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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Thermal Stability of Quasi-1D NbS 3 Nanoribbons and Their Transformation to 2D NbS 2 : Insights from in Situ Electron Microscopy and Spectroscopy

Here in situ electron microscopy imaging and spectroscopy enabled us to study the evolution of quasi-1D NbS 3 -IV nanoribbons with respect to morphology and chemical structure at temperatures between room temperature and 1000 °C. Scanning transmission electron microscopy (STEM) experiments included imaging in the secondary electron, (transmitted) bright field, and high-angle annular dark-field modes while operating in the low kV regime. The results showed that NbS 3 -IV samples transform dramatically from smooth nanoribbons into highly textured configurations featuring polyhedral divots and steps. Similar in situ heating experiments conducted with aberration-corrected STEM revealed that bilayers of NbS 3 -IV chains convert topotactically into aligned 2H-NbS 2 sheets upon loss of sulfur. Atomic resolution imaging, fast Fourier transform analysis, and electron energy loss spectroscopy confirmed these chemical changes, from which we propose an atomistic mechanism for the NbS 3 -IV → 2H-NbS 2 conversion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2009

Analysis of Chromosomal Aberrations after Low and High Dose Rate Gamma Irradiation in ATM or NBS Suppressed Human Fibroblast Cells

A detailed understanding of the biological effects of heavy nuclei is needed for space radiation protection and for cancer therapy. High-LET radiation produces more complex DNA lesions that may be non-repairable or that may require additional processing steps compared to endogenous DSBs, increasing the possibility of misrepair. Interplay between radiation sensitivity, dose, and radiation quality has not been studied extensively. Previously we studied chromosome aberrations induced by low- and high- LET radiation in several cell lines deficient in ATM (ataxia telangactasia mutated; product of the gene that is mutated in ataxia telangiectasia patients) or NBS (nibrin; product of the gene mutated in the Nijmegen breakage syndrome), and gliomablastoma cells that are proficient or lacking in DNA-dependent protein kinase (DNA-PK) activity. We found that the yields of both simple and complex chromosomal aberrations were significantly increased in the DSB repair defective cells compared to normal cells. The increased aberrations observed for the ATM and NBS defective lines was due to a significantly larger quadratic dose-response term compared to normal fibroblasts for both simple and complex aberrations, while the linear dose-response term was significantly higher in NBS cells only for simple exchanges. These results point to the importance of the functions of ATM and NBS in chromatin modifications that function to facilitate correct DSB repair and minimize aberration formation. To further understand the sensitivity differences that were observed in ATM and NBS deficient cells, in this study, chromosomal aberration analysis was performed in normal lung fibroblast cells treated with KU-55933, a specific ATM kinase inhibitor, or Mirin, an MRN complex inhibitor involved in activation of ATM. We are also testing siRNA knockdown of these proteins. Normal and ATM or NBS suppressed cells were irradiated with gamma-rays and chromosomes were collected with a premature chromosome condensation (PCC) technique at the first mitosis post-irradiation. Chromosomes were analyzed using a multicolor fluorescence in-situ hybridization (mFISH) chromosome painting method. Preliminary analysis showed that chromosomal exchanges were increased in the cells treated with the specific ATM inhibitor. Possible cytogenetic signatures of acute and low dose-rate gamma irradiation in ATM or Nibrin deficient and suppressed cells will be discussed.

Hada, M.↗
DOE OSTI2021

Origins of anisotropic transport in the electrically switchable antiferromagnet Fe 1/3 NbS 2

Recent experiments on the antiferromagnetic intercalated transition metal dichalcogenide Fe 1/3 NbS 2 have demonstrated reversible resistivity switching by application of orthogonal current pulses below its magnetic ordering temperature, making Fe 1/3 NbS 2 promising for spintronics applications. Here, we perform density functional theory calculations with Hubbard U corrections of the magnetic order, electronic structure, and transport properties of crystalline Fe 1/3 NbS 2 , clarifying the origin of the different resistance states. The two experimentally proposed antiferromagnetic ground states, corresponding to in-plane stripe and zigzag ordering, are computed to be nearly degenerate. In-plane cross sections of the calculated Fermi surfaces are anisotropic for both magnetic orderings, with the degree of anisotropy sensitive to the Hubbard U value. The in-plane resistance, computed within the Kubo linear response formalism using a constant relaxation time approximation, is also anisotropic, supporting a hypothesis that the current-induced resistance changes are due to a repopulating of antiferromagnetic domains. Our calculations indicate that the transport anisotropy of Fe 1/3 NbS 2 in the zigzag phase is reduced relative to stripe, consistent with the relative magnitudes of resistivity changes in experiment. Finally, our calculations reveal the likely directionality of the current-domain response, specifically, which domains are energetically stabilized for a given current direction.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Disentangling electronic, lattice, and spin dynamics in the chiral helimagnet Cr 1/3 NbS 2

