Engineering topics

Shlichta, P. J.

Publications and source records attributed to Shlichta, P. J..

At least 19 records

NASA NTRS1987

Deep, Precise Etching in Semiconductors

Semiconductors made to accept precise etching after pretreatment. Combination of material destabilization and anisotropic etching permits formation of precise perpendicular-wall cavities in silicon wafers and other semiconductors. New technique extends capabilities of current micromachining technology to fabrication of submillimeter waveguide arrays and filters. Pre-etching process currently used to fabricate thin-walled arrays of submillimeter waveguides for use as dichroic bandpass filters. Possible applications include integration of sensor probes and processing of circuitry on same silicon chip.

Shlichta, P. J.↗

NASA NTRS1986

Feasibility of mapping solution properties during the growth of protein crystals

This paper summarizes the feasibility of using optical techniques for mapping the convection, temperature, and solute concentration in the solution around a growing protein crystal. Convection can be mapped by a variety of techniques which measure either refractive index differences, displacements, velocity, or solute optical absorption. For protein crystal growth, however, ordinary schlieren and interferometric techniques are marginally sensitive and most displacement marking techniques unsuitable; therefore, phase-concentration by the absorption-interferometric technique appears to be quite feasible for protein solutions because of their low dn/dC. Finally, the monitoring of protein crystal growth rates appears to be feasible by double-exposure holography or birefringence.

Shlichta, P. J.↗

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

Ground-based experiments on the minimization of convection during the growth of crystals from solution

Crystals were grown from solution in the earth's gravitational field with the substantial absence of convection by (1) downward unidirectional growth in an isothermally cooled solution and (2) upward unidirectional growth in a positive vertical thermal gradient. Growth rates were 1.3 to 1.8 times the predictions for convectionless growth, and an order of magnitude less than for growth with vigorous convection. Crystals grown in the isothermal configuration were of comparable or superior quality to those grown with substantial convection. The imposition of a 0.5 to 0.8 C/mm gradient greatly stabilized the growth interface so that flat (001) surfaces could be grown on KDP. Crystals grown in a thermal gradient, however, were filled with far more fluid inclusions than crystals grown isothermally.

Nerad, B. A.↗

NASA NTRS1986

Beta Silicon Nitride Whiskers

Process for growing fibrous beta silicon nitride helps meet potentially great demand for silicon nitride ceramics. Ceramics have high tensile strength and resistance to thermal shock, which make them attractive choice for high-temperature engine parts. Process forms whiskers of strong, stable, heatresistant material. Whiskers expected to find application as reinforcement in composite silicon nitride ceramic parts. Corklike material useful in present form for thermal barrier tiles. Process forms whiskers of strong, stable, heat-resistant material.

Holliday, R. J.↗

NASA NTRS1985

Comparison of theory with experiment in convectionless growth of crystals from solution

Wilcox's computer program for predicting the growth rates of crystals in convectionless supersaturated solution is used to model experiments to measure the crystal growth experiments of Simon (1978) and of Nerad and Shlichta (1984), and the results are compared with the experimental data. The predictions of Wilcox's model are found to be in remarkably good agreement with the results of Simon. The data of Nerad and Shlichta are 30 to 90 percent higher than the predictions of the Wilcox model for a certain range of temperature dependence, consistent with the observation of occasional low-level convection in these experiments. These comparisons indicate that the Wilcox model can be used to make reliable order-of-magnitude predictions of growth rates in the absence of convection.

Schlom, D. G.↗

NASA NTRS1985

Method for growth of crystals by pressure reduction of supercritical or subcritical solution

Crystals of high morphological quality are grown by dissolution of a substance to be grown into the crystal in a suitable solvent under high pressure, and by subsequent slow, time-controlled reduction of the pressure of the resulting solution. During the reduction of the pressure interchange of heat between the solution and the environment is minimized by performing the pressure reduction either under isothermal or adiabatic conditions.

Shlichta, P. J.↗

NASA NTRS1985

Minimizing Convection During Crystal Growth

Buoyant convection during crystal growth from solution minimized in experiment cell using boundary-layer stabilizing configurants such as downward isothermal growth or upward growth into thermal gradient.

Shlichta, P. J.↗

NASA NTRS1985

Hot-Dipped Metal Films as Epitaxial Substrates

Multistep process forms semiconductor devices on macrocrystalline films of cadmium or zinc. Solar-cell fabrication processes use hot-dipped macrocrystalline films on low-cost sheet-metal base as substrates for epitaxy. Epitaxial layers formed by variety of methods of alternative sequence paths. Solar cells made economically by forming desired surface substance directly on metal film by chemical reactions.

