Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session N45: Energy - General |
Hide Abstracts |
Sponsoring Units: GERA Chair: Rohit Pant, University of Maryland Room: Room 315 |
Wednesday, March 8, 2023 11:30AM - 11:42AM |
N45.00001: Stable Contact Development for High-Temperature β-Ga2O3 Device Operation Will Callahan, David S Ginley, Andriy Zakutayev, Michael Sanders, Ryan O'Hayre β-Ga2O3 shows promise in the high-temperature power electronics space for high-voltage and high-frequency switching applications. However, due to it being an oxide, metallization presents unique thermodynamic challenges. The most common ohmic contact designs have been repeatedly demonstrated to fail at even moderately elevated temperatures due to a combination of thermodynamically favorable interfacial reactions and kinetically favored diffusion processes. To address this issue, we purposefully leverage a self-limited interfacial reaction scheme by deploying an ohmic contact design (5nm Ti / 100nm Au) with an ultra-thin Ti layer that is designed to fully react, thereby eliminating thermodynamic instability and extraneous diffusion. |
Wednesday, March 8, 2023 11:42AM - 11:54AM |
N45.00002: Native Defects and Extrinsic Dopants in Ultrawide Band Gap (III)BO3 Compounds Emily M Garrity, Cheng-Wei Lee, Andriy Zakutayev, Vladan Stevanovic New ultrawide band gap semiconductors are needed to push the limits of power electronic devices toward higher voltage and power. A recent computational search for n-type semiconductors identified a family of stable calcite-type group-III orthoborates with HSE06 calculated band gaps ranging from 4.8 to 7.8 eV. These (III)BO3 materials are promising for vertical field-effect transistor devices with predicted Baliga figures of merit between 5,500 and 16,000 times that of n-type silicon and room-temperature thermal conductivities between 28 and 76 W/mK. To realize their full potential as semiconductors, the question of dopability remains. Using first-principles calculations, we investigate the formation energetics of native point defects and possibility for extrinsic doping of candidates from this family. In this presentation we will discuss the calculated intrinsic defect chemistry, evaluate the most-suitable extrinsic dopants, and explore the trends in the semiconductor properties across this family. |
Wednesday, March 8, 2023 11:54AM - 12:06PM |
N45.00003: An emerging n-type dopable ternary wide bandgap oxide group: In2{Ge,Si}2O7 Cheng-Wei Lee, Emily M Garrity, Andriy Zakutayev, Vladan Stevanovic New wide band gap (WBG) semiconductors are desirable for optoelectronics and power electronics due to larger electronic band gap and higher Baliga figure of merit (BFOM). BFOM is inversely related to on-state resistance of a conducting transistor under forward bias and is a metric critical for high-power applications. Our previous computational search[1] utilized density functional theory based method and validated semi-empirical models to calculate BFOM and thermal conductivity and screened for promising metal oxides. A few promising groups of ternary compounds are identified using these two metrics that are based on intrinsic material properties. Among them, the group of In2{Ge,Si}2O7 is particularly promising since these ternary compounds are predicted to be likely n-type dopable based on the branch-point energies calculated using HSE06 hybrid functional. To further examine their potentials as semiconductor devices, the next step is to understand their defect chemistries, particularly their dopability and potential dopants. Using the supercell approach that is based on first-principle electronic-structure methods to calculate the defect formation energies, we found that the group In2{Ge,Si}2O7 oxides have the band gap between 2.8 and 5.4 eV and are generally n-type dopable. We also found that Zr impurity is a promising n-type dopant for them. These, together with high BFOM, make In2{Ge,Si}2O7 promising candidates for high-power applications. |
Wednesday, March 8, 2023 12:06PM - 12:18PM |
N45.00004: Achieving very-high current density with GaN nanoscale field emitters array Keshab R Sapkota, Gyorgy Vizkelethy, Harold P Hjalmarson, George T Wang On-chip nanoscale field emission devices are attractive for high-speed operation and radiation hard application due to their combined advantage of traditional vacuum tubes (e.g., high frequency operation, robustness in harsh environment) and modern solid-state technology (e.g., integrability, size, energy efficiency). However, the real-world applications of these devices are limited due to small field emission current up to few µA per device. Here we demonstrate field emission current up to several mA, with >1µA/emitter loading, in the densely packed monolithically integrated GaN lateral field emitter diodes (FED) array. We achieve current density as high as ~200A/cm2 from these arrays which is the highest current density reported for semiconductor field emitters. We will present a novel approach of self-limited electron emission to enable uniform field emission across the arrays of emitters. We will also present theoretical and experimental studies on the electric field screening effect and its impact on electron emission as function of FED density. |
Wednesday, March 8, 2023 12:18PM - 12:30PM |
