Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session S1: Poster Session III (1-4:00pm): Polymer Physics II; Phase Transitions; General Theory; Insulators and Dieletrics; Semiconductors; Supplementary Abstracts; Post-Deadline Abstracts |
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Room: Exhibit Hall A |
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S1.00001: POLYMERIC AND ORGANIC MATERIALS II |
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S1.00002: Transmission Ellipsometry and X-Ray Studies on Shear Induced Order in iPP/CNT Nanocomposites Yaniel Cabrera, Georgi Georgiev, Lauren Wielgus, Bret Stenger, Robert Judith, Peggy Cebe Polymer Carbon Nanotube Composites (PCNs) are the largest commercial application of carbon nanotubes (CNT) in the field of nanotechnology. Isotactic Polypropylene (iPP) is one of the best model systems to study in this field because iPP/CNT PCNs can form alpha, beta, and gamma crystallographic phases under a variety of crystallization conditions such as nonisothermal and isothermal melt crystallization, or application of shear. We prepared iPP/CNT nanocomposites from solution, by co- precipitation from a non-solvent. Films were made by compression molding, with 0.01 - 5.0 wt.{\%} CNT. The morphological structure and the orientation of the crystals, and the impact of CNT on the crystallization kinetics, were evaluated using transmission ellipsometry, wide angle X-ray scattering, and differential scanning calorimetry. CNTs increase the nucleation rate for crystal formation. Ability of the CNTs to promote the formation of smectic phases in iPP will be discussed. [Preview Abstract] |
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S1.00003: Structure and applications of nanohybrid shish-kebabs Eric D. Laird, Bing Li, Christopher Y. Li We describe some of the noteworthy aspects of ``nanohybrid shish-kebabs'' (NHSKs). NHSKs are nanostructures of polymer lamellar single-crystal patterned in regular spacings (a few tens of nm) along carbon nanotubes. These novel composite materials are named for their resemblance to the classical shish-kebab structures observed in polymers crystallized in a shear flow. Morphology and growth mechanisms will be discussed: NHSK can be either 2- or 3-dimensional, and tuning of kebab diameters and spacing is made possible by careful control of the growth conditions. For single walled carbon nanotubes decorated with polyethylene, kebab diameters can be tuned through processing conditions to range from 40-250 nm. This method of functionalization demonstrates adhesion superior to that of most other noncovalent methods. The unique nanoarchitecture of NHSK creates opportunities for a wide variety of novel devices and improvements to existing technology. Thick films of these novel hybrid structures were fabricated by a simple vacuum filtration methods. Their application to electronics and chemical detection will be discussed. [Preview Abstract] |
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S1.00004: Dielectric Relaxation of PVDF/STN Nanocomposites Lei Yu, Peggy Cebe Dielectric relaxation behavior of poly(vinylidene fluoride), PVDF, with Lucentite$^{TM}$ STN nanoclay was investigated over the frequency range from 20 Hz to 1MHz. Lucentite$^{TM}$ STN synthetic nanoclay is based on hectrite structure with an organic modifier contained between the hectrite layers. Composition of the PVDF/STN nanocomposites ranged from 0{\%}-10{\%} STN by weight. Wide angle X-ray and Fourier transform infrared spectroscopy results are consistent with the conclusion that pure alpha phase is formed in PVDF film while STN 1{\%} sample contained majority beta phase, and a tiny amount of alpha phase. When the STN content increased to 5{\%} and 10{\%} only the beta phase was observed. The $\alpha _{a}$ (glass transition) and $\alpha _{c}$ (crystalline) relaxation rates were plotted against the reciprocal of temperature, respectively. The dielectric result shows that the relaxation rate of the $\alpha _{a}$ relaxation, related to the motions of amorphous polymer chains, is increased by the addition of STN. However, the activation energy for the $\alpha _{c}$ relaxation, related to motions of the crystalline chains, remained unchanged with STN addition. A mechanism is proposed to interpret the relative position and interaction between PVDF chains and STN [Preview Abstract] |
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S1.00005: Nanocomposites of Poly(vinylidene fluoride) with Multiwalled Carbon Nanotubes Wenwen Huang, Kyle Edenzon, Luis Fernandez, Shabnam Razmpour, Jenna Woodburn, Peggy Cebe We report the preparation and characterization of nanocomposites of poly(vinylidene fluoride) (PVDF) with mutiwalled carbon nanotubes (MWCNT) with a wide composition range, from 0.1 {\%} to 5.0 {\%} MWCNT by weight. Effect of uniaxial orientation by zone drawing is discussed and compared with unoriented compression molded films. Room temperature two-dimensional wide angle X-ray scattering and Fourier transform infrared spectroscopy were used for phase identification. Differential scanning calorimetry, dynamic mechanical analysis, and thermogravimetic analysis were used to study the thermal properties. Results indicate that: 1) incorporation of MWCNT in PVDF induces a small portion of beta phase crystal in the PVDF/MWCNT bulk films, while zone drawing causes a significant alpha to beta transition; 2) the thermal stability and mechanical properties are improved when MWCNT concentration increases; 3) The glass transition temperature does not change with MWCNT concentration, but a higher glass transition can be obtain by zone drawing. [Preview Abstract] |
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S1.00006: Electrical/dielectric properties and conductivity mechanism of epoxy/expanded graphite composites Athanasios Kanapitsas, Emmanuel Logakis, Christos Pandis, Polycarpos Pissis, Natasa Jovic, Vladimir Djokovic In this work the electrical and dielectric properties, as well as the temperature dependence of the electrical conductivity of epoxy/expanded graphite (EG) composites, are studied by employing dielectric relaxation spectroscopy (DRS). For the preparation of the composites EG was sonicated in acetone for 10h and then the appropriate amount of epoxy resin added to the mixture. The sonication was prolonged for another 3 h. The mixture was dried at 60$^{\circ}$C for a few hours and then the appropriate amount of hardener (triethylenetetramine) was added followed by mechanical stirring for 15 min. Finally, the mixture was cast in a glass mould and outgassed overnight at room temperature. Before they were removed from the mould, all samples were post-cured at 127$^{\circ}$C for 10 min in air. Samples with EG weight fractions ranging from 0 to 8 wt.{\%} were produced. Preliminary DRS results at room temperature indicate that electrical percolation threshold (p$_{c})$ lies between 3-5 wt.{\%} EG. The influence of the EG fillers (for concentrations below p$_{c})$ on the dielectric relaxation mechanisms of the epoxy matrix, as well as the conductivity mechanism (for concentrations above p$_{c})$ are investigated. [Preview Abstract] |
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S1.00007: Effect of interaction on the exfoliation and dispersion of a stack of platelets in a dynamic polymer matrix and solvent particles by a coarse-grained Monte Carlo simulation Barry Farmer, Ras Pandey We consider a stack (layer) of four sheets in host matrix of mobile polymer chains and solvent particles and study their exfoliation and dispersion on a discrete lattice. Sheets and chains are created by tethering particles (nodes) by the bond-fluctuation mechanism. Each component interacts and executes their stochastic motion via Metropolis algorithm. Entropic constraints (excluded volume and entanglement [1]) play a critical role in a relatively dense matrix. Therefore, the density of these constituents and their molecular weight are carefully selected to make this study feasible. Exfoliation of the sheets is examined by varying the interactions among different components, i.e., solvent particles, polymer chains, and platelets. The relaxation time for dispersion in the self-organizing dynamic mixture increases on increasing the molecular weight. Exfoliation ceases in a matrix with chains beyond a certain length. [1] R.B. Pandey and B.L. Farmer, J. Polym. Sci. Part B 46, 2696 (2008). [Preview Abstract] |
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S1.00008: Creating Janus Particles on Polymer Templates Marla McConnell, Matthew Kraeutler, Shu Yang, Russell Composto Gold nanoparticles and their unique optical properties have been the topic of many recent research efforts. These optical properties are associated with the collective oscillations of conduction band electrons, and can be tuned in the visible range by changing the size and shape of the particles. In this study, we assembled spherical gold nanoparticles (13 nm in diameter) on spherical amine-modified silica particles (100 nm - 800 nm), which were covalently linked to a polymeric surface. Because gold has a strong affinity for amines, the modified silica particles served as an ideal template for assembling the gold nanoparticles. By varying the diameters of the silica particles, it is possible to tune the separation between the gold particles, resulting in a change in optical response. Once the gold nanoparticles are attached to the silica spheres, they can be sintered. This technique produces janus particles, because the gold nanoparticles are localized to the top su! rface of the silica particles, due to shadowing. [Preview Abstract] |
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S1.00009: Mechanical Properties of Organized Microcomposites Fabricated by Interference Lithography Srikanth Singamaneni, Sehoon Chang, Ji-Hyun Jang, Whitney Davis, Edwin Thomas, Vladimir Tsukruk We demonstrate that organized, porous, polymer microstructures with continuous open nanoscale pores and sub-micron spacings obtained via interference lithography can be successfully utilized in a highly non-traditional field of ordered microcomposites. Organized microcomposite structures are fabricated by employing two independent strategies, namely, capillary infiltration and in situ polymerization of the rubbery component into the porous glassy microframes. The mechanical properties and ultimate fracture behavior of the single and bicomponent microframes are investigated at different length scales. The ordered single and bi-component microstructures with high degree of control over the microscopic organization of the polymeric phases result in excellent mechanical properties. Combining hard and soft polymer components provides multifunctional materials and coatings with synergetic properties and is frequently utilized for design of advanced polymeric composites. [Preview Abstract] |
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S1.00010: Diamond-shaped small-angle scattering and the deformation of fibrous textures Wenjie Wang, N. Sanjeeva Murthy Small-angle x-ray scattering from materials with fibrous texture are typically characterized by intense diamond-shaped equatorial streaks. Single family of elongated voids aligned along the fiber axis modeled as ellipsoids with a certain orientation distribution yield a fan-like 2D pattern. The diamond-shaped patterns from fibers, such as polyesters, polyamide 6 and polyacrylonitrile, could not be explained with such single class of misoriented voids. Analysis of the orientation distribution and the isointensity contours suggest that there are at least two distinct entities that contribute to this equatorial scattering. Voids with larger cross section ($\sim $ 20 nm dia.), which are likely to be in the interfibrillar regions, give rise to low-q contours with smaller eccentricities and respond poorly to deformation. Entities with smaller cross section ($\sim $ 5 nm dia.), which are likely to be in the intrafibrillar regions, give rise to high-q contours with larger eccentricities and respond to deformation in the same way as crystalline domains. The scattering from these objects appear as two distinct families of elliptical contours with different eccentricities, and the observed diamond-shaped scattering results from the superposition of these two sets of contours. [Preview Abstract] |
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S1.00011: Thin Film Optical Measurements on a Low-bandgap Platinum-Acetylide Conjugated Polymer Developed for Use in Organic Solar Cells Zahra Nasrollahi, Jianguo Mei, Katsu Ogawa, Young-Gi Kim, Nathan Heston, Daniel Arenas, Tracy Mc Carley, David Tanner, John Reynolds, Kirk Schanze An important barrier to overcome in producing high efficiency organic solar cells is to extend light harvesting capabilities into the near infrared. With strong absorption through the visible region and possible involvement of the triplet state in charge generation, Pt-acetylides have received recent attention as interesting and promising materials for photovoltaic applications. This presentation focuses on the thin film optical characterization of p-PtBTD-Th. In order to obtain the absorption coefficient of this material, multiple films of varied thickness were made and characterized by UV to NIR transmission and reflection measurements. We employed a thin film analysis using a Drude-Lorentz model to calculate the optical constants and to estimate the interference effects. From this model we were able to extract the absorption and extinction coefficients. [Preview Abstract] |
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S1.00012: The study of polymer chain structure within macroporous polymer films by breath figure templating method Minsu Lee, Jung O. Park, Mohan Srinivasarao Macroporous films produced by breath figure templating methods have a microstructure with close packed and highly ordered pores. The water droplets condense from humid air flowing over a dilute polymer solution in a volatile solvent, due to evaporative cooling. Then, the water droplets closely pack over and sink into polymer solution. A close packed array of water droplets produces thin walls of polymer films where the polymer chains are confined. In our study, we have some evidence of the deformation of polymer chain within macroporous polymer films in areas where the polymer is confined. We will present our result on the deformation of polymer chain structure within polymer films. [Preview Abstract] |
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S1.00013: Trimerization of Monocyanate ester in Nanopores. Yung Pyo Koh, Qingxiu Li, Sindee L. Simon Nanoconfinement generally results not only in a T$_{g}$ depression, but also in changes in reactivity. Recently, we showed that the polymerization reaction of bisphenol M dicyanate ester is enhanced in nanopores and that the T$_{g}$ of the resulting polycyanurate product is depressed relative to the bulk. In order to examine the importance of an intracyclization side reaction, in this work we investigate the effect of nanoconfinement on the reactivity and the T$_{g}$ of a monocyanate ester and its cyanurate product. Due to the monofunctional nature of the reactant, there is no possibility for the intracyclization side reaction in this system. Using differential scanning calorimetry (DSC), we find the primary T$_{g}$ decreases with decreasing pore size but the secondary (higher) T$_{g}$ is independent of pore size. In addition, we find that the trimerization reaction rate increases as confinement pore size decreases, and in the 8 nm pores, the reactivity is accelerated by a factor of 20. The results are consistent with the T$_{g}$ depression and accelerated reaction found previously for the nanoconfined difunctional reactant. [Preview Abstract] |
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S1.00014: Diblock Copolymers under Nano-Confinement Dong Meng, Yuhua Yin, Qiang Wang Nano-confinement strongly affects and can thus be used to control the self-assembled morphology of block copolymers. Understanding such effects is of both fundamental and practical interest. In this work, we use real-space self-consistent field calculations with high accuracy to study the self-assembled morphology of diblock copolymers (DBC) under nano-confinement for several systems, including 1D lamellae-forming DBC confined between two homogeneous and parallel surfaces, in nano-pores, and on topologically patterned substrates; 2D cylinder-forming DBC on chemically strip-patterned substrates; and 3D gyroid- forming DBC confined between two homogeneous and parallel surfaces. The stable phases are identified through free-energy comparison, and our SCF results are compared with available experiments and Monte Carlo simulations in each case. [Preview Abstract] |
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S1.00015: First-Principles Prediction of Novel Technetium(IV) Halide Polymeric Compounds Philippe F. Weck, Eunja Kim, Frederic Poineau, Kenneth R. Czerwinski We report the crystal structures of novel technetium tetrahalide polymeric compounds, TcX$_4$ [X=F,Br,I], as predicted from first-principles calculations. Similar to TcCl$_4$, TcF$_4$ and TcBr$_4$ compounds are orthorhombic with the centro-symmetric space group $Pbca$, while TcI$_4$ crystallizes in the space group $P2_1/c$. The structures consist of distorted octahedral groups of composition TcX$_6$ linked into endless linear chains. A possible explanation for the differences between these structures is offered in terms of varying degree of bonding withing the polymeric chains. [Preview Abstract] |
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S1.00016: Control of Fibrinogen Assembly by Changing a Polarity of Surfaces Jaseung Koo, Ying Liu, Sara Snow, Pooja Rambhia, Tadanori Koga, Miriam Rafailovich, Dennis Galanakis Thrombogenesis causes various problems associated with an interruption in the blood flow (e.g., myocardial and cerebral infarction), and a hindrance to use of blood-contact vascular biomaterials (e.g., hemodialysis and cardiopulmonary bypass) with long-term patency since undesired adsorption of blood components occurs on vessels or biomaterials, such as surface-induced thrombosis. we showed that this clotting procedure can be occurred on hydrophobic polymeric surfaces without thrombin cleavage. However, the fibrinogen fibers were not formed on the polar surface such as spun-cast polymer film with pyridine and phenol groups. We also found that $\alpha $C domains play an important role in initiation of polymerization on surface. Therefore, molecular association was inhibited on the polar surfaces due to confinement of $\alpha $C chains on the surfaces. These findings were directly applied to stent surface modification. The commercial stent consist of Co-Cr alloy forms undesired fiber formation. However, PS-r-PVPh (13{\%} phenol) coated stent surfaces completely prevent fiber formation. [Preview Abstract] |
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S1.00017: Control self-assembled nanowire using chemically modified substrates Shusuke Aburaya, Satoshi Akasaka, Mikihito Takenaka, Hirokazu Hasegawa, Yasuhiko Tada, Hiroshi Yoshida, Nikos Hadjichristidis Block copolymer lithography is a promising method for fabricating periodical nanopatterns. Strongly segregated block copolymers are required for the formation of smaller size microphase-separated structures. In this study, we used a poly(styrene-b-dimetylsiloxane) (PS-b-PDMS) which has large Flory-Huggins interaction parameter. In addition, we investigated this cylinder-forming PS-b-PDMS has large segregation in the bulk condition by small-angle X-ray scattering (SAXS). Consequently, We demonstrated a fabrication of well-ordered arrays of 15nm period PDMS cylinder on the grating substrate with chemical modification. So, we can obtaine less than 10 nm L/S fabrication. [Preview Abstract] |
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S1.00018: Graphoepitaxy of 2D array of Spheres in Di-block Copolymers Adetunji Onikoyi, Edward Kramer The use of block copolymer (BCP) thin films to create periodic structures on a nanolength scale has proved to be very effective [1-3]. However, removing defects and improving translational order in the periodic structures remain important goals. This study exploits a form of graphoepitaxy as a means to influence translational and orientational order in a polystyrene-b-poly-2-vinylpyridine (PS-b-PVP) diblock copolymer. Here, the domains of the BCP thin film are allowed to order within sub-micron sized wells of various shapes. Effects on order and 2D melting behavior are examined. The wells are patterned into silicon substrates using electron-beam lithography. Secondary ion mass spectroscopy and scanning force microscopy are then used to characterize the self-assembly process. Results show that a near perfect hexagonal 2D lattice can be obtained in diamond shaped wells of appropriate dimensions. Perfect 6 fold symmetry is disfavored in square wells; rather, regions of meta-stable square packing or defect dense regions of hexagonal packing are observed. Further studies are being performed to understand these effects on melting behavior. [1] Segalman et al. Phys. Rev. Lett., 2003, 91, 196101 [2] Kim et al. Nature, 2003, 424, 411 [3] Guarini et al. International Electron Devices Meeting [Preview Abstract] |
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S1.00019: Stress-Strain Relation of Tire Rubber Consist of Entangled Polymers, Fillers and Crosslink Katsumi Hagita, Y. Bito, Y. Minagawa, M. Omiya, H. Morita, M. Doi, H. Takano We presented a preliminary result of large scale coarse-grained Molecular Dynamics simulation of filled polymer melts with Sulfur-crosslink under an uni-axial deformation by using the Kremer-Grest Model. The size of simulation box under periodic boundary conditions (PBC) is set to about 66nm to consider length of entangled polymer chains, size and structure of fillers, and non-uniform distribution of crosslink. We put 640 polymer chains of 1024 particles and 32 fillers into the PBC box. Each filler consists of 1280 particles of the C$_{1280}$ fullerene structure. A repulsive force from the center of the filler is applied to the particles. Here, the particles of the fillers are chosen to be the same as the particles of the polymers and the diameter of the filler is about 15nm. The distribution of the fillers used in this simulation is provided by the result of 2d pattern RMC analysis for 2D-USAXS experiments at SPring-8. Sulfur crosslink are randomly distributed in the system. It is found that stress-strain curves estimated by applying a certain uni-axial deformation to the system in simulations are in good agreement with those in experiments. It is successful to show difference on the S-S curve between existence / absence of fillers and qualitative dependence of attractive force between polymer and filler. [Preview Abstract] |
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S1.00020: In situ Raman Spectroscopy Study of Stress Transfer between Carbon Nanotubes and Amorphous Polymer Minfang Mu, Sebastian Osswald, Yury Gogosti, Karen Winey Stress transfer mechanism in single wall carbon nanotube (SWCNT) / poly(methyl methacrylate) nanocomposites was investigated using Raman spectroscopy on composite fibers. Without specific SWCNT-polymer interactions, the effective stress transfer to SWCNTs is limited to a small strain regime ($<$ 0.5{\%}). At higher strain, the stress on SWCNTs decreases due to debonding at the nanotube-polymer interface. Debonding was also evident by scanning electron microscopy on fracture fiber surfaces produced by tensile testing. Overall, the presence of SWCNTs in composite fibers greatly improves their mechanical properties by two ways: a sufficient stress transfer at SWCNT-polymer interface and a SWCNT-induced polymer chain orientation. It was also observed that longer polymer chains transfer stress more effectively, and we attribute this to a greater extent of nanotube-polymer chain entanglement. [Preview Abstract] |
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S1.00021: MD simulations of nanofibers Robert Liverpool, Joseph Ortiz, Dilip Gersappe We use MD simulations to study the strength of polymeric nanofibers. The simulations will examine the role of chain orientation, internal stresses and surface effects on the modulus of nanofibers. The simulations are performed at above and below the glass transition temperature of the polymer. We also examine the effect of inclusions in the fiber on the modulus. [Preview Abstract] |
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S1.00022: Structure, Dynamics, Loading Capacity, and Volume Phase Transition of Polymer Nanoparticles Kiril Streletzky, John McKenna, Imaan Benmerzouga, Pubudu Peiris, Mekki Bayachou Microgel nanoparticles were synthesized in aqueous solutions of neutral polymer hydroxypropylcellulose (HPC) through self- association of amphiphilic HPC molecules and subsequent cross linking. Dynamic Light Scattering (DLS) was used to study the transport properties of HPC microgels below and above the volume phase transition. Highly non-exponential, multimodal microgel spectra were observed and successfully analyzed by spectral time moment analysis. The structure and dynamics of microgels was found to depend on polymer and salt concentration, crosslinking density, solution temperature, and the rate of heating. HPC microgels undergo a reversible volume phase transition in which microgel volume swells/deswells by as much as a factor of thirty. The study revealed that higher polymer concentration results in smaller microgels with lower shrinking capacity. The effective cross-linking density that yields relatively monodisperse microgels was determined. The angular dependence of scattering demonstrated that microgels are largely spherical particles though sometimes two different particulate sizes are present. Finally, flow- injection amperometry was used to evaluate the loading capacity of microgels. Preliminary results show the moderate injection agent uptake that varies with temperature dependent size of particles. [Preview Abstract] |
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S1.00023: Cleavage Energies of Modified Layered Silicates by Molecular Dynamics Simulation Yao-Tsung Fu, Hendrik Heinz The cleavage energy of organically modified layered silicates indicates the thermodynamic propensity~of exfoliation in polymer matrices. We find substantial cleavage energy differences upon variation in cation exchange capacity (CEC) (90 and 145 meq/100g), head groups (-NH$_{3}$ and --NMe$_{3})$, and chain length of the surfactants (C2 to C14) due to layering effects of the surfactants in the galleries using molecular dynamics simulation. Model systems of full atomistic detail are periodic in the xy plane, open in the z direction, are subjected to sheet separation starting at equilibrium distance. Overall, the cleavage energy, consistent with experimentally measured surface tensions and previous calculations for selected organoclays, shows complex fluctuations as a function of chain length and head group structure. Computed cleavage energies are in the range 25-50 mJ/m$^{2}$ for C2$\sim $C14 (-NH$_{3}$ headgroup) and 40-200 mJ/m$^{2}$ for C2$\sim $C14 (--NMe$_{3}$ headgroup) at two CEC layered silicates. The progression is not linear and related to the packing density of the interlayer of self-assembled surfactant chains and surface reconstruction of the modified layered silicates upon cleavage. [Preview Abstract] |
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S1.00024: Large-scale nanocomposites simulations using hybrid particle/SCFT simulations Scott Sides Preliminary results from 2D simulations of block copolymer nanocomposites (Phys. Rev. Lett. Vol 96, 250601 (2006) have been performed using a hybrid self-consistent field theory (SCFT) algorithm. While these simulation results showed that the presence of nanoparticles could induce changes in block copolymer morphologies, quantitative agreement with experiments for the particle densities at this transition are not yet possible. A feature missing in the 2D hybrid simulations is the packing behavior of real, three-dimensional spherical particles embedded in lamellar layers or hexagonally packed cylinders formed by linear diblock chains. In order to carry out these hybrid particle/SCFT 3D simulations a new object-oriented SCFT framework has been developed. The object-oriented design enables the hybrid/SCFT simulations to be performed in a framework that is both numerically efficient and sufficiently flexible to incorporate new SCFT models easily, In particular, this new framework will be used to investigate the distribution of particle positions in diblock lamellar layers as function of nanoparticle density to study the interplay of patterning due to diblock domain structure and the chain depletion interaction between spherical particles. [Preview Abstract] |
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S1.00025: DNA Electrophoresis: how partially denatured DNA stops moving in a gel. David Sean, Gary Slater During temperature gradient gel electrophoresis (TGGE), a DNA strand travels in a gel with a temperature gradient. As the strand travels in a position of higher temperature, the stability of the double helix is reduced resulting in melted domains. It has been experimentaly observed that in a gel, a partialy melted DNA strand exhibits a steep reduction in mobility ---perhaps even trapping. The sequence dependent melting of DNA can therefore be translated into a sequence dependent position at which the strand appears to stop. Thus, this can be used as an effective method for discriminating between strands that differ only in composition. However, the dominant blocking mechanisms remain unclear. Blocking/trapping events are re-created using Langevin dynamics simulations using the ESPResSo package to understand the physics behind the observed steep reduction in electrophoretic mobility. From these simulations a relation between gel parameters and the mobility of the strand is proposed. [Preview Abstract] |
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S1.00026: Detrapping Particles in a Gel : A Numerical Study Antoine Dub\'e, Francis Torres, Gary W. Slater Pulsed fields are widely used in gel electrophoretic separations to increase resolution. For instance, Boyde \& To [1] presented experimental results for the separation of spherical particles using pulsed fields. They first used alternating fields of fixed amplitudes ($E_\pm =\pm\left| E \right|$) applied in the forward direction for a duration twice as long as in the backward direction. They then used field interruption in order to allow particles to thermally detrap. In both cases, they reported that using a pulsed field makes the particles migrate faster. We model the gel used in electrophoresis as a 2D system of obstacles on a lattice. We use a method that allows us to calculate the exact mean velocity of a particle for Monte-Carlo simulations to first reproduce the experimental results presented above. We then investigate different signals (e.g., telegraph signal) to determine the optimal conditions. Optimal conditions can be either higher velocities or larger velocity differences between particles. \\[4pt] [1] \emph{Pulsed-field acceleration: The electrophoretic behavior of large spherical particles in agarose gels}, Electrophoresis, 1993. [Preview Abstract] |
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S1.00027: Electronic Structure of Aromatic and Quinoidic Oligothiophenes by First-principles Calculations Hiroshi Mizuseki, Yoshiyuki Kawazoe Since the discovery in 1977 that trans-polyacetylene can be made electrically conducting by means of doping[1] several different conjugated polymers with interesting properties in the conducting and semiconducting phases have been discovered. Polythiophene has a typical $\pi $-conjugated system, then many polythiophenes are synthesized and several have been well characterized. Calculation systems based on neutral, doubly charged, and highly charged oligomers whose all ring are linked to have linear chains were studied as model for the polaronic defects in doped polythiophenes. The energetics of the aromatic and quinoid structures is investigated using the both ends of neutral oligomers substituted by dimethyl and dimethylen. To estimate the electronic structures, the difference between corresponding bond lengths along the C-C path of neutral, dicationic, and dianionic oligomers, were investigated. Calculations were performed on systems containing 16 monomers, by using B3LYP/6-31G(d) level of theory. References [1] C. K. Chiang et al., Phys. Rev. Lett. 39, 1098 (1977). [2] http://www-lab.imr.edu/$\sim $mizuseki/nanowire.html [Preview Abstract] |
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S1.00028: Probing Interfaces of Multilayer Polymeric Compensation Films for Liquid Crystal Display system Wumin Yu, Mark Foster Highly anisotropic polymer films formed by rigid-rod like aromatic polyimides show uniaxial negative birefringence and can be used as compensation films to widen the viewing angles of liquid crystal display system (LCD). Fluorinated pendent groups have been introduced to polyimide molecules to improve their solubility in common organic solvents. A new procedure for incorporating the compensation film in the multilayer LCD assembly by directly casting the polyimide film on a LCD unit as a substrate film, e.g. triacetate cellulose (TAC), is preferred in industry for its simplicity and cost-effectiveness. To obtain high quality multilayer films with excellent durability, the compensation films must adhere well to the TAC substrates. X-ray and neutron reflectivity techniques are being used to determine how the interface width between the polyimide film and TAC substrate varies with changes in polyimide chemistry or casting process parameters. [Preview Abstract] |
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S1.00029: Fabrication of Nanostructured Multilayers from Crosslinkable Block Copolymers Dongjune Hwang, Eunhye Kim, Hyunjung Jung, Du Yeol Ryu, Joona Bang In this work, we fabricated three dimensional nanotemplates using crosslinkable block copolymers (BCPs). We synthesized crosslinkable BCP, P(S-$r$-(S-N$_{3}))$-$b$-PMMA, in which 1.5 mol {\%} of crosslinkable azide (N$_{3})$ groups were incorporated. First, 40 nm thick films of P(S-$r$-(S-N$_{3}))$-$b$-PMMA, exhibiting the hexagonal arrays of perpendicularly oriented cylinders, were prepared on the silicon substrates. After crosslinking the films, cylinder- or lamellar-forming BCPs were prepared without disturbing the underlying layers. For cylinder-forming BCPs, it was observed that the cylindrical microdomains in respective layers were exactly registered. For lamellar-forming BCPs, the underlying layers could neutralize the interfacial interactions as PS-$r$-PMMA random copolymers and thus the perpendicular orientation of lamellae was achieved. The detailed structures of nanostructured multilayers were characterized by atomic force microscope (AFM) and scanning electron microscope (SEM), and grazing-incidence small-angle x-ray scattering (GISAXS). [Preview Abstract] |
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S1.00030: Hybrid nanostructured thin films which adapt low adhesive properties in changing environment Sergiy Minko, Roman Sheparovych We describe a nanostructured composite coating constituted of surface-grafted hydrophobic nanoparticles embedded in a hydrophilic, polyethylene oxide molecular brush. The responsive coating undergoes reconstruction from the morphology of rigid hydrophobic asperities, which hide the collapsed polymer brush in air, to the morphology of a hydrophilic brush-like layer engulfing the nanoparticles underwater. Due to this reconstruction, the coating demonstrates low adhesion to hydrophilic, hydrophobic, and amphiphilic materials in both dry and wet environments. The key property of the designed layer is the size of the nanoparticles that is bigger than the collapsed in air and smaller than the stretched in water polymer coil in the brush. This finding provides useful guidelines for the development of low-adhesive surfaces of materials. [Preview Abstract] |
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S1.00031: Glass transition in ultra thin polymeric films measured by differential AC-Chip calorimetry H. Huth, D.S. Zhou, C. Schick The film thickness dependency of glass transition in polymer films is still controversially discussed. For different experimental probes different dependencies are observed and a generally accepted link to molecular mobility is not yet established. Calorimetry has proven to provide useful information about glass transition, because it establishes a direct link to energetic characterization. In several cases a direct comparison with results from other dynamic methods like dielectric spectroscopy is possible giving further insights. For thin films in the $\mu $m{\ldots}nm range standard calorimetric methods are mostly not applicable. In the recent years there are new developments in the field of calorimetry which overcome these limitations. We set up a differential AC-chip calorimeter capable to measure the glass transition in nanometer thin films with pJ/K sensitivity. Changes in heat capacity can be measured for sample masses below one nanogram as needed for the study of the glass transition in nanometer thin polymeric films. No thickness dependency of the glass transition temperature was observed within the error limits - neither at constant frequency nor for the traces in the activation diagrams. [Preview Abstract] |
