Bulletin of the American Physical Society
74th Annual Meeting of the Southeastern Section
Volume 52, Number 13
Thursday–Saturday, November 8–10, 2007; Nashville, Tennessee
Session MC: Surfaces and Interfaces |
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Room: Scarritt-Bennett Center Laskey B |
Saturday, November 10, 2007 8:30AM - 8:42AM |
MC.00001: AFM and LEED of Hybrid Si-based Graphene Interface Nanostructures J.E. (Jack) Rowe, Joseph Tedesco, Andreas Sandin, Zhengang Wang A multi-method approach is described that is being used to create new hybrid nano-scale graphene electronic structures compatible with Si-based technology. Our design uses nanostructured SiC-template graphene channels and high-K dielectrics for RF applications. This method is based on the well-known high temperature annealing procedure that converts SiC into thin layers of graphite called graphene. Initial Atomic Force Microscopy (AFM) measurements of epitaxial SiC on Si(100) and Si(111) shows narrow domains of $\sim $150 nm dimension that have an Auger electron Spectroscopy signature confirming the formation of graphene on the SiC surface. Low Energy Electron Diffraction (LEED) also confirms the well-known pattern of graphene reported earlier by several groups. We find that the conversion temperature appears to be somewhat lower ($\sim $ 1000 -- 1080 C) for these thin films of SiC than for bulk SiC (0001) surfaces which is possibly due to surface dislocations formed during the epitaxial growth process. Additional experiments using Photoelectron Emission Microscopy (PEEM) are in progress that appear to confirm the results found by AFM and give further details of the conversion process on a $\sim $ 10 -- 1000 nm scale. [Preview Abstract] |
Saturday, November 10, 2007 8:42AM - 8:54AM |
MC.00002: Modeling of near surface lithium distribution in lithium fluoride after low energy electron irradiation. Dwight Russell Alkali halides provide a rich response to electron irradiation. Defect formation, recombination and diffusion, thermal and hyperthermal desorption and more play a role in the near surface dynamics. While many experimental results have been modeled accurately, measurements of the depth distribution of lithium and the rate of surface metalization (lithium enrichment) taken by Wurz and Becker in the late 1980's could not be understood with the prevailing models at that time. Since then, additional feature of the dynamics involved, including excited F-center mobility and growth modes on the surface add new possibilities in understanding these data. Here we present the results of including these new features into the modeling and discuss the optimal fit to the data in light of the more recent studies. [Preview Abstract] |
Saturday, November 10, 2007 8:54AM - 9:06AM |
MC.00003: Dynamics of crystal nucleation and growth from large scale simulations Lujian Peng, James Morris, Rachel Aga, Y.C. Lo In previous work, we showed that when simulation size effects and transient nucleation theory were considered, crystal nucleation times from simulations could be predicted using classical theory. We have now extended this to the Lennard-Jones system. Homogeneous crystal nucleation is simulated by large-scale molecular dynamics. We study nucleation dynamics as a function of system size and temperature. We present quantitative comparisons between our results and classical nucleation theory. This is done without parameter fitting, using interfacial free energies and other properties calculated from separate equilibrium simulations. [Preview Abstract] |
Saturday, November 10, 2007 9:06AM - 9:18AM |
MC.00004: Two defect levels for the carbon vacancy carbon antisite pair in 4H-SIC. Geoffrey Ngetich, Mary Ellen Zvanut Due to its possible applications in high power devices, 4H-SiC is a material of keen interest to many researchers. The specific structure of point defects is often studied using electron paramagnetic resonance (EPR) while photo EPR allows for the understanding of their defect level. We are using EPR to look at SI5, a carbon-vacancy-carbon-antisite pair, V$_{C}$C$_{Si.}$ The samples were prepared by halide chemical vapor deposition using gasses with different C/Si ratios. The process produces samples with resistivity activation energy, E$_{a}$, between 0.25 eV and 0.85 eV.The photo EPR was performed at 80 K using a quartz tungsten halogen lamp and a monochrometer. Wavelengths were varied between 388 nm and 2400 nm. Results reveal that SI5 has photo-threshold energy of 0.75 eV for samples with E$_{a }$= 0.25 eV and 0.5 eV while samples with E$_{a}$ of 0.85 eV had a threshold energy of 2.5 eV. In our model, the threshold energy represents the defect level where double negative to negative defect level,V$_{C}$C$_{Si}^{--/-}$, is 0.75 eV below the conduction band edge while negative to neutral, V$_{C}$C$_{Si}^{-/0 }$, is 2.5 eV above the valence band edge. [Preview Abstract] |
Saturday, November 10, 2007 9:18AM - 9:30AM |
