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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
NASA NTRS1973

Oxygen and sulfur interactions with a clean iron surface and the effect of rubbing contact on these interactions

An investigation was conducted to determine the nature of the chemical interactions of oxygen and sulfur with iron when surfaces are stationary and also during sliding in a vacuum environment. Various gases that contained sulfur, oxygen, or both were adsorbed to iron at 23 C. The gases included oxygen, hydrogen sulfide, methyl mercaptan, and sulfur dioxide. Friction experiments were conducted with a hemispherical rider sliding on a rotating disk. An Auger cylindrical mirror analyzer was used to monitor the iron surface chemistry. The results of this study indicate that oxygen will completely displace sulfide films from iron surfaces. Organic thiols containing sulfur, such as methyl mercaptan, adsorb to an iron surface dissociatively. Only sulfur is detected on the iron surface. Sliding inhibits the formation of sulfide films on iron with the adsorption of hydrogen sulfide and methyl mercaptan. With oxygen and sulfur dioxide, the sliding process does not affect adsorption behavior.

Buckley, D. H.↗
NASA NTRS1973

Airborne profiling of ice thickness using a short pulse radar

This paper describes helicopter-borne measurements of ice thickness in Lake Superior, Lake St. Clair, and the St. Clair river as part of NASA's program to develop an ice information system. The profiler described is a high resolution, nonimaging, short pulse radar, operating at a carrier frequency of 2.7 GHz. The system can resolve reflective surfaces separated by as little as 10 cm and permits measurement of the distance between resolvable surfaces with an accuracy of about 1 cm. Data samples are given for measurements both in a static (helicopter hovering), and a traverse mode. Ground truth measurements taken by an ice auger team traveling with the helicopter are compared with the remotely sensed data and the accuracy of the profiler is discussed based on these measurements.

Vickers, R. S.↗
NASA NTRS1974

Argon charge states due to impact of H+ and He+ ions

Charge states of argon produced by bombardment with 100-keV to 1-MeV H+ and He+ projectiles were studied by examining high-resolution L-shell X-ray satellite spectra. Large differences appear in charge-state populations determined from X-ray data and Auger-electron data.-

Oona, H.↗
NASA NTRS1974

The atomic nature of polymer-metal interactions in adhesion, friction and wear

The adhesion, friction, and wear behavior of the solid polymers PTFE and polyimide in contact with various metals were studied using field ion microscopy, Auger emission spectroscopy, and scanning electron microscopy. Results indicate that the polymers will transfer to a clean tungsten surface on simple tough contact, forming a chemical bond. With PTFE, it is hypothesized that the bonding is of the carbon to the metal surface, while with the polyimide, both oxygen and carbon bonding to the tungsten surface are possible. In sliding contact, the friction process itself can initiate polymer film formation. The formation of such films has been suggested as a form of extreme pressure lubrication.

Buckley, D. H.↗
NASA NTRS1975

Effect of adsorbed chlorine and oxygen on shear strength of iron and copper junctions

Static friction experiments were performed in ultrahigh vacuum at room temperature on copper, iron, and steel contacts selectively contaminated with oxygen and chlorine in submonolayer amounts. The concentration of the adsorbates was determined with Auger electron spectroscopy and was measured relative to the saturation concentration of oxygen on iron (concentration 1.0). The coefficient of static friction decreased with increasing adsorbate concentration. It was independent of the metal and the adsorbate. The results compared satisfactorily with an extension of the junction growth theory to heterogeneous interfaces. The reduction in interfacial shear strength was measured by the ratio sub a/sub m where sub a is the shear strength of the interface with an adsorbate concentration of 1.0, and sub m is the strength of the clean metal interface. This ratio was 0.835 + or - 0.012 for all the systems tested.

