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- Electron paramagnetic resonance spectroscopy (6)
- Hyperfine structure (4)
- Electron traps (3)
- Activation energy (2)
- Crystalline solids (2)
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- Crystallographic defects (2)
- Diffuse wave function (2)
- Electron nuclear double resonance (2)
- Electron paramagnetic resonance (2)
- LIBS (2)
- Quantum chemical dynamics (2)
- Semiconductor growth (2)
- Spin-orbit interactions (2)
- Titanium (2)
- #antcenter (1)
- 3-D microfabrication (1)
- 68U10 (1)
- Absorption coefficient (1)
- Algebraic structures (1)
- Analytical chemistry (1)
- Analytical techniques (1)
- Angular dependence (1)
- Annealing (1)
- Anomaly detection (1)
- Bandgap (1)
- Barium gallium selenide (1)
- Blackbody (1)
- Cadmium germanium diphosphide (1)
- Carbon based materials (1)
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Articles 1 - 30 of 43
Full-Text Articles in Physics
Lithium Tetraborate As A Neutron Scintillation Detector: A Review, Elena Echeverria, John W. Mcclory, Lauren Samson, Katherine Shene, Juan A. Colon Santana, Yaroslav V. Burak, Volodymyr T. Adamiv, Ihor M. Teslyuk, Lu Wang, Wai-Ning Mei, Kyle A. Nelson, Douglas S. Mcgregor, Peter A. Dowben, Carolina C. Ilie, James C. Petrosky, Archit Dhingra
Lithium Tetraborate As A Neutron Scintillation Detector: A Review, Elena Echeverria, John W. Mcclory, Lauren Samson, Katherine Shene, Juan A. Colon Santana, Yaroslav V. Burak, Volodymyr T. Adamiv, Ihor M. Teslyuk, Lu Wang, Wai-Ning Mei, Kyle A. Nelson, Douglas S. Mcgregor, Peter A. Dowben, Carolina C. Ilie, James C. Petrosky, Archit Dhingra
Faculty Publications
The electronic structure and translucent nature of lithium tetraborate (Li2B4O7) render it promising as a scintillator medium for neutron detection applications. The inherently large neutron capture cross-section due to 10B and 6Li isotopes and the ease with which Li2B4O7 can be enriched with these isotopes, combined with the facile inclusion of rare earth dopants (occupying the Li+ sites), are expected to improve the luminescent properties, as well as the neutron detection efficiency, of Li2B4O7. The electronic structure of both doped …
Anomaly Detection In The Molecular Structure Of Gallium Arsenide Using Convolutional Neural Networks, Timothy Roche *, Aihua W. Wood, Philip Cho *, Chancellor Johnstone
Anomaly Detection In The Molecular Structure Of Gallium Arsenide Using Convolutional Neural Networks, Timothy Roche *, Aihua W. Wood, Philip Cho *, Chancellor Johnstone
Faculty Publications
This paper concerns the development of a machine learning tool to detect anomalies in the molecular structure of Gallium Arsenide. We employ a combination of a CNN and a PCA reconstruction to create the model, using real images taken with an electron microscope in training and testing. The methodology developed allows for the creation of a defect detection model, without any labeled images of defects being required for training. The model performed well on all tests under the established assumptions, allowing for reliable anomaly detection. To the best of our knowledge, such methods are not currently available in the open …
Intrinsic Point Defects (Vacancies And Antisites) In Cdgep2 Crystals, Timothy D. Gustafson, Nancy C. Giles, Peter G. Schunemann, Kevin T. Zawilski, Kent L. Averett, Jonathan E. Slagle, Larry E. Halliburton
Intrinsic Point Defects (Vacancies And Antisites) In Cdgep2 Crystals, Timothy D. Gustafson, Nancy C. Giles, Peter G. Schunemann, Kevin T. Zawilski, Kent L. Averett, Jonathan E. Slagle, Larry E. Halliburton
Faculty Publications
