Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session C1: Poster Session I (2:00pm - 5:00pm) |
Hide Abstracts |
Sponsoring Units: APS Room: Hall D |
|
C1.00001: POLYMERS AND SOFT MATTER I |
|
C1.00002: Helical Ordering in Chiral Diblock Copolymers -- the Effect of Chirality Wei Zhao, Sung Woo Hong, Gregory Grason, Thomas Russell Introducing molecular chirality into the segments of block copolymers can influence the nature of the resultant morphology. Such an effect was found for poly(styrene-b-L-lactide) (PS-b-PLLA) diblock copolymers where hexagonally packed PLLA helical microdomains (H* phase) form in a PS matrix. However, molecular ordering of PLLA within the helical microdomains and the transfer of chirality from the segmental level to the morphological scale is still not well understood. We used a coarse-grained model to describe the interactions between segments of chiral blocks, and calculated the bulk morphologies of chiral AB diblock copolymers using self-consistent field theory (SCFT). We also performed in situ grazing incidence small angle x-ray scattering experiments to investigate the formation of the helical microdomains by changing solvents. Experiments confirmed that the H* phase is a kinetically trapped, metastable morphology below the melting point of PLLA block, while the SCFT explores the range of thermodynamic stability of helical structures in the phase diagram of chiral block copolymer melts. [Preview Abstract] |
|
C1.00003: ABSTRACT WITHDRAWN |
|
C1.00004: Crystallization of a Cyanurate Trimer in Nanopores Yung P. Koh, Sindee L. Simon Nanoconfinement is known to depress the melting temperature through the well-known Gibbs-Thompson equation. Less well studied is the influence of nanoconfinement on crystallization kinetics. In this work we investigate crystallization of a cyanurate trimer using differential scanning calorimetry. The material shows cold crystallization and melting in the bulk state. Under the nanoconfinement of controlled pore glasses (CPG), cold crystallization and melting shift to lower temperatures, following the shift in the glass transition temperature. More importantly, however, the crystallization kinetics slow down and no crystallization occurs in 13 nm-diameter pores. Isothermal crystallization studies indicate that the Avrami exponent is approximately 2.0 for both bulk and nanoconfined samples. The time scale for crystallization is over one order of magnitude longer for samples confined in 50-nm pores in spite of the fact that samples were crystallized the same distance from T$_{g}$. [Preview Abstract] |
|
C1.00005: Chemical Composition Distribution of Partially Brominated Polystyrenes Wayne Powers, Young Kuk Jhon, Jan Genzer, Chang Ryu Interaction chromatography has been employed to estimate the chemical composition distribution of partially brominated polystyrenes. In particular, random blocky and truly random partially brominated polystyrenes (b-PBrxS and r-PBrxS) differ in the dispersity of their chemical composition distributions, because of the limited accessibility of styrene segments for the bromination at temperature below theta temperature. First, the adsorption-based IC technique was used to fractionate b-PBrxS and r-PBrxS of the same average mole fraction of bromine. Then, these fractions were reinjected, and the peak position of each fraction was analyzed. In addition, the average chemical composition of each brominated polystyrene fraction has been analyzed separately via neutron activation analysis (NAA). The results of this analysis clearly supports that the chemical composition distribution b-PBrxS is narrower than that of r-PBrxS. [Preview Abstract] |
|
C1.00006: Controlled Orientation of Block Copolymer Microdomains on Modified Solid Surfaces Weiyin Gu, Sung Woo Hong, Thomas Russell The interfacial interactions between block copolymers (BCP) and a substrate are important for the self-assembly of BCPs in thin films, especially in terms of orientation of BCP microdomains. A simple, rapid, and robust technique for controlling the alignment of BCP microdomains on modified surfaces is described. End-functionalized poly(styrene-b-ethylene oxide)s (PS-b-PEOs) with different block ratios were end-grafted onto Si substrates creating BCP brushes. Thin films of cylindrical forming PS-b-PEO were prepared on the surface of anchored BCP brushes and thermally annealed. When the fraction of styrene, f, of the anchored BCP was 1, no features were observed in thin film of a PS-b-PEO placed on the surface of the anchored brush due to preferential interaction of the PS block with the brush. When f was varied from 0.3 to 0.7, hexagonally packed cylindrical microdomains oriented normal to the substrate were formed having long range lateral ordering. [Preview Abstract] |
|
C1.00007: Studies on Morphology of PCPDTBT/Fullerene Bulk Heterojunction Organic Photovoltaics Yu Gu, Thomas Russell Low-bandgap conjugated polymer, poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT), has been used in the active layer of the bulk heterojunction (BHJ) solar cells. Though PCPDTBT has a desirable bandgap, the power conversion efficiency (PCE) of the corresponding solar cells is still lower than the expectation. Grazing incidence wide angle X-ray scattering (GI-WAXS) showed that PCPDTBT is amorphous. Dynamic secondary ion mass spectrometry (DSIMS) and small angle neutron scattering (SANS) confirmed that PCPDTBT and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) were uniformly distributed in the active layers. It is likely that the intimate mixing of the two components leads to a recombination of the free charges and the relatively low PCE. With additives, like 1,8-diiodooctane, the crystallinity of PCPDTBT increases and the PCBM segregates, which leads to improved device performances. [Preview Abstract] |
|
C1.00008: Morphology Evolution of Molecular Weight Dependent P3HT: PCBM Solar Cells Feng Liu, Dian Chen, Alejandro Briseno, Thomas Russell Effective strategies to maximize the performance of bulk heterojunction (BHJ) photovoltaic devices have to be developed and understood to realize their full potential. In BHJ solar cells, the morphology of the active layer is a critical issue to improve device efficiency. In this work, we choose poly(3-hexyl-thiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) system to study the morphology evolution. Different molecular weight P3HTs were synthesized by using Grignard Metathesis (GRIM)~method. In device optimization, polymer with a molecular weight between 20k-30k shows the highest efficiency. It was observed that the as-spun P3HT: PCBM (1:1) blends do not have high order by GISAXS. Within a few seconds of thermal annealing at 150 ${^\circ}$ the crystallinity of P3HT increaased substantially and the polymer chains adopted an edge-on orientation. An-bicontinous morphology was also developed within this short thermal treatment. The \textit{in situ} GISAXS experiment showed that P3HT of high molecular weight was more easily crystallized from a slowly evaporated chlorobenzene solution and their edge-on orientation is much more obvious than for the lower molecular weight P3HTs. DSC was used to study the thermal properties of P3HTs and P3HT: PCBM blend. The $\chi $ of P3HT-PCBM was also calculated by using melting point depression method. [Preview Abstract] |
|
C1.00009: Elimination of branching in beta-hairpin self-assembling peptides Sameer Sathaye, Darrin Pochan Nanoscale fibril self-assembly in (VK)4VDPPT (KV)4-NH2 peptides is initiated by intramolecular peptide folding into a beta-hairpin conformation. Once folded, the peptides undergo intermolecular bilayer formation due to hydrophobic collapse of hydrocarbon valine side chains, all located on one face of respective folded beta-hairpins. Subsequent intermolecular hydrogen bonding between folded hairpins leads to fibril formation. A physically crosslinked network structure is formed due to fibrillar entanglement and defects in hydrophobic collapse that nucleate branching points. We attempt to design ``lock and key'' specificity in the hydrophobic faces of the folded beta-hairpins so that only 1-d fibril formation can occur without any branching. The success of the new peptide designs to rid the system of branching and characteristics of the networks afforded by new peptide sequences and blends thereof will be discussed by various characterization techniques such as Rheological Characterization, Circular Dichroism (CD), Transmission Electron Microscopy (TEM) and Small Angle Neutron Scattering (SANS). ~ [Preview Abstract] |
|
C1.00010: Theory of Nanoparticle Interactions Mediated by Reversibly Binding Polymer Chains Stephanie Trittschuh, Gregory Grason In stable polymer-nanoparticle composites, particles must be compatibilized with the polymer matrix to overcome entropically- driven, short-range depletion forces that drive particle aggregation. One strategy is to incorporate end-functional groups to polymers that reversibly bind to particle surfaces via donor- acceptor type interactions, such as hydrogen bonding. The addition of reversibly binding chain ends introduces a new length scale for the effective interaction between two particles due to the possibility of inter-particle bridging conformations available to chains at small particle-particle separations. We use self- consistent field theory to explore the effective pairwise particle potential in a melt of reversibly associating chains and examine how changing particle size, chain length and binding affinity shapes the free energy of interaction and alters higher-order inter-particle organization in nanocomposites. [Preview Abstract] |
|
C1.00011: Thio-amide functionalized polymers via polymerization or post-polymerization modification Ali Ozcam, Adam Henke, Iva Stibingerova, Jiri Srogl, Jan Genzer Decreasing supplies of fresh water and increasing population necessitates development of advanced water cleaning technologies, which would facilitate the removal of water pollutants. Amongst the worst of such contaminants are heavy metals and cyanides, infamous for their high toxicity. To assist the water purification processes, we aim to synthesize functionalized macromolecules that would contribute in the decontamination processes by scavenging detrimental chemicals. Epitomizing this role thio-amide unit features remarkable chemical flexibility that facilitates reversible catch-release of the ions, where the behavior controlled by subtle red-ox changes in the environment. Chemical tunability of the thio-amide moiety enables synthesis of thio-amide based monomers and post-polymerization modification agents. Two distinct synthetic pathways, polymerization and post-polymerization modification, have been exploited, leading to functional thioamide-based macromolecules: thioamide-monomers were copolymerized with N-isopropylacrylamide and post-polymerization modifications of poly(dimethylaminoethyl methacrylate) and poly(propargyl methacrylate) were accomplished via quarternization and ``click'' reactions, respectively. [Preview Abstract] |
|
C1.00012: Charged triblock copolymer self-assembly into charged micelles Yingchao Chen, Ke Zhang, Jiahua Zhu, Karen Wooley, Darrin Pochan Micelles were formed through the self-assembly of amphiphlic block copolymer poly(acrylic acid)-block-poly(methyl acrylate)-block-polystyrene (PAA-PMA-PS). ~Importantly, the polymer is complexed with diamine molecules in pure THF solution prior to water titration solvent processing-a critical aspect in the control of final micelle geometry. The addition of diamine triggers acid-base complexation ~between the carboxylic acid PAA side chains and amines. ~Remarkably uniform spheres were found to form close-packed patterns when forced into dried films and thin, solvated films when an excess of amine was used in the polymer assembly process. Surface properties and structural features of these hexagonal-packed spherical micelles with charged corona have been explored by various characterization methods including Transmission Electron Microscopy (TEM), cryogenic TEM, z-potential analysis and Dynamic Light Scattering. The forming mechanism for this pattern and morphology changes against external stimulate such as salt will be discussed. [Preview Abstract] |
|
C1.00013: Examining the Role of Structure on Charge Transport of Polymer Semiconductors Kiarash Vakhshouri, Enrique Gomez Charge carrier mobility in conjugated semi-crystalline polymers depends critically on the crystallinity, orientation of the crystals, and connectivity between ordered regions. However, the complex interplay between these morphological parameters is not fully understood. By varying the thermal annealing parameters and casting solvents, we have systematically studied charge transport within poly(3-hexylthiophene) and poly(2,5-bis(3-alkylthiophen-2-yl) thieno[3,2-b]thiophene) as a function of the crystallinity. It is found that the crystallinity itself does not always correlate with the charge mobility. Our hypothesis is that the crystallization kinetics can alter the number of tie chains, thereby affecting charge transport in semi-crystalline polymer semiconductors. [Preview Abstract] |
|
C1.00014: Towards quantitative structure-function relationships for organic solar cells Derek Kozub, Kiarash Vakhshouri, Enrique Gomez Organic solar cells belong to a class of devices where the morphology of the active layer has a large impact on device performance. However, characterization of the morphology of organic semiconductor mixtures remains a challenge. We have utilized Grazing Incidence Small Angle X-Ray Scattering (GISAXS), Resonant Soft X-ray Scattering (RSOXS), and Energy Filtered Transmission Electron Microscopy (EFTEM) to characterize the morphology of polythiophene/fullerene mixtures as a function of processing conditions. GISAXS and RSOXS have been used to determine the domain spacing within the active layer, whereas EFTEM has been used to generate images with high contrast between domains. Furthermore, these techniques have been useful in guiding our attempts to control the nucleation of crystals and perturb the structure of the active layer. By comparing our morphological data with device data, we are developing structure-function relationships relevant to organic solar cells. [Preview Abstract] |
|
C1.00015: Polarization Controlled Photomechanical Behaviors of Polydomain Azobenzene Liquid Crystalline Polymer Networks Timothy White, Kyung Min Lee, Vincent Tondiglia, Hilmar Koerner, Richard Vaia, Timothy Bunning We report the polarization controlled photomechanical behaviors of azobenzene liquid crystalline polymer networks (azo-LCNs) as a function of crosslink density and temperature. High modulus, glassy polydomain azo-LCNs were synthesized by copolymerizing RM257 and 2-azo, initiated by 1 wt{\%} of the inorganic photoinitiator Irgacure 784. Crosslinking density of azo-LCNs increases from 2.09 mol/dm$^{3}$ to 7.24 mol/dm$^{3}$ with curing time from 1-120 min. Storage modulus and loss tangent of azo-LCNs also increase with crosslinking density. All azo-LCNs are glassy at room temperature. To increasing temperature, E' begins to decrease through T$_{g}$ to a level dependent on the crosslinking density, and eventually reaching a rubbery plateau region. Interestingly, the bidirectional (forward and reverse) bending angles of the polydomain azo-LCN cantilevers at equilibrium decrease with increasing temperature and crosslinking density. Absorption and bending behaviors of the azo-LCNs with various thicknesses, concentrations and molecular structure of azobenzene monomer will be discussed. [Preview Abstract] |
|
C1.00016: Effects of Sequence Distribution, Concentration and pH on Gradient and Block Copolymer Micelle Formation in Solution Stephen Marrou, Jungki Kim, Christopher Wong, John Torkelson Gradient copolymers are a relatively new class of materials with a gradual change in comonomer composition along the copolymer chain length, which have exhibited unique material properties in comparison to random and block copolymers. Here we extend this architecture to amphiphilic systems that form micelles in solvent, as the effect of a nonuniform comonomer sequence distribution is expected to strongly influence critical aggregation phenomena. Utilizing pyrene as a fluorescence probe, we determined that gradient copolymers present an intermediate critical aggregation concentration in comparison to analogous block and random copolymers. The effect of gradient architecture on a pH-sensitive copolymer was also investigated, concluding that gradient sequencing significantly impacts the solubility and critical aggregation pH when compared to block and random copolymers of similar composition, providing further evidence that gradient architectures introduce a powerful means of tuning properties between block and random copolymers. [Preview Abstract] |
|
C1.00017: Temperature dependence of ionic association of lithium triflate in acetate solutions Dharshani Bopege, Matt Petrowsky, Roger Frech, J.M. Furneaux Ion transport is studied in polymer and organic liquid electrolytes due to the importance of these systems in rechargeable battery applications. We have used Fourier Transform Infrared Spectroscopy (FTIR) to study the temperature dependence of ionic association in solutions of lithium trifluoromethanesulfonate (LiCF$_{3}$SO$_{3}$, LiTf) dissolved in propyl, hexyl, octyl, and decyl acetates. The IR Spectra were recorded for three salt concentrations (0.1, 0.2, 0.5 mol kg$^{ -1}$) from 0 $^{\circ}$C to 80 $^{\circ}$C. Two spectral bands were analyzed at each temperature: the CF$_{3}$ symmetric bend ($\delta_{s}$) in the 740-780 cm$^{-1}$ region and the carbonyl stretch in the 1660-1800 cm$^{-1}$ region. Relative intensities of these bands were calculated by a curve fitting procedure. Three different LiTf ionic species were observed in the $\delta_{s}$(CF$_{3}$) region. The carbonyl band due to coordination with Li ion appears at a lower frequency (1714 cm$^{-1}$) than the pure carbonyl band (1744 cm $^{-1}$). [Preview Abstract] |
|
C1.00018: Organic Molecules and Network Polymers of Intrinsic Microporosity: Structural Characterization via X-ray Scattering and Simulations Amanda G. McDermott, Lauren J. Abbott, Annalaura Del Regno, Kadhum J. Msayib, Bader S. Ghanem, Rupert Taylor, Mariolino Carta, Neil B. McKeown, Peter M. Budd, Flor R. Siperstein, Coray M. Colina, James Runt Like polymers of intrinsic microporosity (PIMs), organic molecules of intrinsic microporosity (OMIMs) are glassy solids featuring a large concentration of pores smaller than 2 nm and large internal surface area as measured by gas sorption experiments. OMIMs are oligomers designed to fill space inefficiently, consisting of several rigid segments joined at one vertex to produce concave faces. Both X-ray scattering patterns and simulations provide insight into the packing geometry and short-range order of these molecules. We also discuss the interpretation of scattering patterns from two- and three-dimensional network PIMs. [Preview Abstract] |
|
C1.00019: Methyl Methacrylate Polymerization in Nanoporous Matrix: Reactivity and Molecular Weight Haoyu Zhao, Sindee Simon The influence of nanoconfinement on the free radical polymerization of methyl methacrylate is investigated. Nanoporous controlled pore glass (CPG) is used as a nanoconfining matrix for the polymerization. The reaction is followed by measuring heat flow as a function of reaction time during isothermal polymerization using differential scanning calorimetry (DSC). Preliminary results indicate several interesting effects for polymerization in 110 nm diameter pores: the induction time increases under nanoconfinement, the effective reaction rate constant increases, the effective activation energy is unchanged, and the gel effect or autoaccleration occurs at earlier times after induction. The latter result concerning the gel effect is presumably due to the decrease in diffusivity under nanoconfinement which results in a decrease in the termination rate of free radicals. The cause of the longer induction times and accelerated reaction rates just after induction are under investigation. The influence of nanoconfinement on molecular weight will also be examined. [Preview Abstract] |
|
C1.00020: The Dynamic Heat Capacity of the Potential Energy Landscape of a Simple Chain Model Jonathan Brown, John McCoy The dynamic heat capacity of a simple (bead-spring) polymeric model glassformer was computed using molecular dynamics simulations by sinusoidally driving the temperature, and recording the resultant energy. The underlying potential energy landscape of the system was probed by taking a time series of particle positions and quenching them with an energy minimization routine. This shows that the long time relaxation of the model glassformer is the direct result of the dynamics of the potential energy landscape. [Preview Abstract] |
|
C1.00021: Characterization of the Morphology and Rapid Expansion of Swellable Organically Modified Silica Lilianna E. Christman, Amanda Logue, Paul L. Edmiston, Susan Y. Lehman Swellable organically modified silica (SOMS) is a novel sol-gel derived material.~ SOMS is hydrophobic and selectively absorbs non-polar liquids and immediately swells 5 to 6 times upon absorption.~ SOMS can be used to remove organic contaminants from water; the contaminant can then be recovered and the SOMS reused.~ We have investigated the SOMS swelling behavior of neat organic liquids usng macroscopic measurements of the force exerted during expansion and through atomic force microscopy (AFM) of the surface. ~A powdered SOMS sample was placed in a cylinder with an adjustable piston.~ Solvent percolated into the cylinder and the piston gradually moved to allow expansion while measuring the force using a load cell.~ During expansion the SOMS exerted forces up to 150 N per gram of material.~ AFM shows the surface of the SOMS is textured with cauliflower-like features.~ In unswollen SOMS, these globules have length scales of a few hundred nanometers, while for SOMS swollen in a solvent the features expand to several micrometers. [Preview Abstract] |
|
C1.00022: ABSTRACT WITHDRAWN |
|
C1.00023: Self-assembly of PtBA-P3HT multi-arms star-like block copolymer at the air/water interface Lei Zhao, Xinchang Pang, Chaowei Feng, zhiqun Lin A novel PtBA-P3HT multi-arm star-like diblock copolymer (BCP) was synthesized via a combination of atom transfer radical polymerization, quasi-living polymerization and click reaction. The self-assembly of PtBA-P3HT multi-arm star-like BCP at the air/water interface was systematically explored using the Langmuir Blodgett (LB) technique. The hydrophobic star-like BCP has 21 arms, with PtBA as the core and P3HT as the shell. At the air/water interface, the BCP molecules gradually assembled into domains composed of bundle-like structures under surface pressure, and finally formed the network structure in a way controlled by PtBA chain folding and P3HT chain stacking. The photoluminescence measurement showed that the formation of P3HT bundle in LB film led to enhanced luminescence due to the reduced inter-chain coupling. [Preview Abstract] |
|
C1.00024: Glassy dynamics of polymers in thin films and monomolecular layers Martin Tress, Emmanuel U. Mapesa, Anatoli Serghei, Friedrich Kremer The glassy dynamics of nanometer thin polymer layers supported on a solid substrate was investigated by Braodband Dielectric Spectroscopy (BDS). The thickness was systematically reduced finally resulting in randomly distributed polymer coils. Highest priority was put on an appropriate sample preparation including an annealing procedure for sufficient long time at elevated temperatures in inert atmosphere to avoid effects due to remaining solvent and chemical degradation. Further, detailed checks of the surface topology by atomic force microscopy (AFM) were performed to verify stability of the samples during the whole measurement. The dynamics is compared to the bulk to trace changes due to the impact of the interface and to give a length scale for the interfacial interactions. [Preview Abstract] |
|
C1.00025: Confinement-Induced Ordering in Dewetting of Polymer Blend Film Mu Wang, Xiao-Chun Chen, Ru-Wen Peng, Guo-Bin Ma, Dajun Shu Dewetting and phase separation of polymer blend film on a periodically modified substrate can generate unique microstructures. Despite external perturbations in previous studies, polymer film remained continuous with the boundary locating at infinity. It is interesting to investigate dewetting and phase separation process in a confined geometry, such as a fishnet-like environment, where unique self- organization process is anticipated. We report here an effect that polymer blend film of polystyrene(PS) and poly (methylmethacrylate)(PMMA) may evolve to a perfectly ordered droplet array on a periodically excavated silicon substrate, and each droplet possesses a PS kernel surrounded by PMMA cofferdam. The formation of regular pattern depends on initial thickness of polymer film and interstitial separation of microholes on substrate, and a scaling has been revealed. Our observation demonstrates a confinement-induced ordering in dewetting of polymer blend film, and suggests a budget and convenient approach to generate regular polymer microstructures over a large area. [Preview Abstract] |
|
C1.00026: Synthesis of polymer brushes by surface-initiated controlled radical polymerization in the presence of free initiators. A Monte Carlo investigation Salomon Turgman-Cohen, Jan Genzer Simultaneous controlled radical polymerization from free and surface-grafted initiators is studied by means of computer simulations. We model ``truly living'' reactions by neglecting chain termination and chain transfer. We study the competition between bulk- (i=b) and surface-initiated (i=s) polymers by monitoring the rates of polymerization (d$<$N$>_{i}$/dt), the average molecular weight ($<$N$>_{i})$, and the polydispersity index (PDI$_{i})$ while varying the initiator grafting density ($\sigma )$, the fraction of surface based polymers ($\eta )$, and the initial number of free monomers (I$_{o})$. We find that d$<$N$>_{B}$/dt$>$d$<$N$>_{S}$/dt and that d$<$N$>_{S}$/dt decreases with increasing $\sigma $. The difference in polymerization rates between the bulk and surface polymerizations results in polymer populations with different $<$N$>$; this has implications for the experimental determination of $\sigma $ and $<$N$>_{S}$. Although $\eta $ affects $<$N$>_{S}$ and $<$N$>_{B}$, it does not influence the PDI. At a specific $<$N$>_{i}$, the PDI$_{i}$ has a value independent of $\eta $. In addition, PDI$_{S}>$PDI$_{B}$; this difference increases with increasing $\sigma $. We therefore conclude that polymerization conditions that yield bulk polymers with low PDI do not guarantee the same PDI for the surface-initiated polymers. [Preview Abstract] |
|
C1.00027: Directed Dewetting of Thin Polymer Films Suchanun Moungthai, Trang Pham, Gus Rajaendran, Gila Stein We present a simple route to generate arrays of microscale polygons by directed dewetting of polystyrene thin films on topographic pre-patterns.\footnote{Yoon et al., Soft Matter, 2008, 4, 1467-1472.} Silicon wafers are patterned with arrays of ca. 10 $\mu$m wide hexagonal holes using photolithography and wet etching. Patterned substrates are coated with thin films of polystyrene and heated above the glass transition temperature to promote dewetting. The dewetting process is monitored \emph{in-situ} with optical microscopy, and final droplet structures are also imaged with atomic force microscopy. The mechanism of polygon formation is driven by Rayleigh instability; Formation rates and final polygon size are controlled by temperature/viscosity, film thickness, and the geometry of the topographic pre-pattern. [Preview Abstract] |
|
C1.00028: Reaction-Diffusion Processes in Ultrathin Films of Photoresist Ginusha Perera, Gila Stein Projection lithography is the primary technology used for patterning semiconductor devices. High-throughput manufacturing requires imaging materials (resists) that are highly sensitive to radiation, and this demand is satisfied through a process termed chemical amplification (CA). CA resists are comprised of a polymer resin (reactant) and photoacid generator (catalyst); a coupled reaction-diffusion mechanism drives image formation, where image resolution is limited by slow diffusion of the acid catalyst. There is evidence that thin film reaction rates deviate from the bulk behavior, and current models for image formation do not capture such effects. We demonstrate that X-Ray Diffraction can measure spatial extent-of-reaction in ultrathin films of a nanopatterned poly(4-hydroxystyrene-co-tertbutylacrylate) CA resist. The feedback acquired is used to construct predictive models for the coupled reaction-diffusion processes that incorporate the physics of confined polymers. [Preview Abstract] |
|
C1.00029: Mechanical properties determination of PDMS films on hard substrate using atomic force microscopy Wenwei Xu, Todd Sulchek Mechanical properties of PDMS thin films adhering on hard substrate were investigated using Atomic Force Microscope (AFM) with a spherical tip. Simulation was implemented using finite element method and was compared to the experiments. The effect of the hard substrate on the mechanical response of the PDMS film becomes significant when the indentation depth exceeds 45{\%} of the sample thickness. This relationship was also verified by comparing Hertz model to the experiments in the whole indentation range. Hertz model is not applicable in the large deformation region because the large deformation violates the assumption on which the Hertz model is based. The point wise Young's modulus as a function of indentation was obtained using Hertz model and also identified the effect of the hard substrate on mechanical responses. Furthermore, the point wise Young's modulus in the linear elasticity region decreases with increasing film thickness, until the sample is thick enough and its modulus reaches that for bulk PDMS. In the point wise Young's modulus plot, the Young's moduli at small indentations were several orders of magnitude higher than those in the linear elasticity region; this phenomenon has been observed in previous research and was also studied in our experiments. [Preview Abstract] |
|
C1.00030: Anisotropic Surface and Interfacial Instabilities in Nanoimprinted Polymer Bilayers Dae Up Ahn, Zheng Zhang, Yifu Ding We illustrate the spontaneous formation of hierarchical polymer patterns driven by surface/interfacial instabilities at mobile and corrugated polymer-polymer interface. Upon thermal annealing of polystyrene (PS) films deposited on (and also confined in) topographic patterns of poly(methylmethacrylate) (PMMA), the PS/PMMA bilayers underwent a sequential event of morphological changes encompassing uniform pattern decay, simultaneous capillary breakup, anisotropic coarsening, and Rayleigh instabilities. Particularly, depending on the geometry of the bilayer pattern, the simultaneous capillary breakup has occurred in different modes. The morphological evolutions and structure formations are unique to the current system, and are drastically different from the polymer film dewettings on a planar surface, a chemically patterned surface, or a topographically patterned rigid surface. Thus, we demonstrate that the direct participations of the viscous topographic interface in the instabilities or assemblies offer a unique strategy to achieve a rich spectrum of highly anisotropic hierarchical structures. [Preview Abstract] |
|
C1.00031: Modification of Silicon Oxide Surfaces with Thermally Annealed Polystyrene Films Steven Kalan, Kevin Cavicchi, Alamgir Karim The modification of silicon with a native oxide surface has been accomplished by annealing thin films of anionically polymerized polystyrene spun-coat from solution at elevated temperature followed by dissolving the film in solvent to leave a thin layer of adsorbed polymer that persisted even after prolonged desorbing in solvent even at elevated temperature. It was found by water contact angle analysis of the samples after washing with organic solvent that annealing is a key step to adsorption of a thin layer of polystyrene on the film surface. X-ray reflectivity analysis also demonstrated that the thickness of the adsorbed layer is proportional to the molecular weight of the polymer. However, the contact angle showed a non-monotonic dependence on molecular weight. The further modification of these surfaces by ultraviolet/ozone treatment will be discussed. This is a novel surface treatment method as it performed with a polystyrene polymer without any additional chemical functionality through straight-forward vacuum annealing and washing with organic solvent. [Preview Abstract] |
|
C1.00032: A closer look on the thermo-responsive behavior of ultrathin pNIPAM films - relating interfacial molecular transitions to macroscopic properties Patrick Koelsch, Volker Kurz, Stefan Zauscher The thermo-responsive behavior of thiol-modified poly(N-isopropylacrylamide) (pNIPAM) films immobilized on gold were probed by in situ broadband sum-frequency generation (SFG) spectroscopy, ellipsometry and capturing bubble contact angle. The pNIPAM films were prepared by atom transfer radical polymerization using a nitro-biphenyl-thiol-SAM on a polycrystalline gold surface as a substrate. Macroscopic properties of the film during the lower critical solution temperature (LCST) are tracked in detail by ellipsometry and capturing bubble contact angle allowing us to measure the thickness and water content within the film as well as the surface energy. These results are correlated with data acquired by in situ SFG spectroscopy, an intrinsic surface specific method probing LCST dynamics on a molecular scale. [Preview Abstract] |
|
C1.00033: Non-Contact Measurements of Stiffness in Confined PS Films by Fluorescence and XPCS Christopher Evans, Suresh Narayanan, Zhang Jiang, John Torkelson Fluorescence is used to detect stiffness in confined polystyrene (PS) films through the intensity ratio (I3/I1) of the dye molecule pyrene. Free-standing PS films show a softening (an increase in I3/I1) when the film thickness decreases below 400 nm, and a stiffening (a decrease in I3/I1) below thicknesses of 200 nm. Silica- and PDMS-supported PS films show no softening but report stiffening for films less than 200 nm thick, a result not in accord with the Tg reductions seen for PS on silica. X-ray photon correlation spectroscopy (XPCS) also reports stiffening in PS on silica through the relaxation times of capillary waves at the polymer surface. A two order of magnitude increase in relaxation time is observed for small in-plane wavevectors (q) in a 30 nm PS film compared to a 120 nm film. Bilayer films of PS supported on various bulk underlayers studied by XPCS indicate that lower substrate modulus leads to faster PS surface relaxation times. These are the first reported non-contact measurements related to stiffness in confined PS on silica. [Preview Abstract] |
|
C1.00034: Interfacial Structure, Dynamics, and Transport of Polyelectrolyte Membrane Materials for Fuel Cells Christopher Soles, K. Page, S. Eastman, S. Kim, S. Kang, J. Dura Polymer electrolyte membranes (PEM) fuel cells show promise for a wide range of applications both in the transportation sector and for stationary power production due to their high charge density and low operating temperatures. While the structure and transport of bulk PEMs have been studied extensively, little is known about these materials at interfaces and under confinement, as they exist within the membrane electrode assembly (MEA). Using neutron/ x-ray reflectivity and polarization-modulation infrared reflection-absorption spectroscopy, we have studied the polymer-substrate interfacial structure, swelling, and water transport as function of humidity, surface chemistry, and film thickness. The interfacial structure is highly dependent upon the substrate surface chemistry and the swelling/water diffusivity are suppressed when the PEM is confined to a thin film. This new information will enable researchers to more accurately model the performance of the MEA as current simulations typically rely on bulk property values to predict water and proton transport under these conditions. [Preview Abstract] |
|
C1.00035: Large and Reversible Plasmon Tuning using Ultrathin Responsive Polymer film Srikanth Singamaneni, Saide Nergiz We demonstrate reversible linear and branched aggregation of gold nanoparticles adsorbed on an ultrathin responsive polymer ((poly(4-vinyl pyridine), P4VP) film. P4VP is a weak cationic polymer, which exhibits a reversible coil to globule transition with change in external pH. Atomic force microscopy revealed that in the coiled state (below the isoelectric point of the polymer) of the polymer chains, gold nanoparticles adsorbed on the polymer layer existed as primarily individual nanoparticles. On the other hand, lowering the pH caused the polymer chains to transition from coil to globule state, resulting in aggregation of the nanoparticles into linear and branched chains. Reversible aggregation of the nanoparticles results in a dramatic change in the optical properties of the metal nanostructures. Apart from the large redistribution of the intensity between the individual (530 nm) and coupled (650 nm) plasmon bands, the coupled plasmon band exhibits a shift of nearly 60 nm with change in external pH. The pH triggered aggregation of the nanoparticles and the dramatic change in the optical properties associated with the same can form an excellent platform for colorimetric sensing. [Preview Abstract] |
|
C1.00036: Mechanical Properties of Nanofibers Revealed by Interaction with Streams of Air Yinan Lin, Daniel Clark, Darrell Reneker Measurements of mechanical properties of electrospun nanofibers are needed for process control [1] and for design of structures that are durable, conformal and hierarchical. A new method, complementing measurements made on miniature mechanical testing devices [2], was developed. Electrospun nanofibers were captured directly between two steel rods that functioned ``grips.'' Tensile deformation was applied by separating grips. The stress information was revealed by the deflections of the nanofibers caused by forces from broad streams of air, flowing perpendicularly to the fibers, at measured velocities. Glints of reflected light that revealed the contour of the deflected nanofibers were recorded with a camcorder. Image analysis of the shapes of the nanofibers was combined with scanning electron microscopy measurements of the diameter of the ends to evaluate the mechanical properties. Stress strain curves and hysteresis loops of selected ultrathin electrospun fibers were obtained. Direct comparisons of mechanical properties were made for a wide range of polymers.\\[4pt] [1] Reneker, D. H.; Yarin, A. L. Polymer 2008, 49, (10), 2387-2425.\\[0pt] [2] Naraghi, M.; Chasiotis, I.; Kahn, H.; Wen, Y. K.; Dzenis, Y. Applied Physics Letters 2007, 91, (15), 151901. [Preview Abstract] |
