Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session A47: Undergraduate Research IIRecordings Available Undergrad Friendly
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Sponsoring Units: APS/SPS Chair: Andrew Zeidell, Wake Forest Univ Room: McCormick Place W-470B |
Monday, March 14, 2022 8:00AM - 8:12AM |
A47.00001: Realtime Vector Field Rendering in Unity Game Engine for STEM Education. Othman Alrawi, Brian Day, Elisabetta A Matsumoto The understanding of physical and mathematical concepts often requires a high level of visualization. This aspect of learning however still remains one of the most overlooked in modern education curriculums. We aspire to fill this void through employing newly available virtual reality technology to transform how students learn into a more interactive and entertaining experience. We are using the Unity game engine as a platform to develop fun and interactive educational programs that are up to date with modern game standards in terms of optimization and graphical fidelity. Particularly, we are working on creating real-time renderings of interactive vector fields. These educational environments are designed with introductory math and physics classes in mind. Our ultimate goal is to enhance the conceptual understanding of topics involving vector fields in undergraduate courses. |
Monday, March 14, 2022 8:12AM - 8:24AM |
A47.00002: Machine Learning the Ground-State and Free Energies of Iron-Vanadium alloys from Molecular Dynamics Simulations via Cluster Expansions Cesar Diaz The ground state energy and the entropy (collectively called the free energy) determine the structure of crystals, so they are from main concern in solid-state physics and materials science. Solids with crystal lattices in nature are always found in the atomic structure that has the lowest free energy, and determining the theoretical atomic arrangement of a system is an important step towards predicting its macroscopic properties. This project intends to predict the ground state energy for different compositions of alloys of iron (Fe) and vanadium (V) by using a machine learning algorithm called Cluster Expansion, which is based on the idea that the properties of a system can be predicted based on the chemical configuration of specific sets of atoms called clusters. After the ground-state value is predicted, entropy is added to the simulation and the value of the Free Energy is simulated to calculate the Phase Transition Diagram for the different compositions of the alloy. A total of 9 Fe-V compositions are simulated using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). A total of 2000 atoms at 10 Kelvin were simulated in each case for the ground-state value calculation. Results include that the Meam potential used was able to predict the ground-state energy for all compositions with less than 0.4% error from the experimental results obtained by Seki et al., and the Cluster Expansions model was able to predict the ground-state value calculated using LAMMPS with less than 1% error in all cases. |
Monday, March 14, 2022 8:24AM - 8:36AM |
A47.00003: Simulation of Ternary Organic Solar Cells as a 3d Grid of Resistors and Photodiodes to Study the Effects of Morphology and Material Properties Alex D Giovannone, Selman P Hershfield We simulate ternary organic solar cells as a 3d grid of resistors and photodiodes to study how a secondary acceptor as a third material affects the overall blend to optimize for power output. We find that the Voc, voltage at zero current, of the donor and third material interfaces should be at least that of the primary system. When the thickness and third material conductivity are high, it is better for a secondary acceptor to stick to the main acceptor due to an asymmetry in current pathways. Otherwise, it is better to place the third material next to the donor to increase the amount of donor:acceptor interfaces. Our results are likely most applicable to the addition of fullerene acceptors into donor:NFA blends, since their potential benefits come from an increased charge mobility and morphology as opposed to increasing the overall absorption spectra. |
Monday, March 14, 2022 8:36AM - 8:48AM |
A47.00004: Constructing a Magnetometer using Hall Effect Probes Storm Simmons, Susan Kempinger, Paul Bloom Three axis magnetometers are used across many areas of physics to measure magnetic fields, but each application has different specific needs for how the magnetometer should be configured. We designed a highly-customizable way to build a magnetometer using Hall effect probes. These probes output a voltage proportional to the perpendicular magnetic field through the sensor. We designed a custom circuit board to provide the probes with constant current, correct for ohmic offset voltage within the probes, and re-scale voltages to be read by LabVIEW software. The code we created reads in the scaled voltage values and converts them to magnetic field strengths. The applications we used this magnetometer for include mapping the magnetic field in the tracker region of the g-2 experiment and calibrating the applied field for a MOKE microscope used to characterize ferromagnetic materials. |
Monday, March 14, 2022 8:48AM - 9:00AM |
A47.00005: Measurement of electrical resistivity using a non-contact method. Jack Zwettler, Damjan Pelc, Zachary W Anderson, Liam Thompson, Sylvia L Griffitt, Martin Greven Reliable measurements of the electrical resistivity are essential to understand the electronic behavior of a material. Conventional methods such as van der Pauw [1] measurements rely on physical contacts for wires, which can be difficult or impossible to make for small and/or delicate samples [2]. In this work, we demonstrate resistivity measurements with a contactless method that involves the generation and detection of eddy currents. Our probe operates between 77 K and 300 K, with very low background signal levels, enabling accurate measurements of sample resistivity. This temperature range could be extended with changes to the design. We will present results for several oxide superconductors that have undergone various heat and pressure treatments aimed to study the effects of plastic deformation [3] and hole doping on resistivity. |
