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At least 325 records · Page 18

All sources NASA NTRS DOE OSTI

DOE OSTI2016

Theoretical evaluation of two dimensional electron gas characteristics of quaternary Al{sub x}In{sub y}Ga{sub 1–x–y}N/GaN hetero-junctions

The two dimensional electron gas (2DEG) characteristics of gated metal-face wurtzite AlInGaN/GaN hetero-junctions including positions of subband energy levels, fermi energy level, and the 2DEG concentration as functions of physical and compositional properties of the hetero-junction (i.e., barrier thickness and metal mole-fractions) are theoretically evaluated using the variational method. The calculated values of the 2DEG concentration are in good agreement with the sparsely available experimental data reported in the literature. According to our simulation results, a considerable shift in the positive direction of threshold voltage of AlInGaN/GaN hetero-junction field-effect transistors can be achieved by engineering both the spontaneous and the piezoelectric polarizations using a quaternary AlInGaN barrier-layer of appropriate mole-fractions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2013

Optical properties of transparent glass–ceramics containing lithium–mica nanocrystals: Crystallization effect

Graphical abstract: Optical properties of transparent Li{sub 2}O–MgO–Al{sub 2}O{sub 3}–SiO{sub 2}–F glasses containing lithium–mica nanocrystals are studied and crystallization condition has been evaluated and optimized to produce transparent glass–ceramics. Crystallization temperatures were determined by differential thermal analysis and crystalline phases were identified and quantified by X-ray diffraction. Scanning electron microscopy was used for morphological variations and UV–vis absorption spectroscopy for comparative analysis of transparency. In order to investigate the optical properties of transparent glass–ceramics, optical band gap, Fermi energy level and Urbach energy are calculated. The results of the investigation illustrate that band gap is reduced with increases in crystallization time and temperature. Enhanced orderliness in the arrangement of atoms might be regarded as possible reasons for the above changes. - Highlights: • The optimum temperature and time of crystallization were determined. • Li–mica nanocrystals with size of <30 nm were formed using a two-step heat-treatment. • Optical band gap and Fermi energy of nanocrystalline materials decreased with increasing of crystallization temperature and time. • Urbach band tailing was decreased with increasing of crystallization condition. - Abstract: Optical properties of transparent Li{sub 2}O–MgO–Al{sub 2}O{sub 3}–SiO{sub 2}–F glasses containing lithium–mica nanocrystals were studied. The crystallization condition of these glasses was evaluated and optimized to produce transparent glass–ceramics. Crystallization temperatures were determined by differential thermal analysis and crystalline phases were identified and quantified by X-ray diffraction. Scanning electron microscopy was used to detect morphological changes and UV–vis absorption spectroscopy was used for comparative analysis of transparency. In order to investigate the optical properties of the transparent glass–ceramics, optical band gap, Fermi energy level and Urbach energy were calculated. The results of the investigation illustrate that the band gap is reduced with increases in crystallization time and temperature. Enhanced orderliness in the arrangement of atoms might be regarded as possible reasons for the above changes.

