Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session C1: Poster Session I: 2:00 pm - 5:00 pm |
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Sponsoring Units: APS Room: Morial Convention Center Exhibit Hall A |
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C1.00001: POLYMERIC AND ORGANIC MATERIALS I |
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C1.00002: Molecular Dynamics of Polymer Systems on Graphic Processing Units (GPUs) Joshua Anderson, Chris Lorenz, Alex Travesset Molecular dynamics (MD) is a powerful, but computationally intensive, simulation technique capable of modeling a wide range of systems in and out of thermodynamic equilibrium. Using traditional computers, simulations large enough to explore the phases of polymer systems require the use of expensive distributed memory clusters. Graphics Processing Units now offer an unprecedented amount of computing power for general purpose applications. They are inexpensive (\$500) and can be added to almost any standard desktop system. MD algorithms are adapted to execute on a single GPU, which is able to attain the same performance as 32 processor cores on a cluster. It is possible for a single system to host up to 4 GPUs, putting the power of a 128 processor core cluster on the desktop. This performance is illustrated in a variety of polymer systems such as low density micellar phases with cubic symmetry, high density lamellar and nanocomposite gyroid systems. GPUs offer unprecedented opportunities for the simulation of polymer systems. [Preview Abstract] |
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C1.00003: An Efficient Algorithm to Calculate Density of State in Large Systems: Generalized Ensemble Means and Compression-Variable Transformation Xin Zhou We present a high efficient algorithm to calculate density of state (DOS, or its logorithm, $S(U)$) of large systems in any macroscopic variable $U$. The algorithm calculate the ensemble means and fluctuations of $U$ in a series of generalized ensembles to form $S(U)$ and its derivative in some adaptively generated $U_{i}$, then interpolate whole the $S(U)$ curve within the required accuracy. We also apply a compression transformation in the $U$ space to focus the most computation cost on extrapolating $S(U)$ in new $U$ region. The algorithm is found to be order of $O(N^{1/2})$ (or faster) as the increasing system size $N$, which is far faster than all current available methods (at least $O(N^{3/2})$). The algorithm satisfies the detailed-balance condition in whole simulations by averaging the ensemble means in each segment of simulation by using their errors as weight, so that it has great numerical stability. The method can be compined with the parallel tempering (PT) algorithm to simulate the low-temperature properties of large complex fluids and decrease the number of the needed replica in original PT, $O(N^{1/2})$, to one in each macroscopic phase. The validity of the new approaches are demonstrated by presenting the simulated results of Lennard-Jone liquids with different size $N$. The approaches even generate DOS of each super-saturated macroscopic phase in the unstable liquid/solid coexistence region, respectively, which provides much more information to understant the phase coexistence and transitions. [Preview Abstract] |
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C1.00004: Understanding Thermodynamics and Surface Dynamics of Pom-pom Branched Polystyrene Sewoo Yang, David T. Wu, Zhang Jiang, Suresh Narayanan, Mark D. Foster We have studied the effect of varying the relative length of the central linear portion of the pom-pom chain on the size of a single chain and on the bulk thermodynamics of blends of the pom-pom branched polystyrenes (PS) with linear analogs. A novel set of pom-pom PS with well-defined molecular architecture was synthesized anionically. The value of the interaction parameter contribution apart from the isotopic labeling for binary blends of linear and branched chains, measured using small angle neutron scattering, increased with a growing disparity in hydrodynamic volumes except for the case of the star polymer. Key aspects of these results are consistent with the predictions of a Gaussian Field Theory. We also investigated surface dynamics of films of pom-pom PS using x-ray photon correlation spectroscopy. Speckle patterns of films of the pom-pom PS of thickness ($\sim $ 100 nm) were measured at temperatures above T$_{g}$ of the bulk chains and both the scattering of a single pattern analyzed and time correlation performed to obtain correlation functions. The temperature dependence for the q-dependent relaxation time was determined and estimates of the surface tensions of the different polymers derived from the static structure factors. [Preview Abstract] |
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C1.00005: Synthesis and characterization of erbium (III)-doped polyimide nanofibers for low temperature thermophotovoltaic applications Zhenxin Zhong, Darrell Reneker Thermophotovoltaic conversion technology is a promising way to convert waste heat to electricity via photons. In this research, erbium (III)-doped polyimide nanofibers mats were prepared as selective emitters to explore the selective thermal emission efficiency in a low operating temperature range ($<$ 500 $^{\circ}$C). The selective emission at 6500 cm$^{-1}$ of erbium (III)-doped polyimide nanofiber mats was measured on mats characterized with scanning electron microscopy, transmission electron microscopy, FT-IR spectroscopy, and thermogravimetric analysis. A small but potentially useful amount of power was obtained from a 2 mg mat. [Preview Abstract] |
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C1.00006: Characterization of an electrospinning jet from videographic observations of glints Kaiyi Liu, Camden Ertley, Darrell Reneker Detailed relationships between glints of light reflected from the electrical bending coils of an electrospinning jet and the path of the jet were established. The path of the jet was observed by illuminating the jet with a short, intense flash of light. Glints were formed simultaneously by a continuous, intense beam of light from a chosen set of directions. As the jet path moved through the continuous beam of light, some segments of the path were oriented so that intense specular reflection (a glint) was recorded by a camera. The motion of the jet path caused a glint to create a trace in the videographic image. A linear glint trace divided into two traces when the segment producing the glint became involved in a bending instability. A smooth turn of a coil of the jet path usually produced two glints in a particular observation direction. When the smooth turn became involved in a smaller electrical bending coil, the two glints divided into many glints. Observations of this sort are expected to lead to new ways to reduce the variability in the diameter of electrospun nanofibers. [Preview Abstract] |
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C1.00007: Viscoelastic Electrospinning Jets: Initial Stresses and Elongational Rheometry Tao Han, Alexander Yarin, Darrell Reneker A novel method of characterization of longitudinal stresses in electrospinning jets is introduced. The measured initial longitudinal stresses in jets of a 6 wt{\%} aqueous solution of polyethylene oxide (M$_{w}$=400 kDa) were of the order of 100 kPa, which is two orders of magnitude larger than in other free viscoelastic jets. This is attributed to strong stretching of polymeric liquids in the transition zone between the Taylor cone and the beginning of the jet, where the stretching rates are 100 to 1000 s$^{-1}$. The velocity of the fluid along the straight segment was determined from the observed jet diameter combined with the laser Doppler velocimeter data. The tensile stress was measured by creating a lateral displacement, near the beginning of the jet, and observing its propagation along the jet. Combination of the velocity with the stress data provided the information needed to determine the modulus and relaxation time of a polymeric liquid subjected to rapid stretching. [Preview Abstract] |
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C1.00008: Molecular Modeling of Thermosetting Polymers Soumya Patnaik, Vikas Varshney, Barry Farmer In this work we present molecular modeling of thermosetting polymers with special emphasis on building atomistic models. Different approaches to building highly cross-linked polymer networks starting from un-crosslinked systems are discussed. A multi-step procedure for relaxing the molecular topology during crosslinking was proposed which allows for minimizing the increase in the residual internal stresses with increasing degree of crosslinking. This methodology was applied to epoxy based thermosets and several materials properties such as density, Young's modulus, glass transition temperature, thermal expansion coefficient and volume shrinkage during curing were calculated and found to be in good agreement with experimental results. Along with the materials properties, the simulations also highlighted the distribution of molecular weight build up and inception of gel point during the network formation. [Preview Abstract] |
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C1.00009: Nafion/poly(1-vinyl imidazole) composite membranes for fuel cell application Dukjoon Kim A base monomer (1-vinyl imidazole, VIDz) was polymerized in Nafion$^{\mbox{{\textregistered}}}$ 112 membrane by UV irradiation in order to reduce methanol permeability of the latter. With increasing content of poly 1-vinyl imidazole (PVI), equilibrium water uptake was decreased due to reduced size of hydrated ion cluster in the composite membrane as confirmed by a small angle X-ray scattering analysis. The electrochemical properties of the membrane such as ion conductivity, methanol permeability and electro-osmotic drag were also affected by equilibrium water uptake and hydrated pore size. Even a minute incorporation of the base polymer showed a significant effect on proton conductivity and methanol permeability. Methanol transport by electro-osmotic drag was evaluated by using relating equations and methanol permeability and limiting current density data obtained in this study. Although the absolute number of electro-osmotic drag was hard to determine, the trend of change could be studied in relation to bulk-like water in composite membranes. This novel composite membrane exhibited an increased cell performance compared with a plain Nafion membrane due to reduced methanol crossover rate. [Preview Abstract] |
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C1.00010: Metastable Structures of poly(lactic acid) Jeff Kalish, Shaw L. Hsu, Kaoru Aou, Meg Starkweather The coexistence of two poly(lactic acid) crystals (alpha' and alpha) and its impact on the double melting peaks in differential scanning calorimetry is investigated. Solubility differences as well as irreversibility of the alpha' to alpha transformation process indicates that the alpha' crystal is the less stable crystal form. The difference in thermal stability is quantified by measurement of crystal melting enthalpies using the Pyda/Wunderlich method. The relative composition of the crystalline fraction can also be determined by the same method. Crystal annealing is found to be accompanied by an increase in both overall crystallinity and the fraction of the alpha crystal relative to the alpha' crystal. Infrared spectroscopy is used to probe the crystal structures. In comparison to the alpha crystal, the alpha' crystal is found to have a weakened carbonyl-carbonyl intermolecular interaction. Results also suggest that the alpha' crystal does not have a 10/3 helix which constitutes the alpha crystal. The coexistence of the two crystal forms has profound implications in interpretation of double melting peaks in its DSC thermogram. [Preview Abstract] |
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C1.00011: Perturbing Effects of Bulky Comonomers on the Chain Conformation of Poly(vinylidene fluoride) Suriyakala Ramalingam, Yuning Yang, Shaw L. Hsu The comonomer effect on structures of poly(vinylidene fluoride- hexafluoropropylene) copolymers P(VDF-HFP) was analyzed by Raman spectroscopy. The HFP content of these copolymers varies from 5{\%} to 15{\%}. Because of steric interactions involving the bulky HFP comonomers, the predominant chain conformation has extensively more gauche conformers in comparison to pure PVDF. Based on both experimental and simulation studies, specific spectroscopic features in the 700 cm$^{-1}$ region have been identified that are characteristic of irregular chain conformations elucidating the perturbing effect of HFP on the equilibrium chain statistics of PVDF in the amorphous phase. In addition, these spectroscopic features were revealed to be extremely sensitive to the relative placement of CF$_{3}$ units respective to other fluorine atoms along the chain. [Preview Abstract] |
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C1.00012: Single Crystals of Diblock Copolymers: Tethered Chain Study Ryan M. Van Horn, Joseph X. Zheng, Huiming Xiong, Roderic P. Quirk, Bernard Lotz, Edwin L. Thomas, Stephen Z.D. Cheng Tethered polymer chains have become an important area of research over the last few decades. Their unique properties make them appealing for various applications. The tethering density of the chains is the most important parameter in determining their properties, as shown by various theoretical and experimental works. Our group uses single crystals of crystalline-amorphous diblock copolymers to study tethered polymer chains. This system provides better control of tethering density and molecular weight as compared to previous methods. Previous work on PS-b-PEO and PS-b-PLLA shows, for the first time, the values of the interacting and brush regime transitions. The systems studied have addressed some issues, molecular weight dependence and solvent quality, but they do not provide general results. The work presented here will look at the role of chain adsorption and crystallization of the tethered chain, using PMMA-b-PLLA and PEO-b-PCL systems. [Preview Abstract] |
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C1.00013: Morphological Control of Segmented Polyurethanes via Crystallization Confinement of Soft Segments Matthew Hood, Bingbing Wang, John LaScala, James Sands, Fredrick Beyer, Josh Orlicki, Mark VanLandingham, Christopher Y. Li Segmented polyurethane (SPU) is a linear, high molecular weight block copolymer comprised of regions of soft and hard segments. The phase separation between these mechanic-contrasting segments is partly the cause of SPU's superior mechanical strength as the hard domains reinforce the soft domains, while the soft domains provide the toughness that allow for good energy adsorption. To achieve the greatest impact absorption the soft segments must remain amorphous surrounding the crystallized hard domains which are held together via hydrogen bonding. We systematically investigated a SPU system with poly(ethylene glycol) (PEG) of various molecular weights as the soft segments. Using differential scanning calorimetry, small angle X-ray scattering and wide angle X-ray diffraction it was observed that as hard segment content increased there was a decrease in soft segment crystallization till PEG crystallization was no longer observed, thus achieving the desired structure. By tailoring the composition it is also possible to control the nano-sized structure altering the morphology on the macro-scale thus increasing the interface density of the SPU such that we produce a transparent film possessing structural capabilities suitable for transparent body armor. [Preview Abstract] |
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C1.00014: Crystal Size Effect on Dielectric Property of PVDF at High Electric Field and Its Effect on Energy Storage and Discharging Behaviors Fangxiao Guan, Steven Boggs, Lei Zhu Improvement of the high energy density capacitor can be achieved by choosing a material with relatively high dielectric constant and/or high electric breakdown strength. In general, their relationship can be described as U=0.5e(r)e(0)Eb$^2$. For certain dielectric polymers, such as poly (vinylidene fluoride) (PVDF), dielectric constant shows strong electric field dependence. Therefore, the energy density cannot be described simply by this equation. In this work, electric field dependent dielectric response of PVDF is studied, and its relation to the energy density stored is discussed. Although the dielectric constants of PVDF with different crystal sizes can be different at high electric field, they all have similar stored energy density. Intriguingly, their energy discharging behaviors are different. The smaller the crystal size, the faster the energy discharging process, and the lower the dielectric loss. From this study, we conclude that a high energy density with fast discharge and low dielectric loss could be obtained by tuning the crystal sizes. [Preview Abstract] |
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C1.00015: Reducing Dielectric Loss by PVDF-CTFE Graft Copolymers Jing Wang, Zhongzhe Yuan, Fangxiao Guan, Steven Boggs, Lei Zhu Polymer film capacitors with high energy density and low loss are very attractive in potential applications. Maintaining the high dielectric breakdown strength in high dielectric constant films with a low loss will also be a challenge. Poly(vinylidene fluoride) (PVDF) and its copolymers are well-known ferroelectric polymers that exhibit excellent electromechanical properties as candidates for high-performance, high-energy-density capacitor. However, the dielectric loss of commercially extruded PVDF films is high (0.02). In our work, lower dielectric loss polystyrene (PS) were introduced to improve PVDF dielectric properties. PVDF-CTFE-g-PS graft copolymers were synthesized via the ``graft from'' process. The quality of films from graft polymer was improved, resulting high energy density and low loss. A series of graft polymers with different electric properties were prepared, since the breakdown strength and dielectric loss of PVDF were influenced by the crystallinities and crystal sizes. [Preview Abstract] |
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C1.00016: Semicrystalline Polymers: A special case of polymer brushes Vikram Kuppa, Gregory Rutledge Monte Carlo (MC) molecular simulations are employed to evaluate the interface between crystalline and amorphous polyethylene. The simulation setup mimics the interlamellar region of a semicrystalline polymer with a low effective molecular weight. All polymer chains are tethered to the crystal surface at one of their ends, thus forming tails with their other (free) ends distributed in the space between crystal lamellae. Two different systems are explored: one, in which the simulations explore a range of molecular weights due to the use of MC moves that exchange beads between different chains; and another, in which strict control of the molecular weight is exercised, thereby constraining chain lengths to a narrow window. The effects of temperature, grafting density, molecular weight distribution and the interaction between brushes on opposing crystal surfaces are investigated by examining monomer density profiles, chemical potentials and bond orientation order parameters. [Preview Abstract] |
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C1.00017: Polydomain Simulation of Liquid Crystalline Polymer Orientation in Channel Flows Jun Fang, Wesley Burghardt The properties of liquid crystalline polymers are strongly affected by the molecular orientation state induced by processing flows. LCP structure development under flow is quite complex, due to the propensity towards 'director tumbling' dynamics in rodlike nematics, and the resulting complicated 'polydomain' distributions of orientation. Many models of LCP structure {\&} rheology begin with a detailed description of the molecular orientation state, possibly including a molecular description of distortional elasticity. While well suited for simulations of fundamental phenomema in simple flows, application of these models to processing flows is far out of reach. Conversely, the phenomenological polydomain model of Larson {\&} Doi is sufficiently simple to allow for its application to process simulations. This is further facilitated by a nearly exact analogy between the Larson-Doi model and the Folger-Tucker model for predicting orientation in fiber dispersions, which is incorporated in commercial process simulation software. We use this available modeling infrastructure to test the ability of the Larson-Doi model to predict orientation distributions in kinematically complex but isothermal channel flows of liquid crystalline polymers, comparing simulation results orientation distribution data previously obtained using in situ x-ray scattering methods. [Preview Abstract] |
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C1.00018: Thin Film morphologies of rod-coil block copolymers Manas Shah, Venkat Ganesan The interplay of microphase separation and liquid crystalline ordering in rod-coil block copolymers leads to complex morphologies distinct from that of conventional flexible block copolymer phases. For many electronic and semi-conducting applications, rod-coil block copolymers need to be patterned into thin films. The final morphology and the nature of orientation of rod units would now depend (in addition to the constituent interactions) on the interactions of the blocks with the confining surfaces. We combine the self-consistent field theory models of rod-coil block copolymers in a thin film framework to understand the effect of confinement on the morphology and the nature of orientation of rod-units. [Preview Abstract] |
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C1.00019: Structural Recovery of Epoxy Films Subjected to CO$_{2}$ Pressure Jumps Shankar Kollengodu-Subramanian, Mataz Alcoutlabi, Lameck Banda, Gregory McKenna This group has previously investigated the impact of structural recovery and physical aging on thermodynamic and mechanical properties of polymers after temperature jumps and compared with plasticizer jumps [1]. Increasing plasticizer content depresses the glass transition temperature (T$_{g})$ in glassy polymers and this results in changes in the mechanical, optical and dielectric properties. Plasticizer jumps using a strong polar molecule have been previously studied by our group and have shown qualitatively similar behavior to temperature jump experiments [2]. In the current work, we report the results on plasticization effects using a weakly polar molecule (CO$_{2})$ on the structural recovery of glassy polymers after plasticization jumps and compare the behavior with temperature formed glasses. \newline \newline [1] Banda, L., Alcoutlabi, M., and McKenna, G.B, J. Polym. Sci. Part B: Polym. Phys., \textbf{44}, 801-814, 2006 \newline [2] Zheng Y, and McKenna, G.B., Macromolecules, \textbf{36}, 2387-2396, 2003 [Preview Abstract] |
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C1.00020: Strain induced non-linear effects in Dynamic Viscosity measurements J.P. Ibar Melt viscosity measurements conducted at increasing $\omega $ and strain, in a parallel plate dynamic rheometer, trigger a roaster of non-linear effects which we review, such as variation from the commanded strain, non-linearity between stress and strain, time dependence of the G' and G'' moduli, and appearance of slip. In addition, melt fracture, at the surface or in the bulk has been reported. Both the Torque and the Normal Force are studied. Results from both a constant strain rheometer (RDAII) and a constant stress rheometer (Bohlin SVO are reviewed. We examine the many aspects of non-linearity and explore the origin(s) of these manifestations, whether due to measurement limitations, melt instability, or purely the expression of non-linear viscoelasticity [Preview Abstract] |
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C1.00021: Topology of Branched Polymers: Effect on Structure and Dynamic Properties Ramnath Ramachandran, Gregory Beaucage, Amit S. Kulkarni, Vassilios Galiatsatos, Douglas C. McFaddin We investigated linear and branched polyethylene (PE) using small-angle neutron scattering (SANS). The experiments were conducted on dilute solutions of PE in deuterated p-xylene. A variety of structural information$^{\dag }$ such as fractal dimension ($d_{f})$, connectivity dimension ($c)$, minimum path dimension ($d_{min})$, long chain branch fraction ($\phi _{br})$, radius of gyration ($R_{g})$ and persistence length ($l_{p})$ were obtained. Such information presents a qualitative and quantitative assessment of branching in polymers. Theoretical models such as `binary contacts per pervaded volume' model$^{\ast }$ were employed to correlate the structural information of the polymer to its entanglement molecular weight ($M_{e})$. $M_{e}$ was used to predict physical properties of the polymer such as plateau modulus ($G_N^0 )$ and zero-shear viscosity (\textit{$\eta $}$_{0})$. $^{\dag }$Beaucage G. \textit{Physical Review E} \textbf{70},031401 (2004) $^{\ast }$Colby \textit{et al}.\textit{ Macromolecules }\textbf{25,} p.996 (1992) [Preview Abstract] |
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C1.00022: Entanglement Percolation Effects on the Dynamics of Polymer Rheology Richard Wool The percolation model of entanglements (Wool 1983) makes unique predictions regarding the dynamics of polymer chains in the terminal relaxation zone of reptating linear polymer melts of molecular weight M. When percolation occurs during relaxation of entangled chains in the terminal zone, we observe some unusual results. These include: (a) for homopolymers of molecular weight M $>>$ M$_{c}$, reptating chains appear to be non-reptating as their ends and centers relax at the same rate during percolation. (b) During stress relaxation, the random coil dimensions R$_{g}$(//) and R$_{g}(\bot )$ are predictably not fully relaxed when the stress and birefringence relax to zero. (c) The matrix molecular weight P effects on relaxation time $\tau $ of the probe chain M $>>$ M$_{c}$ are as follows: Rouse-like dynamics is observed for reptating chains with $\tau \quad \sim $ PM$^{2}$ when M$>>$P and (d) the relaxation time $\tau \quad \sim $ P$^{o}$M$^{3}$ when P$>>$M, in accord with reptation. These unusual results predicted by entanglement percolation are supported by significant experimental data from selectively deuterated polystyrene chains HDH, DHD and DPS. Entanglement Percolation replaces Constraint release and Chain End Fluctuation mechanisms in the understanding of the dynamics of polymers in the melt and concentrated solutions. [Preview Abstract] |
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C1.00023: Determining Local Mechanical Properties of Soft Materials with Cavitation Rheology Jessica Zimberlin, Naomi Sanabria-DeLong, Gregory Tew, Alfred Crosby To guide the development of tissue scaffolds and the characterization of naturally heterogeneous biological tissues, we have developed a method to determine the local modulus at an arbitrary point within a soft material. The method involves growing a spherical cavity at the tip of a syringe needle and monitoring the pressure of the cavity at the onset of a mechanical instability. This critical pressure is directly related to the local modulus of the material, which can be measured on length scales similar to size of a single biological cell. Using model hydrogel, materials, we demonstrate the ability for this technique to quantify the local stiffness of hydrogel networks and its relation to the macroscopic stiffness as measured by shear rheometry. In addition to heterogeneities in equilibrium hydrogel networks, we quantify differences in local stiffness during the gelation of hydrogels. Lastly, we consider the influence of surface energy on the onset of cavitation by using different injected agents to induce the instability. [Preview Abstract] |
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C1.00024: Cavitation Rheology of Polyacrylamide Hydrogels Santanu Kundu, Jessica Zimberlin, Alfred Crosby Cavitation rheology is a new characterization technique for the measurement of mechanical properties on small length scales, e.g. 10 -100 $\mu $m, at any arbitrary location within a soft material. The technique involves growing a cavity at the tip of a syringe needle and monitoring the pressure of the cavity at the onset of instability. This critical pressure is directly related to the local modulus of the material. We used this technique to characterize the network mechanics of polyacrylamide hydrogel materials, a common material used in many biological applications. We compared the cavitation rheology results with that obtained from shear rheometry. This technique was used to investigate the rheological properties of gels with different dimensions and different moduli, which were obtained by varying initial monomer to water ratio. These results provide a quantitative foundation for the extension of this technique to \textit{in vivo} characterization of biological tissues. [Preview Abstract] |
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C1.00025: Polyurea segmented multi-block copolymers: structure and dynamics Jai Pathak, Jeffrey Twigg, C. M. Roland, Peter Mott, Derek Ho, Eric Lin, Mary Vukmir, Thomas Epps We study a Polyurea copolymer by measuring its stress-strain behavior between 100 and 1000 inv. s strain rate and by oscillatory shear rheology, respectively. Polyurea shows elastomeric mechanical response over a wide temperature range, as the rigid domains physically cross-link the soft domains. The modulus increases, while the residual strain in samples stretched to failure decreases with increasing strain rate. SAXS on undeformed specimens reveals two peaks: a higher wave-vector peak from semi-crystalline hard segments (long period 6 nm), and a lower wave-vector peak from micro-phase separated domains of spacing 70 nm. Polyurea specimens quasi-statically stretched to failure show anisotropic scattering, while samples stretched to failure at large strain rates show isotropic scattering, suggesting that deformation effects on morphology are controlled by rigid domain response over the deformation time-scale. Greater molecular reorganization and alignment take place at low strain rates. At large strain rates no molecular reorganization is possible, yielding identical structure as undeformed materials, pronounced strain-rate hardening and low residual strain. [Preview Abstract] |
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C1.00026: Nanoscale Superstructures in Copolymers with Evenly Spaced Charged Groups. Wenqin Wang, Sharlene R. Williams, Timothy E. Long, Ralph H. Colby, Karen I. Winey Multiple copolymers with evenly spaced charged groups have been synthesized: polyethylene (PE) -based ionenes, poly(tetramethylene oxide) (PTMO)-based ionenes, and poly(alkylene oxide)-based sulfonated polyester ionomers. The morphologies of these copolymers are investigated using differential scanning calorimetry, X-ray scattering, and electron microscopy. In both PE- and PTMO-based ionenes, the bulky cationic groups in the backbone reduce the crystallinity of the copolymer and form cation-rich channels perpendicular to the polymer backbone, where the extent of association is influenced by the size of the ionic liquid moiety. In the sulfonated polyester ionomers, the crystallization of long poly(alkylene oxide) segments promotes the formation of ion-rich layers. These results will be compared with our recent work with linear poly(ethylene-\textit{co}-acrylic acid) copolymers and ionomers with precisely spaced acid groups. [Preview Abstract] |
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C1.00027: Phase behavior of polyelectrolyte multilayer investigated by thin film calorimetry H. Huth, R. Mueller, A. Fery, C. Schick Polyelectrolyte multilayer can be easily assembled using spraying or dipping of the different polyelectrolytes [1]. The thickness of the produced layers (nanometer range) is well controlled by the preparation conditions. Only a few methods are available for dynamic investigations, as afm for mechanical properties [2]. AC-chip calorimetry is used as a very sensitive tool for calorimetric investigations of such thin films as demonstrated for thin polymeric films [3]. To investigate the phase behavior of polyelectrolytes the humidity is used as a new parameter in addition to temperature for calorimetry. First measurements with the modified calorimeter for the PSS/PDADMAC polyelectrolyte multilayer system are shown. Further extensions of the calorimeter for better understanding of the phase behavior are discussed. [1] Decher, G. and J.D. Hong, Phys. Chem. Chem. Phys., 1991. 95(11): 1430. [2] Mueller, R., et al. Macromolecules, 2005. 38(23): 9766. [3] Huth, H., Minakov, A. A., Schick, C., J. Polym. Sci. B Polym. Phys. 2006 44: 2996. [Preview Abstract] |
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C1.00028: Stimuli-Response of Charged Diblock Copolymer Brushes Dong Meng, Qiang Wang We have performed self-consistent field calculations to study the stimuli-response of diblock copolymer brushes on a planar substrate. One of the two blocks carries either weakly or strongly dissociating charges, making the brush surface responsive to the solution pH, ionic strength and applied electric field, in addition to the solvent selectivity. We have investigated in detail the influence of these stimuli on the polymer segmental distribution and surface switchability of the brush. Our result can be used to guide the experimental design of ``smart surfaces'' from diblock copolymer brushes. [Preview Abstract] |
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C1.00029: Characterization of polyelectrolyte behavior of the polysaccharides chitosan, heparin, and hyaluronan, by light scattering and viscometry. Soheil Boddohi, Susan Yonemura, Matt Kipper This study on the polyelectrolyte behavior of polysaccharides in solution is motivated by our recent work in development of nanostructured polysaccharide-based surface coatings. Chitosan behaves as a weak polycation, and hyaluronan behaves as a weak polyanion, while heparin behaves as a strong polyanion. The ability to control the conformation of these polysaccharides in solution, by changing the solution ionic strength and pH may offer the opportunity to further tune the nanoscale features of polysaccharide-based surface coatings assembled from solution. In the work reported here, the solution conformation of these polymers is determined from gel permeation chromatography coupled to differential refractive index, light scattering, and viscometry detection. These results are related to the nanostructure of chitosan-heparin and chitosan-hyaluronan surface coatings based on polyelectrolyte multilayers. [Preview Abstract] |
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C1.00030: Competition between liquid crystalline (LC) ordering and block copolymer (BCP) microphase separation in a series of LCBCPs Kishore Tenneti, Xiaofang Chen, Christopher Li, Xinhua Wan, Qi-Feng Zhou, Lixia Rong, Benjamin Hsiao A comprehensive study displaying a rich variety of liquid crystalline (LC) phase structures (SmA, ColN, ColH, ColR) and block copolymer (BCP) morphologies (tetragonal perforated and transverse-parallel lamellae) observed in liquid crystalline LCBCP systems will be presented. The systems under investigation differ in the flexibility of interactions between the mesogen and polymer backbone. Both covalent and non-covalent interactions are investigated in a series of mesogen-jacketed-, side-chain- and hydrogen bonded- LCBCPs and the influence of composition and molecular architecture on the final phase behavior will be presented. The factors that lead to the domination of either LC ordering or BCP microphase separation will also be reported. [Preview Abstract] |
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C1.00031: Symmetry transition in multilayer films of block copolymer/homopolymer blends Vindhya Mishra, E.J. Kramer Multilayer films of spherical domain poly (styrene-b-2vinyl pyridine) (PS-PVP Mn:65000,$f_{pvp} =.12)$ blended with 5 volume{\%} low molecular weight PS homopolymer (Mn:13000) is characterized with grazing-incidence small angle x-ray diffraction (GISAXD) to determine the lattice symmetry and stacking of layers. The structure was also imaged by transmission electron microscopy (TEM). In such films competition between packing preferred at the surfaces with that preferred by the internal layers leads to a transition in the packing symmetry as n, the number of sphere layers, is increased. Pure PS-PVP exhibits hexagonal close packed (HCP) symmetry up through n=4. At n=n*=5 the in-plane symmetry becomes face centered orthorhombic whose lattice parameters approach those of the BCC (110) plane for n$>>$10.GISAXD and TEM data from the blend films one to ten layers thick shows that the addition of 5 vol {\%} PS increases n* to 7. We think that the PS segregates to the interstices in the HCP structure reducing the stretching of the PS blocks and the free energy penalty of HCP versus BCC inner layers. Significant improvement in translational order is also seen in all the films over the copolymer alone. [Preview Abstract] |
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C1.00032: Hierarchical Assemblies of Block Copolymer-Based Supramolecules in Thin Films Shih-Huang Tung, Nisha C. Kalarickal, Thomas Schilling, Ting Xu Diblock copolymer-based supramolecules can be constructed by associating small molecules to the side chain of one block. In bulk, supramolecules self-assemble into a rich library of hierarchical structures. However, the phase behaviors of such systems in thin films have been rarely studied. Here, we present a structural investigation of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) with hydrogen-bonded 3-pentadecylphenol (PDP) to P4VP block in thin films. We show that using the same diblock copolymer, a variety of hierarchical structures can be obtained by varying the stoichiometry of P4VP to PDP. More importantly, the lamellar and cylindrical microdomains can be orientated normally to the substrates after annealed under chloroform atmosphere. The assembly of P4VP/PDP complex, ca. 4nm in size, is oriented within the microdomain as confirmed by GISAXS and AFM. Thus, control over the supramolecular assemblies at two length scales, i.e. tens of nanometers and a few nanometers, can be simultaneously achieved in thin films. [Preview Abstract] |
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C1.00033: Solvent annealing of block copolymer thin films combined with controlled dewetting Tae Hee Kim, Cheolmin Park The treatment of block copolymer thin film with its solvent vapor has been known as an effective way to control both orientation of microdomains with respect to the surface and their registration into a well defined periodic lattice structure. We have recently demonstrated hierarchically ordered cylindrical microdomains in a poly(styrene-b-ethylene oxide)(PS-b-PEO) thin film combined with microcontact printing. Well ordered PEO microdomains in large area was successfully produced by confined dewetting of thin PS-b-PEO films micropatterned on chemically modified surface pattern with self-assembled monolayers during solvent annealing. In order to further control block copolymer thin films upon solvent annealing, we introduce a new patterning method of block copolymer thin films, Plasma Enhanced Polymer Transfer Printing (PEPTP) where a block copolymer thin film spin cast directly on a patterned PDMS mold is easily transferred to a substrate with oxygen plasma. The microstructure of the block copolymer film micropatterned by PEPTP is ordered by the subsequent solvent annealing . The controlled microstructures were characterized by Atomic Force Microscope (AFM), Field Emission Scanning Electron Microscope (FESEM) and Grazing-Incidence Small Angle X-ray Scattering (GISAXS). [Preview Abstract] |
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C1.00034: Morphological Study of ABC Triblock Terpolymers Satoshi Akasaka, Akiko Mitani, Hirokazu Hasegawa, Nikos Hadjichristidis Triblock terpolymers form richer variety of microdomain structures than diblock copolymers. In this study We investigated the microdomain structures in the toluene-cast films of several kinds of ABC triblock terpolymers consisting of polystyrene, polyisoprene and poly(dimethyl siloxane) (PS-b-PI-b-PDMS) by transmission electron microscopy (TEM). As the result we observed various structures composed of lamellae, cylinders and spheres. In addition, we employed electron tomography to analyze the two complex network-forming structures using their three-dimensional images. Consequently, we found that one of them forms core-shell type double gyroid structure in PS matrix, and the other forms core-shell type single gyroid-like structure in PS matrix. [Preview Abstract] |
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C1.00035: Stimuli-responsive block copolymers in ionic liquids Takeshi Ueki, Masayoshi Watanabe, Tim Lodge Ionic liquids (ILs) are room temperature molten salts and have attracted much attention because of their unique properties. The characteristics of ILs (non-volatility, non-flammability, chemical stability, high ionic conductivity) can contribute to high performance energy-conversion materials. On the other hand, some polymers greatly change their solubility in ILs in response to external stimuli such as temperature and light. We have found that poly($N$-isopropylacrylamide) (PNIPAm) and poly(benzyl methacrylate) (PBnMA) show upper critical solution temperature (UCST)-type phase behavior and lower critical solution temperature (LCST)-type phase behavior in an ILs, respectively. Most recently, we also discovered that certain polymers change their solubility induced by photo stimuli. In this study, we describe temperature and photo stimuli responsive self-assembly of AB type block copolymers having at least one stimuli-responsive segment in IL solution. Based on the results, we will aply to construct stimuli-responsive physical gels by using ABA tribock copolymer self assembly in an IL. [Preview Abstract] |
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C1.00036: Polymer translocation through a nanopore in presence of attractive binding particles Aniket Bhattacharya, Kaifu Luo, Tapio Ala-Nissila, See-Chen Ying We use Brownian dynamics simulation to study the translocation of a flexible linear polymer chain through a nanopore into a cell containing particles those bind reversibly to the chain. We study the role of these binding particles [1] by monitoring the mean first passage time, the diffusion of the center of mass, and the net force on the translocating chain as a function of the density of these particles and the strength of the attractive interaction. \newline [1] Roya Zandi,David Reguera, Joseph Rudnick and William M. Gelbart, Proc. Natl. Acad. Sci. USA {\bf 100} 8649 (2003). aniket@bhattacharya:~/aps/aps08 [Preview Abstract] |
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C1.00037: Thin Film Morphology of Block Copolymers Containing Polydimethylsiloxane as a Function of the Surface Tension of the Opposing Block Maurice Wadley, Kevin Cavicchi The self-assembly of block copolymers into ordered nanostructures such as spheres, cylinders, and lamellae in the range of 10-100 nm makes them interesting materials for patterning surfaces. Thin films of block copolymers containing poly(dimethylsiloxane) (PDMS) are attractive for patterning due to their high oxygen etch resistance compared to other polymers. The main disadvantage of these polymers for patterning is the low surface tension of PDMS. This causes the preferential migration of PDMS to the air/film interface driving the formation of domains parallel to the interface and surface wetting layers. In this work a series of AB block copolymers containing PDMS have been prepared where the surface tension of the opposing block was varied. The effect of changing the surface tension mismatch between the blocks on the thin film morphology will be discussed. [Preview Abstract] |
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C1.00038: Novel diblock copolymer morphologies under cylindrical confinement Priyanka Dobriyal, Thomas P. Russell Cylinder forming poylstyrene-b-polybutadiene diblock copolymers were introduced inside nanopores of alumina membrane. The pore diameter was varied in order to study the effect of confinement on diblock copolymer morphologies. The, molecular weights of the copolymers were also varied and similar morphologies were obtained for similar degree of confinement. The morphologies observed were dependent on the structural frustration (D/Lo), where D is the pore diameter and Lo is equilibrium period spacing. D/Lo was varied from 0.75 to 2. A rich variety of novel morphologies that include single helix, torroids and double helices were observed which are not observed in the bulk. These morphologies also depended upon the surface of the pore walls. Different morphologies were obtained when the pore wall was preferential to one of the components of the diblock copolymer and when the pore wall was neutral for same structural confinement. [Preview Abstract] |
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C1.00039: Hard-Surface Effects in Diblock Copolymer Systems Dong Meng, Yuhua Yin, Jacqueline Acres, Qiang Wang Polymer chains near a hard (impenetrable) surface have different conformations from those in the bulk. For diblock copolymers (DBC), a hard surface has both energetic and entropic effects. The decrease of polymer segmental density near a hard surface reduces A-B repulsion and favors self-assembled morphologies with more A-B interfaces near the surface, while the enrichment of chain ends and depletion of middle segments near the surface favor parallel morphologies where chains orient mainly perpendicular to the surface. Using parallel self-consistent field calculations with high accuracy, we have studied in detail the hard-surface effects in three DBC systems: DBC thin films confined between two flat homogeneous surfaces, DBC in nanopores, and DBC nanocomposites. [Preview Abstract] |
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C1.00040: Structural Rearrangement of Miscible Polymer Blends at the Polymer/Substrate Interface Xiguo Zeng, Shaw L. Hsu, Brigitte Wang, Charles W. Paul Structural rearrangement of miscible polymer blends at the polymer/substrate interface has been investigated using Raman Micro-spectroscopy. In this study, blends of crystallizable poly (hexamethylene adipate) (PHMA) and acrylate random copolymer resin were observed on substrates of polycarbonate (PC), polypropylene (PP), and polymethyl methacrylate (PMMA). Results showed distinct selective migration and subsequent adsorption of polymer at the polymer/substrate interface. The final compositional distribution at the interface is determined by the type of substrate. Theoretical calculations based upon the Flory-Huggins theory were carried out relating the interaction parameter (chi) and miscibility of polymer blends and different substrates. The combined theoretical and experimental results clearly demonstrate that specific interactions at the interface are primary causes for structural rearrangement. Furthermore, the chain mobility and molecular weight of polymer blends were also found to be important factors affecting the migrations and consequent surface adsorption ratios. [Preview Abstract] |
