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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Gas chromatography: Possible application of advanced instrumentation developed for solar system exploration to space station cabin atmospheres

Gas chromatography (GC) technology was developed for flight experiments in solar system exploration. The GC is a powerful analytical technique with simple devices separating individual components from complex mixtures to make very sensitive quantitative and qualitative measurements. It monitors samples containing mixtures of fixed gases and volatile organic molecules. The GC was used on the Viking mission in support of life detection experiments and on the Pioneer Venus Large Probe to determine the composition of the venusian atmosphere. A flight GC is under development to study the progress and extent of STS astronaut denitrogenation prior to extravehicular activity. Advanced flight GC concepts and systems for future solar system exploration are also studied. Studies include miniature ionization detectors and associated control systems capable of detecting from ppb up to 100% concentration levels. Further miniaturization is investigated using photolithography and controlled chemical etching in silicon wafers. Novel concepts such as ion mobility drift spectroscopy and multiplex gas chromatography are also developed for future flight experiments. These powerful analytical concepts and associated hardware are ideal for the monitoring of cabin atmospheres containing potentially dangerous volatile compounds.

Carle, G. C.↗
NASA NTRS1985

Defect characterization of silicon dendritic web ribbons

Progress made in the study of defect characterization of silicon dendritic web ribbon is presented. Chemical etching is used combined with optical microscopy, as well as the electron beam induced current (EBIC) technique. Thermal annealing effect on carrier lifetime is examined.

Cheng, L. J.↗
NASA NTRS1986

Laser-assisted solar cell metallization processing

The status of the laser-assisted solar cell metallization processing is described. Metallo-organic silver films were spun-on by argon ion laser beam pyrolysis. The metallo-organic decomposition (MOD) film was spun-on an evaporated Ti/Pd film to produce tood adhesion. In a maskless process, the argon ion laser writes the contact pattern. The film is then built up to obtain the required conductivity using conventional silverplating process. The Ti/Pd film in the field is chemically etched using the plated silver film as the mask. The width of the contact pattern is determined by the power of the laser. Widths as thin as 20 microns were obtained using 0.66 W of laser power. Cells fabricated with the 50 micron line widths of 4 ohm-cm floating zone (Fz) silicon-produced efficiencies of 16.6% (no passivation) which were equivalent to the best cells using conventional metallization/lithography and no passivation.

Meier, D. L.↗
NASA NTRS1986

Rapid thermal processing of Czochralski silicon substrates: Defects, denuded zones, and minority carrier lifetime

Rapid thermal processing (RTP) of Czochralski (Cz) silicon substrates is discussed with its attendant effects on defects, denuded zones, and minority carrier lifetime. Preferential chemical etching and X-ray topography was used to delineate defects which were subsequently correlated with minority carrier lifetime; determined by a pulse metallo-organic decompositon (MOD) test device. The X-ray delineation of grown-in defects was enhanced by a lithium decoration procedure. Results, thus far, show excellent correlation between process-induced defects.

Rozgonyi, G. S.↗
NASA NTRS1987

A V-grooved AlGaAs/GaAs passivated PN junction

A passivated, V-grooved GaAs solar cell offers important advantages in terms of improved optical coupling, higher short circuit current, and increased tolerance to particle radiation when compared to the planar cell configuration. An AlGaAs epilayer has been deposited on a p-type GaAs epilayer grown on an n-type V-grooved GaAs surface using MOCVD. A wet chemical etching process was used to produce a V-pattern with a 7.0 micron periodicity. Reflectivity measurements substantiate the expected decrease in solar reflectance. Scanning electron microscopy techniques were used to confirm the presence of the AlGaAs layer and verify the existence of a pn junction.

Bailey, Sheila G.↗
NASA NTRS1987

Antiphase boundaries in epitaxially grown beta-SiC

When the surface of beta-SiC, grown epitaxially on (001) silicon by chemical vapor deposition, is chemically etched, boundaries appear which may be observed by optical or scanning electron microscopy. Examination by plan-view and cross-sectional transmission electron microscopy shows boundaries in the film which exhibit line or fringe contrast. Convergent beam electron diffraction has been used to show that these boundaries separate domains that are in an antiphase relationship to each other. A model is presented which discusses the formation of these domains from independent nucleation on a stepped substrate surface.