36 MATERIALS SCIENCE↗

NASA NTRS2023

AI-3000K Infrared Line List for Hot CO 2

AI-3000K is a semi-empirical IR line list constructed for hot CO 2 spectra analysis and simulation up to 3000 – 4000 K. Compared to previously published Ames-1000K and UCL-4000, it represents a major upgrade, utilizing a new algorithm for optimization and including the latest improvements in potential energy surface (PES), dipole moment surface (DMS), and room temperature IR line list (Ames-2021 296K). To maximize the success of introducing experimental based accurate line positions, a new PES (X01d) was refined with respect to >800 selected CDSD2019 [Tashkun et al. JQSRT (2019) 228, 124] energy levels in the range of 0 – 24,000 cm -1 , with σ rms = 0.5 – 0.7 cm -1 . Most differences between the X01d PES based levels and CDSD2019 energies are within ± 2 cm -1 . A new DMS is fitted from extrapolated CCSD(T)/aug-cc-pV(T,Q,5)Z dipole calculations, with σ rms = 5.1 × 10 -6 au for 11,155 geometries up to 40,000 cm -1 , denoted Ames-2021–40K. Compared to the best available Ames-2021 DMS and room temperature IR line list [Huang et al J. Phys. Chem. A (2022) 126, 5940], the relative intensity differences are expected to be ∼ 1 ‰. The line position accuracy of ''X01d + Ames-2021–40K'' IR line list is significantly improved by adopting CDSD2019 energy levels up to 24,000 cm -1 (J ≤ 150). The Einstein A21 coefficients for E' < 15,000 cm -1 transitions are replaced by more accurate values from the Ames-2021 296K IR line list. In short, the AI-3000K is the X01d PES and Ames-2021–40K DMS based line list enhanced with the A 21 of Ames-2021 296K line list and CDSD energy levels. It provides continuous coverage from 0 to 20,000 cm -1 for the four most abundant isotopologues: 12 C 16 O 2 (626), 13 C 16 O 2 (636), 16 O 12 C 18 O (628), and 16 O 12 C 17 O (627). The impacts of isotopologue and E'/E'' cutoffs have been examined. Intensity convergence (not accuracy) of AI-3000K line list is quantitatively estimated in 1 cm -1 bins. It is better than 99% in the whole range of 0 – 20,000 (or 10,000) cm -1 at 1000 K (or 2000 K), or better than 90% in the whole range of 0 – 15,000 (or 9000) cm -1 at 2000 K (or 3000 K), respectively. Convergence beyond 3000 K will require a new PES and DMS for E' > 40,000 cm -1 . The AI-3000K and HITEMP based IR simulations are compared to high resolution shock tube experiments for CO 2 -Ar mixture up to 2000 K. With line position accuracy comparable to that of HITEMP, AI-3000K IR line list yields better agreements at more frequencies. Potential sources of discrepancies with experiment are discussed.

AI-3000K↗

DOE OSTI2014

The cyclopropene radical cation: Rovibrational level structure at low energies from high-resolution photoelectron spectra

The cyclopropene radical cation (c-C{sub 3}H{sub 4}{sup +}) is an important but poorly characterized three-membered-ring hydrocarbon. We report on a measurement of the high-resolution photoelectron and photoionization spectra of cyclopropene and several deuterated isotopomers, from which we have determined the rovibrational energy level structure of the X{sup ~+} {sup 2}B{sub 2} ground electronic state of c-C{sub 3}H{sub 4}{sup +} at low energies for the first time. The synthesis of the partially deuterated isotopomers always resulted in mixtures of several isotopomers, differing in their number of D atoms and in the location of these atoms, so that the photoelectron spectra of deuterated samples are superpositions of the spectra of several isotopomers. The rotationally resolved spectra indicate a C{sub 2v}-symmetric R{sub 0} structure for the ground electronic state of c-C{sub 3}H{sub 4}{sup +}. Two vibrational modes of c-C{sub 3}H{sub 4}{sup +} are found to have vibrational wave numbers below 300 cm{sup −1}, which is surprising for such a small cyclic hydrocarbon. The analysis of the isotopic shifts of the vibrational levels enabled the assignment of the lowest-frequency mode (fundamental wave number of ≈110 cm{sup −1} in c-C{sub 3}H{sub 4}{sup +}) to the CH{sub 2} torsional mode (ν{sub 8}{sup +}, A{sub 2} symmetry) and of the second-lowest-frequency mode (≈210 cm{sup −1} in c-C{sub 3}H{sub 4}{sup +}) to a mode combining a CH out-of-plane with a CH{sub 2} rocking motion (ν{sub 15}{sup +}, B{sub 2} symmetry). The potential energy along the CH{sub 2} torsional coordinate is flat near the equilibrium structure and leads to a pronounced anharmonicity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2011

Neutron-Rich {sup 62,64,64}Fe Show Enhanced Collectivity: The Washout of N = 40 in Terms of Experiment, Valence Proton Symmetry and Shell Model

Probing shell structure at a large neutron excess has been of particular interest in recent times. Neutron-rich nuclei between the proton shell closures Z = 20 and Z = 28 offer an exotic testing ground for shell evolution. The development of the N = 40gap between neutron fp and lg{sub 9/2} shells gives rise to highly interesting variations of collectivity for nuclei in this region. While {sup 68}Ni shows doubly magic properties in level energies and transition strengths, this was not observed in neighbouring nuclei. Especially neutron-rich Fe isotopes proved particularly resistant to calculational approaches using the canonical valence space (fpg) resulting in important deviations of the predicted collectivity. Only an inclusion of the d{sub 5/2}-orbital could solve the problem [1]. Hitherto no transition strengths for {sup 66}Fe have been reported. We determined B(E2,2{sup +}{sub 1}{yields}0{sup +}{sub 1}) values from lifetimes measured with the recoil distance Doppler-shift method using the Cologne plunger for radioactive beams at National Superconducting Cyclotron Laboratory at Michigan State University. Excited states were populated by projectile Coulomb excitation for {sup 62,64,66}Fe. The data show a rise in collectivity for Fe isotopes towards N = 40. Results [2] are interpreted by means of a modified version of the Valence Proton Symmetry [3] and compared to shell model calculations using a new effective interaction recently developed for the fpgd valence space [4].

