Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “TiN”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Thematic mapping of likely target areas for the occurence of cassiterite in the Serra do Mocambo (GO) granitic massifs using LANDSAT 2 digital imaging

The applicability of LANDSAT/MSS images, enhanced by computer derived techniques, as essential tools in mineral research was investigated and the Serra do Mocambo granitic massif was used as illustration. Given the peculiar factors founded in this area, orbital imagery permitted the delineation of potential target areas of mineralization occurrences, associated to albitized/greisenized types. Follow up prospection for primary tin deposits in this granitic massif should be restricted to the delineated areas which are less than 5% of the total superficial area of the massif.

Almeidofilho, R.↗
NASA NTRS1984

Silicon film solar cell process

The most promising way to reduce the cost of silicon in solar cells while still maintaining performance is to utilize thin films (10 to 20 microns thick) of crystalline silicon. The method of solution growth is being employed to grow thin polycrystalline films of silicon on dissimilar substrates. The initial results indicate that, using tin as the solvent, this growth process only requires operating temperatures in the range of 800 C to 1000 C. Growth rates in the range of 0.4 to 2.0 microns per minute and grain sizes in the range of 20 to 100 microns were achieved on both quartz and coated steel substrates. Typically, an aspect ratio of two to three between the width and the Si grain thickness is seen. Uniform coverage of Si growth on quartz over a 2.5 x 2.5 cm area was observed.

Hall, R. B.↗
NASA NTRS1985

Simulation studies for surfaces and materials strength

From intermolecular force studies, it is now known that the overall non-additive contribution to the lattice enegy is positive so that analysis based on only pairwise additivity suggests a shallower intermolecular potential than the true value. Two body contributions alone are also known to be categorically unable to even qualitatively describe some configurations of molecular clusters in the gas phase or the general relaxation and reconstruction of fcc crystal surfaces. In addition, the many-body contribution was shown to play a key role in the stability of certain crystal structures. In these recent analyses, a relatively simple potential energy function (PEF), comprising only a two-body Mie-type potential plus a three-body Axilrod-Teller-type potential, was found to be extremely effective. This same parametric PEF is applied to describe the bulk stability and surface energy for the diamond cubic structure. To test the stability condition, the FCC, BCC, diamond cubic, graphite and beta-tin structures were considered.

Halicioglu, T.↗
NASA NTRS1985

Development of metallization process: FSA project, cella and module formation research area

The optimization, evaluation, and demonstration of a novel metallization applied by a screen printing process is examined. Based on previous results of High Resolution, Low Cost Solar Cell Contact Development, a paste consisting of molybdenum, tin, and titanium hydride was selected as the promising composition. No satisfactory cells were made using any of the molybdenum/tin pastes used as a complete replacement for conventional silver pastes. The major problem is the inability to form a bond between the pastes and silicon that withstands soldering.

Garcia, A., III↗
NASA NTRS1984

Experimental investigation of the effects of gravity on thermosolutal convection and compositional homogeneity in Bridgman grown, compound semiconductors

Lead-tin-telluride has been grown in a thermally stable mode (solutally unstable) and in a solutally stable (thermally unstable) mode in a Bridgman configuration. Significant differences in the crystal morphology and the compositional homogeneity have been found between the two configurations. In addition, for the solutally stable configuration, evidence has been found that the flow characteristics in the melt change drastically during the course of the run.

Crouch, R. K.↗
NASA NTRS1984

The mechanisms of formation and prevention of channel segregation during alloy solidification

Using a base chilled configuration, conditions for the formation and prevention of segregation channels are studied in the ammonium chloride-water and lead-tin systems. Such channels develop when the rejected solute is less dense than the solvent and are therefore a result of density inversion, but slow (less than 5 rpm) rates of mold rotation, about axes inclined to the vertical by 20 to 30 deg, throughout the time of solidification, effectively prevent the formation or propagation of these channels. In experiments with artificially created or blocked channels, a simultaneous solute plume in the bulk liquid must be present in order for a channel to develop. The results indicate that channels originate not within the dendritic array, but immediately ahead of the growth front as a result of perturbation from the less dense boundary layer into the bulk liquid. The effect of mold movement is to translate laterally the bulk liquid relative to the growth front so that perturbations are sheared off. The nature of the liquid movement is considered and shown to be a function of the mold dimensions.

Hellawell, A.↗
NASA NTRS1984

Thermocapillary-driven convection in supported and floating-zone crystallization

Marangoni flow was induced in a thin disk of molten tin with an atomically clean surface by heating it from below in an ultra high vacuum apparatus. The radial distribution of temperature was measured and no temperature oscillations were observed. Strong mechanical disturbances introduced at a Marangoni number of about 4300 died out quickly with time indicating that the system was stable. Mathematical models indicate that strong flows in a two cell structure exist under the conditions studied, and that the velocity profile in the cell near the surface is of the boundary layer type which varies rapidly with depth.