We investigate the static and ultrafast magneto-optical response of the hexagonal chiral helimagnet Cr 1/3 NbS 2 above and below the helimagnetic ordering temperature. The presence of a magnetic easy plane contained within the crystallographic $ab$-plane is confirmed, while degenerate optical pump-probe experiments reveal significant differences in the dynamic between the parent, NbS 2 , and Cr-intercalated compounds. Time-resolved magneto-optical Kerr effect measurements show a two-step demagnetization process, where an initial, subpicosecond relaxation and subsequent buildup (τ > 50ps) in the demagnetization dynamic scale similarly with increasing pump fluence. Despite theoretical evidence for partial gapping of the minority spin channel, suggestive of possible half-metallicity in Cr 1/3 NbS 2 , such a long demagnetization dynamic likely results from spin-lattice relaxation as opposed to minority state blocking. However, comparison of the two-step demagnetization process in Cr 1/3 NbS 2 with other 3d intercalated transition metal dichalcogenides reveals a behavior that is unexpected from conventional spin-lattice relaxation, and may be attributed to the complicated interaction of local moments with itinerant electrons in this material system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Persistent exchange splitting in the chiral helimagnet $\mathrm{Cr}_{1/3}\mathrm{NbS}_2$

Here, using high-resolution angle-resolved photoemission spectroscopy and ab initio calculation, we systematically investigate the electronic structure of the chiral helimagnet Cr 1/3 NbS 2 and its temperature evolution. The comparison with NbS 2 suggests that the electronic structure of Cr 1/3 NbS 2 is strongly modified by the intercalation of Cr atoms. Our ab initio calculation, consistent with experimental results, suggests strong hybridization between Nb- and Cr-derived states near the Fermi level. In the chiral helimagnetic state (below the Curie temperature, T c ), we observe exchange splitting of the energy bands crossing the Fermi level, which follows the temperature evolution of the magnetic moment, suggesting a strong interaction between the conduction electrons and Cr spin moments. Interestingly, the exchange splitting persists far above T c with weak temperature dependence, in drastic contrast to the itinerant ferromagnetism described by the Stoner model, indicating the existence of short-range magnetic order. Our results provide important insights into the interplay between the electronic structure and magnetism in Cr 1/3 NbS 2 , which is helpful for understanding the microscopic mechanism of chiral helimagnetic ordering.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Canted antiferromagnetic order in the monoaxial chiral magnets V 1/3 TaS 2 and V 1/3 NbS 2

The Dzyaloshinskii-Moriya (DM) interaction is present in the transition metal dichalcogenides (TMDC) magnets of form M 1 / 3 T S 2 ( M = 3 d transition metal, T ϵ { Nb , Ta } ), given that the intercalants M form 3 × 3 superlattices within the structure of the parent materials T S 2 and break the centrosymmetry. Competition between DM and ferromagnetic exchange interactions has been shown to stabilize a topological defect known as a chiral soliton in select intercalated TMDCs, initiating interest both in terms of fundamental physics and the potential for technological applications. In the current article we report on our study of the materials V 1 / 3 TaS 2 and V 1 / 3 NbS 2 , using a combination of x-ray powder diffraction, magnetization, and single crystal neutron diffraction. Historically identified as ferromagnets, our diffraction results instead reveal that vanadium spins in these compounds are arranged into an A-type antiferromagnetic configuration at low temperatures. Refined moments are 1.37(6) and 1.50(9) μ B for V 1 / 3 TaS 2 and V 1 / 3 NbS 2 , respectively. Transition temperatures T c = 32 K for V 1 / 3 TaS 2 and 50 K for V 1 / 3 NbS 2 are obtained from the magnetization and neutron diffraction results. We attribute the small net magnetization observed in the low-temperature phases to a subtle ( ~ 2 ° ) canting of XY spins in the out-of-plane direction. These new results are indicative of dominant antiferromagnetic exchange interactions between the vanadium moments in adjacent a b planes, likely eliminating the possibility of identifying stable chiral solitons in the current materials.

