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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Materials analysis and particle probe: A compact diagnostic system for in situ analysis of plasma-facing components (invited)

The objective of the materials analysis particle probe (MAPP) in NSTX is to enable prompt and direct analysis of plasma-facing components exposed to plasma discharges. MAPP allows multiple samples to be introduced to the level of the plasma-facing surface without breaking vacuum and analyzed using X-ray photoelectron spectroscopy (XPS), ion-scattering and direct recoil spectroscopy, and thermal desorption spectroscopy (TDS) immediately following the plasma discharge. MAPP is designed to operate as a diagnostic within the {approx}12 min NSTX minimum between-shot time window to reveal fundamental plasma-surface interactions. Initial calibration demonstrates MAPP's XPS and TDS capabilities.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Contactless electroreflectance studies of surface potential barrier for N- and Ga-face epilayers grown by molecular beam epitaxy

Two series of N- and Ga-face GaN Van Hoof structures were grown by plasma-assisted molecular beam epitaxy to study the surface potential barrier by contactless electroreflectance (CER). A clear CER resonance followed by strong Franz-Keldysh oscillation of period varying with the thickness of undoped GaN layer was observed for these structures. This period was much shorter for N-polar structures that means smaller surface potential barrier in these structures than in Ga-polar structures. From the analysis of built-in electric field it was determined that the Fermi-level is located 0.27 ± 0.05 and 0.60 ± 0.05 eV below the conduction band for N- and Ga-face GaN surface, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Growth mechanism and microstructure of low defect density InN (0001) In-face thin films on Si (111) substrates

Transmission electron microscopy has been employed to analyze the direct nucleation and growth, by plasma-assisted molecular beam epitaxy, of high quality InN (0001) In-face thin films on (111) Si substrates. Critical steps of the heteroepitaxial growth process are InN nucleation at low substrate temperature under excessively high N-flux conditions and subsequent growth of the main InN epilayer at the optimum conditions, namely, substrate temperature 400–450 °C and In/N flux ratio close to 1. InN nucleation occurs in the form of a very high density of three dimensional (3D) islands, which coalesce very fast into a low surface roughness InN film. The reduced reactivity of Si at low temperature and its fast coverage by InN limit the amount of unintentional Si nitridation by the excessively high nitrogen flux and good bonding/adhesion of the InN film directly on the Si substrate is achieved. The subsequent overgrowth of the main InN epilayer, in a layer-by-layer growth mode that enhances the lateral growth of InN, reduces significantly the crystal mosaicity and the density of threading dislocations is about an order of magnitude less compared to InN films grown using an AlN/GaN intermediate nucleation/buffer layer on Si. The InN films exhibit the In-face polarity and very smooth atomically stepped surfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Elimination of columnar microstructure in N-face InAlN, lattice-matched to GaN, grown by plasma-assisted molecular beam epitaxy in the N-rich regime

The microstructure of N-face InAlN layers, lattice-matched to GaN, was investigated by scanning transmission electron microscopy and atom probe tomography. These layers were grown by plasma-assisted molecular beam epitaxy (PAMBE) in the N-rich regime. Microstructural analysis shows an absence of the lateral composition modulation that was previously observed in InAlN films grown by PAMBE. A room temperature two-dimensional electron gas (2DEG) mobility of 1100 cm{sup 2}/V s and 2DEG sheet charge density of 1.9 × 10{sup 13} cm{sup −2} was measured for N-face GaN/AlN/GaN/InAlN high-electron-mobility transistors with lattice-matched InAlN back barriers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Effects of aluminum on epitaxial graphene grown on C-face SiC