Gill, W. N.↗
NASA NTRS1985

Moessbauer studies on LaNi(4.7)Sn(0.3) and its hydride

Moessbauer measurements were made on LaNi(4.7)Sn(0.3) at room and liquid nitrogen temperatures. Experimental data yielded a singlet at room temperature and a doublet at liquid-nitrogen temperature. Spectra of the hydrided sample yielded a doublet at liquid-nitrogen temperature with an increase in the quadrupole splitting compared to the unhydrided spectra, but no change in the isomer shift. These data indicate that there is no significant interaction between the tin and the hydrogen. The magnetic character remained the same down to liquid-nitrogen temperature as evidenced by the Moessbauer data. X-ray diffraction measurements on the hydride showed an expanded lattice with the same structure as found for the unhydrided sample. A decrease in particle size was observed upon hydriding.

Oliver, F. W.↗
NASA NTRS1986

Filters for Submillimeter Electromagnetic Waves

New manufacturing process produces filters strong, yet have small, precise dimensions and smooth surface finish essential for dichroic filtering at submillimeter wavelengths. Many filters, each one essentially wafer containing fine metal grid made at same time. Stacked square wires plated, fused, and etched to form arrays of holes. Grid of nickel and tin held in brass ring. Wall thickness, thickness of filter (hole depth) and lateral hole dimensions all depend upon operating frequency and filter characteristics.

Berdahl, C. M.↗
NASA NTRS1985

Crystal Growth Research in Space

The objectives of this work are to develop growth techniques and theory leading to improved bulk growth of semiconductor single crystals. Ground based experiments will be complemented by experiments carried out in the low-g environment provided by the space shuttle. Analytical studies and laboratory investigations are being conducted to better define the causes of crystalline defects and inhomogeneities. The compound semiconductor lead-tin-telluride is being used as the modeling material. Theoretical techniques are being developed to predict the thermal and solutal fields which are present during bulk growth from a melt. Techniques for measuring the thermophysical properties of semiconductors at high temperatures have been developed. During the past year electrochemical etching techniques have been developed for delineation of inhomogeneous regions in crystals. Thermal diffusivity measurements have been completed for the solid and liquid phases of PbTe and PbSnTe. Preliminary results have been obtained on the effects on crystal morphology of gravity, interface shape and interaction between the melt and the container.

Crouch, R. K.↗
NASA NTRS1985

Float Zone Experiments in Space

The objective of this work has been to evaluate whether or not Marangoni flow could be suppressed in molten metals by the presence of very thin oxide films. Experimental work has been carried out on molten Sn under UHV conditions. A disk floating zone arrangement was developed to allow in situ Auger examination of molten surfaces. An electron energy loss technique was developed which allows detection of continuous tin oxide films of 6 A or greater. Experiments were planned to detect the effects of oxide formation upon Marangoni flow by measuring: (1) temperature profiles, (2) solid liquid interface shapes, (3) macrosegregation, and (4) the onset of oscillatory Marangoni flow by detecting oscillating temperature variations. Work on (4) showed that oscillatory temperature variations of frequency or = 10 Hz were not present in the disk float zone geometry under conditions of Ma = 4300 with an oxide free molten surface. The disk float zone geometry was modeled with a finite element analysis and temperature and velocity profiles were determined.

Verhoeven, J. D.↗
NASA NTRS1985

Glass breaking strength: The role of surface flaws and treatments

Although the intrinsic strength of silicon dioxide glass is of the order of 10 to the 6th power lb/sq in, the practical strength is roughly two orders of magnitude below this theoretical limit, and depends almost entirely on the surface condition of the glass, that is, the number and size of flaws and the residual surface compression (temper) in the glass. Glass parts always fail in tension when these flaws grow under sustained loading to some critical size. Research associated with glass encapsulated crystalline-Si photovoltaic (PV) modules has greatly expanded our knowledge of glass breaking strength and developed sizeable data base for commercially available glass types. A detailed design algorithm is developed for thickness sizing of rectangular glass plates subject to pressure loads. Additional studies examine the strength of glass under impact loading conditions such as that caused by hail. Although the fundamentals of glass breakage are directly applicable to thin film modules, the fracture strength of typical numerical glass must be replaced with data that reflect the high temperature tin oxide processing, laser scribing, and edge processing peculiar to thin film modules. The fundamentals of glass breakage applicable to thin film modules and preliminary fracture strength data for a variety of 1 ft square glass specimens representing preprocessed and post processed sheets from current amorphous-Si module manufacturers are presented.

