Bulletin of the American Physical Society
Bridge Program and National Mentoring Community Conference
Volume 63, Number 14
Friday–Sunday, November 16–18, 2018; Google HQ and Stanford University, CA
Session PS2: Graduate Poster Session (11:00AM - 12:30PM) |
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Room: Tressider Oak Lounge |
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PS2.00001: Strontium-Osmium-oxide films by molecular beam epitaxy Tommy Boykin II, Yoshiharu Krockenberger Metallic SrO-OsO$_{\mathrm{2}}$ thin films were grown on (001)-oriented SrTiO$_{\mathrm{3\thinspace }}$and Lanthanum-Strontium-Aluminum-Tantalum (LSAT) substrates by molecular beam epitaxy as a function of substrate temperature from 480 to 650 \textdegree C. We explored the SrO-OsO$_{\mathrm{2}}$ ternary phase diagram to establish appropriate thermodynamic conditions to synthesize the possibly-superconducting Sr$_{\mathrm{2}}$OsO$_{\mathrm{4}}$ phase. X-ray diffraction showed that crystallographic phase of the resulting film depended on substrate temperature. Temperature dependent resistivity was measured by four-probe method from 300 to 4 K. The lowest room temperature resistivity achieved was 0.467 m$\Omega $-cm for a film grown at 480 \textdegree C. The resistivity achieved at 4 K was 0.480 m$\Omega $-cm. Superconducting osmate films have potential applications in quantum computers. [Preview Abstract] |
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PS2.00002: One-dimensional carrier confinement in excitonic nanoshells Luis Royo Romero, Mikhail Zamkov We report on the synthesis and spectroscopy of energy-gradient nanostructures that support the formation of two-dimensional excitons in the shell domain. The developed geometry places a wide-gap semiconductor (CdS) at the core of the composite nanoparticle in order to funnel the photoinduced energy into the low-gap CdSe surface layer. As a result, the quantum confinement is achieved in nanoparticles which total size exceeds the exciton Bohr radius. The formation of excitons in the CdSe shell layer was manifested through a size-tunable emission and the characteristic step-like absorption profile. Transient absorption measurements further elucidate the dynamics of the photoinduced energy relaxation in CdS/CdSe nanoshells providing evidence that excitations of the bulk-like core domain result in a rapid, \textasciitilde 2-ps recovery of the CdS bleach attributed to electron cooling. The charge transport characteristics of nanoshell assemblies were evaluated through a side-by-side comparison with CdSe quantum dot solids. We expect that the developed nanoshell architecture could potentially be extended to a broader range of semiconductors (e.g. CdS/PbS, ZnS/CdS) facilitating the development of quantum confined solids offering improved charge transport characteristics. [Preview Abstract] |
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PS2.00003: Observation of a Dirac state in a half-Heusler material YPtBi Christopher Sims, M. Mofazzel Hosen, Gyanendra Dhakal, Klauss Dmitri, Hongchul Choi, Firoza Kabir, Orest Pavlosiuk, Piotr Wisniewski, Tomasz Durakiewicz, Jian-Xin Zhu, Dariusz Kaczorowski, Madhab Neupane The prediction of non-trivial topological electronic states hosted by half-Heusler compounds makes them prime candidates for discovering new physics and devices as they harbor a variety of electronic ground states including superconductivity, magnetism, and heavy fermion behavior. Here we report a systematic study of normal state electronic properties of the superconducting half-Heusler compound YPtBi using angle-resolved photoemission spectroscopy (ARPES). Our data reveal the presence of a Dirac state at the \(\Gamma\) point of the Brillouin zone at 500 meV below the chemical potential. We observe the presence of multiple Fermi surface pockets including two concentric hexagonal and six half oval shaped pockets at the $\Gamma$ and $\kappa$ points of the Brillouin zone, respectively. Furthermore, our measurements show Rashba-split bands and multiple surface states crossing the chemical potential which are supported by the first-principles calculations. Our findings of a Dirac state in YPtBi play a significant role in establishing half-Heusler compounds as a new potential platform for novel topological phases and explore their connection with superconductivity. [Preview Abstract] |
