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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

The Mariner Mars 1971 orbiter.

The Mariner Mars 1971 (MM '71) orbiter spacecraft, launched toward Mars in the spring of 1971, was designed to offer the first opportunity for sustained observations in the near vicinity of another planet of our solar system. The MM '71 spacecraft, like its predecessors, is fully attitude stabilized about three axes, using the sun and Canopus as references, an orientation which allows use of photovoltaic solar panels for primary power and permits two-way communication to the earth through a high-gain directional antenna. Midcourse and orbit insertion maneuvers use the sun-Canopus orientation as a reference direction for initiating commanded turns. Scientific instruments employed during Mars orbital operations are mounted on a two-degree-of-freedom platform controlled by commands from the central computer and sequencer. Science measurements to be obtained by the MM '71 spacecraft include television visual imaging, infrared radiometry, infrared spectroscopy, ultraviolet spectroscopy, S-band radio occultation, and celestial mechanics.

Scull, J. R.↗
DOE OSTI2023

Measuring Photoexcited Electron and Hole Dynamics in ZnTe and Modeling Excited State Core-Valence Effects in Transient Extreme Ultraviolet Reflection Spectroscopy

Transient extreme ultraviolet (XUV) spectroscopy is becoming a valuable tool for characterizing solar energy materials because it can separate photoexcited electron and hole dynamics with element specificity. We use surface-sensitive femtosecond XUV reflection spectroscopy to separately measure photoexcited electron, hole, and band gap dynamics of ZnTe, a promising photocathode for CO 2 reduction. We develop an ab initio theoretical framework based on density functional theory and the Bethe-Salpeter equation to robustly assign the complex transient XUV spectra to the material's electronic states. Applying this framework, we identify the relaxation pathways and quantify their time scales in photoexcited ZnTe, including subpicosecond hot electron and hole thermalization, surface carrier diffusion, ultrafast band gap renormalization, and evidence of acoustic phonon oscillations.

14 SOLAR ENERGY↗
DOE OSTI2021

Polymer thin films as universal substrates for extreme ultraviolet absorption spectroscopy of molecular transition metal complexes

Polystyrene and polyvinyl chloride thin films are explored as sample supports for extreme ultraviolet (XUV) spectroscopy of molecular transition metal complexes. Thin polymer films prepared by slip-coating are flat and smooth, and transmit much more XUV light than silicon nitride windows. Analytes can be directly cast onto the polymer surface or co-deposited within it. The M-edge XANES spectra (40–90 eV) of eight archetypal transition metal complexes (M = Mn, Fe, Co, Ni) are presented to demonstrate the versatility of this method. The films are suitable for pump/probe transient absorption spectroscopy, as shown by the excited-state spectra of Fe(bpy) 3 2+ in two different polymer supports.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Electrochemical Corrosion and Catalysis Dynamics of Tin Oxide during Water Oxidation

Metal oxide corrosion severely limits anodic electrocatalysis, particularly at high potentials in acidic environments, where degradation pathways remain poorly defined. This study establishes explicit connections between corrosion and electrocatalysis on tin oxide during water oxidation by examining the roles of lattice defects, reactive oxygen species, interfacial pH variations, and speciation of corroded tin in acid. We first demonstrate the presence of structural defects such as oxygen vacancies and substoichiometric Sn(II) species by integrating electron paramagnetic resonance spectroscopy, ultraviolet photoelectron spectroscopy, and Mott–Schottky analysis. Kohn–Sham density functional theory calculations reveal that explicit water structures thermodynamically stabilize reaction intermediates and lower reaction overpotentials. Moreover, we propose that water dissociation leads to hydrogen-bonding networks formed by H* and OH* intermediates, which may span the entire catalyst surface and decrease the interfacial pH to drive corrosion. In contrast, the electrochemical generation of reactive oxygen species is shown to play a minor role in catalyst corrosion during water oxidation using inductively coupled plasma mass spectrometry coupled with selective chemical scavengers. Square-wave voltammetry combined with rotating ring-disk electrodes is used to reveal that under open-circuit conditions, only Sn(IV) cations chemically dissolve from tin oxide, while both Sn(IV) and Sn(II) species electrochemically corrode during water oxidation. Our results unveil a dynamic and complicated interplay between corrosive and catalytic pathways on metal oxide electrocatalysts: a decrease in interfacial pH due to water oxidation exacerbates Sn(II)/Sn(IV) corrosion. Subsequently, the electrochemical corrosion of Sn(II)/Sn(IV) facilitates product formation from lattice oxygen, while the redeposition of corroded Sn(II) as Sn(IV) can enable oxygen exchange with water. By elucidating the roles of defects and interfacial chemistry, this work provides a roadmap for engineering improved electrocatalysts that balance activity and stability, a critical step toward scalable and durable energy technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Interfacial electronic states of misfit heterostructure between hexagonal ZnO and cubic NiO