Cadmium germanium diphosphide (CdGeP2) crystals, with versatile terahertz-generating properties, belong to the chalcopyrite family of nonlinear optical materials. Other widely investigated members of this family are ZnGeP2 and CdSiP2. The room-temperature absorption edge of CdGeP2 is near 1.72 eV (720 nm). Cadmium vacancies, phosphorous vacancies, and germanium-on-cadmium antisites are present in as-grown CdGeP2 crystals. These unintentional intrinsic point defects are best studied below room temperature with electron paramagnetic resonance (EPR) and optical absorption. Prior to exposure to light, the defects are in charge states that have no unpaired spins. Illuminating a CdGeP2 …
Measurement Of Proton Light Yield Of Water-Based Liquid Scintillator, E. J. Callaghan, B. L. Goldblum, J. A. Brown, T. A. Laplace, Juan J. Manfredi, M. Yeh, G. D. Orebi Gann
Measurement Of Proton Light Yield Of Water-Based Liquid Scintillator, E. J. Callaghan, B. L. Goldblum, J. A. Brown, T. A. Laplace, Juan J. Manfredi, M. Yeh, G. D. Orebi Gann
Faculty Publications
The proton light yield of liquid scintillators is an important property in the context of their use in large-scale neutrino experiments, with direct implications for neutrino-proton scattering measurements and the discrimination of fast neutrons from inverse β-decay coincidence signals. This work presents the first measurement of the proton light yield of a water-based liquid scintillator (WbLS) formulated from 5% linear alkyl benzene (LAB), at energies below 20 MeV, as well as a measurement of the proton light yield of a pure LAB + 2 g/L 2,5-diphenyloxazole (PPO) mixture (LABPPO). The measurements were performed using a double time-of-flight method and a …
Feasibility Of Obtaining Surface Layer Moisture Flux Using An Ir Thermometer, Steven T. Fiorino, Lance Todorowski, Jaclyn Schmidt, Yogendra Raut, Jacob Margraf
Feasibility Of Obtaining Surface Layer Moisture Flux Using An Ir Thermometer, Steven T. Fiorino, Lance Todorowski, Jaclyn Schmidt, Yogendra Raut, Jacob Margraf
Faculty Publications
This paper evaluates the feasibility of a method using a single hand-held infrared (IR) thermometer and a mini tower of wet and dry paper towels to psychometrically obtain surface layer temperature and moisture gradients and fluxes. Sling Psychrometers have long been standard measuring devices for quantifying the thermodynamics of near-surface atmospheric gas–vapor mixtures, specifically moisture parameters. However, these devices are generally only used to measure temperature and humidity at one near-surface level. Multiple self-aspirating psychrometers can be used in a vertical configuration to measure temperature and moisture gradients and fluxes in the first 1–2 m of the surface layer. This …
Cu2+ And Cu3+ Acceptors In Β-Ga2O3 Crystals: A Magnetic Resonance And Optical Absorption Study, Timothy D. Gustafson, Nancy C. Giles, Brian C. Holloway, Christopher A. Lenyk, J. Jesenovec, J. S. Mccloy, M. D. Mccluskey, Larry E. Halliburton
Cu2+ And Cu3+ Acceptors In Β-Ga2O3 Crystals: A Magnetic Resonance And Optical Absorption Study, Timothy D. Gustafson, Nancy C. Giles, Brian C. Holloway, Christopher A. Lenyk, J. Jesenovec, J. S. Mccloy, M. D. Mccluskey, Larry E. Halliburton
Faculty Publications
Electron paramagnetic resonance (EPR) and optical absorption are used to characterize Cu2+ (3d9) and Cu3+ (3d8) ions in Cu-doped β-Ga2O3. These Cu ions are singly ionized acceptors and neutral acceptors, respectively (in semiconductor notation, they are Cu− and Cu0 acceptors). Two distinct Cu2+ EPR spectra are observed in the as-grown crystals. We refer to them as Cu2+(A) and Cu2+(B). Spin-Hamiltonian parameters (a g matrix and a 63,65Cu hyperfine matrix) are obtained from the angular dependence of each spectrum. Additional electron-nuclear double resonance …