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PS2.00004: Strontium-iodide (SrI2(Eu2$+))$ scintillator detector crystals in dual energy x-ray absorptiometry (DEXA) for bone densitometry imaging. Kricia Ruano Espinoza, Arnold Burger, Liviu Matei Dual-energy x-ray absorptiometry (DEXA) is a biomedical imaging tool designed to measure soft tissue and bone mineral in patients. The system is comprised of an x-ray source used to radiate over the area of interest, and a scintillator detector that measures the attenuated ray path in the patient at two different energy magnitudes. The low-dose x-rays facilitate the measurement of body composition: one mainly absorbed by bone, and the other by soft tissue. Scintillators are crystals that exhibit luminescence when struck by incoming light, and as a result can be used as radiation sensors in DEXA imaging systems. While there exists a myriad of crystals for use as scintillators, europium-doped strontium-iodide (SrI2(Eu2$+))$ are one of the most promising, low-cost, high-resolution ($\Delta $E$=$ 3.0 {\%}), high light-yield (120,000 photons/MeV), and high effective atomic number (Z$=$ 48) materials. SrI2(Eu2$+)$ is coupled with a pixelated silicon photomultiplier (SiPM) array photosensor, that which generates an electrical signal proportional to the magnitude of the incoming attenuated radiation. A 2D-array can resolve the signals spatially and generate a ``pixel representation'' image of the reference anatomy observed. A limited pixel array system can be used to generate an image of a complex mixture bone sample to prove the concept of operation, and warrant large-scale implementation with multi-pixel detectors for human-scale bone densitometry scanning. [Preview Abstract] |
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PS2.00005: Success is a puzzle: Sorting out the pieces with metaphor analysis Brian Zamarripa Roman, Jacquelyn Chini Women in physics continue to be an underrepresented group, in part due to negative stereotypes and adverse environments that result from a masculine perception of physics. To address this, we explore and highlight feminine perspectives of success in physics. We focus on success because the term is often used by researchers to frame academic achievements; however, not much work explores how different people conceptualize success. For this study we conducted semi-structured interviews of women at various stages of education and careers in physics. One interview question specifically elicited a participant-constructed metaphor of success in physics. The interview data was then examined with metaphor analysis for structural metaphors, which gives us insight into the characteristics of success that are salient to the individual. For example, with the metaphor of a caramel apple one participant highlighted the difficulty (through the apple's tartness) and overall satisfaction of physics (through the caramel's sweetness). [Preview Abstract] |
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PS2.00006: Estimating the cosmic-ray exposure of SuperCDMS detectors Ashley Brooks, John Orrell The Super Cryogenic Dark Matter Search (SuperCDMS) experiment at SNOLAB will use detectors instrumented with phonon and ionization sensors to attempt to measure the recoil energy imparted to Ge and Si nuclei due to collisions of dark matter particles. During fabrication and shipment, the detectors are exposed to cosmic-ray secondaries that collide with the Ge and Si nuclei and through spallation create radioisotopes within the detector crystals. A particular isotope of concern is tritium which has a 12-year half-life and creates a background that diminishes the detectors’ sensitivity to dark matter interactions. To estimate the cosmic-ray exposure of the crystals along shipment routes and to select future routes with minimum cosmic-ray exposure, a MATLAB program was created taking into account geographical location, duration of route, driver rest period (sleeping, refueling, etc.), and elevation. To further understand the cosmic-ray exposure of the detectors, a calculation was reviewed to determine the overburden shielding provided by the Stanford Underground Facility, a shallow underground location used to protect the crystals from cosmic rays during detector fabrication. [Preview Abstract] |
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PS2.00007: 2D Photonic Crystal Bandstructures Dewan Woods The understanding of the nature of light and matter interactions at the interface of novel and exotic materials such as Metamaterials (MMs), Topological Insulators(TIs), and photonic crystals are essential for the continued growth of condensed matter physics and quantum photonics. Much research effort is being made to engineer and enable the ability to tune the optical parameters of such materials, which in turn will tailor their electromagnetic response and thus allow for a better understanding of the photon, giving rise to interesting optical phenomenon in the process. In this theory-based talk, 2D photonic bandstructure-engineering will be investigated. Topological effects in these materials will also be examined. [Preview Abstract] |
