Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session R1: Poster Session III |
Hide Abstracts |
Room: Colorado Convention Center Exhibit Hall F, 1:00pm - 4:00pm |
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R1.00001: POLYMERS II |
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R1.00002: Computer Simulation Studies of Polyurethane Film Formation Shihai Yang, Ras Pandey, Marek Urban Three types of particles (hydrophobic (H, R-NCO), polar (P, R'-OH), aqueous (A) solvent) are used to describe the constituents involved in a polyurethane film formation. Characteristics such as attractive (P,A) and repulsive (H,A) interactions, reaction kinetics, and molecular weight ratios are captured by the model. Each constituent is mobile and forms covalent bonds with appropriate constituents with specific kinetics. Bonded units move and corresponding bonds fluctuate within limits. The aqueous components are also allowed to evaporate. The mobility allows stabilization (equilibration), covalent bonding captures the constituents, and evaporation destabilizes the system. Effects of temperature, initial water concentration, and stoichiometry are considered. With increasing the temperature, film thickness \textit{hs} increases while its roughness \textit{Ws} decreases. With increasing the initial water concentration and NCO:OH ratio, both film thickness \textit{hs} and its roughness \textit{Ws} increases. Simulation data suggest that higher NCO:OH ratios lead to higher urea and urethane contents, however, higher initial water concentration results in higher urea but lower urethane concentration in the film. [Preview Abstract] |
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R1.00003: A ring graph method for approximating atomic short-range order in disordered multi-component systems Zhun-Yong Ong The atomic short-range order (ASRO) in an alloy provides valuable information on the atomic structure to which the disordered alloy is tending. Mean field models with Onsager corrections have been used to calculate the ASRO in lattice models of disordered multi-component alloys. The Onsager correction is composition and temperature dependent and corrects for the over-correlation inherent to mean-field methods so that ASRO calculated satisfies the sum rule. However, it is does not take into account the k-dependence of the corrections. We present an analytical method based on ring graphs which provides for a k-dependent correction to the mean field. The ASRO in a simple ternary Ising model in a FCC lattice with nearest neighbor interactions is calculated using our method and compared to the results obtained from a Monte Carlo simulation. We find that, above the transition temperature, the analytical results are in good agreement with those obtained from simulations. [Preview Abstract] |
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R1.00004: Predicting Short-Range Order in Multicomponent Alloys from an Improved Mean-Field Theory Zhun-Yong Ong, Duane Johnson In alloys the atomic short-range order (SRO) indicates the nascent ordering to which the disordered alloy is tending at high temperatures. Direct first-principles prediction based upon KKR-CPA and mean-field thermodynamics have been successful in predicting system-specific SRO [1], if, at a minimum, corrections are included to satisfy the diffuse scattering sum rule in k-space. However, such models do not account for k-dependence of the corrections. Here, we present an analytic generalization to multicomponent alloys that includes ``cyclic diagrams'' [2,3] for composition, temperature, and k-dependent corrections to SRO. We first explore the improvement to SRO in model fcc ternary alloys via the generalized Ising model. We find that there is much better agreement to Monte Carlo simulations than with standard Bragg-Williams with(out) Onsager corrections. Then we implement this within the KKR-CPA linear-response theory of SRO.\Footnote{Work was supported by DOE (Award DEFG02-03ER46026 and NSF (DMR-0325939).} \newline \newline [1] J.B. Staunton, D.D. Johnson, and F.J. Pinski, Phys. Rev. Lett. 65, 1259 (1990); Phys. Rev. B 50, 1450 (1994); ibid, 57, 15177 (1998). \newline [2] R. Brout, Phys. Rev. 115, 824-835 (1959). \newline [3] R.V. Chepulski, et al, Phys. Rev. 65, 064201-7 (2002). [Preview Abstract] |
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R1.00005: Brownian dynamics simulation of polymer chains incorporating bending and torsion potentials Semant Jain, Ronald Larson Using stretching, bending, and torsion potentials for linear alkanes as described in literature [Ryckaet and Bellemans (1975), Helfand et al. (1980)], we study polymer state transitions, coil size, and storage and loss modulii. As the chain size increases, we compare the coil expansion resulting from bending and torsion forces to the theoretical predictions. Additionally, we compare the effect of Helfand's stretching and bending parameters, commonly used to speed up computation, versus realistic parameters in predicting the impact on coil size. Finally, we vary barrier heights between gauche+/- and trans torsional transition states to identify the limiting factor between bond orientation transitions. We compute individual bond vector and end-to-end vector correlations by combining Brownian force with spring, bending, and torsion forces to predict the contribution of each to the spectrum of polymer relaxation times. [Preview Abstract] |
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R1.00006: Density structure of polymers in the layered host system: the effect of the excluded volume. Alexander Chervanyov, Gert Heinrich We theoretically investigate the density structure of homo-polymers placed inside the host system of alternating layers that have different affinity for polymers. The exact solutions are obtained for the two-point propagator, monomer number density and average Flory radius of the ideal Gaussian polymers immersed in this periodic host structure. For the case where the excluded volume interactions are taken into account, the approximate counterparts of the above exact solutions are found. Based on the comparison of the obtained solutions, the effect of the excluded volume is found to qualitatively change the behaviour of the number density and Flory radius of polymers calculated as a function of the average affinity of the layers and the periodicity of the layered host. The effects (e.g. `polymer localization') of a small number of defects that disturb the perfection of the layered host on the structure of polymers placed in this host are investigated. [Preview Abstract] |
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R1.00007: Origin of Bends in Unperturbed Vinyl Polymers Yergou Tatek, Wayne Mattice Sharp bends are observed in highly dendronized polymers when they are placed on a mica surface. One interpretation assumes that thermal fluctuations are responsible for the formation of bends. An alternative explanation would place the emphasis on the stereochemistry of these polymers. We utilized different techniques to find out which one of the above stated explanations is valid. The first approach is based on the average end-to-end vectors calculation of subchains along the polymer backbone, using rotational isomeric states (RIS) model. Bends are located at sites where a drastic variation of these vectors in term of length and direction are observed. A complementary method is to generate, with RIS based Monte Carlo sampling, ensembles of planar conformations, in order to mimic adsorbed polymers on surfaces. By studying these ensembles, one can discriminate bends due to thermal fluctuations from bends due to stereochemistry. Moreover, results for atactic polymers show that stereochemistry is by far the main cause for bend formation. However, RIS based calculations do not take volume exclusion into account. We therefore performed Monte Carlo simulations using bond fluctuation method, of a single chain adsorption. The results appear to be qualitatively similar to the ones obtained with RIS based Monte Carlo sampling. [Preview Abstract] |
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R1.00008: Molecular dynamics simulations of Poly (Ethylene Oxide) and Poly (Propylene Oxide) Aqueous Solutions as a function of temperature. Oleg Starovoytov, Dmitry Bedrov, Oleg Borodin, Grant Smith Molecular dynamic (MD) simulations of aqueous solutions of poly (ethylene oxide) (PEO) and poly (propylene oxide) (PPO) have been performed using polarizable and non-polarizable force fields. Systematic investigation of thermodynamic and structural properties in PEO/water, PPO/water and PEO/PPO/water solutions as a function of temperature have been conducted and compared with available experiments. Our investigation indicate that polarizable force fields perform better in capturing saddle changes in structural and thermodynamic properties of these solution as a function of temperature and therefore represent a better basis for parameterization of temperature-dependent coarse-grained implicit solvent models. [Preview Abstract] |
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R1.00009: Effective molecular diffusion coefficient in a two-phase gel medium Christine Kingsburry, Gary W. Slater Our group has previously derived a mean-field expression for the effective diffusion coefficient of a probe molecule in a two-phase medium consisting of a hydrogel with large gel-free solvent inclusions. The diffusion coefficient is expressed in terms of the homogeneous diffusion coefficient in the gel and in the solvent, the gel concentration, the relative volume of the inclusions and the viscosities of the two phases. The expression was compared with exact numerical lattice calculations and was found to provide remarkably accurate predictions. The work presented here is an extension of the previously described study. The goal is to investigate more characteristics of a two-phase medium using further exact numerical calculations and then bring everything into one final expression. Some of the parameters we now include are the possible presence of gel fibers inside the inclusions, the local affinity effects (attractive obstacles) and the interfacial effects between the two phases. This work provides robust grounds for the modeling and design of multiphase systems for specific applications, e.g., phase-separated hydrogels as novel food agents or efficient drug-delivery platforms. [Preview Abstract] |
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R1.00010: Surprising non-monotonic dependence of a polymer's diffusion coefficient on the degree of disorder of the medium Owen Hickey, Gary Slater Many studies have found that the diffusion coefficient of a polymer in a disordered array of obstacles is much lower when compared to polymers in an ordered array of obstacles. We present simulation results based on the Bond-Fluctuation Monte Carlo algorithm where we determine the layout of the obstacles using a local harmonic potential well. When the potential is very strong the obstacles take on a periodic structure and the resulting dynamics obey the scaling laws of reptation. As we reduce the strength of the potential the obstacles are able to move small distances and we see an increase in their diffusion coefficient. Eventually, as the strength of the potential goes to zero and the array becomes completely disordered, strong entropic traps form trapping the polymers for long periods of time which dramatically reduces the diffusion coefficient. The surprising increase of the diffusion coefficient for intermediate amounts of disorder appears to be related to reptation inside wider channels [Preview Abstract] |
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R1.00011: Langevin dynamics simulations of PEO brushes in aqueous solutions Fang Yin, Dmitry Bedrov, Grant Smith We have conducted extensive equilibrium and non-equilibrium simulations of poly(ethylene oxide) brushes in aqueous solutions using coarse-grain implicit solvent model. In equilibrium simulation we focused on studying a repulsive force between two brushes as a function of surface coverage and chain length. In the non-equilibrium simulation we attempted to mimic the conditions of the quartz crystal microbalance with dissipation (QCM-D) technique frequently used to analyze the mass change and viscoelasticity of an absorbate. To obtain an understanding of energy dissipation mechanism of PEO brush from a molecular level, we use Langevin dynamics method to study the viscoelasticity of the PEO chains attached on the surface under the oscillation, matching the dissipation shift part measured in QCM-D. We study the effect of frequency and amplitude of the oscillation impacted on the attached surface, grafting density, and grafting pattern (singly-bound and doubly-bound) on both loss tangent and dynamic moduli of PEO brush. Normal mode of PEO brush is also compared with that of PEO solution with equivalent volume fraction. [Preview Abstract] |
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R1.00012: Parallel simulation for block copolymer mesophases Marco Pinna, Xiaohu Guo, Andrei Zvelindovsky We develop parallel large-scale Cell Dynamics Simulation to investigate various block copolymer structures. Effective domain decomposition and implementation of boundary conditions gives perfect scaling of the algorithm as function of number of processors. Little simulation time required and large 3 dimensional simulation boxes achievable make the code a good candidate to be a simulation precursor in combination with heavier simulation techniques. We show results obtained for various block copolymer structures, including block copolymer film formation and block copolymer-colloid complexes. Large simulation boxes allow for a realistic account of defects in the systems, which are not effected in such a case by the box size effect. Our method describes time evolution of the systems, and reaches experimental size and time scales. [Preview Abstract] |
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R1.00013: Microphase Separation Induced by Interfacial Segregation of Isotropic, Spherical Nanoparticles Michael J. A. Hore, Mohamed Laradji In a recent experiment by Chung et al. [Nano Lett. 5, 1878 (2005)] on an immiscible polymer blend containing silica nanoparticles, it was shown that the phase separation of the two polymers can be prevented as a result of the self-assembly of the nanoparticles at the interfaces between the two polymers. This effect is observed despite the fact that these nanoparticles are spherical and isotropic, and therefore fundamentally different from typical anisotropic surfactant particles, known to lead to microphase separated structures. Motivated by these experiments, we performed large scale simulations, based on the dissipative particle dynamics approach, on immiscible binary (A-B) fluids containing moderate volume fractions of isotropic nanoscale spherical particles, N. The nanoparticles preferentially segregate at the interfaces between the two fluids if the pairwise interactions between the three components are such that $\chi_{AB} > |\chi_{AN}-\chi_{BN}|$. We found that at late times, the average domain size saturates to a value, $R \sim r/\varphi$, where $r$ and $\varphi$ are the radius and the volume fraction of the nanoparticles, respectively. The dynamics of the phase separation process, dynamical scaling, and thermodynamic stability of the microphase-separated structures will be discussed. [Preview Abstract] |
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R1.00014: Multi-scale dynamical modes of a tethered membrane by Monte Carlo simulations Ras Pandey, Kelly Anderson, Barry Farmer A tethered membrane can be described by tethered nodes in a flexible sheet. We consider a square sheet with nodes connected by fluctuating bonds on a cubic lattice with each node executing its stochastic movement within the constraints of its bond-lengths. Although each interior node is connected by four of its neighboring node, there can be multiple pathways between two nodes for dynamical modes to propagate. While the motion of the centre of mass provides global dynamics of the membrane, movement of an interior node is crucial in understanding the segmental mode dynamics. Characteristic of sheet is controlled by node-node interaction and bond strength while the empty lattice sites constitute an effective solvent medium via node-solvent interaction. Each node executes its stochastic motion with the Metropolis algorithm subject to bond fluctuations, excluded volume constraints, and interaction energy. Conformational relaxation and dynamics of the sheet are examined at a range of temperatures in different solvent media. Variations of the mean square displacement of the center node of the sheet and that of its center of mass with the time steps exhibit multi-scale mode dynamics, and therefore, visco-elastic responses. Relaxation of the gyration radius are also examined. [Preview Abstract] |
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R1.00015: Dynamics of a Charged, Semi-flexible Polymer with Hydrodynamic Interaction. Won Kyu Kim, Oyeon Kum, Wokyung Sung We study static and dynamic correlation functions of segmental charge density and orientation in a semi-flexible polyelectrolyte. The semi-flexible polymer is described by the mean-field wormlike chain model, where the effective Hamiltonian incorporates bending and stretching energies. Furthermore, we incorporate the Coulombic interaction and hydrodynamic interaction between the beads screened and mediated respectively by ionic fluid environment. We analytically calculate the correlation functions and discuss how conformation and dynamics are affected by net charge value, segmental charge fluctuation, and persistence length. The Brownian dynamic simulations are performed to support and extend the analytical results. [Preview Abstract] |
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R1.00016: Lamellar to inverted hexagonal phase transition in DNA complexes with calamitic, discotic, and cubic shaped cationic lipids Lei Zhu, Li Cui In this study, we report the lipid tail molecular shape/size effect on the mesophase self-assembly of various cationic lipids complexed with double-stranded DNA. The molecular shape of the cationic lipids was tailored from rodlike (a cyanobiphenyl imidazolium salt) to discotic (a triphenylene imidazolium salt), and finally to cubic [a polyhedral oligomeric silsesquioxane (POSS) imidazolium salt]. An increase in the cross-sectional area of the hydrophobic tails with respect to the hydrophilic imidazolium head induced a negative spontaneous curvature of the cationic lipids. As a result, a morphological change from lamello-columnar phase for the DNA-cyanobiphenyl imidazolium salt (DNA-rod) and DNA-triphenylene imidazolium salt (DNA-disk) complexes to an inverted hexagonal phase for the DNA-POSS imidazolium salt (DNA-cube) complex was observed. [Preview Abstract] |
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R1.00017: An investigation of the photovoltaic properties of poly-(3-alkylthiophene):fullerene bulk heterojunction solar cells Anna A. Belak, Michael W. Rowell, Shawn R. Scully, Michael D. McGehee Poly-(3-hexylthiophene) has been the premier semiconducting polymer material for use in organic photovoltaic and transistor devices for some time. Its strong regioregularity yields relatively large crystal domains and a high charge carrier mobility. Some possible limitations in these solar cells are light absorption and hole collection through the polymer matrix. The alkyl side chains may decrease the optical density of the material and interfere with charge transport between polymer chains. We focused our investigation on the use of polythiophene derivatives with side chains of different lengths, poly-(3-hexylthiophene) and poly-(3-butylthiophene), in polymer/fullerene blend cells. We found that P3HT solar cells are most efficient, but P3BT cells are also promising, and their performance could be improved with further optimization. [Preview Abstract] |
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R1.00018: Organic Thin Film Transistors with Gate Dielectrics via Sol-Gel Process June Whan Choi, Sungwon Choi, Jae-Woong Yu, Ho Gyu Yoon, Jai-Kyeong Kim The presents work focuses on the preparation of gate dielectrics by the sol-gel process and the characterization of resultant organic thin film transistor (OTFTs). The basic requirements for the gate dielectric materials of OTFTs are high dielectric constant, low leakage current and the patternability. To obtain suitable gate dielectrics, the feasibility of sol-gel process and UV crosslinking were investigated. Acryl UV resin (DCS-SP210, Dongjin Semichem Co.,Ltd.), titanium n-butoxide, HCl and acetyl acetone were used to prepare a hybrid reaction medium. We obtained the result that the leakage current of dielectric layer was maintained under 10$^{-9}$ A in the OTFTs operating voltage, the dielectric constant was about 9 at 10 KHz and the rms was about 2-3 nm. OTFTs were fabricated with pentacene (45 nm) and the resultant dielectric layer. The field effect mobility and on-off ratio were 1.1 cm$^{2}$/V-s and 10$^{4}$, respectively. The result proved that sol-gel hybrid system was suitable for the gate dielectrics of OTFTs in the requirements of the electric, dielectric property and the patternability. [Preview Abstract] |
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R1.00019: Polarization-dependent Bragg gratings formed by shearing of polymer-dispersed liquid crystals \textit{in situ} during holographic recording Timothy Bunning, Vincent Tondiglia, Lalgudi Natarajan, Richard Sutherland, Pamela Lloyd We report the recording of holographic polymer-dispersed liquid crystal reflection gratings while applying a shear stress parallel to the film plane. The shear is transmitted through the film by moving one glass window with respect to a fixed glass window during the holographic recording in a single beam, total internal reflection geometry. The timing and magnitude of the stress are related to optical properties of the resulting Bragg grating. High diffraction efficiency for light polarized in a direction parallel to the stress is obtained with nearly zero diffraction efficiency for the perpendicular polarization. Contrary to post-recording stress-induced polarization sensitization, the \textit{in situ} process results in permanently polarized gratings. The polarization sensitivity is related to stress-induced morphology changes of liquid crystal droplets that are frozen during the cure process. [Preview Abstract] |
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R1.00020: On the nature of the oligoacene ground state Johannes Hachmann, Jonathan Dorando, Michael Aviles, Garnet Kin-Lic Chan The nature of the oligoacene ground state - its spin, singlet-triplet gap, and diradical character as a function of chain-length - is a question of ongoing theoretical and experimental interest with notable technological implications. Previous computational studies have given inconclusive answers to this challenging electronic structure problem (see e.g. [1]). In the present study we exploit the capabilities of the local \textit{ab initio} Density Matrix Renormalization Group (DMRG) [2], which allows the numerically exact (FCI) solution of the Schr\"{o}dinger equation in a chosen 1-particle basis and active space for quasi-one-dimensional systems. We compute the singlet-triplet gap from first principles as a function of system length ranging from naphthalene to tetradecacene, correlating the full $\pi $-space (i.e. up to 58 electrons in 58 orbitals) and converging the results to a few $\mu $E$_{h}$ accuracy [3]. In order to study the diradical nature of the oligoacene ground state we calculate expectation values over different diradical occupation and pair-correlation operators. Furthermore we study the natural orbitals and their occupation. [1] Bendikov, Duong, Starkey, Houk, Carter, Wudl, \textit{JACS} 126 (\textbf{2004}), 7416. [2] Hachmann, Cardoen, Chan, \textit{JCP }125 (\textbf{2006}), 144101. [3] Hachmann, Dorando, Avil\'{e}s, Chan, \textit{in preparation}. [Preview Abstract] |
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R1.00021: Development of High Refractive Index Conjugated Materials Matthew Graham, Shi Jin, Stephen Z. D. Cheng The goal of this project is to fabricate a polymeric material with a complete 3-D PBG, to bring the tailorable physical, electrical, and optical properties of polymeric materials to 3-D PBG materials. Because of its conjugated nature and the presence of a heavy sulfur atom in its repeat unit, poly(thiophene) (PT) is predicted to have one of the highest polymeric refractive indices, but the reported n values for PT are 1.4 at 633 nm. This discrepancy is because the potential needed to electrosynthesize PT, the only method available to synthesize thick and high quality PT films, is higher than its degradation potential. It was found that by polymerizing thiophene with an optimized monomer concentration, proton trap concentration, and reaction temperature in a strong aprotic Lewis acid solvent, the polymerization potential could be reduced below the degradation potential of PT. The resultant PT film had a significantly elevated n Photonic templates were then constructed using a combination of Colvin's method$^{ }$with monodisperse spheres and mechanical annealing. High n PT was used to infiltrate the templates, and the templates were removed leaving a polymeric inverse opal with the possibility of a complete 3-D PBG. [Preview Abstract] |
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R1.00022: Nanoscale Efficiency Maps for Organic Solar Cell Devices - Initial Results. Benjamin Watts, Andrew Minor, Francis Hellman, Harald Ade Solar cells based on thin blend films of conjugated polymers and/or fullerene derivatives are a promising alternative to the currently available silicon-based solar cells. However, these systems tend to display complex segregation of the organic components during film formation, with the degree of segregation observed shown to depend on parameters such as spincasting spin-speed and solvent type. Many studies in recent years have focused on the influence of film morphology on device performance, often comparing the micron- or nano-scale segregation features observed by scanning probe (AFM, Kelvin probe, NSOM) or electrom microscopies (SEM, TEM) in blend films to the efficiency of fully fabricated macroscopic devices that utilize similarly fabricated active layer blend films. Here, we present details and initial results of two experiments that promise to allow nanoscale observation of the local device efficiency: electron- and soft X-ray beam induced current (EBIC and SoXBIC respectively). EBIC and SoXBIC involve scanning a focused beam of the respective probe across a fully formed photovoltaic device, injecting charges into the active polymer layer and measuring the resulting current between the device electrodes in order to generate 2D efficiency maps. [Preview Abstract] |
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R1.00023: NEXAFS Spectra of Conjugated Polymers: Contrast Mechanisms for Soft X-ray Characterization of Electronic Polymer Structures Tohru Araki, Benjamin Watts, Jan Luning, Harald Ade Electronic devices based on conjugated polymers promise to revolutionize both display and solar cell technologies with significant advantages over conventional inorganic based devices. However, progress in this field is hampered by the fact that many conventional characterization techniques, such as electron microscopy and neutron and hard X-ray scattering and reflectivity, are difficult to apply to polymer blend structures due to poor contrast. On the other hand, polymer structures can be similarly characterized via a variety of soft X-ray techniques that have a strong intrinsic contrast mechanism based on the near edge X-ray absorption fine structure (NEXAFS) resonances of the component polymers. Here, we present a database of calibrated NEXAFS spectra of conjugated polymer materials, including polythiophene, poly phenylenevinylene and polyfluorene based polymers. These spectra illustrate the level of contrast that is achievable with soft X-ray techniques when utilizing specific resonant photon energies, which will be demonstrated with some example data. [Preview Abstract] |
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R1.00024: Charge injection and transport in fluorene-based copolymers. Hon Hang Fong, George G. Malliaras, Tianjian Lu, David Dunlap Fluorene-based copolymer is considered to be one of the most promising hole transporting and blue light-emitting conjugated polymers used in polymeric light-emitting diodes (PLEDs). Time-of-flight (TOF) technique has been employed to evaluate the charge drift mobility under a temperature range between 200 - 400 K at the thick film regime (1-10 micron). Meanwhile, contact ohmicity is studied by Dark Current Space Charge Limited Conduction (DISCLC) technique. Charge injection efficiencies from different electrical contacts are also studied and the corresponding injection barriers are independently investigated by photoemission and electroabsorption spectroscopies. Results show that the copolymers exhibit non-dispersive charge transport behavior and possess superior mobilities of up to 0.01cm$^{2}$V$^{-1}$s$^{-1}$ while single-carrier devices from various electrical contacts such as PEDOT:PSS are varied, depending on the chemical structure of amine component in the fluorene-triarylamine copolymers. Results will shed light on the enhancement of device efficiency and stability in the future polymer electronic devices. [Preview Abstract] |
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R1.00025: Exfoliation and intercalation in a layer of clay platelets: effects of solvent and temperature by a Monte Carlo simulation Barry Farmer, Ras Pandey Effects of the quality of solvent and temperature on the exfoliation of a layered platelets and intercalation of solvent are studied by a Monte Carlo simulation. A platelet is modeled by square sheet consisting of nodes tethered together by fluctuating bonds on a cubic lattice. A stack of four sheets constitutes the layer with a small initial inter-layer distance. A fraction of the lattice sites are randomly occupied by the solvent particles initially; a solvent constituent is modeled by a particle with the size of a node. The interaction strength (attractive and repulsive) between sheet nodes and the solvent particles control the quality of the solvent. Solvent constituents and sheet nodes execute stochastic movement with the Metropolis algorithm subject to bond fluctuation and excluded volume constraints. Density profiles of the sheet and solvent particles and their dynamics are studied for a range of temperatures in different solvent media. The quality of solvent plays a critical role in exfoliation of sheets and intercalation of solvent constituents between the sheet layers particularly at low temperatures. The exfoliation is enhanced on increasing the temperature. [Preview Abstract] |
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R1.00026: Patterning of microgel particles on polymer surfaces controlled by autophobicity and interfacial tension Arif Gozen, Bin Wei, Richard Spontak, Jan Genzer, Paul Gurr, David Solomon, Greg Qiao We investigate the thermal response of microgel particles ($\mu $GPs) composed of a cross-linked divinylbenzene core and poly(methyl methacrylate) (PMMA) arms as they segregate from PMMA homopolymer due to autophobicity. When in contact with a free surface, the particles migrate to the PMMA surface but remain inside the PMMA. When a thin film of polystyrene (PS) is placed on top of a PMMA/$\mu $GP film, the $\mu $GPs segregate to and thus roughen the PMMA/PS interface, as evidenced by AFM analysis. We attribute this behavior to a change in surface vs. interfacial energetics. Specifically, while the high surface energy of the native PMMA film keeps the particles inside the bulk PMMA, placing a thin PS layer on top of the PMMA/$\mu $GP film decreases the PMMA/PS interfacial tension by about an order of magnitude, which consequently permits segregation of the $\mu $GPs to the PMMA/PS interface. We follow the segregation kinetics of core-shell $\mu $GPs with and without fluorescent tagging, and we demonstrate the possibility of patterning the segregated $\mu $GPs by contacting a corrugated poly(dimethylsiloxane) (PDMS) layer to PMMA/$\mu $GP films. Regions of the PMMA/$\mu $GP film touching the PDMS layer exhibit $\mu $GP segregation, while non-contacted regions appear featureless. [Preview Abstract] |
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R1.00027: Microgels: Structure, Dynamics, and Possible Applications. John McKenna, Kiril Streletzky We cross-linked Hydropxypropylcellulose (HPC) polymer chains to produce microgel nanoparticles and studied their structure and dynamics using Dynamic Light Scattering spectroscopy. The complex nature of the fluid and large size distribution of the particles renders typical characterization algorithm CONTIN ineffective and inconsistent. Instead, the particles spectra have been fit to a sum of stretched exponentials. Each term offers three parameters for analysis and represents a single mode. The results of this analysis show that the microgels undergo a transition to a fewer modes around 41C. The CONTIN size distribution analysis shows similar results, but these come with much less consistency and resolution. Our experiments prove that microgel particles shrink under volume phase transition. The shrinkage is reversible and depends on the amount of cross-linker, salt and polymer concentrations and rate of heating. Reversibility of microgel volume phase transition property might be particularly useful for a controlled drug delivery and release. [Preview Abstract] |
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R1.00028: Confinement effects on the glass transition of the hydrogen bonded liquids. Wei Zheng, Sindee Simon The glass transition behavior of glycerol and propylene glycol confined in nanoporous glass is investigated using differential scanning calorimetry. Both silanized and unsilanized porous glasses are used to confine the liquids with nominal pore sizes ranging from 2.5 to 7.5 nm, and the glass transition temperature (T$_{g})$ and the fictive temperature (T$_{f}$') are measured on cooling and heating, respectively. On heating, glycerol confined in the unsilanized pores exhibits a T$_{f}$' similar to that of bulk unconfined material, whereas in the silanized pores a depressed glass transition is observed. For propylene glycol, similar behavior is observed except that an additional glass transition is observed in both silanized and unsilanized systems approximately 30 K higher than the bulk. The measured T$_{f}$'s are compared to the literature results, and the confinement effects are discussed. We also emphasize that changes in T$_{g}$ are not necessarily sufficient to characterize the confinement effects. Dramatic changes are observed for the strength of the transition ($\Delta $C$_{p})$ and for the enthalpy overshoot accompanying the glass transition for the materials confined in unsilanized pores even though no changes in T$_{g}$ are observed. [Preview Abstract] |
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R1.00029: A New Pressurizable Dilatometer for Measuring the Time-Dependent Bulk Modulus of Polymers Yan Meng, Paul O'Connell, Gregory McKenna, Sindee Simon A new piston-cylinder type pressurizable dilatometer controlled by a stepper motor has been developed to measure the time-dependent bulk modulus of polymeric materials. A perfluorinated oil, which surrounds the sample, is used as the confining fluid. By subtracting the volume contribution of the confining fluid from the total volume, the volume response of the polymeric sample can be obtained as a function of temperature, pressure, and time in the glass transition region. We are particularly interested in comparing the width and time scales of the bulk and shear responses in the transition region in order to test Leaderman's hypothesis that the two responses have different molecular origins. PVT measurements and the time-dependent bulk modulus for a polystyrene (Dylene 8) will be reported. [Preview Abstract] |
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R1.00030: Polymeric Template Assisted Formation of Gradient Concentric Metal and Metal Oxide Rings Suck Won Hong, Zhiqun Lin Gradient concentric rings of polymers, including (poly[2-methoxy- 5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and poly (methyl methacrylate) (PMMA), with unprecedented regularity were formed by repeated ``stick-slip'' motion of the contact line in a sphere-on-flat geometry. Subsequently, polymer rings served as templates to direct the formation of concentric metal and metal oxide rings. Three methods were described. The first two methods made use of either UV (i.e., on MEH-PPV) or thermal treatment (i.e., on PMMA) on metal-sputtered polymer rings, followed by ultrasonication. The last method, however, was much simple and robust, involving selective removal of metal and metal oxide and polymer (i.e., PMMA) consecutively. [Preview Abstract] |
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R1.00031: The Shear Response and Structure in Polycyanurate Networks Qingxiu Li, Sindee Simon The shear response of polycyanurate networks with different crosslink densities, varied by changing the ratio of difunctional to monofunctional cyanate ester, is measured from shear stress relaxation and dynamic experiments. Master curves are constructed following the time-temperature superposition principle, and the temperature dependence of the shift factors is examined. The discrete relaxation time spectra are calculated from the viscoelastic responses and are found to be independent of crosslink density. The crosslink density, determined from the rubbery modulus, and the sol content, measured from sol extraction experiments, are modeled for the fully cured polycyanurate networks using the recursive method; a monomer cyclization reaction is assumed in the modeling based upon the chemical composition of the sol which was determined by mass spectroscopy. The effect of monomer cyclization on the conversion at gelation of dicyanate esters is discussed. [Preview Abstract] |
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R1.00032: A New Bio-based Dielectric Material. Mingjiang Zhan, Richard P. Wool Low dielectric constant (low-k) materials are widely used in modern high-speed microelectronics, such as printed circuit boards. A new bio-based composite was developed from soybean oil and chicken feather fibers, which has the potential to replace currently used petroleum-based dielectrics. Feather fibers have a unique hollow structure which distinguishes them from glass fibers and give very attractive properties. Due to the retained air in the hollow fibers, the dielectric constant can be lower than conventional epoxy-based dielectrics at both low and high frequencies. The coefficients of thermal expansion (CTE) of the materials decrease with addition of feather fibers and even can be negative. By controlling the fraction of fibers, delamination caused by CTE mismatch between the dielectric and the metal lines can be avoided. The enhancement of adhesion between copper surface and polymer matrix was investigated. The tough structure of fibers significantly improved the mechanical properties of the composites, such as flexural properties and storage modulus. Supported by USDA [Preview Abstract] |
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R1.00033: Electrical Bending and Mechanical Buckling Instabilities in Electrospinning Jets Tao Han, Darrell H. Reneker The electrospinning jet was a continuous fluid flow ejected from the surface of a fluid when the applied electrical force overcomes the surface tension. The jet moved straight away from the tip and then became unstable and bent into coils. This phenomenon is the electrical bending instability [1]. When the distance between the tip and collector was reduced to less than the maximal straight segment length, the electrical bending instability did not occur. The periodic buckling of a fluid jet incident onto a surface is a striking fluid mechanical instability [2]. When axial compressive stress along the jet reached a sufficient value, it produced the fluid mechanics analogue to the buckling of a slender solid column. In the electrospinning, the buckling instability occurred just above the collector where the jet was compressed as it encountered the collector. The buckling frequencies of these jets are in the range of 10$^{4}$ to 10$^{5}$ Hz. The buckling lengths of these jets are in the range of 10 to 100$\mu$m. \begin{enumerate} \item Reneker,D.H.; Yarin, A. L.; Fong, H.; Koombhongse, S., \textit{Journal of Applied Physics}, 87, 4531, 2000 \item Tchavdarov B.; Yarin, A. L.; Radev S\textit{., Journal of Fluid Mechanics; }253, 593,1993 \end{enumerate} [Preview Abstract] |
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R1.00034: Polymer Micro-scrolls Kyriaki Kalaitzidou, Alfred J. Crosby This research focuses on the spontaneous formation of geometric structures of Au-coated crosslinked polydimethylsiloxane (PDMS) films. The Au-PDMS bilayer is fabricated on a rigid glass substrate that is pre-coated with a sacrificial layer of polyacrylic acid (PAA). Upon dissolution of the PAA, micro-scale, equilibrated structures are formed in a water bath due to a residual stress in the bi-layer film. The residual stress develops due to the difference in coefficients of thermal expansion for the two materials and the constraint at the bi-layer interface. A phase diagram that predicts the shape of the bilayer structures as a function of residual strain, the materials properties, the thickness of the two layers and the lateral sample dimensions is presented. This phase diagram serves as a design tool for fabricating tubes, rings and chiral scrolls on the micron length scale. These structures combined with their demonstrated reversibility have potential as capsules in drug delivery systems and novel conductive composites. [Preview Abstract] |
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R1.00035: The Elastic Constants and Related Mechanical Properties of the Monoclinic Polymorph of the Carbamazepine Molecular Crystal Himansu Mohapatra, Craig J. Eckhardt Polymorphism is the property of a compound to crystallize in two or more crystalline phases containing different arrangements and/or conformations of the molecules in the crystal lattice. The Phenomenon of polymorphism is a major issue in the pharmaceutical industry especially in relation to drug uptake in the body, tablet processing and growth. This has led to considerable interest in predicting and understanding properties of drug polymorphs, and more recently the mechanical properties of the polymorphs. In this work, Brillouin scattering is used to probe the acoustic phonons of the monoclinic ($P$2$_{1}$/$c)$ polymorph of the drug, carbamazepine (CBZ). By sampling a variety of acoustic phonons, the complete elastic constant tensor has been determined for this CBZ polymorph. The observed trend in the elastic constants: C$_{11}<$ C$_{22}\sim $C$_{33}$ is qualitatively associated with the crystal growth pattern seen in CBZ. Investigation into the anisotropy of the intermolecular interactions has been investigated further by calculation of linear compressibilities. [Preview Abstract] |
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R1.00036: Organic Light Emitting Diodes with Opal Photonic Crystal Layer and Carbon Nanotube Anode Raquel Ovalle Robles, Maria del Rocio Nava, Christopher Williams, Mei Zhang, Shaoli Fang, Sergey Lee, Ray Baughman, Anvar Zakhidov We report electroluminescence intensity and spectral changes in light emission from organic light emitting diode (OLEDs) structures, which have thin transparent films of opal photonic crystal (PC). The anode in such PC-OLED is laminated on opal layer from free standing optically transparent multiwall carbon nanotubes (T-CNT) sheets made by dry spinning from CVD grown forests. Silica and polystyrene opal films were grown on glass substrates by vertical sedimentation in colloids in thermal baths and the particle size of opal spheres ranges from 300 nm to 450 nm. The use of T-CNTs, (coated by PEDOT-PSS to avoid shorting) as hole injector, allows to eliminate the use of vacuum deposition of metals and permits to achieve tunneling hole injection regime from CNT tips into Alq$^{3}$ emission layer [Preview Abstract] |
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R1.00037: Flexible OLED with Transparent Multiwall Carbon Nanotubes Electrodes Raquel Ovalle Robles, Christopher Williams, Mei Zhang, Shaoli Fang, Sergey Lee, John Ferraris, Ray Baughman, Anvar Zakhidov We have demonstrated earlier, that transparent carbon nanotube (T-CNT) sheets, prepared by dry spinning of CVD grown multiwall nanotube forests can be used as hole injectors in bright OLEDs with Alq3 as emissive layers [1]. Now we demonstrate here that advantages of mechanically strong, elastomeric T-CNT over traditional ITO can be further favorably used in flexible OLEDs (based on Alq3 emitter) fabricated on mylar or PET substrates. The high work function of T-CNT sheet ($\sim $5.2 eV) and the geometry of sharp tips allows to achieve tunneling charge injection regime at relatively low voltages, which allows to achieve higher hole injection current densities. Moreover we demonstrate, that the use of low quality ITO on PET, combined with T-CNT as tunneling hole injector may have advantages for large area OLED/PLEDs. \newline [1] M. Zhang, S. Fang, A. Zakhidov, S. B. Lee, A. Aliev, R.H. Baughman, Strong, Transparent, Multifunctional, Carbon Nanotube Sheets, \textbf{\textit{Science,}} 309,(2005) 1215 [Preview Abstract] |