Development Of Advanced Machine Learning Models For Analysis Of Plutonium Surrogate Optical Emission Spectra, Ashwin P. Rao, Phillip R. Jenkins, John D. Auxier Ii, Michael B. Shattan, Anil Patnaik
Development Of Advanced Machine Learning Models For Analysis Of Plutonium Surrogate Optical Emission Spectra, Ashwin P. Rao, Phillip R. Jenkins, John D. Auxier Ii, Michael B. Shattan, Anil Patnaik
Faculty Publications
This work investigates and applies machine learning paradigms seldom seen in analytical spectroscopy for quantification of gallium in cerium matrices via processing of laser-plasma spectra. Ensemble regressions, support vector machine regressions, Gaussian kernel regressions, and artificial neural network techniques are trained and tested on cerium-gallium pellet spectra. A thorough hyperparameter optimization experiment is conducted initially to determine the best design features for each model. The optimized models are evaluated for sensitivity and precision using the limit of detection (LoD) and root mean-squared error of prediction (RMSEP) metrics, respectively. Gaussian kernel regression yields the superlative predictive model with an RMSEP of …
Optically Active Selenium Vacancies In Baga4Se7 Crystals, Brian C. Holloway, Timothy D. Gustafson, Christopher A. Lenyk, Nancy C. Giles, Kevin T. Zawilski, Peter G. Schunemann, Kent L. Averett, Larry E. Halliburton
Optically Active Selenium Vacancies In Baga4Se7 Crystals, Brian C. Holloway, Timothy D. Gustafson, Christopher A. Lenyk, Nancy C. Giles, Kevin T. Zawilski, Peter G. Schunemann, Kent L. Averett, Larry E. Halliburton
Faculty Publications
Barium gallium selenide (BaGa4Se7) is a recently developed nonlinear optical material with a transmission window extending from 470 nm to 17 μm. A primary application of these crystals is the production of tunable mid-infrared laser beams via optical parametric oscillation. Unintentional point defects, such as selenium vacancies, cation vacancies (barium and/or gallium), and trace amounts of transition-metal ions, are present in BaGa4Se7 crystals and may adversely affect device performance. Electron paramagnetic resonance (EPR) and optical absorption are used to identify and characterize these defects. Five distinct EPR spectra, each representing an electron …
Beam Formation And Vernier Steering Off Of A Rough Surface, Eric K. Nagamine, Kenneth W. Burgi, Samuel D. Butler
Beam Formation And Vernier Steering Off Of A Rough Surface, Eric K. Nagamine, Kenneth W. Burgi, Samuel D. Butler
Faculty Publications
Wavefront shaping can refocus light after it reflects from an optically rough surface. One proposed use case of this effect is in indirect imaging; if any rough surface could be turned into an illumination source, objects out of the direct line of sight could be illuminated. In this paper, we demonstrate the superior performance of a genetic algorithm compared to other iterative feedback-based wavefront shaping algorithms in achieving reflective inverse diffusion for a focal plane system. Next, the ability to control the pointing direction of the refocused beam with high precision over a narrow angular range is demonstrated, though the …
Single-Shot Positron Annihilation Lifetime Spectroscopy Using A Liquid Scintillator, Joshua R. Machacek, Shawn Mctaggart, Larry W. Burggraf
Single-Shot Positron Annihilation Lifetime Spectroscopy Using A Liquid Scintillator, Joshua R. Machacek, Shawn Mctaggart, Larry W. Burggraf
Faculty Publications
Liquid scintillators provide a fast, single component response. However, they traditionally have a low flashpoint and high vapor pressure. We demonstrate the use of an EJ-309 scintillator (high flashpoint and low vapor pressure variant) to acquire single-shot positron annihilation lifetime spectroscopy spectra using a trap-based positron beam.