36 MATERIALS SCIENCE↗
NASA NTRS1978

Smoke density studies with the Arapahoe and NBS chambers

Smoke density studies on twelve cellulosic and five synthetic materials using the Arapahoe and NBS smoke chambers show an empirical relationship between smoke weight as per cent of initial weight in the Arapahoe test and maximum specific optical density under piloted conditions in the NBS test. The NBS optical density data under piloted conditions exhibited sensitivity to test artifacts such as type of pilot burner.

Hilado, C. J.↗
DOE OSTI2025

Zero-field Hall effect emerging from a non-Fermi liquid in a collinear antiferromagnet V 1/3 NbS 2

Magnetically intercalated transition metal dichalcogenides (TMDs) provide a versatile three-dimensional (3D) material platform to explore quantum phenomena and functionalities that emerge from an intricate interplay among magnetism, band structure, and electronic correlations. Here, we report the observation of a nearly magnetization-free anomalous Hall effect (AHE) accompanied by non-Fermi liquid (NFL) behavior and collinear antiferromagnetism (AFM) in V 1/3 NbS 2 . Our single-crystal neutron diffraction measurements identify a commensurate, collinear AFM order formed by intercalated V moments. In the magnetically ordered state, the spontaneous AHE is tenfold greater than expected from empirical scaling with magnetization, and this strongly enhanced AHE arises in the NFL regime that violates the quasiparticle picture. V 1/3 NbS 2 challenges the existing single-particle framework for understanding AHEs based on one-body Berry curvature and highlights the potential of magnetically intercalated TMDs to unveil new electronic functionalities where many-body correlations play a critical role.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Discovery of Charge Order in the Transition Metal Dichalcogenide Fe x NbS 2

The Fe intercalated transition metal dichalcogenide (TMD), Fe 1/3 NbS 2 , exhibits remarkable resistance switching properties and highly tunable spin ordering phases due to magnetic defects. We conduct synchrotron x-ray scattering measurements on both underintercalated ( x = 0.32 ) and overintercalated ( x = 0.35 ) samples. We discover a new charge order phase in the overintercalated sample, where the excess Fe atoms lead to a zigzag antiferromagnetic order. The agreement between the charge and magnetic ordering temperatures, as well as their intensity relationship, suggests a strong magnetoelastic coupling as the mechanism for the charge ordering. In conclusion, our results reveal the first example of a charge order phase among the intercalated TMD family and demonstrate the ability to stabilize charge modulation by introducing electronic correlations, where the charge order is absent in bulk 2H - NbS 2 compared to other pristine TMDs.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Topological Magneto-optics in the Noncoplanar Antiferromagnet Co 1/3 ⁢NbS 2 : Imaging and Writing Chiral Magnetic Domains

Despite its tiny net magnetization, the antiferromagnetic (AFM) van der Waals material Co 1/3 ⁢NbS 2 exhibits a large transverse Hall conductivity 𝜎 𝑥⁢𝑦 even at zero applied magnetic field, which arises, as recently shown, from the topological nature of its noncoplanar “tetrahedral” AFM order. Here, this triple-𝐪 magnetic order can be regarded as the short-length-scale limit of a magnetic skyrmion lattice and has an intrinsic spin chirality. Here, we show, using optical wavelengths spanning the ultraviolet to infrared (400–1000 nm), that magnetic circular dichroism provides an incisive optical probe of the topological AFM order in Co 1/3 ⁢NbS 2 . Measurements as a continuous function of photon energy are directly compared with first-principles calculations, revealing the influence of the underlying quantum geometry on optical conductivity. Leveraging the power and flexibility of optical methods, we use scanning magnetic circular dichroism microscopy to directly image chiral AFM domains and demonstrate writing of chiral AFM domains.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1973

Far ultraviolet spectral radiance calibrations at NBS.