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S1.00032: Well-defined branched polymers for studying surface segregation Boxi Liu, Shih-Fan Wang, Roderic Quirk, Mark Foster A linear response theory by Wu et al. [1] predicts that the surface segregation of a long-chain branched polymer blended with a linear polymer depends only on the type and number of chain ends or branch points in the linear and branched chains. Our previous neutron reflectivity results suggest that further details of the branching may impact the surface segregation. To better understand the roles of molecular architecture a new set of well defined branched polystyrenes have been synthesized by anionic polymerization. These molecules include a series of 6-arm pom-pom polymers with the same overall number of repeating units, chain ends and branch points, but varying length of central linear portion; a 6-arm star polymer constructed to be a better analog with 6-arm pom-pom polymers; and a deuterated linear polymer more analogous to the branched polymers. Bulk viscosities of these polymers have been measured and their surface segregation is being studied by neutron reflectivity. Reference: 1 Wu, D.T.; Fredrickson, G. H. Macromolecules, 1996, 29, 7919. [Preview Abstract] |
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S1.00033: ``Smart'' Surfaces of Polymer Brushes Qiang Wang, Dong Meng ``Smart'' surfaces, also known as stimuli-responsive surfaces, can change their properties (e.g., wettability, adhesion, friction, elasticity, and biocompatibility) in response to external stimuli (e.g., temperature, pressure, light, solvent selectivity, ionic strength, type of salt, pH, applied electric field, etc.). In this work, we use numerical self-consistent field calculations to study in detail the structure and stimuli- responses of various polymer brushes, including (1) the thermo- response of PNIPAM brushes in water, (2) solvent-response of uncharged diblock copolymer brushes, and (3) the stimuli- response of charged two-component polymer brushes (including both the binary A/B brushes and diblock copolymer A-B brushes) to ionic strength, pH, and applied electric field. Among the many design parameters (e.g., chain lengths, grafting densities, A-B incompatibility, degree of ionization of charged polymers, etc.) we identify those that strongly affect the surface switchability. Such knowledge is useful to the experimental design of these smart polymer brushes for their applications. [Preview Abstract] |
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S1.00034: Adsorption of phospholipid bilayers onto pullulan-modified cellulose surfaces Heejun Choi, Zelin Liu, Alan Esker 1,2-Dimyristoyl-\textit{sn}-glycero-3-phosphocholine (DMPC) vesicle adsorption onto regenerated cellulose and pullulan 4-bromocinnamate (P4BC) modified cellulose surfaces was investigated via surface plasmon resonance (SPR) spectroscopy and quartz crystal microbalance with dissipation monitoring (QCM-D). P4BC with a degree of substitution (DS) of 0.061 $\pm $ 0.002 from UV measurements and 0.058 from $^{1}$H NMR was synthesized from pullulan and 4-bromocinnamic acid to yield P4BC. The deduced thicknesses from SPR for DMPC layers were $\sim $3.7 nm (bilayer) on regenerated cellulose surfaces and $\sim $2.1 nm (monolayer) on P4BC modified cellulose surfaces. Qualitative analysis of the QCM-D data also indicated that the DMPC layers on P4BC modified cellulose surfaces were thinner than on regenerated cellulose surfaces. [Preview Abstract] |
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S1.00035: Robust Self-Assembly of Highly Ordered Complex Structures by Controlled Evaporation of Confined Microfluids Zhiqun Lin, Myunghwan Byun, Suck Won Hong We demonstrate a robust, one-step method of evaporating polymer solutions in curve-on-flat geometries to create versatile, highly regular microstructures in a precisely controlled environment, as well as offering a comprehensive study of the influence of different upper surfaces on complex structure formation via controlled evaporation. Our method further enhances current fabrication approaches to creating highly ordered structures in a simple and cost-effective manner, with the potential to be tailored for use in photonics, electronics, optoelectronics, microfluidic devices, nanotechnology, and biotechnology. [Preview Abstract] |
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S1.00036: A new class of bio-heat resisted polymer blend. Seongchan Pack, Takashi Kashiwagi , Tadanori Koga , Miriam Rafailovich Increasing in oil prices and environmental concerns is a driving force to seek out alternative materials. A completely biodegradable starch is a candidate for the alternative materials. Since the starch is brittle, it must be mixed with other polymers. In order to make a thermoplastic starch (TPS), we need a bio-compatiblizer to increase a degree of compatibilization. The biocompatibilzer can be a small molecules or nanoparticles with the small molecules, which leads to improved material properties. In order to demonstrate a possible biocompatibilzer, we first developed a corn-based starch impregnated with non-halogenated flame retardant formulations. The starch was blended with Ecoflex{\textregistered}, a biodegradable polymer. Using SAXS and USAXS we characterized structures of the compounds with different amount of Ecoflex{\textregistered} by weight. Furthermore, the addition of 5{\%} nanoparticles in the compounds increased the Young's Modulus and impact toughness significantly. The compounds also did flame test. It is indicated that the compound with the addition of the nanopaticles would pass with a UL-94V0 rating. Therefore, the procedure for producing these TPS compounds can be applied to any biodegradable polymers, manufacturing a new bio-heat resisted compound. [Preview Abstract] |
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S1.00037: Controlled morphology of biodegradable polymer blends Sasiwimon Buddhiranon, Thein Kyu Phase diagrams of biodegradable polymer blends containing poly($\varepsilon $-caprolactone) (PCL) and poly(d,l-lactic acid) (PDLLA) having two different molecular weights were established by means of cloud point measurement and differential scanning calorimetry. Subsequently, the theoretical phase diagram was calculated self-consistently based on the combination of Flory-Huggins free energy for liquid-liquid phase separation and phase field free energy for crystal solidification. The phase diagrams thus obtained were LCST type or hour-glass type, which depended on molecular weight of PDLLA utilized. Guided by the phase diagram, the emerged morphology was determined as a function of blend concentration and temperature. It appears that the morphology control is feasible that ultimately affects the end-use property of PCL/PDLLA blends. A wide variety of morphology of biodegradable polymer may be developed with the porous structure and pore size to control scaffold porosity and the rate of drug delivery. [Preview Abstract] |
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S1.00038: A Spectroscopic Investigation on the Structural Evolution of Soy Based Polyurethane Foams Deepa Puthanparambil, Casey Kimball, Shaw L. Hsu Our current research deals with an economical and renewable soy based polyol for use in polyurethane foams. Infrared spectroscopic studies have revealed that the amount of polyurea segments formed and the kinetics of their formation in soy based polyurethane foam systems are considerably different from traditional systems employing ethylene oxide -- propylene oxide based polyols. The most crucial aspect of this research deals with the miscibility of water in the reactive mixtures involving extremely hydrophobic soy-based polyols. High Field Nuclear Magnetic Resonance Spectroscopy (NMR) with D$_{2}$O as the probing agent was employed to determine the miscibility behavior at the molecular level. This technique was able to establish the structure and location of dispersed water, which can be extremely different based on the polyols used, thus affecting the morphology of the foam. The length and amount of polyureas directly impact the kinetics of the phase separation process to form the hard-segment rich domains and associated physical properties. The aggregation of these polyurea hard domains were characterized by the hydrogen bonds formed. This structural transformation as a function of reaction is also reflected in the segmental relaxation kinetics characterized by spin-spin diffusion, measured using a low field NMR instrument. [Preview Abstract] |
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S1.00039: Evaporative Organization of Hierarchically Structured Polymer Blend Rings Myunghwan Byun, Suck Won Hong, Feng Qiu, Zhiqun Lin We report the first study of the controlled, evaporative self-organization of a polymer blend from a sphere-on-flat geometry. In this study, a drop of polystyrene (PS) and poly(methyl methacrylate) (PMMA) toluene solution evaporated in the sphere-on-flat geometry. The combination of controlled, consecutive pinning-depinning cycles (i.e., ``stick-slip'') of the contact line at the edge of the geometry, spontaneous phase separation of incompatible polymers at the microscopic scale, and a dewetting process in the late stage of phase segregation led to the formation of gradient, hierarchically structured polymer blend rings composed of phase-separated PS and PMMA. This facile approach offers a new way of simultaneously processing two or more nonvolatile components via controlled evaporation to produce new kinds of structures with hierarchical order in a simple, robust, and one-step manner. [Preview Abstract] |
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S1.00040: Directing Hierarchical Assembly of Block Copolymer-Based Supramolecules Using Small Molecule Blends Paul Tillberg, Matthew Richards, Ting Xu Block copolymer-based supramolecules can be obtained by selectively hydrogen-bonding amphiphilic small molecules to one block of a diblock copolymer. Through interactions between small molecules and the polymer backbone, and between separate polymer blocks, hierarchical self-assembled structures are achieved on length scales unavailable through traditional top-down engineering methods. We aim to introduce an additional independent design parameter by hydrogen-bonding a mixture of small molecules to the polymer backbone. The phase behavior of the small molecules can be tailored to obtain an extra level of molecular control and generate novel hierarchical structures within block copolymer domains. Ultimately, this principle can be used to generate tri- or multi-block copolymer behavior by hydrogen-bonding different small molecules to simple homo or diblock copolymers. We will present preliminary data obtained by adding fluorinated alkyl phenols to the model block copolymer-based supramolecular system consisting of polystyrene-block-poly(4-vinylpyridine) with alkyl phenols hydrogen-bonded to pyridine groups. [Preview Abstract] |
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S1.00041: Chirality Effect on Flory-Huggins Interaction Parameters in Polylactide-$b$-Poly(ethylene-\textit{co}-1-butene)-$b$-Polylactide Triblock Copolymers Weiqiang Cao, Lei Zhu, Lixia Rong, Benjamin S. Hsiao In this work, a set of well-defined polylactide-$b$-poly(ethylene-\textit{co}-1-butene)-$b$-polylactide (PLA-PEB-PLA) triblock copolymers were synthesized by controlled ring-opening polymerization of corresponding lactide monomers (L-lactide and racemic mixture of D- and L-lactides) using Sn(Oct)$_{2}$ as the catalyst. The volume fractions of PLA in the triblock copolymers were adjusted by tuning its molecular weight. The mesophase morphology and phase transitions in these triblock copolymers were studied by temperature-dependent small-angle X-ray scattering (SAXS). The Flory-Huggins interaction parameter $\chi $ between EB and lactide as a function of temperature were estimated from the order-disorder transition temperature (T$_{ODT})$ using the mean-field critical ($\chi $N)$_{c}$ values. The effects of PLA chirality on both Flory-Huggins interaction parameter and segmental lengths were investigated. [Preview Abstract] |
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S1.00042: Structure of PEO-b-PPO-b-PEO Triblock Copolymer Inclusion Complexes with Beta-Cyclodextrin Chi-Chun Tsai, Stephen Z.D. Cheng, Bernard Lotz, Jin Huang, Yongming Chen Inclusion complexes, formed by non-covalent host-guest interactions, have been extensively investigated because they can be useful as building blocks for constructing supramolecular structures. Cyclodextrins (CDs), due to their good water-solubility and ability to include a wide range of guest molecules, have been the most intensively studied host molecules. CDs are shaped like a shallow truncated cone, with a hydrophilic outer surface as well as primary (narrower end) and secondary (wider end) hydroxyl groups on the rim of the molecule. The cavity, which is constructed with alkyl groups and glycosidic oxygen atoms, is hydrophobic and can act as a host for a great variety of hydrophobic molecular guests. A series of host-guest inclusion complexes were prepared with beta-cyclodextrin (beta-CD) and PEO-PPO-PEO triblock copolymers of varying molecular weights and compositions. The middle PPO block of the copolymers can be selectively included by beta-CD to form an inclusion complex while the PEO blocks cannot. These inclusion complexes can further self-assembled into supramolecular structures in aqueous solution. The inclusion complexes and self-assembled supramolecular structures were characterized by Nuclear Magnetic Resonance, X-ray diffraction, and Differential Scanning Calorimetry experimental methods. [Preview Abstract] |
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S1.00043: Order-to-Order Transitions of Block Copolymer in Film Geometry Changhak Shin, Hyungju An, June Huh, Du Yeol Ryu The phase transition behavior for an asymmetric polystyrene- block-polyisoprene (PS-b-PI) in film geometry, like the order- to-order transition, was investigated by in-situ grazing incidence small angle x-ray scattering (GISAXS). Unlike the bulk behavior, the microdomain (or lattice) orientations in film geometry are influenced by the weak interfacial interactions between the native oxide layer and polyisoprene block due to the efficient interconnectivity, while the random orientation is observed for lamellar (LAM) structure. Compared with the bulk phase behavior, temperature dependence on the morphology leads to the enhancement of LAM morphology, the shifts of transition temperatures for the others, because interactions at the substrate/polymer and polymer/air interfaces influence this free energy balance. [Preview Abstract] |
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S1.00044: Interfacial Polarization and Field Induced Orientation in Self Assembled Nanostructured Soft Ion Conductors Thomas Thurn-Albrecht, Peter Kohn, Klaus Schr\"oter We report about the effects of interfacial polarization in and upon a self assembled nanostructured ion conductor, consisting of an ordered, lamellar block copolymer with a Lithium salt dissolved selectively in one component. Impedance spectroscopy in combination with frequency dependent orientation experiments enable a quantitative analysis of ionic polarization and a direct demonstration of its aligning effect on the interfaces. The transition time from the fast dielectric to the slow ionic interfacial polarization is much longer than expected from classical Maxwell-Wagner-Sillars theory and attributed to the formation of diffuse double layers at the internal interfaces. The much stronger orientation effect of ionic as compared to dielectric polarization offers a new route to align microdomains and therewith the ion conducting paths of the polymer. [Preview Abstract] |
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S1.00045: FTIR Investigation of Ion Environments in PEO-based ``Single Ion'' Polymer Conductors Mingfu Lu, James Runt, Paul Painter The infrared and Raman spectra of ionomers and electrolytes containing sulfonate groups have been previously studied in great depth. If the cation - anion interaction is relatively strong, the doubly degenerate asymmetric SO3- stretching mode becomes split into two components, while the symmetric SO3- stretching mode displays bands that can be assigned to the ``free'' (solvated) anion, neutral pairs and aggregates. In this paper we investigate a series of PEO-based polyester copolymer ionomers, with sulfonate anions covalently bound to the polymer chains, using FTIR spectroscopy. Ion content is systematically varied by changing the ratio of ionic to non-ionic isophthalate groups while keeping a fixed PEO segment molecular weight of 600. In the FTIR spectra of these ionomers, a splitting of the asymmetric mode is observed and only a single symmetric stretching band characteristic of some form of aggregated structure is apparent. There is no evidence that ``free'' or solvated ions are present. In addition, various ethylene oxide modes of vibration are shifted in frequency in a similar manner to those observed in studies of complexes of known structure, indicating their involvement in the formation of the aggregate. [Preview Abstract] |
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S1.00046: Origin of the low-q X-ray scattering behavior in poly(ethylene oxide)-based ionomers Amanda McDermott, Gregory Tudryn, Jan Ilavsky, Andrew Allen, Ralph Colby, James Runt Ultra-small-angle X-ray scattering is used to investigate a series of single-ion-conducting PEO-based polyester copolymers with varying amounts of ionic sulfonate groups covalently bound to the polymer chains. We observe a low-q scattering component found in many polymers, including the neutral version of our material, and generally attributed to impurities. However, both the intensity and power-law slope of this scattering intensity upturn increase at high ion contents, indicating that it contains structural information about intentionally added ions. We discuss the interpretation of this feature with insight from atomic emission spectrophotometry, a critical ion fluctuation model, and the X-ray scattering behavior observed with several different cations and a range of concentrations. [Preview Abstract] |
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S1.00047: New type of Reverse Osmosis Membrane via Layer-by-Layer Assembly Process Junwoo Park, Joona Bang, Jeongju Park, Jinhan Cho As to the commercial RO membranes for desalination, the polyamide (PA) based membranes have been widely used so far. However, they still have limitations, such as low permeability, bio-fouling, etc. In this work, we propose new types of polyelectrolyte-membranes which can overcome such problems. The membranes were designed by layer-by-layer (LbL) method using polyelectrolytes, including poly(allylamine hydrochloride), poly(styrene sulfonate), poly(acrylic acid), etc. Individual layers were adjusted by pH condition and number of deposition. The resulting multi-layered membranes were crosslinked by heat to provide the good durability. The morphologies were characterized by FE-SEM and AFM and the salt rejection was monitored by ion chromatography. By optimizing the membrane structures, we found that the water permeability was enhanced, while the salt rejection was as efficient as RO membranes. We believe that these results can provide the new protocol to design the advanced RO membrane. [Preview Abstract] |
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S1.00048: ABSTRACT WITHDRAWN |
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S1.00049: Simultaneous Prediction of Upper and Lower Critical Temperatures in Polymer Solutions Using a Constant Parameter Set Elizabeth Clark, Jane Lipson Polymer solutions commonly exhibit phase separation and so the ability to predict temperatures and compositions associated with immiscibility is advantageous to experimentalists. We have been applying a simple lattice model that is capable of capturing both upper (UCST) and lower critical solution temperature (LCST) type phase behavior for polymer blends. Most recently we have become interested in mixtures which simultaneously exhibit both types of phase behavior. Examples include polyisobutylene (PIB) in pure and mixed solvents, and cyclohexane/polystyrene mixtures. We have found that with a single set of temperature-independent parameters the lattice theory is capable of capturing all the physics of these solutions; in addition we discuss conditions under which 'hourglass' phase diagrams result. [Preview Abstract] |
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S1.00050: Monte Carlo simulations to study the effect of static and dynamic properties of polymer melts Kiran Khanal, Jutta Luettmer-Strathmann Static and dynamic properties of polymers are affected by the stiffness of the chains. In this work, we investigate structural and thermodynamic properties of a lattice model for semiflexible polymer chains. The model is an extension of Shaffer's bond-fluctuation model and includes attractive interactions between monomers and an adjustable bending penalty that determines the Kuhn segment length. This allows us to model melts of flexible and semiflexible chains. For this work, we performed Monte Carlo simulations for polymer melts with a range of bending parameters and densities. Results for chain dimensions show that the Kuhn segment length increases monotonously with the bending penalty and has a linear dependence for a range of bending parameters. Results for self diffusion constants show that the translational mobility is strongly reduced by increasing chain stiffness. We also investigate the effect of chain stiffness on thermodynamic properties of the melts. [Preview Abstract] |
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S1.00051: Scaling of dynamic properties of polymer melts using friction coefficients of phantom chains - A Monte Carlo simulation study Nenad Stojilovic, Jutta Luettmer-Strathmann A Monte Carlo simulation method is used to investigate two different models of athermal polymer melts. In one model chains are allowed to cross (phantom chains) whereas in the other bond crossing is forbidden (real chains). We confirmed that the conformational properties of both types of polymers are similar and analyzed the differences in chain dynamics due to entanglements of real chains. Phantom chains that are sufficiently long exhibit Rouse dynamics, so that friction coefficients can be extracted from self diffusion coefficients. For real chains, on the other hand, entanglement effects complicate the determination of friction coefficients. In this work, we use friction coefficients from phantom chains to investigate the scaling behavior of dynamic properties of real chains. [Preview Abstract] |
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S1.00052: Tacticity effects on viscoelastic properties of polystyrenes Chien-Lin Huang, Chi Wang Polystyrenes (PS) with a similar molecular weight and distribution but different tacticities, i. e. syndiotactic (s-PS), atactic (a-PS), and isotactic (i-PS), have been used in this study for a fair comparison to reveal their differences in the viscoelastic properties. Our attention was focused on the influence of the PS tacticity on the rheological properties, especially the plateau shear modulus $G_N^0 $ and entanglement molecular weight $M_{e}$. Based on the time-temperature superposition principle, the master curves of dynamic storage modulus $G'(\omega )$, dynamic loss modulus $G?(\omega )$, and \textit{tan}$\delta $ at a reference temperature of 280$^{o}$C were constructed. The feasibility of conventional approaches for determining $G_N^0 $, i. e. minimum \textit{tan}$\delta $criterion, the integration method, and an empirical equation derived by Wu, has been discussed and compared; the corresponding $M_{e}$ is then derived by the classical relation: $M_e =\rho RT/G_N^o $. Our results show that the measured $M_{e}$ and activation energy for flow are similar for s-PS and a-PS, but the highest for i-PS. In addition, the zero shear viscosity of i-PS is ca. one order larger than that of s-PS and a-PS. [Preview Abstract] |
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S1.00053: Stress-induced Mobility in Polymer Glasses During Multistep Creep Deformation Hau-Nan Lee, Keewook Paeng, Stephen Swallen, Mark Ediger, Robert Riggleman, Juan de Pablo An optical photobleaching experiment and molecular dynamics simulations have been used to study the changes in segmental dynamics of a polymer glass during uniaxial creep deformation. Both experiment and simulation observe that segmental mobility increases more than a factor of 100 during deformation. Both show a strong correlation between strain rate and mobility in single step creep. However, in multistep creep and recovery, the correlation between strain rate and mobility is broken in both experiment and simulation; this emphasizes that no simple mechanical variable universally exhibits a simple relationship with molecular mobility. Interestingly, in contradiction to the Eyring model, both experiments and simulations show an increase in segmental mobility immediately follows a significant drop in stress. [Preview Abstract] |
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S1.00054: Unusual Spherulite Radial Growth Rate Kinetics of Poly(ethylene adipate): Observation of a Double Maximum in Growth Rate Curve Kathy Singfield, Ashley Rowe Poly(ethylene adipate) (PEA) is an aliphatic polyester often blended in small amounts with aromatic polyesters in order to impart some of its biodegradability to the resultant blend. Hot-stage polarized-light microscopy and differential scanning calorimetry have been used to investigate the isothermal melt-crystallization kinetics and thermal behaviour of PEA. The unusual spherulite radial growth rate dependence on isothermal crystallization temperature exhibits two maxima. A change in spherulite morphology from banded to non-banded spherulites is associated with the phase behaviour anomaly. The results are interpreted in terms of traditional Hoffmann-Lauritzen growth kinetics. [Preview Abstract] |
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S1.00055: Simultaneous Dielectric Spectroscopy and X-ray Diffraction of Poly(ethylene therephthalate) and PET/Carbon Nanotube Nanocomposites Bret Stenger, Lei Yu, Peggy Cebe The crystallization of poly(ethylene terephthalate) (PET) and a nanocomposite of PET with multi-walled carbon nanotubes (MWCNTs) were studied by simultaneous wide and small angle X-ray diffraction and dielectric relaxation spectroscopy. Our purpose is to determine whether the MWCNTs affect the cold crystallization kinetics or phase structure of the PET host. The nanocomposites contained 2{\%} MWCNT by weight, and were prepared by solution mixing, and then compression molding into film. Dielectric measurements were made at frequencies from 100 Hz to 1 MHz, in parallel plate geometry. Measurements of the samples during cold crystallization (Tc$\sim $100-120\r{ }C) were used to investigate the relationship between the growth of crystals and the restriction of the molecular mobility of the amorphous phase. In agreement with previous work, results indicate that a heterogeneous distribution of amorphous regions exists, implying both interlamellar and interfibrillar/interspherulitic placement of the amorphous chains. Addition of carbon nanotubes to the PET increased the rate of cold crystallization, but did not affect the glass transition relaxation process. [Preview Abstract] |
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S1.00056: Crystallization kinetics and the orientation of crystals under cylindrical nanoconfinement Kyunghee Lee, Euntaek Woo, Kyong Wook Noh, Young Gyu Jeong, June Huh, Kyusoon Shin* Crystallization kinetics, together with crystal orientation, is affected by the imposed geometric constraint. We investigated that crystallization of polymer and metal in nanopores with the variation of pore diameter. Crystallization of PE in nanopores is dominated by nucleation and the crystal growth is restricted by the limited space. On the basis of classical nucleation theory, we found that homogeneous nucleation dominates in larger pores while heterogeneous nucleation governs in smaller pores. We also investigated the orientation of crystal structures of polymer and metal in cylindrical nanopores, and found that the crystal orientation is influenced by crystallization mechanism. In nanoscopic cylindrical pores, the crystal growth is limited and the crystals are preferentially oriented along the pore axis. [Preview Abstract] |
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S1.00057: Crystallization of Polyethylene on nucleating and on passive substrates Thomas Henze, Klaus Schroeter, Thomas Thurn-Albrecht Since the late 1950's it has been known that polymers are able to crystallize epitaxially on suitable crystalline substrates. Whereas epitaxial crystallization experiments have been typically performed from solution, we here present a study of the morphology of thin films of polyethylene crystallized from the melt on a number of substrates with different ability to invoke crystallization, namely mica, NaCl, SiO$_2$ and HOPG. Using intermittent-contact mode AFM very different structures are observed on the surface of the polymer film depending on the kind of substrate as well as film thickness. For very thin films ($\sim$ 30 nm) on NaCl and HOPG edge on lamellae, oriented in domains according to the underlying crystal lattice, show up while for mica and SiO$_2$ flat-on lamellae dominate. With increasing film thickness (up to 130 nm) the orientation of the lamellae on HOPG and NaCl becomes weaker, while on mica and SiO$_2$ a spherulitic morphology develops, which is not present in the case of HOPG and NaCl. [Preview Abstract] |
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S1.00058: Impact of Protein-Metal Ion Interactions on the Crystallization of Silk Fibroin Protein Xiao Hu, Qiang Lu, David Kaplan, Peggy Cebe Proteins can easily form bonds with a variety of metal ions, which provides many unique biological functions for the protein structures, and therefore controls the overall structural transformation of proteins. We use advanced thermal analysis methods such as temperature modulated differential scanning calorimetry and quasi-isothermal TMDSC, combined with Fourier transform infrared spectroscopy, and scanning electron microscopy, to investigate the protein-metallic ion interactions in \textit{Bombyx mori} silk fibroin proteins. Silk samples were mixed with different metal ions (Ca$^{2+}$, K$^{+}$, Ma$^{2+}$, Na$^{+}$, Cu$^{2+}$, Mn$^{2+})$ with different mass ratios, and compared with the physical conditions in the silkworm gland. Results show that all metallic ions can directly affect the crystallization behavior and glass transition of silk fibroin. However, different ions tend to have different structural impact, including their role as plasticizer or anti-plasticizer. Detailed studies reveal important information allowing us better to understand the natural silk spinning and crystallization process. [Preview Abstract] |
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S1.00059: Effects of configurational defects on structural evolution in Poly(vinylidene fluoride-hexafluoropropylene) copolymers Suriyakala Ramalingam, Shaw L. Hsu Crystallization kinetics of various crystallizable segments in Poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] copolymers have been analyzed using thermal techniques. These analyses are supported by spectroscopic and diffraction techniques, which directly measure the presence or absence of specific chain conformations or crystalline forms. Crystallization is constrained due to random distribution of the noncrystallizable bulky comonomer (HFP) along the crystallizable linear PVDF chains. Since the crystallites of different size/VDF chain lengths have different melting temperatures, it is possible to obtain a fraction of each crystallizable segment by selecting the crystallization temperature at various points below melting temperature. This fractionation has been accomplished by following the Successive Self-Nucleation/Annealing (SSA) method. The chain distribution and configurational defects, introduced by HFP, have been evaluated and correlated to the multiple thermal transitions in P(VDF-HFP) copolymers. In addition, it is interesting to find that the thermal fractionation can induce the $\beta $-conformation in highly constrained P(VDF-HFP) copolymers. [Preview Abstract] |
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S1.00060: Polymorphism Behaviors of Electrospun Poly(vinylidene fluoride) Nanofibers Zhenxin Zhong, Darrell Reneker Poly(vinylidene fluoride) (PVDF) and its copolymers have drawn great attention in recent years due to their attractive electrical properties such as ferro-, piezo- and pyro-electricity. Depending on its processing, PVDF can exhibit five different polymorphs. Among them, the beta phase has the highest piezo-, pyro- and ferroelectric activities. Electrospinning was used to produce thin polymer fibers. The polymorphic behavior of electrospun PVDF fibers was observed. Long cylindrical PVDF specimens with cross-sections in the range of 10 nm to 1 micron was obtained by varying the electrospinning conditions. Almost pure beta phase was obtained in electrospun PVDF nanofibers. The morphology and internal structure of single PVDF electrospun nanofibers were studied by transmission electron microscopy. [Preview Abstract] |
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S1.00061: Electrospun Buckling Coils Yu Xin, Darrell Reneker Electrospinning offers a useful way to produce fibers with micron and nanometer scale diameter. The present work deals with the buckling phenomenon characteristic of a jet impinging upon the surface of collector. A viscous jet may have either tensile or compressive forces along its axis. The periodic buckling that is often observed is attributed to the occurrence of compressive forces as the jet decelerates at the collector. With the increase of axial compressive stresses along the jet, a jet with circular cross sections first buckles by formation of sharp folds, and then by formation of coils. The resulting buckling patterns include zigzag patterns and coils that which can be controlled by changing parameters, such as density, viscosity, conductivity, voltage, polymer concentration, distance and volumetric flow rate. Uniformly buckled polymer fibers can be made at a rate of one turn per microsecond. An experimental apparatus was built to continuously collect buckling coils of nylon 6, from a water surface, into a multilayer sheet. These small ``springs'' and sheets will be tested for mechanical properties needed in biomedical applications. [Preview Abstract] |
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S1.00062: Hierarchical Structure on Nanofiber via Combination of Electrospinning and Polymer Crystallization Xi Chen, Bingbing Wang, Rucha Shah, Christopher Li We report the formation of hierarchically ordered polymer nanofiber structures, named as nano fiber shish kebabs (NFSKs), by combining electrospinning and controlled polymer crystallization methods. both poly caprolactone (PCL) and poly (ethylene oxide) (PEO) nanofibers were produced by electrospinning. These polymer nanofibers served as the shish and a secondary polymer (block copolymer) was decorated on the nanofiber in the form of single crystal lamellae by either an incubation (slow crystallization), or a solvent evaporation (fast crystallization) method. The structural parameters of the NSFK such as the fiber diameter, periods, the kebab size etc., were readily controlled by changing the electrospinning and crystallization conditions. This hierarchical architecture is of great technological interest because it provides a platform for incorporating different functionalities into nanoscale polymer fibers in an ordered fashion. [Preview Abstract] |