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R1.00038: Controlling solidification and fiber diameter of Polyethylene oxide nanofibers electrospun from aqueous solution by controlling the partial pressure of water vapor Sureeporn Tripatanasuwan, Zhenxin Zhong, Darrell Reneker Electrospinning is widely in research attention due to its cost effectiveness and straightforwardness for making nanofibers. During the electrospinning process, a charged jet is elongated by repulsive force between electrical charges carried by the jet. The charged jet develops spiral path due to the electrically driven bending instability, which make it possible for the jet to elongate and produce nanofibers in a small space. Solidification has been identified as an important factor that determines the diameter of electrospun nanofibers. The elongation and thinning of a charged jet stops as the charged jet is solidified. Controlling solidification of the charged jet by controlling of partial vapor of water in electrospinning of polyethylene oxide from aqueous solution has been demonstrated in this study. As the partial vapor of water increase, the solidification process of the charged jet becomes slower, allowing elongation of charged jet to continue. [Preview Abstract] |
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R1.00039: Nanoparticles induce raft formation in phospholipid liposomes Bo Wang, Liangfang Zhang, Steve Granick Motivated by general interests in endocytosis, virus transfection and utilization of nanoparticles as cargo for drug delivery, this study focuses on the binding of nanoparticles to model lipid bilayers and the interactions between them. Exploring not only on the ensemble level, with the help of calorimetry, but also on the single-molecule level using fluorescence probes and single-molecule detection, we conclude the following. First, adsorbates capture and slave dynamically the lipids underneath, which results in lipid packing fluctuations, thereby producing rafts in the bilayers. Second, competition between neighboring particles causes further recomposition of heterogeneous lipid distribution. Bearing this insight in mind, we expect coupled motions of lipid and nanoparticles to occur, and confirm this with direct measurements. Going further, collective responses of lipid molecules cast light on the crucial role of support membranes in determining how membrane-based sensors respond to an external stimulus. [Preview Abstract] |
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R1.00040: 2-D Hierarchical Structure of a Block Copolymer and Bio-nanoparticle Composites Dongseok Shin, Yao Lin, Qian Wang, Thomas Russell 2-dimensional hierarchical structures were generated by combining two different self assembling systems; block copolymer and bio-nanoparticle. For this study, a block copolymer having a positively charged component, i.e. poly (styrene-b-N-methyl-4-vinylpyridinium iodide), was used. Thin film composites of this block copolymer and bio-nanoparticles were fabricated by adsorbing bio-particles on the polymer film and subsequently annealing the sample under the presence of solvent vapor. 2-dimensional hierarchical structures, where block copolymer chains microphase separated inside of discrete grains surrounded by bio-nanoparticles, were obtained with rod- like bio-particles (tobacco mosaic virus and M13 phage) as well as with spherical one (ferritin). The pH effect on the assembly of rod-like bio-particles and the morphology of composites was investigated. When the pH of the solution used for the adsorption of bio-particles was low, the bio-molecules aggregated and formed large bundles, while they were dispersed well at high pH. This difference was reflected in the morphology of the resultant complexes. [Preview Abstract] |
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R1.00041: Block Copolymer for Patterning Bio-molecules Dongseok Shin, Yao Lin, Michael Scholle, Liaohai Chen, Brian Kay, Lee Makowski, Thomas Russell The fabrication of a well-defined pattern of bio-molecules is crucial for high throughput diagnostics and cell proliferations. Self-assembling block copolymers are novel candidates for the generation of high density patterns with nanometer scale features. Here, we have used a phage display library to select a peptide sequence that selectively binds to polystyrene. When the selected peptide sequence was incubated on a poly(styrene-b-methylmethacrylate) (P(S-b-MMA)) film, the pattern of the underlying block copolymer microphases was duplicated as a result of the selective binding of the peptide on PS. To utilize this result for the directional assembly of bio-molecules, the selected sequence was engineered into different loops of the fibronectin type III (FN3). The binding of the engineered FN3s was tested using inverted phase P(S-b- MMA), where PS formed cylinders standing normal to the surface. The affinity of engineered FN3s to the film varied depending on the position of the engineered loop. [Preview Abstract] |
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R1.00042: Block Copolymer Films for Organizing Charged Biopolymers Jung Hyun Park, Yujie Sun, Yale Goldman, Russell Composto Amphiphilic block copolymers are attractive templates for organizing biopolymers. In aqueous media, selective attachment is achieved by designing a hydrophilic block that is attractive towards biomolecules. Thin films of poly(styrene-b-tert-butyl acrylate) (PS-b-PtBA) (66.2k-32k) are converted to poly(styrene-b-acrylic acid) (PS-b-PAA) by thermal deprotection resulting in PAA spheres embedded in a PS matrix. Upon exposing PS-b-PAA films to buffered solutions at pH 7.4, PAA spheres, initially below the surface, swell and break through the surface to form a hexagonal array with short range order. To create positively charged patches, PS-b-PAA films are exposed to 3-aminopropyltriethoxysilane (APTES) which selectively cross-link the spherical PAA domains. Because these patches favorably attract negatively charged biopolymers such as F-actin, microtubules, and DNA, the PS-b-PAA thin film provides a tunable template for controlling the number and orientation of biopolymers arranged across the surface. [Preview Abstract] |
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R1.00043: Evolution of the Elastic Modulus and Hardness of Benzocyclobutene During the Curing Process Michael Grzesik, Shivashankar Vangala, William Goodhue, Walter Buchwald Benzocyclobutene (BCB) is a polymer possessing both processing and material properties making it suitable for use as an interlayer dielectric in the fabrication of multi-chip modules and as an adhesive for indirect wafer bonding. Both, the elastic modulus and hardness of BCB were studied as a function of curing percentage. Curing percentage was determined by means of Fourier transform infrared transmission spectroscopy (FTIR). Elastic modulus was measured by nanoindentation, which is demonstrated as a means to determine curing percentage. Measurements were taken spanning the polymers solid phase curing from 48{\%} to fully cured. The reduced modulus was found to decrease from 4.78 GPa at 48{\%} cured to 3.35 GPa at fully cured, while the hardness increased from .191 GPa to .246 GPa. Knowledge of the mechanical properties of the adhesion layer during the curing process allows one to optimize the temperature ramping profile during the bond process, in order to improve yield. [Preview Abstract] |
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R1.00044: Hybrid Nanomaterials: One Dimensional Nanoparticle Assemblies Nikhil Sharma, Darrin Pochan One-dimensional nanoparticle assemblies have potential applications in sensing, as plasmon and energy waveguides and in the conduction of novel signals such as phonons and spin states. Herein we present two strategies for the fabrication of such assemblies. Micro and meso-scale particle assemblies have been produced via a coaxial electrospinning process that results in assemblies of particles (silica and silver) encapsulated within a polymer nanofiber (polyethylene oxide). The method has been demonstrated successfully in the creation of 1D assemblies of differently sized silica particles. The effect of change in solution concentrations and relative flow rates in internal and external channels of the coaxial electrospinning apparatus on the structure of these assemblies has been investigated. Nano-scale assemblies of gold particles have been prepared by templating gold nanoparticles on a 20 amino acid peptide that displays laminated morphology. These assemblies are formed as laterally spaced one-dimensional nanoparticle assemblies. [Preview Abstract] |
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R1.00045: Bicontinuous Mesostructured Inorganic Films from Gold Nanoparticle Induced Phase Transitions in Self-Assembled Polystyrene-b-poly(2-vinylpyridine) Diblock-Copolymer Templates Joshua Petrie, Bumjoon Kim, Glenn Fredrickson, Craig Hawker, Ed Kramer Gold nanoparticles modified by short chain polymers can lead to strong localization at interfaces between blocks in a polystyrene-b-poly(2-vinylpyridine) [PS-PVP] block copolymer. The presence of small volume fractions of these nanoparticles in symmetric PS-PVP films lead to a decrease in the domain spacing of lamellar layers, due to the lowering of interfacial tension. When the volume fraction of nanoparticles is larger than a critical value, the diblock copolymer adopts a bicontinuous morphology. We demonstrate that we can selectively cross-link the PVP domain using diiodobutane with the goal of using these self-assembled films as templates for mesostructured inorganic films by introducing the inorganic precursor into the crosslinked but swellable PVP domain. [R.C.Hayward, B.F. Chmelka and E.J. Kramer, Adv. Materials, 17, 2591 (2005).] [Preview Abstract] |
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R1.00046: Carbon Nanotubes for Polymer Photovoltaics Annick Anctil, Roberta DiLeo, Chris Schauerman, Brian Landi, Ryne Raffaelle Carbon nanotubes are being investigated for optical absorption, exciton dissociation, and carrier transport in polymer photovoltaic devices. In the present work, single wall carbon nanotubes (SWNTs) were synthesized by an Alexandrite pulsed laser vaporization reactor at standard conditions and purified based upon our previously reported TOP procedure. The SWNTs were dispersed in polymer composites for pure MEH-PPV, pure P3HT, and [C60]-PCBM-P3HT (1:1 by weight) as a function of nanotube weight loading (0.1 -- 5{\%} w/w). The AM0 current-voltage measurements for structures sandwiched between PEDOT/PSS coated ITO substrates and an evaporated aluminum contact demonstrate the dramatic effect of SWNT content on the short circuit current density, with conversions efficiencies consistently greater than 1{\%}. The temperature coefficient for nanotube-containing polymer photovoltaics has been compared to conventional PCBM-P3HT devices, and the general relationship of increasing efficiency with increasing temperature is observed. However, the necessity to control nanotube percolation to prevent device shunting has led to recent developments which focus on controlling nanotube length through oxidative cutting, the deposition of intrinsic polymer layers, and the use of aligned carbon nanotube arrays for preferential charge transport. [Preview Abstract] |
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R1.00047: Direct self-catalytic lateral grown NiSi nanowire bridge and their electrical transport Yun-Hi Lee, Hyuk-Sang Kwon* In order to fabricate NiSi nano-interconnector between electrdoes, we introduced self-catalytic direct-lateral growth method. For the growth of NiSi nanowires, Ni/p- or n-type Si bilayer was formed on the thermal oxide coated Si substrate. Then, the layered films were treated in chemical vapour deposition reactor under the flowing of Ar at 900-1500 K. The lateral grown NiSi nanowire bridge showed a high current carrying capacity of 3-10 mA per um at 10 mV of bias voltage. The method introduced in this work suggests that it may be possible to provide building block in nano-electro-spinics. [Preview Abstract] |
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R1.00048: Target Finding Mechanism of Microtubules in a Confined Geometry Mitra Shojania Feizabadi Discovery of a non-equilibrium dynamic of microtubules, called dynamic instability, raised this question: is stochastic polymerization dynamic of microtubules an advantage in the process of finding a chromosome as a target? Previous studies showed that compared to usual reversible polymerization, dynamic instability of microtubules with decreasing length distribution reduced the time required to find a target by several order of magnitude [1]. Dynamic Equations for growing and shrinking microtubules in a confined geometry is theoretically modeled by Govinden and Spillman [2]. This work calculates the target finding time for microtubules with exponentially increasing length distribution in a confined geometry. The efficiency of target finding mechanism based upon different dynamical parameters is discussed. [1] Holy TE, Leibler S. 1994, Proc. Natl. Acad. Sci. USA 91, 5682. [2] Govindan B, Spillman W. 2004, Phys. Rev. E 70, 032901. [Preview Abstract] |
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R1.00049: There and (slowly) back again: Entropy-driven hysteresis in a model of DNA overstretching Stephen Whitelam, Sander Pronk, Phillip Geissler DNA in vivo experiences protein-mediated tensile forces large enough to alter the structure and stability of the hybridized state. Experiments show that double-stranded DNA, when pulled along its axis, elongates abruptly at a force of about 65 pN. Two physical pictures have been developed to describe this overstretched state of DNA. The first introduces a new hybridized phase, called S-DNA, structurally and thermodynamically distinct from standard B-DNA. The second picture proposes that strong forces simply induce a phase transition to a molten state consisting of unhybridized single strands. Little thermodynamic evidence exists to discriminate between these competing pictures. Here we show that within a microscopic model of DNA, the kinetics associated with these two pictures are very different. The nonextensive entropy of unhybridized regions in our model produces hysteresis in a cycle of overstretching and relaxing whenever melting is substantial. Since hysteresis is observed in experiments only at high temperatures, our study requires the proposed S form of DNA in order to account for overstretching kinetics at low temperature. [Preview Abstract] |
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R1.00050: Molecular Dynamics Simulations of Nanopropulsion Engine Jan-Michael Carrillo, Junhwan Jeon, Andrey Dobrynin We have performed molecular dynamics simulations of a nanoscale size engine - nozzle. The engine consists of an end capped cylindrical pore with polymerization sites located on the cap surface. These polymerization sites power the engine by polymerizing chains inside a cylindrical pore. The molecular dynamics simulations are performed with explicit solvent in NVT-ensemble with a Nose-Hoover thermostat. The explicit solvent models hydrodynamic interactions between the engine and its surrounding. The explicit solvent also provides a supply of monomers for the polymerization reaction. Addition of a monomer to a growing polymer chain occurs when a monomer is within a capture radius from the polymerization site. The polymerization induces chain compression, which results in the pressure gradient throughout the length of the nozzle propelling it forward. There is a linear relationship between the average velocity of the nozzle and the chain polymerization rate with a proportionality coefficient dependent on the nozzle geometry such as nozzle length or radius and effective friction brought about by the nozzle itself and the monomers within the nozzle. We compare the motion of the nozzle in solutions and near adsorbing surfaces. [Preview Abstract] |
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R1.00051: Electrostatic Analysis of The Nucleosome Stability Andrew Fenley, David Adams, Alexey Onufriev The wrapping and unwrapping of the DNA around the histone octomer of a nucleosome core particle (NCP) plays a vital role in many cellular processes, such as transcription, replication, and cell differentiation. The exact mechanisms underlying the associated transitions in the NCP are still not well understood. We present a simple, two-state electrostatic model of the NCP that agrees with a number of experiments and suggests mechanisms that could initiate DNA unwrapping \textit{in vivo}. We present and discuss a 2D phase diagram of the system as a function of ambient salt concentration and the net charge of the histone octomer. The model also predicts the free energy of a NCP at physiological conditions. The stability of the system is strongly dependent on the charge of the histone octomer, hinting at possible modes of control in \textit{in vivo} (acetylation and/or pH changes). The model permits analytical solutions in the low and high salt limits. The analysis of these solutions suggests simple physical mechanisms behind the observed folding and unfolding behavior at environmental solvent conditions. [Preview Abstract] |
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R1.00052: Development of a Constitutive Model for Shape-Memory Polymers Containing Reversible H-Bonding Associating Groups Jiahui Li, James Viveros, Mitchell Anthamatten A constitutive model was developed to interpret the shape-memory behavior of elastomers containing reversible H-bonding side-groups. The elastomers studied were copolymerized with butyl acrylate, ureidopyrimidinone (UPy) containing monomer, and crosslinkable monomers. These novel shape-memory elatomers exhibit good shape recovery properties, and more interestingly, their shape recovery rate is tunable due to the dynamics of H-bonding dissociation. Creep experiments at different temperatures were acquired using a thermal-mechanical analysis instrument. By fitting the data using the constitutive model, typical Arrhenius-like temperature dependence was found for the viscosity component of the model. In addition, activation energies were obtained, and correlations between fit activation energies and the activation energy of UPy H-bonding dissociation were discussed. [Preview Abstract] |
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R1.00053: Ultrafiltration of Polymeric Micelles through Nanopores Liangzhi Hong, Chi Wu The micellization of block copolymers in a selective solvent has been extensively studied, a wide range of methods have been used to study the formation kinetics and mechanism of block copolymer micelles. Some questions are still remained to be answered, such as the equilibrium between micelles and individual copolymer chains (unimers) and the strength of interaction between the insoluble blocks in the micelle core. It is rather difficult, if not impossible, to separate micelles from unimers and analyze them separately even by size exclusion chromatography. Recently, using a special double-layer membrane with nanopores, we have, for the first time, observed the predicted discontinues first-order transition in ultrafiltration of flexible linear polymer chains. Namely, the chain could pass through a pore much smaller than its unperturbed radius only when the flow rate is higher than a critical value. Using a similar device, we can separate unimers from micelles by using a specific membrane with a pore size smaller than radii of micelles and unimers and a proper flow rate because micelles can be treated as ?star? polymers. In this way, we can determine the amounts of unimers in the solution. Furthermore, by increasing the flow rate, we can estimate the interaction strength from the critical flow rate at which micelles are broken into unimers to pass through the nanopores. [Preview Abstract] |
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R1.00054: Polymer moving through a small channel: A new Monte Carlo approach to study binding effects and chaperones-assisted Michel Gauthier, Gary W. Slater We recently developed a new approach to study the translocation of long flexible chains through a small channel. In this one-dimensional lattice model, the translocating polymer is represented by a biased random-walker whose dynamics is governed by the entropic pulling of the sub-chains outside the channel, the external force that is driving the translocation (electric field, chemical potential, ...), and the various frictional effects (hydrodynamic drag, pore-polymer friction, ...). The first goal of the present study is to show how this Monte Carlo approach can be adapted to investigate the impact of binding interactions between the polymer and the channel walls on the distribution of translocation times. Secondly, we will present the implementation of a chaperones-assisted driving mechanism and look at the effect of the binding and unbinding rates of these chaperones on the translocation time. [Preview Abstract] |
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R1.00055: ABSTRACT WITHDRAWN |
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R1.00056: Effect of Cross-linking History on Slow Shape Recovery of Disordered Nematic Elastomers Kenji Urayama, Seiji Honda, Toshikazu Takigawa A loosely cross-linked nematic elastomer having a polydomain texture slowly recovers to their initial shape from the distorted state in the order of 1000 s after the imposed field is removed. The mesogen orientation during cross-linking greatly affects the shape recovery dynamics of polydomain nematic elastomers, whereas it has no appreciable influence on their equilibrium properties such as the nematic-isotropic transition temperature, degree of swelling, and field-induced strain. A nematic elastomer formed in the (low-temperature) polydomain nematic state exhibits considerably faster shape recovery than that originally prepared in the (high-temperature) isotropic state because of the memory effect of the initial director distribution during cross-linking. The relaxation time steeply increases as the temperature approaches the transition temperatures; this is independent of the initial mesogen alignment at the cross-linking stage. [Preview Abstract] |
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R1.00057: Effect of Length on the Diffusion of Rodlike Polymers at Concentrations Spanning the Isotropic-Liquid Crystal Transition. Paul Russo, Garrett Doucet The effect of rod length on self-diffusion across the isotropic-liquid crystal phase transition has been examined by comparing Dself vs weight fraction for three molecular weights of polybenzylglutamate (PBLG-24.6, PBLG-134.5, and PBLG-232). The behavior differs, depending on the contour length relative to the persistence length. For PBLGs having a contour length comparable to persistence length, the diffusion coefficient decreases to a value approximately 10 percent of the infinite dilution value. For PBLG with a contour length smaller than the persistence length, the diffusion coefficient decreases even more, to about 1 percent of the dilute solution value. [Preview Abstract] |
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R1.00058: Control of three dimensional alignment in liquid crystalline polymer by magnetic field Toshiaki Ougizawa, Jun Takeda, Keiichi Kuboyama, Tetsuya Uesaka, Takehiro Toyooka The alignment of the aromatic main-chain type liquid crystalline polymer (LCP) by the magnetic field was studied. Magnetic filed was applied to the sample-cells which LCP was sandwiched between the glass substrates or glass substrates with rubbed polyimide. It was found that main chains of LCP were orientated parallel to the magnetic field (Homogeneous alignment). It was also found that LCP chains were oriented even when the magnetic field was applied perpendicularly to the substrates (Homeotropic alignment). By combining these alignments, the three dimensional alignments such as twist nematic like structure and tilt angle changing structure were obtained. Furthermore, it was suggested that there was the possibility of freely controlling three-dimensional alignments of LCP by changing the substrates of the sample cell and the direction of magnetic field. The applications to the optical films for the liquid crystal display were expected. [Preview Abstract] |
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R1.00059: Isoconversion Analysis of the Glass Transition Prashanth Badrinarayanan, Wei Zheng, Sindee Simon At temperatures below their glass transition temperatures (T$_{g}$s), glass forming materials deviate from equilibrium density and form a glass. The kinetic nature of the glass transition process is manifested in the cooling rate dependence of the glass transition temperature and by structural relaxation below T$_{g}$. Various facets of the glass transition kinetics have been well described by phenomenological models of the glass transition, such as the TNM and KAHR model. An important yet frequently questioned assumption in these models is that the apparent activation energy, which describes the temperature dependence of the relaxation time, does not vary during the glass transition process. Some recent reports suggest that the activation energy varies significantly during the glass transition process. In this work we apply an isoconversion analysis to data in the glass transition region which was obtained on cooling from capillary dilatometry and differential scanning calorimetry (DSC) in order to determine whether the apparent activation energy increases as the glassy state is approached. [Preview Abstract] |
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R1.00060: Entanglement in Fullerene End-Capped Linear Polymers Xiaorong Wang, Yuan-Yong Yan We studied the viscoelastic behavior of fullerene (C60) end- caped linear polymers, such as the C60-polybutadiene and C60-poly (butadiene-co-styrene). Those polymers were synthesized through anionic polymerization of butadiene and styrene in hexane, where the living ends were capped with the C60 via an epoxybutane bridging. Rheological measurements showed that for polymer chains of one end attached with C60, the polymer dynamics in the terminal zone were profoundly affected by the presence of fullerene, while the dynamics in the entanglement plateau were nearly unaffected; whereas for polymer chains of two ends attached with two C60, the polymer dynamics in the entanglement plateau were profoundly affected by the presence of fullerene, while the dynamics in the terminal zone were less affected. Given that the diameter for a ``reptation-tube'' is about 5nm, but the diameter for a C60 buckball is only about 0.7 nm, can this phenomenon be explained by the existing reptation models? [Preview Abstract] |
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R1.00061: Precise Characterization of Cyclization Reaction Product Obtained from A Telechelic Polystyrene by HPLC Atsushi Takano, Yuuki Kushida, Yutaka Ohta, Donghyun Cho, Yushu Matsushita Cyclization reaction product synthesized by the end-to-end ring closure reaction of a telechelic polystyrene (Mw=40k) in extremely dilute condition was carefully characterized by using two kinds of HPLC techniques, that is, liquid chromatography at the critical condition (LCCC) and size exclusion chromatography (SEC). Firstly the cyclization reaction product was coarsely separated into linear species and cyclic ones by LCCC, secondly each fraction was analyzed by high resolution SEC. It was found from the HPLC analyses that the cyclization reaction product contains both linear- and cyclic condensation products. Furthermore dimeric, trimeric and more multimeric cyclic molecules with reasonable abundance were identified in the cyclic products in addition to the monomeric cyclic molecule with high yield, as much as 50{\%}. [Preview Abstract] |
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R1.00062: ABSTRACT WITHDRAWN |
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R1.00063: ABSTRACT WITHDRAWN |
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R1.00064: Temperature Coefficients of Unperturbed Chain Dimensions for Flexible Polymers Masashi Osa, Hidetsugu Kanda, Takenao Yoshizaki, Hiromi Yamakawa Until now, we have made a series of experimental studies of dilute solution
behavior of typical flexible polymers on the basis of the helical wormlike
(HW) chain model. From an analysis of experimental data obtained for the
polymers including their oligomers in their respective $\Theta $ states, we
have shown that atactic poly($\alpha $-methylstyrene) (a-P$\alpha $MS) with
the fraction of racemic diads $f_{r}$=0.72 tends to retain large and clearly
distinguishable helical portions in dilute solution while atactic
polyetyrene (a-PS) with $f_{r}$=0.59 does not. In this study, we determined
the temperature coefficient d ln$ |
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R1.00065: Microstructural organization of polydimethylsiloxane based polyurethane block copolymers Rebeca Hernandez, Jadwiga Weksler, Ajay Padsalgikar, James Runt Microphase separation was investigated for polyurethane block copolymers synthesized from MDI and 1,4 butanediol as the hard segments, and poly(hexamethyleneoxide) (MW $\sim $ 700) and bis(6-hydroxyethoxypropyl) poly(dimethylsiloxane) as soft segments (MW $\sim $ 1000). The neat PDMS-based diol presents two segmental relaxations corresponding to the principle siloxane repeat unit and to the hydroxyethoxypropyl end group segments, respectively. When incorporated in the polyurethane, the siloxane units form a phase without intermixing with hard segments and the polyether end group segments are mixed with the second macrodiol and some short hard segment sequences. The microdomain morphology was characterized by atomic force microscopy and small-angle X-ray scattering, and the scattering data were analyzed using an approach based on a modified core-shell model. The model includes core hard segment particles (MDI-BDO), surrounded by a mixed polyether shell (PHMO and hydroxyethoxypropyl end group segments), and a matrix composed of the siloxane units. [Preview Abstract] |
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R1.00066: Dynamics of self-oscillating polymer gels under boundary constraints. Victor Yashin, Anna Balazs Swollen polymer gels, which respond to an on-going oscillatory chemical reaction by rhythmic variations in their size and shape, might serve as chemical-to-mechanical energy transducers. Polymer gels participating in the Belousov-Zhabotinsky reaction (BZ gels) swell and deswell in response to the reduction-oxidation changes of a metal catalyst, which is linked to the polymer. The BZ gels are unique because they exhibit the autonomous oscillations without a precise external control. To serve as a chemomechanical transducer, a self-oscillating gel must be encased and fixed at a surface; this imposes boundary constraints on the gel dynamics. We perform computer simulations of the pattern formation and shape changes in 2D rectangular BZ gels subjected to the boundary constraints. Dynamics of the self-oscillating gel is simulated using the lattice-string model approach. We demonstrate that the developed dynamic patterns depend on whether the gel is expanded or contracted near the boundary, and on the sample dimensions. We also calculate the forces that the self-oscillating gel exerts on the surface. [Preview Abstract] |
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R1.00067: The Rheological Behavior of Natural Rubber Modified by Admicellar Polymerization Technique of Styrene Saman Isahoh, Rathanawan Magaraphan The combination with appropriate polymer component is the one way to improve the mechanical properties and processability of polymer according to gain the industrial importance. The admicellar polymerization is a fine-coating technique to form the ultrathin polymer films on charged surface of another polymer that could be possible to improve its mechanical properties$^{1}$. In this work, the thin polystyrene films are used to coat on natural rubber particles to improve its modulus and impact strength. The study of optimum condition regarding types of surfactant and initiator and amount ratio of monomer/initiator was completed. The thermal analysis, physical properties and rheological behavior of natural rubber modified with 50-mM, 100-mM, 200-mM and 300-mM styrene were also investigated. It was found that the higher contents of polystyrene modified in natural rubber show natural rubber with more plastic. [Preview Abstract] |
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R1.00068: Synthesis and Characterization of Polypyrrole Coated Latex Particles by Admicellar Polymerization Sirinya Chantarak, Rathanawan Magaraphan Polypyrrole (PPy) is good electrical conductive polymer, however, it is poor processibility and its flexibility is limited. To overcome these limitations, natural rubber which is high elongation at break is used by using admicellar polymerization technique. In this research, anionic surfactant; sodium dodecylsulfate (SDS) is used as a reaction template. NaCl is added to decrease electrostatic repulsion between headgroups of surfactants. The polymerization is initiated by iron (III) sulfate at 5$^{o}$C. Thermogravimetric analysis results of admicelled rubbers showed the curves likely to rubber curve with the major decomposition at 349$^{o}$C which revealed the right shift of degradation temperature of PPy by admicellar polymerization. The FT-IR analysis indicated successful coating of PPy on the surface of the rubber particles. The conductivity of admicelled rubber films was measured by two-point probe meter. The higher concentration of monomer and the lower the initiator added showed the higher conductivity. [Preview Abstract] |
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R1.00069: Reversible Self-Assembly of Hydrophilic Inorganic Polyelectrolytes into Highly Conservative, Vesicle-like Structures Melissa Kistler, Anish Bhatt, Guang Liu, Tianbo Liu The hydrophilic polyoxometalate (POM) macroanions are inorganic polyelectrolytes which offer a direct connection between simple ions and organic polyelectrolytes. POM solutions are perfect model systems for studying polyelectrolyte solutions because they are identical in size, shape, mass and charges, with easily tunable charge density. Many types of POM macroanions are highly soluble but undergo reversible self-assembly to form uniform, stable, soft, single-layer vesicle-like ``blackberry'' structures containing $>$1000 individual POMs in dilute solutions. The driving force of the blackberry formation is likely counterion-mediated attraction (like-charge attraction). The blackberry size can be accurately controlled by solvent quality, or the charge density on macroions. Many unexpected phenomena have been observed in these novel systems. Blackberry structures may be analogous to virus shell structures formed by capsid proteins. References: Nature, 2003, 426, 59; JACS, 2002, 124, 10942; 2003, 125, 312; 2004, 126, 16690; 2005, 127, 6942; 2006, 128, 10103. [Preview Abstract] |
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R1.00070: Polyelectrolyte Adsorption and Multilayer Formation: Effects of Fluctuation and pH Qiang Wang, Ying Jiang Using a self-consistent field theory, we have studied the adsorption of flexible polyelectrolytes (PE) on oppositely charged, flat substrates. We examined the effects of PE charge distribution and degree of ionization, substrate charge density, short-range surface-polymer interactions, solvent quality, bulk polymer and salt concentrations, and PE chain length on the conditions under which strong charge inversion can be obtained. The fluctuation effects were studied using the one-loop expansion and revealed by comparing with the mean- field results. We have further modeled the layer-by-layer assembly process using oppositely charged PE. We study in detail the effects of substrate charge density, PE degree of ionization, and bulk salt concentration on the internal structure and charge compensation of the multilayer formed by either strongly dissociating PE or weakly dissociating PE (where the effects of solution pH were examined). A universal rule of charge compensation is found at the steady state, where two consecutively deposited layers carry no net charge. Our results agree with most experimental findings on PE layer-by-layer assembly. [Preview Abstract] |
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R1.00071: Stimuli-Responsive Surfaces from Two-Component Polymer Brushes Ying Jiang, Dong Meng, Qiang Wang Stimuli-responsive surfaces can change their structure and composition in response to subtle changes in the surrounding environment (e.g., temperature, pressure, light, solvent selectivity, ionic strength, type of salt, pH, applied electric field, etc.). Thus the surface properties (e.g., wettability, adhesion, friction, elasticity, and biocompatibility) can be reversibly switched or tuned by these external stimuli. Here we use 3D real-space self-consistent field calculations to study the solvent-response of diblock copolymers A-B grafted to a flat surface by the A block. We focus on the effects of block lengths and grafting density on the surface-layer composition and lateral inhomogeneity of the brush, and compare the copolymer brushes with corresponding binary brushes where both A and B homopolymers are uniformly grafted. We further investigate the use of other external stimuli such as ionic strength, solution pH and applied electric field to enhance the surface switchability and to overcome the lateral inhomogeneity when one of the blocks is charged. [Preview Abstract] |
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R1.00072: Electrostatic force microscopy of DNA under controlled humidity Guoqiang Xia, Nina Markovic Water has profound influence on the properties of DNA. We studied the electrical properties of DNA molecules by electrostatic force microscopy (EFM) experiments under controlled humidity. The phase shift of the oscillation of the cantilever can be related to the conductivity of the sample, allowing us to study the electrical properties of these samples without attaching leads. By stretching DNA on silicon oxide, we found that the DNA molecules are slightly positively charged under low humidity and insulating in micrometer range, but became more conductive at higher humidity. We believe these can be explaind in terms of DNA polymorphism under different hydration and ennhanced ion mobility at higher humidity. [Preview Abstract] |
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R1.00073: Small Angle Neutron Scattering of Mixtures of Linear and Network Polyelectrolyes with an Oppositely Charged Surfactant Wonjoo Lee, Peter Kofinas, Robert M. Briber In general, it has been found solutions containing a (linear) polyelectrolyte and an oppositely charged surfactant exhibit a complex range of phase behavior. We have performed small angle neutron scattering (SANS) on dilute and semi-dilute solutions of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) with sodium dodecylsulfate (SDS). And, a structured hydrogel was formed by crosslinking a semi-dilute PDMAEMA solution containing SDS. SANS intensity of a dilute PDMAEMA solution shows that this polymer in D$_{2}$O has only a few charges. In a dilute PDMAEMA solution with SDS, it was confirmed by SANS that spherical micelle-like structures associated along the polymer chain in a bead-and-necklace structure consistent with what has been observed in the (uncharged) poly(ethylene oxide)/SDS system. As the PDMAEMA concentration increased, a change of a peak position and a scattering shape was observed due to the interaction of the SDS with PDMAEMA. Furthermore, it is shown that the interaction between PDMAEMA and micelles is strong enough to maintain the nanoscale structure formed along the polymer chain, even after crosslinking, leading to a structured hydrogel. [Preview Abstract] |
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R1.00074: Morphology and Rheology of Poly(styrene-\textit{co}-methacrylic acid) Ionomers: Effect of Acid Content, Degree of Neutralization and Cation Type Wenqin Wang, Tsung-Ta Chan, Karen I. Winey Our group has recently applied both scanning transmission electron microscopy (STEM) and x-ray scattering to investigate the size and number density of spherical, ionic aggregates in a poly(styrene-\textit{co}-methacrylic acid) (SMAA) copolymer neutralized with copper. By accounting for the extensive overlap in the STEM image, the imaging and scattering data are in excellent agreement. In this presentation, we will extend our investigation to a wider range of SMAA ionomers to probe the influence of the acid content, the cation type and the level of neutralization. Early results indicate that (1) ionic aggregates form when the acid content is $>$ 5mol{\%} and (2) the size of ionic aggregates in Cu-neutralized SMAA is independent of the percent neutralization. To compliment our morphological studies, rheological properties of these materials are probed in the linear viscoelastic regime. [Preview Abstract] |
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R1.00075: Photopolymerization Induced Directional Crystal Growth in Polymer and Photo Reactive Mixtures Soo Jeoung Park, Thein Kyu Photopolymerization induced crystallization has been demonstrated experimentally in blends of polyethylene oxide (PEO)/diacrylate (DA) at temperatures above the depressed melting temperature of PEO crystals. Upon blending with a multifunctional photo reactive monomer, the melting temperature of the crystalline polymer is depressed due to miscibility or partial miscibility of the system. When photopolymerization was carried out in an isotropic melt state of the PEO/DA monomer mixture by exposing it to UV irradiation, the melting transition curve moves upward and eventually surpasses the reaction temperature, thereby inducing phase separation as well as crystallization. The present paper is the first to demonstrate the occurrence of various directionally solidified interface morphologies of polymer crystals subjected to a photo-intensity gradient. The epitaxially grown seaweed or degenerate structures were observed at the circumference (low intensity region) while the dense branched spherulites developed at the core (high intensity region). These interface structures exhibit striking resemblance to the microstructures formed by directional solidification of small molecule systems such as metal alloys or organic crystals subjected to external thermal gradient. [Preview Abstract] |
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R1.00076: Phase Behavior and Polymerization-Induced Phase Transition of Liquid Crystal Mixtures Namil Kim, Thein Kyu Thermodynamic phase behavior of binary liquid crystal mixtures of UV-curable LC aromatic diacrylate monomer (RM257) and low molar mass LC mixture (E7) has been investigated experimentally and theoretically. Phase transition temperature was measured using differential scanning calorimetry (DSC) and polarized optical microscopy (POM) techniques and compared to the theoretical phase diagram established from the combined Flory-Huggins and Maier-Saupe theory. The simulated phase diagram composed of isotropic, nematic, and crystal region was in good accordance with the experimental results. The behavior of crystal and liquid crystal growth in the neat aromatic diacrylate was investigated with or without UV irradiation. Photo-polymerization-induced phase transition was carried out in both isotropic and nematic regions of the phase diagram to mimic the development diverse morphologies. [Preview Abstract] |
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R1.00077: Rheology-morphology relationships in polytrimethylene terepthalate/liquid crystalline polymer blends Penwisa Pisitsak, Rathanawan Magaraphan The use of thermotropic liquid crystalline polymers as the minor phase of polymer blends has attracted considerable attention because these blends show unique physical, mechanical, rheological and thermal properties. In this work, the reological behaviors of blends of polytrimethylene terepthalate and the liquid crystalline polymer Vectra A950 were characterized with capillary rheometry. Morphology of the rheometer extrudates observed with scanning electron microscopy was compared with the predictions from rheological results. Also, the miscibility of the blends as a result of transeterification reactions was investigated by differential scanning calorimetry (DSC). [Preview Abstract] |
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R1.00078: Molecular Interpretation of Polymer-Polymer Adhesion Suriyakala Ramalingam, Guolin Wu, Shaw L. Hsu Using the techniques developed in our laboratory, the miscibility behavior of various copolymers has been determined experimentally. In addition, these experimental studies were guided by molecular simulation studies. One example deals with blends of poly (vinylidene fluoride-hexafluoropropylene)(PVDF-HFP) copolymers and poly (butyl methacrylate) (PBMA). The interaction parameter ($\chi )$ of the binary systems was determined by composition analysis of the co-existing phases by spectroscopic techniques. Using $\chi $, a generalized Flory-Huggins theory for free energy of mixing has been used to predict the phase diagram of these binary blends. It was concluded from the phase diagram that binary blends with P (VDF-HFP) copolymer content more than 50{\%} by weight are not compatible in solution. This can attributed to the fact that PBMA segment migration into P (VDF-HFP) riche phase is not favorable. Studies were also conducted with Raman microscopy. From further studies on the physical properties of the polymers in the blend, the molecular interpretation of the adhesion behavior of these polymers has been evaluated. [Preview Abstract] |
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R1.00079: Effects of Composition and Crystallinity on the Mechanical Properties of Reactive Ternary Blends Xiguo Zeng, Jayaraman Krishnamoorthy, Shaw L. Hsu, Charles W. Paul , Brigitte Wang Studies were conducted to elucidate the effects of composition, morphology and crystallinity on the mechanical properties of reactive ternary blends. The blends, used as the model system of high performance hot-melt adhesives, contain functionalized crystallizable polyester, functionalized noncrystallizable polyether and an acrylic random copolymer. When mixed, the prepolymers offer a wide range of physical properties. Results indicate the mechanical properties, discussed in terms of tensile strength and modulus, are strongly dependent on morphological features such as degree of crystallinity, crystal size and blend composition. Apart from the bulk mechanical properties, adhesive strength of the blends were also studied on different substrates having different surface energies. From the failure mechanisms and surface analyses of the newly-created surfaces, a correlation was drawn between migration of polymers, surface energy of the substrate and deformation mechanism of the polymer components. [Preview Abstract] |
