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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

High‐Pressure and High‐Temperature Single‐Crystal Elasticity of Cr‐Pyrope: Implications for the Density and Seismic Velocity of Subcontinental Lithospheric Mantle

Abstract Single‐crystal X‐ray diffraction and Brillouin spectroscopy experiments were performed on a natural Cr‐pyrope (Prp 71.0 Alm 12.6 Sps 0.7 Grs 3.5 Uvr 12.2 ) at high pressure and high temperature up to 11.0 GPa and 800 K. Fitting the collected data to the third‐order finite strain equation yields bulk modulus ( K S 0 ), shear modulus ( G 0 ), their pressure ((∂ K S /∂ P ) T and (∂ G /∂ P ) T ) and temperature (( ∂K S /∂T ) P and ( ∂G/∂T ) P ) derivatives, K S 0 = 167.7(8) GPa, G 0 = 91.5(5) GPa, (∂ K S /∂ P ) T = 4.3(1), (∂ G /∂ P ) T = 1.4(1), ( ∂K S /∂T ) P = − 0.0175(1) GPa/K and ( ∂G/∂T ) P = − 0.0073(1) GPa/K. Using the obtained results, we examined whether the elastic properties of the Cr‐pyrope can be accurately calculated from those of endmembers including pyrope, almandine, grossular, and uvarovite assuming a linear relationship between elastic properties and composition (end‐member model). The results indicate that the end‐member model provides a sufficient approximation for the elastic properties of Cr‐pyrope in calculating the density and velocity of the subcontinental lithospheric mantle (SCLM). We modeled the densities and velocities of three typical types of SCLM (Archon, Proton, and Tecton) in order to investigate how the variation of chemical composition influences the SCLM. We obtained that the compositional change from the Archon to the Tecton increases the density of the SCLM significantly, which can be an important prerequisite for SCLM delamination. However, the compositional variation only slightly changes the velocity of the SCLM and the change is within the uncertainty of the calculation. Moreover, in comparison to the velocity, ρ / V P and ρ / V S are much more sensitive to the compositional change of the SCLM.

Xu, Jingui↗
DOE OSTI2019

Single hole spin relaxation probed by fast single-shot latched charge sensing

Hole spins have recently emerged as attractive candidates for solid-state qubits for quantum computing. Their state can be manipulated electrically by taking advantage of the strong spin-orbit interaction (SOI). Crucially, these systems promise longer spin coherence lifetimes owing to their weak interactions with nuclear spins as compared to electron spin qubits. Here we measure the spin relaxation time T 1 of a single hole in a GaAs gated lateral double quantum dot device. We propose a protocol converting the spin state into long-lived charge configurations by the SOI-assisted spin-flip tunneling between dots. By interrogating the system with a charge detector we extract the magnetic-field dependence of T 1 ∝ B -5 for fields larger than B = 0.5 T, suggesting the phonon-assisted Dresselhaus SOI as the relaxation channel. This coupling limits the measured values of T 1 from ~400 ns at B = 1.5 T up to ~60 μs at B = 0.5 T.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Pair distribution function-derived mechanism of a single-crystal to disordered to single-crystal transformation in a hemilabile metal-organic framework

Flexible metal-organic frameworks (MOFs) are materials of great current interest. A small class of MOFs show flexibility driven by reversible bonding rearrangements that lead directly to unusual properties. Cu-SIP-3 is a MOF based on the 5-sulfoisophthalate ligand, where the strong copper-carboxylate bonds ensure that the three-dimensional integrity of the structure is retained while allowing bonding changes to occur at the more weakly bonding sulfonate group leading to unusual properties such as the ultra-selective adsorption of only certain gases. While the integrity of the framework remains intact during bonding changes, crystalline order is not retained at all times during the transformations. X-Ray diffraction reveals that highly crystalline single crystals lose order during the transformation before regaining crystallinity once it is complete. Here we show how X-ray pair distribution function analysis can be used to reveal the mechanism of the transformations in Cu-SIP-3, identifying the sequence of atomic displacements that occur in the disordered phase. A similar approach reveals the underlying mechanism of Cu-SIP-3's ultra-selective gas adsorption.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Relaxation dynamics in see-saw shaped Dy( iii ) single-molecule magnets

Unusual see-saw shaped Dy( iii ) single-molecule magnets, [K(DME) n ][L Ar Dy(X) 2 ] (L Ar = {C 6 H 4 [(2,6- i PrC 6 H 3 )NC 6 H 4 ] 2 } 2− ), X = Cl ( 1 ) and X = I ( 2 ) were synthesized and display high effective energy barriers ( U eff = 1278–1334 K) in zero field.