Wheeler, D. R.↗
NASA NTRS1975

Friction and wear of metals in contact with pyrolytic graphite

Sliding friction experiments were conducted with gold, iron, and tantalum single crystals sliding on prismatic and basal orientations of pyrolytic graphite in various environments, including vacuum, oxygen, water vapor, nitrogen, and hydrogen bromide. Surfaces were examined in the clean state and with various adsorbates present on the graphite surfaces. Auger and LEED spectroscopy, SEM, and EDXA were used to characterize the graphite surfaces. Results indicate that the prismatic and basal orientations do not contain nor do they chemisorb oxygen, water vapor, acetylene, or hydrogen bromide. All three metals exhibited higher friction on the prismatic than on the basal orientation and these metals transferred to the atomically clean prismatic orientation of pyrolytic graphite. No metal transfer to the graphite was observed in the presence of adsorbates at 760 torr. Ion bombardment of the graphite surface with nitrogen ions resulted in the adherence of nitrogen to the surface.

Buckley, D. H.↗
NASA NTRS1975

Wear and interfacial transport of material

Bonding across the interface for two solids in contact and the subsequent transfer of material from one surface to another is a direct result of the interfacial bonds being stronger than the cohesive bonds in either of the two solids. Surface tools such as LEED, Auger emission spectroscopy, field ion microscopy, and the atom probe are used to examine adhesive contacts and to determine the direction, nature, quantity of material transfer and properties of the solids which effect transfer and wear. The electronic nature, cohesive binding energies, surface structure, lattice disregistry and distribution of species in surface layers are all found to effect adhesion and transfer or transport for clean surfaces in solid state contact. The influence of adsorbed and reacted surface films from fractions of a monolayer to multilayer reactive films are considered. It is shown that even fractions of a monolayer of surface active species such as oxygen and sulfur can markedly inhibit adhesion and transport.

Buckley, D. H.↗
NASA NTRS1975

Remote profiling of lake ice using an S-band short pulse radar aboard an all-terrain vehicle

An airborne short-pulse radar system to measure ice thickness was designed. The system supported an effort to develop an all-weather Great Lakes Ice Information System to aid in extending the winter navigation season. Experimental studies into the accuracy and limitations of the system are described. A low power version was operated from an all-terrain vehicle on the Straits of Mackinac during March 1975. The vehicle allowed rapid surveying of large areas and eliminated the ambiguity in location between the radar system and the ground truth ice auger team. It was also possible to the effects of snow cover, surface melt water, pressure ridging, and ice type upon the accuracy of the system. Over 25 sites were explored which had ice thicknesses from 29 to 60 cm. The maximum radar overestimate was 9.8 percent, while the maximum underestimate was 6.6 percent. The average error of the 25 measurements was 0.1 percent.

Cooper, D. W.↗
NASA NTRS1974

Adsorption and condensation of Cu on W single-crystal surfaces

The adsorption and condensation of Cu up to several monolayers in thickness on tungsten 110 and 100 single-crystal surfaces are studied by combining low-energy electron diffraction, Auger electron spectroscopy, thermal desorption spectroscopy, work-function measurements, and quartz microbalance thickness measurements in one experimental system. The results show drastic differences in the evolution of the structure, work function, and desorption behavior between 110 and 100 surfaces. These differences are understandable in terms of the atomic roughness of the surfaces.

Bauer, E.↗
NASA NTRS1975

The surface structure of titanium and its interaction with bromine and chlorine

The surface structure and composition of titanium have been studied by electron diffraction and Auger electron spectroscopy in the temperature range 25 to 850 C. Atomically clean, well-defined Ti surfaces were obtained by a combination of argon ion sputtering and thermal treatment at 700 to 800 C. A series of surface superstructures was observed as the crystal temperature was gradually decreased. The development of the superstructures is best explained as due to surface reconstruction as a result of surface relaxation. The interaction of bromine and chlorine vapors with clean Ti surfaces was investigated in the temperature range 25 to 500 C. Bromine exposure at room temperature gave rise to an amorphous surface layer, which on annealing transformed into an epitaxial TiBr2 structure. Chlorine interaction resulted in the formation of an epitaxial TiCl3 on both cold and hot Ti surfaces. Surface impurities inhibited the chemical interaction process on the Ti surface.