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R1.00080: Statistical Mechanical Theory of Effective Interactions, Structure and Phase Behavior of Polymer Nanocomposites Lisa Hall, K.S. Schweizer Microscopic polymer liquid state theory has been recently developed and extensively applied for the structure, thermodynamics and miscibility of model polymer nanocomposites composed of hard spherical fillers and flexible polymer chains [1]. The complex and often subtle interplay of coupled entropic (translational and packing) and enthalpic (interfacial cohesion) effects results in rich structural and phase behavior. New computational studies have established in detail the role of polymer degree of polymerization on the equilibrium behavior. The theory has been generalized to treat the consequences of soft intermolecular repulsions and van der Waals like attractions between all mixture species. In addition, nonspherical fillers of variable shape and effective dimensionality have been studied including rod, disk and compact molecule-like shapes. Both repulsive force softness and anisotropic filler shape affect the entropic and enthalpic aspects of the problem and can significantly modify their consequences on structure and phase behavior.\newline \newline [1] J.B.Hooper and K.S.Schweizer, \textit{Macromolecules} 38, 8858 (2005); 39, 5133 (2006). [Preview Abstract] |
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R1.00081: Dielectric and Mechanical Relaxation Behavior of PVDF/OMS Nanocomposites Lei Yu, B. Seyhan Ince-Gunduz, Peggy Cebe We report dynamic mechanical (DMA) and dielectric (DEA) relaxation behaviors of poly(vinylidene fluoride), PVDF, and its nanocomposites with Lucentite$^{TM}$ organically modified silicate, OMS. Nanocomposites were made with compositions ranging from 0-4.0 wt.{\%} OMS. Smaller OMS content favors the non-polar alpha crystallographic phase of PVDF, while the larger OMS content favors crystallization into the polar beta phase. Solution cast nanocomposite films were compression molded, and allowed to crystallize by slowly cooling from the melt. DMA (frequency 1-50Hz) and DEA (frequency 10kHz-1MHz) were performed from -120C to 170C. We observe two relaxation peaks in both studies: the lower temperature $\beta $ relaxation, attributed to the amorphous phase glass transition, and the higher temperature $\alpha $ relaxation from the PVDF crystals. The addition of the OMS enhances the strength of the $\alpha $ relaxation. The ratio of the relaxation strength of $\alpha $ to $\beta $ is smallest for pure PVDF, and generally increases as the OMS content increases. Wide and small angle X-ray scattering, Fourier Transform infrared, and differential scanning calorimetery are used to identify the crystalline phase of PVDF and structure of the samples we used in DMA and DEA studies. [Preview Abstract] |
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R1.00082: Thermal and Rheological Properties of Polypropylene/Organoclay/Poly(ethylene-co-octene) Nanocomposites Tongchen Sun, Xia Dong, Kai Du, Kun Meng, Charles C. Han, Ke Wang, Qiang Fu Poly(ethylene-co-octene) (PEOc) is added to polypropylene/organocla\textbf{y(}organic modified montmorillonite-OMMT) nanocomposites which are prepared by a co-rotating twin-screw extruder to improve the properties of these materials. These ternary materials are investigated in details with the combination of XRD, TGA and rheology measurements. The onset and 5{\%} loss temperatures have increased with clay content increasing and reached to a plateau when clay composition is 2{\%} or higher. The degradation temperatures of the ternary nanocomposites are higher than binary nanocomposites. Storage modulus of these two systems show a pseudo-solid like behavior in low frequency region when clay content is 2{\%} or higher. But ternary nanocomposite is more stable and relaxation slower than binary composites. All results indicated that PEOc plays an important role for thermal stability and structure stability of these nanocomposites. [Preview Abstract] |
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R1.00083: Carbon Microtubes from Chicken Feathers. Melissa M. Miller, Richard P. Wool Chicken feathers, an agricultural waste problem, are a promising bio-based alternative to composite reinforcement. Approximately 5 billion pounds of chicken feathers are produced per year in the United States poultry industry alone. Containing 47.83{\%} carbon, chicken feathers are hollow and strong in nature due to the 91{\%} keratin content. Carbonized chicken feather (CCF) fibers are produced by heating to 220 \r{ }C for 26 hours to optimize the crosslinking of the amino acids (predominantly cysteine). The feathers are then heated at 450 \r{ }C for an additional two hours to reduce the content to mainly carbon. Wide angle xray scattering shows a structural change in the carbonized fiber from an interplanar spacing of 4.4 {\AA} (d$_{200})$ in the raw feather to 3.36{\AA} in the CCF, resembling 3.43 {\AA} of commercial fiber. Scanning electron microscopy confirms that the hollow structure is kept intact. Dynamic mechanical analysis shows a 194{\%} increase in the storage modulus of the composite from 0.730 GPa to 2.145 GPa at 35 \r{ }C with the addition of only 3.45 wt{\%} CCF mat. Assuming a density of 1 g/cm$^{3}$ the upper limit of the fiber modulus is approximately 40 GPa, compared to 3 GPa for the natural keratin fiber. The low cost carbon microtubes are being explored for polymer composite reinforcement and Hydrogen Storage substrates. Supported by USDA-NRI. [Preview Abstract] |
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R1.00084: ABSTRACT WITHDRAWN |
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R1.00085: Organobentonite / Polypropylene Nanocomposite for Packaging Application Yukhanthorn Varothai, Atinuch Phandee, Manit Nithitanakul, Rathanawan Magaraphan, Hathaikarn Manuspiya Na-bentonite was treated with several kind of quaternary alkyl ammonium cation by ion exchange reaction to find the high efficiency one to exfoliate the longer of nanoclay. DOEM exhibited the good performance to continue the work. The organomodified bentonite was compounded with polypropylene by using Surlyn$^{\textregistered}$ ionomer as a compatibilizer to produce the packaging film. In addition the organobentonite was modified by ethylene scavenger chemical and characterized by XRD and FT-IR. It was compound with polypropylene to prepare the active packaging film.The gas permeability, ethylene adsorption-desorption, thermal and mechanical properties were investigated. [Preview Abstract] |
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R1.00086: PP/Clay Nanocomposites as Smart Packaging for Evaluating Milk Spoilage Sakkarin Tassanawat, Manit Nithitanakul, Rathanawan Magaraphan, Hathaikarn Manuspiya The color indicator film for fresh milk packaging has been newly developed to evaluate the degree of fresh milk deterioration during storage and distribution. The processing of pH-sensitive material used for milk packaging based on organomodified clay nanocomposites incorporated with indicator dye was focused. The nanoclay composites with indicator dye were melt compounding through a twin screw extruder by using Surlyn as a reactive compatibilizer. Milk deterioration was assessed for titratable acidity (TA), and color changes of the indicator film were measured and expressed as Hunter values as well as total color difference (TCD). TCD values of bromothymol blue (BMB) type indicator also changed continuously with the response of the indicator. The color changes of the indicator film correlated well with TA value of fresh milk. According to the changes in Hunter color values of the indicator within the packages of fresh milk during storage at 25$^{o}$C, the color of the indicator film turned from initially bluish-green to finally yellow. The color changes of the developed indicator film represented properly the degree of deterioration of fresh milk. The pH indicator could be employed an effective smart packaging technology for evaluating fresh milk. [Preview Abstract] |
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R1.00087: Polypropylene Nanocomposites from Porous Clay Materials: Application in Ethylene Scavenger Packaging Films Kasinee Prakobna, Rathanawan Magaraphan, Hathaikarn Manuspiya The PCH is interesting material to use as entrapping system owing to its structure provides high surface area with uniform and specific pore size. In this work, the PCH is synthesized within the galleries of Na-bentonite clay by the polymerization of tetraethoxysilane (TEOS) in the presence of surfactant micelles (cetyltrimethylammonium bromide and dodecylamine). In addition, a mesoporous clay with hybrid organic-inorganic PCH (HPCH) is modified via co-condensation reaction of TEOS and methyltriethoxysilane (MTS). Before the preparation of PCHs and HPCHs, the Na-bentonite clay was adjusted pH into 9, 7, 5 and 3. Furthermore, both PCH and HPCH are utilized as ethylene scavenger and blended with polypropylene (PP) for producing ethylene scavenging films in food packaging application. The eight samples of nanocomposites films including PCH-9, 7, 5, 3 and HPCH-9, 7, 5, 3 (numerals denote the pH-adjusted condition of Na-bentonite clay) will be measured oxygen and ethylene permeabilities; however, the present results obtained from PCH-9 and HPCH-9 nanocomposites films revealed that both oxygen and ethylene permeabilities of these films were less than that of PP virgin film. So these materials could be found new application in active packaging. [Preview Abstract] |
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R1.00088: 0-3 Connectivity of PVDF/BST Piezoelectric Composites Kittikun Kohpaiboon, Hathaikarn Manuspiya Film mechanical sensors, one of the piezoelectric applications, which are focused on this research, are used to measure or detect various mechanical quantities. Film mechanical sensors are primarily based on polymers which are flexible, easy to fabricate and superior in dielectric breakdown strength but have low dielectric permittivity. To compensate this disadvantage, ceramics possessing high dielectric permittivity are introduced. This work extended the range of material properties by fabricating the barium strontium titanate (Ba$_{0.7}$Sr$_{0.3}$TiO$_{3})$ /PVDF composite film. A certain weight fraction of 0.3, 0.5 and 0.7 of barium strontium titanate (Ba$_{0.7}$Sr$_{0.3}$TiO$_{3})$ powder which is environmentally friendly was embedded in a matrix of polyvinylidene fluoride (PVDF) before compression molding into 100-200 $\mu $m thick sheets. The microstructure of the composite was observed using scanning electron microscopy (SEM). Subsequently, thermal properties for 0-3 composites at differential weight fraction of the ceramic were studied. The dielectric constant of composites at {\%}wt 0, 0.3, 0.5 and 0.7 at 1 KHz are 4.28, 8.45, 20.5 and 28.9, the dissipation factor at 1 KHz are 0.01, 0.05, 0.12 and 0.14 respectively. [Preview Abstract] |
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R1.00089: Polymer composites of aligned carbon nanotubes J. A. Fagan, J. R. Simpson, B. J. Landi, L. J. Richter, I. Mandelbaum, R. Raffaelle, A. R. Hight Walker, B. J. Bauer, E. K. Hobbie Model composites of DNA-wrapped single-wall carbon nanotubes (SWNTs) in polyacrylic acid (PAA) are melt-stretched above the glass transition temperature of the PAA to make optically transparent SWNT-PAA films that preserve the optical signature of isolated SWNTs. Optimal nanotube dispersion is confirmed using small-angle neutron scattering (SANS) and near-infrared (NIR) fluorescence spectroscopy. We discuss the factors limiting the dispersion of SWNTs in polymers at the individual nanotube level, and we quantify the degree of SWNT alignment. [Preview Abstract] |
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R1.00090: The Effect of Dielectric Constant on Polyelectrolyte Brushes Grafted to a Spherical Substrate Daniel Sandberg, Thomas Seery, Andrey Dobrynin Polyelectrolyte brushes have been grown from norbornene-coated Stober silica nanoparticles for study under environments of different dielectric constant and pH by dynamic light scattering techniques. Molecular dynamics simulations were also used to study the effect of dielectric constant on the polyelectrolyte brush structure. Polyelectrolytes, having 60 repeating units and a fraction of charged monomers equal to 1/3, are modeled by evenly spaced charged and uncharged Lennard-Jones particles with a diameter of $\sigma $. Polyelectrolyte chains are grafted to a spherical nanoparticle with a radius of 5.14$\sigma $ at grafting densities of 0.277 chains/$\sigma ^{2}$ and 0.544 chains/$\sigma ^{2}$. To model the effect of different dielectric constants we vary the Bjerrum length of the system from 2$\sigma $ to 15$\sigma $. The brush thickness decreases monotonically with increasing Bjerrum length. This decrease is due to counterion condensation into the interior of the brush, resulting in a reduction of the net brush charge and an increase of the correlation-induced attraction between condensed counterions and charges of the polyelectrolyte chains. [Preview Abstract] |
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R1.00091: Electrical Conductivity in Polymer Nanocomposites with Heterogeneous Spatial Distributions of Nanotubes Minfang Mu, Thomas J. Acchione, Jena Deng, Henry Friedman, Karen I. Winey Recent reports have suggested that a heterogeneous spatial distribution of carbon nanotubes or carbon nanofibers might provide improved properties, when a nanotube-rich phase is both the minority phase and continuous through a macroscopic specimen. Here we present an simple method to prepare composite with high electrical conductivities, that coats polystyrene (PS) beads and then compression molds them to form a piece. Optical microscopy indicates that the fillers remain primarily at the boundaries between the particles and form an electrically conductive network. At 0.5 wt{\%} single wall carbon nanotubes (SWNT), the electrical conductivity is higher in samples with heterogeneous rather than homogeneous spatial distribution. Furthermore, the critical concentration for electrical conductivity is smaller for the nanocomposites with this continuous, nanotube-rich phase. In this particular example, ``better'' (more homogeneous) nanotube distribution does not provide higher electrical conductivity. We also explore the effect of bead size on the critical concentration for electrical conductivity. [Preview Abstract] |
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R1.00092: Novel Nanostructures Created by Supercritical Fluid Processing of Polymers Rahmi Ozisik, Kumin Yang, Tong Liu The foaming of polymers using supercritical fluids has been studied extensively and is still the topic of ongoing research. The sudden thermodynamic instability caused by rapid depressurization induces a drop in the gas solubility and produces small cells in large numbers. Novel structures were created using carbon dioxide as the supercritical fluid woth polystyrene and polycarbonate. These structures have nanometer length scales and were previously nbot observed. In addition, the effect of nanoparticles on nucleation aof cells were investigated. [Preview Abstract] |
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R1.00093: Preparation, Structure and Properties of Carbon Nanotube Polymer Composites Yayong Liu, Howard Wang, Kaikun Yang, Zhiyong Xu, Narayan Das, Kunlun Hong, Gyula Eres, David Uhrig Carbon nanotube (CNT)-polymer composites could possess a unique combination of mechanical and transport properties. We have investigated various CNT/polymer composites using randomly oriented and vertically aligned CNTs (VACNTs) via both solution processing and in situ polymerization. VACNTs remain largely unaltered upon forming composites. Nanoindentation tests show that both the elastic modulus and hardness vary along the CNT growth direction due to the varying tube density, alignment order and entanglement. The mechanical properties show an average increase of ca. 60{\%} over the neat polymer, whereas the electric and thermal transport properties increase by several orders of magnitude. Randomly oriented CNT-Polyimide (PI) composites have increased stiffness but decreased toughness comparing to plain PI. Morphology studies on fracture surfaces show weak interfacial adhesion between CNTs and polymer matrix, which might cause the reduced toughness. [Preview Abstract] |
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R1.00094: Dispersion of Carbon Nanotubes in Polymer Matrices using Trifluoroacetic Acid as a Co-solvent Paul Stokes, Harish Mutharaman, Hui Chen, Qun Huo, Saiful Khondaker We report a simple approach of dispersing multi-walled carbon nanotubes (MWNTs) in a polymer matrix using trifluoroacetic acid (TFA) as a co-solvent. TFA is a low boiling point organic acid that is highly miscible with many organic solvents. MWNTs were readily dispersed in organic solvents mixed with 5-10 v{\%} of TFA after mild sonication. The dispersed MWNT solution was then mixed with polymer solution to obtain a uniformly dispersed nanoparticle/polymer mixture solution. From this solution, nanocomposite films were prepared using drawdown bar method. The dispersion of MWNTs in solution and in dried polymer matrix on a glass substrate was studied by dynamic light scattering and scanning electron microscopy. The electrical conductivity of the carbon nanotube/polymer composite films with different loading ratio of MWNTs dispersed on a glass substrate was measured using two probe technique. A percolation threshold of 0.67 wt{\%} MWNTs was found from the nanocomposite films. At a loading ratio of 1.25 wt{\%} of MWNTs, the conductivity of the composite material was increased to the order of 10$^{-3}$ S/cm. [Preview Abstract] |
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R1.00095: Pigment dispersion And Optical property of a TiO$_{2}$ pigmented epoxy coating Haiqing Hu, Lipiin Sung, Xiaohong Gu, Cyril Clerici, Derek Ho The dispersion of pigments in coatings is qualitatively known to affect the appearance and service life of the products. How to characterize pigment dispersion and relate the dispersion with the performance properties still remains challenging. A set of TiO$_{2}$ pigmented epoxy coatings with different states of pigment dispersion was chosen to investigate the effect of pigment dispersion on surface morphology and appearance as well as the weathering durability. Neutron scattering (USANS) and Microscopy (AFM, LSCM) were used to characterize surface morphology and microstructure of unexposed and weathered coatings. Surface optical scattering (OS) and commercial gloss measurements were carried out to study the corresponding optical properties. Preliminary results show that the pigment dispersion affects surface morphology and subsurface microstructure, and consequently affect the optical properties of a coating. Extensive analyses of microscopy, optical scattering, and other results are ongoing to better correlate the pigment dispersion to structure-performance properties. [Preview Abstract] |
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R1.00096: Development of Polythiophene/Acrylonitrile-Butadiene Rubbers for Artificial Muscle Pacharavalee Thipdech, Anuvat Sirivat Electroactive polymers (EAPs) can respond to the applied electrical field by an extension or a retraction. In this work, we are interested in using an elastomeric blend for electroactive applications, acrylonitirle-butadiene rubber (NBR) containing a conductive polymer (Poly(3-thiopheneacetic acid, PTAA); the latter can be synthesized via oxidative polymerization. FT-IR, Thermogravimetric analysis (TGA), $^{1}$H-NMR, UV-visible spectroscopy, and SEM are used to characterize the conductive polymer. Electrorheological properties are measured and investigated in terms of acrylonitrile content, blending ratio, doping level, and temperature. Experiments are carried out under oscillatory shear mode and with applied electric field strength varying from 0 to 2 kV/mm. Dielectric properties, conductivities are measured and correlated with the storage modulus responses. The storage modulus sensitivity, $\frac{\Delta G'}{G'_0 }$of the pure rubbers increases with increasing electric field strength. They attain the maximum values of about 30{\%} and become constant at electric strength at and above 1000 V/mm. [Preview Abstract] |
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R1.00097: Creep and Recovery Behaviors of Polyaniline/Silicone Oil Suspensions under Electric Field Piyanooth Hiamtup, Anuvat Sirivat Creep and recovery behaviors of the PANI/silicone oil suspensions were investigated under action of electric field to explore the effects of field strength and particle concentration, and operating temperature on creep characteristics. At any applied shear stresses, the creep curves of this ER fluid show large instantaneous elastic response whereas the retarded elastic and the viscous responses are relatively small and they disappear as the applied stress is increased further. After the removal of the applied stress, the strain decreases but does not completely relax to the original value which indicates that this fluid exhibites a partially elastic recovery. However, it is noted that the recovery after stress removals disappears when the strain is higher than the critical values $\sim $ 0.4-0.5, independent of particle concentration and field strength. The particle arrangement to the more energy favorable state is suggested to occur. It is also found that above this range of deformation strain, creep resistance of EB/Silicone oil suspension is enhanced with these three parameters. A raise in temperature is additionally observed to increase the pliability of the ER structure. [Preview Abstract] |
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R1.00098: Preparation and Characterization of PPy/PVA blend films Kanokporn Juntanon, Anuvat Sirivat The conductive polymer/hydrogel blends between polypyrrole (PPy) doped with 5-sulfosalicylic acid as model drug and poly (vinyl alcohol) (PVA) were developed as matrix/carriers of drug for the Electrically Controlled Drug Delivery System which is capable of releasing drug at various rates in response to electric field. The PVA films and their blend films were prepared by solution casting using glutaraldehyde as the crosslinking agent, and by mechanical blending of PPy particle within the PVA matrix, respectively. Drug release characteristic of films was studied using a modified Franz diffusion cell. The amount of released drug was analyzed by UV-Visible spectrophotometry. This study was conducted to determine the effects of crosslink ratio, drug concentration, blend composition, and electric field strength on drug release rate from the PVA films and their blend films on the diffusion coefficient. The degree of swelling of PVA films decreases as the crosslink ratio increases. The diffusion coefficient of drug in PVA films decreases with increasing crosslink ratio in absence of electric field. Moreover, the diffusion coefficient of drug in the PVA films depends critically on electric field strength between 0-5 V. [Preview Abstract] |
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R1.00099: The electro-responsive drug delivery from salicylic acid -loaded polyacrylamide hydrogels Sumonman Niamlang, Anuvat Sirivat The release mechanisms and the diffusion coefficients of salicylic acid -loaded polyacrylamide hydrogels were investigated experimentally by using a modified Franz-Diffusion cell at the temperature of 37 $^{0}$C to determine the effects of crosslinking ratio and electric field strength. The fabricated hydrogels retain their physical shapes and sizes during the experiments along with data reproducibility. A significant amount of salicylic is released within 48 hours from the hydrogels of various crosslinking ratios with and without electric field; the release profile follows the Q vs. t$^{1/2}$ relationship. Diffusion coefficients, as determined from the Higuchi equation, increase with electric field strength and reach maximum values at electric field strength of 0.1 V due to the electrophoresis of salicylic drug and become saturated at electric field strengths between 0.5 -- 10 V. [Preview Abstract] |
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R1.00100: Fabrication of Poly(p-phenylene)/Zeolite Composite as a Gas Sensor Material Pimchanok Phumman, Anuvat Sirivat Poly($p$-phenylene) (PPP) is a one of conductive polymers that can be used as a gas sensing material because of its optical and electrical property changes when exposed to a gas. PPP has several advantages such as the ease of synthesis, high stability, and chemical resistance. Sensors are required to have very sharp chemical specificity with high sensitivity toward chemicals. In this work, several zeolites are added into conductive polymer matrix to improve selectivity and sensitivity of the sensors toward a flammable gas such H$_{2}$. The effects of Si/Al ratio, zeolite content, cation type on the electrical conductivity are systematically investigated. [Preview Abstract] |
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R1.00101: Fabrication of Conducting Polymer Nanowires using Blockcopolymer Nano-Porous Templates Jeong In Lee, Phillip Anthony, Jin Kon Kim, Jae Woong Ryu Nanoporous templates have been used for the fabrication of nanostructured materials that have their potential applications in electronics, optics, magnetism, and energy storage. Here, we showed that nanoporous templates based on polystyrene-block- poly(methyl methacrylate) (PS-b-PMMA) were used for the preparation of high density nanowire arrays of polypyrrole (PPy), poly(3,4-ethlenedioxythiophene) (PEDOT), poly(3- hexyltiophene) (P3HT). We found that these conducting polymer nanowires showed much higher conductivity compared with conducting polymer films. This is because of the chain orientation of conducting polymer nanowires during the growing process inside the confined nanohole. The chain orientation of nanowires along the nanoporous template direction was characterized by HR-TEM, XRD and GI-WAXS. [Preview Abstract] |
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R1.00102: Polymer actuators from first principles Nicholas Singh-Miller, Damian Scherlis, Nicola Marzari We investigate the structure and stability of novel molecular architectures based on the actuation of flexible calixarene hinges and conductive oligothiophenes. When oxidized the oligothiophenes drive the actuation via $\pi$-stacking. We investigate from first principles the components of this actuator, paying particular attention to the structure of the hinge, the energetics of $\pi$-stacking in charged oligothiophens, and environmental effects (i.e. solvation and counterions). Since $\pi$-stacking occurs in an oxidized state, the latter effects are of particular importance in screening long range Coulomb interactions and the concentration of the charge. [Preview Abstract] |
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R1.00103: Effect of Temperature on the Electromechanical Properties of Elastomers Ruksapong Kunanuruksapong Acrylic elastomers, SAR, and SIS thin sheets are fabricated through solvent casting and tested towards electroactive applications such as artificial muscle and/or MEMS devices. Experiments were carried under the oscillatory shear mode with applied electric field strength varying from 0 to 2 kV/mm. The effect of temperature on the storage and loss modulus (G' and G"), storage modulus sensitivity ($\Delta $G'/G'$_{0})$, electrical conductivity, and dielectric permittivity of acrylic elastomers (AR70, AR71, and AR72), SAR and SIS D1112P are studied between 300-360 K. SAR possesses the highest storage modulus sensitivity, 104{\%}, whereas AR72 has the lowest storage modulus sensitivity of about 21.5{\%} at E = 2 kV/mm. AR71 has the highest dielectric permittivity ($\varepsilon \prime )$ of 39.31 pF/m, whereas SIS D1112P has the lowest dielectric permittivity of about 20.74 pF/m. The electrical permittivities of the elastomers increase with increasing temperature. There is a correlation between the storage modulus sensitivity of the elastomers and their dielectric constants. [Preview Abstract] |
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R1.00104: Theoretical study of sulfur overlayers on transition metal surfaces Dominic Alfonso In the chemical and petrochemical industries, the deterioration of transition metal-based catalysts by sulfur poisoning incurs great cost to the economy. Investigation of the sulfur-metal interaction will help characterize the problem and may ultimately lend ideas for the development of sulfur-resistant materials. The structures formed by sulfur adsorbed on close-packed surfaces of Ag, Au, Cu, Ir, Ni, Pt, Rh, Co, Re, Ru, Fe and Mo were studied using first-principles calculations. At low coverage, sulfur forms a stable ($\surd $ 3 $\times \quad \surd $ 3) R30\r{ }ordered structure on the fcc (111) metal surfaces. In the case of hcp (0001) and bcc (110) metal surfaces, a stable (2 $\times $ 2) ordered structure was found. These results are in line with experimental findings. The adsorption energy of atomic sulfur varies between -3.58 and -6.30 eV. Notable decrease in the adsorption energy with increasing coverage was found. The lateral interactions among chemisorbed sulfur were investigated to find out what is responsible for the strong coverage effect. In order to explain the binding effects, the projected density of states were also studied in detail. [Preview Abstract] |
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R1.00105: Adsorption kinetics of random copolymers with tunable monomer sequences onto flat surfaces Young Jhon, James Semler, Igal Szleifer, Jan Genzer We report on the adsorption kinetics of heteropolymers with adjustable monomer sequences (HAMS) on flat substrates. Poly(styrene-co-4-bromostyrene) (PBr$_{x}$S) HAMS, where x denotes the mole fraction of 4-bromostyrene (4-BrS), have been prepared by brominating parent polystyrene chains. By adjusting the solvent quality during the bromination reaction a series of PBr$_{x}$S HAMS has been prepared that posses random (good solvent) or random-blocky (poor solvent) distribution of 4-BrS units. We studied the adsorption of PBr$_{x}$S HAMS from various solvents onto flat silica surfaces, where the 4-BrS units possess strong affinity towards silica while the interaction between styrene and the surface is nearly athermal. For a given solvent, the amount of PBr$_{x}$S HAMS adsorbed onto the surface increases with increasing the 4-BrS content and the blockiness in the monomer distribution. Concurrently, the amount of PBr$_{x}$S HAMS on the substrate also increases with decreasing the quality of the solvent from which the copolymer is adsorbed. [Preview Abstract] |
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R1.00106: UVO Tunable Superhydrophobic to Superhydrophilic Wetting Transition on Biomimetic Nanostructured Surfaces Alamgir Karim, Joong Tark Han, Sangcheol Kim A novel strategy for a tunable sigmoidal wetting transition from superhydrophobicity to superhydrophilicity on a continuous nanostructured hybrid film via gradient UV-ozone (UVO) exposure is presented. Along a single wetting gradient surface (40 mm), we could visualize the superhydrophobic ($\theta _{H2O} \quad >$ 165$^{o}$ and low contact angle hysteresis), transition (165$^{ o} \quad > \quad \theta _{H2O} \quad >$ 10$^{ o})$ and superhydrophilic ($\theta _{H2O} \quad <$ 10$^{o}$ within 0.5 s or less) regions simply through the optical image of water droplets on the surface. The film is prepared through layer-by-layer assembly of negatively charged silica nanoparticles (11 nm) and positively charged poly(allylamine hydrochloride) with a initial deposition of fractal manner. The extraordinary wetting transition on chemically modified nanoparticle layered surfaces with submicron to microns scale pores represents a competition between chemical wettability and hierarchical roughness of surfaces as often occurs in nature (e.g., lotus leaves, insect's wings, etc). [Preview Abstract] |
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R1.00107: In silico polymerization: Computer simulation of controlled radical polymerization in bulk and on surfaces Jan Genzer We use Monte Carlo computer simulation to study the effect of several molecular parameters on controlled/``living'' radical polymerization in bulk and on substrates. Specifically, we investigate how the molecular weight and molecular weight distribution of grown polymers depend on the geometry of the substrate, the initial number of initiators, the initial number of monomers, the initiator activation probability, the initial probability of addition of a new monomer to a growing chain, the probability of terminating two ``living'' polymers, and the numbers of ``living'' polymers and their lifetime. We demonstrate that increasing the termination probability and/or decreasing the initial probability of addition of a new monomer to a growing chain broadens the molecular weight distribution. Our results further reveal that the confinement experienced by the surface-initiated polymers leads to an increased number of early terminations, relative to the bulk-initiated polymerization, which in turn, broadens the molecular weight distribution. This effect is enhanced by increasing the grafting density of the initiators on the surface and the concave nature of the substrate. [Preview Abstract] |
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R1.00108: Shear stress measurements on InAs nanowires by AFM manipulation Hakan Pettersson, M. Bordag, A. Ribayrol, G. Conanche, L.E. Fr\"oberg, L. Samuelson, L. Montelius In this paper, we report on a novel approach to measure shear stress between elastic nanowires and a $SiO_2$ surface. The method is based on the fact that the curvature of an elastically deformed nanowire pinned to a flat surface contains information about the maximal static friction force, i.e., the shear stress between the wire and the surface. At rest, the deformed wire is kept in equilibrium by counterbalancing static friction forces and restoring elastic forces. In the present work, $InAs$ nanowires are bent in a controlled manner using the tip of an atomic force microscope (AFM). After the manipulation, the curvature of the most bent state can be determined from AFM micrographs. Assuming bulk values for the Young's modulus, the shear stress can be obtained from straight- forward analyses according to standard theory of elasticity. [Preview Abstract] |
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R1.00109: PS/PMMA Blends in the Presence of Cyclohexane: Selective Solvent Washing or Equilibrium Adsorption? Harald Ade, S. E. Harton, J. Luning, H. Betz Cyclohexane has been frequently used as a selective solvent to remove PS layers or domains from polystyrene:poly(methyl methacrylate) (PS:PMMA) blends and for reorganization or self-assembly of polymer brushes and block copolymers. We have found that cyclohexane is not efficient at PS removal, observing significant residual PS at PMMA surfaces. These results were compared to PMMA surfaces after PS was allowed to adsorb to the surface from a dilute theta solution in cyclohexane. Using near edge X-ray absorption fine structure spectroscopy and inverse gas chromatography, coupled with theoretical calculations using self-consistent mean-field theory, we have demonstrated that selectively washing a polymer from a polymer blend is nearly identical to adsorption of a polymer to a `soft' surface from a dilute solution. Improved knowledge about the effects of selective solvents will improve experimental analysis of washed systems as well as the manipulation of block copolymer and polymer brush reorganization or self-assembly. [Preview Abstract] |
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R1.00110: Homogeneous Crystal Nucleation: To Fold or Not to Fold? Buckley Crist Recent simulations and related theories have addressed interesting aspects of homogeneous nucleation of polymer crystals in very dilute solutions; embryos and very small crystals are composed of folded chains. At the same time there has been renewed activity with experimental studies of homogeneous nucleation in molten polymers, either with dispersed droplets or with microphase-separated block copolymers. Compared to dilute solutions, melts offer enhanced possibilities for nucleation by fringed micelle structures with stems from different chains. Basal or ``end'' surface energy is estimated for unfolded and folded chain nuclei and employed with classical nucleation theory to distinguish between nucleation rates in the two cases. The effect of chain length on the nucleation barrier offers a way to test model predictions. [Preview Abstract] |
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R1.00111: INSTRUMENTATION AND MEASUREMENT |
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R1.00112: Nanometer scale discrimination of mechanical vibrations with a multiple reflections planar glass system Ruggero Micheletto, Katsumi Hamamoto, Yoichi Kawakami An optical vibration sensor is useful where electrical signals cannot be used or are impractical. Also, purely optical vibration sensors have minimal mechanical influence, so they are important for the detection of tiny displacements at a wide range of frequencies. We realized an optical waveguide system to detect in a simple and low-cost manner nanometer scale mechanical vibrations. The system is based on a planar glass waveguide, laser light is internally reflected multiple times in critical angle conditions. Monitoring the light at the exit of the device, results in sensitivity to small angular displacements due to mechanical vibrations. We could demonstrate very high sensitivity; tiny vibrations of 12nm were resolved, this correspond to an angular shift of about $50*10^{-6}$ deg. [Preview Abstract] |
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R1.00113: Simultaneous shear and normal stiffness measurements of a nanoconfined liquid Mircea Pantea, George Matei, Shiva Patil, Peter Hoffmann The nanomechanical behavior of nanoconfined liquids is of great interest in nanotribology, cellular biology and in the development of nanomechanical devices. In our lab, we have developed methods to measure the stiffness and damping in liquid films that are confined to the thickness of only a few molecular layers using a specially designed Atomic Force Microscope. By using two lock-in amplifiers together with a simple compensation circuit we are able to completely separate normal and shear stiffness and measure the two simultaneously as the tip is moved through the film, molecular layer by molecular layer. We will present our technique, the relevant theory and selected results on TEHOS, a model silicone oil. [Preview Abstract] |
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R1.00114: Sagittal acoustic waves in phononic crystals: the k - dependent polarization Betsabe Manzanares-Martinez, Felipe Ramos-Mendieta We have studied the longitudinal and shear contributions to the sagittal vibrations in phononic crystals of one and two dimensional periodicity. As is well known, pressure and shear waves couple to form the saggital oscillations. The question that guides our work is which of the two vibrations predominates in these waves. We demonstrate numerically that the contributions depend on the wave vector, in addition to the structural and material parameters. For calculations we have used a criterion of strain energy balance; the average of the pressure and shear contributions within the unitary cell is obtained. We present the polarization map of sagittal waves in an Epoxy/Sn superlattice and the band polarization for two arrays of cylindrical holes in epoxy. As we shall see the mixed modes can be either predominantly transverse or predominantly longitudinal. [Preview Abstract] |
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R1.00115: Mapping Surface Temperature on Biological Tissues by Infrared Thermography Surya Gnyawali, Yichao Chen, Kenneth Bartels, James Wicksted, Wei Chen In this paper, non-contact and noninvasive infrared thermography in the measurement of skin temperature on a mice model during dye-enhanced laser-tumor treatment coupled with the immunological response is explored. Mice with mammary tumors are injected with light absorption enhancing dye (indocyanine green, ICG) and immunoadjuvant (glycated chitosan, GC) prior to laser light (805 nm) irradiation through optical fiber. Using an infrared temperature probe, images are acquired and analyzed to determine surface temperature measurements. Simulations of the surface temperature measurements are conducted using a Monte Carlo finite difference method. The simulation results are in good agreement with the thermography measurements. [Preview Abstract] |
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R1.00116: All-Reflective, Achromatic Stationary Fourier-Transform Spectrometer David Winters, Philip Schlup, Randy Bartels We present a simplified double-mirror stationary Fourier-Transform spectrometer that measures spectra over a 4.6-octave spectral span between the mid-IR (11 $\mu $m) and the near-UV (400 nm). The results, including octave-spanning spectra, are in good agreement with measurements using conventional grating-based spectrometers. A scanning slit ($\sim $5 $\mu $m in the visible) is used to sample a spatial interferogram formed by overlapping two halves of a spatially-coherent field. An off-axis curved mirror at large incidence angle is used to collect the highly astigmatic beam after the slit and focus it onto a single-element detector, maximizing the system sensitivity and obviating the need for array detectors in the diverse spectral regions. The most common sources of measurement, including errors in collimation, beam pointing, and beam profile, are discussed with reference to their impact on the measured spectra. The calculated deviations are in excellent agreement with measurement results. The spectrometer can be conveniently calibrated using well-characterized sources in the visible, with the calibration remaining unchanged when slit and detector are exchanged for other spectral regions. The spectrometer shows promise for efficient characterization of spectra in the extreme UV. [Preview Abstract] |
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R1.00117: Time-resolved spatial phase measurements with 2-dimensional spectral interferometry Colby Childress, Thomas Planchon, Wafa Amir, Jeff A. Squier, Charles G. Durfee We are using 2-dimensional spectral interferometry for sensitive measurements of spatial phase distortions. The reference pulse and the time-delayed probe pulse are coincident on an imaging spectrometer, yielding spectral and spatial phase information. This technique offers the potential of higher sensitivity than traditional spatial interferometry since there are many fringes of data for each spatial point. We illustrate this technique with measurements of the thermal lensing profile in a cryogenically cooled Ti:sapphire amplifier crystal that is pumped by tens of watts of power from four frequency-doubled Nd:YLF lasers running at 1 kHz. By adjusting the relative delay of the probe and reference pulses, we characterize the thermal transients during and after the pump pulses. We compare the measured transient thermal profiles with those calculated with a finite-element model. [Preview Abstract] |
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R1.00118: Influences of Symmetry in Electromagnetic Scattering by Single Fixed Scatterers Matthew Berg, Christopher Sorensen, Amit Chakrabarti The scattering of a linearly-polarized plane wave by a uniform, non-absorbent single scatterer can be described in terms of phasors in the complex plane representing the secondary waves radiated from the infinitesimal volume elements of the scatterer. Because of the vector nature of the electromagnetic wave, three phasor distributions are needed to fully describe the scattered wave complete with an account of the wave's polarization state. The evolution of the phasor distributions as a function of scattering angle shows how the secondary waves superimpose and interfere to produce the structure of the scattered wave. Much of the analysis involved in the phasor model relies on symmetries of the phasor distributions. In this work, an investigation of the origin and consequences of these symmetries is presented. It is shown that the symmetries of the scattered wave (both in its magnitude and polarization structure) are directly related to symmetries of the scatterer and the scattering arrangement. [Preview Abstract] |
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R1.00119: TOF Electron Energy Analyzer for Spin and Angular Resolved Photoemission Spectroscopy Gennadi Lebedev, Chris Jozwiak, Nord Andresen, Zahid Hussain, Alessandra Lanzara Current pulsed laser and synchrotron x-ray sources provide new opportunities for Time-Of- Flight (TOF) based photoemission spectroscopy to increase photoelectron energy resolution and efficiency compared to current standard techniques. The principals of photoelectron timing front formation, temporal aberration minimization, and optimization of electron beam transmission are presented. We have developed these concepts into a high resolution a TOF Electron Energy Analyzer for photoemission spectroscopy. The electron optical scheme of the analyzer includes an electrostatic objective lens, three columns of transport lenses and a 90 degree energy band pass filter (BPF). High efficiency exchange scattering based spin polarimeter [1] is used for electron spin detection. The analyzer support two modes of operation: Spectrometer Mode allowing the entire spectrum to be measured, and Monochromator Mode in which the BPF passes a specified energy window inside the scope of the electron energy spectrum. [1] J. Graf, C. Jozwiak, A. K. Schmid, Z. Hussain, and A. Lanzara, Physical. Rev. B \textbf{71}, 144429 (2005) [Preview Abstract] |