The combination of materials with dissimilar symmetries can induce a large amount of stress at the interfacial layer of films, thereby promoting the appearance of novel properties in related devices. The study of the interfacial state is critical for determining the inner mechanism. In this work, the misfit heterostructure between cubic NiO films and wurtzite ZnO is investigated. A NiO film grown using molecular beam epitaxy on a ZnO substrate shows a highly (100)-oriented texture featuring three domains with a rotation angle of 30°, which is in agreement with first principles calculations. Misfit-induced dislocations and lattice distortions within the interfacial layers of the NiO film give rise to interfacial electronic states, which are different from those in bulk; these electronic states are analyzed by in situ synchrotron-based x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, x-ray absorption spectroscopy, and ex situ electron energy loss spectroscopy. Additionally, the origin of these interfacial states is discussed. This work aims to provide insights for the integration of semiconducting hexagonal ZnO with other functional materials that have a cubic symmetry. Additionally, we investigate the integration of photon and electron-based techniques to explore the interfacial states of complex interfaces, which is an important aspect of material science.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1981

Integrated material-surface analyzer

These 10 surface-analysis tests can be run without breaking vacuum: secondary-ion mass spectroscopy, ion-scattering spectroscopy, electron-stimulated desorption, residual-gas analysis, auger electron spectroscopy, x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, characteristic-electron energy-loss spectroscopy, scanning electron microscope, scanning low-energy electron probe. Quadruple mass spectrometer, used in first 4 tests, serves as electron transfer lens in last 6 tests.

Grunthaner, F. J.↗
NASA NTRS1981

Ultraviolet slit spectroscopy in the core of 30 Doradus with the International Ultraviolet Explorer

Low resolution (about 7 A) IUE observations of the core of the 30 Doradus Nebula in the Large Magellanic Cloud are presented. Data were obtained through the large entrance aperture at 11 different positions in both the long wavelength (1900-3200 A) and short wavelength (1150-2000 A) cameras. The aperture was stepped in 10-arcsec intervals, in the direction of the long axis of the aperture, effectively yielding a 2-arcmin long slit with the central object, R136, close to the center. The brightness distribution is strongly peaked at the position of R136, but it is found that the far-ultraviolet fluxes are dominated by luminous early-type stars at any position along the slit. The behavior of the ultraviolet colors along the slit implies that the core of 30 Dor lies behind a cloud of dust extending over at least 2 arcmin = 30 pc and suggests that the reddening law changes with distance from R136.

Koornneef, J.↗
DOE OSTI2020

Ultraviolet Photoemission Spectroscopy and Kelvin Probe Measurements on Metal Halide Perovskites: Advantages and Pitfalls

In this essay, a case study is presented on the electronic structure of several metal halide perovskites (MHP) using Kelvin probe (KP)-based surface photovoltage (SPV) measurements and ultraviolet photoemission spectroscopy (UPS) to demonstrate the advantages, but also the pitfalls, of using these techniques to characterize the surfaces of these materials. The first part addresses the loss of halide species from perovskite surfaces upon supragap illumination in vacuum. This has the potential to cause both a long-term alteration of the sample work function and a modification of the KP tip during SPV measurements. If undetected, this leads to a misinterpretation of the MHP surface potential. The second part illustrates the difficulties in determining the valence band maximum (VBM) of MHP surfaces with UPS and stresses the importance of taking into account the low density of states at the VBM edge. Given this circumstance, specific care must be taken to eliminate measurement artifacts in order to ascertain the presence or absence of low densities of electronic gap states above the VBM. This essay also highlights issues such as film degradation, nonequilibrium situations (e.g., SPV), and satellite emissions, which occur during photoemission spectroscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Direct evidence of low work function on SrVO 3 cathode using thermionic electron emission microscopy and high-field ultraviolet photoemission spectroscopy