Monday, March 14, 2022 9:00AM - 9:12AM |
A47.00006: The Evolution of Co2MnGa Topological Magnetic Nanoparticles Danisbel Herrera, Fatai Wahaab, Cole Gibson, Jacob Gayles, Bushra Sabir Magnetic nanoparticles exhibit electronic structure properties that are applicable in biomedicine, optical sensing, and energy harvesting. Heusler compounds are ideal materials for nanoparticles due to their tunability, topological properties, and structural stability. Co2MnGa, a recently discovered cubic Heusler, shows a unique topological electronic structure with Weyl nodes that increase and stabilize dissipationless transport properties needed for many applications. We use first principles calculations to compare a series of bulk materials with electronic structures ranging from topological to half-metallic, including Fe, Co2MnGa, Fe3O4, and CrPt3, to small nanoparticles (<25 nm3). We find the size of the nanoparticle strongly determines the Curie temperature and the Weyl topology still has influence on the nanoparticles. We see that the magnetic texture oscillates in the nanoparticle due to the new boundary conditions. These results allow for atomistic control of magnetization and the spin of electrons in nanoparticles needed for the aforementioned applications. |
Monday, March 14, 2022 9:12AM - 9:24AM |
A47.00007: Design and Implementation of Electron Spin Resonance Capability at Low Temperatures to Study Low-Dimensional Quantum Matter Aulden K Jones, Martin P Mourigal, Michael P Lilly Electron Spin Resonance (ESR) is an experimental technique that gives insight into the unpaired spins of electrons in materials. In low-dimensional spin-1/2 systems, i.e. bulk materials comprising chains of spin or two-dimensional lattices with triangular, square, and honeycomb geometries, spins remain dynamic to very low-temperature as a result of quantum fluctuations, leading to entangled phases of matter called “spin-liquids”. Probing these low-temperature states is important because their elementary excitations are fractional: these “spinons” can propagate independently as pairs over nanometer length scales. ESR, through the line shape of the microwave absorption, is sensitive to the existence and dynamics of spinons. |
Monday, March 14, 2022 9:24AM - 9:36AM |
A47.00008: Engineering thermochromic properties with plasmonics Dongheon Ha, Michaela J McBride, Nikolai Zhitenev Materials with thermochromic properties are useful for real-time temperature sensing, but the application of these materials requires a strong opto-thermal response on the visible spectrum. In this presentation, we show how to enhance the opto-thermal sensitivity of thermochromic materials by taking advantage of plasmonic effects. Before adding plasmonic structures, we compare compounds of vanadium oxide to determine a material with a suitable initial opto-thermal sensitivity. We subsequently evaluate temperature-dependent optical measurements taken for the materials. Finally, we present changes in the opto-thermal sensitivity achieved by the addition of plasmonic structures on the selected thermochromic material. A fifteen percent improvement was observed in the thermochromic response of thin-film vanadium dioxide crystals with self-assembled gold nanoparticles. We propose that this improvement was achievable as a result of the localized surface plasmon resonance of the self-assembled gold structures, as supported by the Maxwell Garnett effective medium theory. |
Monday, March 14, 2022 9:36AM - 9:48AM |
A47.00009: Lateral Structural Phase-Patterning of MoS2 for Nanoelectronic Applications Peter Webb, Kaixuan Ji, Arash Akbari-Sharbaf Van der Waals materials provide atomic-level control in stacking layers with widely varying material properties. Unlike epitaxial growth processes, the weak interplane bonding allows unlimited possibilities for each successive layer during vertical stacking. Thus, precise and complex heterostructures can be assembled. Current lateral patterning, however, relies on traditional lithographic processes that can introduce significant disorder. This disorder destroys fragile quantum electronic states such as fractional quantum Hall effect, Wigner crystallization, and other emergent phases in strongly correlated electron systems. We exploit the metastable structural phases of van der Waals materials to perform polymer-free nanopatterning of MoS2. We use a 30 kV electron beam to selectively convert 2H-MoS2 into its metallic 1T phase and characterize the transition through electrical transport measurements. At a critical beam dosing, the I-V characteristics begin to demonstrate ohmic behavior. The dependence of this dosing on the material thickness is also investigated. This technique unlocks the possibility of using a single material to create various electronic devices such as patterned electrostatic gates, field-effect transistors, Schottky diodes, quantum dots, and nanowires. |
Monday, March 14, 2022 9:48AM - 10:00AM |
A47.00010: A Reliable All-Dry Method to Flip Van der Waals Heterostructures Thomas Barrett, Sharadh Jois, Takashi Taniguchi, Kenji Watanabe, Ji Ung Lee For the development of high-quality graphene-based nanoelectronics, hexagonal boron nitride (hBN) is needed as a substrate due to its large bandgap and atomically smooth surface. We present a method for transferring high-quality continuous graphene onto an hBN substrate free of tears or wrinkles while maintaining a favorable interface between the two. Existing techniques suffer from the difficulty of identifying graphene and cleanly transferring it. Our technique uses a combination of polypropylene carbonate (PPC) and polycarbonate (PC) stamps to flip an hBN-graphene heterostructure using graphene exfoliated on 90nm SiO2/Si substrate. The resulting graphene on hBN is favorable for further stacking or device fabrication and electrical characterization. |
