Bulletin of the American Physical Society
Joint Fall 2012 Meeting of the Texas Sections of the APS, AAPT, and Zone 13 of the SPS
Volume 57, Number 10
Thursday–Saturday, October 25–27, 2012; Lubbock, Texas
Session B9: Posters I: Materials Nanoscience, Biophysics, Chemical Physics (10:30am - 12:15pm) |
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Chair: Charles W. Myles, Texas Tech University Room: Holiday Inn Towers Atrium |
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B9.00001: Towards a Notion of Symmetry for Topological Phases Matthew Titsworth, Tobias Hagge Landau's theory of group symmetry breaking has been hugely successful in the description of classical and quantum phase transitions. However, recently discovered and proposed topological phases lie outside of the Landau paradigm. The primary physical example of these are fractional quantum Hall effect (FQHE) liquids. Topological phases possess no such broken symmetry and cannot be characterized by an order parameter. The effective field theories for topological phases are topological quantum field theories (specifically (2+1)-TQFTs) with a proposed microscopic mechanism in string-net condensation. They possess a number of unique features such as ground state degeneracy and non-trivial quasi-particle exchange statistics. We investigate the mathematical tools used to characterize (2+1) TQFTs/FQHE liquids for the purpose of trying to determine appropriate ``symmetry objects'' for such systems and possible mechanisms for describing their phase changes. [Preview Abstract] |
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B9.00002: Cyclic Transition Processes for Muonium in SiGe Alloys Ganga Jayarathna, Lawrence Hudy, Patrick Mengyan, Brittany Baker, Brent Carroll, Yasar Celebi, Roger Lichti Muonium equivalent of the donor and acceptor levels of H in Si$_{1-x}$Ge$_{x}$ alloy system based primarily on the ionization energies obtained for Mu$_{BC}$ donor and Mu$_{T}$ acceptor centers. We are currently undertaking longitudinal depolarization measurements in SiGe alloys in an attempt to determine acceptor energy over the full alloy range, to determine the position of band-resonant T-site acceptor level for large $x$, and to examine other cyclic transition processes. Critical energies associated with the cycle limiting transitions have been extracted from temperature dependence of the amplitudes associated with various components of the longitudinal signal. We are attempting to fit temperature and field dependences of relaxation rates to models derived from tentative cycle assignments. These results will provide a check of the previous assignments and on the transition energy determinations and should access a few energies that have not previously been determined. Progress to date in modeling the temperature dependence of relaxation rates will be discussed. [Preview Abstract] |
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B9.00003: Probing Local features in Dilute Magnetic Semiconducting ZnGeP2:Mn via MuSR P.W. Mengyan, R.L. Lichti, B.B. Baker, Y.G. Celebi, E. Catek, K.T. Zawilski, P.G. Schunemann The conventional semiconducting properties and the discovery of room temperature ferromagnetism in weakly Mn doped II-IV-V2 chalcopyrite semiconductors make these materials prime candidates for prospective use in the field of spin-electronics. The mechanism responsible for connecting the local magnetic features to the bulk magnetic properties is not yet understood in these materials. Muon Spin Research (MuSR) utilizes the unique sensitivity of 100\% spin polarized and positively charged muons to probe local magnetic and electronic environment. We have initiated a MuSR investigation on dilute magnetic semiconducting II-IV-V2 specifically focused on the, yet to be understood, magnetic features. This contribution presents results of our first set of MuSR measurements on four different ZnGeP2:Mn; each with a different Mn content. We have detected at least three distinct spin fluctuation regimes; antiferromagnetic, ferromagnetic and one that is possibly related to spin polaron formation. Considerable amounts of modeling and measurements are required in order to develop a more complete characterization and assignment for each of these features. These are promising first steps in the larger-scale project of developing a more complete understanding of the magnetic features in DMS systems. [Preview Abstract] |