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

OLED with hybrid emissive layer

A hybrid emissive layer and OLED incorporating the same are provided. The hybrid emissive layer includes a first material having a triplet state energy level T1 H and a singlet state energy level S1 H , a second material having a triplet state energy level T1 F and a singlet state energy level S1 F ; and a third material having a triplet state energy level T1 P and a single state energy level S1 P , where T1 F $\geqslant$ T1 H ; S1 F $\leqslant$ S1 H ; and T1 P < T1 H

Thompson, Mark E.↗

DOE OSTI2016

Transition probabilities of the low-lying levels of Kr XXIV

Energy levels, radiative rates, and wavelengths are calculated for all levels of 3s{sup 2}3p, 3s3p{sup 2}, 3s{sup 2}3d, 3p{sup 3}, 3s3p3d, 3p{sup 2}3d and 3s3d{sup 2} configurations of Al-like krypton ion (Kr XXIV). Multiconfigurational Dirac–Hartree–Fock (MCDHF) method is adopted for calculating energy levels and radiative rates. Transition probabilities are reported for E1 and M2 transitions from the ground level. The valence–valence and core–valence correlation effects are accounted for in a systematic way. Breit interactions and quantum electrodynamics effects are estimated in subsequent relativistic configuration interaction calculations. Comparisons are made with the available data in the literature and good agreement has been found which confirms the reliability of our results.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2020

Solid-state organic intermediate-band photovoltaic devices

In one aspect, solid-state organic intermediate-band photovoltaic devices are provided. A solid-state organic intermediate-band photovoltaic device, in some embodiments, comprises an organic electron donor and an organic electron acceptor, wherein the organic electron donor comprises a singlet energy level separated from a triplet energy level by an energy gap. The device also comprises a triplet sensitizer comprising singlet and triplet energy levels falling within the singlet-triplet energy gap of the electron donor.

14 SOLAR ENERGY↗

DOE OSTI2021

Solid-state organic intermediate-band photovoltaic devices

Rand, Barry P.↗

DOE OSTI2015

Hole traps associated with high-concentration residual carriers in p-type GaAsN grown by chemical beam epitaxy

The hole traps associated with high background doping in p-type GaAsN grown by chemical beam epitaxy are studied based on the changes of carrier concentration, junction capacitance, and hole traps properties due to the annealing. The carrier concentration was increased dramatically with annealing time, based on capacitance–voltage (C–V) measurement. In addition, the temperature dependence of the junction capacitance (C–T) was increased rapidly two times. Such behavior is explained by the thermal ionization of two acceptor states. These acceptors are the main cause of high background doping in the film, since the estimated carrier concentration from C–T results explains the measured carrier concentration at room temperature using C–V method. The acceptor states became shallower after annealing, and hence their structures are thermally unstable. Deep level transient spectroscopy (DLTS) showed that the HC2 hole trap was composed of two signals, labeled HC21 and HC22. These defects correspond to the acceptor levels, as their energy levels obtained from DLTS are similar to those deduced from C–T. The capture cross sections of HC21 and HC22 are larger than those of single acceptors. In addition, their energy levels and capture cross sections change in the same way due to the annealing. This tendency suggests that HC21 and HC22 signals originate from the same defect which acts as a double acceptor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Quantifying adoption rates and energy savings over time for advanced energy-efficient manufacturing technologies