Photoinduced Trapping Of Charge At Sulfur Vacancies And Copper Ions In Photorefractive Sn2P2S6 Crystals, Timothy D. Gustafson, Eric M. Golden, Elizabeth M. Scherrer, Nancy C. Giles, A. A. Grabar, Sergey A. Basun, Jonathan E. Slagle, Larry E. Halliburton
Photoinduced Trapping Of Charge At Sulfur Vacancies And Copper Ions In Photorefractive Sn2P2S6 Crystals, Timothy D. Gustafson, Eric M. Golden, Elizabeth M. Scherrer, Nancy C. Giles, A. A. Grabar, Sergey A. Basun, Jonathan E. Slagle, Larry E. Halliburton
Faculty Publications
Electron paramagnetic resonance (EPR) is used to monitor photoinduced changes in the charge states of sulfur vacancies and Cu ions in tin hypothiodiphosphate. A Sn2P2S6 crystal containing Cu+ (3d10) ions at Sn2+ sites was grown by the chemical vapor transport method. Doubly ionized sulfur vacancies (V2+S) are also present in the as-grown crystal (where they serve as charge compensators for the Cu+ ions). For temperatures below 70 K, exposure to 532 or 633 nm laser light produces stable Cu2+ (3d9) ions, as electrons move from Cu+ ions to …
3-D Fabry–Pérot Cavities Sculpted On Fiber Tips Using A Multiphoton Polymerization Process, Jonathan W. Smith, Jeremiah C. Williams, Joseph S. Suelzer, Nicholas G. Usechak, Hengky Chandrahalim
3-D Fabry–Pérot Cavities Sculpted On Fiber Tips Using A Multiphoton Polymerization Process, Jonathan W. Smith, Jeremiah C. Williams, Joseph S. Suelzer, Nicholas G. Usechak, Hengky Chandrahalim
Faculty Publications
This paper presents 3-D Fabry–Pérot (FP) cavities fabricated directly onto cleaved ends of low-loss optical fibers by a two-photon polymerization (2PP) process. This fabrication technique is quick, simple, and inexpensive compared to planar microfabrication processes, which enables rapid prototyping and the ability to adapt to new requirements. These devices also utilize true 3-D design freedom, facilitating the realization of microscale optical elements with challenging geometries. Three different device types were fabricated and evaluated: an unreleased single-cavity device, a released dual-cavity device, and a released hemispherical mirror dual-cavity device. Each iteration improved the quality of the FP cavity's reflection spectrum. The …
A Fully Quantum Calculation Of Broadening And Shifting Coefficients Of The D1 And D2 Spectral Lines Of Alkali-Metal Atoms Colliding With Noble-Gas Atoms, Robert D. Loper, David E. Weeks
A Fully Quantum Calculation Of Broadening And Shifting Coefficients Of The D1 And D2 Spectral Lines Of Alkali-Metal Atoms Colliding With Noble-Gas Atoms, Robert D. Loper, David E. Weeks
Faculty Publications
We use the Baranger model to compute collisional broadening and shift rates for the D1 and D2 spectral lines of M + Ng, where M = K, Rb, Cs and Ng = He, Ne, Ar. Scattering matrix elements are calculated using the channel packet method, and non-adiabatic wavepacket dynamics are determined using the split-operator method together with a unitary transformation between adiabatic and diabatic representations. Scattering phase shift differences are weighted thermally and are integrated over temperatures ranging from 100 K to 800 K. We find that predicted broadening rates compare well with experiment, but shift rates are …
Applications Of Portable Libs For Actinide Analysis, Ashwin P. Rao, John D. Auxier Ii, Dung Vu, Michael B. Shattan
Applications Of Portable Libs For Actinide Analysis, Ashwin P. Rao, John D. Auxier Ii, Dung Vu, Michael B. Shattan
Faculty Publications
A portable LIBS device was used for rapid elemental impurity analysis of plutonium alloys. This device demonstrates the potential for fast, accurate in-situ chemical analysis and could significantly reduce the fabrication time of plutonium alloys.