The range of NBS radiometric calibration services has been extended into the far ultraviolet region of the spectrum where a dc high-power hydrogen wall-stabilized arc is used as a primary standard of spectral radiance. A capability in the range from 130 to 360 nm (overlapping conventional tungsten strip lamp radiometry) is presently available with estimated uncertainties between 5 and 10%, depending upon wavelength. The status of radiometric source standards in the far ultraviolet is briefly reviewed, and the hydrogen arc and NBS calibration facility are described in detail. The use of commercially available mercury Krefft-Rossler lamps and deuterium arc lamps as transfer or secondary standards is discussed, and the spectra of these lamps calibrated with the hydrogen arc standard are presented.

Ott, W. R.↗
NASA NTRS1975

Current status and future plans for NBS radiometric source standards

The accuracy and long-term stability of currently available NBS radiometric source standards are described. Current research efforts and expected results in this area are outlined. There are over ten NBS radiometric source standards currently available or under development that are of interest for solar measurements or for remote sensing of the earth. The standards and sources are classified and described in terms of the radiometric quantities they represent -- spectral radiance, spectral irradiance and irradiance.

Kostkowski, H. J.↗
NASA NTRS1984

The NBS data management technology program

The National Bureau of Standards (NBS) Data Management Technology Program is discussed. The NBS Data Management Technology Program addresses major problems encountered during the following stages of an application's lifetime: requirements analysis and data base design, system selection and implementation, operations management and conversion. Products developed include standard software specifications, guides to best practice, standard data elements and representations, and reports documenting the experiences of other organizations as they attempt to improve the management of their computing resources. Data base Laboratory facilities are maintained for the investigation and analysis of state of the art data base technology. These facilities support collaborative testing with researchers, vendors, users, and standards developers.

Wood, H. M.↗
NASA NTRS1986

XUV radiometric standards at NBS

The far-UV and XUV detector calibration services at NBS, the properties of the detectors, and the spectrometer calibration facilities at the Synchrotron Ultraviolet Radiation Facility (SURF II) at NBS are described. The method used to calibrate the quantum efficiency of windowless photodiode detectors in the ionization chamber, and the facilities for calibrating photodiodes at various wavelengths are discussed. The cathode and anode of the windowless photodiodes and their operation are examined. Consideration is given to the calculation of spectral irradiance from SURF II; the two stations of the spectrometer facility; the large spectrometer calibration chamber; and sources of error in flux determinations for SURF II.

Ott, W. R.↗
DOE OSTI2020

Materials Data on NbS by Materials Project

NbS is Tungsten Carbide structured and crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Nb2+ is bonded to six equivalent S2- atoms to form a mixture of distorted edge, corner, and face-sharing NbS6 pentagonal pyramids. All Nb–S bond lengths are 2.54 Å. S2- is bonded to six equivalent Nb2+ atoms to form a mixture of distorted edge, corner, and face-sharing SNb6 pentagonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NbS by Materials Project

NbS is Tungsten Carbide-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Nb2+ is bonded to six equivalent S2- atoms to form a mixture of edge, corner, and face-sharing NbS6 octahedra. The corner-sharing octahedral tilt angles are 44°. All Nb–S bond lengths are 2.54 Å. S2- is bonded to six equivalent Nb2+ atoms to form a mixture of distorted edge and corner-sharing SNb6 pentagonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Triggering Anionic Redox Activity in Li 3 NbS 4 Through Cationic Disordering or Substitution

Extensive utilization of Li-ion batteries for varieties of applications necessitates ceaseless improvements of electrode materials for achieving higher energy density. Towards this goal, Li-rich layered oxides exhibiting high capacity due to cumulated cationic and anionic redox activities are under study for nearly a decade. Still, several unanswered questions remain with respect to these Li-driven anionic redox reactions in terms of the activation process and long-term consequences upon cycling. Here, the Li-rich Li 3 NbS 4 phase is focused, and synthesized as two different polymorphs, namely ordered and disordered phases. From analyses of their chemical and electrochemical properties, a crystal-electronic structure relationship is unraveled that triggers the anionic redox activity in these compounds. Moreover, through complementary theoretical calculations, the capability of cationic disorder to trigger anionic redox activity via the hybridization of cationic and non-bonding anionic energy levels is shown. This finding is further supported by the appearance of anionic redox activity by introducing the disorder through cationic substitution. Altogether, the insights derived here can help in designing new anionic redox materials with optimum performances for practical applications.

25 ENERGY STORAGE↗