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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1960

Vacancy-Vacancy Interaction in Copper

The binding energy of two vacancies in a static lattice as a function of their separation and the positions of their displaced neighboring atoms has been calculated using a Morse potential function model for copper. It was found that two vacancies attract one another at separation less than about 7 A. At separations greater than 7 A the vacancies do not interact appreciably. The most stable separation was found to be the first nearest- neighbor separation or the divacancy configuration, for which the binding energy was found to be 0.64 ev. Based on these calculations, it is shown that third-stage annealing in irradiated copper may be accounted for by divacancy migration. The role of the divacancy in copper self-diffusion is also explained.

Girifalco, L. A.↗
DOE OSTI2025

The Many-Body Expansion for Metals: II. Nonadditive Terms in Clusters Composed of Metals with n s 1 , n s 2 , and n s 2 p 1 Configurations

The many-body expansion (MBE) was applied to homometallic and heterometallic trimers of metals with ns 1 , ns 2 , and ns 2 p 1 configurations to investigate its convergence, the magnitude and nature (stabilizing/destabilizing) of the individual terms and seek an understanding of their variation across the different families of clusters. In particular, we examined the series of alkali metals (Li 3 , Na 3 , K 3 , Li 2 Na, LiNa 2 ), alkali metal borides (Li 2 B and LiB 2 ), and alkaline earth metals (Be 3 , Be 2 Mg, BeMg 3 , and Mg 3 ) trimers, as well as sodium clusters Na n , n = 2–5. Here, we found that there is no uniform contribution (stabilizing or destabilizing) across the series in the different families of trimers. For instance, the 2-B term stabilizes the ground states of the Na 3 (doublet), Na 4 (singlet), and Na 5 (doublet) clusters, and the 3-B term destabilizes them; however, the opposite holds for the quartet state of the Li 3 , Li 2 Na, LiNa 2 , and Na 3 clusters (destabilizing 2-B, stabilizing 3-B). Substituting Li with B in the quartet state of Li 3 results in a significant reduction of the 3-B term amounting to 16% (Li 2 B) and 5% (LiB 3 ) of the binding energy. On the contrary, the ground states of the alkaline earth metal clusters (Be 3 , Be 2 Mg, BeMg 3 , and Mg 3 ) are stabilized by the 3-B term, while the 2-B term destabilizes them. Overall, we find that the 3-B terms significantly stabilize the high-spin multiplicity states of the ns 1 configurations and the low-spin states of the ns 2 configurations. Finally, as the size of the metal increases, the contribution of the 3-B term to the binding energy decreases due to the longer metal–metal bond distances.

Alkali metals↗
DOE OSTI2024

X-ray photoelectron spectroscopy of epitaxial films and heterostructures

X-ray photoelectron spectroscopy is a powerful experimental technique that yields invaluable information on a range of phenomena that occur in solids, liquids, and gasses. The binding energy and shape of a photoemission peak is sensitive not only to the atomic number, valence and orbital from which the electron is ejected, but also to complex many-body effects that accompany photoemission. Provided the influences of these different drivers of spectral line shapes can be disentangled, a great deal can be learned about the electronic structures of specific atoms in the material of interest. In addition to these largely local effects, the long-range electrostatic environment and resulting electric potential at the emitting atom have a direct effect on the measured binding energies. Furthermore, this fact opens the door to extracting information about the dependence of the valence and conduction band minima on depth below the surface, which in turn allows both vertical and lateral electrical transport data to be better understood. One purpose of this Report is to describe how the different physical forces described above impact spectral properties of complex oxide epitaxial films. This class of materials typically incorporates transition metal cations in different valences and of all the elements, these exhibit the most complex core-level spectra. A second purpose is to show how a comprehensive understanding of local physical effects in x-ray photoemission allows one to extract detailed information on internal electric fields and band edge discontinuities in heterostructures involving complex oxides from core-level line shapes.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Enhancing carbon dioxide capture under humid conditions by optimizing the pore surface structure

Metal–organic frameworks (MOFs) exhibit significant potential for mitigating carbon emissions due to their high porosity and tunability. Despite numerous reports on CO 2 capture by MOF sorbents, a common challenge is their poor selectivity for CO 2 over water. Moreover, in-depth studies are much needed to elucidate the relationships among the pore surface structure, hydrophobicity, and CO 2 uptake capacity/selectivity. In this work, we investigate the factors influencing CO 2 adsorption capacity and selectivity under humidity in a series of isoreticular pillar-layer structures, Ni 2 (L) 2 (dabco) (L = bdc, ndc, adc). Our study shows that increasing ligand conjugation not only results in increased hydrophobicity, decreased pore size and BET surface area, but also leads to the change of primary binding sites of water molecules and higher binding energy of CO 2 , all of which contribute to largely increased CO 2 uptake capacity under humid conditions. Additionally, increasing ligand conjugation and consequently hydrophobicity slow down and reduce competitive water adsorption drastically. Notably, the MOF made of ligand with the highest conjugation, Ni 2 (adc) 2 (dabco), exhibits significantly enhanced CO 2 adsorption in N 2 /CO 2 binary mixtures under relatively high humidity (50% RH), with an increase of ~31% and ~36% for the composition of 15/85 and 50/50, respectively, compared to dry conditions. An experimental FTIR study and DFT theoretical calculations confirm that H 2 O occupies different primary binding site in Ni 2 (bdc) 2 (dabco) and Ni 2 (adc) 2 (dabco), and under humid conditions a higher binding energy of CO 2 is achieved with preferential H 2 O/CO 2 co-adsorption in Ni 2 (adc) 2 (dabco), potentially creating additional adsorption sites for CO 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Static and dynamic properties of atomic nuclei with high-resolution potentials