The effects of Al layers deposited on graphene grown on C-face SiC substrates are investigated before and after subsequent annealing using low energy electron diffraction (LEED), photoelectron spectroscopy, and angle resolved photoemission. As-deposited layers appear inert. Annealing at a temperature of about 400 °C initiates migration of Al through the graphene into the graphene/SiC interface. Further annealing at temperatures from 500 °C to 700 °C induces formation of an ordered compound, producing a two domain √7× √7R19° LEED pattern and significant changes in the core level spectra that suggest formation of an Al-Si-C compound. Decomposition of this compound starts after annealing at 800 °C, and at 1000 °C, Al is no longer possible to detect at the surface. On Si-face graphene, deposited Al layers did not form such an Al-Si-C compound, and Al was still detectable after annealing above 1000 °C.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

A liquid metal dropper for experiments on the wettability of liquid metals on plasma facing components

A liquid metal dropper has been developed as a part of the Ion-Gas-Neutral Interactions with Surfaces 2 (IGNIS-2) facility at The Pennsylvania State University. The dropper has the capability of directly applying drops to candidate plasma facing materials for nuclear fusion reactors to enable measurements of their liquid metal wetting properties. The results presented here are specific to the use of lithium in the dropper. This paper discusses the design choices of the liquid metal dropper and its chamber, including the heating and temperature control and the dropper’s motorized operation. Lithium drops of masses ranging from 0.05 g up to 0.13 g, equivalent to drop diameters between 5.6 mm to 1 cm, have been consistently dispensed by the dropper. A new algorithm is developed and used to automate the analysis of the contact angle between the liquid drops and substrate material for efficient analysis of video data recorded to study the wetting properties of candidate plasma-facing components.

Instruments & Instrumentation↗
DOE OSTI2026

Initial Assessment of 3D-Printed Molybdenum Lattices as a Substrate for Liquid Metal Plasma-Facing Components

Many liquid metal plasma-facing component concepts for fusion reactors require a capillary porous material to wick the liquid metal to the surface of the component. In this work, samples of 3D-printed molybdenum lattices designed to have pore sizes ranging from 100 to 1000 µm were fabricated by two different suppliers. The dimensions of the lattice structures were characterized using an optical microscope, revealing that the lattice walls were almost systematically thicker than they were designed to be and in turn the pores are all smaller than they were designed to be. In many cases the pores were completely clogged. Several spectroscopic techniques were used to characterize the chemical composition of the materials, collectively indicating the presence of a thick layer of oxygen-rich material extending more than 1 µm below the surface. Compression testing revealed significant asymmetry in the mechanical behavior depending on which direction the force was applied relative to the print direction. Lastly, lithium wetting tests of several lattice samples were performed, and a sample with ~250-µm pores was found to soak up lithium quickly after initial wetting of the surface occurred. The implications of these results for future liquid metal plasma-facing component design are discussed.

Parsons, Matthew S. [Princeton Plasma Physics Labo↗
DOE OSTI2013

THE PHOTOMETRIC AND KINEMATIC STRUCTURE OF FACE-ON DISK GALAXIES. III. KINEMATIC INCLINATIONS FROM H{alpha} VELOCITY FIELDS

Using the integral field unit DensePak on the WIYN 3.5 m telescope we have obtained H{alpha} velocity fields of 39 nearly face-on disks at echelle resolutions. High-quality, uniform kinematic data and a new modeling technique enabled us to derive accurate and precise kinematic inclinations with mean i{sub kin} = 23 Degree-Sign for 90% of these galaxies. Modeling the kinematic data as single, inclined disks in circular rotation improves upon the traditional tilted-ring method. We measure kinematic inclinations with a precision in sin i of 25% at 20 Degree-Sign and 6% at 30 Degree-Sign . Kinematic inclinations are consistent with photometric and inverse Tully-Fisher inclinations when the sample is culled of galaxies with kinematic asymmetries, for which we give two specific prescriptions. Kinematic inclinations can therefore be used in statistical ''face-on'' Tully-Fisher studies. A weighted combination of multiple, independent inclination measurements yield the most precise and accurate inclination. Combining inverse Tully-Fisher inclinations with kinematic inclinations yields joint probability inclinations with a precision in sin i of 10% at 15 Degree-Sign and 5% at 30 Degree-Sign . This level of precision makes accurate mass decompositions of galaxies possible even at low inclination. We find scaling relations between rotation speed and disk-scale length identical to results from more inclined samples. We also observe the trend of more steeply rising rotation curves with increased rotation speed and light concentration. This trend appears to be uncorrelated with disk surface brightness.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Helium flux effects on bubble growth and surface morphology in plasma-facing tungsten from large-scale molecular dynamics simulations

