Bulletin of the American Physical Society
2019 Annual Spring Meeting of the APS Ohio-Region Section
Volume 64, Number 7
Friday–Saturday, March 29–30, 2019; The College of Wooster in Wooster, Ohio
Session F01: Applied Physics and Materials Science |
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Room: Severance Hall 238 |
Saturday, March 30, 2019 9:30AM - 9:45AM |
F01.00001: Grain Growth in Nanocrystalline Metal Deformed in a Confining Environment. Yuejian Wang Stress-induced grain growths were observed in many nanocrystalline metals and alloys. Correct understanding this unique feature is critical in designing and tailoring proper nanostructures for particular applications in mechanically harsh environments, e.g. high-stress concentration, mechanical vibrations. Though extensive researches have been carried out on metals or alloys subjected to deformation, experimental studies on metals deformed in a confining environment are severely lacking. Nearly all of the previous investigations on this theme were carried out either through theoretical simulations or by using TEM to probe grain variation in vacuo. In the present study, we employed a powerful high-pressure technique along with high energy synchrotron X-rays to monitor the grain size evolution in situ, in nanocrystalline Nickel deformed in varied confining environments. Our experimental data demonstrate, for the first time, that grain sizes grow with the increment of the confining pressure. Since plasticity strongly depends on the grain size of a given material, understanding and controlling fundamental mechanisms leading to stress-assisted grain growth may open a new route to improving the mechanical properties of nanocrystalline materials by tuning confining environment within which the deformation is operated. [Preview Abstract] |
Saturday, March 30, 2019 9:45AM - 10:00AM |
F01.00002: Electrical Properties of Molybdenum/4H-Silicon Carbide Schottky Barrier Diode Sai Bhargav Naredla Molybdenum has been recognized as a refractory metal suitable for high temperature applications. In this investigation, silicon carbide (SiC) Schottky diodes have been fabricated using molybdenum (Mo) as the Schottky contact. The Mo contacts were deposited by magnetron sputtering on the n-type 4H SiC at different temperatures from 25 $^{\mathrm{o}}$C to 900 $^{\mathrm{o}}$C. The electrical properties of the diodes were determined by current-voltage, capacitance voltage and current-voltage-temperature measurements. The as-deposited diodes exhibited energy barrier heights ranging from 0.99 to 1.69 eV and ideality factors varying from 1.03 to 1.71. Contacts deposited at 500$^{\mathrm{\thinspace o}}$C produced the optimum barrier height of 1.30 eV and ideality factor of 1.03. After annealing the sample at 500 $^{\mathrm{o}}$C for 24 hours diodes show a barrier height ranges from 1.25 to 1.30 eV and we believe that variation in electrical properties is due to change in crystal quality and formation of silicides. X-ray diffraction results shows the formation of MoSi$_{\mathrm{2}}$, Mo$_{\mathrm{5}}$Si$_{\mathrm{2.}}$ [Preview Abstract] |
Saturday, March 30, 2019 10:00AM - 10:15AM |
F01.00003: Optical and Microstructural Properties of Sputter-Deposited Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ Films. Eduardo Vega, Sundar Isukapati, Tom Oder Gallium oxide (Ga$_{\mathrm{2}}$O$_{\mathrm{3}})$ thin films were deposited on c-plane sapphire substrates by radio frequency magnetron sputtering technique. The deposition gas composition, substrate temperature and post-deposition annealing temperature were varied to optimize the films. Composition and structural properties were studied by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Results indicate that films deposited at 400 \textordmasculine C in argon possess diffraction peaks at 18.6 \textordmasculine , 37.2 \textordmasculine and 58.2 \textordmasculine , which belongs to the (- 2 0 1 ), ( -4 0 2 ) and ( -6 0 3 ) planes of monoclinic gallium oxide ($\beta $-Ga$_{\mathrm{2}}$O$_{\mathrm{3}})$. The optical characteristics obtained by UV-VIS spectroscopy measurements showed excellent transmission of 90 - 95{\%}. Post-deposition annealing in N$_{\mathrm{2}}$ at temperatures below 500 \textordmasculine C did not make any significant improvement in the crystal structure of the films. Addition of tin dopant in the films produced transparent films whose optical bandgaps decreased with increasing dopant concentration in the films. [Preview Abstract] |