Here, we compute ground-state and dynamical properties of 4 He and 16 O nuclei using as input high-resolution, phenomenological nucleon-nucleon and three-nucleon forces that are local in coordinate space. The nuclear Schrodinger equation for both nuclei is accurately solved employing the auxiliary-field diffusion Monte Carlo approach. For the 4 He nucleus, detailed benchmarks are carried out with the hyperspherical harmonics method. In addition to presenting results for the binding energies and radii, we also analyze the momentum distributions of these nuclei and their Euclidean response function corresponding to the isoscalar density transition. The latter quantity is particularly relevant for lepton-nucleus scattering experiments, as it paves the way to quantum Monte Carlo calculations of electroweak response functions of 16 O.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Hard-scattering approach to strongly hindered electric dipole transitions between heavy quarkonia

The conventional wisdom in dealing with electromagnetic transition between heavy quarkonia is the multipole expansion, when the emitted photon has a typical energy of order quarkonium binding energy. Nevertheless, in the case when the energy carried by the photon is of order typical heavy quark momentum, the multipole expansion doctrine is expected to break down. In this work, we apply the “hard-scattering” approach originally developed to tackle the strongly hindered magnetic dipole ( M 1 ) transition [Y. Jia , ] to the strongly hindered electric dipole ( E 1 ) transition between heavy quarkonia. We derive the factorization formula for the strongly hindered E 1 transition rates at the lowest order in velocity and α s in the context of the nonrelativistic QCD, and conduct a detailed numerical comparison with the standard predictions for various bottomonia and charmonia E 1 transition processes. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Assessing the Performance of Exchange‐Correlation Density Functionals in Describing the Iron‐Catalyzed Ammonia Synthesis System

Density functional theory (DFT) has been widely employed for elucidating mechanistic aspects of heterogeneous catalysis. However, the accuracy of DFT calculations relies heavily on selecting an exchange-correlation (XC) functional that correctly describes the electronic structure of materials involved in the reactions. This study assesses the accuracy of several XC density functionals for modeling the iron-catalyzed ammonia synthesis system. In the assessment of functional accuracy, experimental references are compared to DFT-calculated values for the formation energy of gas-phase ammonia and nitrogen, bulk Fe/Fe-nitride (γ′-Fe 4 N) lattice constants and cohesive/formation energies, and nitrogen and ammonia binding energies on Fe(100), Fe(111), Fe(110), and γ′-Fe 4 N(111). It is observed that the experimental value for each of these descriptors is accurately modeled by at least one functional. RPBE alone provides reliable estimates for both the lattice constant and cohesive energy of Fe and γ′-Fe 4 N. Temperature-programmed desorption experiments led to estimates for N and NH 3 adsorption across several Fe-based facets that are best captured by RPBE. These results highlight the importance of choosing an appropriate XC functional that accurately describes experimental systems and offer insights into effectively modeling the interactions between nitrogen and ammonia on Fe-based surfaces.

adsorption↗
NASA NTRS1977

Interpretation of the silver L X-ray spectrum

Silver L X-ray energies were calculated using theoretical binding energies from relaxed orbital relativistic Hartree-Fock-Slater calculations. Theoretical X-ray energies are compared with experimental results.

Chen, M. H.↗
NASA NTRS1979

Bandgap narrowing in moderately to heavily doped silicon

A theoretical model of bandgap narrowing in silicon at high doping levels has been developed. The model takes into account the electrostatic energy of interaction between a minority carrier and the majority carriers surrounding it, which reduces the thermal energy necessary for creation of an electron-hole pair. A pair energy similar to the excitonic binding energy of bound electron-hole pairs in insulators is obtained. Theoretical results are in excellent agreement with experimental results in the doping range from 3 times 10 to the 17th to 1.5 times 10 to the 20th/cu cm at room temperature. These results indicate that at high injection levels such as a transistor biased into the conductivity-modulation regime or a solar cell whose surface is established by ion implantation into an oxide layer, the bandgap narrowing is determined by the injected carrier concentration rather than by the doping level.