Khan, I. H.↗
NASA NTRS1974

Structure and properties of solid surfaces

Difficulties in experimental studies of crystalline surfaces are related to the fact that surface atoms have an intrinsic tendency to react with their environment. A second problem is connected with the effective thickness of surfaces, which ranges from one to several atom layers. The phenomenology of surface interactions with gases are considered, taking into account physical adsorption, chemisorption, and the oxidation of surfaces. Studies of the surface structure are discussed, giving attention to field emission microscopy, field-ion microscopy, electron diffraction techniques, Auger spectroscopy, scanning electron microscopy, electron probe microanalysis, ion microprobe methods, and low-energy backscattering spectroscopy. Investigations of semiconductor surfaces are also described.

Gatos, H. C.↗
NASA NTRS1975

On the controversy about the direction of electrotransport in thin gold films

Annealed 'pure' gold films exhibit electromigration against the electron flow. In contrast, gold films deposited on a transition metal underlayer show mass flow in the same direction as the electron flow. Diffusion of the transition metal from the underlayer into the gold film, deduced from Auger analyses presented herein, is believed to be responsible for this reversal. A new experiment, utilizing an 'inverted temperature profile' gives unambiguous results on the direction of electrotransport.

Hummel, R. E.↗
NASA NTRS1974

Observation of iron-rich coating on lunar grains and a relation to low albedo

The outermost few atomic layers of lunar soil samples were studied by Auger spectroscopy and were found to contain in each case two to three times more iron than the mean bulk composition of the sample. The amount of excess iron is found to be closely correlated with the optical albedo in the manner that would be theoretically expected if the iron provided absorption centers. Crushed lunar rocks of similar mean composition, but lacking the extra iron coating of the soil grains, have a much higher albedo than most lunar soils sampled or observed on the lunar surface.

Gold, T.↗
NASA NTRS1975

Process-induced defects in terrestrial solar cells

Experimental and theoretical work on low resistivity, high efficiency solar cells indicates the dominant role that defects take in determining performance. High doping mechanisms produce gap shrinkage by band tailing, impurity band widening and impurity misfit; altered interband transmission rates result from Auger impact, SRH processes, or from electronic tunneling via defects. Characterizations of cell materials for their defects and their relations to the chosen fabrication processes are proposed.

Lindholm, F. A.↗
NASA NTRS1975

Surface structure and electronic properties of materials

A surface potential model is developed to explain dopant effects on chemical vapor deposition. Auger analysis of the interaction between allotropic forms of carbon and silicon films has shown Si-C formation for all forms by glassy carbon. LEED intensity measurements have been used to determine the mean square displacement of surface atoms of silicon single crystals, and electron loss spectroscopy has shown the effect of structure and impurities on surface states located within the band gap. A thin film of Al has been used to enhance film crystallinity at low temperature.

Siekhaus, W. J.↗
NASA NTRS1975

Enhanced crystallinity of low temperature deposited silicon films on graphite subtrates

The previously developed technique of a sandwich coating for silicon crystallinity enhancement in silicon films deposited at low temperature is applied to graphite substrates. The measured increase in silicon crystallinity is comparable to that observed earlier using a quartz substrate. The distribution of aluminum in the silicon films is determined using Auger spectroscopic depth profiling. Carbon diffusion from the substrate into the silicon film is shown to be negligible at a substrate temperature of 600 C.

Chang, C. A.↗
NASA NTRS1975

Friction differences between aliphatic and aromatic structures in lubrication of titanium

Sliding friction experiments were conducted with a titanium (0001) single crystal surface with various adsorbed aliphatic and aromatic compounds containing the same number of carbon atoms. An Auger emission spectroscopy analysis was used to monitor the presence of the organic lubricating compounds. Results of the investigation indicate that hexane and benzene give the same friction coefficients over a range of loads. At light loads the friction decreased with an increase in the halogen atom size where the halogens chlorine, bromine, and iodine are incorporated into the benzene molecular structure. The aliphatic compounds chlorohexane and bromohexane exhibited lower friction coefficients than the aromatic structures chlorobenzene and bromobenzene.

Buckley, D. H.↗