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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Use of anomolous thermal imaging effects for multi-mode systems control during crystal growth

Real time image processing techniques, combined with multitasking computational capabilities are used to establish thermal imaging as a multimode sensor for systems control during crystal growth. Whereas certain regions of the high temperature scene are presently unusable for quantitative determination of temperature, the anomalous information thus obtained is found to serve as a potentially low noise source of other important systems control output. Using this approach, the light emission/reflection characteristics of the crystal, meniscus and melt system are used to infer the crystal diameter and a linear regression algorithm is employed to determine the local diameter trend. This data is utilized as input for closed loop control of crystal shape. No performance penalty in thermal imaging speed is paid for this added functionality. Approach to secondary (diameter) sensor design and systems control structure is discussed. Preliminary experimental results are presented.

Wargo, Michael J.↗
NASA NTRS1984

One-dimensional thermal modeling of vertical Bridgman-type crystal growth

Articles by Naumann (1982) and Jasinski et al. (1983) examined the axial temperature distribution of the charge during vertical Bridgman-type crystal growth. A comparison of their results demonstrates that Naumann's model is applicable for K (ratio of crucible to charge thermal conductivity) equal to or greater than 1 or for small Biot numbers. The Jasinski model provides a correction for larger Biot numbers and is also applicable for small values of K.

Jasinski, T.↗
NASA NTRS1985

Crystal Growth of Device Quality Gaas in Space

The GaAs research evolves about these key thrust areas. The overall program combines: (1) studies of crystal growth on novel approaches to engineering of semiconductor material (i.e., GaAs and related compounds); (2) investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; and (3) investigation of electronic properties and phenomena controlling device applications and device performance. This effort is aimed at the essential ground-based program which would insure successful experimentation with and eventually processing of GaAs in near zero gravity environment. It is believed that this program addresses in a unique way materials engineering aspects which bear directly on the future exploitation of the potential of GaAs and related materials in device and systems applications.

Gatos, H. C.↗
NASA NTRS1992

Follow up on the crystal growth experiments of the LDEF

The 4 solution growth experiments on the LDEF were presented thoroughly elsewhere. The CaCO3-experiment, and to a certain extent also the TTF-TCNQ-experiments yielded useful results. In Jan. 1992, the next series of solution growth experiments were sent to ESA for shipment to KSC. As on the LDEF, the SGF (solution growth facility) of the EURECA-1 contains 4 large experiments. From the beginning, the planning and developments were introduced. Still, the basic concept was maintained, and the CaCO3-experiment, that showed the best results on the LDEF, will now be repeated with improved technology and in larger scale on the EURECA-1. The contents of the 4 SGF experiments are as follows: (1) growth of calcium-carbonate crystals; (2) formation and transformation of tri-calcium-phosphate; (3) growth of zeolite crystals; and (4) soret coefficient measurements (diffusion). The scientific background for the choice of experiments and the major improvements of the SGF are reviewed. Furthermore, some ideas on basic microgravity solution growth experimentation from ESA's newly established EWG (Expert Working Group) on solution growth are reported.

Nielsen, K. F.↗
NASA NTRS1997

An Innovative Method for Preparing Semiconductor Change Used in Crystal Growth and Shear Cell Diffusion Experiments

An innovative technique for machining semiconductors has been developed. This technique was used to prepare semiconductor charges for crystal growth and shear cell diffusion experiments. The technique allows brittle semiconductor materials to be quickly and accurately machined. Lightly doping the semiconductor material increases the conductivity enough to allow the material to be shaped by an electrical discharge machine (EDM).

Anrold, William A.↗
NASA NTRS1982

Natural convection in melt crystal growth - The influence of flow pattern on solute segregation

The results of two lines of research aimed at calculating the structure of the flows driven by buoyancy in small-scale crystal growth systems and at understanding the coupling between these flows, the shape of the solidification interface, and dopant segregation in the crystal are reviewed. First, finite-element methods are combined with computer-aided methods for detecting multiple steady solutions to analyze the structure of the buoyancy-driven axisymmetric flows in a vertical cylinder heated from below. This system exhibits onset of convection, multiple steady flows, and loss of the primary stable flow beyond a critical value of the Rayleigh number. Second, results are presented for calculations of convection, melt/solid interface shape, and dopant segregation within a vertical ampoule with thermal boundary conditions that represent a prototype of the vertical Bridgman growth system.