Shlichta, P. J.↗

NASA NTRS1984

Purifying Silicon During Crystal Growth

Direct current applied to molten silicon during crystallization causes impurities to migrate away from interface of growing crystal. Method improves purity of crystal without interfering with growth process or requiring additional operator attention.

Shlichta, P. J.↗

NASA NTRS1984

Glass heating panels and method for preparing the same from architectural reflective glass

Electrodes are positioned in intimate contact with an outer surface of a thin electrically insulating protecting layer of architectural reflective glass. Application of a voltage of sufficient magnitude substantially destroys the insulating layer located beneath the electrodes. A subsequent application of voltage results in a passage of current through the underlying thin, light reflective metal or metal oxide layer and in concomitant output of heat.

Shlichta, P. J.↗

NASA NTRS1984

Uncooled IR Detector

Detector combines liquid crystal film with light-sensitive solid-state array. Liquid-crystal film acts as IR detector when maintained just below temperature of transition from opacity to transparancey. When IR radiation is absorbed by film, resultant heating changes visiblelight transmission, modulating uniform visible light beam as it passes through film.

Shlichta, P. J.↗

NASA NTRS1983

Absorbable-susceptor joining of ceramic surfaces

An assembly of ceramic surfaces particularly refractory metal oxides and carbides, abutting a thin sheet of metal susceptor material are placed in a chamber of an enclosure containing inert gas. An RF coil is activated by power supply to melt the susceptor and adjacent zones of the ceramic. Reactive gas such as oxygen or a carbonizing gas is then fed to the chamber and reacts with the susceptor to form compounds which disperse and dissolve in the zones. On cooling, a strong joint is formed. The susceptor may contain inner perforations and outer perforations to aid in distribution of heat.

Schroeder, J. E.↗

NASA NTRS1983

Method and apparatus for minimizing convection during crystal growth from solution

A method and apparatus are disclosed for growing in a gravitational field a microscopic crystal from a solution. The solution is held in a vertical chamber which is relatively thin, the thin being generally perpendicular to the vertical. There is a substrate crystal disposed at either the upper or lower end of the chamber and the crystal grows from this substrate crystal in one direction. The temperature conditions of the solution are controlled so that, as the crystal forms, the effects of buoyant convection within the solution are minimized. This is accomplished in two different ways depending upon whether the crystal is grown from the upper or lower end of the chamber. When grown from the upper end of the chamber, the temperature of the solution is controlled so that it remains essentially isothermal so that there is essentially no heat loss from the solution. When the crystal is grown from the lower end of the chamber, the temperature of the solution is controlled so that there is a differential in temperature throughout the solution which provides a positive thermal gradient within the chamber.

Shlichta, P. J.↗

NASA NTRS1983

Absorbable-Susceptor Welding of Ceramics

Susceptor becomes part of joint. Susceptor is heated to high temperature by RF energy, then melts adjacent ceramic material. Susceptor dissolves in molten ceramic. When cooled, ceramic parts form moloithic assembly. Suitable for joining complex subassemblies in heat exchangers or other ceramic process equipment for high temperatures.

Schroeder, J. E.↗

NASA NTRS1983

Low-Cost Electrically-Heated Glass Panels

Inexpensive process converts architectural reflective-coated glass into electrically heated panels. Technique utilizes reflective layer as heating element in ordinary glass. Panels have many applications, including automobile windows, home-heating panels, temperature-controlled windows or containers, and food warming trays.

Shlichta, P. J.↗

NASA NTRS1982

Electromigration process for the purification of molten silicon during crystal growth

A process for the purification of molten materials during crystal growth by electromigration of impurities to localized dirty zones. In the Czochralski crystal growing process, the impurities are electromigrated away from the crystallization interface by applying a direct electrical current to the molten silicon for electromigrating the charged impurities away from the crystal growth interface. The edge-defined film-fed crystal growth process, a direct electrical current is applied between the two faces which are used in forming the molten silicon into a ribbon. The impurities, migrated to one side only of the crystal ribbon, may be removed or left in place. If left in place, they will not adversely affect the ribbon when used in solar collectors. The migration of the impurity to one side only of the silicon ribbon is especially suitable for use with asymmetric dies which preferentially crystallize uncharged impurities along one side or face of the ribbon.

Shlichta, P. J.↗

NASA NTRS1981

Pressure-Reduction Technique for Crystal Growth

Large crystals grown by varying pressure rather than temperature. In constant temerature pressure-reduction process crystal growth promoted as solubility decreases by factor of more than 10. Technique used to study crystal growth kinetics by "pressure wave"" analog of conventional "thermal wave" experiments. Technique has advantages of faster response and freedom from convective interference.

Shlichta, P. J.↗