|
C1.00037: Structural Characterization of Nanopatterned Surface Gratings with Grazing Incidence X-Ray Scattering Elaine Chan, Dong Hyun Lee, Dmitry Voronov, Howard Padmore, Ting Xu, Thomas Russell, Alexander Hexemer The fabrication of surface gratings with periodic, nanoscale features is a promising route for templating nanopatterned thin film materials with macroscopic lateral order. These materials can be utilized for constructing novel and improved micro- and opto-electronic devices and x-ray optical elements. To characterize the structural features of the grating substrates and templated thin films, grazing incidence x-ray scattering (GISAXS) is becoming an increasingly desirable and emerging technique because the method provides sufficiently high sensitivity. We investigate herein the structural features of gratings with sawtooth topologies using GISAXS. We characterize the GISAXS patterns of gratings prepared from silicon and sapphire substrates, and examine the emergence of specific features that appear for varying sawtooth aspect ratio and at different incident angle values. These features are further analyzed using theoretical calculations where feasible. In this manner we demonstrate the utility of GISAXS for characterizing the structures of nanopatterned surfaces. [Preview Abstract] |
|
C1.00038: Thermal Programmed Desorption of C$_{32}$H$_{66}$ M. Cisternas, V. del Campo, A.L. Cabrera, U.G. Volkmann, F.Y. Hansen, H. Taub Alkanes are of interest as prototypes for more complex molecules and membranes. In this work we study the desorption kinetics of dotriacontane C32 adsorbed on SiO$_{2}$/Si substrate. We combine in our instrument High Resolution Ellipsometry (HRE) and Thermal Programmed Desorption (TPD). C32 monolayers were deposited in high vacuum from a Knudsen cell on the substrate, monitorizing sample thickness \textit{in situ} with HRE. Film thickness was in the range of up to 100 {\AA}, forming a parallel bilayer and perpendicular C32 layer [1]. The Mass Spectrometer (RGA) of the TPD section was detecting the shift of the desorption peaks at different heating rates applied to the sample. The mass registered with the RGA was AMU 57 for parallel and perpendicular layers, due to the abundance of this mass value in the disintegration process of C32 in the mass spectrometers ionizer. Moreover, the AMU 57 signal does not interfere with other signals coming from residual gases in the vacuum chamber. The desorption energies obtained were $\Delta E_{des}$=11,9 kJ/mol for the perpendicular bilayer and $\Delta E_{des}$ = 23,5 kJ/mol for the parallel bilayer. \\[0pt] [1] V. del Campo et al., Langmuir \textbf{25} (22), 12962 (2009); E. A. Cisternas et al., J. Chem. Phys. \textbf{131} (11), 114705 (2009). [Preview Abstract] |
|
C1.00039: Molecular dynamics simulations of dotriacontane films supported on a SiO$_{2}$ surface Sebastian Gutierrez, Raul Araya, Tomas Perez-Acle, Maria Jose Retamal, Ulrich G. Volkmann Dotriacontane (C$_{32}$H$_{66}$, C32) films supported on SiO$_{2}$ surfaces were studied using very high-resolution ellipsometry, atomic force microscopy (AFM) and x-ray reflectivity techniques. For almost complete layers a model was proposed [1] in which the C32/SiO$_{2}$ interfacial region is characterized by a parallel bilayer and perpendicular layers on top. Recent AFM measurements performed on samples forming sea-weed like structures, showed that for these particular perpendicular ``fractal like'' layers the heights are lower than the all-trans length of dotriacontane (42.5 {\AA}). To gain insights on the internal molecular ordering and layering of C32 supported on SiO$_{2}$ surfaces, we used all-atom molecular dynamics to simulate C32 films at different temperatures. Our results confirm the presence of the parallel bilayer suggesting the existence of a mixed layer on top, formed by molecules with both parallel and perpendicular segments. These findings suggest a different molecular architecture for sea-weed like structures of dotriacontane supported on SiO$_{2}$.\\[4pt] [1] H. Mo et al., Chem. Phys. Lett. \textbf{377}, 99-105~ (2003); U. G. Volkmann, et al., J. Chem. Phys. \textbf{116}, 2107 (2002). [Preview Abstract] |
|
C1.00040: Fabricating Stable Superhydrophobic Hierarchical Polyelectrolyte Multilayer Films by Layer-by-Layer Assembly and Nanolithography Xiayun Huang, Nicole Zacharia Recent experiment shows that wetting can be controlled by not only the chemical nature but geometrical structure of the surface also. Even for a hydrophilic surface, it can transit into hydrophobic one when manipulating the roughness of surface. It is also of interest to determine if superhydrophobic surfaces can be created from hydrophilic multilayer films because multilayer is easy to be coated on any place by layer-by-layer assembly. Here, we used water-soluble polycations, PAH (poly(allylamine)), and polyions, SPS (sodium poly(styrene sulfonate)), to form polyelectrolyte multilayers. By nanoimprint lithography and in-situ growth of inorganic patterns in between these polyelectrolyte multilayers, we can include some micro-sized and nano-sized structures for different generations. When controlled introducing micro-sized and nano-sized hierarchical structures into multilayers, we can learn how the surface roughness increasing superhydrophobic properties from geometry view fundamentally. [Preview Abstract] |
|
C1.00041: Adhesion of Nanoparticles Jan-Michael Carrillo, Elie Raphael, Andrey Dobrynin We have developed a new model of nanoparticle adhesion which explicitly takes into account the change in the nanoparticle surface energy. Using combination of the molecular dynamics simulations and theoretical calculations we have showed that the deformation of the adsorbed nanoparticles is a function of the dimensionless parameter $\beta \propto \gamma \left( {GR} \right)^{-2/3}W^{-1/3}$, where $G$ is the particle shear modulus, $R$ is the initial particle radius, $\gamma $ is the polymer interfacial energy, and $W$ is the particle work of adhesion. In the case of small values of the parameter $\beta <$0.1, which is usually the case for strongly cross-linked large nanoparticles, the particle deformation can be described in the framework of the classical Johnson, Kendall, and Roberts (JKR) theory. However, we observed a significant deviation from the classical JKR theory in the case of the weakly cross-linked nanoparticles that experience large shape deformations upon particle adhesion. In this case the interfacial energy of the nanoparticle plays an important role controlling nanoparticle deformation. Our model of the nanoparticle adhesion is in a very good agreement with the simulation results and provides a new universal scaling relationship for nanoparticle deformation as a function of the system parameters. [Preview Abstract] |
|
C1.00042: ABSTRACT WITHDRAWN |
|
C1.00043: Pressure Mapping Within a Tribological Contact with Fluorescence Imaging Mourad Chennaoui, Janet Wong In many lubricated applications from gears to MEMS, the operating pressure must be known in order to achieve optimum performance and design. However, due to the small length scale that exists at the tribological contact, placing sensors is unpractical to allow direct pressure measurement. Instead, the pressure is often inferred from indirect techniques such as film thickness measurements, photo-elasticity or the use of micro-transducers. Although these methods lead to good pressure approximations, they generally involve calibrations on well-defined setups. The results obtained can be difficult to interpret or suffer from limited spatial resolutions. In this work, fluorescent molecules in a lubricating fluid are used as probes for in-situ pressure measurements. The change in the probe's photophysical behaviour with pressure is utilised to quantitatively correlate the pressure distribution in a tribological contact such as the one found in elastohydrodynamic lubrication regimes. [Preview Abstract] |
|
C1.00044: Thermal Properties of specific Nonconjugated Conductive Polymers studied using Differential Scanning Calorimetry Gurudutt Telang, Sapana Shrivastava, Mrinal Thakur Differential scanning calorimeter (DSC) has been used to measure the thermal properties of nonconjugated conductive polymers, poly($\beta $-pinene) and trans-1,4-polyisoprene before and after doping with iodine. The measurements have been made over the temperature range of -50 $^{\circ}$C to 110$^{\circ}$C. The heat capacity of poly($\beta $-pinene) has been observed to increase upon iodine doping. The T$_{g}$ of undoped poly($\beta $-pinene) and the T$_{m}$ of undoped trans-1,4-polyisoprene have been measured and were found to be 77 $^{\circ}$C and 60 $^{\circ}$C respectively. After doping the T$_{g}$ and T$_{m}$ transitions were not clearly observable. X-ray diffraction studies have shown the $\gamma $-phase crystal structure for trans-1,4-polyisoprene film in the undoped state. These results will be discussed considering the molecular and nano-structures of these materials before and after doping. [Preview Abstract] |
|
C1.00045: Complex fluids with robustly tunable optical properties: experiments and theory T. Cong, S.N. Wani, A.S. Sangani, R. Sureshkumar Fluids with tunable optical properties are of fundamental and practical interest. They can be easily processed to manufacture thin films and interfaces for applications such as molecular detection and light trapping in photovoltaics. We use solution phase self-assembly to uniformly distribute various metallic nanoparticles to produce stable suspensions with localized, multiple wavelength or broad-band optical properties. Their spectral response can be robustly modified by varying the species, concentration, size and/or shape of the nanoparticles. Spectral behavior for finite particle concentrations can be predicted by an effective medium theory developed in this work. Structure, rheology and optical properties of these plasmonic suspensions as well as their potential application to high efficiency photovoltaics design will be discussed. [Preview Abstract] |
|
C1.00046: Exploiting redox chemistries to manipulate structure and electrical conductivity in polymer acid-doped polyaniline Jacob Tarver, Joline Fan, Yueh-Lin Loo Template synthesis of polyaniline on poly(2-acrylamido-2-methyl-1-propanesulfonic acid) yields electrostatically stabilized particles that can be aqueously dispersed and cast into thin films; electrical conductivity in these films scales with inter-particle connectivity. Previous research has shown that solvent annealing with dichloroacetic acid (DCA) induces structural rearrangement of polymer chains and consequently enhances the electrical conductivity by up to two orders of magnitude (from 0.4 to 40 S/cm). Alternatively, the electrostatic interactions between polyaniline and its template can be neutralized through chemical reduction with hydrazine monohydrate, after which the polymer undergoes extensive structural rearrangement; subsequent exposure to nitric oxide leads to reassociation of polyaniline and its polymer acid dopant. Enhanced conductivity is observed following this chemical redox process, and is attributed to extensive polymer chain relaxation and concurrent elimination of the particulate nature of template-synthesized polyaniline. [Preview Abstract] |
|
C1.00047: Electromagnetic transport in magnetorheological elastomer composites Darin Zimmerman, Kofi Adu, Richard Bell, Timothy Hooper, Gary Weisel We present systematic measurements of the electron transport properties and optical response of gold-coated-iron (Au/Fe)-elastomer composite materials. By mixing micron-sized Au/Fe particles with silicone-based liquid elastomer, we produce two types of magnetorheological elastomer composites (MREs): those in which the particles are aligned by an external magnetic field prior to elastomer hardening and those in which the particles are left in random arrangement. By applying modest external stress or an external magnetic field to the two types of post-hardened MREs, we control the transport properties and optical response and observe significant differences in their behavior. [Preview Abstract] |
|
C1.00048: Solution Structures of Poly(3-alkylthiophene) Kaikun Yang, Liwei Huang, Narayan Ch Das, Howard Wang Small angle neutron scattering has been used to understand the solution structure of regioregular and regiorandom alkyl-derived polythiophenes, with alkyl side groups varying from 4 to 10 carbons. While poly(3-octylethiophene) (P3OT) remain coil conformations in solution, poly(3-butylthiophene) (P3BT) and poly(3-dodecylthiophene) form gel networks. However, poly(3-hexylthiophene) (P3HT) forms rod-like aggregates over large length scales. At elevated temperatures, all structures dissolve to coil solutions. A temperature dependent study shows that the aggregates (coils, rods and gels) are thermally reversible. The solution structure is reflected in the morphology of as-prepared films cast from the same P3HT solution stored for various time. In general, roughness and large rod-like features in as-cast films increase with storage time. Those long 1D aggregates may form in solution and is responsible for the eventual gelation of P3HT solution, render it useless for casting films for applications. [Preview Abstract] |
|
C1.00049: Generation of conductivity through transfer charge properties, for polyesters and polyamides with characteristic functional groups Carmen Gonzalez, Luis Hernan Tagle, Claudio A. Terraza, Andres Barriga, A.L. Cabrera, Ulrich G. Volkmann Electro-optic properties of $\sigma $-conjugated polymers, as polysilylene; are associated with electron conjugation in the silicon atom, which allows a significant delocalization of electrons along of the chain. Thus, the conductivity is intimately connected to the mobility of charge carriers, which in turn depends on the structure and morphology of the system. We report the characterization of polyesters (PEFs) and polyamides (PAFs). Film thicknesses were obtained by ellipsometry. The vibration frequencies of the groups were determined by FT-IR and corroborated by Raman spectroscopy. Structural information was obtained from X-Ray diffraction (XRD). The structural and surface morphology were studied by scanning electron microscope (SEM). Electrical conductivity of the polymers was measured before and after exposure to iodine vapor, for films of different thicknesses. Morphological differentiation was studied by energy dispersive microscopy (EDX), showing a regular distribution of iodine within the polymer. Preliminary conductivity measurements showed adverse effects when oxidation of the polymer films is induced These effects are related to a certain grade of disorder within the system [Preview Abstract] |
|
C1.00050: Structural symmetry breaking of silicon containing polymers and their relation with electrical conductivity and Raman active vibrations Alejandro Cabrera, Carmen Gonz\'alez , Luis Tagle, Claudio Terraza, Ulrich Volkmann, Andr\'es Barriga, Esteban Ramos, Maximiliano Pavez The incorporation of silicon into the polymeric main chain or side groups can provide an enhancement in chemical, physical and mechanical properties. We report an efficient method for the synthesis of polymers containing silicon in the main chain, from the polycondensation reactions of four optically active carboxylic diacid. The solubility of the polymers, the molecular weight, the glass transition and the thermal stability were studied by standard techniques. Raman spectroscopy was used to probe the conformation of stretching modes as function of the temperature. The conductivity measurements indicated that the alignment of the molecules is a crucial parameter for electrical performance. When the polymers were exposed to iodine, charge transfer increased their mobility and decreased their optical band gaps. These novel properties highlight the possibility to generate alternative active opto-electronics polymers. [Preview Abstract] |
|
C1.00051: Structural Disorder and Thermal Properties of the Alpha' Phase of Poly(l-Lacitc Acid) Jeffrey Kalish, Shaw Ling Hsu Poly(lactic acid) samples rich in alpha' or alpha crystals have been characterized using spectroscopic and thermal methods. Cryogenic infrared and Raman spectroscopy were used to probe the differences in chain conformation and packing. Compared to the alpha crystal, the alpha' crystal has weakened specific carbonyl and methyl interactions. Experimental spectroscopic analysis in conjunction with simulation studies have shown that the alpha' crystal has uniform chain conformational disorder. This disorder in chain conformation and packing leads to different crystalline forms with varying stabilities. The difference in thermal stability was quantified by measuring enthalpic change at melting for both crystalline forms by extrapolation of the glass transition as well as by using small molecule extrapolation. Equilibrium melting enthalpy was determined to be 57 J/g for alpha' and 96 J/g for the alpha crystal. The transformation from the less stable alpha' to the more stable alpha phase has been characterized. This analysis provides an explanation for the double melting peaks usually found in the PLLA samples. [Preview Abstract] |
|
C1.00052: Influence of graphene on the crystallization behavior of polyethylene Shan Cheng, Christopher Li Recent work on polyethylene(PE)/carbon nanotube nanocomposites demonstrates that CNTs can significantly alter PE crystallization. Graphene, a 2D counterpart of CNT, is an excellent candidate for fabricating polymer nanocomposites. We herein report the influence of graphene on crystallization behavior of PE. High density polyethylene (HDPE) was first crystallized in dilute solution in the presence of dispersed single or few-layer graphene sheets. Epitaxial growth of polyethylene on the basal plane of graphene sheets was observed using transmission electron microscopy. PE/graphene nanocomposites with various graphene loading were then fabricated. Both non-isothermal and isothermal crystallization behavior of these nanocomposites were studied using a differential scanning calorimeter. Multiple melting peaks of the nanocomposite were correlated to homo- and heterogeneous nucleation of PE crystallites. Crystallization kinetics was studied using Avrami equation. The results were compared with cabon nanotube/PE system and the difference will be discussed. [Preview Abstract] |
|
C1.00053: Crystallization effects of carbon nanotubes on semicrystalline isotactic polypropylene Georgi Georgiev, Scott Schoen, Devin Ivy, Peggy Cebe When carbon nanotubes are introduced in isotactic polypropylene (iPP) materials the iPP crystals assemble in a fibrillar instead of spherulitic arrangement. We study the effects of concentration and isothermal vs nonisothermal treatments on the rate of crystal formation. Those nanocomposites provide means of controlling the crystal orientation in polymer materials by aligning the nanotubes and creating materials with novel properties. We used Differential Scanning Calorimetry (DSC) as our primary method of investigation due to its ability to give detailed data on the phase transitions of iPP nanocomposites with low concentrations of CNTs (0-5 percent). We analyzed the crystallization of each sample in the DSC at a range of cooling rates (10-20C/minute). We found that increased concentrations of CNTs speed up the nanocomposites' crystallization and decrease the crystal size distribution. [Preview Abstract] |
|
C1.00054: Structure and dynamics of solvent-free polymer grafted nanoparticles: A computational study Alexandros Chremos, Athanassios Panagiotopoulos The structure and dynamics of solvent-free polymer-grafted nanoparticles have been investigated using molecular dynamics simulations. A basic coarse-grained model was used, where the nanoparticle is represented as a single smooth particle with bead- spring polymer chains attached to it. Motivated by the recent advances in nanoparticle ionic materials and nanoparticle organic hybrid materials, we use our model to explore the behavior of these systems over a wide range of parameters and gain insights of their structure and transport properties. In particular, we find that the chain length variation can change the softness of the nanoparticles, so for short chains the system exhibits rich structural characteristics while for long chains display (dilute) liquid-like characteristics. Additionally, we find that by increasing the softness of the particles the structural relaxation of the system becomes less sensitive to temperature variation, indicating a change from the hard-spheres to soft particles. The results confirm the experimental observations that changing the chain length the system can display behavior that spans from glasses to liquids. [Preview Abstract] |
|
C1.00055: A new method to measure the optical trapping energy of nanoparticles Joseph Junio, Jack Ng, Joel Cohen, Zhifang Lin, H. Daniel Ou-Yang A novel method is described for measuring the potential energy of nanoparticles in an optical trap by trapping an ensemble of particles with a focused laser beam. The mechanical force balance between repulsive osmotic and confining gradient-force pressures determines the single-particle trapping potential independent of interactions between the particles. The ensemble nature of the measurement permits evaluation of single-particle trapping energies much smaller than k$_{B}$T. Energies obtained by this method are compared with those of single-particle methods as well as with theoretical calculations based on classical electromagnetic optics. [Preview Abstract] |
|
C1.00056: Spontaneous asymmetry in coated spherical nanoparticles in solution and at liquid-vapor interfaces J. Matthew D. Lane, Gary S. Grest Nanoparticles in solution are often stabilized with functional coatings to prevent aggregation. We'll present recent simulations results showing that small spherical nanoparticles produce highly asymmetric coating arrangements, when coated with simple polymer chains. These coatings are not symmetric even when extremely uniform grafting arrangements and full coverages are employed. I will also discuss the geometric properties which dictate the coating shape. When particles are placed in an anisotropic environment, such as the liquid/vapor interface, the asymmetric coatings are amplified and oriented by the surface. Particle shape and its responsive behavior is seen to strongly influence interactions. Implications and examples of controlled self-assembly will be presented. [Preview Abstract] |
|
C1.00057: ABSTRACT WITHDRAWN |
|
C1.00058: Controlled Evaporative Self-Assembly of Hierarchical Polymer Stripes with Ordered Nanochannels Wei Han, Myunghwan Byun, Lei Zhao, Javid Rzayev, Zhiqun Lin A toluene solution of a bottlebrush block copolymer, polystyrene-polylactide (PS-PLA), was confined in a ``cylinder-on-flat'' geometry, from which the consecutive ``stick-slip'' motion of the contact line of the PS-PLA solution was effectively regulated as the solvent evaporated, thereby forming gradient stripes at the microscopic scale. Upon subsequent solvent vapor annealing, hierarchically organized structures of PS-PLA were produced in which the lamellar nanodomains normal to the substrate were obtained within the stripes. After mild removal the PLA component, channels at the nanoscale wrere formed with the stripes. This facile approach of combining controlled evaporative self-assembly with subsequent vapor annealing opens up a new avenue to rationally organize and engineer self-assembling building blocks into functional materials and devices in a simple, cost-effective and controllable manner. [Preview Abstract] |
|
C1.00059: Supercritical carbon dioxide induced surface melting/recrystallization process in ultrathin PEO films Naisheng Jiang, Mitsunori Asada, Peter Gin, So King Lam, Maya Endoh, Sushil Satija, Tad Koga Crystallization of polymeric materials in nanoconfined geometries has attracted considerable attention in the past decade. In this talk, we will show the novel effects of supercritical carbon dioxide as a plasticizer in order to control the melting/crystallization behavior of semicrystalline polymer thin films. Poly(ethylene oxide) (PEO) thin films with thickness of 10nm-100nm were used for this study. In-situ neutron reflectivity technique was utilized to study the swelling behavior of deuterated PEO films in scCO$_{2}$ at T=50\r{ }C, showing the clear evidence of the surface melting phenomenon even below the bulk melting temperature (65\r{ }C). The surface structures before and after exposure at the different CO$_{2}$ process conditions were then investigated in air by using atomic force microscopy and grazing incidence x-ray diffraction. The results clearly showed that scCO$_{2}$-induced re-crystallization from the amorphous state via pressure quench results in various surface crystalline structures, depending on temperature, pressure, quench rates, and the film thickness. [Preview Abstract] |
|
C1.00060: ABSTRACT WITHDRAWN |
|
C1.00061: Highly Swollen Porous Microstructures in Polyelectrolyte Multilayers Chungyeon Cho, Jeremy Kaiser, Nicole Zacharia We investigated the creation of porous morphologies from polyelectrolyte multilayers (PEMs) consisting of linear poly(ethylenimine) and poly(acrylic acid), and poly (allylamine hydrochloride) and poly (acrylic acid) as a function of pH and immersion time under post-base assembly treatment. The porous transition is linked to the neutralization of the polycations electrolytes as well as ionization of PAA by the exposing LbL films to high pH. This causes PEMs to undergo spinodal decomposition, creating pores and an increase in film thickness. By using reactive wet stamping technique, we were able to locally cause porosity changes under high pH conditions in the LbL films. Further investigation of the mechanical properties of patterned LbL films was done by performing nano-indentation analysis. The results showed clear difference of physical properties such as hardness and modulus between stamped and unstamped regions based on porous transition. [Preview Abstract] |
|
C1.00062: Morphological Change of Poly(4-\textit{tert}-butylstyrene-\textit{block}-4-\textit{tert}-butoxystyrene) in a Wide Range of Segregation Strength Though Hydrolysis Reaction Siti Sarah Abdul Rahman, Daisuke Kawaguchi, Yushu Matsushita Morphological change of symmetric poly(4-\textit{tert}-butylstyrene-\textit{block}-4-\textit{tert}-butoxystyrene)s (BO) upon hydrolysis reaction was investigated by transmission electron microscopy and small-angle X-ray scattering. Segregation strength, \textit{$\chi $N} (\textit{$\chi $}: interaction parameter, $N$: degree of polymerization), which governs the chain dimension, was gradually tuned since poly(4-\textit{tert}-butoxystyrene) (O), a non-polar polymer, can be converted into poly(4-hydroxystyrene) (H), a polar one, through hydrolysis. Samples with different molecular weights and conversion rates of O into H, $f_{H}$s, were prepared. Domain spacing of the lamellar structure, $D$, increased as $f_{H}$ increases where it abruptly increased at a critical $f_{H}$, indicating that the chain stretched perpendicularly to the lamellar interface. The degree of chain stretching compared to a random coil, $D$/$D_{0}$s ($D_{0}$: correlation length at $f_{H}$=0), were scaled by \textit{$\chi $N}. Three regimes can be distinguished in the plot of ($D$/$D_{0})$ vs. \textit{$\chi $N}: (I) the weak segregation regime with $D$/$D_{0}\sim $1 that associates with the scaling behavior of $D\sim N^{0.55}$, (II) the intermediate segregation regime with the scaling behavior of ($D$/$D_{0})\sim $(\textit{$\chi $N})$^{0.34}$, and (III) the strong segregation regime with $D$/$D_{0}\sim $2.3 which corresponds to $D\sim N^{0.67}$. [Preview Abstract] |
|
C1.00063: Frustrated ABC Linear Block-Random Copolymer with a Semicrystalline End Block Bryan S. Beckingham, Richard A. Register The solid-state structure of semicrystalline block copolymers is set either by block incompatibility or by crystallization of one or more blocks. A variety of solid-state morphologies may be observed depending on the block interaction strength, ranging from spherulitic to confined crystallization within preexisting microphase-separated domains. Linear triblock copolymers, polybutadiene-$b$-polyisoprene-$b$-poly(isoprene-$r$-styrene) (A-B-C), are synthesized via lithium-initiated anionic polymerization in cyclohexane. After polymerization of the butadiene block, triethylamine is added to facilitate the random styrene/isoprene copolymerization while also increasing the vinyl content of the polyisoprene block. Selective hydrogenation of the diene units with a Ni-Al catalyst yields a semicrystalline polyethylene endblock, with a frustrated block sequence: $\chi _{BC} > \chi _{AB} >>\chi _{AC}$. For a polymer with block molecular weights of 30-14-14 kg/mol, small-angle x-ray scattering reveals the formation of a well-ordered lamellar melt from which crystallization of the hydrogenated polybutadiene (polyethylene) block proceeds. [Preview Abstract] |
|
C1.00064: Self-Consistent Field Modeling of Diblock Copolymers in Selective Solvents Raghuram Thiagarajan, David Morse The purpose of my poster is to study the driving forces behind the self-assembly of a diblock copolymer AB, consisting of a solventphilic block (B) and a solventphobic block (A), in selective solvents (S). Micellar transformations between spherical, cylindrical, and bilayer curvatures for a model system are tracked using self-consistent field modeling, in real space, in the dilute regime. The transition from a concentrated regime, $\phi_{\rm{AB}} \sim 1$, to a dilute regime, $\phi_{\rm{AB}} \sim 0$, is studied. Phase portrait for the concentrated regime is generated using periodic self-consistent field modeling. The unbinding transition, as seen in the periodic counterpart of self-consistent field theory, is compared with the transformations observed in the dilute regime. The two phase regions in the dilute regime are mapped out for the inverted phases as well. [Preview Abstract] |
|
C1.00065: Synthesis and Characterization of Tapered Block Copolymers Wei-Fan Kuan, Raghunath Roy, JongKeun Park, Thomas Epps Tapered block copolymers offer the opportunity to manipulate copolymer segregation strength independent of molecular weight and chemical constituents, which allows the design of materials with improved mechanical properties while retaining the desired phase separated structures. In this work, we focus on the synthesis and characterization of poly(isoprene-$b$-isoprene/styrene-$b$-styrene-$b$-styrene/methyl methacrylate-$b$-methyl methacrylate) [P(I-IS-S-SM-M)] tapered triblock copolymers. P(I-IS-S) tapered diblock copolymers are synthesized using living anionic polymerization and treated as macroinitiators for activator regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP). ARGET ATRP is employed to make the SM tapered interface and M block, enabling synthesis of tapered triblocks with low polydispersity (M$_{w}$/M$_{n}<$ 1.2). These materials self-assemble into well-defined nanoscale architectures depending on segment volume fractions and taper dimensions. [Preview Abstract] |
|
C1.00066: Gelation of Copolymers Photo-crosslinked by Pendant Benzophenones Scott Christensen, Ryan C. Hayward Copolymers containing pendant benzophenone (BP) groups provide a simple and powerful route to crosslinkable polymer films. While the solution state photo-chemistry of BP is well established, and crosslinking of polymers blended with BP has been studied in detail, the process of crosslinking by covalently attached BP has received comparatively little attention. We have prepared copolymers of BP with several different monomers, and studied gelation as a function of BP content and degree of photochemical conversion. We seek to understand the influence of polymer chemistry on crosslinking efficiency, to guide choices of materials for photo- crosslinkable polymer films and to provide a route for tailoring morphology in polymer blends. [Preview Abstract] |
|
C1.00067: Understanding the phase behavior and equilibration kinetics of PDMS-containing block copolymers Charlotte Stewart-Sloan, Edwin Thomas Block copolymers containing both PDMS and an olefin are of interest because they combine high chi parameters which allow for strong segregation on small length scales with a differential etch resistance to oxygen plasma. In order to understand the phase behavior and how it is affected by thermal treatments, low molecular weight diblocks of PS-PDMS and PI-PDMS were examined at different temperatures using synchrotron radiation. The movement and changes in intensity of the peaks present in the SAXS patterns at different temperatures after long equilibration times provides information about the equilibrium structures present in these materials and the evolution of these patterns over time allows insight into structural kinetics. The ODT was determined for three different compositions and the structure equilibration on heating and cooling were investigated. Of particular interest is the evolution of structure at room temperature after high temperature treatment. [Preview Abstract] |
|
C1.00068: Cloud Point Depression in Dilute Solutions of HEMA/DMAEMA Copolymers with Prescribed Composition Profiles and Gradient Strengths Keith Gallow, Young Jhon, Jan Genzer, Yueh-Lin Loo We have synthesized a random copolymer and gradient copolymers of hydroxyethyl methacrylate and dimethylaminoethyl methacrylate whose instantaneous compositions vary linearly and according to hyperbolic tangent (Tanh) functions along the backbones, all having similar molecular weights and overall compositions. The cloud point of the dilute solution of the random copolymer is 20.0$^{\circ}$C; the transparent-to-turbid transition occurs over 1.0$^{\circ}$C. Dilute solutions of linear gradient copolymers exhibit cloud point depressions of up to 3.5$^{\circ}$C and transition breadths of 1-3$^{\circ}$C compared to that of the random copolymer. The cloud points of dilute solutions of gradient copolymers with Tanh composition profiles are further suppressed by as much as 9.0$^{\circ}$C compared to that of the random copolymer. Our observations demonstrate the importance of monomer sequence distribution in altering the macroscopic solution properties of copolymers. [Preview Abstract] |
|
C1.00069: High area density etching mask for data storage industry based on the block copolymer self-assembly Xiaodan Gu, Thomas Russell, Bin Zhang, Dorsey Paul The application of block copolymer as etching mask for data storage industry was investigated. Higher area density silicon oxide pillars from block copolymer template were generated on the media substrate over several inch square areas. Thin film of PS-b-PVP was spin coated and solvent annealed to generate cylindrical micro-domain normal to surface. The film was then reconstructed in the ethanol alcohol to generate the porous cylindrical micro-domain. Polydimethylsiloxane (\textit{PDMS}) was then spin coated onto the porous film surface. The film was heated to facilitate the movement of PDMS into the pores, and then etched with fluorine and oxygen plasmas to remove the polymeric material, leaving only silicon oxide pillars. The effect of pore diameter on the size and quality of silicon oxide pillar was investigated. Larger pores generated higher quality pillars. Areal densities from 0.5 to 2 Teradots per inch square were achieved. The silicon oxide produced had a good ion-etch resistance, enabling pattern transfer the pillar pattern to underlying magnetic media. [Preview Abstract] |
|
C1.00070: Orientation Control of Block Copolymer Films on Rough Substrates Prepared by E-beam Lithography Youngwoo Choo, Hyo Seon Suh, Hyun-Mi Kim, Myung Rae Cho, Yun Daniel Park, Ki-Bum Kim, Kookheon Char Several researches on the perpendicularly oriented BCP thin films induced from the underlying substrates with surface roughness have been reported. In the present study, we investigated the effect of each roughness factor, such as period or depth of the roughness, on the orientation of BCP thin films. In order to control such roughness factors systematically, we introduced various lithographic techniques. The hydrogen silsesquioxane (HSQ) patterns with controlled period and depth were prepared by the Atomic Image Projection E-beam Lithography (AIPEL), which were realized by adjusting lithographic parameters of AIPEL. In addition, we also prepared silicon oxide patterns using ordinary e-beam lithography. The line width and period of patterns were finely tuned during the E-beam writing while the depth of the patterns was modified by the reactive ion etching on the patterned substrates. On the substrates with specified roughness, we deposited symmetric PS-$b$-PMMA diblock copolymers and observed the effect of individual roughness factors on the orientation of BCP thin films. [Preview Abstract] |
|
C1.00071: Architectural Effects in Thin Films of Poly(styrene-b-methyl methacrylate) Copolymers Nikhila Mahadevapuram, Thai Vu, Gila Stein Block copolymer self-assembly offers a simple route to generate nanostructures over large areas. Control over domain orientation is critical for nanopatterning; typically, the lower-surface energy constituent will segregate at the air interface and drive a parallel orientation of cylindrical or lamellar domains. Recent works by Khanna et al.$\footnote{Khanna et al., Macromolecules, 39, 9346-9356, 2006}$ and Matsen$\footnote{Matsen, Macromolecules, 43, 1671-1674, 2010}$ suggest that molecular architecture can affect surface energetics and domain orientations. We compared the thin film ordering of lamellar poly(styrene-b-methyl methacrylate) (PS-PMMA) diblock copolymers with PMMA-PS-PMMA triblock copolymers. Films that ranged in thickness from $t=L_0-5L_0$ were cast on neutral substrates, annealed under vacuum at 220$^{\circ}$C for 2 days, and then measured with grazing-incidence small-angle X-ray scattering. The triblock copolymers adopt a perpendicular domain orientation near the film surface for all thicknesses considered, while the perpendicular domain orientation was only stable for diblock copolymers when $t\leq L_0$. However, triblock thin films contain defects in the film interior that limit their utility. [Preview Abstract] |
|