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B9.00004: New insights into the surface structure of Pt-Pd core-shell nanoparticles as revealed by Cs-corrected STEM Subarna Khanal, Gilberto Casillas, J. Jesus Velazquez-Salazar, Arturo Ponce, Miguel Jose Yacaman Bimetallic nanoparticles of Pt-Pd core-shell structures have been found to possess significant applications in fuel cells, hydrogen storage, catalysis, etc. However, the cost of Pt makes it unpractical to use in big quantities; therefore, one of the big challenges is to very small catalysts with only a few layers of the active metal in the shell in order to maximize the efficiency in their use. In this work the modified polyol method was used to synthesize Pt-Pd core-shell nanoparticles in the size range of 20 nm and characterized them by Cs-corrected scanning transmission electron microscopy. This technique allowed us to probe the structure at the atomic level of these nanoparticles revealing new structural information. We determined the structure of the three main polyhedral morphologies obtained in the synthesis: octahedral, decahedral and triangular plates. These final shapes of the core-shell structures were determined by the seed morphology. In addition the STEM energy dispersive X-ray spectroscopy (EDS) chemical analysis can be better identified the chemical composition of the nanocrystals. The overgrowth of the thin Pd shells on the Pt cores due to the epitaxial growth modes was observed. In this work, we have been able to observed Shockley partial dislocations, stacking faults, and adatoms at the surfaces of the nanoparticles. [Preview Abstract] |
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B9.00005: Effective Nonradiative Energy Transfer Between Nanocrystal Bilayers Enhanced by 1,6-Hexanediamine Linkers Michael Nimmo, Erick Gonzalez, Niels Ramay, Oliver Seitz, Yves Chabal, Anton Malko Nanostructured materials attract great interest as candidates for producing new, practical photoelectronic devices. Many current devices are based on charge-transfer in which primary photoexcitations are separated into an electron and hole on different sides of the interface. Poor interface quality and carrier transport are issues that result in a lower conversion efficiencies than in inorganic crystalline devices. An alternative is given by non-radiative energy transfer (NRET) based hybrid nanostructures, which combine strongly absorbing components such as nanocrystal quantum dots (NQDs) and high-mobility semiconductor layers. In this work, we compared the effectiveness of 1,6-hexanedithiol vs. 1,6-hexanediamine to link multilayer NQD structures. Steady state photoluminescence (PL) measurements showed that using 1,6-hexanediamine consistently resulted in higher PL counts and passivation of the NQDs. Furthermore, we studied bilayer structures of different size NQD layers (565NQDs on 605NQDs) linked with 1,6-hexanediamine. We performed time-resolved and steady-state PL measurements to quantify the NRET rates between the 565NQD layer and the 605NQD layer. NRET rates were consistently 91{\%}. Hence, we foresee the utilization of bilayer NQD structures linked with 1,6-hexanediamine in energy transfer-based systems. [Preview Abstract] |
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B9.00006: Non-Radiative Energy Transfer Into Nanometer-Scale Thin Semiconducting Films Joseph Gordon, Yuri Gartstein Non-radiative energy transfer (NRET) has gained a lot of attention recently due to its possible utility in new generations of light-emitting and photovoltaic devices. In this process, a ``donor'' species in an excited state transfers its excitation energy resonantly to an ``acceptor'' species. A classical realization of NRET is F\"{o}rster ET between two point-like species. Our interest is in ET between a small donor and an ultrathin acceptor layer. The layers can be realized as planar ensembles of molecules or QDs or as a thin crystalline semiconductor slab. We use two complementary approaches to study the effects of dielectric polarization in thin layers on ET rates: (1) The classical macroscopic electrodynamics treating the acceptor layer as a continuum of certain dielectric permittivity; (2) A direct modeling utilizing planar acceptor lattices, each of the acceptors treated as a polarizable point dipole. Comparison of the results allows us to establish salient qualitative features as well as to clarify the role of local-field factors. Of particular interest is our finding a broad region of the dielectric responses where ET into thinner films \textit{counter-intuitively} turns out to be more efficient than ET into thicker films. [Preview Abstract] |
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B9.00007: Characterization of Energetic Properties of Porous Silicon Blake McCracken Porous silicon has recently been found to explode when under certain oxidation or nitration conditions. However, characterization of the velocity and pressure of these explosions is not been complete, as there are many kinds of porous silicon. We present a simple and inexpensive method to measure these properties using PVDF piezoelectric gauges. Here, the gauges are calibrated qualitatively against common firecrackers, similar to black cats. While the pressure measurements from our results are still being analyzed, the velocity of the shock wave produced by the explosion is faster than the speed of sound, about 430 m/s. [Preview Abstract] |
