Bulletin of the American Physical Society
19th Annual Meeting of the APS Northwest Section
Volume 63, Number 6
Thursday–Saturday, May 31–June 2 2018; Tacoma, Washington
Session C2: Condensed Matter II |
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Chair: Janelle Leger, Western Washington University Room: Thompson Hall 193 |
Friday, June 1, 2018 3:30PM - 4:00PM |
C2.00001: Electron microscopy using structured electrons Invited Speaker: Benjamin McMorran The phase of electron matter waves can be measured and manipulated in analogous ways to light optics. Phase contrast electron microscopy can be used to form images of electron-transparent materials and nanoscale fields, such as topological magnetic domains like Skyrmions in thin films. Nanofabricated diffractive optical elements for electrons provide new ways to measure and control the phase of free electrons. We are developing a scanning electron interferometry using gratings as coherent beamsplitters. We also use these diffractive holographic devices to structure the phase and intensity of the electron beam itself. For example, a forked grating can be used to imprint phase vortices onto the wavefunction of free electrons, giving them quantized orbital angular momentum. This new degree of control over the electron will provide new methods in electron microscopy applied to a wide range of specimens. [Preview Abstract] |
Friday, June 1, 2018 4:00PM - 4:12PM |
C2.00002: Exploring new UV-Semiconductor alloy system Dinesh Thapa, Jesse Huso, Leah Bergman Semiconductors alloys provide by-designed optical and electronic properties as their bandgap can be tailored via the choice of the alloy composition, x. This research aims at the creation of an alloy system named Mg-Zn-Silicate: (Mg$_{\mathrm{x}}$Zn$_{\mathrm{1-x}})_{\mathrm{2}}$SiO$_{\mathrm{4}}$, that its optical and material properties are hardly known. The (Mg$_{\mathrm{x}}$Zn$_{\mathrm{1-x}})_{\mathrm{2}}$SiO$_{\mathrm{4}}$ has optical properties in the deep-UV region in the range 5 -- 7 eV, is environmentally friendly, and with emerging important applications in lighting and wireless communication technologies. In this study, bulk ceramics were synthesized, it was found that the bandgaps shifted deeper to the UV-range as the composition of Mg increased. The preliminary XRD indicated that the diffractions of both samples correspond to the willemite structure. The phonon dynamics of this alloy system as a function of alloy composition will be discussed in terms of lattice and local modes. [Preview Abstract] |
Friday, June 1, 2018 4:12PM - 4:24PM |
C2.00003: Addressing Alloy Broadening in Temperature Dependent Urbach Analysis Amrah Canul, Dinesh Thapa, Jesse Huso, Leah Bergman Modeling the temperature dependent Urbach energy distinguishes defect and thermal contributions to the semiconductor band-edge. \quad The current approach of the Urbach energy analysis relies on linear fitting of the Urbach region in semilogarithmic absorption plots. Determining the fitting range in spectra is relatively straightforward for ZnO. However, by alloying with increasing concentrations of Mg, the band-edge was found to broaden and rendered the fitting of the Urbach range difficult, if not impossible. We introduce a novel analytical approach based on the well-known mathematical description of the Urbach energy. \quad Since the Urbach energy relates to the slope of the semilog plot, we extracted this parameter by using first order derivative spectra. These plots are advantageous by providing a greater degree of clarity and an entirely experimental determination of the Urbach energy, removing all ambiguity in locating and determining the Urbach slopes. The advantage of this method over the conventional method is illustrated in ZnO thin film and its ternary alloys Mg$_{\mathrm{0.07}}$Zn$_{\mathrm{0.93}}$O and Mg$_{\mathrm{0.17}}$Zn$_{\mathrm{0.83}}$O. [Preview Abstract] |
Friday, June 1, 2018 4:24PM - 4:36PM |
C2.00004: Dynamic Phases, Stratification, Laning, and Pattern Formation for Driven Bidisperse Disks Danielle McDermott, Yang Yang, Cynthia Reichhardt, Charles Reichhardt Using numerical simulations, we examine the dynamics of driven two-dimensional bidisperse disks flowing over quenched disorder. The system exhibits a series of distinct dynamical phases as a function of applied driving force and packing fraction such as a phase separated state and a smectic state with liquidlike or polycrystalline features depending on the global disk density. At low driving forces, the system exhibits a clogged phase with an isotropic density distribution, while at intermediate driving forces the disks separate into bands of high and low density, where the high density bands can have either liquidlike structure or polycrystalline structure. In addition to the phase separation in the overall density we find that in some cases there is a fractionation of the disk species, particularly for large size ratio differences. These species phase separated regimes are associated with a variety of patterns such as large disks separated by chains of smaller disks or other types of patterns that are affected by the disk size ratio. [Preview Abstract] |
Friday, June 1, 2018 4:36PM - 4:48PM |
C2.00005: Amorphous to Crystalline Polymorphic Behaviors of TiO$_{2}$ Thin Films Deposited Under Various Oxygen Pressures by Pulsed Laser Deposition Okan Agirseven, James E. S. Haggerty, Janet Tate, Laura T. Schelhas, Michael F. Toney, Lauren Garten, John Perkins, David S. Ginley, John S. Magnum, Brian P. Gorman, Daniil Kitchaev, Wenhao Sun, Gerbrand Ceder TiO$_{2}$ is a versatile wide bandgap transparent semiconducting oxide with three well known polymorphs: Anatase, rutile and brookite. The crystalline polymorphs of TiO$_{2}$ require high temperature annealing processes to form from an amorphous precursor. Our research aims to understand the formation behaviour of these metastable polymorphs of TiO$_{2}$ as related to amorphous precursor properties. In this study, TiO$_{2}$ thin films deposited at room temperature on a-SiO$_{2}$ substrates by PLD under different oxygen pressures and then annealed with same annealing process. Changing the oxygen pressure for each deposition resulted in different phase structures after the annealing processes. We found that lower pressure favors rutile, middle pressure favors brookite, and higher pressure favors anatase formation. Microstructural properties of TiO$_{2}$ thin films are investigated by XRD, Raman spectroscopy, SEM, XPS, and optical transmission and reflection spectroscopy. [Preview Abstract] |
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