C1.00072: From blood dialysis to desalination: A one-size fits all block copolymer based membrane system Nataraj Sanna Kotrappanavar, Paul Zavala-Rivera, Kevin Chonnon, Shaheen S.A. AlMuhtaseb, Easan Sivaniah Asymmetric membrane with ultrahigh selective self-assembled nanoporous block copolymer layer were developed successfully on polyimide (PI) support, which demonstrated excellent thermal, chemical and mechanical stability. Membranes with specific nano- structural architectures and optimized cascades of block assemblies on the top selective skin have been used largely for separation of colour from aqueous streams, wastewater treatment, desalination, blood filtration and gas separation with dense layer transformation. A consistent and reliable method of membrane preparation and measuring separation performance has been adopted. A homologous series of ethylene oxide oligomers covering a large range was used to characterise MWCO of Membrane and were able to provide many points to give a comprehensive description of the membrane performance in the nanofiltration range. [Preview Abstract] |
|
C1.00073: Circular Patterns over Large Areas from The Self-Assembly of Block Copolymers Guided by Shallow Trenches Sung Woo Hong, Xiaodan Gu, June Huh, Shuaigang Xiao, Thomas Russell We report the fabrication of ultra-dense circular nanoarrays of block copolymer (BCP) microdomains over macroscopic areas. These arrays were generated by the directed self-assembly of BCPs on the topographically patterned substrates, where the trenches with circular shape are patterned on a flat substrate. The width of circular trench and the distance between circular trenches are varied for commensurability issues, and difference BPCs are used to demonstrate the generality of this strategy. When a commensurability condition is satisfied, BCPs on the topographically patterned substrates undergo a grapho-epitaxial self-assembly with solvent annealing, resulting in an areal density amplipication of the circular patterns over large areas. The methodology described here may provide an easy approach to high densities of circularly shaped nanopatterns for data storage applications. [Preview Abstract] |
|
C1.00074: Poly (2-vinyl naphthalene-b-acrylic acid) (P2VN-b-PAA) block copolymer pattern formation, alignment and pattern transfer by reactive ion etching (RIE) Xin Zhang, Christopher Metting, R.M. Briber, Sang Hak Shin, Ben Jones P2VN-b-PAA (Mn=30.8-b-24 kDa) lamellar block copolymer was examined for use as a pattern transfer template due to the potential large dry etching contrast between the blocks. As-spun films have a micelle or vertically oriented cylindrical morphology depending on the spinning solvent. Vapor annealing with acetone, a poor solvent for P2VN-b-PAA, resulted rapid reordering to a vertically oriented lamellar morphology within 5 minutes for films $<$50 nm thick. Films between 30 to 50 nm thick were spin coated onto oxide wafers with interdigitated electrodes to examine if an electric field would align the morphology. The lamellae aligned normal to the electrodes within 1 hour by electric field assisted acetone vapor annealing at field strengths as low as 1V/micron. CF$_{4}$ plasma dry etching contrast as high as 1:3.8 (P2VN:PAA) for homopolymer blanket films was measured. The block copolymer pattern was transferred to the silicon substrate in two steps using CF$_{4}$ followed by SF$_{6}$ RIE. [Preview Abstract] |
|
C1.00075: Methods for Self-Assembly of Rod-Coil Diblock Copolymer Thin Films Samantha Collins, Amanda Kamps, Michael Fryd, Russell Composto, So-Jung Park Long range order in diblock copolymer (BCP) thin films can be induced by solvent annealing. First, thin films of semiconducting BCPs were spin-coated onto base-treated and hydroxyl-terminated silicon substrates. These BCP films were then solvent vapor annealed in inert, solvent-saturated atmosphere. Structure was investigated as a function of substrate end group, film thickness, and solvent annealing duration, and an optimized ordering condition was found. Film thickness was varied to direct the morphology perpendicular to the substrate for potential photovoltaic device applications. Second, BCP thin films were processed by novel thermal gradient annealing as an alternative route to directing long range order in the films. The effect of thermal gradient steepness and temperature range on ordering was analyzed for the optimized thickness determined by solvent annealing. [Preview Abstract] |
|
C1.00076: Nanopatterns in a confined triblock copolymer Jumi Lee, Yeongmin Jeon, Jaeup Kim, Junhan Cho Ordered structures in thin films of ABC triblock copolymers are studied experimentally and theoretically in order to be applied to fabrication of nanoscale electronic devices. A field-theoretic simulation method based on the self-consistent field theory is used to generate useful nanopatterns starting with a random configuration of compositions. The main parameters for the phase stability, such as Flory interaction parameters, total chain size, compositions, film thickness, and surface interactions, are considered as controllable variables in the present analysis. By using some typical triblock copolymers, nanopatterns observed in experiments are comparable with those in the simulation. [Preview Abstract] |
|
C1.00077: Hierarchical assembly of coil-rod-coil peptide-based copolymers Nandula Wanasekara, Casey Johnson, LaShanda Korley Coil-rod-coil block copolymers have been shown to exhibit an array of morphologies, from crystalline lamellae, to novel, three-dimensional tetragonal lattices, depending upon coil length and molecular weight. We have been motivated by recent advances in controlled polymerization techniques and the opportunity to develop bio-inspired copolymer motifs to explore the hierarchical self-assembly of coil-rod-coil peptide-based copolymers with variations in peptidic rod length. Thin films were characterized using atomic force microscopy, x-ray scattering and thermal analysis techniques showing random sphere-like nanostructures with alpha-helix peptide secondary structure. Our goal is to utilize these materials to engineer the interface of hierarchically-designed, nature-inspired elastomers. [Preview Abstract] |
|
C1.00078: Enhanced stability of self-assembled polymer nanostructures by molecular crosslinking Mark Stoykovich, Ian Campbell, Brian Perea Self-assembled nanostructures of block copolymers have attracted interest for applications in next generation lithography and advanced materials synthesis. Many of these applications require mechanically and chemically robust nanostructures that cannot be achieved by simple diblock copolymer materials alone. Here we have investigated a method to stabilize block copolymer nanostructures after self-assembly in thin films by incorporating cross-linking molecular components within the self-assembled domains. Polymer blends consisting of a majority symmetric PS-block-PMMA copolymer and equal amounts of PS and PMMA homopolymers were prepared and determined to form lamellar phase morphologies. The PS and PMMA homopolymers were synthesized with a small fraction of glycidyl methacrylate monomer which served as the cross-linking agent in the blends. These nanostructures exhibit enhanced solvent and thermal stability, and have been demonstrated for the fabrication of three-dimensional multilayer structures. [Preview Abstract] |
|
C1.00079: Local segmental dynamics of cis-1,4-polybutadiene, polypropylene, and polyethylene terephthalate via molecular dynamics simulations David Whitley, David Adolf NPT molecular dynamics simulations of cis-1,4-polybutadiene, polypropylene, and polyethylene terephthalate have been performed. The simulation pressure was 1 atmosphere for all systems, with all simulation temperatures being well above each polymer's glass transition temperature. The trajectories have been analysed via autocorrelation functions (ACFs) of chord vectors spanning different numbers of chain backbone bonds. Inverse Laplace transformations of these ACFs using the CONTIN algorithm afforded the corresponding distributions of relaxation times (DRTs) for the simulated dynamics. All DRTs illustrated a peak on fast time scales corresponding to short length scale segmental motion and a peak at longer time scales corresponding to longer length scale relaxations. An intermediate peak between the fast and slow peaks appears as the relaxation dynamics of longer chord vectors are analysed. The temperature dependence of the relaxation dynamics has also been investigated. [Preview Abstract] |
|
C1.00080: Coarse-grained modeling of polystyrene at different concentrations using the Iterative Boltzmann Inversion technique Beste Bayramoglu, Roland Faller We present systematic coarse-graining of several polystyrene models and test their performance under confinement and eventually in brush systems. The structural properties of a dilute polystyrene solution, a polystyrene melt and a confined concentrated polystyrene solution at 450K, 1 bar were investigated in detail by atomistic molecular dynamics simulations of these systems. Coarse-graining of the models was performed by Iterative Boltzmann Inversion Technique (IBI), in which the interaction potentials are optimized against the structure of the corresponding atomistically simulated systems. Radial distribution functions, bond, angle and dihedral angle probability distributions were calculated and compared to characterize the structure of the systems. Good agreement between the simulation results of the coarse-grained and atomistic models was observed. [Preview Abstract] |
|
C1.00081: Identifying Entanglement States of Ring Polymers Using Knot Polynomials Jian Qin, Scott Milner Melts of ring polymers have fixed topologies in the absence of ring opening or reconnecting operations. We identify the topological states by recognizing how rings are knotted with each other, which can be achieved by computing knot invariant polynomials. We used this idea to count the entanglement states of ring polymers, prepared with off-lattice Monte Carlo simulations, in which the system topology is allowed to change by various ring rebridging moves. We project polymer configurations to obtain crossing diagrams, and use algorithms based on knot theory to compute the Jones invariant polynomial. We studied both aperiodic and periodic systems, to estimate the surface effects on entanglements. For the periodic case, we extended the algorithm for aperiodic knots to deal with periodic patterns. These tools enable us to accumulate the probability distribution of topological states for rings of different lengths, from which we determined the entanglement length by identifying the topological entropy as $k_B$ per entanglement strand. [Preview Abstract] |
|
C1.00082: Conformation of a Lennard-Jones Chain in Explicit Solvent: A Solvation Potential Approach Shishir Adhikari, Mark Taylor The conformation of a polymer chain in solution is intrinsically coupled to the chain's local solvent environment. In much of the theoretical work on polymers in solution the effects of solvent are treated implicitly and explicit chain-solvent coupling is ignored. Although a formally exact treatment of chain-solvent coupling can be constructed, the required many-body solvation potential is not practical to compute. Following on our work with hard-sphere and square-well chain-in-solvent systems [1] here we show that for Lennard-Jones (LJ) systems this many-body solvation potential can be made tractable via an ``exact'' decomposition into a set of two-site potentials. We use these exact short chain results, combined with the pure solvent potential of mean force, to construct approximate two-site solvation potentials for long LJ-chains. Monte Carlo simulations for full chain-in-solvent systems verify the accuracy of our solvation potential mapping across the full LJ-solvent phase diagram.\\[4pt] [1] J. Chem. Phys. 127, 184901 (2007); J. Polym. Sci., Part B: Polym. Phys. 45, 3319 (2007). [Preview Abstract] |
|
C1.00083: Differential AC/scanning chip nanocalorimeter for in-situ measurements of vapor deposited glasses Mathias Ahrenberg, Katie Whitaker, Heiko Huth, Mark D. Ediger, Christoph Schick We use nanocalorimetry to investigate the formation of extraordinarily stable glasses prepared by vapor deposition. For that purpose we've built a vapor deposition chamber that allows in-situ characterization of vapor-deposited organic molecules down to liquid nitrogen temperature. The use of commercially available nanocalorimeter sensors permits us to measure the temperature at the sample position directly via heater resistivity. The calibration of this method was done with the frequency dependence of the dynamic glass transition temperature of low molecular glass formers such as toluene over a broad frequency range. This was applied to investigate vapor deposition of glass formers as a function of time as well as vapor deposited samples as a function of temperature. [Preview Abstract] |
|
C1.00084: An apparatus for in situ x-ray scattering studies of polymer melts during homogenous uniaxial extensional flow Wesley Burghardt, Ruinan Mao In situ x-ray scattering methods have been broadly applied to study the structural dynamics of polymers and other complex fluids under flow, and can provide deep insights into the microstructural origins of complex non-Newtonian flow characteristics. Most studies in this vein have employed either homogenous shear flow, or processing flows such as fiber spinning which are complicated by inhomogenous deformation histories and/or nonisothermal operation. Here we present the design and implementation of a new apparatus for in situ x-ray scattering studies of polymer melts during homogenous uniaxial extensional flow. The experiment is based on the commercially-available SER extensional flow fixture, which employs two counter- rotating drums to deform a sample strip of polymer melt. This fixture has been incorporated into a custom-fabricated convection oven designed to facilitate x-ray access to the sample, and operation in a typical synchrotron beam line environment. Preliminary data on extensional flow induced orientation of ordered block copolymers will be used to illustrate the capabilities of this device. [Preview Abstract] |
|
C1.00085: Differential dynamic optical microscopy for the characterization of soft matter: liquid crystal dynamics, volume phase transition of hydrogels, and phase transition of binary mixtures Beom-Jin Yoon, Jung Ok Park, Mohan Srinivasarao, Michael H. Smith, L. Andrew Lyon The structure and dynamics of soft matter were studied by differential dynamic optical microscopy. One can retrieve q-space information through image processing and Fourier analysis, even when the feature sizes in real space image are too small to be resolved or even visible in an optical microscope. The temporal sequence of real space images were Fourier transformed, and analyzed for the temporal and spatial fluctuations of power spectrum. Here, we present the results on liquid crystal dynamics and their elastic properties, volume phase transition of hydrogels when their dimensions are sub-micron, and critical opalescence of binary mixtures (water/2,6-lutidine). [Preview Abstract] |
|
C1.00086: Fast Off-Lattice Monte Carlo Simulations with Soft Potentials Jing Zong, Delian Yang, Yuhua Yin, Xinghua Zhang, Qiang (David) Wang Fast off-lattice Monte Carlo simulations with soft repulsive potentials that allow particle overlapping give orders of magnitude faster/better sampling of the configurational space than conventional molecular simulations with hard-core repulsions (such as the hard-sphere or Lennard-Jones repulsion).\footnote{\textit{Q. Wang and Y. Yin}, \textbf{J. Chem. Phys., 130}, 104903 (2009).} Here we present our fast off-lattice Monte Carlo simulations ranging from small-molecule soft spheres and liquid crystals to polymeric systems including homopolymers and rod-coil diblock copolymers. The simulation results are compared with various theories based on the same Hamiltonian as in the simulations (thus without any parameter-fitting) to quantitatively reveal the consequences of approximations in these theories. [Preview Abstract] |
|
C1.00087: Kinetic Control for the Morphological Transition of Block Copolymer Micelle Complexes Misook Lee, Jinkee Hong, Kookheon Char The morphology of charged block copolymer micelle complexes, consisting of crew-cut poly(styrene-b-acrylic acid) (PS-b-PAA) and poly(styrene-b-4vinyl pyridine) (PS-b-P4VP) micelles, was controlled by pH of aqueous solvent. The charge densities of corona block segments (PAA and P4VP blocks) dispersed in water were sensitive functions of solution pH. The high pH region (pH $>$ 5.5) is particularly interesting in the present case due to the formation of spherical micelle clusters since the degree of ionization of P4VP blocks is negligible while PAA blocks are fully charged in this regime. These spherical clusters were then slowly transformed into different morphologies when the solution pH was adjusted to the range allowing both of the corona blocks to be oppositely charged. The morphological transitions of micelle blends were also monitored by varying experimental parameters such as blending ratio, blending sequence, and the content of co-solvent when coupled with the effect of solution pH. The present study demonstrates that the kinetic pathway for the formation and transformation of micelle complexes at various solution pH is significantly important for the morphological evolution involving charged micelles. [Preview Abstract] |
|
C1.00088: Multigeometry micelles made from self-assembly of block copolymer mixtures via kinetic control Jiahua Zhu, Shiyi Zhang, Yun Lin, Ke Zhang, Caroline Miesch, Todd Emrick, Karen Wooley, Darrin Pochan Multicompartment/multigeometry micellar structures, due to segregation of unlike hydrophobic domains trapped within the same micelle core, have been produced via self-assembly of block copolymer mixtures in tetrahydrofuran/water solution. The mixture is composed of two/or more block copolymers with distinctive hydrophobic blocks but the same poly(acrylic acid) (PAA) hydrophilic block. By taking advantage of the complexation in the hydrophilic corona between the acid side chains of the PAA block and added organoamine molecules, unlike hydrophobic blocks are trapped in the same micelle core and, consequently, locally segregate into compartments. Through designed kinetic pathways, block copolymer design and mixing ratios, both micelle compartment size and shape could be controlled to form multicompartment spheres, sphere-cylinder hybrid micelles and multicompartment cylinders. New mixtures using PAA-containing block copolymers with additional hydrophilic blocks or end-group functionalization produce multigeometry/multicompartment micelles with patterned surfaces in addition to multicompartment cores. [Preview Abstract] |
|
C1.00089: Nanocomposites Consisting of Nanoparticles with Multidentate PS Brushes Mixed with PS Matrices Hyemin Lee, Sanghyuk Wooh, Jaehoon Lim, Matthias Zorn, Rudolf Zentel, Kookheon Char In order to prevent massive phase separation of nanoparticles (NP) in a polymer matrix, the relevant hybridization of NPs with polymer matrices has proven to be an effective method for the high performance of nanocomposites in applications. The surface of inorganic (gold or QD) NPs of various size was modified with polystyrene (PS) polymer brushes, poly(styrene)-block-poly(cysteamine methyl disulfide), by the ligand exchange procedure. The disulfide groups in the PS brushes act as anchoring blocks for NPs. Different PS brushes were prepared with different total molecular weights and mole fractions of disulfide moieties. Compared with NPs dispersed in PS without disulfide anchoring groups, NPs anchored with PS brushes through disulfide groups were uniformly distributed within PS matrices. The dispersion of NPs within a polymer matrix was found to be influenced by the total molecular weight of PS brushes as well as the number of anchoring disulfide groups. Furthermore, the effect of the ratio between relative size of NP and the radius of gyration of a polymer brush as well as the grafting density of PS brushes anchored onto NPs on the NP distribution within a polymer matrix is discussed. [Preview Abstract] |
|
C1.00090: Controlling the Self-Assembly of Inorganic Nanoparticles within Conjugated Rod-Coil Block Copolymers Bryan McCulloch, Rachel Segalman Blends of conjugated polymers and inorganic nanoparticles have been investigated for numerous applications however optimization relies on precise control over the nanoscale morphology. We have designed a conjugated rod-coil block copolymer consisting of poly(3-(2'-ethyl)hexylthiophene)-b-poly(2-vinyl pyridine) (P3EHT-b-P2VP) which self assembles into controllable morphologies. Inorganic nanoparticles reside within the P2VP domain due to the favorable interactions between P2VP and the nanoparticle surface as well as the exclusionary effects of the liquid crystalline P3EHT. The nanoparticle location can be tuned by altering nanocrystal surface chemistry. These findings are used to develop a comprehensive understanding of the self assembly processes in conjugated rod-coil block copolymer nanocomposites. [Preview Abstract] |
|
C1.00091: Experimental and computational studies of finite-size effects in nanocomposites M.P. Roman, E.W. Skau, D.R. Stevens, L.N. Downen, T.J. Hoffman, L.I. Clarke Polymeric nanocomposites are formed when a nanometer-sized particle is embedded within a supporting matrix. Such composites can also be nanostructured - that is, shaped so that characteristic sample length scales may be similar to at least one dimension of the embedded particle [1]. This is particularly true for long aspect-ratio particles such as nanotubes where the length of the particle can approach or exceed the thickness of a thin nanocomposite film or a nanofiber diameter. In these cases, the formation of a particle network (for instance, for mechanical or electrical conductivity enhancement) is affected. We present experimental electrical conductivity and 3-D continuum Monte-Carlo simulation results on such finite-sized percolation effects, which can occur whenever any dimension of the sample is less than ca. 10 times the longest dimension of the particle.\\[4pt] [1] D. R. Stevens, L. N. Downen, and L. I. Clarke, \textit{Phys. Rev. B} \textbf{78}, 235425 (2008). [Preview Abstract] |
|
C1.00092: Nanoparticle Surface Functionalization for Improved Dispersion in Network Composites Adam Richardson, Olivia McNair, Gregory Strange, Mark Early, Daniel Savin Incorporation of inorganic nanoparticles into crosslinked networks has resulted in greater toughening behavior with lower filler content compared to traditional composites. The characteristics that provide these desirable qualities are also responsible for their poor dispersion and, consequently, limiting wide commercial use. This work aims to demonstrate how excellent dispersion can be obtained easily and efficiently in different networks through nanoparticle surface modification. Both epoxy/Jeffamine and thiol-ene based networks were examined with differing molecular weight and chemical functionality tethers. The aggregation behavior of nanocomposite samples were monitored optically and using TEM. Thermomechanical properties were studied using DSC, DMA and MTS. The Tg was dependent on both nanoparticle incorporation and functionality. Toughening was observed in some, but not all, cases. [Preview Abstract] |
|
C1.00093: Effect of Metal-Dielectric Interface on Capacitor Functions of Ag-Polymer Nanocomposites at Low Frequency ($<$ 1 MHz) Ataur Chowdhury, Abhijit Biswas, Ilker Bayer Metal-dielectric interfaces greatly influence the capacitor functions of nanodielectric composites. Nanodielectric composites of silver in PMMA were fabricated by electron-beam-assisted vapor phase codeposition at ambient temperature ($\sim $ 35\r{ } C) in high vacuum. The fabricated samples containing 15- 65{\%} silver reveal unique interfacial structure as studied by X-ray and atomic force microscopy. The capacitance of the as prepared samples were measured with an Agilent LCR meter at frequencies ranging from 20 Hz to 1 MHz. All nanodielectric composites show similar capacitor characteristic with a capacitor density of about 2.0 nF at 20 Hz to about 0.2 nF at 1 MHz., revealing continuous decrease in capacitor density with increasing frequency. This continuous decrease is a direct result of the interface between the silver granules and the dielectric material. This behavior, however, is in clear contrast with our recent study of BTO-PMMA nanocomposites (A. Biswas, et al., NNL, Vol. 1, 111-118, 2009), which show a stable capacitor function over a wide frequency range (20-80 MHz). [Preview Abstract] |
|
C1.00094: A Robust Model for Predicting Charge Mobility in a Random CNT Composite Sample Joshua Brown, Pedro Derosa Experimental results have shown that Carbon Nanotube (CNT) concentrations have significant impact on the conductivities of CNT polymer composites. Two charge transport mechanisms have previously been observed in these composites: covalent hopping and tunneling. Using these mechanisms as a foundation a robust Monte Carlo simulation has been realized. The simulation first creates a CNT composite sample under different initial conditions such as concentration, tortuosity and length. The charge mobility of the sample is then predicted under an applied electric field for CNT concentrations below and above the percolation threshold. [Preview Abstract] |
|
C1.00095: Effect of Single-Walled Carbon Nanotubes on Glass Transition Behavior in Polystyrene Brian Grady, Warren Ford, Abhijit Paul Our group previously investigated (Macromolecules, 2009, 42, 6152) the effect of nanotube addition on the glass transition temperature (Tg) and the heat capacity change at the glass transition (Delta Cp). Tg increased with nanotube addition by $\sim $7\r{ }C at 1 wt{\%} added nanotubes, while the delta Cp had the same qualitative behavior, but with a $\sim $20{\%} decrease instead of an increase. We have extended this work to polymer grafted-to nanotubes, with polystyrene molecular weights of 2800, 15,000 and 50,000 g/mol; the weight fractions of grafted chains were approximately the same. For the two higher grafting densities, Tg showed the same qualitative behavior but quantitatively the increase in Tg was closer to 9\r{ }C. Composites with 50 K grafted nanotubes were statistically identical in terms of the Tg and Delta Cp, although the latter at high nanotube concentrations (20 wt{\%}) did show some anomalous behavior. The decrease in Delta Cp for composites made with the nanotubes having the highest grafting density was linear with added grafted nanotubes to a maximum of a $\sim $35{\%} decrease. Delta Cp for the materials made with 15 K grafted nanotubes showed either a small decrease, or no change in Delta Cp. [Preview Abstract] |
|
C1.00096: Deformation and fracture of Coarse-grained Model of Filled Rubber Composites Katsumi Hagita, Hiroshi Morita, Masao Doi, Hiroshi Takano We presented a result of coarse-grained Molecular Dynamics simulation of filled polymer melts with Sulfur-crosslink under deformation based on the Kremer-Grest Model. Under uni-axial deformation (extension) by setting Poisson's ratio to less than 0.5, facture of this polymer nanocomoposites occurs due to volume increase for increasing the strain. In order to study facture behavior, we use the original Lennard Jones potential formula (with attractive part) as interaction between polymers. The size of simulation box under periodic boundary conditions (PBC) is set to about 133nm. We put 2048 fillers, 5120 polymer chains of 1024 particles, and many crosslink into the PBC box. Due to the crosslink, all polymer chains are connected to one network gel. One filler consists of 320 particles of the C320 fullerene structure. A repulsive force from the center of the filler is applied to the particles of C320 in order to make a sphere whose diameter is about 7nm. We can observe the fracture occurs due to void created near surface of fillers for the case that interaction between polymer and filler is relatively non- attractive. Various cases of Poisson's ratio and interaction between polymer and filler are examined. [Preview Abstract] |
|
C1.00097: SEMICONDUCTORS |
|
C1.00098: Photocatalytic Activity of TiO$_{2}$ Thin Films Obtained by the Sputtering RF in Wastewater Jairo Armando Cardona Bedoya, Wilmer Asmed Sanchez Velandia, Miguel Iban Delgado Rosero, Alex Enrique Florido Cuellar, Orlando Zelaya Angel, Julio G. Mendoza Alvarez The photocatalytic activity of TiO$_{2}$ thin films in wastewater, under an UV irradiation, is studied. The films were prepared on corning glass substrates by the sputtering RF technique. We present evidence on the photocatalytic degradation, carried out by advanced oxidation processes (AOPs) in domestic wastewater pretreated with UASB (upflow anaerobic sludge blanket) reactors. TiO$_{2}$ films were illuminated with ultraviolet light during a time of 4 hours ($\lambda \quad \cong $ 264 nm). We could see the effect of degraded operation in the absorbance measurement using UV-VIS spectrophotometry. The results show an increased rate of degradation of the wastewater by 30{\%} compared to the values reflected biologically treated wastewater by anaerobic reactors. [Preview Abstract] |
|
C1.00099: Afterglow Study of ZnS:Cu,Co Water-soluble Nanoparticles and Potential Applications Lun Ma, Wei Chen ZnS:Cu,Co water-soluble afterglow particles with average size of 4 nm have been prepared by using simple wet chemistry method. The X-ray diffraction pattern of the nanoparticles shows a cubic zinc blende structure as the synthesis temperature is low comparing with solid state reactions. The nanoparticles have two photoluminescence emission peaks. The blue emission is from sulfur defects (vacancies), while the green emission is from Cu$^{2+}$ luminescent center which also contributes to the particle's afterglow. The presence of co-dopant Co$^{2+}$ is critical to perform the afterglow of these nanoparticles. The afterglow intensity and decay vary on different Cu$^{2+ }$and Co$^{2+}$ doping levels. Further conjugation of ZnS:Cu,Co nanoparticles and photosensitizers presents a new method for deep cancer treatment in photodynamic therapy. The successful afterglow observation from water-soluble nanoparticles may find many new applications in biological imaging, detection and treatment. [Preview Abstract] |
|
C1.00100: Characterization of GaN grown on tilt-cut $\gamma $-LiAlO$_{2}$ by molecular beam epitaxy Wen-Yuan Pang, Ikai Lo, Yu-Chi Hsu, Cheng-Hung Shih, Chia-Ho Hsieh, Ming-Chi Chou The non-polar GaN film is a potential candidate for high-efficient optoelectronic devices. This study reports on the characterization of GaN grown on tilt-cut $\gamma $-LiAlO$_{2}$ by plasma-assisted molecular beam epitaxy. The (100) $\gamma $-LiAlO$_{2}$ substrate was tilt-cut about the angle of 11 degree to in-plane. It was found that the GaN thin film tilts to match the atoms of (100) $\gamma $-LiAlO$_{2}$. The basal plan stacking fault and the interface between substrate and thin film have been investigated by transmission electron microscopy. In addition, the characteristics of GaN films for different growth temperatures were studied by X-ray diffraction, scanning electron microscopy, and photoluminescence measurements. From the full width at half maximum of X-ray rocking curve, we found that the quality of GaN film can be improved by tuning the growth temperature. The crystal structure, film surface, and optical properties of the samples will be discussed, as well. [Preview Abstract] |
|
C1.00101: Characterization of $M$-plane GaN film grown on $\beta $-LiGaO$_{2}$ (100) by plasma-assisted molecular beam epitaxy Chia-Hsuan Hu, Ikai Lo, Cheng-Hung Shih, Wen-Yuan Pang, Ying-Chieh Wang, Mitch M.C. Chou Lithium gallate (LiGaO$_{2})$ has an orthorhombic crystal structure that can be described as a wurtzite-like structure. The\textbf{\textit{ M}}-plane basis of GaN wurtzite structure is nearly matched to the selected lattice axes of pseudo-hexagonal LiGaO$_{2}$. \textbf{\textit{M}}-plane GaN thin films have been grown on $\beta $-LiGaO$_{2}$ (100) substrates by plasma-assisted molecular-beam epitaxy in our group. Pure \textbf{\textit{M}}-plane GaN crystal films have been verified by the measurements of x-ray diffraction, micro-Raman scattering, polarization-dependent photoluminescence and atomic force microscopy. The measurements of x-ray diffraction and micro-Raman scattering exhibited the evidences of large compressive stress on the \textbf{\textit{M}}-plane GaN thin films. Based on experimental results, we showed that the large compressive stress is the major source leading to the peeling of \textbf{\textit{M}}-plane GaN thin film off substrate after thermal recycles. [Preview Abstract] |
|
C1.00102: Effect of substrate induced strains on the magnetic and ferroelectric properties of epitaxial bilayer thin films of lead zirconate titanate and cobalt ferrite Devajyoti Mukherjee, Tara Dhakal, Robert Hyde, Pritish Mukherjee, Hariharan Srikanth, Sarath Witanachchi Epitaxial bilayer thin films of cobalt ferrite (CFO) and lead zirconium titanate (PZT) were deposited on MgO (100) and SrTiO$_{3}$ (STO) (100) substrates by pulsed laser deposition. The structural properties were characterized using X-ray diffraction and atomic force microscopy. The magnetic properties were measured at 10 K and 300 K in both parallel and perpendicular magnetic fields. The CFO-PZT bilayers showed enhanced or reduced magnetization compared to the single layer CFO films depending on the substrate of deposition. The ferroelectric properties of the CFO-PZT bilayers showed enhanced polarization compared to PZT single layer films on both types of substrates. A strain compression-relaxation mechanism was proposed in order to explain the structure-property relationships in the CFO-PZT bilayers. [Preview Abstract] |
|
C1.00103: Photochemical synthesis of porous silicon thin films Olivia Skeen, Toni Sauncy Porous silicon thin films were produced by photochemical synthesis~with a solution of hydrofluoric acid (HF) and the oxidizer cobalt~nitrate (Co[NO$_{3}$]$_{2})$. An 11mW HeNe laser was used during synthesis to produce the local electric field~necessary for the formation of the porous matrix on the surface of the~crystalline silicon substrate. Substrates used were n-type (Antimony), and p-type (Boron). Samples~prepared with variations in process time from 15 minutes to 5 hours~were examined using photoluminescence, SEM and Raman spectroscopy. Results indicate that the presence of the~oxidizer during synthesis enhances the intensity and persistence of p-Si~photoluminescence when~compared with samples prepared using only HF. In addition, post process~analysis reveals that the porous layer on the samples is present only~on samples processed for less than 4 hours. [Preview Abstract] |
|
C1.00104: Bipolar resistive switching in Ba$_{0.5}$S$_{r0.5}$Co$_{0.2}$Fe$_{0.8}$O$_{3}$ thin films Zhongwen Xing, Naijuan Wu, Alex Ignatiev Five-component perovskite Ba0.5Sr0.5Co0.2Fe0.8O3 (BSCFO) thin films are reported to have polarized electrical-pulse-induced resistance (EPIR) change at room temperature. Such an EPIR change is attributed to a combined effect of the resistance change of the Schottky barrier and the oxygen ion/vacancy movement near the interface. In the BSCFO, the lower threshold voltage of the electric pulse that leads to nonvolatile resistive changes is close related to its higher oxygen permeability. [Preview Abstract] |
|
C1.00105: Effect of spin-orbit interaction on the ballistic transport properties of nanowires Sheehan Ahmed, Ryan Brennan, Godfrey Gumbs, Antonios Balassis, Danhong Huang We calculated the effects of spin-orbit interaction (SOI) on the energy bands, ballistic conductance ($G$) and the electron-diffusion thermoelectric power ($S_{\rm d}$) of a nanowire by varying the temperature, electron density and width of the wire. We used the effective mass approximation in a model for the quasi-1D electron system that includes a Rashba potential lateral confinement of the 2DEG and a quasi-square potential well confinement transverse to the 2DEG. Both terms ($\alpha$ and $\beta$) give rise to SOI coupling which affects significantly the band structure obtained from numerical solutions of a pair of coupled equations. Comparing our model with the already published work where harmonic confinement was employed to describe the transverse confinement, we found that the energy bands are different and, in addition to crossing effect of the transverse energy bands, there is also anticrossing for specific values of the wavevector $k_y$ along the wire. The $\beta$-term of the Hamiltonian causes a displacement and a deformation of the transverse energy band structure which is more pronounced for large values of the wave vector. [Preview Abstract] |
|
C1.00106: Investigation of first principle thermoelectric properties of compound semiconductor Cem Sevik, Alper Kinaci, Tahir Cagin We analyze relevant electronic and transport properties of several different compound semiconductors, Cu$_{2}$ZnSnX$_{4}$, (X = S, Se, Te), Cu$_{2}$CdSnSe$_{4}$, and Cu$_{3}$SbM$_{3}$, (M = Se, S) to assess their potential as thermoelectric materials. Using density functional theory and Boltzmann transport equations, we determine Seebeck coefficients, conductivities, and power factors for each compound. To assess their potential application as thermoelectrics, we calculated a simple measure: ``maximum'' thermoelectric figure of merit, $ZT_{max}$ at experimentally amenable doping levels. We compared this with results for other well known bulk thermoelectrics (Bi$_{2}$Te$_{3}$ and SrTiO$_{3})$. However, our calculations indicate that it is not possible to reach ZT values higher than 1, so that these materials to be competitive with other materials for power generation and refrigeration applications. [Preview Abstract] |
|
C1.00107: Transport Anisotropy of Epitaxial VO$_{2}$ films grown on (100) TiO$_{2}$ Salinporn Kittiwatanakul, Jiwei Lu, Stuart Wolf Vanadium dioxide (VO$_{2})$ exhibits a metal semiconductor transition (MST) at 340 K. This transition is accompanied by the abrupt change in the electrical conductivity, optical transmittance and reflectance in infrared region, which can be used in the electronic devices such as temperature sensors and electric switches. In this study, Reactive Bias Target Ion Beam Deposition was used for epitaxial VO$_{2}$ thin film growth on TiO$_{2}$ (100) substrates. The out-of-plane and the in-plane XRD scans have been performed to confirm the single phase VO$_{2}$ and the epitaxial relationship between the film and the substrate. The hall bars along the in-plane c-axis and b-axis of R-VO$_{2}$ were fabricated via the photolithographic process. It is found that the maximum conductivity was parallel to c-axis, while the minimum conductivity was parallel to b-axis. The conductivity anisotropy persisted through the metal semiconductor transition. The conductivity anisotropy ratio $\sigma _{c}$/$\sigma _{b}$ was found to be $\sim $16.2 at 300 K, much larger than that of single crystal VO$_{2}$. The temperature dependent anisotropy of the carrier concentration and the mobility is to be discussed. [Preview Abstract] |