Experimental Determination Of The (0/−) Level For Mg Acceptors In Β-Ga2O3 Crystals, Christopher A. Lenyk, Trevor A . Gustafson, Sergey A. Basun, Larry E. Halliburton, Nancy C. Giles
Experimental Determination Of The (0/−) Level For Mg Acceptors In Β-Ga2O3 Crystals, Christopher A. Lenyk, Trevor A . Gustafson, Sergey A. Basun, Larry E. Halliburton, Nancy C. Giles
Faculty Publications
Electron paramagnetic resonance (EPR) is used to experimentally determine the (0/−) level of the Mg acceptor in an Mg-doped β-Ga2O3 crystal. Our results place this level 0.65 eV (±0.05 eV) above the valence band, a position closer to the valence band than the predictions of several recent computational studies. The crystal used in this investigation was grown by the Czochralski method and contains large concentrations of Mg acceptors and Ir donors, as well as a small concentration of Fe ions and an even smaller concentration of Cr ions. Below room temperature, illumination with 325 nm laser light …
Near-Infrared-Sensitive Photorefractive Sn2P2S6 Crystals Grown By The Bridgman Method, O. M. Shumelyuk, A. Y. Volkov, Y. Skrypka, Larry E. Halliburton, Nancy C. Giles, Christopher A. Lenyk, Sergey A. Basun, A. A. Grabar, Y. M. Vysochansky, S. G. Odoulov, D. R. Evans
Near-Infrared-Sensitive Photorefractive Sn2P2S6 Crystals Grown By The Bridgman Method, O. M. Shumelyuk, A. Y. Volkov, Y. Skrypka, Larry E. Halliburton, Nancy C. Giles, Christopher A. Lenyk, Sergey A. Basun, A. A. Grabar, Y. M. Vysochansky, S. G. Odoulov, D. R. Evans
Faculty Publications
Ferroelectric tin hypothiodiphosphate (Sn2P2S6) crystals are well-known for their significant piezoelectric, electro-optic, and nonlinear optical properties. These crystals have usually been grown by a vapor transport technique. We report in this paper on the first study of photorefractive nonlinearity in Sn2P2S6 crystals grown by the Bridgman method. Pronounced photorefraction is observed in the near-infrared region of the spectrum even with no preliminary optical sensitizing.
Radiation-Induced Electron And Hole Traps In Ge1-XSnX (X = 0-0.094), Michael R. Hogsed, Kevin Choe, Norman Miguel, Buguo Wang, John Kouvetakis
Radiation-Induced Electron And Hole Traps In Ge1-XSnX (X = 0-0.094), Michael R. Hogsed, Kevin Choe, Norman Miguel, Buguo Wang, John Kouvetakis
Faculty Publications
The band structure of germanium changes significantly when alloyed with a few percent concentrations of tin, and while much work has been done to characterize and exploit these changes, the corresponding deep-level defect characteristics are largely unknown. In this paper, we investigate the dominant deep-level defects created by 2 MeV proton irradiation in Ge1 -xSnx (x = 0.0, 0.020, 0.053, 0.069, and 0.094) diodes and determine how the ionization energies of these defects change with tin concentrations. Deep-level transient spectroscopy measurements approximate the ionization energies associated with electron transitions to/from the valence band (hole traps) and conduction band (electron traps) …
Analytic Non-Adiabatic Derivative Coupling Terms For Spin-Orbit Mrci Wavefunctions. I. Formalism, Lachlan T. Belcher, Gary S. Kedziora, David E. Weeks
Analytic Non-Adiabatic Derivative Coupling Terms For Spin-Orbit Mrci Wavefunctions. I. Formalism, Lachlan T. Belcher, Gary S. Kedziora, David E. Weeks
Faculty Publications
Analytic gradients of electronic eigenvalues require one calculation per nuclear geometry, compared to at least 3n + 1 calculations for finite difference methods, where n is the number of nuclei. Analytic nonadiabatic derivative coupling terms (DCTs), which are calculated in a similar fashion, are used to remove nondiagonal contributions to the kinetic energy operator, leading to more accurate nuclear dynamics calculations than those that employ the Born-Oppenheimer approximation, i.e., that assume off-diagonal contributions are zero. The current methods and underpinnings for calculating both of these quantities, gradients and DCTs, for the State-Averaged MultiReference Configuration Interaction with Singles and Doubles (MRCI-SD) …
Monte Carlo And Experimental Analysis Of A Novel Directional Rotating Scatter Mask Gamma Detection System, Julie V. Logan, Darren E. Holland, Larry W. Burggraf, Justin A. Clinton, Buckley E. O'Day Iii
Monte Carlo And Experimental Analysis Of A Novel Directional Rotating Scatter Mask Gamma Detection System, Julie V. Logan, Darren E. Holland, Larry W. Burggraf, Justin A. Clinton, Buckley E. O'Day Iii
Faculty Publications
Excerpt: This work demonstrates successful experimental operation of a prototype system to identify source direction which was modeled using a library of signals simulated using GEANT and a novel algorithm....
