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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Monodispersed boron carbonitride hollow spheres with high-performance microwave absorption property

Highlights: • Boron carbonitride hollow spheres were synthesized by a simple precursor. • A novel precursor was synthesized to prepare the hollow spheres. • The products exhibit excellent microwave absorption performance. - Abstract: A novel method, combining polymerization and pyrolysis of single precursor on graphite sheet, has been developed to synthesize monodispersed boron carbonitride hollow spheres in large-scale. The products have hollow architectures (2–3 μm in diameter) with nano-pores on the spherical walls and a composition of B{sub 0.23}N{sub 0.19}C{sub 0.58.} The products exhibit the minimum reflection loss of −42.5 dB at 12.6 GHz (the effective reflection values are obtained in a very wide range of 3.4–17.3 GHz) suggesting a new and high quality microwave absorbent.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Effect of boron on the fracture behavior and grain boundary chemistry of Ni3Fe

The effect of B on the fracture behavior of Ni{sub 3}Fe alloys (24 and 26 at.% Fe) was studied after cathodic charging with hydrogen. In contrast to its disordered state, ordered Ni{sub 3}Fe underwent brittle intergranular fracture at room temperature. Boron addition changed its fracture mode to predominantly ductile transgranular. The grain boundary chemistry of ordered Ni{sub 3}Fe was analyzed by Auger electron spectroscopy. Boron was found to segregate to the grain boundaries of both Ni-24Fe and Ni-26Fe and reduce the hydrogen-induced embrittlement of these alloys in the ordered state.

08 HYDROGEN↗
DOE OSTI2026

Landau–Zener Transition Enhanced Quantum Sensing in Spin Defects of Hexagonal Boron Nitride

Negatively charged boron vacancies (V $^{–}_{B}$ ) in hexagonal boron nitride (hBN) comprise a promising quantum sensing platform, optically addressable at room temperature and transferable onto samples. However, broad hyperfine-split spin transitions of the ensemble pose challenges for quantum sensing with conventional resonant excitation due to limited spectral coverage. While V $^{–}_{B}$ in isotopically enriched hBN using 10 B and 15 N isotopes (h 10 B 15 N) exhibits sharper spectral features, significant inhomogeneous broadening persists. We show that, implemented via frequency modulation on an FPGA, a frequency-ramped microwave pulse achieves around 4-fold greater |0⟩→|−1⟩ spin-state population transfer and thus contrast than resonant microwave excitation and thus 16-fold shorter measurement time for spin relaxation-based quantum sensing. Quantum dynamics simulations reveal that an effective two-state Landau–Zener model captures the complex relationship between population inversion and pulse length with relaxations incorporated. Our approach is robust and valuable for quantum relaxometry with spin defects in hBN, especially in noisy environments.

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

Optical phonon modes in rhombohedral boron monosulfide under high pressure

Raman spectra of rhombohedral boron monosulfide (r-BS) were measured under pressures up to 34 GPa at room temperature. No pressure-induced structural phase transition was observed, while strong pressure shift of Raman bands towards higher wavenumbers has been revealed. IR spectroscopy as a complementary technique has been used in order to completely describe the phonon modes of r-BS. All experimentally observed bands have been compared with theoretically calculated ones and modes assignment has been performed. r-BS enriched by {sup 10}B isotope was synthesized, and the effect of boron isotopic substitution on Raman spectra was observed and analyzed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Theoretical study of the influence of vacancies on the electronic structure of a hexagonal boron nitride monolayer

The influence of boron and nitrogen vacancies and divacancies on the electronic structure of a hexagonal boron nitride h-BN monolayer is studied. In the presence of vacancies in the structure, the introduced states appear in the forbidden band. The position of an introduced state with respect to the upper occupied level and the lower vacant level depends on deformation. Calculations show that, depending on the defect type and the magnitude of the applied deformation, the introduced state can be both localized and not localized on atoms surrounding the defect. When the state is localized in the system, the inhomogeneous distribution of the spin density is observed, resulting in the appearance of the magnetic moment in the system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Raman Scattering by Crystals of Rare-Earth Hexaborides with Different Isotopes of Boron

