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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Magnetic order of tetragonal CuO ultrathin films

Here, we present a detailed low-energy muon spin rotation and x-ray magnetic circular dichroism (XMCD) investigation of the magnetic structure in ultrathin tetragonal (T)-CuO films. The measured muon-spin polarization decay indicates an antiferromagnetic (AFM) order with a transition temperature higher than 200 K. The XMCD signal obtained around the CuL 2,3 edges indicates the presence of pinned Cu 2+ moments that are parallel to the sample surface, and additionally, isotropic paramagnetic moments. The pinning of some of the Cu moments is caused by an AFM ordering consisting of moments that lie most likely in plane of the film. Moreover, pinned moments show a larger orbital magnetic moment contribution with an approximate ratio of m orb /m spin =1.5, indicating that these spins are located at sites with reduced symmetry. Some fractions of the pinned moments remain pinned from an AFM background even at 360 K, indicating that T N >360K. We propose a simple model that explains these experimental findings, showing that the magnetic order of the T-CuO ultrathin films differs from the theoretical predictions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Momentum dependence of the superconducting gap and in-gap states in MgB 2 multiband superconductor

We use tunable laser-based angle-resolved photoemission spectroscopy to study the electronic structure of the multiband superconductor MgB 2 . These results form the baseline for detailed studies of superconductivity in multiband systems. We find that the magnitude of the superconducting gap on both σ bands follows a BCS-like variation with temperature with Δ 0 ~ 7meV. Furthermore, the value of the gap is isotropic within experimental uncertainty and in agreement with a pure s-wave pairing symmetry. We observe in-gap states confined to k F of the σ band that occur at some locations of the sample surface. As a result, the energy of this excitation, ~ 3 meV, was found to be somewhat larger than the previously reported gap on π Fermi sheet and therefore we cannot exclude the possibility of interband scattering as its origin.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Electronic structure of the topological superconductor candidate Au 2 Pb

Here, we use magnetization measurements, high-resolution angle-resolved photoemission spectroscopy (ARPES), and density functional theory (DFT) calculations to study the electronic properties of Au 2 Pb, a topological superconductor candidate. The magnetization measurements reveal three discontinuities at 40, 51, and 99 K that agree well with reported structural phase transitions. To measure the band structure along desired crystal orientations, we utilized polishing, sputtering, and annealing to obtain clean flat sample surfaces. ARPES measurements of the Au 2 Pb (111) surface at 110 K shows a shallow hole pocket at the center and flower-petal-like surface states at the corners of the Brillouin zone. These observations match the results of DFT calculations relatively well. The flower-petal-like surface states appear to originate from a Dirac-like dispersion close to the zone corner. For the Au 2 Pb (001) surface at 150 K, ARPES reveals at least one electron pocket between the Γ and M points, consistent with the DFT calculations. Lastly, our results provide evidence for the possible existence of a Dirac state in this material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Enabling Re-executable Workflows with Near-realtime Visualization, Provenance Capture and Advanced Querying for Mass Spectrometry Data

Mass spectrometry imaging (MSI) enables simultaneous spatially-resolved analysis of numerous ionizable molecules on a sample surface. The current analysis pipeline involves analyzing the data coming off the instrument using a tool called MSI Quickview and saving the results onto a storage drive before moving on to the next experiment. While this works well for single datasets, there is a demand for more scalable, flexible workflows that are re-executable across datasets, support extensive querying and ease collaboration. Here, we present a workflow that moves data analysis from a mere desktop application for single experiments to a more general capability

Re-executable workflow↗
DOE OSTI2025

The development and application of the stirred‐reactor coupon analysis (SRCA) test method

A new technique, termed the stirred‐reactor coupon analysis (SRCA) method, has been developed to measure the rate of glass dissolution in forward‐rate conditions. Monolithic glass coupons are partially masked with an inert material before placement in a large volume of well‐mixed solution with known chemistry and temperature for a predetermined duration. After the test, the mask is removed, and the difference in step height between the protected area and the exposed corroded portions of the sample coupon is measured to determine the extent of glass dissolution. The step height is converted to a rate measurement using the test duration and glass density. Test parameters such as sample surface preparation and test duration were evaluated to determine their effects on the measured rates. Additionally, results from an interlaboratory study (ILS) consisting of 12 laboratories from 11 different institutions are presented, where each laboratory performed 12 independent tests. When removing experimental outlier data, the 95% reproducibility limits for the SRCA method has no statistical difference with previously published standardized test methods used to determine the forward rate of glass dissolution. Overall, this paper describes steps necessary to perform the test method and provides the statistical calculations to evaluate test accuracy.

