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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 163 records · Page 9
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NASA NTRS1977

Auger spectroscopic examination of MgF2-coated Al mirrors before and after UV irradiation

Magnesium fluoride protected Al films were studied since these mirrors are commonly used in astronomical instruments whenever a highly reflecting optical surface is required in the wavelength region from 1100 A to 2000 A. Freshly prepared samples of evaporated Al + 250-A thick MgF2 on glass were analyzed by Auger electron spectroscopy in conjunction with surface erosion by Ar(+) ion bombardment before and after UV irradiation. The analysis showed that a very thin layer of surface contamination and not bulk photolysis in the MgF2 film was reponsible for the irradiation-induced reflectance loss. Postirradiation polishing with a mild calcium carbonate abrasive can restore a mirror's reflectance by removing the photolyzed surface film without disturbing the MgF2 layer.

Heaney, J. B.↗
NASA NTRS1977

The adsorption and early stages of condensation of Ag and Au on W single-crystal surfaces

Silver and gold were evaporated up to several monolayers in thickness onto W single-crystal surfaces of the 110 and 100 plane types in the temperature range between 300 and 1300 K. The mode of growth and the structure of the layers were studied by Auger electron spectroscopy and low-energy electron diffraction. The results are compared with thermal desorption spectroscopy data and work-function change measurements. They show certain similarities but also some striking differences between the two systems Ag/W and Au/W as well as a strong crystallographic anisotropy of adsorption and condensation.

Bauer, E.↗
NASA NTRS1977

The design of an Fe-12Mn-O.2Ti alloy steel for low temperature use

An investigation was made to improve the low temperature mechanical properties of Fe-8 approximately 12% Mn-O 2Ti alloy steels. A two-phase(alpha + gamma) tempering in combination with cold working or hot working was identified as an effective treatment. A potential application as a Ni-free cryogenic steel was shown for this alloy. It was also shown that an Fe-8Mn steel could be grain-refined by a purely thermal treatment because of its dislocated martensitic structure and absence of epsilon phase. A significant reduction of the ductile-brittle transition temperature was obtained in this alloy. The nature and origin of brittle fracture in Fe-Mn alloys were also investigated. Two embrittling regions were found in a cooling curve of an Fe-12Mn-O 2Ti steel which was shown to be responsible for intergranular fracture. Auger electron spectroscopy identified no segregation during solution-annealing treatment. Avoiding the embrittling zones by controlled cooling led to a high cryogenic toughness in a solution-annealed condition.

Hwang, S. K.↗
NASA NTRS1977

The search for the cause of the low albedo of the moon

The effects of different weathering processes on the albedo of the lunar surface cover is discussed. The surface chemical composition of numerous lunar soil and pulverized rock samples was determined by auger electron spectroscopy. The optical albedo of these samples was also measured. The chemical concentration of iron and titanium is greater on the surface of soil samples than it is on the surface of crushed rock samples with similar bulk composition, whereas the albedo of soil samples is lower than that of the crushed rock samples. A correlation is presented between the surface iron + titanium content and the albedo. Results of solar wind simulation experiments show that irradiation of crushed lunar rock samples with a small dose (corresponding to 3000 years of solar wind) of 2-keV energy protons changed the surface chemistry of the rock to that of the soil. A much larger dose of protons (corresponding to 30,000 years of solar wind) was needed to darken crushed rock to the albedo of the soil of similar bulk chemical composition. The mechanism of darkening by solar wind is discussed, and its effectiveness is compared to that of other darkening processes.

Gold, T.↗
NASA NTRS1978

The co-adsorption of copper and oxygen on a tungsten 100 plane-type surface

The coadsorption of Cu on O2 and a W 100 plane-type surface is studied by Auger electron spectroscopy, thermal desorption, low energy electron diffraction and by work function change measurements. It is shown that the presence of Cu on the surface initially decreases the sticking coefficient of O2. For longer oxygen exposures and for higher adsorption temperatures, the coverage of preadsorbed oxygen reaches values larger than those on the clean surface for the same O2 exposure. Except at the highest values and temperatures of the coverage of preadsorbed oxygen, the sticking coefficient for copper is unity and is independent of the oxygen coverage in the range studied. Coadsorption at room temperatures does not produce any long range order while coadsorption at elevated temperature leads to ordered structures. The saturation coverage of the two dimensional coadsorbate at 800 K is given by a relation. The work function is a complicated function of the coverage of preadsorbed oxygen and the coverage of preadsorbed Cu and is determined predominantly by the temperature at which oxygen is adsorbed. At high temperatures the sequence of adsorption has no influence, in contrast to the room temperature behavior.