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C1.00041: A Deuterium NMR Study of Water in a Blend of Soy and Polyether Polyols Yue Zhao, Xia Tong, Shaw L. Hsu The reaction of water with diisocyanate is crucial in formation of polyurethane foams. It yields polyurea hard segments whose lengths and segregation from the polyether soft segments depends, among other things, on the reaction kinetics largely determined by the miscibility of water in the polyether. For soy polyol-based polyurethane formulations, the miscibility issue is further complicated by the use of hydrophobic soy polyols. The question of where water molecules are located in the multicomponent blend is of importance; the answer is key to understanding how the morphology and phase separation evolve and are correlated with foam performance. With water content typically around 5{\%}, it has long been challenging to find a technique that can provide this critical information. We developed an NMR method based on the use of deuterium oxide and found that the signal of resonance of deuterium is sensitive to the chemical environment, which allows water molecules to be quantitatively traced in the phase-separated blend of soy and polyether polyols. Moreover, the resonance signal could serve as a probe to monitor the evolution of phase separation upon composition and temperature change. [Preview Abstract] |
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C1.00042: Surface segregation of end-functionalized homopolymers in a homopolymer matrix Michael Dimitriou, Craig Hawker, Edward Kramer Surface segregation of end-functional poly(2-vinylpyridine) in a blend with P2VP was measured by X-ray photoelectron spectroscopy. A series of chain end functionalized P2VP homopolymers were synthesized \textit{via} either anionic polymerization or Reversible Addition Fragmentation Chain Transfer RAFT and end capped with either a single fluorinated oligomer or a perfluorinated dendrimer. The degree of end functionalization was characterized using NMR spectroscopy, IR spectroscopy and gel permeation chromotagrophy (GPC). [Preview Abstract] |
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C1.00043: Identification of self consistent field interaction parameter from continuum Monte Carlo simulation of model polymer blends Jun Kyung Chung, David Morse Monte Carlo simulations of binary AB polymer blends have been performed to evaluate the effective interaction parameter $\chi_{e}$ of self consistent field theory, and to quantify corrections to RPA predictions for fluctuations. We consider a model with a non-bonded pair interaction $v_{ij}(r) = \epsilon_{ij}f(r)$ for which $f(r)$ is of the repulsive Lennard-Jones form, $\epsilon_{AA}=\epsilon_{BB}$, and $\epsilon_{AB} = \epsilon_{AA} + \Delta \epsilon$. Using thermodynamic perturbation theory, to first order in $\Delta\epsilon$, we obtain an interaction free energy with the composition dependence predicted by Flory-Huggins theory, with an effective interaction parameter $\chi_{e} = \Delta\epsilon z_{c}$. Here, $z_{c}$ is an effective coordination number given by the average of the sum of values of $f(r)$ for interactions between a test monomer and nearby monomers on other chains, in a reference system with $\Delta\epsilon=0$. Results for composition fluctuations in semigrand ensemble simulations of blends with a range of values of $\Delta\epsilon \neq 0$, for several chain lengths, are compared to RPA predictions calculated using this perturbatively defined $\chi_{e}$ parameter. [Preview Abstract] |
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C1.00044: Theory For The Miscibility Windows In Blends Of Polypropylene And Ethylene-$\alpha $-Olefin Copolymers David Wu, Huimin Li, John Curro The miscibility of isotactic polypropylene (iPP) and ethylene-{\&}alpha;-olefin (C2Cx) copolymers has been intensively studied both for its industrial importance and as a model system for complex polymer miscibility behavior. Experiments generally show a window of miscibility for particular regions in the parameter space defined by copolymer composition, volume fraction, and branch chain length. Since the cost of systematic molecular dynamics studies of such systems is still prohibitive, a statistical mechanical approach with the molecular interaction potentials and chain structure as the only input is highly desirable. We present self-consistent Polymer Reference Interaction Site Model (SC-PRISM) calculations of blends of iPP and C2Cx copolymer, where Cx is propylene, butene, and hexene. The calculated enthalpy of mixing is shown to correlate well with experimental trends for the miscibility window. Furthermore, since the theory allows access to molecular-level correlations, insight is provided into the mechanisms for the specific miscibility behavior, including contributions due to chain conformations. [Preview Abstract] |
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C1.00045: MALDI-ToF Analysis of Model Copolymer Blends David Pan, Mark Arnould MALDI-ToF mass spectrometry was used to determine the composition of a low MW styrene (S) / n-butyl acrylate (nBA) copolymer. Bernoullian chain statistics were used to predict the copolymer distribution and confirm that MALDI-ToF detects the correct composition. The copolymer was blended with a low MW polystyrene homopolymer having the same end group as the copolymer at several levels to determine if MALDI-ToF could be used to calculate the amount of homopolymer by subtracting homopolymer peak areas. It is found that, while MALDI-ToF can be used to monitor the amount of homopolymer blended into the copolymer, the observed increase is always greater than the actual amount added, e.g. up to 13{\%} error. This could be due to the fact that the homopolymer ionizes more efficiently than the low MW copolymer. A model to improve the accuracy of the calculated amount of homopolymer in the blend is discussed. [Preview Abstract] |
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C1.00046: Tuning the morphology of polymer nanocomposites: Effect of film thickness and nanoparticle shape Sangah Gam, Aysenur Corlu, Russell J. Composto Adding nanoparticles (NPs) to polymer blend films is an attractive route towards enhancing the mechanical, optical, and electronic properties. Previously, we showed that NPs can segregate to the interphase, jam and produce stable bicontinuous structures. In this study, we show how film thickness effects the phase behavior of poly(methyl methacrylate): poly(styrene-ran-acrylonitrile) (PMMA:SAN) blends containing PMMA-modified silica NPs that partition to the PMMA/SAN interface. As NP loading increased and film thickness decreased, the growth of PMMA domains and correlation length was slowed down. As film thickness increased, the critical concentration to achieve jamming decreased suggesting that lower loading can be used to create bicontinuous structures. To investigate NP shape, hydroxyl and methyl-modified silica nanorods (NRs) were added to PMMA:SAN films. These NRs partitioned into the PMMA-rich domains and produced smaller domain size with increased loading. Compared to spherical NPs, NR loading was more effective at slowing down phase evolution. [Preview Abstract] |
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C1.00047: Synthesis and Characterization of Polyamide Nanocomposites Using Functionalized Carbon Nanotubes Mohammad Moniruzzaman, Karen Winey, Jayanta Chattopadhyay, W. Edward Billups We have synthesized nylon 6,10 nanocomposites using functionalized single-walled carbon nanotubes using our interfacial \textit{in situ} polycondensation method. The specific functional groups -(CH$_{2})_{n}$COCl [n = 4,9] on the sidewalls of SWNT were designed to covalently link the nanotubes to the nylon matrix \textit{via} alkyl segments. The composites show significant improvements in tensile modulus, strength and toughness. The alkyl linkages at the SWNT/nylon 6,10 interface contribute significantly to improving the toughness of the composites. Two extensions of this work will be presented. First, our method will be altered to synthesize nylon 6 via ring opening polymerization in the presence of functionalized nanocomposites. Second, we will adapt our method to other functionalized nanoparticles, possibly graphite. We expect to achieve similar improvements in mechanical properties in these composites. [Preview Abstract] |
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C1.00048: Bulk and Thin film Properties of Nanoparticle-based Ionic Materials Jason Fang Nanoparticle-based ionic materials (NIMS) offer exciting opportunities for research at the forefront of science and engineering. NIMS are hybrid particles comprised of a charged oligomeric corona attached to hard, inorganic nanoparticle cores. Because of their hybrid nature, physical properties --rheological, optical, electrical, thermal - of NIMS can be tailored over an unusually wide range by varying geometric and chemical characteristics of the core and canopy and thermodynamic variables such as temperature and volume fraction. On one end of the spectrum are materials with a high core content, which display properties similar to crystalline solids, stiff waxes, and gels. At the opposite extreme are systems that spontaneously form particle-based fluids characterized by transport properties remarkably similar to simple liquids. In this poster I will present our efforts to synthesize NIMS and discuss their bulk and surface properties. In particular I will discuss our work on preparing smart surfaces using NIMS. [Preview Abstract] |
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C1.00049: Natural Rubber - Layered Silicates Nanocomposites: Mechanical Properties, Structure \& Dynamics Haris Retsos Natural Rubber (NR) is one of the most industrially relevant elastomers due to unique elastic properties. Recently we have been developed NR composites with incorporated natural or synthetic clays. We present structural, dynamical and mechanical properties to justify the influence of different parameters, like silicate dispersion, cross-linking density and strength of polymer/silicate interface, on the reinforcement phenomena of those composites. To understand the improvement of the mechanical properties we have investigated the possibility of any bound rubber formation on the outer surface of fillers like in carbon black or silica composites. Evidence from a rather similar situation have been found in silicate nanocomposites by dielectric spectroscopy and the existence of a possible relaxation mode suggests a strong adhesion with the fillers (interfacially adsorbed polymer IA) that corresponds to a glass transition around 100 \r{ }C higher than the bulk glass transition. [Preview Abstract] |
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C1.00050: Multilayered Polymeric Photonic Structure for THz applications Chen Xia, Louis Kosnosky, Jie Shan, Joseph Lott, Matthew MacKey, Vishwas Pethe, Eric Baer, Anne Hiltner, Christoph Weder Photonic crystal have been widely studied in the visible, and recently become of interest in the THz regime of the electromagnetic spectrum. We have developed a rapid, easy and cost effective method for the preparation of polymeric materials with high refractive indices (RI) for the terahertz (THz) frequencies through extrusion of polymer and nanoparticles of inorganic materials. Using this method, we have fabricated a one-dimensional photonic crystal of polymer/polymer ferroelectric nanoparticles composite with a nearly complete stop band in the THz regime. The result will also be compared to a transfer-matrix calculation [Preview Abstract] |
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C1.00051: Controlled Transdermal Iontophoresis by Polypyrrole/Poly(Acrylic Acid) Hydrogel Phithupha Chansai, Anuvat Sirivat Transdermal drug delivery system delivers a drug into a body at desired site and rate. The conductive polymer-hydrogel blend between polypyrrole (PPy) doped with anionic drug and poly(acrylic acid) (PAA) were developed as a matrix/carrier of drug for the transdermal drug delivery in which the characteristic releases depend on the electrical field applied. The PAA films and their blend films were prepared by solution casting using ethylene glycol dimethacrylate (EGDMA) as a crosslinking agent. A mechanical blending of PPy particles and PAA matrix was then carried out. Drug diffusions in the blended PPy/PAA hydrogel and the non-blended one were investigated and determined by using a modified Franz-diffusion cell with an acetate buffer, pH 5.5, at 37 0C, for a period of 48 hours to determine the effects of crosslinking ratio and electric field strength. Amounts of the released drug were measured by UV-Visible spectrophotometry. The diffusion coefficient of drug was determined through the Higuchi equation via different conditions, with and without an electric field. Moreover, thermal properties and electrical conductivity of the polypyrrole and drug-loaded polypyrrole were investigated by means of the thermogravimetric analysis and by using a two-point probe meter, respectively. [Preview Abstract] |
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C1.00052: Development of PEDOT-PSS/Zeolite Composites as a Gas Sensor Pojjawan Chanthaanont, Anuvat Sirivat Polymer-based gas sensors have received considerable interest in recent years, due to the gas sensing ability through the electrical conductivity changes when exposed to a particular gas. In our work, poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid), PEDOT-PSS, was synthesized via an oxidative polymerization and zeolites were used as selective microporous adsorbent to improve selectivity and electrical conductivity sensitivity of the sensors. PEDOT-PSS were fabricated with zeolites by dry mixing and compressed to form PEDOT-PSS/zeolite composites. Zeolite ZSM-5 of various Si/Al mole ratios were chosen. The composites of zeolite ZSM-5 with different Si/Al mole ratios were investigated for the effect of Si/Al mole ratio on the electrical conductivity sensitivity response when exposed to CO and H2. [Preview Abstract] |
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C1.00053: Effect of Elastomers Types to the Dielectrophoresis Force and Electromechanical Responses Ruksapong Kunanuraksapong, Anuvat Sirivat Electroactive polymers have been well known as materials for using in many applications such as actuators, MEMS devices, and artificial muscles. In our work, we investigated the effect of elastomers type on the dielectrophoresis force and the electromechanical responses at various electric field strengths. The specimens were prepared by solvent casting method and cut into thin films. We studied the dielectrophoresis forces of all elastomers by measuring the deflection distance under various electric field strengths (0-600 V/mm), and calculated the force from non-linear deflection theory of cantilever. Our data show that the electromechanical responses and the dielectrophoresis forces of all elastomers increase almost linearly with increasing electric field strength. The acrylic elastomers (AR71) has the lowest electrical yield point (75 V/mm) and it generates the highest force (389 $\mu $N at E = 600 V/mm). On the other hand, AR70 had the highest electrical yield point (300 V/mm) and it generates the lowest force (321 $\mu $N at E = 600 V/mm). The dielectrophoresis forces appear to depend on several factors such as dielectricity, electrical conductivity, and the storage modulus of elastomers. [Preview Abstract] |
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C1.00054: Development of poly(ether ether ketone)(PEEK) derived from bisphenol-S for proton exchange membrane (PEM) in direct methanol fuel cells (DMFC) Sairung Changkhamchom, Anuvat Sirivat The currently used Proton Exchange Membrane (PEM) in Direct Methanol Fuel Cell (DMFC) is Nafion?, an excellent proton conductivity in fully hydrated membrane. However, it has major drawbacks such as very high cost, and lost of conductivity at elevated temperature and low humidity. In our work, the novel PEM was based on sulfonated poly(ether ether ketone) (S-PEEK) which was synthesized by the nucleophilic aromatic substitution polycondensation of bisphonol-S, 4,4'-dichlorobenzophenone (DCBP), and sodium 5,5'-carbonylbis(2-chlorobenzenesulfonate) (SDCBP). Bisphenol-S is expected to improve thermal stability due to its high melting point (245oC). S-PEEK was characterized by FTIR, 1H-NMR, TGA, DSC, and titration to determine the degree of sulfonation (D.S.). Composite membranes were prepared by using S-PEEK as polymer matrix and heteropolyacid (HPA) as an inorganic filler. The phosphotungstic acid (PTA) was used due to its highly proton conductivity at high temperature and low water uptake. The membranes were characterized by SEM, TGA, DSC, DMTA, and by the measurements of the water uptake ({\%}), the swelling ratio ({\%}), the ion exchange capacities (IEC), the methanol diffusion coefficient, and the proton conductivity. [Preview Abstract] |
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C1.00055: The Titanium-Boron Nitride interaction Gerardo J. Vazquez, Fernando Magana, Eduardo Rangel, Gregorio Ruiz The Boron Nitride (BN) has a structure very similar to that of graphite and this what makes it interesting to study. A sheet of BN has a structure similar to that of the graphene. In this work it was studied, using molecular dynamics based on pseudopotentials theory and Density Functional Theory (DFT), the energy of interaction of a titanium atom with a sheet of BN to obtain the position of adsorption of the titanium in this system. [Preview Abstract] |
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C1.00056: Swelling Behavior of Blended Multilayer Thin Films Using Neutron Reflectivity. Bulent Akgun, Sushil Satija, Hosub Kim, Kookheon Char Surface structure and swelling behavior of polyelectrolyte multilayer films of poly (allylamine hydrochloride) (PAH)/poly(sodium 4-styrenesulfonate) (PSS):poly(methacrylic acid) (PMAA) have been studied using X-ray and neutron reflectivity (NR). Samples have been prepared either using spin-assisted self assembly or dip coating. Swelling measurements were done in a chamber by using saturated salt solutions. PSS:PMAA blend composition was varied from pure PSS to pure PMAA to investigate the effect of strong polyelectrolyte on the swelling of the multilayer film. Multilayer films prepared by spin assisted deposition yields well defined films with much smooth interfaces than the films prepared by dip coating. NR results showed that incorporation of strong polyelectrolyte, PSS, into the multilayer decreases the swelling capacity of the film. [Preview Abstract] |
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C1.00057: Drop retention force as a function of drop size Aisha Leh, Rafael Tadmor, Preeti Yadav, Prashant Bahadur, Kumud Chaurasia, Lan Dang In literature, the force, $f$, required to slide a drop on a surface is often considered as linear with the width of the drop, w, so that $f$/w is constant. Dussan's equation further simplifies this proportionality in the case of advancing and receding contact angles constant with drop size, to show that $f$/V$^{1/3}$ is constant; V being the drop volume. We show experimentally, however, that $f$/V$^{1/3}$ is usually a decaying function of V. The Dussan equation shows that the change of $f$/V$^{1/3}$ with V is also expressed in contact angle variation. Our results, however, illustrate that contact angle variation within the scatter suffices to explain the force variation. It becomes easier to predict contact angle variation based on force variation than vice versa. $f$/V$^{1/3}$ appeared to decrease more with V in the systems studied. [Preview Abstract] |
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C1.00058: Comparison of AFM and Density Functional Theory Force Profiles Keenan Dotson, John McCoy, Daniel McCoy, Sergio Mendez, John Curro, Brett Andrzejewski, Gabriel Lopez, David Keller Monolayer films of tethered poly(N-isopropylacrylamide) in water (and related systems) are investigated with Atomic Force Microscopy. The resulting profiles are analyzed with Density Functional Theory. Of interest are the effects of temperature, degree of polymerization, and surface coverage upon the colloidal force. A particular challenge is the modeling of the adhesive behavior of the film to the coated AFM tip. [Preview Abstract] |
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C1.00059: Influence of Molecular Weight and Processing Conditions on the Thermal Stability of Nanoimprinted Polymer Structures Yifu Ding, Hyunwook Ding, Kyle Alvine, Brian Okerberg, Jing Zhou, Jack Douglas, Alamgir Karim, Christopher Soles We study the influence of both molecular weight of a polymer resist and the nanoimprint process conditions on the thermal stability of the patterned polymer structures. Specifically, we measure the decay rate of the imprinted polymer patterns during thermal annealing by combining diffraction/reflection of X-ray/light and AFM. As a result, highly entangled polymers are found to contain large amount of residual stresses introduced by the imprinting process, which dominates the pattern decay during the annealing. Levels of the residual stresses can be controlled by the imprinting conditions. On the contrast, unentangled polymers behavior like a Newtonian liquid with no sign of residual stress resulted from the patterning process. Furthermore, we also observe correlated lateral pattern instability during the annealing, in addition to the vertical pattern decay. This lateral instability is greatly enhanced when the surfactants were added during the imprint process. Implications of these findings on the nanoimprint fabrication processes will be discussed. [Preview Abstract] |
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C1.00060: Transitions in Nanometer thin films - Investigations by AC Chip calorimetry H. Huth, A. Minakov, C. Schick Calorimetry is known as a very powerful tool for the characterization of a wide variety of materials and their transitions. The combination of silicon technology and calorimetry opens up new possibilities in this research area as demonstrated recently. Based on a differential AC calorimeter we show an improved experimental setup combining the advantages of the different methods. The measurements are done at slow scanning or at constant bath temperature. The frequency chosen provides a well defined time scale of the experiment. In several cases, e.g. at glass transition, a direct comparison with results from other dynamic methods like dielectric spectroscopy is possible. Due to the differential setup we achieve a sensitive in the pico Joule per Kelvin range allowing to measure samples below one nanogram and consequently films down to 1 nm thickness. Because of the small total heat capacity (addenda + sample) not only a high sensitivity is achieved but AC measurements at relative high frequencies are possible too. [Preview Abstract] |
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C1.00061: Adhesion of Surface Ribbons Chelsea Davis, Alfred J. Crosby Inspired by numerous examples in nature, significant research advances have recently demonstrated the ability to use topographic surface patterns to control critical surface properties such as adhesion and friction. Although most efforts have focused on the use of lithographically-fabricated fibrillar structures, alternative patterns such as surface wrinkles have also been shown to be advantageous for the control of adhesion. We present a new surface structure for soft, elastomeric materials called surface ribbons. These surface structure shells are formed by the controlled buckling of a surface-attached film, and offer many advantages for the control of adhesion, including on-command responsiveness. We present methods for the fabrication of these structures, results demonstrating the ability for these structures to enhance adhesion, and scaling relationships that link the structures' geometry, materials properties, and measured surface properties. In addition to providing attractive avenues for the creation of responsive surfaces, these structures offer fundamental insight into the mechanisms controlling general patterned surface adhesion. [Preview Abstract] |
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C1.00062: Analysis of the spincoating of thickness gradient polymer films Monika Michalek, John Dutcher Thickness gradient polymer films can be prepared by dropping one drop of a polymer solution onto a spinning substrate at a position that is displaced from the axis of rotation, resulting in films in which the thickness increases with increasing radial distance. We have studied the spincoating of polystyrene thickness gradient films in two ways: (1) by fitting the measured radial thickness profiles of the dry films to a simple analytical model; and (2) by measuring the drying of the films during the spincoating process by monitoring the time dependence of the intensity of laser light reflected from the film. The results obtained for solutions of polystyrene dissolved in solvents of different volatility will be compared. [Preview Abstract] |
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C1.00063: Segmental dynamics of thin polymer films probed by dye reorientation. Keewook Paeng, Hau-Nan Lee, Stephen Swallen, Mark Ediger We have studied the dynamics of both freestanding and supported polymer thin films (down to 25 nm) by probing reorientation of dilute dye molecules. Well below Tg, dye molecules were photobleached using intense linearly polarized light creating an anisotropic distribution. Anisotropy was measured using circularly polarized light and probing fluorescence parallel and perpendicular to the bleaching beam. Temperature was linearly ramped during anisotropy measurement; near Tg, the anisotropy dropped to zero. The dynamics of a 50 nm poly (tert-butyl styrene) film were faster than bulk dynamics by an amount equivalent to a 5 K shift in Tg. Faster dynamics compared to bulk films were also found for polystyrene and these results will be compared to the previous Tg measurements. Four different polymers, polystyrene, poly (tert-butyl styrene), poly (methyl methacrylate), and poly (2-vinyl pyridine) were studied. [Preview Abstract] |
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C1.00064: Drop retention force as a function of rested time Rafael Tadmor, Aisha Leh, Kumud Chaurasia, Prashant Bahadur, Lan Dang The force, f, required to slide a drop past a surface is shown to be a growing function of the time, t, the drop waited resting on the surface prior to the commencement of sliding along it. In this first report on the ``rest time'' effect we demonstrate the existence of this phenomenon in different systems, which suggests that this phenomenon is general. We show that df/dt is never negative. The shorter the resting times, the higher df/dt is. As the resting time increases df/dt decreases towards zero (plateau) as t tends to infinity. We attribute this phenomenon to the corrugation of the surface by the drop due to the unsatisfied normal component of the Young equation. [Preview Abstract] |
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C1.00065: Controlled Growth of Organic Semiconductor Films Using Liquid Crystal Solvents Kevin Bufkin, Brooks Ohlson, Ben Hillman, Brad Johnson, David Patrick Interest in using organic semiconductors in applications such as large area displays, photovoltaic devices, and RFID tags stems in part from their prospects for enabling significantly reduced manufacturing costs compared to traditional inorganic semiconductors. However many of the best performing prototype devices produced so far have involved expensive or time-consuming fabrication methods, such as the use of single crystals or thin films deposited under high vacuum conditions. We present a new approach for growing low molecular weight organic crystalline films at ambient conditions based on a vapor-liquid-solid growth mechanism using thermotropic nematic liquid crystal (LC) solvents. Tetracene is deposited via atmospheric-pressure sublimation onto substrates coated by a LC layer oriented using rubbed polyimide, producing films that are highly crystalline, with large grain sizes, and possessing macroscopic uniaxial orientation. This poster will describe the growth mechanism, discuss the effects of processing conditions such as LC layer thickness, substrate temperature and flux rate, and compare the results to a model of diffusion limited aggregation accounting for the finite thickness of the solvent layer. [Preview Abstract] |
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C1.00066: Single-chain conformation and dynamics in connected chambers: Theory and simulation of translocation and threading Erica Saltzman, ChiuTai Andrew Wong, Murugappan Muthukumar Confinement in a series of small chambers connected by narrow pores may be viewed as a model system for translocation in the absence of an applied force, as well as for more general instances of spatially heterogeneous confinement relevant to biological and materials applications. Brownian dynamics simulations are performed for single chains equilibrated in this system, and a theoretical treatment is developed. Short chains undergo translocation between chambers, while long chains thread several chambers and diffuse more rapidly. Measures of chain size and mobility are analyzed and compared. [Preview Abstract] |
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C1.00067: Monte Carlo simulations of the selective adsorption of heteropolymers on heterogeneous surfaces Yongmei Wang, Jesse Ziebarth Lattice Monte Carlo simulations are used to study selective adsorption of heteropolymers on heterogeneous surfaces. We focus on how statistical correlation between sequence types and surface patterns affects the critical adsorption point (CAP). We show that statistically patchy and statistically alternating surfaces selectively adsorb blocky and alternating chains, respectively, while surfaces with a random distribution of attractive sites do not selectively adsorb any types of chains. We also show that selectivity is maximized near the CAP. Selectivity of checker-board surfaces have also been examined and we show that higher order parameters describing sequences ands surface patterns are needed to fully characterize the selectivity of these surfaces toward different sequences. [Preview Abstract] |
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C1.00068: Progress on a `spectral filtering' for SCFT algorithms: Removing topological defects in block copolymer simulations Scott Sides, Bobby Sumpter Using block copolymers as mesoscale templates has potential applications for improved photovoltaic devices, fuel-cells and magnetic storage media. For many of these applications the long-range order and orientation of the copolymer phase-separated domains is crucial. Self-consistent field theory (SCFT) for dense polymer melts has been highly successful in describing complex morphologies in block copolymers. Field-theoretic simulations based on SCFT theory are able to access large length and time scales that are difficult or impossible for particle-based simulations such as molecular dynamics. It has been shown that real-space numerical SCFT calculations can describe certain features of topological defects in a bulk copolymer. However, for large SCFT simulations the presence of these topological defects can obscure the identification of the appropriate lowest-energy space group for a complex block copolymer mixture. A 'spectral filtering' algorithm has been shown to help reduce the presence of topological defects in SCFT calculations of block copolymer structure by removing certain frequency components of the chemical potential fields during the simulation. Further progress on this filtering method will be presented and shown to improve the removal of defects in large, 3D-SCFT simulations. [Preview Abstract] |
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C1.00069: Computer simulation of the formation of random-blocky copolymers Lawrence Strickland, Jan Genzer, Carol Hall A recent computational study described a new method for producing random copolymers (RCPs) with tunable monomer sequence distribution; the technique is based on adjusting the size of a homopolymer (say A) coil and performing a chemical reaction (``coloring'') with certain chemical moieties (say B) on the accessible monomers of the homopolymer chain. While experimental evidence exists that can relate the comonomer distribution in the A-B copolymer to the original homopolymer dimension in the solvent, the ``coloring'' mechanism is difficult to reconcile as there exists competing mechanisms, involving the coloring process itself and the tendency for the copolymer to change conformation during the ``coloring'' driven by the changing solubility of the resultant A-B copolymer relative to that of the A homopolymer. In this work we use discontinuous molecular dynamics (DMD) to comprehend the formation of A-B copolymers. Our RCPs were constructed by reacting homopolymers in varying solvents and reactant concentrations. We show how we can selectively tune the randomness by varying chain length and system temperature. While increasing system temperature leads to formation of A-B copolymers with random distribution of segments, increasing monomer solubility leads to A-B copolymers with random-blocky co-monomer sequences. [Preview Abstract] |
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C1.00070: Computational Models of Complex Microstructures of Amphihilic Diblock Copolymers in Dilute Solution Jesse Boer, Apichart Linhananta The formation of micelles and vesicles in dilute solutions of amphihilic diblock copolymers are investigated by the real-space self-consistent field theory (SCFT) in two dimensions and by a Monte-Carlo lattice model in three dimensions. The real-space SCFT method produced rodlike and spherelike micelles and vesicles. It is found that the shapes of the microstructures are determined by the initial conditions in the SCFT algorithms, and that, in general, vesicles have lower free energy than micelles. In contrast, in the Monte Carlo simulation of the lattice model, it is found that as the volume fraction of copolymer increases, the microstructure go from spherelike micelles to rodlike micelles to vesicles and, at high fraction, to the lamellar phase. [Preview Abstract] |
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C1.00071: Secondary Forces as a Driving Mechanism for Thermally Induced Drug Release in ROMP based Polymers Casey Kimball, Shaw L. Hsu, Greg Tew To control drug release via a thermal mechanism is important from both a fundamental and application standpoint. Traditionally, biocompatible polymers with secondary interactions in the backbone have been investigated. Instead, we have synthesized a novel poly(ethylene oxide) crosslinked Ring Opening Metathesis Polymerization based polymer comprised of a polynorbornene derived backbone with multiple substituents groups, including a tetra-ol, diamine, dicarboxylic acid and amino acid based side chains. The strength of secondary interactions based on the functional groups present plays a critical role in chain dynamics and thermal properties. DSC measurements revealed a substantial change in the thermal transitions to be as high as thirty degrees, depending on substituent group and crosslinking properties. Infrared spectroscopy has been employed to characterize the functional groups present. It has been revealed that the strength of the hydrogen bonds strongly correlated with the transition temperature. Additionally the presence of water has a perturbing effect of disrupting the hydrogen bonding network and affecting the chain dynamics of the overall crosslinked system. [Preview Abstract] |
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C1.00072: DNA Electrophoresis using entropic trapping Haobin Luo, Dilip Gersappe We examine the effects of surface patterning on DNA electrophoresis. Using chemically patterned stripes of different widths we can control the separation of DNA. Due to entropic trapping of the chains on the stripes, depending on the width of the stripe and the length of the DNA, we show (using MD simulations) that it is possible to separate chains in increasing order of length and in decreasing order. We show an experimental realization of this effect and illustrate how DNA motion on the surface can be influenced by both the width of the stripe and the periodicity of the pattern. [Preview Abstract] |
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C1.00073: Protein adsorption at calcium oxalate monohydrate crystal surfaces. J. Wesson, X. Sheng, J. Rimer, T. Jung, M. Ward Calcium oxalate monohydrate (COM) crystals are the dominant inorganic phase in most kidney stones, and kidney stones form as aggregates of COM crystals and organic material, principally proteins, but little is known about the molecular level events at COM surfaces that regulate COM aggregation. We have examined the influence of polyelectrolytes on the force of adhesion between chemically modified atomic force microscopy (AFM) tips and selected COM crystal faces in saturated solution. In general, we found that polyanions bind to COM surfaces and block adhesion of a carboxylate functionalized AFM tip, while polycations had no measureable effect on adhesion force under the same conditions. We did observe a unique absence of interaction between poly(glutamic acid) and the COM (100) face compared to other synthetic polyanions, and some native urinary protein structures also exhibited unique face selective interactions, suggesting that simple electrostatic models will not completely explain the data. [Preview Abstract] |
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C1.00074: Phase Transisions in Superparamagnetic Polymer Brush Particles Annette Schmidt, Andreas Kaiser Nanostructured inorganic / organic hybrid materials play an outstanding role in modern technology. We present results on the synthesis and characterization of novel thermo- and magnetoresponsive polymer brush coated particles. The investigated system is composed of nanocrystalline magnetite (Fe$_{3}$O$_{4})$ as an inorganic core and a covalently anchored polystyrene (PS) shell. In cyclohexane, a thermoresponsive magnetic fluid is obtained due to a critical solution behaviour of the PS arms. cyclohexane. Beside the phase transition of Fe$_{3}$O$_{4}$@PS particles, the well known coil-to-globule transition of Fe$_{3}$O$_{4}$@PS particles in cyclohexane is investigated. Both phenomena are compared to the behaviour of linear polymeric arms. The presented results show that magnetic brush particles are well-suited as a model system for the investigation of temperature transitions of surface-attached polymers. [Preview Abstract] |
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C1.00075: 3D Analysis of Lattice Defects in the Gyroid Network Structure of a Block Copolymer/Homopolymer Blend Satoshi Akasaka, Tetsuro Okamoto, Vincent H. Mareau, Hirokazu Hasegawa The bicontinuous microdomain structures known as gyroid cubic phase (\textit{Ia}$^{-}$3$d)$ can be observed in a narrow composition region of a block copolymer system. In the study of the casting process of the polystyrene-block polyisoprene (SI)/homopolystyrene (hS) blend with a particular composition from toluene solution, we observed that sponge phase, an irregular network structure, transformed into gyroid phase by expelling excess hS outside of the gyroid grains. During the growth of the gyroid grains, a variety of interesting lattice defects appear due to the remaining excess hS in the grains. Such defects may be useful in designing photonic band-gap devices based on gyroid cubic phase if we can control them. However, the analysis of the defect structures in gyroid network is not easy since gyroid network itself is too complex. So, we employed a novel technique, electron tomography, to visualize the 3D defect structures in gyroid network. In this presentation, we demonstrate how useful it is and clarify the defects structures in 3D [Preview Abstract] |
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C1.00076: Phase Behavior of Polymer Blends Containing End-Associating Polymers Michelle Wrue, Mitchell Anthamatten Polymer blending is an important route to the creation of new polymeric materials with superior processing and tunability. We are studying the effects of strong, site-specific, hydrogen-bonding groups on the phase behavior of traditional polymer blends exhibiting upper critical solution temperature (UCST) behavior. Ureidopyrimidinone (UPy) functional groups self-associate through the formation of four hydrogen bonds. We have synthesized telechelic ureidopyrimidinone (UPy) functionalized polystyrene (PS) and poly(4-methyl styrene) (P4MS). We have used these materials in ternary polymer-polymer-solvent systems to investigate the miscibility of blends containing UPy-functionalized polymers. Polymer pairs studied include PS/polybutadiene (PB) and PS/P4MS. Phase behavior and end-association were studied using laser light scattering and dilute solution viscometry. Data from PS/PB/toluene blends containing only one functionalized polymer, PS, indicate a reduction in miscibility relative to the corresponding parent blend. PS/P4MS blends in which both polymer components contain the UPy functional group are also being studied. [Preview Abstract] |
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C1.00077: Self-assembly of rod-coil block copolymers from weakly to moderately segregated regimes Raffaele Mezzenga, Nicolas Sary, Georges Hadziioannou, Cyril Brochon We report on the self-assembly behaviour of two homologue series of rod-coil block copolymers in which, the rod, a $\pi $-conjugated polymer, is maintained fixed in size and chemical structure, while the coil is allowed to vary both in molecular weight and chemical nature. This allows maintaining constant the liquid crystalline interactions, expressed by Maier-Saupe interactions, $\omega $, while varying the tendency towards microphase separation, expressed by the product between the Flory-Huggins parameter and the total polymerization degree, $\chi $N. Therefore, the systems presented here allow testing directly some of the theoretical predictions for the self-assembly of rod-coil block copolymers in weakly segregated regime. The two rod-coil block copolymer systems investigated, were poly(DEH-p-phenylenevinylene-b-styrene), whose self-assembly takes place in the very weakly segregated regime, and (DEH-p-phenylenevinylene-b-4vinylpyridine), for which self-assembly behaviour happens under increased tendency towards microphase separation, hereby refereed as moderately segregated regime. Experimental results for both systems are compared with predictions based on Landau expansion theories. [Preview Abstract] |
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C1.00078: Self-Organization on Multiple Length Scales in ``Hairy-Rod''--Coil Block Copolymer Supramolecular Complexes Raffaele Mezzenga, Matthew Hammond, Harm-Anton Klok A peptide-synthetic hybrid block copolymer, poly(ethylene oxide)-block-poly(L-glutamic acid), is demonstrated to form supramolecular complexes with primary alkylamines of varying alkyl chain length (8 to 18 methylene units) in organic solvents via acid-base proton transfer and subsequent ionic bonding. The peptidic block being in the $\alpha $-helical conformation, these materials behave as coil-``hairy rod'' block copolymers, and show hierarchically self-organized nanostructures in the solid state; X-ray scattering measurements show mesomorphic behavior at the length scales of both the overall block copolymer and the polypeptide-alkylammonium complex. [Preview Abstract] |
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C1.00079: Self-Consistent Field Theory Simulations of Confined 2D Block Copolymer Thin Films Su-Mi Hur, Glenn Fredrickson, August Bosse, Edward Kramer, Carlos Garcia-Cervera We present self-consistent field theory (SCFT) simulations of block copolymers confined in a square well in order to guide self-assembly towards defect-free in-plane arrays. In particular, tetragonal (square) packing, which is thought to be crucial to developing novel information storage and electronic devices, has been observed in simulations of thin films of AB diblock copolymers with suitable A homopolymer additives confined in square wells. While the A-B + A system only supports square lattices of limited sizes (up to 4x4), we were able to produce large-area defect-free square lattices using blends of chemically different diblock copolymers with suitable attractive interactions between blocks. Our simulations demonstrate that order originates at the walls and then permeates throughout the system. [Preview Abstract] |
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C1.00080: Orientation Control of Diblock Copolymer Thin Films by the Addition of Amphiphilic Surfactants Jeong Gon Son, Kookheon Char, Paul F. Nealey, Huiman Kang The precise control of the orientation of block copolymer (BCP) thin film is crucial to fully exploit the potential of these materials for applications in nanotechnology. The orientation control is, however, challenging as BCP nanodomains spontaneously self-assemble in a configuration that minimizes the total free energy of the system. The perpendicular orientation of BCP domains, in particular, has potential for device applications. In this presentation, we would like to introduce a new approach for the perpendicular orientation of BCP domains from the top of a BCP film toward a bottom substrate. Our concept is based on the properties of surfactants that naturally locate at interfaces to tailor the surface properties of materials. We demonstrate how the segregation of low molecular weight surfactants, oleic acid (OA) in present case, at the top surface of a PS-b-PMMA BCP thin film can easily create energetically neutral conditions for the BCP, resulting in the desired perpendicular orientation. The main advantage of this new approach is that nano-scale patterns can be generated at the top of a BCP film after short annealing time on any substrates. We verified the structures and mechanisms of the surfactant-assisted perpendicular orientation of thin block films using AFM, SEM, GISAXS and Neutron Reflectivity. [Preview Abstract] |
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C1.00081: Diblock copolymer thin films: Compressed fluid induced order Peter Green, Abraham Arceo We show that liquid and super critical CO$_{2}$ induces long-range order into thin film, symmetric, polystyrene-b-polymethylmethacrylate (PS-b-PMMA) diblock copolymers, supported by SiO$_{x}$/Si substrates, in a temperature range where both bulk and thin films of these materials remain ordered. Under vacuum conditions the substrate induces order the thin films at temperatures significantly above the bulk order-disorder transition temperature. Ordering occurs at $\chi $N=7.94, where $\chi $ is the Flory-Huggins interaction parameter and N is the degree of polymerization, which is below the bulk value of ($\chi $N)$_{bulk}$=10.5. In the presence of CO$_{2}$, the transition shifts to yet lower values of $\chi $N, indicating a more significant degree of incompatibility between the PS and PMMA components under these solvent conditions. This behavior is in contrast to bulk systems, where the PS-b-PMMA systems of $\chi $N$>$10.5 become phase mixed in the presence of liquid or super critical CO$_{2}$. [Preview Abstract] |
