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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Zinc–hydrogen and zinc–iridium pairs in β-Ga 2 O 3

Zinc-doped monoclinic gallium oxide (β-Ga 2 O 3 :Zn) has semi-insulating properties that could make it a preferred material as a substrate for power devices. In this work, infrared and UV/Visible spectroscopy were used to investigate the defect properties of bulk β-Ga 2 O 3 :Zn crystals. As-grown crystals contain a single O-H stretching mode at 3486.7 cm -1 due to a neutral ZnH complex. A deuterium-annealed sample displays the corresponding O-D stretching mode at 2582.9 cm -1 , confirming the O-H assignment. A strong Ir 4+ electronic transition at 5147.6 cm -1 is also observed, along with sidebands attributed to ZnIr pairs. These sidebands show distinct differences compared with Mg-doped samples; most importantly, several peaks are attributed to Ir 4+ paired with a Zn on the tetrahedral Ga(I) site. Annealing under an oxygen atmosphere produced insulating material with a resistance above 1 TΩ.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Optimized in situ crystal growth and disordered quasi-one-dimensional magnetism in Li 2 Mn 2 ( MoO 4 ) 3

We present that the quasi-one-dimensional structure of Li 2 Mn 2 ( MoO 4 ) 3 consists of three mutually distinct chains of Li 1 - x Mn x -centered polyhedra in which Mn ostensibly adopts a J = 5 / 2 Mn 2 + configuration. In situ x-ray scattering experiments carried out as crystallites emerge from a molten oxide solution facilitate the synthesis of large single crystals. Ex situ x-ray diffraction finds no evidence of long-range Li/Mn occupancy ordering, suggesting that the structure is effectively composed of finite chains of Mn moments of statistically varying lengths. UV/visible diffuse reflectance spectroscopy measurements establish a wide 3.43(12)-eV direct charge gap consistent with the local polyhedral coordination of the nominally Mn 2 + species. The temperature T dependence of the DC magnetic susceptibility χ reveals a fluctuating moment of only 2.74 μ B ± 0.01 μ B /Mn, dramatically reduced from the 5.9 μ B /Mn expected for Mn 2 + . Meanwhile, the Weiss temperature Θ W = - 89 ± 1 K reveals antiferromagnetic fluctuations that are stymied from reaching an ordered state apparently by the chemical disorder intrinsic to the polyhedral chains. Measurements of magnetization vs field H at T ≤ 10 K are far from saturation even at H = 5 T and are strongly non-Brillouin-like, instead scaling as H / T 0.24 ( 3 ) and suggesting the presence of quantum fluctuations associated with an eventual quasi-one-dimensional, disordered magnetic phase.

1-dimensional systems↗
DOE OSTI2026

Catalytic Reaction Intermediates Revealed with Femtosecond M-edge XANES (Final Technical Report)

The major goals of this work were to measure the electronic structure of earth-abundant catalysts at key steps in their catalytic cycles using ultrafast UV/Visible, Extreme Ultraviolet, and X-ray spectroscopy. Our central idea was that by using these sophisticated probes, we could uncover hidden reaction mechanisms and provide guidance for catalyst design. A second major goal was the development of Extreme Ultraviolet (XUV) spectroscopy as an accessible, tabletop probe of transition metal electronic structure. Spectra in this 30-100 eV energy range probe 3d→3p transitions in 3d metals and 5p/4f→5d transitions in 5d metals, and share the oxidation state, spin state, and ligand field specificity of hard X-ray spectroscopy. The Vura-Weis group previously established the basic utility of this technique for measuring the excited-state cascades of transition metal chromophores, and in this grant we intended to extend its scope to catalytic intermediates.

36 MATERIALS SCIENCE↗
NASA NTRS1990

CO fundamental lines - Indicators for inhomogeneous atmospheres in cool stars

Carbon monoxide fundamental lines near 4.7 microns are employed to probe the thermal structure of the atmospheres of cool stars. A new non-LTE radiation transfer code is used to analyze high-resolution infrared CO line spectra and derive observation-based stellar atmosphere models. The main results are: (1) the CO-based models developed here deviate strongly from previously published models based on UV/visible observations; (2) varying degrees of agreement between the CO empirical models and predictions based on theoretical radiative-equilibrium atmosphere models are found; and (3) the parameter used to quantify this agreement is anticorrelated with the magnitude of chromospheric activity in the observed stars. These results suggest thermally bifurcated upper atmospheres as the standard case for cool stars.