Energy-efficient manufacturing technologies can reduce energy consumption and lower operating costs for manufacturing facilities, but up-front costs and increased process complexity frequently lead to manufacturers being reluctant to adopt such technologies. To avoid overestimating the benefits of advanced energy-efficient manufacturing technologies, it is necessary to account for how quickly and how widely the technology will be adopted by manufacturers. This work develops a method for estimating manufacturing technology adoption rates using quantitative technology characteristics including energetic, economic, and technical criteria that capture both incentives (such as energy and cost savings) and disincentives (such as increased process complexity) for technology adoption. This method is unique in that it can be applied before or after a technology reaches the market; other adoption rate estimation methods require sales data and can only be applied post-market. Eleven technology characteristics are considered, with each characteristic weighted to reflect its impact on the overall technology adoption rate. Technology characteristic data is used to estimate model parameters for the Bass diffusion curve, which quantifies the change in the number of new technology adopters in a population over time. Finally, energy savings at the sector level are calculated over time by multiplying the number of new technology adopters at each time step with the technology’s facility-level energy savings. The proposed method is demonstrated with an application to glass industry manufacturing technologies using technology data obtained from the U.S. Department of Energy's 2017 bandwidth study. The potential energy savings for each technology and the rate at which each technology is adopted in the sector are quantified and used to identify the technologies which offer the greatest cumulative sector-level energy savings over a period of 20 years.

advanced manufacturing↗

DOE OSTI2019

Radiative rates for E1, E2, M1, and M2 transitions in Ne-like Hf LXIII, Ta LXIV and Re LXVI

Calculations for energy levels, radiative rates and lifetimes have been performed for three Ne-like ions, namely Hf LXIII, Ta LXIV and Re LXVI, for which the general-purpose relativistic atomic structure package (GRASP) has been adopted. Results are presented among the lowest 121 levels of these ions, which belong to the 2s{sup 2}2p{sup 6}, 2s{sup 2}2p{sup 5}3ℓ, 2s2p{sup 6}3ℓ, 2s{sup 2}2p{sup 5}4ℓ, 2s2p{sup 6}4ℓ, and 2s{sup 2}2p{sup 5}5ℓ configurations, but CI (configuration interaction) has been considered among a much larger number of levels. No measurements for energy levels are available but comparisons have been made with the earlier similar theoretical results. Additionally, calculations have also been performed with the flexible atomic code (FAC) in order to assess the effect of (much) larger CI on energy levels.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2015

Frequency-comb referenced spectroscopy of v₄₋ and v₅₋excited hot bands in the 1.5 and μm spectrum of C₂H₂

Doppler-free transition frequencies for v₄₋ and v₅₋excited hot bands have been measured in the v₁ + v₃ band region of the spectrum of acetylene using saturation dip spectroscopy with an extended cavity diode laser referenced to a frequency comb. The frequency accuracy of the measured transitions, as judged from line shape model fits and comparison to known frequencies in the v₁ + v₃ band itself, is between 3 and 22 kHz. This is some three orders of magnitude improvement on the accuracy and precision of previous line position estimates that were derived from the analysis of high-resolution Fourier transform infrared absorption spectra. Comparison to transition frequencies computed from constants derived from published Fourier transform infrared spectra shows that some upper rotational energy levels suffer specific perturbations causing energy level shifts of up to several hundred MHz. These perturbations are due to energy levels of the same rotational quantum number derived from nearby vibrational levels that become degenerate at specific energies. Future identification of the perturbing levels will provide accurate relative energies of excited vibrational levels of acetylene in the 7100–7600 cm⁻¹ energy region.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2015

Luminescence properties of IR-emitting bismuth centres in SiO{sub 2}-based glasses in the UV to near-IR spectral region

We have studied UV excitation spectra of IR luminescence in bismuth-doped glasses of various compositions and obtained energy level diagrams of IR-emitting bismuth-related active centres (BACs) associated with silicon and germanium atoms up to ∼5.2 eV over the ground level. A possible energy level diagram of the BACs in phosphosilicate glass has been proposed. The UV excitation peaks for the IR luminescence of the BACs in the glasses have been shown to considerably overlap with absorption bands of the Bi{sup 3+} ion, suggesting that Bi{sup 3+} may participate in BAC formation. (optical fibres)

36 MATERIALS SCIENCE↗

DOE OSTI2016

Levelized cost of energy for a Backward Bent Duct Buoy

The Reference Model Project, supported by the U.S. Department of Energy, was developed to provide publically available technical and economic benchmarks for a variety of marine energy converters. The methodology to achieve these benchmarks is to develop public domain designs that incorporate power performance estimates, structural models, anchor and mooring designs, power conversion chain designs, and estimates of the operations and maintenance, installation, and environmental permitting required. The reference model designs are intended to be conservative, robust, and experimentally verified. The Backward Bent Duct Buoy (BBDB) presented in this paper is one of three wave energy conversion devices studied within the Reference Model Project. Comprehensive modeling of the BBDB in a Northern California climate has enabled a full levelized cost of energy (LCOE) analysis to be completed on this device.

