Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session A11: Undergraduate Research IUndergrad Friendly
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Sponsoring Units: APS/SPS Chair: Crystal Bailey, American Physical Society Room: 110 |
Monday, March 2, 2020 8:00AM - 8:12AM |
A11.00001: Computational and experimental study of the doping of Bi2Fe4-xMxO9 (M=Ga, Al, or Ge) Joseph Lanier, David Jonathan Pryce Morris Transition metal oxides have attracted interest due to the range of physical properties which are of scientific interest and of interest due to their potential applications. Here we report a study into the doping of Bi2Fe4-xMxO9. Doping the system with M=Ga, Al, or Ge, allows us to modified the magnetic moment on the iron site and alter the ionic and magnetic order of the material. The structure itself consists of metal oxide polyhedron that are seen throughout the entire crystal. Two edge sharing octahedron are connected to a tetrahedron in all locations, where the bismuth sits outside of these polyhedrons. Monte-Carlo simulations have been performed using the Metropolis algorithm to reduce the Coulomb energy - taking into account ionic radii and charge - to determine whether the M sit on the tetrahedron sites, or the octahedron. As well as using the Heisenberg Model to model the overall magnetic moment of the crystal. Crystals of the material with the three options for M have been grown, and we also report results from magnetization and x-ray measurements that test the simulations. |
Monday, March 2, 2020 8:12AM - 8:24AM |
A11.00002: Surface Plasmon Resonance Dispersion Relation of Gold-Aluminum Thin Films Using the Kretschmann Configuration Robert Kent, Abdul Qadeer Rehan, Mariama Rebello Sousa Dias The prevalence of gold (Au) in the excitation of surface plasmon resonance (SPR) has been widely explored, due to these elements’ pronounced dip in reflected intensity in the visible and near-IR spectrum, and their integrity in sensors owing to their resistance to oxidization. Other metals such as aluminum also exhibit SPR, but it remains a challenge to work with because of its propensity to form a surface oxide layer which can inhibit the response. Our research explores SPR in gold-aluminum (AuAl) alloyed thin films. We fabricate the thin films using the co-sputtering technique, with some concentrations (Au0.85Al0.15) showing a higher SPR quality factor than pure gold. The mixture of these elements should reduce the possibility of oxidization of Al, and therefore exhibit a better response. Numerous works have explored SPR using AuAl thin films, but few have done so with such high angular and spectral resolution, over such a wide range, using this many alloys. This is a result of the precision, equipment, and time necessary to take such measurements. We were able to produce high-resolution, homogenous images of SPR for various concentrations of AuAl alloys, that strongly agree with calculations. |
Monday, March 2, 2020 8:24AM - 8:36AM |
A11.00003: Simulating Spin Relaxation in Organic Semiconductors Richard Gerst, Nicholas Harmon Understanding spin lifetimes in organic semiconductors is important for spin-based applications as well as for devices like organic solar cells and OLEDs. Spin relaxation and diffusion in disordered organic semiconductors is explored with numerical simulations. Previous theories and simulations examined the role of nuclear and spin-orbit interactions in relaxing spin [1, 2]. This work extends and explores in more detail the influence of spin-orbit interactions. Spin relaxation is studied in two regimes: one in which hops are uncorrelated with each other (multiple trapping) and the other where hops are correlated (multiple hopping). For multiple trapping we find agreement with analytic solutions [1]. For multiple hopping we find the simulation gives a smaller spin relaxation rate (a factor of 2/3). Both models are studied in either the semi-classical approximation where the carrier spin is a classical vector or in a quantum model where the carrier spin is a quantum object. We find interesting differences emerge between the two approaches when the hopping rates depends on orbital alignment. |
Monday, March 2, 2020 8:36AM - 8:48AM |
