Bulletin of the American Physical Society
2012 Annual Fall Meeting of the APS Prairie Section
Volume 57, Number 14
Thursday–Saturday, November 8–10, 2012; Lawrence, Kansas
Session G2: Condensed Matter Physics IV |
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Chair: Matthew Antonik, University of Kansas Room: Oread Hotel Griffith Room |
Saturday, November 10, 2012 8:30AM - 8:42AM |
G2.00001: PLD Fabrication of CdTe-based Thin Film Solar Cells D. Jake Meeth, Jianwei Liu, Rongtao Lu, Paul Harrison, Bing Li, Judy Wu This work explores \textit{in situ} fabrication of thin film solar cells using pulsed laser deposition (PLD). Optimization of the PLD processing conditions, including laser energy density, substrate temperature, and the PLD chamber pressure, was achieved with respect to pinhole-free CdS and CdTe layers and solar power conversion efficiency. By introducing a novel quantum based structure called Single Offset Superlattice (SOS) to the thin film cell, further increases to the efficiency have been made. SOS allows for tuning of the charge carrier density of the semiconductor. The efficiency of a thin film solar cell can be improved, relatively easily, by pairing the \textit{in situ} capability of PLD with the complicated structure of SOS. High efficiency up to 6.68{\%} has been demonstrated with a CdS (100nm)/CdTe (1500nm) cell and 8.88{\%} efficiency has been achieved with the introduction of SOS structure. Improved performance is expected with optimized PLD conditions and SOS dimensions. [Preview Abstract] |
Saturday, November 10, 2012 8:42AM - 8:54AM |
G2.00002: Al$_{2}$O$_{3}$ Conformal Coating of High-Aspect-Ratio Vertically Aligned Carbon Nanofiber Array Using Atomic Layer Deposition Gary Malek, Judy Wu, Rongtao Lu, Jianwei Liu, Alan Elliot, Logan Wille, Jun Li, Steven Klankowski A vertically aligned carbon nanofiber array (VACNFA) was used as a high-aspect-ratio substrate for atomic layer deposition (ALD) coating of aluminum oxide (Al$_{2}$O$_{3})$. Al$_{2}$O$_{3}$ was deposited on the VACNFA using alternating pulses of trimethylaluminum and distilled water for each cycle. The VACNFA was chosen as the substrate because of its large surface area as a result of the three dimensional structure and its surface reactivity due to outside dangling bonds. ~This reactive nature eliminated the need for functionalization of the VACNFA before ALD deposition. ~Transmission electron microscopy (TEM) was used to verify the Al$_{2}$O$_{3}$ layer conformally coated the VACNFA despite its high-aspect ratio. TEM images also revealed an approximate growth rate of the Al$_{2}$O$_{3}$ layer to be 0.85 {\AA}/cycle. Therefore, we can control the thickness of the Al$_{2}$O$_{3}$ layer on the VACNFA by tuning the number of ALD cycles. [Preview Abstract] |
Saturday, November 10, 2012 8:54AM - 9:06AM |
G2.00003: Fabrication of Nb/Al2O3/Nb Josephson Junctions using Atomic Layer Deposition Rongtao Lu, Alan Elliot, Logan Wille, Bo Mao, Siyuan Han, Judy Wu, John Talvacchio, Heidi Schulze, Rupert Davis, Daniel Ewing, H.F. Yu, G.M. Xue, S.P. Zhao Atomic layer deposition (ALD) provides a promising approach for deposition of ultrathin low-defect-density tunnel barriers, and it has been implemented in a high-vacuum magnetron sputtering system for \textit{in situ} deposition of ALD-Al$_{2}$O$_{3}$ tunnel barriers in superconductor-insulator-superconductor (SIS) Josephson junctions. A smooth ALD-Al$_{2}$O$_{3}$ barrier layer was grown on a Al-wetted Nb bottom electrode and was followed with a top Nb electrode growth using sputtering. The formation of tunnel barriers in these Nb/ALD-Al$_{2}$O$_{3}$/Nb trilayers was strongly indicated at room temperature by using the current-in-plane tunneling technique. Preliminary low temperature measurements of current-voltage characteristics (IVC) of the Josephson junctions made from these trilayers confirmed the integrity of the ALD-Al$_{2}$O$_{3}$ barrier layer. However, the I$_{c}$R$_{N}$ product of the junctions is much smaller than the value expected from the Ambegaokar-Baratoff formula suggesting a significant pair-breaking mechanism at the interfaces. [Preview Abstract] |
Saturday, November 10, 2012 9:06AM - 9:18AM |
G2.00004: The Use of NRS Pulses to Select Among Competing Markov Models for the Same Ion Channel Nick Martinez, Azida Walker Markov models are used to describe the probability of a system being in a certain state and is completely independent of the previous states. If the correct parameters are applied, these models have the ability to predict the random occurrence of protein unfolding to form ion channels. The Markov models of ion channels are used to determine the probability of the channel being in a number of possible states with one or more of these states corresponding to the channel being open. Using the patch clamp technique and data from single channel recordings with stepped potential protocols, Markov models are proposed for different ion channels. The transition rate parameters between states of the models are empirically determined. Using this current technique, researchers have proposed more than one Markov models for the same ion channel. It is argued that by using stepped potentials, the channel is always being observed at equilibrium. We present the use of non equilibrium response spectroscopy (NRS) technique where the randomly generated pulses constantly drive the channel far from equilibrium where the channel is observed. The NRS pulses selected will yield different expectations from competing models for an L-type voltage gated calcium channel. [Preview Abstract] |
Saturday, November 10, 2012 9:18AM - 9:30AM |
G2.00005: Minimum entropy coding of hierarchical mixture data Nathaniel Maddux, John Ralston Many types of data consist of hierarchical mixtures of signals. For example, a fetal electrocardiogram is a linear combination of the maternal and fetal cardiac signals, each of which is composed of signals originating in different muscles and nerves. Linear combinations of the signals are sensed by several electrodes, yet the hierarchy of the component signals is hidden. In this talk, an intuitive geometric picture of hierarchical mixture data is developed by use of synthetic data. Results are shown of minimizing, through gradient descent, the entropy of a code for a synthetic hierarchical mixture dataset. The use of invariant subspaces of a linear operator to express a code for a hierarchical mixture is discussed. The approach is applied to the classification of multi-domain proteins by their essential dynamics. Nine teacup shaped ``proteins'' are constructed by combining 3 differently shaped bodies with 3 differently shaped handles. The impulse response function of each teacup is treated as a vector, the set of vectors is decomposed as a hierarchical mixture, and results are discussed. [Preview Abstract] |
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