Monocrystals of lanthanum hexaboride LaB{sub 6} containing both natural boron and its isotopes {sup 10}B and {sup 11}B have been produced using the solution-melt method. Polyelement hexaboride rare-earths have been grown and the corresponding ceramics have been synthesized for the first time. All these crystals have been studied by means of various techniques, generally using Raman scattering. The Raman spectra attributed to various spectral lines corresponding to nonanalyzable representations have been obtained and interpreted. Frequencies and half-widths of spectral lines have been obtained, the removal of degeneracy and the development of respective splitting of degenerate oscillations induced by defects, mainly by boron isotope inclusions, have been identified. The influence of defects on the Raman spectra has been determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Design and Testing of a Boron Carbide Capsule for Spectral Tailoring in Mixed-Spectrum Reactors

A boron carbide capsule has been designed and used for spectral-tailoring experiments at the TRIGA reactor at Washington State University. Irradiations were conducted in pulsed mode and in continuous operation for up to 4 hours. A cadmium cover was used to reduce thermal heating. The neutron spectrum calculated with MCNP was found to be in good agreement with reactor dosimetry measurements using the STAY'SL computer code. The neutron spectrum resembles that of a fast reactor. Design of a capsule using boron carbide enriched in {sup 10}B shows that it is possible to produce a neutron spectrum similar to {sup 235}U fission.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2012

Introduction to Neutron Coincidence Counter Design Based on Boron-10

The Department of Energy Office of Nonproliferation Policy (NA-241) is supporting the project 'Coincidence Counting With Boron-Based Alternative Neutron Detection Technology' at Pacific Northwest National Laboratory (PNNL) for development of an alternative neutron coincidence counter. The goal of this project is ultimately to design, build and demonstrate a boron-lined proportional tube based alternative system in the configuration of a coincidence counter. This report, providing background information for this project, is the deliverable under Task 1 of the project.

10B↗
DOE OSTI2013

Estimation of Performance of an Active Well Coincidence Counter Equipped with Boron-Coated Straw Neutron Detectors - 13401

He-3, a very rare isotope of natural helium gas, has ideal properties for the detection of thermal neutrons. As such it has become the standard material for neutron detectors and sees ubiquitous use within many radiometric applications that require neutron sensitivity. Until recently, there has been a fairly abundant supply of He-3. However, with the reduction in nuclear weapons, production of tritium ceased decades ago and the stockpile has largely decayed away, reducing the available He-3 supply to a small fraction of that needed for neutron detection. A suitable and rapidly-deployable replacement technology for neutron detectors must be found. Many potential replacement technologies are under active investigation and development. One broad class of technologies utilizes B-10 as a neutron capture medium in coatings on the internal surfaces of proportional detectors. A particular implementation of this sort of technology is the boron-coated 'straw' (BCS) detectors under development by Proportional Technologies, Inc. (PTi). This technology employs a coating of B-10 enriched boron carbide (B{sub 4}C) on the inside of narrow tubes, roughly 4 mm in diameter. A neutron counter (e.g. a slab, a well counter, or a large assay counter designed to accommodate 200 liter drums) could be constructed by distributing these narrow tubes throughout the polyethylene body of the counter. One type of neutron counter that is of particular importance to safeguards applications is the Active Well Coincidence Counter (AWCC), which is a Los Alamos design that traditionally employs 42 He-3 detectors. This is a very flexible design which can accurately assay small samples of uranium- and plutonium-bearing materials. Utilizing the MCNPX code and benchmarking against measurements where possible, the standard AWCC has been redesigned to utilize the BCS technology. Particular aspects of the counter performance include the single-neutron ('singles') detection efficiency and the time constant for the decrease in neutron population in the counter following a fission event (a.k.a. the die-away time). Results of the modeling and optimization are presented. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Growth Dynamics of Millimeter-Sized Single-Crystal Hexagonal Boron Nitride Monolayers on Secondary Recrystallized Ni (100) Substrates

The outstanding physical properties of 2D materials have sparked continuous research interest in exploiting these materials for next-generation high-performance electronic and photonic technology. Scalable synthesis of high-quality large-area 2D hexagonal boron nitride (h-BN) is a crucial step toward the ultimate success of many of these applications. In this work, a synthetic approach in which secondary recrystallized Ni (100) substrates underwent a carburization process, followed by the growth of h-BN in a molecular beam epitaxy system is designed. The h-BN growth dynamics is studied by tuning different growth parameters including the substrate temperature, and the boron and nitrogen source flux ratio. With assistance from density functional theory calculations, the role of interstitial C atoms in promoting h-BN growth by enhancing the catalytic effect of the transition metal, which lowers the nucleation activation energy barrier, is rationalized. Furthermore, through the control of the growth parameters, a single-crystal h-BN monolayer domain as large as 1.4 mm in edge length is achieved. In addition, a high-quality, continuous, large-area h-BN single-layer film with a breakdown electric field of 9.75 MV cm -1 is demonstrated. The high value of the breakdown electric field suggests that single-layer h-BN has extraordinary dielectric strength for high-performance 2D electronics applications.