Bauer, E.↗
NASA NTRS1978

Research on lunar materials

Abstracts of 14 research reports relating to investigations of lunar samples are presented. The principal topics covered include: (1) optical properties of surface and core samples; (2) chemical composition of the surface layers of lunar grains: Auger electron spectroscopy of lunar soil and ground rock samples; (3) high frequency electrical properties of lunar soil and rock samples and their relevance for the interpretation of lunar radar observations; (4) the electrostatic dust transport process; (5) secondary electron emission characteristics of lunar soil samples and their relevance to the dust transportation process; (6) grain size distribution in surface soil and core samples; and (7) the optical and chemical effects of simulated solar wind (2keV proton and a particle radiation) on lunar material.

Gold, T.↗
NASA NTRS1979

Study program to develop and evaluate die and container materials for the growth of silicon ribbons

The development and evaluation of proprietary coatings of pure silicon carbide, silicon nitride, and aluminum nitride on less pure hot pressed substrates of the respective ceramic materials, is described. Silicon sessile drop experiments were performed on coated test specimens under controlled oxygen partial pressure. Prior to testing, X-ray diffraction and SEM characterization was performed. The reaction interfaces were characterized after testing with optical and scanning electron microscopy and Auger electron spectroscopy. Increasing the oxygen partial pressure was found to increase the molten silicon contact angle, apparently because adsorbed oxygen lowers the solid-vapor interfacial free energy. It was also found that adsorbed oxygen increased the degree of attack of molten silicon upon the chemical vapor deposited coatings. Cost projections show that reasonably priced, coated, molten silicon resistant refractory material shapes are obtainable.

Addington, L. A.↗
NASA NTRS1981

Surface chemistry and friction behavior of the silicon carbide (0001) surface at temperatures to 1500 deg C

X-ray photoelectron and Auger electron spectroscopy analyses and friction studies were conducted with a silicon carbide (0001) surface in contact with iron at various temperatures to 1200 or 1500 C in a vacuum of 10 to the minus 8th power Pa. The results indicate that there is a significant temperature influence on both the surface chemistry and friction properties of silicon carbide. The principal contaminant of adsorbed amorphous carbon on the silicon carbide surface in the as received state is removed by simply heating to 400 C. Above 400 C, graphite and carbide type carbine are the primary species on the silicon carbide surface, in addition to silicon. The coefficients of friction of polycrystalline iron sliding against a single crystal silicon carbide (0001) surface were high at temperatures to 800 C. Similar coefficients of friction were obtained at room temperature after the silicon carbide was preheated at various temperatures up 800 C. When the friction experiments were conducted above 800 C or when the specimens were preheated to above 800 C, the coefficients of friction were dramatically lower. At 800 C the silicon and carbide type carbon are at a maximum intensity in the XPS spectra. With increasing temperature above 800 C, the concentration of the graphite increases rapidly on the surface, whereas those of the carbide type carbon and silicon decrease rapidly.

Miyoshi, K.↗
NASA NTRS1981

Development of lead salt semiconductor lasers for the 9-17 micron spectral region

Improved diode lasers of Pb sub 1-x Sn sub x Se operating in the 9-17 micrometers spectral region were developed. The performance characteristics of the best lasers exceeded the contract goals of 500 microW/mode at T 30K in the 9-12 micrometers region and 200 microW/mode at T 18K in the 16-17 micrometers region. Increased reliability and device yields resulted from processing improvements which evolved from a series of diagnostic studies. By means of Auger electron spectroscopy, laser shelf storage degradation was shown to be characterized by the presence of In metal on the semiconductor crystal surfaces. Studies of various metal barrier layers between the crystals and the In metal led to the development of an improved metallurgical contacting technology which has resulted in devices with performance stability values exceeding the contract goal of a one year shelf life. Lasers cycled over 500 times between 300K and 77K were also shown to be stable. Studies on improved methods of fabricating striped geometry lasers indicated that good spectral mode characteristics resulted from lasers which stripe widths of 12 and 25 micrometers.