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PS2.00008: Detonation Initiation in Type Ia Supernovae Gabriel Casabona, Robert Fisher, Pritom Mozumdar Type Ia supernovae play a crucial role as standardizable candles for cosmology, but their stellar progenitors remain mysterious. Underlying this mystery is a crucial physical process: the mechanism of detonation initiation in Type Ia supernovae. Using the FLASH4 code, simulations were run to explore detonation initiation under various initial conditions. Adaptive mesh refinement techniques were utilized in order to refine the limits of successful and unsuccessful detonations. Further research into this topic will clarify the mechanisms giving rise to Type Ia supernovae. [Preview Abstract] |
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PS2.00009: Characterizing the effects of volcanic ash infiltration into 7 wt{\%} yttria stabilized zirconia thermal barrier coatings Chance Barrett, Laurene Tetard, Seetha Raghavan, Ravisankar Naraparaju Volcanic ash (VA) causes thermochemical and thermomechanical degradation on thermal barrier coatings (TBC). The thermomechanical degradation begins after the infiltrated molten VA cools, producing a gradient in stress across the TBC. The thermochemical degradation arises from the phase destabilization caused by VA in the TBC leading to a detrimental volume expansion within the TBC. In this study, our primary interest is to study stress distributions caused by VA infiltration with Raman confocal spectroscopy and Lorentz contact resonance (LCR). All measurements will be carried out on 7wt.{\%} yttria stabilized zirconia (7YSZ) samples with Icelandic VA ingression annealed at a temperature of 1200 for annealing times 10 minutes, 20 minutes, 30 minutes and 60 minutes will be compared. [Preview Abstract] |
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PS2.00010: The Intersection of Identity and Performing Arts for Black Physicist Tamia Williams, Simone Hyater-Adams, Kathleen Hinko, Claudia Fracchiolla, Kerstin Nordstrom, Noah Finkelstein How one negotiates their physics identity is crucial to gaining and maintaining membership in the physics community. However, there is an exclusive culture of physics that has marginalized Black people and leads them to feel that they do not fit the criteria of who a physicist is supposed to be. In an effort to counter the systemic marginalization of Black students in physics, we consider the role performing arts plays in the positive development of science identity. In this work, building on previous studies of physics and racial identities, and studies that demonstrate the positive role of arts for underrepresented groups in STEM, we collect and analyze interviews of thirteen Black physicists. We identify themes that relate to the ways in which Black physicists participate in the performing arts, and map those themes onto the previously- developed Critical Physics Identity (CPI) framework. We find that the performing arts can have positive impacts for Black physicists' identities by serving as a material resource, and can activate ideational resources, which support relational resources or enhance a person's sense of performance/ competence.~ [Preview Abstract] |
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PS2.00011: Stability of Exoplanetary Atmospheres in Contact with Liquid Water Hector Delgado Diaz, Edward Rezayi Kepler, K2, and ground-based telescopes have detected around 3,750 exoplanets with characteristics incomparable to the planets found in our Solar System. However, there are about 10 medium and small exoplanets that sparked interest in continuing to study their atmospheres. The type of planets of interest are rocky planets, which are dependent of the atmospheric conditions in order to be habitable. We will focus in two atmospheric scenarios known to lead to future habitability of the planet: H$_{\mathrm{2}}$/He dominant atmosphere and secondary atmosphere ranging from N$_{\mathrm{2}}$ to CO$_{\mathrm{2}}$. Furthermore, the exoplanet would consist of large bodies of water (i.e. oceans), which played an important role in the evolution of life on Earth. We will determine the stability of nitrogen-containing compounds because it is hypothesized that NH$_{\mathrm{3}}$, HNO$_{\mathrm{3}}$, and HNO$_{\mathrm{4}}$ can be loss due to their solubility in water and thus, depleting the nitrogen from the atmosphere. Molecules such as N$_{\mathrm{2}}$, NH$_{\mathrm{3}}$ are important because they are greenhouse gases that maintain the planet's temperature above the freezing point of water. The lifetimes and long-term stability will be determine using an advance atmospheric chemistry and radiative transfer code (Hu et al. 2012) written in C and the graphs will be plotted using MATLAB. No preliminary results have been achieved This research is important because understanding the atmospheric scenarios that can produce a habitable planet are needed to guide and maximize the efficiency of the future space missions of exoplanet surveys. [Preview Abstract] |