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S1.00063: PP/POSS Nanocomposites: Characterization and Properties of Melt Spun Fibers Byoung-Jo Lee, Sayantan Roy, Sadhan Jana It is known that molecules of polyhedral oligomeric silsesquioxane (POSS) can self-assemble into spherical, fibrillar, or lamellar nanoparticles by bottom-up self assembly process during mixing with host polymers. This study capitalizes on such nanoparticle formation to increase the melt strength and tensile properties of polyolefin blown films and spun fibers. A novel method was developed whereby a sorbitol-type nucleating agent was used as dispersion aids for POSS. The nucleating agent also served as templates for self-assembly of POSS molecules into nanoparticles of 25-200 nm in diameter. A typical polypropylene formulation containing 0.3 wt{\%} nucleating agent and 5-10 wt{\%} POSS was spun into fibers with close to 70{\%} reduction in diameter and 40-45{\%} increase in modulus and 70-75{\%} increase in yield strength compared to unfilled PP. An optimum concentration of POSS was identified. [Preview Abstract] |
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S1.00064: Affine deformation in polymer networks Anindita Basu, Qi Wen, Paul Janmey, Arjun Yodh An affine deformation is one where a macroscopic deformation applied on a body is translated uniformly to the microscopic level. Much existing theory, ranging from simple rubber elasticity to non-linear elasticity in biological polymer networks, is based on the assumption that deformations are affine. We explore the validity of the affine assumption by embedding micron-sized fluorescent beads within model polymer networks and quantifying their displacements when the sample is put under shear deformation. We quantify the non-affine deformations as functions of polymer chain density, cross-link concentration and find our results to be in qualitative agreement with current theories of rubber elasticity. [Preview Abstract] |
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S1.00065: Length and Structure Dependence of Electron Transport in Organic Molecules Shashi Karna, Govind Mallick, Haiying He, Ravindra Pandey The electron transport through organic molecules are affected by a number of structural parameters, such as the length, dihedral angle, rotation around a single-bond, symmetry and charge distribution of frontier molecular orbitals. In addition, in a molecule-solid hybrid system, the chemistry and physics of the molecule-solid interface plays an extremely important role on electron transport through organic molecules. In order to gain an enhanced understanding of the effects of length, geometry and solid-molecule interface we have investigated electron transport through $\pi $-conjugated molecules of increasing lengths in contact with Au substrate by non-equilibrium Green's function method within \textit{ab initio }molecular orbital theory, density functional theory and semi-empirical methods. The effects of rotation around a single bond, change in dihedral angle and the length of the molecule on the transport properties are investigated. The results suggest a complex dependence of electron transport on one-electron energy levels, spatial characteristics of the wave function and geometry of the molecules. Further, the local density of states and location of metal Fermi level are also found to affect electron transport characteristics in a metal-molecule hybrid system. [Preview Abstract] |
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S1.00066: PHASE TRANSITIONS AND STRONGLY CORRELATED SYSTEMS |
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S1.00067: Color change of Ruby investigated by Raman and UV-vis Sean Breckling, Ying Zou, Shishir Ray, Larry Buroker, Somaditya Sen, Mark Williamsen, Prasenjit Guptasarma The origin of a distinctive red color in Ruby (Al$_{2}$O$_{3}$:Cr$^{3+})$ continues to be a fundamental unsolved question [1]. We report the synthesis of a series of samples of 2{\%} Cr$_{2}$O$_{3 }$by solid state reaction [2] at temperatures varying between 900$^{o}$ and 1300$^{o}$C. We observe a visible change in color at every stage, from light green, to grey, and to pink, indicating progressive incorportation of Cr$^{3+}$ ions into the Al$_{2}$O$_{3}$ lattice. We report further investigations of x-ray diffraction analysis, Raman and UV-visible spectroscopy, and correlate the observed color changes with the evolution of vibration modes of the cage around CrO$_{6}$ and band-gap states resulting from Cr incorporation. We also plan to report results from single crystals grown using a floating zone. [1]J.M. Garcia-Lastra, M.T. Barriuso, J.A. Aramburu and M. Moreno, Phys. Rev. B 72(2005)113104 [2]L.W. Finger and R.M. Hazen, J. Appl. Phys. 49(1978)5823 [Preview Abstract] |
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S1.00068: ABSTRACT WITHDRAWN |
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S1.00069: Scattering of the Transverse Acoustic Phonon by Polar Nanodomains in the Relaxor Ferroelectric KTa$_{1-x}$Nb$_{x}$O$_{3}$ (KTN) Jean Toulouse, Eugene Iolin, Bernard Hennion, Daniel Petitgrand, Ross Erwin We show that, in relaxors, the transverse acoustic (TA) mode displays a particularly original behavior, due its coupling to the transverse optic (TO) mode as well as to the polarization \textbf{\textit{P}} of the Polar Nano-Domains (PND) that are ubiquitous in these special ferroelectrics. A neutron scattering study of the TA phonon frequency and damping, and especially of their \textbf{\textit{q}} dependence, reveals that the PNDs condense in the form of platelets. In the relaxor range of temperatures, in which elastic diffuse scattering is also observed, the TA mode is strongly scattered by the PNDs. We compare our results with those from thermal conductivity studies of inhomogenous solids and similar neutron results obtained in other perovskite systems. We also present a theoretical model that describes the scattering mechanism specific to relaxors, the TA-\textbf{\textit{P}}-TO interaction, is shown to fit the acoustic data well and also provides an estimate of the TO mode frequency and damping. [Preview Abstract] |
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S1.00070: $^{93}$Nb NMR investigation of the multiferroic system Ba$_3$NbFe$_3$Si$_2$O$_{14}$ Lloyd Lumata, M.J.R. Hoch, H.D. Zhou, J.S. Brooks, P.L. Kuhns, A.P. Reyes, C.R. Wiebe We present $^{93}$Nb nuclear magnetic resonance spectroscopy and relaxation data on the new multiferroic system Ba$_3$NbFe$_3$Si$_2$O$_{14}$. The spin-lattice relaxation rate $^{93}$1/T$_1$ and spin-spin relaxation rate $^{93}$1/T$_2$ show a peak at 26 K accompanied by broadening of the NMR lineshapes, characteristic of N\'{e}el ordering. Salient features of $^{93}$Nb NMR lineshapes in the ordered phase and temperature-dependent $^{93}$Nb Knight shifts will be discussed in relation to the possible bulking or tilting of the NbO$_6$ octahedra (caused by magneto-lattice coupling) around the transition. [Preview Abstract] |
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S1.00071: Phase Diagram of Floating Zone grown Multiferroic SmMnO$_{3}$ and Mn site substitutions. Somaditya Sen, Larry Buroker, Ying Zou, Shishir Ray, Mark Wiliamsen, Prasenjit Guptasarma SmMnO$_{3}$, a member of a Rare Earth manganite series of current interest due to the observation of multiferroic magnetoelectricity, anisotropy in magnetic properties and an unconventional ``compensation temperature'' $\sim $8K possibly arising from antiparallel Sm--Mn exchange interactions. Of particular interest here is charge disproportionation of Mn, competing magnetic and orbital order, and the proximity to a metal-insulator transition [1]. We report detailed studies of a high-quality single crystal of SmMnO$_{3}$ grown from a floating zone, and the result of Mn-site substitution by elements with multiple valence states and octahedral coordination. We discuss magnetization, crystal structure refinement, and dielectric spectroscopy in 0.3$<$T$<$300 Kelvin and 0$<$H$<$9Tesla. [1] Kurbakov, et.al., A, Physics of the Solid State, 46 -9~(2004) 1704 [Preview Abstract] |
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S1.00072: Magnetic and Specific Heat Studies of Multiferroic Hexagonal DyMnO$_{3}$ ~ Ying Zou, Shishir Ray, Somaditya Sen, Mark Williamsen, Prasenjit Guptasarma Rare earth (R) manganites ~(RMnO$_{3})$ are well known to exhibit novel magnetic and magnetoelectric multiferroic properties. Under normal conditions, R=La through Dy yields orthorhombic lattice symmetry, whereas R=Ho through Lu yields hexagonal lattices. We confirm however that DyMnO$_{3}$ single crystals, when grown in Argon from a floating zone, have a hexagonal lattice structure [1]. ~We further report new features in the H-T phase diagram in the range 0.3-300K and 0-9 Tesla. Specific heat measurements show two transitions at 4K and 63K in the absence of a magnetic field. dc-Magnetization shows a cusp at 4K, which we attribute to a Dy3+ spin ordering. Time-dependent relaxation and frequency dependent shifting in ac susceptibility reveals a spin-glass behavior at this temperature, possibly suggesting an incommensurate Dy magnetic structure. An interesting bifurcation occurs for the high temperature transition (T=63K) in ac susceptibility with increase in frequency of the ac field. \newline [1] V.Y.Ivanov et al, Phys.Solid State, 48(2006)1726 [Preview Abstract] |
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S1.00073: Low Temperature Phase Transitions in Single Crystal Magnetoelectric GdMnO$_{3}$ Mark Williamsen, Shishir Ray, Somaditya Sen, Ying Zou, Prasenjit Guptasarma GdMnO$_{3}$ is proposed to have a magnetic phase transition from paramagnet to incommensurate antiferromagnet at 43K, further ordering to canted antiferromagnetism around 23K, followed by Gd magnetic ordering at 6.5K[1]. We present further studies of a large single crystal of orthorhombic GdMnO$_{3}$ grown by us from a floating zone, revealing additional features at lower temperature. Dielectric spectroscopy measurements confirm these new features. We also report dc-magnetization, frequency dependent ac-magnetization 2-300K, and specific heat 0.4-300K in a variable magnetic field 0-9T, and propose additional features in the magnetoelectric phase diagram. [1]T. Kimura,Phys.Rev.B 71,224425(2005) [Preview Abstract] |
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S1.00074: Local structure studies of multiferroic RMn2O5 (R=Bi, Pr, Gd) G. Fabbris, N.E. Massa, E. Granado, G.A. Maciel, J.A. Souza, J.A. Alonso, M.J. Martinez, G.M. Azevedo EXAFS measurements from 20 K to 300K were used to investigate the local structure of multiferroic RMn$_{2}$O$_{5}$ (R = Bi, Pr, Gd, TM~TC~40K) in transmission mode at the Mn K- and R L$_{3}$- edges in the XAFS2–LNLS beamline and analyzed using the IFEFFIT and FEFF codes. For BiMn$_{2}$O$_{5}$, Mn K-edge reveals very small temperature dependence of the Debye-Waller factor (DWF) and an Einstein temperature (ET) from Mn-O bonds of 675$\pm$22 K, suggesting that MnO polyhedra are rigid. We find structural distortions in the first coordination shell at the Bi L$_{3}$-edge associated to vibrational anomalies in the Bi-O bonds. The quantitative analysis relates the origin of such distortions to two very distinct values of DWT and ET (294$\pm$7K and 462$\pm$28K) for these bonds on first shell. Similar behavior is observed for PrMn$_{2}$O$_{5}$, and GdMn$_{2}$O$_{5}$. [Preview Abstract] |
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S1.00075: Magnetism, disorder and non-Fermi liquid behavior in a Na$_{0.78}$CoO$_{2}$ single crystal Alexander Feher, A. Zorkovska, M. Kajnakova, A. Baran, C.T. Lin, J.P. Peng, J.S. Xia, L. Yin, M.W. Meisel In recent years, significant interest has been devoted to high Na-doped cobaltates, in which the competition between geometric frustration, strong electronic correlations, and magnetic interactions leads to disorder, either correlated or non-correlated, and a variety of ground states with possible QPTs are expected. Specific heat down to 100 mK and the ac-susceptibility at several frequencies and temperatures, down to 40 mK and in fields up to 10 T, of a layered Na$_{0.78}$CoO$_{2}$ single crystal have been measured. The results will be discussed in terms of disorder induced non-Fermi liquid behavior, related to the spin dynamics of the ferromagnetic nano-domains coexisting with antiferromagnetically correlated regions in the system. [Preview Abstract] |
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S1.00076: Transport and Magnetic Properties of ErNi2B2C W.C. Lee We measured the magnetization M(H,T) and magnetoresistivity $\rho $(H,T) of ErNi2B2C single crystal for magnetic fields perpendicular and parallel to the c-axis and with the current along the c-axis at low temperature regions. From the magnetoresistivity measurements with the current along c-axis, we constructed the H$_{c2}$(T) curves for magnetic perpendicular and parallel to the c-axis and those were compared for curves with the current perpendicular to the c-axis. Also we constructed a magnetic phase diagram only the magnetic field perpendicular to the c-axis [Preview Abstract] |
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S1.00077: Antisymmetric Exchange in Antiferromagnetic Materials of Rhombohedral Structures Alexander Bazhan Carriers transferrings, determined by wave functions and energy levels of i j magnetic and oxygen ions, which are determined by rhombohedral oxygen crystal fields and their particularities, are in discussions for identification of antisymmetric, Dzyloshinskii-Moria exchange, \textbf{D}$_{z}${\{}\textbf{S}$_{ix}$\textbf{S}$_{jy}-$\textbf{S}$_{iy}$\textbf{S}$_{jx }${\}}, taking into account Hubbard Hamiltonians, including spin-orbit interactions. Wave functions symmetry dependence are described by, depending on trigonal symmetry $\alpha $, $\beta $ coefficients in wave functions of energy levels of magnetic ions. Particularities of i j oxygen crystal fields are concerned with rotations of j fields at angles 60 degrees with respect to i fields. Taking spin-orbit, transferrings as perturbations, exchange symmetric,$_{ }$antisymmetric parts of spin Hamiltonians are H$_{ex}=\Sigma _{i,j}$J$_{i,j}$(\textbf{S}$_{i}\cdot $\textbf{S}$_{j})+\Sigma _{i,j}$\textbf{D}$_{i,j}$[\textbf{S}$_{i}\times $\textbf{S}$_{j}$], where J$_{i,j}$ and \textbf{D}$_{i,j}$ are determined by carriers transferrings, kinetic energies, Coulomb interactions, magnetic and oxygen energy levels. As examples, after some assumptions \textbf{D}$_{ij }$= J$\cdot (-\lambda )\cdot $i$\cdot ${\{}$\Sigma _{m}\langle \psi _{im }$/\textbf{L}$_{i}$/$\psi _{i0}\rangle ^{\ast }$/($\varepsilon _{im}-\varepsilon _{i0})\cdot $(t$_{im,kn}$/t$_{i0,kn})$ - $\Sigma _{m}\langle \psi _{jm}$/\textbf{L}$_{j}$/$\psi _{j0}\rangle ^{\ast }$/($\varepsilon _{jm}-\varepsilon _{j0})\cdot $(t$_{kn,jm}$/t$_{kn,j0})${\}}, \textbf{D}$_{z}\sim $J$\cdot \alpha \beta \cdot ${\{}$\lambda $/($\varepsilon _{m}-\varepsilon _{0})${\}}$\cdot ${\{}(t$_{im,kn}$/t$_{i0,kn}-$t$_{kn,jm}$/t$_{kn,j0})${\}}. Energy levels and Pauli requirements, determine depending on spin-orbit interactions, carriers transferrings between magnetic -oxygen -magnetic ions, which determine vectors \textbf{D}$_{z}$, oriented, according to trigonal symmetry, along trigonal - z axis. [Preview Abstract] |
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S1.00078: Infinite-randomness quantum critical points induced by dissipation Chetan Kotabage, Jose Hoyos, Thomas Vojta We develop a strong-disorder renormalization group to study quantum phase transitions with continuous $O(N)$ symmetry order parameters under the influence of both quenched disorder and dissipation. For Ohmic dissipation, as realized in Hertz' theory of the itinerant antiferromagnetic transition or in the superconductor-metal transition in nanowires, we find the transition to be governed by an exotic infinite-randomness fixed point in the same universality class as the (dissipationless) random transverse-field Ising model. We determine the critical behavior and calculate key observables at the transition and in the associated quantum Griffiths phase. We also briefly discuss the cases of superohmic and subohmic dissipation. [Preview Abstract] |
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S1.00079: Phase-transition behavior of Selenium confined in periodic mesoporous silica: an x-ray scattering study Kuangmin Li, Congshang Wan, Gang Chen Confinement of semiconductors in nanoporous media provides a new opportunity to modify their physical properties such as electric conductivity, thermal conductivity, and phase transition temperatures. To understand the effect of nanoscale confinement on the melting behavior of selenium, we now conduct x-ray scattering experiments on selenium that are confined in periodic mesoporous silica (PMS). Hexagonal MCM-41 and SBA-15 with cylindrical pores (2 - 30 nm in diameter) are synthesized and utilized as the host for selenium, which is filled into the periodic pores by vapor phase condensation. The PMS are characterized by small-angle x-ray scattering, from which the pore size and the pore wall thickness are determined. Wide-angle x-ray scattering are used to measure the melting points of selenium confined in cylindrical pores of various widths. Relation between pore width and melting point of Se is established and compared with the Gibbs--Thomson theory. Our study provides fresh insights into the applicability of the Gibbs--Thomson theory to inorganic semiconductors confined in nanoporous media. [Preview Abstract] |
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S1.00080: Critical exponents taking into account dynamic scaling for adsorption on small-size one-dimensional clusters. Vladimir Udodov, Andrey Taskin Adsorption on small-size one-dimensional clusters is investigated using the Monte Carlo method. The effect of temperature and system size variations on adsorption is studied. Critical coefficients of the correlation length and dynamic critical coefficient z are calculated taking into account the hypothesis of dynamic scaling. The results obtained demonstrate that non-equilibrium adsorption in nanosystems can occur in a much different fashion than in macrosystems. [Preview Abstract] |
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S1.00081: Finite Size Scaling of Melting in Two Dimensions Keola Wierschem, Efstratios Manousakis The melting transition of a two-dimensional Lennard-Jones fluid is studied using classical Monte Carlo methods. Melting in two dimensions is expected to occur via a two-stage process, with separate transitions for translational and orientational order. The second moments of the translational and orientational order parameters are analyzed, and dimensionless quantities are constructed. According to finite size scaling theory, such quantities should be a function of the ratio of system size to the correlation length of the appropriate order parameter. Using the theoretical temperature dependence of the correlation length, and the fact that the correlation length approaches infinity at the critical point, the two melting transitions may be determined. [Preview Abstract] |
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S1.00082: Probability Density Function at the 3D Anderson Transition Alberto Rodriguez, Louella J. Vasquez, Rudolf Roemer The probability density function (PDF) for the wavefunction amplitudes is studied at the metal-insulator transition of the 3D Anderson model, for very large systems up to $L^3=240^3$. The implications of the multifractal nature of the state upon the PDF are presented in detail. A formal expression between the PDF and the singularity spectrum $f(\alpha)$ is given. The PDF can be easily used to carry out a numerical multifractal analysis and it appears as a valid alternative to the more usual approach based on the scaling law of the general inverse participation rations. [Preview Abstract] |
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S1.00083: Quantum simulation of Fermi-Hubbard models in semiconductor quantum-dot arrays Na Young Kim, Tim Byrnes, Kenichiro Kusudo, Yoshihisa Yamamoto We propose a solid-state quantum simulator device to investigate a Fermi-Hubbard model including long-ranged Coulomb interactions. The device consists of an array of coupled quantum dots in a GaAs-based two-dimensional electron gas system. We launch an artificial lattice potential electrostatically by applying DC voltage to a periodically patterned thin film on top of the two-dimensional electron gas system. We tune both two competing energy terms -- Coulomb interaction energy and kinetic energy- and the density of electrons independently, which enables us to construct a Hubbard phase diagram via differential conductance measurements. We consider the case of high average trapped electron density where more than the first bands are occupied. In this case, high mobility is still preserved and the effects of the Hubbard model would not be masked by impurities or disorder. We believe that a metal-Mott insulator quantum phase transition and a $d$-wave superconducting phase are observable in our proposed device according to the estimates of Hubbard parameters. [Preview Abstract] |
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S1.00084: GENERAL THEORY (THEORETICAL METHODS) |
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S1.00085: Coexistence of phases in final one-dimensional systems Vladimir Udodov, Ivan Naumov Within the framework of L.D. Landau (1908-1968) approach it is shown, that two-phase equilibrium is possible in linear macrosystems of the final size at low temperatures. At further downturn of temperature two-phase equilibrium becomes unstable and the system passes in a single-phase state. These results remain in force and at the account of interaction of interphase borders with each other and with the ends of linear system. Following Landau [1] we shall consider the linear system made of alternating pieces of two various phases. Points of contact between various phases (interphase borders) we shall present as a weak solution. For linear system of the limited size\textit{ L (L$>>$} 1) at low temperatures a single-phase state is stable. The increase in temperature will lead to phase transition of the first order in a two-phase state. The original cascade of phase transitions of the first order, because of increase of quantity of interphase border \textit{of item } will be observed actually. 1. L.D.Landau, E.M.Lifshits. Theoretical physics. Statistical physics. A part 1. 4 edition. Moscow (In Russian): the Science publisher, 1995. [Preview Abstract] |
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S1.00086: Variational Ground State of the One Dimensional Bose-Hubbard Modelel J.D. Mancini, V. Fessatidis, S.P. Bowen, R.K. Murawski Recently Eichenberger and Baeriswyl [PRB \textbf{76}, 180504R, (2007)] have introduced a novel variational ansatz to study the two dimensional Hubbard model. Their scheme involves choosing a trial ket which consists of an exponential operator constructed from the Hamiltonian which then operates on a mean field ground state $\left\vert \psi _{0}\right\rangle $. In this study, we wish to extend this ansatz by combining it with a second ansatz in which a variational basis is constructed by systematically taking derivatives with respect to a (set) of variational parameters. The model we will study is the one dimensional Bose-Hubbard Hamiltonian which is used to investigate the properties of interacting bosonic atoms in a one-dimensional optical lattice. The Hamiltonian is given by \[ H_{\mathrm{bh}}=-J\sum_{l=1}^{M}(a_{l}^{\dag }a_{l+1}+{\mathrm{h.c.}})+\frac{U% }{2}\sum_{l=1}^{M}n_{l}\left( n_{l}-1\right) , \]% where $a_{l}$ ($a_{l}^{\dag }$) creates a boson at the lowest level localized on the $l$-th site, $J$ is the hopping energy and $U>0$ is the onsite repulsion. Our results are then compared with other approximation methods such as Hartree-Fock-Bogoliubov theories and the variational Bijl-Dingle-Jastrow method. [Preview Abstract] |
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S1.00087: Variational Ground-State of the One-Dimensional Heisenberg Model J.D. Mancini, V. Fessatidis, R.K. Murawski, W.J. Massano, S.P. Bowen We wish to study the ground state of a spin system described by the Heisenberg Hamiltonian% \[ H=-\frac{1}{2}J\sum_{l}\left\{ 2\left( \sigma _{l}^{+}\sigma _{l+1}^{+}+\sigma _{l}^{-}\sigma _{l+1}^{-}\right) +\sigma _{l}^{z}\sigma _{l+1}^{z}\right\} , \]% where $\sigma ^{\pm }=\sigma _{x}\pm i\sigma _{y}$ and $J$ is the interaction strength. We choose as our trial ket $\left\vert \psi _{0}\left( \lambda \right) \right\rangle =e^{\lambda \hat{S}}\left\vert \phi _{0}\right\rangle $ where $\left\vert \phi _{0}\right\rangle $ is chosen to be the ferromagnetic state with all spins aligned downward, and $\hat{S}$ is the operator $\hat{S}=\sum_{l}\sigma _{l}^{+}\sigma _{l+1}^{+}$ with $% \lambda $ a variational parameter. We then construct our variational basis by systematically taking derivatives of $\left\vert \psi _{0}\left( \lambda \right) \right\rangle $ with respect to $\lambda $: $\left\vert \psi _{N}\left( \lambda \right) \right\rangle =\partial _{\lambda }^{N}\left\vert \psi _{0}\left( \lambda \right) \right\rangle $. The lowest eigenvalue of the Hamiltonian matrix $E_{0}\left( \lambda \right) $ is then minimized with respect to $\lambda $. Comparisons are then made with other approximation schemes. [Preview Abstract] |
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S1.00088: Variational Moments Expansion R.K. Murawski, J. Mikalopas, J.D. Mancini, V. Fessatidis, S.P. Bowen A number of years ago, a generalized moments expansion, \textrm{GMX}$\left( m,n\right) $ was derived as a novel way to calculate ground-state energies of many body systems [PLA \textbf{349}, 320, (2006)]. This scheme was based on a theorem by Horn and Weinstein for the \textquotedblleft \emph{t}-expansion\textquotedblright\ and was shown to be a generalization of an earlier connected moments expansion \textrm{CMX}, in which $\mathrm{CMX=GMX}\left( 1,1\right) $. Here we wish to extend the \textrm{GMX} method, which involves matrix elements of moments of the Hamiltonian, to include a recent variational ansatz in which a variational basis is constructed by taking successive derivatives with respect to a (variational) parameter $\lambda $ that is introduced in a trial ket. The \textrm{GMX} expression for the ground state, $E_{0}(\lambda )$ is then minimized within a given subspace of the Hilbert space. [Preview Abstract] |
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S1.00089: Variational Approach to a Class of \textit{P-T} Symmetric Hamiltonian Systems J. Mikalopas, J.D. Mancini, V. Fessatidis, F.A. Corvino In the usual study of non-relativistic Quantum Mechanics, one chooses a real (Hermitian) potential so as to ensure a real energy spectrum for the corresponding Schr\"{o}dinger equation. In recent years, a number of authors have studied a class of complex potentials which are invariant under the combined symmetry \emph{P-T} (here the operator \emph{P} represents parity reflection and the operator \emph{T} represents time reversal). For such \emph{P-T} symmetric systems it has been shown that the energy eigenvalues of the Schr\"{o}dinger equation are real so long as the \emph{P-T} symmetry is not spontaneously broken. Thus it would appear that rather than the usual demand for Hermiticity, it may be sufficient to have a \emph{P-T} invariant Hamiltonian so long as the energy spectrum remains real. It should be noted however that this conjecture has not been proven, but rather has been demonstrated to be true for several sample Hamiltonian systems. Here we wish to apply a recently developed ansatz wherein a variational basis is constructed by systematically taking derivatives of an initial trial state with respect to a (set) of variational parameters. In particular we shall study the spectrum of the Hamiltonian $H=p^{2}+x^{2}(ix)^{\alpha }$ ($\alpha $ real) as a test case for the ansatz. [Preview Abstract] |
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S1.00090: Single Hole Dynamics in a 2D quantum antiferromagnet in a stripe-ordered by fluctuating background Satyaki Kar, Efstratios Manousakis We study the dynamics of a hole in a $2D$ lattice in a stripe-ordered background. Starting from $t-J$ Hamiltonian, we treat the $J$-term using the linear spin wave theory and we linearize the hole hopping in terms of spin-deviation operators. We find the dispersion relation of the eight different spin-wave modes and we solve the Dyson's equation within the non-crossing approximation for the eight hole green's functions. We investigate the hole energy bands, the spectral functions and the quasi-particle peak broadening. [Preview Abstract] |
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S1.00091: Towards a two dimensional lattice gas with dynamical geometry Anna Klales, Donato Cianci, Zachary Needell, Peter Love We report on simulations using a lattice gas automaton in which the lattice is replaced by a triangulation of an arbitrary two-dimensional manifold. If the manifold is 2D Euclidean space the particles move on the Kagome lattice. We report results of simulations of channel flow for the flat space model and of simulations in which the particle state can change the geometry of the triangulation through the Pachner moves. [Preview Abstract] |
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S1.00092: Quantum Monte Carlo Studies of Buckling of the Si(100) Surface Wendy Lampart, Richard Christie, Daniel Schofield, Kenneth Jordan The quantum Monte Carlo method is used to study the role of electron correlation on the buckling of Si-Si dimers on the Si(100) surface. The buckling is addressed using cluster models with one to three surface dimers. In addition to the diffusion Monte Carlo method, calculations are also carried out using various density functional methods, multi-reference MP2, multi-reference MP3, and approximate multi-reference coupled cluster approaches. The calculations show that high-order correlation effects are important for determining the relative stability of the buckled and unbuckled structures, favoring the buckled structure. [Preview Abstract] |
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S1.00093: Quantum Monte Carlo study of water-acene systems Jiawei Xu, Richard Christie, Kenneth Jordan Electronic structure quantum Monte Carlo methods are used to calculate the energies of a water molecule interacting with benzene, anthracene, and coronene. Localized orbitals represented as spline functions are used to reduce the computational cost of the calculations for larger water-acene complexes. The prospects of using this approach to determine the interaction energy between water and graphite is discussed. [Preview Abstract] |
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S1.00094: Ab initio study of ferroelectricity in quantum-confined nanostructures Ghanshyam Pilania, Ramamurthy Ramprasad In the present ab initio study, we have employed density functional theory to investigate the size dependence of ferroelectric properties of BTO quantum wires and quantum dots. In the case of quantum wires, the ferroelectric well depth was calculated as a function of size. We find that the ferroelectric well depth corresponding to bulk BTO is recovered in quantum wires with diameters larger than 1 nm. Analysis of the decomposed density of states indicates that the central BTO unit behaves bulk like, whereas the peripheral units result in defect states in the band gap (with density depending on facet terminations). Complex polarization patterns were also observed, and were strong functions of the surface termination of the nanostructures. For instance, in non-stoichimetric quantum wires with all surface facets terminated with TiO2, strong axial polarization was dominant. However, in BaO terminated quantum wires, polarization in the ``shell'' region is radial, while in the ``core'' region the polarization is axial. The BTO quantum dots that were studied displayed even more complex polarization patterns, reminiscent of the ``vortex'' patterns anticipated earlier based on effective hamiltonian calculations. [Preview Abstract] |
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S1.00095: On the interplay between spin polarization, orbital polarization and spin-orbit coupling in actinides from Pa to Cm Md Islam, Asok Ray We present a systematic investigation of the effects of spin polarization, orbital polarization and spin-orbit coupling in six actinide elements, namely Pa, U, Np, Pu, Am and Cm using relativistic full-potential augmented plane wave with local orbital basis method. Our calculation shows that the $5f$ electrons in lighter actinides are itinerant with no magnetic effects. In heavier actinides, the $5f$ electrons are strongly correlated and quite sensitive to spin polarization, although the difference between FM and AFM energies tends to be very small. The orbital polarization has strongest effect in NM order and nearly vanishes for spin polarized calculations in almost all cases. The $5f$ electrons in $\alpha $-Pu are close to being delocalized and their behavior is similar to that of lighter actinides. Among all the elements studied in this work, $\delta $-Pu exhibits the most complex behavior. All forms of correlation effects are comparable in $\delta $-Pu and significantly affect volume, bulk modulus and ground state energy. [Preview Abstract] |
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S1.00096: Strain-dependence of the superconducting critical temperature Tc in Al and Nb simple crystals from first-principles M. Salvetti, N. Bonini, M. Calandra, D. Parks, N. Marzari, J. Minervini In the past 20 years, efforts have been devoted to predict the critical current density $J_{c}$ of superconducting magnets based on the Nb$_{3}$Sn compound. The use of Nb$_{3}$Sn magnets for high-field applications has highlighted the dependence of $J_{c}$ on strain. We present calculations of the $T_{c}$-dependence of Al and Nb crystals on pressure, uni-axial and shear strains using the DFT \textit{PWscf} package from the Quantum-ESPRESSO distribution to evaluate the phonon linewidth and the \textit{el-ph} coupling parameter using very dense \textbf{\textit{k}}-space samplings of the IBZ. The superconducting critical T$_{c}$ is calculated by using the McMillan formula as a fit to the solution of the Migdal-Eliashberg equations. Favourable comparisons with available experimental data have been obtained and will be presented. The modelling of the $T_{c}$-dependence on strain in Nb$_{3}$Sn crystals is an ongoing effort. The potential for modelling the $T_{c}$-dependence on strain in Nb$_{3}$Sn is discussed. In this regard, recent advances in the implementation of the Wannier formalism give access to the sampling of the dense \textbf{\textit{k}}-point grids required to calculate fully-converged electron-phonon coupling quantities. This approach opens the possibility to extend the study of the $T_{c}$-dependence on strain to unit cells characterized by a higher number of atoms or electronic complexity. [Preview Abstract] |
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S1.00097: TDDFT+{\it U} for transition-metal complexes Xiaofeng Qian, Davide Ceresoli, Elise Li, Heather J. Kulik, Nicola Marzari Time-dependent density functional theory (TDDFT) has been used to successfully predict excited-state properties of various organic and inorganic molecular systems, such as optical absorption and circular dichroism. On the other hand, it is known that orbital-independent exchange-correlation functionals, such as LDA and GGA, tend to underestimate exchange interactions, delocalize electrons, and suffer from qualitative failures originating in self-interaction errors. In transition-metal complexes these often lead to incorrect multiplicities and charge and spin distributions already in the ground states. We implement a Hubbard-like {\it U} correction [1] to TDDFT calculations in Quantum ESPRESSO [2], using a real-time propagation scheme, and examine the effect of the Hubbard term in TDDFT predictions of optical properties. [1] H. J. Kulik, M. Cococcioni, D. A. Scherlis, and N. Marzari, Phys. Rev. Lett., 2006, 97, 103001. [2] http://www.quantum-espresso.org/ [Preview Abstract] |
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S1.00098: Internal inconsistency of Kohn-Sham equations in density-functional-theory Boyan Obreshkov The conflict of DFT Kohn-Sham equations with the Ritz variational principle will be demonstrated rigorously. It will be shown that the ground-state charge density of the material is not representable by auxiliary one-electron orbitals of variational character. This inconsistency is also expressed by a charge-sloshing effect in attempt to solve these equations self-consistently. \\[0pt] [1] B.~D.~Obreshkov , submitted to Phys.~Rev.~A (2008). [Preview Abstract] |
