Bulletin of the American Physical Society
Fall 2009 Meeting of the Four Corners Section of the APS
Volume 54, Number 14
Friday–Saturday, October 23–24, 2009; Golden, Colorado
Session K7: Materials Physics III |
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Chair: Tim Ohno, Colorado School of Mines Room: Hill Hall 202 |
Saturday, October 24, 2009 1:50PM - 2:02PM |
K7.00001: A shadow-edge contact for epitaxial nanostructures on silicon Samuel K. Tobler, Peter Bennett We have developed a method to apply a thin (5 nm) metal film with a sharp edge (100 nm) onto the surface of a silicon sample in ultrahigh vacuum, to provide a counter-electrode for the study of electrical properties of epitaxial nanostructures. Film sheet resistance, Rs, is monitored continuously during deposition, to identify ``electrical closure'' of small grains. Film roughness, $\sigma $, is measured ex situ using Atomic Force Microscopy and in situ using Scanning Tunneling Microscopy. We find that Pt is more suitable than Au, attaining $Rs\approx 300\Omega /sq$ and $\sigma \approx 10nm$ versus $Rs\approx 1000\Omega /sq$ and $\sigma \approx 50nm$ for Au. [Preview Abstract] |
Saturday, October 24, 2009 2:02PM - 2:14PM |
K7.00002: The Search for Effective p-Type Material in GaN-Based Devices: Past, Present, and Future Reid Juday, Alec Fischer, Fernando Ponce, Russell Dupuis In the continued drive towards viable, large-scale solid state lighting, GaN and its alloys with In and Al have risen to the forefront of current research. Regardless of GaN's success in LEDs and laser diodes, certain technological obstacles have remained. Since the beginning of GaN fabrication, the ability to reliably and effectively create p-type material has been a major concern. Mg is the most widely used and successful acceptor in GaN and appears to behave even more favorably in In$_{x}$Ga$_{1-x}$N with small values of x ($<$ 0.1). It is commonly accepted, however, that Mg-H complexes form during growth, inhibiting hole formation. This talk will focus on comparing the techniques most commonly used to activate p-GaN, such as thermal annealing and low-energy electron beam irradiation in a scanning electron microscope, as well as the properties of low-indium content p-type InGaN thin films. [Preview Abstract] |
Saturday, October 24, 2009 2:14PM - 2:26PM |
K7.00003: Experimental discrimination of geminate versus non-geminate recombination in a-Si:H Sang-Yun Lee, Thomas Herring, Dane McCamey, Craig Taylor, Klaus Lips, Jian Hu, Feng Zhu, Arun Madan, Christoph Boehme Hydrogenated amorphous silicon (a-Si:H) is an important material for solar cells, thin film transistors, and other devices. An open fundamental question in a-Si:H is which excess charge carrier recombination processes are geminate (correlated) or non-geminate (non-correlated). While both mechanisms cause photoluminescence (PL), only non-geminate recombination impacts photocurrent (PC). To answer this question, we have conducted pulsed Optically and Electrically Detected Magnetic Resonance (pODMR and pEDMR) spectroscopy on a-Si:H. The results allow an assignment of non-geminate and geminate processes to various previously known recombination mechanisms. [Preview Abstract] |
Saturday, October 24, 2009 2:26PM - 2:38PM |
K7.00004: Investigation of Interactions of Atomic Hydrogen with Amorphous Carbon Films Bhavin N. Jariwala, Cristian V. Ciobanu, Sumit Agarwal Hydrogenated amorphous carbon (a-C:H) films are generally deposited using plasma enhanced chemical vapor deposition from hydrocarbon feed gases. The structure and properties of these films are defined by the sp$^{2}$-to-sp$^{3}$ hybridization ratio and the H content. Interaction of H generated in the plasma results in local and overall transformations to a diamond-like structure due to various reactions. We have employed classical molecular-dynamics (MD) simulations based on the modified extended Brenner potential and experiments to study atomic H interactions with a-C:H thin films. Using MD, we first developed a procedure for creating realistic a-C:H thin films and formulated a scheme to characterize the sp$^{2}$-to-sp$^{3}$ hybridization ratio. These films were then impinged with H atoms at random locations and the specific chemical reactions of the H atoms with the a-C:H surface were identified through a detailed analysis of the MD trajectories. The reaction mechanisms for the hydrogenation reaction, H-atom abstraction and chemical erosion through desorption of stable hydrocarbon species have been identified and shown to be consistent with experimental measurements. Support from NSF award number DMR-0820518 is gratefully acknowledged. [Preview Abstract] |
Saturday, October 24, 2009 2:38PM - 2:50PM |
K7.00005: An initial analysis of short- and medium-range correlations potential non-Pt catalysts in CoNx Joe Peterson A potential show stopper for the development of fuel cells for the commercial automotive industry is the design of low-cost catalysts. The best catalysts are based on platinum, which is a rare and expensive noble metal. Our group has been involved in the characterization of potential materials for non-Pt catalysts. In this presentation, I will present some preliminary neutron scattering data from a nanocrystalline powder sample of CoNx. It is apparent that the diffraction data cannot be analyzed with standard Riedveld refinement, and we have to invoke pair distribution function (PDF) analysis. The PDF provides insight into short-range correlations, as it measures the probabilities of short- and mid-range interatomic distances in a material. The analysis reveals a strong incoherent scattering response, which is indicative of the presence of hydrogen in the sample. After correcting for the incoherent scattering, one obtains the normalized scattering function S(Q), whose Fourier transform yields the PDF. [Preview Abstract] |
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