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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Probing Boron Vacancy Complexes in h-BN Semi-Bulk Crystals Synthesized by Hydride Vapor Phase Epitaxy

Hexagonal BN (h-BN) has emerged as an important ultrawide bandgap (UWBG) semiconductor (Eg~6 eV). The crystal growth technologies for producing semi-bulk crystals/epilayers in large wafer sizes and understanding of defect properties lag decades behind conventional III-nitride wide bandgap (WBG) semiconductors. Here we report probing of boron vacancy (VB)-related defects in freestanding h-BN semi-bulk wafers synthesized by hydride vapor phase epitaxy (HVPE). A photocurrent excitation spectroscopy (PES) was designed to monitor the transport of photoexcited holes from deep-level acceptors. A dominant transition line at 1.66 eV with a side band near 1.62 eV has been directly observed, which matches well with the calculated energy levels of 1.65 for the VB-H deep acceptor in h-BN. The identification of VB complexes via PES measurement was further corroborated by the temperature-dependent dark resistivity and secondary ion mass spectrometry measurements. The results presented here suggested that it is necessary to focus on the optimization of V/III ratio during HVPE growth to minimize the generation of VB-related defects and to improve the overall material quality of h-BN semi-bulk crystals. The work also provided a better understanding of how VB complexes behave and affect the electronic and optical properties of h-BN.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Ultrawide bandgap semiconductor h-BN for direct detection of fast neutrons

III-nitride wide bandgap semiconductors have contributed on the grandest scale to many technological advances in lighting, displays, and power electronics. Among III-nitrides, BN has another unique application as a solid-state neutron detector material because the isotope B-10 is among a few elements that have an unusually large interaction cross section with thermal neutrons. A record high thermal neutron detection efficiency of 60% has been achieved by B-10 enriched h-BN detectors of 100 μm in thickness in our group. However, direct detection of fast neutrons with energies above 1 MeV is highly challenging due to the extremely low interaction cross section of fast neutrons with matter. We report the successful attainment of 0.4 mm thick freestanding h-BN 4"-diameter wafers, which enabled the demonstration of h-BN fast neutron detectors capable of delivering a detection efficiency of 2.2% in response to a bare AmBe neutron source. Furthermore, it was shown that the energy information of incoming fast neutrons is retained in the neutron pulse-height spectra. A comparison of characteristics between h-BN fast and thermal neutron detectors is summarized. Neutron detectors are vital diagnostic instruments for nuclear and fusion reactor power and safety monitoring, oil field exploration, neutron imaging and therapy, as well as for plasma and material science research. With the outstanding attributes resulting from its ultrawide bandgap (UWBG), including the ability to operate at extreme conditions of high power, voltage, and temperature, the availability of h-BN UWBG semiconductor detectors with the capability of simultaneously detecting thermal and fast neutrons with high efficiencies is expected to open unprecedented applications that are not possible to attain by any other types of neutron detectors.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Imaging of a van der Waals spin-orbit torque system using spin ensembles in hBN

Recently, optically active spin defects embedded in two-dimensional (2D) van der Waals (vdW) crystals have emerged as a transformative quantum sensing platform to explore cutting-edge materials science. Taking advantage of excellent solid-state integrability, this new class of spin defects can be readily arranged in nanoscale proximity to target materials, showing great promise for realizing in-situ quantum sensing of microscopic spin and charge behaviors in vdW heterostructures. Here we report hexagonal boron nitride-based quantum imaging of field-free deterministic magnetic switching and electric current distributions in an all-vdW spin-orbit torque (SOT) system. By visualizing variations of nanoscale magnetic stray field profile of room-temperature 2D magnet Fe 3 GaTe 2 under different SOT conditions, we show how the magnetic switching evolves from deterministic to stochastic behavior due to the interplay between spin orientations, anisotropy and Joule heating. Micromagnetic simulations rationalize our results well, revealing the role of field-like SOT in inhibiting thermal fluctuation driven stochastic switching and chaotic multi-domain competition. This understanding, which is otherwise difficult to access by conventional transport measurements, offers valuable insights into material design, testing, and performance evaluation of next-generation vdW spintronic devices.