marine hydrokinetic energy development↗

DOE OSTI2025

Structure of odd-mass Ne, Na, and Mg nuclei

The island of inversion is a region of neutron-rich nuclei around 31 Na that are deformed in their ground states. In this region, less is known about the energy levels of odd-mass nuclei, how they evolve with increasing neutron numbers, and how they can be organized into rotational bands. We perform ab initio coupled-cluster calculations of spectra in odd-mass Ne, Na, and Mg nuclei based on an interaction of chiral effective field theory. In conclusion, our results confirm some tentative spin and parity assignments, predict the structure of nuclei near the neutron dripline, and inform us about rotational bands in this region of the nuclear table.

20 ≤ A ≤ 38↗

NASA NTRS1988

Generation of high-power nanosecond pulses from laser diode-pumped Nd:YAG lasers

Simulation results are used to compare the pulse energy levels and pulse energy widths that can be achieved with LD-pumped Nd:YAG lasers for both the pulse-transmission mode (PTM) and pulse-reflection mode (PRM) Q-switching methods for pulse energy levels up to hundreds of microjoules and pulse widths as short as 1 ns. It is shown that high-power pulses with pulse widths as short as 1 ns can be generated with PTM Q-switched in LD-pumped Nd:YAG lasers. With the PRM Q-switching method, pulse widths as short as 2 ns and pulse energy at the level of a few hundred microjoules can also be achieved but require pumping with 8-10-mJ AlGaAs laser diode arrays.

Chan, Kinpui↗

DOE OSTI2015

Poole-Frenkel-effect as dominating current mechanism in thin oxide films—An illusion?!

In many of the publications, over 50 per year for the last five years, the Poole-Frenkel-effect (PFE) is identified or suggested as dominating current mechanism to explain measured current–electric field dependencies in metal-insulator-metal (MIM) thin film stacks. Very often, the insulating thin film is a metal oxide as this class of materials has many important applications, especially in information technology. In the overwhelming majority of the papers, the identification of the PFE as dominating current mechanism is made by the slope of the current–electric field curve in the so-called Poole-Frenkel plot, i.e., logarithm of current density, j, divided by the applied electric field, F, versus the square root of that field. This plot is suggested by the simplest current equation for the PFE, which comprises this proportionality (ln(j/F) vs. F{sup 1/2}) leading to a straight line in this plot. Only one other parameter (except natural constants) may influence this slope: the optical dielectric constant of the insulating film. In order to identify the importance of the PFE simulation studies of the current through MIM stacks with thin insulating films were performed and the current–electric field curves without and with implementation of the PFE were compared. For the simulation, an advanced current model has been used combining electronic carrier injection/ejection currents at the interfaces, described by thermionic emission, with the carrier transport in the dielectric, described by drift and diffusion of electrons and holes in a wide band gap semiconductor. Besides the applied electric field (or voltage), many other important parameters have been varied: the density of the traps (with donor- and acceptor-like behavior); the zero-field energy level of the traps within the energy gap, this energy level is changed by the PFE (also called internal Schottky effect); the thickness of the dielectric film; the permittivity of the dielectric film simulating different oxide materials; the barriers for electrons and holes at the interfaces simulating different electrode materials; the temperature. The main results and conclusions are: (1) For a single type of trap present only (donor-like or acceptor-like), none of the simulated current density curves shows the expected behavior of the PFE and in most cases within the tested parameter field the effect of PFE is negligibly small. (2) For both types of traps present (compensation) only in the case of exact compensation, the expected slope in the PF-plot was nearly found for a wider range of the applied electric field, but for a very small range of the tested parameter field because of the very restricting additional conditions: first, the quasi-fermi level of the current controlling particle (electrons or holes) has to be 0.1 to 0.5 eV closer to the respective band limit than the zero-field energy level of the respective traps and, second, the compensating trap energy level has to be shallow. The conclusion from all these results is: the observation of the PFE as dominating current mechanism in MIM stacks with thin dielectric (oxide) films (typically 30 nm) is rather improbable!.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