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S1.00099: Loop voltage, inductance, and impurity ion velocity in toroidal discharges D. H. McNeill Strong co-current drift and substantial heating of impurity ions were reported in some early ($\sim $1960) toroidal devices with low magnetic field B and high loop voltage, V$_{L}$ (Sceptre and ZETA in Britain and Al'fa in Russia). High frequency spikes in V$_{L}$ suggest rapid changes in the discharge inductance; V$_{L}$ should be treated as the sum of resistive [IR] and inductive [d(LI)/dt] terms. Experimental data can be used to estimate the resistive and inductive contributions. High-energy electrons and (impurity and hydrogenic) ions were observed, but the average energies were a few tens of eV. Calculations using a 1-D momentum equation with a toroidal electric field as driver and slowing in Coulomb collisions and inelastic processes yield impurity ion (average) drift velocities and apparent temperature (drift driven by voltage spikes) that are consistent with spectroscopic observations on Al'fa. These early experiments contrast with modern tokamaks, which are comparatively quiescent and usually have relatively higher toroidal B and lower V$_{L}$. On the other hand, ZETA was a precursor of the reversed field pinch (RFP), some of whose characteristics seem related to their high V$_{L}$. Toroidal drift ("rotation") velocities for tokamaks and RFPs can be calculated in the same way. [Preview Abstract] |
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S1.00100: Finite Difference Time Evolution of the Quantum Wigner Function in the Presence of a Magnetic Field Timothy Bergstresser, Tomas Materdey Numerical results from the finite-difference solution of a quantum Vlasov equation that governs the dynamics of the Wigner function in the presence of a magnetic field will be presented. Effects of absorbing boundary conditions in phase space and use of higher order finite-difference approximations will be discussed. [Preview Abstract] |
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S1.00101: Red Shifts and Existing Speculations Sol Aisenberg There are many current flaws, mysteries, and errors in the standard model of the universe - all based upon speculative interpretation of many excellent and verified observations. The most serious cause of some errors is the speculation about the meaning of the redshifts observed in the 1930s by Hubble. He ascribed the redshifts as due to ``an apparent Doppler effect''. This led to speculation that the remote stars were receding, and the universe was expanding -- although without observational proof of the actual receding velocity of the stars. The age of the universe, based upon the Hubble constant is pure speculation because of lack of velocity demonstration. The belief in expansion, the big bang, and of inflation should be reexamined. Also, the redshift cannot always be used as a distance measure, particularly for photons from quasars containing massive black holes that can reduce photon energy through gravitational attraction. If the linear Hubble constant is extrapolated to the most remote super novae and beyond, it would eventually require that the corresponding photon energy go to zero or become negative -- according to Hubble linear relationship. This should require a reexamination of the meaning of the red shift and the speculative consequences and give a model with fewer mysteries. [Preview Abstract] |
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S1.00102: Challenging the fundamental interactions in nature: Can ${1/r}$-interactions, like the gravitational and Coulomb interactions, be induced interactions? Bo E. Sernelius Two of the fundamental interactions in nature, the Coulomb interaction and the gravitational interaction, vary with distance as ${1/r}$. Here we address the question if an induced, as apposed to fundamental, interaction could have this distance dependence. We show that in theory it is possible to obtain a Casimir interaction potential that varies with distance as ${1/r}$. We achieve this by invoking hypothetical particles having a harmonic oscillator interaction potential. These particles generate fields that are different from the ordinary electromagnetic fields. The derivation parallels the derivation of the Casimir-Polder interaction between atoms in electromagnetism. The derivation relies on the harmonic oscillator interaction between the particles and Einstein's two postulates in special relativity. [Preview Abstract] |
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S1.00103: Reinterpreting Relativity's Negative Solutions: An Introduction to the Theory of Symmetry Physics B.G. Szabo Using basic algebra, it can be shown that Einstein's renowned equation E = mc$^2$ is only half correct. Just as the equation: x$^2$ = 9 has two equally valid solutions, i.e. x = +3 and x = -3, there are two equally valid solutions to the useful relativistic equation: E$^2$ = (pc)$^2$ + (mc$^2$)$^2$, When the object is at rest (p = 0) E$^2$ = (mc$^2$)$^2$ or, as above E = +mc$^2$ and E = -mc$^2$ Furthermore, it can be shown that this negative solution is found throughout relativity. In general, there are two equally valid mathematical solutions to the Pythagorean theorem and this concept can be extended to the foundation of relativity -- the Einstein hypotenuse. Are the negative solutions merely a mathematical curiosity or a fundamental physical reality? Current physics, discards the negative solution as not physically realizable. It is believed that this mathematically deficient practice results in physically ``inexplicable'' phenomena, e.g. the apparent matter-antimatter asymmetry, apparent CP violation, etc... However, by applying the basic premise of Symmetry Physics these phenomena have natural, experimentally falsifiable explanations: For all matter there exists equal but opposite antimatter. Or more precisely with deference to particle/wave duality: For every particle/wave there exists an equal but opposite antiparticle/antiwave. Further information can be found at http://www.symmetryphysics.com [Preview Abstract] |
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S1.00104: Origin of Everything and the 21 Dimensions of the Universe Mark Loev The Dimensions of the Universe correspond with the Dimensions of the human body. The emotion that is a positive for every dimension is Love. The negative emotion that effects each dimension are listed. All seven negative emotions effect Peace, Love and Happiness. 21st Dimension: Happiness Groin \& Heart 20th Dimension: Love Groin \& Heart 19th Dimension: Peace Groin \& heart 18th Dimension: Imagination Wave Eyes Anger 17th Dimension: Z Wave / Closed Birth 16th Dimension: Electromagnetic Wave Ears Anger 15th Dimension: Universal Wave Skin Worry 14th Dimension: Lover Wave Blood Hate 13th Dimension: Disposal Wave Buttocks Fear 12th Dimension: Builder Wave Hands Hate 11th Dimension: Energy Wave Arms Fear 10th Dimension: Time Wave Brain Pessimism 9th Dimension: Gravity Wave Legs Fear 8th Dimension: Sweet Wave Pancreas Fear 7th Dimension: File Wave Left Lung Fear 6th Dimension: Breathing Wave Right Lung Fear 5th Dimension: Digestive Wave Stomach Fear 4th Dimension: Swab Wave Liver Guilt 3rd Dimension: Space Wave Face Sadness 2nd Dimension: Line Wave Mouth Revenge 1st Dimension: Dot Wave Nose Sadness The seven deadly sins correspond: Anger Hate Sadness Fear Worry Pessimism Revenge Note: Guilt is fear [Preview Abstract] |
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S1.00105: INSULATORS AND DIELECTRICS |
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S1.00106: Searching for a possible universal character of non-equilibrium fluctuations A. Oprisan, J. Hegseth, S. Oprisan, A. Teklu, C. Lecoutre, Y. Garrabos, D. Beysens Light scattering due to microscopic fluctuations was used to investigate possible universal laws. We used two significantly different physical systems: a pure fluid near critical temperature in microgravity and silica or gold colloids under the influence of gravity. The direct visualization and analysis of thermal fluctuations and phase separating in pure fluids near critical temperature in microgravity provides invaluable information about cooperative phenomena and the role played by the thermodynamic fluctuations in determining the critical behavior. Scattering from a non-equilibrium macroscopic concentration gradient in a free diffusion experiment for two colloidal samples under the influence of gravity is determined both by diffusion and the buoyancy. Using image processing techniques for series of recorded images from both experiments, we extracted both the static and dynamic structure factor. We implemented algorithms for detecting and extracting quantitative features from snapshots of images recorded near critical point. Additionally, the radial average of the power spectra for images recorded in both experiments presented the characteristic ``ring'' that determined the most likely wave number associated with the fluctuations. [Preview Abstract] |
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S1.00107: Electronic Structure of Aluminum compounds A.R. Chourasia, Hong Dong, S.D. Deshpande The valence and conduction bands of aluminum and aluminum compounds (AlB, AlN, and Al2O3) have been studied using a DFT computational approach implemented in CRYSTAL06. The Becke exchange with the LYP correlation has been employed. The atomic basis sets with diffusive and polarization functions have been optimized for each configuration in these materials. The density of states in the valence and conduction bands has been computed in each case. The projected density of states of the constituents has also been computed. The band gap and the dielectric constant have been calculated for these materials. These values have been compared with the available experimental data. The correlation between the partial density of states and the chemical bonding will be presented. [Preview Abstract] |
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S1.00108: Insights into the structure of the stable and meta-stable (GeTe)$_m$(Sb$_2$Te$_3$)$_n$ compounds Juarez L.F. Da Silva, Aron Walsh, Hosun Lee Phase-change materials such as (GeTe)$_m$(Sb$_2$Te$_3$)$_n$ (GST) have been considered as one of the most natural candidates for the development of non-volatile memory devices, however, there is no common consensus on the structure of those compounds. Using first-principles calculations, we identify the mechanisms that lead to the lowest energy structures for the crystalline GST compounds, namely, strain energy release by the formation of superlattice structures along of the hexagonal [0001] direction and by maximizing the number of Te atoms surrounded by three Ge and three Sb atoms (3Ge-Te-3Sb rule), and Peierls-type bond dimerization. The intrinsic vacancies form ordered planes perpendicular to the stacking direction in both phases, which separate the GST building blocks. The 3Ge-Te-3Sb rule leads to the intermixing of Ge and Sb atoms in the (0001) planes for Ge3Sb2Te6 and Ge$_2$Sb$_2$Te$_5$, while only single atomic species in the (0001) planes satisfy this rule for the GeSb$_2$Te$_4$ and GeSb$_4$Te$_7$ compositions. [Preview Abstract] |
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S1.00109: TEM study of Pt nanoparticles on gamma Al$_{2}$O$_{3}$/NiAl support Zhongfan Zhang, Long Li, Judith Yang Pt gamma Al$_{2}$O$_{3}$ as one of the most important catalysts has attracted much attention in research. Moving beyond the current phenomenological understanding of the nanoparticle support interaction necessitates the examination of the Pt/ $\gamma $-Al2O3 interface at the atomic level. To produce the model interface, NiAl(110) single crystal was oxidized at 1223K in order to fabricate gamma Al$_{2}$O$_{3 }$(440). The crystallinity and uniformity of the oxide film was characterized by X-ray diffraction (XRD), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Nanometer sized Pt particles were deposited through vapor deposition method onto the film. Cross sectional TEM samples were prepared using a Focused Ion Beam (FIB). The Pt gamma Al$_{2}$O$_{3}$ interface will be examined by cross-sectional transmission electron microscopy (TEM) methods to elucidate the atomic, defect and electronic structure of the interface. [Preview Abstract] |
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S1.00110: Structural properties and electronic structures of amorphous HfO$_{2}$/Si(001) interface Chen Guohong, Hou Zhufeng, Gong Xingao Using the projector augmented wave method within the generalized gradient approximation, we have performed \textit{ab-initio }molecular dynamics simulations to generate an atomic structure model of amorphous hafnium dioxide ($a$-HfO$_{2})$ by a melt-and-quench scheme, and have investigated the structural and electronic properties of $a$-HfO$_{2}$ /Si(001)-$c$(2$\times $2) interface. The structure of $a$-HfO$_{2}$ sample is analyzed via atomic coordination number and partial pair-radius distribution functions. Our results show the average Hf-O nearest-neighbor distance is 2.06 ?, which is comparable with the Hf-O bond lengths (in the range from 2.04? $\sim $ to 2.25?) in monoclinic HfO$_{2}$ crystalline, and also indicate the generated sample essentially reflects the experimentally measured structural characteristics of $a$-HfO$_{2}$. Most importantly, it is found that the valence band offset of $a$-HfO$_{2}$/Si interface is about 2.97eV, and our results suggest that the coordination of Si atoms at interface would significantly affect the electronic properties of interface. [Preview Abstract] |
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S1.00111: Experimental Studies of the Giant Dielectric Constant Materials CaCu$_{3}$Ti$_{4}$O$_{12}$ Jianjun Liu, Wai-Ning Mei, Robert W. Smith We present results of four different experimental studies, namely (1) scanning electron microscopy, (2) dielectric measurements, (3) \textit{in-situ} high-pressure and X-ray and (4) low-temperature specific heat, on the insulating giant dielectric constant material CaCu$_{3}$Ti$_{4}$O$_{12}$. From analyzing the results, we first deduce the electronic and mechanical properties of the samples and conclude that the mechanism for high-dielectric constant phenomena is mostly extrinsic. In addition we propose a phenomenological model to explain the high dielectric constant behaviors at both low and high frequency regions. [Preview Abstract] |
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S1.00112: Dielectric tensors of high-k {\it Pbnm} perovskites from first principles Sinisa Coh, David Vanderbilt Among the materials under consideration for future high-k dielectrics in MOSFET and other microelectronic devices are several perovskites having space group {\it Pbnm}. Among these are LaLuO$_3$, SrBO$_3$ (B = Zr, Hf), AScO$_3$ (A = La, Pr, Nd, Sm, Gd, Tb, Dy), and LaB$_{1/2}$Zr$_{1/2}$O$_3$ (B = Ca, Mg) (with lower symmetry), which are all compatible with growth on silicon and can have higher dielectric constants than HfO$_2$.\footnote{ D. G. Schlom, S. Guha, S. Datta, MRS Bull. {\bf 33}, 1017 (2008).}$^,$\footnote{Thin Films and Heterostructures for Oxide Electronics, S.~B.\ Ogale, Ed. (Springer, New York 2005), pp.~31-78.} Using first-principles DFT methods with ultrasoft pseudopotentials and GGA energy functionals, we compute the dielectric tensors, structural properties, and phonon spectra of these materials. We analyze the dependence of these properties on chemical composition, and compare with experiments where possible. We also focus on correlation between dielectric tensor anisotropy and octahedra rotation angles. [Preview Abstract] |
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S1.00113: Thickness dependent multiferroicity in relaxor Pb(Fe$_{2/3}$W$_{1/3}$)O$_{3}$ thin films Ashok Kumar, Ram S. Katiyar Epitaxial multiferroic Pb(Fe$_{2/3}$W$_{1/3})$O$_{3}$ thin films were fabricated on MgO substrates by pulse laser deposition. The surface morphology indicates homogeneous distribution of grain with an average surface roughness $\sim $ 2-5 nm. Highly frequency dispersive spectra were observed between 120 K to 220 K suggests relaxor-like nature of epitaxial PFW thin films. Relaxor behavior was suppressed and dielectric dispersion increased with decrease in thickness from 300 nm to 50 nm. Modified Curie-Weiss law was used to analyze the relaxor character of films. Dielectric characteristic were further studied using different DC bias field $\sim $ 5 kV/cm over wide range of temperature to investigate the polarization properties below freezing temperature. The impedance spectroscopy was carried out to check the grain and grain boundary effects near the dielectric dispersion regions. Magnetization vs. applied magnetic field displayed weak ferromagnetic properties. Temperature dependent polarized Raman spectroscopy were carried out to investigate the change in crystal structure, lower frequency F$_{2g}$ phonon mode, A$_{1g}$ phonon mode near the dielectric dispersion region. In plane compressive strain plays vital role to suppress relaxor behavior in thin films compare to single crystal/bulk counter part. [Preview Abstract] |
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S1.00114: Multiferroic properties of artificially designed Perovskite-Spinel Heterostructures Sandra Dussan, Manoj K. Singh, Ram S. Katiyar Multiferroics materials are a class of functional material that combines two or more ordered parameters i.e. ferromagnetic, ferroelectric and ferroelastic. The recent finding of multiferroic composite material with the coexistence of these properties has attracted the attention of various researchers due to its potential applications in highly sensitive sensors and actuators as well as multistate memory devices. We synthesized and characterizatied CoFe$_{2}$O$_{4}$-BiFeO$_{3}$ (CFO-BFO) heterostructure thin films grown on SrTiO$_{3 }$(111), (100) substrates using Pulsed laser deposition. The XRD patterns of CFO-BFO multilayered films evidenced that all picks correspond to CFO and BFO structure also confirmed by their respective Raman spectra. We observed three peaks at 136, 168, and 215 cm$^{-1}$ that can be assigned to A$_{1}$(TO) modes of the BFO pure phase and at 468 and 695 cm$^{-1}$ correspond to CFO. Room temperature M-H exhibited well-shaped magnetization hysteresis loops, good saturation and high coercivity. Preliminary results evidenced the existence of ferroelectricity and magnetic properties in heterostructure. [Preview Abstract] |
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S1.00115: Single Phase multiferroics Pb\{(Zr$_{1/2}$Ti$_{1/2}$)$_{x}$(Fe$_{1/2}$Ta$_{1/2}$)$_{1-x}$\}O$_{3}$ thin films Dilsom A. Sanchez, Ashok Kumar, Ram S. Katiyar The epitaxial Pb{\{}(Zr$_{1/2}$Ti$_{1/2})_{1-x}$(Fe$_{1/2}$Ta$_{1/2})_{x}${\}}O$_{3}$ (PZTFT) (x = 0.1, 0.2, 0.3) thin films were fabricated by pulsed laser deposition. X-ray diffraction (XRD) patterns of all compositions showed single phase at room temperature without any pyrochlore phase. These materials showed good ferroelectric and ferromagnetic properties at room temperature. Room temperature multiferroicity were observed in PZTFT for x $>$ 10{\%}. PZTFT illustrated high dielectric constant and low loss at room temperature. The dielectric maximum temperature shifted to lower temperature side with increase in iron and tantalum concentration. Magnetization vs. applied magnetic field (M-H) curves showed well defined hysteresis with ramanent magnetization ($\sim $ 0.004- 0.13 emu/gm) and very small coercive field (900 Oe). Preliminary results indicate that PZFT is a promising candidate of room temperature multiferroic materials. AC and DC conductivity of PZTFT showed very low conductivity $\sim $ 10$^{-9}$ to 10$^{-7}$ S/cm$^{-1}$ at room temperature. [Preview Abstract] |
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S1.00116: ABSTRACT WITHDRAWN |
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S1.00117: Strain induced electric field driven relaxor ferroelectricity in BaZr$_{x}$Ti$_{1-x}$O$_{3}$ system Tanmoy Maiti, Ruyan Guo, Amar Bhalla A revised complete phase diagram of Ba(Zr$_{x}$Ti$_{1-x})$O$_{3}$ (0.0$\le $x$\le $1.0) has been developed based on evaluation of their crystallographic, dielectric, and ferroelectric properties. A new understanding of the relaxor behavior in this system, e.g. associated with the local elastic strains at the nanoscale, has been gained and presented in this paper. Two different kinds of relaxor behaviors are observed in the BZT system; one is dominated by polar Ti-rich regions and another by non-polar Zr-rich regions. BZT relaxor compositions are characterized by measurement of their dielectric (under bias), pyroelectric, and thermal expansion properties in a wide range of temperatures. The structure of the BZT compositions was evaluated by X-ray and neutron diffraction studies. Their local structure has been also probed by micro-Raman spectra. Although the global symmetry of BZT relaxors is cubic from neutron diffraction studies, non-cubic local symmetry is evident based on the micro-Raman spectra of BZT relaxors. [Preview Abstract] |
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S1.00118: Comparative study of electronic structures and nonproportionality of scintillator materials Wahyu Setyawan, Romain Gaume, Robert Feigelson, Stefano Curtarolo The electronic structures of selected scintillator materials for gamma-ray detection are calculated. We use Vienna Ab-initio Simulation Package with projector augmented waves pseudopotentials and exchange-correlation functionals as parameterized by Perdew-Burke-Ernzerhof. Curvatures of the top of valence band and the bottom of conduction band are calculated. Parameters are introduced to measure the degree of nonproportionality of photon response of the scintillators. Tha data show an interesting correlation between the band curvatures and the nonlinearity. The results can be used to guide the design of future proportional scintillators. [Preview Abstract] |
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S1.00119: Synthesis and Characterization of Alumina/Titania Nanofibers R.K. Feaver, D.A. Perhay, A.F. Lotus, E.T. Bender, G.G. Chase, R.D. Ramsier, N. Stojilovic Both alumina and titania nanofibers are promising materials for use in high-temperature applications. In an attempt to access the properties of these two materials systems simultaneously we synthesize alumina/titania nanofibers by electrospinning. We characterize their properties using different analytical methods (scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, and infrared, and X-ray photoelectron spectroscopies). We compare the properties of these mixed fibers with pure alumina and pure titania nanofibers and investigate the effects of annealing. [Preview Abstract] |
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S1.00120: Controlled TiO$_{2}$ nanoparticles on solid substrate for high gate dielectric of a pentacene based organic thin film transistor (OTFT) Himadri Acharya, Jinwoo Sung, Geun Tak Lee, Tae Hee Kim, Byung Gil Min, Cheolmin Park Ordered high$ k$ TiO$_{2}$ nanoparticles on substrate in large area have been developed using self assembled poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) and Ti-precursors by simple spin coating method. Calcination at 600$^{0}$C in ambient atmosphere removes both blocks of the polymers from the substrate and results in well ordered arrays of TiO$_{2}$ nanoparticles. Subsequent spin coating of polystyrene (PS) insulator was performed to generate gate dielectric film with higher permittivity on which pentacene based organic thin film transistor (OTFT) was developed to investigate the permittivity effect on transistor performance. The arrays of TiO$_{2}$ nanoparticles firmly adhering to substrate exhibit a significant dielectric constant enhancement when used for capacitance measurement. The incorporation of single walled carbon nanotube (SWNT) during the formation of TiO$_{2}$ nanoparticles on substrate further improves the transistor behavior by electrostatic coupling of high $k$ TiO$_{2 }$dielectric ($\sim $ 80) with SWNT. [Preview Abstract] |
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S1.00121: SEMICONDUCTORS |
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S1.00122: Low-bias Transport Features in a Quantum Point Contact with a Variable Aspect Ratio Bryan Hemingway, Tai-Min Liu, Andrei Kogan, Steven Herbert, Michael Melloch Quantum Point Contact (QPC) devices frequently display a zero- bias conductance anomaly (ZBA), the origin of which is not fully understood. To investigate a possible connection between the ZBA and the device geometry, we use a four-gate QPC device patterned on a GaAs/AlGaAs semiconductor heterostructure, aiming to achieve independent control over the transverse and the longitudinal potential profiles. In several regimes, we find a narrow ZBA that shows a pronounced temperature dependence for T$<$100 mK. Coulomb peaks arise under certain device settings, suggesting a weakly bound state located in the QPC. For other settings, we observe a plateau below the first conductance step. The plateau's conductance varies as the aspect ratio of the confining potential is changed. We describe a series of magnetic field measurements that show splitting of the ZBA and compare the findings to our measurements in a different, very short device which displayed no ZBA. [Preview Abstract] |
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S1.00123: Magnetooptical and magnetic studies of Co and Cr doped CdMnTe S. Shen, X. Liu, Y.J. Cho, J. Furdyna, M. Dobrowolska, Y.H. Hwang, Y.H. Um We investigate the magnetooptical and magnetic properties of two new CdMnTe-based diluted magnetic semiconductors. The first system consists of a series of Cd$_{1-x-y}$Mn$_ {x}$Cr$_{y}$Te alloys with Mn concentration x fixed at $\sim$0.37 and controlled Cr concentration y in the range $0 < y < 0.07$. The second system is the quaternary Cd$_{1-x-y}$Mn$_{x}$Co$_{y}$Te alloy, with the same Mn concentration (x = 0.37) and the Co concentration y in the range $0 < y < 0.009$. These systems are of interest in that they are expected to involve interactions of the minority magnetic ions (Cr and Co, respectively) with the surrounding majority Mn ions. Indeed, optical absorption and MCD spectra observed on these alloys reveal a series of new ``impurity'' peaks that are not present in the Cd$_{0.63}$Mn$_{0.37}$Te control samples. It is interesting that the magnetic field dependence of the MCD spectra as well as SQUID measurements reveal a ferromagnetic-like hysteresis loop in Cd$_{1-x-y}$Mn$_ {x}$Cr$_{y}$Te samples with Cr concentration y in the range of $0 < y < 0.03$. Surprisingly, the FM loop survives up to 295 K. But this ferromagnetic behavior is not observed in samples with $y > 0.05$. One should note that FM loops were not observed in Cd$_{1-x-y}$Mn$_{x}$Co$_{y}$Te samples. [Preview Abstract] |
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S1.00124: Experimental investigation of spin interference phenomena in InGaAs/InAlAs rectangular loop arrays Sebastien Faniel, Takaaki Koga, Yoshiaki Sekine We report spin interference experiments in rectangular loop arrays built from InGaAs quantum wells. Low $T$ magnetotransport measurements in such systems exhibit Alt'shuler-Aronov-Spivak (AAS) oscillations stemming from the interference between closed loop trajectories in clockwise and counterclockwise directions. In InGaAs devices, that show a large, gate-controllable spin-orbit (SO) interaction, this interference can be tuned by means of a front gate voltage, leading to a modulation of the AAS oscillations. The present work focuses on the anisotropic interplay between the Rashba and the Dresselhaus contributions to the SO interaction. Along the [-110] and the [110] crystallographic directions, the Rashba and the Dresselhaus effective magnetic fields are expected to be added or subtracted to/from each other. To probe this anisotropy, we study rectangular loop array interferometers whose sides are aligned along these two particular crystallographic directions. We analyze our results using a model that includes both the Dresselhaus and the Rashba SO interactions and accounts for phase decoherence in the devices. This work was supported by KAKENHI (19684009) and also partially by Support Center for Advanced Telecommunications Technology Research, Foundation (SCAT). [Preview Abstract] |
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S1.00125: Zero-field spin-splitting and spin lifetime in $n$-InSb/In$_{1-x}$Al$_{x}$Sb quantum wells A.M. Gilbertson, M. Fearn, J.H. Jefferson, B.N. Murdin, P.D. Buckle, L.F. Cohen The Rashba and Dresselhaus coupling parameters are calculated for a range of carrier densities in [001]-grown $\delta $-doped $n$-type InSb/In$_{1-x}$Al$_{x}$Sb quantum wells using an established 8 band k.p formalism [1]. It is shown that both sets of parameters scale approximately linearly with carrier density. In contrast to other material systems the Dresselhaus contribution to spin splitting is found to be of significant and comparable value to the Rashba mechanism under certain conditions. The inherently large BIA induced SO coupling in these systems is shown to have considerable effect on the spin lifetime$\tau _{s[1\bar {1}0]} $for spins oriented along $[1\bar {1}0]$based on D'yakonov-Perel' mechanism [2]. The relaxation rate of spins oriented in the [001] direction is found to be dominated by the k-linear Rashba and Dresselhaus coupling parameters and at least an order of magnitude greater than in the $[1\bar {1}0]$ direction [3]. Comparison to recent experimental results in similar structures is presented. [1] P. Pfeffer and W. Zawadzki, PRB \textbf{59}, 8 R5312 (1999) [2] Averkiev \textit{et al.}, J. Phys.:Condens. Matter \textbf{14} (2002) [3] A.M.Gilbertson \textit{et al.}, PRB \textbf{77} (16), 165335 (2008) [Preview Abstract] |
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S1.00126: Nuclear Effects on Electron Spin Resonance in Gallium Arsenide Aaron Jones, John Colton, Benjamin Heaton, Daniel Jenson, Michael Johnson Electron spin properties in gallium arsenide (GaAs) are investigated by electron spin resonance (ESR), the signal being detected via optical Kerr rotation. Experiments in ESR have shown broadened and shifted resonance peaks due to the hyperfine nuclear interaction. Simultaneous nuclear magnetic resonance (NMR) reduces the nuclear effects by preventing the nuclei from responding to the changing electron polarization. However, low NMR power still permits the electron spins to have a great effect on the nuclei, which then affect the electrons in return. We have developed a tunable, impedance-matched, lumped-element rf circuit which increases the output power at the resonant frequencies of the three nuclei ($^{75}$As, $^{69}$Ga, and $^{71}$Ga). Improved ESR data resulting from stronger NMR is presented. [Preview Abstract] |
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S1.00127: ABSTRACT WITHDRAWN |
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S1.00128: Generation of spin polarized current in a semiconductor by an ohmic contact containing ferromagnetic particles Leonardo Castelano, Yu-Chang Chen, S.-R. Eric Yang, Lu Sham We investigate the possibility of injection of spin polarized current into a semiconductor from an ohmic contact containing ferromagnetic metal (FM) nanodots. The polarization is created by the spin-dependent scattering of the current carriers with the FM dots with aligned magnetizations. The usually inefficient polarization generation due to the resistance mismatch between the metal electrode and the semiconductor is mitigated by the reduction of the mismatch between the FM dots and the heavily doped electrode. When the paramagnetic semiconductor is connected by two such electrodes containing FM dots forming a spin valve system, the magnetoresistance is calculated to be sizable. We report the calculation results for two examples: (i) silicon connected to electrodes of poly-silicon contain the FM dots and (ii) the heavily doped region of InAs as contact. [Preview Abstract] |
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S1.00129: Spin polarization of doped II-VI nanocrystals Savas Delikanli, William Falls, Mesut Yasar, Athos Petrou, Hao Zeng The photoluminescence of Mn2+ doped CdSe nanoparticles synthesized by solution phase method has been studied as a function of nanocrystal size and the circular polarization of the light emitted from Cd$_{1-x}$Mn$_{x}$Se nanoparticles has been investigated as a function of applied magnetic field in the 7-100 K temperature range. Spin polarized photoluminescence emission from Cd$_{1-x}$Mn$_{x}$Se was observed and strongly depends on the growth time of the nanoparticles. They show negatively spin polarized photoluminescence emission and the behavior of spin polarization strongly depends on the applied field. Spin polarization initially saturates between 1-3 Tesla and shows an unexpected linear increase beyond 3 Tesla. Magnetization of Cd$_{1-x}$Mn$_{x}$Se nanoparticles shows mostly paramagnetic behavior with some hysteresis at low temperatures. [Preview Abstract] |
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S1.00130: Effect of pressure on spin-carrier interactions in Sb$_{2-x}$V$_{x}$Te$_{3}$ and Sb$_{2-x}$Cr$_{x}$Te$_{3}$ single crystals Matthew L. Bowers, Jeffrey S. Dyck, Cestmir Drasar, Petr Lostak Bulk, single crystal samples of diluted magnetic semiconductors Sb$_{2-x}$Cr$_{x}$Te$_{3}$ and Sb$_{2-x}$V$_{x}$Te$_{3}$ are being studied in an effort to understand the electrical and magnetic mechanisms that cause these and other similar DMS materials to undergo a ferromagnetic transition at low temperature.~ By taking advantage of the fact that hydrostatic pressure alters the carrier concentration in these materials, our aim is to examine the carrier-mediated magnetic interactions at work.~ Electrical resistivity and Hall effect measurements were made as a function of temperature and pressure for a variety of samples with varying concentration of magnetic impurity. The results show that the Curie temperature is increased for values of x = 0.08 in Cr-doped samples, and was decreased for x = 0.02 or 0.03 for both Cr- and V-doped samples.~ A model based on the full oscillatory nature of the RKKY interaction, incorporating the pressure dependence of both carrier concentration and magnetic impurity separation, has been developed for comparison to our experimental results. [Preview Abstract] |
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S1.00131: SQUID measurements of Mn$_{x}$Sc$_{(1-x)}$N and Fe$_{0.1}$Sc$_{0.9}$N Films Grown by Molecular Beam Epitaxy Han-Jong Chia, Costel Constantin, Kangkang Wang, Abhijit Chinchore, Arthur Smith, John Markert We report SQUID magnetic measurements on N-rich and N-poor Mn$_{x}$Sc$_{(1-x)}$N and Fe$_{0.1}$Sc$_{0.9}$N films grown on ScN(001)/MgO(001) substrates by radio frequency plasma assisted molecular beam epitaxy. Ferromagnetism is present in both the Mn doped (x ranging from 3 to 15\%) and the Fe doped ScN samples. Measurements on N-poor Mn$_{0.03}$Sc$_{0.97}$N and Mn$_{0.15}$Sc$_{0.85}$N (x=15\%) show Curie temperatures of 383 K and 361 K, respectively. The Fe$_{0.1}$Sc$_{0.9}$N film shows a Curie temperature above 350 K as well. Further studies will be required to determine the origin of the ferromagnetism and the Curie temperature of the remaining Mn$_{x}$Sc$_{(1-x)}$N films. This work is supported by: Seton Hall: University Research Council; Ohio University: DOE-BES Grant No. DE-FG02-06ER46317 and NSF Grant No. 0730257; and UT Austin: NSF Grant Nos. DMR-0605828 and DGE-0549417, Welch Foundation Grant No. F-1191. [Preview Abstract] |
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S1.00132: Probing current and temperature effects on the direct insulator-quantum Hall transition Kuang Yao Chen, C.-T. Liang, N. Aoki, Y. Ochiai, K.A. Cheng, Li-Hung Lin, C.F. Huang, Yu-Ru Li, Yen Shung Tseng, Chun-Kai Yang, Po-Tsun Lin, Jau-Yang Wu, Sheng-Di Lin We report a magneto-transport study on the two-dimensional electron system (2DES) in an AlGaAs/GaAs heterostructure. The direct insulator-quantum Hall transition is observed at different temperatures by increasing the magnetic field $B$ perpendicular to the 2DES. Such a transition can also be observed by varying the current $I$ since the electron temperature is given by $T _{e} = CI ^{\alpha}$ in both the insulator and quantum Hall sides of the transition. Here $\alpha$ denotes the exponent for the power law and $C$ is a constant at a particular magnetic field. The value of $\alpha$ may be determined by comparing the temperature and current dependences. Our results show that $\alpha$ takes on different values on either sides of the transition point, indicating the presence of different heating mechanisms in the low-field insulator and in the quantum Hall liquid. The effects due to electron-electron interaction and scattering are also discussed. [Preview Abstract] |
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S1.00133: The Quantum Hall Effect Revisited Tobias Kramer, E.J. Heller, R.E. Parrott, C.-T. Liang, C.F. Huang, K. Y. Chen, L.-H. Lin, J.-Y. Wu, S.-D. Lin Experiments shown here reveal inflection points of the Hall resistivity at half-integer filling factors 5/2 and 7/2 which become more pronounced with increasing current and finally lead to half-integer plateau like structures. These features contradict the edge-state picture of the quantum Hall effect (QHE) and also the disorder picture of the QHE, which cannot explain a gap directly in the middle of a Landau level. We present a novel approach to the quantum Hall effect, which allows us to calculate the electronic transport in a highly non-uniform Hall field, which is present in two opposite corners of a Hall bar, the hot-spots. Precisely in one corner electrons are injected into the device and we derive the local density of states there. We obtain a self-consistent equation for the current-voltage relation through the Ohmic contact and thus a computable theory of the quantum Hall effect, which predicts a unique modulation and splitting of Landau levels caused by the presence of a high electric field exactly in line with the experimental observations. [Preview Abstract] |