2D↗
DOE OSTI2017

Boron Nitride-supported Sub-nanometer Pd 6 Clusters for Formic Acid Decomposition: A DFT Study

A periodic, self-consistent planewave DFT study was carried out to explore the potential use of Pd 6 clusters supported on a boron nitride sheet as a catalyst for the selective decomposition of formic acid (HCOOH) to CO 2 and H 2 . The competition between formate (HCOO) and carboxyl (COOH) paths on catalytic sites, with different proximities to the support, was studied. Based on energetics alone, the reaction may mainly follow the HCOO route. Slightly lower activation energies were found at the lateral sites of the cluster as compared to top face sites. This is particularly true for the bidentate to monodentate HCOO conversion. Through comparison of results with similar studies on HCOOH decomposition on extended Pd surfaces, it was demonstrated that the existence of undercoordinated sites in the sub-nanometer cluster could play a key role in preferentially stabilizing HCOO over COOH, which is a common CO precursor in this reaction. A hydrogen spillover mechanism was also investigated; migration toward the boron nitride support is not favorable, at least in the early stages of the reaction. However, hydrogen diffusion on the cluster has low barriers compared to those involved in formic acid decomposition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Optical Properties of Low‐Defect Large‐Area Hexagonal Boron Nitride for Quantum Applications

Intrinsic defects and their concentrations in hexagonal boron nitride (h-BN) play a key role in single-photon emission. In this study, the optical properties of large-area multilayer h-BN-on-sapphire grown by metal-organic chemical vapor deposition are explored. Based on the detailed spectroscopic characterization using both cathodoluminescence (CL) and photoluminescence (PL) measurements, the material is devoid of random single-point defects instead of a few clustered complex defects. The emission spectra of the measurements confirm a record-low-defect concentration of ≈10 4 cm −2 . Post-annealing, no significant changes are observed in the measured spectra and the defect concentrations remain unaltered. Through CL and PL spectroscopy, an optically active boron vacancy spin defect is identified and a novel complex defect combination arising from carbon impurities is revealed. This complex defect, previously unreported, signifies a unique aspect of the material. In these findings, the understanding of defect-induced optical properties in h-BN films is contributed, providing insights for potential applications in quantum information science.

42 ENGINEERING↗
DOE OSTI2017

Tailoring N-Terminated Defective Edges of Porous Boron Nitride for Enhanced Aerobic Catalysis

Tailoring terminated edge of hexagonal boron nitride (h–BN) for enhancing catalysis has turned to be an imperative for the rational design of a highly active aerobic catalyst. Herein, a tailoring N–terminated porous BN (P–BN) strategy is reported with a zinc (Zn) salt as a dual–functional template. The Zn salt acts as both an in situ template and an N–terminated defective edges directing agent. The zinc salt template turns to Zn nanoparticles (Zn NPs) and functions as physical spacers, which are subsequently removed at a higher temperature, for producing P–BN, whose high surface area is high to 1579 m 2 g –1 . Moreover, because of the lower electronegativity of Zn, boron (B) atoms are partly replaced by Zn atoms and ultimately preferred to N–terminated edges with the volatilization of Zn NPs. Owing to the moderate dissociative energy of oxygen atoms on N–terminated edges, the N–terminated edges are proved to be the origin of an enhanced aerobic catalytic activity by density functional theory (DFT) calculations. Furthermore, the DFT calculation result is experimentally verified.