Linden, K. J.↗
NASA NTRS1981

Adhesion and friction of transition metals in contact with nonmetallic hard materials

Sliding friction experiments were conducted with the metals yttrium, titanium, tantalum, zirconium, vanadium, neodymium, iron, cobalt, nickel, tungsten, platinum, rhenium, ruthenium, and rhodium in sliding contact with single crystal diamond, silicon carbide, pyrolytic boron nitride, and ferrite. Auger electron spectroscopy analysis was conducted with the metals and nonmetals to determine the surface chemistry and the degree of surface cleanliness. The results of the investigation indicate the adhesion and friction of the transition metals in contact with diamond, silicon carbide, boron nitride, and ferrite are related to the relative chemical activity of the metals. The more chemically active the metal, the higher the coefficient of friction and the greater amount of transfer to the nonmetals.

Miyoshi, K.↗
NASA NTRS1981

Assessment of high temperature metallizations for I(2)L and CMOS technologies

High temperature barrier metallizations were assessed and tested for I(2)L and CMOS applications. Life tests were accelerated to 375 C in view of the -55 C to +300 C temperature range established for engine-located electronics without fuel cooling. The gold-refractory metallizations evaluated were Au-TiW-PtSi, Au-TiW/TiO2/TiW-PtSi and Au-TiW(N)-PtSi. These metallization systems were thermally annealed to at least 375 C for up to 250 hours. The critical requirement for stable diffusion barrier is the TiW grain size. Small grain (250A-500A) films were observed to be stable up to 375 C. Deposition to TiW diffusion barrier in the presence of oxygen and nitrogen also results in an effective diffusion barrier. Auger electron spectroscopy profiles of the PtSi indicates some penetration by the TiW. In the case of PtSi/TiW interface, the redistribution of oxygen further passivates the system by forming a TiO2 layer at the interface.

Christou, A.↗
NASA NTRS1981

Amorphous metallizations for high-temperature semiconductor device applications

The initial results of work on a class of semiconductor metallizations which appear to hold promise as primary metallizations and diffusion barriers for high temperature device applications are presented. These metallizations consist of sputter-deposited films of high T sub g amorphous-metal alloys which (primarily because of the absence of grain boundaries) exhibit exceptionally good corrosion-resistance and low diffusion coefficients. Amorphous films of the alloys Ni-Nb, Ni-Mo, W-Si, and Mo-Si were deposited on Si, GaAs, GaP, and various insulating substrates. The films adhere extremely well to the substrates and remain amorphous during thermal cycling to at least 500 C. Rutherford backscattering and Auger electron spectroscopy measurements indicate atomic diffussivities in the 10 to the -19th power sq cm/S range at 450 C.

Wiley, J. D.↗
NASA NTRS1981

Stuffed MO layer as a diffusion barrier in metallizations for high temperature electronics

Auger electron spectroscopy was employed to characterize the diffusion barrier properties of molybdenum in the CrSi2/Mo/Au metallization system. The barrier action of Mo was demonstrated to persist even after 2000 hours annealing time at 300 C in a nitrogen ambient. At 340 C annealing temperature, however, rapid interdiffusion was observed to have occurred between the various metal layers after only 261 hours. The presence of controlled amounts of oxygen in the Mo layer is believed to be responsible for suppressing the short circuit interdiffusion between the thin film layers. Above 340 C, its is believed that the increase in the oxygen mobility led to deterioration of its stuffing action, resulting in the rapid interdiffusion of the thin film layers along grain boundaries.

Boah, J. K.↗
NASA NTRS1980

An investigation of the kinetics for hydrogen chemisorption on iron metal surfaces

A quasi-isothermal approach was used to study the kinetics of hydrogen and hydrogen sulfide chemisorption onto iron film in an effort to understand the environmental degradation of steels. The coverage of chemisorbed hydrogen or chemisorbed sulfur was observed as a function of time for fixed conditions of substrate temperature. Auger electron spectroscopy was used to observe the sulfur and chemisorption-induced resistance change was employed to monitor hydrogen coverage. To compare the results obtained from studying the kinetics by two different techniques, the kinetics of oxygen chemisorption onto iron films was also studied. A reaction model utilized to interpret the H2/Fe2 chemisorption kinetics was applied to data from an earlier study on the desorption kinetics for H2 chemisorbed onto nicket films in the vicinity of the Curie temperature of the film. This analysis permitted a separation of the gross desorption process into individual components so that the influence of the magnetic phase transition on the rate constants could be determined.