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R1.00120: Table Top Extreme Ultraviolet Holography. Present and future capabilities Przemyslaw Wachulak, Mario Marconi, Randy Bartels, Carmen Menoni, Jorge Rocca We report nanometer-scale spatial resolution obtained with Gabor holography using a highly coherent table-top capillary discharge laser. This compact table-top laser provides highly coherent illumination at $\lambda $= 46.9 nm. The hologram was recorded with high spatial resolution in a photoresist and subsequently digitized using an atomic force microscope to reveal the topography of the imprinted pattern. The final image was numerically reconstructed with a Fresnel propagator. Optimal reconstruction parameters and quantification of spatial resolution were obtained with a wavelet analysis and image correlation. [Preview Abstract] |
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R1.00121: Characterization of medium-range order in disordered materials by fluctuation x-ray microscopy Lixin Fan, D.J. Paterson, I. McNulty, M.M.J. Treacy, D. Kumar, P. Du, U. Wiesner, J.M. Gibson Measuring medium-range order is a challenging problem in the structural study of disordered materials. We have developed a technique which we call fluctuation x-ray microscopy that offers quantitative insight into medium-range correlations in disordered materials at nanometer- and larger-length scales. The technique examines spatially resolved fluctuations in the intensity of x-ray speckle patterns. To demonstrate this new technique at micron-length scales, we studied a model system comprised of polystyrene latex spheres. Using nanofocusing optics, we have further developed fluctuation x-ray microscopy for the study of nanomaterials. The medium-range order in two hybrids of \textit{PI-b-PEO/ aluminosilicates }was quantitatively examined and compared. by fluctuation x-ray microscopy. [Preview Abstract] |
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R1.00122: CW Coherent Soft X-Ray Laser Marvin Niimura CW Soft X-Ray Laser (CW-SXL) lasing at the ``water window" wavelengths (2.3 - 4.4 nm) is indispensable for CW structural (3D) study of biological polymers such as DNA and proteins. Unlike pulsed X-ray (laser) sources, CW-SXLs have a higher beam quality and do not rely on a high power pulsed laser. The electronic structure necessary for lasing soft X-ray lines is obtainable from a CW source of highly charged ions (HCIs). Soft X-ray emission due to the interaction of HCIs with neutral atoms is taking place in the quasar and cometary gases. Solar and (quasar's) stellar winds are naturally occurring CW sources of HCIs, for which a modern electron cyclotron ion source (ECRIS) can be used in laboratory. Appropriate X-ray cavity (equipped with Bragg reflector) and re-circulating neutral gas atoms can achieve the laser action at water window. Population inversion takes place naturally since the electron transfer from neutral gas atom to HCI is readily a Rydberg pumping, no TW pump laser, as used for pulsed X-ray source, is needed. My preliminary calculation has indicated that the achievable gain-length product gL =2.16 -6.48 with the laser output power P $>$ 26.4 kW, exceeding the level of pulsed X-ray source. [Preview Abstract] |
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R1.00123: Ultra-High NA Structured Illumination Microscopy Michael Beversluis, Stephan Stranick We measure the three-dimensional point-spread function and compare the resolution of three high numerical aperture objectives (NA) in a structured illumination fluorescence microscope using three-dimensional images of single quantum dots. Compared with conventional 1.30 and 1.42 NA objectives, the ultra-high 1.65 NA TIRF objectives offer significantly improved lateral spatial resolution of better than 75 nm using 488 nm excitation. [Preview Abstract] |
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R1.00124: Sensing of an electromagnetic field with photon-assisted Fano resonance in 1D quantum dots Serhii Shafraniuk Photon-assisted Fano resonance in 1D quantum dots for sensing of an electromagnetic field (EF) is suggested. The EF is sensed with a $\Delta$-shape carbon nanotube junction. Such a $\Delta$- sensor involves two carbon nanotube sections C$_l$ and C$_r$ misaligned by a finite angle and attached to three normal metal leads N$_r$ ($r=1,2,3$). The Fano resonance originates from a photon- assisted indirect coupling between the quantized states in C$_l$ and C$_r$ via continuous states in N$_r$. The resonance results in series of singularities observed in the linear conductivity of the $\Delta$-sensor. The position and magnitude of the singularities is uniquely determined by the frequency, amplitude and polarization of the EF. [Preview Abstract] |
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R1.00125: Improving the performance of hot-electron bolometers and solid state coolers with disordered alloys Ilari Maasilta, Jenni Karvonen, Lasse Taskinen Normal metal-insulator-superconductor tunnel junctions were used as thermometers at sub-Kelvin temperatures to study the electron-phonon (e-p) interaction in thin aluminum films doped with manganese, as a function of manganese concentration. The temperature dependence of the e-p interaction is consistent with an existing theory for disordered metals. The strength of the interaction decreases with increasing manganese concentration, providing a means to improve sensitivity of detectors and the base temperature of solid state coolers. In addition, we discuss the effect of non-uniform heating on the temperature profiles in mesoscopic wires. Even in good conductors such as Cu, thermal gradients develop quite easily at sub-Kelvin temperatures. [Preview Abstract] |
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R1.00126: Magnetic Resonance Force Microscopy Combined with Surface Topography Shigenori Tsuji, Yohsuke Yoshinari In this presentation, we will show magnetic resonance force microscopy imaging combined with surface topography. The individual and combined images taken in the same coordinate are presented for extraction of the position, shapes and spin density distribution of target phantoms. This imaging technique is useful applied when the surface needs to be investigated in relation to the influence of a material buried below the surface. In our method, the surface topography was observed by the AFM with tapping mode. The spin density distribution was measured by the MRFM with the cyclic saturation technique. The AFM and MRFM experiments were made one after another by using the same experimental set-up, and their images were merged together afterwards. The sample consists of two kind of materials, one is DPPH containing unpaird spins and the other is a glass bead. DPPH particles with the size of 5$\sim $8 micrometer and a 8.8 micrometer single bead were glued on a commercial cantilever. [Preview Abstract] |
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R1.00127: Theoretical simulations of non-contact atomic force microscopy in aqueous environment Masanori Harada, Masaru Tsukada Most of the theoretical simulations of atomic force microscopy (AFM) use the models consisting of only the tip and sample and have been in qualitative agreement with the experimental images especially of inorganic surfaces in vacuum. However, such models are not suitable for the AFM experiments performed in liquid. One methodology to improve the models is to incorporate the liquid molecules into the models as they exist in experimental environments. However, the methodology needs more enormous computational costs because of the increase of atom number and the increase of the time scale of simulations in order to reproduce the equilibrium property of the liquid. To overcome this difficulty, Koga et al. used statistical method called RISM for contact mode AFM simulations using the artificial model of tip and sample [1]. We use the similar methodology for nc-AFM simulations of more realistic models of tip and sample. [1] K. Koga et al., Phys. Rev. B 60, 14328 (1999). [Preview Abstract] |
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R1.00128: A technique for removing distortion due to thermal drift in scanning probe microscope images Brian S. Salmons, Matthew L. Trawick A common source of distortion in scanning probe microscope images is the slow thermal expansion of different materials in the sample and microscope due to small fluctuations in temperature over the course of a scan. We model this distortion as a low-order polynomial function of time (and thus of the slow scan axis), and determine the polynomial coefficients by comparing the original image to a second, partial scan on which the fast and slow axes have been reversed. Our method searches all possible sets of polynomial coefficients to find the unique set that would be consistent with both images. Because the algorithm compares the entirety of both images for each possible set of coefficients, we expect it to be robust against common local imaging artifacts such as streaking and pixel noise. We also address speed considerations in implementing this computationally intensive technique. [Preview Abstract] |
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R1.00129: Detection of a live cell in a microfluidic system by scanning capacitance microscopy S. Y. Sung, I. J. Yi, Y. J. Choi, J. Y. Kim, Y.S. Kim, C. J. Kang In recent years, many studies on the biosensors using a microfluidic system have been performed. The system fabricated with polydimethylsiloxane (PDMS) has many advantages such that it is portable, disposable, cost effective, and automatable. Scanning capacitance microscope (SCM) that has a good capacitance pickup sensor attached to an atomic force microscope (AFM) is capable of measuring the capacitance variation with a resolution of better than 10$^{-18}$F/V between a conducting tip and the sample. In this work, we present possibility of SCM as a biosensor by measuring a live cell which flows in the microchannel. By measuring the consecutive capacitance line profiles of a cell, which represent the charge distribution of a cell surface resulting from the ion channel or cell activity, we can get more information on the cell analysis and provide one solution for the realization of a lab-on-a-chip. [Preview Abstract] |
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R1.00130: Theoretical simulation of non contact atomic force microscopy 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 frequency shift dependence of the image contrast, discuss its origin, and compare it to the experimentally observed images. [Preview Abstract] |
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R1.00131: APPLICATIONS |
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R1.00132: Plasma Physics Applied (New Book) Crockett Grabbe \hspace{0.5cm} Plasma physics applications are one of the most rapidly growing fields in engineering \& applied science today. The last decade alone has seen the rapid emergence of new applications such as dusty plasmas in the semiconductor and microchip industries, and plasma TVs. In addition, this last decade saw the achievement of the 50-year Lawson breakeven condition for fusion. With new discoveries in space plasma physics and applications to spacecraft for worldwide communication and space weather, as well as new applications being discovered, this diversity is always expanding. The new book Plasma Physics Applied reviews developments in several of these areas. Chapter 1 reviews the content and its authors, and is followed by a more comprehensive review of plasma physics applications in general in Chapter 2. Plasma applications in combustion and environmental uses are presented in Chapter 3. Lightning effects in planetary magnetospheres and potential application are described in Chapter 4. The area of dusty plasmas in both industrial and space plasmas and their applications are reviewed in Chapter 5. The particular area of Coulomb clusters in dusty plasmas is presented in Chapter 6. The variety of approaches to plasma confinement in magnetic devices for fusion are laid out in Chapter 7. Finally, an overview of plasma accelerator developments and their applications are presented in Chapter 8. [Preview Abstract] |
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R1.00133: Ab initio study of H2 adsorption in graphitic BC2N Yi Zhang, Hong Sun, Changfeng Chen We report results of first-frinciples density functional and quantum Monte Carlo (QMC) calculations on the H2 adsorption in graphitic BC2N. The binding energy and kinetics of H2 at various adsorption sites and coverages are systematically examined. The obtained results provide insights into the mechanism and capacity of hydrogen storage in graphitic BC2N. [Preview Abstract] |
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R1.00134: Thermodynamic properties of calcium alanate from first-principle calculations Xuezhi Ke, Changfeng Chen, Ole Martin Lovvik The potential hydrogen-storage material calcium alanate has been studied by density functional theory at the GGA level, and by phonon calculations using the harmonic approximation. The stability and thermodynamic properties of this system have been studied in detail. [Preview Abstract] |
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R1.00135: Design of tailored carbon nanostructures for hydrogen storage Philippe F. Weck, Eunja Kim, Naduvalath Balakrishnan, Hansong Cheng In a time of increasing scarcity of fossil fuel resources worldwide, hydrogen is widely regarded as a potential cost-effective, renewable and clean energy alternative to petroleum, especially in the transportation sector. However, storage of hydrogen has revealed to be particularly challenging so far. In the present work, we report our progress on the computational study of functionalized carbon nanostructures for hydrogen storage. Structures and properties of these nanostructures consisting of single-walled carbon nanotubes constrained by spacers were calculated using the density functional theory (GGA, PW91). Particular emphasis was given to understanding the role of the chirality and diameter of small single-walled carbon nanotubes on the overall thermal stability and storage capacity of such nano-frameworks. [Preview Abstract] |
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R1.00136: Silicon Light Source for Optical Computing and Communications Ryan Lu, A.D. Ramirez, S.A. Campbell, U. Kortshagen, R. Ligman, R. Liptak, X. Pi Silicon is the choice of material in modern microelectronics but, as an indirect-bandgap semiconductor, it is not an efficient light emitter in its bulk form, as a laser or a light-emitting diode (LED). A silicon laser will be advantageous for monolithic integration with current CMOS technology in order to eliminate the interconnect bottleneck. Silicon LEDs, on the other hand, may revolutionize solid-state lighting and displays because of the low cost and environmental friendliness of silicon. One of the most challenging problems of silicon-based lighting and displays is the lack of a reliable and efficient full visible spectrum emission. Here we show an all gas-phase high-production-yield synthesis of silicon nanocrystals that emit light from red to blue despite oxidation in air. The quantum yields of these oxidized silicon nanocrystals can be as high as 65 percent. Furthermore, this approach is compatible with microelectronic manufacturing. The present findings advance the development of photonic applications especially silicon-based lighting and display technology. [Preview Abstract] |
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R1.00137: Surface Thermal Imaging of VCSELs by Thermoreflectance Microscopy Maryam Farzaneh, Reja Amatya, Dietrich L\"{u}er{\ss}en, Kathryn Greenberg, Whitney Rockwell, Janice Hudgings We report on high resolution surface temperature measurements of vertical cavity surface emitting lasers (VCSELs) under operating conditions by means of thermoreflectance microscopy. Convex refractive index profiles, corresponding to measured radial surface temperature distributions, are found to be consistent with previously observed thermal lensing phenomena in VCSELs. The measured change of the average surface temperature, which varies linearly with the change in dissipated power, compares well with the temperature of the top DBR mirror of an oxide confined single mode VCSEL, obtained from the wavelength shift of the spontaneous emission. [Preview Abstract] |
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R1.00138: Further demonstration of a local evanescent field array coupled (LEAC) biosensor concept Guangwei Yuan, R. Pownall, M. Stephens, D. Dandy, T. Chen, P. Nikkel, K. Lear Low-cost, label-free immunoassay biosensors are needed for point-of-care clinical diagnostics, food safety, environmental monitoring, and biosecurity applications. A novel local, evanescent-field, array coupled (LEAC) photonic biosensor that can simultaneously sense multiple viruses, proteins, or DNA oligomers is being investigated. The sensing mechanism relies on the formation of a biological adlayer via specific binding of an analyte target to one of several localized patches of immobilized biological molecule probes (antibodies, ssDNA, aptamers). The attached analytes modify the waveguide cross-section and thus the optical field. A buried array of evanescently coupled photodetector elements along the length of the waveguide, each opposite a region of specific antibody type, locally sense the modification in the evanescent field due to adlayers of bound analytes. Proof-of-concept experiments have demonstrated strong optical modulation responses to artificial adlayers varying from 17 to $\sim $100 nm in thickness as observed by near-field scanning optical microscopy. LEAC sensors with electronic readout circuits are have been fabricated in a commercial 0.35 $\mu $m CMOS technology. Currently, research efforts are characterizing the effect of different polymer and organic molecules adlayers on the detected optical signal using these sensors. [Preview Abstract] |
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R1.00139: Temperature Dependence of Polysilicon Photodetectors for Integrated Optical Sensors and Electronics Applications Robert Pownall, Guangwei Yuan, Kevin L. Lear While single-crystal silicon photosensors are frequently integrated with CMOS electronics, polycrystalline silicon photodetectors allow more flexibility in processing. Integrated polysilicon detectors have promise in areas as diverse as biological sensors and optical interconnects for electronic circuits. Temperature dependence studies reveal information about the photoconduction process in polysilicon, including the function of traps or carrier reinjection/generation at the contacts in addition to the known variation of the absorption coefficient. Measurement of the photoresponse of metal-semiconductor-metal polysilicon photodiodes incorporated in a commercial CMOS process produced activation energies of 0.35eV and 0.54eV for photocurrent and dark current, respectively, indicating an acceptable contrast penalty for many applications. The mobility-lifetime product is estimated by fitting DC photoresponse versus electrode spacing, and the results compared to AC measurements to derive additional insight into the underlying physical processes. [Preview Abstract] |
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R1.00140: Processing Gallium Antimonide and Indium Arsenide for MWIR and LWIR LEDS Dennis Norton, Mark Boley, Thomas Boggess Novel materials made from the semiconductors gallium antimonide (GaSb) and indium arsenide (InAs) play a vital role in the development of mid-wave infrared (MWIR) and long-wave infrared (LWIR) optoelectronic devices such as light-emitting diodes (LEDs). A significant barrier to achieving high output power from LEDs arises from total internal reflection at the LED-air interface. In order to increase extraction efficiency, an InAs-GaSb LED structure containing angled side walls has been designed to redirect horizontally emitted light to the surface and enhance LED output power. An isotropic etch recipe resulted in angled sidewalls of 53 degrees along with a depth of 9 microns. All samples reported on were characterized using a Leitz Ergolux microscope and an atomic force microscope, where surface, as well as cross sectional, pictures were taken. [Preview Abstract] |
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R1.00141: Magnetic Field Effects on Current Instability in a Weakly Modulated 2DEG M. Tahir, K. Sabeeh, Vassilios Fessatidis, Norman J.M. Horing, Jay D. Mancini We have examined the collective excitation spectrum of a weakly modulated two dimensional electron magnetoplasma, analyzing the role of a steady current which induces drift instability. The inter- and intra-Landau band plasmon spectrum in quantizing magnetic field is derived within the self-consistent-field approximation with weak density modulation. In this, we determine the conditions on drift speed for the occurrence of magnetoplasmon instability. [Preview Abstract] |
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R1.00142: Generic Quantum Rate Equations and 1st Order coherent resonant tunneling through an interacting coupled-quantum-dot interferometer and current noise Bing Dong, X.L. Lei, Norman J.M. Horing, Jay D. Mancini We analyze coherent resonant tunneling through an Aharonov-Bohm (AB) interferometer in the weak tunneling limit. The interferometer consists of two vertically coupled quantum dots (CQD) in a parallel arrangement. In this, we establish a set of quantum rate equations (QREs) in terms of the eigenstate-representation, which are valid for arbitrary bias-voltage, temperature and interdot hopping strength. Furthermore, we derive the current and frequency-independent shot noise formulae in terms of reduced density matrices. We find that the QREs involve some new coherence terms associated with effective dot-dot hopping due to tunneling to leads which appear in a finite bias-voltage regime even for a CQD in a series configuration, as well as in a parallel arrangement. These terms play a decisive role in determining asymmetric transport features of a series CQD. Moreover, the combined effects of the additional coherence terms and the interference terms between the two path branches give rise to interesting transport features for a parallel CQD: finite-bias-induced AB oscillations of current, and magnetic-flux-controllable negative differential conductance and a huge Fano factor. [Preview Abstract] |
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R1.00143: Single and Multijunction InGaP PIN-Diode Radioisotope Batteries Cory Cress, Ryne Raffaelle A direct-conversion radioisotope battery (DCRB) utilizes a semiconductor diode to convert the high energy nuclear emissions of a radioisotope source into electrical power. Research regarding the experimentally measured single junction (PIN) diode performance and computer-simulated multijunction (PINI) diode performance of InGaP DCRBs will be presented. InGaP p/n and PIN diodes with various layer thicknesses and doping concentrations were grown using organometallic vapor phase epitaxy. The power output of these devices measured under simulated air mass zero (AM0) illumination and under alpha- and beta-particle irradiation, is provided. In addition, the radiation-tolerance of the devices is assessed by measuring the power output under simulated AM0 illumination as a function of total alpha-particle fluence. The computer-simulated performance of multijunction PINI devices under photon illumination and alpha-particle irradiation are also provided. The multijunction diode structure increases the energy absorption cross section of the device thereby increasing its theoretical efficiency. Additionally, the selective contacting scheme results in drift-field assisted minority carrier extraction, which reduces the influence of radiation-induced lattice defects on minority carrier lifetime. [Preview Abstract] |
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R1.00144: Effects of Annealing Cool-down Rate on Torque Transducer Response Function in 4340 High-Alloy Steel Bryan G. Hecox, Joseph L. Wiewel, Mark S. Boley We have investigated the change in magnetoelastic torque transducer response as the annealing cool-down rate is changed in 4340 high-alloy steel. In many commercial power-train applications, measurement of torque via a non-contact method is highly desirable. Three separate solid steel 1-inch diameter shafts underwent a common hardening process conducted in a helium atmosphere followed by a five hour annealing process at 843$^{\circ}$ C. Subsequently, the three samples were cooled down at rates of 10$^{\circ}$ C, 15$^{\circ}$ C, and 20$^{\circ}$ C, respectively. Prior and subsequent to heat treatment, the axial magnetic hysteresis properties of the samples were measured and their external field signals were mapped over the magnetically polarized regions both with and without torque (applied shear stress up to 3500 psi). The faster annealing cool-down rate increased the torque response (sensitivity) and the field map height the most. The heat treatment improved the Gaussian field map shape and removed the remnants of old domain walls. Linearity of response remained consistent before and after heat treatment. [Preview Abstract] |
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R1.00145: Size Effects on Magnetoelastic Sensitivity and Polarized Domain Wall Profiles in ESR-420 Steel Matthew W. Beckner In earlier research in our laboratory, we have found that the 14{\%} chromium stainless tool steel, ESR-420, is an excellent candidate for torque sensing applications. My work has focused on producing solid and hollow sensory shafts of diameters ranging from 18 mm down to 5 mm with subsequent heat treatment processes in order to enhance their magnetoelastic behaviors. After the measurement of torque load sensitivities, and axial and circumferential magnetic hysteresis parameters such as retentivity and coercivity, the technique of magnetic force microscopy (MFM) is used to more closely examine the center domain wall between the two circumferentially magnetically polarized regions in the torque sensor section of the shaft. By fitting the sequential MFM scans, we were able to directly measure the domain wall width and height for each sample and correlate these to sensor diameter and the other measured magnetic properties. Additionally, a direct correlation was observed between the total domain wall region area (product of width and height) and the torque load sensitivities. [Preview Abstract] |
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R1.00146: Ambient Temperature Dependence of Magnetoelastic Response in Steel Torque Transducers Patrick Szczypinski, Jason Orris, Mark Boley Changes in magnetoelastic response with ambient temperature of three commonly applied steel torque transducers, PMT-15, Kapstar, and ESR-420 are investigated. Applications of these transducers in real mechanical settings are often in an immersed fluid environment (such as engine coolant or engine oil) where the ambient temperature can fluctuate between 0\r{ }C and 100\r{ }C on an irregular basis. Reliability in such a setting will be dependent on the designer mapping magnetoelastic response in the applicable temperature regions and programming this map into the associated sensory electronics. Our studies over the easily attainable ambient temperature ranges in our laboratory from 20\r{ }C to 56\r{ }C clearly show that in these three samples there is little or no gain or loss to magnetoelastic response to applied torque (less than 0.1 mG/N-m/\r{ }C in either direction), but rather that the magnetic background signal in these transducers has a very definite positive slope with temperature of around 10 mG/\r{ }C. Our laboratory tests were performed first with the sensor torqued on the upstroke and released from torque on the downstroke, then with the test repeated in the reverse case. Thus, appropriately programming the transducer's sensory electronics to include the slope of magnetic background signal with temperature, will ensure transducer reliability. [Preview Abstract] |
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R1.00147: Effect of Low Nickel Dopant on Torque Transducer Response Function in High-Chromium Content ESR Stainless Tool Steels Joseph L. Wiewel, Bryan G. Hecox, Jason T. Orris, Mark S. Boley The change in magnetoelastic torque transducer response was investigated as a low nickel content (up to 0.2{\%}) is alloyed into an ESR (Electro-Slag-Refining) stainless tool steel with a chromium content of around 13{\%}, which our previous studies have proven to be the ideal level of chromium content for optimal transducer performance. Two separate hollow steel 3/4-inch diameter shafts were prepared from ESR 416 and ESR 420 steel, respectively, the first having no nickel content and the second having 0.2{\%} nickel content. The heat treatment of these steels consisted of a hardening process conducted in a helium atmosphere at 1038$^{\circ}$C, followed by an annealing at 871$^{\circ}$C for 5h and a 15$^{\circ}$C cool down rate. Prior and subsequent to the heat treatment processes, the circumferential and axial magnetic hysteresis properties of the samples were measured and their external field signals were mapped over the magnetically polarized regions both with and without applied shear stress up to 2500 psi on the samples. It was found that the effect of the low nickel dopant was to improve torque transducer sensitivity and linearity, but heat treatment worsened the performance of both samples. [Preview Abstract] |
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R1.00148: Comparison of Solid and Hollow Torque Transducer Shaft Response in a High Alloy Stainless Steel Christopher L. Milby, Bryan G. Hecox, Joseph L. Wiewel, Mark S. Boley Recent investigations of the torque transducer response function (ambient field signal versus applied torque or shear stress) have been conducted in a 13{\%} chromium and 8{\%} nickel stainless steel alloy in both the hollow shaft and solid shaft configuration. An understanding of both is needed for applications with differing yield strength and hardness requirements. Axial hysteresis measurements conducted before and after heat treatment exhibited little difference in coercivity and retentivity between the two sample types. However, the field mapping and transducer sensitivity studies showed the hollow shaft configuration to have a far superior degree of polarization in the sensory region and to exhibit an enhanced sensitivity, especially after heat treatment. This is most likely due to its more efficient provision of closed circumferential geometry for the field lines and improved grain alignment during heat treatment. [Preview Abstract] |
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R1.00149: Nanopositioning for Magneto-optic Imaging of Nanostructures and Materials Naser Qureshi, Oleg Kolokoltsev, Roberto Ortega-Martinez A positioning system with nanometer resolution has been developed based on mechanical motor and screw systems. This has been applied to the near- and far-field magneto-optical imaging of nanostructures and to imaging of spin waves in magnetic thin films. This system shows remarkably low levels of drift and vibration compared to more widely used piezoelectric systems, and typically does not require position feedback during fixed-position data acquisition processes. During scanning processes, non-repeatability problems typical of mechanical positioning systems are reduced using a new electronic motor control scheme and software feedback. As a result, we are able to demonstrate an average mechanical resolution of 1.45nm and near diffraction-limited imaging using scanning confocal imaging. We thus demonstrate a highly simplified mechanical approach to spatially resolved magneto-optical measurements. [Preview Abstract] |
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R1.00150: Polarization switching enhanced by optical feedback in polarization-mode hopping VCSEL Da-Long Cheng, Tsu-Chiang Yen, Wei Chang Polarization mode hopping (PMH) is characterized by a stochastic exchange of power between two polarization states of vertical-cavity surface-emitting laser (VCSEL). This investigation presents an experimental study of the current driven polarization switching (PS) properties of the PMH VCSEL with polarization-selective optical feedback (PSOF). Experimental results indicate that PMH noise could be suppressed by the PSOF while the VCSEL subjected to current modulation at a rate of 50 MHz. The signal to noise ratio (SNR) of the PS increased above 30 dB by the PSOF. These results can be used to greatly improve the performance of the PS in data transmission. [Preview Abstract] |
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R1.00151: Recovering single-mode operation from multi-transverse mode VCSEL by wavelength-selective optical feedback Da-Long Cheng, Tsu-Chiang Yen, Chuan-Pi Hsu, Kuo-Sheng Kao It is known that VCSEL can emit multiple high-order transverse modes due to spatial hole burning. The multi-transverse mode character of VCSEL is useful for applications in high-speed multimode data links and networks. However, for numerous applications in optical interconnects, optical recording, and optical communications, single-mode operation is essential. This work presents a self-seeding configuration of VCSEL by wavelength selective element (Etalon). Experimental results show that the laser was retrieved to a single high-order mode with low intensity noise and high spectrum purity. Selection of a particular high-order transverse mode has been achieved. The shorter feedback distance (10 cm) significantly increases the stability and the applicability of this technology in conventional laser systems. [Preview Abstract] |
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R1.00152: Recovery and switching missing longitudinal modes in a semiconductor laser Tsu-Chiang Yen, Da-Long Cheng, Jun-Juh Yan This investigation, for the first time, recovered and maintained a stable oscillation of every missing longitudinal mode in a hysteresis type mode-hopping gap of a Fabry-Perot semiconductor laser. The experimental method was to feedback the laser's beam with a polarization orthogonal to the laser's output polarization. An application of this technology was demonstrated, in which the laser's wavelength was switched among recovered modes with a speed that potentially could be up to several hundreds of megahertz. A special feature of this method is that both the laser power and spectral purity are preserved during mode recovery and mode switching. [Preview Abstract] |
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R1.00153: The optimization of Stirling refrigerator and Stirling heat engine Xin-Mei Zhu The optimization of an irreversible Stirling refrigerator or a Stirling heat engine is an important research subject for a long time. Taking into account of the influence of mixed thermal resistance and regeneration loss in the performance study, we have derived the optimal relation of both of them. For Stirling refrigerator, we have deduced the optimal relation between the thermal resistance coefficient and the efficiency. To the Stirling heat engine, we have deduced the optimal relation between the power output and the efficiency. The conclusions obtained mirror the observed performance of the Stirling refrigerator or the Stirling heat engine quite well. Thus, the results may provide a new theoretical guidance to the optimal design and the selection of optimal operating condition of the Stirling refrigerator or the Stirling heat engine. [Preview Abstract] |
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R1.00154: Phase-Locking of Two Laser Diodes to Femtosecond Frequency Comb for frequency standard of THz radiation Chao-Kuei Lee, C.Y. Kou, Chih-Yu Wang, Tze-An Liu, Jin-Long Peng In this work, we demonstrated the depressed beat signal linewidth of 100 kHz, and generated frequency-tunable terahertz radiation with tuning ranges from 0.2 THz to 1.24 THz from two external-cavity diode lasers. [Preview Abstract] |
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R1.00155: A Study of Excitation Dynamics of Strained Saturable Bragg Reflector by Exploiting Pulse Shaping Technique. Chao-Kuei Lee, Y.S. Lin, C.C. Hsu In this work, we utilized pulse shaping technology to study chirp response of SSBR and attempt to analyze contribution of SSBR in mode-locked process. A home-made pulse shaping system (based on 4f scheme) with Freezing algorithm and Gerchberg-Saton algorithm was demonstrated. Decrease of pulse compression with increasing power of negative chirp incident pulse was characterized. Unclear power dependence for positive chirp case was also performed. These could be due to competition of band-filling and pump dump process. In addition, higher reflectivity and tendency of lower saturation fluence of SSBR for negative chirp incident pulse were observed. [Preview Abstract] |
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R1.00156: A Study of Excitation Dynamics of LT-GaAs by Chirp-Controlled Pump-Probe Technique Chao-Kuei Lee, C.K. Huang, L.Y. Liao In this work, a home made chirp-controlled pump-probe measurement system has been developed and the chirp-controlled pump-probe measurement system with temporal resolution of around 100 femtosecond and chirp parameter tuning from --350 fs$^{2}$ to +650 fs$^{2}$ was demonstrated. Meanwhile, using chirp-controlled pump-probe measurement system, ultrafast dynamics of photogenerated carrier in low-temperature growth GaAs in different chirp by was characterized. The shorter relaxation time of low-temperature growth GaAs in positive chirp pump pulse was observed and the result was explained by the Pump-Dump process in negative chirp pump pulse and similar band-filling effect in positive chirp pump pulse. [Preview Abstract] |
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R1.00157: Sub-100 nm scale ablation by direct focusing of an extreme ultraviolet laser Herman Bravo, Fernando Brizuela, Georgiy Vaschenko, Carmen Menoni, Jorge Rocca, Oscar Hemberg, Bradley Frazer, Scott Bloom, Weilun Chao, Erik Anderson, David Attwood We have demonstrated single-shot ablation of sub-100 nm nanoscale holes using a focused extreme ultraviolet (EUV) laser beam. Very clean ablation craters with smooth walls were realized in in poly-methyl methacrylate (PMMA) by focusing the 46.9 nm wavelength light from a table-top capillary discharge laser with a free-standing Fresnel Zone Plate (FZP). The smallest craters, 82 nm in diameter, were obtained by placing the sample near the third order focal plane of the FZP. The high quality of the ablation is mainly the result of chain scissions at EUV wavelengths and strong localization of the absorbed energy. This proof-of-principle demonstration sets the path for the development of new nanoprobes and nanomachining tools. [Preview Abstract] |
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R1.00158: Single electron behaviors of DNA-mediated Au Nanoparticle Assebly Sung-In Kim, Young-Wook Chang, Jeong-Do Yang, Kyung-Hwa Yoo We have fabricated single electron transistors (SET) using DNA-assisted assembly of Au nanoparticles and investigated electrical transport properties of fabricated devices. Most devices exhibited clear Coulomb blockade and Coulomb oscillations, indicating that DNA molecules play a role of tunneling barriers. However, in contrast to conventional single electron transistors, the different periods of Coulomb oscillations are found at different temperatures. Based on orthodox Coulomb blockade model, we propose that the temperature dependence of Coulomb oscillation period is ascribed to the temperature dependence of junction capacitances. [Preview Abstract] |
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R1.00159: Electrical transport properties of electrodeposited polypyrrole/single-walled carbon nanotubes Ji Hun Kim, Je Seung Oh, Young Wook Chang, Seung Hwan Yoo, Hyang Hee Choi, Kyung-Hwa Yoo Single-walled carbon nanotubes (CNT) coated by conducting polypyrrole (PPy) have been synthesized by electrochemical polymerization of pyrrole on CNTs. In order to study the influence of PPy on the electrical transport properties of CNTs, the temperature dependences of the conductivity have been measured on bare CNTs and CNT/PPy. At room temperatures, the conductivity of CNT/PPy was reduced with thin PPy layers, whereas it was enhanced with thick PPy layers. In addition, depending on the PPy thickness, different temperature dependences of conductivity have been observed. Possible electrical transport mechanisms are discussed. [Preview Abstract] |
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R1.00160: One-dimensional Metal Nanoparticle Necklace that Exhibits Coulomb Blockade at Room Temperature Jennifer Kane, Vivek Maheshwari, Ravi Saraf One-dimensional (1D) nanostructures are attractive materials for fabricating electronic devices because the structure serves both as a device and circuit element to integrate external power source and extract the signal. Necklace of nanoparticles is a versatile avenue to build 1D nanostructures where the chemistry and diameter of the nanoparticle can be tailored. To date, nanoparticle necklaces have been self-assembled using isolated DNA chains, microorganisms, block copolymers, and polyelectrolyte films. However, the electrical conductivity of these structures has not been demonstrated. Here we present an approach to self-assemble a necklace of Au nanoparticles onto a chain of (flexible) polymer wherein the particles are then cemented with an inorganic material. The electrical properties of the cemented necklace show a coulomb blockade at room temperature. Interestingly, the blockade is over 1 V compared to 50 mV for a single particle. Furthermore, the blockade voltage blue-shifts as temperature decreases. We will present the fabrication process and explain the observations in terms of a simple model. [Preview Abstract] |
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R1.00161: Investigations of Biofilm-Forming Bacterial Cells by Atomic Force Microscopy Prior to and Following Treatment from Gas Discharge Plasmas K.G. Vandervoort, J.C. Joaquin, C. Kwan, J.D. Bray, R. Torrico, N. Abramzon, G. Brelles-Marino We present investigations of biofilm-forming bacteria before and after treatment from gas discharge plasmas. Gas discharge plasmas represent a way to inactivate bacteria under conditions where conventional disinfection methods are often ineffective. These conditions involve bacteria in biofilm communities, where cooperative interactions between cells make organisms less susceptible to standard killing methods. \textit{Rhizobium gallicum} and \textit{Chromobacterium violaceum} were imaged before and after plasma treatment using an atomic force microscope (AFM). In addition, cell wall elasticity was studied by measuring force distance curves as the AFM tip was pressed into the cell surface. Results for cell surface morphology and micromechanical properties for plasma treatments lasting from 5 to 60 minutes were obtained and will be presented. [Preview Abstract] |
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R1.00162: Scanning Probe Microscopy on DNA-CNT Conjugated Structures Danda P. Acharya, Wei Lu, Liwei Chen, Saw W. Hla Single stranded DNA (ssDNA) interacts strongly with carbon nanotubes (CNTs) to form a stable DNA-CNT hybrid that effectively disperses CNTs in aqueous solution. In our experiment, ss-DNA oligonucleotide~with a repeating G-T sequence was used. Atomic Force Microscopy and Low Temperature Scanning Tunneling Microscopy are used to image the structures of DNA-CNT on gold substrate. Our experimental result shows an entangled DNA with CNT. The Voltage dependent LT-STM images demonstrate that DNA molecules become transparent at low bias voltages at constant current mode. This work is financially supported by Ohio University \underline {Biomimetic Nanoscience and NanoTechnology} (BNNT) and the US Department of Energy Basic Energy Sciences grant no. DE-FG02-02ER46012 . [Preview Abstract] |
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R1.00163: Evanescent field response to affinity binding on a planar optical waveguide. Matthew Stephens, Guangwei Yuan, Kevin Lear, David Dandy The need for a selective, multianalyte biosensor capable of detecting target molecules with high sensitivity has long been recognized. In this project, a novel means of detecting target affinity binding interactions is under development, whereby a shift in the evanescent wave surrounding the core of an ultra thin ($<$ 1 micron) optical waveguide is monitored. The bound analytes cause a localized refractive index change at the surface of the waveguide, which in turn causes the evanescent field to shift. In this study, analyte binding is determined from a two-dimensional light intensity plot generated by a near field scanning optical microscope (NSOM) as a hollow AFM tip is rastered across the surface of the waveguide. The probe/analyte regions are physically mimicked using several techniques such as (1) direct contact printing of proteins or polystyrene spheres, (2) capture of conjugated nanoparticles using the avidin-biotin interaction in an immunoassay, and (3) microfluidic networks. The evanescent field response characteristics of the sensor to these features determined using NSOM are presented. [Preview Abstract] |