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PS2.00012: Spin-1 Ising model simulations of Nuclear pasta Daniel Silva To construct neutron star crust models requires knowledge of condensed matter and statistical physics. We use a lattice model and Monte Carlo sampling to simulate nuclear pasta, a frustrated phase of matter which is thought to occur near the bottom of the inner crust of a neutron star. Frustration, a phenomenon characterized by the existence of a very large number of low-energy configurations, occurs because it is impossible to simultaneously minimize all elementary interactions. Somewhat above $10^{17} $ kg m$^{-3}$ nuclei can no longer exist, they coalesce into a uniform plasma of nearly-pure neutron matter with a few percents of protons and electrons. The potential energy in the inner crust of a neutron star consists of a sum of a short-range nuclear interaction between nucleons and a long-range Coulomb interaction between protons, treating the electrons as a uniform gas. We compute the long-range interaction using the Ewald method. We model the short-range nucleon interaction as a nearest-neighbor Ising interaction in a grand-canonical ensemble. This simple model should capture the Coulomb frustration of the neutron-star matter. We probe the parameter space of the spin-1 Ising model which can reproduce the conditions of nuclear pasta, that is extreme isospin asymmetry. [Preview Abstract] |
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PS2.00013: Study of the effect of ball milling parameters on defect introduction in h-BN for heterogeneous catalytic applications Fernand Torres-Davila, Yi Ding, Katerina Chagoya, Alan Felix, David Nash, Richard Blair, Laurene Tetard The quest for a new generation of metal-free heterogeneous catalysts as alternatives to noble metals for CO\textlnot 2 capture and conversion to added-value products has recently gained traction. It was previously shown that defect-laden hexagonal Boron Nitride (dh-BN) becomes reactive for hydrogenation reactions, where defects such as boron or nitrogen vacancies or edges, are considered to play a key role. However, the study of process-structure-catalytic property relationships to determine optimal conditions for economical and effective implementation of these catalysts remains incomplete. In this study, we consider ball milling as a method to produce dh-BN and monitored the effect of milling parameters on the efficiency of the catalyst in terms of reagent gas molecule uptake on the flakes. We compare the effect of milling duration, material, and ball dimensions on the resulting catalytic performance. Morphological and structural properties are considered to identify the optimal conditions. Lastly, using the fluorescent properties of dh-BN exposed to air, we estimate the density of the defect introduced in the flakes during milling. We highlight some critical conditions that guide the performance of the material for catalytic functions. [Preview Abstract] |
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PS2.00014: A Preliminary Synthesis of Ruthenium-doped Oxyfluoride Perovskites Michael Shah, Ritesh Uppuluri Layered perovskites are structures of anionic perovskite blocks interleaved with metal cations and their rich chemistry makes them amenable topochemical reactions. Layered oxide materials are used in diverse applications such as superconductors, semiconductors, ferroelectrics and photovoltaics. Late transition metal perovskites are particularly interesting due to their correlated electronic properties. This study sought to create ruthenium-doped layered oxyfluoride perovskites due to ruthenium's d$^{\mathrm{n}}$ electrons which may give rise to metallic phases and can also be exfoliated. Ruthenium-doped oxyfluoride perovskites were synthesized by first preparing a titano-niobate phase (LaNbTiO$_{\mathrm{6}})$ followed by intercalation of rubidium fluoride (RbF). Samples were characterized using X-ray diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy to give phase and composition information. The precursor phase LaNbTiO$_{\mathrm{6}}$ was produced during the heating process and conditions were optimized.. Ruthenium doping on the B'-Site (Titanium) was shown to have increased the occurrence of the impurity phase (LaNbO$_{\mathrm{4}})$, whilst doping on the B-Site (Niobium) was shown to have decreased this impurity phase but gave rise to a pyrochlore phase (La$_{\mathrm{2}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}})$. Phase pure doped samples were made. [Preview Abstract] |