Moore, D.↗
NASA NTRS1986

Method of making macrocrystalline or single crystal semiconductor material

A macrocrystalline or single crystal semiconductive material is formed from a primary substrate including a single crystal or several very large crystals of a relatively low melting material. This primary substrate is deposited on a base such as steel or ceramic, and it may be formed from such metals as zinc, cadmium, germanium, aluminum, tin, lead, copper, brass, magnesium silicide, or magnesium stannide. These materials generally have a melting point below about 1000 C and form on the base crystals the size of fingernails or greater. The primary substrate has an epitaxial relationship with a subsequently applied layer of material, and because of this epitaxial relationship, the material deposited on the primary substrate will have essentially the same crystal size as the crystals in the primary substrate. If required, successive layers are formed, each of a material which has an epitaxial relationship with the previously deposited layer, until a layer is formed which has an epitaxial relationship with the semiconductive material. This layer is referred to as the epitaxial substrate, and its crystals serve as sites for the growth of large crystals of semiconductive material. The primary substrate is passivated to remove or otherwise convert it into a stable or nonreactive state prior to deposition of the seconductive material.

Shlichta, P. J.↗
NASA NTRS1986

Development status of first Tethered Satellite System

An MOU between NASA and Italian research organizations has assigned the responsibilities for the development, payload integration, launch and operation of a Tethered Satellite System (TSS). The TSS will include a deployer mounted on a Spacelab pallet, science equipment on a customized mission support structure and a satellite connected to the Orbiter by a tether. The satellite is 1.6 m in diameter and can weight up to 500 kg. The deployer will be insulated from the Orbiter because of the conductive nature of the tether. The first mission is to demonstrate the TSS technology, perform electrodynamic investigations of the interaction of the tether with ambient space plasma, and gather data on atmospheric interactions in the lower thermosphere, geomagnetic phenomena and gravimetric characteristics. The first TSS will be deployed 20 km outward from the Orbiter and the earth on a strand of tin-coated copper wire wrapped in Teflon insulation, braided Kevlar and a Nomek jacket. The first strand is designed to accommodate 53 N tension. The satellite on the end of the tether will be a multimission platform for facile changeout of the scientific package from mission-to-mission.

Sisson, J. M.↗
NASA NTRS1986

Practical method for highly accurate large-scale surface calculations

An accurate and efficient film linearized muffin-tin orbital (FLMTO) technique for surface electronic-structure calculations is presented which uses only 60-70 basis functions, as opposed to the 300 functions used in the linear augmented plane-wave method. Calculations for three different (3d and 4d) transition-metal films resulted in high quality results for five-layer slabs of Cu(001), Fe(001), and Ru(001), in addition to good results for the work functions and projected density of states. By retaining the LMTO small basis size, computer time and memory are reduced, making practical the study of systems with a larger number of atoms in the two-dimensional unit cell.

Fernando, G. W.↗
NASA NTRS1987

Pretreatment of Platinum/Tin Oxide-Catalyst

Addition of CO to He pretreatment doubles catalytic activity. In sealed, high-energy, pulsed CO2 laser, CO and O2 form as decomposition products of CO2 in laser discharge zone. Products must be recombined, because oxygen concentration of more than few tenths of percent causes rapid deterioration of power, ending in unstable operation. Promising low-temperature catalyst for combining CO and O2 is platinum on tin oxide. New development increases activity of catalyst so less needed for recombination process.

Hess, Robert V.↗
NASA NTRS1987

The alloy undercooling experiment on the Columbia STA 61-C space shuttle mission

An Alloy Undercooling experiment was performed in an electromagnetic levitator during the Columbia STS 61-C mission in January 1986. One eutectic nickel-tin alloy specimen was partially processed before an equipment failure terminated the experiment. Examination of the specimen showed evidence of undercooling and some unusual microstructural features.

Harf, Fredric H.↗
NASA NTRS1987

Catalysts for long-life closed-cycle CO2 lasers

Long-life, closed-cycle operation of pulsed CO2 lasers requires catalytic CO-O2 recombination both to remove O2, which is formed by discharge-induced CO2 decomposition, and to regenerate CO2. Platinum metal on a tin (IV) oxide substrate (Pt/SnO2) has been found to be an effective catalyst for such recombination in the desired temperature range of 25 to 100 C. This paper presents a description of ongoing research at NASA-LaRC on Pt/SnO2 catalyzed CO-O2 recombination. Included are studies with rare-isotope gases since rare-isotope CO2 is desirable as a laser gas for enhanced atmospheric transmission. Results presented include: (1) achievement of 98% to 100% conversion of a stoichiometric mixture of CO and O2 to CO2 for 318 hours (greater than 1 x 10 to the 6th power seconds), continuous, at a catalyst temperature of 60 C, and (2) development of a technique verified in a 30-hour test, to prevent isotopic scrambling when CO-18 and O-18(2) are reacted in the presence of a common-isotope Pt/Sn O-16(2) catalyst.

Schryer, David R.↗