Bulletin of the American Physical Society
2006 Four Corners Section of the APS Fall Meeting
Friday–Saturday, October 6–7, 2006; Logan, Utah
Session D1: Thin Films and Quantum Dots |
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Chair: Heinz Nakotte, New Mexico State University Room: Eccles Conference Center Room 216 |
Friday, October 6, 2006 1:30PM - 1:42PM |
D1.00001: The Effect of Voltage Ramp Rate on Dielectric Breakdown of Thin Film Polymers Anthomas Thomas, J. Dennison, Steve Hart, Ryan Hoffmann When a sufficient electric field is placed across a dielectric material, electrical breakdown occurs. The field strength at which this occurs is referred to as the dielectric strength or electrostatic discharge (ESD) voltage. The dielectric strength of thin (25 $\mu $m to 250 $\mu $m) film polymer samples (low density polyethylene, Teflon, Kapton, Mylar, and other fluorocarbon polymers) have been measured by placing them between parallel plate electrodes and increasing the voltage until breakdown occurs across the dielectric barrier creating a path for the flow of large discharge currents. The results are affected by the rate at which the applied potential is increased and the incremental increases. Rates between 20 V/s and 500 V/s and voltage increments between 10 V and 500 V have been studied. Larger rates cause a premature breakdown compared to a slower ramping speed. This may be due to a kind of conditioning of the sample; the stress of the high voltage is easier to handle if taken in small increases. [Preview Abstract] |
Friday, October 6, 2006 1:42PM - 1:54PM |
D1.00002: Orientation Studies of Recrystallized Vanadium Dioxide Felipe Rivera, Laurel Burk, Robert Davis, Richard Vanfleet Crystalline films and isolated vanadium dioxide particles (up to 700nm in diameter) were obtained through thermal annealing of amorphous vanadium dioxide thin films on silicon dioxide. Vanadium dioxide undergoes a metal to insulator transition changing from a monoclinic to tetragonal phase near 66 $^{\circ} $C. Orientation Imaging Microscopy (OIM) was used to study the phase and orientation of the crystals formed, as well as to differentiate from different vanadium oxide crystal structures. Kikuchi patterns for the tetragonal phase of vanadium dioxide were used for indexing as the Kikuchi patterns for the monoclinic phase are indistinguishable, by OIM, from those of the tetragonal phase. There is a preferred orientation for the growth of these crystals with the c axis in the plane of the specimen. [Preview Abstract] |
Friday, October 6, 2006 1:54PM - 2:06PM |
D1.00003: Characterization of Crystallization of Silicon on Alumina Brady Cox My research at Brigham Young University this summer focused on studying the crystallization of silicon on alumina (Al$_2$O$_3$). I deposited amorphous silicon ($\alpha$-Si) layers of two thicknesses onto various substrates in order to study how the silicon would crystallize at various temperatures and annealing times. The preliminary results indicate that $\alpha$-Si does not crystallize at temperatures below 630$^\circ$C when annealed for an hour on these substrates, but does crystallize at temperatures above 700$^\circ$C when annealed for the same amount of time. There appear to be no noticeable differences in crystallization between substrates. At the temperatures at which crystallinity was observed, there appears to be no preferred orientation for crystal formation. Further research will focus on determining the lowest temperature(s) at which crystallization begins and studying the early stages of crystal formation at these temperatures. [Preview Abstract] |
Friday, October 6, 2006 2:06PM - 2:18PM |
D1.00004: Characterization of GeSbTe Thin Films for Phase-Change Applications C.D. Grijalva, C.E. Inglefield, T. Herring, Heng Li, P.C. Taylor Thin films of the alloy GeSbTe are of interest because of current and potential applications in rewritable optical media and reconfigurable electronics. These applications stem from the fact that reflectivity and electrical conductivity are very different in the amorphous and crystalline phases of GeSbTe\textbf{, }and rapid switching between these phases is possible\textbf{. }We have grown amorphous GeSbTe using RF sputtering on quartz substrates, and used laser-induced heating to switch regions of the film from amorphous to crystalline phases. Previously, atomic force microscopy (AFM) showed that, during this transition, a substantial amount of ablation (several hundred nanometers) of the film occurred. The laser treatment has been revised to reduce the film ablation to the point that it is nearly undetectable by AFM. In addition, the AFM scans of films did not show any ordered structure on the scale we were able to resolve. Future work with these films includes looking at direct measurements of electrical conductivity on a similar scale. [Preview Abstract] |
Friday, October 6, 2006 2:18PM - 2:30PM |