Pirouz, P.↗
NASA NTRS1987

Improved beta-SiC heteroepitaxial films using off-axis Si substrates

All beta-SiC films grown using on-axis (001) Si substrates that have been examined with transmission electron microscopy exhibit a high density of interfacial twins, stacking faults, and antiphase disorder. The antiphase boundaries can be decorated by chemical etching, sputter etching, wet oxidation, and beta-SiC growth in the presence of diborane. All traces of antiphase disorder are eliminated when the heteroepitaxial growth is carried out on vicinal (001) Si substrates that are tilted 2 deg about a 110-line axis. In addition, growth on the off-axis Si produces beta-SiC films that are significantly smoother than on-axis films. The density of stacking faults is apparently unaffected by growth on the off-axis substrates.

Powell, J. A.↗
NASA NTRS1987

A V-grooved AlGaAs/GaAs passivated pn junction

A passivated, V-grooved GaAs solar cell offers important advantages in terms of improved optical coupling, higher short-circuit current, and increased tolerance to particle radiation when compared to the planar cell configuration. An AlGaAs epilayer has been deposited on a p-type GaAs epilayer grown on an n-type V-grooved GaAs surface using MOCVD. A wet chemical etching process was used to produce a V-pattern with a 7.0-micron periodicity. Reflectivity measurements substantiate the expected decrease in solar reflectance. Scanning electron microscopy techniques were used to confirm the presence of the AlGaAs layer and verify the existence of a pn junction.

Bailey, S. G.↗
NASA NTRS1989

Roughening Surfaces Of Solar Cells

Proposed treatment involving bombardment by ions gives silicon solar cells rough surfaces and increases amount of light absorbed by cells. First step of treatment, wafer of single-crystal silicon held at temperature of 70 degree C or higher while bombarded with argon or hydrogen ions at kinetic energies between 100 and 2,000 eV. This high dose produces damaged layer on surface, consisting of outer polycrystalline sublayer and underlying sublayer containing extended defects. Bombarded wafer then etched chemically. Photovoltaic conversion efficiency increases with number of reflections at surface of silicon cell because large part of light absorbed at each reflection. Deeply textured surface provides opportunities for multiple reflections.

Singh, Ranbir↗
NASA NTRS1988

Development of optimized, graded-permeability axial groove heat pipes

Heat pipe performance can usually be improved by uniformly varying or grading wick permeability from end to end. A unique and cost effective method for grading the permeability of an axial groove heat pipe is described - selective chemical etching of the pipe casing. This method was developed and demonstrated on a proof-of-concept test article. The process improved the test article's performance by 50 percent. Further improvement is possible through the use of optimally etched grooves.

Kapolnek, Michael R.↗
NASA NTRS1989

Diffusion of Si in thin CoSi2 layers

Evidence of silicon diffusion in 100-A CoSi2 layers grown by room-temperature codeposition and annealing on Si(111) substrates was from Auger peak height ratios, which were interpreted in terms of a Si overlayer. It was found that this layer could be removed by chemical etching and reformed by subsequent annealing. By measuring the intensity of the plasmon energy loss peak associated with the CoL23 VV Auger peak, the effective thickness of the Si overlayer was measured as a function of annealing temperature, by calibrating the plasmon loss data against known overlayer thicknesses on unannealed samples. Similar results were found for samples grown both with and without the addition of a 10-A Si cap to prevent pinhole formation in the CoSi2; moreover, Si diffusion was also observed at temperatures well below the point where pinhole formation is first found, suggesting that Si diffusion does not depend on the presence of observable pinholes.

Schowengerdt, F. D.↗
NASA NTRS1990

Optical and microwave detection using Bi-Sr-Ca-Cu-O thin films

Recent progress at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) in the development of optical and microwave detectors using high temperature superconducting thin films is described. Several objectives of this work have been accomplished, including: deposition of Bi-Sr-Ca-Cu-O thin films by laser abation processing (LAP); development of thin film patterning techniques, including in situ masking, wet chemical etching and laser patterning; measurements of bolometric and non-bolometric signatures in patterned Bi-Sr-Ca-Cu-O films using optical and microwave sources, respectively; analysis and design of an optimized bolometer through computer simulation, and investigation of its use in a Fourier transform spectrometer. The focus here is primarily on results from the measurement of the bolometric and non-bolometric response.

Grabow, B. E.↗
NASA NTRS1990

Electrical characterization of chemically modified YBa2Cu3O(7-x) surfaces

Results on electrical characterization of YBa2Cu3O(7-x) thin-film surfaces treated with a Br/ethanol chemical etch are presented. Electrical measurements of YBa2Cu3O(7-x)/Au/Nb device structures fabricated using polycrystalline, post-annelaed YBa2Cu3O(7-x) films with Br-etched surfaces, show improvements of approximately one or two orders of magnitude in current densities and resistivities (resistance-area products) relative to unetched devices. The existence of supercurrents in these structures has been confirmed by observation of the ac Josephson effect, and by magnetic field and temperature studies of the critical currents. The Br-etch process has produced 10 x 10 sq micron devices with critical current densities greater than 400 A/sq cm and resistivities as low as 4 x 10 to the -7th ohm/sq cm.

