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At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

The structure of 110 tilt boundaries in large area solar silicon

The models of Hornstra and their connection to the repeating group description of grain boundaries (7-10) are discussed. A model for the Sigma = 27 boundary containing a zig-zag arrangement of dislocations is constructed and it is shown that zig-zag models can account for the contrast features observed in high resolution transmission electron micrographs of second and third order twin boundaries in silicon. The boundaries discussed are symmetric with a 110 tilt axis and a (110) boundary plane in the median lattice (the median plane). The median lattice is identical in structure and halfway in orientation between the crystal lattices either side of the boundary.

Ast, D. G.↗
NASA NTRS1983

Analysis of defect structure in silicon. Characterization of SEMIX material. Silicon sheet growth development for the large area silicon sheet task of the low-cost solar array project

Statistically significant quantitative structural imperfection measurements were made on samples from ubiquitous crystalline process (UCP) Ingot 5848 - 13C. Important correlation was obtained between defect densities, cell efficiency, and diffusion length. Grain boundary substructure displayed a strong influence on the conversion efficiency of solar cells from Semix material. Quantitative microscopy measurements gave statistically significant information compared to other microanalytical techniques. A surface preparation technique to obtain proper contrast of structural defects suitable for quantimet quantitative image analyzer (QTM) analysis was perfected and is used routinely. The relationships between hole mobility and grain boundary density was determined. Mobility was measured using the van der Pauw technique, and grain boundary density was measured using quantitative microscopy technique. Mobility was found to decrease with increasing grain boundary density.

Natesh, R.↗
NASA NTRS1983

Large-area sheet task: Advanced dendritic-web-growth development

Thermally generated stresses in the growing web crystal were reduced. These stresses, which if too high cause the ribbon to degenerate, were reduced by a factor of three, resulting in the demonstrated growth of high-quality web crystals to widths of 5.4 cm. This progress was brought about chiefly by the application of thermal models to the development of low-stress growth configurations. A new temperature model was developed which can analyze the thermal effects of much more complex lid and top shield configurations than was possible with the old lumped shield model. Growth experiments which supplied input data such as actual shield temperature and melt levels were used to verify the modeling results. Desirable modifications in the melt level-sensing circuitry were made in the new experimental web growth furnace, and this furnace has been used to carry out growth experiments under steady-state conditions. New growth configurations were tested in long growth runs at Westinghouse AESD which produced wider, lower stress and higher quality web crystals than designs previously used.

Duncan, C. S.↗
NASA NTRS1983

Large-area sheet task advanced dendritic web growth development

The thermal stress models were used to test the effect of melt level on stress generation and growth velocity. The results indicate that melt level has only small effects on stresses but significant effects on growth velocity. These results are consistent with experimental growth from measured melt levels. A new low-stress design concept is being evaluated with the models. A width-limiting version of the low-stress J460 configuration was tested experimentally with results consistent with the design goals.

Duncan, C. S.↗
NASA NTRS1983

Large-area sheet task advanced dendritic web growth development

Modeling in the development of low stress configurations for wide web growth is presented. Parametric sensitivity to identify design features which can be used for dynamic trimming of the furnace element was studied. Temperature measurements of experimental growth behavior led to modification in the growth system to improve lateral temperature distributions.

Duncan, C. S.↗
NASA NTRS1982

Observations of a gamma-ray burst and other sources with a large-area, balloon-borne detector

Observations of a weak cosmic gamma ray burst of integrated intensity 2 x 10 to the -6th erg/sq cm, two solar flare events, and pulsed emission profiles of A0535+26 and NP0532 are reported for several energy intervals in the energy range from 45 to 520 keV. The measurements were made with a NaI(Tl) detector array flown on a balloon to 4 g/sq cm residual atmosphere from Palestine, Texas, on October 6-8, 1980, for 28 hours. The detector is a prototype of the Burst and Transient Source Experiment (BATSE) to be flown on the Gamma-Ray Observatory (GRO).

Wilson, R. B.↗
NASA NTRS1983

Production of large-area single-crystal wafers of cubic SiC for semiconductor devices

A reproducible process is described for growing a thick single-crystal layer of cubic SiC on a single-crystal Si wafer by chemical vapor deposition. A buffer layer, grown in situ, is used between the cubic SiC and the Si substrate to minimize the effect of lattice mismatch. Layers of up to 34 microns thick and several sq cm in area have been grown. Wafers are obtained by chemically removing the Si substrates from the grown layers. Excellent electron channeling patterns produced by these wafers indicate very good crystal quality. Preliminary electrical measurements have yielded electron mobilities up to 380 sq cm/Vs.

Nishino, S.↗
NASA NTRS1985

Polyurethane Masks Large Areas in Electroplating

Polyurethane foam provides effective mask in electroplating of copper or nickel. Thin layer of Turco maskant painted on area to be masked: Layer ensures polyurethane foam removed easily after served its purpose. Component A, isocyanate, and component B, polyol, mixed together and brushed or sprayed on mask area. Mixture reacts, yielding polyurethane foam. Foam prevents deposition of nickel or copper on covered area. New method saves time, increases productivity and uses less material than older procedures.

