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Leipold, M. H.

Publications and source records attributed to Leipold, M. H..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Fracture toughness of silicon

The paper presents a study to determine the fracture toughness and to characterize fracture modes of silicon as a function of the orientation of single-crystal and polycrystalline material. It is shown that bar specimens cracked by Knoop microhardness indentation and tested to fracture under four-point bending at room temperature were used to determine the fracture toughness values. It is found that the lowest fracture toughness value of single crystal silicon was 0.82 MN/m to the 3/2 in the 111 plane type orientation, although the difference in values in the 111, 110, and 100 planes was small.

Chen, C. P.↗
NASA NTRS1980

Cost of Czochralski wafers as a function of diameter

The impact of diameter in the range of 10 to 15 cm on the cost of wafers sliced from Czochralski ingots was analyzed. Increasing silicon waste and decreasing ingot cost with increasing ingot size were estimated along with projected costs. Results indicate a small but continuous decrease in sheet cost with increasing ingot size in this size range. Sheet costs including silicon are projected to be $50 to $60/sq m (1980 $) depending upon technique used.

Leipold, M. H.↗
NASA NTRS1980

Materials of construction for silicon crystal growth

The performance of materials for construction and in contact with molten silicon for crystal growth is presented. The basis for selection considers physical compatibility, such as thermal expansion and strength, as well as chemical compatibility as indicated by contamination of the silicon. A number of new high technology materials are included as well as data on those previously used. Emphasis is placed on the sources and processing of such materials in that results are frequently dependent on the way a material is prepared as well as its intrinsic constituents.

Leipold, M. H.↗
NASA NTRS1980

Low cost silicon-on-ceramic photovoltaic solar cells

A technique has been developed for coating low-cost mullite-based refractory substrates with thin layers of solar cell quality silicon. The technique involves first carbonizing one surface of the ceramic and then contacting it with molten silicon. The silicon wets the carbonized surface and, under the proper thermal conditions, solidifies as a large-grained sheet. Solar cells produced from this composite silicon-on-ceramic material have exhibited total area conversion efficiencies of ten percent.

Koepke, B. G.↗
NASA NTRS1979

Structure of deformed silicon and implications for low-cost solar cells

The paper reports on an investigation of the microstructure and minority carrier lifetime of silicon in uniaxially compressed silicon samples, the objective of which was to determine if it is feasible to produce silicon solar cells from sheet formed by high temperature deformation. It is reported that recrystallization was found to be incomplete in both fine and large grained materials, and that the major mode of recrystallization appears to be migration of existing boundaries into the deformed regions. Also, minority carrier diffusion length was found to be drastically reduced after deformation, perhaps due to contamination or cooling rate, and recovered only slightly with annealing. It is concluded that these results suggest that high temperature deformation of silicon for direct production of sheet for high efficiency solar cells is not practical. It is noted that potential may exist for its use as a coarse grained substrate.

Mardesich, N.↗
NASA NTRS1978

Structure of deformed silicon and implications for low cost solar cells

The microstructure and minority carrier lifetime of silicon were investigated in uniaxially compressed silicon samples. The objective of the investigation was to determine if it is feasible to produce silicon solar cells from sheet formed by high temperature rolling. The initial structure of the silicon samples ranged from single crystal to fine-grained polycrystals. The samples had been deformed at strain rates of 0.1 to 8.5/sec and temperatures of 1270-1380 C with subsequent annealing at 1270-1380 C. The results suggest that high temperature rolling of silicon to produce sheet for cells of high efficiency is not practical.

Mardesich, N.↗
NASA NTRS1978

Compatibility Studies of Various Refractory Materials in Contact with Molten Silicon

The production of low cost, efficient solar cells for terrestrial electric power generation involves the manipulation of molten silicon with a present need for noncontaminating, high temperature refractories to be used as containment vessels, ribbon-production dies, and dip-coated substrates. Studies were conducted on the wetting behavior and chemical/physical interactions between molten silicon and various refractory materials.

Odonnell, T.↗
NASA NTRS1978

Structure development in silicon sheet by shaped crystallization

Models are presented for the development of a parallel twinned structure of the 110 plane type and the 112 line type in silicon ribbons. The models are believed to be mutually compatible and operable. The first model relates the requirements for super-cooling during crystallization. The existence of reentrant angles associated with the twin structure is proposed to provide a rough interface to reduce super-cooling. The spacing of the twins is proposed to be limited by the geometrical relationship between the thermal gradient in the liquid and the dimensions of the twinned crystallization front. The second model relates the thermal stress configuration to detail dislocation reactions which would be expected to develop twins. While a specific dislocation mechanism cannot yet be defined, a number of alternatives are presented. All of these various dislocation mechanisms would result in the observed crystalline configuration and the choice among them is not critical.