Wiedemann, Guenter↗
NASA NTRS1991

SOHO - A high resolution solar physics mission

The present study discusses SOHO (Solar and Heliospheric Observatory), a satellite with a pointing stability of 1 arcsec that will be launched in 1995 to the L1 Lagrangian point between the sun and the earth. In situ measurements, at approximately 1 AU, are to trace the results of solar wind expansion. The SOHO mission aims are discussed: to obtain long and uninterrupted series of solar oscillation measurements either in flux or in velocity in order to sound the solar interior using high resolution in the frequency domain; to probe the upper atmosphere with high-resolution UV/EUV imager/spectrometers and UV/visible coronagraphs and photometers in order to bring new constraints on the coronal heating; and to measure in situ the solar wind flow in front of the earth and thus establish the link between the sun and the near-earth environment. The satellite and instrumentation are reviewed in relation to the specific capabilities that they offer.

Lemaire, P.↗
NASA NTRS1990

Four lunar astronomical observatories - Concepts developed in the NASA 90-day study for the Human Exploration Initiative

A number of astrophysical observatory concepts were studied under the overall direction of the NASA Astrophysics Division in support of NASA's 90-day study of the Human Exploration Initiative. The four observatory concepts described here were investigated at JPL. In three of them, interferometric techniques would be used to acquire high resolution synthetic aperture images in several different parts of the electromagnetic spectrum: in the UV/visible near infrared; the submillimeter; and the very low frequency (1 to 30 MHz region). The fourth is a gravitational wave detector which uses laser optical interferometry to measure the strains induced by the passage of a gravitational wave. The observatory concepts reflect the constraints on lunar surface science deployment anticipated for the Human Exploration Initiative in the period 2002 through 2015.

Cutts, James A.↗
NASA NTRS1993

Post-flight analyses of the crystals from the M0003-14 quartz crystal microbalance experiment

Quartz Crystal Microbalances constructed by QCM Research were flown on the leading and trailing edges of LDEF as one of the sub-experiments of M0003. Response of the crystals coated with 150 A of In2O3 was recorded during the first 424 days of the mission. A second QCM with crystals coated with 150 A of ZnS was also flown but not monitored. After the flight, the QCM's were disassembled and analyzed in The Aerospace Corporation laboratories. The samples included the crystals from the leading and trailing edge samples of both types of coatings along with the reference crystals, which were inside the QCM housing. Analyses were performed by scanning electron microscopy, energy dispersive x-ray analyses, x-ray photoelectron spectroscopy, ion microprobe mass analysis, and reflectance spectroscopy in the infrared and UV/visible regions. The crystals are contaminated predominantly with silicone compounds. The contamination is higher on the leading edge than on the trailing edge and higher on the exposed crystals than on the reference crystals.

Stuckey, W. K.↗
NASA NTRS1993

Effect of plasma ion bombardment on the reflectance of Io's trailing and leading hemispheres

The possible effect of a net difference in the ion bombardment flux to the surface of Io on the ratio of the reflectance spectra is investigated. Io's vapor-deposited surface layers are simulated by a laboratory-produced film of vapor-deposited SO2 with a small admixture (about 3 percent) of H2S and (about 0.1 percent) H2O. It is shown that the reflectance ratio in the UV/visible of the surface bombarded by keV ions to the unbombarded surface is surprisingly similar to the observed ratio of Io's trailing to leading hemispherical reflectance. The changes produced are either structural or involve products of species originally present in the sample.

Sack, N. J.↗
NASA NTRS1994

Ozone and NO2 measurements from Aberystwyth and Lerwick

Measurements of the total column of ozone and NO2 were obtained by a SAOZ UV/Visible spectrometer at Aberystwyth (52.4 deg N, 4.1 deg W) and Lerwick (60.1 deg N, 1.2 deg W) during the period March 1991 - April 1992. NO2 measurements show a marked decrease in 1992 compared with 1991, due to the effect of aerosols from Mt. Pinatubo. Ozone measurements appear to have been affected by the aerosols - comparisons with both Dobson and TOMS measurements are presented.