Deep Donors And Acceptors In Β-Ga2O3 Crystals: Determination Of The Fe2+/3+ Level By A Noncontact Method, Christopher A. Lenyk, Trevor A . Gustafson, Larry E. Halliburton, Nancy C. Giles
Deep Donors And Acceptors In Β-Ga2O3 Crystals: Determination Of The Fe2+/3+ Level By A Noncontact Method, Christopher A. Lenyk, Trevor A . Gustafson, Larry E. Halliburton, Nancy C. Giles
Faculty Publications
Electron paramagnetic resonance (EPR), infrared absorption, and thermoluminescence (TL) are used to determine the Fe2+/3+ level in Fe-doped β-Ga2O3 crystals. With these noncontact spectroscopy methods, a value of 0.84 ± 0.05 eV below the conduction band is obtained for this level. Our results clearly establish that the E2 level observed in deep level transient spectroscopy (DLTS) experiments is due to the thermal release of electrons from Fe2+ ions. The crystals used in this investigation were grown by the Czochralski method and contained large concentrations of Fe acceptors and Ir donors, and trace amounts of Cr …
Analytic Non-Adiabatic Derivative Coupling Terms For Spin-Orbit Mrci Wavefunctions. Ii. Derivative Coupling Terms And Coupling Angle For Khe (A2Π1/2) ⇔ Khe B2Σ1/2), Lachlan T. Belcher, Charlton D. Lewis, Gary S. Kedziora, David E. Weeks
Analytic Non-Adiabatic Derivative Coupling Terms For Spin-Orbit Mrci Wavefunctions. Ii. Derivative Coupling Terms And Coupling Angle For Khe (A2Π1/2) ⇔ Khe B2Σ1/2), Lachlan T. Belcher, Charlton D. Lewis, Gary S. Kedziora, David E. Weeks
Faculty Publications
A method for calculating the analytic nonadiabatic derivative coupling terms (DCTs) for spin-orbit multi-reference configuration interaction wavefunctions is reviewed. The results of a sample calculation using a Stuttgart basis for KHe are presented. Additionally, the DCTs are compared with a simple calculation based on the Nikitin’s 3 × 3 description of the coupling between the Σ and Π surfaces, as well as a method based on Werner’s analysis of configuration interaction coefficients. The nonadiabatic coupling angle calculated by integrating the radial analytic DCTs using these different techniques matches extremely well. The resultant nonadiabatic energy surfaces for KHe are presented.
Quantitative Analysis Of Cerium-Gallium Alloys Using A Hand-Held Laser Induced Breakdown Spectroscopy Device, Ashwin P. Rao, Matthew Cook, Howard L. Hall, Michael B. Shattan
Quantitative Analysis Of Cerium-Gallium Alloys Using A Hand-Held Laser Induced Breakdown Spectroscopy Device, Ashwin P. Rao, Matthew Cook, Howard L. Hall, Michael B. Shattan
Faculty Publications
A hand-held laser-induced breakdown spectroscopy device was used to acquire spectral emission data from laser-induced plasmas created on the surface of cerium-gallium alloy samples with Ga concentrations ranging from 0–3 weight percent. Ionic and neutral emission lines of the two constituent elements were then extracted and used to generate calibration curves relating the emission line intensity ratios to the gallium concentration of the alloy. The Ga I 287.4-nm emission line was determined to be superior for the purposes of Ga detection and concentration determination. A limit of detection below 0.25%was achieved using a multivariate regression model of the Ga I …
Variations Of Heavy Ion Abundances Relative To Proton Abundances In Large Solar Energetic (E > 10 Mev) Particle Events, J. F. Round, Robert D. Loper, Omar A. Nava, Stephen W. Kahler
Variations Of Heavy Ion Abundances Relative To Proton Abundances In Large Solar Energetic (E > 10 Mev) Particle Events, J. F. Round, Robert D. Loper, Omar A. Nava, Stephen W. Kahler
Faculty Publications