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B9.00008: Dilution factor measurement setup for a vibrating steel string Moises Castillo, Trevor Guston, Cade Daniel, Joe Avila, Juan Vazquez, Gianpietro Cagnoli, Mario Diaz Measurements of mechanical losses have been done in the past in configurations parallel and perpendicular to the gravitational potential of earth with different sample shapes. Gravity will modify the quality factor of resonances when the restoring force depends on it, like in a pendulum. The proposed configuration used for this experiment involves a steel string under tension. The restoring force will be due to the tension rather than gravity. The goal is to quantify the relation between the tension of a steel string and its quality factor for varied resonant modes. [Preview Abstract] |
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B9.00009: Properties of the Oxidized Cu(110) Surface: The DFT study Antoine Olenga, N.G. Fazleev The study of adsorption of oxygen on transition metal surfaces is important for the understanding of oxidation, heterogeneous catalysis, and metal corrosion. In this work we have studied from first principles the changes of electronic properties of the Cu(110) surface due to oxygen adsorption. Especially, we have focused on studies of changes in the work function, electronic density, interlayer spacing, density of states and band structure with oxygen coverage. Calculations of electronic properties from first principles have been also performed for the (110) and surface of Cu$_{2}$O to use for comparison. The first-principles calculations in this work have been performed on the basis of the Density Functional Theory and using DMOl3 code. The obtained theoretical results have been compared with available experimental data. [Preview Abstract] |
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B9.00010: Properties of Carbon Nanotubes Samina Masood, Daniel Bullmore, Michael Duran, Michael Jacobs Different synthesizing methods are used to create various nanostructures of carbon; we are mainly interested in single and multi-wall carbon nanotubes, (SWCNTs) and (MWCNTs) respectively. The properties of these tubes are related to their synthetic methods, chirality, and diameter. The extremely sturdy structure of CNTs, with their distinct thermal and electromagnetic properties, suggests a tremendous use of these tubes in electronics and medicines. Here, we analyze various physical properties of SWCNTs with a special emphasis on electromagnetic and chemical properties. By examining their electrical properties, we demonstrate the viability of discrete CNT based components. After considering the advantages of using CNTs over microstructures, we make a case for the advancement and development of nanostructures based electronics. As for current CNT applications, it's hard to overlook their use and functionality in the development of cancer treatment. Whether the tubes are involved in chemotherapeutic drug delivery, molecular imaging and targeting, or photodynamic therapy, we show that the remarkable properties of SWCNTs can be used in advantageous ways by many different industries. [Preview Abstract] |
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B9.00011: Study of plasmonic crystal to metamaterial transition in dielectric doped two-dimensional periodic structures Shivkumar Gourshetty, Charles Regan, Luis Grave de Peralta, Ayrton Bernussi We investigated experimentally the transition from plasmonic crystal to metamaterial in dielectric-loaded plasmonic two-dimensional periodic structures with different lattice periods and lattice symmetries. The transition occurs due to changes in the effective refractive index of the plasmonic crystals when the period and/or the size of the patterned features are varied. The effective refractive index of the plasmonic structure can be further modified when an object (i.e. a virus, a bead, a cell, etc.) is placed on the top of the sample, thus altering the transition. This can be prospectively used for nanosensing applications. The samples investigated here were fabricated using a combination of electron-beam lithography and liftoff techniques and consisted of a glass substrate, a thin film of gold, and periodic arrays of air holes defined on PMMA doped with Rhodamine 6G. The plasmonic crystal to a metamaterial transition region was investigated using the leakage radiation microscopy technique. We determined that the transition occurs for lattice periods 262 nm and 310 nm for samples with square and hexagonal lattice symmetries, respectively. [Preview Abstract] |