N45.00005: How numerical simulations can advance wide bandgap materials and devices: a case study on the optical spectrum of visible light-emitting diodes Nick Pant, Xuefeng Li, Elizabeth DeJong, Daniel Feezell, Rob Armitage, Emmanouil Kioupakis Numerical simulations can help accelerate the development of wide bandgap materials and devices by bringing unique insights that are otherwise inaccessible by experiments alone. A paradigmatic example of wide bandgap semiconductor technology that can be found in nearly every U.S. household today is the visible light-emitting diode (LED) based on InGaN semiconductors. Despite their success, the color purity of green and longer wavelength InGaN LEDs severely degrades at high operating currents, thus limiting their utility to low-power applications. In this work, we show how our combined theoretical and experimental study has helped resolve the mystery of why the color purity of InGaN LEDs degrades at high operating currents. This has led to new insights on device designs that improve the high-power color purity of visible LEDs. In light of this success, we discuss how our multi-scale modeling approach can be generalized to accelerate advances in emerging wide bandgap optoelectronic and photovoltaic technology. |
Wednesday, March 8, 2023 12:30PM - 12:42PM |
N45.00006: Hybrid Energy Harvesting System to Improve Power Efficiency of Organic Photovoltaics in Indoor Light Sources Hyojeong Choi, Yongju Lee, Selim Han, SWARUP BISWAS, Hyeok Kim The Internet of Things (IoTs) is rapidly developing, and research on developing sustainable energy is becoming crucially indispensable. Among various energy harvesters, Organic Photovoltaic (OPV), which produces energy through light absorption, has a lot of advantages. However, since OPV is greatly affected by the surrounding environment, it is difficult to harvest energy that can be always operated. Accordingly, by incorporating a Triboelectric Nanogenerator (TENG) into the system, want to overcome the limit. We developed TENG with newly synthesized Deco-flex® with good elasticity which has a high resolution of 0.4 kPa and is sensitive enough to obtain a maximum output of 5 V and 1.34 μA. This was combined with OPV in series and measured at low illumination (LED 1000 lux: 0.32 mW/cm2). As a result, the output of about 8.5 V and 1.3 μA was come out, respectively. About 4.6 times of single OPV and 1.7 times more power than a single TENG were obtained. Through this, the OPV-TENG hybrid energy harvesting system can harvest energy under 1-Sun (AM 1.5: 100 mW/cm2) and low light sources and is expected to supply sustainable power by supplementing the low open circuit voltage (VOC) of OPV through TENG. |
Wednesday, March 8, 2023 12:42PM - 12:54PM |
N45.00007: Etching SiO2 on Si wafers to develop an array of tip well-trench structures for potential freestanding graphene energy harvesting. Floyd T Lancaster, Ferdinand Harerimana, Paul M Thibado Freestanding graphene is so flexible it moves under the slightest influence. In this study, we use is a silicon wafer to create a stable platform on which to potentially capture this kinetic energy. A 1 cm by 1 cm chip is cut from a silicon wafer having a 2-micron thick thermal oxide on top. We spin coat the chip with polymethyl methacrylate and bake. Next we use electron beam lithography to pattern the surface. The pattern is an array of well-trench structures. However, the well pattern contains a "hat" at its center to block surface etching. The chip is then submerged in a buffered oxide etchant (BOE) for 5 to 10 minutes. The BOE undercuts the "hat" to naturally form a cone shaped tip in the SiO2 at the center of the well due to isotropic etching. We characterize the etched surface using optical and atomic force microscopy. The goal is to have the trench depth around 1 micron. The well is square shaped with a width around 7 microns. The top of the SiO2 tip is 0.5 microns below the top surface of the wafer, which is where the graphene is ultimately suspended from. |
Wednesday, March 8, 2023 12:54PM - 1:06PM |
N45.00008: Efficiency of an intermittent, flexible propeller Benjamin Thiria In this talk, I will present a study addressing the problem of propulsion using intermittent dynamics. The system consist of body moving forward using a propeller that has the possibility of changing shape depending on whether the propeller is rotating or not. The nature of the intermittent dynamics consist of alternating active phase (when the propeller in rotating) and passive phase where the body uses inertia to sustain the motion. |
Wednesday, March 8, 2023 1:06PM - 1:18PM |
N45.00009: Investigation of the structure and dynamics of molten salt LiF-NaF-UF4 using first-principles molecular dynamics Vitor Ferreira Grizzi, Y Z Molten salts are considered to play a key role in a future low-carbon economy, especially in nuclear energy and energy storage. However, very little is understood about their dynamics and thermophysical properties since the experimental investigation is difficult due to their corrosiveness and the high temperatures of interest. Currently, the state of the art to study molten salts computationally is through first-principle molecular dynamics (FPMD) simulations and machine learning (neural network potentials). In this work we thoroughly investigated the structure and dynamics of LiF-NaF-UF4 (54.5-36.4-9.1 mol%), a candidate salt for next-generation molten salt reactors, using FPMD. Structural properties such as pair distribution function and structure factor, and transport and thermophysical properties such as specific heat, density, viscosity, and diffusion were calculated. Some of the results we obtained can be directly compared to neutron scattering experiments for validation. This in-depth understanding of the salt’s properties is important to facilitate the screening of molten salt candidates in different industrial applications, and to gain insights into the dynamics of ionic liquids. |