2D↗
DOE OSTI2013

Boron neutron capture therapy (BNCT) for liver metastasis in an experimental model: dose–response at five-week follow-up based on retrospective dose assessment in individual rats

Boron neutron capture therapy (BNCT) was proposed for untreatable colorectal liver metastases. Employing an experimental model of liver metastases in rats, we recently demonstrated that BNCT mediated by boronophenylalanine (BPA-BNCT) at 13 Gy prescribed to tumor is therapeutically useful at 3-week follow-up. The aim of the present study was to evaluate dose–response at 5-week follow-up, based on retrospective dose assessment in individual rats. BDIX rats were inoculated with syngeneic colon cancer cells DHD/K12/TRb. Tumor-bearing animals were divided into three groups: BPA-BNCT (n = 19), Beam only (n = 8) and Sham (n = 7) (matched manipulation, no treatment). For each rat, neutron flux was measured in situ and boron content was measured in a pre-irradiation blood sample for retrospective individual dose assessment. For statistical analysis (ANOVA), individual data for the BPA-BNCT group were pooled according to absorbed tumor dose, BPA-BNCT I: 4.5–8.9 Gy and BPA-BNCT II: 9.2–16 Gy. At 5 weeks post-irradiation, the tumor surface area post-treatment/pre-treatment ratio was 12.2 +/- 6.6 for Sham, 7.8 +/- 4.1 for Beam only, 4.4 +/- 5.6 for BPA-BNCT I and 0.45 +/- 0.20 for BPA-BNCT II; tumor nodule weight was 750 +/- 480 mg for Sham, 960 +/- 620 mg for Beam only, 380 +/- 720 mg for BPA-BNCT I and 7.3 +/- 5.9 mg for BPA-BNCT II. The BPA-BNCT II group exhibited statistically significant tumor control with no contributory liver toxicity. Potential threshold doses for tumor response and significant tumor control were established at 6.1 and 9.2 Gy, respectively.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2017

Electron Paramagnetic Resonance and X-ray Diffraction of Boron- and Phosphorus-Doped Nanodiamonds

Powders of boron- and phosphorus-doped detonation nanodiamonds and sintered pellets of non-doped nanodiamond powders were studied using electron paramagnetic resonance and x-ray diffraction. Doping of detonation nanodiamond crystals with boron and phosphorus was demonstrated to be possible. These methods could be used to diagnose diamond nanocrystals doped during shock-wave synthesis.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Four-coordinate six-membered ketiminate and diketiminate boron complexes. Synthesis, structure, reactivity, and application in the design of nitrogen heterocycles

The data on ketiminate and diketiminate boron complexes are first reviewed. The present review is focused on the synthesis and chemical transformations of these chelates. The special attention is paid to the application of these boron chelates in the synthesis of nitrogen heterocycles including CF{sub 3}-substituted derivatives.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Vibrational spectra and electronic structure of 11-vertex boron-containing clusters: a comparative study of [B{sub 11}H{sub 11}]{sup 2–}, [CB{sub 10}H{sub 11}]{sup –}, and C{sub 2}B{sub 9}H{sub 11}

Vibrational spectroscopy studies of 11-vertex boron-containing clusters [B{sub 11}H{sub 11}]{sup 2–}(1), [2-CB{sub 10}H{sub 11}]{sup –} (2), and 2,3-C{sub 2}B{sub 9}H{sub 11} (3) revealed two low-frequency large-amplitude modes in their spectra and, therefore, structural nonrigidity of these polyhedra in contrast to related 12-, 10-, and 6-vertex closo-clusters. The nonrigidity originates from specific features of the electron density distribution. According to calculations within the framework of the 'Atoms in Molecule' (AIM) theory, these polyhedra are characterized by the lack of many bond paths localized on corresponding edges, in particular, between boron atoms with coordination numbers of 6 and 5 (6k and 5k). Consequently, these polyhedra are composed of not only trigonal faces, i.e., formally do not have the closo-structure that was traditionally ascribed to them based on formal count of (2n + 2) valence electrons. According to calculations of three-center delocalization indices, the absence of bond paths is not equivalent to the lack of interaction between corresponding atoms since this interaction occurs through open three-center bonds. The mechanism and reasons for signal averaging observed in {sup 11}B NMR spectra of compounds 1 and 2 in contrast to 3 are analyzed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Solid-phase synthesis of boron carbides ReB{sub 2}C (Re = Ho, Tm, Lu) of rare earth elements

Approaches to solid-phase synthesis of boron carbides of heavy rare-earth elements using the hydride phase have been considered. Synthetic procedures with the use of carbon in the forms of carbon black and pyrographite were tested under atmospheric pressure, in medium and high vacuum. The obtained samples were characterized by X-ray and chemical (elemental) analyzes. A technique for obtaining compact samples of boron carbides of Ho, Tm, and Lu, which are homogeneous in the phase composition, has been developed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