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B9.00012: Effect of Diameter on Radiation Emitted by Carbon Nanotubes in Microwave Fields Sarah Ferguson, Daniel Gonzales, Brandon Cavness, Nieman McGara, Scott Williams Carbon Nanotubes have been observed to emit ultraviolet, visible, and infrared radiation when placed in microwave fields. We have irradiated nanotubes of different diameters with 2.45 GHz microwaves and studied the spectra of the emitted radiation. We have also compared the spectra after several irradiation and cooling cycles in order to try and determine the mechanisms responsible for observed phenomena. [Preview Abstract] |
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B9.00013: Study of Surface Plasmon Polariton propagation in Plasmonic Waveguides Willis Agutu, Charles Regan, Ayrton Bernussi, Luis Grave-De-Peralta Using surface plasmon polariton (SPP) tomography techniques, we study the propagation of SPPs in dielectric-loaded plasmonic waveguides. Surface emission and Fourier plane tomography images were used to characterize SPP propagation and losses in straight and curved, single and multimode waveguides. This study shows the imaging and characterization capabilities of SPP tomography. [Preview Abstract] |
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B9.00014: Manipulating the Crystal Growth of Organic Energetic Materials on Substrates Xin Zhang, Gengxin Zhang, Brandon Weeks Organic energetic materials (OMEs) have been attracted a lot of attention due to its wide application in military weapon. One of the most compelling researches is manipulating the crystal structure of OEMs due to their performances, such as ignition and burning rate, which depend strongly on the crystalline structure. The crystalline structure of OEMs on substrates has strong dependence on the experimental parameters, such as the deposition rate and external factors. This report demonstrates a new technique for manipulating the crystal growth of OEMs on substrates by micro-contact printing. The methodology depends on coating a polymer stamp with a surfactant, which has a strong affinity for the OEMs deposited on the substrate. The coated stamp selectively removes OEMs in contact areas when the stamp was lifted. And then the OEMs that were left on the substrates grew to the crystals. By careful choice facile film preparation method and optimal stamp pattern, this technique provides a new methodology for fabricating OEMs crystals from hexagon single crystals, dendrite crystals to micro-rod crystals and manipulating the size and distribution of these crystals. [Preview Abstract] |
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B9.00015: Properties and Applications of Carbon Nanotubes Daniel Bullmore, Michael Duran, Michael Jacobs, Samina Masood Different synthesizing methods are used to create various nanostructures of carbon; we are mainly interested in single and multi-wall carbon nanotubes, (SWCNTs) and (MWCNTs) respectively. The properties of these tubes are related to their synthetic methods, chirality, and diameter. The extremely sturdy structure of CNTs, with their distinct thermal and electromagnetic properties, suggests a tremendous use of these tubes in electronics and medicines. Here, we analyze various physical properties of SWCNTs with a special emphasis on electromagnetic and chemical properties. By examining their electrical properties, we demonstrate the viability of discrete CNT based components. After considering the advantages of using CNTs over microstructures, we make a case for the advancement and development of nanostructures based electronics. As for current CNT applications, its hard to overlook their use and functionality in the development of cancer treatment. Whether the tubes are involved in chemotherapeutic drug delivery, molecular imaging and targeting, or photodynamic therapy, we show that the remarkable properties of SWCNTs can be used in advantageous ways by many different industries. [Preview Abstract] |
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B9.00016: Influence of RF plasma power on structural properties of AlN thin layers grown by PAMBE on Si (111) Mahesh Pandikunta, Oleg Ledyaev, Sergey Nikishin AlN grown by plasma assisted molecular beam epitaxy (PAMBE) is attractive for fabrication of high-power and high-frequency electronic devices. The Si substrate is used for deposition of AlN due to its low cost, high thermal conductivity, and compatibility with existing Si technologies. The growth of AlN layers with desirable Al- or N-face polarity on Si (111) is still a challenge for researchers. In this work, the influence of RF plasma power on initial nucleation and subsequent growth of AlN layers on Si (111) substrate by PAMBE was studied. Six AlN samples were grown at RF power in the range of 150-450 W when the N2 flow rate was set to 0.6 sccm. The surface reconstruction was controlled in situ by reflection high energy electron diffraction (RHEED). The RHEED pattern was 1 x 1 for AlN grown at RF power of 300-450 W, while the samples grown at lower RF power had 3 x 6 reconstruction related to N-face polarity. We found that crystalline quality of AlN strongly depends on the RF power. The screw and edge dislocation densities for the best AlN sample grown at 150 W were estimated to be 1.4E9 and 5.9E9 cm-2, respectively. [Preview Abstract] |