Beasley, J. L.↗
NASA NTRS1983

Land cover change monitoring within the east central Louisiana study site: A case for large area surveys with LANDSAT multispectral scanner data

Results established for four digital procedures developed for characterizing the radiometric changes between multidate LANDSAT spectral data sets into meaningful measures of land cover/use dynamics are documented. Each technique's performance was contrasted against digitized land use change maps, which were produced from contemporaneous, retrospective aerophoto coverage, in a cell by cell comparison over a one half by one degree area in east central Louisiana as a standard for comparison. The four techniques identify from 10.5 to 13.0% loss in area of forestland in a five year period; however, they differ more by how accurately this amount of change is distributed, the need for ancillary ground truth, and amount of usable information that is extractable. All require some method of digitally co-registering the two data sets. All are capable of providing tabular statistics as well as map products. Two are capable of detecting changes and identifying their locations. The other two, in addition to this, provide information to qualify land cover conditions at each end of the study interval.

Burns, G. S.↗
NASA NTRS1984

Large-area sheet task advanced dendritic web growth development

The thermal models used for analyzing dendritic web growth and calculating the thermal stress were reexamined to establish the validity limits imposed by the assumptions of the models. Also, the effects of thermal conduction through the gas phase were evaluated and found to be small. New growth designs, both static and dynamic, were generated using the modeling results. Residual stress effects in dendritic web were examined. In the laboratory, new techniques for the control of temperature distributions in three dimensions were developed. A new maximum undeformed web width of 5.8 cm was achieved. A 58% increase in growth velocity of 150 micrometers thickness was achieved with dynamic hardware. The area throughput goals for transient growth of 30 and 35 sq cm/min were exceeded.

Duncan, C. S.↗
NASA NTRS1982

Large area space solar cell assemblies

Results of the development of a 34.3 sq cm space solar cell and integral glass cover are presented. Average AM(0) cell efficiency is 14 percent. The cell design includes a high performance back surface reflector yielding a thermal alpha of approximately 0.66. A novel process is described which integrates cell fabrication and encapsulation thereby achieving a reduction of encapsulation cost. Test results indicate the potential of this new technology.

Nowlan, M. J.↗
NASA NTRS1985

Proportional drift tubes for large area muon detectors

A proportional drift chamber which consists of eight rectangular drift tubes with cross section of 10 cm x 5 cm, a sense wire of 100 micron phi gold-plated tungsten wire and the length of 6 m, was tested using cosmic ray muons. Spatial resolution (rms) is between 0.5 and 1 mm over drift space of 50 mm, depending on incident angle and distance from sense wire.

Cho, C.↗
NASA NTRS1984

Advances in large area polycrystalline solar cells

Polycrystaline silicon is presently routinely processed into low cost 10 cm by 10 cm solar cells. However assuming minimal handling difficulties, only minor equipment modifications and no increase in processing complexity, the fabrication of even larger geometries would be economically advantageous. This investigation addressed the feasibility of developing 10 cm by 15 cm solar cells from research through pilot line production stages. The major thrust was to minimize costing by using existing production equipment and proven techniques wherever possible. Accordingly methods were developed to section larger substrates from existing cast ingots, a simple solar cell was designed and low cost processes implemented. After numerous preliminary experiments, pilot line production of 1500 cells was completed. Of these approximately 62 percent exhibited efficiencies greater than 7.0 percent, 53 percent were greater than 8.0 percent and 15 percent were greater than 9.0 percent. Based on this study, the regular production of 10 cm by 15 cm solar cells was determined to be both feasible and cost effective using existing processing methods.

Vendura, G. J., Jr.↗
NASA NTRS1983

A large area experiment to determine cosmic ray isotopic abundances

Measurements of the isotopic composition of cosmic rays have shown that the cosmic ray isotope ratios, Ne-22/Ne-20 and (Mg-25 + Mg-26)/Mg-24, exceed the solar abundance ratios by factors of 2.7 and 1.8, respectively. There are several processes which could be responsible for the observed excess of neutron-rich isotopes. The considered models imply neutron enrichment in the case of other, less abundant species, and a measurement of the involved isotopic abundances could provide a basis for the determination of the dominating processes occurring in cosmic ray sources. However, an experiment utilizing special equipment is necessary to conduct the required measurements. Such an experiment, the Aluminum Isotopic Composition Experiment (Alice), is being designed in a joint effort involving NASA and a West German university. Alice uses a Cherenkov-range technique to determine the isotopic composition of elements from oxygen through argon.

Mauger, B. G.↗
NASA NTRS1985

Large area CCD image sensors for scientific applications

The designs of the 512 x 512 pixel and 2048 x 2048 pixel CCD sensors developed for scientific imaging are described. Both sensors are manufactured using the three phase, three level polysilicon gate technology, and the architecture of the chips is series-parallel-series. The components of the two different on-chip amplifiers are examined. The sensors are thinned and operated in the back side illumination mode to ensure the highest quantum efficiency. The performances of a number of front side illuminated devices and two thinned rear illuminated chips are evaluated. It is observed that the sensors equal or exceed their proposed charge transfer efficiency of 0.99999, the noise level of 2 e- and 20 e- at 50 kp/s, the quantum efficiency of 40 percent at 400 microns and 70 percent at 700 microns, and of the well capacity of greater than 500 ke-/pixel.

Blouke, M. M.↗
NASA NTRS1985

Large-area high-efficiency ion-implanted cells and flat-plate modules

This paper reports the development of a flat-plate module based on highly efficient ion-implanted silicon solar cells. The cells are 53 sq cm in area and have exhibited AM 1.5 efficiencies of over 18 percent. The use of back surface reflectors to reduce module operating temperature is discussed. A comparison of various approaches to cell design is made, and module test data for these designs are presented. Module efficiency of 14 percent (25 C) is reported.

Spitzer, M. B.↗