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R1.00164: Thermodynamic and electrical properties of ferroelectric domains in films Igor Luk'yanchuk, Laurent Lahoche, Francois De Guerville The energetically unfavorable depolarization field produced in ferroelectric materials by the surface bound charges is screened in the macroscopic samples by either intrinsic or electrode charge carries. In the micro- and nanoscale case, however, formation of periodic polarization domains seems to be more efficient mechanism of the reducing of the depolarization field that makes the physics of these devices different to the bulk samples. We present the results of modeling of ferroelectric domains and domain textures in ferroelectric thin films and periodic paraelectric/ferroelectric superlattices, basing on the self-consistent solution of the coupled electrostatic and Ginzburg-Landau equations. Our principal result is that, two different types of domain structure occur in micro- and nanoscopic samples. (a) Soft domains with gradual sinus-like polarization profile can exist in the large temperature interval below transition temperature Tc in thin nanometric films. (b) Hard domains with flat Kittel-like polarization profile and narrow domain walls are realized at low temperatures and in thick ferroelectric films. We calculate the temperature dependence of the dielectric susceptibility for the both types of domains and compare results wit experiment. [Preview Abstract] |
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R1.00165: Light-induced dispersion and its application in slow and fast light propagation Qiguang Yang, Jaetae Seo, Wei Gong, Seongmin Ma, Linwood Creekmore, Liting Huang, Bagher Tabibi, Sungsoo Jung, Jinha Heo, Wanjung Kim, Wansoo Yun, Donghwa Ha, Min Namkung The slow and fast light propagation of a Gaussian pulse in Kerr like nonlinear optical materials have been investigated. We found that both the slow and fast light propagation was caused by the slow finite response of the nonlinear materials. Even far away from resonance, both normal and abnormal dispersions may be induced by a strong CW pump or by the pulse itself through two-wave mixing processes in the materials. Both the light-induced group velocity dispersion (GVD) and third-order dispersion (TOD), which leads to pulse distortion, have been studied. [Preview Abstract] |
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R1.00166: Resonance of SSR in Mid- and Near-Infrared Regions Jing Yang, Jungseek Hwang, Thomas Timusk We have fabricated periodic Au SSR (Split-Ring Resonator) patterns on Si substrates by electron-beam lithography. The dimension and periodicity of the SSRs can be confined to fairly small sizes, in microns and sub-microns. We will investigate the reflectance and transmittance spectra of the samples with a Bruker IFS 66v/s Fourier-transform spectrometer and an infrared microscope. The optical measurements will be performed with polarized light source. The samples are expected to exhibit electronic and magnetic resonances in the mid- and near-infrared regions. [Preview Abstract] |
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R1.00167: Lattice Dynamics Simulations of Phonon Thermal Conductivity in SiGe Alloys Shang-Fen Ren, Wei Cheng Thermoelectric Properties of SiGe alloys and Si/SiGe alloy superlattices have attracted a great research attention in recent years because their potential applications in thermoelectric devices and other applications. By using a microscopic lattice dynamics model developed to investigate phonon properties in semiconductor nanostructures, we have calculated phonon thermal conductivities of Si/Ge superlattices in both the growth and in-plane directions [1]. In this research, we have calculated the phonon thermal conductivity of SiGe alloy with various alloy compositions at different temperatures. The calculated results are compared with available experimental measurement [2] with good agreement. We are expecting that these calculations can help with the searching for the most efficient thermoelectric materials for various applications. References: 1. Lattice Dynamics Investigations of Phonon Thermal Conductivity of Si/Ge Superlattices with Rough Interfaces, S.F. Ren, W. Cheng , G. Chen , J. Appl. Phys. (in print 2006). 2. The influence of the composition of SiGe mixed~crystals on thermal diffusivity photoacoustic approach, A. Patrin, N. Abrosimov, M. Mali!nski, L. Bychto, Solar Energy Materials {\&} Solar Cells 72 (2002) 579. [Preview Abstract] |
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R1.00168: Organic Photovoltaic Devices with Ga-doped ZnO$_{2}$ electrode M. S. Son, J. Owen, K. -H. Yoo, B. D. Ahn, S. Y. Lee We report two organic photovoltaic devices using a Ga-doped ZnO$_{2}$ (GZO) film as a transparent conducting electrode. In the first structure, the conventional In$_{2}$O$_{3}$:Sn (ITO) hole-collecting anode was replaced by GZO and an efficiency of 0.35 {\%} was obtained. The second has the inverse structure where GZO was used as the electron-collecting cathode and gave a nonoptimized device efficiency of about 1.4 {\%}. Furthermore, this inverse structure of GZO devices provides a passivation layer to protect the active layer from the atmosphere. [Preview Abstract] |
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R1.00169: AlGaAs quantum-well solar cell junctions on beryllium telluride grown on silicon Kevin Clark, Eduardo Maldonado, Fatima Amir, Robert Bate, Wiley Kirk A bandgap combination of 1.7 eV and 1.1 eV offers the highest theoretical efficiency for a series-connected tandem-junction solar cell. The monolithic structure of aluminum gallium arsenide grown on silicon is a natural implementation, but has long-standing crystal-quality challenges such as lattice mismatch and island growth of AlGaAs. We address the growth issues by use of an interlayer of BeTe on silicon. AlGaAs grown on BeTe has a strong tendency for island formation, which is suppressed by low-temperature growth initiation. A barrier for electrical transport at the p-BeTe/p-AlGaAs interface is also reduced by low-temperature growth, and BeTe anneal under arsenic rather than tellurium flux. Al$_{0.15}$Ga$_{0.85}$As-GaAs multiple quantum-well p-i-n junction structures were grown on both Si/BeTe and GaAs substrates for electrical characterization. In preliminary results, the short-circuit photocurrent J$_{SC}$ and open-circuit voltage V$_{OC}$ is lower in the Si/BeTe based junction than the GaAs based junction, with about twice the fractional reduction of V$_{OC}$ than of J$_{SC}$. A graded-bandgap emitter structure with different n+GaAs top contact layer thicknesses exhibited J$_{SC}$ reduction less than 15{\%}. [Preview Abstract] |
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R1.00170: PHASE TRANSITION AND STRONGLY CORRELATED SYSTEMS |
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R1.00171: Influence of Cation Vacancies on Structural and Dielectric Properties of Pr-modified SrBi$_{2}$Ta$_{2}$O$_{9}$ Jorge Mata*, Alejandro Duran, Eduardo Martinez, Jesus Siqueiros Dielectric and ferroelectric properties were studied in Sr$_{0.85-y}$Pr$_{0.15}$V$_{y}$Bi$_{2}$Ti$_{2}$O$_{9 }$polycrystalline samples where cation vacancies were induced. DRX characterization shows that the Aurivillius structure can accept only 10{\%} of induced vacancies without precipitation of second phases in $A2_{1}$\textit{am }space group. The replacement induces change in the crystal structure and as consequence dielectric properties are affected. Thermoelectric analysis and ferroelectric hysteresis measurements show that the vacancies modify the transition temperature Tc and slightly the polarization values. From the $\varepsilon $-T curves it was observed that the polarization magnitude and Tc are affected as a consequence of the induced vacancies. A broad peak at Tc, typical of the diffuse phase transition behavior of this material was also observed. Furthermore, the induced vacancies in praseodymium-modified SBT produce an increased on Tc from $\sim $180 to $\sim $240 $^{o}$C, these facts show that induced vacancies in the structure are a tuning mechanism for the dielectric and ferroelectric properties. Thanks to DGAPA-UNAM and CONACYT for funds through Proj. No. 40604-F, 47714-F, IN116703, IN100903 and to J. Peralta {\&} P. Casillas. [Preview Abstract] |
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R1.00172: Study of the Structural Stability in Lithium and Sodium Undergoes High Pressures Gerardo Vazquez-Fonseca, Gregorio Ruiz-Chavarria, Fernado Maga\~na In this work we made a study of the structural stability of lithium and sodium undergoes high pressures using a first principles local pseudopotential. This kind of study was made previously successfuly in magnesium [1]. We used the total energy like comparison criterion to investigate the structural stability of studied metals and have studied three structures: fcc, bbc and hcp. We have simulated the different pressures on the metals having varied the $r_s$ parameter, which is related with the electronic density parameter $n_0$. Finally, we found a prediction correct with the reports for the lithium, whereas for the sodium is partially correct the prediction obtained. \newline \newline [1] Ruiz-ChavarrĂa, Gregorio. Phys. Lett. A,{\bf 336},210 (2005) [Preview Abstract] |
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R1.00173: $^{75}$As NMR Study of the Antiferroelectric Transition in NH$_{4}$H$_{2}$AsO$_{4}$ Ozge Gunaydin-Sen, Phil Kuhns, Arneil Reyes, Naresh Dalal $^{75}$As NMR on single crystals has been used to investigate the mechanism of the antiferroelectric phase transition in NH$_{4}$H$_{2}$AsO$_{4}$ (T$_{N }$= 216 K), using the temperature dependence of $^{75}$As chemical shift at high Zeeman fields. Angular variation of the NMR spectra was studied with the Zeeman field in the crystal ab and ac (bc) planes. Frequency sweeps were made at fixed fields between 3 T and 11.75 T and at a temperature range of 300 K-200 K. Temperature dependence has also been measured at a fixed angle (H//c and H//a or b) to understand whether the mechanism involves a displacive character. For that purpose, we utilized the fact that an anomaly in the isotropic chemical shift $\delta _{iso} $ at a transition provides a direct evidence for a displacive behavior of the transition, since $\delta _{iso} $ is not affected by any reorientational change or a spatial displacement that are involved in an order-disorder behavior [1]. Standard models of phase transition mainly involve the order-disorder dynamics of the H's above the phase transition, and their ordering in the O-H{\ldots}O bonds below the transition temperature. Whether the mechanism also involves displacive behavior of the H$_{2}$AsO$_{4}^{-}$ units, as reported for ferroelectric KD$_{2}$PO$_{4}$ [1] will be discussed. [1] A. Bussmann-Holder, N.S. Dalal, R. Fu, R. Migoni, J. Phys.:Condens. Matter 13, (2001), L231-L237. [Preview Abstract] |
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R1.00174: Dielectric Response and Heat Capacity Measurement of Ammonia Borane (NH$_{3}$BH$_{3})$ N. Kaur, O. Gunaydin Sen, A. Harter, R. Vasic, J.S. Brooks, N.S. Dalal Ammonia Borane (NH$_{3}$BH$_{3})$, henceforth AB, has attracted a lot of interest recently because of its potential as a hydrogen storage material. It is known to exhibit a solid-solid phase transition at T$_{P} \quad \sim $225 K but the underlying mechanism is unclear. AB being a classical example of donor-acceptor complex, a high dipole moment is expected in the solid, with a probable ferroelectric or antiferroelectric behavior$^{1}$. We thus carried out dielectric measurements on AB using an ac impedance bridge technique over a temperature range of 200--250 K, and found a dielectric transition at 225 K. The dielectric constant was measured at 100 Hz, 1 kHz and 10 kHz, and, was calibrated against standard materials$^{2}$. It is found to decrease with increase in frequency. We also observed the hysteresis at 10 kHz frequency using a ramping rate of 0.25 K/min. The hysteresis behavior is consistent with an antiferroelectric transition at 225K. The transition mechanism was studied also by specific heat measurements, clearly indicating a first-order transition, with a half width at half height of 0.3 K, in contrast to literature values of 10-K. Details of sample preparation, experimental procedure and data analysis will be explained in the presentation. [1] Weaver et al, \textit{J. Chem. Phys.} 1958, 29, 1-2. [2] Bull. Acad. Sci. USSR, \textit{Phys. Ser.} 1960, 24, 1327. [Preview Abstract] |
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R1.00175: Slow dynamics at the smeared phase transition of randomly layered magnets Shellie Huether, Ryan Kinney, Thomas Vojta We investigate a model for randomly layered magnets, viz.\ a three-dimensional Ising model with planar defects. The magnetic phase transition in this system is smeared because static long-range order can develop on isolated rare spatial regions. Here, we report large-scale kinetic Monte Carlo simulations of the dynamical behavior close to the smeared phase transition which we characterize by the spin (time) autocorrelation function. In the paramagnetic phase, its behavior is dominated by Griffiths effects similar to those in magnets with point defects. In the tail region of the smeared transition the dynamics is even slower: the autocorrelation function decays like a stretched exponential at intermediate times before approaching the exponentially small asymptotic value following a power law at late times. Our Monte-Carlo results are in good agreement with recent theoretical predictions based on optimal fluctuation theory. [Preview Abstract] |
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R1.00176: Zero-Temperature Magnetic Transition in an Easy-Axis Kondo Lattice Model --- An NRG Study Jian-Xin Zhu, Stefan Kirchner, Ralf Bulla, Qimiao Si Antiferromagnetic heavy fermion metals close to their quantum critical points display a richness in their physical properties unanticipated by the traditional approach to quantum criticality. Here we address the quantum transition of a spin-$\frac{1}{2}$ antiferromagnetic Kondo lattice model with an easy-axis anisotropy within the extended dynamical mean field theory. We derive results [1] in real frequency using the bosonic numerical renormalization group (bNRG) method and compare them with Quantum Monte Carlo results in Matsubara frequency. The bNRG results show a logarithmic divergence in the critical local spin susceptibility, signaling a destruction of Kondo screening. The $T=0$ transition is nearly second order, with any jump in the magnetic order parameter {\em not} exceeding a few percents of the full moment. The bNRG results also display some subtle features; we discuss their possible origins and suggest means for further microscopic studies. [1] J.-X. Zhu, S. Kirchner, R. Bulla, and Q. Si, cond-mat/0607567. [Preview Abstract] |
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R1.00177: Correlating off-stoichiometric doping and nanoscale electronic inhomogeneity in high-$T_c$ superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ Sen Zhou, Hong Ding, Ziqiang Wang A microscopic theory is presented for the dopant induced nanoscale electronic disorder observed by scanning tunneling microscopy in superconducting Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. We demonstrate that the essential phenomenology is consistent with the existence of two types of interstitial oxygen dopants in the doped Mott insulator. The nonlinear screening of the dopant potential produces atomic scale variations in the doped hole concentration and electronic inhomogeneity in the CuO$_2$ plane. Based on a spatially unrestricted Gutzwiller approximation of the extended t-$J$ model including the dopant potential, we provide a consistent explanation of the weak correlation between the observed dopant location and the pairing gap and its spatial evolutions. We show that the off-plane oxygen dopants are the primary cause of both the pairing gap disorder and the quasiparticle interference patterns. [Preview Abstract] |
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R1.00178: Ferroelectric and structural characterization of Bi$_{4}$Ti$_{3}$O$_{12}$ doped with Pr$^{3+}$and Eu$^{3+}$ Polycrystals Abril Munro, Jorge Mata, Eduardo Martinez, Jesus Siqueiros Bismuth Titanate; BiTi$_{3}$O$_{12}$ (BIT) is a ferroelectric material useful for NVFRAMs. Bismuth ions in BIT have been replaced by rare earth elements such as Pr and Eu to form new ceramics. A solid-state reaction route was adopted for the synthesis. This study reports the structure and electric properties of the polycrystals. Crystal structures were determined accurately by X-ray diffraction and structure refinement using Rietveld analysis revealed that the all the samples is single phase. The dielectric constant showed higher values for BIT-Pr and BIT-Eu and the dielectric loss was low. Replacement of RE ions for Bi in the BIT structure produces a considerable decrease of the Curie temperature (Tc) from 675 to 450 $^{o}$C. The change in the values of ferroelectric polarization with the addition of rare earths to BIT appears to be gradual. Homogeneous grain growth, the grain morphologies were observed. The density was increased by the replacement of cations of rare earth in the structure. The authors would like to thank P. Casillas, M. Sainz, J. Peralta and J. Palomares for their technical assistance. This work is partially supported by CONACyT M\'{e}xico, projects 47714-F and 40604-F and DGAPA-UNAM projects IN116703 and IN100903. [Preview Abstract] |
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R1.00179: ESR study of the (super)conducting charge-transfer salts $\beta ^{\prime\prime}$-(ET)$_4$\-[(H$_3$\-O)M\-(C$_2$\-O$_4$)$_3$]{\it S} Alessandro Narduzzo, Amalia Coldea, Arzhang Ardavan, John Singleton, Vasile Bercu, Luca Pardi, Akane Akutsu-Sato, Hiroki Akutsu, Scott Turner, Peter Day We present a spin resonance investigation of the family of quasi- two-dimensional organic (super)conductors {$\beta^{\prime\prime} $-(ET)$_4$\-[(H$_3$\-O)M\-(C$_2$\-O$_4$)$_3$]{\it S}} (M = Cr$^ {3+}$, Fe$^{3+}$;~{\it S}~is a guest molecule). The spin systems are probed by means of both resonant cavity perturbation and field modulation techniques in the frequency range 50-313 GHz. The role of the different solvent molecules in determining the degree of spin-orbit coupling and the local symmetry at the metal ion site is established. Intensities, positions and widths of the resonant lines reveal significant modifications of the spin-orbit coupling, and of the inter- and intra-ionic spin-spin interactions below $T=10$K. Despite the onset of a weak antiferromagnetic internal field at low temperature, the ultimate narrowing of the lines suggests spin-lattice interactions are still the dominant relaxation process. Additional lineshifts observed below $B~=~2.5$~{\rm T} and $T~=~4 $~{\rm K}, attributed to the presence of diamagnetic currents in the mixed state of the superconducting samples, provide a threshold for full field penetration within the ``insulating" anion layers. [Preview Abstract] |
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R1.00180: ABSTRACT HAS BEEN MOVED TO H12.00013 |
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R1.00181: ABSTRACT WITHDRAWN |
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R1.00182: Hydrostatic pressure effects on {\it{T$_N$}} for single-crystal U(Pt$_{0.98}$Pd$_{0.02}$)$_3$ Diana Cuff, Michael Graf Substitution of Pd for Pt in the heavy-fermion superconductor UPt$_3$ is known to suppress superconductivity and induce conventional antiferromagnetic order for x $\ge$ 0.006. It has been postulated that the primary effect of Pd is to exert a negative pressure, and that there is an antiferromagnetic quantum critical point (QCP) at x = 0.006. We are testing this through application of hydrostatic pressure on a single crystal sample of U(Pt$_{0.98}$Pd$_{0.02}$)$_3$ with ordering temperature {\it{T$_N$}} = 3.30 K by crossing the QCP from the ordered state. Our first measurements for temperatures above 2 K indicate that the pressure required to suppress the {\it{T$_N$}} to 0 K is approximately 6 +/- 1 kbar. We are now extending our measurements to lower temperatures (a) to refine this estimate, and (b) to look for signatures of quantum critical behavior in the low-temperature transport when {\it{T$_N$}} = 0 K. [Preview Abstract] |
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R1.00183: Kondo-holes in La-doped CeOs$_{4}$Sb$_{12}$ Costel R. Rotundu, Bohdan Andraka CeOs$_{4}$Sb$_{12}$ is an example of an interesting class of systems with low carrier concentrations in which strongly electron correlated states develop at low temperatures. 2{\%} of La introduced for Ce suppresses the 1.1 K ordering and leads to exotic heavy fermion behavior. Electrical resistivity of weakly La-doped alloys, studied down to 20 mK, is proportional to the square of temperature, but with the proportionally coefficient (A) being negative. Such a temperature variation is characteristic of Kondo-hole systems. The absolute value of A (-45 $\mu \Omega $cm/K$^{2}$ for Ce$_{0.98}$La$_{0.02}$Os$_{4}$Sb$_{12})$ implies presence of massive quasiparticles. Magnetic fields reduce the absolute value of A and, for sufficiently strong fields, lead to a Fermi-liquid temperature variation (positive A). [Preview Abstract] |
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R1.00184: Fermi-surface topology and field-dependent effective masses in the skuttuderite PrOs$_4$As$_{12}$ Pei-Chun Ho, John Singleton, W. Yuhasz, T. Yanagisawa, T. Sayles, Brian Maple, Paul Goddard, A. Pietraszko, Z. Henkie, Hisatomo Harima Comprehensive magnetic-field-orientation dependent studies of the de Haas-van Alphen effect have been carried out on single crystals of the skuttuderites PrOs$_4$As$_{12}$ and LaOs$_4$Sb$_{12}$ using fields of up to 60 T. The Fermi- surface topologies of the two compounds are found to be very similar; in addition, they are in reasonable agreement with the predictions of bandstructure calculations for LaOs$_4$Sb$_{12}$. However, whilst the quasiparticle effective masses in LaOs$_4$Sb$_{12}$ are field- independent, those in PrOs$_4$As$_{12}$ are found to decrease with increasing field, possibly reflecting the gradual suppression of magnetic fluctuations associated with proximity to the low-temperature, low-field antiferromagnetic state. [Preview Abstract] |
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R1.00185: Critical Fidelity at the Metal-Insulator Transition Joshua Bodyfelt, Gim Seng Ng, Tsampikos Kottos Using a Wigner Lorentzian Random Matrix ensemble, we study the fidelity, $F(t)$, of systems at the Anderson metal-insulator transition subject to small perturbations that preserve the criticality. We find that there are three decay regimes as perturbation strength increases: the first two are associated with a Gaussian and an exponential decay respectively and can be described using Linear Response Theory. For stronger perturbations, $F(t)$ decays algebraically as $F(t) \sim t^{-D_2^\mu}$, where $D_2^\mu$ is the correlation dimension of the Local Density of States. [Preview Abstract] |
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R1.00186: Separation observation of metal-insulator transition and structural phase transition in VO$_{2}$ Hyun-Tak Kim, Bong-Jun Kim, Yong Wook Lee, Byung Gyu Chae, Sun Jin Yun, Soo-Young Oh, Yong-Sik Lim An intermediate monoclinic metal phase between the metal-insulator transition (MIT) and the structural phase transition (SPT) is observed with VO$_{2}$-based two-terminal devices and can be explained in terms of the Mott MIT. The conductivity of this phase linearly increases with increasing temperature up to $T_{SPT} \approx $ 68$^{\circ}$C and becomes maximum at $T_{SPT}$. The SPT is confirmed by micro-Raman spectroscopy. Optical microscopic observation reveals the absence of a local current path in the metal phase. The current uniformly flows throughout the surface of the VO$_{2}$ film when the MIT occurs. This device can be used as a programmable critical temperature sensor. (References: New J. Phys. 6 (1994) 52 (http://www.njp.org); Appl. Phys. Lett. 86 (2005) 24210); Physica B 369 (2005) 76; cond-mat/0607577; cond-mat/0608085; cond-mat/0609033). [Preview Abstract] |
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R1.00187: Studies on the Insulator to Metal Phase Transition in Vanadium Dioxide Mike Clemens, Felipe Rivera, Brady Cox, Robert Davis, Richard Vanfleet Vanadium dioxide undergoes an insulator to metal transition changing from a monoclinic to tetragonal phase near 66 $^{\circ} $C. Crystalline films and isolated vanadium dioxide particles (up to 700nm in diameter) were obtained through thermal annealing of amorphous vanadium dioxide thin films on silicon dioxide. Orientation Imaging Microscopy (OIM) was used characterize the resulting film and particles, and to differentiate them from different vanadium oxide crystal structures. A study of this phase transition is being performed through Trasnmision Electron Microscopy, as well as with resistance and Capacitance measurements. The results of this study will be presented. [Preview Abstract] |
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R1.00188: On the validity of the Luttinger liquid description of the Holstein model David K. Campbell, Ka-Ming Tam, Shan-Wen Tsai, Antonio H. Castro Neto We show that the scaling relations between various correlation functions of the Luttinger liquid are not valid for the Holstein model with the system size attainable by reliable numerical calculations. Hence, the recent controversy about the existence and the proposed nature of the metallic phase of the zero- temperature half-filled one-dimensional Holstein model is reexamined without using the scaling relations of the Luttinger liquid. The competition between the singlet pairing and the charge ordering are determined by the Monte Carlo calculation. [Preview Abstract] |
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R1.00189: Optical spectral weight changes accompanying ferromagnetic transition in EuB6 E. J. Choi, Jungho Kim, C. C. Homes, B. K. Cho, Young-June Kim EuB6 have drawn much attention for the last decade due to their interesting electrical and magnetic properties. As a prerequisite to the understanding of these unconventional phenomena, the band structure of EuB6 was extensively studied both theoretically and experimentally. However, there is no consensus of opinion on the electronic ground state. We present temperature dependent optical reflectivity and spectroscopic ellipsometry measurements on ferromagnetic EuB$_{6}$ taken over a wide spectral range 0.002-5.5 eV. In addition to a large blue shift of the plasma frequency below T$c$=15.5 K, two prominent changes in the interband region are observed: a systematic decrease of the interband spectral weight below 3.3 eV and the splitting of 4 eV peak with a decrease in T. We can explain the observed optical spectral weight changes within the semi-metal picture of EuB6. [Preview Abstract] |
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R1.00190: CHEMICAL PHYSICS |
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R1.00191: Path Integral Sampling Techniques Jennifer Barry, Amy Bug In this study, we evaluate several Monte Carlo methods with the goal of simulating a light particle in a fluid. We present a simulation that allows Metropolis sampling, Wang-Landau sampling, or multicanonical sampling for a Lennard-Jones fluid within a canonical or grand canonical ensemble. We compare these methods and show that the results from each are self-consistent. We also present a simulation that performs Metropolis Path Integral Monte Carlo or Wang-Landau Path Integral sampling for a light particle. Simulating a quantum particle in a simple harmonic potential, we demonstrate that our results match analytical calculations for finite bead numbers. The two sampling methods yield results that are in agreement for the light particle interacting with the fluid via a potential meant to represent He within Ar. Finally, we show benchmarks that indicate how the performance of Wang-Landau and Metropolis sampling compare for these systems where efficient means of equilibration and sampling are needed. [Preview Abstract] |
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R1.00192: Inertial effects in the fractional diffusion of a Brownian particle in a double-well potential William Coffey, Yuri Kalmykov, Sergey Titov The anomalous translational diffusion including inertial effects of nonlinear Brownian oscillators in a double well potential $V(x)=ax^2/2+bx^4/4$ is considered. An exact solution of the fractional Klein-Kramers (Fokker-Planck) equation is obtained which allows one to calculate via matrix continued fractions the positional autocorrelation function and dynamic susceptibility describing the position response to a small external field. The result is a generalization of the solution for the normal Brownian motion in a double well potential to fractional dynamics (giving rise to anomalous diffusion). [Preview Abstract] |
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R1.00193: Production of Molecular Oxygen using a Radio-Frequency Discharge in a Carbon Dioxide Gas Mixture George Brooke, Greg Schwartz We have measured the concentration of molecular oxygen in a capacitively-coupled radio-frequency discharge in a carbon dioxide (CO$_{2})$ gas mixture. The gas mixture was composed of 95{\%} CO$_{2}$ and was maintained at a pressure of approximately 5 torr in order to simulate Martian atmospheric conditions. Continuous-wave cavity ring-down spectroscopy was used to measure the absolute concentration of ground state molecular oxygen in the discharge volume using the b-X (1,0) transition. Our results will be compared to the measurements and a numerical model of another group[1]. \newline [1] T.H. Dinh, Dissertation, Old Dominion University, Department of Physics (2002). [Preview Abstract] |
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R1.00194: High Temperature Adsorption Isotherms on Equilateral Triangular Terraces Alain Phares, David Grumbine, Jr., Francis Wunderlich The adsorption isotherms on infinitely long equilateral triangular terraces are obtained at high temperature. Within the context of a lattice-gas model, the computations are conducted for terraces with an increasing number $M $of atomic sites in width using long double precision arithmetic. The entropy per site divided by Boltzmann's constant reaches a maximum of ln2 at half coverage for all values of $M$, and there are (3$M-$4)/4$M$ first-neighbors per site and (3$M-$6)/4$M$ second-neighbors per site. All possible occupational configurations of the terraces are obtained for arbitrary width $M$ at half coverage. [Preview Abstract] |
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R1.00195: A simple and efficient approach to calculating the density of states of a fluid Chengju Wang, Richard M. Stratt Knowledge of the density of states (DOS) is not only of fundamental thermodynamic significance but is also critical to designing stochastic methods in molecular simulations. Contrary to conventional methods which include bias from temperature or other order parameters, we showed that sampling the potential energy surface by a random walk in the \textit{energy landscape ensemble} enables us to calculate DOS directly from the potential energy distribution of the configurations within the ensemble. The ensemble itself is defined to include all the configurations with a potential energy less than a given value. Using this approach, we studied the relationship between the configuration entropy and the configurational temperature for the Kob-Andersen model, a typical glassy system. The results were in excellent agreement with the literature reports while showing a significant improvement in computational efficiency. [Preview Abstract] |
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R1.00196: Anomaly in the heat capacity of nitrobenzene and dodecane Nathan Utt, D.T. Jacobs The heat capacity C$_{p}$ of the liquid-liquid mixture nitrobenzene+dodecane has been precisely measured using our own computer-based data acquisition and control, adiabatic calorimeter. A step process of adding heat and then waiting several minutes for a stable temperature assures equilibrium values for the heat capacity from the known heat added and the resulting change in temperature. For a sample at the critical concentration, we observe behavior in the heat capacity consistent with the Ising Model and determine the amplitudes in the one- and two-phase regions to test universal predictions. We acknowledge support from NSF-REU grant DMR 0243811. [Preview Abstract] |
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R1.00197: Dynamic Light Scattering Study of Carbon Nanoparticles Aggregating in Aerosol Phase Rajan Dhaubhadel, Amitabha Chakrabarti, Christopher M. Sorensen Intensity correlation function was measured using ALV5000 correlator for the aerosol system created inside an optical chamber by exploding a mixture of a hydrocarbon (Acetylene) and oxygen. The observations were taken at two $q$ (scattering wave vector) values 8.81 $\mu $m$^{-1}$ and 24.20 $\mu $m$^{-1}$, which for \textit{$\lambda $} = 488nm correspond to scattering angles 40$^{o}$ and 140$^{o}$ respectively. For a system with medium volume fractions ($\sim $ 8 x 10$^{-5})$ or higher it was observed that the decay in intensity correlation was exponential initially for up to about 1 minute and then transited to stretched exponential with stretched exponent of about 0.45 for $q$ = 24.20 $\mu $m$^{-1}$and 0.65 for $q$ = 8.81 $\mu $m$^{-1}$. The value of intensity correlation function at small time is also found to decrease a little bit with time at both $q$. This indicates of the development of static scatterer in the scattering volume with time (gelling of the cluster). This also introduced non-ergodicity in the system. [Preview Abstract] |
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R1.00198: Aqueous Surfactant Self-Assembly at Solid-Liquid Interfaces Alberto Striolo, Nage Rajesh Tummala, Camille Gutig, Brian Grady We conducted a series of experimental adsorption isotherms for aqueous non-ionic (C12E6) and ionic (CTAB) surfactants on Au (hydrophobic), SiO$_{2}$ (partially hydrophilic), and Al$_{2}$O$_{3}$ (hydrophilic) surfaces at room temperature. The amount of surfactant adsorbed per unit surface area was measured as a function of the surfactant bulk concentration by means of a Quartz Crystal Microbalance. To assess the equilibrium adsorbed structures we conducted all-atom molecular dynamics (MD) simulations for surfactants at the water-graphite and water-SiO$_{2}$ interfaces. The results not only provide a molecular interpretation for the experimental data, but also allow us to identify the driving forces responsible for the surfactant self-assembly. For example, our MD calculations predict that SDS form hemicylindrical structures at water-graphite interfaces, in agreement with solution AFM studies (Wanless and Ducker, JPC 100, 1996, 3207). By conducting test simulations for SDS-like surfactants in which we suppressed surfactant head -- counter ion electrostatic interactions we proved that the hemicylindrical structure forms because of the condensation of counter ions near the hydrophilic SDS surfactant heads. [Preview Abstract] |
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R1.00199: Fractal Hierarchy in Isotopic Positional Correlations in Crystals Alexander A. Berezin From subatomic particles to superclusters of galaxies, nature has nested hierarchial fractal-like organization (R.L. Oldershaw). Earlier I discussed formation of isotopic superlattices due to self organizational dynamics among isotopes (A.A. Berezin, SolidStComm, 1988). Informationally (in spirit of ``Maxwell's demon'' engine), formation of isotopic superlattices can be inferred from Maximum Entropy Principle (C.E. Shannon, E.T. Jaynes). In spite that effects of gravitation for isotopes (due to their nuclear mass difference) are very small, they can, nevertheless, manifest in such subtle effects as gravitationally-induced reduction (collapse) of wave functions (F. Karolyhazy, R. Penrose, A.A. Berezin). Since Planck mass (which is combination of h, G and c) is about 0.02 mg, size of desired isotopic fluctuation should be about 100 mkm (mesoscipic). Experimentally, isotopic correlations, micron and sub-millimeter isotopic fluctuations, isotopic clusters and isotopic fractal-type distribution can be probed by Rayleigh scattering (sampling at various wavelengths) and/or such high electric field effects as hopping conductivity (B. Ya. Shklovsky) in which isotopic clusters act as trapping or scattering centers. Other aspects of purposeful isotopic structuring (isotopic engineering) include isotopic fiber optics (A.A. Berezin) when core and cladding has varied (step or gradual) isotopic content which causes total internal reflection and light confinement. [Preview Abstract] |
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R1.00200: ABSTRACT WITHDRAWN |
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R1.00201: First-principles Helical Elasticity in Carbon Nanotubes H.M. Lawler, J.W. Mintmire, D.A. Areshkin, D. Gunlycke, C.T. White As an application of a unique, one-dimensional first-principles method with screw-symmetric boundary conditions, we derive a helical elastic tensor, and with it express several fundamental physical quantities of extended quasi-one dimensional, helical systems, including torsional and longitduinal speeds of sound, radial-breathing frequencies, and Poisson's ratio. These quantities are then calculated for nearly every nanotube structure from 0.4 to 1.4 nm, and the results are interpreted through the in-plane elastic response of graphene. [Preview Abstract] |
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R1.00202: Anomalous steady state nonlinear dielectric and Kerr effect relaxation responses in superimposed ac and dc electric fields William Coffey, Yuri Kalmykov, Sergey Titov It is shown how the Debye rotational diffusion model of polar molecules (which may be described in microscopic fashion as the diffusion limit of a discrete time random walk on the surface of the unit sphere) may be extended to anomalous nonlinear dielectric relaxation and the dynamic Kerr effect by using a fractional kinetic equation for the Havriliak-Negami (HN) model. The equation is obtained via a generalization of the noninertial kinetic equation of conventional rotational Brownian motion to fractional kinetics governed by the HN relaxation mechanism and is solved using matrix continued fractions yielding the complex nonlinear dielectric susceptibility and the Kerr function. [Preview Abstract] |
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R1.00203: Superhydrophobic silicone fiber mats fabricated by electrospinning from solution Bonnie Ludwig, Aneta Clark, Steven Snow, Randal Hill, Randall Schmidt, Brad Fogg, Peter Lo Fine silicone fibers of 1 -- 20 $\mu $m diameter were fabricated from solution via electrospinning. These are the first examples of fine fibers prepared from silicone homopolymers. Fiber morphology (beaded, ribbon-like, smooth) and diameter were controlled. The nanoscale surface roughness of nonwoven fiber mats created with silicone fibers produced a superhydrophobic surface that had a water contact angle of $\sim $160$^{o}$. The superhydrophobic surface was made reversibly hydrophilic with exposure to oxygen plasma. The combination of high surface area and superhydrophobicity suggests potential applications in the areas of water-repellent textiles, filtration, adsorption and chemical separations, wound dressings, and fuel cells. [Preview Abstract] |
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R1.00204: Nonadiabatic MD simulations of IBr$^{-}$(CO$_{2}$)$_{n}$ photodissociation Matthew A. Thompson, Joshua Martin, Joshua Darr, Jack Barbera, Vladimir Dribinski, W. Carl Lineberger, Robert Parson Potential energy curves for the ground and valence excited states of IBr$^{-}$ have been calculated at the MRCI level using the MOLPRO \emph{ab initio} package. Spin-orbit coupling was calculated via a spin-orbit ECP. Charge densities, transition moments, and nonadiabatic coupling matrix elements constructed from a distributed multipole analysis of the \emph{ab initio} wavefunctions~\footnote{Maslen, Faeder and Parson, Molecular Physics, 1998} were then used to carry out nonadiabatic molecular dynamics simulations of the photodissociation of IBr$^{-}$ in CO$_{2}$ clusters. Experimental studies have demonstrated a large variation in ground-state recombination times which are supported by our simulations. We propose a mechanism of excited-state trapping and a configurational transition state which leads to recombination times on the order of 10-20 ps for $n$=5,13 up to 1 ns for $n$=8,10. [Preview Abstract] |
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R1.00205: Ultrafast Pump-Probe Study of Halide Dependence in Primary Reaction Dynamics of Halorhodopsin Takumi Nakamura, Satoshi Takeuchi, Mikihiro Shibata, Hideki Kandori, Tahei Tahara Halorhodopsin is a retinal protein in \textit{Haloarchaeal} cell membrane. The light-induced all-trans to 13-cis isomerization of the retinal chromophore triggers unidirectional chloride-ion pump in millisecond timescale. Here, we present pump-probe study of the primary ultrafast dynamics of \textit{Natronobacterium pharaonis} halorhodopsin that contains Cl$^{-}$, Br$^{-}$ or I$^{-}$. All the temporal behaviors of the S$_{1}$ absorption, ground-state bleaching, and stimulated emission consisted of three components, and their time constants showed halide-ion dependency. The $\sim $50-fs component corresponds to the spectral shift of the S$_{1}$ absorption and stimulated emission bands, which is due to the wavepacket motion from the Franck-Condon region, forming the reactive and nonreactive S$_{1}$ states. Referring to previous reports, the $\sim $2-ps component is assignable to the isomerization process from the reactive S$_{1}$ state to the ground-state 13-\textit{cis} form via the conical intersection, while the $\sim $5-ps component to the internal conversion of the nonreactive S$_{1}$ state. Quantitative analysis indicated that the isomerization quantum yield increased in order of Cl$^{-}$, Br$^{-}$ and I$^{-}$. On the basis of the halide-ion dependence observed, we discuss the relation between the initial halide-ion pump process and the isomerization mechanism. [Preview Abstract] |
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R1.00206: Light harvesting and carrier transport in core/barrier/shell semiconductor nanocrystals. Patanjali Kambhampati, Eva Dias, Samuel Sewall Excitation transfer pathways in colloidal core/barrier/shell nanomaterials are investigated in the CdSe/ZnS/CdSe system. Absorption of light in the outer CdSe shell results in emission from the band edge of the CdSe core. The CdSe quantum shell acts as a light harvester which indirectly increases the brightness of the CdSe quantum dot core. Spectroscopic evidence is provided which suggests that the CdSe core and shell are coupled by tunneling of excitons through the ZnS barrier. Competition kinetic analysis shows that charge transport competes effectively with hole capture by pyridine at the outer CdSe shell, and exciton relaxation within the outer CdSe shell. Femtosecond experiments are underway to monitor and control the charge transport dynamics in these core/barrier/shell nanostructures. [Preview Abstract] |
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R1.00207: Enhanced Fluorescence Blinking of CdSe/ZnS Quantum Dot Clusters Ming Yu, Alan Van Orden Semiconductor quantum dots (QDs) have been studied for many years to understand their unique, size tunable optical properties, and to investigate their potential applications in optoelectronic devices and biological imaging. In particular, much effort has been devoted to the phenomenon of fluorescence intermittency, or blinking, of individual QDs. In our work, we used spatially correlated single molecule fluorescence spectroscopy and atomic force microscopy (AFM) to study the structures and fluorescence blinking of single CdSe/ZnS core-shell QDs, small ensembles of two or more isolated QDs, and close-packed clusters containing two or more QDs. When multiple isolated QDs were probed simultaneously, the fluorescence behavior was consistent with independent blinking of the particles. However, when close-packed QD clusters were probed, the fluorescence intermittency became much more rapid and intense than could be explained by the summation of multiple particles blinking independently.[1] This suggests when the QDs cluster together, they become electronically coupled in some way that enhances the fluorescence. One possible explanation for this coupling is that the trapping of photoexcited electrons from one or more of the QDs can enhance the fluorescence properties of neighboring QDs by passivating external trap sites available to the neighboring QDs. [1]. Yu, M.; Van Orden, A. Phys. Rev. Lett., Accepted for publication. [Preview Abstract] |
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R1.00208: A Density Functional Theory Study of Silicon-Molecule-SWCNTs Nanodevices Brahim Akdim, Ruth Pachter Electronic devices comprised of oligo(phenylene-ethynylene) and its derivatives, bridged between a silicon slab and a single walled carbon nanotubes (SWCNTs) mat, have been shown to exhibit bistable states, driven by an applied voltage (He et al. Nature Materials 5, 2006). In light of these reports, we present a theoretical study on the switching mechanism of the nitro-oligo(phenylene-ethynylene), via the non-equilibrium Green's function formalism and the density functional theory (DFT) method. We report on the conformational changes of nitro-OPE induced by an applied field, as well as on the interaction at the interface of the SWCNT, emphasizing their effects on the electronic transport of the system (Si---Molecule---SWCNT). DFT properties such as structural parameters, electronic structures, and the density of states near the Fermi level as a function of an applied field, will be outlined. In conjunction with the DFT results, the electron transport obtained via the non-equilibrium Green's function formalism will be discussed. [Preview Abstract] |