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S1.00134: The doubling of von Klitzing's constant h/e$^{2}$ Keshav Shrivastava The Hall resistivity is found to become a function of spin. For positive spin, one value is found but for negative sign in the spin, another value occurs. In this way, there is never only one value of the resistivity but there is doubling of values. The value of the von Klitzing's constant is a special case of more general dependence of resistivity on the spin. We investigate the effect of Landau levels. For extreme quantum limit, n=0, the effective charge of the electron becomes (1/2)ge. The fractional charge arises for finite value of the angular momentum. The fractional as well as the integral values of the charge are in full agreement with the experimental data. The generalized constant is h/[(1/2)ge]e which under special conditions becomes h/e$^{2}$ which is the von Klitzing's constant [1]. [1] K. N. Shrivastava, Phys. Lett. A 113,435(1986); A326,469(2004); Mod. Phys. Lett. 13,1087(1999); 14,1009(2000); AIP Conf. Proc. 909, 43-49(2007); 909.50-56(2007);1017, 422-428(2008);1017,326-330(2008); 1017, 47-56(2008), Proc. SPIE(USA)7155,71552F1-8[7155{\_}86](2008). [Preview Abstract] |
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S1.00135: Correlating exciton localization with compositional fluctuations in InGaN/GaN quantum wells grown on the GaN (0001) and (1-101) surfaces Daniel Rich, Stanislav Khatsevich, Xingang Zhang, Daniel Dapkus We have used spatially and temporally resolved cathodoluminescence (CL) to study the carrier recombination dynamics of InGaN quantum wells (QWs) grown on GaN (0001) and (1-101)-oriented facets of GaN triangular prisms prepared by lateral epitaxial overgrowth in a MOCVD system. Recently, growth on non-[0001]-oriented crystal planes is being considered for creating more favorable parameters for devices, owing to significant reductions of the internal field that otherwise reduces the electron-hole oscillator strength for radiative recombination. The effects of In migration during growth on the resulting QW thickness and composition were examined. We employed a modified variable temperature time- resolved CL imaging approach that enables a spatial correlation between regions of enhanced exciton localization, luminescence efficiency, and radiative lifetime with the aim of distinguishing between excitons localized in In-rich quantum dots and those in the surrounding Ga-rich QW regions. A thermally activated nonradiative recombination model was invoked to explain a reversal in the spatial dependence of lifetime between cases of high and low temperatures, in which we show that nonradiative recombination is linked to an enhanced exciton dissociation at high temperatures. [Preview Abstract] |
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S1.00136: Enhanced Luminescence in an amorphous AlN:Ho thin film by co-doped Gd+3 Cathodoluminescence Muhammad Maqbool, Hugh Richardson, Martin Kordesch Sputter deposited thin films of amorphous AlN:Ho (1 at. {\%}) emits in the green (549 nm) region of the visible spectrum under electron excitation. The addition of Gd (1 at. {\%}) in the film enhances the green emission linearly after thermal activation at 900 \r{ }C for 40 minutes in a nitrogen atmosphere. The luminescence enhancement saturates when the gadolinium concentration reaches four times the holmium concentration.. The optical bandgap of amorphous AlN is about 210 nm, so that the film is transparent in the ultraviolet, allowing us to observe the ultraviolet emission at 313 nm from Gd. No significant quenching of the Gd emission is observed. EDX spectra confirm the increasing concentration of Gd. XRD analysis shows no peaks other than those arising from the Si (111) substrate, confirming that the films are amorphous. [Preview Abstract] |
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S1.00137: The carrier property of Al$_{x}$Ga$_{1-x}$N/GaN nanowire fabricated by a dual-beam focused ion beam Jenn-Kai Tsai, W.Y. Pang, Y.H. Chang, Ikai Lo In this study, the Al$_{x}$Ga$_{1-x}$N/GaN high electron mobility transistor structure was grown on GaN template substrate using a radio frequency plasma assisted molecular beam epitaxy. The undoped GaN template substrate was grown on c-sapphire substrate by metal organic vapor phase epitaxy system. The carrier property was performed by a Hall effect measurement. The mobility and carrier density obtained of the as-grown HEMT was 1814 cm$^{2}$/V s and 1.29x10$^{14}$ cm$^{-2}$, respectively. The nanowire was patterned on the Al$_{x}$Ga$_{1-x}$N/GaN heterostructure by a dual-beam focused ion beam. The first step was to process a Hall bar pattern. The second step was to reduce the width of active channel. The wire width of 100 nm of nanowire was fabricated successfully. The carrier property of nanowire was evaluated at the different temperature from 4 to 300 K. [Preview Abstract] |
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S1.00138: Magneto-transport Study on the nanometer-scaled quantum-ring interferometer made of Al$_{x}$Ga$_{1-x}$N/GaN heterostructures Wen-Yuan Pang, Ikai Lo, Yu-Chi Hsu, Yen-Liang Chen, Ming-Hong Gau, Yung-Hsi Chang, Ying-Chieh Wang, Jih-Chen Chiang, Jen-Kai Tsai The quantum-ring interferometer has been proposed for spintronic application. The Al$_{x}$Ga$_{1-x}$N/GaN samples were grown on GaN-template buffer layer by plasma-assisted molecular beam epitaxy. We obtained the mobility and carrier density of two-dimensional electron gas to be 19845 cm$^{2}$/Vs and 5.18x10$^{12}$ cm$^{-2}$ by conventional van der pauw Hall measurement at temperature of 4.2 K, respectively. The samples were used to fabricate quantum-ring field-effect-transistors with different widths of conducting channel by Focus Ion Beam. The magneto-resistance measurement at temperature of 0.35 K and magnetic field up to 12 T was performed on these samples. The electronic characterization of nanometer-scaled quantum-ring made of high-mobility Al$_{x}$Ga$_{1-x}$N/GaN heterostructures has been studied. [Preview Abstract] |
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S1.00139: High Electron Mobility Al$_{x}$Ga$_{1-x}$N/GaN Heterostructures Grown by PAMBE on GaN Templates Prepared by MOCVD Yen-Liang Chen, Wen-Yuan Pang, Ming-Hong Gau, Yu-Chi Hsu, Wan-Tsang Wang, Jih-Chen Chiang, Ikai Lo, Chia-Ho Hsieh, Jenn-Kai Tsai A series high mobility Al$_{x}$Ga$_{1-x}$N/GaN heterostructures samples were grown on MOCVD-grown GaN templates by molecular beam epitaxy with different Al fractions(x = 0.017$\sim $0.355). The highest mobility in this series samples at liquid nitrogen temperature is 14110 cm$^{2}$/Vs with carrier concentration 2.87 x 10$^{12}$ cm$^{-2}$ and Al fraction x = 0.022. In our experiments, the carrier density decreases as Al content reduces. While the carrier density decreases from 1.54 x 10$^{13}$ cm$^{-2}$ to 2.87 x 10$^{12}$ cm$^{-2}$, the mobility increases. But as the carrier density decreases from 2.87 x 10$^{12}$ cm$^{-2}$, the mobility decreases. [Preview Abstract] |
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S1.00140: Electron heating in disordered 2DEG GaAs/AlGaAs structures by THz radiation Rahul Ramaswamy, Kai Wang, Matthew Bell, Andrei Sergeev, Aleksandr Verevkin, Gottfried Strasser, Vladimir Mitin, Darold Wobschall While numerous applications of heterostructures with two-dimensional electron gas (2DEG) in electronics require high-mobility of carriers, slow momentum relaxation creates substantial problems for employing these structures as various detectors of electromagnetic radiation. Significant kinetic inductance of carries does not allow one to use 2DEG-based sensors in combination with ordinary antennas and readouts, designed for Ohmic detectors. Keeping in mind sensor applications, we investigate the electron heating in disordered AlGaAs/GaAs structures at liquid nitrogen temperatures. In our experiments, 2DEG was overheated by DC current or THz radiation. The devices were fabricated from AlGaAs/GaAs structures and have widths of 50-150 $\mu$m and lengths varying from 3-50 $\mu$m. 2DEGs of various levels of disorder are used to change the kinetic inductance of our devices and to study effects of disorder on electron heating. Steady-state and quasi-optical THz heating measurements provide consistent data and allows us to determine basic parameters, such as electron-phonon relaxation rate, electron heat capacity of 2DEG, and radiation coupling. [Preview Abstract] |
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S1.00141: High-Frequency Electron Pumps used as an Entangler S. J. Wright, Godfrey Gumbs, Michael Pepper, M. D. Blumenthal, Danhong Huang We calculate the exchange interaction of two interacting electrons that are captured in the quantum dot (QD) formed by the DC electric potential applied to a pair of gates. A giga hertz AC pulse is applied to one of the gates to pump electrons from below the Fermi level. We shall discuss the mechanism for capturing and ejecting electrons from the quantum dot and the characteristics of the pumped current as a function of the DC voltage. A simple model for the observed temperature dependence of the pumped current will be presented. The measured current shows plateaus at $Nef$, where $N=1,2,\cdots$, $e$ is the magnitude of the electron charge and $f$ is the frequency of the pulse. The QD capturing the electrons is modeled by a harmonic confining potential. We calculate the spin singlet and spin triplet energies which then determine the exchange interaction $J$ for $N=2$. As the QD moves from just above the Fermi level to a height when the electrons are ejected, the confinement is strong just after the capture but the size of the QD continues to increase. When the size of the QD is increased, we show that the energy of the spin singlet and spin triplet state gets larger over a range of values for the size of the QD. We will present calculated results for the energies of entangled electrons and possible related experiments. [Preview Abstract] |
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S1.00142: TEM analysis of Microstructure of AlN/sapphire grown by MOCVD B. Cai, M. L. Nakarmi AlN and Al-rich AlGaN have emerged as promising deep ultraviolet (UV) materials for the development of deep ultraviolet optoelectronic devices such as light emitting devices and detectors in the spectral range down to 200 nm. High quality AlN/sapphire can be used as templates to grow nitride based ultraviolet and deep ultraviolet photonic devices due to high thermal conductivity and transparency of the light. The performance of the devices depends of the microstructures of the templates. We report on the microstructure analysis of AlN epilayer grown on sapphire. Both plane and cross section views are investigated by high resolution transmission electron microscopy. It has been revealed that the dislocations are greatly reduced by using high temperature buffers. Density of edge dislocations dominates the total density of dislocations. The microanalysis of Al-rich AlGaN epilayers grown on AlN/sapphire templates will also be presented. Implications of our finding for the applications in deep UV optoelectronic devices will be discussed. [Preview Abstract] |
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S1.00143: Reduction of the Specific Contact Resistance in p-type GaN-based Devices via Polarization Doping. Jacob Melby, Jason Gu, Li Huang, Yuhrenn Wu, Lisa Porter, Robert Davis The power efficiency of GaN-based devices is sensitive to energy loss at p-type semiconductor contacts. Low resistance contacts to p-type GaN are difficult to achieve due to limitations in extrinsic acceptor doping. These limitations can be avoided via polarization doping. Au/Ni contacts deposited on a 2nm thick strained In$_{x}$Ga$_{1-x}$N capping layer atop a p-type GaN layer exhibited three orders of magnitude reduction in the specific contact resistance versus the single layer p-type GaN control. Increased band bending near the interface due to the polar field resulted in a reduced tunneling barrier width and a decrease in the specific contact resistance. At a minimum critical capping layer thickness, a two-dimensional hole gas (2DHG) forms in the In$_{x}$Ga$_{1-x}$N layer. The effect of the composition and thickness of the capping layer on the specific contact resistance and the hole concentration in a 2DHG has been determined using self-consistent solutions to the Schr\"{o}dinger and Poisson equations and will be reported in the presentation. The results of these simulations will also be compared with data from electrical measurements on actual In$_{x}$Ga$_{1-x}$N/GaN heterostructures. [Preview Abstract] |
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S1.00144: Kinetic Monte Carlo Simulation Studies of Nanocolumn Formation in Two-Component Epitaxial Growth Shu Zheng, Wenguang Zhu, G. Malcolm Stocks, Zhenyu Zhang Recent experimental studies have revealed that well-ordered one-dimensional column structures are formed via self-assembly during two-component epitaxial growth of a variety of materials, including diluted magnetic semiconductors and high-Tc superconductors. Here we use~kinetic Monte Carlo simulations to study the morphological evolution of a two-component epitaxial system, based on a (1+1)-dimensional lattice model. We find that in systems where the atom-atom interactions obey the relationship of E$_{AB} \quad <$ (E$_{AA}$+E$_{BB})$/2, ordered nanoscale columns can be formed during the growth. The dependence of the ordering on the growth temperature and deposition rate and on the relative concentration of the two components is also explored. [Preview Abstract] |
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S1.00145: ABSTRACT WITHDRAWN |
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S1.00146: Improved conductivity observed in doped layered oxysulfides [Cu$_{2}$S$_{2}$][Sr$_{n+1}M_{n}$O$_{3n-1}$] Koichi Ushiyama, Hiraku Ogino, Shigeru Horii, Jun-ichi Shimoyama, Kohji Kishio [Cu$_{2}$S$_{2}$][Sr$_{n+1}M_{n}$O$_{3n-1}$] is a group of semiconducting oxyslfides which are composed of alternate stackings of Cu$_{2}$S$_{2}$ antifluorite layers and perovskite-based $M$O$_{2}$ planes$^{[1]}$. Perovskite structures are expected to show interesting properties such as high-temperature superconductivity and magnetoresistance. However they have attracted less attention because they have relatively high resistivity and there are only a few reports of career doping$^{[2]}$. In this study, we found Na substitution was especially effective on [Cu$_{2}$S$_{2}$][Sr$_{2}$CoO$_{2}$]. Systematic decreases in lattice parameter with increasing doping levels indicated that Na was successfully substituted at the Sr site. Remarkable decrease in resistivity was observed especially at low temperatures, from 10$^{3} \quad \Omega $cm (undoped) to 0.15 $\Omega $cm at 50 K. This value is lowest ever reported in the [Cu$_{2}$S$_{2}$][Sr$_{n+1}M_{n}$O$_{3n-1}$] oxysulfides. [1] K. Ueda\textit{ et al.}, \textit{Chem. Mater.} \textbf{13} (2001) 1880 [2] K. Ito \textit{et al.}, \textit{J. Appl. Phys.} \textbf{99} (2006) 08F705 [Preview Abstract] |
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S1.00147: Temperature dependent structural disintegration of delafossite CuFeO$_{2}$ P. Shojan, Ashok Kumar, Ram Katiyar Single phase delafossite p-type CuFeO$_{2}$ (CFO) semiconductor was synthesized by modified solid state reaction technique. X-ray diffraction (XRD) and X-ray photo spectroscopy (XPS) studies suggest pure phase of CFO and Energy dispersive X-ray spectroscopy (EDX) also revealed that the atomic ratio Cu and Fe is 1:1. The XPS spectra showed two intense Cu 2p3/2 and 2p1/2 peaks at 932.5 eV and 952 eV and two Fe 2p3/2 and 2p1/2 peaks at 710 eV and 725 eV suggesting Cu and Fe ions are in +1 and +3 state with high spin S=5/2. The room temperature Raman spectra of CFO displayed two main strong active modes at 351 cm$^{-1}$ and 692 cm$^{-1}$ that matched with other delaffosite structure. Temperature dependent Raman spectra indicate that the lowest mode vanished or overdammped at $\sim $ 400 K where as higher modes shifted to lower frequency side with significantly decreased in intensity. We have also observed a low frequency (E$_{2} \quad ^{low})$ mode at 79 cm$^{-1}$ using 532 nm ($<$5MHz line width) laser line. The line width and intensity of the lowest mode indicates temperature independent behavior. Raman Spectra were carried out from 80 K to 1300 K which revealed structural disintegration in CFO over 800 K in air. The structural degradation is counter confirmed by XPS, XRD, DTA measurements. Around 800 K in air, CFO disintegrates to form CuO and CuFe$_{2}$O$_{4}$. [Preview Abstract] |
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S1.00148: Structural and transport studies on nanostructured SnS synthesized by solvothermal process Pratima Agarwal, Gouri S. Paul Nanostructured SnS has a lot of interest due to its potential application in optoelectronic devices such as solar absorber, near-infrared detector and as a holographic recording medium. SnS usually exhibits p-type conduction and reported to have a direct band gap of about 1.32-1.5 eV and an indirect band gap of 1-1.3 eV dependent of the condition of preparation. In this work we report structural and transport studies on nanostructured SnS synthesized by solvothermal process for different reaction time (RT). Structural and morphological analyses are carried out by XRD, SEM and TEM. It is observed that structure of the as-prepared SnS powder samples vary with RT. SAED patterns reveal that as synthesized SnS are single crystals. Transport measurements done on thin films prepared by Doctor's blade techniques show that films are thermally stable and uniform through out the surface. The conductivity of the SnS thin films is measured in coplanar geometry in the temperature range (303--463) K. The films show thermally activated conduction and the curves are identical for both heating and cooling cycle. [Preview Abstract] |
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S1.00149: Weak ferromagnetism in single crystalline Zn$_{1-x}$Co$_{x}$O thin films H.-J. Lee, B.-G. Park, J.-Y. Kim, J.-H. Park, Y. H. Jeong Diluted Magnetic Semiconductors (DMS) have been actively searched for many years; a prospect of spintronic devices. Transition metal doped oxide materials, especially ZnO-based DMS, have been of particular interest as a high Tc material. Co doped ZnO thin films, for example, were reported to show ferromagnetic properties at room temperature. However, various subsequent studies including ours do not seem to converge on a definite picture and controversy continues. The observed ferromagnetism in DMS is very sensitive to the preparation methods and conditions. Therefore, what is needed to resolve the situation are well synthesized and thoroughly characterized samples. Zn$_{1-x}$Co$_{x}$O thin films were epitaxially grown on sapphire (0001) substrates by PLD technique and monitored by In-situ RHEED. Surface morphology and crystallographic characteristic evaluated using AFM and XRD. The magnetization, resistivity, and Hall effect measurements were carried out systematically as a function of Co contents using a QD PPMS. To clarify the electronic structure and the magnetic properties associated with the Co ions in Zn$_{1-x}$Co$_{x}$O, we have performed X-ray Absorption Spectroscopy and X-ray Magnetic Circular Dichroism measurements. These results and their implications for the understanding of ferromagnetism in Zn$_{1-x}$Co$_{x}$O will be discussed. [Preview Abstract] |
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S1.00150: Transport Measurements and Synchrotron-Based X-Ray Absorption Spectroscopy of Iron Silicon Germanide Grown by Molecular Beam Epitaxy Nader Elmarhoumi, Ryan Cottier, Greg Merchan, Amitava Roy, Chris Lohn, Heike Geisler, Carl Ventrice Jr., Terry Golding Some of the iron-based metal silicide and germanide phases have been predicted to be direct band gap semiconductors. Therefore, they show promise for use as optoelectronic materials. We have used synchrotron-based x-ray absorption spectroscopy to study the structure of iron silicon germanide films grown by molecular beam epitaxy. A series of Fe(Si$_{1-x}$Ge$_{x})_{2}$ thin films (2000 -- 8000{\AA}) with a nominal Ge concentration of up to x = 0.04 have been grown. X-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) measurements have been performed on the films. The nearest neighbor co-ordination corresponding to the $\beta $-FeSi$_{2}$ phase of iron silicide provides the best fit with the EXAFS data. Temperature dependent (20 $<$ T $<$ 350 K) magneto transport measurements were done on the Fe(Si$_{1-x}$Ge$_{x})_{2}$ thin films via Van Der Paw (VDP) Hall configuration using a 0.5-1T magnetic field and a current of 10-200 $\mu $A through indium ohmic contacts, the Hall coefficient was calculated. Results suggest semiconducting behavior of the films which is consistent with the EXAFS results. [Preview Abstract] |
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S1.00151: Effect of N to In flux ratio on the InN surface morphologies grown on single crystal ZnO (000$\overline 1 )$ substrate by plasma-assisted molecular beam epitaxy Cheng-Hung Shih, Ikai Lo, Wen-Yuan Pang, Shih-Hung Chuang, Chia-Hsuan Hu, Chia-Ho Hsieh The surface morphology of InN epitaxial films grown on ZnO (000$\overline 1 )$ substrate by plasma-assisted molecular beam epitaxy has beam investigated. We found that the evolution of InN surface morphology was sensitive to the N/In flux ratio. With N/In flux ratio decreasing, the growth mode was changing from 3D to 2D growth. In addition, we found that In$_{2}$O$_{3}$ layer was formed at the interface between InN and ZnO when the N/In flux ratio was lower than 32 by the observation of XRD and TEM. [Preview Abstract] |
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S1.00152: Effect of negatively charged excitons on the phase coherent photorefractive effect in ZnSe quantum wells A. Kabir, H.P. Wagner We investigate the effect of negatively charged excitons (trions) on the efficiency and dephasing rate of the phase coherent photorefractive (PCP) effect in ZnSe/Zn$_{0.9}$Mg$_{0.1}$Se single quantum wells using 90 fs light pulses. Intensity, temperature and spectrally dependent measurements are performed in a transient four-wave mixing configuration. In the presence of trions the PCP effect is composed of both a fast dephasing component that is caused by the formation of a trion grating and a slower decaying component caused by an exciton grating. With decreasing temperature the trion dephasing rate significantly increases while the exciton dephasing rate remains almost constant. The trion dephasing rate also increases with decreasing barrier width between the ZnSe quantum well (QW) and the GaAs substrate which is attributed to an enhanced electron density of captured substrate electrons in the QW. Model calculations based on the optical Bloch equations are in agreement with the experimentally observed PCP traces. [Preview Abstract] |
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S1.00153: Effect of annealing temperature of ZnO seed layer on growing aligned ZnO nanorods Jenn-Kai Tsai, Chu-Yu Wei, Yi-Chi Chen, You-Cheng Jheng, Teen-Hang Meen Vertical aligned ZnO nanorod arrays were synthesized by hydrothermal method on the Si substrate with a sputtered thin ZnO seed layer on it. Different annealing temperatures of ZnO seed layer were studied in order to understand the ZnO nanorod growth mechanisms. The results show that ZnO nanorods grow faster if the seed layer annealed at higher temperature. The photoluminescence spectra exhibit ultraviolet emission and a broad green emission. The green emission is attributed to the oxygen vacancies in the ZnO nanorods. Further investigations using the scanning electron microscopy, x-ray diffraction, atomic force microscopy were also demonstrated. [Preview Abstract] |
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S1.00154: High Quality Epitaxial ZnO Films Grown Using Magnetron Sputtering Tom Oder Zinc oxide films were sputter-deposited at 500 $^{\circ}$C on sapphire, SiC and GaN substrates using different mixtures of Ar and O$_{2}$. Post-deposition annealing up to 900 $^{\circ}$C in N$_{2}$ with rapid thermal processor resulted in films whose crystalline quality improved with the annealing temperature. The effects of deposition and annealing using different Ar-O$_{2}$ gas mixtures were also investigated. Films grown on sapphire in a 1:1 Ar-O$_{2}$ mixture and annealed in N$_{2}$ at 900 $^{\circ}$C for 5 min had the best quality. Room-temperature photoluminescence spectroscopy measurements revealed a near band edge luminescence at 3.25 eV with a FWHM value of 126 meV. The two-theta XRD measurements of these films showed a peak at 34.8$^{\circ}$, which corresponds to the diffraction from the (0 0 2) plane of the ZnO and indicates a strong c-axis orientation perpendicular to the surface at the sapphire substrate. Results from the transport properties of these films determined using Hall-effect measurements will be discussed. [Preview Abstract] |
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S1.00155: IR-Dielectric functions of ZnBeTe alloys determined by spectroscopic ellipsometry Nirajan Mandal, Frank Peiris, Oleg Maksimov, Maria Tamargo Using spectroscopic ellipsometry, we have determined the complex dielectric function of a series of ZnBeTe II-VI semiconductor alloys between a spectral range of 2000 nm and 40,000 nm. A standard inversion technique was used to obtain the dielectric functions from the measured ellipsometric spectra. By modeling the dielectric functions as a collection of oscillators, representing longitudinal and transverse optical phonons associated with the ZnBeTe lattice, we were able to recover the phonon spectra for this alloy system. It is argued that the the additional phonon modes that are obtained from ellipsometry are best understood from the recently-proposed percolation model. [Preview Abstract] |
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S1.00156: A Method for Determining Refractive Indices of Compound Materials of Epilayers of Multilayer Quantum Structure Gagik Shmavonyan A method of determining the refractive indices of compound materials of epilayers of multilayer quantum structures of optoelectronic devices has been suggested. The difficulty with the determination of the refractive indices of the above-mentioned epilayers is that the exactness of the determination of the same parameters of compound materials of epilayers is not high as their values obtained by various methods are quite different. Therefore, the difference between values of bulk and epitaxially grown materials is great. For that reason beam profiles of light emitted from multilayer quantum structure of optoelectronic devices are experimentally investigated and theoretically calculated. The latter allows us to determine the refractive indices of compound epilayers of multilayer active layer of nanostructured optoelectronic devices. As this method consists in the confrontation of theoretical calculations and experimental results, it allows to precisely determine the refractive indices of compound epilayers. [Preview Abstract] |
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S1.00157: Synthetic Cu$_{2}$O crystals with various morphologies prepared by thermal oxidation Shahin Mani, Joon Jang, John Ketterson Cuprous oxide (Cu$_{2}$O) is an extensively studied semiconductor with a rich history in exciton related physics; it has also been a popular solar cell material. A major impediment to workers studying this material has been the difficulty in fabricating high quality crystals. Achieving a low concentration of impurities and defects is an essential requirement in obtaining increased exciton lifetimes. We have prepared high-quality crystals of Cu$_{2}$O by an improved thermal oxidation technique. Using this strategy we have formed crystals in various geometries including; i) platelets, ii) cylindrical wires, iii) hollow cylindrical structures, and iv) spheroids. The formation of hollow cylindrical structures or tubules of Cu$_{2}$O by oxidizing copper wires in air is especially surprising. We will discuss photoluminescence experiments involving one- and two-photon excitation and optical absorption measurements at 2 K from the synthetic samples, which in some respects out perform natural (geological) crystals. The more unconventional structures of Cu$_{2}$O may be utilized to confine excitonic matter or serve as high density exciton-polariton cavities [Preview Abstract] |
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S1.00158: Effects of atomic randomness on the band structure calculation of Si$_{1-x}$Ge$_{x}$ via density functional theory Md Hossain, Jonathan Freund, Harley Johnson Electronic band structure calculations for compound semiconductors are usually performed by averaging fitting parameters using the virtual-crystal-approximation in either the pseudopotential method or the tight binding method. The effect of atomic randomness is completely ignored in such calculations. In this work, without using any fitting parameters, density functional theory is employed to calculate the band structure of the Si$_{1-x}$Ge$_{x}$ alloy system taking into account the effect of atomic randomness and, correspondingly, the local strain relaxation. The variation of band gap with 16 different Ge fractions in the alloy is computed to find bowing parameters for the two distinct composition ranges: 0 $\le $ x $\le $ 0.85 and 0.85 $\le $ x $\le $1.0. The calculation is carried out for a supercell of 64 atoms with P1 symmetry, and the randomly positioned atoms are relaxed up to a force tolerance of 0.0001eV/{\AA}. Our results show much better agreement with experimental results for bandgaps, especially near Si$_{0.85}$Ge$_{0.15,}$ than available empirical methods do. The results demonstrate the importance of accounting for the effect of randomness and local strain in band structure calculations. [Preview Abstract] |
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S1.00159: High Yield Microsphere Formation Using an Excimer Laser Ryan Lu, Teresa Emery, Ayax Ramirez The need for low-cost photonic devices has stimulated a significant amount of research in silicon photonics. Although silicon photonics is less well-developed as compared to III--V technologies, it has the potential to make a huge impact on the optical communications industry. Silicon is transparent in the standard ITU optical communication bands, which makes silicon the material of choice for passive and active optoelectronic devices. Recently, microspheres are gaining an important place in the optical microcavity resonator community due to their high quality factor morphology-dependent resonances (MDRs). Silicon microspheres with high quality factor morphology dependent resonances are used for resonant detection and filtering of light in the near infrared. The experimentally measured quality factors are limited by the sensitivity of the experimental setup, however, the microsphere quality factor is several magnitudes of order higher than current microring resonators. These optical resonances provide the necessary narrow linewidths, that are needed for high resolution micro-photonic applications. A reproducible process to quickly fabricate uniform microsphere particles with a narrow distribution of diameters and high yield is presented in this paper. [Preview Abstract] |
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S1.00160: Nitric-phosphoric acid etching effects on the surface chemical composition of CdTe thin film. Irfan Irfan, Huanjun Ding, Wei Xia, Hao Lin, Ching W. Tang, Yongli Gao Nitric-phosphoric (NP) acid etching has been regarded as one of the most successful methods for the formation of low resistance back contact with the metal electrode in CdTe based solar cells. We report back surface chemical composition for eight different durations of NP etching of CdTe polycrystalline thin film. We studied the surfaces with x-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), inverse photoemission spectroscopy (IEPS) and atomic force microscopy (AFM). Etching dependence on the back surface composition and electronic structure was observed. Valence and conduction band shifts relative to the Fermi level of the system with different etching duration were analyzed. The sample was left in open ambient condition for three weeks and XPS data were obtained again in order to study the difference in surface chemical composition with the pristine CdTe film. Unetched and highly etched part of the sample were sputtered and the depth profile analyzed. [Preview Abstract] |
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S1.00161: ABSTRACT WITHDRAWN |
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S1.00162: Elastic strain sharing in silicon nanomembranes from a silicon nitride stressor layer Anna Clausen, Don E. Savage, Max G. Lagally Strained-silicon (001) nanomembranes have increased electron mobility relative to their unstrained counterparts and are therefore of considerable interest for ultra-fast flexible electronics [1]. The increased mobility is caused by the strain splitting of the delta valleys in the conduction band and the concomitant reduced inter-valley scattering of charge carriers. Previous work using SiGe as the stressor layer on silicon-on-insulator (SOI) requires epitaxial growth and is restricted to tensilely straining Si. We grow polycrystalline SiN on SOI by PECVD to form tensilely as well as compressively strained Si nanomembranes. When the SiN/Si film is released from the buried oxide layer, the strain in the SiN layer is elastically shared with the Si layer. The strain-relaxed nanomembrane is then bonded onto a new substrate. XRD, Raman, and TEM are used to characterize the strain transfer and the presence or absence of dislocations in the Si nanomembrane. Our results are in good agreement with predictions from continuum elasticity theory. [1] Yuan, H-C. et al., Semicond. Sci. Tech. \textbf{22}, S72-S75 (2007). [Preview Abstract] |
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S1.00163: Chemical, Electrical and Thermal Characterization of Nanoceramic Silicon Carbide Hervie Martin, Malek Abunaemeh, Cydale Smith, Claudiu Muntele, Satilmish Budak, Daryush Ila Silicon carbide (SiC) is a lightweight high bandgap semiconductor material that can maintain dimensional and chemical stability in adverse environments and very high temperatures. These properties make it suitable for high temperature thermoelectric converters. At the Center for Irradiaton of Materials (CIM) we design, manufacture and fabricate nanoceramic SiC, and perform electrical, thermal and chemical characterization of the material using particle induced X-ray emission (PIXE), Rutherford backscattering spectroscopy (RBS), Seebeck coefficient, electrical conductivity, and thermal conductivity measurements to calculate its efficiency as a thermoelectric generator. We are looking to compare the electrical and thermal properties of SiC ceramics with some other materials used for the same purposes. [Preview Abstract] |
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S1.00164: Mechanical Properties of Nanoceramic Silicon Carbide Ipidapo Ojo, Malek Abunaemeh, Cydale Smith, Claudiu Muntele, Daryush Ila Generation IV nuclear reactors will use the TRISO fuels, a type of micro fuel particle. It consists of a fuel kernel coated with four layers of isotropic material. One of the materials considered for these layers is silicon carbide ceramic. This lightweight material can maintain chemical and dimensional stability in adverse environments at very high temperatures up to 3000\r{ } C, and it is chemically inert. It is widely used as a semiconductor material in electronics because of its high thermo conductivity, high electric field break down strength, and high maximum current density, which makes it more desirable than silicon. Silicon carbide has a very low coefficient of thermal expansion and has no phase transition that would discontinue its thermal expansion. At the Center for Irradiation of Materials (C.I.M.) we are developing a new fabrication process for nanopowdered silicon carbide for TRISO fuel coating purposes. We also study the mechanical properties of the material produced. Among the different test being performed are particle induced X-ray emission (PIXE) an Rutherford backscattering spectroscopy (RBS). The mechanical properties of interest are hardness (measured by Vickers Hardness machine), toughness (measured by the Anstis equation, K$_{IC}$= 1.6 x 10$^{-2}$(E/H)$^{1/2}$(P/C$_{0}^{3/2}$, where P=load, C$_{0}$=crack length, E=Young's modulus and H=Vickers Hardness), tensile strength and flexural strength (measured by a three point bend test). Results will be presented during the meeting. [Preview Abstract] |