We investigate helium flux effects on helium transport and surface evolution in plasma-facing tungsten using molecular dynamics. The simulations span two orders of magnitude, from ITER-relevant levels to those more typical of simulations published to date. Simulation times of up to 2.5 µs (corresponding to actual fluences of 1.4 x 10 21 m -2 ) are achieved, revealing concerted bubble-bursting events that are responsible for significant and very sudden changes in surface morphology. The depth distribution of helium depends very strongly on helium flux: helium self-trapping becomes more probable near the surface at high flux, and a layer of near-surface bubbles forms. Helium retention prior to the onset of bubble bursting is also substantially lower at low flux than it is at high flux. Surface features at low fluence are correlated with the positions of bubbles, but at high fluence, bubbles tend to coalesce, venting to the surface at one or more locations and leaving large interconnected cavities below the surface. Ruptured bubbles may serve as pathways deeper into the material, allowing helium to bypass the layer of near-surface bubbles and fill deeper, potentially much larger, bubbles that can produce more substantial surface features. Deeper bubbles also emit prismatic dislocation loops that can fill in cavities closer to the surface. Our results suggest that nearly all molecular dynamics simulations published to date are hampered by finite-size effects, and that helium flux is a very important parameter in determining the behavior of helium in plasma-facing components.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Spectroscopic measurement of increases in hydrogen molecular rotational temperature with plasma-facing surface temperature and due to collisional-radiative processes in tokamaks

Abstract Spatially resolved rotational temperature of ground state hydrogen molecules desorbed from plasma-facing surface was measured in QUEST, LTX-β, and DIII-D tokamaks, and the increases of the rotational temperature with the surface temperature and due to collisional-radiative processes in the plasmas were evaluated. The increase due to collisional-radiative processes was calculated by solving rate equations considering electron and proton collisional excitation and deexcitation and spontaneous emission. The calculation results suggest a high sensitivity for the rotational temperature to electron and proton densities, but a negligible sensitivity to the electron, proton, and surface temperatures. In the three tokamaks with different plasma parameters and plasma-facing surface materials, the spatial profile of the rotational temperature was estimated using Fulcher-α emission lines (600–608 nm). In QUEST, the spatial profile of the rotational temperature was estimated from spatially resolved spectra. In the other tokamaks, the rotational temperature was evaluated assuming a single point emission with a location determined from the Fulcher-α emission profile as measured with a filtered camera. In metal-walled devices QUEST and LTX-β, the rotational temperature increased with the surface temperature, and the calculated collisional-radiative increase is consistent with measured increase assuming that the rotational temperature at the surface is approximately 500–600 K higher than the surface temperature. In DIII-D with carbon walls, a larger collisional-radiative increase than the other tokamaks was observed because of the higher density leading to a large difference from the calculated increase compared to the other smaller tokamaks. Measurement of the Fulcher-α emission profile with higher spatial resolution in DIII-D may reduce the difference and reveal the effect of the surface temperature on the rotational temperature. These results show the increases in the rotational temperature with the surface temperature and due to the collisional-radiative processes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

MAPPING CLOUDS AND TERRAIN OF EARTH-LIKE PLANETS FROM PHOTOMETRIC VARIABILITY: DEMONSTRATION WITH PLANETS IN FACE-ON ORBITS