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B9.00017: Two photon excited fluorescence from diamond nanoparticles Ankit Singh, Mathias Ajaeroh, Samar Mohanty, Suresh sharma The possibility of two photon eaxcited fluorescence by diamond nanoparticles is an interesting nonlinear phenomenon. We have grown 20-100 nm diamond nanoparticles by using chemical vapor deposition (CVD) and characterized their properties by using complementary techniques of AFM, SEM, and Raman spectroscopy.\footnote{R. Chakraborty, S. C. Sharma, and J. K. LaRoque, J. Nano Research, \textbf{12}, 1123 (2010)}$^,$\footnote{R. Chakraborty and S. C. Sharma, Physica B, \textbf{406}, 4170 (2011)} In this work, we have utilized femtosecond laser based two-photon excitation to study the emission of visible light ($\sim$ 530 nm) as functions of the excitation wavelength (750-850 nm), excitation power, and size of the NPs. These results and their potential applications will be discussed. [Preview Abstract] |
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B9.00018: Study of growth mechanism and atomic structure of Au-Pd core-shell nanocube by Cs-corrected scanning transmission electron microscopy Nabraj Bhattarai, Gilberto Casillas, Arturo Ponce, Miguel Jose-Yacaman Au-Pd core-shell nanocubes of controlled sizes from 14 nm to 30 nm were synthesized using seed mediated growth process. The Pd shell layers were controlled from some monolayers to 10 nm. The stepwise growth mechanism from nucleation and growth of Au nanoparticles to final core-shell nanocube was studied by using conventional transmission electron microscopy (TEM) and Cs-corrected scanning transmission electron microscopy (STEM). It was found that the nanocubes grew from octahedral Au seeds due to fast growth along \textless 111\textgreater directions and concavity occurred because of high reduction rate of ascorbic acid (AA). The concave nanocube showed a change in strain-release mechanism as the Pd shell grew from a few layers to a 30 nm nanocube. Shockley partial dislocations (SPD), stacking faults (SF) and edge dislocations were found to be the mechanism to release the mismatch strain. Also, those concave nanocubes present high index facet surfaces which are found to be more active than low index facet surfaces. Moreover, the smallest size nanocube with HIFs will be suitable in order to maximize the catalytic activity per unit weight and mass specific activity. [Preview Abstract] |
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B9.00019: Analysis of Crystalline Structure of Synthetic Opals Based on Their AFM Scans Darkhan Tuyenbayev, Liliana Ruiz Diaz, Malik Rakhmanov Synthetic opals are made of silica nano spheres by means of self-assembly techniques. Formation of the opals is a somewhat random process and can lead to different close-packed crystalline structures and defects. In most cases the opals form the face centered cubic lattice and sometimes the hexagonal close packed lattice. Moreover, the opals consist of multiple domains and can have various crystalline defects. To study the structure of opals at the nano scale we analyze their surfaces with Atomic Force Microscope (AFM). We developed an algorithm to analyze the profile of the scanned surfaces and separate adjacent packing layers from which we obtain the positions of the individual silica nano spheres. This technique allows us to determine the crystalline structure of the opal domains, the presence of defects within the structure, and assess the uniformity of the opal sample. The results of this analysis can be used for optical characterization of opals and other nano structured materials. [Preview Abstract] |