D1.00005: Morphological study on dot-chains using molecular beam epitaxy and \textit{in-situ} scanning tunneling microscopy Haeyeon Yang, Dongjun Kim, Edward Everett, Richard Wilson We report scanning tunneling microscopy (STM) study on nano dots with a linear alignment. Strained but flat InGaAs epilayers were grown on nominal (001) surfaces of GaAs substrate by molecular beam epitaxy (MBE) at low temperature below 400\r{ }C. Real-time reflection high energy electron diffraction observations suggest that the strained surfaces are crystalline during the deposition process.\textit{ In-situ} scanning tunneling microscope (STM) shows that the strained surfaces are atomically flat but the surface reconstructions are not uniform, mixed with various structures. Upon heating the strained layers above 450 \r{ }C under arsenic pressure, the strained layers undergo roughening transition, resulting in nanodots. The nano dots were formed very closely along a line to form dot-chains during the annealing process. The alignment lines are mostly along the [1-10] azimuthal direction and some within 35 degrees off the [1-10] azimuthal direction. Furthermore, the size and shape of dots depend on the annealing temperature and strain amount. Effect of strain amount and the annealing temperature on the morphology of dots will be discussed. [Preview Abstract] |
Friday, October 6, 2006 2:30PM - 2:42PM |
D1.00006: Linear alignment of InGaAs quantum dots on nominal GaAs(001) surfaces Dong Jun Kim, Addison Everett, Haeyeon Yang We report linear alignment of quantum dots (QDs) by direct deposition on smooth surfaces. A single deposition of InGaAs with 37{\%} indium was carried out on a smooth GaAs(001) surface using molecular beam epitaxy (MBE) after a 1$\mu $m thick GaAs buffer, whichwas grown at 580$^{\circ}$ to get a flat surface. The substrate was then cooled down to the InGaAs growth temperature, 500$^{\circ}$C. \textit{In-situ} scanning tunneling microscopy (STM) confirmed that the buffer surface was smooth with well ordered 2x4 reconstruction. STM images of the dots show that they are aligned along a terrace edge line as shown while these dots are aligned along the dimer row direction but not along a step edge. The lines in the contour plot indicate the terrace edges and separate terraces with height difference of one monolayer. The effect of growth parameters on linear alignment of self-assembled quantum dots will be discussed. [Preview Abstract] |
Friday, October 6, 2006 2:42PM - 2:54PM |
D1.00007: Variation and effects of As$_{4}$ flux on morphology of InGaAs quantum dots E. Addison Everett, Dong Jun Kim, Haeyeon Yang We present a comprehensive \textit{in-situ} scanning tunneling microscopy (STM) study of InGaAs quantum dots (QDs) on GaAs (001) substrates as a function of arsenic flux using molecular beam epitaxy (MBE). With all other MBE growth parameters fixed, changes in arsenic flux result in changes in the morphology of InGaAs QDs and the critical thickness to form 3D islands. Under arsenic-rich conditions, islands with flat tops are formed while reduced arsenic flux results in formation of islands with rounded tops. Decreasing numbers of InGaAs QDs result from increasing arsenic flux. Reflection high energy electron diffraction patterns taken before InGaAs deposition show that the surface reconstruction changes from a 2x4 to c4x4 with an increase of arsenic flux. STM imaging shows no dots with high As$_{4}$ flux, low density of dots with medium As$_{4}$ flux, and high density of dots with low As$_{4}$ flux, with a deposition amount of 7ML for all samples studied. Effects of arsenic flux on the changes in surface reconstruction surface morphology and density of QDs, and the critical thickness to form the self-assembled QDs will be discussed. [Preview Abstract] |
Friday, October 6, 2006 2:54PM - 3:06PM |
D1.00008: Structural Characterization of Nanopolar Domains in PZN-PT Vayee Vue, Branton Campbell Pb(Zn$_{1/2}$Nb$_{2/3})$O3-PbTiO3 (abbreviated as PZN-PT) is of currently of great interest because of its potential as a ferroelectric-relaxor material and because it has the highest known piezoelectric constant. Piezoelectricity is the ability of a crystalline material to generate an electric potential difference when an external stress is applied, or conversely, to generate a physical strain (i.e. stretch or compress) when an external electric field is applied. The physical mechanism that facilitates the special properties of PZN-PT is not well understood. The existence of local structural distortions called nanopolar domains (NPDs) have been suggested as a likely mechanism. We present three-dimensional computer-generated defect models that embody all of the structural freedom an NPD is likely to possess. Individual defect models are evaluated by simulating the x-ray diffuse scattering distribution that results and comparing against experimental data collected at the Advanced Photon Source at Argonne National Laboratory. The DISCUS software package is used to generate the defect models and simulated diffuse scattering patterns, while Crystal Maker is used to visualize the results. [Preview Abstract] |
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