chemical durability↗
DOE OSTI2017

Microbial contamination and good manufacturing practices in school kitchen

Abstract This study evaluated microbial contamination and good manufacturing practices (GMP) in school kitchens. Thus, the kitchen of four municipal schools have been assessed through microbiological analysis performed in their cutting boards ( n = 12), kitchen sinks ( n = 12), dish cloths ( n = 12), hands of food handlers ( n = 22), kitchen sponges ( n = 12), milk ( n = 10), and water ( n = 10). A questionnaire was also applied to food handlers in order to access their profiles and get to know their daily practices inside school kitchens. The results this study showed that all samples (surfaces, cutting boards, kitchen sponges, milk, and water) were contaminated with heterotrophic bacteria. Staphylococcus aureus was found on the surface of sinks, dish cloths, cutting boards, and on the hands of food handlers. Fecal coliforms were found on sinks, water, and milk. Results from the survey reveal that food handlers know about GMP, but they do not perform these activities in school kitchens. Practical applications The presented study shows that the schools there are failures in good manufacturing practices (GMP), which increase the risks of food contamination. In addition, we also showed microbial contamination on surface, cutting boards, kitchen sponges, and in food (milk and water) on schools which it make a risk for the development of foodborne diseases, since children have a relatively lower immunity than adults, additional safety measures are needed to protect them from foodborne pathogens and high microbial contamination in school. The microbial contamination in schools show that although the food handlers know about GMP, but there is a necessity for correct surface cleaning in food preparation to avoid foodborne illnesses proliferation in schools

Rossi, Eliandra Mirlei↗
DOE OSTI2022

In-plasma photo-assisted etching of Si with chlorine aided by an external vacuum ultraviolet source

Photo-assisted etching of p-type Si was previously found to occur in a chlorine-containing, Faraday-shielded, inductively coupled plasma (ICP), and this was attributed to the vacuum ultraviolet (VUV) light generated by the plasma. Other causes for the very high etching rates were ruled out, including ion bombardment. In the present study, the substrate in the main Cl2/Ar ICP was subjected to extra VUV light that was generated in an independently controlled, auxiliary Ar/He ICP in tandem with the main ICP. The ICPs were separated by a tungsten mesh and a bundle of high-aspect-ratio quartz tubes in a honeycomb configuration. There was no measurable perturbation of the main plasma by the auxiliary plasma. The etching rate was found to be enhanced by 11%–51% with the additional VUV light provided by the auxiliary ICP. With absolute measurements of the auxiliary ICP photon flux at the sample surface, as described elsewhere, incredibly large etching yields of 90–240 Si atoms per photon were obtained. It is argued that etching is not a result of electron–hole pair formation but is instead ascribed to a photocatalytic chain reaction.

42 ENGINEERING↗
DOE OSTI2018

Electronic structures and unusually robust bandgap in an ultrahigh-mobility layered oxide semiconductor, Bi 2 O 2 Se

Semiconductors are essential materials that affect our everyday life in the modern world. Two-dimensional semiconductors with high mobility and moderate bandgap are particularly attractive today because of their potential application in fast, low-power, and ultrasmall/thin electronic devices. We investigate the electronic structures of a new layered air-stable oxide semiconductor, Bi 2 O 2 Se, with ultrahigh mobility (~2.8 × 10 5 cm 2 /V∙s at 2.0 K) and moderate bandgap (~0.8 eV). Combining angle-resolved photoemission spectroscopy and scanning tunneling microscopy, we mapped out the complete band structures of Bi 2 O 2 Se with key parameters (for example, effective mass, Fermi velocity, and bandgap). The unusual spatial uniformity of the bandgap without undesired in-gap states on the sample surface with up to ~50% defects makes Bi 2 O 2 Se an ideal semiconductor for future electronic applications. In addition, the structural compatibility between Bi 2 O 2 Se and interesting perovskite oxides (for example, cuprate high–transition temperature superconductors and commonly used substrate material SrTiO 3 ) further makes heterostructures between Bi 2 O 2 Se and these oxides possible platforms for realizing novel physical phenomena, such as topological superconductivity, Josephson junction field-effect transistor, new superconducting optoelectronics, and novel lasers.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Channeling of Neutrons in the Potential Well of a Planar Waveguide

The channeling of neutrons in a three-layer planar waveguide with a neutron-optical potential well is studied. Neutrons incident on a sample surface, which propagate in a middle layer and escape from the waveguide end in the form of a narrow divergent beam, are detected. The decay parameter of a neutron wave inside the waveguide is measured as a function of the potential well depth. Experimental results are compared with a theory.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Modification of Graphene on a Copper Grid during Femtosecond Laser Irradiation: Electron Diffraction and Raman Spectroscopy Studies

The modification of a graphene sheet, which was fabricated by chemical vapor deposition on a close-meshed copper grid, during powerful femtosecond laser irradiation is studied. The process of long-term irradiation of a sample in vacuum is found to be accompanied by (1) breaking carbon bonds, which is indicated by a decrease in the intensities of the reflections corresponding to electron-beam diffraction by graphene and (2) the formation of new products, which is indicated by the appearance of new diffraction rings and a change in the Raman spectrum of the sample. The compositions of the forming chemical compounds are analyzed. Copper oxides Cu{sub 2}O and CuO are shown to form predominantly on the sample surface as a result of the chemical reactions induced by powerful femtosecond laser pulses.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Damage formation in Si under irradiation with PF{sub n}{sup +} ions of different energies