We develop an inversion technique of annual scattered light curves to sketch a two-dimensional albedo map of exoplanets in face-on orbits. As a test bed for future observations of extrasolar terrestrial planets, we apply this mapping technique to simulated light curves of a mock Earth-twin at a distance of 10 pc in a face-on circular orbit. A primary feature in recovered albedo maps traces the annual mean distribution of clouds. To extract information of other surface types, we attempt to reduce the cloud signal by taking the difference of two bands. We find that the inversion of reflectivity difference between 0.8-0.9 and 0.4-0.5 {mu}m bands roughly recovers the continental distribution, except for high latitude regions persistently covered with clouds and snow. The inversion of the reflectivity difference across the red edge (0.8-0.9 and 0.6-0.7 {mu}m) emphasizes the vegetation features near the equator. The planetary obliquity and equinox can be estimated simultaneously with the mapping under the presence of clouds. We conclude that the photometric variability of the scattered light will be a powerful means for exploring the habitat of a second Earth.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

A LACK OF RESOLVED NEAR-INFRARED POLARIZATION ACROSS THE FACE OF M51

The galaxy M51 was observed using the Mimir instrument on the Perkins Telescope to constrain the resolved H-band (1.6 {mu}m) polarization across the galaxy. These observations place an upper limit of P{sub H} < 0.05% on the H-band polarization across the face of M51, at 0.6 arcsec pixel sampling. Even with smoothing to coarser angular resolutions, to reduce polarization uncertainty, the H-band polarization remains undetected. The polarization upper limit at H band, when combined with previous resolved optical polarimetry, rules out a Serkowski-like polarization dependence on wavelength. Other polarization mechanisms cannot account for the observed polarization ratio (P{sub H}/P{sub VRI} {approx}< 0.05) across the face of M51.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Formation of graphene atop a Si adlayer on the C-face of SiC

The structure of the SiC(000$\overline{1}$) surface, the C-face of the {0001} SiC surfaces, is studied as a function of temperature and of pressure in a gaseous environment of disilane (Si 2 H 6 ). Various surface reconstructions are observed, both with and without the presence of an overlying graphene layer (which spontaneously forms at sufficiently high temperatures). Based on cross-sectional scanning transmission electron microscopy measurements, the interface structure that forms in the presence of the graphene is found to contain 1.4–1.7 monolayers (ML) of Si, a somewhat counter-intuitive result since, when the graphene forms, the system is actually under C-rich conditions. Using ab initio thermodynamics, it is demonstrated that there exists a class of Si-rich surfaces containing about 1.3 ML of Si that are stable on the surface (even under C-rich conditions) at temperatures above ~400 K. The structures that thus form consist of Si adatoms atop a Si adlayer on the C-face of SiC, with or without the presence of overlying graphene.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Face Recognition Oak Ridge (FaRO): A Framework for Distributed and Scalable Biometrics Applications

The facial biometrics community has seen a recent abundance of high-accuracy facial analytic models become freely available. Although these models' capabilities in facial detection, landmark detection, attribute analysis, and recognition are ever-increasing, they aren't always straightforward to deploy in a real-world environment. In reality, the use of the field's ever growing collection of models is becoming exceedingly difficult as library dependencies update and deprecate. Researchers often encounter headaches when attempting to utilize multiple models requiring different or conflicting software packages. Face Recognition Oak Ridge (FaRO) is an open-source project designed to provide a highly modular, flexible framework for unifying facial analytic models through a compartmentalized plug-and-play paradigm built on top of the gRPC (Google Remote Procedure Call) protocol. FaRO's server-client architecture and flexible portability allows easy construction of modularized and heterogeneous face analysis pipelines, distributed over many machines with differing hardware and software resources. This paper outlines FaRO's architecture and current capabilities, along with some experiments in model testing and distributed scaling through FaRO.