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S1.00165: Investigation on Ge induced GaAs(001)-(1x2) structure Jun Nara, Akihiro Ohtake, Takahisa Ohno It is known that at the initial stage of the Ge growth on GaAs(001), a reconstructed structure with a (1x2) periodicity is formed. A structure model with Ga-Ge dimers on an As-terminated surface has been proposed for the (1x2) reconstruction. On the other hand, the previous studies have shown that As atoms segregate to the growing Ge surface at the initial growth stages. We have reexamined the atomic structure of the Ge-induced (1x2) reconstruction experimentally and theoretically. We show that the initial growth of Ge on GaAs(001) induces the formation of Ga-As dimers as a result of the site exchange between deposited Ge atoms and subsurface As atoms. We confirmed that this atomic geometry is energetically favored compared with the previously proposed Ga-Ge dimer model, by using first-principles calculations. Our proposed structure model accounts well for the experimental results. This work was partly supported by the RISS project in IT program and a Grant-in-Aid for Scientific Research (No.17064017) of MEXT of the Japanese Government. [Preview Abstract] |
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S1.00166: Monte Carlo Calculations of the Specific Heat in Quantum Critical Metals John Gaddy, Wouter Montfrooij, Thomas Vojta Quantum critical magnetic metals have unusual low temperature response such as an anomalous temperature dependence of the electronic specific heat (c$_{v}\sim $ T lnT). This dependence originates in the competition between ordering local magnetic moments and the conduction electrons shielding the moments. The Kondo Temperature, T$_{K}$ when moments become shielded depends on the inter-atomic distances. In most systems that have been investigated experimentally quantum criticality is obtained through lattice expansion by chemical substitution, one can expect a distribution of T$_{K}$ reflecting altered local inter-atomic distances. The random removal of these moments leads to the formation of magnetic clusters in quantum critical metals which has indeed been observed in quantum critical CeRu$_{0.5}$Fe$_{1.5}$Ge$_{2}$. We investigate the dependence of the specific heat through the formation through magnetic cluster formation. Once a cluster separates itself from the lattice, it should order and affect the specific heat.. Using a Monte Carlo simulation we calculate the changes in specific heat associated with cluster formation for various Kondo temperature distributions, and we compare our results to those measured in 122-systems like CeRu$_{0.5}$Fe$_{1.5}$Ge$_{2}$. [Preview Abstract] |
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S1.00167: Study of oxidation of titanium by x-ray photoelectron spectroscopy Hong Dong, A.R. Chourasia, R.L. Miller The oxidation of titanium has been investigated using the technique of x-ray photoelectron spectroscopy. Thick films of titanium have been deposited on silicon substrates by e-beam method. The Oxford Applied Research EGN4 was used for this purpose. The titanium substrate was kept at different temperatures (100, 200, 300, 400, 500, and 600\r{ }C). These substrates were exposed to oxygen at different partial pressures. The titanium 2p and oxygen 1s regions have been investigated by XPS. The magnesium anode (energy = 1253.6 eV) has been used for this purpose. The spectral data have been recorded at 45\r{ } take-off angle. The spectral data for different temperatures and oxygen partial pressures have been analyzed to ascertain the complete oxidation of the titanium substrate. [Preview Abstract] |
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S1.00168: Synthesis and characterization of TiO2 nanocrystals through sol-gel and hydrothermal methods Corina Ileana Orha, Carmen Lazau, Cornelia Elena Ratiu, Paula Sfirloaga, Paulina Vlazan, Paul Barvinschi, Ioan Muscutariu, Ioan Grozescu Nanomaterials with special and interesting properties, which can be different comparing to the macro scale materials, offer a large area of practical applications in all social-economical fields. Incorporating metallic and non-metallic dopant ions into the titanium dioxide particles can influence the performance of these photocatalysts. This affects the dynamics of electron-ion recombination and interfacial charge transfer. In this paper it was synthesized undoped and doped TiO2 nanocrystals with metallic (Ag) and non-metallic (N) ions through sol-gel and hydrothermal methods. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX), diffuse reflectance UV-VIS, thermogravimetric analysis (TG) and differential thermal analysis (DTA). [Preview Abstract] |
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S1.00169: Observation of acousto-elastic hysteresis in kinking nonlinear elastic solids Peter Finkel, Aiguo Zhou, Michel Barsoum Using bulk acoustic waves we studied the nonlinear mechanical properties and hysteresis of the acousto-elastic effect in kinking nonlinear elastic, KNE, solids. The experiments reviewed here present direct observation of nonlinear hysteretic scattering and attenuation of ultrasonic waves in Ti$_{3}$SiC$_{2}$ and Ti$_{3}$AlC$_{2}$, representatives of KNE solids, as a function of quasi-static cyclic compressive stresses. We attribute this dynamic behavior to the interaction of the acoustic waves with dislocation in incipient kink bands. The relevance of these findings to possible sensor applications of hysteretic KNE solids is briefly discussed. [Preview Abstract] |
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S1.00170: Spectral Calculations for columnar Thin Films Deposited on Periodically Decorated Substrates Jon Mease, Tariq Gilani, Akhlesh Lakhtakia Using a morphological model of a class of nano-engineered materials called columnar thin films (CTFs) deposited on periodically decorated substrates, we compute their optical reflection and transmission spectra. The calculation procedure involves the use of the MIT Electromagnetic Equation Propagation (Meep) software libraries. The deposition geometry and the spatial periodicity affect the spectra in technologically significant ways. Our current efforts are focused~on a narrowband, linear-polarization rejection filter.~~ [Preview Abstract] |
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S1.00171: Light reflection from semiconductor surface with submonolayer cover of metal particles Irina Bariakhtar, Valeri Lozovski, Tatiana Mishakova In the framework of the Green function method, the effective susceptibility of submonolayer of metal particles covering the surface of semiconductor is calculated. The main point of calculations is taking into account the size and the shape of the particles. The particles are assumed to have the shape of the ellipsoid of revolution. The effective susceptibility was obtained in the form:${\rm X}_{ij} ({\rm {\bf k}},\omega )=\left[ {\chi _{ij}^{-1} (\omega )-nG_{ji} ({\rm {\bf k}},\omega )} \right]^{-1}$, where$ n$ is the concentration of the particles, $G_{ji} ({\rm {\bf k}},\omega )$ is the Green function of the substrate, and $\chi _{ij}^ (\omega )$ is the liner response function of the single particle in the surface. Based on this, the exact form of the effective linear response function is calculated. As a result, the reflection coefficient is readily obtained via effective susceptibility and Green function. This approach allows studying the dependence of the reflection coefficient on the particle concentration and its shape, and development of the theory of ellipsometry. [Preview Abstract] |
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S1.00172: Electronic Properties of Large-scale Graphene Chemical Vapor Synthesized on Nickel and on Sapphire Helin Cao, Liyuan Zhang, Yong Chen, Qingkai Yu, Hao Li We have studied the electronic transport properties of \textit{large area} few-layer graphene/graphitic films grown by two different chemical vapor based methods. The first type of samples (metal-transfer graphene) is synthesized by carbon segregation from Ni, then transferred to SiO2/Si substrates. The second type of samples is synthesized by direct chemical vapor deposition (CVD) on sapphire. We measured these samples under variable temperatures (from 2K to 300 K) and transverse magnet fields (from 0 to 7 T). For both types of samples, we found a negative magnetoresistance at low field, and carrier mobilities on the order of several hundreds of cm$^{2}$/V-s. For metal-transfer graphene in particular, we were able to measure a moderate field effect response, using the highly doped Si substrate as back gate. The observed magnetoresistance shows characteristic features of weak localization, from which we extract various carrier scattering lengths in the metal-transfer graphene samples. Comparison with those measured in mechanically exfoliated graphene suggests possibly different carrier scattering mechanisms for graphene materials prepared with different methods. [Preview Abstract] |
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S1.00173: All-electron KKR Calculations for Metallic Systems with Thousands of Atoms Per Cell via Sparse Matrix Iterative Solvers Suffian Khan, Aftab Alam, Duane Johnson To perform electronic-structure calculations for inherently large systems, such as a quantum dots or interfaces like domain walls, we must perform the calculations over very large unit cells (10$^{4}$ to 10$^{8}$ atoms). For the inverse Green's function G$^{-1}$, KKR methods typically solve for G by direct inversion. Using a screened, k-space hybrid KKR, we solve Dyson's equation for the Green's function using a reference state via G = G$_{ref}$ [ I - (t - t$_{ref}$) G$_{ref}$]$^{-1}$, scattering matrices t and t$_{ref}$ are known and the non-Hermitian tensor G$_{ref}$ is chosen for convenience and sparsity [1]. The approach is O(N) for bandgap materials, whereas it is O(N$^2$) for metals but with a potentially large prefactor. Based upon Sparse Approximate Inverse (or SPAI) technique [2], we generalize the algorithm for complex, non-Hermitian matrices, then use the method as a preconditioner for the inversion to reduce the iteration counts (hence, reduce the prefactor) of the iterative Krylov-space inverses, such as TFQMR, to address large-scale metallic systems. Parallel iterative and energy contour solves are made also. We explore the numerical efficiency and scaling versus atoms per unit cells. \newline [1] Smirnov and Johnson, Comp. Phys. Comm. 148, 74-80 (2002). \newline [2] Grote and Huckle, SIAM J. Sci. Comput. 18, 8 [Preview Abstract] |
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S1.00174: Many-flavor electron gas approach to electron-hole drops Gareth Conduit, Peter Haynes A many-flavor electron gas (MFEG) is analyzed, such as could be found in a multivalley semiconductor or semimetal. Using the rederived polarizability for the MFEG, an exact expression for the total energy of a uniform MFEG in the many-flavor approximation is found; the interacting energy per particle is shown to be $-0.574447(E_{h}a_{0}^{3/4}m*^{3/4})n^{1/4}$, with $E_h$ being the Hartree energy, $a_0$ being the Bohr radius, and $m*$ being the particle effective mass. The short characteristic length scale of the MFEG motivates a local-density approximation, allowing a gradient expansion in the energy density and the expansion scheme is applied to electron-hole drops, finding a new form for the density profile and its surface scaling properties. The formalism is verified using both Quantum Monte Carlo and density-functional theory calculations. [Preview Abstract] |
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S1.00175: 3D Quantum Dot Density of States in a Magnetic Field N.J.M. Horing, S.Y. Liu, V. Fessatidis We have analyzed the detailed quantum dynamics of a 3D quantum dot in a magnetic field. The dot is taken to be lodged in a bulk medium in a high magnetic field and it is represented by a three-dimensional Dirac delta function potential which would support just one subband state if there were no magnetic field. The integral equation for the retarded Green's function of this system is solved in closed form analytically and the single particle subband energy spectrum and the density of states are examined taking account of splintering of the subband spectrum by Landau quantization. [Preview Abstract] |
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S1.00176: SUPPLEMENTARY ABSTRACTS |
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S1.00177: Boron-catalyzed growth of multi-wall carbon nanotubes and their mechanical properties Fumio Kokai, Takashi Okada, Iori Nozaki, Akira Koshio, Toru Kuzumaki Carbon nanotubes have received widespread interests in basic and applied research fields. However, many applications of carbon nanotubes are hindered by a lack of control of their precise morphology and microstructures. We report here an efficient synthesis of multi-wall carbon nanotubes (MWNTs) by laser vaporization in inert gas atmosphere. We used a continuous-wave Nd:YAG laser (600 kW peak power) to irradiate a graphite target containing boron carbide (boron content: 1-60 at.{\%}) at room temperature. The pressure of He, Ne, or Ar gas was 0.05-0.90 MPa. The yield and morphology of MWNTs were strongly dependent on the inert gas type and pressure and the boron content. Ar provided higher yields and He led to lower yields. The maximum yield ($\sim $60{\%}) of MWNTs was obtained for 20-30 at.{\%} boron content and 0.1 MPa Ar gas. For He, Ne, and Ar, the outer diameters of the MWNTs were 4-40, 4-60, and 5-70 nm, and their lengths were up to 2, 5, and 30 $\mu $m, respectively. Young's moduli of MWNTs were also measured by nanoprobe manipulation in a TEM. The modulus was 680 GPa for a MWNT produced in 0.1 MPa Ar for 20 at.{\%} boron content, which is much higher than those ($\sim $10 GPa) of MWNTs grown by CVD. [Preview Abstract] |
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S1.00178: How Mass Changes with Velocity and Energy? Lianxi Ma It is well known that mass of an object $m$ can increase with its speed $v$, which is one reason that we believe that the speed of light $c$ is the ultimate limit for all objects. As the $v$ is approaching to the speed of light, the $m$ becomes larger and larger so the acceleration becomes more and more difficult. It is also well known that $m$ is related to the energy $E$. Energy is released in the nuclear reaction while the mass is lost and this has been the theoretical basis for nuclear fission and fusion reactions. However, argument exists over how to interpret the relationship between mass and velocity and energy. In the text, we don't want to discuss if the use of relativistic mass is appropriate. Instead, we discuss two examples that seem to be confusing in the teaching of special relativity. A harmonic spring oscillator and a proton accelerated in an electric field are chosen as examples to discuss the mass change with energy and velocity. We show that the two equations $m=\gamma m_0 $ and $m=\frac{E}{c^2}$ agree each other if potential energy and related mass are properly considered. [Preview Abstract] |
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S1.00179: Manipulation of thermal emission via gold gratings Jones Tsz-Kai Wan The photon density of states of a structured metallic surface is strongly modified by various plasmonic excitations; as a result, thermal emission of photons can be manipulated through the control of plasmonic excitations. In this work, the author studies the emission properties of gold gratings, and investigates the effects due to the groove depth and periodicity. By systematically increasing the groove depth, the polarization of the emitted photons can be controlled. In addition emission at particular frequencies could be tuned to achieve that of the blackbody radiation limit, whereas the emission in other frequency ranges does not have noticeable changes. [Preview Abstract] |
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S1.00180: Absorption spectrum of the Single Molecule Magnet [Ni(dbm)(MeOH)Cl]$_4$ Daniel J. Arenas, Dimitrios Koukis, Saiti Datta, Chao Cao, Hai-Ping Cheng, David B. Tanner, Stephen Hill, Christopher Beedle, David Hendrickson The room temperature optical absorption of the single-molecule magnet [Ni(dbm)(MeOH)(Cl)]$_4$ has been measured in the near-infrared-visible spectral region. The spectra show a strong absorption band around 3 eV and bands characteristic of d-d transitions in nickel. The results will be compared to various theoretical models in the literature; including DFT and DFT+\textit{U} calculations [\textit{Phys. Rev. Lett.} \textbf{100}, 167206] that predict different energy gaps for the HOMO to LUMO optical transitions. [Preview Abstract] |
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S1.00181: POST-DEADLINE ABSTRACTS |
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S1.00182: BioCARS: A State-of-the-art Facility for Time-resolved Crystallography with 100ps Time Resolution Robert Henning, Tim Graber, Vukica Srajer, Yu-Sheng Chen, Zhong Ren, Friedrich Schotte, Philip Anfinrud, Keith Moffat BioCARS, a national facility located at the Advanced Photon Source (APS), recently upgraded the undulator beamline (14-ID) to become one of the best facilities in the world for conducting experiments with 100ps time resolution. Improvements in both the x-ray and laser capabilities were required in order to extend experiments into the sub-ns time domain. The more intense and strongly focused x-ray beam was achieved by using a KB mirror pair which provides a focal spot size of 35x90 $\mu $m$^{2}$ (VxH). The high heat loads that can be achieved with this configuration required the development of a new water-cooled heat-load chopper. The continuously rotating, air-bearing based chopper intercepts the white beam upstream of the mirrors and reduces the heat load on the downstream components by $\sim $99{\%}. BioCARS ultra-fast rotating chopper used for selection of X-ray pulses was modified so individual x-ray pulses (100 ps) could be isolated in the standard operating mode of the APS (24 bunch). A new Spectra Physics picosecond laser system and beam transport optics have been installed and can deliver $\sim $35ps tunable laser pulses to the sample position. [Preview Abstract] |
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S1.00183: Raman spectroscopy measurement of MoS$_{2}$ to 43 GPa Yanzhang Ma, Boheng Ma, Hongyang Zhu, Ming Chyu MoS$_{2}$ has a typical layered crystal structure. The two-dimensional lattice vibration, in conjunction with the strong (ionic) and weak (Van de Waals) bonding, is a very interesting subject. Among many of the interesting properties of MoS$_{2}$ is the physical performance in response to the substantial reduction of distance between the layers of the MoS$_{2}$ network along with the increase of interaction between them. We compressed MoS$_{2}$ in a diamond anvil cell to 43 GPa and carried out \textit{in situ} Raman spectroscopy measurement. We found that the vibration energy of the A$_{1g}^1 $and E$_{2g}^1 $modes was elevated with increasing pressure. At about 27 GPa, the peak of E$_{2g}^1 $ mode split into two peaks while the A$_{1g}^1 $ peak did not show any abnormality. We believe that this reflects a structural phase transformation due to a minimal distortion of the MoS$_{2}$ network within the layer. We also found that non-hydrostatic compression on the sample lowered the pressure-induced energy elevation of the vibration modes, indicating that the differential stress applied on a MoS$_{2}$ crystal resists the atomic vibration. [Preview Abstract] |
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S1.00184: $MgB_2$ under pressure; band-filling, phonon hardening and electrical anisotropy Jesus Vazquez, Sabina Ruiz-Chavarria, Pablo de la Mora The electrical two-dimensional character has been accepted as an important factor in the high $T_c$ superconductors. In $MgB_2$ it is the almost two dimensional $\sigma$-bands that are responsible for the superconductivity. On the other hand in $MgB_2$ the band-filling and phonon hardening have been found to be the responsible for the high $T_c$ [1]. But previous calculations [2] have shown that with pressure both, electrical anisotropy and $T_c$ are reduced. Thus the question arises: Is the electrical anisotropy, together with band-filling and phonon hardening, also responsible of the high $T_c$ in $MgB_2$? Using the $WIEN2k$ package the $MgB_2$ superconductor is analyzed as function of pressure. At each pressure the cell parameters are optimized and the $\sigma$-$DOS$, the $E_{2g}$-phonons and the electrical anisotropy of the $\sigma$-bands are calculated and, with the use of the Hopfield expression, are analyzed to see what the correlation of these elements with $T_c$ is. [1] J Kortus, \textit{Physica C} \textbf{456} (2007) 54-62 [2] U Esteves and P de la Mora, \textit{Rev. Mex. Fis.} \textbf{53} (2007) 95-98 [Preview Abstract] |
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S1.00185: ABSTRACT WITHDRAWN |
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S1.00186: Magnetic properties of $Sr_2IrO_4$ a $DFT$ stud Pablo de la Mora, Carlos Cosio-Castaneda, Gustavo Tavizon $Sr_2IrO_4$ is a magnetic insulator with a small $Ir$-magnetic moment [1]. $IrO_4$ rotations (due to the $I41/acd$ space group) allow non-collinear magnetic ordering, thus this material could have weak ferromagnetism (non-collinear antiferromagnetically ordered $Ir$ magnetic moments); other possible explanation is band-magnetism. Simple $DFT$ calculations give a non-magnetic conductor. Intra-atomic electron repulsion can generate magnetic moments in the $d$-orbitals (via the Hubbard $U$ ($U_H$)), but due to extended character of these $5d$-orbitals the $U_H$ should be quite small. $Sr_2IrO_4$ is analyzed with the $WIEN2k$ package. Different magnetic configurations with varying $U_H$ are calculated in order to try to explain the observed magnetic behaviour. [1] C Cos\'io-Castaneda, G Taviz\'on, A Baeza and R Escudero, \textit{J. Phys.: Cond. Matter} \textbf{19} (2007) 446210 [Preview Abstract] |
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S1.00187: Magnetic behaviour of the $Bi_{2-x}Sr_xIr_2O_7$ pyrochlore Carlos Cosio-Castaneda, Gustavo Tavizon, Pablo de la Mora, Francisco Morales, Roberto Escudero Polycrystalline compounds of the $Bi_{2-x}Sr_xIr_2O_7$ solid solution have been synthesized. These compounds were obtained by the solid state reaction method in the $0 < x < 0.9$ range with the $\alpha$-pyrochlore crystal structure. This material was characterized with Crystalline Rietveld refinement and cyclic voltammetry. These analyzes permitted the understanding of the unit-cell modifications and valence states of Iridium as a function of the strontium content. Electrical characterization of samples in the $10$-$300K$ range shows a metallic character that remains for the whole solid solution. Magnetically this system behaves as a Curie-Weiss paramagnetic in the $2$-$300K$ range. The measured magnetic moment values suggest the presence of $Ir^{5+}$ in some compounds of the solid solution. [Preview Abstract] |
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S1.00188: Phase behavior of colloid-polymer mixtures in two-dimensions Amir Amini, Marc Robert Phase behavior of mixtures of colloidal particles and non-adsorbing polymer chains bounded to two dimensions with various polymer-to-colloid size ratios are investigated. Mixtures are trapped at the air-water interface and pressure-area isotherms are obtained using the Langmuir-Blodgett technique. Different regions of the phase diagram are explored by changing temperature and the concentration of the colloid and the polymer. Brewster angle microcopy is then used to identify the microstructure of the formed phases. [Preview Abstract] |
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S1.00189: How Local Anesthetics affect the structural and dynamical properties of bio-membranes Zheng Yi, Michihiro Nagao, Dobrin Bossev To address the question of how local anesthetics influences the structural and dynamical properties of bio-membranes, neutron-spin echo spectroscopy (NSE) has been performed on 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DMPC) unilamellar vesicles (ULV) with different concentrations of Lidocaine in D2O to study the influence of Lidocaine on the bending elasticity of DMPC ULV bilayers in fluid crystal (L{\_}alpha) phase and the ripple gel (P{\_}beta') phase; The measurement of small-angle neutron scattering (SANS) has been performed to determine the bilayer thickness as a function of the concentration of Lidocaine. In the existence of molecules of Lidocaine the bending elasticity of DMPC bilayers was increased 30{\%} -100{\%} in L{\_}alpha phase. The NSE data confirmed that fluid crystal/ripple gel transition temperature of DMPC bilayers was depressed by the addition of local anesthetics, which has also been examined via differential scanning calorimetry (DSC). [Preview Abstract] |
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S1.00190: Landau-Zener Interference in Multilevel Superconducting Flux Qubits Driven by Strong Fields Yang Yu, Xueda Wen We proposed a model to investigate the Landau-Zener (LZ) interference in multilevel superconducting flux qubits driven by large-amplitude microwave fields. The calculated interference patterns agree remarkably with those of the experiments. Moreover, the interference depends on the driving-frequency and dephasing rate. The dephasing generally destroys the interference while increasing frequency rebuilds the interference at large dephasing rate. At certain driving frequency and dephasing rate, the interference shows some anomalous features as observed in recent experiments. Our results can be used to understand the LZ interference in multilevel quantum systems under different driving frequencies and decoherence rates. [Preview Abstract] |
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S1.00191: A Logic-Based Technique that Charaterizes the Class of Boolean Networks Producing a Given Biological Pathway Guanyu Wang, Chen Zeng A central theme in biophysics is the relationship between structure and function. The question~ becomes especially intricate at the systems level in which the objects of study are biological networks composed of large numbers of interacting molecules. To what extent does the requirement of carrying out a specific function constrain the structural and more general dynamical properties of a network? Does the biological network optimally designed? Here we present an efficient logic-based technique that captures the ensemble of all the networks that realize the same biological function. The biological function is first represented by a dynamical trajectory in the state space, which impose constraints to the network space. Through some Boolean reasoning we can discover the fundamental building blocks of the network space, namely the irreducible edges and minimal networks. The approach is applied to a cell cycle model and reveals some interesting properties. The full network has 34 edges, but only 23 edges are essential for the cell cycle function. Moreover, this 23 edge minimal network alone can guarantee the robustness of the cell cycle function. In total there exists 40320 such minimal networks, but the naturally occurring one is specially selected by nature, because it has many good properties: high robustness, large designability, etc. [Preview Abstract] |
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S1.00192: Controlling the spatial correlation of entangled photon states using engineered crystal patterns S.N. Zhu, X.Q. Yu, P. Xu In this work, we will illustrate a scheme to tailor and manipulate the spatial mode of the quantum entanglement of two photons by carefully engineering a nonlinear crystal. We study the entangled state generated from a crystal of lithium tantalite with parallel stripes at intervals of 200 micrometres. These stripes are periodically poled with the period of $\Lambda $ = 7.548 $\mu $m. The longitudinal nonlinearity works for quasi-phase-matched spontaneous parametric down conversion (QPM-SPDC), whereas the transverse modulation is used to manipulate the two-photon state's spatial mode. When a 532 nm laser is directed on the crystal, it can split the 532nm photon into two degenerate 1064 nm photons. They must be entangled and the structural information in periodic crystal patterns would be transferred into their spatial mode. We performed a far-field interference experiment with such entangled photon pairs. The coincidence count shows a multi-beam two-photon sub-wavelength interference pattern with the peak interval of 3.72 mm and the visibility of the fringe is 0.82$\pm$0.03. The result implies that it is possible to control the spatial properties of the entangled photons simply by changing the periodic patterns of nonlinear crystal. [Preview Abstract] |
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S1.00193: Flexoelectricity in nanostructures and ramifications for the dead-layer effect in nanocapacitors and ``giant'' piezoelectricity Ravi Maranganti, Mohamed Majdoub, Pradeep Sharma Thin films of high-permittivity dielectrics are considered ideal candidates for realizing high charge density nanoscale capacitors for use in next generation energy storage and nanoelectronics applications. The experimentally observed capacitance of such film nanocapacitors is, however, an order of magnitude lower than expected. This dramatic drop in capacitance is attributed to the so-called ``dead layer'' -- a low-permittivity layer at the metal-dielectric interface in series with the high-permittivity dielectric. Recent evidence suggests that this effect is intrinsic in the sense that its emergence is evident even in ``perfectly'' fabricated structures. The exact nature of the intrinsic dead-layer and the reasons for its origin still remain somewhat unclear. Based on insights gained from recently published \textit{ab initio} work on SrRuO$_{3}$/SrTiO$_{3}$/SrRuO$_{3}$ and our first principle simulations on Au/MgO/Au and Pt/MgO/Pt nanocapacitors, we construct an analytical model that isolates the contributions of various physical mechanisms to the intrinsic dead layer. In particular we argue that strain-gradients automatically arise in very thin films even in complete absence of external strain inducers and, due to flexoelectric coupling, are dominant contributors to the dead layer effect. [Preview Abstract] |
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S1.00194: ABSTRACT WITHDRAWN |
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S1.00195: NaCl and Cationic lipid bilayer dynamics Markus S. Miettinen, Andrey A. Gurtovenko, Ilpo Vattulainen, Mikko Karttunen Positively charged lipid bilayer systems hold promise for safer and more efficient gene and drug delivery. Here we studied cationic bilayers comprising binary mixtures of cationic dimyristoyltrimethylammoniumpropane (DMTAP) and zwitterionic dimyristoylphosphatidylcholine (DMPC) lipids. Using molecular dynamics simulations we addressed the effects of bilayer composition (cationic to zwitterionic lipid fraction) and NaCl electrolyte concentration on the dynamical properties of these systems. We found that despite the DMPC lipids form complexes via Na$^+$ ions that bind to the lipid carbonyl oxygens, NaCl concentration had a rather minute effect on the lipid diffusion. The residence times of sodium ions in the carbonyl region appeared to lack a characteristic time scale, although observed a simulation period of over 200 ns. These prolonged dynamics of the sodium ions could be interesting for the physics of the whole membrane, especially to its interaction dynamics with charged macromolecular surfaces. 1. A. A. Gurtovenko {\em et al.}, J. Phys. Chem. B {\bf 109}, 21126 (2005) 2. M. Miettinen {\em et al.}, J. Phys. Chem. B,{\em (submitted)} [Preview Abstract] |
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S1.00196: Achieving quantum-like interference in ostensibly ``classical" systems through closed timelike curves M.J. Rave It was recently shown [1] that quantum interference can be understood heuristically as a quasi-probability effect as opposed to being interference in the traditional sense. Surprisingly, this interpretation requires one to think of closed loops in time (represented by products of probability amplitudes) as fundamental quantum entities, much as we think of state vectors normally. (These entities, incidentally, share similarities to Berry's geometric phase.) The question naturally arises: can this closed-loop paradigm elucidate QI, making its idiosyncracies more mundane? We show that this new way of thinking about QI leads to a whole new class of ``classical'' systems and analogies that exhibit pseudo-QI effects. [1] M.J. Rave, Found. Phys. 38, 1073 (2008). [Preview Abstract] |
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S1.00197: Crack branching and viscous fingering at nanoscale in brittle material Deeder Aurongzeb Cracked surfaces of soda lime glass and single crystal silicon are studied using atomic force microscopy simply by breaking them with impulsive force. We find traces of cavities and reorganized surface structures in both surfaces. At micron scale fractured glass surface exhibits viscous fingering and fractured silicon surface exhibit nanoscale crack branching showing two materials responds to sudden fracture differently. Crack branched surface of Si shows unusually low self --affine exponent and faceted nanoscale organized islands. [Preview Abstract] |
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S1.00198: Raman spectroscopic studies of monoclinic Gallium Oxide ($\beta $-Ga$_{2}$O$_{3}$) Nanostructures: A comparison between nanowires vs. nanobelts Aurangzeb Khan, Saima Khan, Wojciech Jadwisienczak, Martin Kordesch Nanostructures of monoclinic gallium oxide ($\beta $-Ga$_{2}$O$_{3})$, nanowires and nanobelts were synthesized via a very simple thermal evaporation process by using Ga metallic ignots and $\beta $-Ga$_{2}$O$_{3 }$powder as source materials for gallium and oxygen, respectively. The structural properties of the as grown nanostructures were characterized by using SEM, XRD and EDS. Raman studies were also performed for the grown nanostructures and Raman shifts were compared with the LDA calculated values of the peaks as well as with their bulk counterpart which exhibited good agreements with most of the peaks for both the nanostructures. In addition to this, there are some more Raman shifts which are the characteristics of the nanostructures as they have larger surface to volume ratio compared to their bulk counterparts. [Preview Abstract] |
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S1.00199: Surface Effects on Amyloid Fibril Formation Brad Moores, Janet Simons, Zoya Leonenko Amyloid fibrils are insoluble aggregates composed of proteins in beta-sheet conformation, which are implicated in at least 20 diseases for which no cure is currently available. Although fibril plaque formation is associated with biological membranes in vivo, most of earlier research on fibrillogenesis has been performed in a solution phase, in which only a protein-protein interactions are considered. On the other hand, the surface of plasma membrane could provide the environment in which amyloid forming proteins could cluster. In order to get an insight into the understanding of the effect of the surface of plasma membrane, and the surfaces in general, on amyloid fibril formation, we used Atomic force microscopy to study binding of amyloid beta 1-42 peptide and amyloid fibril formation on model surfaces, such as chemically modified positively charged, negatively charged and hydrophobic substrates. The results show that structure, size and amount of larger fibrils and smaller aggregates depend on the type of surface, and differ from aggregation observed in solution. [Preview Abstract] |
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S1.00200: High Resolution TEM Imaging of Graphene by use of aberration-free microscope, R005 Takayuki Tanaka, Yuusuke Abe, Hidetaka Sawada, Eiji Okunishi, Yukihito Kondo, Kunio Takayanagi Free-standing Graphene is imaged by use of a novel transmission electron microscope (TEM), R005, equipped with newly-designed Cs Correctors for TEM and STEM. The R005 microscope is fitted with 300kV cold-field emission gun (CFEG) to minimize the chromatic aberration, resulting in achievement of 50pm resolution. Its high phase contrast allows direct imaging of graphene without image reconstruction. The TEM Image of graphene can be distinguished from that of graphite and confirmed by simulation. The adatoms and defects of single carbon atom, which cause the modulation of electronic properties, are also observed. [Preview Abstract] |