The elemental composition of heavy ions (with atomic number Z > 2) (hi-Z) in large gradual E > 10 MeV nuc-1 SEP events has been extensively studied in the 2-15 MeV nuc-1 range to determine the acceleration processes and transport properties of SEPs. These studies invariably are based on abundances relative to those of a single element such as C or O and often neglect H and He, the elements of primary interest for space weather. The total radiation of an SEP event is determined not only by the H and He properties but also by those of hi-Z ions …
Influence Of Basis-Set Size On The X2Σ+1/2, A2Π1/2, A2Π3/2, And B2Σ1/2 Potential-Energy Curves, A2Π3/2 2 Vibrational Energies, And D1 And D2 Line Shapes Of Rb+He, L. Aaron Blank, Amit R. Sharma, David E. Weeks
Influence Of Basis-Set Size On The X2Σ+1/2, A2Π1/2, A2Π3/2, And B2Σ1/2 Potential-Energy Curves, A2Π3/2 2 Vibrational Energies, And D1 And D2 Line Shapes Of Rb+He, L. Aaron Blank, Amit R. Sharma, David E. Weeks
Faculty Publications
The X 2 Σ + 1 / 2 , A 2 Π 1 / 2 , A 2 Π 3 / 2 , and B 2 Σ + 1 / 2 potential-energy curves for Rb+He are computed at the spin-orbit multireference configuration interaction level of theory using a hierarchy of Gaussian basis sets at the double-zeta (DZ), triple-zeta (TZ), and quadruple-zeta (QZ) levels of valence quality. Counterpoise and Davidson-Silver corrections are employed to remove basis-set superposition error and ameliorate size-consistency error. An extrapolation is performed to obtain a final set of potential-energy curves in the complete basis-set (CBS) limit. This …
Semiconductor Color-Center Structure And Excitation Spectra: Equation-Of-Motion Coupled-Cluster Description Of Vacancy And Transition-Metal Defect Photoluminescence, Jesse J. Lutz, Xiaofeng F. Duan, Larry W. Burggraf
Semiconductor Color-Center Structure And Excitation Spectra: Equation-Of-Motion Coupled-Cluster Description Of Vacancy And Transition-Metal Defect Photoluminescence, Jesse J. Lutz, Xiaofeng F. Duan, Larry W. Burggraf
Faculty Publications
Valence excitation spectra are computed for deep-center silicon-vacancy defects in 3C, 4H, and 6H silicon carbide (SiC), and comparisons are made with literature photoluminescence measurements. Optimizations of nuclear geometries surrounding the defect centers are performed within a Gaussian basis-set framework using many-body perturbation theory or density functional theory (DFT) methods, with computational expenses minimized by a QM/MM technique called SIMOMM. Vertical excitation energies are subsequently obtained by applying excitation-energy, electron-attached, and ionized equation-of-motion coupled-cluster (EOMCC) methods, where appropriate, as well as time-dependent (TD) DFT, to small models including only a few atoms adjacent to the defect center. We consider the …
Electron Paramagnetic Resonance Study Of Neutral Mg Acceptors In Β-Ga2O3 Crystals, Brant E. Kananen, Larry E. Halliburton, Elizabeth M. Scherrer, K. T. Stevens, G. K. Foundos, K. B. Chang, Nancy C. Giles
Electron Paramagnetic Resonance Study Of Neutral Mg Acceptors In Β-Ga2O3 Crystals, Brant E. Kananen, Larry E. Halliburton, Elizabeth M. Scherrer, K. T. Stevens, G. K. Foundos, K. B. Chang, Nancy C. Giles
Faculty Publications
Electron paramagnetic resonance (EPR) is used to directly observe and characterize neutral Mg acceptors (Mg0Ga) in a β-Ga2O3 crystal. These acceptors, best considered as small polarons, are produced when the Mg-doped crystal is irradiated at or near 77 K with x rays. During the irradiation, neutral acceptors are formed when holes are trapped at singly ionized Mg acceptors (Mg−Ga). Unintentionally present Fe3+ (3d5) and Cr3+ (3d3) transition-metal ions serve as the corresponding electron traps. The hole is localized in a nonbonding p orbital on a threefold-coordinated oxygen ion …
Sn Vacancies In Photorefractive Sn2P2S6 Crystals: An Electron Paramagnetic Resonance Study Of An Optically Active Hole Trap, Eric M. Golden, Sergey A. Basun, D. R. Evans, A. A. Grabar, I. M. Stoika, Nancy C. Giles, Larry E. Halliburton