A11.00004: Electrically conductive gels of single wall carbon nanotubes and PEDOT:PSS Angelo Porcu, Luis D. Rivas Baguer, Anamaris Melendez, Idalia Ramos, Arjun G Yodh, Mohammad F Islam The development of lightweight, flexible, and electrically conductive carbon aerogels has important technological applications. Their high surface area to volume ratio and electrical conductivity make them suitable for energy storage and chemical sensing. Here, we report on preparation and characterization of highly porous (void volume ~0.9) gels with a range of shapes and sizes and composed of co-networks of single wall carbon nanotubes (SWCNTs) and the conducting polymer poly(3,4-ethylenedioxythiophene)–poly(styrene sulfonate) (PEDOT:PSS), at ratios ranging from 1:5 to 1:9 using concentration dependent sol-gel method. We validated the porous, filamentous microstructure of these gels by imaging their cross-sections using scanning electron microscopy. The aerogels exhibited good electrical conductivity of ~100 S/cm, determined from four-point I-V measurements. We will also present how to enhance the electrical conductivity of the co-gels by the addition of dopants and to fabricate mechanically robust, highly electrically conducting fibers. |
Monday, March 2, 2020 8:48AM - 9:00AM |
A11.00005: Applying uniaxial strain to graphene devices fabricated on flexible substrates Justin Oh, Brian T Schaefer, Veronika Sunko, Kenji Watanabe, Takashi Taniguchi, Clifford W. Hicks, Andrew P. Mackenzie, Katja Nowack Strain engineering is a promising avenue for tuning the band structure and electronic properties of two-dimensional materials. We report progress toward applying uniaxial strain to bilayer graphene devices with the ultimate goal of studying their magnetic properties using scanning superconducting quantum interference device (SQUID) microscopy. We fabricate graphene devices on flexible polyimide substrates and use a spring-based strain apparatus [1] to apply uniaxial strain by compressing or stretching the substrate, achieving a planar geometry compatible with scanning probe microscopy. We use Raman microscopy to monitor changes in the Raman peaks of graphene in response to uniaxial strain. Finally, we discuss the effects of strain on the band structure of bilayer graphene and outline our plans for studying this system using scanning SQUID microscopy. |
Monday, March 2, 2020 9:00AM - 9:12AM |
A11.00006: Novel Technique for Inducing Large Area Uniaxial Strain in Graphene Lucas Hanson, Angela Coe, Guohong Li, Eva Andrei The effect of uniaxial strain on the electronic band structure of graphene is an exciting topic of inquiry, for both studies into the fundamental physics of 2D electron systems as well as applicative investigations in the design of “straintronics”. Tight binding calculations of the effect of strain in graphene have shown that strain on the order of 20 percent causes the Dirac points to merge, resulting in the formation of a band gap. However, experimental realization of this prediction has yet to be achieved, as current techniques for inducing strain in graphene cannot generate strain exceeding a few percent. We have devised a novel technique for inducing large uniaxial strain in graphene using a piezoelectric mechanism. The mechanism allows for controllable and continuously variable strain, with an expected upper limit on the inducible strain set only by the tearing of graphene at 26 percent. Device functionality and performance are discussed, and strained graphene samples are characterized by Raman spectroscopy. Results are compared with existing Raman spectra of strained graphene. |
Monday, March 2, 2020 9:12AM - 9:24AM |
A11.00007: Quantum Transport in a Graphene-Superconductor Hybrid Device Elizabeth Zhou, Vivek Manu Kakani, Jian Liao, Xurui Zhang, Xiaoyan Shi The interplay of superconductivity and the two-dimensional (2D) quantum Hall edge states is of great current interest for both fundamental science and applications. It could be an ideal platform to realize the non-Abelian zero modes, which is crucial for topological quantum computation. Here we fabricated an encapsulated few-layer graphene flake, which is in proximity to s-wave superconducting leads to form a Josephson-junction-like structure. At temperatures down to 20 mK, we have studied the magnetotransport properties of the device in a wide range of magnetic fields (both parallel and perpendicular orientations). In addition, the differential resistance has been measured as well. Experiments show multiple peaks at low fields, which may indicate the existence of Andreev reflections. |
Monday, March 2, 2020 9:24AM - 9:36AM |