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C1.00082: Crystal Orientation of Polyethylene oxide in a Defect-Free 1D Confined System of Poly ethylene oxide-b-Polystyrene Diblock Copolymer Single Crystals Ming-Siao Hsiao, Joseph X. Zheng, Ryan M. Van Horn, Roderic P. Quirk, Stephen Z. D. Cheng, Bernard Lotz, Edwin L. Thomas, Hsin-Lung Chen Highly oriented crystalline-amorphous block copolymers under a large amplitude shear open a window for studying crystal orientation evolution within a one-dimensional confined environment at different degrees of supercooling; however, inevitable defects and internal stresses are the main cause of releasing the confinement effect on polymer crystallization. Defect-free, 1-D confined lamellae of 10 nm PS-b-PEO solution grown single crystal mats were used to study the crystal orientation evolution as a function of crystallization temperature (Trc) via recrystallization. From DSC and temperature dependent SAXS, it was found that a hard-confined environment for PEO crystallization is created by vitrified PS layers while the middle PEO layer is in the melt state. From the analysis of 2D WAXD patterns, it is shown that the PEO c-axis orientation changes from homogeneous at low Trc to homeotropic at higher Trc. The mechanism inducing crystal orientation change is investigated in detail in this publication. [Preview Abstract] |
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C1.00083: Well-Defined Fullerene-Containing Diblock Copolymers Based on Regioregular Poly(3-hexylthiophene) and Poly(methyl methacrylate): Synthesis and Photovoltaic Properties Jea Uk Lee, Won Ho Jo, Ali Cirpan, Todd Emrick, Thomas Russell Polymer solar cells based on conjugated polymer and fullerene materials have opened a new avenue to develop economically renewable energy resources. Recently, bulk heterojunction solar cells fabricated by simple blending regioregular poly(3- hexylthiophene) with fullerene derivatives have resulted in great improvement in the power conversion efficiency. Although a remarkable progress has been made, bulk heterojunction solar cells still have several problems. First, in all of the bulk heterojunction solar cells, the conjugated polymer and electron acceptor have been randomly interspersed throughout the film. Second, the blend of conjugated polymer and fullerene derivatives usually results in macrophase separation, limiting the charge separation and thus the power conversion efficiency in a photovoltaic device. We have designed and synthesized novel diblock copolymers composed of regioregular poly(3-hexylthiophene) and fullerene containing poly(methyl methacrylate). The diblock copolymers self-assemble into nanostructured morphologies (lamellae or hexagonally packed cylinder), which provide exitons with large interfaces for charge separation on the nanometer scale. [Preview Abstract] |
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C1.00084: Point Mutations Effects on Charge Transport Properties of the Tumor-Suppressor Gene $p53$ Rudolf A. Roemer, Chi-Tin Shih, Stephan Roche We report on a theoretical study of point mutations effects on charge transfer properties in the DNA sequence of the tumor-suppressor $p53$ gene. On the basis of effective tight-binding models which simulate hole propagation along the DNA, a statistical analysis of mutation-induced charge transfer modifications is performed. In contrast to non-cancerous mutations, mutation hotspots tend to result in significantly weaker {\em changes of transmission properties}. This suggests that charge transport could play a significant role for DNA-repairing deficiency yielding carcinogenesis. [Preview Abstract] |
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C1.00085: Endohedral Fullerenes in Organic Thin Film Photovoltaic Devices Russel Ross, Edward VanKeuren, Martin Drees, Claudia Cardona, Brian Holloway, Dirk Guldi Cost factors in inorganic solar cells have opened up a new path to less expensive manufacturing techniques using bulk heterojunction polymer/fullerene based solar cells. Using empty cage fullerene derivatives as the acceptor material, state-of-the-art organic photovoltaics currently display $\sim$5\% overall conversion efficiency. One of the main factors limiting the efficiency in organic solar cells is the low open circuit voltage. The open circuit voltage is governed by the molecular orbitals of the donor and acceptor material; therefore better matching of the orbitals will lead to improved voltages. We present a novel acceptor material based on TRIMETASPHERE$^{\textregistered}$ carbon nanomaterials (TMS). TMS are endohedral metallofullerenes that consist of a trimetal nitride cluster enclosed in a C80 cage. First-generation TMS derivatives have been synthesized; electrochemical and photophysical studies show behavior consistent with C60 but with improved molecular orbitals. The electrochemical data suggests a maximum voltage increase of up to 280 mV over C60-PCBM-based devices. Organic solar cell devices are currently under construction and performance results will also be presented. [Preview Abstract] |
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C1.00086: Multilayer polymer light emitting diode (PLED) devices studied using resonant soft x-ray reflectivity Cheng Wang, B. Watts, T. Araki, H. Ade, A. Hexemer, A. Garcia, T.-Q. Nguyen, G.C. Bazan, K.E. Sohn, E.J. Kramer The performance of multilayer PLED devices is likely to be strongly affected by the structure of the interface between the active layers. Using resonant soft x-ray reflectivity (RSoXR), the contrast between polymer components can be greatly enhanced by tuning the photon energy to absorption resonances near 285 eV and the interfacial width can be measured. The interfacial widths $w$ of model bilayers of poly[9,9-bis(6'-N,N,N,-trimethylammoniumhexyl)fluorene-co-alt-1,4 phenylene~ bromide] (PFNBr)/poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) on SiO2 substrates were manipulated by changing the sample preparation process and were measured by RSoXR, allowing $w$ to be correlated to device performance. In addition, for a real PLED device with a more complicated multilayer structure, but missing the top Al electrode, it was demonstrated that the top four interfaces can be fully characterized using RSoXR, adjusting the material contrast in order to selectively observe different layers by tuning to different photon energies. [Preview Abstract] |
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C1.00087: Breath Figure Templated Assembly of Ordered and Disordered Array of Holes in Polymer Films Vivek Sharma, Sai M. Gogineni, Matija Crne, Mohan Srinivasarao Breath figures are patterns formed when water vapor from our breath condenses over a cold substrate. These patterns, which mimic the behavior of dew or chemical vapor deposition, comprise of drops with range of self-similar sizes, and form through coalescence assisted growth. Water drops that condense over evaporating polymer solutions can organize into close packed arrays, and template nicely ordered arrays of holes in polymer films. Using experiments and theory, we examine the role of various parameters that contribute to the formation of ordered assembly. We will present our findings about how the choice of polymer and polymer concentrations and air flow conditions influences the extent of order and the pore size. [Preview Abstract] |
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C1.00088: Carbon nanotube based gecko inspired self-cleaning adhesives Sunny Sethi, Liehui Ge, Pulickel Ajayan, Dhinojwala Ali Wall climbing organisms like geckos have unique ability to attach to different surfaces without use of any viscoelastic material. The hairy structure found in gecko feet allows them to obtain intimate contact over a large area thus allowing then to adhere using van der Waals interactions. Not only high adhesion, the geometry of the hairs makes gecko feet self cleaning, thus allowing them to walk continuously without worrying about loosing adhesive strength. Such properties if mimicked synthetically could form basis of a new class of materials, which, unlike conventional adhesives would show two contradictory properties, self cleaning and high adhesion. Such materials would form essential component of applications like wall climbing robot. We tried to synthesize such material using micropatterened vertically aligned carbon nanotubes. When dealing with large areas, probability of defects in the structure increase, forming patterns instead of using uniform film of carbon nanotubes helps to inhibit crack propagation, thus gives much higher adhesive strength than a uniform film. When carbon nanotube patterns with optimized aspect ratio are used, both high adhesion and self cleaning properties are observed. [Preview Abstract] |
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C1.00089: Understanding the Structure and Phase Behavior of Model DNA-Linked Nanoparticles by Monte Carlo Simulations. Juan Araque, Athanassios Panagiotopoulos, Marc Robert The high specificity and selectivity of DNA hybridization makes nucleic acid recognition a powerful tool for bottom-up assembling approaches. Here, we propose a coarse-grained model to address the question of how nanoparticles tethered with single stranded DNA self-assemble in solution. Our approach employs a computationally efficient discretization of hard-core interactions and a high-coordination lattice, in combination with parallel tempering and multicanonical Monte Carlo simulations. This simplified model of DNA strands not only accounts for all physically relevant interactions, but also enables a significant reduction of the problem dimensionality. We discuss the effects of a number of system parameters and assembling architectures on the equilibrium structures and phase behavior. In addition, we establish the relation of these results with experimental observations. [Preview Abstract] |
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C1.00090: Relationship Between Interfacial Strength and Materials Properties in Hybrid Organic/Inorganic Nanomaterials Chad Snyder, Mickey Richardson, Jing Zhou, Gale Holmes, Alamgir Karim, Nandika D'Souza Thermal interface materials (TIM's) are critical to the semiconductor electronics industry for heat dissipation, a potential show-stopper for future technology nodes. Essentially, an epoxy nanocomposite, TIMs suffer from a series of typical nanocomposite limitations including heat conduction in nanoscale inclusions, nanoparticle dispersion, void formation with thermal cycling, and interfacial resistance between the matrix and filler. It is postulated that the interfacial adhesion between the matrix and nanofiller is at the root cause of many of these difficulties, however, few techniques exist to characterize this critical property. Compounding this are the overall difficulties associated with characterizing these materials in their ultimate applications, i.e., thin films. To this end, a novel series of organic/inorganic hybrid nanostructured materials based on layered double hydroxides in epoxy matrices were designed as a test bed to develop the measurement techniques needed to elucidate the relationship between the material structure and dynamics and the ultimate materials properties. Initial results are presented based on characterization by mechanical, dielectric, and thermal spectroscopies. [Preview Abstract] |
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C1.00091: Control of Polymer Translocation with External Forcing Santtu Ollila, Kaifu Luo, Tapio Ala-Nissila, See-Chen Ying We investigate the dynamics of driven polymer translocation through a nanopore using two-dimensional Langevin dynamics simulations within the bead-spring model. A pulling force $F$ is exerted on the first monomer whilst there is an opposing force $F_E$ in the pore. For this setup, we calculate the distribution of translocation time $\tau$, which is defined as the time for the polymer to traverse from one side of the membrane to the other, and the waiting time $t_W$, which is defined as the time between the translocations of the $i$th and the $(i+1)$th bead. As our main result, we characterize the fluctuations and the positions of the beads along the direction of $F$ with respect to the position of the segments in the nanopore, and with respect to the position of the pore. Implications of these results to actual sequencing experiments are discussed. [Preview Abstract] |
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C1.00092: Structural Relaxation of Stacked Ultrathin Polystyrene Films Yung P. Koh, Sindee L. Simon The kinetic behavior of stacked polystyrene ultrathin films is investigated by differential scanning calorimetry (DSC) and compared to the behavior of bulk polystyrene. The fictive temperature (Tf) was measured as a function of cooling rate and as a function of aging time for aging temperatures below the nominal glass transition temperature (Tg). The stacked thin films show enthalpy overshoots in DSC heating scans which are reduced in height but occur over a broader temperature range relative to the bulk response for a given change in fictive temperature. The cooling rate dependence of the limiting fictive temperature, T$_{f}$' is also found to be higher for the stacked thin film samples; the result is that the magnitude of the T$_{g}$ depression between the thin film sample and the bulk is inversely proportional to the cooling rate consistent with other results in the literature. We also find that the rate of physical aging of the stacked thin films is comparable to the bulk when aging is performed at the same distance from Tg; however, when conducted at the same aging temperature, the thin film samples show accelerated physical aging due to their depressed Tg values. This result is in contrast to recent work in the literature on PMMA ultrathin films and on o-TP confined in nanopores. [Preview Abstract] |
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C1.00093: Surface Dynamics Of Homopolymer Brushes Gokce Ugur, Bulent Akgun, Zhang Jiang, Suresh Narayanan, Sanghoon Song, Heegu Lee, William J. Brittain, Hyunjung Kim, Sunil K. Sinha, Mark D. Foster The surface dynamics of polystyrene (PS) and poly($n$-butyl acrylate) (P$n$BA) homopolymer brushes were investigated by X-ray photon correlation spectroscopy for the first time. Within the range of time (0.2 -1100 s) and length scale (0.2-5 um) studied, no fluctuations of the brush surfaces were detectable. When PS brushes of thicknesses in the range of 9-101 nm and high grafting density ($>$0.5 chains/nm\^{}2) were considered at temperatures up to Tg+130C, no relaxation was visible within our window of in-plane wave-vector. Even reduction of the grafting density from 0.6 to 0.1 chains/nm\^{}2 did not bring the relaxation into the window. Likewise, no relaxation was observed for P$n$BA brushes up to 170C above Tg. The suppression of surface fluctuations is a result of covalent tethering. [Preview Abstract] |
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C1.00094: Mass Transport through Dynamic Polymer Networks Containing Reversibly Associating Side-Groups Jiahui Li, Andrew Hilmer, Mitchell Anthamatten, Hung Chung, James McGrath Dynamic polymer networks containing both covalent crosslinks and reversibly associating side-groups were synthesized. Those polymers exhibit novel shape-memory properties due to strong temperature dependence of side-group association. Diffusion of different molecules through polymer networks were studied using three techniques: gravimetric sorption, dye permeation, and fluorescence recovery after photo-bleaching. The dependence of diffusion on temperature, network architecture, solute size, and the interaction between the solute and the network will be discussed. Results show polymer networks with reversibly associating side-groups exhibit unusually strong temperature dependence. This study highlights the potential of these and other dynamic networks to serve as precision drug or reagent release devices. [Preview Abstract] |
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C1.00095: Nanoscale building blocks for the development of novel proton-exchange membranes fuel cells: A first-principles study Philippe F. Weck, Eunja Kim, Chulsung Bae, Naduvalath Balakrishnan We propose a new type of sulfonated aromatic polyarylenes as candidate building blocks for proton-exchange membranes (PEMs) and investigate their electronic and structural properties using first-principles methods. Density functional theory calculations and ab initio molecular dynamics (MD) simulations suggest that desulfonation is limited at high temperatures, owing to the strong aryl-SO3H bond induced by the electron-deficient aromatic ring, and that the proposed polymers exhibit good thermomechanical stability due to the robust aromatic main-chain repeating unit. MD simulations of solvated sulfonated aromatic polyarylenes also emphasize the importance of the Grotthuss-type mechanism for the hydrated proton transport in the vicinity of the sulfonic acid groups. Simulations show that hydrated protons form fluxional defects in the hydrogen bonded network surrounding protogenic groups, the transport mechanism involving inter-conversion between the Eigen cation and the Zundel cation as limiting structures. [Preview Abstract] |
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C1.00096: Meso-scale modeling of block copolymer/colloid nano-composites Marco Pinna, Ignacio Pagonabarraga, Andrei Zvelindovsky We develop a coarse grained simulation technique to study dynamics in soft nano-composites. The system consists of block copolymer melt or solution with nano-size colloidal particles. The time evolution of the system is described by a multiscale approach: a field based simulation for block copolymer component and a particle based method for nano-colloids. The block copolymer is modelled by cell dynamics simulation technique, and colloids are modelled in a spirit of dissipative particles dynamics. A cross interaction term is controlling the interplay of dynamics of both components. The influence of colloids on block copolymer morphology is investigated. [Preview Abstract] |
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C1.00097: Fundamentals of the reinforcement of hairy nanoparticles in rubber compounds Xiaorong Wang The reinforcement of nano-sized polymeric hard core-hairy shell particles in a polymer matrix of chemically identical chains was investigated by dynamical mechanical measurements. We found that the magnitude of reinforcement depended strongly on the phase behavior of the nanoparticles in the polymer matrix. In one phase region, the mechanical response was nearly linear, and the reinforcement was approximately described by the Guth- Smallwood relationship in terms of filler concentration. In two phase region, however, the mechanical response was largely nonlinear, even for strain lower than 1\%, and the reinforcement at low strains was an exponential function of the filler concentration. We show that by tailoring the filler interaction potentials the entire reinforcing mechanism can be changed. [Preview Abstract] |
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C1.00098: Thermoporosimetric Measurements of Network Heterogeneity: Melting Point Depression, Gibbs-Thomson and Flory-Huggins Jinrong Wu, Gregory McKenna To improve understanding the heterogeneity and structure of polymer networks, thermoporosimetry was performed on four model networks of polydimethylsiloxanes (PDMS), which were obtained by tetrakis(dimethylsiloxy)silane crosslinking vinyl terminated PDMS having different molecular weights. The effects of solvent molecular size, solvent quality and PDMS chain length between cross-linkages on the anomalous melting point depression of solvents in these model networks were systematically investigated. The results are analyzed in termos of both the Gibbs-Thompson (GT) equation and the Flory-Huggins (FH) model. Furthermore, we also compared the the pore size distributions obtained from thermoporosimetry for these model networks with the molecular distribution of their oligomers as determined by Matrix Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry. [Preview Abstract] |
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C1.00099: Statistics and dynamics of blends of linear and ring polymers. Michael Lang, Michael Rubinstein This work focuses on conformations and dynamics of blends of linear and ring polymers. Rings in a melt of homo-polymer rings are compressed due to topology, if rings are significantly larger than the entanglement length. Dilute rings with degree of polymerization, $N_{r}$, immersed in a melt of linear polymers with degree of polymerization, $N_{l}$ are almost ideal if $N_{l} > N_{r}^{1/2}$ and swell if $N_{l} < N_{r}^{1/2}$. Dynamics of pure ring melts is enhanced as compared to pure linear melts. Thus, minority of linear chains immersed in ring melt experiences enhancement of diffusion and relaxation. On the other hand, minority of long entangled rings immersed in melt of long entangled linear chains gets temporarily trapped. This leads to a clear reduction in diffusion coefficient while keeping relaxation (as determined by half ring relaxation) almost unaffected. [Preview Abstract] |
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C1.00100: Spectroscopic Analysis of Amorphous Structure in Fluorinated Polymers Shaw L. Hsu, Yuning Yang, Suriyakala Ramalingam High-quality polarized Raman spectra have been obtained for various poly(vinylidene fluoride) (PVDF) structures, crystalline and amorphous. These data encouraged us to revisit the Raman band assignment, especially within the conformational sensitive region (400-1100 cm$^{-1})$ and use the new understanding to characterize the amorphous region. Vibrational bands have been assigned on the basis of observed polarization characteristics and the calculated potential energy distribution (PED). The simulated results agree well with the experimental polarized Raman study. On the basis of the calculated PED, combined with simulation of different conformational sequences (\textit{tttt}, \textit{tttg}, \textit{tgtg}$\prime $, \textit{tggg}, \textit{gggg}), spectroscopic features (band intensity at 648 cm$^{-1}$ and the frequency change of the 856 cm$^{-1}$ band) were associated with the distribution of rotational isomeric states. Two rotational isomeric state (RIS) models were analyzed and compared in the simulation study of the amorphous state. On the basis of the spectroscopic features of experimental and simulated Raman spectra, the conclusion was reached that the model which predicts a higher gauche population more accurately describes the amorphous state. This analysis provides an opportunity to describe the amorphous state in a quantitative manner. [Preview Abstract] |
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C1.00101: Equilibrium Pathyway of Spin-coated Polymer Films Ophelia Tsui, Yong Jian Wang, Fuk Kay Lee, C.-H. Lam, Zhaohui Yang Spin-coating is a common method of making thin polymer films. Recent experiments show that polymer films produced by this method are highly non-equilibrated. By monitoring the temporal evolution of the surface structure of freshly sin-cast polystyrene films on Si with molecular weights, 2.3 $\le $ M$_{w }\le $ 393 kg/mol, we find that the relaxations can be fully accounted for by thermal excitations of surface capillary waves on the film surface. Modeling of the data based on this relaxation scheme leads to excellent agreement between the viscosity of the films and that of the bulk polymers. Our results provide compelling evidence that thickness uniformity is the major cause of the non-equilibration of the films. [Preview Abstract] |
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C1.00102: COMPLEX STRUCTURED MATERIALS |
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C1.00103: Crystal structures and physical properties of nanostructured [(PbSe)$_{0.99}$]$_{m}$(WSe$_{2}$)$_{n}$ (m, n=1-5) Qiyin Lin, Colby Heideman, Clay Mortensen, Ngoc Nguyen, David C. Johnson, Paul Zschack, Catalin Chiritescu, David G. Cahill We report a class of nanostructured misfit layered compounds [(PbSe)$_{0.99}$]$_{m}$(WSe$_{2}$)$_{n}$ (m,n=1-5) synthesized using a modulated elemental reactant technique. The structures are built of two subsystems alternately stacking along the c direction - a distorted rock salt structure (PbSe) and a transition metal dichalcogenide (WSe$_{2}$). These nanostructured compounds have ultra low thermal conductivities, as small as 0.06Wm$^{-1}$K$^{-1}$, which can be attributed to the structural misfit between the components resulting in an unusual balance of order and disorder. Annealing samples under different partial pressures of selenium can be used to control electrical conductivity and the value of the Seebeck coefficient. The relationship between nanostructures and physical properties will be discussed. [Preview Abstract] |
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C1.00104: Low Temperature Study of Mechanically Alloyed EuFeO$_{3}$ Suman Khatiwada, Dereje Seifu Rare-earth (R) and transition metal (T) perovskite Oxides RTO$_{3}$ are of great interest in Physics, besides potential applications in variety of devices. Here, we present study of EuFeO$_{3}$ synthesized by mechanical alloying. The M\"{o}ssbauer measurement on EuFeO$_{3}$ is one of the rare cases where both the R and the T sites are probed in the same compound. Room temperature M\"{o}ssbauer study is already reported [1], here we report low temperature M\"{o}ssbauer measurements. Measurements indicate that hyperfine magnetic field increased with decreasing temperature. The $^{57}$Fe M\"{o}ssbauer spectra depicts that there is only a magnetic sextet at 20K implying pure ferromagnetic state. As temperature increased two non-magnetic states appeared and their propensity increased with temperature. The $^{151}$Eu M\"{o}ssbauer measurements show that the line width at half maxima has a peak between 50K and 100K. [1] Seifu, D., Takacs, L., Kebede, A., ``$^{151}$Eu and $^{57}$Fe M\"{o}ssbauer study of mechanically alloyed EuFeO$_{3}$.'' J. of Mag. and Mag. Matt., \textbf{302}, pp 479 -- 483, 2006. [Preview Abstract] |
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C1.00105: Production of metal cluster patterns using Focused Ion Beams (FIB) Farhad Ghaleh, Niklas Gr\"{o}nhagen, Heinz H\"{o}vel, Lars Bruchhaus, Sven Bauerdick, J\"{u}rgen Thiel, Ralf Jede Nanometer sized pits on graphite (HOPG) substrates can be used as nucleation centers to produce clusters with a narrow size distribution. In previous experiments [1] nanometer sized pits were produced by sputtering and oxidizing the sample. As a result we get nanopits which are a few nanometers wide and only one monolayer deep, distributed at random locations on the surface. In the present study a focused beam of gallium ions is used to produce nanopits in a given pattern on the substrate. The FIB instrument (Raith ionLiNE) is capable of a resolution below 10 nm [2]. Using the nanopits as nucleation centers we are able to produce gold islands as well as silver clusters in a given pattern by depositing metal atoms. Furthermore the nanopit distribution on the surface in combination with Monte Carlo simulations helps investigating the ion beams, e.g. ion distribution, recoils as well as the penetration depth of the ions [3]. In this respect the oxidation of HOPG-samples provides a method to study the ion impact effects. \par \noindent [1] H. H\"{o}vel, Appl. Phys. A 72 (2001) 295; [2] J. Gierak et al., Appl. Phys. A 80 (2005) 187; [3] F. Ghaleh, R. K\"{o}ster, H. H\"{o}vel, L. Bruchhaus, S. Bauerdick, J. Thiel, R. Jede, J. Appl. Phys. 101 (2007) 044301. [Preview Abstract] |
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C1.00106: The role of low frequency vibrational modes localization properties in the glass transition and mechanical stability of glasses Gerardo Naumis It is surprising that although glasses present low frequency vibrational anomalies like floppy modes or the Boson peak, not so much effort has been made in order to understand the relationship between glass transition and low frequency anomalies, which we know are fundamental in the stability of solids. We will show that rigidity theory allows to understand in a systematic way such relationship. Then, the effects of flexibility and chemical composition in the variation of the glass transition temperature are obtained by using the Lindemann criteria, that relates melting temperature with atomic vibrations, and rigidity theory. Using this criteria and that floppy modes at low frequencies enhance in a considerable way the average cuadratic displacement, we show that the consequence is a modified glass transition temperature. This approach allows to obtain in a simple way the empirically modified Gibbs-DiMarzio law, which has been widely used in chalcogenide glasses to fit the changes in the glass transition temperature with the chemical composition [1]. The method predicts that the constant that appears in the law depends upon the ratio of two characteristic frequencies (or temperatures). This constant is estimated for the Se$_{1-x-y}$(Ge$_{y}$As$_{1-y}$)$_{x}$ glass by using the experimental density of vibrational states, and the result shows a good agreement with the experimental fit from glass transition temperature variation. [1] G.G. Naumis, Phys. Rev. B 73, 172202 (2006). [Preview Abstract] |
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C1.00107: Density of States Simulations of Confined Glasses Roland Faller, Jayeeta Ghosh Glassy systems under confinement have been studied with great enthusiasm and effort for the last decades. They are relevant both fundamentally and technically because there is still debate about the nature of glass transition in small geometries which is important for lithographic processes in the semiconductor and other industries. In this work we are using the Wang-Landau approach also known as Density of States Monte Carlo to study glassy systems in bulk and under confinement. We apply the technique to a model binary Lennard Jones glass as well as the small organic glass former Ortho-terphenyl (OTP). For Lennard Jones glasses we use a well tested model. For OTP we start from a united atom model and then derive systematically a coarse grained representation by replacing each phenyl ring with a bead and using the Iterative Boltzmann Inversion. The properties of bulk Lennard Jones model show very good agreement with literature values. The atomistic and coarse grained representations of ortho-terphenyl in the bulk are in good agreement with experiments. Unsupported freestanding films show a lower glass transition than the bulk value. [Preview Abstract] |
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C1.00108: Evolution of SiC nanoclusters from carbon fullerene: A density functional theoretic study. Muhammad N. Huda, Asok K. Ray Formation of SiC fullerene type structures is still an unsolved issue as there is no experimental confirmation reported so far regarding their existence. However, theoretical research results are available in the literature where carbon fullerenes were taken as a base model for SiC fullerene type structures. In this presentation, we show by a systematic study on C$_{20}$ fullerene based SiC structures that this approach may not always reproduce the ground state structures; rather, the energetically favorable structure based on C$_{20}$ could be highly distorted and open structures. In general, Si atoms tend to cluster on the C$_{20}$ base structures. We observed a very systematic linear trend in the evolution of binding energies of SiC clusters from carbon fullerene and a detailed set of results on the electronic and geometric structures of these clusters will be presented. [Preview Abstract] |
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C1.00109: Strong correlation effect in Fullerene C20 Fei Lin, Erik Sorensen, Catherine Kallin, John Berlinsky Successful synthesis of the gas-phase dodecahedral C20 molecule [Nature 407, 60 (2000)] has stimulated great interest in this material. In this talk we report exact diagonalization and quantum Monte Carlo simulation results on the C20 molecule and a possible solid structure [Phys. Rev. B 76, 033414 (2007)]. Our results suggest that strong electronic correlations suppress the Jahn-Teller effect on the dodecahedral molecule, and make the solid an insulator. We also determine the critical value of the interaction strength for the metal-insulator transition. [Preview Abstract] |
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C1.00110: Development of a Semi-empirical Hamiltonian for Boron and the Prediction of Structures for Intermediate-Size Boron Clusters Paul Tandy, Chris Leahy, James Simrall, Yu Ming, Chakram Jayanthi, Shi-Yu Wu In this work, we will present a semi-empirical Hamiltonian for Boron that includes environment-dependent terms and electron correlation terms with the on-site charge calculated self-consistently. This Hamiltonian developed within the LCAO framework has been shown previously to be successful in predicting the properties of intermediate-size silicon and carbon clusters, silicon nanowires and carbon nanotubes, and surface reconstructions of Si(100) and Si(111) surfaces [1]. One of the goals of this work is to obtain the parameterized Hamiltonian for Boron by fitting the properties of small boron clusters (B$_{2 }$to B$_{6})$ and of the bulk phases of Boron, as obtained by our method, to ab-initio calculations [2,3]. The optimized parameters for Boron will be used to predict the structure and stability of intermediate-size Boron clusters. [1] C. Leahy, M. Yu, C.S. Jayanthi, and S.Y. Wu, Phys. Rev. B 74, 155408 (2006) [2] G. Kresse and J. Furthmuller, Phys. Rev. B 54, 11169 (1996). [3] M. J. Freese et al., Gaussian 03, Gaussian Inc. (2004). [Preview Abstract] |
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C1.00111: Electronic Properties of Boron Nitride Nanotubes Brahim Akdim, Ruth Pachter In this work, we present a first-principles study coupled with Green's function formalism to investigate changes in the electronic properties of Boron Nitride Nanotubes (BNNTs) due to analyte adsorption, including hexadecanol, benzaldehyde, and benzoic acid. A transverse electric field representing a gate source is also included in our calculations to study band-gap modulation due to the Giant Stark effect. Effects of the analytes-adsorption on the electronic band structure, density of states, and transport properties will be outlined. [Preview Abstract] |
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C1.00112: Charge noise in liquid-gated single-wall carbon-nanotube transistors Jaan Mannik, Iddo Heller, Anne Jannsens, Serge Lemay, Cees Dekker Inherent electrical noise determines the performance limits of single-wall carbon nanotube transistors (SWNT-FETs) for various applications such as biosensors or components of electronic circuits. Recently, several models have emerged for the noise properties of SWNT-FETs. Here, we aim to verify these models by studying the gate- voltage dependence of noise in SWNT-FETs. We use electrolytic solutions as a gate electrode to be able to map out extensive range of gate voltages. Our data are in contrast with the Hooge's model but support a recently proposed model where noise power is proportional to the square of the derivative of current with respect to gate voltage, i.e. charge noise model. Furthermore, we find that the charge noise scales approximately as the inverse of the length of the SWNT, down to lengths where ballistic transport of charge carriers through SWNT is expected. Our measurements also show that the salt concentration of the electrolyte has a minimal effect on the magnitude of noise in SWNT-FETs. [Preview Abstract] |
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C1.00113: Interaction Effects in Quasi-Ballistic One-Dimensional Channel in AlGaAs/GaAs Structures Matt Bell, Andrei Sergeev, Vladimir Mitin, Aleksandr Verevkin We investigated the interaction effects in a quasi-ballistic one-dimensional channel in AlGaAs/GaAs 2D-electron gas structure. The one-dimensional high-mobility channel was formed using the split-gate technique from the AlGaAs/GaAs 2D-electron gas. Negative bias applied to the split-gates deposited on top of the hall bar allowed us to deplete electrons under the gates and to form an adjustable narrow (width $\sim$ 500nm) and long (length $\sim$ 100$\mu$m) conductive channel with smooth boundaries. This structure allowed us to study electron transport in the quasi-ballistic regime, $T\tau \gg 1$, where $\tau$ is the elastic electron scattering time. We observe a significant difference in the temperature-dependent conductivity of the one-dimensional channel and conductivity of the initial 2D structure. These changes are attributed to the modification of interaction effects in low dimensions. [Preview Abstract] |
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C1.00114: Quantum conductance of carbon nanotube at finite temperature: effect of electron-phonon interactions Narjes Gorjizadeh, Amir A. Farajian, Yoshiyuki Kawazoe Effect of inelastic electron-phonon interaction is studied on electronic transport of semiconducting carbon chains and carbon nanotubes. Absorption and emission of individual phonon modes are investigated as well as collective modes in order to reveal the nature of the interactions and the role of vibrations in quantum transport at finite temperature. The conductance in this study is calculated using non-equilibrium Green's function formalism combined with a tight-binding Hamiltonian description. The phonon spectrum is obtained from frozen-phonon approach and the electron-phonon interaction appears in the calculations as a coupling matrix determined by atomic displacements and phonon eigenvectors. Our results show that the effect of individual electron-phonon interaction on quantum conductance depends on temperature and energy of the phonon mode, regarding absorption and emission processes. The type of the phonon mode is in fact a determining part of the interactions. Decrease of conductance due to e-ph scattering is stronger when the process is scattering of electron out of in-plane phonons which make the in-plane C-C bonds of nanotube or chain vibrate with higher length. The effect of collective modes also suggests the temperature dependent nature of the conductance of a finite size carbon chain and nanotube. [Preview Abstract] |
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C1.00115: Detection of multiple tumor markers using ultra-long carbon nanotube devices Hye-Mi So, Dong-Won Park, Beom Soo Kim, Ki-jeong Kong, Gyoung-Ho Buh, Hyunju Chang, Jeong-O Lee, Jing Kong For the simultaneous detection of multiple tumor markers, we have fabricated ultra-long carbon nanotube sensors that can detect carcinoembryonic antigen (CEA) and prostate specific antigen (PSA), simultaneously. Ultra-long carbon nanotubes, several millimeters long, were grown by ethanol CVD, and fabricated as FET sensors by using conventional photolithography. To functionalize each segment of a single ultra-long nanotube device with multiple-tumor markers, we first functionalize the entire device with CDI-Tween 20 linking molecules, and then immobilized CEA and PSA antibodies using the microfluidic channel. The electrical conductance from CEA-antibody functionalized and PSA-antibody functionalized segment of a ultra-long carbon nanotube device was monitored simultaneously with Ag/AgCl reference electrode as a liquid gate. We will discuss the advantages of long-nanotube device in detail. [Preview Abstract] |
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C1.00116: Low-temperature electronic transport in ferromagnetic cluster embedded carbon nanotubes Caterina Soldano, Swastik Kar, Robert Vajtai, Saikat Talapatra, Saroj Nayak, Pulickel Ajayan We present the electronic transport properties of ferromagnetic material embedded alumina template grown carbon nanotubes. Zero-field temperature dependence of the conductance in ferromagnetic cluster-embedded tubes (FM-MWNT) reveals a L\"{u}ttinger liquid type of behavior in the higher temperature region. Differential conductance measurements for discrete applied magnetic field show the appearance of field-dependent oscillations at low temperatures. The properties of the FM-MWNT were found to change permanently under the application of a magnetic field, indicating that the charge transport is sensitive to the relative magnetic orientations (random or aligned) of the nanoclusters. Those measurements suggest differences between charge transport in a L\"{u}ttinger liquid under the influence of ``random'' and ``ferromagnetically aligned'' impurities. [Preview Abstract] |
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C1.00117: Local-gated single-walled carbon nanotube field effect transistors assembled by AC dielectrophoresis Paul Stokes, Saiful I. Khondaker Carbon nanotube field effect transistors (CNT-FETs) have displayed exceptional electrical properties that are superior to the traditional silicon MOSFET. Directed assembly of individually addressable CNT-FETs at selected positions of the circuit with high throughput needs to be demonstrated for future integrated circuits. Here, we present a simple and scalable technique for the fabrication of CMOS compatible {\&} local gated CNT-FETs. The approach is based on directed assembly of individual single-walled carbon nanotube from dichloroethane via AC dielectrophoresis (DEP) onto pre-patterned source and drain electrodes with a local Al gate in the middle. We find that both metallic and semiconducting nanotubes can be assembled and the centered aluminum gate does not affect the DEP assembly. We also show that the measured device performance such as subthreshold swing of local-gated semiconducting nanotube FET is superior compared to the global back gated device possibly due to channel controlled operation. Directed assembly of local gated CNT-FETs at selected position of the circuit via DEP pave the way for large scale fabrication of CMOS compatible nanoelectronic devices. [Preview Abstract] |
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C1.00118: Microwave Magnetoelectric Coupling in Ferromagnetic-Piezoelectric Nanostructures Yu.J. Pukinsky, M.I. Bichurin, V.M. Petrov, A.V. Filippov, S.V. Bely, G. Srinivasan A theory is presented on the effect of an external electric field on ferromagnetic resonance (FMR) spectra of nanobilayers, nanopillars and nanowires of ferrite and piezoelectrics on MgO or gadolinium gallium garnet substrates. Expressions have been obtained relating the FMR line shift to ME coupling constants. Estimates of ME coupling constants are given. With increasing substrate thickness, the theory predicts a decrease in the ME interaction due to the clamping effect. The strongest ME coupling is expected for ferrite nanopillars in a piezoelectric matrix when the pillar height is large compared to substrate thickness. Numerical estimations are obtained for nanostructures of nickel ferrite and PZT or PMN-PT, yttrium iron garnet and PZT or PMN-PT on MgO or gadolinium gallium garnet substrates. The theory is useful for measurements of ME constants and for the design and analysis of electrically controlled high frequency devices. [Preview Abstract] |
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C1.00119: Enhancement of Magnetoelectric Effect in Ferromagnetic-Piezoelectric Nanostructures at Electromechanical Resonance A.V. Kozin, M.I. Bichurin, Yu.J. Pukinsky, V.M. Petrov, G. Srinivasan A theoretical model is presented for giant magnetoelectric (ME) coupling in nanobilayers, nanopillars and nanowires of ferrite and piezoelectrics on MgO substrates or templates in the electromechanical resonance region (EMR). We take into account clamping effect of the substrate in determining the ME voltage coefficient. ME coefficients are obtained from known material parameters (piezoelectric modules, magnetostriction, stiffness, geometrics) using the solution of the elastodynamic and electrostatic equations. With increasing substrate thickness the theory predicts a shift in the resonance frequency along with a decrease in the ME interaction due to the clamping effect. The strongest interactions are expected for ferrite nanopillars in a piezoelectric matrix when the pillar height is large compared to substrate thickness. As an example, the ME voltage coefficients are estimated for nanostructures based on nickel and cobalt ferrites and piezoelectric PZT and PMN-PT. Although the estimates here are based on bulk material parameters, it can easily be refined to take into account parameters for nanosized components. [Preview Abstract] |
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C1.00120: Electronic Properties of XB$_{6}$ rods: a theoretical study Guangping Li, Jing Lu, R.F. Sabirianov, W.N. Mei, C.L. Cheung, X.C. Zeng Metal hexaborides have varieties of interesting properties and are utilized frequently in technological applications: LaB$_{6}$ has low work function (WF=2.6 eV), and is used as electron emitter. Experiments indicated LaB$_{6}$ nanorods generate stronger electric current than in the bulk case. We focus on the electronic structure of quasi-1D XB$_{6}$ nanorods (X = Si, Ca, Sr, Y, Ba, and most of the rare earth elements) with various widths and breadths for studying the relationship between WF and rod shape by using density functional theory with many-body and relativistic effect included included. Then the electronic structure properties such as Fermi energy and and electrostatic potential are calculated to deduce the work function. Cluster model with several cross section areas is used to investigate the size dependence of ionization potential which is found to decrease with the increasing number of unit cells: 3.3 eV for 1-cell and 2.7 eV for 6-cell cluster. The trend is in reasonable agreement with the experimental studies. [Preview Abstract] |
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C1.00121: Optical Determination of the Flexural Rigidity of Carbon Nanotube Ensembles Prabhakar Bandaru, Chinung Ni, Christian Deck We demonstrate two simple and consistent optical methods for quantitatively determining the flexural rigidity (\textit{EI, }where$ E $is the elastic modulus and $I$, the moment of inertia), a quantity of practical importance in determining the deflection and buckling characteristics of carbon nanotubes (CNTs). This is done through monitoring the deflection of patterned arrays of CNTs subject to fluid flow. In addition to mechanical characterization of filamentous nanostructures, the implications of our work extend to the monitoring of nanoscale fluid flows, for tactile and shear force sensors and the characterization of the mechano-sensor response of cilia in physiology. [Preview Abstract] |
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C1.00122: ABSTRACT WITHDRAWN |