Bolme, David↗
DOE OSTI2018

A Comparison Study of the Performance of South/North Facing vs East/West-Facing Bifacial Modules under Shading Condition

Horizon obstructions can decrease the diffuse and direct light received by photovoltaic (PV) modules. In this paper, we compare the performances of the two bifacial PV system orientations: optimally tilted facing south/north (Bi S/N ), and vertically installed facing east/west (Bi E/W ) under no-shading and shading conditions. We considered multiple locations with different latitudes and weather types and observed that without any horizon obstructions, Bi S/N outperforms Bi E/W for most locations. However, certain types of obstructions cause Bi E/W to have higher energy yield than Bi S/N . For sunnier and lower latitude locations such as Albuquerque, NM, a very large obstruction at south causes this result. On the other hand, for higher latitude locations (e.g. Anchorage, AK), much smaller obstructions at south is enough to have higher energy yield for Bi E/W than Bi S/N . Under certain shading conditions Bi E/W produces up to 75 kWh/year more energy than Bi S/N.

14 SOLAR ENERGY↗
DOE OSTI2013

Elevated CO2 increases tree-level intrinsic water use efficiency: insights from carbon and oxygen isotope analyses in tree rings across three forest FACE sites

Elevated CO2 increases intrinsic water use efficiency (WUEi) of forests, but the magnitude of this effect and its interaction with climate is still poorly understood. We combined tree ring analysis with isotope measurements at three Free Air CO2 Enrichment (FACE, POP-EUROFACE, in Italy; Duke FACE in North Carolina and ORNL in Tennessee, USA) sites, to cover the entire life of the trees. We used 13C to assess carbon isotope discrimination ( 13C ci/ca) and changes in WUEi, while direct CO2 effects on stomatal conductance were explored using 18O as a proxy. Across all the sites, elevated CO2 increased 13C-derived WUEi on average by 73% for Liquidambar styraciflua, 77% for Pinus taeda and 75% for Populus sp., but through different ecophysiological mechanisms. Our findings provide a robust means of predicting WUEi responses from a variety of tree species exposed to variable environmental conditions over time, and species-specific relationships that can help modeling elevated CO2 and climate impacts on forest productivity, carbon and water balances.

Battipaglia, Giovanna↗
DOE OSTI2012

Effect of target-substrate distance on properties of flexible InZnSnO films grown by linear facing target sputtering

The authors have investigated the effect of target-to-substrate distance (TSD) on the electrical, optical, and structural properties of flexible InZnSnO (IZTO) films grown on polyethylene terephthalate substrates using linear facing target sputtering (LFTS) at room temperature. The electrical and optical properties of IZTO film grown by LFTS were significantly influenced by TSD while the structural and surface properties of IZTO film were not affected by TSD, unlike conventional magnetron sputtering. Regardless of TSD, all IZTO film showed completely amorphous structure with very low root mean square roughness of 0.33 nm, due to the low kinetic energy of sputtered IZTO atoms and a substrate position that did not directly face the targets. Based on the figure of merit value, the optimized TSD for deposition of flexible IZTO films is 2.5 cm. At optimized conditions, the IZTO film showed a sheet resistance of 23.1 {Omega}/sq and an optical transmittance of 80%.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Applying an Oriented Divergence Theorem to Swept Face Remap

Here we present a novel oriented divergence theorem and apply the results to a swept face remap method (conservative data transfer between two meshes) in arbitrary Langrangian–Eulerian hydrodynamics. In our setting, we compute the material flux along swept regions between corresponding faces in the source and target meshes. Since the swept region may add material, subtract material, or do both when it intersects itself, we cannot apply the conventional divergence theorem without accounting for orientation and self-overlaps. In this work, we encode the swept region orientation and geometry with a map from the unit n -dimensional cube, and then apply an oriented analog of divergence theorem to compute the material flux. We present efficient implementation strategies for the presented method. We also provide numerical evidence supporting our results and discuss extensions to more general mesh topologies.

97 MATHEMATICS AND COMPUTING↗