MC.00005: Probing the Surface Potential of Ag(001) with Hyperthermal K$^+$ Ion Scattering M.P. Ray, R.E. Lake, C.E. Sosolik Using hyperthermal (10-400 eV) K$^+$ scattering, we probe the surface potential of Ag(001) in the energy regime where ion beam epitaxy and sputtering occur. In these measurements, hyperthermal energy K$^+$ ions were scattered from a clean Ag(001) target into a detector. The K$^+$ were incident at an angle of 45 degrees from the surface normal and energy spectra of the scattered ions were measured at various coplanar final angles with up to three distinct energy peaks observed. We have found that the energy of the scattered ions is dependent on the trajectory of the K$^+$ near the Ag(001) surface. The open lattice of Ag(001) allows the K$^+$ to undergo several well-defined scattering events, and using the kinematic factor and the classical scattering simulation SAFARI, we are able to identify the three energy peaks in our data as quasi-single, quasi-double and \textit{zig-zag} ion collisions. Comparing the data to the simulation results, we extract a K$^+$/Ag surface potential in this important energy range. [Preview Abstract] |
Saturday, November 10, 2007 9:30AM - 9:42AM |
MC.00006: Polymer LED interfaces studied with resonant soft x-ray reflectivity Cheng Wang, B. Watts, T. Araki, H. Ade, A. Hexemer, A. Garcia, T.-Q. Nguyen, G.C. Bazan, K.E. Sohn, E.J. Kramer Multilayered polymer structures produced by alternate spin casting from polar and non-polar solvents are promising for polymer light emitting diodes (PLEDs). The structure of the interface between the active layers most likely significantly affects the device efficiency, yet little is known about the interfacial structure and how it affects properties of such devices. Recently, it has been shown that Resonant Soft X-ray Reflectivity (RSoXR) is an excellent tool to study polymeric thin films without the need for deuteration. RSoXR can enhance the sensitivity to a particular interface by using specific photon energies. We have used RSoXR and characterized the interfacial width of bilayers of poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) and poly[9,9-bis(6'-N,N,N,-trimethylammoniumhexyl)fluorene-co-alt-1,4 phenylene bromide] (PFNBr), materials relevant to PLED devices. MEH-PPV is a neutral conjugated polymer spun-cast from toluene (non-polar solvent) and PFNBr is a charged conjugated polymer (conjugated polyelectrolyte) spun-cast from methanol (polar solvent). [Preview Abstract] |
Saturday, November 10, 2007 9:42AM - 9:54AM |
MC.00007: A Method for Studying Atomic Diffusion by STM Tip-Crash Induced Vacancy Island Coalescence R.E. Lake, A.P. Lange, M.P. Ray, C.E. Sosolik The study of vacancy and adatom island motion on single crystal metals with the scanning tunneling microscope (STM) has explained many of the underlying atomic diffusion mechanisms responsible for movement of atoms on a surface. We present a new method for vacancy island creation at room temperature using a controlled mechanical tip-surface interaction. The method allows us to control the relative positions and initial sizes of vacancy islands with respect to one another and to surface defects. Complicated and closely spaced vacancy island configurations can also be engineered. This enhances our ability to collect statistics on the movement of the macro-scale vacancy islands and distinguish between mass transport channels. To demonstrate the technique, time series analysis of coalescence events on the surface of Ag(111) is presented. Diffusion coefficients of the Ag surface atoms obtained with this method are in general agreement with previous stochastic methods for creating vacancy islands such as low-dose sputtering [1]. [1] M. E{\ss}er, K. Morgenstern, G. Rosenfeld, G. Comsa, Surf. Sci. \textbf{402-404}, 341 (1998). [Preview Abstract] |
Saturday, November 10, 2007 9:54AM - 10:06AM |
MC.00008: Heteroepitaxial Growth and Phase Transition Properties of Vanadium Dioxide Thin Films Joyeeta Nag, Eugene Donev, Jae Suh, Leonard Feldman, Richard Haglund Vanadium dioxide thin films were deposited on R(012) and C(001) planes of sapphire and titanium dioxide substrates using pulsed laser deposition. Growth conditions were optimized to obtain epitaxial growth of films up to 100 nm thick. As is typical for oxide thin films, oxygen pressure and temperature are the main parameters governing the formation of the well-known VO$_{2}$ phase that exhibits the semiconductor-to-metal transition near 68$^{\circ}$C. A systematic study of the optical transmission and reflection in the near-infrared was done as a function of temperature between 20$^{\circ}$C and 90$^{\circ}$C. The samples were analyzed by X-ray diffraction, ion-beam channeling and scanning electron microscopy in order to determine epitaxy and crystal quality. The results show that the growth of VO$_{2}$ has strong substrate dependence. Tungsten doping of the epitaxial VO$_{2}$ films was also carried out in order to lower the phase transition temperature and lattice locations of the dopant atoms were determined. [Preview Abstract] |
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