Brown, R. A.↗
NASA NTRS1980

The effect of growth rate, diameter and impurity concentration on structure in Czochralski silicon crystal growth

It is demonstrated that maximum growth rates of up to 80% of the theoretical limit can be attained in Czochralski-grown silicon crystals while maintaining single crystal structure. Attaining the other 20% increase is dependent on design changes in the grower, to reduce the temperature gradient in the liquid while increasing the gradient in the solid. The conclusions of Hopkins et al. (1977) on the effect of diameter on the breakdown of structure at fast growth rates are substantiated. Copper was utilized as the test impurity. At large diameters (greater than 7.5 cm), concentrations of greater than 1 ppm copper were attained in the solid (45,000 ppm in the liquid) without breakdown at maximum growth speeds. For smaller diameter crystals, the sensitivity of impurities is much more apparent. For solar cell applications, impurities will limit cell performance before they cause crystal breakdown for fast growth rates of large diameter crystals.

Digges, T. G., Jr.↗
NASA NTRS1986

Crystal growth and transport rates of the GeSe-xenon system under microgravity conditions

The analysis of the STS-7 flight experiments of the GeSe-xenon system yielded positive results which surpass the original objectives of these experiments. The mass transport rates of GeSe observed in microgravity environment are in close agreement with theoretically predicted values for diffusion limited mass transport. This supports the earlier proposed hypothesis for the interpretation of flux anomalies observed in previous space experiments. In addition, the STS-7 flight experiments led to the observation of unexpected crystal growth phenomena. The largest GeSe single crystals obtained in microgravity grew in the ampul without direct wall contact which could suggest homogeneous nucleation. The space grown crystals are much larger and have considerably improved surface and bulk morphologies relative to corresponding ground control specimens. The combined results are of basic scientific importance and of technological significance.

Wiedemeier, H.↗
NASA NTRS1992

Thermocapillary convection instability in microgravity crystal growth

Energy and linear stability theories are applied to study the stability properties of thermocapillary convection in a half zone model of the float zone crystal growth process. The analyses yield results which provide sufficient conditions for both stability and instability, respectively, and therefore, lower and upper bounds for the Marangoni numbers at which oscillatory thermocapillary convection will appear. The results of the analyses are compared with available experimental and numerical data.

Neitzel, G. P.↗
NASA NTRS1996

Semiconductor crystal growth in crossed electric and magnetic fields: Center Director's Discretionary Fund

A unique growth cell was designed in which crossed electric and magnetic fields could be separately or simultaneously applied during semiconductor crystal growth. A thermocouple was inserted into an InSb melt inside the growth cell to examine the temperature response of the fluid to applied electromagnetic fields. A static magnetic field suppressed time-dependent convection when a destabilizing thermal field was applied. The simultaneous application of electric and magnetic fields resulted in forced convection in the melt. The InSb ingots grown in the cell were polycrystalline. An InGaSb crystal, 0.5 cm in diameter and 23-cm long, was grown without electromagnetic fields applied. The axial composition results indicated that complete mixing in the melt occurred for this large aspect ratio.

Mazuruk, K.↗
DOE OSTI2021

Crystal growth, density functional theory, and scintillation properties of Tl 3 LnCl 6 :Ce 3+ and TlLn 2 Cl 7 :Ce 3+ (Ln = Y, Gd)

In this paper we report on the crystal growth, density functional theory (DFT) calculations and scintillation properties of Tl 3 LnCl 6 :Ce and TlLn 2 Cl 7 :Ce(Ln = Y, Gd). Crystals were grown by the Vertical Bridgman technique up to 16 mm in diameter and 25 mm long. Crystals of Tl 3 YCl 6 :Ce and Tl 3 GdCl 6 :Ce belong to the family of the Nesohalides which have the monoclinic crystal structure. Crystals of TlY 2 Cl 7 :Ce and TlGd 2 Cl 7 :Ce belong to the family of the Phyllohalides which have either the monoclinic or the orthorhombic crystal structure. We report the light yields of these Nesohalides and Phyllohalides are typically on the order of 35,000–40,000 ph/MeV.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1985

Solutal Convection and Its Effects on Crystal Growth and Segregation in Binary and Pseudo-Binary System with Large Liquidus-Solidus Separation

This research program is composed of theoretical and experimental studies of solutal convection and its effects on crystal growth and segregation in binary and pseudo-binary systems with large liquidus-solidus separation. The theoretical program has resulted in the development of a transient simulation of the growth of concentrated alloys in microgravity and has been used to study the dynamics of GeSi, PbSnTe, HgCdTe growth. Finite element analysis has also been developed for studying the interactions of buoyancy-driven convection in the melt caused by temperature and concentration variations with melt-solid interface morphology and alloy segregation in the grown crystal. These calculations are being compared directly to experimental measurements of segregation and interface shape for GeSi growth and GaGe growth. The results for SiGe indicate that careful design of the thermal system can result in almost diffusion-controlled growth on Earth because of the stablizing influence of the concentration gradient ahead of the solidification front.