|
C1.00108: Transport Characteristics of Amorphous Borocarbides: A Variable Range Hopping Treatment Naseer Dari, Donald Priour, Jr We calculate the temperature dependent conductivity of amorphous borocarbide materials within a variable range hopping framework. We study the impact of disorder on borocarbide transport characteristics by beginning with a regular rombahedral lattice of periodically placed icosahedral arrangements of boron and carbon atomic species. A self consistent numerical procedure is used to calculate the charge occupancy factors. Three dimensional lattices containing several hundred icosahedral clusters are considered; disorder is introduced in the form of random translational displacements of the icosahedral cages. In addition, we use stochastic rotations about three independent randomly selected axes to implement orientational disorder for each of the icosahedral clusters. We find the sensitivity to random lateral displacements of the boron-carbon icosahedra to be on the order of 5\%, whereas the effects of even appreciable orientational disorder appears to be negligible within the assumptions of our model. In sum, we find temperature and the density of icosahedral clusters to have the strongest effect on the conductivity, while the transport characteristics are largely robust with respect to the introduction of disorder. [Preview Abstract] |
|
C1.00109: Temperature dependent adsorption and dissociation of water molecules on the Si(001)-$(2\times1)$ surface Ja-Yong Koo, Yong-Sung Kim, Hanchul Kim, Sang-Yong Yu The dissociative adsorption of water molecules on the Si(001)- $(2\times1)$ surface was studied up to 850 K by scanning tunneling microscopy (STM). A water molecule is dissociated into on-dimer (OD) and inter-dimer (ID) configurations and the population ratio $n_{ID}$/$n_{OD}$ changes from $\sim$5 at room temperature to $\sim$0.5 above 500 K. A quantitative analysis was made by considering the flipping motion of Si dimers to overcome the discrepancy between the experiment and theoretical estimations from the model of simple energy barrier. The flipping motion of Si dimers plays a dominant role in the dissociation of water molecules on the Si (001)-$(2\times1)$ surface. [Preview Abstract] |
|
C1.00110: Asymmetric Double Quantum Dot Energy States in a Quantizing Magnetic Field Norman Horing, Spencer Horton, Sina Bahrami This work is concerned with electron states and propagation in a two-dimensional asymmetric quantum double-dot system embedded in a two dimensional host sheet subject to Landau quantization. The two dots are represented by two Dirac delta function potential terms of differing depths each of which would support just one subband state if the other were absent, if there were no magnetic field. The integral equation for the Schrodinger Green's function for this double-dot system is solved exactly in closed form in terms of the infinite sheet Green's function for two dimensional electrons subject to Landau quantization with no quantum dots. The dispersion relation for the double dot subband energies is formulated and examined by analyzing the frequency poles of the Green's function with Landau-quantization-like splintering of the levels by the magnetic field. The effects of the asymmetry in regard to the potential well depths are analyzed as functions of the well-depth difference and dot-separation. [Preview Abstract] |
|
C1.00111: Core level XAS study on high pressure solids Min Wu, Jianzhong Jiang, John Tse We investigated the K and L-edge core level X-ray absorption spectra of solid CO2 and Silica (SiO2) under high pressure, using methods based on pseudopotentials and all-electron Bethe-Salpeter Equation. A comparison of the calculated spectra with both methods is present. We found that the calculated Si K and L-edge spectra of quartz and stishovite are in good agreement with experiment. Particularly, the origin of the second peak in the O K-XAS observed in compressed silica which is often used as an indication of six-fold coordinate is explained. Preliminary calculations show both the full core hole and no core hole approximations failed to reproduce quantitatively the observed C and O K-edge XAS. [Preview Abstract] |
|
C1.00112: An Ab Initio Study of Hydrogenation induced Metallization of SiC001 (3x2) James Westover, Abdelkader Kara We will present results for the band structure of hydrogenated Silicone Carbide (001) (3x2) surface with various levels of hydrogenation. These band structures were obtained using density functional theory with a generalized gradient exchange correlation function. Further, the calculations reveal the following scenario. Initially, Hydrogen atoms saturate all the dangling bonds of the surface dimers. This in turns allows for the subsequent H atoms to bind with Si atoms in the second layer. Those new bonds for the appropriately hydrogenated surface cause a ``metallization'' of the surface. Hydrogenation beyond that brings the system to its semiconducting state. [Preview Abstract] |
|
C1.00113: Band offsets at semiconductor interfaces with hybrid functionals and the GW approximation Roberto Longo Pazos, Leeor Kronik, Jeffrey Neaton The ability to predict and understand how the electronic structure of a semiconductor is altered at an interface is important for many technological applications, carrier injection and confinement properties. While it is somewhat routine to compute band offsets at semiconductor interfaces with density functional theory (DFT) within standard approximations, mean-field Kohn-Sham band structures are well known to underestimate band gaps and neglect nonlocal correlations across the interface. Here, we use many-body perturbation theory within the GW approximation to compute band gaps and band offsets at a well-studied interface formed from two heterovalent semiconductors, GaAs and ZnSe, that have a small lattice mismatch. Comparing our results to calculations with standard DFT and hybrid functionals, we elucidate the quantitative importance of Fock exchange, and static and dynamic correlation effects, in developing an accurate picture of the electronic behavior at this interface, and in differentiating the interfacial electronic structure from that of bulk GaAs and ZnSe. [Preview Abstract] |
|
C1.00114: Electron affinities of d1 transition metal chloride clusters and onset of super halogen behavior Swayamprabha Behera, Jorly Joseph, Purusottam Jena Geometry, electronic structure, and electron affinity of d1 transition metal chloride clusters (MCl$_{n}$, M = Sc,Y, La; n = 1--5) have been calculated using density functional theory. Chlorine atoms are chemically bound in all cases except for MCl$_{5}$. The electron affinities of MCl$_{n}$ (n = 1--3) are small and increase only marginally as a function of n until the valence of the metal atom is consumed. Beyond this, they rise sharply and reach a value of 5.96, 6.03 and 5.90 eV for ScCl$_{4}$, YCl$_{4}$ and LaCl$_{4}$, respectively and remain high for n = 5. MCl$_{n}$, (n = 4,5) clusters, therefore, behave as superhalogens. Results are compared with available experimental data [Preview Abstract] |
|
C1.00115: Calculation of the Electronic Structure for the AlGaAs Quantum Well Chin-Sheng Wu Quantum wells are important in semiconductor lasers because they allow some degree of freedom in the design of the emitted wavelength through adjustment of the energy levels. We apply the various the well width w and barrier height $V $ in order to match the device information made by Willander. Solving the Schr\"{o}dinger equation with exchange- correlation energy and effective mass of electrons for a finite potential will produce values of the energy levels within the well. Alternating GaAs-AlGaAs layers produce high and low energy gaps. The result is the generation of quantum wells. The electrons in the donor section AlGaAs diffuse into the low band gap GaAs section, where is free of impurity atoms, therefore the effective mass of electrons reduces and the mobility increases. Dispersion relations in conduction band and valence band are applied for the effective mass approximation. Because of the presence of quantum wells the electrons have discrete energies and these appear as peak in the absorption measurements. [Preview Abstract] |
|
C1.00116: Carrier cooling and Auger heating in Si doped InN thin films Y.-G. Zeng, D. -J. Jang, C.-F. Tzen, M.-E. Lee, L.-W. Tu Silicon doped InN thin films grown on sapphire substrates by plasma-assisted molecular beam epitaxy have been studied using time-resolved photoluminescence (TRPL) upconversion technique. The back ground carrier densities vary from 6.2$\times $10$^{18}$ to 1.27$\times $10$^{20}$ cm$^{-3}$. The carrier temperature curves, derived from the TRPL at different time delay, indicate that the hot carriers lost most of their excess energy within the first 10 ps after photoexcitaiton. For low doping densities, the carrier cooling curves can be explained by carriers releasing excessive energy through the carrier--LO-phonon interaction. The extracted effective phonon emission times decreased as the photoexcited carrier concentration reduced. The radiative and nonradiative decay rates were obtained with the TRPL signals and the nonlinear dependence of the PL intensity on the carrier concentration. The derived radiative recombination rates were consistent with the theoretical predications. The Auger recombination was found to increase with the doping concentration. The reduced carrier cooling rates for large doping densities can be accounted for by the Auger heating occurred during carrier relaxation. [Preview Abstract] |
|
C1.00117: Radiative and nonradiative recombination rates of Si:InN thin films S.-F. Wang, D. -J. Jang, C.-F. Tzen, M.-E. Lee, L.-W. Tu Silicon doped InN thin films with background carrier densities vary from 6.2$\times $10$^{18}$ to 1.27$\times $10$^{20}$ cm$^{-3}$ were investigated by time-resolved photoluminescence (TRPL) upconversion technique. The radiative and nonradiative decay rates as a function of carrier density were derived from the TRPL signals. The Shockley-Read-Hall, radiative recombination, and Auger recombination coefficients were obtained by fitting the derived decay rates with the rate equation. The defect density can be determined from the differences of doped and undoped carrier densities. We found that the SRH coefficient is proportional to the defect density. The capture cross sections, determined from the SRH coefficient, defect density, and thermal velocity, were 1.5$\sim $3.0 $\times $ 10$^{16}$ cm.$^{2}$ The radiative decay times determined from the rate equation were compared with those determined by a model developed by Gourdan and Lavallard, which is recently used to determine radiative lifetimes of InN by several reports. We found the discrepancy of radiative lifetimes determined by these two approaches is attributed to the large nonradiative recombination rates in these samples. [Preview Abstract] |
|
C1.00118: Differential reflectance study of InN M.-S. Wang, D. -J. Jang, M.-E Lee, L.-W Tu Time-resolved differential reflectance (TRDR) of Si:InN thin films grown on sapphire substrates by plasma-assisted molecular beam epitaxy were investigated. The background carrier densities of 4.4 $\times $10$^{18}$ $\sim $ 1.27$\times $10$^{20}$ cm$^{-3}$ were measured by van der Pauw Hall geometry for undoped and Si doped InN thin films. The energy of the degenerated pump and probe beams were tuned from 1.37 to 1.65 eV. All the signals were measured at room temperature. The intensity and the temporal position of the TRDR peak intensity increase with the pumping intensity and show trivial dependence on photoexcitation energy. The TRDR intensity exhibits single-exponentially decay for photogenerated carrier density up to 6$\times $10$^{18}$ cm$^{-3}$. For higher excited carrier density, two decay times must be employed to describe the decay behavior. The rate equation includes the Shockley-Read-Hall, radiative, and Auger recombination were used to fit the decay rate. While the Auger recombination is insignificant for low photoexcitation, it becomes the dominated recombination mechanism within 10 ps for high photoexcitaiton. The dominated recombination mechanism for different pumping energy will be discussed. [Preview Abstract] |
|
C1.00119: Precision Bandgap Control of Titanium Dioxide Nanoparticles by Ultrasonication Robby Flaig, Lester Lampert, Jorge Camacho, James Hamilton TiO2 is a commonly used material in many areas of industry including photocatalysis and pigments. Band gap narrowing and particle size are engineered with a high level of control. We report precision bandgap control by ultrasonication in novel stable solvent systems in which unmodified TiO2 can be suspended. The effects of ultrasonication in these unique solvent systems are monitored by optical band gap (UV-Vis), scanning electron microscopy (SEM), atomic force microscopy (AFM), and x-ray diffraction (XRD). [Preview Abstract] |
|
C1.00120: Seung-Nelson representation for singular thin sheets Thomas Witten, Jin Wang We extend the popular Seung-Nelson model [1] to better study thin elastic sheets with singular or multi-scale structures, which are common phenomena in thin sheets [2]. Because it requires a uniform distribution of lattice points over the simulated sheets, the original model is ill-equipped to study these singular structures. Our extended model retains the essence of the original one, but it allows lattice points to be concentrated as needed in regions of large curvatures. We will compare the two methods by applying them to study the energy of the core region of a developable cone [3]. \\[4pt] [1] H. S. Seung and D. R. Nelson, {\sl Phys. Rev. A} {\bf 38}, 1005 (1988). \newline [2] T. A. Witten, {\sl Rev. Mod. Phys.} {\bf 79}, 643 (2007). \newline [3] E. Cerda, S. Chaieb, F. Melo, and L. Mahadevan, {\sl Nature} {\bf 401}, 46 (1999). [Preview Abstract] |
|
C1.00121: Hamiltonian monodromy Chen Chen, John Delos, Megan Ivory, Seth Aubin We say that a system exhibits monodromy if we take the system around a closed loop in its spectrum space, and we find that the system does not come back to its original state. We report a method for experimental realization of a newly discovered dynamical manifestation of monodromy by investigating the behavior of atoms in a trap. The trapping potential has long range attraction to and short range repulsion from the center. Calculations include two parts. First we consider atoms as classical particles for which we can choose any desired set of initial conditions. As was shown previously for different systems, when we take the system around a monodromy circuit, a loop of initial conditions evolves into a topologically different loop. Second, we incorporate the limitations that would appear in experimental implementation. The atoms have a range of initial angles, initial angular momenta, and initial energies. Our work shows how real atoms can be driven by real forces around a monodromy circuit, and thereby shows how one can observe dynamical monodromy in a laboratory. Finally, we extend classical dynamical monodromy to quantum dynamical monodromy by examining wave function evolution under comparable conditions. [Preview Abstract] |
|
C1.00122: The complete interpretation of the fractions in quantum Hall effect Keshav Shrivastava We propose that the modified cyclotron energy is given by (h/2$\pi )\omega _{c}$(1/2)g(n+1/2) so that the fractional charge is given by the angular momentum with both signs of spin, j = $l \pm $ s. In addition to the (i) principal fractions given by (1/2)g our theory with effective charge e*=(1/2)ge, has (ii) resonances at $\nu _{1}-\nu _{2}$ and (iii) two-particle states at $\nu _{1}+\nu _{2}$ and there are (iv) clusters with spin $>$1/2, where $\nu $ is a filling factor. This theory explains all of the 101 fractions and full graphene series. The fractional charges of graphene [2] are also explained. The series also explains the even denominators for S=0,1,2, {\ldots}, as in electron clusters. The S=0, L=0, corresponds to half filled Landau level. S=1/2, L=0 with negative sign before s in j gives the zero-energy state. All of the predicted fractions agree with the data. \\[4pt] [1] K. N. Shrivastava, AIP Conf. Proc. 1150, 59-67 (2009). \\[0pt] [2] K. I. Bolotin, et al, Nature 462, 196(2009). [Preview Abstract] |
|
C1.00123: Trial Wavefunctions and Ground State Energies of Some Non-Laughlin Correlated Quantum Hall Systems John Quinn In the lowest Landau level (LL0), incompressible quantum liquid (IQL) states occur at the Laughlin-Jain sequence of filling factors $\nu = n (2 p n \pm 1)^{-1}$, where n and p are positive integers. In all of these states, Laughlin correlations (avoidance of pair states with the largest repulsion) are the cause. In the first excited Landau level (LL1), IQL states occur at $\nu' = \nu - 2 = 1/2$. This state and daughter states of Laughlin quasiparticles with $\nu_{QE} = 1/3$ cannot be caused by Laughlin correlations. Paired states described by the Moore-Reed Pfaffian wavefunction and by a novel wavefunction with different pairing correlations are studied as candidate wavefunctions. The energy of each of these states is evaluated analytically for an arbitrary pair pseudopotential $V(L_2)$, where $L_2$ is the pair angular momentum. Explicit results are derived for a six particle system. The generalization to N particle systems is proposed and compared for both trial functions. [Preview Abstract] |
|
C1.00124: Density functional study of the effects of doping and stoichiometry on gallium diffusion in gallium arsenide J.T. Schick, C.G. Morgan Previous experimental [1-4] and theoretical [5,6] work on the properties of diffusion of gallium within gallium arsenide has produced some results that are apparently at odds with each other. We present results of a wide theoretical survey of the point defects that form in this material with special attention paid to the formation and diffusion of excess-gallium-related point defects. In this study we applied density functional theory in the local density approximation [7]. Diffusion was examined through the use of the nudged elastic band method [8]. After considering the accuracy of the approximations used, the calculations yield information compatible with the experimental situation and capable of shedding light on areas of apparent disagreement.\\[4pt] [1] G B\"{o}sker \emph{et al.}, Phys.\ Rev.\ B {\bf{52}}, 11927 (1995). [2] G B\"{o}sker \emph{et al.}, J. Appl.\ Phys.\ {\bf{86}}, 791 (1999). [3] H Bracht and S Brotzmann, Phys.\ Rev.\ B {\bf{71}}, 115216 (2005). [4] H Bracht \emph{et al.}, Physica B {\bf{308-210}}, 831 (2001). [5] K Levasseur-Smith and N. Mousseau, J. Appl.\ Phys.\ {\bf{103}}, 113502 (2008). [6] PA Schultz \emph{et al.}, Mod.\ and Sim.\ in Mat.\ Sci.\ and Engr.\ {\bf{17}}, 084007 (2009). [7] G. Kresse and J. Hafner, Phys. Rev. B {\bf{47}}, 558 (1993); \emph{ibid.} {\bf{49}}, 14251 (1994). [8] H. J\'{o}nsson \emph{et al.}, ``Classical and quantum dynamics in condensed phase systems,'' (World Scientific, 1998) Chap.\ 16, pp. 385-404. [Preview Abstract] |
|
C1.00125: Investigation of Mg- and Si- doped AlN epilayers by Transmission Electron Microscopy Bo Cai, M.L. Nakarmi Aluminum nitride (AlN) has emerged as a promising deep ultraviolet (UV) material for the development of optoelectronic devices operating in deep UV region. Low dislocation density AlN on sapphire substrate has been achieved by metal organic chemical vapor deposition technique. Doping in AlN is very crucial in order to use it in active devices. Silicon and magnesium are usually used for n- and p- type doping in III-nitride materials. We report on microstructure analysis of Mg- and Si- doped AlN epilayers by transmission electron microscopy (TEM). The samples were grown on low dislocation density AlN/sapphire templates. Cross section and plan view TEM images were taken to characterize the threading dislocations in these samples during the growth process. High resolution TEM images are also taken to study the detailed nature of the dislocations, and their generation and propagation. The TEM images will be compared with the undoped AlN epilayers to investigate the effect of doping in the generation/annihilation of threading dislocations. Implications of our finding for the applications in deep UV optoelectronic devices will be discussed. [Preview Abstract] |
|
C1.00126: Spin transport and spin minibands in a magnetic superlattice: dependence on geometrical and physical parameters Nammee Kim, Jinwoo Kim, Heesang Kim We have studied the spin miniband structure and the ballistic spin-polarized transport through a magnetic superlattice, formed by inhomogeneous magnetic field in a semiconductor nanowire. Based on the transfer matrix theory and the Bloch's theorem, we calculate the energy dispersion having spin miniband and minigap due to Bloch periodicity and spin dependent ballistic conductance for various geometrical and physical parameters. It is shown that full spin polarization in the ballistic conductance of the system occurs clearly for each spin, and that the fully spin polarized range for each spin can be enhanced by modulation of geometrical and physical parameters. [Preview Abstract] |
|
C1.00127: Magnetocurrent of a multiferroic resonant tunneling diode Nammee Kim, Heesang Kim We study the resonant tunneling magnetoresistance of a multiferroic resonant tunneling diode, which is hybridized of ferroelectric double barriers and a ferromagnetic quantum well. Magneto-current is calculated, focusing on its dependence on $\phi $, the angle between an external magnetic field and the spontaneous magnetic field in the diluted magnetic semiconductor quantum well, by using the non-equilibrium Green's function method. The magneto-current varies from zero to 440{\%}, and the spin polarization of the current varies from zero to 1 by changing the angle $\phi $. We also perform controlling of the transmission energy level by reversing the direction of dipole polarization in ferroelectric barriers. Therefore, the magneto-current and its current spin polarization through this multiferroic resonant tunneling diode can be manipulated either by the direction of the external magnetic field in the diluted magnetic semiconductor quantum well or by the direction of the dipole polarization in ferroelectric barriers. This study shows the possible application of this structure to a multiferroic spin device to control the amount of current and spin polarization of current through it. [Preview Abstract] |
|
C1.00128: Effect of disorder on the Curie temperature of GaMnN and InMnN diluted magnetic semiconductors Ahmad Alsaad The critical Curie temperatures of GaN, InN, CrN, and MnN diluted magnetic semiconductors and those of ordered and disordered diluted (Ga,Mn)N and (In,Mn)N magnetic semiconductors are investigated by using the classical Heisenberg model within the mean field approximation with the structural parameters are obtained from first principles total energy calculations. We show that Curie temperature depends on the Mn and Cr concentrations. Our calculations on these systems have shown that above room-temperature can be observed. Ferromagnetic stability in GaN, InN, CrN, and MnN is systematically studied. Our results indicate that 3d Mn and Cr impurities in GaN and InN favor the ferromagnetic state rather than the spin-glass phase. The mechanism behind this behavior is discussed and explained in details. [Preview Abstract] |
|
C1.00129: Spin resolved transverse electron focusing in wide leads due to diffuse collimation in InSb/InAlSb two-dimensional electron gases L.F. Cohen, A.M. Gilbertson, A. Korm\'anyos, C.J. Lambert, M. Fearn, T. Ashley, S.A. Solin Using the transverse electron focusing geometry, we report spin-resolved cyclotron motion in an InSb two-dimensional electron gas (2DEG). A zero field spin spitting$^{1}$ causes electrons from different spin subbands to have slightly different cyclotron radii in external field which manifest as a splitting in the first focusing peak.$^{2}$ Traditionally in focusing experiments, electrons are emitted and collected via quantum point contacts that host only a few open channels. We show that spin resolved electron focusing is observable in $wide$ leads with many open channels due to diffuse collimation of ballistic electrons emitted into the bulk 2DEG region. The results are compared to a semiclassical model$^{3}$ from which a Rashba-type spin-orbit coupling parameter of $\alpha = 5x10^{-11}$ eVm is deduced at 2 K. We compare these results to values determined from the beating of Shubnikov-de Haas oscillations.$^{4}$ We also present ballistic transport results extending over 3 $\mu$m.\\ $^{1}$A. M. Gilbertson, et al., Phys. Rev. B 77, 165335 (2008). $^{2}$L. P. Rokhinson, et al., Phys. Rev. Letts. 93, 146601 (2004). $^{3}$A. Kormanyos, Phys. Rev. B 82, 155316 (2010). $^{4}$A. M. Gilbertson, et al., Phys. Rev. B 79, 235333 (2009). [Preview Abstract] |
|
C1.00130: Spin-orbit coupling in InAs-based wurtzite quantum wells J.Y. Fu, Poliana H. Penteado, J. Carlos Egues By folding down the 8$\times$8 Kane model, accounting for the $s$-$p_z$ orbital mixing, we derive an effective Hamiltonian for the conduction electrons. In this derivation, we consider the renormalization of the spinor component of the conduction band wave function. In addition to the Rashba-type term arising from the bulk inversion asymmetry of the wurtzite lattice, we obtain the usual linear in momentum Rashba term induced by the structural inversion asymmetry of the well. We also find a new Rashba-like contribution, proportional to the well profile only and not to its derivative. We self-consistently calculate the spin-orbit coupling parameters for single and double wurtzite InAs-based wells with two subbands. By gating the structures, we find that the new Rashba term shows a distinctive voltage dependence as compared to that of the usual Rashba coupling. Finally, for the double-well case, we find that both the intersubband spin-orbit coupling and the Dresselhaus term for each subband show a resonant behavior for the symmetric configuration of the well. [Preview Abstract] |
|
C1.00131: 2D Waveguides as spin devices: spin-orbit and lead effects Lilia Meza-Montes Straight waveguides with different shapes have been proposed as devices to control the spin polarized transport, with Rahsba spin-orbit interaction as the mechanism to induce spin mixing. Several theoretical approaches have been applied, mostly based on transfer-matrix method. Here, the Schroedinger equation is solved by means of the Finite-Element Method,finding good agreement with previous calculations. It is known that positions of the leads influence the ballistic transport in this sort of cavities due to changes in the spatial symmetry. The role of the lead positions on the transmission and, in turn on the spin polarization, will be discussed for several geometries. The linear Dresselhaus interaction is taken into account to consider zincblende structure. Implications for quantum dots is also addresed. [Preview Abstract] |
|
C1.00132: First principles calculations of magnetic properties of Gd-doped ZnSiN J. Rufinus Diluted metal-doped chalcopyrite compounds have recently attracted a great attention due to some experimental confirmations on their ability to achieve high temperature ferromagnetism. Such a material would likely play a role in building future spintronic devices. First principles calculations of the magnetic properties of Gd-doped ZnSiN$_2$, a semiconductor chalcopyrite, have been performed using the density functional theory within generalized gradient approximation. Our results show, independent of the substitutional sites, the lowest energy structure is ferromagnetic. [Preview Abstract] |
|
C1.00133: Zitterbewegung-induced Spin Resonance in Quantum Wires Marco O. Hachiya, Gonzalo Usaj, J. Carlos Egues Recently, the \textit{Zitterbewegung} in quantum wires was proposed theoretically by Schliemann \textit{et al.} [1]. This effect is characterized by an oscillatory motion in the position and spin components of an electron wave packet injected along the quantum wire with spin-orbit coupling. We investigate the \textit{Zitterbewegung} evaluating time dependent expectation value for the spin operators. Here we consider the \textit{Zitterbewegung} in a multi-band quantum wire with both the Rashba and Dresselhaus spin-orbit interactions. We find that an external magnetic field perpendicular to the quantum wire can be used to tune the probability of spin flip, i.e., the resonance condition. A possible experimental scenario to observe this effect is proposed using injection via a quantum point contact.\\[4pt] [1] J. Schliemann, D. Loss, and R.M. Westervelt, Phys. Rev. Lett. \textbf{94}, 206801 (2005). [Preview Abstract] |
|
C1.00134: Deep level transient spectroscopic study of oxygen-implanted ZnO single crystal Ziran Ye, Guangwei Ding, Jincheng Fan, Chi Chung Ling ZnO single crystal samples were implanted by oxygen with the energy of 150keV. After the pretreatment of hydrogen peroxide [1], Schottky contacts were fabricated with Au film deposited by thermal evaporation. Deep level defects were studied by deep level transient spectroscopy (DLTS). The activation energy of the 0.29eV deep trap was observed in the as-implanted sample and samples anneal at 350 ${^\circ}$C , 650 ${^\circ}$C and 750 ${^\circ}$C. Three peaks were identified in the DLTS spectra of the 900 ${^\circ}$C sample, with the activation energies of 0.11eV, 0.25eV and 0.37eV respectively. The thermal evolutions of the deep levels up to the temperature of 1200 ${^\circ}$C were also investigated. \\[4pt] [1] Q. L. Gu, C. C. Ling, X. D. Chen, C. K. Cheng, A. M. C. Ng, C. D. Beling, S. Fung, A. B. Djuri\v{s}i\'c, L. W. Lu, G. Brauer and H. C. Ong, Appl. Phys. Lett. 90, 122101, (2007). [Preview Abstract] |
|
C1.00135: ABSTRACT WITHDRAWN |
|
C1.00136: Observation of defects in CuInSe$_{2}$ by 300kV aberration corrected scanning transmission electron microscope Akane Takeshita, Takayuki Tanaka, Tadahiro Kubota, Hideto Miyake, Hidetaka Sawada, Yukihito Kondo, Yoshifumi Oshima, Yasumasa Tanishiro, Kunio Takayanagi Vacancies (V$_{Cu}$, V$_{In})$ and substitutional atoms (In$_{Cu}$, Cu$_{In})$ in CuInSe$_{2}$ crystal, which is the key semiconductor material for thin film solar cell applications, were directly observed by 300kV aberration-corrected high angle annular dark field scanning transmission electron microscope (HAADF-STEM). The atomic columns of Cu, In and Se were independently observed from CuInSe$_{2}$ [100] crystal zone axis by HAADF-STEM. Some In and Cu columns showed reduced and increased intensities from that of column without defect, respectively. On the other hand, no defects in Se columns were observed. The intensity analysis suggests In substitution of Cu site (In$_{Cu})$ and Cu substitution of In site (Cu$_{In})$. The concentrations of Cu and In substitutions were evaluated based on comparison with the multi-slice calculation. [Preview Abstract] |
|
C1.00137: LaF3:Ce/CdTe nanocomposites for radiation detection application Mingzhen Yao Radiation detection demands new scintillators with high quantum efficiency, high energy resolution, and short luminescence lifetimes. Nanocomposites consisting of quantum dots and Ce$^{3+}$ doped nanophosphors may be able to meet these requirements. Here, we report the luminescence enhancement of LaF$_{3}$:Ce/CdTe nanocomposites which were synthesized by a wet chemistry method. The results show that CdTe luminescence in LaF$_{3}$:Ce/CdTe nanocomposites is enhanced about five times. Energy transfer, light reabsorption, and defect passivation are the likely reasons for the luminescence enhancement [Preview Abstract] |
|
C1.00138: Determination of property in semiconductors Carlos Figueroa, Ra\'ul Riera, Mart\'In Molinar In this work it is doing a comparative study of the most conventional semiconductors in electronics, such as silicon (Si), germanium (Ge) and gallium arsenide (GaAs). We present the mathematical development of the magnitude that determines the intrinsic semiconductor property, which is the concentration of charge carriers, and is discussed in each case with respect to temperature variation. On the other hand, in the case of extrinsic semiconductors is calculated potential barrier of a pn junction. The task to make in this work is to use the intrinsic concentration of each material and their respective potential barrier to verify their behavior in relation to temperature. In the case of reverse bias generates a graphical output capacitance associated with these quantities. It is also used matlab to solve the transcendental equation that defines the relationship between voltage, resistance and current of a semiconductor diode bias. These demonstrations and concepts are important because they govern the operation of basic electronic devices and can characterize the differences between the Si, Ge and GaAs. [Preview Abstract] |
|
C1.00139: SURFACES, INTERFACES AND THIN FILMS |
|
C1.00140: Modeling the Self- and Directed-assembly of Viruses on Surfaces Daniel Sullivan, George Gilmer, Cristian Ciobanu The exploitation of naturally self-assembling viruses has received much attention recently in regards to fabrication of nanomaterials and devices. Formation of dense viral mono- and multilayers as well as viral immobilization via chemospecific surface functionalization can be studied by modeling viruses as colloidal particles. We use a modified Lennard-Jones (LJ) potential, characterizing each colloid as an integrated collection of LJ particles, to describe intercolloidal and colloid-surface interactions. By carefully selecting the LJ interaction parameters and performing molecular dynamics simulations, we are able to replicate experimentally observed behavior of viruses on both strongly and weakly interacting surfaces in our surrogate colloidal system. Kinetic properties of the computational system are monitored and we find them to be in good agreement with predictions based on experimental data. We provide a basis for further investigation into the capabilities and limitations of modeling self-assembly of viral systems of technical interest using classical molecular dynamics. [Preview Abstract] |
|
C1.00141: Silicon Nanoparticle Formation Analysis and Optical Properties Daniel Frasier, Greg Spencer, Anup Bandyopadhyay, Wim Geerts In this study, the formation of silicon nanoparticles by thermal annealing of an initial silicon-on-insulator (SOI) structure is being performed. The SOI samples are synthesized by thermal oxidation of Si (100) wafers followed by magnetron and ion beam sputtering of a thin Si top layer. The thermal anneals are performed in a rapid thermal anneal system at temperatures ranging from 600\r{ }C to 900\r{ }C under atmospheric pressure of Ar gas. The nanoparticle formation process is being studied as a function of the thermal anneal maximum temperature, anneal time, and Si layer thickness. The annealed samples are measured by atomic force microscopy to determine the resulting nanoparticle size distributions and synthesis details. Electron microscopy is also being used for physical analysis in addition optical properties being studied through Effective Medium Approximations (EMA) proposed in the Lorentz-Lorenz (LL), Maxwell-Garnett (MG), and Bruggeman methods. Results for these experiments as well as comparisons with the work of others will be presented. [Preview Abstract] |
|
C1.00142: A study of the structure and dynamics of the interface between a nanoparticle and a surface: the case of Cu and Ag James Borrelli, James Westover, Abdelkader Kara We performed a Molecular Dynamics study using the Embedded Atom Method for interatomic potentials for silver and/or copper nanoparticles projectiles incident on Ag and/or Cu (100) surfaces. Nanoparticles in the range of 1 to 2 nm in diameter were used with incident energies ranging from 50 to 500 meV/atom; while the surface temperature is kept at a temperature ranging between 300 and 700K. After collision and thermalization, distributions of nearest neighbor distances show a variety of values that reflect the strength of the local bonding. Using a Real Space Green's Function approach, we have determined the vibrational densities of states and the corresponding thermodynamical functions for a limited number of cases. Results for the vibrational dynamics show a strong effect at the high frequency end of the densities reflecting the stiffness of the bond at the interface. Results for the vibrational enery, entropy, lattice heat capacity as well as Debye temperatures will be presented. [Preview Abstract] |
|
C1.00143: Cluster growth driven by long range de-wetting interactions in thin films Adi Constantinescu, Leonardo Golubovic, Artem Levandovsky Long range de-wetting inteactions acting across thin films, such as the van der Waals forces, may drive the formation of large clusters (tall multi-layer islands). We study, by analytic arguments and simulations, the growth of these clusters within a unified model explicitly incorporating de-wetting interactions. The ultimate cluster growth scaling laws at long times are universal: Short and long range de-wetting interactions yield the same coarsening exponents. However, long range de-wetting interactions introduce a long lasting early-time scaling behavior characterized by a slow growth of the cluster height/lateral size aspect ratio (i.e., a time-dependent Young angle). This stage of cluster evolution is characterized by effective coarsening exponents that we calculate from our simulations and from an analytic approach. [Preview Abstract] |
|
C1.00144: Insights in to hetero diffusion and growth: A DFT Study H. Yildirim, Subramanian Sankaranarayanan, Jeff Greeley We report the results of first principles calculations performed to study heteroatom diffusion on the terraces and step edges of fcc(001) surfaces on a series of 3d, 4d and 5d transition metals. For each adsorbate-substrate pair, we report the most stable adsorption sites and the corresponding adsorption energies. The corresponding terrace diffusion barriers are also reported, and periodic trends in the barrier heights are related to differences in adsorbate adsorption energies, cohesive energies of both adsorbate and substrate, and the differences in bond length/strength. Diffusion barriers and mechanisms at the step edges are also reported. Finally, insights into the possibility of 2D vs. 3D growth for each studied system are discussed via the calculated Ehrlich-Schwoebel barriers. [Preview Abstract] |
|