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R1.00209: Electron Transport Properties of Co Nanodot Arrays Chae-Hyun Kim, Seongjin Jang, Wenjie Kong, Hao Zeng The DC electron transport properties of Co nanodot arrays have been investigated. The device was produced by e-beam evaporation of cobalt through the nanoporous alumina masks. The masks were mounted on substrates with 2 um-wide gap between electrodes, fabricated using photolithography before evaporating cobalt. The sizes and interdot spacings of the Co nanodots can be adjusted by widening the pores of the mask for different durations. Metal-insulator transition has been observed as the interdot spacing changes, as evidenced by different temperature dependent resistivity behavior. Magnetoresistance has been measured, and its dependence on structural parameters and temperature will be discussed. Work supported by NSF DMR 0547036. [Preview Abstract] |
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R1.00210: Pair State Analysis of the Hubbard Hamiltonian in One-Dimension William Hodge, N. A. W. Holzwarth, W. C. Kerr Recently, there has been renewed interest in using a variational determination of the two-particle reduced density matrix $^2D$ to find the ground state energy of an $N$-electron system. This interest can be partly attributed to progress in solving this constrained optimization problem using semidefinite programming algorithms (SDPA).\footnote{Nakata, Nakatsuji, and co-workers, J. Chem. Phys. {\bf{114}}, 8282 (2001), Hammond and Mazziotti, Phys. Rev. A {\bf{73}}, 062505 (2006).} We use the one-dimensional Hubbard model for comparing several variations of the SPDA appproach with the exact results, considering either even or odd numbers $N$ of electrons, either periodic or fixed boundary conditions, and various values of the Coulomb energy parameter $U/t$. It is convenient to use the two-electron eigenstates of the pair Hubbard Hamiltonian as a basis for representing the $^2D$ matrix using the normalization ${\rm{Tr}}(^2D)= N(N-1)/2$. For example, for $N=4$ at half filling, using all of the two-particle constraints along with the appropriate physical constraints, we find the SDPA ground state energies to differ from the exact ones by less than $4\times10^{-4}t$. In addition, the diagonal elements of $^2D$ generally differ from the exact ones on the order of $10^{-2}$. [Preview Abstract] |
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R1.00211: POSTDEADLINE |
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R1.00212: Thermal stability and oxidation resistance of protective coating on stainless steel interconnect for SOFC H. Chen, J. A. Lucas, W. Priyantha, M. Kopczyk, R.J. Smith, P.E. Gannon, M. Deibert, V.I. Gorokhovsky The possibility of an anode-supported SOFC with ferritic stainless steel interconnects is particularly promising because of its low cost and flexibility. An effective, dense and well adherent AlCrTiCoMnYO coating was deposited on 430SS using filtered arc deposition technique. Rutherford backscattering with He$^{+}$ and non-Rutherford scattering with H$^{+}$ were used to characterize the composition and the thermal stability of the coatings. The chromium volatility of the coated steel plates at 800 $^{o}$C was measured using ion beam analysis. Significant reductions in oxidation rates as well as reduced Cr volatility were observed for the coated alloys. [Preview Abstract] |
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R1.00213: Catalyst free synthesis and luminescence of well aligned ZnO nanorods Aurangzeb Khan, Wojciech Jadwisienczak, Martin Kordesch Quasi-aligned undoped ZnO nanorods with diameter in the range 100-300 nm and length of several micrometers have been grown catalyst free on Si (100) wafer in a one-step process by direct heating of Zn powders. All nanowires are single crystals and are well aligned vertically to the substrate surface with $c$-axis preferred orientation. XRD, HRTEM and Raman studies revealed that the ZnO nanorods have wurtzite phase, are highly crystalline and well aligned with the lattice parameters $a$ = 0.32 nm and $c$ = 0.52 nm. The PL spectra measured at different temperatures are dominated by excitonic emission at 380 nm and less intense below bandgap emission band centered at 520 nm. The intensity ratio between these two bands changes with temperature. [Preview Abstract] |
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R1.00214: Aharonov-Bohm Effect in Concentric Quantum Double Rings Guang-Yin Chen, Yueh-Nan Chen, Der-San Chuu We propose a theoretical model to study the single-electron spectra of the concentric quantum double ring fabricated lately by self-assembled technique. Exact diagonalization method is employed to examine the Aharonov-Bohm effect in the concentric double ring. It is found the appearance of the AB oscillation in total energy depends on the strength of the screened potential. Variations of the energy spectra with the presence of coulomb impurities located at inner or outer ring are also investigated. [Preview Abstract] |
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R1.00215: Translocation Model for Intermediate-Length Polymer Dynamics Erica J. Saltzman, Murugappan Muthukumar A description is presented of polymer translocation among a series of spherical chambers separated by narrow pores. This system is a useful model for studying polymer dynamics in the intermediate molecular weight regime. A simple free energy barrier approach is adopted, and the barrier associated with large-scale chain motion is expressed in terms of the barrier for translocation of a subchain between adjacent chambers. The characteristic relaxation time and diffusion constant are calculated and exhibit a molecular weight dependence stronger than that predicted by the reptation model. [Preview Abstract] |
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R1.00216: Diffusion coefficient in hydrogel under high-frequency ultrasound Akira Tsukamoto, Kei Tanaka, Tatsuya Kumata, Yoshiaki Watanabe, Shogo Miyata, Katsuko Furukawa, Takashi Ushida Modulating hydrogel properties by external stimuli can be applied for drug delivery system. For example, ultrasound can enhance drug release from hydrogel by the mechanism which is not fully understood. We measured diffusion coefficient in hydrogel under high-frequency ultrasound to understand mass transport property. To estimate diffusion coefficient, FRAP (fluorescence recovery after photobleaching) technique was applied with time-lapse fluorescence microscopy and we analyzed fluorescence recovery after photobleaching of FITC-dextran (4$\sim $40 kDa) which was fully fused in agarose gel (1$\sim $3 {\%}). As a result, diffusion coefficient was altered when agarose gel was sonicated by 1MHz ultrasound with 400kPa (peak-peak). We discussed several possible underlying mechanisms such as cavitation, heat and phase transition with extended experimental data. [Preview Abstract] |
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R1.00217: High-sensitivity interlayer tunneling study of Bi-2212 Timothy Benseman, John Cooper, Geetha Balakrishnan We have performed interlayer tunneling measurements on the high-T$_{c}$ superconductor Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$, using micron-scale `mesa' structures containing a few intrinsic Josephson junctions in series. The dI/dV spectra of these devices were studied with high resolution at closely-spaced temperatures ranging from 1.2K to 300K. Interesting new aspects of our data are compared with the results of spatially resolved STM measurements reported recently by Lee \textit{et al. }[1]. The authors would like to acknowledge Professor Vladimir Krasnov of the University of Stockholm, and Professor Jeff Tallon of Victoria University of Wellington, for helpful discussions and advice regarding this work. [1] Lee et al. Nature Vol. 442/3, 546-550 (2006) [Preview Abstract] |
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R1.00218: Growth and properties of epitaxial Fe$_{2-x}$Ti$_{x}$O$_{3}$ thin films Manuel Bibes, Herve Ndilimabaka, Elena Popova, Niels Keller, Yves Dumont While Fe$_{2}$O$_{3}$ and FeTiO$_{3}$ are both antiferromagnetic insulators with N\'{e}el temperatures of 950K and 60K, respectively, Fe$_{2-x}$Ti$_{x}$O$_{3}$ (0.2$<$x$<$0.8) solid solutions are semiconducting and exhibit a finite magnetization with critical temperatures close to or above room temperature. As such, Fe$_{2-x}$Ti$_{x}$O$_{3}$ samples are intrinsic ferromagnetic semiconducteurs with potential for spintronics. We have grown films of FeTiO$_{3}$ and Fe$_{1.5}$Ti$_{0.5}$O$_{3}$ by pulsed laser deposition on c-Al$_{2}$O$_{3}$ substrates in a wide range of deposition pressures. The films are epitaxial and their transport properties depend critically on the growth pressure. We will present the results of the optimization of their structural, magnetic and magneto-optical properties. [Preview Abstract] |
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R1.00219: Statics and dynamics of elastic manifolds in media with long-range correlated disorder Andrei Fedorenko, Pierre Le Doussal, Kay Wiese We study the statics and dynamics of an elastic manifold in a disordered medium with quenched defects correlated as $\sim r^{-a} $ for large separation $r$. We derive the functional renormalization group equations to one-loop order, which allow us to describe the universal properties of the system in equilibrium and at the depinning transition. Using a double $\varepsilon=4-d$ and $\delta=4-a$ expansion, we compute the fixed points characterizing different universality classes and analyze their regions of stability. The long-range disorder-correlator remains analytic but generates short-range disorder whose correlator exhibits the usual cusp. The critical exponents and universal amplitudes are computed to first order in $\varepsilon$ and $\delta$ at the fixed points. At depinning, a velocity-versus-force exponent $\beta$ larger than unity can occur. We discuss possible realizations using extended defects. [Preview Abstract] |
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R1.00220: Spin-Transfer Torque in Double Barrier Magnetic Tunnel Junction. Ioannis Theodonis, Alan Kalitsov, Nicholas Kioussis The transport properties in double-barrier magnetic tunnel junctions (DBMTJ) are determined by the spin polarized quantum well states(QWS) formed in the middle ferromagnetic(FM) region. Using tight-binding approach to the Keldysh formalism, we have studied the effect of the QWS on spin-transfer torque(STT) exerting on the middle FM region in non-collinear DBMTJ, with components parallel,$T_{\vert \vert } $, and perpendicular,$T_\bot $, to the interface. Our results reveal that both \textit{local} STT $T_{\vert \vert (\bot ),i} $exerting on atomic layer i in the middle FM region can be dramatically enhanced for values of the thickness of the middle FM region, b, for which spin-up and spin-down QWS are in close proximity to each other and lie within the bias window. This enhancement though, is cancelled out for the \textit{total} STT, $T_{\vert \vert (\bot )} =\sum\limits_{i=1}^b {T_{\vert \vert (\bot ),i} } $ due to the oscillations of $T_{\vert \vert ,i} $and $T_{\bot ,i} $, as a function of i. In addition we show that the bias dependence of $T_{\vert \vert } $ for different b and different orientations of the magnetizations of the leads varies due to the QWS and symmetry respectively. We also show that the angular dependence of both $T_{\vert \vert } $ and $T_\bot $deviates from the sinusoidal behavior. Interestingly$T_\bot $, which measures the non-equilibrium exchange coupling, exhibits an enhanced biquadratic term in its angular dependence. [Preview Abstract] |
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R1.00221: Structural comparison of Ag-Ge-S bulk glasses and thin films Fei Wang, Mukul Jain, Porter Dunn, Carter De Leo, Punit Boolchand Ternary glasses of composition (GeS$_{3})_{1-x}$Ag$_{x}$ (x=0.1 and 0.2) are studied in form of bulk and thin films. Bulk glasses are synthesized and examined in Raman scattering and SEM. Raman scattering results of bulk glasses show that with increasing x, an increasing fraction of the Ag additive enters the base glass as Ag$^{+}$ with S$^{-}$anions serving to form thiogermanate species with one, two and three non-bridging S$^{-}$ species. SEM measurements of the bulk glass show the material is intrinsically phase separated. White colored islands are observed distributed in a dark base. The EDS measurements show islands are Ag rich and the base is relatively Ag deficient. The Ag rich islands are expected to be mainly glassy phase Ag$_{2}$S. Thin films of same compositions are fabricated using thermal evaporation. Films are evaporated following two different procedures to prevent the material from spitting. One method was preheating outgas and the other method was using tungsten mesh wrapped boats. The stoichiometry and molecular structure of films under each procedure are analyzed by Raman scattering and SEM to be compared with bulk glasses. [Preview Abstract] |
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R1.00222: First-Principles electronic transport calculations in finite elongated systems: A divide and conquer approach Oded Hod, Juan E. Peralta, Gustavo E. Scuseria We present a \textit{first-principles} method for the evaluation of the transmittance probability and the coherent conductance through \textit{finite-elongated} systems composed of a repeating molecular unit and terminated at both ends. Our method is based on a divide and conquer approach in which the Hamiltonian of the elongated system can be represented by a block tridiagonal matrix, and therefore can be readily inverted. This allows us to evaluate the transmittance and the conductance using first-principles electronic structure methods without explicitly dealing with calculations involving the entire system. A proof of concept model based on a \textit{trans}-polyacetylene chain bridging two aluminum leads indicates that our divide and conquer approach is able to capture all of the features appearing in the transmittance probability curves of a full scale calculation. Using our method we investigate the edge effects on the electronic structure of finite sized carbon nanotubes as a function of their length and identify the limit at which the electronic structure converges to that of an infinite system. [Preview Abstract] |
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R1.00223: Breakdown Waves Propagating into a Neutral Medium Mostafa Hemmati The propagation of breakdown waves in a gas has been investigated by applying a set of one-dimensional, steady state, three component fluid equations. The results of electron-fluid theory of breakdown waves as developed so far has been in good agreement with experimental results at velocities above and below the ionization velocity for the gas. Our set of equations consists of equations of conservation of mass, momentum, and energy, coupled with the Poisson's equation. Breakdown waves are composed of a thin dynamical region (the shock layer) followed by a thicker thermal region. In the shock layer, which often is referred to as the sheath region, the electric field reduces to zero and the electrons come to rest relative to ions and neutral particles at the trailing edge of the sheath. For breakdown waves propagating into a non-ionized medium, the set of electron-fluid dynamical equations has successfully been integrated through the shock layer. Our solutions fulfill the expected physical conditions at the trailing edge of the shock layer. For breakdown waves moving into a non-ionized medium, we will present the method of integration of the electron-fluid dynamical equations through the shock layer. Also, for two wave speeds, we will present the wave profile for electric field, electron velocity, ionization rate, electron number density, and electron temperature inside the shock layer. [Preview Abstract] |
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R1.00224: Order-disorder phase transition in Fe/Pt(110) Chanyong Hwang, S.W. Han, W. Kim, In-Ho Lee, H. Kim, M. B. Hossain, C.K. Kim, Y.P. Lee, J. Hong Order-disorder phase transition in binary alloy has been studied for long time but so far not much microscopic studies on its behavior have been made. The surface of (110) platinum shows missing row structure, which results in (2x1) structure. At room temperature, small amount of Fe overlayers on top of this surface destroys the surface order, while the surface order at low temperature is maintained. This means that the Fe atoms can fill the missing row at low temperature, which results in ordered state of surface alloy. Upon increasing the temperature, this ordered state became disordered. The most remarkable result is that with the atom-resolved STM measurement, we can actually count the entropy of the system, which is important in determining the free energy at this elevated temperature. The importance in magnetic phase in determining the ground state will be discussed. Also the disordering pathway will be shown. Also this order-disorder phase transition has been explained with the Ising model of the spin system in magnetic filed. [Preview Abstract] |
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R1.00225: An \textit{Ab Initio }Full Potential Fully Relativistic Study of the (0001) Surface of Double Hexagonal Close Packed Americium* Da Gao, Asok Ray The electronic and geometric properties of bulk dhcp Am as well as quantum size effects in the surface energies and the work functions of the dhcp Am (0001) ultra thin films up to seven layers have been examined at nonmagnetic, ferromagnetic, and anti-ferromagnetic configurations via full-potential all-electron density-functional calculations with a mixed APW+lo/LAPW basis. The anti-ferromagnetic state including spin-orbit coupling is found to be the ground state of both bulk and the (0001) surface of dhcp Am with the 5$f$ electrons primarily localized. Our results show that magnetic configurations and spin-orbit coupling play important roles in determining the equilibrium lattice constant, the bulk modulus as well as the localized feature of $5f$ electrons for dhcp Am. Quantum size effects are found to be more pronounced in work functions than in surface energies. *This work is supported by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U. S. Department of Energy and the Welch Foundation, Houston, Texas. [Preview Abstract] |
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R1.00226: Sound-wave-like plasmonic excitations in atomic-scale metal chains T. Nagao, C. Liu, S. Yaginuma, T. Inaoka, T. Nakayama In his pioneering work in 1950, Tomonaga has theoretically proven the existence of a sound-wave like excitation in one-dimensional array of Fermi particles that follows Bose statistics [1]. We have been searching for such one-dimensional (1D) collective excitation in high electron density-limit in atomic-scale metal chains supported on dielectric substrates. Electron energy loss spectroscopy using highly collimated slow electron beam has detected a characteristic sound wave-like excitations that propagate along the wire showing strong anisotropy [2]. These excitations occur in dipole scattering regime and their lifetime rapidly drops as a function of momentum. From these features, the observed losses are identified as one-dimensional collective excitation (plasmon) that Tomonaga has mentioned. These plasmons are highly metallic as judged from their high intensity near the elastic peak, but at low temperatures ($<$70K), some of the atom wires show reduced density of states which indicates gap opening at the Fermi level, due to Peierls-type metal to insulator transition. [1] S. Tomonaga, Progress of Theoretical Physics Vol. 5, No.4, 544 (1950). [2] T. Nagao, S. Yaginuma, T. Inaoka, S. Sakurai, Phys. Rev. Lett. 97, 116802 (2006). [Preview Abstract] |
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R1.00227: LEED Structure Factor analysis of ultra-thin Ag and Ti films on the crystalline Al(100) surface M. Kopczyk, W. Priyantha, H. Chen, D. S. Choi, R. J. Smith The surface structure for one monolayer of Ag deposited on the Al(100) surface at room temperature has been studied using low energy electron diffraction (LEED). The LEED pattern is analyzed using structure factor calculations to find the theoretical relative intensities of the LEED spots. From the LEED pattern, we infer that Ag on the Al(100) surface forms a quasi-hexagonal structure in a (5x1) coincidence lattice with the fcc-structure of the Al(100) substrate surface, i.e. the surface layer of Ag atoms is coincident with the Al(100) surface unit cell, having a repeat distance of 5 Al(100) interatomic spacings in the [110] direction. The LEED pattern shows a double-domain (5x1) structure with additional intensity in those spots corresponding to a (111) close-packed hexagonal layer. Study of an ultra-thin layer of Ti deposited on the Al(100) surface reveals a much simpler c(2x2) LEED pattern. [Preview Abstract] |
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R1.00228: Reactions of atomic oxygen with the D-covered Si(100) surfaces. Arifur R. Khan, Fauzia Khanom, Faridur Rahman, Akira Takeo, Hidetaka Goto, Akira Namiki We have studied D abstraction by O on the D/Si(100) surfaces using a continuous as well as a modulated O-beam. Both D$_{2}$ and D$_{2}$O molecules are desorbed during the O-exposure. The D$_{2}$ desorption takes places more efficiently on the saturated dideuteride surface containing dideuterides than on the 1.0 ML monodeuteride surface. The modulated beam experiments exhibit occurrence of both slow and a fast desorptions. The reaction order of D$_{2}$ desorption is found to be a second-order on the monodeuteride surface and 3.5-th order on the dideuteride surface. Possible mechanisms for the O-induced desorption from the D/Si(100) surface are discussed. [Preview Abstract] |
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R1.00229: Energetics and transport coherence in spatially non-uniform temperature microscopic heat engines Ronald Benjamin We study via numerical simulations the energetics and thermal transport of a microscopic Brownian heat engine based on a non-uniform temperature profile. [Preview Abstract] |
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R1.00230: ABSTRACT WITHDRAWN |
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R1.00231: Development of a Scaling Law for Fractal Aggregate Sintering from Molecular Dynamics Simulation Takumi Hawa, Michael Zachariah A simple modification to the Frenkel sintering law is developed for nanoparticle fractal aggregates, based on molecular dynamics (MD) simulations. The fractal aggregates investigated consist of up to 110 primary particles of silicon, with primary particles of 2.5 nm in diameter. Aggregates of Fractal dimension of 1 (wire), 1.9 (complex), and 3 (compact) were considered. Sintering of aggregates consists of three steps, a) reaction between particles to minimize surface defects, (b) sintering of multiple secondary branches to the primary branch, and (c) contraction of the primary branch. The sintering times normalized by the primary particle diameter showed a universal relationship that only depends on the number of particles in an aggregate and its fractal dimension. This result was found to be consistent with a continuum viscous flow mathematical model we developed. Finally the results for the sintering of arbitrary fractal aggregates can be approximated with a power law modification of the Frenkel viscous flow equation, to include a dependence on the number of particles in a fractal aggregate and fractal dimension. [Preview Abstract] |
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R1.00232: High-Pressure Vibrational Spectroscopy of Polymers Erik Emmons, Richard Kraus, Srividya Duvvuri, Jeffrey Thompson, Aaron Covington Polymers are often subjected to extreme conditions of high pressure and temperature in shock compression experiments and in their use as binders in high explosives. We have begun a program to examine polymeric materials at high pressures in a diamond anvil cell using infrared and Raman vibrational spectroscopies. There is a significant lack of measurements of basic spectroscopic data on scientifically and technologically interesting polymeric materials at high pressure. Data for different materials, including pressure-dependent FTIR absorption spectroscopy of poly (methyl methacrylate) (PMMA) will be presented. The data were analyzed to determine mode Gr\"uneisen parameters and vibrational anharmonicities. Such measurements are useful for interpreting experimental studies of shock compression of polymers as well as benchmarking theoretical models of the behavior of polymers under pressure. [Preview Abstract] |
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R1.00233: Energy Eigenstates in Systems Weakly Coupled to Environments:Decoherence to Pointer States Wenge Wang We study decoherence of superpositions of energy eigenstates in a generic system with nondegenerate discrete spectrum, which is quite weakly coupled to a generic environment. We show that $t_e \gg \tau_f$ in most cases, where $t_e$ is the time before which energy eigenstates are robust and $\tau_f$ is a time scale related to decoherence of superpositions of energy eigenstates. Energy eigenstates are shown to be pointer states between the two time scales. [Preview Abstract] |
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R1.00234: Glassy worms of PS-PEO block copolymers Kandaswamy Vijayan, Debbie Cheng, Dennis Discher A novel class of rigid worm micelles formed by PS-PEO dilock copolymers are described. The worms exhibit unique hinged motion about defects, with the defect density falling drastically at higher molecular weights. The glassiness of the system is demonstrated using FRAP analysis. Stiffness of the worms is estimated in terms of tangent-tangent correlation along the backbone, and by the magnitude of angle fluctuations about the hinges. The backbone flexibility is found to be only weakly dependent on the temperature up to 80 $^{o}$C. Breaking of glassiness, including stiffness and morphology control using organic solvents and a fluid diblock, are described. A simple method to engineer worm shape during formation process is presented. The rheological properties of the worms studied under parallel plate geometry, along with visualization of the worms under shear are presented. [Preview Abstract] |
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R1.00235: Rodent Brain Imaging with X-ray CT Youngho Seo, Tomoki Hashimoto, Yoshitsugu Nuki, Bruce Hasegawa, Benjamin Franc High resolution compact computed tomography (CT) systems have become increasingly important for examining morphology in small animal models of human biology and disease. However, functional measurements of blood flow and tissue perfusion are more challenging due to limited temporal resolution and need for x-ray absorptive contrast media. We therefore have developed methodologies which use x-ray CT for imaging hemorrhagic stroke in the brain of the intact rat. The head of the anesthetized rat was secured in an immobilization device, followed by \textit{in vivo} imaging with a dedicated small animal CT scanner (X-O{\texttrademark}, Gamma Medica-Ideas, Northridge, CA). Imaging was performed without iodine contrast to visualize a very small volume (less than 0.1 ml) of arterial blood in a rat model of intracranial hemorrhage, and with iodine contrast (iopromide, 300 mgI/ml) to visualize carotid and cerebral arteries in order to study aneurysms and other vascular formations that may precede or indicate intracranial hemorrhage. [Preview Abstract] |
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R1.00236: Normal-mode coupling of rare-earth-metal ions (Pr$^{3+})$ in a crystal (Y$_{2}$SiO$_{5})$ to a macroscopic optical cavity mode Kouichi Ichimura, Hayato Goto Coupling of rare-earth ions (Pr$^{3+})$ in a crystal (Y$_{2}$SiO$_{5})$ to a macroscopic cavity mode was demonstrated by observing optical bistability and normal-mode peaks, which is sometimes described as vacuum Rabi splitting, due to sweeping-laser-induced population redistribution of the ions. The experimentally evaluated coupling constant between the individual ions and the single cavity mode is 15 kHz, which is comparable with or larger than the dissipation of the ions. The coupling constant will exceed the cavity dissipation with a narrowing of the mode waist of the cavity to the wavelength. The results advance the application of a coupled system of rare-earth ions in a crystal and an optical cavity for quantum information processing. [Preview Abstract] |
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R1.00237: Stimulated Raman adiabatic passage with a rare-earth-ion-doped crystal Hayato Goto, Kouichi Ichimura We report experimental study of stimulated Raman adiabatic passage (STIRAP) with a rare-earth-ion-doped crystal (Pr$^{3+}$:Y$_{2}$SiO$_{5})$. We have investigated two types of STIRAP: $\Lambda $ type and tripod type. We have demonstrated efficient population transfer between two ground states of Pr$^{3+}$ ions in Y$_{2}$SiO$_{5}$ via $\Lambda $ STIRAP. We have confirmed that the dependence of the efficiency of the population transfer on the delay time of the pulse sequence is in agreement with theoretical prediction. We have also experimentally investigated tripod STIRAP with Pr$^{3+}$:Y$_{2}$SiO$_{5}$. The observed population transfers and the comparison with numerical simulation in this case indicate that these are mainly due to a coherent process similar to STIRAP, not optical pumping. [Preview Abstract] |
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R1.00238: Variation of the glass transition temperature with rigidity and chemical composition Gerardo Naumis 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 . 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-Ge-As glass by using the experimental density of vibrational states, and the result shows a very good agreement with the experimental fit from glass transition temperature variation. [Preview Abstract] |
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R1.00239: Three-body interactions in sociophysics and their role in coalition forming Gerardo Naumis An study of the effects of three-body interactions in the process of coallition formation is presented. In particular, we modify an spin glass model of bimodal propensities to include a particular three-body hamiltonian that reproduces the main features of the required interactions. As an application, we analyze a simplyfied model of the Iraq war , which shows that three-body effects are sometimes more important than friendship. [Preview Abstract] |
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R1.00240: Dynamical Studies of Phonon Polaritons by Femtosecond X-ray Diffraction Matteo Rini, Robert W Schoenlein, Eric Statz, David W Ward, Keith A Nelson, Simon Wall, Chris Simpson, Andrea Cavalleri In solids, light propagation near resonances can be described in terms of polaritons, mixed excitations with both phonon- and photon-like character arising from the coupling of the oscillating electromagnetic field to polar lattice vibrations. Here we use time-resolved x-ray diffraction with 200-fs synchrotron pulses to directly measure the coherent lattice distortions associated with the propagation of THz phonon polaritons in ferroelectric LiTaO$_{3}$. THz radiation was generated by fs IR pulses via impulsive stimulated Raman scattering. The lattice motion component of polariton propagation was measured as time-dependent modulation of the 006 structure factor. The comparison with a time-domain simulation of THz propagation allowed extracting the absolute atomic displacements along the coordinate of the A$_{1}$ normal mode with 1-m{\AA} resolution. Our experiments reveal a polariton wave with a 1.5-THz frequency and a 5-m{\AA} peak displacement of the Ta atom with respect to the plane of the oxygen atoms. Complementing optical techniques which measure the time-dependent electrical polarization, femtosecond X-ray experiments directly monitor amplitude and phase of all structural degrees of freedom. [Preview Abstract] |
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R1.00241: Neutron Reflection Studies on Nanophase-Separated Structures of Block Copolymers with Composition Distribution Atsushi Noro The effect of composition distribution on nanophase-separated structures of AB diblock and BAB triblock copolymers was investigated by neutron reflectometry. Three monodisperse polystyrene-$d_{8}$-\textit{block}-poly(2-vinylpyridine) (DP), three labeled triblocks (PDP) with constant molecular weight and with different volume fractions, and unlabeled counterparts were prepared by living anionic polymerizations. The selective labeling method was employed by blending three parent copolymers for segmental distribution studies while three labeled polymers were mixed for interfacial studies. Blend thin films were produced by spin-coating and successive thermal annealing. It was confirmed by morphological observation that all samples having composition distribution show simple alternating lamellar structures. It was found that a longer chain is localized at the center of the domain while a shorter chain is localized near the domain interface. Furthermore, interfacial thickness increases with an increase in composition distribution index for both diblock and triblock systems. The increment of the increase for the triblock system was larger than that for the diblock system. [Preview Abstract] |
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R1.00242: Predicting Ecosystem Response to Perturbation from Thermodynamic Criteria Karo Michaelian, Vasthi Alonso-Chavez The response of ecosystems to perturbations is considered from a thermodynamic perspective by acknowledging that, as for all macroscopic systems and processes, the dynamics and stability of ecosystems is subject to definite thermodynamic law. For open ecosystems, exchanging mass and energy with the environment, the thermodynamic criteria come from non-equilibrium or irreversible thermodynamics. For ecosystems during periods in which the boundary conditions may be considered constant, it is shown that criteria from irreversible thermodynamic theory are sufficient to permit a quantitative prediction of ecosystem response to perturbation. [Preview Abstract] |
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R1.00243: Electronic Structure of Electron-doped Sm$_{1.86}$Ce$_{0.14}$CuO$_{4}$ : Strong `Pseudo-Gap' Effects and Nodeless Gap S. R. Park, Y. S. Roh, Y. K. Yoon, C. S. Leem, J. H. Kim, B. J. Kim, H. Eisaki, N. P. Armitage, C. Kim Angle resolved photoemission (ARPES) data from the electron doped cuprate superconductor Sm$_{1.86}$Ce$_{0.14}$CuO$_{4}$ shows a much stronger pseudo-gap or ``hot-spot" effect than that observed in other optimally doped n-type cuprates. Importantly, these effects are strong enough to drive the zone-diagonal states below the chemical potential, implying that d-wave superconductivity in this compound would be of a novel ``nodeless" gap variety. The gross features of the Fermi surface topology and low energy electronic structure are found to be well described by reconstruction of bands by a root 2 times root 2 order. Comparison of the ARPES and optical data from the same sample shows that the pseudo-gap energy observed in optical data is consistent with the inter-band transition energy of the model, allowing us to have a unified picture of pseudo-gap effects. [Preview Abstract] |
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R1.00244: Photon transport in low-dimensional nanostructures Teemu Ojanen, Tero Heikkila At low temperatures when the phonon modes are effectively frozen, photon transport is the dominating mechanism of thermal relaxation in metallic systems [1]. Starting from a microscopic many-body Hamiltonian using the equation-of-motion technique for nonequilibrium Green's functions, we study the energy transport by photons in nanostructures. We obtain a formally exact expression for the energy current between a metallic island and a one-dimensional electromagnetic field supported by a parallel strip transmission line. From this expression we derive the quantized thermal conductance as well as show how the electron shot noise affects the photon transport. Frequency-dependent current noise essentially determines the transport process, thus providing a close connection between electron transport and photon transport [2]. \newline \newline [1] M. Meschke, W. Guichart and J. P. Pekola, Nature {\bf 444}, 187 (2006). \newline [2] T. Ojanen and T. T. Heikkil\"a, to be published. [Preview Abstract] |
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R1.00245: Thermoelectric miniband transport in superlattice cross-plane direction Zhixi Bian, M. Zebarjadi, R. Singh, A. Shakouri, J-H. Bahk, G. Zeng, J. Bowers Thermoelectric materials can be used for solid-state refrigeration and thermal-to-electric power conversion. The thermoelectric transport performance can be optimized by adjusting the charge carrier concentration in bulk semiconductor materials. Further improvement can be achieved by using low dimensional structures such as multiple quantum wells. In the current transport direction parallel to the quantum well plane, this is attributed to the quantum confinement effect and the highly asymmetric electronic density of states; while in the multiple quantum well cross-plane direction, it was explained by the energy filtering of charge carriers by the band edge offset. We study the thermoelectric transport of superlattices in the cross-plane direction using the multiple-miniband structure. The barrier height and width of superlattices are optimized and the results are compared with the bulk materials. [Preview Abstract] |
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R1.00246: Progress towards the development of a source of entangled photons for Space Alessandro Fedrizzi, Thomas Jennewein, Rupert Ursin, Anton Zeilinger Quantum entanglement offers exciting applications like quantum computing, quantum teleportation and quantum cryptography. Ground based quantum communication schemes in optical fibres however are limited to a distance of the order of $\sim $100 km. In order to extend this limit to a global scale we are working on the realization of an entanglement-based quantum communication transceiver for space deployment. Here we report on a compact, extremely bright source for polarization entangled photons meeting the scientific requirements for a potential space to ground optical link. The pair production rate exceeds 4*10\^{}6 pairs/s at just 20mW of laser diode pump power. Furthermore, we will present the results of various experiments proving the feasibility of quantum information in space, including a weak coherent pulse single-photon downlink from a LEO satellite and the distribution of entanglement over a 144km free space link, using ESAs optical ground station. [Preview Abstract] |
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R1.00247: Dynamic Monte Carlo rate constants for magnetic Hamiltonians coupled to a phonon bath Lazarus Solomon, Mark Novotny For quantitative comparisons between experimental time- dependent measurements and dynamic Monte Carlo simulations, a relation between the time constant in the simulation and real time is necessary. We calculate the transition rate for spin S system using the lattice frame method for a rigid spin cluster in an elastic medium [1]. We compare this with the transition rate for an Ising spin $\frac{1}{2}$ system using the quantum- mechanical density-matrix method [2] with the results of ref [1,3]. These transition probabilities are different from those of either the Glauber or the Metropolis dynamics, and reflect the properties of the bosonic bath. Comparison with recent experiments [4] will be discussed. \newline \newline [1] E. M. Chudnovsky, D. A. Garanin, and R. Schilling (PRB 72, 2006) \newline [2] K. Park, M. A. Novotny, and P. A. Rikvold (PRE 66, 2002) \newline [3] K Saito, S. Takesue, and S. Miyashita, (PRE 61, 2002) [4] T. Meunier et al (Condensed Matter, 2006) [Preview Abstract] |
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R1.00248: Pairing in an one-dimensional interacting electron gas M. Fortes, R. Mendoza, M. A. Sol\'{\i}s We study an N-electron gas in one dimension with two electrons above, or two holes below, the Fermi surface interacting via a Cooper/BCS pairwise interaction model, taking full account of the Fermi sea of N-2 background electrons. We study the structure of possible Cooper-pair formation through the Bethe- Salpeter equation in the ladder approximation. When the unperturbed ground state is simply that of the ideal Fermi gas, we obtain the well-known result for the binding energy of electron pairs if hole pairs are completely ignored. Also obtained is a linear center-of-mass momentum, correction term leading to pair breakup for somewhat larger values for the total center-of-mass momentum, K. The same result but with opposite sign is obtained for a hole pair below the Fermi surface. But when both electron- and hole-pairs are considered via the same model interaction, no solution exists as the energy is purely imaginary. However, by performing a Bogoliubov transformation to replace the ideal Fermi gas sea as the unperturbed ground-state by a correlated BCS ground-state, two solutions are found. For sufficiently small K, we derive a highly-nontrivial solution of the moving Cooper pair which is also linearly-dispersive for small K. These results are consistent with similar calculations in 2D and 3D. [Preview Abstract] |
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R1.00249: Negating Negative Heat Capacity in Nanoclusters Karo Michaelian, Ivan Santamaria-Holek It is shown that ``negative heat capacity'' in nanoclusters is an artifact of applying equilibrium thermodynamic formalism on a ``small'' system trapped out of equilibrium in a particular structural motif representing only part of the energetically available phase space volume. Trapping may occur in either the canonical or microcanonical ensemble, but it is unavoidable in the microcanonical. A more general consequence of trapping is that all macroscopic quantities determined for nanoclusters will depend on the initial conditions. [Preview Abstract] |
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R1.00250: Density Functional Theory and Noncollinear Magnetism Juan Peralta We present a generalization of the treatment of the electronic spin degrees of freedom in density functional calculations to the case where the spin can vary in any direction in space. This generalization is applied not only to the local--spin density and generalized--gradient approximations, but also to meta--generalized gradient energy functionals that include the kinetic energy density and the Laplacian of the density in their ingredients, as well as to hybrid functionals including Hartree--Fock exchange. The expression of the generalized exchange and correlation potential matrix elements is explicitly derived for all cases. We discuss the model case of planar Cr clusters that exhibit ground states with noncollinear spin densities due to geometrically frustrated antiferomagnetic interactions. [Preview Abstract] |
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R1.00251: Investigations of Abrupt Movements of Optically Trapped Water Droplets Shawntel Murphy, Lowell I. McCann We have used a single beam optical trap (optical tweezers) to capture individual water droplets in air. A 3-dimensional viewing system consisting of a two axis microscope allows the trapped droplet to be viewed from the top and the side simultaneously. The position of the droplet is determined with a digital camera at a rate up to 700Hz. We have observed abrupt movements along the beam in two situations: As a pure water droplet evaporates, the movements occur at specific size intervals as the diameter decreases. For non-evaporating saltwater droplets the movements rapidly occur for certain ranges of beam power, and not at all for other ranges of power. [Preview Abstract] |
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R1.00252: First-principles calculation of anharmonic force constants Keivan Esfarjani, Harold Stokes Calculation of anharmonic force constants in a crystal is a challenging task due to their large number, especially in a low symmetry crystal. Using the symmetry properties of the force constants coming from rotational, translational, as well as space group operation invariance, we formulate the exact constraints the latter have to satisfy. The other relations they have to satisfy come from total energy and forces for different atomic configurations. Using a singular value decomposition, we extract the force constants from the available linear relations and constraints. They will be used to calculate the phonon spectra and lifetimes, as well as scattering rates needed for the calculation of the thermal conductivity. This approach being systematic, can be extended to all crystals for which a first-principles-based interatomic potential up to fourth order can be obtained and used for molecular dynamics simulations. [Preview Abstract] |
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R1.00253: Spin-dependent Quantum Well States in Magnetic Tunnel Junctions Yan Wang, XiuFeng Han, Zhong-Yi Lu, X.-G. Zhang MgO crystalline oxide based magnetic tunnel junctions (MTJs) and double barrier MTJs (DBMTJs) have attracted much recent attention due to the observation of large tunneling magnetoresistance (TMR) ratio and realization of quantum size effect in epitaxial structures. Using first-principles calculations, we show that the TMR ratio is reduced by an ultrathin Mg insertion layer although experimentally it can improve the orientation of the MgO(001) barrier layer. We also confirm that spin-dependent quantum well (QW) states exist in the middle film in DBMTJs, and large TMR can be realized by resonant tunneling effect through these states. However, at a small bias, large MgO thickness for DBMTJs is prerequisite for achieving TMR as high as single barrier MTJs without resonant tunneling effect. We also discover that the Coulomb blockade effect plays a dominant role in the smearing of the QW resonances. [Preview Abstract] |