Lanyon, H. P. D.↗
NASA NTRS1979

The hydrodynamics of off-center explosions

The behavior of off-center supernova explosions is investigated using a two-dimensional hydrodynamic code. An important application of these calculations is the possible formation of high-velocity pulsars. The dependence of the final velocity of the collapsed remnant on the location and energy of the explosion is computed. The largest remnant velocities result from explosions located at a mass fraction of 0.5. An explosion energy 50% greater than the binding energy of the star ejects 0.51 solar masses, producing a 1.4 solar mass remnant with a velocity of 400 km/s. However, this energy must be generated in a very small region of the star in order to create the required asymmetry in the explosion. Because of this, a specific energy of about 10 to the 20th ergs/g is needed. Nuclear reactions can produce no more than about 5 x 10 to the 17th erg/g, and it is unclear how the energy produced in gravitational collapse models can be sufficiently localized. Unless a supernova mechanism can be found which can produce enough energy in a small region of the star, off-center explosions do not provide a satisfactory explanation for high-velocity pulsars.

Fryxell, B. A.↗
NASA NTRS1984

Surface analysis of space telescope material specimens

Surface analysis by electron spectroscopy for chemical analysis (ESCA) was used to characterize a number of the material samples for the space telescope. With ESCA, the sample is irradiated with monoenergetic soft X-rays and the resulting emitted electrons are energy analyzed to determine the binding energy of electrons to the surface atoms. The major peaks were used in the quantitative determination of the surface composition. The presence of trace elements (impurities below 1% atomic composition) was also detailed. Initially a survey scan was run for each sample to deduce the elemental composition. Then the major peaks of interest and those of the trace elements were individually examined. After this, the samples were argon sputtered to etch away surface layers, and then additional measurements were carried out in order to obtain depth profile information. In this way it was possible for those species present only on the surface to be distinguished from those having a significant depth distribution within the sample.

Fromhold, A. T.↗
NASA NTRS1989

Gravitational effects on planetary neutron flux spectra

The effects of gravity on the planetary neutron flux spectra for planet Mars, and the lifetime of the neutron, were investigated using a modified one-dimensional diffusion accelerated neutral-particle transport code, coupled with a multigroup cross-section library tailored specifically for Mars. The results showed the presence of a qualitatively new feature in planetary neutron leakage spectra in the form of a component of returning neutrons with kinetic energies less than the gravitational binding energy (0.132 eV for Mars). The net effect is an enhancement in flux at the lowest energies that is largest at and above the outermost layer of planetary matter.

Feldman, W. C.↗
DOE OSTI2025

Ionization dynamics of intense laser-produced argon plasmas revealed by NLTE modeling

The ionization dynamics and transient behavior of under-dense plasma irradiated by an intense laser are investigated. We report two significant effects in the ionization behavior: (1) a surprisingly large delay in ionization response and (2) a stepwise ionization process which involves collisional and laser-driven photoionization (LDP) processes. Ionization induced by intense lasers can exhibit delayed responses due to rapid changes in conditions, particularly when atomic transition processes occur more slowly than the relevant time scales. Furthermore, modeling reveals that the two-step ionization process—collisional excitation followed by LDP—plays an important role in this ionization delay, with collisional excitation acting as the bottleneck. Even low-energy photons (∼3.5 eV) can predominantly ionize plasmas, challenging the conventional belief that such energies are insufficient to overcome the binding energy of bound electrons. These findings underscore the necessity of including such processes into plasma simulations for various laser-plasma experiments.

Collisional excitation↗
DOE OSTI2024

Hole doping and electronic correlations in Cr substituted BaFe$_{2}$As$_{2}$

For a significant composition range, the suppression of the spin density wave transition temperature (T SDW ) in Cr- and Mn-substituted BaFe 2 As 2 (CrBFA and MnBFA, respectively) coincides as a function of Cr/Mn content, despite the distinct electronic effects of these substitutions. Additionally, for any Cr/Mn content superconductivity (SC) is absent and this topic is particularly less explored in the case of CrBFA. Here, in this work, we employ angle-resolved photoemission spectroscopy (ARPES) and combined density functional theory plus dynamical mean field theory (DFT+DMFT) to address the evolution of the Fermi surface (FS) and electronic correlations in CrBFA. Our findings reveal that incorporating Cr leads to an effective hole doping of the states near the FS, which is well described within the virtual crystal approximation (VCA). Moreover, analysis of the ARPES spectra of the bands with main d yz -orbital character reveals a fractional scaling of the imaginary part of self-energy as a function of the binding energy, a signature property of Hund's correlations. Our DFT+DMFT calculations support these experimental findings. We conclude that CrBFA is a correlated electron system for which the changes in the FS as a function of Cr are unrelated to the suppression of T SDW . In addition, we suggest that the absence of SC is primarily due to the competition between Cr local moments and the Fe-derived itinerant spin fluctuations.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