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PS2.00015: Noise Spectroscopy of Simulated Coupled Transmons in the Noisy Intermdiate Quantum Scale Jonathon Miller Thermal noise from electrical circuit components and noise due to fluctuations in energy levels of Transmon circuits have the cumulative effect of decreasing the coherence time of these systems. As coupled Transmon systems scale to the noisy intermediate quantum scale, noise accumulation is not well characterized in its effects on coherence time and quantum logic gate fidelity. The answer this work aims to provide is the limitations on the coherence time imposed by the noise as the system scales from a few to many (50-100) qubits. The noise analysis is being carried out by a computational simulation of a linear Transmon chain forced into a confinement and surrounded by a bath of thermal photons characteristic of the circuit component radiation. [Preview Abstract] |
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PS2.00016: $\backslash $pardProperties of Diffuse gas to Prestellar Cores$\backslash $pard Luz Jimenez Vela, David Collins h $-abstract-$\backslash $pardWhile star structure and star evolution are generally agreed theories, star formation is one of the least understood processes in cosmic evolution. That is because the formation of stars is a complex process combining turbulence, magnetic fields, and gravity. Turbulence is a chaotic process and adds kinetic energy; magnetic fields act like rubber bands, and are difficult to observe; and when the mass of a gas achieves Jeans mass, it can potentially collapse under the force of gravity. These are three physical processes and each may play a dominant role in molecular cloud collapse and hence star formation. As a consequence, the following question arises: how much of which drives the collapse of molecular clouds? In this study we ran a simulation of a supersonic turbulent molecular cloud with magnetic fields and self gravity to follow the properties of the gas from its diffuse state to high density prestellar cores. By using Lagrangian tracer particles that follow the history of the gas which composes the cores, we can study how the density, magnetic energy, and kinetic energy evolve. The simulation of the molecular cloud is performed using an adaptive mesh refinement (AMR) magnetohydrodynamic (MHD) code Enzo, and we use the yt software to analyze its data.$\backslash $pard-/abstract-$\backslash $pard$\ [Preview Abstract] |
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PS2.00017: Raman Spectra as a probe of localized strain in perovskite solar cells Kuntal Talit, David A. Strubbe Hybrid organometallic perovskites are a promising new material for cheap, flexible, and high-efficiency photovoltaics, although a major obstacle preventing commercialization is rapid degradation under illumination. During processing, strain may develop in the material due to thermal expansion mismatch with the substrate. Polycrystallinity in thin films may result in inhomogeneous strains around grain boundaries, which in turn can affect carrier mobility, non-radiative recombination etc. Absorption of light can also generate strain within the perovskite material, which may be related to degradation processes. Vibrational frequencies are shifted due to strain in a material and we want to enable use of this phenomenon to map local stress-strain behavior within a perovskite material via Raman spectroscopy, as is done in crystalline silicon. We calculate the slope of the shift for applied strains along different crystal directions to provide a calibration curve for measuring local strains. Our study also gives insight about vibrational mode characters which may help to understand degradation in perovskites. [Preview Abstract] |
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PS2.00018: The mechanics of cytoskeletal bundles Kristian D. Barajas Adam J. Levine Semiflexible filament networks are ubiquitous in biology. One example is found in the cytoskeleton, a network of stiff protein filaments transiently cross linked and driven by molecular motors. These networks are well known to form large bundles (“stress fibers”) containing tens of nearly parallel filaments. We explore how the collective mechanical properties of these fibers emerge from the interactions of their constituent filaments with transient cross-linkers using large-scale Brownian dynamics simulations. Filaments making up the bundles are treated as flexible but nearly inextensible beams. They are cross linked by small molecule elastic elements that are in chemical equilibrium with a solution of such linkers. We observe that, under bending and torsional stresses applied at the boundary, the cross-linker distribution evolves, allowing for stress relaxation in the bundle. The time evolution of these internal degrees of freedom make the collective bundle mechanics viscoelastic. We comment on the implications for these measurements for in vitro experiments and cellular mechanics. [Preview Abstract] |
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