Perovskite SrVO 3 has recently been proposed as a novel electron emission cathode material. Density functional theory (DFT) calculations suggest multiple low work function surfaces, and recent experimental efforts have consistently demonstrated effective work functions of ~2.7 eV for polycrystalline samples, both results suggesting, but not directly confirming, that some fraction of even lower work function surface is present. In this work, thermionic electron emission microscopy (ThEEM) and high-field ultraviolet photoemission spectroscopy (UPS) are used to study the local work function distribution and measure the work function of a partially oriented- (110)-SrVO 3 perovskite oxide cathode surface. Our results show direct evidence of low work function patches of about 2.0 eV on the cathode surface, with a corresponding onset of observable thermionic emission at 750 °C. We hypothesize that, in our ThEEM and UPS experiments, the high applied electric field suppresses the patch field effect, enabling the direct measurement of local work functions. This measured work function of 2.0 eV is comparable to the previous DFT-calculated work function values of the SrVO-terminated (110) SrVO 3 surface (2.3 eV) and SrO-terminated (100) surface (1.9 eV). The measured 2.0 eV value is also much lower than the work function for the (001) LaB 6 single crystal cathode (~2.7 eV) and comparable to the effective work function of B-type dispenser cathodes (~2.1 eV). If SrVO 3 thermionic emitters can be engineered to access domains of this low 2.0 eV work function, they have the potential to significantly improve thermionic emitter-based technologies.

36 MATERIALS SCIENCE↗
NASA NTRS1988

High-resolution detectors for imaging and spectroscopy at ultraviolet and soft X-ray wavelengths

The Multi-Anode Microchannel Arrays (MAMAs) are a family of pulse-counting imaging array detectors designed specifically for astrophysical investigations in space. The MAMAs have a number of unique performance characteristics which make them particularly suitable for imaging and spectroscopy at ultraviolet and soft X-ray wavelengths. First, they employ 'solar blind' photocathodes eliminating the 'red leak' problem associated with solid state arrays such as the CCDs. Second, they operate with zero readout noise, yielding photon-statistics limited signals. Third, they utilize a random readout technique and can determine both the location of a detected photon and also its arrival time to an accuracy of the order of 100 ns. This paper gives an overview of the construction, mode of operation, and performance characteristics of the MAMA detectors and describes the current status of the development program.

Timothy, J. G.↗
DOE OSTI2019

Pressure-induced tuning of lattice distortion in a high-entropy oxide

Abstract As a new class of multi-principal component oxides with high chemical disorder, high-entropy oxides (HEOs) have attracted much attention. The stability and tunability of their structure and properties are of great interest and importance, but remain unclear. By using in situ synchrotron radiation X-ray diffraction, Raman spectroscopy, ultraviolet–visible absorption spectroscopy, and ex situ high-resolution transmission electron microscopy, here we show the existence of lattice distortion in the crystalline (Ce 0.2 La 0.2 Pr 0.2 Sm 0.2 Y 0.2 )O 2−δ HEO according to the deviation of bond angles from the ideal values, and discover a pressure-induced continuous tuning of lattice distortion (bond angles) and band gap. As continuous bending of bond angles, pressure eventually induces breakdown of the long-range connectivity of lattice and causes amorphization. The amorphous state can be partially recovered upon decompression, forming glass–nanoceramic composite HEO. These results reveal the unexpected flexibility of the structure and properties of HEOs, which could promote the fundamental understanding and applications of HEOs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1997

XPS Study of Plasma- and Argon Ion-Sputtered Polytetrafluoroethylene

The similarity of plasma-polymerized tetrafluoroethylene (PPTFE) and the fluoropolymer film deposited by rf (radio frequency) plasma sputtering (SPTFE) of polytetrafluoroethylene (PTFE), noted earlier in the literature, has been reconfirmed. FT-IR (Fourier Transform Infrared), XPS (X ray Photoelectron Spectroscopy) and UV (ultraviolet) spectroscopy has been employed in apparently the first study to involve preparation of PPTFE and SPTFE in the same reactor and under comparable low-power plasma conditions. Most of the work concerned the use of He or Ar as sputtering gas, but some runs were also carried out with the other rare gases Ne, Kr and Xe. The C1s XPS spectra of SPTFE films displayed a relatively higher content of CF2 groups, and yielded higher F/C (fluorine / carbon) ratios, than PPTFE films, while the SPTFE films were somewhat more transparent in the UV than PPTFE. The F/C ratios for SPTFE were essentially independent of the rare gas used for sputtering. Increasing rf power from 10 to 50 W for Xe plasma-sputtering of PTFE resulted in successively lower F/C ratios (1.55 to 1.21), accompanied by sputtering of the glass reactor occurring at 40 W and above. Some limited XPS, FT-IR and UV data are presented on Ar ion-sputtered PTFE.

