Bulletin of the American Physical Society
2006 73rd Annual Meeting of the Southeastern Section of the APS
Thursday–Saturday, November 9–11, 2006; Williamsburg, Virginia
Session EC: Nanoscience |
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Chair: Seong-Gon Kim, Mississippi State University Room: Williamsburg Hospitality House Yorktown |
Thursday, November 9, 2006 4:15PM - 4:27PM |
EC.00001: Long-range interactions and Pseudo-relativistic Phenomena in Disordered Graphene: The Zero-bias Anomaly William Shively, Dmitri Khveshchenko Two-dimensional graphene creates a window into new and unusual transport phenomena, which can be in terms of the propagation of non-interacting Dirac quasiparticles (DQP). In such a system, Coulomb interactions also remain unscreened, and it is of interest how such long-ranged correlations might significantly affect DQP excitations. Using single-particle tunneling measurements, the DQP densities of states are computed analytically, in the presence of mild impurities and for energies ranging between the diffusive and the ballistic limits. Interesting interplay between the Coulomb interactions and the Dirac quasiparticles is best revealed in the ballistic regime, whereas in the diffusive limit we recover what is essentially the conventional 2DEG. The evolution of the anomalous exponent characterizing the ``zero-bias'' anomaly in the ballistic regime is discussed. [Preview Abstract] |
Thursday, November 9, 2006 4:27PM - 4:39PM |
EC.00002: Modeling of nanoscale graphite superlattices and its applications Reza Rock, Wing Tat Pong The study of superlattices on graphite surfaces by scanning tunneling microscopy is hampered by the lack of a method for reproducibly creating these superlattices for laboratory study. Computer models have been used to simulate these structures using the Moire pattern mechanism as the cause for superlattices. However, it is difficult to perform quantitative analyses using this simple model because the calculated corrugation amplitude of the atomic lattice is unrealistically large compared to the amplitude of the superlattice. We made the modeling results more useful and realistic by averaging the surface profile within an optimum radius around each data point. This has the effect of simulating the finite sharpness of a tunneling tip. The averaging radius controls the ratio of the atomic corrugation to the superlattice corrugation, and can be adjusted to achieve more realistic simulation results. With this model, it is now possible to perform useful analyses on the cross sections of the model superlattices. We present analyses of the layer coefficient ideality, impact of the angle of misorientation of the top graphite layer on superlattice corrugation, attenuation factor, and coexisting superlattices. [Preview Abstract] |
Thursday, November 9, 2006 4:39PM - 4:51PM |
EC.00003: DFT study of Br and Cl Electrodeposition on Ag(100) Tjipto Juwono, Ibrahim Abou Hamad, Per Arne Rikvold Ab-initio density-functional methods have been used to find the lowest energies of Br and Cl adsorbates on Ag(100) surfaces with coverages of $1/9$, $2/9$, $1/3$, and $1/2$. The supercell slab method was used to calculate the electron density distributions for each configuration. The electron transfer function, surface dipole moments, adsorbate resident charge, and lateral interaction energies were calculated and compared with results from electrochemical adsorption exeperiments. The calculated quantities are weakly dependent on the coverage, and the overall shape of electron transfer function is nearly coverage independent. The calculations also show electron sharing between neighbouring Br atoms at 2/9 coverage, reminescent of Br$_2$ molecules. This effect is much weaker or absent for Cl. [Preview Abstract] |
Thursday, November 9, 2006 4:51PM - 5:03PM |
EC.00004: Molecular dynamics simulations of crack nucleation near nanoparticle inclusions. Jeffery Houze, Bohumir Jelinek, Seong-Gon Kim We studied nucleation of cracks near a nanoparticle embedded in a matrix under tension with molecular dynamic simulations using Modified Embedded Atom Method (MEAM) potentials for Al and Mg. Uniaxial tension was applied to an Al(fcc) matrix containing an embedded Mg(hcp) nanoparticle. The same study was performed with an Al nanoparticle embedded in a Mg matrix. Animations showing the damage evolution in both alloying situations and the effect of the materials different tensile strengths on crack nucleation will be presented. [Preview Abstract] |
Thursday, November 9, 2006 5:03PM - 5:15PM |
EC.00005: Molecular Dynamics Simulation of Sintering of Nanopowders Amitava Moitra, Sungho Kim, Seong-Gon Kim Nanopowder metallurgy is an emerging technology that fabricates sophisticated metal parts by sintering of nano-scale metal powders. Consolidated nanopowders are known to have enhanced mechanical properties compared to conventional micron-size powders. Nanopowders also offer the promise of improving the sintering process since, due to their higher surface area to volume ratio, they can be densified more fully and much quicker resulting lower sintering temperature and higher fracture toughness. To understand the fundamental mechnisms of sintering of nanopowders, molecular dynamics simulations of tungsten nano-particles were performed using the Modified Embedded Atom Method (MEAM). The effects of various heating cycles on sintering process as a function of size of the nanopowders will be presented. [Preview Abstract] |
Thursday, November 9, 2006 5:15PM - 5:27PM |
