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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

The dynamics of charged particles in the near wake of a very negatively charged body - Laboratory experiment and numerical simulation

A numerical simulation that is cylindrical in configuration space and three-dimensional in velocity space has been initiated to test a model for the near-wake dynamics of a very negatively charged body, with reference to the plasma environment around spacecraft. The simulation parameters were closely matched to those of a laboratory experiment so that the results can be compared directly. The laboratory study showed that the electrons and ions can display different temporal features in the filling-in of the wake; and that they can both be found within one body diameter of an object with a highly negative body potential. It was also found that the temperature of the electrons in the very near wake could be somewhat colder than the ambient value, suggesting the possibility of a filtering mechanism being operative there. The simulation results to date largely corroborate the density findings.

Morgan, M. Alvin↗
DOE OSTI2024

A study of charge symmetry violation in fragmentation functions extracted from semi-inclusive electroproduction of charged pions from protons and deuterons

We have measured the flavor dependence of multiplicities for ?+ and ?? production in semi- inclusive deep-inelastic scattering (SIDIS) on proton and deuteron targets. We used a 10.6 GeV electron beam at Jefferson Lab, and 4 msr solid angle spectrometers (HMS for electrons, SHMS for pions), the lepton vertex spanned the kinematic range 0.3 < ? < 0.6, 2 < ?2 < 5 GeV2, and 4 < ?2 < 11 GeV2. The pion fractional momentum range was 0.3 < ? < 0.7 and the small transverse momentum range was 0 < ?? < 0.25 GeV. We used the multiplicities to form sum-and- difference ratios, testing the validity of factorization. We extracted two favored and two unfavored flavor-dependent fragmentation functions (FFs) using these multiplicities. Assuming factorization at low ?? , we find that these two FFs allow for isospin breaking (charge symmetry violation) at low ?, while converging to a common flavor independent value at the highest ? of this experiment, where the factorization is most applicable.

Bhatt, Hem↗
DOE OSTI2021

On the Equilibrium Electrostatic Potential and Light-Induced Charge Redistribution in Halide Perovskite Structures

Lead halide perovskites are semiconductor materials which are employed as nonintentionally doped absorbers inserted between two selective carrier transport layers (SCTL), realizing a p-i-n or n-i-p heterojunction. In our study, we have developed and investigated a lateral device, based on methylammonium lead iodide (MAPbI3) in which the p-i-n heterojunction develops in the horizontal direction. Our research suggests that the effective doping level in the MAPbI3 film should be very low, below 1012 cm-3. Along the vertical direction, this doping level is not enough to screen the electric field of the buried heterojunction with the SCTL. The perovskite work function is therefore affected by the work function of the SCTL underneath. From drift-diffusion simulations, we show that intrinsic perovskite-SCTL structures develop mV range surface photovoltages (SPVs) under continuous illumination. However, perovskite-SCTL structures can develop SPVs of hundreds of mV, as confirmed by our measurements. We therefore analyzed the compatibility between low doping and low defect densities in the perovskite layer and such high SPV values using numerical modeling. It is shown that these high SPV values could originate from electronic processes due to large band offsets in the buried perovskite-SCTL heterojunctions, or at the SCTL-transparent conductive oxide (TCO) buried heterojunction. However, such electronic processes can hardly explain the long SPV persistence after switching off the illumination.

defects↗
DOE OSTI2022

Pseudo-Polymorphism in Layered FeS Intercalates: A Competition between Charged and Neutral Guest Species

Systematic synthesis studies of the formation of tetrahedral FeS-ethylenediamine intercalates resulted in the synthesis of a new compound, [Fe 9.4(2) S 10 ][Fe(en) 3 ] 0.6(1) ·en 0.9 ( 3 ). The composition and complex crystal structure were determined based on a synergistic combination of elemental composition, decomposition behavior, high-resolution synchrotron X-ray diffraction and total scattering, 57 Fe Mössbauer spectroscopy, and electron diffraction. The structural model was derived based on a systematic comparison to the previously reported structures [Fe 8 S 10 ][Fe(en) 3 ] 1 ·en 0.5 and tetragonal FeS. The new compound has flat Fe 9.4 S 10 layers, analogous to those in superconducting binary FeS. In the crystal structure of [Fe 9.4 S 10 ][Fe(en) 3 ] 0.6 ·en 0.9 , the interlayer space is occupied by [Fe(en) 3 ] 2+ complexes and neutral ethylenediamine molecules in a ~2:3 ratio. Interlayer species are not randomly oriented but ordered as evidenced by superstructural diffraction peaks in both high-resolution X-ray diffraction and electron diffraction patterns. Magnetic studies reveal no superconducting transition down to 2 K, indicating that the presence of minute amounts (~6%) of iron vacancies at the Fe-S layer in [Fe 9.4 S 10 ][Fe(en) 3 ] 0.6 ·en 0.9 is still sufficient to shift the position of the Fermi level resulting in an adjustment of the properties. Here, our work shows the importance of detailed characterization of the crystal structure of intercalated compounds to understand the origin of the observed properties and develop proper structure–property relationships.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