Sn Vacancies In Photorefractive Sn2P2S6 Crystals: An Electron Paramagnetic Resonance Study Of An Optically Active Hole Trap, Eric M. Golden, Sergey A. Basun, D. R. Evans, A. A. Grabar, I. M. Stoika, Nancy C. Giles, Larry E. Halliburton
Faculty Publications
Electron paramagnetic resonance (EPR) is used to identify the singly ionized charge state of the Sn vacancy (V−Sn) in single crystals of Sn2P2S6 (often referred to as SPS). These vacancies, acting as a hole trap, are expected to be important participants in the photorefractive effect observed in undoped SPS crystals. In as-grown crystals, the Sn vacancies are doubly ionized (V2−Sn) with no unpaired spins. They are then converted to a stable EPR-active state when an electron is removed (i.e., a hole is trapped) during an illumination below 100 K …
Investigation Of 186Re Via Radiative Thermal-Neutron Capture On 185Re, David A. Matters, Andrew G. Lerch, A. M. Hurst, L. Szentmiklosi, J. J. Carroll, B. Detwiler, Zs. Revay, John W. Mcclory, Stephen R. Mchale, R. B. Firestone, B. W. Sleaford, M. Krticka, T. Belgya
Investigation Of 186Re Via Radiative Thermal-Neutron Capture On 185Re, David A. Matters, Andrew G. Lerch, A. M. Hurst, L. Szentmiklosi, J. J. Carroll, B. Detwiler, Zs. Revay, John W. Mcclory, Stephen R. Mchale, R. B. Firestone, B. W. Sleaford, M. Krticka, T. Belgya
Faculty Publications
Partial 𝛾-ray production cross sections and the total radiative thermal-neutron capture cross section for the 185Re(n,𝛾)186Re reaction were measured using the Prompt Gamma Activation Analysis facility at the Budapest Research Reactor with an enriched 185Re target. The 186Re cross sections were standardized using well-known 35Cl(n,𝛾)36Cl cross sections from irradiation of a stoichiometric natReCl3 target. The resulting cross sections for transitions feeding the 186Re ground state from low-lying levels below a cutoff energy of Ec=746keV were combined with a modeled probability of ground-state feeding from levels above E …
Identification Of The Zinc-Oxygen Divacancy In Zno Crystals, Maurio S. Holston, Eric M. Golden, Brant E. Kananen, John W. Mcclory, Nancy C. Giles, Larry E. Halliburton
Identification Of The Zinc-Oxygen Divacancy In Zno Crystals, Maurio S. Holston, Eric M. Golden, Brant E. Kananen, John W. Mcclory, Nancy C. Giles, Larry E. Halliburton
Faculty Publications
An electron paramagnetic resonance (EPR) spectrum in neutron-irradiated ZnO crystals is assigned to the zinc-oxygen divacancy. These divacancies are observed in the bulk of both hydrothermally grown and seeded-chemical-vapor-transport-grown crystals after irradiations with fast neutrons. Neutral nonparamagnetic complexes consisting of adjacent zinc and oxygen vacancies are formed during the irradiation. Subsequent illumination below ∼150 K with 442 nm laser light converts these (V2−Zn − V2+O)0 defects to their EPR-active state (V−Zn − V2+O)+ as electrons are transferred to donors. The resulting photoinduced S = 1/2 spectrum of the …
The Closo-Si12C12 Molecule From Cluster To Crystal: A Theoretical Prediction, Xiaofeng F. Duan, Larry W. Burggraf
The Closo-Si12C12 Molecule From Cluster To Crystal: A Theoretical Prediction, Xiaofeng F. Duan, Larry W. Burggraf
Faculty Publications
The structure of closo-Si12C12 is unique among stable SinCm isomers (n, m > 4) because of its high symmetry, π–π stacking of C6 rings and unsaturated silicon atoms at symmetrical peripheral positions. Dimerization potential surfaces reveal various dimerization reactions that form between two closo-Si12C12 molecules through Si–Si bonds at unsaturated Si atoms. As a result the closo-Si12C12 molecule is capable of polymerization to form stable 1D polymer chains, 2D crystal layers, and 3D crystals. 2D crystal structures formed by side-side polymerization satisfy eight Si valences on each monomer …