EC.00006: Large Cubic Nonlinearity of Silver Nanoparticles S.M. Ma, Q. Yang, R. Battle, L. Creekmore, B. Tabibi, J.T. Seo, W.J. Kim, J.H. Heo, W.S. Yun, D.H. Ha, S.S. Jung, E. Bryant, C. Payne, W. Yu, V. Colvin The cubic nonlinearity of Ag nanoparticles (NPs) with average sizes of $\sim $ 112 nm and $\sim $4 nm were investigated using polarization-resolved degenerate four-wave mixing (DFWM) at the regions of non surface plasmon resonance (SPR). The absorption spectra and TEM pictures of Ag NPs with an average size of $\sim $112 nm indicated wide morphology of size and shape distributions, and those of Ag NPs with an average size of $\sim $4 nm provided narrow size distribution. The SPR absorption peaks of Ag NPs with average sizes of $\sim $ 112 nm and $\sim $4 nm were $\sim $420 nm with an inhomogeneous spectral shape and $\sim $424 nm with a homogeneous shape. The excitation source was a spatially Gaussian shaped, $\sim $6 ns pulsed laser with 10-Hz repetition rate operating at 1064- and 532-nm wavelengths for the DFWM spectroscopy. The concentration- and polarization-resolved DFWMs revealed that the hyperpolarizabilities of Ag NPs with average sizes of $\sim $ 112 nm and $\sim $4 nm were $\sim $1.05$\times $10$^{-20 }$esu and $\sim $4.19$\times $10$^{-21 }$esu, and $\sim $3.05$\times $10$^{-26 }$esu and $\sim $6.6$\times $10$^{-27 }$esu for parallel and orthogonal polarizations. The possible origins of large hyperpolarizability enhancement with the Ag NPs with average size of $\sim $112 nm are a dielectric resonance and edge effects of the existing nanorods and nanoplates in the NPs. [Preview Abstract] |
Thursday, November 9, 2006 5:27PM - 5:39PM |
EC.00007: Automated Tracking of Nanometer-Scale Feature Evolution Using an STM Russell Lake, Adam Dean, Niru Maheswaranathan, Chad Sosolik Time-resolved measurements of vacancy pits and adatom islands on monatomic metallic surfaces (e.g. Ag(111) [1]) have provided valuable insight into the underlying atomic diffusion processes that drive dynamics at nanometer length scales. Utilizing our variable temperature scanning tunneling microscope or STM, we are extending this probing method to more complex systems, such as the AuCu and NiAl alloys. To increase the rate of successful data acquisition for these measurements, we have developed automated tracking routines that allow for the continuous monitoring of evolving surface features with minimal operator involvement. Post-acquisition image analysis is further enhanced utilizing feature detection algorithms. Current proof-of-concept results spanning several hours of acquisition time on single crystal metal surfaces are presented. [1] K. Morgenstern et al., Phys. Rev. B 63, 045412 (2001). [Preview Abstract] |
Thursday, November 9, 2006 5:39PM - 5:51PM |
EC.00008: Actuation of High-Aspect-Ratio Magnetoelastic Nanorod Arrays B.A. Evans, A.R. Shields, R.L. Carroll, R. Superfine Nanoscale arrays of actuable rods may have applications as nanoscale mechanical stirrers for microfluidics systems, mechanical actuators, or active antibiofouling surfaces, and may produce interesting photonic effects. In addition, our group is interested in using such nanorod arrays as a model for biological cilia, in order to study fluid flow and mucociliary clearance in the human lung. We have produced nanorod arrays both by lateral self-assembly of metallic rods and by templation of a curable magnetoelastomer. Paramagnetic rods respond to torque applied by magnetic fields and forces applied by magnetic field gradients. We have developed an energy-minimization model which inputs the magnetic, geometric, and elastic properties of our rod arrays and calculates the degree of bending due to magnetic effects. The spatial modulation of 30 microns in the actuation of biological cilia presents a challenge in designing actuating fields for our biomimetic model. We will present a strategy based on our mathematical model to produce spatial modulation of this magnitude in our nanorod arrays. [Preview Abstract] |
Thursday, November 9, 2006 5:51PM - 6:03PM |
EC.00009: The Functionalized Double-Walled Nanotube S.J. Frankland, G.M. Odegard, T.S. Gates Functionalized nanotube materials are being proposed as fillers in polymer matrix materials for aerospace applications. Chemical modification (functionalization) of nanotubes enables better association with the polymer, but in doing so, changes in the molecular structure of the nanotube. In functionalized double-walled nanotubes (f-DWNT), the outer nanotube is made compatible with the polymer while the inner nanotube is pristine. In the present work, molecular dynamics (MD) simulation and the equivalent continuum method are used to calculate mechanical properties of f-DWNTs. Young's moduli have been calculated for multiple f-DWNT systems. MD simulations also demonstrate that the f-DWNT have friction coefficients on the order of one reducing the degree of nanotube slippage in a composite. The paper will present results for the Young's modulus and friction coefficients of f-DWNT systems. [Preview Abstract] |
Thursday, November 9, 2006 6:03PM - 6:15PM |
EC.00010: Tuning Silicon Photonic Crystal Band Gap by Oxidation and Etching. Makhin Thitsa, Sacharia Albin Tunability of photonic bandgap is restricted by the limited number of parameters that can be varied. In triangular silicon photonic crystal consisting of silicon pillars in air background, it is difficult to fine tune the photonic band gap because the gap is too sensitive to the change in atom radius. When silicon atom is etched from the radius of 0.28*a (a = lattice constant), to 0.1* a, the TM band gap drastically changes from 0.095 to 0.16 normalized frequency value, and the midgap frequency shifts from 0.325 to 0.49. In this paper it is demonstrated that by oxidizing the silicon and etching the silicon dioxide, the band gap can be tuned in a much finer scale by varying the oxide thickness. Plane wave expansion method is used for modeling the process. In our model, when silicon pillars are oxidized so that silicon is consumed and silicon radius goes from 0.28*a to 0.1*a, the band gap changes very slowly from 0.095 to 0.1 and the midgap from 0.325 to 0.42. After that the silicon dioxide is etched, and the band gap and midgap frequency changes slowly with the oxide thickness. Along this path the band gap moves from 0.1 to 0.16 and the midgap frequency from 0.42 to 0.49. [Preview Abstract] |
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