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B9.00020: Self-Assembled Nano-energetic Gas Generators based on Bi$_{2}$O$_{3}$ Mkhitar Hobosyan, Tyler Trevino, Karen Martirosyan Nanoenergetic Gas-Generators are formulations that rapidly release a large amount of gaseous products and generate a fast moving thermal wave. They are mainly based on thermite systems, which are pyrotechnic mixtures of metal powders (fuel- Al, Mg, etc.) and metal oxides (oxidizer, Bi$_{2}$O$_{3}$, Fe$_{2}$O$_{3}$, WO$_{3}$, MoO$_{3}$ etc.) that can generate an exothermic oxidation-reduction reaction referred to as a thermite reaction. A thermite reaction releases a large amount of energy and can generate rapidly extremely high temperatures. The intimate contact between the fuel and oxidizer can be enhanced by use of nano instead of micro particles. The contact area between oxidizer and metal particles depends from method of mixture preparation. In this work we utilize the self-assembly processes, which use the electrostatic forces to produce ordered and self-organized binary systems. In this process the intimate contact significantly enhances and gives the ability to build an energetic material in molecular level, which is crucial for thepressure discharge efficiency of nano-thermites. The DTA-TGA, Zeta-size analysis and FTIR technique were performed to characterize the Bi$_{2}$O$_{3}$ particles. The self-assembly of Aluminum and Bi$_{2}$O$_{3}$ was conducted in sonic bath with appropriate solvents and linkers. The resultant thermite pressure discharge values were tested in modified Parr reactor. In general, the self-assembled thermites give much higher-pressure discharge values than the thermites prepared with conventional roll-mixing technique. [Preview Abstract] |
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B9.00021: Modeling of oxidation of aluminum nanoparticles by using Cabrera Mott Model Zamart Ramazanova, Maxim Zyskin, Karen Martirosyan Our research focuses on modeling new Nanoenergetic Gas-Generator (NGG) formulations that rapidly release a large amount of gaseous products and generates shock and pressure waves. Nanoenergetic thermite reagents include mixtures of Al and metal oxides such as bismuth trioxide and iodine pentoxide. The research problem is considered a spherically symmetric case and used the Cabrera Mott oxidation model to describe the kinetics of oxide growth on spherical Al nanoparticles for evaluating reaction time which a process of the reaction with oxidizer happens on the outer part of oxide layer of aluminum ions are getting in contact with an oxidizing agent and react. We assumed that a ball of Al of radius 20 to 50 nm is covered by a thin oxide layer 2-4 nm and is surrounded by abundant amount of oxygen stored by oxidizers. The ball is rapidly heated up to ignition temperature to initiate self-sustaining oxidation reaction. As a result highly exothermic reaction is generated. In the oxide layer of excess concentrations of electrons and ions are dependent on the electric field potential with the corresponding of the Gibbs factors and that it conducts to the solution of a nonlinear Poisson equation for the electric field potential in a moving boundary domain. Motion of the boundary is determined by the gradient of a solution on the boundary. We investigated oxidation model numerically, using the COMSOL software utilizing finite element analysis. The computing results demonstrate that oxidation rate increases with the decreasing particle radius. [Preview Abstract] |
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B9.00022: Investigation of using N and P Doped Graphene to Fabricate a Transistor Kyle Joseph Drake The atomic structure of graphene causes it to have a zero-energy band gap, where its valence and conduction bands meet at the Dirac point. By doping the graphene, a band gap can be created and it can then be used as a semiconductor similar to silicon. Nitrogen and Boron doped graphene will be used as n-type and p-type semiconductor materials to fabricate n-p-n transistors. The graphene will be doped with nitrogen to be the n-type semiconductor and boron to be the p-type semiconductor. This will be done by chemical vapor deposition (CVD) methods. [Preview Abstract] |
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B9.00023: Kinetic Parameter Extraction of Square Wave Voltammograms from DNA-Modified Gold Electrodes Marc McWilliams, Chris Wohlgamuth, Jason Slinker The field of surface bound electrochemistry is important in a variety of applications specifically sensing. A fundamental understanding of the processes involved could help to improve detection limits, optimize rates of detection and direct changes in device design. Accurate extraction of electrochemical kinetic parameters such as the rate constant $k$ and charge transfer coefficient \textit{$\alpha $} from cyclic voltammograms can be challenging when confronted with large background currents and relatively weak signals. The commonly used technique of Laviron analysis is both time consuming and somewhat subjective. Square wave voltammetry (SWV) is therefore an ideal alternative method given that it maximizes signal while minimizing capacitive effects. In this experiment kinetic parameters of DNA-modified gold electrodes are obtained from SWV curves through background subtraction followed by nonlinear least squares fitting using a first order quasi-reversible surface process model. The fitting is accomplished using the Nelder-Mead simplex algorithm with standard parameters and a convergence condition of less than 0.0001{\%}. General agreement with experimental data is shown with varying levels of confidence. Difficulties specific to this experiment are discussed as well as the possible benefits of utilizing the Bayesian statistical approach of nested sampling when confronted with multiple peaks of interest and the background source is well defined. [Preview Abstract] |