Saturday, March 30, 2019 10:15AM - 10:30AM |
F01.00004: Emergent mechanics of bird nests. Nichalas Weiner, Hunter King, Yashraj Bhosale, Mattia Gazzola A bird nest is stable bulk material comprised of many individual sticks and, in the simplest case, contains no adhesives and is held together only through internal friction between the components. A lot of research has been done on similar aggregate structures of low aspect ratio components (grains, soil, etc.) in the field of granular materials, however, very little has been done in exploring the mechanics of aggregate materials made up of high aspect ratio components. We designed experiments to probe the stress-strain behavior of an artificial simplified nest, made up of \textasciitilde 2500 homogeneous sticks of aspect ratios above 50. We are exploring how the internal structure (coordination number, contact slipping, etc.) of the material changes during loading and unloading cycles, as well as how the bulk stress strain behavior changes will different loading procedures. We are also creating a simulation model to match our system in the limited cases of different properties we can explore experimentally. Providing useful information that cannot be extracted easily from the experiment (force chains, contact point location, etc.). Initial results for the experimental system will be presented, as well as preliminary hypotheses for why the system behaves in the unique ways observed. [Preview Abstract] |
Saturday, March 30, 2019 10:30AM - 10:45AM |
F01.00005: The Role of Surface Morphology in Aerodynamics of Biomimetic Fog Harvesting Aida Shahrokhian, Jiansheng Feng, Hunter King Harvesting water from atmospheric fog has been considered in regions where surface water is scarce. Namib desert beetles with bumpy elytra in this context have been frequently cited as a source of biological inspiration in a narrative where the difference in wetting properties of the bumps and the valleys accelerates the transport of accumulated water to the mouth of the beetle. However, the accumulation step depends solely on fluid dynamics. In this study, using a custom wind tunnel, we investigate how bumps as aerodynamic features take advantage of the competition between drag and inertia of the fog droplets to induce collisions. Results indicate that even slight modification of the surface morphology can play a significant role. Here we show that by addition of millimetric bumps the efficiency increases to three times the efficiency of a smooth surface of identical wettability. [Preview Abstract] |
Saturday, March 30, 2019 10:45AM - 11:00AM |
F01.00006: Hyperdoping silicon for intermediate band photoconductivity Yining Liu, Wenjie Yang, Quentin Hudspeth, Jeffrey Warrender, James Williams, Jay Mathews Hyperdoped silicon is a promising material for infrared detection. Supersaturated solutions of impurities in Si are produced in order to create intermediate bands (IBs) in between the valence and conduction bands. This new IB serves on sub-band gap absorption. Ion implantation followed by pulsed laser melting has been demonstrated as a method to produce concentrations of impurities in Si that are well above the solid solubility limit. In this work, we look at Si hyperdoped with Au or Ti. To achieve devices that could be commercialized for FPAs or other demanding applications, efficient ones will require significant optical absorption and high quality Ohmic contacts for carrier extraction. We fabricated Si layers hyperdoped with Au or Ti at varying concentrations, measured the optical absorption enhancement relative to Si, and attempted to form Ohmic contacts to the layers. The results show significant enhancement of optical absorption by increasing the implant dose. For making Ohmic contacts to hyperdoped materials, we tried several treatments, including boron or phosphorus shallow doping, rapid thermal annealing of contact, etching off the top metallic layer, and modifying the PLM process to suppress dopant segregation. Recipes for Ohmic contacts to each layer were demonstrated. [Preview Abstract] |
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