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C1.00123: Crystallization of titania nanotubes powders synthesized by anodization in chloride ions containing solutions Eugen Panaitescu, Latika Menon Titanium oxide nanotubes show good promise in solar energy harvesting for photovoltaic cells and photocatalysis. Pristine anodic titania nanotubes are amorphous, and annealing procedures are employed for their crystallization. We investigated the crystallization process of titania nanotubes powders - obtained by anodization of titanium foils in chloride ions containing solutions - by means of differential scanning calorimetry. We analyzed the influence of parameters such as annealing temperature, annealing time, and temperature scan rate on the phase transition, and on the crystalline properties of the final product. The crystalline powders have been characterized using XRD, RAMAN and diffuse reflection measurements. SEM and TEM imaging has been employed for the investigation of structural properties before and after annealing, and optimal annealing conditions have been identified. [Preview Abstract] |
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C1.00124: The size controlled structural and optical properties of ZnO nanorods Yanwei Chen, Guoliang Yang, Qian Qiao, Yichun Liu In comparison with zero dimensional (0D) nanostructures, one-dimensional (1D) semiconducting nanostructures can facilitate more efficient carrier transport due to decreased grain boundaries, surface defects and disorders, and discontinuous interfaces. In order to utilize 1D ZnO nanostructures for optoelectronic nanodevices, it is essential to have detailed information about their size and other properties and to have the ability to tune these properties in the fabrication process. The application of the 1D nanostructures depend on this tenability. At present, it is still a challenge to fabricate well-controlled 1D ZnO nanostructures and to characterize their properties. We used convenient and flexible sol-gel and hydrothermal methods to synthesize 1D ZnO nanorods with diameters in the order of 10 to 20 nm. The crystallite size, morphology, the structural and optical properties could be well controlled by modulating the crystal nucleus quantity, the solution concentration and the reaction time. We obtained a strong ultraviolet exciton emission for the ZnO nanorods with a size about 10 nm, and also observed the size effect on the photoluminescence. [Preview Abstract] |
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C1.00125: Linear optical response of (6,0) boron nitride nanotubes adsorbed with molecular hydrogen Norberto Arzate, Raul A. Vazquez-Nava, Jorge E. Mejia We performed a study of the molecular adsorption of hydrogen on BN nanotubes. We present {\em ab initio} calculations for the linear optical response of single wall zigzag BN(6,0) nanotubes as a function of the hydrogen adsorption on the exterior surface of the nanotube. The calculation of the linear optical response is performed by using density functional theory with the use of plane waves and pseudopotentials. We consider four different nanotube-structures adsorbed with different coverage of molecular hydrogen. We find optimized atomic coordinates for such structures and calculate binding energies for the molecule of hydrogen on the nanotube. After having the linear response of the considered structures, we have calculated their energy loss function spectra. [Preview Abstract] |
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C1.00126: Magnetoelectric effects in a bilayer of PZT and magnetostriction-graded ferrite G. Srinivasan, V.M. Petrov Magnetoelectric (ME) effects in a piezoelectric-magnetostrictive composite are mediated by mechanical stresses. The effect, in particular, will be enhanced in the electromechanical resonance region (EMR) where the electrical subsystem shows resonance. We show here that further enhancement of the strength of ME interaction is possible with the use of magnetostriction-graded ferromagnet. A material with the grading axis perpendicular to the sample plane is considered. In this case, the thickness dependence of the piezomagnetic coefficients leads to an additional bending strain, resulting in an increase in the ME voltage. Estimates are provided for a bilayer of Zn-doped nickel ferrite and lead zirconate titanate, length 12 mm in length and 2 mm in thickness. The ME voltage coefficient is predicted to increase by a factor of two compared to bilayers with homogeneous ferrite compositions. [Preview Abstract] |
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C1.00127: Magnetoelectric properties of a bilayer of magnetostrictive and piezoelectric nanofilm- studies on substrate pinning effects Gopalan Srinivasan, V.M. Petrov A model is presented for magnetoelectric (ME) effects in the electromechanical resonance region (EMR) for bilayers of magnetostrictive and piezoelectric films on a substrate. The clamping effect of the substrate has been considered in determining the ME voltage coefficient for longitudinal (or radial) and bending modes. The ME effect is predicted to be weak due to pinning and is dependent on the substrate volume. It is shown that the dependence of ME effect on the substrate thickness is much weaker for bending modes than for radial or longitudinal modes. For increasing volume of the substrate, the EMR frequency decreases dramatically. In the case of a rectangular nickel ferrite-PZT nanobilayer on an MgO substrate, the EMR frequency is predicted to be minimum when the substrate is clamped at one end. [Preview Abstract] |
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C1.00128: Theory of magnetoelectric coupling in magnetostrictive-piezoelectric bilayer at bending modes A.V. Filippov, N.A. Fedotov, M.I. Bichurin, V.M. Petrov, G. Srinivasan, Ce-Wen Nan Magnetoelectric (ME) couplings in bilayers of magnetostrictive and piezoelectric phases result from mechanical deformation. Reports to-date focused mainly on enhancement of the ME effect in the electromechanical resonance (EMR) corresponding to radial modes. Recent investigations, however, showed a similar enhancement and a giant ME effect for the bending modes of EMR in ferromagnetic-piezoelectric layered structures. Such bending modes are expected to occur at a much smaller frequencies than radial modes. Here we provide the frequency dependence for longitudinal and transverse ME voltage coefficients using a simultaneous solution of electrostatic, magnetostatic and elastodynamics equations. The resonance ME effect in a bilayer is shown to be strong, depending on boundary conditions. A giant ME coefficient for bending modes is predicted for a bilayer fixed at one end and free at the other. The ME voltage coefficients are estimated from known material parameters (piezoelectric coupling, magnetostriction, elastic constants, etc.) and are compared with data. [Preview Abstract] |
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C1.00129: Photo-formation of Gold Nanoparticles in Au(III)-chitosan-silica aerogels: Dependence on Wavelength and Duration of Exposure Narayanan Kuthirummal, Adam Dean, Richard Smith, Alem Teklu Porous transparent monoliths of Au(III)-chitosan-silica aerogels have been exposed to UV light (320 nm and 207 nm). The photoacoustic spectra of UV-exposed sample revealed a new peak around 526 nm, which corresponded to the plasmon resonance band of gold nanoparticles. Scanning electron microscopic and elemental analysis revealed the presence of gold particles. The plasmon peak is found to shift significantly to the blue side upon irradiating the sample for a longer time interval. It is possible that the nanoparticle heats a bit and could anneal its surface surrounding leading to a slight reduction in size. Electron microscopic observations show morphological changes upon increasing the UV exposure time. A relatively larger shift is observed upon exposing the sample to 200 nm light. Based on the present results, it is concluded that the gold particle size can be altered by changing the duration of light exposure or by using a different wavelength. [Preview Abstract] |
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C1.00130: Elasticity and mechanical properties of nanostructured carbon Maria Fyta, Ioannis Remediakis, Pantelis Kelires We present a theoretical study of nanostructured carbon, emphasizing on diamond nanocomposites. These are materials that consist of diamond nanocrystallites surrounded by a dense amorphous carbon matrix, in a highly stable configuration. We study the properties of such materials by employing a combination of tight-binding molecular-dynamics and empirical-potential Monte-Carlo simulations. We aim to investigate the role of the sp$^2$ component and the grain size on the mechanical properties of these structures. We calculate the rigidity of these materials and their elastic recovery under hydrostatic pressure, and find them to be considerably high compared to those of dense single-phase amorphous carbon. We find that the inter-grain fracture of these materials under shear and tensile load on these materials occurs at the weakly bonded sp$^3$ sites in the amorphous matrix. [Preview Abstract] |
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C1.00131: Thermal conductivity of Cu/carbon nanotube composite films Jung Joon Yoo, Ho-Ki Lyeo, Jae Yong Song, Sungjun Lee, Jin Yu We report the thermal conductivity of Cu/carbon nanotube (CNT) composite films measured by time-domain thermoreflectance, an optical pump-probe method, which measures the time-evolution of temperature change. The thermal and electrical conductivities of sputter-deposited Cu, electroplated nanocrystalline (nc) Cu, and Cu/CNT composite films are measured with a varying content (0 $\sim $ 2 wt{\%}) of CNT in Cu matrix. Both conductivities of nc-Cu films grown on a seed layer of sputtered Cu decrease significantly compared to those of bulk Cu. The thermal conductivity of Cu/CNT composite films made of nc-Cu and randomly oriented CNTs decreases further with the increase of CNT in the films. With the increasing amount of CNT, we also measure the decreasing thermal conductance of interface between Cu/CNT composite film and Al layer that is used as a transducer for the measurement. We will discuss the relations between CNT content and the measured reduction of thermal conductivity and conductance, depending upon the microstructure and impurities of composite films. [Preview Abstract] |
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C1.00132: Percolation Studies of Metal-insulator Composites at Microwave Frequencies Kelly Martin, Jeremy Cardellino, Earnie Johnson, Nicholas Miskovsky, Gary Weisel, Darin Zimmerman, JunKun Ma We present a systematic study of the effective dc conductivity ($\sigma _{eff} )$, complex permittivity ($\varepsilon _{eff} )$, and complex permeability ($\mu _{eff} )$ at microwave frequencies, of metal-insulator mixtures up to and beyond the critical volume fraction ($p_c )$ for conductive percolation. Samples made with varying concentrations of Teflon and micron-sized metallic inclusions of copper, silver, cobalt, and tungsten were subjected to separated microwave electric and magnetic fields of a 2.45 GHz, TM$_{010}$ resonant cavity. Using cavity perturbation techniques, the real and imaginary components of $\varepsilon _{eff} $ and $\mu _{eff} $ were thus measured at room temperature. We observe the expected strong dependence of $\sigma _{eff} $, $\varepsilon _{eff} $, and $\mu _{eff} $ on volume fraction near $p_c $ and analyze the results using McLachlan's Generalized Effective Medium (GEM) theory to extract $p_c $ and the percolation exponents $s$ and $t$. [Preview Abstract] |
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C1.00133: The electronic spectrum of a quasiperiodic potential: from the Hofstadter butterfly to the Fibonacci chain Gerardo Naumis We show that the electronic spectrum of a tigth-binding Hamiltonian defined in a quasiperiodic chain with an on-site potential given by a Fibonacci sequence, can be obtained as a superposition of Harper potentials. Since the spectrum of the Harper equation as a function of the magnetic flux is a fractal set, known as Hofstadter butterfly, here we show that is possible to follow the transformation of the butterfly to a new one that contains the Fibonacci potential and related approximants. As a result, the equation in reciprocal space for the Fibonacci case has the form of a chain with long range interaction between Fourier components. Then we explore the transformation between both spectra, and specially the origin of energy gaps due to the analytical calculation of the components in reciprocal space of the related potentials. As an application, we calculate the correlator of each potential, which allows to obtain some of the localization properties. [Preview Abstract] |
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C1.00134: Ab initio studies of molecular physisorption on graphene David Carey, Daniel Henwood Ab initio studies of the hydrogen and oxygen molecular physisorption have been made on a graphene using both the local density approximation (LDA) VWN and generalized gradient approximation (GGA) PW91 functionals. Binding energies and optimum molecular separations for different graphene lattice sites have been calculated. It was found that the most stable binding energy is for the hydrogen molecule to lie at a hexagon mid-point with a binding energy of 93 meV as calculated for a 96 carbon atom graphene layer using the LDA functional. Lower values of hydrogen molecular binding were found with the GGA functional. [1] Analysis of the charge distribution showed little charge transfer between the molecule and graphene sheet. Oxygen physisorption is shown to be significantly stronger than hydrogen physisorption with calculations using the LDA functional showing binding energies of 280 meV. [1] Daniel Henwood and J David Carey, Phys. Rev. B 75, 245413 (2007). [Preview Abstract] |
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C1.00135: The Transport of Graphene in a Parallel Field Adam Friedman, Anish Mokashi, Latika Menon The recent discovery of graphene and its remarkable properties has generated an enormous amount of research and has led some to contemplate it as a replacement for silicon in the next generation of computer chips. A large amount of theoretical work has been completed, but very little experimental work has been done to verify the theory. In particular, experiments have neglected the effect of a magnetic field applied parallel to the 2-D surface plane. Theory [1] has predicted that this orientation of magnetic field will split the spectra of particles and holes, which will then interact with each other through attractive Coulomb forces, driving a metal to gapped insulator transition. We will report the results of experimental studies of the transport in graphene in a parallel magnetic field at low temperatures. [1] I. L. Aleiner, D. E. Kharzeev, and A. M. Tsvelik, arXiv:cond-mat/0708.0394 \newline [Preview Abstract] |
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C1.00136: Numerical study of electronic transport in a graphene superlattice Di Wu, Wei-Qiang Chen, Fu-Chun Zhang Using tight-bonding model, We calculate the transport properties of charge carriers through graphene superlattices consisting of monolayer or bilayer graphene with an applied external potential barrier. Emphasis is placed on inter-valley scattering between two inequivalent Dirac cones in our systems. It is shown that transmission probabilities for two kinds of graphene structure exhibit different features due to distinct intrinsic properties of charge carriers in these superlattices. The co-existence of inter-valley and intra-valley scattering in the monolayer lattice declines the phenomenon of perfect transmission predicted by Klein paradox. [Preview Abstract] |
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C1.00137: Magnetic edge states in graphene. Sunghun Park, H.-S. Sim We theoretically study the magnetic edge states of the Dirac fermions in graphene, formed along the boundary between the two domains in a spatially nonuniform magnetic field, B$_{0}$ in one domain and B$_{1}$ in the other domain, in the quantum Hall regime. The energy spectra of the magnetic edge states depend on whether B$_{0}$ is parallel or antiparallel to B$_{1}$. For the parallel case, the n=0 magnetic edge states are dispersionless, while they split into electron-like and hole-like levels for the antiparallel case. Here, n is the graphene Landau level index. These features are attributed to the coupling between the pseudo-spin of the magnetic edge states and the direction of the external magnetic field. We also study the modification of the energy spectra when the finite Zeeman spin splitting or an electrostatic step-like potential is considered. An Aharonov-Bohm interferometry, which can identify the existence of the magnetic edge states, is suggested for experimental study. [Preview Abstract] |
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C1.00138: Organic-inorganic Schottky diode based on few layers of graphene Maria Abreu, Idalia Ramos, Nicholas Pinto A Schottky diode was fabricated using several layers of graphene and a n-doped semiconductor and electrically characterized. The diode current-voltage characteristics show that it is forward biased in the first quadrant and reverse biased in the third. The diode turn on voltage is weakly dependent on temperature and increases slightly upon lowering the temperature. The diode rectification ratio (I$_{on}$/ I$_{off})$ decreases as temperature is lowered consistent with the semiconducting nature of graphene. In addition, we have studied the diode behavior in the presence of nitrogen and ammonia gas. The diode characteristics are unaffected by nitrogen but in the presence of ammonia they are similar to that obtained by two back-to-back Schottky diodes. We believe that this change could be due to a slight modification of the surface states and the n-doping of the graphene layer caused by ammonia. [Preview Abstract] |
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C1.00139: Ferromagnet proximity effect in graphene bilayer Yuriy Semenov, John Zavada, Ki Wook Kim A well-known effect of ferromagnet proximity in metallic thin film results in the giant magneto-resistance (GMR). In case of graphene monolayer, the effect of dielectric ferromagnet layer (DFL) proximity leads to formation of spin-dependent electron potential and electron spin rotation in effective exchange field. We theoretically consider the ferromagnet proximity effect in graphene bilayer (GBL), where bottom and top layers are affected by arbitrary oriented DFL. Our calculations show a drastic reconstruction of energy band structure with the top DFL magnetization rotation compared to the bottom one, which is assumed to be fixed by an antiferromagnetic substrate. If the top and bottom magnetic moments are parallel and equal, we obtain a simple spin split gapless band structure. As soon as symmetry between the top and the bottom GBL is broken by rotation of top DFL magnetization, the gap is opening; it reaches the magnitude of exchange field at antiparallel configuration. Calculated conductivity of GBL strongly depends on magnetic configuration demonstrating efficiency of the new mechanism of GMR. [Preview Abstract] |
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C1.00140: The Magnetic effect of Nonmagnetic Defect on Graphene Hideki Kumazaki, Dai Hirashima We study the effect of a nonmagnetic defect on magnetism of graphene. Magnetism in carbon-based materials has been a controversial problem. Apart from magnetic defects, the nonmagnetic-defect-induced mechanism is the most probable mechanism in those materials. In this presentation, we focus on vacancy-induced magnetism. Electrons in graphene can be described with a half-filled Hubbard model on a honeycomb lattice. We then introduce a vacancy as a short-range strong scattering potential on a lattice point. Resorting to a mean field approximation and diagonalizing the approximated Hamiltonian, we can determine the electron number and spin densities at each lattice point. We then find that a vacancy induces short-range ferrimagnetic order around itself. This order is caused by a quasilocalized vacancy state induced by a strong potential. In cases with extended vacancies, the moment formation depends on the geometrical structure and the difference in the numbers of vacancies on two sublattices. The magnetic moment is necessarily induced when the number of vacancies on one sublattice is unequal to that on the other sublattice, in accordance with Lieb's theorem. We further discuss the possible magnetic moment formation on realistic edges in graphene. [Preview Abstract] |
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C1.00141: Pseudospin Magnetism in Graphene Hongki Min, Giovanni Borghi, Marco Polini, Allan H. MacDonald We predict that neutral graphene bilayers are pseudospin magnets in which the charge density-contribution from each valley and spin spontaneously shifts to one of the two layers. The band structure of this system is characterized by a momentum-space vortex which is responsible for unusual competition between band and kinetic energies leading to symmetry breaking in the vortex core. We discuss the possibility of realizing a pseudospin version of ferromagnetic metal spintronics in graphene bilayers based on hysteresis associated with this broken symmetry. [Preview Abstract] |
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C1.00142: Electron-electron and spin-orbit interactions in armchair graphene ribbons Mahdi Zarea, Nancy Sandler The effects of intrinsic spin-orbit and Coulomb interactions on low-energy properties of finite width graphene armchair ribbons are studied by means of a Dirac Hamiltonian. It is shown that metallic states subsist in the presence of intrinsic spin-orbit interactions as spin-filtered edge states, in contrast with the insulating behavior predicted for graphene planes. A charge-gap opens due to Coulomb interactions in neutral ribbons, that vanishes as $\Delta \sim 1/W$, with a gapless spin sector. Weak intrinsic spin-orbit interactions do not change the insulating behavior. Explicit expressions for the width-dependent gap and various correlation functions are presented. [Preview Abstract] |
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C1.00143: Electrical modulation in Graphene based devices Hassan Raza, Edwin Kan Graphene due to its unique dispersion has attracted great attention lately. In a nanoribbon form, it can result in unique `bulk like' states for armchair and edge states for zigzag nanoribbon. Both can be manipulated by an applied bias in the width direction and can result in interesting device concepts. Furthermore, the edge states can be engineered by modifying the edge termination, although atomic-precision is likely required. Moreover, a bandgap can be introduced in a bilayer using an electric field in the bilayer direction. This bandgap opening critically depends on the numbers of graphene layers. Motivated by this rich physics in one and two dimensional graphene structures, we present different bandstructure calculations of nanoribbons and multilayers of graphene. We extract important dispersion parameters from the above calculations. We further study the effect of electric field on these structures. Finally, we present the substrate effect on the electronic structure of graphene layers. We conclude by presenting transport calculations through nanoribbons in longitudinal direction with gate electric field in the width direction. [Preview Abstract] |
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C1.00144: Spin channels in functionalized graphene nanoribbons Giovanni Cantele, Young-Su Lee, Domenico Ninno, Nicola Marzari Graphene nanoribbons have attracted lot of interest, due to high potentiality in technological applications, mostly in graphene-based nanoelectronics. Electronic and transport properties may strongly be influenced by the crystallographic orientation as well as by the presence of defects and different chemical functionalizations. Among the possible edges, the zigzag ones deserve special attention, because it has been shown that magnetic ordering is obtained in the ground state, so as half-metallicity and spin-filtering behavior could in principle be observed under suitable experimental conditions. Here we show how the chemistry of the ribbon edge and surface may strongly affect the transport properties. Quantum conductance is calculated, with ab-initio accuracy, by combining a maximally localized Wannier function approach and the Landauer formula. We show that proper functionalization of the edges may strongly modify the electronic properties. Chemical species adsorbed on the nanoribbon surface can, on the other hand, significantly affect the spin channels, giving rise in some cases to an almost perfect spin-filtering behavior. [Preview Abstract] |
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C1.00145: Ab initio study of alkali metal adsorption on various forms of graphene nanoribbons Seon-Myeong Choi, Seung-Hoon Jhi Electronic and magnetic properties of graphene nanoribbons (GNRs) are very unique depending on their edge shape. While many theoretical studies of GNRs show such intriguing features, clear experimental proofs of atomic edges and their effect on electronic structures have not been explicitly demonstrated. One of the issues is the difficulty of identifying GNRs edges. In this study, we calculated the adsorption energy of alkali metal atoms on various forms of GNRs using the pseudopotential density functional method. We present the distribution of adsorbed atoms on armchair- and zigzag-edged GNRs using the calculated adsorption energy. This approach can help classify the edge of GNRs from the distribution of adsorbed atoms. [Preview Abstract] |
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C1.00146: Electronic structure and bonding properties of hydrogen on K(2x2)/Graphene. C\'esar Acosta, Jorge Alejandro Tapia, Romeo de Coss The effect of the adsorption of hydrogen atom on the electronic properties of K(2x2)/graphene system, are studied by means of fist-principles principles calculations. The results were obtained with the pseudopotentials LCAO method (SIESTA code) and the Generalized Gradient Approximation (GGA) for the exchange-correlation potential. The structural parameters, bonding properties, and electronic structure of the H atoms on K/graphene system are calculated by molecular dynamics. We find an important charge transfer from the substrate towards the H adatoms. The strong H-C chemical bond produced a considerable deformation in the graphene layer. The bonding energy of hydrogen is larger for the K/graphene system than for the single layer of graphene. The present results suggest that the hydrogen adsorption on layered cabon systems could be stimulated by the pre-adsorption of simple metals. [Preview Abstract] |
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C1.00147: Spontaneous Decay and Two-Qubit Entanglement in Ion-Doped Carbon Nanotubes Igor Bondarev, Natalia Noginova We study theoretically surface electromagnetic phenomena, such as spontaneous decay and entanglement of two-level atoms (qubits) close to a carbon nanotube surface[1]. The research is motivated by the progress in growth of cm-long single-walled nanotubes[2], single atom encapsulation into nanotubes[3], and the need for nanomaterials with long quantum coherence lifetimes for advanced applications in modern optoelectronics. We demonstrate the strong coupling of atomic qubits to nanotube surface virtual photon modes, which, via the virtual photon exchange, results in the two-qubit entanglement of the two spatially separated atoms (ions) encapsulated into small-diameter metallic nanotubes. We discuss how to employ Eu$^{3+}$ ions to test our predictions as they are known to be excellent probes to study optical effects in spatially confined systems[4,5], owing to the dominant $^{5}$D$_{0}$--$>^{7}$F$_{2}$ electric dipole transition that essentially creates a two-level (qubit) system. [1] I.V.Bondarev, J. Electron. Mat. 36, 1579 (2007). [2] L.X.Zheng, et al., Nature Mat. 3, 673 (2004). [3] G.-H.Jeong, et al., Phys. Rev. B. 68, 075410 (2003). [4] S.V.Gaponenko, et al., J. Lightwave Technol. 17, 2128 (1999). [5]N.Noginova, et al., J. Appl. Phys., in print. [Preview Abstract] |
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C1.00148: Uptake and isosteric heats of gases adsorbed inside carbon nanotubes Daniel Robertson, Silvina Gatica We studied the properties of gases adsorbed in the interior of open-ended single wall carbon nanotubes for a wide range of pressures and temperatures from tenths to hundreds of Kelvin. The gases studied are Argon, Methane, Hydrogen and Helium in a classical regime. Using the method of Grand Canonical Monte Carlo Simulations we computed the adsorption isotherms, the isosteric heat of adsorption and the configurations at different T,P values. The thresholds values of the pressure and maximum uptake were calculated as a function of the temperature. At the lower temperatures the adsorption of atoms on the axis of the tube is observed as a discontinuous step in the isotherms. [Preview Abstract] |
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C1.00149: Acetylene-Boosted Growth of Vertically Aligned SWNTs by Alcohol CCVD Method Rong Xiang, Jun Okawa, Erik Einarsson, Yuhei Miyauchi, Shigeo Maruyama We present an interesting growth boost of vertically aligned SWNTs achieved by introducing a very small amount of acetylene into the conventional Alcohol Catalytic CVD (ACCVD) system. This acetylene assisted ACCVD, as investigated \textit{in situ} by optical absorption, not only provides us a way to enhance the SWNT growth rate by an order of magnitude, but also confirms that 0.1{\%} of acetylene can reach the same activity as ethanol. Considering that acetylene is one of the products of thermal decomposition of ethanol at our growth temperature, we need to consider the chemical pathway to form SWNTs via acetylene besides the direct pathway from ethanol. A no-flow ACCVD condition fully utilizes this decomposed acetylene as the growth promoter. Since this highly efficient growth through acetylene is only observed with sufficient accompanying ethanol, the critical roles of ethanol and acetylene are discussed. [Preview Abstract] |
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C1.00150: The evolution of helical forms in nanotube and nanofiber growth: Thermodynamic Model and Experiment Prabhakar Bandaru, Apparao Rao Several models, none of them completely satisfactory, have been proposed to understand the synthesis of nanotubes and nanocoils. In this presentation, we first briefly review the models in vogue and point out their shortcomings. Second, we introduce a thermodynamic model, based on exclusion volume principles, common in chemical and biological systems that could potentially explain coiling in nanostructures. Here, the observation of helices and coils in nano-tube/-fiber syntheses is explained on the basis of the interactions between specific catalyst particles and the growing nanostructure. Third, we make specific predictions for the optimal growth of nano-coils/-helices with the hope that these could be used as a guide for rational synthesis. Finally, our own experimental results conforming to the above model, on the role of Indium catalyst particles and local CVD reactor temperature in influencing the coil pitch in coiled nanostructures, will be presented. [Preview Abstract] |
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C1.00151: Electroluminescence of a ZnS-based powder phosphor So Yeon Jun, Jin-Young Kim, Sang Hyeun Park, SeGi Yu Electrouminescence (EL) and photoluminescence (PL) spectra of carbon nanotube (CNT) incorporated ZnS:Cu,Al inorganic powder phosphors under an AC voltage were analyzed by comparing with bare ZnS:Cu,Al powder. The spectra was obtained at room temperature with a He-Cd laser and a single grating monochrometer. By varying the frequency of the applied ac voltage, the PL and EL spectra yield distinct difference in the peak position, width, and intensity of the luminescence. As the concentration of CNTs were increased, the separation between the two luminescence peaks, which were analyzed by the Gaussian fitting, shrank. However, the spectra showed little different behavior for the voltage variation at fixed frequency. The underlying mechanism for this frequency dependence on CNT incorporation and EL performance enhancement will be mentioned in this poster. [Preview Abstract] |
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C1.00152: Oscillatory Behavior of a Double Wall Carbon Nanotube Near an Infinite Surface Adrian Popescu, Lilia Woods, Igor Bondarev Theoretical calculations of a double wall carbon nanotube oscillator with its axial direction perpendicular to an infinite surface are presented. The model for this work is based on the continuum approach of the pair-wise Lennard-Jones type of interaction in the double wall nanotube and between the nanotube and the surface. We investigate the oscillation frequency as a function of the distance between the nanotube and the surface, the length of the nanotube, and the magnitude of the initial extrusion. Our calculations show that the oscillatory behavior is in the GHz region and it can be changed significantly by these factors. Based on these results, we suggest that the carbon nanotube oscillator can be used as a scanning device for surfaces in a similar manner as an atomic force microscope tip. [Preview Abstract] |
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C1.00153: Influence of surfactant concentration on the absorption and emision of light in single-wall carbon nanotubes Cristiano Fantini Optical absorption and photoluminescence have been largely used in the study and characterization of carbon nanotube samples, usually dispersed in aqueous solution wrapped with some surfactant. In this work we present a systematic investigation about the influence of the surfactant on the absorption and emission of light by carbon nanotubes. Carbon nanotubes dispersed in solution at different concentrations and wrapped with some different surfactant such as sodium dodecyl sulfate, sodium cholate, sodium dodecyl benzenesulfonate and segments of DNA were used in the experiments. Optical absorption and photoluminescence spectra were measured and the effects of both the kind of surfactant and the nanotube and surfactant concentrations on the photoluminescence efficiency were investigated. By comparing the intensities of absorption and emission is possible to obtain the best nanotube and surfactant concentration for a higher efficiency in the emission of light. Changes in the absorption and emission energies are observed due to the environment screening on the exciton binding energies. Finally, we determine the structural assignment of the nanotubes and compare the dependence of the photoluminescence efficiency as a function of the surfactant and nanotube concentrations for different nanotube chiralities in the samples. [Preview Abstract] |
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C1.00154: Theory of superplasticity and atomic relaxation in nanotubes and fullerenes Feng Ding, Kun Jiao, Yu Lin, Jianyu Huang, Boris I. Yakobson Plastic relaxation of carbon nanotubes under tension and at high temperature have been described in terms of dislocation theory and with atomistic computer simulations. Now we show how the glide of pentagon-heptagon defects and a particular type of their pseudo-climb [1], with the atoms directly breaking out of the lattice, work concurrently to maintain the tube perfection. Derived force diagram quantifies the balance between these mechanisms, while simulations show both helical and longitudinal movement of the kinks. Mass reduction also represents a compelling problem [2], and we present a mechanism of high-temperature sublimation of carbon nanotubes and giant fullerenes [3]. It does not destroy their ordered makeup even upon significant loss of mass. The atoms depart to the gas phase from the pentagon-heptagon dislocation cores, while the bond disruption is immediately repaired, and the 5$\vert $7 seamlessly propagate through the lattice. This explains a broad class of unsettled phenomena when at high temperature or under radiation the nanotubes do not become amorphous but rather shrink in size nearly flawlessly. We also will present our recent [1] F. Ding, et. al., Phys. Rev. Lett. 98, 075503 (2007) [2] F. Ding, et. al., Nano Lett. 7, 681 (2007) [3] J. Huang, et. al., Phys. Rev. Lett. 99, 175503 (2007) [Preview Abstract] |
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C1.00155: Carbon metal interactions and epitaxy in nanotube growth: Towards chirality-selected nanotube production Feng Ding, Peter Larsson, J. Andreas Larsson, Rajeev Ahuja, Arne Ros\'en, Kim Bolton, Boris I. Yakonson The nucleation of carbon nanotubes (CNTs) on catalyst cluster surfaces was studied by both molecular dynamics (MD) simulation and density functional theory (DFT) calculations. The analysis reveals the two important necessary conditions for the CNT growth: (i) weak tube wall-catalyst interaction and (ii) strong carbon dangling bond-catalyst interaction. A model of CNT growth is proposed to explain the efficiency of the catalyst and the chirality-selective nucleation of carbon nanotubes. [1] F. Ding, et al. J. Phys. Chem. B 108, 17369 (2004). [2] F. Ding, et al. J. Chem. Phys. 121, 2775 (2004). [3] F. Ding, et al. Nanotechnology 17, 543 (2006). [4] F. Ding, et al. Carbon 43, 2215 (2005). [Preview Abstract] |
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C1.00156: Structural dependence of carbon nanotube orbital magnetic susceptibility: tight binding calculations O. N. Torrens, J. M. Kikkawa Recent ab initio calculations of the orbital magnetic susceptibility anisotropies in carbon nanotubes (CNTs) have shown large, systematic differences among zigzag CNTs of similar diameters [1]. We theoretically investigate the origin of these trends by applying the zone-folding method within the nearest-neighbor tight-binding approximation to all chiral and achiral semiconducting CNT species with diameters between 0.6 nm and 1.7 nm. Our results show qualitative agreement with the ``mod 1'' and ``mod 2'' trends of the ab initio theory and additionally distinguish between trigonal warping and curvature-related effects as physical reasons for the predicted species-dependent spread. Our calculations show (2n+m) patterns similar to those in a recent, experimentally-motivated ``fan-out'' diagram [2] and can be likewise fit to an analytical four-term chirality expansion. [1] Marques, M. A. L.; d'Avezac, M. {\&} Mauri, F.,\textit{ Phys. Rev. B, }\textbf{2006}$, 73$, 125433 [2] Torrens, O. N.; Milkie, D. E.; Ban, H. Y.; Zheng, M.; Onoa, G. B.; Gierke, T. D. {\&} Kikkawa, J. M., \textit{J. Am. Chem. Soc., }\textbf{2007}$, 129$, 252-253 [Preview Abstract] |
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C1.00157: Calculations of optical injection and coherent control in graphene Julien Rioux, John E. Sipe We calculate injection spectra for one- and two-photon absorption in graphene, as well as optically injected currents from coherent control of $1+2$ excitation. We compare \emph{ab initio} pseudopotential calculations to analytical expressions of an effective tight-binding model expanded in $\vec{k}$ about the $K$ symmetric point. We find that the spectra from full-zone band structure calculations deviate from the simple model at energies above a few hundred meV's. [Preview Abstract] |
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C1.00158: Titanium Doped Carbon Nanotubes for Hydrogen Storage Jake Fennick, James Lewis An efficient method of storing hydrogen is necessary before fuel cells can become practical. Previous computational results show that a single titanium atom adsorbed on the surface of a carbon nanotube can bind up to 4 hydrogen molecules. We pursue simulations of hydrogen packed between two titanium-doped carbon nanotubes. The highest percentage weight of storage and the manner in which these parallel nanotubes pack is of particular interest. Calculations are performed with the classical MD program GULP. After computation, automated analysis will choose the combination of parameters that results in the most efficient hydrogen storage for these titanium-doped carbon nanotube systems. \newline [1] Yildrim, T.; Ciraci, S. Phys. ReV. Lett. 2005, 94, 175501. [Preview Abstract] |
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C1.00159: Organic Light Emitting Diodes Using a Single Wall Nanotube Film Anode Evan Donoghue, Ken Graham, Matthew Craps, Zhuangchun Wu, Ryan M. Walczak, John R. Reynolds, Andrew G. Rinzler To investigate single-walled carbon nanotube (SWNT) films as a replacement for indium tin oxide (ITO) as the anode in organic light emitting diodes (OLEDs), OLEDs constructed on SWNT films are compared to OLEDs on PEDOT:PSS/ITO. It is found that a simple, single polymer based device design of SWNT /poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV)/Ca/Al can perform comparably with PEDOT:PSS/ITO OLEDs. For thick polymer layers of 300nm, both devices achieve a maximum light output of 700 cd/m$^{2}$ with efficiencies between 0.7-0.8 cd/A. The ITO device performance improves when a thinner MEH-PPV layer is used however variations in the SWNT film surface cause shorting if the MEH-PPV layer is substantially reduced in the SWNT anode devices. The advantages of a SWNT anode as well as the potential for future improvements will be discussed. [Preview Abstract] |
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C1.00160: Extremely Long Multiwall Carbon Nanotube Arrays for Spinning Yarn Chaminda Jayasinghe, Pravahan Salunke, Lucy Lee, Emily Head, Nilanjan Mallik, YeoHeung Yun, Chandrashekhar Pendyala, Mark J. Schulz, Vesselin N. Shanov Centimeter long Multiwall Carbon Nanotube (MWCNT) arrays have been grown by CVD from H$_{2}$-C$_{2}$H$_{4}$-H$_{2}$0-Ar gas mixture at 750\r{ } C in an Easy Tube furnace from First Nano Inc. The arrays were characterized by AFM, SEM, TEM and Raman spectroscopy. The diameter of the CNT was found to be affected by the substrate design. The substrate preparation had great impact on the nanotube diameter. The CVD growth has been optimized with respect to the length and the purity of the CNT. It was found that the CVD growth conditions affect dramatically the quality of the arrays. Base on the optimized process 15 mm long CNT arrays were synthesized and preliminary data were obtained on spinning them into yarns. [Preview Abstract] |
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C1.00161: Formation of highly-conductive SrTiO$_{3-\delta }$ by pulsed laser deposition of TiO$_{2}$ on SrTiO$_{3}$ substrate Kunitada Hatabayashi, Taro Hitosugi, Yutaka Furubayashi, Yasushi Hirose, Toshihiro Shimada, Tetsuya Hasegawa We report on formation of highly conductive SrTiO$_{3-\delta }$ by pulsed laser deposition of TiO$_{2}$ on SrTiO$_{3}$ substrate under relatively reducing atmosphere. Anatase TiO$_{2}$ thin films were grown on SrTiO$_{3}$(001) and (LaAlO$_{3})_{0.3}$(Sr$_{2}$AlTaO$_{6})_{0.7}$ (LSAT)(001), for comparison, by pulsed laser deposition under oxygen pressure of $P$o$_{2 }$= 5x10$^{-8}$ Torr. In-situ RHEED (reflection high energy electron diffraction) measurements during film deposition revealed a clear streak pattern of 4x1 reconstruction, indicating growth of high quality anatase (001) films. Meanwhile, the anatase (001) films deposited on LSAT with thickness of $>$2 nm showed spotty RHEED patterns, indicating formation of oxygen-poor TiO$_{2-x}$. These facts lead us to a conclusion that oxygen atoms in SrTiO$_{3}$ substrate diffuse into anatase TiO$_{2}$ during the film growth process. In the TiO$_{2}$/SrTiO$_{3- \delta }$ heterostructure, we observed high mobility of 1x10$^{4}$ cm$^{2}$/Vs (5K) and Shubnikov-de Haas oscillation (0.5K), proving formation of clean SrTiO$_{3- \delta }$ without structural deformation. [Preview Abstract] |
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C1.00162: On the Electronic Structures of Ge Based Nanotubes. Somilkumar Rathi, Asok Ray In the context of elucidating the properties of Ge-based nanotubes, we provide here a systematic \textit{ab initio} study of the electronic and geometric structures of three different types of armchair silicon germanium nanotubes from (3, 3) to (11, 11) and compare them with the corresponding properties of Ge and GeC nanotubes. The finite cluster approach with dangling bonds terminated with hydrogen has been used. The theoretical formalism used is hybrid density functional theory incorporating HF exchange with DFT exchange-correlation functional. Full geometry and spin optimizations with unrestricted symmetry have been performed. A detailed comparison of the structures and stabilities of the nanotubes with dependence of the electronic band gaps on the respective tube diameters, energy density of states, dipole moments as well as Mulliken charge distributions have been investigated for all the tubes. Radial buckling of the tubes along with bond length variations is also studied and implications for band gap engineering will be discussed. [Preview Abstract] |
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C1.00163: Wigner Function for a Quantum Wire with an Impurity Yi Tang, Tomas Materdey We present the Wigner function for a Gallium Arsenide (GaAS) quantum wire subjected to a magnetic field with an off-center donor impurity. The Wigner function is more sensitive to detecting changes than the variational wavefunction for smaller scale differences in a quantum wire with an impurity. [Preview Abstract] |
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C1.00164: Computational Models for Catalyzed Growth of Si Nanowire. Seunghwa Ryu, Wei Cai We present molecular simulation models for the growth of silicon nanowires from gold catalyst particles.~ Because the number of atoms involve in this process is above 1000, it is infeasible to use ab initio models.~ Hence our first step is to develop an interatomic potential model for Au-Si using the modified embedded-atoms method (MEAM) \newline framework.~ For the first time, we computed the Au-Si phase diagram entirely from the interatomic potential.~ The melting points are computed from free energy methods with uncertainties less than 1K.~ Molecular simulation of the interaction between the gold nanoparticle with the Si substrate and Si NW is presented. [Preview Abstract] |
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C1.00165: Rapid Beam Shaping For Pulsed Laser Processing Using Tunable Acoustic Gradient Index Lenses Craig Arnold, Alexander Mermillod-Blondin, Euan McLeod Rapid shaping of an incident Gaussian laser beam enables spot-to-spot control over local material properties in pulsed and CW applications. Here we present a new device, the tunable acoustic gradient index (TAG) lens, which provides a rapid, high throughput alternative for spatially modifying incident beams and we discuss its effect on pulsed laser micromachining. The TAG lens is a resonant cylindrical cavity for acoustic radial standing waves that modulate the density and thereby create a gradient in index of refraction within the filling fluid. With CW illumination, a single driving frequency will produce a multiscale Bessel beam, or under multiple-frequency operation it can generate a superposition of Bessel beams, approximating any radially-symmetric pattern. When synchronizing a pulsed laser illumination to the lens, rapid switching between instantaneous patterns at frequencies as high as 100-1000 kHz is possible. The theory behind the operation of the lens, its speed, and applicability to pulsed laser processing will be presented. [Preview Abstract] |