C1.00145: Initial growth of CrAs on GaAs(001)-c(4$\times$4)$\alpha$ Kazuma Yagyu, Shigeru Kaku, Junji Yoshino CrAs is a ferromagnetic material which has a hexagonal structure. It is, however, predicted by first-principles calculation that zincblende (ZB) CrAs shows ferromagnetism and has a halfmetaric electronic structure [1-3]. Although ferromagnetism of a CrAs epitaxial film was confirmed so far, its crystal structure is still unclear. It turned out that ferromagnetism originated at the interface. In this study, initial growth of CrAs film has been investigated with scanning tunneling microscopy at 80 K. CrAs was grown on a GaAs(001)-c(4$\times$4)$\alpha$ surface by means of exposing Cr as well as As$_4$ atoms at 250$^{\circ}$ C, followed by annealing at the same temperature. Randomly grown CrAs islands were observed form larger islands in proportion to the annealing time. Dimer structure which is similar to that of the substrate was confirmed on the surface of CrAs islands. This means that a CrAs island may have a ZB structure. The detailed structure and electric state of CrAs islands are discussed in the presentation. \\[4pt] [1] H. Akinaga et al., Jpn. J. Appl. Phys. 39 (2000) L1118 \\[0pt] [2] M. Shirai, Physica E 10 (2001) 143 \\[0pt] [3] A. Sakuma, J. Phys. Soc. Jpn. 71 (2002) 2534 [Preview Abstract] |
|
C1.00146: Effect of deposition temperature on the properties of ZnO thin films Ali Er, Ashraf Farha, Yuksel Ufuktepe The effect of deposition temperature on the surface morphology of zinc oxide thin films prepared by spray pyrolysis has been studied. The surface morphology of the films was studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The effects of substrate temperature during deposition on the structure with optical properties of ZnO thin films were determined. Surface parameters were calculated and compared for different thin films. It showed that the films were polycrystalline with hexagonal wurtzite structure and $c$-axis was perpendicular to the substrate. The grain size of the films changed from 240 to 440 nm with different substrate deposition temperatures. It was found that growth temperature has significantly affected the morphological (grains size, surface roughness) as well as optical properties of ZnO films. [Preview Abstract] |
|
C1.00147: ABSTRACT WITHDRAWN |
|
C1.00148: Investigation of Chemical Reactivity at the Co/CuO interface by X-ray Photoelectron Spectroscopy J. Edmondson, Y. Judie, A. Chourasia The technique of x-ray photoelectron spectroscopy has been utilized to investigate the chemical reactivity between cobalt and copper oxide at the Co/CuO interface. Thin films of copper (about 15 nm) were deposited on silicon substrates by the e-beam method. Such samples were oxidized in an oxygen environment in a quartz tube furnace at 400\r{ }C. The formation of CuO was checked by the XPS spectral data. Thin films of cobalt were then deposited on these CuO samples. The cobalt 2p, oxygen 1s and copper 2p regions were investigated by XPS. The magnesium anode (energy = 1253.6 eV) has been used for this purpose. The spectral data show chemical reactivity at the Co/CuO interface. The samples were annealed afterwards in air at 400\r{ }C. The spectral data were recorded at different take-off angles. Diffusion of copper through the cobalt overlayer with the formation of CuO is observed in the annealed samples. [Preview Abstract] |
|
C1.00149: High resolution scanning tunneling microscope (STM) image of SrTiO$_3$(100)-$\sqrt{5}\times\sqrt{5}-R26.6^\circ$ surface Ichiro Shiraki, Kazushi Miki, Shuheng Pan SrTiO$_3$(100)-$\sqrt{5}\times\sqrt{5}-R26.6^\circ$ surfaces were studied by scanning tunneling microscope (STM) in ultra-high vacuum conditions at room temperatures. STM images with truly atomic resolution in filled states, which have never been reported, were successfully obtained. The atomic arrangement in $\sqrt{5}\times\sqrt{5}$ unit cell is clearly seen. It is currently assumed that Ti and its fourfold site O atoms were separately imaged with varying bias voltages, which indicates that TiO$_2$ plane is a basic plane of $\sqrt{5}\times\sqrt{5}$ surface superstructures. The dI/dV images simultaneously taken with topographic images were also obtained in filled states. Comparing our experimental results with the previous works, especially a theoretical study of O-vacancy model [1] and an experimental and theoretical study of Sr adatom model [2], possible structures on $\sqrt{5}\times\sqrt{5}$ surfaces will be discussed.\\[4pt] [1] Z. Fang and K Terakura, Surf. Sci. 470, L75(2000)\\[0pt] [2] T. Kubo and H. Nozoye, Phys. Rev. Lett. 86, 1801(2001) [Preview Abstract] |
|
C1.00150: Molecular-scale Structure of Pentacene at Functionalized Electronic Interfaces Soonjoo Seo, Guowen Peng, Manos Mavrikakis, Rose Ruther, Robert Hamers, Paul Evans, Hee Jae Kang A dipolar interlayer can cause dramatic changes in the device characteristics of organic field-effect transistors or photovoltaics. We have conducted a series of experiments in which different molecular linkages are placed between a pentacene thin film and a silicon substrate. Interface modifications with different linkages allow us to predict the nature of tunneling through pentacene on modified Si surfaces with different dipole moment. The molecular-scale structure and the tunneling properties of pentacene thin films on modified Si (001) with nitrobenzene and styrene were examined using scanning tunneling spectroscopy. Electronic interfaces using organic surface dipoles can be used to control the band lineups of a semiconductor at organic/inorganic interfaces. Our results can provide insights into the charge transport characteristics of organic thin films at electronic interfaces. [Preview Abstract] |
|
C1.00151: Chemisorption of Anthracene on Cu(110) Jeronimo Matos, Abdelkader Kara We use density functional theory (PBE) to calculate the adsorption of an Anthracene molecule on Cu(110). Anthracene adsorbs at a height of 2 {\AA} above the surface and has a binding energy of 562 meV/molecule. We also found noticeable changes in the atomic and electronic structures of both the molecule and the substrate. The molecule is bent while the surface atoms experience a buckling. The dz$^{2}$ state of the copper atoms that are directly under carbon atoms presents new states near the Fermi level. These effects, in addition to a change in the work function, classify this system as chemisorption. We also determined the barrier for diffusion along the Cu(110) channel to be 77 meV. [Preview Abstract] |
|
C1.00152: A low friction coefficient between graphane coated surfaces Can Ataca, Hasan Sahin, Salim Ciraci Using first-principles calculations, we investigate the electronic properties and stability of recently synthesized 2D hydrocarbon in honeycomb structure, namely graphane. Varios charge analysis result that in graphane geometry negatively charged carbon atoms are sandwiched between positively charged hydrogen atoms bound from both sites. In addition high frequency vibration modes associated with C-H bonds are well separated from the rest of the spectrum. The repulsive interaction between two graphane layers due to mainly strong Coulomb interaction serves as if a boundary lubricant and prevents the sliding graphane surfaces from being closer to each other even under high normal forces. As a result, calculated lateral force variation generated during sliding has small magnitude under high constant loading forces. Superlow friction observed earlier between diamondlike carbon-coated surfaces can be understood strong and stiff carbon-carbon and carbon-hydrogen bonds which do not favor energy dissipation. [Preview Abstract] |
|
C1.00153: Tribological Properties of Atmospheric Pressure Plasma Polymerized Silica-like Films Bing Han, James Boerio Thin silica-like films were deposited on ferrotype plate and polycarbonate (PC) substrates with an atmospheric pressure plasma jet using hexamethyldisiloxane (HMDSO) as the precursor. It was found that the thickness and properties of the film were sensitive to the flow rate of the precursor, the deposition distance, and the radio frequency power Residual methyl groups were incorporated into the film when the distance between the nozzle of the plasma jet and the substrate was increased, or when the RF power used in deposition was decreased. This was confirmed by an increase in Si-CH$_{3}$ peak intensity in the Fourier transform infrared spectroscopy spectra of the films. The atomic compositions and chemical bonding of HMDSO-air plasma-polymerized SiO$_{x}$C$_{y}$ were analyzed by X-ray photoelectron spectroscopy. Low precursor flow rates produced smoother, more continuous, and more uniform films than high precursor flow rates. Low precursor flow rates produced films with atomic composition of Si:O:C=1:2.37:0.2. The deposited films presented mainly inorganic characteristics without adding oxygen or argon gas to the ionization gas mixture, as is common in the literature. Scratch resistance of the films was measured using a scratch tester with a diamond indenter under progressive load. Post scratch image and surface morphology of the substrate and the film was obtained by scanning electron microscopy and atomic force microscopy. [Preview Abstract] |
|
C1.00154: Diamagnetic Levitation Cantilever System for the Calibration of Normal Force Atomic Force Microscopy Measurements Jahn Torres, Jin-Woo Yi, Colin Murphy, Kyung-Suk Kim In this presentation we report a novel technique for normal force calibration for Atomic Force Microcopy (AFM) adhesion measurements known as the diamagnetic normal force calibration (D-NFC) system. The levitation produced by the repulsion between a diamagnetic graphite sheet and a set of rare-earth magnets is used in order to produce an oscillation due to an unstable mechanical moment produced by a silicon cantilever supported on the graphite. The measurement of the natural frequency of this oscillation allows for the calculation of the stiffness of the system to three-digit accuracy. The D-NFC response was proven to have a high sensitivity for the structure of water molecules collected on its surface. This in turns allows for the study of the effects of coatings on the structure of surface water. [Preview Abstract] |
|
C1.00155: Modeling of charged particles trajectories in order to optimize the design of a new, higher resolution, Time of flight- Positron Annihilation Induced Auger Electron Spectroscopy (TOF PAES) System Prasad Joglekar, L. Lim, Suman Satyal, Sushant Kalaskar, K. Shastry, Alex Weiss Time of Flight Positron Annihilation Induced~Auger Electron Spectroscopy~(TOF PAES) is a surface analytical technique with high surface selectivity. TOF PAES is used to study elemental composition, surface defects, and various energy loss mechanisms. Positrons incident on the sample surface at low energies can be trapped in an image-potential well just above the surface Prior to annihilation. Consequently it is possible to use positron annihilation related signals to selectively probe the top-most atomic layer. This poster presents the results of modeling of the charge particle beam transport system performed in connection with the optimization of the the design of the new TOF-PAES system currently under construction at U T Arlington. The system will incorporate a 2 m long drift tube in order to achieve better energy resolution than our previous TOF-PAES system design which used a 1 m long drift tube [Preview Abstract] |
|
C1.00156: Coherent x-ray surface scattering applied to Pt (001) Michael S. Pierce, Daniel Hennessy, Kee-Chul Chang, Vladimir Komanicky, Alec Sandy, Joseph Strzalka, Hoydoo You Scattering using highly coherent light provides information about the very small scale, but over a very large area suitable for an ensemble measurement. We have used coherent x-ray diffraction to study the surfaces Pt (001) single crystal surfaces at high temperature in vacuum and compare them with earlier measurements of Au (001) in similar conditions. Both metals possess a temperature dependent quasi-hexagonal surface reconstruction. The speckled scattering patterns can be quantitatively compared against each other to determine how quickly configuration is changing, even when the macroscopically the system appears in equilibrium. We have been able to obtain measurements of the dynamic temperature dependent surface processes for these two different systems. For Pt (001) we have also directly observed step-flow motion of the terraces, obtaining step-edge velocity as a function of temperature. Our results point to two very different mechanisms at work in lifting the surface reconstruction at high temperature in vacuum. [Preview Abstract] |
|
C1.00157: Ion neutralization as a probe to study electronic dynamics on clean and nanostructured surfaces Hee Suk Lee, Ryan O'Connell, Andrew Schmitz, John Shaw, Himadri Chakraborty Resonant charge transfer in ion-surface collisions is a classic tool to explore the surface electronic structure. Using the Crank-Nicholson propagation [1] we solve the time-dependent Schroedinger equation to simulate electrons' motion during the interaction of a H$^{-}$ anion with clean, nanostepped, and nanolayered metal surfaces. Ion survival from a clean surface is found to depend adiabatically on the metal band gap, but for the fast (diabatic) ion-speed perpendicular to the surface interactions with image states dominate [2]. For larger distance of ion's closest approach, however, the image interaction intrudes the adiabatic region. For the stepped surfaces, conversely, the survival is found to depend on the ion speed parallel to the surface from super-lattice sub-band effects, resulting in rich structures in the survival probability. Electrons that populate a nanolayered surface, in contrast, are found to modify the Shockley surface state and image states by inducing standing waves in the direction perpendicular to the surface.\\[4pt] [1] Chakraborty et al., \textit{Phys. Rev.} A \textbf{70}, 052903 (2004);\\[0pt] [2] Schmitz et al., \textit{Phys. Rev.} A \textbf{81}, 042901 (2010). [Preview Abstract] |
|
C1.00158: Electronic structure of oxygen di-vacancies on the (110) surface of rutile Willie Maddox, Branden Kappes, Christian Ciobanu We report the results of electronic structure calculations for the reduced surface of rutile (110). We have performed density functional theory calculations in the framework Hubbard-corrected generalized gradient approximation (GGA+U) to investigate the electronic signatures of single and di-vacancies on rutile (110) slabs, both neutral and positively charged. We have also carried out Bader charge analysis to evaluate the charge transfer that occurs upon the reduction of the rutile surface. We observe n-type character for the neutral systems and p-type character for the positive slabs. For U=3 eV, we observe mid-gap states for the neutral system, while for U=6 eV, we observe mid-gap states for the positively charged system as well. Bader analysis shows that the atoms associated with mid-gap states are those that experience a larger charge transfer. The dependence of the band gap on the U parameter was also investigated, and the results were compared with experimental observations in the literature for both electronic properties and for structural atomic relaxations. [Preview Abstract] |
|
C1.00159: ABSTRACT WITHDRAWN |
|
C1.00160: Electronic structure of alkali/Si(111):B semiconducting interfaces Laurent Chaput, Antonio Tejeda, Cedric Tournier-Colletta, Yannick Fagot-Revurat, Luis Cardenas, Bertrand Kierren, Daniel Malterre, Patrick Lefevre, Francois Bertran, Amina Taleb-Ibrahimi We have evidenced by LEED and STM a novel $2\sqrt{3} \times 2\sqrt{3}$ surface reconstruction for K, Rb and Cs on Si(111):B.\footnote{L. A. Cardenas et al, Phys. Rev. lett. 103, 046804 (2009)} The $2\sqrt{3}$ charge ordering occurring mainly in Si dangling bonds has been evidenced by high resolution photoemission measurements on core levels whereas the k-dependent photoemission spectral function agrees with the $2\sqrt{3}$ symmetry establishing a full gap higher than 1 eV.\footnote{C. Tournier-Colletta et al., Phys. Rev. B 82, 165429 (2010)} These results will be discussed in the light of ab initio calculations giving evidence for strong atomic distortions associated with a possible full charge ordering in dangling bonds, in connection to a large energy gap,\footnote{ L. Chaput et al., to be published} which is compatible with a bi-polaronic scenario. [Preview Abstract] |
|
C1.00161: Scanning Tunneling Spectroscopy Observation of New Type of Resonances on the Dense Pb Overlayer on the Si(111) Shin-Ming Lu, H.Y. Chou, Y.P. Chiu, W.B. Su, P.H. Chu, C.L. Jiang, C.S. Chang, H.L. Hsiao, Tien T. Tsong We use scanning tunneling spectroscopy (STS) to investigate the electronic structures of the dense Pb overlayers of 1$\times $1, $\surd $7$\times \surd $3 and stripe incommensurate (SIC) phases grown on the Si(111) surface. Although their atomic structures are all very different, very surprisingly the STS spectra of these three phases show a nearly identical oscillatory feature with two resonance peaks. These resonances are not the common quantum-well states but the energy bands originating from the dominant 1$\times $1 potential in these phases. However, the local electronic states found by STS on the $\surd $7$\times \surd $3 and SIC phase exhibit that the resonances can be affected locally by the superstructures of two phases. It reflects that there exists a weak additional one-dimensional periodic potential on the $\surd $7$\times \surd $3 phase and the SIC phase is of the local variation of the work function. [Preview Abstract] |
|
C1.00162: Effect of substrate strain on the charge dynamics of Nd$_{0.5}$Sr$_{0.5}$MnO$_3$ investigated by pump-probe technique Munkhbaatar Purevdorj, J.S. Kim, H.Y. Hwang, K. Myung-Whun We present the polarization and time dependent transmittance of Nd$_{0.5}$Sr$_{0.5}$MnO$_{3}$ (NSMO) thin films grown on SrTiO$_3$ (STO) (100) and STO (110) substrates. We used the normal transmission technique and the pump-probe technique for the measurement. While the transmittance of NSMO film on STO (100) is isotropic, the transmittance of NSMO on STO (110) measured with the electric field parallel to [-110] direction (E$//$[-110]) is larger than that of E$//$[100]. The time dependent transmittance change of NSMO film on STO (100) shows a sharp increase near the zero time delay and exponential decreases as the time delay between the pump and the probe pulse increases. The transmittance change of NSMO film on STO (110) shows almost the same time dependence. The time dependent transmittance change of NSMO film on STO (100) shows no significant polarization direction dependence, however the magnitude of time dependent transmittance change of NSMO on STO (110) is different depending on the polarization direction. The mechanism of the polarization dependence of transmittance change and the polarization direction independent relaxation will be discussed in terms of the substrate strain and its effect on the charge dynamics. [Preview Abstract] |
|
C1.00163: Angular Distributions and Total Yields of Bi Sputtered by 20 keV He$^{+}$, Ne$^{+}$ and Ar$^{+}$ Naresh Deoli, Lucas Phinney, Jose Pacheco, Duncan Weathers The angular distributions of neutral atoms sputtered from the surface of solid Bi by normally incident 20 keV He$^{+}$, Ne$^{+}$ and Ar$^{+}$ ions have been measured. The sputtered atoms were collected on pure aluminum foils under ultrahigh vacuum conditions, and the collector foils were subsequently analyzed using heavy ion Rutherford backscattering spectroscopy. The angular distributions obtained were integrated to determine the total sputtering yields of Bi for the different incident ions. Details of the measurements and data analysis are presented. [Preview Abstract] |
|
C1.00164: Segregation of impurities at $\gamma'$ (L12) / $\gamma$ (fcc) interfaces in a Ni-based superalloy De Nyago Tafen, Michael Gao One of the most technologically advanced energy conversion devices is the gas turbine used in aerospace jet engines and gas- fired land-based turbines for electricity generation, fabricated from Ni-based superalloys. However, these materials lack of long- term mechanical and microstructure stability, which is largely due to an excessive coarsening of $\gamma'$ that can cause substantial loss of creep resistance and mechanical instability at high temperatures. Theoretical prediction of the creep rate of these important compounds is very imperative, but yet is extremely challenging. Interfacial energy is one of the most important factors that control the coarsening kinetics of these important phases. It indirectly determines the creep resistance of the alloy through the coarsening rate of the strengthening precipitate phase. In this talk, we will present the results of various $\gamma'$/$\gamma$ interfaces of a Ni-based superalloy obtained using DFT calculations. Then, we will discuss the segregation of impurities at these interfaces. Minor alloying elements in superalloys can alter the interfacial energy between $\gamma$ and $\gamma'$, and change the strength behavior of the alloy. Alloying elements or impurity species can segregate to interfaces. A favorable segregation would result in enhancing the interfacial cohesion and thus lower the energy. [Preview Abstract] |
|
C1.00165: METALS |
|
C1.00166: Structural properties of nanometric HfN/VN superlattices P. Prieto, M. Villareal, C. Escobar, J.C. Caicedo, G. Cabrera, L. Yate, J. Esteve, A. Lousa HfN and VN systems have broadly been used as protective hard and anticorrosive coatings. [HfN/VN]n multilayered were deposited on silicon substrates by two target-r.f. magnetron sputtering with alternatively changing the sputtering plasma composition between pure Hf and V elements under a reactive mixture Ar/N$_{2}$. HfN/VN bilayer period varied from nanometric range (15 nm) to higher nanometric range (600 nm) values. Structural, morphological and stoichiometric of the coatings were analyzed by high angle and low-angle X-ray diffraction, X-ray photo electron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), atomic force microscopy (AFM) and cross sectional transmission electron microscopy (TEM). We determined multilayer period, $\Lambda $, and individual layer thicknesses. We found a cube-on-cube epitaxial growth structure with an epitaxial relationship between layers inside each columnar crystallite given by (111)[100]$_{HfN}$//(200)[100]$_{VN}$. [Preview Abstract] |
|
C1.00167: Synthesis and Characterization of Multifunctional Epitaxial Metal-oxide Films Jie Xiong, Junyi Zhai, Guifu Zou, Haiyan Wang, Li Yan, Mujin Zhuo, Yingying Zhang, Bowan Tao, Yanrong Li, J.L. MacManus-Driscoll, Quanxi Jia Transition metal-oxides have attracted great attention due to their versatile properties. Multilayers, and/or artificial superlattices, are especially interesting since these architectures usually exhibit unique physical properties in comparison with single phase thin films. Furthermore, the lattice strains and the coupling in the multilayered systems can strongly affect the films' growth and their physical properties. We have grown and characterized different multilayered metal-oxide thin films using laser molecular beam epitaxy (MBE). Specifically, we have prepared [(BiFeO$_{3})_{n}$/(La$_{0.7}$Sr$_{0.3}$MnO$_{3})_{n}$]$_{m}$ and [(BiFeO$_{3})_{n}$/(BiMnO$_{3})_{n}$]$_{m}$ superlattices and strained BiFeO$_{3}$ (BFO)$_{ 0.5}$: BiMnO$_{3}$ (BMO)$_{ 0.5}$ films. We have systematically investigated the strain states on the magnetic properties of these multilayer films. [Preview Abstract] |
|
C1.00168: Origin of interfacial gap states in Ga$_{2}$O$_{3}$ layer grown on GaAs surface and interface passivation by F and Gd Weichao Wang, K. Xiong, Robert M. Wallace, Kyeongjae Cho III-V compound semiconductors are potential candidates to replace Si as the channel of future high performance n-MOSFETs. However, the poor III-V/dielectric interface quality leads to low performance of device operations. Prior to any high-k deposition on III-V, a passivated III-V surface could help to obtain a high quality high-k/III-V interface. We examine the native oxides of Ga$_{2}$O$_{3}$ on GaAs with density functional theory to determine the origin of gap states and propose possible ways to passivate the interface. Ga$_{2}$O$_{3}$ molecular species is gradually added in first principles molecular dynamics until one monolayer formed on the top of GaAs at 700 K within 3 ps. During the growth process, O atoms tend to diffuse into GaAs, and Ga-Ga dimer forms as well. The interface states originate from the Ga dangling bonds, Ga-Ga dimers and under-coordinated Ga suboxides Based on the understanding of the origin of the gap states, F and Gd are proposed to remove the gap states. [Preview Abstract] |
|
C1.00169: Crystal Growth of MoO$_{2}$ and K$_{x}$MoO$_{2-\delta}$ B.S. de Lima, C.A.M. dos Santos, L.M.S. Alves, S.S. Benaion, A.D. Bortolozo, M.R. Andreeta, J.J. Neumeier During the last years our group has searched for new quasi-one- dimensional (1D) conductors, which led to the discovery of K$_ {x}$MoO$_{2-\delta}$. The electrical resistivity of this compound is well described by a power law in temperature [1]. In this presentation, progress on the crystal growth of K$_{x} $MoO$_{2-\delta}$ will be discussed. Crystal growth of the parent compound MoO$_{2}$ utilizes chemical vapor transport (CVT) with iodine as transport agent. Crystal growth of K$_{x} $MoO$_{2-\delta}$ by CVT was carried out using high purity K$_ {2}$MoO$_{4}$, MoO$_{3}$, and Mo powders which were mixed in appropriate amounts (0 $\leq$ x $\leq$ 0.25) and sealed with I$_ {2}$ in quartz tubes, followed by heat treatment in temperature gradients from 750 to 950$^{o}$C for 100 h. The crystals were characterized by X-ray diffraction, scanning electron microscope (SEM), Raman spectroscopy, electrical resistance and magnetization measurements.\\[4pt] [1] L. M. S. Alves $\emph{et al.}$; Phys. Rev. B 81, 174532 (2010) and references therein. [Preview Abstract] |
|
C1.00170: Induced Magnetic Behavior and Anomalous X-ray Fluorescence Spectra of Thermally Tailored Copper Patrick Bradley, Claire Chanenchuk, Chris Nagel When a high purity ($>$99.98 wt\%) copper ingot was melted, subjected to high temperature thermal cycling including rapid electromagnetic field oscillation (thermally tailored), the resultant solidified metal exhibited unexpected magnetic regions with unique spectroscopic behavior. A high-resolution magnetic microscope was used to provide current density imaging with resultant surface mapping of magnetic fields of the magnetically active regions on the copper ingot. Energy-dispersive, X-ray fluorescence (XRF) analysis of the magnetic regions exhibited energy emissions inconsistent with the known starting composition of the material. An analysis of the magnetic field and XRF data shows them both to be a result of the tailoring process and eliminates the possibility of causation by impurities accumulated during the process. [Preview Abstract] |
|
C1.00171: Crystal structure and electrical properties of the Bi$_{2-y}$Sr$_{y}$Ir$_{2}$O$_{7}$ $\alpha$-pyrochlore solid solution Carlos Cosio-Castaneda, Gustavo Tavizon, Pablo de la Mora, Francisco Morales In this work we report the synthesis and crystal structure of the Bi$_{2-y}$Sr$_{y}$Ir$_{2}$O$_{7}$. From structural Rietveld refinements we show that in this system the local geometry of the IrO$_{6}$ passes from a trigonal antiprism (y$<$0.4); a regular octahedron (y=0.5), reaching a new trigonal antiprism at the end compositions (y$>$0.5). Experimentally, this is a metallic system with a conductivity that decreases as a function of the Sr content in the (10-300 K) low temperature range. By means of electronic structure calculations, using WIEN2k to study Bi$_{2}$Ir$_{2}$O$_{7}$ and two hypothetical compounds, BiSrIr$_{2}$O$_{7}$ and h-BiSrIr$_{2}$O$_{7}$, we show that a) the main contribution to conductivity come from the shift of the oxygen towards the Ir atoms; b) the lattice imperfections (random occupation of Sr) and lattice vibrations are responsible for the drop of the electrical conductivity, and c) the IrO$_{6}$ local geometry (and crystal field configuration, t$_{2g}^{5}$ e$_{g}^{0}$/e$_{g}^{4}$a$_{1g}^{1}$b$_{2g}$b$_{1g}$ change), this last one does not seem to affect the electrical conductivity. [Preview Abstract] |
|
C1.00172: Effect of Temperature, Pressure and Precursor flux ratios on InSb Thin film Growth: Morphology and Properties Samuel Mensah, Alexander Vogel, Joerg Wittemann, Johannes de Boor, Volker Scmhidt We have investigated the growth of InSb thin films on InAs and GaAs substrates by Chemical Beam Epitaxy (CBE). Raman spectroscopy measurements show that the optical properties of the grown layers is not greatly affected even when varying the growth conditions over a wide range (varying the V/III flux ration between 1 and 10, growth temperature between 390-480$^{\circ}$C). The lattice mismatch between the layers and substrates, results in regions of no growth during the deposition of InSb layers. To circumvent this problem, the growth process is preceded by a 10 mins exposure of the substrates to TMIn. This step eliminates the regions of no growth. Our results show that at constant pressure, the growth rate decreases with increasing temperature and with increasing V/III flux ratio. A much slower response was observed for increasing antimony partial pressure. The lattice mismatch between the layer and substrate give rise to stacking fault and twins. A decrease in particle size from 34.89 to 9.95nm was observed for increasing flux ratio and an increase from11.31 to 32.68nm for increasing temperature. Evidence of Raman spectroscopy results confirms the crystalline nature of the deposited films. Details of our results will be presented at the meeting. [Preview Abstract] |
|
C1.00173: Growth of thin, transparent and high quality phase pure hBN films Muhammad Sajjad, Xioan Zhang, Peter Feng A simple approach using pulse laser deposition technique was made in order to obtain multi layers transparent hexagonal boron nitride films at low substrate temperature (700 $^{\circ}$C) with iron nano-particles as catalyst. The catalyst helped in creating reactive species of boron and nitrogen to react quickly and formed h-BN base layer. The formation of film layers were studied systematically with increasing amount of catalyst keeping same experimental conditions and steps. Transparent and ultra thin base layer was obtained using small amount of catalyst. However, with increasing amount of catalyst, few more layers were formed on the base layer which affected the transparency of the films. Therefore, it was revealed that with optimized amount of catalyst helped in nucleating ultra thin transparent layers of BN with clear variation in atomic wall layers, sharp edge of the film, shape and surface smoothness. Scanning Electron Microscopy was used to analyze the surface images of hBN thin films whereas Energy Dispersive X-Ray spectroscopy (EDS) verified dominance of boron and nitrogen in the structure. The crystalline structure of the films was analyzed with Raman spectroscopy and XRD technique. [Preview Abstract] |
|
C1.00174: Magnetic and thermodynamic properties of Americium-II: An \textit{Ab Initio }Study Jianguang Wang, Li Ma, Asok Ray Hybrid density functional theory based method has been used to study the structural, magnetic, electronic, and thermodynamic properties of Americium-II. Non-magnetic, ferromagnetic (FM), and anti-ferromagnetic (AFM) configurations without and with spin-orbit coupling (SOC) have been considered. The experimental NM ground state configuration is indeed obtained for Am-II at a level of 40{\%} HF exchange with SOC and the computed structural properties and electronic density of states are in good agreement with experimental observations. The importance of SOC is found to be significant. The phonon related properties of Am-II are presented for the NM ground state configuration and the computed heat capacity and entropy are in good agreement with the experimental measurements. The lattice constant, bulk modulus, heat capacity, and entropy of Am-II are predicted to be 9.44 a.u., 21.7 GPa, 24.3 JK$^{-1}$mol$^{-1}$, and 55.7 JK$^{-1}$mol$^{-1}$, respectively. [Preview Abstract] |
|
C1.00175: Characterization of Doped $\mathbf{CeCoIn_5}$ A.R. Treat, J.C. Cooley, C.P. Opeil Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467. Los Alamos National Laboratory, Los Alamos, New Mexico 87545. $\mathrm{CeCoIn_5}$ is an unconventional, d-wave, heavy fermion superconductor with a critical temperature of $\sim$2.3K. The physical properties of doped samples of $\mathrm{CeCo_{1-x}M_{x}In_5}$, where M is Fe, Cr, Rh, Ru, Ir, Mn, Ni, V, or Cu for $\rm{x} \le 0.03$, are characterized. Resistivity, magnetoresistance, and magnetization are measured in a temperature range 5 - 300K and magnetic field up to 9 Tesla; the magnetization is measured using a capacitive cantilever magnetometer. The effect of the dopants on resistivity and magnetization, with regard to percentage x present in the sample, provides valuable insight into the character of the parent material $\mathrm{CeCoIn_5}$. Implications of magnetic, diamagnetic, and non-magnetic doping of $\mathrm{CeCoIn_5}$ will be discussed. [Preview Abstract] |
|
C1.00176: A Universal Relation between Heat Conduction and Diffusion Sha Liu, Baowen Li We rigorously prove a useful equality relating the heat current autocorrelation function and the mean square displacement of the energy diffusion. From this equality, we are able to recover the existing theories for normal diffusion and normal heat conduction. Moreover, we are also able to obtain a connection between anomalous diffusion and anomalous heat conduction. We are results are applicable to all isotropic systems with any dimension. [Preview Abstract] |
|
C1.00177: Study of the angular-dependence of the L-alpha and L-beta radiation produced by 0-15 kev photons incident on Au targets of various thicknesses Sebastian Requena, Scott Williams We report the results of experiments involving the L-alpha and L-beta x-ray lines produced by 0-15 keV bremsstrahlung incident on gold targets of various thicknesses at forward-scattered angles ranging from 20 to 160 degrees. Previous reports [1, 2] have shown the L-beta peaks to be isotropic and the L-alpha peaks to be anisotropic due to the symmetry/asymmetry associated with the orbital being filled during the transition. The relative intensities are compared to the predictions of the Monte Carlo code, PENELOPE. \\[4pt] [1] K. S. Kahlon, et al., Phys. Rev. A 44, 7 (1991) \\[0pt] [2] L. Demir, et al., Radiat. Phys. And Chem., 59, 355-359 (2000) [Preview Abstract] |
|
C1.00178: Hexagonal motifs on the Ir(100) surface reconstructions from a first-principles study Wan-Sheng Su, Feng-Chuan Chuang, Ken-Ming Lin, Tsan-Chuen Leung The hexagonal motifs of the Ir(100) surface overlayer are examined by using first-principles calculations. The studied hexagonal motifs are formed on the Ir(100) surface overlayer with (5x1), (8x1), (12x1), and (14x1) periodicities. Our results showed that the unstrained (5x1) phase is the most stable phase, which is consistent with not only previous theoretical calculations but also experimental findings. Further analysis on the strain-induced phase transition among various hexagonal reconstructions is presented. Such a phenomenon can be further qualitatively elucidated by analyzing the computed average standard deviation of angles. [Preview Abstract] |
|
C1.00179: An \textit{Ab Initio }Study of FCC Pu$_{1-x}$Ga$_{x}$ Kinjal Gandha, Asok Ray As is known, the addition of a few atomic percent of Ga stabilizes the fcc $\delta $ -- phase of Pu at room temperature. In this work, conventional and hybrid density functional theory have been used to study the electronic, geometric, and magnetic structure properties of Pu$_{1-X}$Ga$_{x }$with varying Ga concentrations in the fcc $\delta $ phase. The calculations have been performed using the all-electron full-potential linearized augmented plane wave plus local orbitals basis method and the \textit{WIEN2k }software. Each compound has been studied at the non-magnetic, ferromagnetic, and anti-ferromagnetic configurations with and without spin-orbit coupling (SOC) and full geometry optimizations. The ground state structures are found to be anti-ferromagnetic with a contraction of the lattice constants from pure $\delta $-Pu. The obtained lattice parameters are in satisfactory agreement with experimental data. [Preview Abstract] |
|
C1.00180: Spectroscopic ellipsometry of NTO/ultrathin Cu/NTO films Jun Woo Park, Hyung Keun Jang, Hosuk Lee, Hosun Lee, Jun-Hyuk Park, Han-Ki Kim, Bo Hyun Kong, Hyung Koun Cho NTO/Cu/NTO/glass thin films were grown using sputtering deposition. The thickness of the Cu film (t) varied between 1.5 nm and 50 nm. The ellipsometric angles ($\Psi $, $\Delta )$ of the NTO/Cu/NTO/glass thin films were measured by using spectroscopic ellipsometry. The thicknesses and dielectric functions of the Cu films in the NTO/Cu/NTO/glass were estimated by using a multi-layer model analysis with the parametric optical constant and Drude models. Transmission electron microscopy measurements showed that the Cu layers evolved from aggregates of Cu nanoparticles to coalesced Cu thin films as the Cu film thickness increased. According to sheet resistance data, the Cu films thinner than 8 nm were aggregations of Cu nanoparticles that were not well-connected and the Cu films thicker than 8 nm were above the percolation threshold. From the Drude model, the plasmon frequency ($\omega _{p})$ and the electron relaxation time ($\tau )$ were estimated and were found to increase with increasing film thickness. We obtained the second derivatives of the dielectric function spectra that were composed of several peaks near 1.5, 2.1, 2.5, 3.5, and 4.3 eV, and attributed to interband transitions. The peak energies (except 1.5 eV) matched to the band structure calculations found in the literature. [Preview Abstract] |
|
C1.00181: Magnetic properties of Mn$_{11}$Si$_{19}$ and Mn$_{4}$Si$_{7}$ in their bulk and powdery states Kiyotaka Hammura, Haruhiko Udono, Tomosuke Aono, Isao Ohsugi, Elisa De Ranieri, Ken-ichi Yajima, Yusuke Ujiie The purpose of this paper is to determine by experiment whether Mn$_{11}$Si$_{19}$ and Mn$_{4}$Si$_{7}$ in their bulk and powdery states have a finite magnetic moment or not. High quality bulk samples for both were prepared using the temperature gradient solution growth method. Powery samples for both were prepared by pounding bulk crystals in a mortar. Magnetisation measurements were carried out using both SQUID system and Kerr rotation system. SQUID measurements revealed that Mn$_{11}$Si$_{19}$ has finite magnetism while Mn$_{4}$Si$_{7}$ does not in their bulk states. It was also confirmed that Mn$_{4}$Si$_{7}$ became magnetic and Mn$_{11}$Si$_{19}$ exhibited a distinctive hysteresis, in their powdery state. The enhancement of magnetism in their powery states implied that the surface of the samples was to a great extent linked to its magnetism. [Preview Abstract] |
|