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R1.00254: Influence of Filling of Polymer with Nanoparticles on Relaxation Processes and Glass Transition Ivan Joel Lopez, Vladimir Dolidze, Fouad Aliev We report the results of the investigations of the influence of filling of polymer with Aerosil nanosize particles on the glass transition and dynamics of the alpha- and the beta-relaxation processes in poly(butylmethacrylate) by dielectric spectroscopy and differential scanning calorimetry (DSC). The polymer was filled with hydrophilic and hydrophobic Aerosil particles of 12 nm diameter. Both the alpha- and the beta- relaxation processes were observed in filled polymer. However in filled polymers the characteristic frequency of the alpha-process was shifted to higher frequencies in comparison with pure bulk polymer. This suggests that the filling of the polymer with nanoparticles has resulted in the shift of its glass transition temperature T$_{g}$. This change in T$_{g}$ was mainly due to the existence of a developed pore wall/solid particle-polymer interface and the difference in the dynamic behavior of the polymer in the surface layers compared to that in the bulk. This result was in agreement with DSC experiments. Variations of size of filling particles and their concentration are helpful in understanding of relaxation properties at polymer -- solid interface as well as of a role of surface interactions in glass transition. [Preview Abstract] |
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R1.00255: Relaxation Processes and Phase Transitions in Nanoconfined Liquid Crystal Edwin Arroyo, Sarmistha Basu, Vladimir Dolidze, Fouad Aliev The results of static and dynamic light scattering (DLS), broadband dielectric spectroscopy (DS) and differential scanning calorimetry (DSC) investigations of the influence of confinement on the dynamic behavior and phase transitions of liquid crystal-8CB dispersed in porous matrices with randomly oriented, interconnected pores with average pores sizes of 10nm and 100nm will be presented. The combination of these methods allow us to obtain detail information about orientational fluctuations of director-collective mode (DLS) the dynamics of molecular modes (DS) as well as phase transitions (DSC and static light scattering). The influence of confinement on physical properties under investigation was strongly pore size dependent and was resulted in absence of clear phase transitions in narrow pores (10nm). In large pores (100nm) broadening and shift of phase transitions was observed. The dynamics of both molecular and collective modes was also drastically affected by confinement. [Preview Abstract] |
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R1.00256: Enhancement of heat exchange by on-chip engineered heat sink structure Yonuk Chong, Paul D Dresselhaus, Samuel P Benz We report a method for improving heat exchange between cryo- cooled high power consuming devices and coolant. We fabricated a micro-machined monolithic heat sink structure on a high integration density superconducting Josephson device, and studied the effect of the heat sink on cooling of the device in detail. The monolithic heat sink structure showed a significant enhancement of cooling efficiency, which markedly improved the chip operation. The detailed mechanism of the enhancement still needs further modeling and study in order to optimize the design of the heat sink structure. [Preview Abstract] |
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R1.00257: Optimization of the design of superconducting hybrid wires Ilya Grigorenko, Alexander Balatsky We study the transition temperature and critical current in inhomogeneous superconducting nanowires using a numerical solution of the Bogolubov-de Gennes equations. Optimized geometry thay allows one to maximize the critical current and transition temperature from these solutions is determined for axially symmetric design of nanowires. Specifc geometry we focus on is composed of N-S-N-S-...-N-S material layered along the radial axis with a variable thickness of each individual layer. We found critical currents and transition temperatures of these composite objects to be sensitive to the wires' radius and to the individual thickness of layers. Critical currents and transition temperatures exceeding the corresponding bulk values for optimally designed configurations. Possible experimental realizations of the proposed structures are discussed. [Preview Abstract] |
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R1.00258: Room temperature high efficiency heterodyne THz QW detector based on quantum coherence Hamid Javadi, Kishor Kapale THz devices are used for Earth's (and other planets) atmospheric remote sensing, astronomical investigation of interstellar dust medium, and life detection instruments for in-situ probing of the planet's surfaces. As the radio astronomy science community demands observations at higher THz frequencies, there is a technology development push for high power tunable THz sources, high efficiency room temperature heterodyne detectors that need low power local oscillators, and high dynamic range near-quantum-noise-limit detectors. THz technology gap is being filled up by traditional optics and microwave communities. Quantum coherence promises to be the enabling technology in many technical areas [including Electromagnetically Induced Transparency (EIT) based magnetometer, all optical switch, single photon counter, quantum computer, micro-K laser cooling). Quantum coherence phenomena have been demonstrated successfully in select (gaseous) atoms, and in few (crystalline) solids. We will discuss a heterodyne THz QW detector device based on quantum coherence with prospects of performing near-quantum-noise-limit at room temperature with high quantum efficiency, where the need for high power THz source is eased, and phase-matching is no longer restrictive. THz down-conversion concept via closed-loop four-wave-mixing will be discussed. [Preview Abstract] |
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R1.00259: Controllable Coupling between Flux Qubit and Nanomechanical Resonator Ying-Dan Wang, Fei Xue, Changpu Sun, Hajime Okamoto, Hiroshi Yamaguchi, Kouichi Semba We propose an active mechanism for coupling the quantized mode of a nanomechanical resonator to the persistent current in the loop of superconducting flux qubit. This coupling is independently controlled by an external coupling magnetic field. The whole system forms a novel solid-state cavity QED architecture in strong coupling limit which has broad applications in demonstrating quantum optical phenomena in solid state system and solid-state quantum computing. The coupling mechanism is applicable for more generalized situations where the superconducting Josephson junction system acts as a multi-level quantum system. We also address the practical issues concerning experimental realization. [Preview Abstract] |
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R1.00260: Quantum Monte Carlo simulation of the dissipative granular array Munehisa Matsumoto, Matthias Troyer We develop a new cluster algorithm for the dissipative granular arrays and apply it to the one-dimensional (1D) array. The problem in the simulation of the dissipative granular array arises from the competition between the phase difference terms and the on-site charging energy terms in the action. We divide these two kinds of terms into on-site terms and inter-site terms. A cluster update for the latter is combined with the Metropolis method for the former, being in the same spirit as was done for the resistively-shunted Josephson-junction array [1]. The on-site charging energy is calculated for the 1D array and its dependence on the strength of dissipation is discussed in comparison to several theoretical predictions [2]. [1] P. Werner and M. Troyer: Phys. Rev. Lett. 95 (2005) 060201. [2] K. B. Efetov and A. Tschersich: Europhys. Lett. 59 (2002) 114; A. Altland, L.I. Glazman, A. Kamenev: Phys. Rev. Lett 92 (2004) 026801. [Preview Abstract] |
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R1.00261: Electrostatics of DNA complexes with cationic lipids Andrey Cherstvy We present the exact solutions of the linear Poisson-Boltzmann theory for several problems relevant to electrostatics of DNA complexes with cationic lipids. We calculate the electrostatic potential and energy for lamellar and inverted hexagonal phases, concentrating on the effects of water-membrane dielectric boundaries. Our results for the complex energy agree qualitatively well with the known numerical solutions of the nonlinear Poisson-Boltzmann equation. Using the solution for the lamellar phase, we calculate its compressibility modulus and compare our findings with experimental data available suggesting a new scaling dependence on DNA-DNA separations in the complex. Also, we treat analytically charge-charge electrostatic interactions across, along, and in between two low-dielectric membranes. We obtain an estimate for the strength of electrostatic interactions of 1D DNA smectic layers across a lipid membrane. We discuss also some aspects of 2D DNA condensation and DNA-DNA attraction in DNA-lipid lamellar phase in the presence of di- and tri-valent cations and analyze the equilibrium intermolecular separations using the recently developed theory of electrostatic interactions of DNA helical charge motifs. [Preview Abstract] |
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R1.00262: Strong and weak adsorptions of polyelectrolyte chains onto oppositely charged spheres Andrey Cherstvy, Roland Winkler We investigate the complexation of long thin polyelectrolyte chains with the oppositely charged sphere. In the limit of strong adsorption, when strongly charged polyelectrolyte chains adapt definite wrapped conformations on the sphere surface (solenoidal, tennis-ball-like, etc.), we analytically solve the linear Poisson-Boltzmann equation and calculate the electrostatic potential and energy of the complex. We discuss some biological applications of the obtained results, including those for DNA wrapping in the nucleosome core particles and for aggregate formation of DNA with oppositely charged nano-spheres studied in vitro. For weak adsorption, when a flexible weakly charged polyelectrolyte chain is localized next to the sphere in solution, we solve the Edwards equation for the chain conformations in the Hulth\'en potential. The latter is used as an approximation for the screened Debye-H\"uckel potential of the sphere. For arbitrary sphere radius, we predict the critical conditions for polyelectrolyte adsorption as a coupling between critical sphere and polyelectrolyte charge densities, sphere radius, temperature, and ionic strength in solution. We find that the critical charge density of the sphere exhibits a distinctively different dependence on the Debye screening length than for polyelectrolyte adsorption onto a flat surface. We compare our findings with experimental measurements on complex formation of various polyelectrolytes (DNA, PSS, AMPS, etc.) with oppositely charged colloidal particles and cationic micelles, where similar universal scaling relations for the sphere charge density have been revealed. [Preview Abstract] |
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R1.00263: Ferromagnet/Superconductor Systems: Effects of Magnetic Domain Structure Charles Moreau, Reza Loloee, William Pratt, Norman Birge Ferromagnet/Superconductor (F/S) hybrid systems have received considerable interest owing to the interplay between their competing types of order. A number of open questions remain about these systems. In particular, several groups have observed ``superconducting spin switch'' behavior in F/S/F trilayers, occasionally with conflicting results [1,2]. There is concern that the magnetic domain structure may be playing an important role in some experiments. To address this issue, we have measured the resistance $R$ of S/F bilayers as a function of magnetic field $H$ in the vicinity of their superconducting transitions. One expects either dips (enhancement of superconductivity) or peaks (diminishment of superconductivity) in $R(H)$ at the coercive field of the F layer. The latter is due to stray fields from F in S, whereas the former is due to averaging of the exchange field over the superconducting coherence length [3]. Our preliminary data on Nb/Ni films indicate only peaks in $R(H)$ when the Ni magnetization switches, indicating that the stray magnetic field is the dominant of the two effects in this material system. [1] I. Moraru \textit{et al.,} Phys. Rev. B \textbf{74}, 220507(R) (2006). [2] A. Yu. Rusanov \textit{et al.,} Phys. Rev. B \textbf{73}, 060505(R) (2006). [3] A. Yu. Rusanov \textit{et al.}, Phys. Rev. Lett. \textbf{93}, 057002 (2004). Work Supported by DOE Award ER46341 [Preview Abstract] |
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R1.00264: Photoconductivity of Single-Walled Carbon Nanotubes Measured by Terahertz Time-Domain Spectroscopy Hugen Yan, Yang Wu, Gordana Dokovic, Louis Brus, Tony Heinz THz time-domain spectroscopy has been employed to probe the change in the conductivity of single-walled carbon nanotubes induced by optical excitation. Two types of ensemble samples, namely bundled and isolated HiPCO nanotubes embedded in polymer matrices, were examined. Here we report on the response for frequencies from 0.2 -- 2 THz, which complements the higher frequency range probed previously by another group.$^{1}$ For our spectral range, the response was found to be Drude-like for the bundled nanotubes, but significantly different characteristics were measured for the sample of isolated nanotubes. In the latter case, a generalized Drude model.$^{2}$ that takes into account velocity persistence after scattering provides a better fit of the experimental conductivity data. Defects, disorder and the shorter nanotube length associated with the nanotube debundling process may account for the different behavior of the isolated nanotubes. \newline $^{1 }$L. Perfetti, T. Kampfrath, F. Schapper, et al., Phys. Rev. Lett. \textbf{96}, 027401 (2006). \newline $^{2 }$N. V. Smith, Physical Review B \textbf{64, }155106 (2001). [Preview Abstract] |
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R1.00265: K-12 Teaching and Physics Enrollment Samina Masood We have collected and analyzed the relevant data from public schools in greater Houston area of Texas. Based on this analysis, we propose a few recommendations towards the improvement of science education in Texas Schools, in general, and greater Houston area schools in particular. Our results indicate that the quality of science education can be improved by organizing teacher training programs at K-12 level as school education plays a pivotal role in the decrease in physics enrollment at the higher level. Similar analysis can actually be generalized to other states to find out the best way to increase the physics enrollment. [Preview Abstract] |
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R1.00266: Experiments Using Force-Detected Nuclear Magnetism Han-Jong Chia, Wei Lu, Samaresh Guchhait, Rosa Cardenas, Isaac Esteve, Michelle Millan, John Markert We present progress on our Nuclear Magnetic Resonance Force Microscopy (NMRFM) experiments, interferometer instrumentation, and double-torsional oscillator fabrication. Our new $^3$He probe is in the final stages of testing and will be utilized to perform single-spin feasibility experiments at 300 millikelvin. We are also currently scanning for the boron resonance in MgB$_2$ using our $^4$He probe. With our room-temperature probe we are currently studying double and multiple resonance effects in NH$_4$PF$_6$ and are preparing to study dynamics and diffusion in soft condensed matter. In addition we will present results from our fabricated double-torsional oscillators using electron beam lithography with a minimum detectable force of $1.8\times 10^{-18} \textrm{N}/\sqrt{\textrm{Hz}}$. [Preview Abstract] |
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R1.00267: The free energies of six-vertex models and the n-equivalence relation. Kazuhiko Minami The free energies of six-vertex models on general domain D with various boundary conditions are investigated with the use of the n-equivalence relation which classifies the thermodynamic limit properties. It is derived that the free energy of the six-vertex model on the rectangle is unique in the limit where both the height and the width go to infinity. It is derived that the free energies of the model on D are classified through the densities of left/down arrows on the boundary. Specifically the free energy is identical to that obtained by Lieb and Sutherland with the cyclic boundary condition when the densities are both equal to 1/2. This fact explains several results already obtained through the transfer matrix calculations. The relation to the domino tiling (or dimer, or matching) problems is also noted. [Preview Abstract] |
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R1.00268: Statistical properties of granular gas under microgravity --- one dimensional inelastic hard rod system Masaharu Isobe, Akinori Ochiai We have studied numerically statistical properties of granular gas in a one-dimensional inelastic (viscoelastic) hard rod model under microgravity, which is designed to the mimic experimental granular vibrated beds by introducing a velocity- dependent restitution coefficient. Our systematic simulations show that various macroscopic properties of this model are quantitatively different from a linear combination of the previous simulations based on the constant restitution coefficient. The present results are significantly important to study a vibration response and dynamics of granular gas especially in microgravity experiment. [Preview Abstract] |
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R1.00269: Dephasing of a superconducting flux qubit Kosuke Kakuyanagi, Takayoshi Meno, Shiro Saito, Hayato Nakano, Kouichi Semba, Hideaki Takayanagi, Frank Deppe, Alexander Shnirman In order to gain a better understanding of the origin of decoherence in superconducting flux qubits, we have measured the magnetic field dependence of the characteristic energy relaxation time $T_{1}$ and echo phase relaxation time $T_{2}^{echo}$ near the optimal operating point of a flux qubit. We have measured $T_{2}^{echo}$ by means of the phase cycling method. At the optimal point, we found the relation $T_{2}^{echo} \quad \sim 2T_{1}$. This means that the echo decay time is limited by the energy relaxation ($T_{1}$ process). Moving away from the optimal point, we observe a linear increase of the phase relaxation rate ($1/T_{2}^{echo})$ with the applied external magnetic flux. This behavior can be well explained by the influence of magnetic flux noise with a $1/f$ spectrum on the qubit. \begin{flushright} K.Kakuyanagi, et al., cond-mat/0609564 \end{flushright} [Preview Abstract] |
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R1.00270: Theory of superconductivity in carbon nanotubes and graphene Ken-ichi Sasaki, Jie Jiang, Riichiro Saito, Seiichiro Onari, Yukio Tanaka The energy spectrum of the pi-electrons near the Fermi level of graphene consists of not only delocalized bulk states but also localized edge states. The edge states play a decisive role at the interface between carbon nanotube and an electronic contact because they enhance the local density of states. The contact is also important for emergence of superconductivity observed in multi-wall carbon nanotubes. Thus, it is valuable to examine the effect of the edge states on the superconductivity. Using the Eliashberg equation, we obtain an appreciable transition temperature for the edge states. As a result, a metallic zigzag carbon nanotube having open boundaries can be regarded as a natural Superconductor/Normal Metal/Superconductor junction system, in which superconducting states are developed locally at both ends of the nanotube and a normal metal exists in the middle. In this case, a signal of the edge state superconductivity appears as the Josephson current which is sensitive to the bandwidth of the edge states, the position of the Fermi energy and the length of a nanotube. (arXiv:cond-mat/0611452) [Preview Abstract] |
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R1.00271: Magnetic and structural studies of double perovskites La(2-x)Sr(x)RuCrO$_{6}$ Hirotoshi Terashita The B-site ordered double perovskites La(2-x)Sr(x)RuCrO$_{6}$ were prepared using solid state reaction. X-ray powder diffraction showed all specimens to be single phase. The best structural model is a cubic structure with space group Fm-3m, in which RuO6 and CrO6 octahedra are alternatively located (rock salt type). Samples with 0$\le $x$\le $1 show antiferromagnetic behavior with T$_{N} \quad \sim $ 300K. Anomaly, which may result from charge-ordering, is observed below T$_{N}$. [Preview Abstract] |
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R1.00272: Scattering and Guiding by Atomic Walls J. Y. Vaishnav, J. D. Walls, M. Apratim, E. J. Heller We propose the possibility of using a wall of atoms to guide matter waves, e.g. electrons or other atoms, in a manner similar to which a fiber optic guides light. Such walls could be engineered from individual atoms by STM, for instance. We model the atomic wall as a quasi-1D array of scatterers embedded in 2D; our theoretical study reveals the interplay of scattering phenomena with bands and conduction along the array. We discuss the conditions under which straight or curved arrays of atoms can guide a beam focused on one end of the array. [Preview Abstract] |
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R1.00273: The Living Feature of PBLG-Grafted SiO$_{2}$ Polypeptide Composite Particles Jianhong Qiu, Sibel Turksen-Selcuk, Erick Soto-Cantu, Paul Russo Silica-polypeptide composite particles (SiPCPs) have a SiO$_{2}$ core and polypeptide shell. The length of poly(carbobenzoxy-L-lysine (PCBL) polypeptide chains on the SiPCP surface is proportional to the concentration of monomer when the particles are dispersed in $m$-cresol . The same is true for poly(benzyl-L-glutamate (PBLG) SiPCPs in pyridine; the hydrodynamic radius increases each time monomer is added and the reaction after each addition of monomer is mostly completed in one day. The radius of gyration stays level, reflecting the fact that the core is predominantly responsible for the scattering and confirming that the particles are not aggregated. The amount of monomer added at the first step is crucial because it determines the number of polypeptide chains formed on the SiO$_{2}$ particle surface. The living feature also allows us to graft co-block polypeptide PBLG/PCBL on SiO$_{2}$ core. Thus, silica-polypeptide particles of defined size and complex shell structure can be produced. [Preview Abstract] |
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R1.00274: Reversible Transfer of Optical to Atomic States Andreea Boca, Allen David Boozer, Russell Miller, Tracy Northup, H. Jeff Kimble Using a single atom strongly coupled to a high-finesse cavity, optical states can be reversibly transferred to superpositions of atomic internal states. We demonstrate this by transferring a weak coherent state to a superposition of F=3 and F=4 atomic ground states in a single trapped Cesium atom. To confirm that the process is reversible, we transfer the atomic superposition back to an optical state, which is shown to be phase coherent with the original coherent state. [Preview Abstract] |
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R1.00275: Release kinetics of volatiles from clay minerals Pascal Clausen Smectite clay minerals are known to have interesting sorption properties, but the prediction of the kinetics of desorption of volatile molecules from such clays remains a challenge. The aim of this work is to relate the isothermal rate of desorption of volatile molecules from cation exchanged smectite clays to the chemical structures and geometries of the interacting species (clay platelet surface, type of counter-ion, type of volatile). It is thought that the rate of desorption of the volatiles at a given time is governed by their instantaneous diffusion in the clay and in the gas phase, which in turns is dependent on the volatile's interaction with its chemical and geometrical environment. Therefore, in addition to isothermal desorption rate measurements by thermogravimetry, activation energies of desorption are measured and calculated and the interacting compounds are characterized in terms of their chemical structure and geometry. [Preview Abstract] |
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R1.00276: Electronic spectrum and superconductivity in cuprates:effective p-d Hubbard model Nikolay Plakida, Viktor Oudovenko A microscopic theory of electronic spectrum and superconducting pairing for the CuO2 plane within an effective p-d Hubbard model is formulated. The Dyson equation for the normal and anomalous Green functions in terms of the Hubbard operators is derived by applying the Mori-type projection technique. Self-consistent solution of the Dyson equation with the self-energy evaluated in the noncrossing approximation for electron scattering on spin fluctuations is obtained. Doping and temperature dependence of electron dispersions, spectral functions, the Fermi surface are studied for a hole doped case. Superconducting pairing mediated by antiferromagnetic exchange and spin fluctuations induced by the kinematical interaction results in the d-wave superconductivity with high-T$_c$ proportional to the Fermi energy. [Preview Abstract] |
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R1.00277: Total energy calculations using the transcorrelated method: wavefunction approach for solids Keitaro Sodeyama, Rei Sakuma, Shinji Tsuneyuki To calculate the electronic structures of solids including
electron correlation effects, we have developed the
transcorrelated (TC) method which was first proposed by Boys and
Handy. In this method, the wave function is represented by a
correlated wave function $F \Phi$, where $\Phi$ is a single
Slater determinant and $F$ is a Jastrow function,
$F=\exp[-\sum_{i |
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R1.00278: AFM Simulations of H-terminated Si surfaces Akira Masago, Satoshi Watanabe, Katsunori Tagami, Masaru Tsukada Si currently plays an important role in electronics. In order to search for more powerful and novel devices based on Si, significant attention has been recently focused on the fabrication of hybrid structures using organic molecules on Si surfaces, and a number of investigations have been reported. In such a situation, atomic force microscopy (AFM) and scanning tunneling microscopy (STM) are powerful techniques for observation and manipulation. In particular, since AFM can be used not only for conductors but also semiconductors and insulators, it has been widely used for observations or manipulations of various materials. However, compared to STM, there have been few reports on AFM of organic molecules adsorbed on Si surfaces. We guess that this is due to the difficulty in analyzing the AFM images of such systems. In this situation, simulations are expected to be useful, and our major objective is the development of such simulators. Thus far, we have performed non-contact AFM simulations of bare, hydrogen and methyl-terminated Si surfaces using the density-functional based tight-binding method. Results of these simulations are in good agreement with experiments quantitatively. In the present report, we talk about such Si surfaces including various defect types. [Preview Abstract] |
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R1.00279: Structural properties of ZnO thin films grown on glass substrate by pulsed laser deposition Toshihiko Maemoto, Hiroaki Ishii, Shigehiko Sasa, Masataka Inoue High quality ZnO epitaxial films on Corning glass substrates were produced by pulsed laser ablation. These films were characterized by x-ray diffraction, optical transmittance, photoluminescence (PL), and Hall effect measurements. The high crack density that results from the mismatch of the thermal expansion coefficients between the ZnO film and glass substrate, make it difficult to grow ZnO films directly. In order to improve the quality of ZnO thin films grown on such a substrate, we introduced low-temperature grown ZnO (LT-ZnO) buffer layers between the films and the glass substrates. The surface of the ZnO films grown on the LT-ZnO buffer is very smooth, with a root-mean-square roughness of 1 nm. Highly c-axis oriented ZnO(0002) reflections corresponding to the wurtzite-phase were observed. Moreover, the LT-ZnO buffer layers affected the structural and optical properties of subsequently grown un-doped ZnO films. The full width at half maximum (FWHM) values of the PL spectra was reduced with increments in the buffer thickness. Details of the structural properties, optical properties, and electrical properties for the ZnO thin films grown on glass substrates will be discussed. [Preview Abstract] |
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R1.00280: Phase diagrams of titanium and titanium oxide at high pressure Yahya Al-Khatatbeh, Kanani Lee, Boris Kiefer The nature of bonding in titanium (Ti) and, in particular, titanium oxide (TiO2) are of significant interest since TiO2 forms a superhard material.~ Using density-functional theory-based ab-initio computations, we have investigated the structural phase transitions of both Ti and TiO2 at high pressure. For titanium, the hexagonal close-packed (hcp), hexagonal ($\omega )$, distorted hcp ($\gamma )$, distorted bcc ($\delta )$, body-centered cubic (bcc), faced-centered cubic (fcc) and simple cubic (sc) structures were studied up to a pressure of~ $\sim $ 200 GPa. The structural phase transition sequence is as follows: hcp -$>{\rm g}\omega ->{\rm g}\gamma ->{\rm g}\delta ->$ bcc, in good agreement with both experimental and theoretical results. Furthermore, we test the stability of bcc to other cubic and close-packed phases (fcc, sc, and hcp) and find that bcc is the most stable structure of Ti under pressures between 156 and $\sim $200 GPa. For titanium oxide, rutile, anatase, columbite, baddeleyite, fluorite, pyrite, brookite, and cotunnite structures were also studied under high compression. For both Ti and TiO2, our transition pressures compare well with previous studies. [Preview Abstract] |
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R1.00281: Spin-Blockade in One-Dimensional Strongly-Correlated Systems Yao Yao, Hui Zhao, Chang-Qin Wu We investigate the charge/spin dynamics in a one-dimensional strong repulsive Hubbard chain by using an adaptive time-dependent density-matrix renormalization group method. It's well known that there exists the spin-charge separation in a non-half-filling Hubbard model since it exhibits Luttinger liquid behavior. By adjusting the spin-dependent hopping on a bond, we realize the spin-blockade on the bond while the charge propagating freely on the chain. The spin storage as well as its directional transmit are discussed. [Preview Abstract] |
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R1.00282: Wetting of liquid crystal surfaces and induced smectic layering at the nematic-liquid interface Masafumi Fukuto, Oleg Gang, Benjamin Ocko, Kyle Alvine, Peter Pershan We present a synchrotron x-ray reflectivity (XR) study of the interfacial behavior of a bulk nematic 8CB surface that is coated by a thin wetting film of an immiscible liquid, perfluoromethylcyclohexane (PFMC). The thickness of the wetting film was controlled by the temperature difference $\Delta T_{\mu }=T$ -- $T_{res}$ between the sample and a reservoir of bulk PFMC. Interfacial electron density profiles have been extracted from the x-ray interference between the PFMC-vapor interface and the surface induced smectic order. The observed $\Delta T_{\mu }$ dependence of thickness of the PFMC film, $L \quad \propto $ ($\Delta T_{\mu })^{-1/3}$, is consistent with complete wetting. The liquid crystal side of the nematic-liquid interface is characterized by a density oscillation whose period is equal to the smectic layer spacing and whose amplitude decays exponentially towards the nematic subphase. The results indicate that the homeotropic orientation of the 8CB molecules is preferred at the PFMC-8CB interface and that the observed temperature dependence of smectic layer growth is consistent with a critical adsorption mechanism, independent of the PFMC film thickness. [Preview Abstract] |
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R1.00283: Mechanical properties and electronic structure of Ta4AlC3 Songyou Wang, Ming Xu, Gang Yin, Liangyao Chen, Fengchuan Chuang, Yu Jia The mechanical properties and electronic structure of Ta4AlC3 have been studied using the first-principles calculations. Optimized structural parameters of the crystal structure and the calculated bulk modulus are in good agreement with the experimental data. The calculated bulk modulus reaches up to 262.40 GPa, which is the largest among all the known materials with MAX phases in the literature, the band-structure and the density of states suggest that Ta4AlC3 is metallic. Further analysis shows that the alternating stacks of relatively strong Ta-C bonding and weak Ta-Al bonding lead to the large bulk modulus of Ta4AlC3, but softening in shear. [Preview Abstract] |
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R1.00284: Morphological instability of the solid-liquid interface under a thin shear flow with a free surface-ripples on icicles and stalactites Kazuto Ueno Icicles and stalactites grow when their surfaces are covered with a thin film of flowing water through which latent heat of fusion and carbon dioxide are released to the surrounding air by diffusion and convection. Despite the complete difference in their basic growth mechanism, their surfaces often have ripples of centimeter-scale wavelengths. We consider the underlying common mechanism of ripple formation and find that the mean thickness of the water film and the capillary length associated with the surface tension of the water-air surface are common important characteristic lengths in determining the centimeter-scale wavelength of ripples. This is the first theoretical work on the morphological instability of solidification front during icicle and stalactite growth from a thin shear flow with one side being a free surface, in which we take into account the change of shape of the water-air surface when the shape of the solid-liquid interface is changed. [Preview Abstract] |
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R1.00285: Band structure calculations using the transcorrelated method Rei Sakuma, Keitaro Sodeyama, Shinji Tsuneyuki We have been developing a new wave-function-based method for calculating the electronic properties of solids. The main feature of this method, called the transcorrelated (TC) method, is a similarity transformation of the Hamiltonian using the Jastrow-Slater trial wave function, which leads to an effective non-hermitian Hamiltonian with three-body interactions. Correlation effects are incorporated in the effective Hamiltonian via the similarity transformation. The wave function is optimized by solving a set of Hartree-Fock-like single particle equations derived by minimizing the variance of the effective Hamiltonian. In this work, the TC method is applied to the band structure calculations of \textit{sp} semiconductors. In the TC method, Koopmans' theorem holds, in which the eigenenergies of the single particle orbitals are interpreted as the ionization energies and electron affinities. By applying the Jastrow function derived from the random phase approximation (RPA), the screening effect is incorporated in the effective Hamiltonian, which significantly reduces the value of band gaps of semiconductors from their Hartree-Fock values. [Preview Abstract] |
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R1.00286: A Dynamical System Having Deterministic Behavior Governed by Statistics Martha-Elizabeth Baylor, Dana Anderson, Zoya Popovic We describe a holographic optoelectronic circuit whose dynamics to lowest order is described by a Lotka-Volterra system in which the parameters are determined by the second- and fourth- order statistical moments of a collection of input signals. The system is multistable, metastable, or monostable, depending on whether the input signal statistical fourth moments are sub-Gaussian, Gaussian, super-Gaussian, or a mixture of statistical classes. More generally the circuit gain is directly derived from the input-space statistical characteristic function. We use the dynamical properties to demonstrate the cocktail party effect in which the circuit unscrambles a mixed pair of audio or radio frequency signals in the absence of any \textit{a priori} information about the mixture. [Preview Abstract] |
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R1.00287: TOF measurements of He and D$_{2}$ molecules scattered from clean and H-covered Si(100) surfaces. S. Ueno, A.R. Khan, Y. Kihara, S. Sato, Y. Narita, A. Namiki Angular distribution of He or H$_{2}$ (D$_{2})$ scattered from Si(100) surfaces has been found to be broad. In case of H$_{2}$, such a broad scattering was considered as evidence of physisorption. Our aim is to know whether light atoms and molecules such as He or D$_{2}$ are physisorbed upon collision with Si (100) surfaces. Using 300 K effusive beam, we measured Time-Of-Flight (TOF) distributions of He and D$_{2}$ molecules scattered from clean and H-terminated Si(100) surfaces at surface temperature T$_{s}$ = 300 and 600 K. We found that for T$_{s}$ = 300 K the scattered He atoms show a Maxwellian velocity distribution characterized with translational temperature of T$_{t}$=300 K. At T$_{s}$ = 600 K, on the other hand, the net increase in translational temperature was found to be very small, about 340 K. Similar results were also found on the H-terminated surfaces. These results indicate that the scattered atoms or molecules have not accommodated with the surface, suggesting physisorption does not take place. [Preview Abstract] |
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R1.00288: Nonequilibrium Green's functions approach to artificial atoms: Nonequilibrium behavior Michael Bonitz, Karsten Balzer, Niels Erik Dahlen, Robert van Leeuwen Using a nonequilibrium Green's functions approach we directly compute the nonequilibrium behavior of quantum confined charged particles, which is of relevance for quantum dots, metal clusters or trapped ions. We study the nonlinear response to a strong laser pulse by solving the Keldysh-Kadanoff-Baym equations for the two-time Green's functions [1] where equilibrium initial correlations are selfconsistently included via computation of the Matsubara Green's functions. This method fully conserves momentum total energy and sum rules. Here we apply it to an inhomogeneous system -- N charged fermions in a one-dimensional parabolic trap extending earlier results for atoms and molecules [2]. The results include the selfconsistently coupled intra and intersubband dynamics in the laser field [3]. [1] D. Semkat and M. Bonitz, chapter in ``Introduction to Computational Methods for Many Body Systems'', Rinton Press, Princeton 2006, M. Bonitz and D. Semkat (eds.) [2] N.E. Dahlen, R. van Leeuwen, and A. Stan, J. Phys: Conf. Ser. 35 (2006) [3] K. Balzer, M. Bonitz, N.E. Dahlen, and R. van Leeuwen, submitted for publication [Preview Abstract] |
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R1.00289: Quantum Stark confined strongly correlated indirect excitons in quantum wells P. Ludwig, A. Filinov, M. Bonitz, H. Stolz, Yu. E. Lozovik We consider small ensembles of optically excited indirect excitons (IE) in a quantum well. Using path integral Monte Carlo simulations we compute from first principles the spatial separation of electrons (e) and holes (h) and the lateral quantum Stark confinement in the quantum well due to a strong electric field from a tip electrode [1]. Electrons and holes are shown to form permanent dipoles with a strong repulsion giving rise to interesting correlation and quantum effects [2,3]. By changing the field strength, tip to sample distance and excitation intensity (IE number) we predict the parameter range where exciton crystallization is expected to be observable in experiments on ZnSe based quantum wells. [1] P. Ludwig et al., phys. Stat. Sol. (b) 243, 2363 (2006) [2] A. Filinov et al., phys. Stat. Sol. (c) 3, 2457 (2006) [3] A. Filinov et al., J. Phys. Conf. Ser. 35, 197 (2006) [Preview Abstract] |
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R1.00290: Crystallization in mass-asymmetric electron-hole bilayers P. Ludwig, A. Filinov, M. Bonitz, H. Stolz, Yu. E. Lozovik We analyze hole crystallization [1] in an electron-hole bilayer system and specifically study the effect of the hole to electron mass ratio M. Varying M between 1 and 100 at a fixed layer separation at low temperature and high density, we demonstrate that the hole behavior can be tuned from delocalized (liquid-like) to localized (crystal-like), while the electrons remain delocalized all the time. As was recently demonstrated [1] in bulk systems holes undergo a crystallization transition if M exceeds a critical value of 83. Here we extend this analysis to bilayer systems and demonstrate that the critical mass ratio can be drastically reduced by properly choosing the layer separation. The complicated interplay between Coulomb correlations and quantum effects of electrons and holes is fully taken into account by performing first principle path integral Monte Carlo simulations. [1] M. Bonitz, V.S. Filinov, V.E. Fortov, P.R. Levashov, and H. Fehske, Phys. Rev. Lett. 95, 235006 (2005) and J. Phys. A: Math. Gen. 39, 4717 (2006); Phys. Rev. Focus, December 2 2005 [2] P. Ludwig, A. Filinov, Yu. Lozovik, H. Stolz, and M. Bonitz, Contrib. Plasma Phys. (2007) [Preview Abstract] |
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R1.00291: Superfluidity in small 2D systems of trapped charged bosons J. Boening, A. Filinov, M. Bonitz, Yu. E. Lozovik Superfluidity in a trapped cloud of quantum particles is defined using the cloud's response to a rotation of the external potential (non classical moment of inertia, NCRI). While NCRI originates from inter-particle interactions. in finite trapped quantum systems, due to the discrete nature of the spectrum, the NCRI effect occurs in any case regardless of the presence of interactions. We investigate small bosonic systems in order to distinguish between effects related to a finite system size, inter-particle interactions and quantum statistics. Our results are obtained with first principle path-integral Monte-Carlo (PIMC) simulations [1] and are compared to analytical expressions for the ideal case based on permutations cycles [2], respectively. Finally, coexistence of a mesoscopic bosonic crystal and superfluidity is studied. [1] A. Filinov and M. Bonitz, in: ``Introduction to Computational Methods in Many Body Physics'', M. Bonitz and D. Semkat (eds.), Rinton Press Inc., Princeton 2006 [2] J. Schneider and H. Wallis, Eur. Phys. J. B 18, 507 (2000) [Preview Abstract] |
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R1.00292: Quantum potential for confined charged particles in nonequilibrium A. Fromm, M. Bonitz, J.W. Dufty The idea of treating quantum systems by semiclassical methods using effective quantum pair potentials (forces) has been successfully used in equilibrium by many authors, see e.g. [1] and refs. therein. Here, we extend this idea to quantum systems in an external field in nonequilibrium. Using nonequilibrium Green's functions techniques we derive a gauge-invariant equation of motion for an effective quantum potential which modifies an external confinement potential by quantum effects. This equation is solved by an iteration procedure. Results include the nonequilibrium spectral function and density of states of a weakly inhomogeneous electron system. [1] A. Filinov, V. Golubnychiy, M. Bonitz, W. Ebeling, and J.W. Dufty, Phys. Rev. E. 70, 046411 (2004) [2] M. Bonitz and J.W. Dufty, Cond. Matt. Phys. 7, 483 (2004) [Preview Abstract] |
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R1.00293: Cooperative epitaxial growth of rutile TiO$_{2}$ nanorods Guobin Ma, Mu Wang, Nai-Ben Ming One-dimensional (1-D) inorganic nanostructures are of both theoretical and technological interest, as these structures exhibit a wide range of electrical and optical properties that depend on both size and shape. Investigation of their microstructures is essential for understanding properties and growth mechanisms of 1-D nanocrystals, therefore it is an important issue. Taking rutile TiO$_{2}$ nanorods as a model material, here we report a new growth mechanism of nanorods. Rutile TiO$_{2}$ nanorods are prepared by a hydrothermal method. The nanorods, although having well-defined side surfaces, actually can be regarded as bunches of thinner nanowires with slight misorientations as indicated by high-resolution transmission electron microscopy analysis. We propose a growth mechanism, the cooperative epitaxial growth method, to explain this formation phenomenon. Nanorods of various materials reported in literatures also imply these growth features, suggesting that they should be governed by the same mechanism. [Preview Abstract] |
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R1.00294: Schottky Anomaly Observed in NMR of Metallic Si:P Minki Jeong, Myeonghun Song, Tomohiro Ueno, Meng-Yuan Chen, Takao Mizusaki, Yutaka Sasaki, Akira Matsubara, Kohji Fukuda, Meiro Chiba, Soonchil Lee We studied the $^{31}\mathrm{P}$ nuclear magnetic relaxation of metallic Si:P with doping concentration of $\sim6 \times10^{19}\mathrm{cm}^{-3}$ at very low temperatures from 3.5 K down to 45 mK and magnetic field of 7.4 T. Below 1 K, Nuclear spin-lattice relaxation studied by inversion recovery method showed two-step recovery in magnetization due to the effects of finite heat capacity of conducting electrons. Under given experimental conditions, the heat capacity of nuclear spins becomes comparable to that of conducting electrons, so the conducting electrons cannot be considered as a heat reservoir. Still, however, the initial magnetization recovery or the corresponding time constant $\mathrm{T}_1$ followed the Korringa’s law very well. Nuclear spin-spin relaxation time $\mathrm{T}_2$ above 1.5 K was ~14 msec independent of temperature and explained by dipolar fields from $^{31} \mathrm{P}$ and $^{29}\mathrm{Si}$ nuclear spins. As temperature decreased below 1.5 K, however, $\mathrm{T}_2$ started falling and again became constant of $\sim1.3$ msec below 600 mK. [Preview Abstract] |
