Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B67: Undergraduate Research IIUndergraduate
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Sponsoring Units: APS/SPS Chair: Crystal Bailey, American Physical Society Room: BCEC 050 |
Monday, March 4, 2019 11:15AM - 11:27AM |
B67.00001: Visualizing Contact Area Growth in Frictional Interfaces Thomas Pilvelait, Shmuel Rubinstein, Samuel Dillavou Seemingly static interfaces between two solids are in fact dynamic. These multicontact interfaces (MCIs) exert enormous stresses on tiny contact areas, causing time-dependent deformation, also known as aging. Though these phenomena are ubiquitous in engineering and the sciences (e.g from micromachines to plate tectonics), their underlying mechanisms are not yet well understood. Quantitative, 2D measurements of the real contact area between a polymer solid and a glass plate are obtained over a variety of normal loads and time steps. By varying geometric and elastic properties of our samples, we induce variations in the 2D structure of contact growth, which give insight into the mechanisms that produce aging in frictional interfaces. |
Monday, March 4, 2019 11:27AM - 11:39AM |
B67.00002: Ultrafast Laser Ablation of Graphene under Water Immersion Ethan Richman, Mac Selesnick, Yu-Tien Chou, Yanpei Deng, Logan Kaelbling, Ziwei Liang, Grey McAlaine, Cameron Miller, Christopher LaFratta, Paul Cadden-Zimansky We report on a technique to pattern 2-D materials by ultrafast laser ablation. This resist-free method is performed in single step using a Ti:sapphire laser coupled to a microscope with a programmable x-y stage. While close examination of samples ablated in ambient air revealed persistent defects, a novel modification to the technique by carrying out the ablation under water immersion dramatically reduced the observed defects. In addition to using this technique to create submicron graphene wires, its application to other other 2-D materials, such as hexagonal boron nitride, is detailed. |
Monday, March 4, 2019 11:39AM - 11:51AM |
B67.00003: Theoretical Study of Amorphous Graphene Victor Barone, Blair Tuttle Amorphous graphene is a two-dimensional sheet of carbon atoms with three fold coordination. The atoms in amorphous graphene mostly form hexagons but there are regions of interconnected 5, 6, 7 and 8 sided objects with carbon atoms at the vertices. Here we use density functional calculations to explore the mechanical and electronic properties of amorphous graphene. |
Monday, March 4, 2019 11:51AM - 12:03PM |
B67.00004: Mechanism to Generate Larger Strain in Two-Dimensional Materials Melissa Bowman, Angela Coe, Guohong Li, Eva Andrei Two-dimensional (2D) materials, especially graphene, are very sensitive to strain due to every atom residing at the surface. Theory predicts that when graphene experiences large strain, its electronic properties change dramatically. In particular for strain in excess of 20% a strain-dependent gap is expected to develop in its band structure, providing a mechanism to switch its transport properties on and off. Thus far however strain levels achieved with standard techniques could not exceed a few percent. We present a piezoelectrically controlled technique that can introduce, in a controlled way, a continuously variable amount of uniaxial strain in 2D materials reaching up to ~25% where graphene ruptures. |
Monday, March 4, 2019 12:03PM - 12:15PM |
B67.00005: Effect of Lattice Mismatch Strain in Oxygen Deficient Strontium Titanate Films Francis Walz, Joseph Cartelli, Azriel Weinreb, Anton Wiggins, Jeffrey Simpson, Rajeswari M Kolagani, Oleksiy Svitelski SrTiO3 (STO) is a quantum paraelectric material which exhibits electronic phenomena that are interesting for technological applications. Applications of STO include its use as a dielectric layer in semiconductor devices, and as a photocatalytic material. Varying the oxygen content in STO affects the crystal structure and electronic properties which are important for such applications. In oxygen deficient STO (SrTiO3-y), the valence of the titanium ion and the average ionic sizes are different from those of the stoichiometric form (SrTiO3), leading to structural and electronic changes. Our study focuses on the structure and electronic properties of oxygen deficient epitaxial thin films of STO grown by Pulsed Laser Deposition on substrates with varying degrees of lattice mismatch. Previous work in our laboratory has shown that tensile strain promotes oxygen deficiency in epitaxial thin films of another perovskite oxide CaMnO3-y. Such coupling may be employed to engineer novel phases in thin films. We explore whether a similar coupling between strain and oxygen stoichiometry is present in STO. We will present the results of x-ray diffraction, electrical conductivity, Raman spectroscopy and atomic force microscopy studies. |