C1.00182: Polarization-dependent optical excitations in AB-stacked graphite Chih-Wei Chiu, Yuan-Cheng Huang, Feng-Lin Shyu, Ming-Fa Lin The band structure of AB-stacked graphite exhibits two pairs of parabolic bands, where the band-edge states induce the peaks and shoulders in the density of states and in the joint density of states (JDOS). The dipole matrix element M$^{cv}$ plays an important role in the relationship between the spectral function A($\omega$) and JDOS. It is strongly dependent on the polarization directions ${\bf {\hat{E}}}$ of the laser beams, showing a anisotropic property. The optical excitations do not fully reflect the special structures of JDOS. For ${\bf {\hat {E}}}$ on the graphene plane, A($\omega$)$'$s are isotropic and include one sharp peak and some shoulders. As for ${\bf {\hat {E}}}$ along the stacking direction, A($\omega$) is much weaker, and only shows a broadened peak. The spectra contrast sharply with those of AA-stacked graphite. [Preview Abstract] |
|
C1.00183: Correlation effect investigations on the Magneto-optical Kerr Spectra of Co-based Heusler alloys from first principles Miyoung Kim, Hanjo Lim, Jae Il Lee Here, we report our \textit{ab-initio} calculational results on the electronic structures and magneto-optical (MO) properties of the ferromagnetic Co$_{2}$Mn$X$ full Heusler alloys. Employing the +U corrections for the transition metal 3$d$ bands in addition to the local density approximation (LDA), we investigate the correlation effect on the MO spectra in polar geometry as well as the detailed electronic structures using FLAPW [1] method. Results show that the correlation effect results in a blue-shift of the peak positions and large enhancement of the low energy MO spectra, which are attributed to the increased t$_{2g}$-e$_{g}$ splitting of spin minority Co and Mn $d-$bands indicating the suppression of diagonal elements of optical conductivity at energy region of 1$\sim $2 eV where the interband transitions are forbidden.\\[4pt] [1] E. Wimmer, K. Krakauer, M. Wienert, and A.J. Freeman, Phys.Rev B 24, 864 (1981). [Preview Abstract] |
|
C1.00184: Theoretical Study of tip apex electronic structure in Scanning Tunneling Microscope Heesung Choi, Min Huang, John Randall, Kyeongjae Cho Scanning Tunneling Microscope (STM) has been widely used to explore diverse surface properties with an atomic resolution, and STM tip has played a critical role in controlling surface structures. However, detailed information of atomic and electronic structure of STM tip and the fundamental understanding of STM images are still incomplete. Therefore, it is important to develop a comprehensive understanding of the electronic structure of STM tip. We have studied the atomic and electronic structures of STM tip with various transition metals (TMs) by DFT method. The d-electrons of TM tip apex atoms show different orbital states near the Fermi level. We will present comprehensive data of STM tips from our DFT calculation. Verified quantification of the tip electronic structures will lead to fundamental understanding of STM tip structure-property relationship. This work is supported by the DARPA TBN Program and the Texas ETF. [Preview Abstract] |
|
C1.00185: Exchange constants and spin waves of MnV$_{2}$O$_{4}$ from first principles DFT calculations Ravindra Nanguneri, Sergey Savrasov We present results of DFT calculations of exchange constants of the magnetic spinel MnV$_{2}$O$_{4}$. The starting point is the one-particle eigenfunctions of the Kohn-Sham auxiliary Hamiltonian as a function of the self-consistent, converged charge density. Using linear response and perturbation theory, the exchange constants between the magnetic ions Mn and V are calculated in both the collinear and non-collinear, orbital-ordered phases of the spinel. The collinear exchanges have exchange constants proportional to the unit matrix, which means they are isotropic. On the other hand, the non-collinear exchanges have unequal diagonal elements and in addition have off-diagonal elements, revealing anisotropic magnetic interactions. The anisotropy is traced to the orbital-order and non-collinear spin structure of the low-temperature ground-state. We find that the interactions between the V atoms can sometimes be anti-ferromagnetic. The V atoms are located at the vertices of a corner-sharing tetrahedral lattice, commonly known as a pyrochlore lattice. AFM interactions on such a lattice are geometrically frustrated because all pair-wise bond energies cannot be simultaneously minimized with a classical spin configuration. It has been experimentally found that as the temperature is lowered, MnV$_{2}$O$_{4}$ undergoes a transition from a paramagnet with a cubic symmetry structure phase to a ferrimagnetic with cubic symmetry phase at 56 K. [Preview Abstract] |
|
C1.00186: Comparative Studies of Constitutive properties of Nanocrystalline and Bulk Iron During Compressive Deformation Xiaohui Yu, Jianzhong Zhang, Liping Wang, Yusheng Zhao We present a comparative study of mechanical properties of bcc nano-crystalline iron and microncrystalline iron by in-situ high-pressure synchrotron x-ray diffraction under tri-axial compression. For nano-Fe with a starting high dislocation density of 10$^{16}$ m$^{-2}$, the peak broadening is almost reversible upon unloading from 8.6 GPa to ambient pressure, indicating that no additional dislocations are built up during compressive deformation inside grains, at grain boundaries or twin boundaries. Furthermore, an orientation dependent surface strain is found to be stored in the surface layer of the bcc nano Fe, which is in agreement with the core-shell model of the nano crystals. For micron-Fe, a significant and continuous peak sharpening and the associated work softening were observed after the sample is yielded at pressures above 2.0 GPa, which can be presumably attributed to a pressure-induced dislocation annihilation. This finding/interpretation supports the hypothesis that the annihilation of dislocations is one of the dominant mechanisms underlying the plastic energy dissipation. The determined yield strength of 2.0 GPa for nano-Fe is more than 15 times higher than that for micron-Fe (0.13 GPa), indicating that the nano scale grain-size reduction is a substantially more effective strengthening mechanism than the conventional carbon infusion in iron. [Preview Abstract] |
|
C1.00187: Density functional study of the mechanical properties in single-layered graphene sheet Jorge Tapia, Francis Aviles, Ricardo Peon, Gabriel Canto By means of the density functional theory, we studied the structural and mechanical properties (the Young's modulus, shear modulus and Poisson's ratio) of single-layered graphene sheets (SLGS). The calculations were performed with a linear combination of atomic orbitals method using pseudopotentials and the generalized gradient approximation for the exchange-correlation potential. The uniaxial stress is applied along the one preferential direction for the range of $\pm $10{\%} in the unitary deformation. We found that the bond lengths between carbon atoms in SLGS are larger than the experimental value of graphite and the mechanical properties showed good agreements with the data available in the literature. [Preview Abstract] |
|
C1.00188: The morphological evolution and migration of inclusions in thin-film interconnects under electric loading Yinfeng Li, Xi Wang, Zhonghua Li The paper reports the result of an investigation into electromigration-driven morphological evolution of inclusions in finite scale thin-film interconnects using a phase field method. In examples, two types of inclusion defect are simulated and discussed. The results show that the morphological evolution and migration of inclusion is proportional to the electric field strength applied on thin-film interconnects. It is also seen from the result that the inclusion with anisotropic diffusion interface will move faster than one with isotropic interface under the identical electric field, and the one with anisotropic diffusion interface may evolves into an irregular shape with protuberance. [Preview Abstract] |
|
C1.00189: Calculation of the Peierls barrier of screw dislocations in bcc metals and its dependence on stress Roman Groger, Vaclav Vitek Plastic deformation of bcc metals at low temperatures is governed by thermally activated glide of $1/2\langle 111 \rangle$ screw dislocations over Peierls barriers. Thermodynamic models of the dislocation glide depend on the shape of the Peierls barrier and its changes under stress. Atomistic simulations provide only the maximum slope of the Peierls barrier and, therefore, its overall shape as well as the path of the dislocation are generally unknown. We introduce a new approach by which the Peierls barrier and its changes under stress can be calculated if a suitable set of constraints is imposed to prevent the dislocation from falling into the nearest potential minima. The state of the system at any point along the path is described by the position of the intersection of the dislocation with the perpendicular \{111\} plane. Hence, both the Peierls barrier and the transition path are obtained directly. This is a clear advantage over the currently used approach, where one calculates the path of the system of $N$ atoms through the space of $3N$ degrees of freedom. We compare the results of these two approaches by employing the Finnis-Sinclair potential for tantalum. [Preview Abstract] |
|
C1.00190: Hydrogen Segregation in Crystalline Palladium and Effects on Mechanical Properties Hieu Pham, Amine Benzerga, Tahir Cagin Calculations of tensile strength and tensile modulus were carried out to investigate the effects of hydrogen interactions, diffusion and segregations in palladium single crystal, high-vacancy crystal and bicrystal, by using the embedded atom method. Elevated temperature, hydrogen absorption and defects such as vacancy and grain boundary (GB) individually induce a loss in mechanical strength of palladium in a monotonous manner. The hydrogen-induced mechanical degradation was noticed at the grain boundary, as well as in bulk. The failure induced by hydrogen in palladium up to x$_{H}$=0.1 is plastic rather than brittle, even around grain boundary region, by formation of dislocations. At high H absorption, the global hydrogen concentration is a dominant factor over crystal defects. However, a high-angle grain boundary such as $\sum $5 (2 1 0) provides a great driving force for diffusion and tendency for physical trapping of hydrogen. Therefore, the existence of grain boundary makes materials more susceptible and easily exposed to high hydrogen absorption and segregation. Also, our simulation shows that hydrogen maintains the highest localization at GB in the vicinity of ambient temperatures; and this finding coordinates with experimental observation that hydrogen embrittlement are generally observed at room temperatures. [Preview Abstract] |
|
C1.00191: Atomic analyzis and photocurrent studies of isolated sub-100 nm diameter silicon nanowires Didier Stievenard, Tao Xu, Bruno Grandidier, Yannick Lambert, Christophe Kreminsky, Abdellatif Akjouj, Yan Pennec, Bahram Djafari-Rouhani, Wanghua Chen, Rodrigue Larde, Emmanuel Cadel, Philippe Pareige n-doped Si NWs were synthesized by the vapor-liquid-solid mechanism using the chemical vapor deposition (CVD) technique.The nanowires were grown to a nominal length of 10 $\mu $m with a diameter ranging typically from 60 to 110 nm. Atom Probe Tomography analyzes evidence a gradient of concentration of the phosphorous atom dopants, inducing a built-in potential accros the nanowires. Photocurrent on isolated nanowires was performed with a monochromator source. Depending on the light energy and on the nanowire diameters, we measure various absorption thresholds. Calculations have been performed on a periodic array of wires of varying diameters and with different periodicity by using a Finite Difference Time Domain (FDTD) method. The results evidence a clear dependence of the optical absorption with the nanowire diameters. This work was supported by DGA REI contract N\r{ }2008.34.0031. [Preview Abstract] |
|
C1.00192: Raman Study of the Verwey Transition in Magnetite (Fe$_3$O$_4$) at High Pressure and Low Temperature: Effect of Aluminum Doping Z. Shirshikova, L. Gasparov, V. Struzhkin, A. Gavriliuk, H. Berger Raman spectra of pure and doped magnetite provide a set of markers allowing one to study how the Verwey transition in magnetite changes with the change of pressure. At ambient pressure Verwey transition temperature, Tv, of the single crystals of magnetite, Fe3O4, is determined to be 123K. High-pressure experiment indicates strong dependence of the change of pressure vs. change in the Verwey transition temperature on the amount of impurities: for pure Fe$_3$O$_4$ the change is -0.2 GPa/K; for doped iron, Fe$_{2.98}$Al$_{0.02}$O$_4$, the change is -0.09 GPa/K. Aluminum-doped magnetite (Fe$_{2.98}$Al$_{0.02}$O$_4$) where Al substitutes Fe$^{+2}$ and Fe$^{+3}$ atoms, represents a 2\% aluminum doping, which shifts the Verwey transition temperature to T$_v$=118.5K. The rate with which the Verwey temperature decreases with pressure is further discussed based on the molar specific heat measurements. [Preview Abstract] |
|
C1.00193: INSTRUMENTATION AND MEASUREMENTS |
|
C1.00194: Design and Construction of a Radio Telescope for Undergraduate Research Christopher Stathis Radio telescopes provide a practical and economical alternative to optical observatories for astrophysics research and education at primarily undergraduate physics and astronomy institutions. Ithaca College is in the testing phase of development for a low cost, flexible frequency band radio telescope which I have developed as the research component of my undergraduate thesis. I have constructed a three-stage low noise superheterodyne radiometer on custom printed circuit boards for signal detection, which is mounted on a 3 meter parabolic antenna. Data collection and signal processing is achieved using custom software written in MATLAB. We are currently performing preliminary drift continuum observations of the Sun and Milky Way at Ku band frequencies. We expect that the receiver can also be easily adapted to measure spectral emission of neutral hydrogen and OH masers at L band. I present my design methods for the radiometer and printed circuit boards, including measured noise characteristics and SPICE simulations, as well as an overview of applied signal processing methods and a discussion of observable celestial sources. [Preview Abstract] |
|
C1.00195: Synthesis and characterization of ZnO nanostructures for sensor application Xiaoyan Peng, Jin Chu, Boqian Yang, Peter Feng ZnO nanostructures including nanoparticles (diameter about 50nm), nanorods (diameter about 150 nm and length about 1-1.5$\mu $m) and nanoparticles (diameter $\sim $ 20 nm) were prepared onto Si (100) substrates using both r.f sputtering and PLD technique, respectively. Thermal annealing was performed at 800 $^{o}$C in atmosphere for 2 hours to improve the qualities of ZnO crystalline structures. X-ray diffraction, electron scanning microscope and Raman scattering have been used to characterize all these nanostructured samples After synthesis and initial characterizations, the ZnO nanostructure-based field effect transistor sensors have been designed, fabricated, and tested. High sensitivity (few PPM), quick time response (less than 1 second) of the newly designed sensors have been achieved. Experimental data indicate that the sensitivity of the sensor highly relies on the operating temperature. [Preview Abstract] |
|
C1.00196: Doped and functionalized ZnO nano films and their applications for gas sensors Jin Chu, Xiaoyan Peng, Peter Feng We demonstrate efficient gas sensors using Cu-doped ZnO nanowires and Li atoms-modification of ZnO nanorods. Various Cu-doped ZnO nanowires were synthesized on Si substrates by plasma sputtering at 300 $^{\circ}$C with deposition duration of 30 minutes, while Li-coated ZnO nanorods were prepared by coating Li on the surface of the as-grown nanorods. Raman and EDX data indicated that the obtained ZnO nanowires and nanorods have wurtzite structure with Cu-doping concentration of 1 wt.{\%} and ZnO nanorods with Li-coated concentration of 3 wt.{\%}, respectively The sensing properties were examined by being exposed to H$_{2}$, N$_{2}$ and CH$_{4}$ gases with a home-made system that can facilitate the detection of the resistance change and the control of gas flow as well as temperature. The sensitivities of both samples increased with the operating temperature from RT to 200 $^{\circ}$C and signal intensity of the sensor increased with gas concentration at each type of gas. Experimental data indicates that both types of samples-sensors showed highly sensitive to H$_{2}$ and selectivity against N$_{2}$ and CH$_{4}$. However, the response time for Li-coated ZnO nanorods-based sensor is less than 1 second, much quicker than that for Cu-doped ZnO nanowires-based sensors. [Preview Abstract] |
|
C1.00197: First-principles study of $\gamma$-ray detector materials : heavy alkali metal compounds Hosub Jin, Jung-Hwan Song, Arthur J. Freeman, Bruce W. Wessels, Mercouri G. Kanatzidis In an effort to find good candidate materials for $\gamma$-ray detectors, alkali metal based chalcogenide semiconductors containing heavy elements were investigated. We performed ab- initio density functional theory calculations using the highly precise full-potential linearized augmented plane wave (FLAPW) method\footnote{Wimmer, Krakauer, Weinert, Freeman, Phys. Rev. B, {\bf 24}, 864 (1981)} to estimate their electronic characteristics. The state-of-the-art screened-exchange LDA scheme was adopted to correct the underestimation of the band gap in the LDA method. Several candidate materials for $\gamma$- ray detectors such as Cs$_2$Cd$_3$Te$_4$ and Cs$_2$Hg$_6$S$_7$ were suggested based on the electronic properties like band gaps, effective masses, absorption coefficients, and work functions. Lattice degrees of freedom such as static dielectric constants and bulk modulus were also calculated, and are reported. [Preview Abstract] |
|
C1.00198: ZSM-5, Y, and Mordenite Zeolites as Sensing Materials for Ethanol Vapor Anuvat Sirivat, Intira Yimlamai The effects of the framework type, the charge balancing cation type, and the Si/Al ratio of ZSM-5, Y, and Mordenite zeolites on the electrical conductivity responses towards ethanol vapor have been investigated. All zeolites were characterized using XRD, FT-IR, SEM, TGA, BET, and NH$_{3}$-TPD techniques. For the effect of the framework type, H$^{+}$Y has a higher electrical conductivity sensitivity value than that of H$^{+}$MOR because of a greater pore volume and available surface area. For the effect of the charge balancing cation, all NH$_{4}^{+}$ZSM-5 zeolites (Si/Al = 23, 50, 80, 280) show negative responses, whereas the H$^{+}$Y zeolites (Si/Al = 30, 60, 80) and the H$^{+}$MOR zeolites (Si/Al = 30, 200) show positive responses. These differing behaviors can be traced to the interactions between ethanol molecules and the reactive sites of the zeolites. For the effect of Si/Al ratio, the electrical conductivity sensitivity towards the ethanol decreases with increasing Si/Al ratio or decreasing Al content, and there is a lesser degree of interaction between ethanol molecules and the active sites of the zeolites. The interactions between the ethanol molecules and the zeolites were investigated through infrared spectroscopy. [Preview Abstract] |
|
C1.00199: Apparatus for the analysis of surfaces in gas environments using Positron Spectroscopy Suman Satyal, Lawrence Lim, Prasad Joglekar, Sushant Kalaskar, Karthik Shastry, Alexander Weiss Positron spectroscopy performed with low energy beams can provide highly surface specific information due to the trapping of positrons in an image potential surface state at the time of annihilation. Here we present design details of a new positron beam system for the analysis of surfaces gas environments. The new system will employ differential pumping to transport the positrons most of the way from the source to the sample under high vacuum. The positrons will then be transported through a thin gas layer surrounding the sample. The positrons will be implanted into the sample at energies less than $\sim $10 keV ensuring that a large fraction will diffuse back to the surface before annihilation. The Elemental content of the surface interacting with the gas environment will then be determined from the Doppler broadened gamma spectra. [Preview Abstract] |
|
C1.00200: High-resolution X-ray Emission Spectroscopy as a Microprobe Imaging Modality Joseph Pacold, Gerald Seidler, Brian Mattern, Matthew Haave, Robert Gordon Hard x-ray microprobe beamlines at third generation light sources have made significant impacts in several fields of science and technology. Such facilities permit rapid 2-dimensional studies of multiphase materials on submicron length scales using a variety of pixel-by-pixel imaging modalities (e.g., x-ray diffraction, x-ray absorption near edge fine structure, or x-ray fluorescence). Here, we aim to expand hard x-ray microprobe imaging modalities to include high-resolution x-ray emission spectroscopy (XES). When performed at 1-eV resolution, such measurements can provide quite direct atomic-level information on ionic valence, spin, and local electronic and chemical environment. Ongoing work in our research group has improved the efficiency of XES via the development of a new type of compact and inexpensive x-ray spectrometer design, the ``miniature x-ray spectrometer'' or ``miniXS'' paradigm. We will report preliminary 2-dimensional XES studies of planar multiphase materials, with specific applications to samples of interest for geophysics and catalysis science. [Preview Abstract] |
|
C1.00201: Measurements of chemical bonds using diffraction of electronic waves traveling through crystals Robert Lanning, Cristian Bahrim We propose a simple and intuitive procedure for discovering the atomic arrangement and the chemical bonds in transparent crystals using the diffraction of light or electronic waves by crystals. This study can help to improve methods of optical imaging, electronic microscopy, microbiology, and crystallography. Using fundamental principles of quantum mechanics, we also explain the formation of electronic wave packets when a free electronic beam passes through the atoms of a solid target. The atoms in solids act as the narrow slits of a diffraction grating producing a Fourier transform of the sinusoidal waves associated to free electrons incident on the solid target. Such a model allows measuring the chemical bonds within 1{\%} precision. This research project was done under a NSF-DUE-sponsored program, called STAIRSTEP [1], which was designed to engage STEM undergraduate students in high-quality research in several fields of science including physics, at Lamar University.\\[4pt] [1] Doerschuk P, Bahrim C, Daniel J, Kruger J, Mann J, and Martin Ch, \textit{39th ASEE/IEEE Frontiers in Education Conference,} San Antonio 2009, M3F-1-2. [Preview Abstract] |
|
C1.00202: Negative thermal expansion in Prussian Blue analogs S. Adak, H. Nakotte, L. Daemen While many Prussian Blue (PB) analogs are known to display negative thermal expansion (NTE), few have been studied in detail. Not all compounds in this family exhibit NTE. Because it is possible to systematically vary ion size and charge in these materials, they represent an interesting playground to study NTE and possible correlations with electronic and crystal structures. By contrast with many silicates displaying NTE and in which tetrahedral units are linked with apical oxygens, the octahedral units in PB compounds are linked with a linear cyanide ligand. This introduces more degrees of freedom in the (mostly) cubic PB structures compared to the silicates. Polycrystalline samples of PB analogs, $M^{II}_{2}$\textit{[Fe}$^{II}$\textit{(CN)}$_{6}]$ and $M^{III}_{2}[A^{III}$\textit{(CN)}$_{6}]_{2}$\textit{(M = Mn, Co, Ni, Cu, Zn; A = Cr, Fe, Co) }were synthesized via standard chemical precipitation. Variable temperature X-ray powder diffraction patterns were collected \textit{in-situ} in the range 300-123 K to study the T-dependence of the lattice parameter and to obtain an average coefficient of thermal expansion (CTE). Lattice parameters were extracted using the Rietveld refinement technique with the General Structure Analysis System (GSAS) software. The determined average CTEs, for the compounds showing NTE behavior, are in the range -4.9 x 10$^{-6 }$K$^{-1}$ to -39.5 x 10$^{-6}$ K$^{-1}$ while the CTEs for the other materials showing positive TE behavior are in the range 5.9 x 10$^{-6 }$K$^{-1}$ -- 59.2 x 10$^{-6}$ K$^{-1}$. [Preview Abstract] |
|
C1.00203: New Approach to Image Aerogels by Scanning Electron Microscopy Francisco Sol\'a, Frances Hurwitz, Jijing Yang A new scanning electron microscopy (SEM) technique to image poor electrically conductive aerogels is presented. The process can be performed by non-expert SEM users. We showed that negative charging effects on aerogels can be minimized significantly by inserting dry nitrogen gas close to the region of interest. The process involves the local recombination of accumulated negative charges with positive ions generated from ionization processes. This new technique made possible the acquisition of images of aerogels with pores down to approximately 3nm in diameter using a positively biased Everhart-Thornley (E-T) detector. Well-founded concepts based on known models will also be presented with the aim to explain the results qualitatively. [Preview Abstract] |
|
C1.00204: Three-axis positional drift correction in scanning probe microscopy Nathan D. Follin, Christopher J. Musalo, Matthew L. Trawick Positional drift in scanning probe microscopy can cause image distortion and metrological errors of tens of nanometers or more. It can arise from thermal drift, due to thermal expansion of materials in the sample and microscope while scanning, or from piezo creep, particularly along the z axis. We present a technique for correcting positional drift errors in all three axes. Our method works by comparing each scanned topographical image to a second, partial scan, taken immediately afterwards, on which the fast and slow scan axes have been reversed. We model the positional distortion as a low-order polynomial function in three dimensions, searching for the set of correctional coefficients that minimizes the difference between the two scans. Using this technique we have successfully reduced positional errors from 50 nm to 0.5 nm in the z axis, and from 40 nm to 2 nm (about half of a single pixel) in the xy plane. [Preview Abstract] |
|
C1.00205: Three Electrode Control of the NanoDeposition of Gold Nanoparticles With Atomic Force Controlled Capillary Electrophoresis Aaron Lewis, Talia Yeshua, Mila Palchan, Yulia Lovsky, Hesham Taha Controlled deposition of the metallic features such as nanoparticles with high spatial accuracy has a great interest in different applications such as surface plasmons, surface enhanced Raman scattering (SERS), nanophotonics and nano biophysics. Lithography based scanning probe microscopy techniques have been shown as a potential methodology for accurate and localized deposition of material in the nanometer scale. Here we report an accurate deposition of high resolution features of single gold nanoparticles using Three Electrodes and atomic force microscopy (AFM) controlled capillary based fountain pen nanolithography. In this methodology three electrodes are attahced one on the outside of the metal coated glass probe, one on the inside of the hollow probe in the solution contained in the capillary and a third electrode on the surface on which the writing is to take place. The three electrodes provide electrical pulses for accurate control of the deposition and retraction of the liquid from the surface. We will demonstrate depositing of single gold nanoparticle with size of 1.2nm onto surfaces such as semiconductors. [Preview Abstract] |
|
C1.00206: Have some large structures? Try small-angle neutron scattering (SANS) Lisa DeBeer-Schmitt, Kathy Bailey, Lilin He, George Wignall, Yuri Melnichenkov, Ken Littrell The small-angle neutron scattering (SANS) beam line, CG-2, has been in operation since 2007. CG-2 has been optimized so that structures from 0.5 to 200 nm can be thoroughly investigated. HFIR's cold source places the flux at CG-2 among the best in the world. Along with high flux, many varied sample environments can easily be integrated into the beam line which gives the user a versatile temperature range from 1.5 K to 1000 K. In addition there are two cryomagnets (horizontal 4.5 T and vertical 7 T), pressure cells and load frames available to users allowing for the availability of multiple configurations of experimental setups. Due to all the above equipment and the flux at CG-2, there have been many diverse and intriguing scientific developments. One such outcome is the study of flux-line lattices found in Type-II superconductors including the highly touted iron pnictides. Besides superconductors, other science studied on CG-2 ranges from molecular self-assembly and interactions in complex fluids to phase separation to grain growth and orientation in metallurgical alloys. [Preview Abstract] |
|
C1.00207: Characterization and Modeling of Off-Specular Neutron Scattering for Analysis of Two Dimensional Ordered Structures Christopher Metting, Brian Maranville, Paul Kienzle, Robert Briber, Joseph Dura, Chuck Majkrzak The University of Maryland along with NIST Center for Neutron Research (NCNR) and the NSF funded DANSE project are currently developing off-specular neutron reflectometry modeling software for fitting scattering data from multilayer samples. The software includes a robust sample representation scheme for easy development of various models. Theory functions are being calculated using a variety of approximations. The suite of approximations allows for the evaluation of each calculation's usefulness in representing the scattering data. In this presentation we describe corrections made to a purely Born approximation that capture dynamical scattering and resolution effects seen in measured data. We then show modeled data taken on the Advanced Neutron Diffractometer/Reflectometer (AND/R) at the NIST Center for Neutron Research (NCNR) from a sample of gold pillars using a substrate modified Born approximation, and compare it to a model which uses a purely Born approximation. [Preview Abstract] |
|
C1.00208: On-demand Control of Micro Quartz Resonator in Scanning Probe Microscopy Junghoon Jahng, Wonho Jhe, Bongsu Kim We demonstrate generalized theoretical analysis and experimental realization of active feedback control for the self-oscillating quartz tuning-fork (QTF) which is a widely used probe for sensing applications in scanning probe microscopy. In this work, we present the damping control, feedback cooling, resonance control and nonlinear dynamics for the QTF by implementing active feedback control scheme. Finally, we suggest the prospect of several novel applications in scanning probe microscopy by using the active feedback control of QTF such as increasing the force sensitivity, reducing the thermal noise and modulating the resonance of the sensor. [Preview Abstract] |
|
C1.00209: Low Temperature Scanning Probe Microscope(LT-SPM) operating in a Cryogen-Free Cryostat, 1.5-300K Ozgur Karci, Munir Dede, Yury Bugoslavsky, Renny Hall, Ahmet Oral We present the design of a Low Temperature Scanning Probe Microscope(LT-SFM) operating in a vibration-free cryogen-free cryostat. A 0.5W ultra now noise Pulse Tube cryocooler is integrated into the cryostat with a 9T magnet. Stick slip coarse approach mechanism is used to bring the sample in to close proximity of the sample. The sample can be moved in XY directions within 3 mm range, while the position is measured with capacitive encoder with 3$\mu $m accuracy. An improved fiber interferometer with $\sim $12fm/$\surd $Hz noise level is used to detect cantilever deflection. The resonance of the cantilever controlled by a digital Phase Locked Loop (PLL) integrated in our Control Electronics with 5mHz frequency resolution. We can achieve $\sim $1nm resolution in AFM mode {\&} $<$10nm resolution in MFM mode. Results from different imaging modes; non-contact AFM, MFM, Piezoresponse, Conductive AFM etc. will be presented. [Preview Abstract] |
|
C1.00210: A 129 GHz dynamic nuclear polarizer in a wide-bore superconducting magnet Lloyd Lumata, Richard Martin, Ashish Jindal, Craig Malloy, A. Dean Sherry, Mark S. Conradi, Matthew Merritt Dynamic nuclear polarization via fast dissolution method has allowed production of solutions containing highly-polarized nuclei ($>$10,000-fold enhancement of the room-temperature liquid-state NMR signal) of bio-molecules for \emph{in vitro} and \emph{in vivo} metabolic nuclear magnetic resonance spectroscopy (MRS) and imaging (MRI). Here we present the construction and use of a 129 GHz dynamic nuclear polarizer in a 4.6 T wide-bore superconducting magnet. The relatively large bore (150 mm) of the superconducting magnet allows the use of a cryostat separate from the magnet and routing of the microwaves such that the waveguide does not have to be removed before dissolution. A 100 mW microwave source operating at 129 GHz was used to irradiate the samples. The cryostat has a 10-liter liquid Helium capacity which lasts for 10-12 hrs of continuous operation. Base temperature of 1.15 K is achieved with a 450 m$^{3}$/hr roots blower pump. Preliminary results will be discussed. [Preview Abstract] |
|
C1.00211: Diffuse Reflectance Spectroscopy and Colorimetry as a Diagnostic Tool for Acanthosis Nigricans Bensachee Pattamadilok, Suneetha Devpura, Zain U. Syed, Pranita Vemulapalli, Marsha Henderson, Steven J. Rehse, Iltefat Hamzavi, Bassel H. Mahmoud, Henry W. Lim, Ratna Naik The purpose of this study was to quantify skin color changes due to Acanthosis Nigricans, a disorder common among prediabetic and obese individuals. The non-invasive optical technique diffuse reflectance spectroscopy (DRS) was used to determine skin melanin, oxyhemoglobin and deoxyhemoglobin content through the measured absorption spectrum. Colorimetery was used to measure skin color based on the standard Tristimulus values (L*, a*, and b*). Data was obtained from eight patients, spanning eight months of treatment. Measurements were obtained from lesion tissue on the neck and healthy skin was used as a control. L*, a* and b* values showed significant differences between lesion and normal controls, whereas melanin was the only parameter which showed statistical significant differences in DRS measurements. Future work will use more sensitive chemometric methods to increase diagnostic accuracy based on the raw spectra of the DRS. [Preview Abstract] |
|
C1.00212: Toward contrast-enhanced, optically-detected NMR spectroscopy Carlos Meriles, Daniela Pagliero Optical detection of Nuclear Magnetic Resonance (NMR) takes place via a two-step process that relies on the interaction between optical photons and electrons on the one hand, and the hyperfine coupling between electrons and nuclear spins on the other. The latter depends on the material system under consideration while the former is dominated by the difference between the illumination and optical transition wavelengths. Here we use optical Faraday rotation to monitor nuclear spins in real time after resonant radio-frequency excitation at high-magnetic field. Comparison between inductively and optically detected NMR spectra in model sample fluids indicates that each of these mechanisms can lead to alternate forms of spectral contrast. Extension of these findings may find application in solvent suppression protocols, sensitivity-enhanced NMR of metalloproteins, or the characterization of molecular orbitals in diamagnetic systems. [Preview Abstract] |
|
C1.00213: STATISTICAL AND NONLINEAR PHYSICS |
|
C1.00214: DEFINITION of (so MIScalled) "Complexity" as UTTER-SIMPLICITY!!! VERSUS DEVIATIONS From It As COMPLICATEDNESS-MEASURE(S) F. Young, Edward Carl-Ludwig Siegel (so MIScalled) "complexity" with INHERENT BOTH SCALE-Invariance Symmetry-RESTORING, AND 1/w\^{}(1.000..) "pink" Zipf-law Archimedes-HYPERBOLICITY INEVITABILITY power-spectrum power-law decay algebraicity. Their CONNECTION is via simple-calculus SCALE-Invariance Symmetry-RESTORING logarithm-function derivative: (d/d$\omega )$ ln($\omega )$ = 1/$\omega $ , i.e. (d/d$\omega )$ [SCALE-Invariance Symmetry-RESTORING]($\omega )$ =1/$\omega $ . Via Noether-theorem continuous-symmetries relation to conservation-laws: (d/d$\omega )$ [{\{}inter-scale 4-current 4-div-ergence{\}} = 0]($\omega )$ = 1/$\omega $. Hence (so MIScalled) "complexity" is information inter-scale conservation, in agreement with Anderson-Mandell [Fractals of Brain/Mind, G. Stamov ed.(1994)] experimental-psychology!!!], i.e. (so MIScalled) "complexity" is UTTER-SIMPLICITY!!! Versus COMPLICATEDNESS either PLUS (Additive) VS. TIMES (Multiplicative) COMPLICATIONS of various system-specifics. COMPLICATEDNESS-MEASURE DEVIATIONS FROM complexity's UTTER-SIMPLICITY!!!: EITHER [SCALE-Invariance Symmetry-BREAKING] MINUS [SCALE-Invariance Symmetry-RESTORING] via power-spectrum power-law algebraicity decays DIFFERENCES: ["red"-Pareto] MINUS ["pink"-Zipf Archimedes-HYPERBOLICITY INEVITABILITY]!!! [Preview Abstract] |
|
C1.00215: A Revelation: Quantum-Statistics and Classical-Statistics are Analytic-Geometry Conic-Sections and Numbers/Functions: Euler, Riemann, Bernoulli Generating-Functions: Conics to Numbers/Functions Deep Subtle Connections R. Descartes, G.-C. Rota, L. Euler, J. D. Bernoulli, Edward Carl-Ludwig Siegel Quantum-statistics Dichotomy: Fermi-Dirac(FDQS) Versus Bose-Einstein(BEQS), respectively with contact-repulsion/non-condensation(FDCR) versus attraction/ condensationBEC are manifestly-demonstrated by Taylor-expansion ONLY of their denominator exponential, identified BOTH as Descartes analytic-geometry conic-sections, FDQS as Elllipse (homotopy to rectangle FDQS distribution-function), VIA Maxwell-Boltzmann classical-statistics(MBCS ) to Parabola MORPHISM, VS. BEQS to Hyperbola, Archimedes' HYPERBOLICITY INEVITABILITY, and as well generating-functions[Abramowitz-Stegun, Handbook Math.-Functions--p. 804!!!], respectively of Euler-numbers/functions, (via Riemann zeta-function(domination of quantum-statistics: [Pathria, Statistical-Mechanics; Huang, Statistical-Mechanics]) VS. Bernoulli-numbers/ functions. Much can be learned about statistical-physics from Euler-numbers/functions via Riemann zeta-function(s) VS. Bernoulli-numbers/functions [Conway-Guy, Book of Numbers] and about Euler-numbers/functions, via Riemann zeta-function(s) MORPHISM, VS. Bernoulli-numbers/ functions, visa versa!!! Ex.: Riemann-hypothesis PHYSICS proof PARTLY as BEQS BEC/BEA!!! [Preview Abstract] |
|
