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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 1,189 records · Page 66
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Interpretation of scanning tunneling quasiparticle interference and impurity states in cuprates

We apply a recently developed method combining first principles based Wannier functions with solutions to the Bogoliubov–de Gennes equations to the problem of interpreting STM data in cuprate superconductors. We show that the observed images of Zn on the surface of Bi 2 Sr 2 CaCu 2 O 8 can only be understood by accounting for the tails of the Cu Wannier functions, which include significant weight on apical O sites in neighboring unit cells. This calculation thus puts earlier crude “filter” theories on a microscopic foundation and solves a long-standing puzzle. We then study quasiparticle interference phenomena induced by out-of-plane weak potential scatterers, and show how patterns long observed in cuprates can be understood in terms of the interference of Wannier functions above the surface. Furthermore, our results show excellent agreement with experiment and enable a better understanding of novel phenomena in the cuprates via STM imaging.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Enhanced sensitivity to trace 238 U impurity of sapphire via coincidence neutron activation analysis

Sapphire has mechanical and electrical properties that are advantageous for the construction of internal components of radiation detectors such as time projection chambers and bolometers. However, it has proved difficult to assess its 232 Th and 238 U content down to the picogram per gram level. Here, this work reports an experimental verification of a computational study that demonstrates 𝛾⁢𝛾 coincidence counting, coupled with neutron activation analysis (NAA), can reach ppt sensitivities. Combining results from 𝛾⁢𝛾 coincidence counting with those of earlier single-𝛾 counting based NAA shows that a sample of Saint Gobain sapphire has 232 Th and 238 U concentrations of <0.26 ppt and <2.3 ppt, respectively; the best constraints on the radiopurity of sapphire.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Ab Initio Study of Carbon Impurities in Cu$_2$ ZnSnS$_4$

Cu 2 ZnSnS 4 (CZTS) is a highly promising absorber material for efficient and low-cost solar cells. In a cost-effective method of production of high-quality CZTS, nanocrystals of precursor compounds, solved in an amine solution, are deposited on a substrate and sulfurized. Here, this can generally lead to considerable residual carbon in the final samples, in the form of separate amorphous layers as observed experimentally, but also incorporated in the CZTS matrix. In this study, preferred configurations, bonding characteristics, formation energies, and ionization levels of carbon-related defects in CZTS are calculated, including interstitials, single- and double-carbon antisites, and complexes of those with intrinsic defects. For different growth conditions of carbon, the set of dominant defects is determined, and the resulting total carbon concentrations are discussed with respect to experimental values.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Impact of impurities on the α-LiIO{sub 3} crystal growth: Technique for measuring the “dead zone”

Lithium iodate (α-LiIO{sub 3}) single crystal is a promising nonlinear optical material, which used for efficient laser radiation conversion in the visible and near-IR regions. A technique for measuring the “dead zone” (ΔТ{sub dz}) of LiIO{sub 3} solutions has been developed; data on the impact of Fe(IO{sub 3}){sub 2}, AgIO{sub 3}, CsOH, H{sub 3}PO{sub 4}, and methyl methacrylate on the growth of the (100) face of α-LiIO{sub 3} crystals have been presented; and the dependences of the nucleation and motion of single steps on the degree of supersaturation have been measured. It is shown that the ΔТ{sub dz} value makes it possible to estimate the validity of solutions for growing α-LiIO{sub 3} crystals. The results of measuring the face growth rates and step velocities for KDP and α-LiIO{sub 3} crystals are compared.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Radiation−condensation instability in tokamaks with mixed impurities

Radiation−condensation instability (RCI) is one of the possible mechanisms behind the formation of microfaceted asymmetric radiation from the edge (MARFE) of a tokamak. It has been previously shown by the authors that RCI in carbon-seeded plasma can be stabilized using neon injection. Recently, beryllium- and tungsten-seeded plasmas became a subject of great interest. Therefore, in the present paper, RCI stability analysis of the edge plasma seeded with beryllium, tungsten, nitrogen, and carbon is performed. The influence of neutral hydrogen fluxes from the wall on the marginal stability limit is studied as well.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