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C1.00166: Floating Tip Nanolithography Yehiam Prior, Kaiyin Zhang, Alexander Milner, Michael Karpovski We introduce a new mode of operation to standard atomic force microscopes, working under ambient conditions, for truly noncontact nanolithography. A phase-locked loop, based on tiny oscillations ($<$1 nm) of the cantilever at a frequency far from its mechanical resonance, is used to maintain the gap between the tip and the sample at a predetermined value of 1 - 4 nanometers continuously for long times without the tip ever touching the surface. In a geometry characteristic for Apertureless Scanning Near Field Optical Microscope, the tip is illuminated by a focused beam of a femtosecond laser (800 nm, 20 fsec, 100 mw ) for nano-patterning of the area under the tip. Under the laser irradiation the tip apex heats to a few hunderd degrees as verified by a direct measurement of Raman line shifts, and the elecrtomagnetic enhancement under the tip is used when the laser irradiates the actual tip apex. We demonstrate Floating Tip Nanolithography of two different types, both with lateral resolution of 10-20 nm. With a hot tip (the laser is not in contact with the surface) we thermally pattern the surface of a polymer film, and based on the electromagnetic field enhancement under the sharp tip we ablate narrow lines on a gold film. Future applications will be discussed. [Preview Abstract] |
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C1.00167: Laser Desorption Ionization from Laser Induced Silicon Microcolumns: Surface Morphology and Chemistry Bennett N. Walker, Guerman Pasmanik, Akos Vertes Nanomaterials and mesostructures, such as laser induced silicon microcolumn arrays (LISMA), offer new matrix-free platforms for laser desorption ionization (LDI) of biomolecules. The morphology and surface chemistry of LISMAs depend on the processing environment and the laser parameters. Column diameters and lengths as well as periodicity, observed by AFM and SEM, depend on processing conditions (processing medium, laser pulse energy, pulse length and angle of incidence, etc.). Capillary waves at the molten silicon--processing liquid interface seem to initiate the development of LISMA structures. This is reflected by the correlation between the array morphology and the processing liquid density and interfacial tension. Ion yields from the various surfaces are dramatically affected by the pH of the processing environment, indicating a strong influence of the OH-terminated sites on the silicon surface. Ion generation from LISMAs also significantly depends on the angle of the desorbing laser incidence, potentially suggesting energy coupling through an antenna array mechanism. [Preview Abstract] |
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C1.00168: Internal Energy of Ions Produced by Laser Desorption/Ionization from Laser Induced Silicon Microcolumn Arrays Jessica A. Stolee, Akos Vertes Laser induced silicon microcolumn arrays (LISMA) were demonstrated as effective matrix-free laser desorption/ionization substrates for the mass spectrometry of biomolecules. Structure specific fragmentation of the produced ions primarily depends on their internal energy. To gain insight into the internal energy of ions laser desorbed from native LISMAs and LISMAs derivatized through silane chemistry, the cations of eight benzyl-substituted benzylpyridinium salts were used as thermometer ions (TI). Survival yields of their unimolecular decomposition were determined and correlated to their internal energy through RRKM calculations. On both native and perfluorophenyl-derivatized surfaces, TIs showed no change in their internal energy over a wide range of laser fluence. While the survival yields for these preformed ions are stable, results on peptides indicate fluence dependent fragmentation. These results point to a different fragmentation mechanism for peptides mediated by hydrogen radicals formed through the recombination of protons, produced from residual solvents, and electrons, emitted from the silicon surface upon laser irradiation. [Preview Abstract] |
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C1.00169: Nanoparticle Formation of Compound Materials Omar Musaev, Vladimir Dusevich, David Wieliczka, Jerzy Wrobel, Michael Kruger UV pulsed laser radiation was applied to synthetic polycrystalline hydroxyapatite, the mineral that is the main component of bone. The process was carried out in deionized water. The ablated nanoparticles have been studied with Raman spectroscopy, TEM and XPS. According to transmission electron microscopy micrographs, the ablated particles were approximately spherical and had a size of $\sim $ 100 nm. Raman spectroscopic analysis indicated that particles had the same structure as the original crystal. XPS demonstrated that the surface chemical composition is similar to that of the original material. The advantage of this method in comparison with ablation in vacuum and gas is that due to the confinement conditions produced by the water, the composition of the ablated nanoparticles remains the same as the target material. Another advantage is in the simplicity of the method in comparison to both ablation in vacuum or low pressure gas and to chemical methods for nanoparticle synthesis. [Preview Abstract] |
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C1.00170: Universal disorder in the microwave conductance spectra of doped silicon nanowire arrays Clark Highstrete, Mark Lee, Aaron Vallett, Sarah Eichfeld, Joan Redwing, Theresa Mayer Microwave conductance spectra of doped silicon nanowire (SiNW) arrays were measured from 0.1 to 50 GHz at temperatures between 4 K and 293 K. SiNWs were synthesized by VLS growth, assembled into arrays on co-planar waveguides and measured using microwave vector network analysis. The complex conductance of the arrays was found to increase with frequency at all temperatures as $f^{s}$, with 0.25 $<$ s $<$ 0.4, and to agree with the expected Kramers-Kronig relations. This AC conductance is consistent with behavior found universally in disordered systems. The likely cause is disorder from Si/SiO$_{x}$ interface states dominating the conduction due to the high surface-to-volume ratio of the nanowires. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. Penn State authors acknowledge partial support from NSF DMR-0213623 and NSF NIRT ECCS-0609282. [Preview Abstract] |
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C1.00171: Size-dependent ionization of impurities in GaN nanowires Joonah Yoon, Ilan Shalish, L. R. Ram-Mohan, Venkatesh Narayanamurti The integration of nanowires into devices requires having dielectric materials in contact with the nanowire. Therefore understanding the effect of surrounding dielectric materials on properties of nanowires becomes quite relevant for the device integration of nanowires. In this work we present the effect of dielectric surroundings on electrical properties of gallium nitride nanowires. The conductivity of unintentionally n-doped gallium nitride nanowires is measured from 4.2 to 300 Kelvin. The ionization energies of impurities are extracted from the conductivity versus temperature measurements. These ionization energies are found to display a dependence on the radius of nanowires. This size dependence is explained by the self-energy correction due to the image charges formed at the surface of nanowires. We would like to emphasize this work is the first experimental work to report on the size-dependent ionization of impurities in nanowires [Preview Abstract] |
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C1.00172: Highly electron-emitting states of boron-nitride nanotubes derived from the free-electron-like conduction band states Binghai Yan, Changwon Park, Jisoon Ihm, Gang Zhou, Wenhui Duan, Noejung Park We investigate electronic structures and field emission properties of boron-nitride nanotubes(BNNTs) using the first-principles method and electron dynamic simulations. To introduce a feasible transport channel we choose to dope alkali atoms to BNNTs. We show that the nearly free electron (NFE) state could shift down to the Fermi level, preserving the free-electron-like dispersion along the axial direction. Meanwhile the downshifted NFE state bears s-wave characters, which is necessary for an efficient electron field emission. Our dynamic simulations of emission current reveal that the BNNTs are much favorable for electron field emission, owing partially to the presence NFE states as well as low electron affinity. We suggest that a high-performance field emission devices could be fabricated using n-type doped BNNTs. [Preview Abstract] |
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C1.00173: ABSTRACT HAS BEEN MOVED TO SESSION S30 |
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C1.00174: ABSTRACT HAS BEEN MOVED TO SESSION S30 |
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C1.00175: ABSTRACT HAS BEEN MOVED TO SESSION V30 |
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C1.00176: Free standing carbon nanotubes growth on large-area by nanoimprint and plasma-enhanced chemical vapor deposition. Won Seok Chang, Dae-Geon Choi, Jun-ho Chung, Kab-Soo Huh Among various synthesis methods for carbon nanotube growth, chemical vapor deposition (CVD) method has been widely used for various advantages such as high quality, vertical alignment, controlled diameter and length of nanotubes and so on. Especially, vertically aligned multi-wall carbon nanotube could be grown using plasma-enhanced chemical vapor deposition (PECVD). In this paper, we presented growth of free standing carbon nanotubes by PECVD for the fabrication of nano-electrode. For the growth of nanotubes on the large area 50 mm x 50 mm, catalyst dots were formed by nanoimprint and lift-off process. The synthesis of carbon nanotube requires a metal catalyst layer, etchant gas, and a carbon source. Ammonia (NH3) and acetylene (C2H2) were used as the etchant gas and carbon source, respectively. And iron (Fe) of catalyst metal was deposited on silicon wafer substrates. To form Fe nano dots with diameter of 150 nm and thickness of 50 nm, nano holes patterned imprint resin was used for lift-off process. Carbon nanotubes were grown on pretreated substrates at approximately 30{\%} C2H2:NH3 flow ratios for 40 min. [Preview Abstract] |
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C1.00177: Ab inito calculation of intrinsic spin-Hall effect in graphene nanostructures Bin Wang, Jian Wang, Hong Guo We report a theoretical analysis of intrinsic spin-Hall effect in a four-probe graphene nanostructure in the absence of spin orbit interaction and magnetic field. The nanostructure consists of a finite size graphene sheet connected to the outside world by two zigzag graphene nano-ribbons (ZGNR) and two armchair graphene nano-ribbons (AGNR), forming a cross- shaped two-dimensional device. Due to edge states induced magnetism at ZGNR boundaries, our result suggests that a pure spin-current without an accompanying charge current, is intrinsically induced giving rise to a spin-Hall effect. We have calculated the spin-Hall conductance by an atomic first principles method where density functional theory is carried out within the Keldysh nonequilibrium Green's function framework. [Preview Abstract] |
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C1.00178: Electronic properties of bilayer graphene ribbons with Bernal stacking in a strong magnetic field Yuan-Cheng Huang, Cheng-Peng Chang, Ming-Fa Lin We employ the Peierl coupling tight-binding method to study magneto-electronic properties of bilayer graphene ribbons with Bernal stacking. Because of the interlayer interactions, the magnetic energy bands of a bilayer graphene ribbon are different from those of a monolayer ribbon in the Landau-level energies, the energy spacing, the state degeneracy, and the number of the Landau levels. The low-frequency magneto- absorption spectra reveal the characteristics of the electronic properties. The spectra exhibit denser Landau peaks than those of a monolayer ribbon do. Meanwhile, the transition channels of the Landau peaks are also identified. The selection rule is $\Delta {\tilde n}=\pm 1$. [Preview Abstract] |
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C1.00179: NEGF Transport Simulation on Pd$_4$-cluster Functionalized CNTs Chao Cao, Alexander Kemper, Yao He, Hai-Ping Cheng We have investigated the conductance response of the Pd-cluster functionalized CNTs to hydrogen environment using DFT+NEGF method. Experiments find that the semiconducting CNTs behave very differently from metallic CNTs, and suggest that the semi-conducting ones are good candidates for hydrogen sensors. By comparing the simulation results for the (5,5) metallic and the (8,0) semiconducting CNTs, we are able to reveal the underlying physics behind this phenomena. This work is supported by the DOE grant number DE-FG02-02ER45995. The authors want to thank NERSC, CNMS/ORNL and the University of Florida High Performance Computing Center for providing computational resources and support that have contributed to the research results reported within this paper. [Preview Abstract] |
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C1.00180: QUANTUM FLUIDS AND SOLIDS |
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C1.00181: Spin-charge separation in a strongly correlated spin-polarized chain Shimul Akhanjee, Yaroslav Tserkovnyak We combine the first-quantized path-integral formalism and bosonization to develop a phenomenological theory for spin- charge coupled dynamics in one-dimensional ferromagnetic systems with strong interparticle repulsion, at low temperatures. We assume an effective spin-charge separation and retain the standard Luttinger-liquid plasmon branch, which is explicitly coupled to a Heisenberg ferromagnetic spin-wave texture with a quadratic dispersion. The dynamic spin structure severely suppresses the plasmon peak in the single-particle propagator, in both fermionic and bosonic systems. Our analysis provides an effective theory for the new universality class of one-dimensional ferromagnetic systems, capturing both the trapped spin and propagating spin-wave regimes of the long-time behavior. [Preview Abstract] |
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C1.00182: Implementation of High Temperature Superconducting Leads in research cryostats Yuko Shiroyanagi, Gokul Gopalakrishnan, Dongkyun Ko, Sanghun An, Thomas Gramila While High Temperature Superconducting (HTSC) Magnet Leads are available for use in high current applications when combined with active cryocoolers, they are typically not used in liquid Helium based research cryostats because of the difficulty of implementation. We have successfully implemented a HTSC lead system for Helium based cryostats in which baffles provide thermal coupling to the outgoing Helium gas. The increase in the Helium boiloff rate at full current (110amps) has been measured to be 0.4L/day as compared with the zero current boiloff. An essential element of the design is maintaining a temperature at the warm end of the HTSC leads which is well below the critical temperature. Measurements indicate that this temperature is roughly 65K at 110A. The basic design approach and actual implementation of this novel HTSC lead system, as well as its measurement, are discussed. [Preview Abstract] |
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C1.00183: QUANTUM INFORMATION, CONCEPTS, AND COMPUTATION I |
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C1.00184: PT-Symmetric Quantum Evolution and Logic Torey Semi, Mark Coffey There has been much recent interest in PT-symmetric quantum mechanics (QM) as an alternative formulation of quantum theory. We investigate the potential of this formulation for quantum computation and simulation. PT-symmetric QM replaces the usual postulate that a system's Hamiltonian must be Hermitian. It argues instead that the Hamiltonian can be symmetric with respect to combined parity and time-reversal and, for certain parametric regions, still produce real eigenvalues and maintain unitary time evolution. Besides being of fundamental interest, this approach allows for a fresh perspective on many QM applications. It is known that for one-qubit PT-symmetric systems the evolution time from an initial state to a final state can be made arbitrarily small. We report on applying PT-symmetric Hamiltonians for two-qubit systems to quantum logic. [Preview Abstract] |
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C1.00185: Two-particle Interferometry with Filtering Operations S.-S. B. Lee, H.-S. Sim We generalize the conventional two-particle interferometer by including filtering operations. We find that after appropriate local filtering operations, the concurrence, a two-particle entanglement measure, can be directly obtained from the visibility of the two-particle interference, even for mixed states. This indicates that entanglement is associated with experimentally feasible properties. [Preview Abstract] |
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C1.00186: Entanglement of magnetic impurities via electron scattering with asymmetric coupling constants Guillermo Cordourier-Maruri, Romeo de Coss, Yasser Omar We study the entanglement generated by electron scattering between two fixed magnetic impurities, located in a 1-D quantum wire. The impurities were considered distant and only interact through the spin of a scattered electron. We analyzed the asymmetric case produced by the effect of considering different exchange coupling electron-impurity factor for each impurity. We used the quantum waveguide theory approach to find the probability of electron transmission for each espinorial configuration of the system, taking into account the possible changes in the directions of the impurities and electron spins. We find resonance behavior in the evolution of the probability of electron transmission with respect to the impurities separation. We show results for the cases where the average and the difference of the exchange coupling electron-impurity factor are constant. From the probabilities of electron transmission the entanglement is calculated using the von Neumann entropy. We show that the entanglement can be maximized changing the initial conditions of the system, like the impurities separation distance and the ratio of the electron-impurity exchange coupling factor. [Preview Abstract] |
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C1.00187: Squeezed State Effects on Continuous Variable Quantum Erasing Peter Bonanno, Vijay Kasisomayajula, Onofrio Russo Experimental verification of complementarity using quantum erasing for the continuous variable (CV) infinite dimensional Hilbert space has been considered. [1] The complemetary pair is that of the canonically conjugate amplitude and phase quadratures of light. The amplitude quadrature is labeled to a squeezed meter signal by quantum nondemolition (QND) [2] entanglement coupling. [3] Knowledge of \textit{which eigenstate} (WE) can be obtained by measuring this amplitude in the meter state, and can thereafter be `lost' by measuring the quadrature phase of the meter, thus restoring the quadrature phase of the signal beam in a process known as \textit{quantum erasure.} [4] The coupling, i.e. the labeling of the signal state to the meter state, is implemented with a beam splitter coupled to the squeezed light meter beam. [4] We investigate the effects of using the unitary squeeze operator S(z)=exp$\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $(z*a$^{2}$ - za$^{+2}$) where z = re$^{i(squeezing angle)}$ on selected coherent states under certain conditions. [5,6] [1] U. L. Anderson et al., Phys. Rev. Lett. 93, 100403 (2004). [2] V. B. Braginsky et al., Science 209, 547 (1980). [3] R. Bruckmeimer et al., Phys. Rev. Lett. 79, 43 (1997). [4] P. Grangier et al., Nature 396, 537 (1998). [5] C. M. Caves, Phys. Rev. D 23, 1693 (1981). [6] D. Stoler, Phys. Rev. D. 1, 3217 (1970), D. Stoler, Phys. Rev. D. 4, 1925 (1971). . [Preview Abstract] |
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C1.00188: Hidden variables in quantum mechanics: Generic models, set-theoretic forcing, and the appearance of probability Robert A. Van Wesep The hidden-variables (HV) program in quantum mechanics proposes that physical states have properties that are not observable in the ordinary sense and which uniquely determine the outcome of any observation. It is well known that one cannot consistently assign values to all propositions in a Hilbert space of dimension $\ge 3$, but for systems of commuting propositions one always can, so there is some interest in HV in this limited setting. But the same objection has been raised against HV as against the many-worlds view (MW), viz., that it cannot accommodate the notion of probability, specifically the Born rule. We have shown that the Born rule is actually derivable in MW[1]. In the present work we do the same in the HV setting[2]. Specifically, we show that the HV premise implies that the sequence of values assigned by a given HV state to a set of commuting propositions is indistinguishable from a sequence randomly generated according to the Born rule. In fact, the same is true for systems of noncommuting propositions satisfying a natural condition[3]. The sequences demanded by HV are \emph{generic} in the set-theoretic sense. The fascinating ontology of generic objects in set theory therefore applies to HV states in physics.\newline \noindent [1] R.A. Van Wesep, Ann. Phys. 321 (10) (2006) 2438--2452.\newline \noindent [2] R.A. Van Wesep, Ann. Phys. 321 (10) (2006) 2453--2475.\newline \noindent [3] R.A. Van Wesep, Ann. Phys. 321 (10) (2006) 2476--2490. [Preview Abstract] |
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C1.00189: Intrinsic Friction Microscopy Daniel Knorr, Rene Overney A novel scanning probe methodology based on lateral force microscopy is presented wherein kinetic friction measurements, obtained as a function of velocity for various temperatures, are used to deduce apparent Arrhenius-type activation energies for surface and subsurface molecular mobilities. Depending on the coupling strength (cooperativity) between molecular mobilities involved the dissipation energy can carry a significant entropic energy contribution, accounting for the majority of the apparent Arrhenius activation energy. The intrinsic friction methodology also provides a means of directly separating enthalpic energy contributions from entropic ones by employing absolute rate theory. As such, the degree of cooperativity in the system is readily apparent. This methodology is illustrated with nanoscale tribological experiments on two systems, (1) monodisperse, atactic polystyrene and (2) self assembling molecular glassy chromophores. In polystyrene, dissipation was found to be a discrete function of loading, where the $\gamma $-relaxation (phenyl group rotation) was recovered for ultra low loads and the $\beta $-relaxation (local backbone translation) for higher loads in the same temperature range, indicating sensitivity to surface and subsurface mobilities. For self assembling glassy chromophores, the degree of intermolecular cooperativity was deduced using the methodology, resulting in an increased understanding of the interactions between self assembling molecules. [Preview Abstract] |
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C1.00190: HIGH PRESSURE PHYSICS |
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C1.00191: Influence of Shockwave Profile on Ejection of Micron-Scale Material From Shocked Tin Surfaces Michael Zellner, Jim Hammerberg, Robert Hixson, Russel Olson, Paulo Rigg, Gerald Stevens, William Turley, William Buttler This effort investigates the relation between shock-pulse shape and the amount of micron-scale fragments ejected (ejecta) upon shock release at the metal/vacuum interface of shocked Sn targets. Two shock-pulse shapes are considered: a supported shock created by impacting a Sn target with a sabot that was accelerated using a powder gun; and an unsupported or triangular-shaped Taylor shockwave, created by detonation of high explosive that was press-fit to the front-side of the Sn target. Ejecta production at the back-side or free-side of the Sn coupons were characterized through use of piezoelectric pins, Asay foil, optical shadowgraphy, and X-ray attenuation. [Preview Abstract] |
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C1.00192: Pressure induced valence changes in YbTe studied by resonant inelastic x-ray emission (RXES) Ravhi Kumar, Andrew Cornelius, Yuming Xiao, Paul Chow, Malcolm Nicol We have performed high resolution x-ray absorption (XAS) and resonant inelastic x-ray emission (RXES) experiments to probe the pressure dependence of Yb valence in YbTe as high as 20 GPa. XAS spectra were collected in the partial fluorescence yield (PFY) mode at the Yb L3 edge. The RXES spectra were recorded by fixing the incident energy and collecting the transferred energy as a function of pressure in 2eV steps. The results show a continuous valence change of Yb towards 3+ from the mixed valent state, similar to other mixed valent Yb compounds under pressure [1, 2]. The experimental details with the PFY and RXES results will be presented. 1. C. Dallera, M. Grioni, A. Shukla, G. Vanko, J. L. Sarrao, J. P. Rueff and D. L. Cox Phys. Rev. Lett., 88, 196403 (2002) 2. C. Dallera, E. Annese, J. P. Rueff, A. Palenzona, G. Vanko, L. Braicovich, A. Shukla and M. Grioni, Phys. Rev. B., 68, 245114 (2003 [Preview Abstract] |
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C1.00193: Sugar pucker in nucleosides as a function of pressure Scott Lee Infrared and Raman experiments of adenosine (rA), deoxyadenosine (dA), cytidine (rC) and deoxycytidine (dC) have been performed at room temperature as a function of pressure. Phase transitions are observed to occur near 2 and 4 GPA in rA and dA and near 4 GPa in rC and dC. Based on theoretical calculations of the vibrational frequencies, these transitions appear to be due to changes in the sugar moiety. The most likely explanation is that the sugar pucker changes at these pressures. These observations are relevant to our understanding of the A-to-B transition observed in DNA. [Preview Abstract] |
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C1.00194: First-order polymorphic phase transition in supercooled liquid Silicon P. Ganesh, Mike Widom We perform first-principles molecular dynamics simulation of liquid and supercooled liquid Silicon.~ Looking at the volume dependence of the pressure at different supercooled liquid temperatures, we find a van der-Waals loop, indicating a possible liquid-liquid first-order phase transition.~ It appears that the transition can be seen only at pressures of about a few GPa.~ We analyze our data using the zero'th moment of the tetrahedral order parameter, $q_i =1-\frac{3}{8}\sum\limits_{j>k} {[\cos \theta _{ijk} +\frac{1}{3}]^2} $[1], where $\theta _{ijk} $ is the angle formed between neighbors `$j$' and `$k$' and the central atom `$i$'. For a perfect tetrahedral arrangement ($\cos \theta _{ijk} =-\frac{1}{3})$ the value of the order-parameter is `1' and for an uncorrelated system its distribution is peaked at `0'. We find that the low temperature liquid has a more tetrahedral open network than the high temperature one, indicating that the transition is between a high-density and a low-density liquid. The electronic density of states along an isochore indicates a sharp drop in metallicity across the transition temperature, which we believe lies around T = 1100K. [1] M. Scott Shell and Pablo G. Debenedetti and Athanassios Z. Panagiotopoulos, Physical Review E \textbf{66}, 011201, (2002) [Preview Abstract] |
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C1.00195: Formation of nano-domains during the ZB-B1 high-pressure transition in bulk ZnSe R.E. Tallman, B.A. Weinstein, P. Zhang, V. Iota, H. Rhee, M.A. Marcus Raman scattering and x-ray absorption spectroscopy (XAS) are applied to explore the early-stage nucleation of the zincblende-rocksalt high-pressure transition in ZnSe. The Raman spectra (300K) of both natural ZnSe and high-quality vapor-grown ZnSe exhibit extreme broadening in the region of the TO($\Gamma )$ phonon for pressures $\sim $ 2.5 GPa below the onset of the opaque high-pressure phase. At the same time sharp features persist in the spectra, $e.g.$, due to the resonantly enhanced LO($\Gamma )$ peak and the 2TA(X) and 2TA(L) critical points. These results indicate that the high-pressure rocksalt phase in ZnSe tends to form in nanoscale domains due to a high density of nucleation sites. In order to explore the nucleation process further, XAS measurements are carried out under applied pressure on a ZnSe film containing $\sim $ 10$^{21}$ cm$^{-3}$ As-impurities as an easily identifiable source of nucleation sites. Comparisons of the XAS results at 1 atm. and 6.5 GPa support the early onset of disorder consistent with nano-domain formation and the Raman findings. [Preview Abstract] |
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C1.00196: A first-principles investigation of ionic vacancies and diffusion in high-pressure silica polymorphs Ashok Verma, Bijaya Karki We have performed the density functional theory based simulations within the local density and pseudopotential approximations to investigate the effects of pressure and structural changes on the formation and migration energies of the ionic vacancies in crystalline silica. The simulations use supercells of 72 atoms for $\alpha $-quartz, stishovite and CaCl$_{2}$-type and 96 atoms for $\alpha $-PbO$_{2}$ and pyrite type silica. The simulations are performed up to 250 GPa pressure. The atomic positions are fully optimized. Our results show a discontinuous change in Schottky formation enthalpy at phase transitions which involve cation coordination number change. In fact increase in cation coordination number leads in reduction of Schottky formation enthalpy. For example, at 0 GPa pressure Schottky formation enthalpies of 4-fold ($\alpha $-quartz), 6-fold (stishovite) and (6+2)-fold (pyrite) coordinated silica are 16.12 eV, 11.02 eV and 7.73 eV respectively. Calculations of migration enthalpies, activation enthalpies and activation volumes all are also carried out up to 250 GPa pressure. [Preview Abstract] |
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C1.00197: GENERAL |
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C1.00198: Two Theories Are Better Than One Robert Jones All knowledge is of an approximate character (B. Russell, Human Knowledge, 1948, pg 497 and 507). Our formalisms abstract, idealize, and simplify (R. L. Epstein, Propositional Logics, 2001, Ch XI and E. Bender, An Intro. to Math. Modeling, 1978, pg v and 2). Each formalism is an idealization, often times approximating in its own DIFFERENT ways, each offering somewhat different coverage of the domain. Having MULTIPLE overlaping theories of a knowledge domain is then better than having just one theory (R. Jones, APS general meeting, April 2004). Theories are not unique (T. M. Mitchell, Machine Learning, 1997, pg 65-66 and Cooper, Machine Learning, vol. 9, 1992, pg 319). In the future every field will possess multiple theories of its domain and scientific work and engineering will be performed based on the ensemble predictions of ALL of these. In some cases the theories may be quite divergent, differing greatly one from the other. This idea can be considered an extension of Bohr's notion of complementarity, ``...different experimental arrangements...described by different physical concepts...together and only together exhaust the definable information we can obtain about the object.'' (H. J. Folse, The Philosophy of Neils Bohr, 1985, pg 238) [Preview Abstract] |
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C1.00199: What's in a Name?FRAMING:Martin-Bradshaw DYSfunctionality = Siegel ``Buzzwordism,Bandwagonism\&Sloganeering For: Fun, Profit,Survival,Ego": From SOC to FLT Proof to High-Tc to Spintronics to Giant-Magnetoresistance: Ethics??? SHMETHICS!!! Rampant Sociolog Edward Siegel Buzzwordism,Bandwagonism,Sloganeering for:Fun,Profit,Survival, Ego=ethics DYSunctionality: Digits log-law: Siegel INVERSION: bosons=digits; Excluded d=0? P(0)=oo V P(1)$<$oo: DIGITS gapFUL BEC!1881$<$QM! EXPANSION: 1/w Zipf-power-law; PF: units=base= SCALE-INVARIANCE! DARPA spintronics V Overhauser-effect: 1954$<$1988! Anderson-localization V graph-thy Rayleigh(short-cut):1870$<$1958! CCNY Siegel[FUZZYICS]Pythagorean-thm+dimension-thy+category-semantics simple FLT pf.=vector-subtraction+Fermat least-action V Wiles: 1964$<$1994! Bak SOC,long-after Siegel[PSS(a)601,1971;Scripta(Acta)Met.1974(1977);Intl.Conf.AE,JIPA,1977;MRS Symp.Scaling,1990-proving SOC=F=ma Fourier-transform=AE]: 1971$<$1987: Not Per Bak, but PRE Bak!(ie Pure Bunk!) Bednorz-Mueller cuprates V Raveau-Chu TRUE high-Tc! Emery SC 3-band V Siegel multi-band Hubbard-mdls[J.Mag.Mag. Mtls.(1976-1980);APS March Mtgs.,1987-on];Intl.Conf.High-Tc:Stanford,1987;Berkeley,1987); WorldCong.SC, 1992]: 1970s$<$1993! Anderson SC RVB V Overhauser CORRECT SS/CDWs:1960s$<$1987. Fert-Grunberg GMR V decade-earlier Siegel[JMMM.7,31(1978);Mayo,Village Voice,p.40(8/21/78):1978$<$1988!!!A la Brian Martin-John Bradshaw addictions 12-step recovery programs[Healing SHAME That BINDS YOU]: One is only as SICK as one's SECRETS! Ethics? SHMETHICS! RAMPANT ethical DYSfunctionality!!! [Preview Abstract] |
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C1.00200: GENERAL THEORY INCLUDING COMPUTATIONAL METHODS: MANY BODY AND STRONGLY CORRELATED SYSTEMS |
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C1.00201: A nonlinear quantum master equation symmetric with respect to particles and holes C.F. Huang, K.-N. Huang A nonlinear master equation symmetric with respect to particles and holes has been introduced for systems composed of non-interacting identical fermions. [1,2] It can be reduced to semiclassical irreversible equation in the incoherent limit, and can be generalized to model interacting and/or open quantum systems. [2,3] To prove the validity of Pauli's exclusion principle, we note that such a principle holds true if and only if the density matrix for holes is a positive one. Suitable mathematical structures have been constructed to complete the proof when there exists an upper bound for the transition rate. Extensions based on BCS-type symmetry are taken into account to incorporate both particle-particle and particle-hole pairings. References: [1] K. Burke, R. Car, and R. Gebauer, Phys. Rev. Lett. \textbf{94}, 146803 (2005) [2] C. F. Huang and K. --N. Huang, quant-ph/0604054. [3] R. Alicki and K. Lendi, ``Quantum Dynamical Semigroups and Applications'' (Springer, Berlin Heidelberg 2007) [Preview Abstract] |
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C1.00202: A new Variational Approach to the Hydrogen Atom I. Djuric, F.A. Corvino, V. Fessatidis, J.D. Mancini Over a decade ago, a systematic scheme for improving the variational wave functions and corresponding energy levels for quantum systems was developed. By expanding the wave function around a variational parameter value(s), a family of independent functions may be systematically generated. The eigenstates are then obtained by diagonalizing the Hamiltonian basis and optimized with respect to variational parameter(s). In this work we wish to apply this scheme to the well studied and understood ground state of the hydrogen atom. For a trial (starting vector) state we make two choices: $% e^{-\alpha r}$ and $e^{-\beta r}$ where $\alpha $ and $\beta $ are variational parameters. Our two (variational) basis are then constructed by taking derivatives with respect to these parameters. We then choose a linear combination of the two states $e^{-\alpha r}$ and $e^{-\beta r}$ as our initial state and minimize with respect to both parameters. This leads to questions of the optimal number of each derivative $\partial _{\alpha }^{p}$, $\partial _{\beta }^{q}$, which will yield the lowest ground state energy for a given basis size $N$ ($p+q=N$). [Preview Abstract] |
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C1.00203: Variational Bound States of Screened Potentials J.D. Mancini, V. Fessatidis, S.P. Bowen, W.J. Massano A number of years ago, a calculational scheme was introduced by Stubbins (Phys.~Rev.~\textbf{A}48, 220 (1993)) to compute the energies of both the Hulth\'{e}n and Yukawa potentials. The method introduces a particular ansatz for solving the Schr\"{o}dinger equation with screened Coulomb type potentials. In this work we wish to review the method of Stubbins and to show that it is, in fact, equivalent and a subset of a more systematic (and hence more useful) variational scheme (Zhou et al.~Phys.~Rev.~\textbf{A}51, 3337 (1995)). This variational approach involves the construction of a basis by taking derivatives of the variational parameters of the system. The eigenvalues of the Hamiltonian matrix are then minimized with respect to these parameters yielding a ``best guess" upper bound on the energies. [Preview Abstract] |
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C1.00204: Translational Invariance in Parameter Space: An Alternate Variational Coupled Cluster Method V. Fessatidis, J.D. Mancini, S.P. Bowen, R.K. Murawski Over the past few decades the Coupled Cluster Method (CCM) has proven to be a useful tool for both chemists and physicists in the calculation of ground state energies. The CCM scheme is also a viable method in calculating the correlation energies of a number of diverse quantum systems such as atoms, molecules, electron gases as well as for magnetic lattice systems. In this work a new many-body calculational scheme is developed by merging the CCM scheme with a relatively new variational ansatz wherein a basis is constructed by taking derivatives with respect to the variational parameters of the system. A novel translational operator is then introduced leading to a generalization of Bloch's Theorem in parameter space. [Preview Abstract] |
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C1.00205: Microsolvation Effects on the Excited-State Dynamics of Protonated Tryptophan Matteo Guglielmi, Sebastien Mercier, Oleg Boyarkin, Anthi Kamariotis, Ivano Tavernelli, Michele Cascella, Ursula Roethlisberger, Thomas Rizzo To better understand the complex photophysics of the amino acid tryptophan, which is widely used as a probe of protein structure and dynamics, we have measured electronic spectra of protonated, gas-phase tryptophan solvated with a controlled number of water molecules and cooled to $\sim$10 K. We observe that, even at this temperature, the bare molecule exhibits a broad electronic spectrum, implying ultrafast, nonradiative decay of the excited state. Surprisingly, the addition of two water molecules sufficiently lengthens the excited-state lifetime that we obtain a fully vibrationally resolved electronic spectrum. Quantum chemical calculations at the RI-CC2/aug-cc-pVDZ level, together with TDDFT/pw based first-principles MD simulations of the excited-state dynamics, clearly demonstrate how interactions with water destabilize the photodissociative states and increase the excited-state lifetime. [Preview Abstract] |
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C1.00206: The One-Hole, One-Dimensional Hubbard Model at $U = \infty$ William Hodge, Natalie Holzwarth, William Kerr The Hubbard Hamiltonian is the simplest model that describes interacting electrons on a lattice. In this work, we use the properties of stochastic matrices to examine the ground state with an even number of lattice sites and one electron less than half-filling. We show that there exists a highly symmetric state with energy $-2$ (in units where $t = 1$) at all \textit{U}. At $U = \infty$ this state becomes the lowest energy state, consistent with the established lower energy bound. \footnote{S. A. Trugman, Phys. Rev. B \textbf{42}, 6612 (1990)} Using this result, several properties of the strongly coupled ground state are derived, including the chemical potential and momentum distribution. This method may be applicable to other models as well. Disagreements between our results and previous work are examined. [Preview Abstract] |
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C1.00207: Direct extension to $n$-leg models in the density-matrix renormalization group method: An approach on the ground state of two-dimensional triangular Hubbard model Susumu Yamada, Masahiko Okumura, Masahiko Machida In order to examine the ground state of two-dimensional triangular Hubbard model, we directly extend the density-matrix renormalization group (DMRG) method to $n$-leg lattice model. The leg extension requires not only an enormous memory space but also a huge CPU cost. Therefore, we propose an efficient and scalable parallel algorithm of the direct DMRG method and actually perform parallel numerical simulations of triangular 4- to 6-leg Hubbard models using 128 to 512 CPU's on SGI Altix 3700Bx2 in JAEA. In this presentation, we will briefly introduce the parallelization strategy, the implementation way, and show its performance including its scalability and accuracy. Furthermore, we reveal peculiar particle density distributions on $n$-leg triangular Hubbard models. These results are compared with the future experiments on atomic Fermi gases loaded on triangular optical lattices. [Preview Abstract] |
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C1.00208: s-Wave Superconductivity Phase Diagram in the Inhomogeneous Two-Dimensional Attractive Hubbard Model Karan Aryanpour, Thereza Paiva, Warren E. Pickett, Richard T. Scalettar We study s-wave superconductivity in the 2-D square lattice attractive Hubbard Hamiltonian for inhomogeneous patterns of interacting sites. Using the Bogoliubov-de Gennes (BdG) mean field approximation, we obtain the phase diagram for inhomogeneous patterns with on-site electron interaction $U_i$ taking on two values, $0$ and $-U/(1-f)$ ($f$ the non-interacting sites concentration) as a function of electron density per site $n$ as $f$ varies. Inhomogeneity can result in a larger average pairing amplitude at $T=0$ and also a higher superconducting $T_c$, relative to a uniform system. Superconductivity can also vanish due to charge ordered phase formation. $T_c$ enhancement due to inhomogeneity is robust as long as $n<2(1-f)$ regardless of the pattern. Also, for certain inhomogeneous patterns, when $n=2(1-f)$, raising temperature works against the stability of existing charge ordered phases for large $f$ and as a result, enhances $T_c$. [Preview Abstract] |
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C1.00209: Simple dynamic exchange-correlation kernel of the uniform electron gas Lucian Constantin, J.M. Pitarke We propose a simple dynamic exchange-correlation kernel of the uniform electron gas. We model the reduction of the electron-electron interaction due to short-range exchange-correlation effects by introducing a frequency-dependent error-function effective interaction. By imposing the fulfillment of the compresibility and the third-frequency-moment sum rules, as well as the correct asymptotic behavior at large wave vectors, we find an accurate and simple dynamic exchange-correlation kernel that accurately reproduces the wave-vector analysis and the imaginary-frequency analysis of the correlation energy of the uniform electron gas. [Preview Abstract] |
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C1.00210: Critical parameters for the disorder-induced metal-insulator transition in FCC and BCC lattices Andrzej Eilmes, Andrea M. Fischer, Rudolf A. Roemer We use a transfer matrix method to study the disorder-induced metal-insulator transition for. We take isotropic nearest- neighbour hopping and an onsite potential with uniformly distributed disorder. Following previous work done on the simple cubic lattice, we perform numerical calculations for the face centred cubic (FCC) and body centred cubic (BCC) lattices, which are more common in nature. We obtain the localisation length from calculated Lyapunov exponents for different system sizes. This data is analysed using finite size scaling to find the critical parameters. We create an energy-disorder phase diagram for both lattice types, noting that it is symmetric about the band centre for the BCC lattice, but not for the FCC lattice. We find a critical exponent of approximately 1.5-1.6 for both lattice types for transitions occurring either at fixed energy or at fixed disorder, agreeing with results previously obtained for other systems belonging to the same orthogonal universality class. We notice an increase in critical disorder with the number of nearest neighbours, which agrees with intuition. [Preview Abstract] |
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C1.00211: The Gutzwiller Ansatz: A new Approach J.D. Mancini, V. Fessatidis, I. Djuric, S.P. Bowen The search for calculational methods for dealing with strongly correlated electron systems ranging from high ${\mathrm{Tc}}$ superconducting compounds and other transition metal oxide materials to $f$-electron bearing elements is a long and continuous one. There are a number of well documented failures of such schemes as the local density approximation and the generalized gradient approach. Although these methods partially address the issues related to the strongly correlated electrons, a comprehensive theory is still lacking. The choice of including electrons correlations using the Gutzwiller variational wave function has proved over the years to be a useful one in the interpolation between the strong electron correlation (large $U$) and weak electron correlation (small $U$) limits. In this work a novel variational ansatz is applied to strongly correlated systems by using the Gutzwiller wave function as our initial vector, and then systematically constructing a basis by taking derivatives with respect to the variational parameters of the system. The eigenvalues of the Hamiltonian matrix with this basis are then minimized to yield a variational upper bound on the ground state energy. [Preview Abstract] |
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C1.00212: Solution of the Electron Fluid Dynamical Equations Mostafa Hemmati To describe the breakdown waves, we use a one-dimensional, steady-state, three-fluid, hydro-dynamical model with a shock front. We assume that the electron gas partial pressure is much larger than the partial pressures of the other species and therefore provides the driving force for the propagation of the wave. The wave is composed of two distinct regions: a thin dynamical transition layer followed by a relatively thicker thermal layer. In the transition region, the electrons slow down to speeds comparable to those of heavy particles as the electric filed falls to zero. In the thermal layer, the high temperature electron gas will cool, resulting in more ionization. The set of equations used to investigate these waves consists of the equation of conservation of mass, momentum, and energy coupled with Poisson's equation, and is known as the electron fluid dynamical (EFD) equations. We have replaced the assumption of ionization rate being a function of temperature only, by a computation based on the free trajectory theory by Fowler; in which the ionization rate changes from accelerationnal ionization at the front of the wave to directed velocity ionization in the intermediate stages of the wave to thermal ionization at the end of the wave. Using Fowler's equation to calculate the ionization rate, we have been able to integrate the EFD equations through both, the transition and thermal layers of the wave. The results conform to the expected conditions at the end of both layers. Wave profile for the electric field, ionization rate, and electron velocity, temperature, and number density will be presented. [Preview Abstract] |