C1.00216: RANDOMNESS of Numbers DEFINITION(QUERY:WHAT? V HOW?) ONLY Via MAXWELL-BOLTZMANN CLASSICAL-Statistics(MBCS) Hot-Plasma VS. Digits-Clumping Log-Law NON-Randomness Inversion ONLY BOSE-EINSTEIN QUANTUM-Statistics(BEQS) . Z. Siegel, Edward Carl-Ludwig Siegel RANDOMNESS of Numbers cognitive-semantics DEFINITION VIA Cognition QUERY: WHAT???, NOT HOW?) VS. computer-``science" mindLESS number-crunching (Harrel-Sipser-...) algorithmics Goldreich "PSEUDO-randomness"[Not.AMS(02)] mea-culpa is ONLY via MAXWELL-BOLTZMANN CLASSICAL-STATISTICS(NOT FDQS!!!) "hot-plasma" REPULSION VERSUS Newcomb(1881)-Weyl(1914;1916)-Benford(1938) "NeWBe" logarithmic-law digit-CLUMPING/ CLUSTERING NON-Randomness simple Siegel[AMS Joint.Mtg.(02)-Abs. {\#} 973-60-124] algebraic-inversion to THE QUANTUM and ONLY BEQS preferentially SEQUENTIALLY lower-DIGITS CLUMPING/CLUSTERING with d = 0 BEC, is ONLY VIA Siegel-Baez FUZZYICS=CATEGORYICS (SON OF TRIZ)/"Category-Semantics"(C-S), latter intersection/union of Lawvere(1964)-Siegel(1964)] category-theory (matrix: MORPHISMS V FUNCTORS) "+" cognitive-semantics'' (matrix: ANTONYMS V SYNONYMS) yields Siegel-Baez FUZZYICS=CATEGORYICS/C-S tabular list-format matrix truth-table analytics: MBCS RANDOMNESS TRUTH/EMET!!! [Preview Abstract] |
|
C1.00217: Collective states of interacting Yang-Lee anyons in 1D: the golden chain's twin Eddy Ardonne, Jan Gukelberger, Andreas Ludwig, Simon Trebst, Matthias Troyer Collective states of interacting non-Abelian anyons have recently been studied mostly in the context of exotic quantum Hall states. In this talk we will further expand this line of research and present certain non-unitary generalizations of the original golden chain model. In particular, we introduce the notion of Yang-Lee anyons, discuss their relation to the `Gaffnian' quantum Hall wave function, and describe an elementary model for their interactions. A one-dimensional version of this model can be fully understood in terms of an exact algebraic solution and numerical diagonalization. We discuss the gapless phases of these models, and comment on the physical implications of the non-unitarity of their underlying critical theories. [Preview Abstract] |
|
C1.00218: Long-range in a system of thermal brownian particles Alexandro Heiblum, Francisco Sevilla, Victor Dossetti We present a model that exhibits an order-disorder phase transition in two spatial-dimensions. The model considers a collection of $N$ thermal Brownian particles moving in a square of length $L$ subjected to periodic boundary conditions and to velocity-alignment forces. The alignment force affects only the velocity direction in a way that it makes it equal to the velocity direction of the nearby group. Our results contrast with those obtained from the well known model of Vicsek {\it et al.} [Phys. Rev. Lett. {\bf 75}, 1226 (1995)] where such a transition occurs out of equilibrium. [Preview Abstract] |
|
C1.00219: Long-range order in a system of thermal Brownian particles Alexandro Heiblum, Francisco J. Sevilla, Victor Dossetti We present a model that exhibits an order-disorder phase transition in two spatial-dimensions. The model considers a collection of $N$ thermal Brownian particles moving in a square of length $L$ subjected to periodic boundary conditions and to velocity-alignment forces. The alignment force affects only the velocity direction in a way that it makes it equal to the velocity direction of the nearby group. Our results contrast with those obtained from the well known model of Vicsek {\it et al.} [Phys. Rev. Lett. {\bf 75}, 1226 (1995)] where such a transition occurs out of equilibrium. [Preview Abstract] |
|
C1.00220: Investigating Low Dimensional Chaos with Nearly Elastic Spheres Alex Sabey, Corey LaFontaine, Jeffrey Olafsen An experimental and numerical study of the dynamics in a system which is prone to chaotic motion is implemented via a shaking plate and two nearly elastic particles. Confined to move in the vertical direction, one spherical particle is driven by the shaking plate while the other sphere is driven by collisions with the first. The motion of the two particles and the plate were captured with a relatively high speed ($\sim $340 fps) CCD camera via image analysis algorithms written in IDL. Measurements of position, velocity, acceleration, and energy and are used to formulate a thorough description of the system. The experimental results are compared to those of a numerical simulation to explore phase space for chaotic orbits of the two trajectories as well as phase synchronization between the particles and the plate. A thorough investigation of the phase space to describe the low dimensional system as well as to examine the dynamics for phase synchronization between the two particles will be presented. [Preview Abstract] |
|
C1.00221: Simulation studies of diffusion limited ballistic growth of particles from a surface Stephen M. Kuebler, Aniket Bhattacharya Motivated by electroless deposition of metals on polymeric surfaces we plan to study evolving morphologies of deposited particles from a surface using Monte Carlo simulation in continuum which shares characteristics of both diffusive and ballistic behavior. In the proposed model we assume that the particles residing at the surface of a growing pattern are capable of attracting particles those are within a certain range. Once one of these seed particles attracts a particle it transfers its attractive characteristics to the newly adsorbed particle which then acquires this characteristics for further growth. The motion of the particles in the bulk is diffusive. However, once they are within the range of an ``active'' particle they move ballistically along a straight line and gets adsorbed to a cluster unless hindered by other particles on its way. We plan to report the characteristics of the evolving patterns as a function of density of the diffusive particles, the range of the attractive particles, and the speed of ballistic moves. [Preview Abstract] |
|
C1.00222: Intermittency and ergodicity breaking in a system of interacting self-propelled particles Francisco J. Sevilla, Victor Dossetti A comprehensive dynamical model for cooperative motion of self-propelled particles [Dossetti et al. Phys. Rev. E 79, 051115 (2009)], that combines velocity alignment interactions, spatial interactions, and angular noise, is studied. The noise considered in this model comes about nonlinear with correlations that decay in time, leading to a unique collective behavior. In particular, for a certain arrangement of the parameters, the system develops intermittent behavior and some sort of ergodicity breaking. In this work, we characterize these phenomena by studying the distributions of time intervals between turbulent bursts and changes between metastable states, respectively. [Preview Abstract] |
|
C1.00223: Non-Equilibrium Statistical Dynamics of River Network Evolution Xu-Ming Wang, Ping Zhang, Jie Huo, Rui Hao According to the erosion rule in a natural process, a Langevin Equation describing the prolongation of river channel is defined. The determinate prolongation is given by consideration of the characteristics of the early stage in the development of a river channel. The random growth (diffusion) is expressed by the fluctuations of the related stochastic variables or factors. A Fokker-Planck equation that describes the evolution of the distribution of the channel length is derived from this Langevin Equation. The solution presents the transition probability and exceedence probability with a Power-Exponent function which indicates that the channel length distributes in a complicated way. The details show that there exists a critical time, before which river network is developing and marked by exponent distribution., and beyond which river network is developed and marked by power distribution. On the basis of Hack's law, the transition probability of river's area and the corresponding exceedence probability are obtained. They are in excellent agreement with them obtained by field observations. [Preview Abstract] |
|
C1.00224: Introduction to the Mu-bit Florentin Smarandache, V. Christianto Mu-bit is defined here as `multi-space bit'. It is different from the standard meaning of bit in conventional computation, because in Smarandache's multispace theory (also spelt multi-space) the bit is created simultaneously in many subspaces (that form together a multi-space). This new `bit' term is different from multi-valued-bit already known in computer technology, for example as MVLong. This new concept is also different from qu-bit from quantum computation terminology. We know that using quantum mechanics logic we could introduce new way of computation with `qubit' (quantum bit), but the logic remains Neumann. Now, from the viewpoint of m-valued multi-space logic, we introduce a new term: `mu-bit' (from `multi-space bit). [Preview Abstract] |
|
C1.00225: Stochastic Phase Decoupling in Dynamical Networks William Sulis Network models and their theories play a central role in the understanding of complex systems, in particular complex social systems such as societies and organizations. An important problem is to understand how agent attributes become organized within the connectivity structure of a network. The effective matching of agent attributes is important for the expression of functionality by a network. The creation of static networks relative to some control parameter has been extensively studied and gives rise to order-disorder phase transitions. This paper extends this work to dynamic networks. Several models of dynamic networks are created relative to two control parameters and their associated stochastic phase transitions are examined. Under conditions of weak coupling between the control parameters, it is shown that the relevant stochastic phase transitions become decoupled from one another, each qualitatively distinct and dependent on a single (distinct) control parameter. [Preview Abstract] |
|
C1.00226: Range of spectral exponents in rigor-state muscle fibers -- a 1/f noise family affair? Caroline Ritz-Gold Using EPR spectroscopy, we have followed changes in crossbridge state in rigor-state muscle fibers as a function of time. These observed changes were of two types -- erratic fluctuations taking place on multiple time scales, and slowly-relaxing transients in response to substrate analog. For both types of change, the resulting power spectra had a 1/f-like power-law form with spectral exponents ranging from near 0 (white noise) to around 2 (brown noise). The average exponent was around 1 (pink noise). This observed broad range of spectral exponents is similar to that seen in the extended-family model of 1/f noise processes -- a model that includes members ranging from white noise to pink to brown (JM Halley, Trends. Ecol. Evoln. \underline {11}, 33, 1996). Properties of this extended family model include self-affinity, long correlation times (memory), and non-stationarity (JM Halley {\&} P Inchausti, Fluct. Noise. Lett \underline {4}, R1, 2004). We conclude that the broad range of spectral exponents observed in rigor-state muscle fibers reflects a type of underlying 1/f process. However, this particular type of process is unusual in that, although produced by a \underline {single} biological source (rigor muscle fibers), it appears to include not just one but \underline {all} of the members of the extended 1/f noise family -- from white to pink to brown. [Preview Abstract] |
|
C1.00227: Self organization of social hierarchy in competitive societies Takashi Odagaki, Ryo Fujie We investigate self organization of social hierarchy in a competitive society where all individuals have rights to participate in fighting. The winning probability of an individual against an opponent depends on the difference of their wealth. We introduce cost to participate in the fighting and show that the emergence of the hierarchical society depends strongly on the ratio of the cost to the reward for the winner. We show numerically and analytically that the phase transition occurs in two steps for most values of the ratio. Furthermore, we determine the phase diagram as a function of the ratio and the probability of participating in fighting. We show that there are four different phases in the parameter space, one egalitarian phase and three distinct hierarchical phases [Preview Abstract] |
|
C1.00228: Fermi Acceleration in a Periodically Driven Fermi-Ulam Model O.F. de Alcantara Bonfim The dynamics of a particle bouncing between two harmonically vibrating walls is analyzed in the context of the static wall approximation. Fermi acceleration is observed for a wide range of the ratio between the frequencies of the oscillating walls and their relative phases. However, no acceleration is observed if the frequency ratio is an integer. In the phase versus frequency-ratio diagram, the region in which Fermi acceleration is observed is separated by an upper and lower boundary. At the lower boundary, after a large number of collisions the particle average velocity increases with the square-root of the number of collisions ($n$) with the walls. Between the lower and upper boundaries, the particle average velocity behaves as $V(n) \sim n^{\beta}$, with $\beta$ in the interval [0.5, 1.0]. Below and near the lower boundary, the average particle velocity initially grows with the number of collisions until it eventually reaches a plateau. In this region, for a fixed frequency ratio, the velocity of the particle exhibits scaling properties over a range of the relative phases of the vibrating walls. Inelastic collisions with the walls cause suppression of the Fermi acceleration inside the previously accelerating region and lead to the particle velocity exhibiting scaling properties with respect to changes in the coefficient of restitution. [Preview Abstract] |
|
C1.00229: Moment ratios and dynamic critical behavior of a reactive system with several absorbing configurations Wagner Figueiredo, Marcelo Freitas de Andrade We determine the critical behavior of a reactive model with many absorbing configurations. Monomers A and B land on the sites of a linear lattice and can react depending on the state of their nearest-neighbor sites and temperature of the catalyst. We consider that monomers of the type A are allowed to react with nearest-neighbor monomers A or B, but reactions between monomers B are forbidden. Besides the temperature of the catalyst, we also include lateral interactions between pairs of nearest-neighbor monomers. We employ Monte Carlo simulations and finite-size scaling arguments to calculate the moments of the order parameter of the model as a function temperature. Some ratios between pairs of moments are independent of temperature and are in the same universality class of the Contact Process. We also find the dynamical critical exponents of the model and we show that they are in the direct percolation universality class whatever the values of temperature. [Preview Abstract] |
|
C1.00230: Simulating Electroweak Baryogenesis in the Standard Model Andrew Blaikie, R. Mike Winters, Deva O'Neil One explanation for the abundance of matter over anti-matter in the universe is Electroweak Baryogenesis, which proposes that an excess of baryons was created during the electroweak phase transition, when particles first acquired mass. This transition, which occurred about one-tenth of a nanosecond after the Big Bang, proceeded through bubble nucleation, with the walls of the ``bubbles'' expanding until the electroweak symmetry was broken everywhere in space. We modeled this process in Mathematica using the Standard Model. Although current mass limits for the Higgs boson rule out Electroweak Baryogenesis in the Standard Model, our simulation can provide the basis for modeling more sophisticated scenarios. We used the sonification software SuperCollider to create an audio representation of the growth of the bubbles. [Preview Abstract] |
|
C1.00231: Shannon's entropy decreases spontaneously in certain isolated systems Satoru Sato In this study, we present an isolated system in which the Shannon's entropy decreases spontaneously. Of course physical entropy must increase in an isolated system according to the second law of thermodynamics. But Shannon's entropy which depends on the view point of an observer can decrease in certain isolated systems entailed by the increase of the physical entropy. As Shr\"{o}dinger said in his famous book ``entropy, taken with the negative sign, is itself a measure of order''[1]. However, the order of living organisms is not just the decrease of the physical entropy itself, but something in larger scale, for example proteins. This fact suggests that the formation of order does not necessarily involve the emission of physical entropy from the view point of information theory.\\[4pt] [1] E. Shr\"{o}dinger, WHAT IS LIFE?, first published 1944 [Preview Abstract] |
|
C1.00232: Trajectory Analysis for Inelastic Gravitational Billiards Andy Yost, Jeffrey Olafsen We present an analysis for an experiment [1] involving the motion of a gravitational billiard undergoing inelastic collisions with a sloped boundary. The inelastic particle is set into ballistic motion within three types of boundary shapes: parabolic, hyperbolic, and wedge geometries. The two-dimensional experimental cell is oriented vertically with respect to gravity and motion is maintained by horizontal shaking. Trajectories for various boundary shapes, shaking frequencies, and amplitudes are analyzed to determine regions of periodic and chaotic behavior. The shaking is provided by a DC-motor and armature that allows for control of both the shaking amplitude and frequency. Comparison of the experimental results to numerical methods provides a sensitive test of the velocity dependence of the coefficient of restitution. The trajectories may also be examined to extract a Lyapunov exponent for the motion. \\[4pt] [1] S. Feldt and J. S. Olafsen, Phys. Rev. Lett.\textbf{ 94}, 224102 (2005). [Preview Abstract] |
|
C1.00233: Nonlinear dynamics of an electronic model of one-way coupling in one and two dimensions Aaron Doud, Barbara Breen, Jamie Grimm, Andrew Tanasse, Stuart Tanasse, John Lindner, Katsuo Maxted One-way or unidirectional coupling is a striking example of how topological considerations -- the parity of an array of multistable elements combined with periodic boundary conditions -- can qualitatively influence dynamics. Here we introduce a simple electronic model of one-way coupling in one and two dimensions and experimentally compare it to an improved mechanical model and an ideal mathematical model. In two dimensions, computation and experiment reveal richer one-way coupling phenomenology: in media where two-way coupling would dissipate all excitations, one-way coupling enables soliton-like waves to propagate in different directions with different speeds. [Preview Abstract] |
|
C1.00234: Gauss Modular-Arithmetic Congruence = Signal X Noise PRODUCT: Clock-model Archimedes HYPERBOLICITY Centrality INEVITABILITY: Definition: Complexity= UTTER-SIMPLICITY: Natural-Philosophy UNITY SIMPLICITY Redux!!! E. E. Kummer, Edward Carl-Ludwig Siegel Clock-model Archimedes [http://linkage.rockeller.edu/ wli/moved.8.04/ 1fnoise/ index. ru.html] HYPERBOLICITY inevitability throughout physics/pure-maths: Newton-law F=ma, Heisenberg and classical uncertainty-principle=Parseval/Plancherel-theorems causes FUZZYICS definition: (so miscalled) "complexity" = UTTER-SIMPLICITY!!! Watkins[www.secamlocal.ex.ac.uk/people/staff/mrwatkin/]-Hubbard[World According to Wavelets (96)-p.14!]-Franklin[1795]-Fourier[1795;1822]-Brillouin[1922] dual/inverse-space(k,w) analysis key to Fourier-unification in Archimedes hyperbolicity inevitability progress up Siegel cognition hierarchy-of-thinking (HoT): data-info.-know.-understand.-meaning-...-unity-simplicity = FUZZYICS!!! Frohlich-Mossbauer-Goldanskii-del Guidice [Nucl.Phys.B:251,375(85);275,185 (86)]-Young [arXiv-0705.4678y2, (5/31/07] theory of health/life=aqueous-electret/ ferroelectric protoplasm BEC = Archimedes-Siegel [Schrodinger Cent.Symp.(87); Symp.Fractals, MRS Fall Mtg.(89)-5-pprs] 1/w-"noise" Zipf-law power-spectrum hyperbolicity INEVITABILITY= Chi; Dirac delta-function limit w=0 concentration= BEC = Chi-Quong. [Preview Abstract] |
|
C1.00235: Network-Physics(NP) BEC DIGITAL({\#})-VULNERABILITY VERSUS FAULT-TOLERANT ANALOG G. K. Alexander, M. Hathaway, H. E. Schmidt, E. Siegel Siegel[AMS Joint Mtg.(2002)-Abs.973-60-124] digits logarithmic-(Newcomb(1881)-Weyl(1914; 1916)-Benford(1938)-"NeWBe"/"OLDbe")-law algebraic-inversion to ONLY BEQS BEC:Quanta/Bosons= digits: Synthesis reveals EMP-like SEVERE VULNERABILITY of ONLY DIGITAL-networks(VS. FAULT-TOLERANT ANALOG INvulnerability) via Barabasi "Network-Physics" relative-``statics''( VS.dynamics-[Willinger-Alderson-Doyle(Not.AMS(5/09)]-]critique); (so called)"Quantum-computing is simple-arithmetic(sans division/ factorization); algorithmic-complexities: INtractibility/ UNdecidability/ INefficiency/NONcomputability / HARDNESS(so MIScalled) "noise"-induced-phase-transitions(NITS) ACCELERATION: Cook-Levin theorem Reducibility is Renormalization-(Semi)-Group fixed-points; number-Randomness DEFINITION via WHAT? Query(VS. Goldreich[Not.AMS(02)] How? mea culpa)can ONLY be MBCS "hot-plasma" versus digit-clumping NON-random BEC; Modular-arithmetic Congruences= Signal X Noise PRODUCTS = clock-model; NON-Shor[Physica A,341,586(04)] BEC logarithmic-law inversion factorization:Watkins number-thy. U stat.-phys.); P=/=NP TRIVIAL Proof: Euclid!!! [(So Miscalled) computational-complexity J-O obviation via geometry. [Preview Abstract] |
|
C1.00236: Finite-Size-Scaling at the Jamming Transition: Corrections to Scaling and the Correlation Length Critical Exponent Stephen Teitel, Daniel V{\aa}gberg, Daniel Valdez-Balderas, Michael Moore, Peter Olsson We carry out a finite size scaling analysis of the jamming transition in frictionless bi-disperse soft core disks in two dimensions. We consider two different jamming protocols: (i) quench from random initial positions, and (ii) quasistatic shearing. By considering the fraction of jammed states as a function of packing fraction for systems with different numbers of particles, we determine the spatial correlation length critical exponent $\nu\approx 1$, and show that {\it corrections to scaling} are crucial for analyzing the data. We show that earlier numerical results yielding $\nu<1$ are due to the improper neglect of these corrections. [Preview Abstract] |
|
C1.00237: Response of Jammed Ellipsoid Packings Zorana Zeravcic, Andrea Liu, Sidney Nagel We investigate the nature of the jamming transition for packings of spheroids by examining the elastic moduli as a function of the aspect ratio of the particles $\varepsilon$ and the compression. Irrespective of the particle aspect ratio, both shear modulus $G$ and bulk modulus $B$ show the same scaling as a function of compression as is found for packings of spheres. Moreover, for any value of $\varepsilon$, $G$ is proportional to the excess of the coordination number above that found at the jamming threshold; this recovers the result for frictionless spheres at $\varepsilon=1$. Our results imply a new diverging length scale associated with the loss of rigidity of these spheroid packings. The critical behavior of ellipsoid packings is an extension of that found for spheres. [Preview Abstract] |
|
C1.00238: A new solution to the statistics of hard elongated objects Mohammad H. Ansari We propose a formalism that helps to study elasticity of hard elongated objects (e.g. needles, rectangles, ellipses, etc) analytically. For this aim, we introduce an approximation to the exact model that simplifies the Gibbs free energy to be solved analytically and then extract some formulations for a collective number of Gibbs related physical quantities. Interestingly, this formalism reproduces the numerical results of the exact model. The simplicity and the accuracy of this formalism allows to study some previously unknown properties of of elongated objects in different compressions, such as the elasticity coefficients of objects with curved boundary shapes. Moreover we introduce a new quantity, i.e. the mean inverse distance, and investigate how it behaves under different compressions. [Preview Abstract] |
|
C1.00239: Multiscale Modeling of Biomimetic Self-Healing Materials German Kolmakov, Amy Scarbrough, Chet Gnegy, Isaac Salib, Krzysztof Matyjaszewski, Anna Balazs We use a hybrid computational approach to examine the self-healing behavior of polymeric materials composed of soft nanogel particles crosslinked by a network of both stable and labile bonds. The latter are highly reactive and therefore, can break and readily reform. To capture the multiscale structure of the material, we take advantage of the multi-level Hierarchical Bell Model (mHBM) where the labile crosslinks are organized into M levels of interconnected elements, each of them represents a number of bonds that lie in parallel and is described by a single-level HBM. We vary the number of hierarchical levels M and the number of labile bonds in each element to determine optimal conditions for improving strength and toughness of the material. We also compare the properties of the multiscale material with those for the gel, in which only single-level interconnections are presented. This study takes its inspiration from biological systems that show remarkable resilience in response to mechanical deformation. [Preview Abstract] |
|
C1.00240: (BNL/DoE-hyped) "Self-Organized-Criticality"(SOC) is Merely Newton's(1687) Third Law of Motion F = ma REdiscovery: LONG PRE-"Bak"!!! P.R.E. Bak, I. Newton, Edward Carl-Ludwig Siegel "Bak"/BNL/DoE "self-organized-criticality"(SOC) usual BNL/DoE media-hype P.R spin-doctoring "show-biz" "Bush-waaa-...-aaah!!!" is manifestly-demonstrated in two distinct ways to be nothing but Newton's Third Law of Motion F = ma REdiscovery!!! PHYSICS: (1687) cross-multiplied F = ma rewritten as 1/m = a/F = OUTPUT/INPUT = EFFECT/ CAUSE = inverse-mass mechanical-susceptibility = X ("w "); X ("w ") $\sim $(F.-D. theorem-equivalence /proportionality)$\sim $ P("w ") "noise" power-spectrum; E $\sim $ w ; and E $\sim $(any/all media upper-limiting-speeds)$\sim $ m. Thus: w $\sim $ E $\sim $ m; inversion yields: 1/w $\sim $ 1/E $\sim $ 1/m $\sim $ a/F = X ("w ") $\sim $ P("w "); hence: F = ma dual/inverse-integral-transform is "'SOC"'s" P(w ) $\sim $ 1/w\^{}(1) !!! ; "PURE"-MATHS: F = ma double-integral time-series s(t) = [vot + (1/2) at\^{}(2)] inverse/dual-integral-transform formally defines power-spectrum: P(w ) = S {\{}s(t) e\^{}[-(i OR no i)w t]{\}} dt = S {\{}[vot + (1/2) at\^{}2)] e\^{}[-(i OR no i)w t]{\}} dt = vo S {\{}t e\^{}[-(i OR no i)wt]{\}} dt + (1/2) S {\{}[a =/= a(t)] e\^{}[-(i OR no i)wt){\}} dt = vo (d/dw ) Delta (w ) +(1/2) [a =/= a(t)] (d/dw )\^{}(2) Delta (w) = vo/w \^{}(0) +(1/2) [a=/=a(t)] /w \^{}1: if a = 0, then P(w ) $\sim $ 1/w \^{}0, VS. if a =/= a(t) =/= 0, then P(w ) $\sim $ 1/w; = by physics: ``SOC'' RE-expresses F = ma!!!: ``just `a tad' late/tardy'' REdiscovery of F=ma: LONG PRE-"Bak"!!! [Preview Abstract] |
|
C1.00241: Deformation of Entangled Random Fiber Networks Catalin Picu, Gopinath Subramanian The mechanics of random fiber networks which are not bonded or cross-linked but are subjected to topological constrains imposed by the excluded volume of the fibers is studied by means of a computational model. The fibers do not cross, have linear constitutive behavior in the axial and bending deformation modes and interact with each other frictionally. The system-scale response is highly-non-linear (power law) and hysteretic. The system exhibits a rich dynamics in response to imposed deformation, characterized by intermittency and spatial and temporal correlations of localized deformation (fiber-fiber sliding events). The role of friction in defining the overall system response is discussed. [Preview Abstract] |
|
C1.00242: Study of Transient Nuclei near Freezing Masaharu Isobe, Berni Alder The molasses tail in dense hard core fluids is investigated by extensive event-driven molecular dynamics simulation through the orientational autocorrelation functions. Near the fluid- solid phase transition, there exist three regimes in the relaxation of the pair orientational autocorrelation function, namely the kinetic, molasses (stretched exponential), and diffusional power decay. The density dependence of both the molasses and diffusional power regimes are evaluated and the latter compares with theoretical predictions in three dimensions. The largest cluster at the freezing density of only a few sphere diameter in size persist for only about 30 picoseconds ($\sim 2.8 \times 10^{-11}$[s]). The most striking observation through the bond orientatinal order parameter is the dramatic increase of the cluster size as the freezing density is approached. [Preview Abstract] |
|
C1.00243: COMPLEX STRUCTURED MATERIALS I |
|
C1.00244: From 2D graphene to 1D graphene nanoribbons: dimensional crossover signals in the structural thermal fluctuations Ariel Dobry, Sebasti\'an Costamagna I this work, by analyzing the thermal excited rippling in the graphene honeycomb lattice, we find clear signals of an existing dimensional crossover from 2D to 1D while reducing one of the dimensions of the graphene layer. Trough a joint study, using montecarlo atomistic simulations and analytical calculation based, we find that the normal-normal correlation function $G(q)$ does not change the power law behavior valid on the long wavelength limit, however the system size dependency of the quadratic out of plane displacement $h^2$ shows a breakdown of its corresponding scaling law. In this case we show that a new scaling law appear which correspond to a truly 1D system. On the basis of these results, and having explored a wide number of realistic systems size, we conclude that narrow nanoribbons presents strongest corrugations than the square graphene sheets. This result could have important consequences on the electron transport properties of freestanding graphene systems. [Preview Abstract] |
|
C1.00245: Properties of anisotropically etched graphene devices C.M. Reynolds, A. Roberts, A.S. Sandhu, B.J. LeRoy Mechanically exfoliated graphene on a SiO2 substrate was etched using a solution of nickel nanoparticles. Using an atomic force microscope, etch lines 10 nm in width were observed. In addition, etch lines made angles of only 60 and 120 degrees and did not cross one another indicating that the etching occurs along a crystallographic edge. This resulted in structures such as equilateral triangles and nanoribbons as narrow as 35 nm wide. We have investigated these devices using Raman spectroscopy and scanning tunneling spectroscopy to determine the quality of the crystallographic edges and the local electronic properties. [Preview Abstract] |
|
C1.00246: Anisotropy and edge roughness scattering in the thermal conductivity of graphene nanoribbons Zlatan Aksamija, Irena Knezevic We present a calculation of the thermal conductivity of graphene nanoribbons, based on solving the Boltzmann transport equation with the full phonon dispersions, a momentum-dependent model for edge roughness scattering, as well as three-phonon and isotope scattering. The interplay between strong edge roughness scattering and the anisotropy of the phonon dispersions results in thermal conduction that strongly depends on the chiral angle of the nanoribbon. A minimum occurs in the armchair direction and a maximum is attained in zig-zag nanoribbons. We also show that both the thermal conductivity and the amount of armchair/zig-zag anisotropy depend strongly on the width of the nanoribbon and the rms height of the edge roughness, with smallest and most anisotropic thermal conductivities occuring in narrow GNRs with rough edges. We conclude that physical width of the nanoribbon and the rms roughness of its line edges can be used along with angular direction as parameters to tailor the value of the thermal conductivity. [Preview Abstract] |
|
C1.00247: Electro-Mechanical Actuation of Carbon Nanotube Yarns, Sheets, Composites Jiyoung Oh, Mikhail Kozlov, Mei Zhang, Shaoli Fang, Ray Baughman We report preparation of highly conductive carbon nanotube yarns and sheets. The materials aim at such applications as electronic textiles, electro-mechanical actuators, and conductive coatings. The electro-mechanical response of the specimens was measured using custom made force transducer operating in an isometric mode. The measurements were carried out at room temperature in aqueous and organic electrolytes; square-wave potential of variable amplitude was applied with a potentiostat. It was found that the maximum isometric stress generated by nanotube actuators could be as large as 12 MPa. This approaches the stress generation capability of commercial ferroelectrics and is significantly larger than that of natural muscles. A variety of applications of the materials is discussed. [Preview Abstract] |
|
C1.00248: Convenient growth of millimeter-long, few-walled carbon nanotube forests Raquel Ovalle-Robles, Xavier Lepro, Marcio Lima, Ray Baughman We report the efficient growth of 3 mm long, few-walled carbon nanotube (FW-CNT) forests by chemical vapor deposition on Si substrates. High yields (nearly 90{\%}) of FW-CNTs were grown in a continuous and controlled way in 3 hours without resorting to water-assisted growth. TEM and SEM images of 1 and 3 mm long FW-CNTs show that the forests are comprised of mostly carbon double walled nanotubes and single walled nanotubes having large diameters. The number of walls was controlled by the catalyst thickness (ranging from 0.2 to 0.6 nm) and nanotube length was controlled by adjustment of gas pressures (ethylene, hydrogen and argon), temperature and residence time. The Al$_{2}$O$_{3}$ buffer layer was critically important for this controlled synthesis. [Preview Abstract] |
|
C1.00249: Super acid processing of Single walled carbon nanotube (SWNT): effect of SWNT aspect Ratio on Macroscopic properties Natnael Behabtu, Anson Ma, Dmitri Tsentalovich, Colin Young, Matteo Pasquli Single walled carbon nanotubes are exceptional building blocks that combine great mechanical, electrical and thermal properties with low density. A number of processing techniques have been proposed to manufacture macroscopic articles made purely of carbon nanotubes. Superacid processing is the most flexible and promising of all since it allows dissolution of a wide range of carbon nanotube materials, including hundreds of micron long carpets. Here we show how SWNT aspect ratio influences the rheology (both shear and extensional) of SWNT/super acid solution. The longest SWNT ($\sim $10 microns as measured by cryo-TEM) are able to form stable, highly aligned fibrils under elongational flow. Fibrils thus made can be recovered and further characterized. These fibrils have some of the lowest resistivity of SWNT based material to date (160 $\mu $m-cm). These materials can also be processed into conducting and transparent films via dip coating and vacuum filtration. Films made with the longest SWNT gave a sheet resistance of 150 Ohm/sq at 90{\%} transparency. We have also mixed long SWNT at high concentration (10 wt{\%}) and, as expected, they form liquid crystalline solution. Surprisingly, we find that the viscosity of highly concentrated solution is not a function of the aspect ratio of the constitutive molecules (unlike dilute solutions). This allows for the high concentration solutions to be successfully spun into neat SWNT fibers. [Preview Abstract] |
|
C1.00250: Development of Side-gated Carbon Nanotubes for Terahertz Studies Chris McKitterick, Joel Chudow, Daniel Santavicca, Daniel Prober, Philip Kim The single-walled carbon nanotube is a truly one-dimensional conductor. The currently accepted theory describing propagation of electrons in the nanotube is Luttinger liquid theory, which predicts collective charge modes moving at a velocity greater than the Fermi velocity. By modeling the carbon nanotube as a transmission line, this propagation velocity can be determined from the standing wave resonances in the system. Due to the high resistance of carbon nanotubes, a length on the order of one micron must be used, resulting in resonances which occur at terahertz (THz) frequencies. These resonances can be measured using the heating of the nanotube electron system [1]. To avoid the use of a conducting substrate that absorbs THz, we use a side gate. We describe the development of nanotube samples with side gates for the proposed THz experiment. \newline \newline [1] D.F. Santavicca, J.D. Chudow, D.E. Prober, M.S. Purewal and P. Kim, Nano Lett. 10, 4538 (2010). [Preview Abstract] |
|
C1.00251: Understanding the emission current limiting step in the carbon nanotube based polymer composite cathodes David Carey, Thomas Connolly, Richard Smith Carbon nanotube (CNT) based electronic applications often make use of the intrinsically high electrical conductivity of the nanotubes for charge transport. One attractive area for the exploitation of nanotubes is to combine their high electrical conductivity with their high aspect ratio leading to the development CNT based cathodes. In the presence of an electric field the field lines concentrate on the tip of nanotube and the resultant high local electric field (few V/nm) can result in electron tunneling (Fowler -- Nordheim tunneling) from the tip and emission. Embedding a nanotube in a polymer matrix opens up the possibility of a large area and a solution processable way to produce cathodes [1]. We have studied the factors that control the rate limiting step for electron transport in functionalized CNTs in polyvinyl alcohol composites. We demonstrate excellent emission and current transport for nanotube volume fractions down to as low as 1 vol.{\%} and that in the range from 1 vol.{\%} to 7 vol.{\%} the threshold field for emission does not significantly depend on nanotube content. Key to good emission is the ability to disperse the nanotubes efficiently. \\[4pt] [1] T. Connolly, R. C. Smith, Y. Hernandez, Y. Gun'ko, J. N. Coleman and J. D. Carey, Small \textbf{5}, 826 (2009). [Preview Abstract] |
|
C1.00252: In-Air Growth of Carbon Nanotubes Christopher Huynh, Ryan Lu, Ayax Ramirez, Debjyoti Banerjee Carbon nanotubes were fabricated using catalytic metal growth methods in air. Their microstructures were characterized using scanning electron microscopy and micro Raman spectroscopy. The results indicate non-aligned carbon nanotubes. In-air growth would facilitate implementation of wide-area growth of carbon nanotubes in a variety of DoD and commercial applications. [Preview Abstract] |
|