Monday, March 14, 2022 10:00AM - 10:12AM |
A47.00011: Thermal-Field Emission from Cones and Wires Mia K Dhillon, Daniel Finkenstadt, Kevin L Jensen Field emission electron sources generally have sharp geometries in the form of cones and wires. Because they are often driven hard, their elevated current leads to elevated temperatures resulting in thermal-field emissions. A sharply curved emitter affects the emission barrier past which the electrons must be emitted, as does space charge in metal-insulator-metal (MIM) and metal-oxide-semiconductor (MOS) devices. Modeling the temperature profile of the emitter based on its resistivity gives the temperature gradient along the surface that determines total emission. Therefore, the physical capabilities, stability, and operation of the emitter depending on the material properties of the wire impacts are dependent on the temperature gradient. Specifically to model beam characteristics of hot rods and cones, modifications to the current density are based on the newly developed quadratic barrier GTF model which requires repeated evaluations along numerous differential surface elements. This model of field emission has a diverse array of applications associated with nano-devices and carbon fibers along with field emission with different material parameters. |
Monday, March 14, 2022 10:12AM - 10:24AM |
A47.00012: Effects of Strain on Single Electron Devices Edgar J Garcia Gate-defined quantum dots have various potential applications including their use in quantum information science and metrology. The requirement that these devices be operated at extremely low temperatures coupled with the difference in thermal expansion between the metallic gates and the semiconductor crystal results in a complicated strain profile during operation. To better understand the effects of this strain profile, we perform finite-element simulations of the gate-induced strain and how it impacts the electron states in these devices. In agreement with previous studies, our results suggest that strain can lead to changes in quantum dot location as well as the formation of unintentional quantum dots. Building on these results, we incorporate the electrostatics from the gates into our simulations providing a more complete picture of these devices. Ultimately, we aim to accurately predict quantum dot location as well as the energy associated with any strain-induced unintentional charge traps. |
Monday, March 14, 2022 10:24AM - 10:36AM |
A47.00013: Crystallization of Titanium Doped Niobium Dioxide for Neuromorphic Computing Applications Carl A Ventrice, Karsten Beckmann, Nathaniel Cady, Matthew C. Sullivan, Timothy N Walter, Hans Cho, Alexander C Kozen, Emma G Sargent, Alexander Mesiti Niobium Dioxide (NbO2) is a promising material for future-generation computer architectures. NbO2 undergoes an insulator to metal transition (IMT) that could be used as a switch for certain neuromorphic computing architectures. However, the IMT occurs at high temperature (around 800°C), and only in fully crystallized material. Doping the NbO2 with titanium is one promising approach to both reduce the IMT temperature and lower the required annealing temperatures to crystallize NbO2. In this work, amorphous titanium-doped NbOx was deposited using physical vapor deposition, and was annealed in a reducing environment at temperatures ranging from 700 – 1000°C for times ranging from 0 - 60 minutes. After annealing, the samples were analyzed for the amount of crystallization. These crystals were first identified with Raman Spectroscopy, and then an optical microscopy technique was used to determine the percent crystallization across a large area on each sample. It was found that titanium does not change the crystallization temperature of NbO2, within the range of doping concentrations studied. IMT temperature measurements are ongoing. |
Monday, March 14, 2022 10:36AM - 10:48AM |
A47.00014: An Experimental Study of the Magnetic Properties of Cryogel* Alan J Sherman Motivated by the desire to improve thermal insulation techniques employed to isolate MRI cryo-coils from the live animals being imaged, the aerogel-based material known as Cryogel®-Z [1] was identified. The low temperature thermal properties have been reported [2], so the purpose of this work is to characterize the electromagnetic properties and response. Using a commercial magnetometer, the temperature dependence of the low magnetic field(0.1 Tesla) susceptibility was studied from 2 K to 300 K and the magnetic field dependence of the isothermal (5 K) magnetization was investigated up to 7 Tesla. The analysis of these data will be presented with the goal of making the results available via FAIR data management practices [3]. Extensions of the work to explore high frequency response (nominally in the range used in MRI instruments) may be presented. |
Monday, March 14, 2022 10:48AM - 11:00AM |
A47.00015: Characterization of the Magnetic Properties of Pyrogel* Quinton L Wiebe During the design and construction of a furnace for materials processing in high magnetic fields being built to operate in the 89 mm, room-temperature bore of a 9.4 Tesla superconducting magnet [1], the aerogel-based insulating material known as Pyrogel® [2] was located. To provide magnetic "fingerprints" of the material, the first step was to use a commercial magnetometer to study the temperature dependence of the low magnetic field (0.1 Tesla) susceptibility from 2 K to 300 K and the magnetic field dependence of the isothermal (5 K) magnetization up to 7 Tesla. The analysis of these data will be presented with the goal of making the results available via FAIR data management practices [3]. Extensions of the work to explore the high temperature (> 300 K) properties may be presented. |
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