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C1.00213: INSTRUMENTATION AND MEASUREMENTS |
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C1.00214: Branching Transport Model of NaI (Tl) Scintillator Boian Alexandrov, Kiril Ianakiev, Peter Littlewood The time dependence of NaI(Tl) fluorescence was measured long time ago with the delayed coincidences method and two decay time components were observed. Because 95{\%} of the total light yield is collected within the first 800 ns, the influence of the second component has been neglected. We claim that there are two dominant \textit{nonexponential} light components with strong temperature redistribution. We experimentally measured the time dependence of the NaI(Tl) light-emission pulses and found that the amplitude ratio of these two components shows Arrhenius temperature dependence. We found that the slow component occupies up to 40{\%} of total light at -20$^{\circ}$C. Our model for the temperature-dependent behavior of the NaI(Tl) scintillators is based on two dominant pathways for reaching the Tl level in the scintillator, which lead to two effective, main \textit{nonexponential} components of the time shape of the light pulse. These two effective exponents correspond to the two different transport processes in the crystal. First of them is hopping transport from Self Trapped Exciton (STE) levels to Tl activator sites, and the second is multi-phonon assisted dissociation of the STE followed by binary diffusion of separated holes and electrons to the Tl level. [Preview Abstract] |
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C1.00215: Optimization of MOKE Setups: Analyzing Experimental Assemblies Using Jones Matrix Formalism Srinivas Polisetty, Jeremy Scheffler, Sarbeswar Sahoo, Christian Binek We report on the optimization of Magneto Optical Kerr setups. Photoelastic modulation and phase sensitive detector methodology have been used to measure the first and second harmonics of the reflected light intensity related to the magnetization-dependent off-diagonal reflection coefficients $r_{ps/sp}$ of the sample's dielectric tensor. The latter elements determine the Kerr ellipticity \textit{$\varepsilon $}$_{K}$ and rotation \textit{$\theta $}$_{K}$. Jones matrix formalism has been used to analyze a large variety of arrangements of the optical elements involved in setups for longitudinal Kerr measurements with incoming s-polarized light. Relative analyzer and polarizer orientations have been varied with respect to each other and with respect to the retardation axis of the modulator. Different configurations have been analyzed and experimentally studied by measuring magnetic Kerr-hysteresis loops on a Co/CoO bilayer sample. We find that one configuration stands out by doubling the first as well as second harmonic intensities and, hence, the signal to noise ratio. Inefficient setups show first and second harmonic signals involving non-magnetic background contributions of $r_{p}$ and $r_{s}$. [Preview Abstract] |
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C1.00216: Electromagnetic modulation of the ultrasonic signal for nondestructive detection of small defects and ferromagnetic inclusions in thin wall structures Peter Finkel We report on new nondestructive evaluation technique based on electromagnetic modulation of ultrasonic signal for detection of the small crack, flaws and inclusions in thin-walled parts. The electromagnetically induced high density current pulse produces stresses which alter the ultrasonic waves scanning the part with the defect and modulate ultrasonic signal. The excited electromagnetic field can produces crack-opening due to Lorentz forces that increase the ultrasonic reflection. The Joule heating associated with the high density current, and consequent thermal stresses may cause both crack-closure, as well as crack-opening, depending on various factors. Experimental data is presented here for the case of a small crack near holes in thin-walled structures. The measurements were taken at 2-10 MHz with a Lamb wave wedge transducer. It is shown that electromagnetic transient modulation of the ultrasonic echo pulse tone-burst suggest that this method could be used to enhance detection of small cracks and ferromagnetic inclusions in thin walled metallic structures. [Preview Abstract] |
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C1.00217: Detection of nerve agents and biological molecules using embedded piezoresistive microcantilever sensors. Timothy Porter, Tim Vail, Amanda Wooley Embedded piezoresistive microcantilever (EPM) sensors have been used in the detection of a variety of analyte species. EPM sensors utilize a tiny piezoresistive microcantilever partially embedded into a sensing material to produce a sensing element that is compact, simple, resistant to movement and shock, and suitable for remote sensing applications. In the current project, we have used sensing materials comprised of an immobilizing polymer functionalized with either target enzymes or antibodies to detect two biological agents, bacillus globigi (BG) and Diisopropyl fluorophosphate (DFP). DFP is an organophosphate used as a simulant for organophosphate nerve agents, while BG is a large bacterial spore used as a simulant for other bacterial spores such as bacillus anthracis. Sensing results are presented for both types of EPM sensors. [Preview Abstract] |
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C1.00218: Micro-Oscillators for Ultra-Sensitive Force Detectors Wei Lu, John Markert Recently, we have improved the microfabrication process for ultra-sensitive double-torsional mechanical micro-oscillators. Starting with silicon-on-insulator wafers (with 300 nm Si surface layers), we grow a protective layer of oxide, then pattern 2-mm $\times$ 0.5-mm ``windows" that result in a thin Si film after two-sided wet chemical etching. Patterning these film windows with electron-beam lithography then provides the final micro- oscillator structures. Our designs include multimode structures, particularly double-torsional modes; we have achieved excellent geometric symmetry and small sizes ($\sim 30\ \mu$m laterally and 300~nm thick). These oscillators have excellent force sensitivity, yet provide stronger mechanical structures than typical ultrafloppy cantilevers designs. For example, an antisymmetric double-cantilever mode provides a minimum detectable force of $1.6\times 10^{-16}$~N/$\sqrt{\rm Hz}$ at room temperature, corresponding to $F_{\rm min} = 5 \times 10^{-18}$~N/$\sqrt{\rm Hz}$ at $^3$He temperatures. A double torsional mode typically provides enhanced sensitivity, so minimum detectable forces on the order of $10^{-19}$--$10^{-20}$~N/$\sqrt{\rm Hz}$ are now targeted. [Preview Abstract] |
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C1.00219: Surface Plasmon Based Spectrometer Andrew Wig, Ali Passian, Philip Boudreaux, Tom Ferrell A spectrometer that uses surface plasmon excitation in thin metal films to separate light into its component wavelengths is described. The use of surface plasmons as a dispersive medium sets this spectrometer apart from prism, grating, and interference based variants and allows for the miniaturization of this device. Theoretical and experimental results are presented for two different operation models. In the first case surface plasmon tunneling in the near field is used to provide transmission spectra of different broad band-pass, glass filters across the visible wavelength range with high stray-light rejection at low resolution as well as absorption spectra of chlorophyll extracted from a spinach leaf. The second model looks at the far field components of surface plasmon scattering. [Preview Abstract] |
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C1.00220: Atomic Force Microscopy Simulation in Aqueous Environment by RISM Theory Masanori Harada, Masaru Tsukada Many theoretical simulations of atomic force microscopy (AFM) have been performed so far to clarify the underlying physics in experimental AFM images which were difficult to understand intuitively. Most of the simulations use the models consisting of only tip and sample atoms and successfully reproduce experimental AFM images obtained in vacuo. However, those models are not suitable to simulate the AFM experiments performed in liquid or gaseous environments. Reference Interaction Site Model (RISM) is used in our simulation to incorporate liquid effect. This method is based on statistical mechanics and has the advantage of low computational cost over all-atom molecular dynamical simulations. To investigate the efficiency of the method, we simulated the force-distance curves and 2D force maps in constant height mode for a few simple models. The overall methodology is referred to the studies of Koga et al.[1], specially for the AFM-RISM interface. [1] K. Koga and X. C. Zeng, Phys. Rev. B 60, 14328 (1999). [Preview Abstract] |
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C1.00221: Two Meter Flight Path - Time of Flight Positron Annihilation Induced Auger Electron Spectrometer S. Mukherjee, K. Shastry, W. Maddox, A.H. Weiss Details of the design and construction of a new time of flight positron annihilation induced Auger electron (TOF-PAES) spectrometer are presented. The new spectrometer will be equipped with a 2 meter long ``TOF'' tube that can be biased at a potential different from that of the sample in order to increase or decrease the kinetic energy of the electrons traveling through the tube. The time of flight will be determined from timing signals obtained from the detection of the annihilation gamma (signaling the start of the flight) and detection of the annihilation induced Auger electron at the end of the 2 meter flight path (signaling the end of the flight). The 2 meter long flight path is a factor of two longer than used in previous TOF-PAES systems. The longer flight path can be expected to result in a fractional energy width: delta E/ E that is $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $ as large as the current UTA lab based TOF-PAES spectrometer. [Preview Abstract] |
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C1.00222: Theoretical simulation of nc-AFM images of mica surface in water Katsunori Tagami, Masaru Tsukada Based on molecular dynamics simulations, the non-contact atomic force microscopy (nc-AFM) images are simulated of mica surface in water. The tip is modeled by the carbon nanotube apex and the temperature is assumed to be 300 K. The interatomic interactions used in the calculations are listed in CHARMM22 and CLAY force field models. The force curves show oscillatory behaviours near the surface and their amplitudes are found to significantly depend on the scanning points, which produces highly resolved images of the surface structure. In the talk we will make a presentation on the relationship between the normal force and water density profile. [Preview Abstract] |
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C1.00223: Micromechanical force detectors for measuring magnetization at high magnetic fields and the magnetic response of Ba3Cr2O8. K. Ninios, H.B. Chan, Y. J. Jo, L. Balicas, A. Aczel, G. M. Luke We report magnetization measurements of Ba3Cr2O8 using micromechanical faraday balance magnetometers. The magnetometers consist of a movable polysilicon plate (500 by 500 micrometers) supported~ by four springs 2.75 micrometers above a fixed electrode. When small samples of the magnetic material are placed at the center of the movable plate, the natural gradient of the field creates a force on the sample that changes the capacitance between the plate and electrode, while the response to magnetic torque is minimized. The absolute magnetization of the sample can be determined provided that the magnetic field gradient is known. The device is used to measure the magnetization of a small sample of Ba3Cr2O8 with mass of 1 microgram. At high fields, our measurements reveal an asymmetric dome like structure in the temperature-magnetic field phase diagram, possibly related to the Bose-Einstein condensation of spin triplet degrees of freedom. [Preview Abstract] |
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C1.00224: Characterization and Modeling of Off-Specular Neutron Scattering for Analysis of Two Dimensional Ordered Structures Christopher J. Metting, Robert M. Briber, Julie A. Borchers, Brian Maranville, Paul Kienzle, Chuck F. Majkrzak, Joseph A. Dura Work is currently being done to expand further neutron reflectometry to the off-specular regime for the characterization of thin films with two-dimensional, ordered in- plane structures. The combination of this two-dimensional, in- plane information with the depth-profile that is routinely obtained from reflectivity data can produce a complete, 3-D description of both the structure and magnetic characteristics of these films. The University of Maryland along with the NIST Center for Neutron Research (NCNR) are developing software which can easily be integrated into existing neutron modeling package such as Reflpak, and will expand the accessibility of off-specular neutron reflectometry to the general scientific community. In this presentation, we show data obtained using a position sensitive detector on the AND/R instrument at the NCNR facility for a range of model systems. Preliminary analysis has been completed on several sample sets with wire and diffraction grating geometries. In addition, patterned gold samples are being lithographically produced in order to test models for a variety of standard feature structures and patterns. [Preview Abstract] |
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C1.00225: Upgraded varied-line-space PGM beamline at CAMD Pingheng Zhou, Eizi Morikawa CAMD is a synchrotron research center at the Louisiana State University. Recently, the center's aging plane-grating vuv soft x-ray monochromator beamline was upgraded to a varied-line-space plane-grating monochromator beamline. Preliminary experiments results show performance improvements in the resolving power from 1000 to 5000 and the throughput from 10$^{9}$ to 10$^{11}$ photons/sec.100 mA. A polarization aperture providing right and left circular polarized photon beams from the bending magnet radiation is scheduled to be installed in the front-end section of this beamline that will provide the opportunity to perform X-ray Magnetic Circular Dichroism(XMCD) spectrum experiments spectroscopy in the future. [Preview Abstract] |
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C1.00226: Free-electron laser-based pulsed electron paramagnetic resonance Susumu Takahashi, Mark S. Sherwin, Gerald Ramian, Louis-Claude Brunel, Johan van Tol High-power pulsed electron paramagnetic resonance (EPR) is extremely useful to study the ultrafast dynamics of spins. At present, most high-power pulsed EPR spectrometers operate near the X-band frequency of 9.5 GHz with kW-level power. A trend in the evolution of next generation pulsed EPR is for higher magnetic field and frequency, both for finer spectral and time resolution and because motional averaging becomes negligible. Since the linewidth of resonances studied by pulsed EPR tends to be extremely narrow, the source radiation also has to be stable and have narrow bandwidth. High-power pulsed EPR, using few-ns pulses to rapidly manipulate spins for spin-echo and related experiments, has been demonstrated at 95 GHz using kW- power Klystron-based sources. A bottleneck for higher frequency pulsed EPR spectroscopy is a lack of sources with high power and narrow bandwidth. The University of California Santa Barbara (UCSB) free-electron lasers (FEL) are potential sources for high-power pulsed EPR because they generate ~kW of power tunable from 120 GHz to 4.7 THz. We present the current status of the UCSB FEL-based 240 GHz pulsed EPR spectrometer. [Preview Abstract] |
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C1.00227: Directed Self-assembly of Nanostructures to Develop AFM-Based Biomaterial-to-Electronic Interface Mehdi Yazdanpanah, Mahdi Hosseini, Santosh Pabba, Scott Berry, Vladimir Dobrokhotov, Abdelilah Safir, Robert Keynton, Robert Cohn Very flexible and rugged Ag$_{2}$Ga nanoneedles of constant diameter (sub 100 nm diameter, 7-70 microns long) can be securely grown onto AFM tips at room temperature. These nanoneedles are electrically conductive and have stiffness well matched to viscoelastic properties of complex fluids and biological materials. This talk specifically presents the abilities of the needles to (1) make precise AFM measurements of surface tension, contact angle, evaporation rate, and shear viscosity of polymeric liquids, (2) measure complex viscoelastic properties of cell membranes and organelles of blood and endothelial cells, (3) capture and be surrounded by single live endothelial cells within a few seconds, (4) polymerize and detect the growth of protein nanofibers on the end of the nanoneedles and (5) Functionalize the end of the needles with protein nanofibers and use them for imaging the cell receptors. [Preview Abstract] |
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C1.00228: Force measurement with a scanning tunneling microscope Kai-Felix Braun, Saw-Wai Hla We present a method to measure the interaction force between single atoms with a scanning tunneling microscope [1]. During experiments for atomic manipulation with a scanning tunneling microscope the tip height curve is recorded. It is shown here that the amplitude of the manipulation curve is a measure for the interaction force between the microscopes tip and a single atom adsorbed on a surface. A simple formula is derived and tested. Extensions of this scheme to different surfaces shall be discussed. [1] K.-F. Braun and S.W. Hla, Physical Review B \textbf{75} (2007), 033406. [Preview Abstract] |
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C1.00229: ESR-MRI Using Low-Temperature Magnetic Resonance Force Microscopy Shigenori Tsuji, Tatsuya Fujimoto, Yohsuke Yoshinari, Kohsuke Inomata The low-temperature operation of Magnetic Resonance Force Microscopy (MRFM) leads to a significantly better signal-to-noise ratio (SNR) than at room temperature, because of an increase of the spin magnetization and a reduction of the thermo-mechanical noise of the cantilever. We have built a low-temperature equipment, which is capable of operating in vacuum at liquid helium temperature. Our setup employed the sample-on-cantilever design at present. A magnetic needle with $100~{\rm \mu m}$ in diameter was placed on a stage to generate magnetic field gradient $11.3~{\rm G/\mu m}$ at the magnetic field $714~{\rm G}$. The 3D closed-loop stage based on slip-stick principle allows a $200 \times 200 \times 200~{\mu m}^3$ scan range with $50~{\rm nm}$ resolution. The experimental results of the 2D magnetic resonance force map carried out on diphenylpicrylhydrazil (DPPH) at $T = 14~{\rm K}$ are shown and an improvement of the SNR by 154 compared with the results at room temperature is confirmed. The 2D reconstructed images will be shown as well. [Preview Abstract] |
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C1.00230: High-Resolution Combined Low-Temperature Scanning Tunneling/Atomic Force Microscope for 3D Force Spectroscopy B.J. Albers, M. Liebmann, T.C. Schwendemann, M.Z. Baykara, M. Heyde, M. Salmeron, E.I. Altman, U.D. Schwarz We present the design and first results from a new home-built low-temperature scanning probe microscope enabling high-resolution experimentation in both scanning tunneling microscopy (STM) and non-contact atomic force microscopy (NC-AFM) modes. A tuning fork based $Q$-plus style sensor is used to allow for flexibility in choosing probe tip materials. The system features an on-top cryostat, where the microscope is enclosed in a double set of thermal shields. Tip as well as sample can be changed in-situ at low temperatures to keep turn-around times low. By opening the front shutters of the shields, unrestricted access from dedicated flanges permits the direct deposition of molecules or atoms on either tip or sample while they remain cold. As examples for the microscope's performance, we present data measured on Cu(111) in STM mode as well as on graphite in NC-AFM mode, featuring atomic resolution with corrugations of 4-5 pm and corrugations below 1 pm could be measured. In addition, atomic resolution data obtained by local force spectroscopy is shown. [Preview Abstract] |
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C1.00231: Using Nuclear Magnetic Resonance Force Microscopy with Cross-Polarization for Nuclear Magnetization Enhancement and Heteronuclear Decoupling Rosa Elia C\'ardenas, John T. Markert We report our progress in applying Nuclear Magnetic Resonance Force Microscopy (NMRFM) to study position-dependent cross-polarization effects in ammonium hexafluorophosphate (NH$_4$PF$_6$). Cross polarization (CP) is typically used either to enhance the polarization of a weak or rare species, or to decouple one species from its dipolar interactions with another, that is, for line narrowing. With the added local probe abilities of NMRFM, particularly the presence of a strong field gradient, new techniques for coupling spins in nearby resonant slices are possible. The NH$_4$PF$_6$ system has three NMR-active nuclei: the stronger $^1$H and $^{19}$F nuclear moments, and the weaker and more rare $^{31}$P moments. We will examine the various effects of coupling $^1$H and/or $^{19}$F with $^{31}$P, including efficient frequency-sweep matching for optimization of the CP rate. We will also examine local effects dependent on excitation and detection slice geometry, and the dynamical effects of NH$_4^+$ and PF$_6^-$ reorientations. [Preview Abstract] |
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C1.00232: Tip-Sample Gap control for truly noncontact operation on an AFM Yehiam Prior, Alexander Milner A new mode of operation is introduced to standard atomic force microscopes, working under ambient conditions, for noncontact operation at a small predetermined Tip Sample Gap (TSG) of a few nanometers. A phase-locked loop, based on tiny oscillations ($<$1 nm) of the cantilever at a frequency far from the cantilever mechanical resonances, is used to maintain the gap between the tip and the sample at a range of 1 - 4 nanometers. The noncontact hovering of the tip is maintained for long times without the tip ever touching the surface. The TSG is calibrated by the far field scattering of evanescent fields over transparent samples. A typical measurement run provides, in addition to the standard topography, information about the amplitude and phase of the new oscillations, as well as information about the shear forces based on lateral oscillation of the sample relative to the tip. In a geometry characteristic for Apertureless Scanning Near Field Optical Microscope, the tip is illuminated by a focused beam of a femtosecond laser (800 nm, 20 fsec, 100 mw ) for nano-patterning of the area under the tip. [Preview Abstract] |
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C1.00233: A physically founded model of the efficiency curves of coaxial Germanium detectors Yunxia Guan, Lianbin Niu, Yan Ma, Jianzhang Xue, Qing Kang A semi-empirical formula for the full energy peak efficiency of coaxial Germanium detectors in the range from 60 to 2614 keV is presented. Both equations are linear with respect to the fitting parameters. They were obtained by combining, and minor adjusting, the terms in the asymptotic expressions for the probabilities of the processes (photoelectric absorption, Compton Scattering and pair production) through which $\gamma$-rays interact with matter. Both equations were found to be able to fit very well in wide energy ranges the efficiency curves of coaxial Ge detectors detecting $\gamma $-rays from point or plane sources, as well as from cylindrical volume sources. [Preview Abstract] |
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C1.00234: Derivation of sensitivity of a Geiger mode APDs detector from a given efficiency to estimate total photon counts Kiyotaka Hammura In quantum key distribution (QKD) experiments based on a single photon stream, a single photon detector incorporating Geiger mode avalanche photodiodes (APDs) is mostly used for detecting photons. It is important to estimate prior to experiment how many photons the detector can detect in total for a simple single photon stream. We propose a method of estimating it using intrinsic detection sensitivity (DS) instead of extrinsic detection efficiency (DE). We derive DS using figures to give the DE for some specific configuration and a quantity, designated by NB, of how many photons are ignored due to a blanking operation of the detector to suppress dark counts originating from after pulsing. \begin{equation} DS = \frac{\mbox{(How many photons have been counted per second)}} {\mbox{(How many photons have arrived per second} - N_B)} \end{equation} resulting in 0.27. Applying this value of DS to our experimental configuration, the total photon counts are estimated at 81,000 counts/second. DE under these configurations is estimated at 0.16, which is found to be smaller than that at a lower triggering rate configuration. [Preview Abstract] |
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C1.00235: METALS |
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C1.00236: ABSTRACT WITHDRAWN |
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C1.00237: Dynamic acoustic effects and hysteresis in dislocation-based kinking nonlinear elastic solids under stresses Peter Finkel We argue that proposed recently mechanism explaining inelastic hysteresis in non-linear elastic systems indeed can be explained by means of formation of dislocation-based incipient kink bands (IKB). Using acoustic waves we investigated possible dislocation related mechanisms responsible for nonlinear dynamic response of IKB solids. In this work, for the first time we observed and reversibility of IKB formation directly under stress using ultrasonic waves and acoustic emission signatures during compression test of nanolaminated layered ternary carbide (MAX phases) and hexagonal metal samples. We confirm here that the dynamic behavior of these non-linear elastic systems is due to the interaction of dislocations with the stress waves. [Preview Abstract] |
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C1.00238: Direct Estimation of Strain Gradient Maps in Plane Strain Indentation Tejas Murthy, Chihyung Huang, Srinivasan Chandrasekar Indentation is a widely used non-destructive means for assaying mechanical properties of metals. \textit{In-situ} Experimental investigations on the extent of deformation and the distinct features of the deformation field around a plane strain wedge indenter were performed. A rigid plastic material (lead) was indented under plane strain conditions with different deformation rates and wedge angles. The region around the indenter was directly observed by tracking asperity movements on the surface of the specimen using high-speed imaging. The digitized images were analyzed using particle image velocimetry (PIV) to obtain velocity fields. Strain rate fields and strain maps were also obtained through analysis of this velocity field. Estimates of the strain gradients at a macro scale have afforded detailed analysis of the size effects in indentation and validation of flow theories at a macroscopic scale. [Preview Abstract] |
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C1.00239: Ab initio simulations of grain boundary sliding in aluminum and nickel Jivtesh Garg, Nicola Marzari The Hall-Petch relationship predicts an increase in material yield strength with decreasing grain size. However, a breakdown has been reported at smaller grain sizes, where plastic deformation gradually becomes grain-boundary dominated. Studying grain-boundary sliding processes is therefore key to understanding the mechanical properties of polycrystalline materials. In the present work, we use density-functional theory to examine the microscopic processes that accompany grain boundary sliding in aluminum and nickel for different grain boundary structures. Sliding of tilt boundaries is also accompanied with grain boundary migration, where grain boundary movement normal to the boundary surface takes place. The effect of adding W to the sliding process in Ni-W alloys is also reported. [Preview Abstract] |
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C1.00240: Laser induced patterning of metal films via weakly bound layers on surfaces Micha Asscher, Ori Stein, Yigal Lilach, Leonid V. Zhigilei, Zhibin Lin Pulsed laser heating of weakly bound layers has been employed for selective removal of these layers. The ablated films (Xe) are then used as templates for metallic clusters and film patterning. The method enables patterning over most substrates that absorb the laser light, e.g. Ru(001) single crystal, soft surfaces prepared from self assembled monolayers (SAM) and SiO$_{2}$/Si(100). Patterns obtained from interfering laser beams result in a ratio of laser wavelength to width of pattern's edge less than 1:40, better than most standard optical, mask-less patterning techniques. In-situ optical diffraction has been utilized to study the thermal stability of the patterned weakly bound films against surface diffusivity and desorption. Molecular Dynamics simulations of a Xe film composed of 15,000 atoms attached in 14 layers, has demonstrated a threshold for ablation at 100J/m$^{2}$. At identical laser energy above threshold and 3-10 psec pulse duration range, longer pulses result in better patterning resolution. [Preview Abstract] |
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C1.00241: Laser-induced dewetting nanomorphology and nanostructure in immiscible bilayer metal films H. Krishna, R. Sureshkumar, R. Kalyanaraman Spatially ordered patterns of nanoparticles result under ns laser-induced dewetting of immiscible bilayer metallic films (Co and Ag) on inert substrates like SiO$_{2}$. The morphological pathway during dewetting is different for the two individual metals: occurring through development of bicontinuous structures in the case of Ag and by progression of cellular networks for Co. On the other hand, dewetting in bilayer structures of Ag/Co/SiO$_{2}$ or Co/Ag/SiO$_{2}$ shows that the morphology evolution is dictated by the thicker of the two films. Linear stability analysis predicts that the self-organized length scales from the bilayer film dewetting is smaller than a single layer of either metal with the same total thickness. This was also verified experimentally and shows that the metal-metal interfacial dynamics significantly influences bilayer dewetting. Electron microscopy investigations show that the individual nanoparticles consist of Ag and Co in their individual elemental crystal phase. These ns laser dewetting experiments provide novel ways to create multi-metal patterns and nanostructures. [Preview Abstract] |
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C1.00242: An Evaluation of the Rigid Band Model and the Virtual Crystal Approximation in the Transition Metals Dimitrios Papaconstantopoulos, Fred Iacoletti, Alex Koufos The Schrodinger equation was solved using the Augmented Plane Wave (APW) Method for transition metals in both the body centered cubic (bcc) and face centered cubic (fcc) structures. This method accurately predicts the equilibrium lattice parameter and the ground state of all transition metals. The Rigid Band Model tests based on the group eight and group nine transition metals was applied to predict the density of states (DOS) at the Fermi level for the rest of the transition metals. This test agreed with direct calculations quite well with only a few exceptions in the hexagonal structures. The APW method was also applied using the virtual crystal approximation to obtain the DOS of binary alloys. The results will be compared with direct calculations of ordered and disordered structures. [Preview Abstract] |
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C1.00243: The Density Functional Calculation for Surface Capacitance of Metal-Semiconductor Junction Chin-Sheng Wu We use the density functional theory to find the density of the surface electronic charge around metal-semiconductor junction. We use the local approximation for the inhomogeneous dielectric function around the junction. Therefore this surface charge can be applied to find dielectric constant, which is a function of the electron density. The capacitances are calculated on the junction by their shapes and dielectric constants for various metal and semiconductor densities. [Preview Abstract] |
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C1.00244: Comparison of the Phase Field Crystal Free Energy Functional and the Second Order Density Functional Theory of Freezing Akusti Jaatinen, Cristian Achim, Jari Jalkanen, Tapio Ala-Nissila, Ken Elder We present a numerical study of the recently established connection between the phenomenological free energy functional of the phase field crystal model (PFC) and the second-order density functional theory of freezing (DFT) [1]. We have used liquid state structural data of iron and copper near their melting points to study their freezing properties by both DFT and PFC functionals. The results obtained by the two functionals differ from each other significantly, DFT being superior to PFC in predicting crystal structures, density profiles and coexistence densities. We conclude that the fitting procedure outlined in [1] does not provide quantitatively accurate predictions of phase diagrams. [1] K. R. Elder, N. Provatas, J. Berry, P. Stefanovic and M. Grant, Phys. Rev. B 75, 064107 (2007) [Preview Abstract] |
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C1.00245: ABSTRACT WITHDRAWN |
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C1.00246: STATISTICAL AND NONLINEAR PHYSICS |
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C1.00247: Doebner-Goldin Equation for Electrodynamic Model Particle \& Applications J.X. Zheng-Johansson We set up based on Maxwell's equations the classical wave equation for the total wave of a particle composed of an oscillatory charge of zero rest mass and the resulting electromagnetic waves traveling in the force field of an usual potential and an additional frictional force $f$. The equation decomposes into a component equation describing the particle kinetic motion, which for $f=0$ identifies with the usual Schr\"odinger equation. The $f$-dependent probability density presents generally an observable diffusion current of a real diffusion constant; this and the particle's usual quantum diffusion current as a whole are under adiabatic condition conserved and obey the Fokker-Planck equation. The extra, $f$- dependent Hamiltonian operator identifies with that obtained by Doebner and Goldin. The friction produces to the particle's wave amplitude a damping that can describe well the effect due to a radiation (de)polarization (RD) field, which is always by- produced by the particle's oscillatory charge in a (nonpolar) dielectric medium; such a friction and the resulting observable diffusion as intrinsically accompanying the particle motion was as strikingly conjectured in the Doebner and Goldin original discussion. The RD field in a dielectric vacuum exerts on another particle an attractive, depolarization radiation force which overall resembles Newton's gravity, and on the particle itself an attractive, self depolarization radiation force whose time rate gives directly the $f$ (full paper: SNMP2007). [Preview Abstract] |
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C1.00248: The Effects of Popping Popcorn Under Reduced Pressure Paul Quinn, Amanda Cooper In our experiments, we model the popping of popcorn as an adiabatic process and develop a process for improving the efficiency of popcorn production. By lowering the pressure of the popcorn during the popping process, we induce an increase in popcorn size, while decreasing the number of remaining unpopped kernels. In this project we run numerous experiments using three of the most common popping devices, a movie popcorn maker, a stove pot, and a microwave. We specifically examine the effects of varying the pressure on total sample size, flake size and waste. An empirical relationship is found between these variables and the pressure. [Preview Abstract] |
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C1.00249: Dynamic localization and transport of a quantum particle in an optical lattice. Panagiotis Maniadis, George P. Tsironis We study the localization and the transport of a quantum particle in an optical lattice under the influence of an AC electric field. For the description of the particle we use a generalized Discrete Nonlinear Schr\"odinger equation with local and nonlocal nonlinearities Depending on the parameters of the system, and the external driving field, different behavior is observed (hopping, diffusion, dynamic localization). We explore numerically the behavior of the particle for different values of the external field and the internal nonlinearity parameters, and we compare our results with experimental observations. [Preview Abstract] |
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C1.00250: Hysteresis-induced long-time tails Guenter Radons Many systems ranging from magnetic materials to shape memory alloys, or fluids in porous structures show complex hysteretic behavior in the sense that besides major loops, subloops and non-local memory effects are observed. The most prominent phenomenological model to account for such effects is the so-called Preisach model [1]. For this model it is shown analytically that uncorrelated input in time is transformed into output showing power-law decay of correlations and 1/f-noise. The characteristic exponents are shown to depend on the tails of the input density and the Preisach density. Universality classes leading to these results are identified. \newline [1] G. Bertotti, I. D. Mayergoyz (Eds.), The Science of Hysteresis, Vol.1-3 (Academic Press, London, 2006). [Preview Abstract] |
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C1.00251: Reaction-Diffusion Processes on Networks Kyungsik Kim, Soon-Hyung Yook, Soo Yong Kim, Ki-Ho Chang We study the novel reaction-diffusion process of three-species on scale-free networks, which is significantly different from the numerical calculation manipulated on regular and small-world lattices. The inverse particle density for three-species process scales as the power-law behavior with $\alpha=1.5$ for $\gamma>3 $. However we find that the inverse particle density scales in a different way depending on time $t$ when $\gamma<3$. In the early time regime, $\alpha\simeq 1.5$ but the inverse particle density increases exponentially as time increases. We also discuss the possible relationship to the dynamical properties of random walks. Particularly, we measure the ratio between the number of inactive and active bonds which shows the segregation of the particles. [Preview Abstract] |
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C1.00252: A node-weight description on a kind of cooperation-competition networks Dan Shen, Da-Ren He Cooperation and competition between elements usually appear together in complex systems. We consider the kind of the systems, which can be described by bipartite graphs. In the networks there are two types of nodes: some activities, organizations or events, and the participators. The traditional bipartite graph statistical properties may describe the configuration of the cooperation-competition, and the statistical properties about a node weight may describe the different role of a node in cooperation or competition result. We shall present some empirical investigations on Chinese Movie Network, Beijing Restaurant Network and IT product Network as examples. [Preview Abstract] |
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C1.00253: IT product competition Network Xiu-Lian Xu, Lei Zhou, Jian-Jun Shi, Yong-Li Wang, Ai-Xia Feng, Da-Ren He Along with the technical development, the IT product competition becomes increasingly fierce in recent years. The factories, which produce the same IT product, have to improve continuously their own product quality for taking a large piece of cake in the product sale market. We suggest using a complex network description for the IT product competition. In the network the factories are defined as nodes, and two nodes are connected by a link if they produce a common IT product. The edge represents the sale competition relationship. 2121 factories and 265 products have been investigated. Some statistical properties, such as the degree distribution, node strength distribution, assortativity, and node degree correlation have been empirically obtained. [Preview Abstract] |
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C1.00254: The combined traffic network of China Chang-Gui Gu, Si-Jun Pan, Kai-Jun Li, Yan-Qing Qu, Chao Qiao, Yu-Mei Jiang, Da-Ren He From a new viewpoint, we study the combined traffic network of china including the intercity bus network, the railway network, and the airplane network. Some statistical properties, such as averaged distance, clustering coefficient, assortativity, degree distribution, and degree correlation have been empirically investigated for each traffic network and the combined one. From the results we found that the cumulative distribution of cluster coefficient is in a good agreement with the node degree distribution. In order to describe the jumping between the sub-networks, we define and discuss some new statistical properties, such as the jump-convenience and average jumping distance. This may be the first investigation on a combined traffic network. [Preview Abstract] |
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C1.00255: Chinese Mainland Movie Network Ai-Fen Liu, Yu-Hua Xue, Da-Ren He We propose describing a large kind of cooperation-competition networks by bipartite graphs and their unipartite projections. In the graphs the topological structure describe the cooperation-competition configuration of the basic elements, and the vertex weight describe their different roles in cooperation or results of competition. This complex network description may be helpful for finding and understanding common properties of cooperation-competition systems. In order to show an example, we performed an empirical investigation on the movie cooperation-competition network within recent 80 years in the Chinese mainland. In the net the movies are defined as nodes, and two nodes are connected by a link if a common main movie actor performs in them. The edge represents the competition relationship between two movies for more audience among a special audience colony. We obtained the statistical properties, such as the degree distribution, act degree distribution, act size distribution, and distribution of the total node weight, and explored the influence factors of Chinese mainland movie competition intensity. [Preview Abstract] |
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C1.00256: A network description on fruit nutritive factor system Yan-qing Qu, Yu-Mei Jiang, Da-Ren He We propose describing a kind of cooperation-competition systems by node-weighted bipartite graphs. In the systems the nodes can be divided into two types. One type expresses a kind of activities, organizations or events, named ``acts''; the other expresses the ``actors'' participating the acts. In each act the actors basically show collaboration relationship, however they play different role in the cooperation. This is a kind of competition. The node weight usually signify the role or ``importance degree'' of each actor. We propose using some statistical properties for the description of such kind of systems. The properties without considering node-weight can describe the cooperation situation and configuration. The properties with node-weight considered may describe the competition results. We report an example system, the fruit nutritive factor network, to show the description method and the corresponding empirical investigation results. It is our wish that the description method could be widely effective for the kind of systems in variety different scientific fields. [Preview Abstract] |
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C1.00257: A Collaboration Network Model Of Cytokine-Protein Network Sheng-Rong Zou, Ta Zhou, Yu-Jing Peng, Zhong-Wei Guo, Chang-gui Gu, Da-Ren He Complex networks provide us a new view for investigation of immune systems. We collect data through STRING database and present a network description with cooperation network model. The cytokine-protein network model we consider is constituted by two kinds of nodes, one is immune cytokine types which can be regarded as collaboration acts, the other one is protein type which can be regarded as collaboration actors. From act degree distribution that can be well described by typical SPL (shifted power law) functions [1], we find that HRAS, TNFRSF13C, S100A8, S100A1, MAPK8, S100A7, LIF, CCL4, CXCL13 are highly collaborated with other proteins. It reveals that these mediators are important in cytokine-protein network to regulate immune activity. Dyad in the collaboration networks can be defined as two proteins and they appear in one cytokine collaboration relationship. The dyad act degree distribution can also be well described by typical SPL functions. [1] Assortativity and act degree distribution of some collaboration networks, Hui Chang, Bei-Bei Su, Yue-Ping Zhou, Daren He, Physica A, 383 (2007) 687-702 [Preview Abstract] |
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C1.00258: An Empirical Study of Immune System Based On Bipartite Graphs Yu-Jing Peng, Sheng-Rong Zou, Zhong-Wei Guo, Ta Zhou, Chang-gui Gu, Da-Ren He Immune system is the most important defense system to resist human pathogens. We present an immune bipartite graph model. Firstly we collect data through COPE database and then construct an immune cell-mediator network. In the net the immune cells can be regarded as collaboration acts and the mediators can be regarded as collaboration actors. The act degree distribution of this network is proved to be power-law with a scaling exponent 1.8. From our analysis, we found that some mediators with high degree are very important in the process of regulating immune activity, such as TNF-alpha, IL-8, TNF-alpha receptors, CCL5, IL-6, IL-2 receptors, TNF-beta receptors, TNF-beta, IL-4 receptors, IL-1 beta, CD54 and so on. We also found that the assortativity coefficient of the immune network is -0.27. [Preview Abstract] |