Imaging techniques↗
DOE OSTI2020

Reversible writing of high-mobility and high-carrier-density doping patterns in two-dimensional van der Waals heterostructures

A key feature of two-dimensional materials is that the sign and concentration of their carriers can be externally controlled with techniques such as electrostatic gating. However, conventional electrostatic gating has limitations, including a maximum carrier density set by the dielectric breakdown, and ionic liquid gating and direct chemical doping also suffer from drawbacks. In this work, we show that an electron-beam-induced doping technique can be used to reversibly write high-resolution doping patterns in hexagonal boron nitride-encapsulated graphene and molybdenum disulfide (MoS 2 ) van der Waals heterostructures. The doped MoS 2 device exhibits an order of magnitude decrease of subthreshold swing compared with the device before doping, whereas the doped graphene devices demonstrate a previously inaccessible regime of high carrier concentration and high mobility, even at room temperature. We also show that the approach can be used to write high-quality p–n junctions and nanoscale doping patterns, illustrating that the technique can create nanoscale circuitry in van der Waals heterostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Hall effect for Dirac electrons in graphene exposed to an Abrikosov flux lattice

The proposals for realizing exotic particles through coupling of quantum Hall effect to superconductivity involve spatially non-uniform magnetic fields. As a step toward that goal, we study, both theoretically and experimentally, a system of Dirac electrons exposed to an Abrikosov flux lattice. Here, we theoretically find that the non-uniform magnetic field causes a carrier-density-dependent reduction of the Hall conductivity. Our studies show that this reduction originates from a rather subtle effect: a levitation of the Berry curvature within Landau levels broadened by the non-uniform magnetic field. Experimentally, we measure the magneto-transport in a monolayer graphene-hexagonal boron nitride-niobium diselenide (NbSe 2 ) heterostructure, and find a density-dependent reduction of the Hall resistivity of graphene as the temperature is lowered from above the superconducting critical temperature of NbSe 2 , when the magnetic field is uniform, to below, where the magnetic field bunches into an Abrikosov flux lattice.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRSDate not supplied

NASA-GRC Research Activities in High Voltage (HV) Electrical Insulation

This presentation gives an overview of recent research activities at NASA Glenn Research Center (GRC). The presentation covers research associated with materials for high voltage aerospace electrical insulation applications.

Aerospace Materials Aerospace electrical insulatio↗
DOE OSTI2020

Materials Data on BN by Materials Project

BN is Boron Nitride structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is two-dimensional and consists of two BN sheets oriented in the (0, 0, 1) direction. B3+ is bonded in a trigonal planar geometry to three equivalent N3- atoms. All B–N bond lengths are 1.45 Å. N3- is bonded in a trigonal planar geometry to three equivalent B3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on WN by Materials Project

NW1 is Boron Nitride structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. W3+ is bonded in a rectangular see-saw-like geometry to four equivalent N3- atoms. There are one shorter (2.00 Å) and three longer (2.08 Å) W–N bond lengths. N3- is bonded in a rectangular see-saw-like geometry to four equivalent W3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PdN by Materials Project

PdN is Boron Nitride structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is two-dimensional and consists of two PdN sheets oriented in the (0, 0, 1) direction. Pd2+ is bonded in a trigonal planar geometry to three equivalent N2- atoms. All Pd–N bond lengths are 1.95 Å. N2- is bonded in a trigonal planar geometry to three equivalent Pd2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on IrN by Materials Project

IrN is Boron Nitride structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Ir3+ is bonded in a rectangular see-saw-like geometry to four equivalent N3- atoms. There are three shorter (2.04 Å) and one longer (2.10 Å) Ir–N bond lengths. N3- is bonded in a rectangular see-saw-like geometry to four equivalent Ir3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BeH by Materials Project

BeH is Boron Nitride structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Be is bonded in a rectangular see-saw-like geometry to four equivalent H atoms. All Be–H bond lengths are 1.67 Å. H is bonded in a rectangular see-saw-like geometry to four equivalent Be atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on RhBr by Materials Project

RhBr is Boron Nitride structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Rh is bonded in a rectangular see-saw-like geometry to four equivalent Br atoms. There are one shorter (2.43 Å) and three longer (2.53 Å) Rh–Br bond lengths. Br is bonded in a rectangular see-saw-like geometry to four equivalent Rh atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaBr by Materials Project

CaBr is Boron Nitride structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Ca is bonded in a rectangular see-saw-like geometry to four equivalent Br atoms. There are one shorter (2.96 Å) and three longer (3.01 Å) Ca–Br bond lengths. Br is bonded in a rectangular see-saw-like geometry to four equivalent Ca atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CuBr by Materials Project

CuBr is Boron Nitride-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is two-dimensional and consists of two CuBr sheets oriented in the (0, 0, 1) direction. Cu1+ is bonded in a trigonal planar geometry to three equivalent Br1- atoms. All Cu–Br bond lengths are 2.39 Å. Br1- is bonded in a trigonal planar geometry to three equivalent Cu1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BN by Materials Project

BN is Boron Nitride-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is two-dimensional and consists of two BN sheets oriented in the (0, 0, 1) direction. B3+ is bonded in a trigonal planar geometry to three equivalent N3- atoms. All B–N bond lengths are 1.45 Å. N3- is bonded in a trigonal planar geometry to three equivalent B3+ atoms.

36 MATERIALS SCIENCE↗