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 K4: Thin Films and Surfaces |
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Chair: Mark Siemens, JILA, University of Colorado at Boulder Room: Green Center 263 |
Saturday, October 24, 2009 1:50PM - 2:02PM |
K4.00001: Reconstruction of many-body excitation configurations via nonlinear absorption in semiconductor quantum wells Ryan P. Smith, Andrew Funk, Hanno Steiner, Jared K. Wahlstrand, Martin Schaefer, Mackillo Kira, Stephan Koch, Steven Cundiff Detailed electronic many-body configurations are determined by analyzing quantitatively measured time-resolved nonlinear absorption spectra of resonantly excited GaAs quantum wells with a fully consistent microscopic theory. The measured reflection and transmission probabilities across a broad spectrum allowed a model of the sample structure to be fixed using a transfer matrix calculation. Quantitative comparison of co-linear and co-circular polarization pump-probe excitation schemes reveal consequences of spin selection rules on scattering. An observed strong transient probe gain is attributed to the optically induced coherent polarization under low dephasing conditions. Radiative and internal sources of dephasing are quantified. Unexpectedly, it is found that true exciton populations do not significantly contribute to spectral broadening whereas the strong resonance blue shifts are dominated by the excited carrier densities. [Preview Abstract] |
Saturday, October 24, 2009 2:02PM - 2:14PM |
K4.00002: Ge$_{0.98}$Sn$_{0.02}$/Si $p-i-n$ Heterostructure Photodiodes for Telecommunications Applications Jay Mathews, Jose Menendez, Shui-Qing Yu, Radek Roucka, Junqi Xie, John Kouvetakis In this study, $p-i-n$ heterostructure photodiodes were fabricated from Ge$_{0.98}$Sn$_{0.02}$ films grown directly on Si substrates using complementary metal-oxide-semiconductor (CMOS) compatible processes. The devices characterized with respect to their dark currents and their quantum efficiency in the near IR. The structures were grown on boron-doped (p-type) Si(100) with resistivity 0.01 $\Omega $cm. A 350nm thick layer of intrinsic Ge$_{0.98}$Sn$_{0.02}$ was deposited first as the active region, followed by 64nm of phosphorus-doped (n-type) Ge$_{0.98}$Sn$_{0.02}$. The current-voltage characteristics of the devices yielded distinctly diode-like behavior. The measured photoresponse yielded higher quantum efficiencies than comparable pure-Ge devices over a broader spectrum as a result of the lower direct band gap and broadening of the absorption edge due to alloying. The significant responsivity obtained at wavelengths as long as 1750 nm confirms the advantages of the GeSn approach for telecom applications. [Preview Abstract] |
Saturday, October 24, 2009 2:14PM - 2:26PM |
K4.00003: Hybrid plasmon/dielectric waveguide for integrated silicon-on-insulator optical elements Jonathan Banks, David Flammer, Charles Durfee, Tom Furtak, Reuben Collins, Russell Hollingsworth We present a hybrid plasmon/dielectric single-mode single-polarization waveguide on silicon-on-insulator wafers. The structure is fabricable using VLSI processing techniques and minimizes losses due to surface roughness and metallic losses. Because only a single mode and single polarization is admitted, birefringent effects are eliminated. Both simulations and experimental verification of the modes are presented. Simulations show the waveguide can be tuned for either very long propagation lengths or sub-wavelength confinement by changing a patterned metal line width and oxide thickness, which are easily done with VLSI methods. Simulations show sub-wavelength confinement modes with propagation lengths greater than 100 microns, and micron-scale confinement modes with 7mm propagation lengths. This structure naturally forms an MOS capacitor that may be used for active device integration. [Preview Abstract] |
Saturday, October 24, 2009 2:26PM - 2:38PM |
K4.00004: Binding of N$_{2}$, O$_{2}$, CO and H$_{2}$O$_{2}$ on graphene in the presence of Co Shyam Kattel, Boris Kiefer One of the largest challenges in the current century is the production of energy to meet the increasing societal demands. Bio-inspired carbon based catalytic materials have been invoked as a possible solution to this challenge. We use density-functional-theory (DFT) to study molecule-Co-graphene interactions. Our results show that the most stable Co binding site is above the center of C6 hexagons of the graphene sheet (H) site in agreement with previous work. For molecule-Co-graphene interactions we find that N$_{2}$, O$_{2}$ and CO physiosorb onto the Co-graphene system only if the molecule and Co are on the same side of a graphene sheet. Therefore unaltered graphene is unlikely to be a catalytically active. In contrast we observe that H$_{2}$O$_{2}$ chemisorbs. These two different behaviors may explain selectivity of some catalytic materials toward O$_2$. We also observe that Co modifies the charge density only locally and which indicates that electronic transport properties of the underlying carbon structure are not enhanced and remain a bottleneck for the development of carbon based catalytic materials. [Preview Abstract] |
Saturday, October 24, 2009 2:38PM - 2:50PM |
K4.00005: New Lowest Energy Graphene Allotropes Utilizing 8 Membered Defect Rings David Appelhans, Mark Lusk The combination of Stone-Thrower-Wales (STW) and the recently identified Inverse-Stone-Thrower-Wales (ISTW) defects in graphene allow a wide range of graphene allotropes to be constructed. This is accomplished by applying combinations of these defects in a periodic template on pure graphene. For instance, the three lowest energy Haeckelite structures can be constructed in this way as has a new class of low energy graphene allotropes, Dimerites, which use only ISTW defects. All of these Haeckelites and Dimerites, though, are composed of 5-, 6-, and 7-membered rings. We have focused on 8-membered rings and predict a new family of carbon allotropes. One of these, Appelite R568, is only 194 meV/atom higher in energy than graphene. This is the lowest energy graphene derivative predicted. We outline a pathway of defect creation leading to the structure. [Preview Abstract] |
Saturday, October 24, 2009 2:50PM - 3:02PM |
K4.00006: Spin Dynamics for Wavepackets in Monolayer Graphene and Rashba systems Bailey Hsu, Jean-Francois Van Huele Spintronics, a technology to manipulate spin degrees of freedom in addition to the charge of an electron, has attracted considerable interest for its potential to increase computational power. Two current candidates for promising spintronics devices are graphene and materials with Rashba spin-orbit coupling. The Hamiltonians for these two systems involve combinations of momentum operators and spin operators. In this talk, we use the quantum propagator method to analyze the spin dynamics for localized wavepackets in these two physical systems and we discuss the occurences of interesting localization features with animated 2D plots. [Preview Abstract] |
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