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B9.00024: Temperature Dependent Kinetics DNA Charge Transport Chris Wohlgamuth, Marc McWilliams, Jason Slinker Charge transport (CT) through DNA has been extensively studied, and yet the mechanism of this process is still not yet fully understood. Besides the benefits of understanding charge transport through this fundamental molecule, further understanding of this process will elucidate the biological implications of DNA CT and advance sensing technology. Therefore, we have investigated the temperature dependence of DNA CT by measuring the electrochemistry of DNA monolayers modified with a redox-active probe. By using multiplexed electrodes on silicon chips, we compare square wave voltammetry of distinct DNA sequences under identical experimental conditions. We vary the probe length within the well matched DNA duplex in order to investigate distance dependent kinetics. This length dependent study is a necessary step to understanding the dominant mechanism behind DNA CT. Using a model put forth by O'Dea and Osteryoung and applying a nonlinear least squares analysis we are able to determine the charge transfer rates (k), transfer coefficients ($\alpha$), and the total surface concentration ($\Gamma^*$) of the DNA monolayer. Arrhenius like behavior is observed for the multiple probe locations, and the results are viewed in light of and compared to the prominent charge transport mechanisms. [Preview Abstract] |
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B9.00025: Biological Effects of Electromagnetic Fields on Cellular Growth Beheshte Eftekhari, James Wilson, Samina Masood The interaction of organisms with environmental magnetic fields at the cellular level is well documented, yet not fully understood. We review the existing experimental results to understand the physics behind the effects of ambient magnetic fields on the growth, metabolism, and proliferation of in vitro cell cultures. Emphasis is placed on identifying the underlying physical principles responsible for alterations to cell structure and behavior. [Preview Abstract] |
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B9.00026: Multiscale Molecular Dynamics Simulations of Beta-Amyloid Interactions with Neurons Liming Qiu, Mark Vaughn, Kelvin Cheng Early events of human beta-amyloid protein interactions with cholesterol-containing membranes are critical to understanding the pathogenesis of Alzheimer's disease (AD) and to exploring new therapeutic interventions of AD. Atomistic molecular dynamics (AMD) simulations have been extensively used to study the protein-lipid interaction at high atomic resolutions. However, traditional MD simulations are not efficient in sampling the phase space of complex lipid/protein systems with rugged free energy landscapes. Meanwhile, coarse-grained MD (CGD) simulations are efficient in the phase space sampling but suffered from low spatial resolutions and from the fact that the energy landscapes are not identical to those of the AMD. Here, a multiscale approach was employed to simulate the protein-lipid interactions of beta-amyloid upon its release from proteolysis residing in the neuronal membranes. We utilized a forward (AMD to CGD) and reverse (CGD-AMD) strategy to explore new transmembrane and surface protein configuration and evaluate the stabilization mechanisms by measuring the residue-specific protein-lipid or protein conformations. The detailed molecular interactions revealed in this multiscale MD approach will provide new insights into understanding the early molecular events leading to the pathogenesis of AD. [Preview Abstract] |
