Bulletin of the American Physical Society
2012 Annual Meeting of the California-Nevada Section of the APS
Volume 57, Number 13
Friday–Saturday, November 2–3, 2012; San Luis Obispo, California
Session D2: Condensed Matter II: Nanotechnology and Materials |
Hide Abstracts |
Chair: Ben Wang, Svaya Nanotechnologies Room: Business 003 0112 |
Friday, November 2, 2012 4:12PM - 4:24PM |
D2.00001: Single Layer Multipolymer Photovoltaics Grant Olson, Ryan Blumenthal, Spencer Herrick, Daniel Spaizman, Robert Echols Polymer (Plastic) solar cells are an exciting and quickly developing area of study in photovoltaics. Our research group uses a blend of high and low bandgap polymers to create solar cells with broad spectral response, while maintaining a simple single active layer. Devices created have power conversion efficiencies as high as 2.0\%, with a spectral response that spans from 400 to 900nm, the portion of the solar spectrum with the highest photon flux. [Preview Abstract] |
Friday, November 2, 2012 4:24PM - 4:36PM |
D2.00002: Defects as qubits in SiC Luke Gordon, Anderson Janotti, C.G. Van de Walle The NV- center in diamond has been extensively studied as a promising qubit for quantum computing applications. However, technological limitations of the NV center in diamond impel a search for alternative defects in other materials which possess NV-like characteristics. Using first-principles calculations based on hybrid density functional theory, we explore possible defects in 4H- and 3C-SiC that hold potential as new solid-state qubits. Specifically, the divacancy in 4H and 3C -SiC and N-V centers in 3C-SiC are investigated. The calculated excitation and emission energies of the divacancy in 4H-SiC can explain the experimental data. In addition, our results indicate that the neutral divacancy and the negatively-charged N-V center in 3C-SiC are promising candidates as qubits; both defects are stable in n-type 3C-SiC, opening a pathway for possible coupling with charge carriers. [Preview Abstract] |
Friday, November 2, 2012 4:36PM - 4:48PM |
D2.00003: First-principles lineshapes of defect luminescence bands Audrius Alkauskas, Daniel Steiauf, John L. Lyons, Chris G. Van de Walle We present a theoretical study of broadening of defect luminescence bands due to vibronic coupling. Numerical proof is provided for the commonly used assumption that a multi-dimensional vibrational problem can be mapped onto an effective one-dimensional configuration coordinate diagram. Our approach is implemented based on density functional theory with a hybrid functional, resulting in luminescence lineshapes for important defects in GaN and ZnO that show unprecedented agreement with experiment. We find clear trends concerning effective parameters that characterize luminescence bands of donor- and acceptor-type defects, thus facilitating their identification. [Preview Abstract] |
Friday, November 2, 2012 4:48PM - 5:00PM |
D2.00004: Absolute surface energies of polar and non-polar planes in GaN Cyrus Dreyer, Anderson Janotti, Chris G. Van de Walle Growth of high quality single crystals and epitaxial layers of GaN is very important for producing optoelectronic devices. {\it Ab initio} calculations can help in determining absolute surface energies, which are key quantities that control crystal-growth rates and fracture toughnesses. By means of hybrid functional calculations, we have determined absolute surface energies for the non-polar $\{11{\bar 2}0\}$ and $\{10{\bar 1}0\}$ and polar $(0001)$ and $(000{\bar 1})$ planes in wurtzite GaN. Low energy reconstructions of the bare and hydrogenated surfaces were considered under various conditions chosen to correspond to growth by molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD). We find that the non-polar planes are close in energy, and lower in energy than the reconstructed $(000{\bar 1})$ polar plane under all conditions considered. The reconstructed $(0001)$ plane is lower in energy than the $(000{\bar 1})$ plane over the whole range of conditions, and lower in energy than the non-polar reconstructions for Ga-rich chemical potential conditions. From these surface energies, lower bounds on the anisotropic fracture toughness of GaN are determined. Surface energies of polar planes for other III-nitrides will be compared to those of GaN. [Preview Abstract] |
Friday, November 2, 2012 5:00PM - 5:12PM |
D2.00005: Electromagnetic Interaction in Plasmonic Artificial Molecules Sarah Grefe, Yohannes Abate Plasmonic hotspots located in the nanogaps of infrared optical antennas are mapped in the near-field. The enhanced evanescent fields are imaged as a function of excitation wavelength, polarization, particle length, gap size, and tip material. The near-field resonance behavior of antennas composed of rods, ``bowtie'' and ``fourtie'' infrared antenna structures reveals that field enhancement strongly depends on the particle length and interparticle gaps. In rod antenna-field imaging using scattering probes, the probe tip can be considered as a load in the gap of the antenna, and the antenna response to tips can be directly understood by using nanocircuit theory. Experimental results are in agreement with finite-difference time-domain (FDTD) simulations. [Preview Abstract] |