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C1.00259: A bipartite graph of Neuroendocrine System Zhong-Wei Guo, Sheng-Rong Zou, Yu-Jing Peng, Ta Zhou, Chang-gui Gu, Da-Ren He We present an empirical investigation on the neuroendocrine system and suggest describe it by a bipartite graph. In the net the cells can be regarded as collaboration acts and the mediators can be regarded as collaboration actors. The act degree stands for the number of the cells that secrete a single mediator. Among them bFGF (the basic fibroblast growth factor) has the largest node act degree. It is the most important mitogenic cytokine, followed by TGF-beta, IL-6, IL1-beta, VEGF, IGF-1and so on. They are critical in neuroendocrine system to maintain bodily healthiness, emotional stabilization and endocrine harmony. The act degree distribution shows a shifted power law (SPL) function forms [1]. The average act degree of neuroendocrine network is h=3.01, It means that each mediator is secreted by three cells on average. The similarity, which stands for the average probability of secreting the same mediators by all neuroendocrine cells, is observed as s=0.14. Our results may be used in the research of the medical treatment of neuroendocrine diseases. [1] Assortativity and act degree distribution of some collaboration networks, Hui Chang, Bei-Bei Su, Yue-Ping Zhou, Daren He, Physica A, 383 (2007) 687-702 [Preview Abstract] |
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C1.00260: Triangle-3star-Correlations in the mean-field solution of equilibrium ensembles of undirected networks with 3-edge interactions Peter Fleck, Noshir Contractor We study the equilibrium statistical mechanics of ensembles of undirected networks with triangle- and 3-star-type interaction among bi-valued edges. We discuss the analytical expressions for the statistics' averages in mean-field approximation as a function of these interaction parameters. We find these averages to be highly correlated for a large region of the parameter space. Quantifying these correlations we especially find triangle- and 3-star-motifs to correlate with one another. Markov Chain Monte Carlo simulations confirm the analytical mean-field results in an important part of parameter space. Implications for the analysis of network topologies are being discussed. [Preview Abstract] |
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C1.00261: Multifractal Behaviors in Foreign Exchange Markets Kyungsik Kim, Soo Yong Kim , Gyuchang Lim, Enrico Scalas, Dong-In Lee The market information and its intensity for the context of two-phase phenomenon is introduced in financial exchange markets. To find the underlying process of the formation of market information, we investigate the multifractal properties of the market information in terms of the multifractal and the detrended fluctuation analysis and also examine the higher order correlations between successive pieces of market information. Although the multifractal properties of the market information process is clearly confirmed, the simple binomial multiplicative process is not appropriate to catch its dynamics. It means that the market information process can be essentially different from the fully developed turbulence. [Preview Abstract] |
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C1.00262: Universality in rank distributions due to multiplicative processes : from power laws to stretched exponentials Gerardo Naumis, Germinal Cocho Although power laws have been used to fit rank distributions in many different contexts, they usually fail at the tails. Stretched exponentials and log-normal distributions have been used to solve the problem, but unfortunately they are not able to fit at the same time both ending tails. Here we show that many different data in rank laws, like in granular materials, codons, author impact in scientific journal, etc. are very well fitted by a beta-like function ({a,b} distribution). Since this distribution is indeed ubiquitous, it is reasonable to associate it to the product of correlated probability distributions. In particular, we have found that the macrostates of the product of discrete probability distributions imply stretched exponential-like frequency-rank functions, which qualitatively and quantitatively can be fitted with the {a,b} distribution in the limit of many random variables [1]. We prove this by transforming the problem into an algebraic one: finding the rank of successive products of a given set of numbers. [1] New J. Phys. 9 (2007) 286. (2007). [Preview Abstract] |
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C1.00263: Dynamical Behaviors of rainfalls in Korean peninsula Kyungsik Kim, Soo Yong Kim , Gyuchang Lim, Ki-Ho Chang, Jae-Won Jung, Sang-Bum Park, Myung-Kul Yum Application of ideas from fractal and chaos theories to characterize rainfall is one of the most active and exciting areas of research in this field. Many studies performed thus far have yielded evidence of the existence of fractal and chaos properties in rainfall. In this work, we present a singularity spectrum of a rainfall time series to provide strong evidence of multifractality. A curdling cascade process in a well developed turbulence is presented as a candidate to describe the rainfall, and the analogy between the rainfall and turbulence is confirmed via the validity of the binomial multiplicative process to describe both systems. [Preview Abstract] |
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C1.00264: Colloids in a periodic potential: driven lattice gas in continuous space Ronald Dickman, Fabricio Potiguar Motivated by recent studies of colloidal particles in optical tweezer arrays, we study a two-dimensional model of a colloidal suspension in a periodic potential. The particles tend to stay near potential minima, approximating a lattice gas. The interparticle interaction, a sum of Yukawa terms, features short-range repulsion and attraction at somewhat larger separations, such that two particles cannot occupy the same potential well, but occupation of adjacent cells is energetically favored. Monte Carlo simulation reveals that the equilibrium system exhibits condensation, as in the Ising model/lattice gas with conserved magnetization; the transition appears to be continuous at a half occupancy. We study the effect of biased hopping, favoring motion along one lattice direction. This system is found to exhibit features of the driven lattice gas: the interface is oriented along the drive, and appears to be smooth. A weak drive facilitates ordering of the particles into high- and low-density regions, while stronger bias tends to destroy order, and leads to very large energy fluctuations. We also study ordering in a {\it moving} periodic potential. Our results suggest possible realizations of equilibrium and driven lattice gases in a colloidal suspension subject to an optical tweezer array. [Preview Abstract] |
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C1.00265: Disordered contact process in two and three dimensions: rare regions, Griffiths effects, and infinite randomness Adam Farquhar, Jason Mast, Thomas Vojta We investigate the effects of quenched spatial disorder on the directed percolation universality class in two and three space dimensions. To this end we perform large-scale Monte-Carlo simulations of the contact process on a randomly diluted lattice for times up to $10^{10}$ and system sizes up to $6 \times 10^7$ sites. We study both the nonequilibrium phase transition and the associated Griffiths region between the clean and disordered critical points. Rare strongly coupled regions lead to slow dynamics characterized by a nonuniversal power-law density decay in the entire Griffith region. In two dimensions, we also perform a detailed scaling analysis of the critical behavior right at the phase transition. We find an infinite-randomness critical point with activated rather than power-law dynamical scaling. However, the critical region is narrow and the approach to the asymptotic dynamics is extremely slow, which hampers the precision of our critical exponent estimates. We discuss the generality of our findings and relate them to a broader theory of rare region effects at phase transitions with quenched disorder. [Preview Abstract] |
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C1.00266: Phase diagram, depinning and sliding friction in the Phase Field Crystal model Tapio Ala-Nissila, Cristian Vasile Achim, Ken R. Elder, Mikko Karttunen, Enzo Granato, See Chen Ying We present results for commensurate-incommensurate transitions and non-linear sliding friction for a two-dimensional crystal lattice in the presence of an external pinning potential in the Phase Field Crystal model. This model provides a continuum description of lattice system, such as adsorbed monolayers or two-dimensional vortex lattice. The competition between the length scales associated with the intrinsic ordering and the pinning potential leads to commensurate-incommensurate transitions. The dynamical response of the system in the presence of a driving force has also been studied via the time dependent Ginzburg-Landau equation. We present results on non-linear dynamics and sliding mechanisms for commensurate phases. [Preview Abstract] |
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C1.00267: Development of a Fracture Network: blocks and springs model Martin Ferer, Adam Jozwick, Duane Smith Since flow in fractured reservoirs is significantly enhanced by clusters of inter-connecting fractures, it's important to understand their inter-connectedness. In these fractured reservoirs, one often finds two sets of fractures due to two separate geologic events. We have developed a blocks and springs model to study how the second generation fractures intersect the first generation of. We find a percolation-like transition where the cluster size grows with increasing strain leading to system-spanning fractal clusters. Increasing the thickness of the layer being fractured leads to sparser system-spanning fracture clusters with smaller fractal dimension. We have studied how the thickness of the layer affects the fractal character of the fracture clusters as well as their number distribution, and the correlations within the large fracture cluster. [Preview Abstract] |
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C1.00268: Cyclic deformation of polymer glasses in the yield regime by a contact method Antoine Chateauminois, Christian Fretigny Cyclic strains in the yield regime are characterized by a slow evolution of the mechanical response of polymer glasses toward a poorly understood stationary state. In this study, the dynamics of plastically deformed polymer glasses is analysed by a contact method where a thin film is geometrically confined and sheared within a contact between two elastic substrates. As opposed to conventional mechanical testing using bulk polymers, this approach allows to investigate the cyclic plastic behavior without the complications arising from fracture. From a measurement of the lateral contact response, we have shown that the shear properties of the film can be determined both in the linear and in the non linear regime. Using this approach, the time and strain dependent shear response of polymer glasses in the yield regime will be discussed. In addition, linear viscoelastic measurements carried out after the application of cyclic yield provides information about the dynamics of plastically deformed glass and its recovery. [Preview Abstract] |
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C1.00269: Numerical studies of the Zaitsev (Robin Hood ) model Perry Fox, Gabriel Cwilich, Sergey Buldyrev, Fredy Zypman The Zaitsev[1] model of depinning of interfaces has been widely used to discuss motion of dislocations, low temperature flux creep, and more recently dry friction. The properties of this model have been discussed theoretically in one dimension, and numerically verified with precision in the isotropic case. We are studying here the effect of anisotropy in the distribution of the ``mass'' among the neighbors in the updating of the sites, which is known to modify the critical exponents of the model in one dimension. We have considered the validity of the scaling laws in higher dimensions, which might be relevant for the case of friction [2], by computing several of the exponents of the model for the avalanche size distribution, average avalanche size, avalanche fractal dimension and distribution of jumps between extremal sites of activity. The much richer space of parameters of anisotropy in two dimensions has been explored. [1] S.I. Zaitsev , Physica \textbf{A189}, 411 (1992). [2] S. Buldyrev, J. Ferrante and F. Zypman Phys. Rev \textbf{E64}, 066110, (2006) [Preview Abstract] |
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C1.00270: A physical mechanism for enhanced orientational order of self propelled hard rods Aparna Baskaran, Cristina Marchetti We consider a model of 2D hard rods on a substrate. The rods interact through energy and momentum conserving binary collisions. Self propulsion is implemented as a center of mass force acting along the long axis of each rod. The nonequilibrium statistical mechanics for this microscopic model is systematically developed. In the overdamped regime, the dynamics is described by a modified Smoluchowski equation that includes new momentum transfer contributions that arise from self propulsion. Hydrodynamic equations for the density, polarization and nematic order parameter are derived by coarse graining the Smoluchowski equation. The homogeneous equations yield an isotropic-nematic transition at lower densities than the Onsager density corresponding to an equilibrium system of hard rods. This enhanced ordering arises from the additional momentum transfer associated with self propulsion and is expected to be a generic feature of a broad class of active systems. [Preview Abstract] |
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C1.00271: Statistics preserving formation of chaotic swarmers Iuliana Oprea, Ioana Triandaf, Ira Schwartz We present a class of models for self-propelled multi-agent systems of autonomous vehicles that accomplish common tasks while preserving the formation moments of inertia. The models are based on simple, local interaction rules that create prescribed overall complex patterns in which coupling and communication are key elements. We use a statistics-preserving algorithm with a Duffing-like term added to the equations of motion to control the moments of the pattern formation. We concentrate on those parameters in the neighborhood of a resonant situation. This allows us to obtain interesting patterns of behavior similar to those observed in parametrically forced systems near resonance. [Preview Abstract] |
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C1.00272: Modular Networks in the Neocortex H.G.E. Hentschel We will describe our approaches to characterizing the network architecture of active neurons in mouse neocortex in terms of modules and functional motifs, in order to extract their information processing capabilities. The raw data comes from fast two photon microscopic techniques recently developed using flourescent Ca2+ indicators to record the spontaneous and evoked activity from hundreds of identified cells in mouse. This ensemble of active neurons can be considered as a complex network linked by synaptic connections, and represented as a graph of nodes connected by edges. Information processing in the network requires interaction of neurons in different functional assemblies (microcircuits) over time. We will describe the information we have been able to uncover on these microcircuits and their function. [Preview Abstract] |
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C1.00273: Study on the hierarchical property between the functional classes in protein-protein interaction network Young-Jin Ko, Soon-Hyung Yook, Yup Kim Detecting community structures and hierarchy among communities have been one of the most attractive research topics in complex network studies. In this study we regard each protein as an oscillator which interacts with its neighboring proteins. In order to define the hierarchy among the functional classes based on the synchronizability of each functional classes, we introduce a parameter $r_{link}$. Here $r_{link}$ represents the fraction of all possible links whose ends nodes are synchronized. From the numerical simulations we find that the hierarchical structure between functional classes does not depend on the coupling strength. We expect that this result provides a clue to understand the mechanism to form the specific structure of PIN. Some possible relationships between the observed hierarchical structure of the functional classes and the properties of the PIN are also discussed. [Preview Abstract] |
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C1.00274: Phase synchronization induced by common external telegraphic noise Ken Nagai Generally, noise desynchronizes phase of nonlinear oscillators. However, when a neuron receives a randomly fluctuating input current, its reliability of spike generation improves compared with the case of a constant input current [Mainen and Sejnowski, Science $\textbf{268}$, 1503 (1995)]. Like this phenomenon, phase synchronization between uncoupled nonlinear oscillators subject to a common external noise occurs in some systems. Phase synchronization between uncoupled limit-cycle oscillators is induced by common external telegraphic noise that jumps between two values randomly [Nagai and Nakao, Phys. Rev. E, $\textbf{71}$, 036217 (2005)]. We observed this phenomenon with an electric circuit and analyzed it. When the switching time of the input current is sufficiently long, the internal state of the oscillator randomly jumps between two limit cycles corresponding to the input values, which can be described by random phase maps. We determined the phase maps experimentally and discussed the synchronization of oscillators subject to fluctuating inputs, using this maps. The Lyapunov exponents of the maps corresponded to damping rate of the variance of the phase. [Preview Abstract] |
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C1.00275: Thin-film morphology dependence on adatom-substrate interaction energy Nuno A.M. Araujo, Cristovao S. Dias, Antonio Cadilhe We study, by kinetic Monte Carlo, the influence of adatom-substrate interaction energy on the morphology of heteroepitaxial film growth. We take the case of (1+1)-dimensions for sake of simplicity. We also define $\alpha$ as the quotient between the above interaction and the adatom-adatom interaction. We measure the roughness in time. We show that changing the value of $\alpha$ it is possible to range from a wetting regime to a non-wetting one. We also show that above a critical thickness, film growth becomes independent of adatom-substrate interaction. [Preview Abstract] |
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C1.00276: Agent based spin model for financial markets on regular lattices and complex networks Hong-Joo Kim, Soon-Hyung Yook, Yup Kim We study an agent based microscopic model for price formation in financial markets on various topologies motivated by the dynamics of agents. The model consists of interacting agents (spins) with localand global couplings. The local interaction denotes the tendency of agents to make the same decision with their interacting partners. On the other hand, the global coupling to the self-generating field represents the process which maximizes the profit of each agent. In order to incorporate more realistic situations, we also introduce an external field which changes in time. This time-varying external field represents any internal or external interference in the dynamics of the market. For the proper choice of model parameters, the competition between the interactions causes an intermittency dynamics and we find that the distribution of logarithmic return of price follows a power-law. [Preview Abstract] |
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C1.00277: Complexity and Ability in Ising Games Ayax Ramirez, Michael George In previous work [1, 2], we discussed various facets of designs in games, and considered the evolution [2] of Ising games. The traditional aspect of game theory, with its focus on rational decisions, was not considered in this work. Instead, there was a predominant interest in the time evolution of design toward a goal design, and resulting levels of frustration. There was also a concern with time- reversal properties. In the new work, our goal is to consider the \textquotedblleft molecular structure\textquotedblright\ of the Ising model as it evolves, and to associate this molecular structure with feedback into the structure that can be understood in algorithmic terms. We develop an analogy with the famous Malthusian argument concerning exponential population increase, associating ability to cope with complexity, and algorithmic complexity, and discuss biological implications of the ideas associated with these games. [1] M. George, A nonequilibrium statistical model based on latin squares, paper presented at WorldComp'07, Las Vegas, Nevada, June 25-28, 2007. [2] M. George, Classical and quantum Ising games, paper presented at Fourth International Conference in Applied Mathematics and Computing, Plovdiv, Bulgaria, August, 2007. [Preview Abstract] |
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C1.00278: Wrinkling induced by poking a free-floating film under tension Narayanan Menon, Jiangshui Huang, Enrique Cerda, Wim de Jeu, Thomas Russell We study experimentally and theoretically the out-of-plane deformation in a floating polystyrene film induced by depressing the centre of the film by a distance, d. When this depth exceeds a critical value d{\_}c, the smooth conical deformation of the film becomes unstable to an elastic instability in which a radial wrinkling pattern develops. The wrinkles have a finite length, and originate a finite radius from the centre. This observation is completely reproduced by a calculation starting from the von Karman equations. Experimental results and theoretical predictions for the critical depth as a function of the thickness and elasticity of the films are in good agreement. We also present theoretical results for the number and the length of the wrinkles, and the radius of the cone of smooth deformation. [Preview Abstract] |
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C1.00279: Percolation density profiles and lattice structures Robert Ziff, Peter Kleban, Jacob Simmons, Christian Scullard This poster presents a visual display of results on percolation density profiles from anchor points and intervals along the side, demonstrating our theoretical predictions of various forms of factorization of the three point functions into products of two-point functions (some with square roots). We also show a gallery of numerous lattice structures where the percolation threshold can be found exactly through the triangle-triangle transformation, or approximately (to very high precision) by generalizations of known formulas. Studies of various classes of lattices shows slight but non-zero corrections for most non-triangular configurations. Methods to numerically find the threshold (hull generation, cluster growth, and cluster-coalescence) are also presented. [Preview Abstract] |
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C1.00280: SIEGEL GMR [DECADE PRE-Fert] $->$ Diffusive-MR $->$ Magnetic-H-Valve $->$ HINDENBURG-EFFECT $->$ FLYING-WATER Makes New H2O in New Places, TERRAFORMING via ONLY H MAX-Buoyancy on Geomorphology: H-Up; H2O-Down: Renewables-H-H2O: ONLY H IS FLYING-WATER Edward Siegel ``G/CMR'' 2007 Physics Nobel/Wolf/Japan-Prizes ``a tad'' PREdated by SIEGEL[www.flickr.com; search on GMR]{@:WAPD/PSEG/IAEA/ABB(1973-77)}[J.Mag.Mag.Mtls.,7,312 \& 334(1978); -``mysteriously'' ``not yet scanned'' by Elsevier!?; A.Mayo, Village Voice,p.40(Aug.21,1978) in (so miscalled)``super''alloys:[Ni-based \& Fe-based stainless-steels: ANY/ALL!!!] generic endemic: Wigner's[JAP,17,857(1946)]-disease/Ostwald-ripening/ spinodal-decomposition/overageing-embrittlement/thermo-mechanical-INstability[Daniel Horner, www.Platts.com or LexisNexis.com; or www.animatedsoftware.com's nuc"el"ar sector: rhoffman@animatedsoftware.com; 760-720-7261]. Enabled Ertl-Radd-Youdelis-Herring-Alefeld-Siegel[Intl..Conf. Alt.-Energy, Bal Harbor; Hemisphere/ Springer(1980)-vol.5,page 459!; W Sci. Talent-Search(1957)] H-ion/proton-band diffusive-magnetoresistance enabled magnetic-H-valve enabled HINDENBURG-EFFECT(H-up; H2O-down) enabled FLYING-WATER, enables in new places making new water/glaciers(only possible way!) \& rebaseifying now acidifying-(dying)-oceans [U.McFarling, L.A. Times,Aug.3(2006))]and TERRAFORMING [D.Biello,Sci.Am.News(Mar.9,2007); D.Rosenfeld, Science 315,1396(Mar.9,2007) (http:/earth.huji.ac.il/research.asp)]a drought-parched Earth via ONLY HYDROGEN MAXIMAL Archimedes-buoyancy's geomorphology/ gravitational-potential-energy differences: WATER!!! [Preview Abstract] |
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C1.00281: Does mean mean MEAN!? Digits For A Very Long Time Giving Us The Finger!: 1881 Statistics Log-Law was: Quanta=Digits!: BEC; Zipf 1/f-Law; Information-Thy; Random-{\#}s = Euler V Bernoulli; Q-Computing = Arithmetic; P=/=NP SANS Complexity: Euclid 3-Mille Edward Siegel Classic statistics digits Newcomb[Am.J.Math.4,39,1881]-Weyl[Goett.Nachr.1912]-Benford[Proc.Am.Phil.Soc.78,4,51,1938]("NeWBe")probability ON-AVERAGE/MEAN log-law: $<$P$>$=log[1+1/d]=log[(d+1)/d][google:``Benford's-Law'';"FUZZYICS": Siegel[AMS Nat.-Mtg.:2002{\&}2008)]; Raimi[Sci.Am.221,109,1969]; Hill[Proc.AMS,123,3,887,1996]=log-base=units=SCALE-INVARIANCE!. Algebraic-inverse d=1/[e\^{}(w)-1]: BOSONS(1924)=DIGITS($<$1881): Energy-levels:ground=(d=0),first-(d=1)-excited ,... No fractions; only digit-integer-differences=quanta! Quo vadis digit $<$P(d=0)$>$=oo vs. $<$P(d=1)$> \quad <<<$oo)?: DIGITS gapFUL BE(``NeWBe'')C! Siegel[Schroed.Cent.Symp.1987] e\^{}(w)-term expansion: d$\sim $1/[[1+w+...]-1]=1/w\^{}(1.000...)Zipf-law Pareto power-law decay algebraicity, Siegel[Symp.Fractals,MRS Fall-Mtg.,1989-5!] ``FUZZYICS'' explains INEVITABILITY via Lawvere-Goguen-Siegel-Baez ``CATEGORICAL-SEMANTICS'' HYBRID:CATEGORY-THEORY+COGNITIVE-SEMANTICS! Averages dominate physics: expectations,ensemble, time,ANY/ALL experiments!: What if any don't follow digits log-law? Must they always?; Do YOURS?; ALWAYS?; No fluctuations from it allowed?; Never?; Ever?; Never Ever? Ponder long/hard digits' log-law's MEANING for physics/ sciences! Could statistics' ``mean'' REALLY MEANS ``MEAN!''? "Does `mean' mean ``MEAN''!?": ``quantum-computing'' is/was always alive/well in/since 1881: in $<$1 + 1 = 2$>$,... simple-arithmetic! [Preview Abstract] |
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C1.00282: Beijing restaurant network Chun-Hua Fu, Pei-Fang Zhnag, Yong-Li Wang, Jian-Jun Shi, Ai-Xia Feng, Da-Ren He We have empirically studied the restaurants in Beijing and suggested a network description on the system. We define the restaurants as nodes and connect a link between two nodes if the two restaurants sell a common dish. The edge represents the sale competition relationship. In order to describe the competition, we define a node weight, which is the mark given by consumers on an evaluation network (http://www.dianping.com), to the restaurant in cooking the dish. 3338 nodes and 688 dishes have been investigated. We find that both the total node weight, which is defined as the sum of the node weight in all the dishes, and the so-called dish weight, which is defined as the sum of the node weight in one dish, show a rather nice power law distribution. [Preview Abstract] |
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C1.00283: PHASE TRANSITIONS AND STRONGLY CORRELATED SYSTEMS |
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C1.00284: Adsorption and Dissociation of Molecular Oxygen on the (0001) Surface of Double Hexagonal Close Packed Americium Pratik Dholabhai, Raymond Atta-Fynn, Asok Ray Oxygen molecule adsorption on (0001) surface of double hexagonal packed americium has been studied in detail within the framework of density functional theory using a full-potential all-electron linearized augmented plane wave plus local orbitals method. The most stable configuration corresponded to molecular dissociation with the oxygen atoms occupying neighboring three-fold hollow h3 sites. Chemisorption energies and adsorption geometries for the adsorbed species, and change in work functions, magnetic moments, partial charges inside muffin-tins, difference charge density distributions and density of states for the bare Am slab and the Am slab after adsorption of the oxygen molecule will be discussed. The effects of chemisorption on Am 5$f$ electron localization-delocalization in the vicinity of the Fermi level and the reaction barrier calculation for the dissociation of oxygen molecule to the most stable h3 sites will be discussed. [Preview Abstract] |
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C1.00285: Mott transition studied by cellular dynamical mean field theory Yuzhong Zhang, Masatoshi Imada, Claudius Gros, Roser Valenti We study metal-insulator transitions between Mott insulators and metals. The transition mechanism completely different from the original dynamical mean field theory (DMFT) emerges from a cluster extension of it. A consistent picture suggests that the quasiparticle weight $Z$ remains nonzero through metals and suddenly jumps to zero at the transition, while the gap opens continuously in the insulators. This is in contrast with the original DMFT, where $Z$ continuously vanishes but the gap opens discontinuously. The present results arising from electron differentiation in momentum space agree with recent puzzling bulk-sensitive experiments on CaVO$_3 $ and SrVO$_3$. Details of the mechanism of Mott transition is studied through doublon-doublon, doublon-holon and spin-spin dynamical susceptibilities. [Preview Abstract] |
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C1.00286: Pressure Induced Metallization In ACrO$_{3}$ Perovskite Compounds Changqing Jin, L.X. Yang, Y.W. Long, H.Z. Liu, G.Y. Shen, H.K. Mao, J.S. Zhou, J.B. Goodenough We have studied the electrical conductivity of ACrO$_{3}$ (A=alkaline earth) perovskites performed at various pressures up to 60 GPa using diamond anvil cell techniques. The samples were synthesized under high pressure high temperatures. Pressure induced metallizations were observed in both samples. However the x ray diffraction experiments with synchrotron radiation source indicated no discernable crystal structural transition up to 60 GPa. Therefore the pressure induced metallizations were ascribed to electronic type phase transitions. It possibly came from the change of electronic structure due to an orbital ordering evolution induced by pressure. [Preview Abstract] |
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C1.00287: Ultrasonic Study of the Yb-based Heavy Fermion Compound YbCo$_2$Zn$_{20}$ Yoshiki Nakanishi We present experimental results of elastic constants as a function of temperature and magnetic field performed on a single crystal of the Yb-based heavy fermion system YbCo$_2$Zn$_{20}$. A marked elastic softening toward low temperature was observed in a longitudinal elastic constant C11 and transverse ones (C11 -C11)/2, C44. The softening is suppressed unexpectedly in a weak applied field of 2 T. Our results strongly suggest a large degeneracy of a 4f state of the Yb ion at low temperature and the Heavy Fermion state is quenched by the applied weak field. Thus, it is expected that this highly degenerated situation due to the almost spherical CEF, realized by the unique crystal structure, would form such a heavy fermion state and a lift of the degeneracy would bring about the disappearance. We discuss these results in the context of a crystalline electric field (CEF) ground state. [Preview Abstract] |
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C1.00288: Multifractal Analysis of the Metal to Insulator Transition in the Three-Dimensional Anderson Model Louella Vasquez, Alberto Rodriguez, Rudolf Roemer The wavefunctions at the metal to insulator transition (MIT) of a disordered system within the Anderson model of localization have been shown to be of multifractal nature. In this paper we use a multifractal analysis to compute for the singularity spectra of very large wavefunctions at the band center. We will show that the singularity spectrum at the MIT is independent of the system size. We compare our results with recent findings and the Wegner prediction. [Preview Abstract] |
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C1.00289: Superconductivity induced by non-local electron-phonon interaction Ka-Ming Tam The effects from commensurate filling, typically in the one-dimensional half-filled systems, often lead to finite charge gap and instability of long wavelength density wave ordering. Various proposals have been suggested recently that some of the one-dimensional electron-phonon coupled systems can be metallic with zero charge gap. However, subsequent studies of these proposals have obtained divergent results. We study an electron-phonon model with non-local electron-phonon interaction, its low energy effective theory unambiguously possess dominant charge gapless superconducting phase at half filling. In this model, the spin-charge coupling at high energy is weakened by the non-local electron-phonon interaction and the charge gap can be destroyed by the suppression of the umklapp process. The existence of the dominant pairing instability in the half-filled system may have an implication on the role plays by the phonon modes in the cuprate superconductor, suggesting that non-local or long range electron-phonon interactions may favor the formation of pairing. [Preview Abstract] |
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C1.00290: $^{1}$H NMR Measurements on the Phase Transition of (NH$_{4}$)$_{3}$H(SO$_{4}$)$_{2}$ Single Crystal S.H. Choi, K.S. Han, S.K. Kwon, S.K. Nam, H.H. Choi, Moohee Lee, Ae Ran Lim $^{1}$H nuclear magnetic resonance (NMR) experiments have been performed in the temperature range of 30 - 300 K at 7 T to investigate~the phase-dependent nature of the dynamic network of hydrogen bonds~in a (NH$_{4})_{3}$H(SO$_{4})_{2}$ single crystal. The crystal has six phases, which are ferroelectric, antiferroelectric, incommensurate, antiferroelectric, ferroelastic, and superionic conductor with the respective transition temperatures of 63, 133, 139, 256, and 413 K. The spin-lattice relaxation time T$_{1}$ of $^{1}$H NMR is similar for the ammonium protons and the hydrogen-bond protons in all range of experimental temperature. T$_{1}$ of $^{1}$H NMR gradually decreases down to 120 K and then starts to steeply increase below 100 K. Then T$_{1}$ shows an abrupt decrease below 68 K with a sharp minimum at 63 K, where the ferroelectric transition occurs. The $^{1}$H NMR spectrum shifts to the high frequency side below 63 K due to the ferroelectric phase transition. This temperature dependence of T$_{1}$ and spectrum confirms a dramatic change in the dynamics of hydrogen bonds~associated with~the ferroelectric phase transition at 63 K. [Preview Abstract] |
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C1.00291: Exact thermodynamics of electron hole pairing and ferroelectricity in attractive Hubbard nanoclusters. Armen Kocharian, Gayanath Fernando, Kalum Palandage, Jim Davenport Using analytical diagonalization and symmetries in the small Hubbard clusters, we demonstrate exact mapping between $U>0$ and $U<0$ models in the ground state and at finite temperatures for general electron concentration and magnetic field. We establish equivalency between corresponding phase diagrams for one hole off half-filling at $U>0$ and in the low spin region for half filled $U<0$ models. The $U<0$ model exhibits Fulde-Ferrell-Larkin-Ovchinnikov phase separation into spin-rich and spin-poor regions analogous to electron pairing for $0U_F$ [1]. The calculated phase diagrams resemble a number of metal dielectric transitions, inhomogeneous paired phases, superconductivity, ferromagnetism and ferroelectricity found recently in transition metal and Nb nanoparticles [3], etc. [1] A.N.Kocharian et. al., Phys. Rev. B{\bf 74}, 024511 (2006); Phys. Lett. A{\bf 364}, 57 (2007). [2] G.~W.~Fernando, et. al., Phys.~Rev. B{\bf 75}, 085109 (2007). [3] X.~Xu et al., Phys. Rev. Lett. {\bf 93}, 086803 (2004). [Preview Abstract] |
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C1.00292: Reversible pressure-induced phase change in eutectic GeSb Dmitry Shakhvorostov, Lia Krusin-Elbaum, Glenn J. Martyna, Dennis M. Newns, Cyril Cabral, Jr., Simone Raoux, Zak E. Hughes, Martin H. M\"{u}ser, Yang Song In phase-change materials (PCM), typically Ge-Te-Sb based glassy semiconductors, a reversible transformation between a highly resistive (amorphous) and a highly conductive (crystalline) phase is accomplished by Joule heating that melt-quenches PCM into the amorphous state, and thermally anneals it back to the crystalline state. Here we report a room-temperature pressure driven \emph{reversible} phase change in a binary eutectic GeSb system. From structural and Raman spectroscopy studies, we demonstrate abrupt hysteretic amorphous-to-crystalline and intra- crystalline transitions under a compressive load---unique to the Te-free system---that access with pressure the two extreme GeSb states previously obtained by thermal programming. Using \emph {ab-initio} molecular dynamics simulations we show that the reverse process occurs under a tensile load. The role of the Peierls gap and Anderson localization in the pressure induced phase change accompanying a metal-insulator transition will be discussed. [Preview Abstract] |
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C1.00293: Micron-Scale Observation of Nucleating Water Vapor Bubbles Scott Parker, Sung Chul Bae, Chang-Ki Min, David Cahill, Steve Granick Surface plasmon microscopy is used to detect nucleation and lift-off of vapor bubbles in water. Vapor bubbles are generated under pool boiling conditions by heating with a focused Ti-Sapphire laser in the near-infrared region. These bubbles modulate the local index of refraction, thereby altering the local excitation of the surface plasmon which are excited in the Kretchmann geometry and observed with a CCD camera. Altering the surface roughness, we observe how bubbles interact in their earliest stages. [Preview Abstract] |
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C1.00294: The condensation phenomena of conserve-mass aggregation model with mass-dependent fragmentation Dong-Jin Lee, Sungchul Kwon, Yup Kim We study a conserved mass aggregation model with mass-dependent fragmentation in regular lattice and scale-free networks. In the model, the whole mass $m$ of a site isotropically diffuse with unit rate. With rate $\omega$, a mass $m^{\lambda}$ is fragmented from the site and moves to a randomly selected nearest neighbor site. Since the fragmented mass is smaller than the whole mass $m$ of a site for $\lambda < 1$, the on-site attractive interaction exists for the case. For $\lambda = 0$, the model is known to undergo the condensation phase transitions as the density of total masses ($\rho$) increases beyond a critical density $\rho_c$. For $0< \lambda <1$, we numerically confirm for several values of $\omega$ that $\rho_c$ diverges with the system size $L$. Hence in thermodynamic limit, the condensed phase disappears and no transitions take place in one dimension. We also explain that there are no transitions in any dimension. On scale-free networks with degree distribution $P(k) \sim k^{-\gamma}$, we numerically confirm for $\gamma >3$ that the condensation transitions occurs at $\rho_c >0$ and its nature is the same as that in regular lattice. However, for $\gamma \leq 3$, the condensation always takes place for $\lambda < \lambda_c$ and masses distribute uniformly without aggregation for $\lambda \geq lambda_c$. We derive $\lambda_c = 1/{\gamma-1}$ via mean-field argument. [Preview Abstract] |
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C1.00295: Universal and nonuniversal supercritical adsorption in pores Hye-Young Kim, S.M. Gatica, A.D. Lueking, J.K. Johnson, M.W. Cole A recent study of gas adsorption in porous carbons found a common trend in the gas uptake as a function of reduced pressure at the same relative supercritical temperature, with the exception of hydrogen [1]. Using analytical expressions (Henry's law) and computer simulations (quantum and classical) we demonstrate that the ``universal'' behavior of the classical gases and the ``deviant' behavior of hydrogen can both be understood from simple combining rules and the role of quantum effects. Thus, we reject a hypothetical explanation of the data in terms of small pores permitting just hydrogen to enter.\newline [1] D. F. Quinn, Carbon 40, 2767 (2002). [Preview Abstract] |
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C1.00296: ABSTRACT WITHDRAWN |
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C1.00297: Observation of field-induced magnetic disorder state in one-dimensional antiferromagnet BaCo$_{2}$V$_{2}$O$_{8}$ from NMR C.S. Lue, C.N. Kuo, T.H. Su, Zhangzhen He, Mitsuru Itoh We report the results of a $^{51}$V nuclear magnetic resonance (NMR) study on the single crystal BaCo$_{2}$V$_{2}$O$_{8}$ at temperatures between 3k and 300k. This material has been a subject of current interest due to indications of the field-driven magnetic order-disorder transition above 4T. For the present NMR study, we found no abrupt changes in the NMR shift and line width at low temperature as a constant field 7.06T was applied along the $c$-axis, indicative of the absence of magnetic long-range ordering under this field. Hence, the NMR results establish unequivocally the field-induced magnetic disorder state in BaCo$_{2}$V$_{2}$O$_{8}$. [Preview Abstract] |
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C1.00298: Reentrant Morin Transition in Natural Haematite Crystal at Low Temperature Seong-Joo Lee, Hyunok Jung, Soonchil Lee, Joonghoe Dho We investigate the magnetic properties of natural haematite ($\alpha$-Fe${}_{2}$O${}_{3}$) crystal at low temperature using a SQUID and ${}^{57}$Fe nuclear magnetic resonance (NMR). The M (T) curve shows that the net magnetization in the (111) plane vanishes at Morin transition occurring around 260 K but reappears as temperature decreases below 30 K. The M(H) curve shows that the hysteresis exists in the (111) plane and the spin-flop transition also occurs when strong external field is applied in parallel with the [111] direction at low temperature. We obtain the NMR spectra in external magnetic field of up to 7 T at 4.2 K. Comparison of the M(H) curve and the field dependence of the NMR resonance frequency suggests that the antiferromagnetic and the weak-ferromagnetic phases coexist at low temperature. Assuming that the weak- ferromagnetic state at low temperature is the same with that above Morin transition, the amount of the weak-ferromagnetic phase in the antiferromagnetic bath at low temperature is about 3 $\%$. [Preview Abstract] |
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C1.00299: New Phase transitions in ceramic SrSnO3: Raman scattering and differential thermal analysis Manoj Singh, N.K. Karan, Ram S. Katiyar, J.F. Scott, H.M. Jang We report a continuous or nearly continuous order-disorder transition from orthorhombic (pseudo-tetragonal) to orthorhombic on heating in SrSnO$_{3}$ at 377 $^{\circ}$C. The transition at 377 $^{\circ}$C is manifested in an order of magnitude increase in Raman linewidths and in a $\lambda $-shaped anomaly in the specific heat. Previous work [Mountstevens et al., Phys. Rev. B71, 220102R (2005)] has interpreted the Pnma -- Imma transition at ca. 636 $^{\circ}$C as a continuous order-disorder transition and emphasized that this would be unique for an octahedron-tilting transition in oxide perovskite, which are always displacive. Our work on Raman scattering and Differential Thermal Analysis shows that the disorder sets in at much lower temperatures 377 $^{\circ}$C, so that the 636 $^{\circ}$C transition is disorder-disorder, or a displacive transition within an already highly-disordered lattice. Hence it may not be as unusual as had been claimed. [Preview Abstract] |
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C1.00300: $^{11}$B NMR Study of Spin Structure and Dynamics in TbB$_{4}$ Single Crystal S.K. Kwon, B.J. Mean, S.K. Nam, S.H. Choi, H.H. Choi, Moohee Lee, B.K. Cho $^{11}$B NMR measurements have been performed on the single crystal of TbB$_{4}$ to investigate $4f $spin structure and dynamics. $^{11}$B NMR spectrum, shift, $1/T_{1}$ and $1/T_{2}$ are measured down to 5 K at 8 T perpendicular to the (110) plane. $^{11}$B NMR shift and linewidth are huge and strongly temperature-dependent due to the $4f$ moments of Tb. In addition, both are proportional to the magnetic susceptibility, indicating that the hyperfine field at the boron site originates from the $4f$ spins of Tb. Below $T_{N}$ = 43 K, the single broad resonance peak of $^{11}$B NMR splits into several peaks reflecting the onset of internal magnetic fields due to the antiferromagnetic spin arrangements. Assuming that the $4f$ moments are aligned antiferromagnetically and collinearly in the basal plane perpendicular to the c-axis, we have calculated dipolar fields at the 16 boron nuclear sites from the $4f$ spins of Tb. The results show that the various peaks of $^{11}$B NMR spectrum at 5 K are generally consistent with the calculation confirming that the collinear spin arrangement is correct. The longitudinal and the transverse relaxation rates, $1/T_{1}$ and $1/T_{2}$, are independent of temperature above $T_{N}$ and then decreases tremendously indicating the huge suppression of spin fluctuations below $T_{N}$. [Preview Abstract] |
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C1.00301: $^{11}$B NMR Study of Spin Structures and Dynamics in GdB$_{4}$ Single Crystal S.K. Nam, B.J. Mean, S.K. Kwon, S.H. Choi, H.H. Choi, Moohee Lee, B.K. Cho We have performed $^{11}$B NMR measurements on a single crystal of GdB$_{4}$ to investigate $4f $spin structures and dynamics. $^{11}$B NMR spectrum, shift, $1/T_{1}$ and $1/T_{2}$ are measured down to 5 K at 8 T perpendicular to the c-axis. $^{11}$B NMR shift and linewidth are huge and strongly temperature-dependent due to the $4f$ moments of Gd. In addition, both are proportional to the magnetic susceptibility, indicating that the hyperfine field at the boron site originates from the $4f$ spins of Gd. Below $T_{N}$ = 42 K, the single broad resonance peak of $^{11}$B NMR splits into various peaks reflecting the onset of internal magnetic fields due to the antiferromagnetic spin arrangements. Assuming that the $4f$ moments of are aligned noncollinearly along the $<$110$>$ direction in the basal plane perpendicular to the c-axis, we have calculated dipolar fields at the 16 boron nuclear sites from the $4f$ spins of Gd. The results show that the various peaks of $^{11}$B NMR spectrum at 5 K are generally consistent with the calculation confirming that the noncollinear spin arrangement is correct. The relaxation rates, $1/T_{1}$ and $1/T_{2}$, are independent of temperature above $T_{N}$ and then decreases tremendously indicating the huge suppression of spin fluctuations below $T_{N }$. [Preview Abstract] |