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R1.00295: Fabrication of magnetic random access memory based on nanoring-type magnetic tunnel junctions and spin-polarized current driving X.F. Han, H.X. Wei, Z.L. Peng, H.D. Yang, J.F. Feng, G.X. Du, Z.B. Sun, L.X. Jiang, Q.H. Qin, M. Ma, Y. Wang, Z.C. Wen, D.P. Liu, W.S. Zhan Nanoring-type magnetic tunnel junctions (NR-MTJs) of Ta/IrMn/CoFe/Ru/CoFeB/Al-O/CoFeB/Ta/Ru were nano-fabricated on the Si/SiO$_2$ substrate. The small NR-MTJs with the outer- and inner-diameter of 100 and 50 nm were nano-fabricated and the corresponding NR-MTJ array integrated above the transistors in CMOS circuit for 4x4 MRAM DEMO devices. The magnetoresistance (R) versus current (I) loops for a spin-polarized current switching were measured and the TMR ratio larger than 20$\%$ at room temperature were observed. The critical switching current for the free CoFeB layer between parallel and anti-parallel magnetization states is smaller than 750 $\mu$A in such NR- MTJs. After each positive and negative pulse writing current the high and low resistance of a NR-MTJ as a MRAM bite were read out using a low read current of between 10 and 20 $\mu$A. It shows that the MRAM fabrication with the density higher than 5 Gbite/inch$^2$ are possible based on 1 NR-MTJ + 1 transistor structure and spin-polarized current switching. [Preview Abstract] |
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R1.00296: Effect of hydrogen coating on the shape of silicon nanoclusters Takumi Hawa, Michael Zachariah The effect of hydrogen coating on the shape of silicon nanoclusters has been investigated using molecular dynamics simulation. We use Kohen-Tully-Stillinger potential to model the Si-H system. We consider bare and hydrogen coated silicon nanoclusters, which have crystal structure of cubic and truncated octahedron shapes and amorphous spherical shape for sizes between 2 nm and 10 nm. For bare Si clusters, truncated octahedron clusters are the most stable shape and amorphous spherical clusters are the least stable shape. On the other hand, cubic clusters are the most stable shape and amorphous spherical clusters are the least stable shape for hydrogenated Si clusters. Transition of the cluster shape was also observed from the MD simulation. This prediction explains the production of cubic Si clusters in the plasma synthesis. [Preview Abstract] |
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R1.00297: Hysteretic phenomena in multiferroic HoMnO$_{3}$ Eduard Galstyan, Bernd Lorenz, Marin Gospodinov, Karen Martirosyan, Paul Chu The hexagonal HoMnO$_{3}$ is multiferroic with ferroelectric transition at T$_{C}$=875 K, the Mn$^{3+}$ moments order at T$_{N}$=72 K, Mn$^{3+}$- spin reorientation transitions occur at T$_{sp1}$=34 K and T$_{sp2}$=4.9 K, and magnetic Ho$^{3+}$ orders at T$_{Ho }\sim $ 5.2 K. Our dc susceptibility measurements of HoMnO$_{3}$ single crystal under both zero-field cooled (ZFC) and field-cooled (FC) conditions at low applied magnetic fields reveal un unusual anomaly. In particular, below 4.9 K, the out-of-plane susceptibility ($c$-axis magnetization) is higher in the case of a ZFC measurement compared with that of a FC measurement. Above 4.9 K, the ZFC curve is lower than the FC curve, as well as for the in-plane susceptibility measurement in the temperature range below T$_{N}$=34 K. We assume that these phenomena are related to the magnetic and ferroelectric domain boundary structures and sensitively respond to changes of the magnetic structure such as spin-rotations at the phase transitions. We also have observed a sizable difference in the magnetization of HoMnO$_{3}$ polycrystalline samples with nano and micro size particles. [Preview Abstract] |
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R1.00298: Morphological Characterization of type I collagen fibrils network Sejin Han The self-assembly, termed fibrillogenesis of type I homozygous mutant and wild-type collagen revealed substantial differences in the kinetics and morphology. Computational Homology, in particular, Betti numbers, is used as a measure of the structural differences in collagen fibrils network. The Betti numbers are the most computable algebraic topological invariant, remaining constant under deformations, as primarily describing the connections between different components. In collagen network, it can implicate that the 0$^{th}$ betti number represents the number of disjointed fibers; the 1st betti number is the maximum number of cuts and 2$^{nd}$ betti number is the number of cavities in network. [Preview Abstract] |
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R1.00299: Structural NMR investigation of antimony pentafluoride C. Trevenen, F. Rivera, H. Martin, J. Futia, R. Michalak Antimony pentafluoride, SbF5, is a very viscous liquid at room temperature whose structural details are not well understood. The distribution and relative abundances of fluorine coordination clusters as a function of temperature are of great interest for the emerging catalyst role of doped SbF5. We have carried out fluorine NMR studies between the vaporization and solidification temperatures of SbF5. Three distinct fluorine coordinations are identified and the changes of their relative abundances are studied as a function of heating and cooling. [Preview Abstract] |
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R1.00300: ABSTRACT HAS BEEN MOVED TO B9.00015 |
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R1.00301: Magnetoresistance and Hall Effect in Electrochemically Doped $\beta $-Ag$_{2-\delta}$Te Paige Lampen, Justin Copenhaver, Harold Schnyders The magnetoresistance (MR) and Hall effect of $\beta $-Ag$_{2-\delta }$Te are measured over a range of precise, electrochemically-established silver concentrations. In the extrinsic regime, positive MR is seen at all studied values of silver deficiency. However, it is largest and most linear within the narrow range of $\delta $ where the Hall coefficient abruptly changes sign. [Preview Abstract] |
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R1.00302: TSP Thermodynamic Properties Felix Marin We investigate the thermodynamic properties of the traveling salesman problem (TSP). This research is widely based in a statistical mechanics analogy which we introduced a few years ago. Indeed, we introduced an order parameter for the TSP which is a discrete version of the angular momentum of a fictitious particle moving along the TSP configurations. Following the analogy mentioned above and the new order parameter behavior we define specific heat and susceptibility for the TSP. These are evaluated along a simulated annealing and show peaks around the transition temperature associated to the TSP order parameter. [Preview Abstract] |
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R1.00303: Ballistic rectification in four-terminal InAs/AlGaSb nanostructures Masatoshi Koyama, Hiroshi Takahashi, Tatsuya Inoue, Toshihiko Maemoto, Shigehiko Sasa, Masataka Inoue Rectification effects based on ballistic electron transport properties occur in four-terminal InAs/AlGaSb nanostructures. We have investigated rectification effects in a sample application employing these properties. InAs/AlGaSb ballistic rectifiers consisting of two voltage probes and two current injection waveguide structures with a triangular anti-dot or slanted current injection waveguides [1]. In the anti-dot type device, rectification effects relying on the ballistic transport were observed at 77 K and 4.2 K. The voltages, V$_{LU}$ were generated between lower and upper contact of the devices, which have a negative polarity regardless of the sample current polarity. The current-voltage characteristics showed good agreement with calculations from the multi-terminal Landauer-B\"{u}ttiker formula [2]. For the latter device, the introduction of additional waveguide structures to one of the voltage probes facilitated room temperature operation. We report not only on the nonlinear electron transport properties but also on the temperature dependence from 4.2K to room temperature. [1] M. Koyama \textit{et al}., presented at the 28$^{th}$ ICPS, Vienna (2006). [2] A.M. Song, PRB 59, 9806 (1999). [Preview Abstract] |
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R1.00304: Comparison of the Wetting Behavior of Dotriacontane Films Adsorbed on SiO$_{2}$ Surfaces by Physical Vapor Deposition with that of Films Dip-coated in Solution E.A. Cisternas, T. Corrales, V. del Campo, U.G. Volkmann, H. Taub, F.Y. Hansen We have used high resolution ellipsometry and Atomic Force Microscopy (AFM) to compare the structure and morphology of dotriacontane ($n$-C$_{32}$H$_{66}$ or C32) films deposited by two different methods on Si(100) wafers coated with their native oxide. The vapor deposition was done in high vacuum with a substrate temperature below the C32 bulk melting point, while the dip-coated samples were prepared at room temperature. Heating/cooling cycles at a rate of 2 K/min were performed in air on both types of samples and monitored simultaneously by high resolution ellipsometry and stray light intensity measurements to determine the film thickness and roughness, respectively. The samples had a thickness range of 20\textbf{-}160 {\AA} and were optically smooth, but AFM measurements showed the dip-coated films to be less homogeneous and rougher on a nanometer length scale. During the first three heating/cooling cycles, the phase transitions and the wetting behavior of both types of samples differed significantly, particularly as revealed by their stray light intensity. [Preview Abstract] |
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R1.00305: Design and Characterization of Silicon Cantilevers for Use as Force and Torque Sensors Michelle Chabot Using custom-designed cantilevers can significantly improve the sensitivity of many novel measurement techniques such as magnetic force microscopy and micro-torque magnetometry. We have designed custom cantilevers with these specific measurement techniques in mind and fabricated them using standard semiconductor techniques. These cantilevers were characterized in order to determine their sensitivities at room temperature when implemented as either force or torque sensors. The sensitivities far exceed those of commercially available cantilevers. Extensive finite element modeling was performed to predict specific cantilever characteristics such as resonance frequency and mode shapes. [Preview Abstract] |
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R1.00306: The Radiationless Decay Mechanism of Cytosine: An \textit{Ab Initio} Study with Comparisons to the Fluorescent Analog 5-Methyl-2-Pyrimidinone (5M2P) Kurt Kistler, Spiridoula Matsika The radiationless decay mechanism of photoexcited cytosine has been supported by exploring the important potential energy surfaces using multi-reference configuration-interaction \textit{ab initio} methods for the gas-phase keto-tautomer. At vertical excitation the bright state is S$_{1}$ ($\pi \pi $*) at 5.14 eV, with S$_{2}$ (n$_{N}\pi $*) and S$_{3}$ (n$_{O}\pi $*) at 5.29 eV and 5.93 eV, respectively. Minimum energy paths connect the Franck-Condon region to a minimum on S$_{1}$ at 4.31 eV. Two energetically accessible conical intersections with the S$_{0}$ surface are shown to be connected to this minimum: one involves N$^{3}$ distorting in a sofa conformation at 4.27 eV, and the other involves a twisting about the C$^{5}$-C$^{6}$ bond at 3.98 eV. Studies on the fluorescent 5M2P reveal very similar distortions throughout the decay paths of both bases. The different photophysical behavior of the two bases is attributed to energetic differences. Vertical excitation in cytosine occurs at a higher energy, creating more vibrational energy than 5M2P, and the S$_{1}$ minimum for 5M2P is too low to access an intersection with S$_{0}$, causing population trapping and fluorescence. [Preview Abstract] |
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R1.00307: Resistance Memory Switching behavior in MnOx, FeOx, CoOx, and NiOx thin films. Ranju Jung, Sunae Seo, Doungchirl Kim, Chang-won Lee, Inkyung Yoo, SangHoon Kim, Baeho Park We have fabricated the ReRAM(Resistance change Random Access Memory) with some ferromagnetic transition metal(Co, Fe, Mn) oxides materials. Antiferromagnetic NiOx film is well known to show non-volatile resistance switching property. Here, we have studied the relationship between magnetic property and resistance switching properties. We have deposited the MnOx, FeOx, CoOx, and NiOx thin films on Pt/Ti/SiO$_{2}$/Si (111) by using Pulsed Laser Deposition (PLD), and then analyzed the structural properties of these oxides thin films by using X-Ray diffraction (XRD) and Scanning Electron Microscope (SEM), surface properties using Atomic Force Microscope (AFM), and electrical properties using probe station. Every thin film shows poly-crystalline behaviors and reproducible resistance switching behaviors. We have performed the temperature-dependent electrical property measurement across the Neel temperature. [Preview Abstract] |
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R1.00308: Switching behaviors of Co nanorings in the current-perpendicular-to-plane configuration T. Yang, A. Hirohata, M. Hara, T. Kimura, Y. Otani We fabricated current-perpendicular-to-plane pseudo-spin-valve (CPP PSV) nanopillars comprising a thick and a thin Co rings with deep submicron lateral sizes. The dc current can effectively induce the flux-closure vortex states in the rings with desired chiralities. Abrupt transitions between the vortex states are also realized by the dc current and detected with the giant magnetoresistance (GMR) effect, which are interesting on such technological applications as magnetic random access memory(MRAM) . Both the Oersted field and the spin-transfer torque are found important to the magnetic transitions. They can be designed to cooperate with each other in the vortex-to-vortex transitions by carefully setting the chirality of the vortex state in the thick Co ring. Detailed results on the magnetic switching behaviors induced by both the DC current and the in-plane external field will be presented. [Preview Abstract] |
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R1.00309: A challenge to develop a continuous centrifuge for precision particle size fractionation Jun-ichi Kawahara, Yoichiro Ito In producing particles, including nanoparticles, of narrow particle size distribution, synthetic methods have been widely used, since considerable amounts of products could rather simply be obtained. On the other hand, such sort of processes have a significant drawback, since applicable range of materials is rather limited. Under such circumstances, we have started to develop a continuous centrifuge for precision particle size fractionation, which could be applied, in principle, to any material, in stark contrast to synthetic processes. Besides, continuous systems could realize not only considerable processing capacity but also the exact particle sizes we want, in contrast to batch systems. Furthermore, since such methodology is based upon principles completely different from those of synthetic processes, it could complement them, by further sharpening the size distribution of the products, for example. We chose liquid phase as separation medium, since it enables high processing capacity and also suppresses the possible aggregation of the particles. At present, there are no continuous particle size fractionation systems in liquid phase applicable to the size range below several micrometers. The designs to widen this range down to submicrometers and further, together with realization of high resolution, are to be discussed. [Preview Abstract] |
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R1.00310: Effect of annealing temperature on microstructure and optical properties of ZnO thin films prepared by sol-gel method. Idris Sorar, Fatma Z. Tepehan, Galip G. Tepehan Transparent ZnO thin films were prepared on corning 2947 substrates by sol-gel spin coating method. ZnO films were annealed for 1 hour at 100, 250, 350 and 550$^{\circ}$C. These temperatures were determined from TGA results. Effect of annealing temperature on microstructure and optical properties were investigated. Optical properties of the films were determined by an NKD spectrophotometer and their structural properties were investigated by an X-ray diffractometer and atomic force microscopy. All ZnO thin films were highly transparent and had Rms values 7.497, 1.158, 0.528 and 3.287 nm for annealing temperatures of 100, 250, 350 and 550$^{\circ}$C, respectively. [Preview Abstract] |
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R1.00311: On-line Monitoring of Ultrasonic Polymer Chain Scission Ali Aky\"uz, Ahmet Giz, Huceste \c{C}atalgil-Giz Poly vinyl pyrrolidone in dilute aqueous solution was subjected to ultrasonic scission. The decrease of the molecular weight was monitored by light scattering via a BIMwA molecular weight analyzer. The on-line data was compared with the theoretical models of Schmid, Malhorta, Price, Madras and Berlin, Doulah,. The models were compared on the bases of $\chi ^{2}$ analysis and fit quality. It is seen that on-line data can discriminate among theoretical models. [Preview Abstract] |
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R1.00312: The design of an antireflective filter using TiO$_2$--ZnO and TiO$_2$ thin films Dursen Saygin Hinczewski, Michael Hinczewski, Idris Sorar, Fatma Z. Tepehan, Galip G. Tepehan In the present work, we designed an antireflective filter for the visible region composed of TiO$_2$ and ZnO--TiO$_2$ thin films. Initially, single layers of the films were coated on both sides of the substrate using the sol-gel spin coating method. UV--visible spectroscopy was used to measure the transmittance and reflectance of the films. The thicknesses, refractive indices and extinction coefficients were determined by fitting to a modified Tauc-Lorentz model. Having determined the appropriate film thicknesses and refractive indices needed for an antireflective filter in the desired wavelength region, the single layers were combined to build the filter. The theoretical model of Ref.[1], which accounts for the densification occurring during the construction of the multilayer stack, was adapted to extract the optical properties of the individual layers in the stack, which were then compared to the single layer results. [1] D. Saygin Hinczewski, M. Hinczewski, F.Z. Tepehan and G.G. Tepehan, Solar Energy Materials and Solar Cells 87, 181 (2005). [Preview Abstract] |
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R1.00313: Diffuse scattering study of the elastic effect on thin polystyrene films at melt Youngsuk Byun, Daeyong Eom, Young-Joo Lee, Heeju Lee, Sanghoon Song, Hyunjung Kim, Zhang Jiang, S.K. Sinha We have measured x-ray diffuse scattering of thin polystyrene films at melt. We carried out the measurements with varying thicknesses and molecular weights as a function of temperature. We observed a deviation from conventional capillary wave theory for viscous liquids when the film thickness is close to the radius of the polymer. We shall discuss the deviation and modification of liquid theory with the model considering elastic effect. [Preview Abstract] |
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R1.00314: X-ray scattering studies of surface and pore morphologies on nanoporous organosilicate films Jeeun Kim, Heeju Lee, Youngsuk Byun, Sanghoon Song, Hyunjung Kim, Sungkyu Min, Taehoon Lee, Gunwoo Park, Heewoo Rhee, Gwangwoo Kim, Xuefa Li, Jin Wang We have studied surface and pore morphologies and structure of nanoporous organosilicate films. We have employed the grazing incidence small angle x-ray scattering (GISAXS) and x-ray reflectivity (XRR) for characterizing the pore size distribution, shape, porosity, and electron density, roughness, respectively. We have measured in situ the pore morphologies depending on the types of porogens, loading densities along the pore generation process. The results will be discussed with the mechanical properties for finding the optimized condition for low dielectric constant. [Preview Abstract] |
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R1.00315: Relation between structural, electronic, and magnetic properties in ferromagnetic (Ga,Fe)N A. Bonanni, C. Simbrunner, T. Li, M. Wegscheider, M. Quast, A. Navarro-Quezada, M. Kiecana, M. Sawicki, H. Przybylinska, R. Jakiela, T. Dietl In order to shed light on the origin of high temperature ferromagnetism observed in magnetically doped semiconductors and oxides, we have undertaken comprehensive studies of MOCVD grown (Ga,Fe)N, which combine a detailed space-resolved chemical analysis by TEM and EDS with a thorough magnetic, optical, and electric characterization. Our results, partly presented in cond-mat/0612200, reveal the presence of coherent nanocrystals, presumably Fe$_{x}$N, with the composition and lattice parameter imposed by the GaN host. Their presence and their non-uniform distribution over the film volume affect in a decisive way the magnetic, optical, and transport properties of the films. We find, in particular, ferromagnetic signatures such as spontaneous magnetization, which persist well above room temperature and whose magnitude increases with the Fe concentration above the solubility limit. We explain these observations in terms of a high blocking temperature associated with magnetic- and shape-anisotropy of the Fe$_{x}$N nanocrystals. [Preview Abstract] |
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R1.00316: The structure and dynamics of thin poly(styrene)-b-(polybutadiene) copolymer films studied by x-ray scattering Sanghoon Song, Youngsuk Byun, Jeeun Kim, Daeyong Eom, Wonsuk Cha, Hyunjung Kim We have investigated the structure and dynamics of thin diblock copolymer films of poly(styrene)-b-poly(butadiene) using x-ray reflectivity, diffuse scattering, grazing incidence small angle scattering (GISAXS), and x-ray photon correlation spectroscopy (XPCS), respectively. The measurements were performed at temperatures below and above the order-disorder transition temperature (ODT) of bulk with different film thicknesses. The x-ray reflectivity and GISAXS results show that the structural changes appear at lower temperature than ODT of bulk. These results will be discussed with the findings from the XPCS. [Preview Abstract] |
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R1.00317: ABSTRACT WITHDRAWN |
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R1.00318: EuPd$_{3}$ ultrathin layers on MgO(001) Pawel Maslankiewicz, Zbigniew Celinski, Jacek Szade Ultrathin layers (0.8 -- 4 nm thick) of EuPd$_{3}$ intermetallic compound were grown on MgO(001) substrates by molecular beam epitaxy from elemental sources. In-situ X-ray photoelectron spectroscopy studies revealed a dominant trivalent europium component, in agreement with available data on bulk EuPd$_{3}$ (e.g. [1, 2]). As demonstrated by reflection high energy electron diffraction and X-ray photoelectron spectroscopy, growth by co-deposition at elevated temperature ($\sim $500 \r{ }C) or post-growth annealing of Pd/Eu/Pd layers resulted in formation of islands. Formation of EuPd$_{3}$ occurs at lower temperatures. Trivalent europium at Pd layers interface was observed even at room temperature. 250 \r{ }C is sufficient to form EuPd$_{3}$ from individual Pd and Eu layers. [1] I.R. Harris, G.V. Raynor, J. Less-Common Met. \textbf{9}, 263 (1965). [2] W.-D. Schneider, C. Laubschat, I. Nowik, G. Kaindl, Phys. Rev. B, Condens. Matter \textbf{24}, 5422 (1981). [Preview Abstract] |
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R1.00319: The physics of magnetic resonance in the proximity of energy instability Michael Pechan, Chengtao Yu, Ryan Bennett, Jordan Katine, Liesl Folks, Matthew Carey We are investigating the magnetization dynamics of a ferromagnetic system in the proximity of an unstable equilibrium. The test system utilized is permalloy in thin film and nano-scale dot geometries with the magnetization along the film normal at fields close to saturation (4$\pi $M$_{eff})$. For sub-critical fields (H$_{appl.}$ = 4$\pi $M$_{eff})$, the magnetization equilibrates at some angle $\theta $, but has no energy minumum in the azimuthal angle $\phi $, therefore no resonance condition exists. Slight misalignment of the field removes the degeneracy in $\phi $ resulting in an energy minimum in both the $\theta $ and $\phi $ directions. This produces finite resonances at sub-critical fields. This sub-critical energy minimum resembles an asymmetrical `bowl' that changes shape with field and misalignment angle. We model measured frequency/field dispersion curves in terms of the Landau-Lifshitz equations of motion about the equilibrium position and interpret the results in terms of the `bowl' geometries. We also explain the observance of a local minimum, close to 4$\pi $M$_{eff}$, resulting in the three resonances in a constant frequency/swept field scan. [Preview Abstract] |
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R1.00320: Phase Transformation of Self-Assembled Nanostructure of PS-P2VP/HAuCl4 Hybrid System Chi-An Dai, Chun-Jie Chang, Yi-Huan Lee, Wei-Fang Su In this study, we investigated the effect of the addition of chloroauric acid (HAuCl4) in polystyrene-b-poly (2-vinyl pyridine) (PS-P2VP) on the morphology and phase transformation of the mixture system. Nanosturcture of ordered array of spheres, cylinders, gyroids, lamellae as well as different shapes of micellar phases of the system can be obtained by choosing appropriate PS-P2VP diblock copolymer, by changing molar ration of the gold salt to the copolymer, and by choosing different solvents. The phase diagram of the hybrid system are determined and related to intermolecular interactions on nano- and mesoscopic scale. The self-assembled nanostructure is characterized by TEM, WAXS and SAXS. [Preview Abstract] |
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R1.00321: Magnetic anisotropy in Iron-phosphate crystal RbNa$_{3}$Fe$_{7}$(PO4)$_{6}$ Chengtao Yu, Michael Pechan, Wendy Queen, Shiou-Jyh Hwu, Lei Wang Low dimensional iron-phosphate single crystal RbNa$_{3}$Fe$_{7}$(PO4)$_{6}$ has been synthesized using high temperature methods in molten-salt media. The crystal consists of FeO$_{n}$ polyhedra chains (direction a), bridged via the long oxygen band of the polyhedra and the PO$_{4}$ tetrahedra to form a three dimensional framework. Magnetic properties of the compound have been investigated down to 2 K. Both susceptibility and magnetization as function of temperatures indicate the compound is paramagnetic at high temperatures and has a ferromagnetic phase transition around 15K. Magnetization loops at low temperatures show large coercivities and saturation fields. For example, the coercive fields at 2 K are about 1.5 and 1.6 Tesla along and perpendicular to the chain direction, respectively. The magnetic loops also reveal that the chain direction is the magnetic easy axis, though the sample cannot be completely saturated even at a maximum field of 9 Tesla. Magnetic torque measurements show that the sample possesses uniaxial anisotropy with magnetic easy axis in the chain plane and hard axis perpendicular to the chain plane. [Preview Abstract] |
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R1.00322: Coherent Transport on Carbon Nanotube Junctions under a Magnetic Field Monica Pacheco, Luis Rosales, Zdenka Barticevic, Claudia Rocha, Andrea Latge In this work we study the effects of a magnetic field on the electronic and transport properties of different carbon-nanotube based heterostructures (CNHs) like single junctions and single and double quantum dots [1]. All of them are formed by joining two zigzag tubes using a single pentagon-heptagon pair defect. Emphasis is put on the analysis of the local density of states (LDOS), the conductance, and on the characteristic curves of current versus voltage of the CNHs. We described the system by means of a tight-binding Hamiltonian and the LDOS is calculated using real-space renormalization techniques [2]. The conductance is calculated using the Landauer formula in the Green functions formalism and the characteristic curves of current is calculated numerically through the Landauer- B\"{u}ttiker formalism. All the Green functions are obtained numerically and the effects of the magnetic field are described within the Peierls phase approximation. [1] L. Rosales, C. Rocha, A. Latg\'{e}, M. Pacheco and Z. Barticevic, cond-mat/0611380, submitted to Phys. Rev. B (2006). [2] M. Ferreira, A. Latg\'{e}, R. Muniz, T. Dargam, Phys. Rev. B 62, 16040 (2000). [Preview Abstract] |
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R1.00323: The Effect of Ligands on the Unoccupied Density of States in Mn12 Acetate Molecular Magnets: An X-ray Absorption Near-Edge Study Nadia Leyarovska, Monica Soler, George Christou, Carlo Segre, Jeff Terry Mn K-edge x-ray absorption spectra have been collected from three different samples of the Mn Acetate family of Single Molecule Magnets (SMM). The XANES region of the spectra shows large differences due to the presence of Mn ions of different oxidation state ( II, III, IV ) and different ligand environment. Self-consistent calculation of the local density of states (LDOS) and the x-ray absorption coefficient of the above samples were performed and compared to experimentally measured near edge absorption spectra (XANES). The good agreement between the calculated and measured absorption coefficient in the preedge and near edge regions for the three compounds with different ligand environment gives an opportunity for systematic correlation between the electronic and magnetic properties of this rapidly developing class of nanomagnets. [Preview Abstract] |
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R1.00324: Magnetic and Higher Order Lattice Excitations in LaFe(1-x)Cr(x)O(3) Perovskites Jakob Andreasson, Joakim Holmlund, Mikael K\"all, Lars B\"orjesson, Christopher S. Knee, Benjamin Schulz, Michael R\"ubhausen, Sten G. Eriksson The resonance behavior of the oxygen breathing mode at 700 cm(- 1) and its higher orders is studied between 1.8 eV (676 nm) and 4.2 eV (300 nm) in the perovskite LaFe(0.5)Cr(0.5)O(3). The Franck-Condon induced higher order scattering present in the x=0.1, 0.5 and 0.9 compounds dominates the Raman spectrum in the visible energy region while a feature in the 1400 cm$^{-1}$ energy region dominates using UV lasers. The energy location of this peak coincides both with the second order Franck-Condon mode as well as similar feature seen in the x=0 and 1 compounds (and to some extent in the low doping compounds (x=0.02, 0.04, 0.06 and 0.08)) using the 2.41 eV ($\lambda $=514) laser, believed to be a two-magnon caused by a spin-flip excitation in the AFM spin-state. Thus the complex magnetism in the Fe/Cr perovskite is likely to be influenced by the competition between the magnetically ordered state and the lattice dynamics through the resonant Franck- Condon effect. [Preview Abstract] |
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R1.00325: $^{11}$B Nuclear Magnetic Resonance Measurements of Antiferromagnetic HoB$_{4}$ Single Crystals J.H. Kim, B.J. Mean, K.H. Kang, I.N. Hyun, S.K. Kwon, S.K. Nam, S.H. Choi, S.H. Kim, Moohee Lee, B.K. Cho, J.H. Cho $^{11}$B nuclear magnetic resonance (NMR) measurements have been performed on single crystals of HoB$_{4}$ to investigate local electronic structures and $4f$ spin dynamics. $^{11}$B NMR spectrum, Knight shift, spin-lattice and spin-spin relaxation rates were measured in the temperature range of 3.5 - 300 K under magnetic field of 8 T. $^{11}$B NMR shift and linewidth are huge and strongly temperature-dependent due to $4f$ moments of Ho. The spin-lattice relaxation rate $1/T_{1}$ is independent of temperature above $T_{N }$=8 K whereas it decreases significant below $T_{N}$ indicating huge suppression of $4f$ spin fluctuation. Also the spin-spin relaxation rate $1/T_{2}$ shows similar behavior characteristic of $4f$ electronic spin dynamics change associated with antiferromagnetic ordering. [Preview Abstract] |
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R1.00326: Structural and Energetic Study of PtxPd98-x Nanoparticles Alvaro Posada-Amarillas, Dora Julia Borb\'on-Gonz\'alez, Lauro Oliver Paz-Borb\'on, Roy L. Johnston Cluster structure, composition and degree of mixing or segregation all play important roles in determining the physical and chemical properties of bimetallic nanoparticles such as PtPd, which are currently the subject of intense research mainly due to their important catalytic properties. In this work we present an exhaustive study of the structure and energetic of PtxPd98-x nanoparticles, obtained by a Genetic Algorithm which incorporates the Gupta potential for bimetallic atoms. Excess energy and stability function indicate that the most stable configurations correspond to those compositions approximately with 50 \% Pd and 50\% Pt atoms. Segregation is observed for the lowest energy structures meanwhile mixing is predominant for disordered higher energy nanoparticles. [Preview Abstract] |
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R1.00327: $^{11}$B Nuclear Magnetic Resonance Measurements of Antiferromagnetic DyB$_{4}$ Single Crystals I. N. Hyun, B. J. Mean, K. H. Kang, J. H. Kim, S. K. Kwon, S. K. Nam, S. H. Choi, S. H. Kim, Moohee Lee, B. K. Cho, J. H. Cho $^{11}$B pulsed nuclear magnetic resonance (NMR) measurements have been performed to investigate local electronic structures and $4f$ spin dynamics in antiferromagnetic DyB$_{4}$ single crystals. $^{11}$B NMR spectrum, Knight shift, spin-lattice and spin-spin relaxation rates, $1/T_{1}$ and $1/T_{2 }$, were measured down to 4.3 K under magnetic field of 8 T. The $^{11}$B NMR shift and linewidth are huge and strongly temperature-dependent due to $4f$ moments of Dy. In addition, both are proportional to magnetic susceptibility, indicating that the hyperfine field at the boron site originates from the $4f$ spins of Dy. Below$ T_{N}$ =20 K. the single broad resonance peak of $^{11}$B NMR splits into several peaks reflecting the local magnetic fields developed due to the antiferromagnetic spin arrangement. The relaxation rates $1/T_{1}$ and $1/T_{2}$ are very large and independent of temperature much above $T_{N}$ and then decrease significantly below $T_{N }$ confirming the suppression of spin fluctuation and the huge change in $4f$ spin dynamics associated with the antiferromagnetic ordering. [Preview Abstract] |
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R1.00328: Nonclassicality and decoherence of photon-subtracted squeezed states Asoka Biswas, Girish S. Agarwal Single-photon subtracted squeezed vacuum states are equivalent to Schrodinger kitten states and show non-Gaussian nature in phase space. Such states are useful in entanglement distillation, loophole-free test of Bell's inequality, and quantum computing. We discuss nonclassical properties of these states in terms of the sub-Poissonian statistics and the negativity of the Wigner function. We derive a compact expression for the Wigner function from which we find the region of phase space where Wigner function is negative. We find an upper bound on the squeezing parameter for the state to exhibit sub-Poissonian statistics. We then study the effect of decoherence on the single-photon subtracted squeezed states. We present results for two different models of decoherence, viz. amplitude decay model and the phase diffusion model. In each case we give analytical results for the time evolution of the state. We discuss the loss of nonclassicality as a result of decoherence. We show through the study of their phase-space properties how these states decay to vacuum due to the decay of photons. We show that phase damping leads to very slow decoherence than the photon-number decay and the state remains nonclassical at long times. [Preview Abstract] |
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R1.00329: Donor impurities in elliptic quantum disks: magnetic-field effects Zdenka Barticevic, Monica Pacheco, Pablo Ulloa We present a theoretical study of the optical energy spectrum of donor impurities in elliptic semiconductor quantum disks in the presence of magnetic fields. We work in the framework of the effective mass theory adopting a model of parabolic bands, valid for donor impurities in the majority of the semiconductors III-V. We calculate the energy spectrum and binding energies of donor impurities by assuming high geometrical confinement along the quantum disk growth direction, and a lateral confinement modeled by a parabolic potential of elliptic geometry. We study the effects of the loss of the cylindrical symmetry of the lateral potential on the energy spectrum and binding energies of impurities located in different positions in the quantum disk. We found that the presence of a uniform magnetic field perpendicular to the quantum disk induces remarkable changes in the energy spectrum of the confined impurity. By changing the magnitude of the field it is possible to obtain and to modify, in a wide range of energies, different impurity optical transitions in the quantum disk. [Preview Abstract] |
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R1.00330: ABSTRACT WITHDRAWN |
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R1.00331: A new UV femtosecond pulse shaper for controlling organic photochemistry Dorian Parker, Abigail Nunn, Kiera Jones, Helen Fielding We present a femtosecond pulse shaper that operates in the UV. Using a dual array 640 pixel SLM within a reflective mode 4-f configuration, visible light at 508nm is shaped and subsequently doubled in a SHG crystal to give shaped light in the UV at 254 nm. This device is to be used in a pump probe scheme with a constrained feed back optimisation to coherently control benzene S1 photochemistry in order to reach ground state fulvene. [Preview Abstract] |
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R1.00332: Switching and negative differential resistance in a gated single-molecule transistor: Effects of fixed and shifting states Amir Farajian, Rodion Belosludov, Hiroshi Mizuseki, Yoshiyuki Kawazoe, Tomihiro Hashizume, Boris Yakobson The quantum transport in a gated nanodevice based on polythiophene is studied. The functional polythiophene molecule is attached to two gold electrodes which are used as drain and source contacts. A third electrode, assumed to act as gate, is considered to shift the energy levels of the functional molecule. We use density functional theory to obtain the self- consistent electronic structure of the system under bias. The electronic structure is then used within the nonequilibrium Green's function approach to calculate conductance and current- voltage characteristics. We show that this molecular field effect transistor possesses two the of the main features of electronic components, namely abrupt switching and negative differential resistance. Ab- initio based explanations of these features are provided by distinguishing fixed and shifting conducting states, which are shown to arise from the interface and functional molecule, respectively. Optimization of the device characteristics by choosing proper bias range and doping is also discussed. [Preview Abstract] |
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R1.00333: Hydrogen inside fullerene nanocage Olga Pupysheva, Amir Farajian, Boris Yakobson We model fullerene nanocages filled with hydrogen using density functional theory. Stability of such endohedral complexes is studied depending on the amount of encapsulated hydrogen. It is shown that some of the hydrogen atoms can be chemisorbed on the inner surface of the nanocage. The mechanism of cage breaking is investigated by ab initio molecular dynamics simulations, and the hydrogen chemisorption, which weakens the fullerene C-C bonds, is proved to play the key role in this process. We also discuss the mechanical properties of fullerene nanocage and find the internal hydrogen pressure on the nanocage. [Preview Abstract] |
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R1.00334: Aggregation and electrorheology in nanotube suspensions under applied electric field Amir Farajian, Olga Pupysheva, Howard Schmidt, Boris Yakobson We consider the electrostatic response, i.e., polarization, mutual interactions and aggregation, of the nanotubes in solution under applied electric field. We model the nanotubes as rigid cylindrical rods with hemispherical ends. The surface charge densities of the nanotubes are obtained by solving an integral equation numerically. The calculated charge densities are then used to derive the interaction energies of the nanotubes with the applied field, as well as among each other. In addition to the electrostatic response, this would be a reasonable estimate of the radio-frequency (RF) electrodynamic response, as the RF wavelength is typically much larger than the nanotubes lengths. Our results show that nanotubes alignment with the electric field is very sensitive to their diameter. Nanotubes with larger diameters, e.g. multiwall or bundles, can overcome Brownian aggitation of the solvent molecules more effectively. The semiconducting nanotubes response is around two orders of magnitude lower than that of the metallic ones. The response is also proportional to the square of the applied field. The conditions for chain-like aggregation of the nanotubes are also explored using our results. We find that the calculated rupturing forces provide an estimate for the yield stress, which is in qualitative agreement with experimental results. [Preview Abstract] |
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R1.00335: Slow Modes in Dynamic Light Scattering of Hydroxypropylcellulose---Comparison to Fluorescence Photobleaching Recovery. Derek Dorman, Paul Russo, Young-wook Choi Less is understood of semidilute solutions than dilute solutions of macromolecules. As concentration increases, multiple decays rates are observed. This multimodal phenomena of 1 MDa hydroxypropylcellulose was investigated using dynamic light scattering and fluorescent photobleaching recovery. The resulting decays were fitted using two exponential fits and CONTIN. Several gammas and amplitudes were obtain with each CONTIN fit but the two with the highest amplitude were determined to be the gammas of interest---a fast and slow mode. FPR data, using a two exponential fit, also exhibited a fast and slow mode. The two experimental techniques were compared to elucidate the dynamic behavior of semidilute hydroxypropylcellulose. [Preview Abstract] |
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R1.00336: Electron Energy Loss Spectroscopy study of surface plasmon resonances in noble metal nanostructures. Shaul Aloni Nobel metal nanostructures are of great interest because of their unique optical properties. Their optical properties are determined by the surface plasmon resonance of conduction electrons, the frequency of which is determined not only by the nature of the metal or alloy of which the particle is made but also by the particle's size and shape. Moreover, the properties can be further tailored by forming nanoparticle assemblies and by controlling the surrounding dielectric medium We focus on study of the shape effects of the plasmonic excitation in silver and gold nanostructures.The silver and gold nanostructures were synthesized by solution phase synthesis yielding highly faceted nanocrystals including cubes triangular plates bi-pyramids and rods of aspect rations up to 1:20. The results show that the optical properties of individual metallic nanoparticles, as extracted from the low-loss spectrum, can be correlated with the properties predicted based on the particle size, shape and composition. . [Preview Abstract] |
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R1.00337: Wetting morphologies on chemically nanopatterned surfaces Antonio Checco, Oleg Gang, Benjamin M. Ocko We study the wetting of simple, volatile liquids on model chemical nanopatterns created using Local Oxidation Nanolithography. This technique makes use of a biased, metallic AFM tip to locally oxidize the methyl-terminations of a self-assembled monolayer (octadecylthrichlorosilane) into carboxylic acid termination[1]. With this method we have realized parallel, 50 to 500 nm wide, wettable stripes (carboxylic) embedded into a non-wettable (methyl) surface. Several organic (polar, non-polar), volatile liquids have been condensed onto the wettable stripes and the resulting droplet morphologies have been studied in-situ by using an environmental AFM. We show that close to saturation and for droplet thickness less than 10 nm long-range forces are relevant to the nanoliquid shape. These results are well described by Density Functional Theory assuming dispersive molecular interactions. In addition, we explore the dynamics of condensation/evaporation of the liquid nanodrops. [Preview Abstract] |
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R1.00338: Thermoelectric Properties of Nanotube Junctions Keivan Esfarjani, Leif Poorman We calculate the thermoelectric properties of several kinds of carbon nanotube junctions using the Landauer formalism. Several junction geometries are considered, including end-to-end, side-by-side, and crossed tubes. All of these geometries should be present in nanotube mats. [Preview Abstract] |
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R1.00339: Carbon Nanotubes as Nucleobase Sensors Leif Poorman We compute the conductance change of a carbon nanotube when one nucleobase is adsorbed. Different bases cause similar, but potentially distinguishable, conductance changes. We discuss possible applications of this effect in DNA sequencing. [Preview Abstract] |
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