Monday, March 4, 2019 12:15PM - 12:27PM |
B67.00006: Annealing and Characterization of Niobium Oxide Films Deposited With Atomic Layer Deposition Andrew H. Rowley, Zachary Robinson, Alexander C. Kozen, Mark Twigg, Sharka Prokes Niobium oxides have seen a rise in interest due to their potential usefulness in optical, electronic, and memristive devices. Specifically, Nb2O5 and NbO2 have bandgaps of ~3.5 eV and ~1.2 eV, respectively. Nb2O5 is a high-k dielectric (k~41) and has a high refractive index (n~2.2). Both materials have the potential to be used in nonvolatile or volatile memristor devices. Amorphous thin-films of Nb2O5 and NbO2 were grown with atomic layer deposition on 4” Si(110) wafers with native oxide. The wafers were diced into 1 cm squares, and annealed in both inert and reducing environments in an atmospheric pressure tube furnace. The anneals were performed for up to 120 minutes, with temperatures ranging from 550 ○C up to 1000 ○C. It was found with X-ray diffraction and Raman spectroscopy that the amorphous Nb2O5 crystallizes at 550 ○C, and nucleates crystalline NbO2 islands at 750 ○C. Anneals performed at 1000 ○C were found to be fully recrystallized as NbO2. As-deposited amorphous NbO2 was found to crystallize at similar temperatures. For both NbO2 and Nb2O5, trends were observed in the sample morphology, indicating that annealing temperature and duration are important in the reduction and recrystallization of as-grown Nb2O5 and NbO2 on SiO2. |
Monday, March 4, 2019 12:27PM - 12:39PM |
B67.00007: Perovskite Films on Plasmonic Metamaterials Assata Acey, Giorgio Adamo, Harish Krishnamoorthy, Cesare Soci, Michael Lim Perovskites are of rising importance for current applications in the field of sustainable energy. Of particular interest are the optical properties of patterned perovskite films. The properties of these gratings have been studied with simulations in COMSOL, providing predictions of how the reflection and absorption at different wavelengths may be tuned by varying the configuration of perovskite-coated gratings. Using inputs values for n and k determined through ellipsometry of the perovskite film, this work has led to promising grating designs that are now candidates for testing. One fabricated grating did not perform according to prediction, implying degradation in the material over time that was later confirmed. |
Monday, March 4, 2019 12:39PM - 12:51PM |
B67.00008: Optical properties of AlAu alloyed and intermetallic thin films Abdul Qadeer Rehan, Mariama Rebello Sousa Dias Noble metal alloys have been widely investigated as an alternative to pure metals for improving the optical response of optoelectronic devices operating in the visible range of the electromagnetic spectrum. However, their use is hardly extended to the ultra-violet (UV) range. As an alternative, aluminum-based alloys could expand the functionality of photonic devices into the UV range of the spectrum. In this work, we fabricated and measured the optical response of a binary mixture of gold (Au) and aluminum (Al) thin films. The thin films were deposited on a glass substrate via the co-sputtering method. The dielectric functions were measured using spectroscopic ellipsometry. Also, we investigated how the optical response of the thin films changed under a wide range of temperatures, from 25°C to 200°C. We demonstrate that, in some cases, a bimetallic material can outperform their pure metal counterparts after the temperature treatment, e.g., Al0.15Au0.85 shows an increased quality factor of its localized surface plasmon (QLSP) than pure Au and Al. Moreover, we observe that Al-rich thin films are stable, no significant changes were noticed in its dielectric function, as temperature increased. |
Monday, March 4, 2019 12:51PM - 1:03PM |
B67.00009: Exploring the effects of bismuth clustering on the energy band gap of GaBixAs1-x semiconductors John Carlton, Arthur Lin, Garnett Bryant Substituting Bi anions in place of As allows for effective tuning of the energy band gap |
Monday, March 4, 2019 1:03PM - 1:15PM |
B67.00010: Effects of Temperature on the Vibrational Mode Dynamics of Cubane Anthony Froehlich, Guoping Zhang Ab initio calculations and the Boltzmann distribution are utilized to determine the effects of temperature on the vibrational modes of cubane. Attention is paid to the propagation of energy throughout the normal modes as temperature changes, providing information about chemical and physical characteristics of cubane and their relationship to temperature. The order in which the energy levels of normal modes increase, the effect of this energy on the movement of atoms in a molecule, and the effects of this movement on chemical characteristics are the desired results of this project. |