Leipold, M. H.↗
NASA NTRS1978

Recent developments in low cost silicon solar cells for terrestrial applications

A variety of techniques may be used for photovoltaic energy systems. Concentrated or not concentrated sunlight may be employed, and a number of materials can be used, including silicon, gallium arsenide, cadmium sulfide, and cadmium telluride. Most of the experience, however, has been obtained with silicon cells employed without sunlight concentration. An industrial base exists at present for producing solar cells at a price in the range from $15 to $30 per peak watt. A major federal program has the objective to reduce the price of power provided by silicon solar systems to approximately $1 per peak watt in the early 1980's and $0.50 per watt by 1986. The approaches considered for achieving this objective are discussed.

Leipold, M. H.↗
NASA NTRS1976

Some observations on the characteristics of low-cost silicon sheets

To meet the need for low cost silicon sheet material in the ERDA/JPL photovoltaics program, JPL has initiated a wide ranging technology development effort in crystal growth that includes several different technology thrusts. They range in scope from innovative ingot growth and multislice wafering, to shaped growth techniques, substrate-related processes and hot forming techniques. In this paper, some salient observations on materials resulting from these processes are reported. Included are multiblade wafering-induced damage studies, interface morphology studies on the heat exchanger cast silicon, some diffusion length measurements in thin silicon layers on ceramic substrates, and results on the equilibrium structure found in laser zone ribbon growth.

Digges, T. G., Jr.↗
NASA NTRS1976

Economic analysis of low cost silicon sheet produced from Czochralski grown material

This study shows that the lower limits for manufacturing add-on costs to convert polysilicon to wafers is in the range of $22 to $26/sq m with the cost about equally divided between the crystal growth and wafering processes. However, the $22 to $26/sq m cost limit should be viewed as an asymptote since it is based on multicharge or continuous growth configurations, solidification rates in excess of 2 Kg/hr, multiblade wafering and a slice plus kerf of .045 cm. It should also be emphasized that the results of this study are based on as-sawn wafers, 100% yields (growth and slicing) and no profit. To the first approximation, the limiting cost factors are crucible material and furnace parts for growth and blade material and slurry for slicing.

Koliwad, K. M.↗
NASA NTRS1974

Mechanical behavior of polycrystalline ceramics: Brittle fracture of SiC-Si3N4 materials

The first study area involved magnesium oxide and the role of anion impurities, while the second area was directed toward slow crack growth in silicon nitride-silicon carbide ceramics. The oxide program involved development of fabrication techniques for anion doped materials and evaluation of the role of these anions in the hot pressing response, grain boundary diffusion of nickel doped material, grain boundary microhardness, and grain growth.

Leipold, M. H.↗
NASA NTRS1974

Space processing of ceramic materials

A review was made of the processing of ceramic materials in space and of those space environment factors appearing to be useful in the processing of this class of materials. Applicability of these factors to various processing procedures appropriate to ceramics, such as containerless melting, is discussed. Specific applications of these procedures in developing new and improved products and processes are reviewed.

Savage, C. H.↗
NASA NTRS1974

Mechanical behavior of polycrystalline ceramics: Brittle fracture of SiC-Si3N4 materials

Various properties of ceramic materials were investigated. Magnesium oxide and the role of anion impurities were investigated together with the slow crack growth in silicon nitride-silicon carbide ceramics. The oxide program involved development of fabrication techniques for anion doped materials and evaluation of the role of these anions in the hot pressing response, grain boundary diffusion of nickel doped material, grain boundary microhardness, and grain growth. The carbide-nitride work employed commercial materials and the research involved evaluation of a recently reported technique for study of slow crack growth and the development of data for these commercial materials.

Leipold, M. H.↗
NASA NTRS1973

O(minus 2) grain boundary diffusion and grain growth in pure dense MgO

Grain growth behavior in fully dense compacts of MgO of very high purity was studied, and the results compared with other similar behaving materials. The activation energy for the intrinsic self-diffusion of Mg(2minus) is discussed along with the grain boundary diffusion of O(2minus). Grain boundary diffusion of O(2minus) is proposed as the controlling mechanism for grain growth.

Kapadia, C. M.↗
NASA NTRS1973

Grain boundary mobility in anion doped MgO

Certain anions OH(-), F(-) and Gl(-) are shown to enhance grain growth in MgO. The magnitude of their effect decreases in the order in which the anions are listed and depends on their location (solid-solution, second phase) in the MgO lattice. As most anions exhibit relatively high vapor pressures at sintering temperatures, they retard densification and invariably promote residual porosity. The role of anions on grain growth rates was studied in relation to their effect on pore mobility and pore removal; the atomic process controlling the actual rates was determined from observed kinetics in conjunction with the microstructural features. With respect to controlling mechanisms, the effects of all anions are not the same. OH(-) and F(-) control behavior through creation of a defect structure and a grain boundary liquid phase while Cl(-) promotes matter transport within pores by evaporation-condensation. Studies on an additional anion, S to the minus 2nd power gave results which were no different from undoped MgO, possibly because of evaporative losses during hot pressing. Hence, the effect of sulphur is negligible or undetermined.

Kapadia, C. M.↗