Bartlett, L. M.↗
NASA NTRS1995

Solid-state image sensor with focal-plane digital photon-counting pixel array

A photosensitive layer such as a-Si for a UV/visible wavelength band is provided for low light level imaging with at least a separate CMOS amplifier directly connected to each PIN photodetector diode to provide a focal-plane array of NxN pixels, and preferably a separate photon-counting CMOS circuit directly connected to each CMOS amplifier, although one row of counters may be time shared for reading out the photon flux rate of each diode in the array, together with a buffer memory for storing all rows of the NxN image frame before transfer to suitable storage. All CMOS circuitry is preferably fabricated in the same silicon layer as the PIN photodetector diode for a monolithic structure, but when the wavelength band of interest requires photosensitive material different from silicon, the focal-plane array may be fabricated separately on a different semiconductor layer bump-bonded or otherwise bonded for a virtually monolithic structure with one free terminal of each diode directly connected to the input terminal of its CMOS amplifier and digital counter for integration of the photon flux rate at each photodetector of the array.

Fossum, Eric R.↗
NASA NTRS1993

Asteroid approach covariance analysis for the Clementine mission

The Clementine mission is designed to test Strategic Defense Initiative Organization (SDIO) technology, the Brilliant Pebbles and Brilliant Eyes sensors, by mapping the moon surface and flying by the asteroid Geographos. The capability of two of the instruments available on board the spacecraft, the lidar (laser radar) and the UV/Visible camera is used in the covariance analysis to obtain the spacecraft delivery uncertainties at the asteroid. These uncertainties are due primarily to asteroid ephemeris uncertainties. On board optical navigation reduces the uncertainty in the knowledge of the spacecraft position in the direction perpendicular to the incoming asymptote to a one-sigma value of under 1 km, at the closest approach distance of 100 km. The uncertainty in the knowledge of the encounter time is about 0.1 seconds for a flyby velocity of 10.85 km/s. The magnitude of these uncertainties is due largely to Center Finding Errors (CFE). These systematic errors represent the accuracy expected in locating the center of the asteroid in the optical navigation images, in the absence of a topographic model for the asteroid. The direction of the incoming asymptote cannot be estimated accurately until minutes before the asteroid flyby, and correcting for it would require autonomous navigation. Orbit determination errors dominate over maneuver execution errors, and the final delivery accuracy attained is basically the orbit determination uncertainty before the final maneuver.

Ionasescu, Rodica↗
NASA NTRS2000

Space Environmentally Stable Polyimides and Copolyimides

Polyimides with a unique combination of properties including low color in thin films, atomic oxygen (AO), ultra-violet (UV) radiation resistance, solubility in organic solvents in the imide form, high glass transition (T(sub g)) temperatures and high thermal stability have been prepared and characterized. The polymers were prepared by reacting a novel aromatic diamine with aromatic dianhydrides in a polar aprotic solvent. The solubility of the polymers in the imide form as well as the color density of thin films were dependent upon the chemical structure of the dianhydride. Several thin films (25-50 mm thick) prepared by solution casting of amide acid or imide solutions exhibited very low color and high optical transparency (approximately 90%) as determined by UV/visible spectroscopy. The polymers exhibited T(sub g)s >200 C depending upon the structure of the dianhydride and temperatures of 5% weight loss approximately 500C in air as determined by dynamic thermogravimetric analysis. Thin films coated with silver/inconel were exposed to a high fluence of AO and 1000 equivalent solar hours of UV radiation. The effects of these exposures on optical properties were minor. These space environmentally durable polymers are potentially useful in a variety of applications on spacecraft such as thin film membranes on antennas, second-surface mirrors, thermal/optical coatings and multi-layer thermal insulation (MLI) blanket materials. The chemistry, physical and mechanical properties of the polymers as well as their responses to AO and UV exposure will be discussed.

Watson, Kent A.↗
NASA NTRS2005

Temperature-dependent optical properties of Cd(1-x),Zn(x),Te substitute material

In this study, we report cryogenic optical properties of Cd(l-x), Zn(x), Te wafers that are used as substrate seed layers in the manufacturing of HgCdTe focal-plane array detectors. These studies are motivated by the fact that the substrate optical properties influence the overall detector performance. The studies consist of measuring the substrate frequency dependent transmittance T(W) and reflectance R(W) above and below the optical band-gap in the UV/Visible and infrared frequency ranges, and with temperature variation of the sample from 5 to 300 K. Determination of the optical absorption from these measurements show that the optical absorption energy gap near 1.6 eV shows a substantial increase as the temperature is reduced from 300 to 5 K. Furthermore, we observe the presence of infrared-active optical phonons whose peak frequency shifts as the temperature of the sample is varied over the measured temperature range. The theoretical frequency dependent optical conductivity, with allowance for redistribution of spectral weight among the interband transition charge carriers, will be discussed.