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B9.00027: Detection and Monitoring of Neurotransmitters - a Spectroscopic Analysis Felicia Manciu, Kendall Lee, William Durrer, Kevin Bennet In this work we demonstrate the capability of confocal Raman mapping spectroscopy for simultaneously and locally detecting important compounds in neuroscience such as dopamine, serotonin, and adenosine. The Raman results show shifting of the characteristic vibrations of the compounds, observations consistent with previous spectroscopic studies. Although some vibrations are common in these neurotransmitters, Raman mapping was achieved by detecting non-overlapping characteristic spectral signatures of the compounds, as follows: for dopamine the vibration attributed to C-O stretching, for serotonin the indole ring stretching vibration, and for adenosine the adenine ring vibrations. Without damage, dyeing, or preferential sample preparation, confocal Raman mapping provided positive detection of each neurotransmitter, allowing association of the high-resolution spectra with specific micro-scale image regions. Such information is particularly important for complex, heterogeneous samples, where modification of the chemical or physical composition can influence the neurotransmission processes. We also report an estimated dopamine diffusion coefficient two orders of magnitude smaller than that calculated by the flow-injection method. [Preview Abstract] |
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B9.00028: Influence of strain on the work functions of carbon nanotubes investigated by the first-principles method Wan-Sheng Su, Han Hu The responses of work functions to uniaxial strain for infinite-length single-walled armchair (AC) [(2,2) and (7,7)], and zigzag (ZZ) [(3,0) and (12,0)] carbon nanotubes (CNTs) are investigated based on density functional theory. It is found that as the strain is increased, the work function of ZZ (3,0) tubes decreases monotonically from 6.2 to 5.7 eV, whereas that of AC (2,2) tubes varies between 4.6 and 4.8 eV in a somewhat complicated manner. As for ZZ (12,0) and AC (7,7) tubes with large diameters, the work functions of ZZ (12,0) change almost linearly from 4.3 to 4.7eV, while for AC (7,7) the work function values grow monotonically from 4.2 to 4.6 eV. Finally, the changes of the energy band give a qualitative understanding of how work function is affected by the uniaxial strain. [Preview Abstract] |
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B9.00029: Dynamical Properties of the Triangular Bouncer Matthew Holtfrerich, Bruce Miller This poster presents research on the dynamical properties of a Fermi bouncer with a triangular driving function using numerical simulation. A Fermi bouncer consists of a mass confined to move in one dimension that bounces on an oscillating floor. It will be shown that, for the elastic case of this bouncer, Fermi acceleration and stability islands exist. Periodic and quasiperiodic motion can be found with the exception of period 1 motion. The elastic version of the bouncer is a one parameter system. When the parameter's value is changed, the behavior of the system can change drastically. However, if the collisions of the system are inelastic, the system becomes a two parameter system that can change its behavior as either parameter is varied. Here, the new parameter arises from the velocity dependence of the coefficient of restitution. As in the elastic case, the inelastic case shows stable islands representing periodic and quasiperiodic motion. Not surprisingly, Fermi acceleration does not occur. An interesting observation is that, when the new parameter is varied, islands can be created or destroyed and complex patterns arise in the island structure. [Preview Abstract] |
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B9.00030: Molecular Dynamics Simulation of the Transport Properties of Molten Transuranic Salt Mixtures Austin Baty, Peter McIntyre, Akhdiyor Sattarov, Elizabeth Sooby The Accelerator Research Laboratory at Texas A\&M is proposing a revolutionary design for accelerator-driven subcritical fission in molten salt (ADSMS), a system that destroys the transuranic elements in spent nuclear fuel. The transuranics are the most enduring hazard of nuclear power, since they contain high radiotoxicity and have half-lives of a thousand to a million years. The ADSMS core is fueled by a homogeneous chloride-based molten salt mixture containing the chlorides of the transuranics and NaCl. Knowledge of the density, heat capacity, thermal conductivity, etc. of the salt mixtures is needed to accurately model the complex ADSMS system. There is a lack of experimental data on the density and transport properties of such mixtures. Molecular dynamics simulations using polarizable ion potentials are used to determine the density and heat capacity of these melts as a function of temperature. Green-Kubo methods are employed to calculate the electrical conductivity, thermal conductivity, and viscosity of the salt using the outputs of the model. Results for pure molten salt systems are compared to experimental data when possible to validate the potentials used. Here we discuss potential salt systems, their neutronic behavior, and the calculated transport properties. [Preview Abstract] |
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