The generation of structural damage in silicon irradiated with atomic (P{sup +}) and molecular (PF{sub 4}{sup +}) ions is experimentally studied in a wide range of ion energies. A strong molecular effect caused by the over-lapping of collision cascades created by atoms comprising a molecular ion is revealed near the sample surface in all cases considered. Theoretical assessments of the depths of possible nonlinear process have shown good agreement with experimental data. Calculations have also shown that the role of nonlinear energy spikes decreases with an increase in the energy of the ion.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Laterally localizing potential as a tool for controlling the electron spin relaxation time in GaAs quantum wells

The coherent spin dynamics of electrons localized in a plane of GaAs quantum wells is studied experimentally by the application of an electrically controlled potential. The localizing potential is produced with the use of a metal gate with submicrometer windows deposited onto the sample surface. The photoinduced spin Kerr effect is used to study the electron spin lifetime as a function of the temperature, applied bias, and magnetic field for gates with different sets of windows. It is shown that, with an electrically controlled laterally localizing potential, it is possible to gradually change the electron spin lifetime from several hundreds of picoseconds to several tens of nanoseconds. The dependence of the electron spin relaxation time on the sizes of the lateral localization region is in good qualitative agreement with theoretical prediction.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Formation of a memristor matrix based on titanium oxide and investigation by probe-nanotechnology methods

The results of investigation of a memristor-matrix model on the basis of titanium-oxide nanoscale structures (ONSs) fabricated by methods of focused ion beams and atomic-force microscopy (AFM) are presented. The effect of the intensity of interaction between the AFM probe and the sample surface on the memristor effect in the titanium ONS is shown. The memristor effect in the titanium ONS is investigated by an AFM in the mode of spreading-resistance map. The possibility of the recording and erasure of information in the submicron cells is shown on the basis of using the memristor effect in the titanium ONS, which is most promising for developing the technological processes of the formation of resistive operation memory cells.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Conditions of Electrochemical Etching on the Morphological, Structural, and Optical Properties of Porous Gallium Arsenide

The properties of porous GaAs samples produced by the electrochemical etching of single-crystal n-GaAs(100) wafers are studied by X-ray diffraction analysis, electron microscopy, and infrared and ultraviolet spectroscopy. It is possible to show that, by choosing the composition of the electrolyte and the conditions of etching, samples can be produced not only with different degrees of porosity and pore sizes (nanopores/micropores), but with another type of sample surface as well. The etching of n-GaAs(100) wafers under the conditions chosen in the study does not change the orientation of the porous layer with respect to the orientation of the single-crystal GaAs(100) substrate. At the same time, etching induces a decrease in the half-width of the diffraction peak compared to that for the initial wafer, a splitting of the phonon mode in the infrared spectra and a partial shift of the components in accordance with the parameters of anodic etching, and a change in the optical properties in the ultraviolet region.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Hyperfine Interaction and Shockley–Read–Hall Recombination in Semiconductors

Experimental and theoretical studies on optical orientation and spin-dependent recombination in a semiconductor in a magnetic field under the normal incidence of circularly polarized radiation onto the sample surface are reviewed. The experiments were carried out on GaAs{sub 1 –x}N{sub x} solid solutions, in which Ga{sup 2+} interstitial displacement defects play the role of deep paramagnetic centers responsible for spin-dependent recombination. It is established that, in the investigated materials, the hyperfine interaction of a localized electron with one nucleus of the paramagnetic center remains strong even at room temperature. The theory is compared with an experiment conducted in the steady-state excitation mode and under two-pulse pump-probe conditions. An analytical formula for spin beats in a magnetic field is derived.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Delayed demagnetization jumps in (NdDy)(FeCo)B magnets in a steady-state magnetic field

Spontaneous demagnetization jumps are observed in sintered magnets (Nd{sub 0.6}Dy{sub 0.4}){sub 16}(Fe{sub 0.77}Co{sub 0.23}){sub 78}B{sub 6} in a constant magnetic field after a sharp decrease in an external magnetic field from the value corresponding to the saturation to a value close to the coercive force. It is shown that the number of the magnetization jumps is proportional to their amplitudes. A low value of the autocorrelation coefficient between the jump amplitude and the time of its appearance (R < 0.1) demonstrate the stochasticity of the jumps. It is found that the spectral jump density is independent of the frequency, i.e., a white magnetic noise is observed. The distribution of the magnetic field gradient has been obtained near the sample surface that makes it possible to distinguish domains and the grain magnetization in the dependence on the direction of the texturing of the sintered magnet.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