Brown, R. A.↗
NASA NTRS1982

Heat transfer analysis of the Bridgman-Stockbarger configuration for crystal growth. Part 1: Analytical treatment of the axial temperature distribution

All first order effects on the axial temperature distribution in a solidifying charge in a Bridgman-Stockbarger configuration for crystal growth are analyzed on the basis of a one dimensional model whose validity can be verified through comparison with published finite difference ana;uses of two dimensional models. The model presented includes an insulated region between axially aligned heat pipes and considers the effects of charge diameter, charge motion, thickness, and thermal conductivity of a confining crucible, thermal conductivity change at the crystal-melt interface, generation of latent heat at the interface, and finite charge length. Results are primarily given in analytical form and can be used without recourse to computer work for both improve furnace design and optimization of growth conditions in a given thermal configuration.

Jasinski, T. J.↗
NASA NTRS1990

Thermocapillary flow and melt/solid interfaces in floating-zone crystal growth under microgravity

Computer simulation of steady-state axisymmetrical heat transfer and fluid flow was conducted to study thermocapillary flow and melt/solid interfaces in floating-zone crystal growth under microgravity. The effects of key variables on the extent of thermocapillary flow in the melt zone, the shapes of melt/solid interfaces and the length of the melt zone were discussed. These variables are: (1) the temperature coefficient of surface tension (or the Marangoni number), (2) the pulling speed (or the Peclet number), (3) the feed rod radius, (4) the ambient temperature distribution, (5) the heat transfer coefficient (or the Biot number), and (6) the thermal diffusivity of the material (or the Prandtl number).

Lan, C. W.↗
NASA NTRS1990

Transient natural convection heat and mass transfer in crystal growth

A numerical analysis of transient combined heat and mass transfer across a rectangular cavity is performed. The physical parameters are selected to represent a range of possible crystal growth in solutions. Good agreements with measurement data are observed. It is found that the thermal and solute fields become highly oscillatory when the thermal and solute Grashof numbers are large.

Han, Samuel S.↗
NASA NTRS1993

Stability and instability of thermocapillary convection in models of the float-zone crystal-growth process

This project was concerned with the determination of conditions of guaranteed stability and instability for thermocapillary convection in a model of the float-zone crystal-growth process. This model, referred to as the half-zone, was studied extensively, both experimentally and theoretically. Our own earlier research determined, using energy-stability theory, sufficient conditions for stability to axisymmetric disturbances. Nearly all results computed were for the case of a liquid with Prandtl Number Pr = 1. Attempts to compute cases for higher Prandtl numbers to allow comparison with the experimental results of other researchers were unsuccessful, but indicated that the condition guaranteeing stability against axisymmetric disturbances would be a value of the Marangoni number (Ma), significantly higher than that at which oscillatory convection was observed experimentally. Thus, additional results were needed to round out the stability picture for this model problem. The research performed under this grant consisted of the following: (1) computation of energy-stability limits for non-axisymmetric disturbances; (2) computation of linear-stability limits for axisymmetric and non-axisymmetric disturbances; (3) numerical simulation of the basic state for half- and full-zones with a deformable free surface; and (4) incorporation of radiation heat transfer into a model energy-stability problem. Each of these is summarized briefly below.

Neitzel, G. P.↗
NASA NTRS1980

Practical aspects of silicon float zone crystal growth

The float zone (FZ) growth method for silicon crystallization has advantages and disadvantages when compared to the other principal growth method, the Czochralski (CZ) technique. CZ growth is attractive for the following reasons: large diameters, high single crystal yields, low thermal gradients, low operator skill requirements, efficient power utilization, and low feed material costs. Some areas where FZ growth is advantageous include high purity, axial resistivity uniformity (on a macroscale), visibility of the growth region, low consumable material costs, and high growth rates.

Ciszek, T. T.↗