Monday, March 4, 2019 1:15PM - 1:27PM |
B67.00011: Monte-Carlo Simulations of Magnetic Ising Models for Sodium Cobaltate Joseph Lanier, Patrick T Gemperline, David Morris Sodium cobaltate is a material whose physical properties depend strongly on the concentration of sodium. It is unique because it acts as a thermoelectric material, and a superconductor at different concentrations of sodium. The sodium ions move within layers sandwiched between CoO2 layers. The sodium ions can occupy two different types of site; one low energy and one high energy. These sites neighbor each other, and by representing the two sites as pseudospin vectors pointing to the occupied site, we can study the ordering of sodium ions by simulating how the pseudospins interact with each other via the Ising Hamiltonian. This is done with the use of a Monte-Carlo Metropolis simulation with the results being presented here. The code is used to study the lowest energy structure of sodium cobaltate at different sodium concentrations. |
Monday, March 4, 2019 1:27PM - 1:39PM |
B67.00012: WITHDRAWN ABSTRACT
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Monday, March 4, 2019 1:39PM - 1:51PM |
B67.00013: Investigating the Far-IR Optical Properties of Hg1-xCdxSe Semiconductor Alloys John W Lyons, Frank C Peiris, Gregory N Brill Far-IR reflectivity was used to analyze phonon modes and obtain dielectric functions of a series of Hg1-xCdxSe thin films deposited on both ZnTe/Si(112) and GaSb(112) substrates. The data were supplemented by ellipsometric scans in the mid-IR to visible range to assist in modeling the dielectric functions. The combination and simultaneous modeling of these data allowed the determination of not only the phonon and free-carrier activity but also the complex dielectric function over an extremely large range of energies. |
Monday, March 4, 2019 1:51PM - 2:03PM |
B67.00014: Floquet Hofstadter Butterfly on the Kagome and Triangular Lattices Ariel Barr, Liang Du, Qi Chen, Aaron Barr, Gregory Fiete Recently, the interactions of materials with light have attracted considerable interest from the materials science community. “Hofstadter’s butterfly” refers to a fractal energy spectrum which occurs when a perpendicular magnetic field of extreme magnitude distributes the electronic energy levels of a lattice in a pattern resembling a butterfly. Lattices with a Hofstadter spectrum exhibit quantum Hall conductance, and under the influence of periodic driving, produce pairs of counter-propagating chiral edge modes which are robust against static disorder. We use Floquet theory to theoretically study the influence of a periodic driving potential provided by monochromatic circularly and linearly polarized light on the Hofstadter butterfly energy spectrum and Chern numbers of Kagome and triangular lattices. We find that as the lattices are exposed to driving, dramatic changes in the energy spectrum occur: reflection symmetry is broken, band width is altered, band inversion is observed, and polarization directional dependence can be identified. Further, we identify polarization-directional dependence of the Chern numbers. This work is currently under review at Phys Rev B, and can be found on Arxiv: arXiv:1808.02057 |
Monday, March 4, 2019 2:03PM - 2:15PM |
B67.00015: Cytoskeletal Dynamics of Neurons Measured by Combined Fluorescence and Atomic Force Microscopy Peter Moore, Cristian Staii Mechanical properties of neurons represent a key factor that determines the functionality of neuronal cells and the formation of neural networks. The main source of mechanical stability for the cell is a biopolymer network of microtubules and actin filaments that form the main components of the cellular cytoskeleton. This biopolymer network is responsible for the growth of neuronal cells as they extend neurites to connect with other neurons, forming the nervous system. Here we present experimental results that combine atomic force microscopy (AFM) and fluorescence microscopy to produce systematic, high-resolution elasticity and fluorescence maps of cortical neurons. This approach allows us to apply external forces to neurons, and to monitor the dynamics of the cell cytoskeleton. We measure how the elastic modulus of neurons changes upon changing the ambient temperature, and identify the cytoskeletal components responsible for these changes. These results demonstrate the importance of taking into account the effect of ambient temperature when measuring the mechanical properties of cells. |
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