Wednesday, March 8, 2023 1:18PM - 1:30PM |
N45.00010: Ab initio Study of Point Defects in Uranium Oxides Monica M Herrera, Carlos I Hernandez, Nicholas J Wilson, Eduardo Montoya, Todd N Lombardi, Eunja Kim Uranium dioxide (UO2) is naturally occurring, which is also a central component in the production of nuclear energy. Although highly studied, there are still questions regarding the degradation process of UO2 when exposed to the environment (i.e., humidity, oxygen-rich conditions, high pressure, heat, radiation, etc). We carried out density functional theory (DFT) calculations to investigate the structural and chemical changes in UO2. In order to see the path taken, we introduced different types of defects within the baseline UO2 structure. Those defects included Frenkel, Schottky, vacancy, and interstitial, all of which we tested independently. Among the point defects we investigated, we found that the interstitial defect of oxygen had the lowest formation energy and occurred spontaneously leading to the formation of U4O9. This formation is consistent with previous theoretical and experimental findings. Further oxidation to U4O10 may occur under oxygen-rich conditions. The structure that provided the best results was a combination of defects (interstitial and Schottky) leading to a U3O8 structure, corroborating previous experimental observations. |
Wednesday, March 8, 2023 1:30PM - 1:42PM |
N45.00011: Strictly localized basis sets for Uranium and Plutonium Raymond Atta-Fynn, Sarah C Hernandez, Roxanne M Tutchton The properties of allotropes and selected compounds of plutonium (Pu) and uranium (U) are evaluated using a first-principles approach with strictly localized basis sets as implemented in the density functional theory code SIESTA. The lattice parameters, first-order elastic properties, and phonon density of states of the allotropes and compounds are in good agreement with available experimental data and prior calculations based on plane-wave methodologies. The advantage of the localized basis set approach is a good balance between speed and accuracy, which is demonstrated by modeling, for the first time, the properties of large systems of U using parameter-free ab initio molecular dynamics. |
Wednesday, March 8, 2023 1:42PM - 1:54PM |
N45.00012: Electronic structure and transport properties of [Fe(qsal)2][Ni(dmit)2] molecular spin crossover complex. Mohammad Z Zaz, Thilini K Ekanayaka, Esha Mishra, Kayleigh A McElveen, Gauthami Viswan, Jack Rodenburg, Alpha T N’Diaye, David A Shapiro, Rebecca Y Lai, Robert Streubel, Peter A Dowben We report on the electronic structure of a mixed metal spin crossover molecular complex [Fe(qsal)2][Ni(dmit)2]. This spin crossover molecular complex exhibits an atypical low resistivity making the system of interest for nonvolatile molecular memory applications, but the availability of the device functionality depends on a good understanding of the electronic structure. Photoemission indicates a typical Fe(III) complex in the high spin state at room temperature with a ferromagnetic coupling between Fe and Ni evident in X-ray magnetic circular dichroism. Absorption spectra obtained using circularly polarized light with opposite polarization indicate the system exhibits chiral behavior. This chirality can be attributed to the loss of inversion symmetry due to the presence of [Ni(dmit)2]. There is the prospect of realizing a topologically protected spin current in such systems if used as the transistor channel. |
Wednesday, March 8, 2023 1:54PM - 2:06PM |
N45.00013: Investigating the role of interactions on the stability of magnetic anisotropy in L10 magnetic materials Nica Jane B Ferrer, Gursagar Singh, Cy Elliott, Benjamin J Wieder, Gregory A Fiete, Laura H Lewis Recent studies have revealed the superior magnetic properties of L10 magnetic materials which lead to a vast number of applications ranging from magnetic recording to medical imaging. While there is a wealth of experimental studies and numerical simulations aimed at finding ways to tune the magnetic properties of these L10 magnetic materials, there is inadequate attention given to understanding the underlying mechanisms that govern the magnetic properties of these materials, such as their magnetic anisotropy. Hence, this study aims to elucidate how fundamental interactions such as the electron-electron interaction combined with crystal symmetry affect the magnetic anisotropy of L10 magnetic materials. To achieve this, the material is modeled by a tight-binding Hamiltonian with electron-electron interactions accounted for using a Hartree-Fock mean-field approximation. This approach allows us to calculate the magnetic anisotropy as a function of the interaction strength and work through crystal symmetry-related trends in the anisotropy. These trends can be directly compared against material-specific ab initio calculations. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700