A11.00008: Growth of ZnO on Nanosphere templates by Glancing Angle Vapor Deposition and Growth Modeling Derick DeTellem, Pritish Mukherjee, Sarath Witanachchi Growth of coatings on a curved surface at steep angles enables the formation of pillar structures. In this research glancing angle laser deposition method was used to deposit Zinc Oxide (ZnO) nanostructures on silica nanoparticle templates in the size range of 3.5um to 250 nm. Self-assembled silica nanosphere templates were prepared by the Langmuir-Blodgett technique. It was observed that the diameter of the pillars and the number of pillars on each nano sphere decreased with decreasing sphere size. A simple model based on the nucleation theory that is adopted for nucleation and growth on a curved surface was developed to predict the evolution of the nanopillar structures. Results pertaining to the morphology, structure, and composition investigated for varying template sphere sizes by SEM, EDS, AFM, and XRD will also be presented. |
Monday, March 2, 2020 9:36AM - 9:48AM |
A11.00009: First order reversal curves simulation for core-shell nanoparticles via 3D-Ising model Nicolás Vergara, Edwin ER RAMOS, Juan Ramirez We studied the magnetic properties of the 3D-Ising model employing Montecarlo simulations. The system is built with a cubic unit cell compound of spherical nanoparticles with a core-shell structure. We have recovered the dynamical magnetic properties such as the susceptibility, energy, heat capacity and equilibrium magnetization for Ferro and Anti-Ferro magnetic couplings. All these properties were studied as a function of nanoparticle size. We found a nanoparticle critical-size limit below which the magnetic properties depart from those of the bulk. In addition, in simulating first order reversal curves (FORC) of the core-shell structures, we found that we were able to identify features on the FORC diagram that allowed us to decouple individual magnetic reversal mechanisms of the core, shell and the interface. Our results suggest that nano-confinement modify bulk properties and that FORC is able to separate individual magnetic contributions to the magnetism that are otherwise hidden in the isothermal hysteresis loops. |
Monday, March 2, 2020 9:48AM - 10:00AM |
A11.00010: Plasmonic interactions of gold nanoparticles with MoS2-WS2 Heterostructures Mumtaz Hassan, Hana Hrim, Sharad Ambardar, Dmitri v Voronine Scanning probe force microscopic techniques and optical spectroscopy have been widely used for sensing applications. Raman scattering and photoluminescence (PL) signals provide vital spectroscopic information about low vibrational modes and electronic properties of two-dimensional transition metal dichalcogenides (2D TMD). Since Raman signals are generally weak, chemical and electromagnetic mechanisms can enhance these signals using plasmonic materials such as gold nanoparticles (NPs) leading to surface-enhanced Raman scattering (SERS). The effects of the gold NPs deposited on lateral MoS2-WS2 heterostructures has been investigated using a combination of optical spectroscopic techniques. Changes in surface topography have been observed using atomic force microscopy (AFM), Kelvin probe force microscopy (KPFM), Tip-enhanced PL (TEPL) and Raman (TERS) spectroscopy. Contact potential difference obtained through KPFM has decreased as a result of high accumulation of gold NPs. Raman spectroscopy peak intensities have decreased, and PL peaks have been observed to become sharper and narrower which could be a result of the formation of surface cavities on TMD’s after the deposition of gold nanoparticles. This information can be applied to nano-optoelectronics and biosensing. |
Monday, March 2, 2020 10:00AM - 10:12AM |
A11.00011: Atomistic and Coarse-Grained MD Simulation Studies of the Energetics and Interactions of Regulatory Dib1 Protein Inside a Highly Dynamic Pre-Catalytic Spliceosomal Macromolecular Complex Preceding Pre-Messenger RNA Splicing in Eukaryotic Cells Rachel Goldstein, Sara Cheng, Gabrielle Orr, Christian Schreib, Corina Maeder, Kwan Cheng The spliceosome is a complex RNA/protein macromolecular machine responsible for catalyzing the removal of introns from pre-messenger RNA in eukaryotic cells. As part of the highly dynamic spliceosome assembly pathway, the key protein Dib1 must depart the pre-catalytic B complex prior to pre-mRNA splicing. Experimentally, we have identified several Dib1 temperature-sensitive mutants that disrupt splicing activity and spliceosome assembly. However, the molecular mechanisms underlying how these mutations perturb protein-protein and protein-RNA interactions in the B complex are not known. Using 200ns of atomistic and 2µs of coarse-grained MD simulations, the interactions between Dib1 and its neighboring molecules were determined for spliceosomal B complexes containing wild-type and mutant Dib1 at conditions similar to biochemical experiments. We observed specific changes in the interaction energy, residue-contact, and hydrogen-bonding propensity at the interfacial region between Dib1 and neighboring RNAs and proteins. Our results offer an explanation for the experimental finding that the Dib1 mutations disrupt the transition from B to Bact complexes in the splicing pathway. |