Hunt, B. D.↗
NASA NTRS1990

Cosmogenic neon from individual grains of CM meteorites - Extremely long pre-compaction exposure histories or an enhanced early particle flux

This paper presents the results on cosmogenic Ne extracted from individual meteoritic grains by a laser extraction system which used, at different times, two CW lasers: an Ar-ion laser and an Nd:YAG laser, with 20 and 70 W of deliverable power, respectively. Chemical etching was used to select grains exposed to solar flare VH particles. Results show that most of the grains with solar flare VH tracks (but not those which did not exhibit such tracks) contain spallation-produed Ne in significant excess of that due to the nominal cosmic-ray exposure, providing evidence for extensive energetic particle exposure during the precompaction era.

Hohenberg, Charles M.↗
NASA NTRS1990

Revealing the microstructure of materials

The objectives are to demonstrate how the microstructure of materials may be revealed by abrasive polishing and chemical etching, and to illustrate how microstructural information is used to monitor manufacturing processes, provide in-depth inspection, and perform failure analysis. Microstructural analysis is the procedure used to reveal the internal microstructural details of a material or part by sectioning and polishing the cut surface so that it may be examined under a suitable microscope. A printed wiring board was selected as the test material because it contains both metals and nonmetals that have distinctive microstructures, and because this technique is used throughout the electronic industry as a key quality control tool. The three principle component materials in printed circuit boards are glass/epoxy laminates faced with copper foil; copper, deposited by both electroless and electrolytic plating; and tin/lead solder. Sample preparation, mounting, grinding, polishing, and examination and analysis are discussed.

Nelson, James A.↗
NASA NTRS1991

Thermal shock testing for assuring reliability of glass-sealed microelectronic packages

Tests were performed to determine if thermal shocking is destructive to glass-to-metal seal microelectronic packages and if thermal shock step stressing can compare package reliabilities. Thermal shocking was shown to be not destructive to highly reliable glass seals. Pin-pull tests used to compare the interfacial pin glass strengths showed no differences between thermal shocked and not-thermal shocked headers. A 'critical stress resistance temperature' was not exhibited by the 14 pin Dual In-line Package (DIP) headers evaluated. Headers manufactured in cryogenic nitrogen based and exothermically generated atmospheres showed differences in as-received leak rates, residual oxide depths and pin glass interfacial strengths; these were caused by the different manufacturing methods, in particular, by the chemically etched pins used by one manufacturer. Both header types passed thermal shock tests to temperature differentials of 646 C. The sensitivity of helium leak rate measurements was improved up to 70 percent by baking headers for two hours at 200 C after thermal shocking.

Thomas, Walter B., III↗
NASA NTRS1991

Process for the manufacture of seamless metal-clad fiber-reinforced organic matrix composite structures

A process for producing seamless metal-clad composite structures includes providing a hollow, metallic inner member and an outer sleeve to surround the inner member and define an inner space therebetween. A plurality of continuous reinforcing fibers is attached to the distal end of the outside diameter of the inner member, and the inner member is then introduced, distal end first, into one end of the outer sleeve. The inner member is then moved, distal end first, into the outer sleeve until the inner member is completely enveloped by the outer sleeve. A liquid matrix material is then injected into the space containing the reinforcing fibers between the inner member and the outer sleeve. Next a pressurized heat transfer medium is passed through the inner member to cure the liquid matrix material. Finally, the wall thickness of both the inner member and the outer sleeve are reduced to desired dimensions by chemical etching, which adjusts the thermal expansion coefficient of the metal-clad composite structure to a desired value.

Bluck, Raymond M.↗
NASA NTRS1991

Matrix plasticity in SiC/Ti-15-3 composite

An experimental method is described which allows for the observation of slip bands due to matrix plasticity in the SiC/Ti-15-3 composite system. A post-test heat treatment and subsequent chemical etch is employed to reveal slip bands in the titanium matrix. Composite specimens of various laminates were examined after tensile testing at room temperature. This method definitively shows that matrix plasticity has occurred in all the laminates investigated and at load/strain levels which were insufficient to cause fiber breakage.

Lerch, Bradley A.↗