Quijada, Manuel A.↗
NASA NTRS2007

Ares V an Enabling Capability for Future Space Astrophysics Missions

The potential capability offered by an Ares V launch vehicle completely changes the paradigm for future space astrophysics missions. This presentation examines some details of this capability and its impact on potential missions. A specific case study is presented: implementing a 6 to 8 meter class monolithic UV/Visible telescope at an L2 orbit. Additionally discussed is how to extend the mission life of such a telescope to 30 years or longer.

Stahl, H. Philip↗
NASA NTRS2007

Temperature Evolution in Excitonic Absorptions of Cd(0.96)Zn(0.04) Materials

We report cryogenic optical properties of Cd(0.96)Zn(0.04)Te wafers that are used as substrate seed layers in HgCdTe focal-plane array detectors. These studies are motivated by the fact that the substrate optical properties influence the overall detector performance. The studies consist of measuring the sample frequency dependent transmittance (T) and reflectance (R) above and below the optical band-gap in the UV/Visible and infrared frequency ranges, and with temperature variation of the sample from 5 to 300 K. These measurements show that the optical gap near 1.49 eV at 300 K increases to 1.62 eV at 5 K. Finally, we observe sharp absorption peaks near this gap energy at low temperatures. The close proximity of these peaks to the optical transition threshold suggests that they originate from the creation of bound electron-hole pairs or excitons. The decay of these excitonic absorptions may contribute to a photoluminescence and transient background response of these back-illuminated HgCdTe CCD detectors.

Quijada, Manuel A.↗
NASA NTRS2007

Temperature Evolution of Excitonic Absorptions in Cd(1-x)Zn(x)Te Materials

The studies consist of measuring the frequency dependent transmittance (T) and reflectance (R) above and below the optical band-gap in the UV/Visible and infrared frequency ranges for Cd(l-x),Zn(x),Te materials for x=0 and x=0.04. Measurements were also done in the temperature range from 5 to 300 K. The results show that the optical gap near 1.49 eV at 300 K increases to 1.62 eV at 5 K. Finally, we observe sharp absorption peaks near this gap energy at low temperatures. The close proximity of these peaks to the optical transition threshold suggests that they originate from the creation of bound electron-hole pairs or excitons. The decay of these excitonic absorptions may contribute to a photoluminescence and transient background response of these back-illuminated HgCdTe CCD detectors.

Quijada, Manuel A.↗
NASA NTRS2009

In-flight Performance of the Detectors on HST/Wide Field Camera 3

Wide Field Camera 3 (WFC3) is a powerful new imager recently installed on the Hubble Space Telescope during Servicing Mission 4. WFC3 covers wavelengths from the near UV (200nm) to the near infrared (out to 1.7microns), in two channels. The UV/visible (UVIS) channel utilizes two low-noise, UV-enhanced 2Kx4K CCD detectors from e2v, while the IR channel incorporates a 1Kx1K 1.7micron cutoff HgCdTe array, custom-developed for the WFC3 program by Teledyne. We report here on the performance of the detectors in-flight as observed in this summer's Servicing Mission Orbital Verification program.

Kimble, Randy↗
NASA NTRS2010

WFC3: In-Flight Performance Highlights

Wide Field Camera 3 (WFC3), a powerful new imager for the Hubble Space Telescope (HST), was successfully installed in the telescope in May 2009 during the first dramatic spacewalk of space shuttle flight STS-125, also known as HST Servicing Mission 4. This new camera offers unique observing capabilities in two channels spanning a broad wavelength range from the near ultraviolet to the near infrared (200-1000nm in the UV/Visible [UVIS] channel; 850-1700nm in the IR channel). After an initial outgassing period, WFC3 was cooled to its observing configuration in June. In the following months, a highly successful Servicing Mission Observatory Verification (SMOV4) program was executed, which has confirmed the exciting scientific potential of the instrument. Detailed performance results from the SMOV 4 program are presented in a number of papers in this session. In this paper, we highlight some top-level performance assessments (throughput, limiting magnitudes, survey speeds) for WFC3, which is now actively engaged in the execution of forefront astronomical observing programs.

Kimble, Randy A.↗