Monday, March 2, 2020 10:12AM - 10:24AM |
A11.00012: Electrodepositing switchable photovoltaic window electron and hole transport layers Rachel Tham, Kevin Prince, Anica Neumann, Caleb Boyd, Lance Wheeler Vertical glass facade buildings, such as skyscrapers, have significant potential for generating electricity using solar window technologies, such as SwitchGlaze, a switchable photovoltaic window, containing a perovskite layer that absorbs visible and UV light. To commercialize these perovksite solar cells, it is essential to optimize electrodeposition, a scalably and controllably fabricate stable transport layers. This technique can then be used to fabricate back contact solar devices to decrease delamination occurrence and allow for more sunlight to directly interact with the perovskite and increase device efficiency. Nickel oxide and tin oxide, are promising transport layers due to higher stability and electron mobility, respectively. A three-electrode system was used to determine, in a range of 0.03 M to 0.1 M electrolyte concentrations, the electrodeposition times, current densities, and annealing times would electrodeposit that produced most uniform, least surface roughness, and thinnest transport layers. Initial results have produced solar cell devices up to about 12% efficiency. |
Monday, March 2, 2020 10:24AM - 10:36AM |
A11.00013: Manipulating Generation and Spatial Distribution of Plasmon-Generated Hot Electrons via Oxygen Vacancies on Au/TiO2 Heterostructures for Photochemistry Grace Rohaley, Jiawei Huang, April Lo, W. David Wei Utilizing hot electrons on plasmonic metal/oxide heterostructures offers unique opportunities for solar photocatalysis. However, the role that surface oxygen vacancies (OVs) play in governing plasmon-driven photochemical reactions is poorly understood. Here, we demonstrate that surface OVs on Au/TiO2 heterostructures manipulate plasmon-generated hot electrons in the generation process and spatial distribution for visible-light methylene blue (MB) degradation. Hot electrons originating from the plasmon-mediated electron transfer (PMET) pathway (i.e. the electron transfer from Au to TiO2) and the plasmon-induced energy transfer (PIRET) pathway (i.e. the generation of electrons in TiO2) accumulate under λ > 435 nm excitations, occupying surface OVs. Together, they result in ca. 5x enhancement in MB degradation than that under λ > 495 nm excitations, in which hot electrons only originate from the PMET pathway. Taken together, our study demonstrates an essential role played by surface OVs in plasmon-driven photochemistry and reveals two distinct mechanisms clarifying visible-light photocatalytic activity under different excitation conditions. |
Monday, March 2, 2020 10:36AM - 10:48AM |
A11.00014: Molecular Dynamics Simulations of the Anorthite-Water System Under Extreme Conditions Devon Romine, Robert Mayanovic Incorporation of water plays an important role in modifying the physical and chemical properties of silicate melts. Water reacts with the melt constituents causing depolymerization and reduces the viscosity of the melt which directly impacts the eruptive power of magmas and the transfer of mass in magmatic processes. Anorthite is a Ca-bearing aluminosilicate having the chemical formula CaAl2Si2O8. It is an end member of the feldspar series and an important constituent of the rocks comprising the Earth’s crust. We have made large simulation-cell molecular dynamics calculations in order to develop a detailed quantitative structural analysis of an hydrous anorthite melt system. ReaxFF reactive force fields are utilized to simulate the reaction between an anorthite melt and water at extreme temperatures. An analysis of bond lengths, pair correlations and bond angles within the hydrous melt is being made in order to determine how the structural properties of the system change under the extremes of pressure and temperature. The extent of depolymerization of the hydrous aluminosilicate melt, as determined from the transformation of Si – O – Si, Si – O – Al, and Al – O – Al bonds into terminating, non-bridging Si – OH and Al – OH bonds, will be discussed. |
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