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C1.00302: ABSTRACT HAS BEEN MOVED TO SESSION B33 |
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C1.00303: Atomic Adsorptions on the (020) Surface of $\alpha $-Pu: A Density Functional Study Raymond Atta-Fynn, Asok Ray Adsorptions of atomic carbon, nitrogen, and oxygen on the (020) surface of $\alpha $-Pu have been investigated using the full-potential linearized augmented plane wave plus local basis method. The surface was modeled by a 4-layer periodic slab consisting of a total of 32 Pu atoms. Adsorption energies have been optimized with respect to the distance of the adatom from the Pu surface for four adsorption sites, namely the one-fold top, one-fold hollow, two-fold short bridge, and the two-fold long bridge sites. The short bridge site was the most stable adsorption site for C with chemisorption energy of 6.038. The long bridge site was the most stable adsorption site for N and O with chemisorption energies of 6.067 eV and 7.362 eV respectively. The work function and net spin magnetic moments respectively increased and decreased in all cases upon chemisorption compared to the bare surface. The density of states and difference charge density have been used to analyze the adsorbate-induced changes in the surface electronic structure. [Preview Abstract] |
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C1.00304: Valence Instability and Mass Enhancement in an Extended Periodic Anderson Model Takashi Sugibayashi, Yasuhiro Saiga, Dai Hirashima In CeCu$_2$Si$_2$, CeCu$_2$Ge$_2$ and CeRh$_{1-x}$Ir$_x$In$_5$, the shape of the superconducting region is asymmetric and the superconducting transtition temperature $T_c$ reaches its maximum far away from the antiferromagnetic quantum critical point. Onishi and Miyake ascribed the asymmetric behavior of $T_c$ to the enhanced valence fluctuations. They introduced the repulsive interaction $U_{cf}$ between a conduction electron and an $f$ electron, in addition to the Coulomb interaction $U$ between $f$ electrons and studied the periodic Anderson model (PAM) with both $U$ and $U_{cf}$ (which is the so-called extended PAM). We investigated the valence instability in the extended PAM and two-fold degenerate extended PAM with the dynamical mean field theory. In these models, we found that the valence instability is observed when $U_{cf}$ is larger than the conduction band width $2W$ and the $f$-electron level $\epsilon_f$ is deeper than the lower bound of the conduction band, $-W$. It is also found that the orbital degeneracy suppresses the valence instability. In the parameter region of inducing the valence instability, we investigate the mass enhancement factor $Z_f^{-1}$ which is related to the specific heat. [Preview Abstract] |
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C1.00305: Experimental Evidence of Fermi-Luttinger Liquid State. Philippe Debray, Mustafa Muhammad, Steven Herbert, Richard Newrock We have measured Coulomb drag between spatially separated parallel quantum wires, made on AlGaAs/GaAs heterostructures by the split-gate technique, in the absence of tunneling to experimentally probe drag by small forward momentum transfer. Drag between wires of lengths 500 and 300 nm was measured in the one-dimensional transport regime at temperatures in the range 30 mK -- 1.2 K. We have observed both positive and negative drag. The temperature dependence of drag of both types is in excellent agreement with that predicted by the recently proposed Fermi-Luttinger liquid (FLL) theory that takes into account the curvature in the fermionic dispersion. Positive drag occurs when the curvature is positive, while negative drag occurs when it is negative. [Preview Abstract] |
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C1.00306: Low Temperature Differential Conductance in Al/AlOx/Sc Tunnel Junctions Sheng-Shiuan Yeh, Juhn-Jong Lin We have fabricated several Al/AlO$_{x}$/Sc tunnel junctions and measured the differential conductances $G\equiv dI/dV$ at low temperatures. Our objective is to study the effect of the coupling between tunneling electrons and localized magnetic impurities (which sat in the insulating barrier) on $G(V,T)$. We observed a crossover from the weak coupling regime to the strong coupling regime. We found that, in both regimes, the $dI/dV$ spectra could be well described by the Appelbaum's $s$-$d$ exchange interaction theory, with a Kondo temperature $T_{K}^{Appelbaum} \approx 34.8$ K. On the other hand, our measured zero-bias conductances could be well described by a scaling form predicted by the NRG calculations and a $T_{K}^{NRG} \approx$ 38 K was deduced, being in close agreement with the value of $T_{K}^ {Appelbaum}$. A magnetic field of 4 T was applied at 2.5 K, but no Zeeman splitting in the $dI/dV$ spectra was observed. This absence of Zeeman splitting resulted as a consequence of the high $T_{K}$ value found in our junctions. [Preview Abstract] |
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C1.00307: Large drop in dielectric constant at ferrimagnetic ordering of CoCr$_{2}$O$_{4}$ thin film as observed by terahertz time domain spectroscopy K.R. Mavani, M. Nagai, M. Shirai, K. Tanaka, D.S. Rana, I. Kawayama, M. Tonouchi Multiferroic spinel CoCr$_{2}$O$_{4}$ shows ferrimagnetic transition at $\sim $95 K and, at further low temperatures, it shows development of magnetic spin spirals simultaneous to a ferroelectric transition. We have deposited epitaxial CoCr$_{2}$O$_{4}$ thin film on MgO$ (100) $substrate and studied the film using temperature dependent terahertz (THz) time-domain spectroscopy. There is a large drop in the dielectric constant (\textit{$\varepsilon $}$_{1})$ to nearly half of its initial value at ferrimagnetic transition of CoCr$_{2}$O$_{4}$ thin films in the THz frequency range. This is contrary to few earlier studies by capacitance measurements which showed no significant change in the dielectric constant (\textit{$\varepsilon $}$_{1})$ at ferrimagnetic transition [1]. At lower temperatures, two dielectric anomalies were observed in the temperature dependent \textit{$\varepsilon $}$_{1,}$ which correspond to the onset of short-range magnetic spin spirals ($\sim $50 K) and the long-range ordering of the spirals at lower temperature ($\sim $26 K). Our results indicate a magnetoelectric effect at the ferrimagnetic transition of CoCr$_{2}$O$_{4}$ thin film in THz frequency range. [1] G. Lawes \textit{et al.}, Phys. Rev. B 74, 24413 (2006). [Preview Abstract] |
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C1.00308: Consequences of magnetoelectric interactions on ferroelectric domain structures P. Mahanandia, A.S. Tatarenko, G. Srinivasan The standard lift mode of electrostatic force microscopy (EFM) has been utilized to study the influence of magnetoelectric (ME) effect on ferroelectric domain structures in a YIG-PZT bilayer. A PZT disk of thickness=250$\mu $m was bonded on to a (111) single crystal YIG on GGG substrates. Randomly oriented domains of PZT are observed in the absence of a dc magnetic filed H. The domains are transformed into a columnar structure when H= 120 Oe is applied to the bilayer. The H-induced changes are mediated by mechanical forces; when a magnetic field is applied to the layered composite, the magnetostriction exerts a stress on PZT, resulting in an induced electric polarization and changes in the domain structure. [Preview Abstract] |
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C1.00309: MIS and MFIS Devices: DyScO$_{3 }$ as a gate-oxide and buffer-layer R. Melgarejo, N.K. Karan, J. Saavedra-Arias, D.K. Pradhan, R. Thomas, R.S. Katiyar Metal-Ferroelectric-Insulator-Semiconductor (MFIS) structure is of importance in nonvolatile memories, as insulating buffer layer that prevents interdiffusion between the ferroelectric (FE) and the Si substrate. However, insulating layer has some disadvantages \textit{viz}. generation of depolarization field in FE film and increase of operation voltage. To overcome this, it is important to find a FE with low $\varepsilon _{r}$ (compared to normal FE) and an insulating buffer layer with high $\varepsilon _{r }$ (compared to $\varepsilon _{r}$ = 3.9 of SiO$_{2})$. High-k materials \textit{viz}. LaAlO$_{3}$, SiN, HfO$_{2}$, HfAlO etc. have been studied as buffer layers in the MFIS structures and as gate-oxide in metal-insulator-silicon (MIS). Recently, a novel gate dielectric material, DyScO$_{3}$ was considered and studies indicate that crystallization temperature significantly increased and the film on Si remained amorphous even at 1000\r{ }C annealing. Considering the requirements on crystallization temperature, $\varepsilon _{r}$, electrical stability for high-$k $buffer layers, DyScO$_{3}$ seems to be very promising for future MFIS device applications. Therefore, the evaluations of MOCVD grown DyScO$_{3}$ as gate-oxide for MIS and the buffer layers for Bi$_{3.25}$La$_{0.75}$Ti$_{3}$O$_{12}$ based MFIS structures are presented. [Preview Abstract] |
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C1.00310: Magnetodielectric Effects and Transport Study in LuFe$_{2}$O$_{4}$ Single Crystal Tae Hwan Jang, Sang Youn Park, Hai Joon Lee, Sun Hee Kang, Tae Yeong Koo, Sung Baek Kim, Ill Won Kim, Yoon Hee Jeong, Sang Wook Cheong Magnetic, dielectric, and magnetodielectric properties of geometrically frustrated mixed valance LuFe$_{2}$O$_{4}$ single crystal are discussed to clarify the charge order based ferroelectricity and its coupling with magnetism. From the magnetization and dielectric constant measurement, a new anomalous temperature point T$_{N\mbox{'}}(\sim $160 K) in both magnetization and dielectric constant versus temperature curve below the ferrimagnetic transition temperature T$_{N}(\sim $225 K) has been observed. The sign of magnetodielectric effect (MDE) also changes from positive T $>$ T$_{N\mbox{'}}$ into negative T $<$ T$_{N\mbox{'}}$. No field hysteresis in positive MDE temperature region was found. However a large hysteretic behavior in negative MDE below T$_{N\mbox{'}}$ with the same magnetic coercive field measured in M (H) curve was observed. This indicates a strong coupling between magnetism and ferroelectricity in the charge and spin frustrated ferrimagnetic LuFe$_{2}$O$_{4}$ system. [Preview Abstract] |
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C1.00311: Effect of epitaxial strain on magnetization and photo-control of spontaneous polarization in BiFeO$_{3}$ films on (LaAlO$_{3})_{0.3}$(Sr$_{2}$AlTaO$_{6})_{0.7} (110)$ substrate D.S. Rana, I. Kawayama, H. Murakami, M. Tonouchi Recent researches on thin films of BiFeO$_{3}$ have been driven by the need to obtain better multiferroic properties by either inducing epitaxial strain or fabrication of magnetoelectric superlattices. The BFO $(100)$ thin films on (LaAlO$_{3})_{0.3}$(Sr$_{2}$AlTaO$_{6})_{0.7} \quad (100)$ substrate are highly strained with different physical properties than that of bulk [1]. Given the dependence of ferroelectric polarization of BFO on crystallographic directions, epitaxial thin films -- 70nm and 180nm - of BFO were deposited on LSAT $(110)$ substrate. Structure and surface morphology of BFO/LSAT$(110)$ films show that the films with thickness $\le $ 80 nm possess a strong in-plane strain while thicker films (150-200nm) are partially relaxed with a bulklike structure. Though the magnetic properties of BFO/LSAT$(110)$ films are nearly independent of structure, the spontaneous polarization and the ferroelectric properties (probed by terahertz emission) are strong characteristic of structure. These results emphasize the importance of epitaxial strain induced tailoring of the ferroelectric properties of BiFeO$_{3}$ film along $(110)$ crystallographic direction. 1. D.S. Rana \textit{et al}, Phys. Rev. B \textbf{75}, 060405 (2007). [Preview Abstract] |
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C1.00312: Anomalies in the thermoelectric power in cuprates from strong electron correlation Shiladitya Chakraborty, Dimitrios Galanakis, Philip Phillips The thermoelectric power data in hole-doped cuprates show a sign change on increasing the hole doping from the underdoped to the overdoped regime. The origin of this anomaly is debatable, and there exist multiple explanations for it. Phonon drag is one of the more widely accepted explanations. Our approach,instead, is to investigate the behaviour of the thermoelectric power from a purely electronic perspective. We employ Cluster Dynamical Mean Field Theory (CDMFT) on a four site square plaquette to study the thermoelectric power in the 2-d Hubbard model as a function of hole doping , temperature and $U/t$ ratio. We observe a sign change in the thermoelectric power in qualitative agreement with experimental data. The sign change vanishes for small values of $U/t$, suggesting that strong electron correlations are responsible for this phenomenon. [Preview Abstract] |
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C1.00313: POST-DEADLINE ABSTRACTS |
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C1.00314: ABSTRACT WITHDRAWN |
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C1.00315: Rectification effects in InAs/AlGaSb three-terminal ballistic junctions Masatoshi Koyama, Tatsuya Inoue, Naoki Amano, Toshihiko Maemoto, Shigehiko Sasa, Masataka Inoue We report on the fabrication and the DC characterization of InAs/AlGaSb three-terminal ballistic junctions consisting of three quantum-wire T-shaped structures. InAs/AlGaSb quantum wells were grown by molecular beam epitaxy, and the three-terminal ballistic junctions were defined using electron beam lithography. Typical electron mobility of 80,000 -- 200,000 cm$^{2}$/Vs and sheet carrier density of 1.0 -- 2.0 x 10$^{12}$ cm$^{-2}$ were observed at 77K. Ballistic electron transport properties are due to the one-dimensional (1D) nature of electrons in InAs and dramatic changes in scattering probability from the 2D electron system, which are expected to occur at higher temperatures. We measured the rectified output voltage, $V_{C}$ at the central branch of the devices at various temperatures. Nonlinearity and negative voltages at the central branch, regardless the polarities of the source-drain (left and right branch) voltage, were observed at each temperature. Clear rectification effects were observed in the ballistic junctions even at room temperature. Details of the triode characteristics in the InAs/AlGaSb ballistic devices will be discussed at the conference. [Preview Abstract] |
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C1.00316: MnScN(001)/MgO(001) films grown by molecular beam epitaxy: a possible dilute magnetic semiconductor. Arthur R. Smith, Costel Constantin, Utkur Mirsaidov, John Markert Considerable interest has been of late in finding a room temperature dilute magnetic semiconductor. Recently, theoretical calculations had predicted Curie temperature to be above 400 K for the films with 3{\%} Mn concentration into the Mn$_{x}$Sc$_{(1-x)}$N system\footnote{ Aditi Herwadkar and Walter R. L. Lambrecht, Phys. Rev. B \textbf{72}, 235207 (2005).\par \par }. In this study, Mn$_{x}$Sc$_{(1-x)}$N films (with x = 3-5{\%}) were grown on ScN(001)/MgO(001) substrates by radio frequency plasma assisted molecular beam epitaxy. The buffer layer of ScN(001) was grown on top of MgO(001) at T$_{S}\sim $ 800 $^{^{\circ}}$C and with a thickness of $\sim $ 50 nm. The MnScN film was grown at T$_{s}\sim $ 520 $^{^{\circ}}$C and with a thickness of $\sim $ 290 nm. Post-growth x-ray diffraction measurements show that Mn$_{x}$Sc$_{(1-x)}$N alloys follow the Vegard's law. The hysteresis magnetic data measured with the superconducting quantum interference device show possible ferromagnetic behavior for the Mn$_{0.03}$Sc$_{0.97}$N films with a Curie temperature of $\sim $50 K, but additional data is needed to establish the conclusiveness of the results. Work supported by NSF. [Preview Abstract] |
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C1.00317: Characterization of p-InGaAsSb/n-GaSb and p-GaAs/n-GaAs Structures for the Fabrication of Fusion-Stacked Solar Cells M.L. Gomez-Herrera, J.L. Herrera-Perez, P. Rodriguez-Fragoso, J.G. Mendoza-Alvarez, I. Riech, G. Torres-Delgado We are developing a two-stacked solar cell, using for the infrared portion a p-InGaAsSb/n-GaSb heterostructure, and a p-GaAs/n-GaAs for the visible part. Both structures were grown using the liquid phase epitaxy growth technique, and doping at different levels the p-type layers in order to obtain p-n junctions with different electrical characteristics and depletion layer depths. We present results on the characterization of both structures using the photoluminescence spectroscopy to characterize the layer crystalline quality, and the photoacoustic effect to characterize the layer-substrate interface for both structures. Also, we present the results on the I-V characterization and spectral response of both p-n structures for the different doping levels in the p-type layers used. Finally, details on the fusion process to stack the two solar cells are discussed. [Preview Abstract] |
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C1.00318: Optical Properties of GaN$_{x}$As$_{1-x}$ Thin Films Grown on Si Substrates by r f. Sputtering J.G. Mendoza-Alvarez, O. Zelaya-Angel, A. Cruz-Orea, J.S. Arias-Ceron, J.A. Cardona-Bedoya GaN$_{x}$As$_{1-x}$ ternary alloys in the GaN-rich side, are expected theoretically to have band-gap energies in the full range of the visible spectrum for just a small change in the nitrogen concentration in the range of about 70-85{\%}. Using the r. f. sputtering and the laser ablation film deposition techniques, we have reported the growth of ternary GaNAs layers with band-gap energies in the range between 1.4 to 2.6 eV. In this work we report the growth of GaNAs thin films on Si substrates using the r. f. sputtering technique at high substrate temperatures; the r. f. power was varied in order to control the nitrogen incorporation in the films. The low temperature photoluminescence (PL) and the photoacoustic (PA) spectroscopies were used to characterize the optical properties of the series of GaN$_{x}$As$_{1-x}$ As films grown with different stoichiometries. We discuss the origin of the transitions observed in the PL spectra and the shoulders around 2.5 eV observed in the PA spectra. [Preview Abstract] |
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C1.00319: Differential Magnetoresistance Oscillations induced by Microwave and DC Electric Fields Maxim Khodas, Maxim Vavilov We study magnetoresistance oscillations in two-dimensional electron systems induced by AC and DC fields. We find the position of the maxima and minima in the differential magnetoresistance, $r(\epsilon^{ac},\epsilon^{dc})$ and evaluate the amplitude of magneto-oscillations in terms of various microscopic parameters of the system. We compare our findings with the results of recent experiments by W. Zhang, Phys. Rev. Lett. 98, 106804 (2007). [Preview Abstract] |
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C1.00320: First-Principles Theory of Ordering, Phase Separation, and Phonon Scattering in Thermoelectric LAST (Lead-Antimony-Silver-Telluride) alloys Sergey V. Barabash, Vidvuds Ozolins, Chris Wolverton Bulk LAST (Pb$_{2-x-y}$Ag$_{y}$Sb$_{x}$Te$_{2})$ alloys exhibit$^{\ast }$ high thermoelectric figure of merit (ZT$\sim $2 at 800K, considerably exceeding ZT of pure PbTe or AgSbTe$_{2})$, and nano-scale inhomogeneities, origin of which is poorly understood. The atomic structure of the nano-regions, as well as that of the pure AgSbTe$_{2}$, remains the subject of an experimental debate. Using density-functional theory (DFT), we calculate the composition-temperature phase diagram and vibrational spectra of Pb$_{2-x-y}$Ag$_{y}$Sb$_{x}$Te$_{2}$ alloys. We predict that the experimentally observed nanoscale inhomogeneities are due to the precipitation of ordered AgSbTe$_{2}$ phases. Two types of cation order type closely compete in AgSbTe$_{2}$, the dominant order type being D4; the predicted hypothetical order-disorder transition temperature exceeds the melting temperature of pure AgSbTe$_{2}$. The miscibility gap between solid PbTe and AgSbTe$_{2}$ phases is highly asymmetric, with a high solubility of PbTe in ordered AgSbTe$_{2}$. We also characterize the shape of coherent precipitates. Finally, the phonon spectra of AgSbTe$_{2}$ and PbTe suggest that boundary scattering of acoustic phonons causes the observed suppression of thermal conductivity. $^{\ast }$K.F. Hsu \textit{et al.}, Science \textbf{303}, 818 (2004). [Preview Abstract] |
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C1.00321: Oxygen adsorption on Cu/ZnO (0001) --Zn. Patricio H\"aberle, Matthias Batzill, Ulrike Diebold, Paola Lazcano By using plasma assisted deposition we have adsorbed oxygen onto the Cu/ZnO(0001)-Zn surface. Cu was deposited on the sputtered-annealed ZnO substrate at room temperature, which was later exposed to oxygen. Using X-ray photoelectron spectroscopy (XPS) we verified the effect of the oxidation procedures on the electronic structure of the interface. Our results are consistent with a partially oxidized Cu layer, in which CuO is mainly located at the interface between ZnO and the adsorbed Cu islands. Further Cu deposition induces the formation Cu$_{2}$O. Annealing the sample in UHV induces further oxide reduction. The oxidation is reversible and metallic Cu is recovered on the top layer. [Preview Abstract] |
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C1.00322: Nucleation and stochiometry dependence of rutile-TiO$_{2}$ thin films grown by plasma-assisted molecular beam epitaxy Costel Constantin, Kai Sun, R.M. Feenstra Considerable interest has been shown of late in transition-metal oxides. One case is the titanium dioxide system, which can have applications as a high-k dielectric gate insulator for Si-based devices\footnote{Z. J. Luo \textit{et al.}, Appl. Phys. Lett. \textbf{79}, 2803}. In this study, rutile-TiO$_{2}$ thin films were grown on GaN(0001) substrates by oxygen plasma-assisted molecular beam epitaxy. Two sets of films were grown, one in which the initial GaN surface is prepared WITH the pseudo 1$\times $1 Ga-rich surface reconstruction, and the other set, WITHOUT the pseudo 1$\times $1. On top of these two type of surfaces, the rutile-TiO$_{2}$ thin films were grown at T$_{s}\sim $ 600 $^{o}$C, and with a thickness $\sim $ 40 - 50 nm.~During growth, reflection high-energy electron diffraction indicated a reversible stoichiometry transition from O-rich to Ti-rich growth. Post-growth x-ray diffraction measurements performed on the samples WITHOUT the GaN pseudo 1$\times $1, show the presence of additional peaks at 2$\theta $ = 52.9$^{o}$, which implies the existence of additional phases. In addition, the high-resolution transmission electron microscopy performed on these samples show a high degree of disorder, as compared to the samples prepared WITH the pseudo 1$\times $1. Work supported by ONR. [Preview Abstract] |
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C1.00323: Study of the crystalline structures of the syndiotactic polystyrene (sPS) under mechanical deformation Suguru Nagasaka, Atsushi Hotta Polystyrene (PS) has become one of the important, yet complicated semi-crystalline materials since the successful synthesis of the syndiotactic PS (sPS) by Ziegler-Natta catalyst. Since then, sPS has been actively investigated and four different crystalline forms ($\alpha $, $\beta $, $\gamma $ and $\delta )$, two mesomorphic forms and various clathrate forms have been found, indicating complex feature of its crystalline structures. Among the four crystalline forms, $\alpha $ and $\beta $-crystals can be obtained by different annealing processes and both crystalline structures comprise the same all-trans planar conformation. In this work, $\beta $-crystal structure was made by high temperature annealing and the sPS with $\beta $-crystal structure was mechanically stretched above the glass transition temperature of sPS, followed by the crystalline transition analysis studied by FT-IR. [Preview Abstract] |
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C1.00324: Magnetic Field Effects on Intersystem Crossing in Polaron-Pair, Excitonic, and Charge-Transfer States in Organic Semiconducting Materials Liang Yan, Bin Hu The singlet-triplet intersystem crossing can be magnetic field dependent in organic semiconducting molecules. This field-dependent intersystem crossing accounts for the magnetic properties of these non magnetic organic semiconducting molecules. Therefore, the study of the dependence of magnetic field on the intersystem crossing can enhance the understanding of intrinsic magnetic responses of excited states and also expend the application of non magnetic organic materials to magnetic devices. In this report we will present our recent investigations: magnetic field effects on singlet-triplet intersystem crossing based on the selected polaron-pair, excitonic, and charge-transfer excited states by using magnetic field-dependent electroluminescence, photoluminescence, and photocurrent. Our experimental results show that the intersystem-crossing dependence of magnetic field significantly decreases as the internal electron-hole distance is reduced in an excited state. This phenomenon indicates that the electron-hole distance essentially determines the intersystem-crossing dependence of magnetic field through the competition between the Zeeman splitting of triplet sublevels caused by applied magnetic field and the intrinsic singlet-triplet energy difference generated by the distance-dependent spin-exchange interaction. As a result, changing the electron-hole distance presents a new mechanism to magnetically tune the optoelectronic properties of non magnetic organic semiconducting molecules. [Preview Abstract] |
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C1.00325: Using genetic algorithms to search for an optimal portfolio strategy and test market efficiency Haowen Xi, Edward Mandere In this numerical experiment we used genetic algorithms to search for an optimal portfolio investment strategy. The algorithm involves having a ``manager'' who divides his capital among various ``experts'' each of whom has a simple fixed investment strategy. The expert strategies act like population of genes which experiencing selection, mutation and crossover during evolution process. The genetic algorithm was run on actual portfolio with stock data (DowJones 30 stocks). We found that the genetic algorithm overwhelmingly selected optimal strategy that closely resembles a simple buy and hold portfolio, that is, evenly distribute the capital among all stocks. This study shows that market is very efficient, and one possible practical way to gauge market efficiency is to measure the difference between an optimal portfolio return and a simple buy and hold portfolio return. [Preview Abstract] |
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C1.00326: Magnetic Study of Exciton-Charge Reaction in Organic Phosphorescence-Based Light-Emitting Diodes Ming Shao, Bin Hu The capture of electron and hole leads to the singlet and triplet exciton formation at 1:3 ratio in organic light-emitting diodes (OLEDs) of fluorescent conjugated molecules. This significantly limits the quantum efficiencies of singlet light emission from OLEDs. The alternative option is to use triplet emission from phosphorescent molecules to ultimately increase the quantum efficiencies of OLEDs. In this report we will present our recent studies of triplet exciton-charge reaction in most efficient phosphorescence-based OLEDs by using magnetic field-dependent electroluminescence and excited state-related magnetoresistance. Our experimental results show that the electrically generated excitons can react with charge carriers with two consequences: detrapping charge carriers or splitting electrons and holes in excited states. Nevertheless, the triplet exciton-charge reaction presents a significant challenge to increase the quantum efficiencies of OLEDs towards the theoretical limit of 100{\%}. Furthermore, we observed that the triplet-charge reaction can be adjusted by changing the balancing degree of bipolar electron and hole injection. Therefore, tuning the bipolar injection can forms a mechanism to control the triplet-charge reaction and to consequently improve the quantum efficiencies of phosphorescence-based OLEDs. [Preview Abstract] |
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C1.00327: Enhanced Photovoltaic Effect from Nanocomposite of Treated PbS quantum dots and $\pi -$conjugated polymers Xiaomei Jiang, Jian Zhang We report novel type of hybrid solar cells based on nanocomposites of conjugated polymers (polythiophene) and IR-sensitive PbS nanocrystals that have a size-tunable energy gap between ca. 0.7 and 1.6 eV. Thin film cells show very good diode characteristics and sizable photovoltaic response. The good performance of our devices in both photovoltaic and photodiode regimes indicates quite efficient charge separation between the polymer and QD components. To further facilitate charge separation and transport in these composite structures, we applied various ligands exchange (pyridine, butylamine and octylamine) to the quantum dots prior to device fabrication. We find noticable increase of photocurrent due to more efficient charge separation when the original bulky oleic acid ligand of the nanocrystals was replaced by these much smaller ligands. We have conducted mobility measurement of PbS QDs with different sizes, both in pure QD film and the hybrid nanocomposite with polymers. Both electronic and optical device characterizations were carried out. Specifically, we observe indications of a rapid increase in the photocurrent at spectral energies in correlation with the size-dependent energy gap of the QD component. [Preview Abstract] |
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C1.00328: Studies on the parameters affecting the adhesion between Diamond-Like Carbon (DLC) films and polyolefin substrates Yuuma Nakamura, Terumitsu Hasebe, Aki Kamijo, Kouki Takahashi, Tetsuya Suzuki, Atsushi Hotta Polyolefins coated with thin Diamond-Like Carbon (DLC) films are particularly attractive for effective control of the surface and mechanical properties of the polyolefins and the adhesion between the DLC and the polyolefins determines the major properties: if the adhesion force is not sufficient, DLC film is easily peeled off from the polyolefin substrate, eventually degrading the whole highly-controlled DLC-polyolefin system. In this work, we evaluated the adhesion between DLC films and various polyolefin substrates through T-peel testing using tensile tester. DLC films were deposited on each polyolefin substrate by plasma enhanced chemical vapor deposition (CVD) method using acetylene gas. High-density polyethylene (HDPE), low-density polyethylene (LDPE), linear-low-density polyethylene (LLDPE), isotactic polypropylene (iPP) and syndiotactic polypropylene (sPP) were introduced as polyolefin materials. It was found that molecular structures and annealing conditions had significant effects on the adhesion between DLC and the polyolefins. [Preview Abstract] |
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C1.00329: Raman scattering from the CaC$_6$ superconductor A. Mialitsin, J. Kim, R. Kremer, G. Blumberg \def\prb{Phys. Rev. B} \def\prl{Phys. Rev. Lett.} \def\pla{Phys. Lett. A} \def\pr{Phys. Rev.} \def\MgB2{MgB$_{2}$} \def\cm-1{cm$^{-1}$\,} \def\cmT-1{cm$^{-1}$/T\,} \def\E2g{$E_{2g}$} \def\A1g{$A_{1g}$} \def\2DS{$2\Delta_{S}^{E}$} \def\DL{$2\Delta_{L}^{E}$} \def\2DA{$2\Delta^{A}$} \def\D0{$2\Delta_{0}$} \def\CaC6{CaC$_6$} A polarized Raman scattering study has been performed on bulk 1st stage intercalated graphite CaC$_6$ crystals at sub-$T_c$ temperatures. We identify all three Raman active E$_g$ bands expected for the Rm$\overline{6}$ space group of CaC$_6$ at 440, 1120 and 1508\,\cm-1 and find them to be in agreement with zone center modes predicted by first principles calculations of phonon dispersion.$^1$ In addition the equivalents of the graphite D and G bands are observed at respective frequencies. Inherent to the disorder induced double resonant scattering process$^2$ the D band shifts from 1308\,\cm-1 to 1332\,\cm-1 upon the change of the excitation laser wavelength from 647\,nm to 476 \,nm. Assuming linear dependence of the D band peak position as a function of excitation energy this translates to the frequency shift of 35\,\cm-1$/$\,eV. By comparing the integrated intensity of the G band at 1582\,\cm-1 in \CaC6 to the one in kish graphite the relative fraction of higher stage domains to the 1st stage intercalation is estimated to be less then 0.2\%. Finally upon the superconducting phase transition we observe a 2$\Delta$ peak with the frequency of 24\,\cm-1 at $5\,\rm{K}$. With temperature increase this peak persists shortly up to the SC phase transition at 11.6\,K and shows temperature dependence consistent with the strong coupling regime. $^1$M.~Calandra and F.~Mauri, PRL $\mathbf{95}$, 237002 (2005). $^2$C.~Thomson and S.~Reich, PRL $\mathbf{85}$, 5214 (2000). [Preview Abstract] |
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C1.00330: Ni-Impurity Effect in High-$T_{\rm c}$ Cuprates Studied by Neutron Scattering and XAFS Spectroscopy Haruhiro Hiraka, Shuichi Wakimoto, Masaaki Matsuda, Daiju Matsumura, Yasuo Nishihata, Jun-ichiro Mizuki, Kazuyoshi Yamada Neutron scattering experiments using La$_{2-x}$Sr$_x$Cu$_{1-y}$Ni$_{y}$O$_{4}$ clarified that the parallel spin-density modulations (SDMs) in the superconducting phase are susceptible to Ni, in the same way as the diagonal SDMs in the insulating spin-glass phase. Ni substitution reduces the mobile hole concentration from $x$ down to $x-y$. Polarized XAFS measurements using Ni $K$-edge probe two types of Ni valence states; Ni$^{2+}$ and Ni$^{(2+\alpha)+}$. It indicates that a strong hole localization occurs around Ni, resulting in an effective spin-$1/2$ value at Ni sites. Therefore, a charge dopant nature of Ni is most likely realized when $x \ge y$. [Preview Abstract] |
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C1.00331: Spin transfer torque switching in perpendicular magnetic tunnel junctions with Co based multilayer Toshihiko Nagase, Katsuya Nishiyama, Masahiko Nakayama, Naoharu Shimomura, Minoru Amano, Tatsuya Kishi, Hiroaki Yoda It has been reported that spin transfer torque switching in the perpendicular magnetic device has the advantage of improving the spin-torque efficiency in comparison with the in-plane one [1, 2]. Our previous study was the first time to demonstrate the spin transfer switching in perpendicular magnetic tunnel junctions (MTJs) using TbCoFe alloy. In this paper, we report studies on the spin-torque efficiency in MgO based perpendicular MTJs consisting of CoFeB wedge/[Pd/Co]x2/Pd free layer and FePt/CoFeB reference layer. The damping constant $\alpha $ of the free layer increases in the thinner parts of the CoFeB thickness because of the effect of spin pumping. The ratio of the switching current density to the thermal stability factor (Jc/$\Delta )$, which corresponds to the spin-torque efficiency, was estimated. It was found that the free layer with the thicker CoFeB had a lower Jc/$\Delta $ because of its smaller $\alpha $. Our results experimentally clarify that reducing $\alpha $ leads to achieving the low switching current. [1] S. Mangin et al., Nature Materials 5, 210 (2006) [2] M. Nakayama et al., BB-09, 52nd MMM conference (2007). [Preview Abstract] |
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C1.00332: Electric Field-Induced Effects on Single-Walled Carbon Nanotube Photoluminescence Anton Naumov, Sergei Bachilo, R. Bruce Weisman An investigation of the fluorescence emission of single-walled carbon nanotubes (SWNTs) in electric fields will be described. HiPco SWNTs were embedded in poly(methylmethacrylate) (PMMA) films deposited onto the surface of microscope slides with ITO or interdigitized gold electrodes. The fluorescence of individual semiconducting SWNTs was then observed using a microscope coupled to a near-IR spectrograph and an InGaAs 2-D camera. Bulk samples of SWNTs in polymer were studied with a spectrofluorometer. When SWNTs in PMMA were subjected to electric fields of up to 10$^{7}$ V/m, a drastic decrease in fluorescence intensity was observed. This quenching is well described as a single-parameter inverse hyperbolic cosine function of applied field. The quenching effect is also dependent on the angle between SWNT and field, the length of the SWNT, and SWNT diameter (exciton binding energy). The quenching mechanism may involve both exciton dissociation in an electric field and free carrier effects. The latter were suggested by studies of long nanotubes. [Preview Abstract] |
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C1.00333: Scaling Laws for NanoFET Sensors Qi-Huo Wei, Fu-Shan Zhou In this paper, we report our numerical studies of the scaling laws for nanoplate field-effect transistor (FET) sensors by simplifying the nanoplates as random resistor networks. Nanowire/tube FETs are included as the limiting cases where the device width goes small. Computer simulations show that the field effect strength exerted by the binding molecules has significant impact on the scaling behaviors. When the field effect strength is small, nanoFETs have little size and shape dependence. In contrast, when the field-effect strength becomes stronger, there exists a lower detection threshold for charge accumulation FETs and an upper detection threshold for charge depletion FET sensors. At these thresholds, the nanoFET devices undergo a transition between low and large sensitivities. These thresholds may set the detection limits of nanoFET sensors. We propose to eliminate these detection thresholds by employing devices with very short source-drain distance and large width. [Preview Abstract] |
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C1.00334: Fabrication and magnetic characterization of ferromagnetic nanotubes Rehana Sharif, Shamaila Shahzadi, Han Yunan, Ming Ma, Han Xiu-Feng During the last decade, interesting properties of magnetic nanowires have attracted much attention. Besides their interesting basic properties, there is evidence that these can be used in the fabrication of new nanodevices. Recently magnetic nanotubes have been successfully fabricated and have become a symbol of new and fast developing research area of nanotechnology because of their technological applications in patterned recording media,magentic sensors and magnetic biotechnology. Ferromagnetic nanotubes have been fabricated using templates (Alumite, PCTE) which can provide us a straight forward route to fabrication of the nanotubes.The anisotropy of the tubes is governed by shape anisotropy and the switching field of the tubes is consistent with that expected from curling mechanism in which the magnetization rotates within the plane of the tube wall. [Preview Abstract] |
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C1.00335: Possible nano-graphene devices having topology origin edge states Koichi Kusakabe In nanometer scale graphene structures, edge-localized surface states may appear in specified edges. Evidences of the edge states has been given by the ultrahigh vacuum STM/STS observation of well-characterized edges of graphene structures.[1,2] The density functional theory supported both appearance of edge states and existence of localized magnetism in a characterized Hydrogenated graphene structure within the local-spin-density approximation.[3] In this study, we reconsider appearance of the edge states due to network topology of $\pi $ orbitals of graphene, which is used in designed structures for nano-meter scale graphene-based devices. We consider graphene structures bridging two metallic Ni electrodes. For the Ni (111) surface, epitaxial growth of graphene is possible. We assume that the Ni electrode has a sharp straight edge. The interface between graphene and Ni structure creates a boundary condition for conducting electrons in the graphene, since it is known that a gap is formed in the electronic states of graphene pasted on Ni. The gap is much enhanced by fluorination of graphene on Ni. There are two types of boundary for the graphene structures, which may be classified into zigzag and Klein's edges. Thus, we can design a graphene-based magnetic FET structure with Ni electrodes by possible partial fluorination of graphene. First-principles electronic structure calculations for this structure is given. [1] Y. Kobayashi, K. Fukui, T. Enoki, K. Kusakabe and Y. Kaburagi, Phys. Rev. B 71, 193406-1-4 (2005). [2] Y. Kobayashi, K. Fukui, T. Enoki and K. Kusakabe, Phys. Rev. B 73, 125415-1-8 (2006). [3] K. Kusakabe and M. Maruyama, Phys. Rev. B 67, 092406-1-4 (2003). [Preview Abstract] |
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C1.00336: Demixing of Charged Nanoparticle-Polymer Mixtures: A Simulation Study Ben Lu, Alan R. Denton The phase behavior of mixtures of charged nanoparticles and neutral polymers is studied by computer simulation. Adapting the classic Asakura-Oosawa-Vrij model, the polymers are modeled as coarse-grained effective spheres that are mutually ideal (theta solvent), but can overlap the nanoparticles with a penetration energy that mimics a loss of chain conformational entropy. Although monodisperse in chain length, the polymers fluctuate in radius of gyration in response to the nanoparticles. Within the primitive model of charged colloids, the nanoparticles are modeled as charged hard spheres, governed by effective electrostatic interactions, including a repulsive screened-Coulomb (Yukawa) pair potential and a one-body volume energy. To investigate demixing behavior, constant-NPT Gibbs ensemble Monte Carlo simulations are performed over ranges of nanoparticle-polymer size ratio, nanoparticle charge, and salt concentration. In the limit of neutral nanoparticles, simulation results are compared with predictions of density-functional theory. [Preview Abstract] |
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C1.00337: Topological Validation of Morphology Modeling by Reverse Monte Carlo Analysis of Two-dimensional Scattering Patterns Katsumi Hagita, Takashi Teramoto We presented a new method of morphology modeling using coarse- grained particles from multiple two-dimensional (2D) patterns of structure factors, which can be obtained from small angle x- ray scattering (SAXS). Reverse Monte Carlo (RMC) technique is extended for multiple 2D patterns. It is motivated by SAXS experiments of kinetic pathway from hexagonal perforated lamellar structure to double gyroid (DG) structure in the surfactant/water systems. For the first test, we examine reproducibility of a DG morphology. As a reference configuration, we obtain positions of particles forming DG morphology are generated in a computer using the equation of DG’s surface. Inputs of this extended RMC method are calculated from this reference configuration. The configurations obtained from this extended RMC method are examined by the Betti numbers which are mathematical indexes to classify complicated inter- connected three-dimensional structures and are given by Computational homology (CHomP) analysis. Combination of RMC and CHomP is examined as a new and useful approach for connecting scattering experiments to mathematics for 3D morphology. [Preview Abstract] |
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C1.00338: Thermal Deflection of Nanojets Wei Kang, Uzi Landman Generation of fluid jets of reduced sizes, down to the nanoscale [1], is a topic of continuing interest from both basic science and technological perspectives. One of the challenges pertains to the ability to control the direction of propagation of the jet. For macroscopic jets, including those with radii in the several micron range, a common method to vary the propagation direction is through the deflection of charged droplets, or as suggested more recently, via asymmetric heating that affects the surface tension and viscosity of the jet. Here we discuss a jet-bending method based on asymmetric heating of a fluid flowing in a cylindrical nozzle, where the main contribution to the deflection of the emanating nanojet is due to asymmetric evaporation near the exit, which results in a directional thrust that deflects the nanojet. Molecular dynamics simulations demonstrating bending of propane nanojets are discussed. [1] M. Moseler, U. Landman, Science 289, 1165 (2000) ; W. Kang, U. Landman, Phys. Rev. Lett. 98, 064504 (2007). [Preview Abstract] |
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C1.00339: Clustering Dynamics of Ultra-fine Particulate Systems Meenakshi Dutt, James Elliott Length scales of particles and their surrounding medium strongly determines the nature of their interactions with one another and their responses to external fields. We are interested in systems of ultrafine particles (0.1 - 1.0 micron) such as volcanic ash, solid aerosols, or fine powders for pharmaceutical ihalation applications. We develop a numerical model for these systems using the Derjaguin-Muller-Toporov (DMT) adhesion theory along with the van der Waals attraction between the particles and their contact mechanical interactions. We study the dynamics of these systems in the absence and presence of gravity by controlling the particle size, and thereby, the surface properties of the particles. The high surface energies of these particles causes them to agglomerate as they gravitationally settle. We explore their internal structure as a function of their particle size. [Preview Abstract] |
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C1.00340: Qubit Entanglement Driven by Remote Optical Fields Muhammed Yonac We examine the entanglement between two qubits, supposed to be remotely located and driven by independent quantized optical fields. No interaction is allowed between the qubits, but their degree of entanglement changes as a function of time. We report a collapse and revival of entanglement that is similar to the collapse and revival of single-atom properties in cavity QED. [Preview Abstract] |
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C1.00341: Optical Characterization of Biological Tissues Frederick Barrera, Dhiraj Sardar, Andrew Tsin University of Texas at San Antonio, San Antonio, Texas 78249. An in-depth characterization of optical properties of biological tissues has been performed. The wavelength-dependent total diffuse reflection ($R_{d})$ and total transmission ($T_{t})$ measurements have been taken for individual tissue by using a double-integrating sphere setup. The index of refraction of the tissue will be determined using conventional optical techniques. The Inverse Adding Doubling (IAD) computational method is applied to the measured values of $n$, $R_{d}$, and $T_{t}$ to calculate the optical absorption and scattering coefficients as well as the scattering anisotropy coefficients of these tissues. The $R_{d}$ and $T_{t}$ determined by the IAD method were compared with those generated by the Monte Carlo simulation technique. A thorough comparison of the scattering characteristics of these tissues has been made. Furthermore, a comparison of these optical scattering and absorption coefficients calculated by IAD method were compared to the values determined by the Kubelka-Munk model. [Preview Abstract] |
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