Shanabarger, M. R.↗
NASA NTRS1982

Surface chemistry and wear behavior of single-crystal silicon carbide sliding against iron at temperatures to 1500 C in vacuum

X-ray photoelectron and Auger electron spectroscopy analyses and morphological studies of wear and metal transfer were conducted with a single-crystal silicon carbide 0001 surface in contact with iron at various temperatures to 1500 C in a vacuum of 10 to the minus 8th power pascal. The results indicate that below 800 C, carbide-carbon and silicon are primarily seen on the silicon carbide surface. Above 800 C the graphite increases rapidly with increase in temperature. The outermost surficial layer, which consists mostly of graphite and little silicon at temperatures above 1200 C is about 2 nm thick. A thicker layer, which consists of a mixture of graphite, carbide, and silicon is approximately 100 nm thick. The closer the surface sliding temperature is to 800 C, the more the metal transfer produced. Above 800 C, there was a transfer of rough, discontinuous, and thin iron debris instead of smooth, continuous and thin iron film which was observed to transfer below 800 C. Two kinds of fracture pits were observed on the silicon carbide surface: (1) a pit with a spherical asperity; and (2) multiangular shaped pits.

Miyoshi, K.↗
NASA NTRS1982

Friction wear and auger analysis of iron implanted with 1.5-MeV nitrogen ions

The effect of implantation of 1.5-MeV nitrogen ions on the friction and wear characteristics of pure iron sliding against steel was studied in a pin-on disk apparatus. An implantation dose of 5 x 10 to the 17th power ions/sq cm was used. Small reductions in initial and steady-state wear rates were observed for nitrogen-implanted iron riders as compared with unimplanted controls. Auger electron spectroscopy revealed a subsurface Gaussian nitrogen distribution with a maximum concentration of 15 at. % at a depth of 8 x 10 to the -7th m. A similar analysis within the wear scar of an implanted rider after 20 microns of wear yielded only background nitrogen concentration, thus giving no evidence for diffusion of nitrogen beyond the implanted range.

Ferrante, J.↗
NASA NTRS1982

Tribological characteristics of nitrogen (N+) implanted iron

The effect of implantation of nitrogen ions (1.5 MeV) on the friction and wear characteristics of pure ion sliding against M-50 steel (unimplanted) was studied in a pin-on-disk sliding friction apparatus. Test conditions included room temperature (25 C), a dry air atmosphere, a load of 1/2 kg (4.9 N), sliding velocities of 0.043 to 0.078 m/sec (15 to 25 rpm), a pure hydrocarbon lubricant (n-hexadecane), or a U.S.P. mineral oil and nitrogen ion implantation doses of 5x10 to the 15th power and 5x10 to the 17th power ions/sq cm. No differences in wear rates were observed in the low dose experiments. In the high dose experiments, small reductions in initial (40 percent) and steady state (20 percent) wear rates were observed for nitrogen implanted iron riders as compared with unimplanted controls. No differences in average friction coefficients were noted for either dose. Auger electron spectroscopy combined with argon ion bombardment revealed a subsurface Gaussian nitrogen distribution with a maximum concentration of 6 atomic percent at a depth of 0.8 microns. Similar analysis within the wear scar of an implanted rider after 20 microns of wear yielded only background nitrogen concentration. No inward migration of nitrogen ions was observed.

Jones, W. R.↗
NASA NTRS1982

An investigation of the kinetics of hydrogen chemisorption on iron metal surfaces

The isothermal kinetics of H2, H2S, and O2 chemisorption onto epitaxially grown (III) oriented Fe films were studied. The measurements were made using the techniques of chemisorption induced resistance change and Auger electron spectroscopy (for adsorbed sulfur and oxygen). Also the origin of the chemisorption induced resistance change for these systems and its applicability to kinetic measurements were established. The chemisorption kinetics were interpreted as dissociative chemisorption via an adsorbed molecular species. The applicable rate constants were established. In none of the studies were the rate constants observed to be coverage dependent. By comparing the temperature dependence of the rate constants with absolute rate theory, the binding energies and activation energies of all the kinetic processes were obtained for the H2/Fe system. The initial sticking coefficient was pressure dependent for both the H2/Fe and H2S/Fe systems. This results from the step between the adsorbed molecular state and the dissociated chemisorbed state being the rate limiting step for absorption at certain pressures and temperatures. Estimates were obtained for the temperature dependence of the rate constants for the O2/Fe system.

Shanabarger, M. R.↗