Golub, Morton A.↗
DOE OSTI2025

Time-resolved vacuum-ultraviolet photoelectron spectroscopy of the à 1 A u state of acetylene

Ultrafast time-resolved photoelectron spectra are reported for the vacuum-ultraviolet (VUV) photoionization of acetylene following excitation to the à 1 A u state via UV absorption at 200 nm. The excitation energy lies above the lowest dissociation threshold to C 2 H X̃ 2 Σ + + H, as well as above the threshold for adiabatic dissociation of the à 1 A u state to form C 2 H (à 2 Π) + H. The time-dependent mass spectra and photoelectron spectra provide insight into the intramolecular decay processes of the à 1 A u state. In addition, photoelectron spectra of the à 1 A u state with VUV light access both the X̃ 2 Π u and à 2 Σ g + states of the ion, as well as the predicted, but previously unobserved, 1 2 Π g state, which corresponds to a two-hole, one-particle configuration that lies in close proximity to the à 2 Σ g + state. The 1 2 Π g state is split into 2 A 2 + 2 B 2 and 2 A g + 2 B g states in the cis and trans configurations, respectively. In conclusion, electronic structure calculations, along with trajectory calculations, reproduce the principal features of the experimental data and confirm the assignment of the 1 2 Π g state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1986

High-resolution pulse-counting array detectors for imaging and spectroscopy at ultraviolet wavelengths

The performance characteristics of multianode microchannel array (MAMA) detector systems which have formats as large as 256 x 1024 pixels and which have application to imaging and spectroscopy at UV wavelengths are evaluated. Sealed and open-structure MAMA detector tubes with opaque CsI photocathodes can determine the arrival time of the detected photon to an accuracy of 100 ns or better. Very large format MAMA detectors with CsI and Cs2Te photocathodes and active areas of 52 x 52 mm (2048 x 2048 pixels) will be used as the UV solar blind detectors for the NASA STIS.

Timothy, J. Gethyn↗
NASA NTRS1985

Electron temperature and average density in spherical laser-produced plasmas - Ultraviolet plasma spectroscopy

The average values of the electron temperature Te and the electron density Ne in the corona plasmas of spherically irradiated high-Z targets have been estimated. Targets composed of the elements Cu through Br, Rb, and Mo were irradiated using the fundamental (1.06 microns) and the frequency-tripled (351 nm) output of the Omega laser system. Spectra were recorded in the wavelength region 15-200 A. Using various extreme ultraviolet spectroscopic techniques, it is found that for the case of a Mo plasma produced by frequency-tripled laser irradiation, Te = 2600 + or - 600 eV and Ne is greater than 6 x 10 to the 20th/cu cm. This is consistent with a 'flux limit' smaller than 0.1. The estimated values of Te and Ne are lower in the corona plasmas produced using the fundamental (1.06 micron) irradiation.

Goldsmith, S.↗
NASA NTRS1994

Geometry and physical conditions in the stellar wind of AG Carinae

AG Carinae is one of the prototypes of the class of Luminous Blue Variables (LBVs). Since 1990 the star has continuously brightened in its visual continuum. We report on a multi-instrument and -wavelength observing campaign to monitor the current activity phase of AG Car. Ground-based photometry, polarimetry, spectroscopy, and space-ultraviolet spectroscopy and spectropolarimetry have been obtained. From the variability of the polarization at ultraviolet and optical wavelengths we detect significant intrinsic polarization. P(sub int) greater than or equal to 0.5% is a large value for a hot, luminous star, suggesting departure from spherical symmetry in the wind of AG Car. The intrinsic polarization is variable on a timescale of 2 months or less. The measured ultraviolet polarization (intrinsic + interstellar) dropped to 0.5% in 1992 May and returned to 1% in 1992 July. The results are interpreted in terms of a variable outflow with a density enhancement in the equatorial plane. A similar model was suggested for the related object R127 in the Large Magellanic Cloud (LMC). This geometry is reminiscent of the large-scale morphology of the gas nebula and dust 'jet' surrounding AG Car. It is therefore likely that physical conditions close to the stellar surface are responsible for the geometry of the spatially resolved circumstellar material around AG Car. Despite the drastic change of the photospheric conditions, the mass-loss rate did not increase. We find no evidence for a positive correlation between wind density and stellar radius. This makes models that explain the radius increase by opacity effects in the outflow unlikely. The mechanism responsible for the temperature and radius variations is still unknown but most likely has its origin in subphotospheric regions.

Leitherer, Claus↗