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S1.00201: Affordable Integrated Technology Projects Science Education towards New Horizons Franco Paoletti, Lisa Marie Carlucci The new-era concept of education supports a type of instruction whereby technology directly acts as a conduit of change, fundamentally altering what is learned, how it is learned, and the role of the educator in the classroom. In our current world, the learning about technology itself has become a goal and a means to successful participation in today's society. Efficient integration of technology to enhance and support the educational process will: 1) provide educators with the resources and the freedom to actualize innovative educational programs; 2) allow educators to be successful in challenging each student to reach his/her highest potential to ultimately increase academic achievement. This study analyzes what technology integration into education means identifying the benefits and the challenges that educators need to meet in order to be successful in their efforts while providing examples of how to successfully implement effective programs under budgetary constraints. [Preview Abstract] |
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S1.00202: In-situ High Resolution TEM Observation of Dynamic Structural Changes of Au/TiO2 Catalyst Exposed to Oxygen and Hydrogen Kentaro Sano, Takayuki Tanaka, Hidetaka Sawada, Yukihito Kondo, Kunio Takayanagi Recently atomic structures of Au nanoparticles (NPs) / TiO2 catalyst are discussed in relation to its high catalytic activity. In addition, the importance of in-situ experiments in gas environments has been increased. We have developed a novel gas-injection holder, which allows in-situ observations at high pressures about 100 Pa. We observed Au NPs on TiO2 exposed to gas including oxygen and hydrogen. The exposure to oxygen induced growth of buffer layer on TiO2 surface. The buffer layer attached Au NPs and often covered Au NPs. The growth of buffer layer has been not reported so far, while it appears to cause the substrate roughening, Au-NPs sintering and small protrusions, reported in the past STM experiments. The EELS experiments suggest that the buffer layer is highly oxidized titania. On the contrary the exposure to hydrogen induce a slight change of TiO2 surface and remarkable changes of Au NPs morphology. These in-situ observations greatly contribute the clarification of catalysis of Au NPs / TiO2. [Preview Abstract] |
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S1.00203: Upper bounds on photonic bandgaps in two and three dimensions Mikael Rechtsman, Salvatore Torquato A 20-year search has been on to find photonic crystals (periodic dielectric structures) with the largest possible full photonic bandgaps. A large, robust bandgap is key to the many applications of these materials, which include near-lossless waveguiding, optical filtering, optical computing, and others. A number of three-dimensional structures with large gaps have been proposed (e.g., a diamond lattice of spheres [1], the ``Woodpile'' structure [2]), and in two dimensions, structural optimizations to find the largest-bandgap structure have been performed, (e.g., [3], [4]). So far, however, there has been no work on finding rigorous limits on how high the bandgap may be. In this talk, I present upper bounds on the bandgaps of two- and three-dimensional photonic crystals.\\ \noindent $[1]$ Phys. Rev. Lett. {\bf 65}, 3152 (1990)\\ $[2]$ J. Mod. Opt. {\bf 41}, 231 (1994)\\ $[3]$ Appl. Phys. B. {\bf 81}, 235 (2005) \\ $[4]$ Phys. Rev. Lett. {\bf 101}, 073902 (2008) \\ [Preview Abstract] |
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S1.00204: Anomalous Brownian motion and viscoelasticity of the ear's mechanoelectrical transducer Daniel Andor-Ard\'o, Andrei Kozlov, A.J. Hudspeth The Brownian motion of a particle in a complex environment is known to display anomalous power-law scaling in which the mean squared displacement is proportional to a fractional power of time. Using laser interferometry and analytical methods of microrheology, we examine nanometer-scale thermal motions of hair bundles in the internal ear and show that these cellular organelles undergo fractional Brownian motion. This anomalous scaling is caused by viscoelasticity of the gating springs, elements that transmit energy in a sound to the mechanosensitive ion channels. These results demonstrate a connection between rheology and auditory physiology, and indicate that statistical properties of the thermal noise in the ear can be determined by dynamics of a small number of key molecules. [Preview Abstract] |
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S1.00205: ABSTRACT WITHDRAWN |
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S1.00206: ABSTRACT WITHDRAWN |
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S1.00207: Label-free detection of DNA interactions by terahertz spectrometry Anis Rahman, Bruce Stanley, Aunik Rahman Terahertz (THz) spectrometry has the potential to analyze DNA and other molecular interactions without fluorescent labeling. THz spectrometry is conducted in time domain where the temporal signal is acquired on a sub-pico-second scale. The temporal signal converted to frequency domain via Fourier transform constitutes a signature of the interaction under study. An important advantage of this technique is that the delay time can be tuned from tens of femto-seconds to tens of pico-seconds. This gives a means of probing a molecular ``event'' (e.g., a vibrational state or bond position or bending, or a conformational state, etc.) in an appropriate time window. This is a powerful ability because different molecular events exhibit different time response based on their physical and chemical nature. For example, a molecular relaxation occurs over a longer time scale compared to a bond vibration. Similarly, compositional or conformational difference of a given molecule results in different signature with appropriate time response that can be accurately probed. The terahertz signature is unique and provides a means of identifying and/or characterizing many molecular interactions. Some exemplary results of biological system will be discussed. [Preview Abstract] |
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S1.00208: Void collapse in energetic structural materials Derek Reding, Sathya Hanagud A spherically symmetric pore collapse model is introduced that incorporates internal and physical state variable plasticity models for a mixture. This model is based on the modified Carroll-Holt model by Nesterenko. Mixture rules are formulated for the density and yield strength. Previous spherically symmetric model studies consider single constituent porous mixtures. This study investigates the pore collapse in the Ni+Al + void system during shock loading. This material is part of a larger class of energetic structural materials. The proposed model is incorporated into a gas-gun simulation via an algorithm that uses the bisection method for robustness. Results show close agreement between simulation and experiments for shock pressures up to 6 GPa. The proposed mixture pore collapse model is useful for incorporation into a continuum level simulation of the gas-gun experiment. [Preview Abstract] |
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S1.00209: Evidence for a disorder-phase transition in the condensation of $^{4}$He in aerogels Fabien Bonnet, Mathieu Melich, Laurent Puech, Pierre Etienne Wolf Although widely studied, capillary condensation of fluids in disordered mesoporous media is not fully understood. A central question is the origin of the hysteretic behavior between adsorption and desorption. It has been recently proposed that this hysteresis could result from the disorder of the porous media. Based on mean-field theoretical calculations, a disorder-driven transition is predicted, similar to that occurring in the Random Field Ising Model. Our earlier results on the condensation of helium in silica aerogel, combining thermodynamic (adsorption isotherms) and optical measurements, have provided a first evidence for such a transition. Here, we report new measurements on aerogels (porosity: 95\%, 97\% and 98.5\%) , which further support the disorder scenario, and allow us to study the interplay between temperature and disorder. We also compare the case of aerogels to that of Vycor. Although a transition is not observed in Vycor, the dynamics of the adsorption and desorption processes lead us to conclude that disorder is also important in this case. F. Bonnet et al. Europhys. Lett. 82, 56003 (2008) [Preview Abstract] |
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S1.00210: Ambient Detection of Energetic Materials by Matrix Assisted Laser Desorption and Photofragmentation-Fragment Detection Stephen Roberson, Rosario Sausa We detect energetic materials TNT and RDX by Matrix Assisted Laser Desorption (MALD) followed by photofragmentation-fragment detection (PF-FD) in real time at ambient conditions. A pump laser irradiates a mixture of energetic material and laser dye freeing the energetic material from the surface, and a second laser fragments the resulting energetic molecule to create the characteristic nitric oxide (NO) fragment, which is subsequently ionized and then detected by resonance-enhanced multiphoton ionization (REMPI). Our studies on the effects of pump and probe laser energy, dye concentration, and analyte concentration on the ion signal intensity, as well as the RDX and TNT limits of detection will be reported at the meeting. The PF-FD technique exhibits great potential for detecting trace energetic materials on surfaces because of its high sensitivity and selectivity. It is not restricted to TNT and RDX, and can be extended to other energetic materials. [Preview Abstract] |
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S1.00211: Molecular dynamics simulations of electrostatics and hydration distributions around RNA and DNA motifs Ashley E. Marlowe, Abhishek Singh, Andrey V. Semichaevsky, Yaroslava G. Yingling Nucleic acid nanoparticles can self-assembly through the formation of complementary loop-loop interactions or stem-stem interactions. Presence and concentration of ions can significantly affect the self-assembly process and the stability of the nanostructure. In this presentation we use explicit molecular dynamics simulations to examine the variations in cationic distributions and hydration environment around DNA and RNA helices and loop-loop interactions. Our simulations show that the potassium and sodium ionic distributions are different around RNA and DNA motifs which could be indicative of ion mediated relative stability of loop-loop complexes. Moreover in RNA loop-loop motifs ions are consistently present and exchanged through a distinct electronegative channel. We will also show how we used the specific RNA loop-loop motif to design a RNA hexagonal nanoparticle. [Preview Abstract] |
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S1.00212: Disentanglement and Re-entanglement of Polymer Solutions after Large Step Shearing Deformation Yangyang Wang, Shi-Qing Wang Double-step strain and elastic recovery experiments were carried out to explore the disentanglement and re-entanglement kinetics in entangled 1,4-polybutadiene solutions after large step shearing deformation. In double-step strain experiments, startup shear measurements were interrupted at different strains, and resumed after different waiting times. When the interrupted strain was small, the magnitude of stress overshoot in the resumed shear remained unchanged. However, at a large strain, the magnitude of stress overshoot would first decrease with increasing waiting time and only become higher after longer waiting time. This observation reveals evidence that disentanglement occurs after a large step deformation. Subsequent healing in the form of re-entanglement allows the sample to relax normally in quiescence. In elastic recovery experiments, the data at small strains fall onto a master-curve, whereas the recovery at large strains shows much stronger strain dependence, confirming occurrence of chain disentanglement beyond a critical strain amplitude. [Preview Abstract] |
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S1.00213: Phonons in strongly correlated materials from Hubbard-corrected density-functional-perturbation theory Andrea Floris, Matteo Cococcioni, E.K.U. Gross, Stefano de Gironcoli In this contribution, density functional perturbation theory is generalized to the DFT+U approach. The goal is to compute the vibrational frequencies of strongly correlated systems whose ground-state electronic properties are well reproduced within the DFT+U method. The formalism, extended to both norm-conserving and Vanderbilt ultrasoft pseudo-potentials, allows us to compute phonon frequencies with a computational cost that is independent of the q-vector, thus permitting an efficient exploration of the entire Brillouin zone. The correction to the perturbed self-consistent potential and to the dynamical matrix due to the inclusion of the Hubbard U term, as well as the main features of their implementation will be discussed along with several applications. [Preview Abstract] |
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S1.00214: Extended LDA+U+V approach for covalently bonded systems Vivaldo Leiria Campo Jr, Matteo Cococcioni A novel DFT+U energy functional (named DFT+U+V) is introduced based on a corrective Hubbard Hamiltonian that includes both on-site (U) and inter-site (V) electron-electron interactions. The competition between these couplings allows for more general localization regimes (e.g., on hybrid, molecular states). Systems as diverse as Mott insulators and covalent semiconductors can be described within the same theoretical framework. Also, phenomena like electron-transfer reactions or formation and breaking of bonds, whose modeling within ``standard" (e.g., LDA or GGA) approximations to DFT or with the ``on-site" DFT+U approach is problematic, will be addressed with higher precision. Accurate energetics is guaranteed by the consistent evaluation of V that can be obtained, at no additional cost, from the same linear-response approach used to calculate U [1]. The flexibility and reliability of the novel functional are demonstrated by its application to covalent (Si) and ionic (GaAs) semiconductors and to charge-transfer insulators (NiO). [1] M. Cococcioni and S. de Gironcoli, Phys. Rev. B 71, 035105 (2005). [Preview Abstract] |
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S1.00215: Physical Properties of Various Materials Relevant to Granular Flow Kurt Rosentrater Because of the ubiquitous nature of granular materials, ranging from natural avalanches to industrial storage and processing operations, interest in quantifying and predicting the dynamics of granular flow continues to increase. The objective of this study was to investigate various physical properties of common biological bulk solids (i.e., grains) which are relevant to granular flow. Particle size, shape, loose bulk density, compacted bulk density, angle of repose, and angle of marginal stability will be presented and discussed. Flow properties depend, in large measure, upon the size and shape of the particles themselves; thus information generated from this study may be useful to future experimental and simulation studies of bulk flow. [Preview Abstract] |
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S1.00216: Bismuth nanowire array fabrication and measurements Richard Greco Bismuth Nanowire Arrays (BNAs) are semiconducting materials that can potentially lead to radiation detectors with better spectral resolution and efficiency than cooled high purity germanium because of the high atomic number of bismuth and expected nanowire electronic properties. Bismuth, which is normally a semi-metal, becomes a semiconductor when it is fabricated in wire form with a diameter smaller than 50 nanometers (nm). Arrays of bismuth nanowires are produced by vapor deposition into electrochemically-fabricated alumina templates. The electronic bandgap of a bismuth wire is a function of its diameter, varying from 0 eV at 50 nm to 0.7 eV at 5 nm. In this paper we present an improved fabrication technique and recent measurements on BNAs. [Preview Abstract] |
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S1.00217: Organic non-volatile memories from ferroelectric phase separated blends Kamal Asadi, Dago de Leeuw, Bert de Boer, Paul Blom Ferroelectric polarisation is an attractive physical property for non-volatile binary switching. The functionality of the targeted memory should be based on resistive switching. Conductivity and ferroelectricity however cannot be tuned independently. The challenge is to develop a storage medium in which the favourable properties of ferroelectrics such as bistability and non-volatility can be combined with the beneficial properties provided by semiconductors such as conductivity and rectification. In this contribution we present an integrated solution by blending semiconducting and ferroelectric polymers into phase separated networks. The polarisation field of the ferroelectric modulates the injection barrier at the semiconductor--metal contact. This combination allows for solution-processed non-volatile memory arrays with a simple cross-bar architecture that can be read-out non-destructively. Based on this general concept a non-volatile, reversible switchable Schottky diode with relatively fast programming time of shorter than 100 microseconds, long information retention time of longer than 10$^{ }$days, and high programming cycle endurance with non-destructive read-out is demonstrated. [Preview Abstract] |
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S1.00218: Manganese doping of group IV semiconductor surfaces and nanostructures Petra Reinke, Christopher Nolph, Kiril Simov The combination of Si and Ge with Mn is a critical step in the development of novel spintronics devices. We investigate the magnetic doping of Si, Si-surfaces and Ge- quantum dots with Mn. A surface-driven route is used for the addition of Mn and allows a stringent control of the Mn-Si and Mn-Ge interaction. The evolution of nanostructures is observed with STM and PES. Monoatomic Mn-wires form on the Si(100) surface in the low-mobility regime and dissolve into sub-surface structures at elevated temperatures. The phase diagram for Mn-Si nanostructures is developed and leads to embedded Mn structures. The interaction of Mn with Ge-quantum dots poses a new set of constraints. The Mn-addition leads to the formation of surface clusters on the wetting layer whose spatial distribution is driven by the surface relaxation. The Mn-adatom clusters on the {105} facet of the Ge-quantum dots are oriented with respect to the surface reconstruction, which predetermines diffusion pathways into the Ge-QD. The characteristics of Mn-nanostructure formation and the possibility of the synthesisof magnetic structures will be discussed. [Preview Abstract] |
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S1.00219: The impact of the market index on the topology of financial networks Edward Mandere, Haowen Xi We study the financial network generated from stock price returns correlation. The network topology has been used to explore and visualize the relationships between stocks. These networks have also been used in reconstructing less noisy correlation matrices for portfolio optimization. In this work, we explore the effect of adding the market index to the rest of stock network. We show that there is a very strong clustering around the index, both in S{\&}P500 and DJIA. The mechanism that leads to these strong clustering as well as the implication to reconstructed correlation matrices will be explored. [Preview Abstract] |
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S1.00220: Second harmonic generation in $\rm N@C_{60}$ and $\rm P@C_{60}$ Megan Morris, Nicole Perigo, Guoping Zhang The successful implantation of nitrogen and phosphorus into $\rm C_{60}$ opens many new applications. For instance, both $\rm N@C_{60}$ and $\rm P@C_{60}$ are ideal candidates for quantum computing. In this paper, we show that $\rm N@C_{60}$ and $\rm P@C_{60}$ can be used to generate the second harmonic generation. If N and P are at the center of the buckyball, the signal is zero, but if they are off the center, the signal comes out. Therefore, the oscillation of N and P atoms will generate a 0-1-0-1 bit, when detected along the incident light direction. If this signal is sent to another $\rm N@C_{60}$ and $\rm P@C_{60}$, they can control the sequence of bits. The intensity sensitively depends on the laser energy and polarization. This process can be useful for quantum control by $\rm N@C_{60}$ and $\rm P@C_{60}$ themselves. All the results are obtained using the first-principles method. [Preview Abstract] |
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S1.00221: Quantum correlated light pulses from sequential superradiance of a condensate Mehmet Emre Tasgin, Mehmet Ozgur Oktel, Li You, Ozgur Esat Mustecaplioglu We discover an inherent mechanism for entanglement swap associated with sequential superradiance from an atomic condensate. As a result, Einstein-Podolsky-Rosen (EPR)-type quantum correlated photons can be detected among the scattered light pulses. [Preview Abstract] |
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S1.00222: Doping effects on charge density wave state in o-TaS$_{3}$ Damir Dominko, Damir Stare\v{s}inic, Katica Biljakovic, Peter Lunkenheimer, Alois Loidl, Jean Claude Lasjaunias We present the effects of the isoelectronic supstitution of Ta by (0.2 and 0.5 {\%}) Nb atoms on the charge density wave (CDW) properties in o-TaS$_{3}$. The characteristic, primary relaxation process which gives the maximum in the dielectric constant near 100 K disappears with slight doping. At the same time the minimum in threshold field in the same temperature range disappears as well, which is expected from well known relation between E$_{T}$ and low frequency dielectric constant [1]. This implies that the primary process it mainly due to polarization on order of domain scale, which decreases by doping. The secondary process, on the other hand, as well as low energy excitation contribution to specific heat (C$_{LEE})$, seem to be unchanged. Only the amplitudes of the two are increased [1, 2], as both are due to the local excitations of the CDW phase in vicinity of defects described by two level system (TLS) model. [1] Stare\v{s}inic et. al, Phys. Rev. B, \textbf{65}, 165109 (2002) [2] Biljakovic et. al, \textit{Europhys. Lett.}, \textbf{62 }(4), pp. 554--560 (2003) [Preview Abstract] |
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S1.00223: Nature of Light Sunil Thakur How do we perceive light? We assume that we have to absorb a photon to perceive light. When we set out to confirm this assumption experimentally then we find that everything we knew about light is wrong. We can perceive light wherever it is, provided light is in the perceivable range of our eyes. More than one photon detector can simultaneously detect a single photon. Obviously, a single photon cannot be absorbed by more than one detector. We can see a laser beam refract as it enters water from air but we find no refraction when we view the laser beam from the side of the container. It is possible only if we can see the light without having to absorb the light. Perception of the total solar eclipse as it occurs confirms this observation. All light sources emit only energy, light is produced by the object that absorbs this energy. Only difference between a luminous object and an illuminated object is that luminous objects generate their own energy to radiate light whereas illuminated objects need energy from an external source to radiate light. The observations are conclusively validated in several other advanced experiments. These experiments also show that the idea of motion cannot be associated with the light; illusion of motion of light is created due to movement of energy through the medium that produces light. These experiments conclusively invalidate theory of relativity, standard model of cosmology, and standard model of particle physics. [Preview Abstract] |
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S1.00224: Phonon Spectroscopy by Electrical Measurement in Coupled Quantum Dots Akiko Ueda, Mikio Eto We propose a phonon spectroscopy by electrical measurement in coupled quantum dots. We consider T-shaped double quantum dots, in which one of the dots is connected to external leads (dot 1) and the other is disconnected (dot 2). The differential conductance shows a dip at the midpoint of the two peaks by resonant tunneling through bonding or antibonding orbitals between the two dots, when the energy levels are tuned in the dots. The dip is caused by the destructive interference between the electron waves passing by the molecular orbitals. We calculate differential conductance under finite bias $V_{\rm bias}$ using Keldysh Green function method.\footnote{A.\ Ueda and M.\ Eto, Phys.\ Rev.\ B {\bf 73}, 235353 (2006); New J.\ Phys.\ {\bf 9}, 119 (2007).} The conductance dip is diminished by electron-phonon interaction since phonon emission from dot 2 destroys the interference between electron waves passing through only dot 1 and waves passing through both dots. The dip as a function of $V_{\rm bias}$ reflects a product of the density of states for phonons at $eV_{\rm bias}$ and strength of electron-phonon coupling in dot 2. This implies a new method of electrically detected phonon spectroscopy. [Preview Abstract] |
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S1.00225: Transport Properties for Biphenyl-Based Molecular Junction System Hisashi Kondo, Jun Nara, Takahisa Ohno In the present study, the transport properties of an biphenyl-based molecule [$X$-BP-$X$ ($X$: the end-group atom),$ X$=O, S, Se, and Te] sandwiched between Au(111) electrodes are theoretically investigated using the non-equilibrium Green's function method based on the density functional theory. The end-group atom $X$ has an influence on the interaction between the molecule and electrodes and the interaction between the two phenyl rings. For $X$ =S, Se, and Te, similar transport properties are obtained, while the system with $X$ =O exhibits much different properties from the other $X$s. In case of $X$ =O, the interaction between the molecule and electrodes becomes the weakest and that between $\pi $-type orbitals of the two phenyl rings, which mainly contributes to the transmission around the Fermi energy, becomes the strongest. As a result, this system has a larger transmission around the Fermi energy. We also investigate the dependence on dihedral angle between the two phenyl rings for all $X$s. This study was supported by the RISS project and a Grant-in-Aid for Scientific Research (No.17064017) of MEXT of the Japanese Government. The present calculations were performed by using the Numerical Materials Simulator in National Institute for Materials Science. [Preview Abstract] |
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S1.00226: Electronic structure and Fermi surface of Pr$M$In$_5$ ($M$=Co, Rh, and Ir) compounds Saad Elgazzar, Ingo Opahle, Manuel Richter, Peter Oppeneer We report density functional calculations of the electronic structure, Fermi surface, and de Haas-van Alphen (dHvA) quantities of the Pr$M$In$_5$ ($M$=Co, Rh, and Ir) compounds. Our investigation is carried out within the framework of the local density approximation (LDA), using a relativistic, full-potential band structure method (FPLO). A critical analysis of the electronic structures and the de Haas-van Alphen quantities is performed, which shows that good agreement with recent measurements is obtained when we assume the Pr $4f$-states to be localized. The topology of the Fermi surface is calculated to be similar to that of non-4$f$ reference compounds, as, e.g., LaRhIn$_5$. The similarities of the Fermi surfaces and the dHvA extremal orbits among the compounds in the series are discussed. We furthermore compare our calculated effective masses with experimental measurements and discuss the differences between them. [Preview Abstract] |
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S1.00227: Capillary interactions in nano-particles suspensions Dobrin Bossev, Garfield Warren We have investigated the structures formed by colloidal particles suspended in solvents at volume fractions below 10{\%} and interacting through capillary bridges. Such systems resemble colloidal gas of sticky nano-spheres that form pearl-necklace like chains that, in turn, induce strong viscoleasticity due to the formation of 3-D fractal network. The capillary force dominates the electrostatic and Van der Waals forces in solutions and can bridge multiple particles depending of the volume of the capillary bridge. We have investigated the morphology of the structures formed at different fractions of the bridging fluid. Computer simulations of a pearl necklace-like chain of spheres is conducted to explain the structure factor when capillary bridges are present. Alternatively, we have analyzed the slope of the neutron scattering intensity at low Q in a double logarithmic plot to determine the dimension of the fractal structures formed by the particles at different volume fraction of the bridging fluid. We have also studied the properties of the capillary bridge between a pair of particles. The significance of this study is to explore the possibility of using capillary force as a tool to engineer new colloidal structures and materials in solutions and to optimize their viscoelastic properties. [Preview Abstract] |
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S1.00228: Capillary interactions between silica-particles in organic solvents Garfield Warren, Dobrin Bossev Small-angle neutron scattering (SANS) is used to study the interactions of silica nano-particles with an average diameter of 10 nm in methanol and methanol/toluene mixtures at 25 $^{o}$C. SANS intensities are analyzed as a product of a form factor and a structure factor. The form factor is experimentally determined in methanol after addition of simple electrolyte at a concentration of 100 mM to suppress the interparticle interactions. The data is successfully fitted by Hayter-Penfold mean spherical approximation (HPMSA) that yielded the specific area of surface charge in methanol. The phase behavior, viscosity and interparticle interactions are studied as a function of fraction of toluene in methanol/toluene mixtures at a constant particle volume fraction of 3.7 {\%}. At intermediate fractions of toluene, between 44 and 65 {\%}, the viscosity increases by two orders of magnitude which suggests formation of two dimensional network of silica particles. Computer simulations of a pearl necklace-like chain of spheres is conducted to explain the structure factor at these intermediate fraction of toluene. The capillary force is thought to be the driving force for the network formation. To verify this hypothesis, anionic and cationic surfactants are tested to disintegrate the particle chains. [Preview Abstract] |
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S1.00229: Superconductivity in (La$_{1-x}$Th$_{x})$PtSi and LaPt$_{1-x}$Si systems W.H. Lee, H.H. Sung, J.Y. Chen, K.J. Syu As revealed in the powder x-ray diffraction and crystallographic data, the partial substitution of La with Th in (La$_{1-x}$Th$_{x})$PtSi is able to be systematic up to the solubility limit near x = 0.5 and the parent compound LaPtSi admits considerable vacancies up to 20{\%} on the Pt sublattice while still retaining its tetragonal symmetry. The refined lattice parameters show that both the c-axis and the volume of the unit cell v shrink clearly due to the doping with Th or the existence of vacancies in the compound. These results are consistent with what one would expect from a chemical pressure effect. We will present the static magnetization and specific heat data for these pseudo-ternary compounds investigated in the necessary temperature range. Discussion of the change in the superconducting critical temperature T$_{c}$ will be directed toward the changes of electron number density as well as the lattice parameters with respect to pure LaPtSi. [Preview Abstract] |
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S1.00230: Crystal structure and superconductivity in (La$_{1-x}$Y$_{x})$NiC$_{2}$ H.H. Sung, K.J. Syu, T.F. Liao, W.H. Lee As observed in the powder X-ray diffraction and crystallographic data, the partial substitution of La with Y in (La$_{1-x}$Y$_{x})$NiC$_{2}$ could be systematic up to the solubility limit near x = 0.35. The variation of room temperature lattice parameters, a, b, c and v of these substitute compounds are consistent with what one would expect from a chemical pressure effect. Magnetic, electrical and heat capacity measurements indicate that the change in T$_{c}$ with x is similar to the change in the lattice parameter. It is found that the T$_{c}$ change rate is dT$_{c}$/dx = --7.0 K and dT$_{c}$/dv = 0.46 K/{\AA}$^{3}$. According to the BCS theory, the stiffening of the lattice under pressure may change both the electron-phonon coupling strength V and the electron density of states at the Fermi level, N(0), which will lead to the change of T$_{c}$. Analysis of the electron density of states at Fermi level N(0) from the specific heat data indicates that the effect of N(0) on T$_{c}$ dominates in the (La$_{1-x}$Y$_{x})$NiC$_{2}$ system. [Preview Abstract] |
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S1.00231: Unbinding Dynamics of weakly adhered vesicle on a substrate Sunita Chatkaew, Marc Georgelin, Marc Leonetti Unbinding dynamics of a vesicle adhering weakly on a substrate by hydrodynamic force is characterized in our works. Vesicle shapes on a substrate are governed by adhesion energy, gravity and curvature energy. Several regimes of unbinding dynamics are observed from inflated vesicles until the deflated ones. Water film growth between the membrane and the substrate and the reduction of contact area are monitored. In the case of inflated vesicle, the unbinding dynamics shows the growth of water film with the same contact area. After this lag time, the radius of the contact area decreases strongly following a 1/2 power law. When the vesicles are more deflated, the unbinding is then just a strong reduction of the contact area at a constant thickness of water film. Lipidic tube can be found in the case of a strong applied hydrodynamic force on a deflated vesicle occupying a large contact area. [Preview Abstract] |
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S1.00232: Particle-Tracking Velocimetric Investigation of Large Amplitude Oscillatory Shear of Entangled Polymer Melts Gregory Zartman, Yangyang Wang, Shi-Qing Wang Large amplitude oscillatory shear (LAOS) experiments were carried out on a series of entangled monodisperse styrene-butadiene random copolymers (SBR). The deformation field during the measurements was monitored with a particle-tracking velocimetric technique. It was found that when the applied frequency was higher than the overall relaxation rate of the sample, the entangled melt would undergo uniform deformation at small strains, but exhibit shear banding at large strains. The inhomogeneity of the deformation field suggests that yielding through chain disentanglement cannot take place uniformly. This is the first report of shear banding in LAOS for melts and consequently rules out any speculation that shear banding could originate from concentration variation (due to shear induced phase separation) in entangled solutions. [Preview Abstract] |
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S1.00233: Elementary charge-transfer processes in mesoscopic conductors Mihajlo Vanevic, Yuli Nazarov, Wolfgang Belzig We determine charge-transfer statistics in a quantum conductor driven by a time-dependent voltage and identify the elementary transport processes. At zero temperature unidirectional and bidirectional single-charge transfers occur. The unidirectional processes involve electrons injected from the source terminal due to excess dc bias voltage. The bidirectional processes involve electron-hole pairs created by time-dependent voltage bias. This interpretation is further supported by the charge- transfer statistics in a multiterminal beam-splitter geometry in which injected electrons and holes can be partitioned into different outgoing terminals. The probabilities of elementary processes can be probed by noise measurements: the unidirectional processes set the dc noise level, while bidirectional ones give rise to the excess noise. For ac voltage drive, the noise oscillates with increasing the driving amplitude. The decomposition of the noise into the contributions of elementary processes reveals the origin of these oscillations: the number of electron-hole pairs generated per cycle increases with increasing the amplitude. The charge- transfer statistics at finite temperature can be interpreted in terms of multiple-charge transfers with probabilities which depend on energy and temperature. [Preview Abstract] |