Harriman, Katie L. M.↗
DOE OSTI2013

Mechanical properties of irradiated single-layer graphene

The mechanical properties of irradiated single-layer graphene sheets are determined as a function of inserted vacancy concentration. We find that the vacancy-induced crystalline-to-amorphous transition is accompanied by a brittle-to-ductile transition in the failure response of irradiated graphene sheets for inserted vacancy concentrations of 8%-12%. While point defects and larger voids appreciably degrade the strength of pristine graphene, we find that even heavily damaged samples ({approx}20% vacancies) exhibit tensile strengths of {approx}30 GPa, in significant excess of those typical of engineering materials. Our results suggest that defect engineering of graphene is feasible without incurring a complete loss of its desirable mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Ellipsometric characterization and density-functional theory analysis of anisotropic optical properties of single-crystal α-SnS

We report on the anisotropic optical properties of single-crystal tin monosulfide (SnS). The components ε{sub a}, ε{sub b}, and ε{sub c} of the pseudodielectric-function tensor (ε)=(ε₁)+i(ε₂) spectra are taken from 0.73 to 6.45 eV by spectroscopic ellipsometry. The measured (ε) spectra are in a good agreement with the results of the calculated dielectric response from hybrid density functional theory. The (ε) spectra show the direct band-gap onset and a total of eight above-band-gap optical structures that are associated with the interband-transition critical points (CPs). We obtain accurate CP energies by fitting analytic CP expressions to second-energy-derivatives of the (ε) data. Their probable electronic origins and implications for photovoltaic applications are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Specific heat of Nb{sub 3}Sn: The case for a single gap

The important influence of multiple gaps in the superconductivity of MgB{sub 2} and Fe-based compounds, especially because of the possibility that manipulation of a second gap can significantly raise the upper critical field H{sub c2}, has refocused attention on Nb{sub 3}Sn because anomalies in both specific heat and point-contact tunneling studies have led to the proposal that Nb{sub 3}Sn is also a two-gap superconductor. Here, we search for evidence of the second gap in a careful study of the influence of the homogenization temperature on the sample uniformity. We show that it is very difficult to fabricate samples that are both homogeneous and stoichiometric. We find so-called “second-gap” anomalies disappear only after high temperature and long-term annealing. Such a well-annealed sample shows only a strong, electron-phonon-coupled, single-gap behavior. In contrast, samples reacted and annealed at lower temperatures, as in the earlier two-gap studies, show small chemical composition variations of the A15 phase. We propose that the second gap sightings are actually due to variation of T{sub c} within very difficult-to-fully homogenize samples. A curiosity of the A15 Nb{sub 3}Sn phase is that almost any mixture of Nb and Sn tries to form a stoichiometric A15 composition, but the residue of course contains off-stoichiometric A15, Nb, and other phases when the Nb:Sn ratio departs from the true 3:1 stoichiometry.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Single-walled carbon nanotube transparent conductive films fabricated by reductive dissolution and spray coating for organic photovoltaics

Solutions of unbundled and unbroken single-walled carbon nanotubes have been prepared using a reductive dissolution process. Transparent conductive films spray-coated from these solutions show a nearly twofold improvement in the ratio of electrical conductivity to optical absorptivity versus those deposited from conventional aqueous dispersions, due to substantial de-aggregation and sizable nanotube lengths. These transparent electrodes have been utilized to fabricate P3HT-PCBM organic solar cells achieving power conversion efficiencies up to 2.3%, comparable to those of solar cells using indium tin oxide transparent electrodes.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Anisotropic small-polaron hopping in W:BiVO{sub 4} single crystals

DC electrical conductivity, Seebeck and Hall coefficients are measured between 300 and 450 K on single crystals of monoclinic bismuth vanadate that are doped n-type with 0.3% tungsten donors (W:BiVO{sub 4}). Strongly activated small-polaron hopping is implied by the activation energies of the Arrhenius conductivities (about 300 meV) greatly exceeding the energies characterizing the falls of the Seebeck coefficients' magnitudes with increasing temperature (about 50 meV). Small-polaron hopping is further evidenced by the measured Hall mobility in the ab-plane (10{sup −1 }cm{sup 2 }V{sup −1 }s{sup −1} at 300 K) being larger and much less strongly activated than the deduced drift mobility (about 5 × 10{sup −5 }cm{sup 2 }V{sup −1 }s{sup −1} at 300 K). The conductivity and n-type Seebeck coefficient is found to be anisotropic with the conductivity larger and the Seebeck coefficient's magnitude smaller and less temperature dependent for motion within the ab-plane than that in the c-direction. These anisotropies are addressed by considering highly anisotropic next-nearest-neighbor (≈5 Å) transfers in addition to the somewhat shorter (≈4 Å), nearly isotropic nearest-neighbor transfers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Coherent (photon) vs incoherent (current) detection of multidimensional optical signals from single molecules in open junctions

The nonlinear optical response of a current-carrying single molecule coupled to two metal leads and driven by a sequence of impulsive optical pulses with controllable phases and time delays is calculated. Coherent (stimulated, heterodyne) detection of photons and incoherent detection of the optically induced current are compared. Using a diagrammatic Liouville space superoperator formalism, the signals are recast in terms of molecular correlation functions which are then expanded in the many-body molecular states. Two dimensional signals in benzene-1,4-dithiol molecule show cross peaks involving charged states. The correlation between optical and charge current signal is also observed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Direct evidence of single quantum dot emission from GaN islands formed at threading dislocations using nanoscale cathodoluminescence: A source of single photons in the ultraviolet

Intense emission from GaN islands embedded in AlN resulting from GaN/AlN quantum well growth is directly resolved by performing cathodoluminescence spectroscopy in a scanning transmission electron microscope. Line widths down to 440 μeV are measured in a wavelength region between 220 and 310 nm confirming quantum dot like electronic properties in the islands. These quantum dot states can be structurally correlated to islands of slightly enlarged thicknesses of the GaN/AlN quantum well layer preferentially formed in vicinity to dislocations. The quantum dot states exhibit single photon emission in Hanbury Brown-Twiss experiments with a clear antibunching in the second order correlation function at zero time delay.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