C1.00253: Molecular dynamics simulations of oxide memory resistors (memristors) Alexander Bratkovsky, S.E. Saveliev, A.S. Alexandrov, R.S. Williams Reversible bipolar nano-switches that can be set and read electronically in a solid-state two-terminal device are very promising for applications. We have performed molecular- dynamics simulations that mimic systems with oxygen vacancies interacting via realistic potentials and driven by an external bias voltage. The competing short- and long-range interactions among charged mobile vacancies lead to density fluctuations and short-range ordering, while illustrating some aspects of observed experimental behavior, such as memristor polarity inversion. The simulations show that the ``localized conductive filaments'' and ``uniform push/pull'' models for memristive switching are actually two extremes of one stochastic mechanism [1]. \\[4pt] [1] S. E. Savel'ev, A. S. Alexandrov, A. M. Bratkovsky, R. Stanley Williams, arXiv:1010.5656v1 [Preview Abstract] |
|
C1.00254: The electrical and magnetic properties of C-doped ZnO film Dong Hak Kim, Joon Won Park, Daeyoung Lim The theoretical explanation on the room temperature ferromagnetism (RTF) in ZnO:C is based on the C incorporation at the O-site and the consequent exchange interaction between the localized C2p spins and valence-band holes. Here, we investigated the C incorporation site and the electrical properties of C-doped ZnO films grown by pulsed laser deposition (PLD) at both an oxygen rich and a poor conditions. Contrary to the theoretical explanations, all the C-doped ZnO films exhibited n-type conductivity. Furthermore, most of the carbons were not incorporated at the O-site, but rather at the interstitial or Zn site, or formed C clusters. Our experimental results indicate that the defect-induced ferromagnetism mechanism can better explain most of the observed RTF in the PLD grown ZnO:C films. [Preview Abstract] |
|
C1.00255: Molecular Simulations of Graphene-Based Electric Double-Layer Capacitors Raja K. Kalluri, Deepthi Konatham, Alberto Striolo Towards deploying renewable energy sources it is crucial to develop efficient and cost-effective technologies to store electricity. Traditional batteries are plagued by a number of practical problems that at present limit their widespread applicability. One possible solution is represented by electric double-layer capacitors (EDLCs). To deploy EDLCs at the large scale it is necessary to better understand how electrolytes pack and diffuse within narrow charged pores. We present here simulation results for the concentrated aqueous solutions of NaCl, CsCl, and NaI confined within charged graphene-based porous materials. We discuss how the structure of confined water, the salt concentration, the ions size, and the surface charge density determine the accumulation of electrolytes within the porous network. Our results, compared to data available for bulk systems, are critical for relating macroscopic observations to molecular-level properties of the confined working fluids. [Preview Abstract] |
|
C1.00256: Capture and release of carbon dioxide by carbon nanotubes via temperature cycling Deniz Rende$^{2}$, Nihat Baysal, Rahmi Ozisik Carbon nanotubes (CNTs) received remarkable attention since they were shown to possess many unique properties as well as being effective and stable adsorbent materials that make them potentially useful for gas storage and separation of various gas mixtures. In this study, the effect of temperature variations on carbon dioxide (CO$_{2}$) capture via single walled carbon nanotubes (SWNTs) and multi walled carbon nanotubes (MWNTs) were investigated with molecular dynamics simulations. SWNTs of type (10,10), (15,15), and (20,20) and MWNTs formed from the combination of these were simulated. The temperature was varied between 300 and 360 K. The results suggest that absorption of CO$_{2}$ into the CNTs were directly related to the internal volume of the nanotube, but the cross-sectional area of the tube entrance had a significant effect on the number of CO$_{2}$ molecules retained. The number of CO$_{2}$ molecules collected in CNTs gradually decreases with increasing temperature. Separate simulations were performed to understand the potential use of CNTs as thermal pumps to collect/discharge CO$_{2}$ molecules via temperature cycling. [Preview Abstract] |
|
C1.00257: Half-Metallic Sandwich Molecular Wires with Negative Differential Resistance and Sign-Reversible High Spin-filter Efficiency Lu Wang, Xin Yan, Jing Zhou, Jing Lu, Zhengxiang Gao, Xingfa Gao, Shigeru Nagase, Stefano Sanvito, Yutaka Maeda, Takeshi Akasaka, Wai-Ning Mei Using density functional theory and non-equilibrium Green's function method, we construct organometallic nanowires that consist of Fe or V atoms sandwiched between composite molecules (Cp$^{\ast }$FeCp$^{\ast }$, where Cp$^{\ast }$ is C$_{5}$(CH$_{3})_{5})$. For the first time, we demonstrate that half-metallicity, negative differential resistance, and sign-reversible high spin-filter capability can coexist remarkably in one organometallic nanowire (FeCp$^{\ast }$ wire). This renders FeCp$^{\ast }$ wire promising in electronics and spintronics. [Preview Abstract] |
|
C1.00258: An investigation on work-function enhancement in multilayer graphene Abbas Ebnonnasir, Branden B. Kappes, Cristian V. Ciobanu Using density functional theory calculations, we perform a detailed analysis of the electronic properties of multilayer graphene on a generic substrate. A range of the possible substrate effects is simulated by systematically changing the interlayer distance between the first two graphene layers and leaving the other layers at the nominal graphite spacing. We find that the work function on the graphite-like side varies with the number of layers and with the distance between the first two layers, and we analyze the charge transfer distribution and the surface dipole moment as a function of the distance between the first two graphene layers. We correlate our results with reported experimental observations and provide possible explanations of pronounced work-function variations. [Preview Abstract] |
|
C1.00259: Scanning Tunneling Microscopy Study of Grain Boundaries in Graphene Grown by Chemical Vapor Deposition on Copper Foil Justin Koepke, David Estrada, Joshua Wood, Eric Pop, Joseph Lyding There have been few scanning tunneling microscopy studies of graphene grown by CVD on Cu [1] and no atomic scale studies of the electronic properties of the films' grain boundaries. We present the electronic nature of grain boundaries in polycrystalline graphene grown by CVD on Cu foil and transferred to SiO2 substrates. These grain boundaries are continuous across large protrusions and wrinkles in the graphene and other surface topography. We observe misorientation angles of approximately 7\r{ }, 23\r{ }, and 30\r{ } across the grain boundaries and standing wave patterns adjacent to the grain boundaries with a decay length on the order of 1 nm. The spectroscopy shows enhanced conduction in empty states at the grain boundaries. The graphene is grown on 1.4 mil copper foil by CVD. After growth the graphene was transferred onto a SiO$_{2}$/Si substrate using PMMA and FeCl$_{3}$. Raman spectroscopy and atomic force microscopy are used to characterize the roughness and quality of the graphene. The sample was degassed in the UHV-STM system at 600 -- 700 \r{ }C for 24 hours.\\[4pt] [1] X. Li et al., Science 324, 1312 (2009) [Preview Abstract] |
|
C1.00260: CVD graphene growth on different substrates P. H\"aberle, A. Cortes, C. Celedon, V. Del Campo Graphene growth on solid substrates have the advantage of growing high quality epitaxial graphene. In this sence it is important to choose substrates and precursors having in mind the final application and an efficiency if the process. In this work we grow graphene by CVD on three different substrates, changing temperatures and precursor concentration. For graphene growth on copper foil we heat the sample up to 1000 $^{\circ}$ C in the presence of a hydrogen and acethylene flux. The same process is performed for graphene growth on copper oxide thin films. These thin films ($\sim $400 nm) are prepared by conventional sputtering on SiO$_{2}$ substrates and the reduced inside the preparation chamber. The advantage of this process is that copper undergoes a dewetting process during graphene growth, so at the end we have graphene suported on the SiO$_{2}$ substrate. To monitor graphene growth we use Raman spectrometer. For graphene growth on Ru(0001) we heat the substrate, temperature between 840$^{\circ}$C and 1000$^{\circ}$C in ultra high vacuum (UHV). We introduce ethylene in the vacuum chamber and cool down the sample. To monitor graphene growth we use Low Energy Electron Diffraction. [Preview Abstract] |
|
C1.00261: Controlling the Thermal Decomposition of Silicon Carbide into Graphene David Torrance, Tien Hoang, David Miller, Baiqian Zhang, Walt de Heer, Phillip First The quality of epitaxial graphene films grown by thermal decomposition of silicon carbide depends on experimental control of the net silicon desorption rate. Such control has been previously demonstrated by three techniques: tight confinement within an induction furnace, growth in 1-atm Ar buffer gas, or introduction of a silane overpressure. Our goal is to study the physics of these methods. We have constructed an all-graphite UHV induction furnace with maximum temperature over 1700$^\circ$ C and gas handling that allows process gas pressures from UHV to 1 atm. Sample holders with different orifices are used to vary the furnace confinement. Our initial systematic measurements of the effect of Ar buffer gas pressure establish that the silicon sublimation rate is adequately described by a 1D diffusion model with geometry-dependent parameters. [Preview Abstract] |
|
C1.00262: Large area growth of single layer graphene on the C-face SiC Baiqian Zhang, Ming Ruan, Michael Sprinkle, Yike Hu, John Hankinson, Claire Berger, Walt A. de Heer High quality graphene, from monolayer to many layers are consistently grown on the carbon terminated face of 4H-SiC, using the confinement controlled sublimation growth method in an induction furnace. Here we show large area monolayer graphene grown on silicon carbide substrates with this method. C-face 1cmx1cm SiC samples were graphitized by carefully controlling silicon sublimation. Ellipsometry measurements demonstrate an essentially uniform high quality graphene layer over the entire surface. The SiC chip is entirely covered by monolayer graphene, with less that 5{\%} of bi-layer region. The thickness homogeneity is confirmed by photoemission electron microscopy, Raman spectroscopy, Atomic force microscopy (AFM). We also present transport measurements on single graphene layer C-face sample. [Preview Abstract] |
|
C1.00263: Micellization and phase transitions in a triblock copolymer-D$_{2}$O system Hosanna Odhner, Alison Huff, Kelly Patton, D.T. Jacobs, Bryna Clover, Sandra Greer The triblock copolymer (``unimer'') of PPO-PEO-PPO (commercially known as 17R4) has hydrophobic ends and a hydrophilic center. When placed in D$_{2}$O at lower concentrations and temperatures, only a network of unimers exists. However, at higher concentrations or temperatures, micelles of different geometries can form. We have measured the micellization line marking the transition from only unimers to some micelles, as well as a one- to two-phase transition at higher temperatures. This second transition is an Ising-like, LCST critical point, based on the shape of the coexistence curve. We find the LCST to not correspond to the minimum of the cloud point curve, which indicates polydispersity as described by Sollich. [Preview Abstract] |
|
C1.00264: INSULATORS AND DIELECTRICS |
|
C1.00265: The T$_{g}$ of polycyanurate in cylindrical nanoporous confinement Siyang Gao, Sindee Simon The glass transition behavior of materials under nanoconfinement is often different than their behavior in the bulk. A leading explanation is that enhanced mobility at free surfaces or neutral interfaces results in depressions in Tg, whereas attractive interfaces result in increases in Tg. In this work, we examine the Tg of a polycyanurate using differential scanning calorimetry for both material confined in cylindrical nanopores and for freely-standing nanocylinders. Preliminary results using an alumina nanofilter for the confining matrix indicate that the Tg depression for the supported and freely standing nanocylinders are similar. The implications of the results will be discussed. [Preview Abstract] |
|
C1.00266: Band Alignment of atomic layer deposited HfO2 on clean and N passivated Germanium surfaces Abdul Rumaiz, Joseph Woicik, Gabriella Carini, Peter Siddons, Eric Cockayne, Patrick Lysaght, Daniel Fischer Hard x-ray photoelectron spectroscopy (HAXPES) has been used to study the band alignment between atomic layer deposited (ALD) HfO2 on clean Ge (100) and nitrogen treated Ge (100) surfaces. The position of the valence-band maximum was determined by convolving theoretically calculated density of states from first-principles calculations and comparing with experimental valence-band data. The valence-band offset was found to be 3.2 $\pm $ 0.1 and 3.3 $\pm $ 0.1 eV for the samples grown on clean and N passivated Ge, respectively. The oxide charge however shows a significant increase between the two samples. The small change in the band offset between the two systems strongly indicates negligible contribution of the interface to the conduction/valence-band barrier and the band alignment of the heterojunctions. [Preview Abstract] |
|
C1.00267: Spectroscopic Ellipsometry of Gadolinium Gallium Oxide Multilayers Kaleb Gilbert, Kunal Bhatnagar, Steve Jackson, Ravi Droopad, Wilhelmus Geerts The dielectric parameters of Gadolinium Gallium Oxide (GGO) multilayer structures have been investigated with spectroscopic ellipsometry and modeled with a simplified modeling technique. The GGO thin films are of varying thickness and the simple four parameter model was effective in determining consistent values for the dielectric constants of this important high k dielectric material. Ellipsometric data was collected in two different acquisition configurations to insure the merit of the model. The model is further confirmed by the determination of film thickness values within an acceptable range when compared with those reported by the sample grower. The dielectric parameters are then used to determine the band gap of GGO. [Preview Abstract] |
|
C1.00268: The existence of an isopermitive point of water at low frequencies Hilda Mercado, Abril Angulo Water has been studied extensively since the last past century and it continues to be a subject of great interest because it has special properties and a relevant role in biological functions. One of the most used techniques to study water is the dielectric spectroscopy. Normally, the studies with this method are carried out at frequencies higher than 1 MHz. We have studied the relative permittivity of water at low frequencies (100 Hz to 1 MHz), and we found that this varies strongly as a function of the frequency. In addition, we found a specific frequency where this parameter is independent of temperature and we called it the isopermitive point. Below this point the relative permittivity increase with temperature, above, it decreases. Our explanation of this behavior is that water can be considered as a system of two species: dipoles and ions. The first obey the Maxwell-Boltzmann statistics, while the second causes the Maxwell-Wagner-Sillars effect. At the isopermitive point the effect of both mechanisms in the relative permittivity compensate each other. [Preview Abstract] |
|
C1.00269: An \textit{Ab Initio }Study of rare gases in uranium dioxide Li Ma, Asok Ray Hybrid density functional theory has been used to study the stability and behavior of rare gases (He, Ne, Ar, Kr and Xe) in uranium dioxide. The calculations have been performed using the all-electron \underline {f}ull-\underline {p}otential \underline {l}inearized \underline {a}ugmented \underline {p}lane \underline {w}ave plus \underline {l}ocal \underline {o}rbitals basis (FP-L/APW+lo) method. Three insertion sites are considered: the octahedral interstitial position and the oxygen and uranium substitution sites. The defect formation energy, the optimized lattice constants and the volume variation induced by gaseous atom incorporation, and the electronic structure are studied for each rare gas in anti-ferromagnetic UO$_{2}$ phase without and with spin-orbit coupling (scalar vs. ``full'' relativistic). The results indicate that the lattice constants and formation energies increase with the increase of the radius of the rare gases. The octahedral interstitial position is the most favorable occupation site. All incorporation energies are found to be positive implying an exothermic process. [Preview Abstract] |
|
C1.00270: Ab initio study of adatom adsorption on topological insulator thin film Kyung-Hwan Jin, Seung-Hoon Jhi Recently topological insulator has attracted great attention due to its intriguing electronic and transport properties. Topological insulator has bulk energy gap but conducting surface states which are chiral with a linear energy-momentum relation. These surface states are robust against external perturbations as they are protected by the time reversal symmetry. We studied the electronic structure of topological insulator Bi$_{2}$Te$_{3}$ thin film and investigated how it is modified upon the adsorption of single atomic impurities using first-principles calculations. We chose nitrogen (N), oxygen (O), sodium (Na) and cobalt (Co) atoms to study their adsorption on top of Bi$_{2}$Te$_{3 }$surface. We investigated the effect of non-magnetic and magnetic impurities on the surface states, and the band splitting due to the inversion symmetry-breaking by the Rashba field. [Preview Abstract] |
|
C1.00271: Phonons in Bi2Te3 and Bi2Se3 Thin Films Shang-Fen Ren, Wei Cheng Bi2Te3 and Bi2Se3 are topological insulators attracted great research attention in recent years. In this research, some of calculated results on phonons in Bi2Te3 and Bi2Se3 bulk and single quintuple thin films are presented. The effects of spin-orbit couplings on phonon properties in these materials are discussed. Some features of Raman observations of these materials are explained. [Preview Abstract] |
|
C1.00272: Performance of the spin- and angle- resolved photoemission spectrometer with highly efficient VLEED spin detector K. Miyamoto, T. Okuda, A. Kimura, H. Miyahara, K. Kuroda, H. Namatame, M. Taniguchi Because of the growing scientific interests in the spin-related exotic materials such as topological insulators, spin- and angle- resolved photoemission with much improved efficiency is strongly desired. In this report, we present the current status of a new SARPES with significantly improved energy- ($\Delta E)$ and angular resolutions ($\Delta \theta )$, which is under construction at beam line BL-9B in Hiroshima Synchrotron Radiation Center. The system consists of high performance hemispherical analyzer (VG-Scienta R-4000) and highly efficient spin detector based on very low energy electron diffraction of Fe(001)p(1x1)-O, which has 100 times higher efficiency than conventional Mott spin detector. Owing to the high efficiency of the detector, the highest $\Delta E$ and $\Delta \theta $ have been improved to be 7.5 meV and 0.37$^{o}$. Moreover, high-resolution ARPES measurement ($\Delta E \quad \sim $ 2meV, $\Delta \theta \quad \sim $ 0.2$^{o})$ and Fermi surface mapping in the sample temperature range from 8K to room temperature can be efficiently performed by hemispherical analyzer equipped with multi-channel detector and motorized 5 axis goniometer. These features of the SARPES enable us to observe detailed spin-dependent band structures of topological insulators very precisely and efficiently. [Preview Abstract] |
|
C1.00273: Statistics of Josephson vortices in topological superconductors Eytan Grosfeld, Ady Stern In recent years there has been an intensive search for Majorana fermions in condensed matter systems. Predicted to be localized on cores of vortices in certain non-conventional superconductors, their presence is known to render the exchange statistics of bulk vortices non-Abelian. In this talk I will present novel results regarding the persistence of Majorana zero modes into insulating barriers, providing a way to coherently and effectively manipulate them. A method to probe the Majorana modes will be presented. [Preview Abstract] |
|
C1.00274: Van der Waals epitaxial growth and transport properties of Bi2Se3 thin films Jian-Hao Chen, Jack Hellerstedt, William Cullen, Michael Fuhrer Thin films of Bi$_{2}$Se$_{3}$ with high carrier mobility are grown with van der Waals epitaxy method in ultra-high vacuum environment on single crystal Sapphire (0001) and single crystal SrTiO$_{3}$ (111) surfaces. \textit{Ex-situ} transport measurement revealed weak-antilocalization-like behavior at small out-of-plane magnetic field (B$_{o})$ and non-linear Hall conductance versus Bo. The carrier concentration of the Bi$_{2}$Se$_{3}$ can be substantially tuned with applied electric field through the SrTiO$_{3}$ substrate. [Preview Abstract] |
|
C1.00275: Electronic properties at the interface in oxide BiFeO$_{3}$/Nb-doped SrTiO$_{3}$ semiconductor Yu-Ting Chen, Ya-Ping Chiu, Min-Chuan Shih, Jan-Chi Yang, Yi-Chun Chen, Ying-Hao Chu In oxide systems, the interface of the heterojunctions had attracted much attention due to the interesting properties of the low-dimensional electron confinement. In this work, by using cross-sectional scanning tunneling microscopy, the direct and local information of structural and electronic properties across the$ p-n$ heterojunction in the multiferroic BiFeO$_{3}$ films grown on Nb-doped SrTiO$_{3}$ substrate was investigated. Spectroscopy analysis of the point-to-point electronic properties allows us to realize how the asymmetrically electronic band alignment is formed at the interface. Further analysis of the evolution of the potential field across the interface also reveals that surface charge states, spontaneous polarization, and the $p-n$ contact contribute to the formation of the build-in field pointing from BiFeO$_{3}$ films to Nb-SrTiO$_{3}$ semiconductors. [Preview Abstract] |
|
C1.00276: Size dependent anomalous dielectric behavior in nanoparticle Gd$_{2}$O$_{3}$ : SiO$_{2}$ glass composite system Sudip Mukherjee, Yu-Hsing Lin, Ting-Hui Kao, C.C. Chou, H.D. Yang Gd$_{2}$O$_{3}$ (0.5 mol{\%}) nanoparticles have been synthesized in a silica glass matrix by the sol-gel method at calcination temperatures of 700 $^{\circ}$C and above. Compared with the parent material SiO$_{2}$, this nano-glass composite system shows enhancement of dielectric constant and diffuse phase transition along with magnetodielectric effect around room temperature. Observed conduction mechanism is found to be closely related to the thermally activated oxygen vacancies. Magnetodielectric behavior is strongly associated with magnetoresistance changes, depending on the nanoparticle size and separation. Such a material might be treated as a potential candidate for device miniaturization. [Preview Abstract] |
|
C1.00277: Study of field-dependent coupling of mixed phases in highly-strained BFO by impedance spectrum Jhih-Wei Chen, Yi-Chun Chen, H.J. Chen, W.I. Liang, Ying-Hao Chu In this study, we investigated the dielectric mechanism of highly-strained BFO epitaxial films with Tetragonal (T)-like and rhombohedral (R)-like monoclinic phases. The ratio of R-like BFO to T-like BFO is controllable by varying the film thickness through the relaxation of substrate stress. The impedance spectrum of T-like and R-like samples showed conducting-system dispersive (CSD) peaks at 20 kHz and 6.7 MHz, respectively. By contrast, the T+R-BFO had an additional dielectric-system dispersive (DSD) mechanism at relatively low frequency of 4.2 kHz. Moreover, the distribution range of relaxation time for this mechanism depended on the switching history, implying that the mechanism is related to the ferroelastic interaction between the two monoclinic phases. This result suggested intermediate states through phase transformation will reduce energy barrier for polarization switching. The effect of interfacial capacitance between sample and electrode was also discussed. [Preview Abstract] |
|
C1.00278: Monoclinic phase transition in stress-induced BiFeO3 epitaxial films Yen-Chin Huang, Y.C. Chen, C. Cheng, K.I. Lin, J.S. Hwang, W.I. Liang, H.J. Chen, Y.H. Chu Material system near morphotropic phase boundary usually attracted a lot of attention due to their unique physical properties. The key issue of the mechanism is to reveal the coupling between the multiple phases or the intermediate states during phase transformation. Recently, highly-strained multiferroic BiFeO3 (BFO) films had been reported to possess a particular isosymmetric boundary between tetragonal(T) and rhombohedral(R) phases. In this study, we investigated the as-grown state of mixed-phase BFO and the evolution of phases under external stimulus. Through first principle study and Raman measurement, we found the mixed phase BFO films at room temperature included two monoclinic phases, MA(Cm) and MC (Pm). When the temperature was increased to about 420 K, MC phase transformed to a R-like phase. The MA and the R-like phase coexisted until 620 K; after that, the R-like phase disappeared while the MA lasted to higher temperatures. This result showed the possible path of transition near the morphotropic phase boundary. [Preview Abstract] |
|
C1.00279: Tunnel electroresistance in ferroelectric tunnel junctions A. Chanthbouala, A. Crassous, V. Garcia, K. Bouzehouane, S. Fusil, J. Grollier, C. Deranlot, X. Moya, N. Mathur, M. Bibes, A. Barthelemy In tunnel junctions with a ferroelectric barrier, large resistance changes can arise upon switching the ferroelectric polarization direction. This tunnel electroresistance (TER) effect has recently been observed by scanning probe techniques on electrode/barrier bilayers (e.g. LSMO/BaTiO$_{3}$), yielding giant TER values in the 50000\% range at room temperature. Beside their fundamental interest to elucidate the interplay between electrostatic effects, changes in the interfacial density of states, piezoelectricity and quantum-mechanical tunneling, ferroelectric tunnel junctions undoubtedly present a great potential for application as memory devices with simple, non-destructive readout and low-power write operations. We will present our progress towards the realization of solid-state ferroelectric tunnel junctions and discuss their potential as next-generation non-volatile memories. [Preview Abstract] |
|
C1.00280: Structural and Magnetic Study of YCrO$_{3}$ Doped with Calcium Eduardo Verdin, Francisco Morales, Raul Escamilla, Roberto Escudero, Alejandro Duran In recent years there has been much interest in multiferroic materials. The coupling between ferromagnetic and ferroelectricity on the same material is important from both basic science and applications. Here we address the behavior observed in YCrO$_{3}$ doped with Ca. The pure material presents a ferroelectric transition at about 473 K, and ferromagnetism at about 140 K. The magnetic transition is due to canted spins, so ferromagnetism and antiferromagnetism coexist. In this presentation we will show the studies on Ca doped YCrO$_{3}$. We show that Ca does not affect the magnetic transition ($T_{N}$), but the dielectric behavior is strongly affected by the increase of the electrical conductivity ($\sigma_{ac}$) in the range of 35 to 200 $^{\circ}$C. [Preview Abstract] |
|
C1.00281: Surface magnetization of a multiferroic with linear \textbf{M}-to-\textbf{P} coupling: The case of FeTiO$_{3}$ James Glasbrenner, Kirill Belashchenko A multiferroic material with linear coupling between the magnetization \textbf{M} and electric polarization \textbf{P} could serve as an electric switch of magnetization. However, for applications it is necessary to couple its magnetization to a proximate ferromagnet through exchange bias at the interface. Symmetry considerations indicate that multiferroics with linear \textbf{M}-to-\textbf{P} coupling should also have a boundary magnetization, which is not directly coupled to \textbf{P} but is rather determined by the surface normal direction. This magnetization can present an obstacle for electric switching of exchange bias. Here we investigate the (001) surface magnetization of LiNbO$_{3}$-type FeTiO$_{3}$ using first-principles PAW calculations with spin-orbit coupling. The surface magnetization appears through spin canting of the surface moments. This canting is found for different surface terminations and compared with the bulk behavior. [Preview Abstract] |
|
C1.00282: Impact of Step Defect on Surface States of Topological Insulators Degang Zhang, C.S. Ting Recent topological insulators have attracted much attention in the condensed matter community due to the existence of surface states. The Dirac-cone topological surface states, which preserve time-reversal symmetry, are produced by strong spin- orbit coupling. In recent STM experiments, the modulations of local density of states (LDOS) induced by a step defect were observed. In this work, we investigate electron tunneling in the presence of $\delta(x)$ or $\delta(y)$ potential on the surface of topological insulators in the framework of quantum mechanics and calculate the LDOS near the $\delta $ potential. The STM experiments could be interpreted by an additional spin torque term in the wave function. We also figure out the oscillatory features of the LDOS produced by the $\delta(x)$ and $\delta(y)$ potentials, respectively. [Preview Abstract] |
|
C1.00283: Current-Induced Spin Polarizations in Surfaces of Topological Insulators Tetsuro Misawa, Shuichi Murakami Topological Insulators (TI) have gapless conducting states on their surfaces, which are largely spin-split. Former studies have showed that in spin-orbit coupled systems, current can induce a spin polarization. In this research, we calculate the response of the TI surface state to the dc electric field, that is, transverse conductivity and the induced in-plane spin polarization in the presence of delta-function impurities using Kubo formula. Additionally, in ${\rm Bi}_{2}{\rm Te}_{3}$, the shape of Fermi surface is warped to be 6-fold rotationally symmetric; thereby the transport properties are modified. In this warped Fermi surface, we predict that the current induces a component of spin polarization perpendicular to the surface as a nonlinear response. This out-of-plane polarization may be easier to detect than in-plane polarization. Using the 6-fold rotational symmetry, we discuss the nonlinear response of spin accumulation to the current and its implications on ${\rm Bi}_{2}{\rm Te}_{3}$. We also study another non-linear effect, the inverse Faraday effect, where the oscillating electric field induces the dc spin polarization. [Preview Abstract] |
|
C1.00284: GENERAL PHYSICS I |
|
C1.00285: Blowpipe Mineralogy for Physics/Environment: Highest-Possible-Tc SuperConductor (Beyond: (but via!!!) MgB2, Cuprates, Pnictides) Quest; BOTH PERMANENT FOREVER Carb-IDES SOLID-State Sequestration AND Drought(s)-Elimination Kurt Segler, Wendell Williams, Edward Siegel Detailed are old blowpipe new applications: charcoal-block reduction of borates to yield ("N-NW" of MgB2) Overhauser-[PR 35,1,411(1987); Intl.J.Mod.Phys.1, 2 {\&} 4, 927(1987)]-"land" predicted high-EST-POSSIBLE Tc SC $\sim $ "LiD2"; very-early: Siegel[Phys.Stat.Sol.(a)11,45(1972);Semiconductors.and Insulators 5: 39,47,62(1979)] carb-IDES SOLID-state phase-TRANSITIONED CHEMICALLY-REDOX"-REACTED STABLE PERMANENT LONG-term NOT "CO2" BUT C-sequestration: PROFITABLE "Grab and Sell" TRUMPS "cap and trade"!!!; Mott alloying/vertical metal-insulator transitions in "borax-(GLASS)-beads"; and very-earlySiegel [\underline {3rd Intl.Conf.Alt.Energy }(1980)-vol.5/p.459!!!] "FLYING-WATER" Hindenberg-effect (H2-UP;H2O-DOWN) via Hydrogen-maximal-Archimedes-buoyancy "chemical-rain-in-pipelines", only via Siegel proprietary "magnetic-hydrogen-valve"(MHV): Renewables-Hydrogen-Water flexible versatile agile scaleable retrofitable integrated operating-system for PERMANENT drought(s)-elimination FOREVER!!! [Preview Abstract] |
|
C1.00286: Consciousness can reduce the voltage of the output signal of solar cell Dayong Cao When the sun's light radiate on the solar cell, it can produce the output signal as the pho- tocurrent. We use the Data Acquisition Modules to record the voltage of the output signals. The v1 is voltage of the photocurrent of solar cell1; The v2 is the one of solar cell2. And these two solar cells stay side by side. When we record the voltages from the morning to the noon, the voltages will go up, and the v1 is bigger than the v2 during this time. But in other experi- menter, not only sun's light ratiade on two solar cells, but also consciousness act on two solar cells. Not only I can use consciousness to reduce the growth voltage of the output signals, but also can change the v1 to be littler than the v2. The experiment was conducted on Sep. 2010. When light of lamp radiate on two solar cells, I can reduce v1, at the same time, can augment v2. These experiments had been finished in Los Angeles, Oct. 26th. And the experiment show that the consciousness active function differ from the passive function of conditioned reflex (of Pavlov). There is the physical system of the mass, energy, space and time-MEST; There is the spirited system of the mind, consciousness, emotion and desire-MECD; the information system is the code system. We can use the consciousness change the electron-structure of solar cell by the interaction of the information. [Preview Abstract] |
|
C1.00287: FLYING-WATER Renewables-H2-H2O TERRAFORMING: PERMANENT Drought(s)-Elimination FOREVER!!! G. Ertl, G. Alefeld, W. Youdelis, H. Radd, G. Oertle, Edward Siegel "H2O H2O everywhere; ne'er a drop to drink"[Coleridge(1798)]; now: "H2 H2 everywhere; STILL ne'er a drop to drink": ONLY H2 (or methane CH4) can be FLYING-WATER(F-W) chemical-rain-in-pipelines Hindenberg-effect (H2-UP;H2O-DOWN): {\{}O/H2O{\}}=[16]/[18] $\sim $90{\%}; O already in air uphill; NO H2O pumping need! In global-warming driven H2O-starved glacial-melting world, rescue is possible ONLY by Siegel [\underline {3rd Intl. Conf. Alt.-Energy }(1980)-vol.5/p.459!!!] Renewables-H2-H2O purposely flexible versatile agile customizable scaleable retrofitable integrated operating-system. Rosenfeld[Science 315,1396(3/9/2007)]-Biello [Sci.Am.(3/9/2007)] crucial geomorph-ology which ONLY maximal-buoyancy H2 can exploit, to again make "Mountains into Fountains", ``upthrust rocks trapping the clouds to precipitate their rain/snow/H2O'': "terraforming"(and ocean-rebasificaton!!!) Siegel proprietary magnetic-hydrogen-valve (MHV) permits H2 flow in already in-ground dense BCC/ferritic-steels pipelines-network (NO new infrastructure) counters Tromp[Science 300,1740(2003)] dire warning of global-pandemics (cancers/ blindness/famine) Hydrogen-economy CATASTROPHIC H2 ozone-layer destruction sobering cavat to dangerous H2-automotion-economy panacea hype!!! [Preview Abstract] |
|
C1.00288: FRAUD/SABOTAGE Killing Nuclear-Reactors Need Modeling!!!: "Super"alloys GENERIC ENDEMIC Wigner's-Disease/.../IN-stability: Ethics? SHMETHICS!!! Joseph O'Grady, Arlden Bument, Edward Siegel Carbides solid-state chemistry domination of old/new nuclear-reactors/spent-fuel-casks/refineries/jet/missile/rocket-engines is austenitic/FCC Ni/Fe-based (so miscalled)"super"alloys(182/82;Hastelloy-X,600,304/304L-SSs,...690!!!) GENERIC ENDEMIC EXTANT detrimental(synonyms): Wigner's-disease(WD) [J.Appl.Phys.17,857 (46)]/Ostwald-ripening/spinodal-decomposition/overageing-embrittlement/thermal-leading-to-mechanical(TLTM)-INstability: Mayo[Google: $<$ "If Leaks Could Kill" $>$;-Siegel[J.Mag.Mag.Mtls.7,312(78)=at flickr.com search on "Giant-Magnotoresistance" $<<<$"Fert" [PRL(1988)]-"Gruenberg"[PRL(1989)] 2007-Nobel]necessitating NRC inspections on 40+25=65 Westin"KL"ouse PWRs(12/2006)]-Lai [Met.Trans.AIME, 9A,827(78)]-Sabol-Stickler[Phys.Stat.Sol.(70)]-Ashpahani[\underline {Intl.Conf. Hydrogen in Metals}, Paris(1977]-Russell [Prog.Mtls.Sci.(1983)]-Pollard [last UCS rept.(9/1995)]-Lofaro [BNL/DOE/NRC Repts.]-Pringle [\underline {Nuclear-Power:From Physics to Politics}(1979)]-Hoffman [animatedsoftware.com], what DOE/NRC MISlabels as "butt-welds" "stress-corrosion cracking" endpoint's ROOT-CAUSE ULTIMATE-ORIGIN is WD overageing-embrittlement caused brittle-fracture cracking from early/ongoing AEC/DOE-n"u"tional-la"v"atories sabotage!!! [Preview Abstract] |
|
C1.00289: Horizons and Phase Space Richard Kriske This author has previously suggested that the CMBR may not be entirely due to the generalized Red-Shift, but may be due to the curvature of the Universe in that the time dimensional axis would gradually tilt away from the observer at great distances in the same way that the height dimension tilts away from the observer on the surface of the Earth. There is a well known theory used by navigators that uses Euclidean Geometry to gauge this effect on the surface of the Earth, but when used in 4 space this method lacks the height needed to calculate the distance to the horizon in that the height is the time dimension. A similar height like variable can be found in QED however in the phase that is calculated from the Lagrangian. This author is suggesting that QED needs to be corrected in adding an additional phase that comes about from information conveyed in the wave-function at the time it is created giving it information about the direction of the time dimension which is rotated as the wave function moves and ultimately changes the frequency of the photon. This is field information that resembles current theories. [Preview Abstract] |
|
C1.00290: Interface Defect States and Charge Transport Properties in Low-Cost Photovoltaic Devices made from Scalable Deposition Methods Andrew Marin, David Munoz-Rojas, Diana Iza, Talia Gershon, Judith MacManus-Driscoll Electrochemical deposition and Atmospheric Atomic Layer Deposition (AALD) are high-throughput, scalable methods that can be used to produce low-cost transition metal oxides for photovoltaic devices. Previous work by our group has used electrochemical deposition to fabricate ZnO/Cu$_{2}$O cells, however the performance of these cells is limited by poor Cu$_{2}$O transport properties and recombination at interface states. AALD has been shown to produce much smoother films of Cu$_{2}$O but little work has been done to characterize the electrical properties of these films. Similarly little work has been done to show the ability of AALD to reduce interface defect states. In this investigation, we use impedance spectroscopy and illuminated solar cell performance to examine the electrical properties of Cu$_{2}$O films and ZnO/Cu$_{2}$O photovoltaic devices. We also show how AALD can deposit seed layers for further improved electrochemical deposition. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700