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S1.00234: On the Salecker-Wigner-Peres Clock and Quantum Tunneling Luiz Manzoni, Jose Lunardi, Marcos Calcada We consider the Salecker-Wigner-Peres clock formalism and show that in the approach introduced by Peres it can be directly applied to quantum tunneling. Then we apply this formalism to the determination of the tunneling time of a non relativistic particle through a double barrier potential. In special, we consider the case in which the clock runs only when the particle can be found inside the region \emph{between} the barriers and analyze the limit of opaque barriers in order to discuss the generalized Hartmann effect. [Preview Abstract] |
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S1.00235: Restricted height discrete model Jin Min Kim We introduce a discrete growth model following the Edward- Willikinson equation with a conservative noise. The surface width $W(h,t)$ of our model follows $W^2(L,t)=W_i^2- L^{2\alpha}f(t/L^z)$, where $W_i$ is an intrinsic width. By subtracting the surface width from the intrinsic width, the roughness exponent $\alpha \approx -d_s/2$ and the growth exponent $\beta \approx -d_s/4$ are successfully obtained for the substrate dimension $d_s=1, 2$ and $3$. Various discrete models with conserved noise are also discussed. [Preview Abstract] |
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S1.00236: Growth of the Graphene Nanoribbons on the Vicinal 6H-SiC(0001) Surface Ilyou Kim, E. Cho, C. Hwang, W. Kim Graphene nanoribbons (GNR) are currently considered as one of the most promising materials for future nanoelectronic devices due to its exceptional physical properties. We investigated the possibility of the growth of GNR on the vicinal 6H-SiC(0001) surface using Scanning Tunneling Microscopy. We observed the formation of the ribbon-like single-layer graphene with sharp edge structures at the initial stage of thermal graphitization process of the SiC(0001) surface. However, the overall long-range ordering of the steps of the bare vicinal surface was found out to be lost during graphitization process, and only the local short range ordering of the steps with graphene layer patches existed on the entire surface. From the atom-resolved STM images, we clearly identified the armchair edge structure of graphene for several ribbon-like graphene nanostructures. Scanning tunneling spectroscopy experiment was also carried out over the ribbon-like graphene patches to examine the local electronic states at the edge structures. [Preview Abstract] |
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S1.00237: First Principles Study of Nature of Binding Energies in Solid Hydrogen Hari Paudel, Sitaram Byahut The study of solid hydrogen is of utmost importance since it can be used as renewal source of energy. In the present work, we have quantitatively studied the properties of solid molecular hydrogen. The Hartree-Fock method, together with electron correlation effects included by many-body perturbation theory, has been utilized in this work. Study of geometry and binding energy using different basis sets will be presented. In addition to this, the effect on energy due to orientations of hydrogen molecule at lattice point will be presented and compared with available experimental data. A comparison of binding energy using pair energy approximation and cluster energy approximation methods will be discussed. [Preview Abstract] |
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S1.00238: Elastic yielding after step shear and shear banding in LAOS: Is there any edge effect? Xin Li, Shi-Qing Wang One of the most striking findings in our recent exploration of nonlinear rheological behavior of entangled polymers is the discovery that a suddenly sheared sample cannot relax quiescently. In both solutions [1] and melts [2], particle-tracking velocimetric (PTV) observations reveal macroscopic motions after a large step shear. The present work takes a significant step forward to examine whether such cohesive failure upon shear cessation could arise from the experimental imperfection due to the presence of the free surface, i.e., the meniscus. By adopting a new setup to insure that the edge only undergoes a small strain and therefore suffers no failure of any kind, we determine how the sample interior would undergo elastic yielding in the form of macroscopic motions during stress relaxation upon a large step strain. The same device also allows us to illustrate that the previously observed shear banding in large amplitude oscillatory shear (LAOS) [3] is also an inherent response to the imposed LAOS, free of any edge effects. [1] S. Ravindranath and S. Q. Wang, Macromolecules 40, 8031 (2007). [2] P. Boukany and S. Q. Wang, Macromolecules, to be submitted (2009). [3] S. Ravindranath and S. Q. Wang, J. Rheol. 52, 341 (2008). [Preview Abstract] |
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S1.00239: Exploring origins of nonlinearity in large amplitude oscillatory shear of different viscoelastic materials Xin Li, Xiaorong Wang, Shi-Qing Wang The present work studies nonlinear behavior in large amplitude oscillatory shear (LAOS) of three different polymeric materials using both rheometric and particle-tracking velocimetric measurements. We show that nonlinearity in LAOS is often not inherent response of the polymers that are capable of rearranging their microstructures over time. For instance, a highly viscoelastic material made of nano-sized polybutadiene particles exhibits homogeneous deformation and a nearly perfect single-harmonic sinusoidal wave in its stress response despite strong strain softening. In a second example of a well entangled polymer solution, the structural alternation in LAOS occurs non-homogeneously, where the nonlinearity also took a finite time to develop to its fullest. In the last example of wall slip, contrary to the literature claim that it should violate the mirror symmetry, the stress response only involves odd-harmonics, i.e., there is equivalence during steady-state wall slip in LAOS when the direction of shear is reversed. [Preview Abstract] |
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S1.00240: Undulatory swimming of a sandfish lizard in granular media Daniel Goldman, Ryan Maladen, Chen Li, Yang Ding We study the locomotion of the desert dwelling sandfish lizard ({\em Scincus scincus}) as it dives into and swims beneath the surface of sand ($300 \mu m$ glass beads). Above the surface, the animal uses a diagonal gait to move rapidly across the sand. High speed x-ray imaging reveals that once subsurface the animal no longer uses limbs for propulsion but instead folds the limbs against the body and generates thrust using a large amplitude undulatory motion consisting of a traveling wave with frequency $f$ that propagates down the body with one wave period. The forward swimming speed $v$ (maximum 10 cm/sec) increases with increasing $f$. We measure $v$ versus $f$ as a function of packing fraction of the material $\phi$. To predict $v$ as a function of $f$ and $\phi$, we model the animal as a series of elements, each which produces thrust and experiences drag along its surface. We measure thrust and drag coefficients by performing drag measurements on a small stainless steel rod (grain-rod friction comparable to the animal's skin) as a function of rod angle, rod speed, and $\phi$. Integrating the drag law over a sinusoidal wave form accurately predicts the $v-f$ relationship of the animal in loose and close packed granular media. [Preview Abstract] |
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S1.00241: Characteristics of top-gate ZnO thin film transistors grown on glass substrate by pulsed laser deposition Toshihiko Maemoto, Kenji Fujiwara, Taichi Yoshida, Shigehiko Sasa, Masataka Inoue We report on the fabrication and characterization of top-gate ZnO thin film transistors (TFTs) using glass substrates. High quality ZnO epitaxial films were grown on glass substrates (Corning {\#}1737) by pulsed laser deposition. The thickness of the films was in the range of 50-100 nm. The growth temperature was set to 380$^{\circ}$C. These films were characterized by x-ray diffraction, and Hall effects measurements. Highly c-axis oriented ZnO(0002) reflections corresponding to the wurtzite-phase were observed for all the films, indicating that these films grow epitaxially as a crystalline single phase on a glass substrate. The Hall effects measurements show that we have succeeded in fabricating a ZnO film with an electron mobility of 36 cm$^2$/Vs on a glass substrate. Top-gate ZnO TFTs were fabricated by photolithography and wet chemical etching. The ohmic contact metal Ti/Au was deposited by electron beam evaporation. The top gate electrodes and the gate insulator SiO$_2$ were finally deposited by electron beam evaporation. A room temperature characteristic of ZnO TFT with 50 $\mu $m gate length was an n-channel depletion type with a transconductance of 5.4 mS/mm. The off current was less than 10$^{-9}$ A and the on/off current ratio was about 10$^6$ at V$_{DS}$=5V. [Preview Abstract] |
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S1.00242: Stabilization of Ti-Zr-Ni quasicrystals by hydrogen and application as renewable energy storage materials Sang-hwa Lee, Jae-kyun Jeon, Soo-bin Choi, Jae-yong Kim We prepared quasicrystal samples by rapidly quenching of Ti$_{50-x}$Zr$_{30+x}$Ni$_{20}$ alloys (where 0$\le $x$\le $10), and measured equilibrium vapor pressures of hydrogen using a lab-built computer-controlled-absorption apparatus at elevated temperatures. To activate the hydrogen absorption, we removed a thin oxygen layer on the surface of the sample by using a plasma etching in a partial pressure of Ar and applied an immediate thin Pd coating by using a physical vapor deposition. As a result, the equilibrium vapor pressures of hydrogen in the QCs were lower than 5 Torr at below 300${^\circ}$, and were increased as lowering the temperature. The maximum value of the H/M was also increased as increasing the temperature. Interestingly, the coherence length of the QCs was increased from 180 to 270 ? as performing the absorption/desorption cycling at elevated temperature suggesting that diffusion of hydrogen might enhance the stability of QCs structure. An applaud explanation about the relation of increased coherence length with hydrogen diffusion in QCs will be discussed. [Preview Abstract] |
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S1.00243: Semiconductor-metal transition of Se in Ru-Se Catalyst Nanoparticles P.K. Babu, Adam Lewera, Eric Oldfield, Andrzej Wieckowski Ru-Se composite nanoparticles are promising catalysts for the oxygen reduction reaction (ORR) in fuel cells. Though the role of Se in enhancing the chemical stability of Ru nanoparticles is well established, the microscopic nature of Ru-Se interaction was not clearly understood. We carried out a combined investigation of $^{77}$Se NMR and XPS on Ru-Se nanoparticles and our results indicate that Se, a semiconductor in elemental form, becomes metallic when interacting with Ru. $^{77}$Se spin-lattice relaxation rates are found to be proportional to $T$, the well-known Korringa behavior characteristic of metals. The NMR results are supported by the XPS binding energy shifts which suggest that a possible Ru$\to $Se charge transfer could be responsible for the semiconductor$\to $metal transition of Se which also makes Ru less susceptible to oxidation during ORR. [Preview Abstract] |
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S1.00244: Morphology Characterization of Polymer Nanocomposites using Electron Tomography and Analytical TEM Lawrence Drummy, Richard Vaia Polymer nanocomposites often display complex hierarchical structures that require high resolution morphological and chemical analysis. Here we describe methods for and quantitative results from electron tomography of polymer/layered silicate nanocomposites. High angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and subsequent tomographic reconstruction produced fully segmented 3D data sets from the nanocomposites. A 3D power spectrum of the fast Fourier transform (FFT) was calculated, radially integrated, and compared with the one dimensional SAXS from the same sample. As a tool for determination of nanoparticle global dispersion, the analysis revealed good agreement between the techniques from the sub-nm regime up to a length scale of 1 micron. Currently, energy filtered TEM and energy dispersive spectroscopy in STEM mode are being investigated for providing high spatial resolution chemical information at interfaces and inhomogeneities in polymer nanocomposites. [Preview Abstract] |
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S1.00245: Interlayer Thermal Coupling of Hot Dirac Fermions in Epitaxial Graphene Dong Sun, Charles Divin, Ted Norris, Claire Berger, Walt de Heer, Phillip First Degenerate and nondegenerate ultrafast pump-probe spectroscopy is used to study interlayer thermal coupling of hot Dirac Fermions in carbon face epitaxial graphene. The hot carriers in lightly doped and undoped graphene layers are selectively excited by the pump laser while leaving the carriers in the heavily doped layer not directly excited. Within the 500fs, carries at elevated temperature in the heavily doped layer is observed, which is excited due to the interlayer thermal coupling of the hot carriers. [Preview Abstract] |
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S1.00246: Exploring origin of instabilities in pressure-driven flow of entangled polymers using particle-tracking velocimetric method Xiangyang Zhu, Shi-Qing Wang Well entangled polymeric materials undergo extrudate distortions commonly known as sharkskin (surface melt fracture) and gross melt fracture. Particle-tracking velocimetric (PTV) observations have been carried out to explore the relationship between gross melt fracture and entry flow instability based on polybutadiene melts. The sharkskin formation process has also been investigated based on PTV visualization of the flow field at the die exit. These instabilities have been studied in terms of the material parameters. [Preview Abstract] |
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S1.00247: Morphology and structure of the self assembled Ag nanodots on undoped Si(100) under ambient conditions Jeffrey Parks, Indrajith Senevirathne Self assembly is an important bottom up design approach in making nanostructures on substrate. Therefore understanding the self assembly mechanisms is very important. Morphology and structure of the self assembled of Ag nano dots via sputter deposition on the chemically cleaned ambient undoped si(100) wafer at RT ($\sim $300K) is observed via contact mode Atomic Force Microcopy (AFM). At a Ag coverage of $\sim $60ML nucleation of the nanodots were seen, implying StranskiKrastanov growth mode. At a coverage of $\sim $120ML the self assembled nanodots are clearly seen. These nanodots are observed to have $\sim $40nm in width and $\sim $10nm in height. At increase Ag coverage ($\sim $120ML and $\sim $180ML) it is observed the number density of Ag nanodots increase in lock step. Higher the coverage size characteristics observed to show a higher variance. When annealed at successively higher temperatures ($\sim $373K, $\sim $473K, $\sim $573K) for an interval of 5min the structures seem to dissolve, implying kinetically limited growth. Conductivity measurements on these nanostructures will also be discussed. [Preview Abstract] |
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S1.00248: Study on the formation of rhenium borides by density functional calculations R.R. Agundez, G. Soto, M.G. Moreno, A. Reyes-Serrato The searching of hard and superhard materials is a hot topic in material science. Two known factors are fundamental to get high hardness: (1) high valence-electron density; and (2) high number of electron in covalent bonds. The 5d-transition metals comply with requirement (1); so, the task is to fulfill condition (2) without expanding its native structure. Supposedly this is possible by developing interstitial alloys with elements of moderate electronegativity, like boron and/or carbon. This idea materializes in the very hard ReB2, which scratches the surface of diamond. This work is a study in the formation of rhenium borides by density functional calculations. Here, we want to reveal the changes that would occur in the hexagonal close packed lattice of Re as B is inserted into its interstitial sites. We cover compositions in ReBx from x = 0 to x = 3 in x steps of 0.125. B is positioned in octahedral and tetrahedral interstices of Re, and for each arrangements we have calculated cell volume, cohesive energy, bulk modulus, valence electron concentration, and energy density. Supported by FONDOS CONACYT I0013, SNI-ESTUDIANTES 2008-01, SOLICITUD: 103909 [Preview Abstract] |
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S1.00249: Magnetic force microscopy studies of vortex states in type II superconductors and ferromagnetic microstructures Jeffrey Wright, Evgueni Nazaretski, P.C. Hammel, Roman Movshovich A variable temperature, high sensitivity Magnetic Force Microscope (MFM) was used to study vortices in a superconducting niobium thin film, as well as ferromagnetic microstructures, whose magnetization forms a vortex ground state. The highly sensitive interferrometric detection of the cantilever displacement allowed for detailed measurements of the magnetic field profile produced by individual vortices. The MFM's variable temperature ability and superconducting magnet allowed for field cooling of the niobium sample in an external magnetic field either parallel or anti-parallel to the orientation of the cantilever magnetic tip.~ MFM studies of 50 nm thick and 4 $\mu $m diameter permalloy microstructiures were performed at room temperature and at 4.2K. At room temperature, the sample's magnetization exhibited the dipole structure while at 4.2 K it showed the evidence for the vortex state. By bringing the MFM tip close to the sample we were able to reverse the orientation of individual vorteces. [Preview Abstract] |
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S1.00250: Simulation Coherent Quantum Processes in Many-Body Systems Using Classical Trajectories Craig Martens We describe a method for the simulation of coherent quantum dynamics in many-body systems. The approach is based on the semiclassical limit of the multistate quantum Liouville equation and solution using classical trajectory ensembles. The method is applied to modeling nonadiabatic quantum dynamics and the creation, evolution, and decay of quantum coherence in condensed phase systems. The role of environmental interactions in inducing---or delaying---ultrafast electronic decoherence of molecules in condensed phases is investigated. In addition, simulations of vibrational dephasing of an I$_{2}$ diatomic molecule in cryogenic rare gas matrices are described. For I$_{2}$ in Kr, excellent agreement with recent experimental results is obtained. [Preview Abstract] |
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S1.00251: Effect of Atmospheric Conditions on Type and Depth of Polymer Damage Due to Ultra Violet Radiation MacKenzie Sinden-Redding, Firouzeh Sabri, J. Cole, N. Leventis The Earth's atmosphere scatters, absorbs, and reflects the sun's total incoming radiation reducing it by nearly 55\%, thus also reducing UV which causes material damage at the Earth's surface. Visually noticeable material changes often associated with UV exposure is a color shift, typically towards a yellow tint. In this work, we have explored the relationship between free radical generation and the color shift of two types of material: RTV 655 and Silica aerogels. The impact of atmosphere on the amount and nature of free radicals generated, as well as the color shift, is the prime focus of this work. Both materials are of particular interest in space-related applications such as calibration targets for Mars landers. Investigative tools implemented are ESR technique, UV-Vis spectral analysis and X-ray diffraction studies. Both material types demonstrate a significant and similar spectral shift regardless of the presence or absence of atmospheric oxygen. However, not both exposure circumstances lead to a detectable ESR signal. [Preview Abstract] |
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S1.00252: Study of nonlinear optical effects in dye solutions using the Z-scan technique and two-photon fluorescence Milan Poudel, Alexandre Kolomenski, Jinhai Chen, Hans Schuessler A systematic study of the power and intensity dependences of the two-photon fluorescence of methanol solutions of DCM dye under action of 50 femtosecond laser pulses was performed using the Z-scan technique. Various competing nonlinear processes, including self-focusing, ionization, de-focusing, self-phase modulation, continuum generation and the saturation effect were studied. Filamentation and intensity clamping were visible to the eye, when observing the two-photon fluorescence. The simultaneous measurements of two-photon fluorescence and transmission, or white light continuum generation were performed to better understand the interplay of these phenomena. The effect of a linear chirp on the two-photon fluorescence signal during a Z-scan was also investigated. The results for the DCM dye were compared to those obtained previously for Coumarin-30 dye solutions. [Preview Abstract] |
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S1.00253: Ultrafast dynamics of plasma microclouds induced by strong-field ionization in atomic and molecular gases Ryan Compton, Alex Filin, Dmitri Romanov, Robert Levis The model presented for the ultrafast dynamics of laser-induced plasma channels reveals the connections among the fundamental processes of laser-induced tunnel ionization, plasma cooling dynamics of the produced plasma channel, and the residual fluorescence of the channel. The results obtained link the dynamic behavior of the underdense plasma formation with the internal degrees of freedom of the constituent species suggesting that related processes of much current interest, such as laser induced breakdown, laser induced ablation, and, further, atmospheric filamentation will depend sensitively on atomic and molecular constituents. This opens the way to optimizing plasma channel characteristics (bandwidth, coherence, brightness) to that desired for a particular experiment. [Preview Abstract] |
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S1.00254: Attosecond dynamics of strong-field multielectron excitation in small molecules: the case of carbon dioxide Stanley Smith, Dmitri Romanov, Xiaosong Li, H. Bernhard Schlegel, Robert Levis The electron dynamics of CO$_{2}$ interacting with a short IR (1.63 eV) three cycle pulse was theoretically investigated, as manifested by the instantaneous dipole oscillations. The pulse envelope shape (Gaussian or trapezoidal) is shown to control the residual dipole oscillations spectrum (which excited states are populated) and amplitude (or relative population in each state). The carrier envelope phase (for either envelope shape) changes markedly the excited state amplitudes. The windowed Fourier transform was used to extract the attosecond electron excitation dynamics during the pulse. This analysis shows the nonlinear excitation process to be much more complicated than the traditional excited state ladder climbing. In particular, (i) electron transfer plays a major role in the nonlinear excitation dynamics, and (ii) the two pronounced spectral peaks at $\sim $5 and $\sim $8.5 eV do not correspond to any single-photon dipole-allowed transitions. The electron response in the directions orthogonal to the molecular axis was also simulated and, as expected, this response was smaller in magnitude than the response along the molecular axis. [Preview Abstract] |
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S1.00255: Doping the golden buckyball: M@Au$_{16}^{-}$ clusters Lei-Ming Wang, Wei Huang, Lai-Sheng Wang The 16-atom gold cluster (Au$_{16})$ was previously found to possess an unprecedentedly hollow cage structure. Using photoelectron spectroscopy and density functional theory, we have investigated the possibility of doping the Au$_{16}$ cage with an external atom, M@Au$_{16}^{-}$ (M = Cu, Ag, Zn, In, Si, Ge, Sn, Fe, Co, Ni). We have found that doping the Au$_{16}^{-}$ cluster with a Cu, Ag, Zn or In atom does not significantly alter its structure, and the dopant atom sits inside with little distortion to the parent cage. However, the Si, Ge, Sn, atoms cannot be doped inside the Au$_{16}$ cage and they are found to completely change the structure of the parent cage due to the strong M-Au local interactions. The transition-metal-atom-doped species, M@Au$_{16}^{-}$ (M = Fe, Co, Ni), are found to be endohedral in nature with atomic-like magnetic moments and some minor structural distortions. [Preview Abstract] |
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S1.00256: Correlations Between Thin-Film Manganite Morphology, Phase Separation, and Dead Surface Layers Investigated with STM Simon Kelly, Federica Galli, Ivan Komissarov, Jan Aarts Thin-film colossal magnetoresistance manganites such as La$_ {0.67}$Ca$_{0.33}$MnO$_{3}$ (LCMO) have now been intensely studied for more than a decade, but the issue of possible nanoscale electronic phase separation remains unresolved. Scanning Tunneling Microscopy / Spectroscopy (STS) has been pivotal in studying phase separation, but is hindered by being surface- rather than bulk-sensitive. For our sputtered LCMO films the data indicates a strong correlation between surface morphology and phase separation; rough films are phase separated while atomically flat films are homogeneous but have a more or less inactive surface layer. Regardless of surface morphology, the film-bulk is electronically and magnetically active. Many of the reported conclusions about electronic inhomogeneities measured by STS have been confused by this issue. [Preview Abstract] |
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S1.00257: Enhancement in flux pinning in superconducting Bi-Sr-Ca-Cu-O H. Yetis, A. Kilic, K. Kilic, A. Altinkok, M. Olutas It is shown that the pinning properties of Bi$_{1.7}$Pb$_{0.3}$Sr$_2$Ca$_2$Cu$_3$O$_x$ (BSCCO) can be increased by drilling a macroscopic cylindrical hole (CH). To observe the enhancement in flux pinning two different standard and reverse procedures in measuring of the $I - V$ curves were performed as functions of transport current ($I$), temperature ($T$) and external magnetic field ($H$). For a better description, during the measurements, the sweep rate (d$I$/d$t$) of transport current in $I - V$ curves was varied. As the current cycles in up and down direction, it was observed that the presence of CH drilled in BSCCO sample causes a dramatic increase in the hysteresis effects in $I - V$ curves depending on d$I$/d$t$ and changes the evolution of $I - V$ curves as compared to that of similar measurements carried out in BSCCO sample before drilling CH. Another important observation is the increase in the critical current value of BSCCO with CH for increasing branch of $I - V$ curve. The increase in width of hysteresis loops of $I - V$ curves was interpreted as a kind of superheated state. We show in this study that the surface effects in superconductors can be studied by applying the reverse procedure in $I - V$ curves. Finally, it is also shown that the macroscopic cylindrical hole act as a macroscopic pinning center for flux lines. [Preview Abstract] |
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S1.00258: The new piezoelectric single crystal obtained by the Ge doping in the $\alpha $-quartz structure M. Miclau, A. Grozescu, R. Bucur, M. Poienar, P. Vlazan, I. Grozescu, N. Miclau, I. Muscutariu The most interesting properties of the quartz-like crystals are its piezoelectric properties, which are strongly influenced by the intrinsic structural distortions of the material and the crystal growth conditions. Thus, physical properties such as coupling coefficient, the $\alpha \leftrightarrow \beta $ transition can be directly related to structural distortions in terms of the bridging angle. We propose a new way to increase the structural distortion, using Ge to dope the SiO2 structure with respect to $\alpha $-quartz structure type. Growth of $\alpha $ -SixGe1-xO2 crystal was realized hydrothermally using a temperature gradient method. Single crystals were investigated by electron microprobe analysis, X-ray diffraction and atomic force microscopy. The results open the possibility to tune the piezoelectric properties of these materials by varying the chemical composition. [Preview Abstract] |
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S1.00259: Fabrication and Characterization of Si Nanorod Arrays as Subwavelength Antireflection Structures Yi-Ruei Lin, Jr-Hau He The structure of antireflection (AR) is widely utilized to suppress undesired reflection between different optical media for various optical applications. For example, Multilayered coatings are used on the surface of optical and optoelectronic devices. However, it is also suffered from the problems such as poor adhesion, thermal instability, and lattice mismatch. An alternative to multilayered coatings is to pattern the surface with a periodically structured array with the periodicity smaller than the wavelength of the incident light. Compared with multilayered AR coatings, subwavelength structure (SWS) surfaces are more stable and durable, because the AR structures are directly etched in the surface and there are no other materials involved. So far SWSs has been fabricated on silicon have been fabricated through various methods. In the present work, we demonstrated a simple method, which combines sub-wavelength-scale monolayer spheres with a reactive ion etching process, to fabricate AR structures of Si nanorod arrays (NWAs) with structural stability, low cost and low temperature procedures. It was found that the reflectivity of Si substrates with NWAs was dramatically decreased at the wavelength of light from 400 to 800 nm. The reflectivity as a function of size of Si NWAs was discussed. [Preview Abstract] |
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S1.00260: Reduction of thermal conductivity on n-type silicon germanium bulk alloy with nano-pores formation Xiaowei Wang, Hohyun Lee, Yucheng Lan, Gaohua Zhu, Giri Joshi, Dezhi Wang, Jian Yang, Mildred Dresselhaus, Gang Chen, Zhifeng Ren Silicon-Germanium (SiGe) alloys have been the main thermoelectric materials in power generation devices operating from 500.\r{ }C to 1000 .\r{ }C. The main challenge for enhancement of thermal performance of Si-Ge system is the reduction of thermal conductivity. Here we report that by creating nano-pores, the thermal conductivity can be reduced to around 2 Wm$^{-1}$K$^{-1}$ with a little lower power factor. The nano-structured bulk alloy was made by first forming alloyed nano powders from commercial grade Si and Ge chunks with the dopant phosphorous (P) powder and sulfur powder and then by hot pressing the powders for their compaction. Followed by annealing at 1050 .\r{ }C, nano pores were created inside the bulk disc. Our results showed that nano pores are very effective to scatter phonons, thus reduce the thermal conductivity. [Preview Abstract] |
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S1.00261: The Transition of Two Dimensional Hard Spheres Under Gravity from the Liquid to Solid State Using a Global Equation of State Alison E. Koser, Paul V. Quinn, Sr. Using a global equation of state, derived empirically from Luding, we can accurately model the density profile of two-dimensional hard spheres with diameter d and mass m under gravity given a temperature $T$. [\textit{Physica A}, \textbf{271}, 192 (1999)] We then compare our theoretical graphs to MD simulated data. In a given system, if the temperature is below some critical value T$_c$ obtained by the density profile, then crystallization occurs and we can solve for the number of frozen layers. Again, we compare out theoretical values for number of frozen layers with the number of frozen layers from the simulated data. In addition, we use the global equation to solve for the center of mass and its fluctuations as a function of $T$. [Preview Abstract] |
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S1.00262: Examination of the Motion of a System of Granular Material Subjected to Vertical Vibration Carl E. Faust, Paul V. Quinn, Sr. Experiments are conducted using various granular materials subject to a vertical vibration. Qualitative data for the angle of repose is collected as a function of the initial height of the material in the container. Data is used to determine empirical relationships between the maximum angle of repose and container size. This is done for various materials of differing grain size. Also, qualitative observations are made of the surface shape and precession of the angle of repose. [Preview Abstract] |
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S1.00263: Unusual pseudogap features observed in iron-oxypnictide superconductors Y. Ishida, T. Shimojima, K. Ishizaka, T. Kiss, M. Okawa, T. Togashi, S. Watanabe, X.-Y. Wang, C.-T. Chen, Y. Kamihara, M. Hirano, H. Hosono, S. Shin Laser photoemission spectroscopy is employed to investigate the electronic structures of LaFeAsO:F and LaFePO:F [1] exhibiting $T_{c}$ = 26 and 5 K, respectively [2]. We find that the high-$T_{c}$ LaFeAsO:F exhibits a temperature-dependent pseudogap extending over $\sim $0.1 eV about the Fermi level at 250 K, whereas such a feature is absent in low-$ T_{c}$ LaFePO:F. We also find $\sim $20-meV pseudogap features and signatures of superconducting gaps both in LaFeAsO:F and LaFePO:F. We discuss possible origin of the pseudogaps through comparison with the cuprates. [1] Y. Kamihara \textit{et al.}, \textit{JACS }\textbf{128}, 10012 (2006);\textbf{ 130}, 3296 (2008). [2] Y. Ishida \textit{et al.}, arXiv:0805.2647. [Preview Abstract] |
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S1.00264: Study of the operational properties of the Capillary Plasma Electrode (CPE) discharges Jose Lopez, David Jacome, Wei-Dong Zhu, Margaret Figus, Kurt H. Becker Various approaches have been pursued to create stable atmospheric pressure discharges by extending the lifetime of the diffuse phase of the discharge to hundreds of microseconds. Previous research showed that the stability of the diffuse mode is dependent on the frequency (in the kHz range), gas type power, mode of the excitation, and geometrical confinement. Some of the most promising approaches are based on the recognition of the arc formation in high-pressure plasmas can be avoided and stable high-pressure plasma can be generated and maintained when the plasma are spatially constricted to the dimensions of tens to hundreds of microns. The Capillary Plasma Electrode (CPE) discharge is stable to produce stable atmospheric pressure nonequilibrium plasma. The CPE is similar in design to the Barrier Electrode Discharge, but has perforated dielectrics. The configuration, aside from exhibiting a diffuse mode of operation, also exhibits the so-called ``capillary jet'' mode, in which the capillaries “turn on” and a bright plasma jet emerges from the capillaries. The capillary jets from adjacent capillaries overlap so that the discharge appears uniform when the electrode contains an array of holes. There appears to be a threshold frequency for the capillary jet formation, which is strongly dependent on the L/D ratio of the capillaries, where D is diameter of the capillary and L its length. However, the operating principles and basic properties of this behavior are not well understood. The current work explores these modes of operations of the CPE by characterizing the electrical and optical emission properties of this discharge by examining a multi-hole discharge as well as a single capillary discharge reactor. [Preview Abstract] |
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S1.00265: Direct Current Cathode Boundary Layer Xenon Discharge Wei-Dong Zhu, Luan To, Jose Lopez, Kurt Becker Cathode boundary layer (CBL) discharges are high-pressure glow discharges generated between a planar cathode and a ring-shaped anode, separated by a dielectric layer with a thickness of several hundred micrometers. Self-organized patterns formation, excimer emission, and electrical properties of CBL discharges in a direct current operation have been thoroughly studied by Schoenbach and co-workers at various pressures in xenon with mainly molybdenum as the electrode material. However, no detailed assessment of the effect of the cathode material on the cell-organized pattern formation and cathode material modification by the CBL discharge has been reported. This study focuses on the electrical characteristics, excimer emission of xenon around 172 nm, and self-organized pattern formation in CBL discharge with various cathode material at pressures of 100 Torr and 250 Torr. Cathode material modification by CBL discharge will also be briefly assessed. [Preview Abstract] |
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