Friday, November 2, 2012 5:12PM - 5:24PM |
D2.00006: LAMMPS Simulations of Ternary CuTiZr Metallic Glasses Sara Cheng, Lev Gelb Metallic glasses are a family of amorphous solids which display highly desirable material properties. These include high magnetic permeability, high hardness, and absence of micro structures such as grains and phase boundaries (Miller 2011). In this computational study we apply a three-step heating treatment to a ternary mixture of copper, titanium, and zirconium to study glass formation and recrystallization. We empirically apply a Second Moment Approximation Tight Binding Potential with adjustable parameters, outlined in Dalgic \textit{et al.} (2011), Qin \textit{et al. }(2011), and Rosato \textit{et al. }(1993). We calculate the temperature, volume, pressure, and total energy of the system as functions of simulation time. We also calculate the radial distribution function for the entire system as well as grouped atom constituents. We employ common neighbor analysis to qualify the structure of clusters of atoms in terms of either face-centered-cubic, hexagonal close packed, icosahedral, or unknown configurations. [Preview Abstract] |
Friday, November 2, 2012 5:24PM - 5:36PM |
D2.00007: Copper Phthalocyanine Thin Film Morphology Impact on Impedance Spectrum Kyle Robinson, Thomas Gredig Copper phthlacyanine thin films play an important role as the active layer in gas sensors, organic solar cells, and organic field-effect transistors. The surface morphology of such thin films can be controlled via modification of thermal deposition parameters. Thin films were deposited onto platinum interdigitated electrodes for impedance measurements to study the effect of structure on charge transport. The average grain size increases and changes from $\alpha $- and $\beta $-phase for samples deposited in the temperature range of 295-534 K. AC measurements in the temperature range of 295-385 K reveal relaxation peaks in the impedance spectra. From this spectrum, essential properties are retrieved, such as relaxation times and effective capacities, and correlated with the film morphology. Subject to both photo- and 5-day-dark current trials, photodecay rates are extracted via effective impedance circuit analysis using a phenomenological model that includes contributions from the grain boundary and the bulk part of the grain. Results indicate that the resistance contribution of low frequency relaxation peaks decrease while approaching the phase transition temperature, and vice versa for capacitance. We attribute the low-frequency peaks to grain boundaries, which are reduced in high temperature deposited samples. Hyper $\beta $-phase deposition temperatures show a sudden rise in resistance and lower capacitance due to increased roughness of samples. [Preview Abstract] |
Friday, November 2, 2012 5:36PM - 5:48PM |
D2.00008: Synthesis of Gadolinium and Neodymium Nanoparticles through the Reverse Micelle Method Ryan Fukuda, Maya Castro De La Torre, Pei-Chun Ho, Saeed Attar, Melissa Golden, Dennis Margosan Nanotechnology is a growing field that can be applied to several technologies such as electronics and medicine. Due to micro-scale materials reaching their limit, nano-scale development of materials is becoming the new focus. In reaction to this trend, our lab has aimed to synthesize Gd and Nd nanoparticles through the reverse micelle method. This method uses a molecule with a polar head and nonpolar tail, known as a surfactant, to form and contain nanoparticles. In this study, we used the surfactant Aerosol OT (AOT) with polar methanol and nonpolar hexane. The geometry of AOT's two nonpolar tails favors the formation of reverse micelles in a hexane solution containing small ``pools'' of methanol. The ``pools'' contain the rare earth compounds that are reduced by using sodium borohydride as a reduction agent. Samples have been examined using scanning electron microscopy, energy dispersive x-ray analysis, and a Leica microscope. The reduction of gadolinium chloride has been confirmed, but is not seen in spherical particles. The same procedure was used for neodymium chloride and neodymium nitrate, but further testing is required. Future work will be done to improve the purity of our sample, generate spherical reverse micelles, and develop smaller particles. [Preview Abstract] |
Friday, November 2, 2012 5:48PM - 6:00PM |
D2.00009: Electronic Properties of Graphene Multilayers Hamed Sadeghi, Julius de Rojas, Andreas Bill We determine numerically the tight-binding band structure, the density of states and the plasmon spectrum of N stacked graphene layers beyond the Dirac cone approximation. We calculate the polarizability in the random phase approximation and determine the dielectric function $\epsilon$({\bf q},$\omega)$. This allows to determine the acoustic and optical modes of the plasmon spectrum. Because we do not limit ourselves to the Dirac cone approximation we cannot use the semi-analytic approach usually proposed for graphene in the literature. Instead we use a combination of numerical procedures to determine the collective modes of graphene multilayer. [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