NASA Scientific and Technical Aerospace Reports

inconsistent with the theory on which the current model is based for the limited number of glasses tested. It should be noted
that these glasses cover a narrow compositional region. With respect to the impact on viscosity, the data suggest that there may
be a bias in the model. That is, the model currently does not contain a U3O8 or ThO2 term - but perhaps it should to account
for their contributions to the measured (or actual) viscosity results. In addition, a series of glasses were produced to assess the
impact of higher waste loadings on select glass properties. The PCT results suggest that durable glasses can be made at
relatively high WLs (exceeding 40 wt percent). Comparisons between the measured PCTs and their predictions indicate that
the current model is applicable, with all of the quenched glasses falling within the 95 percent confidence bands. The viscosity
data for the higher WL glasses suggest that the current model may be extremely accurate for some systems but for different
regions the model may be biased high or low - an observation that is consistent with that of Harbour et al. (1999).
NTIS
Glass; Uranium; Thorium Oxides; Substitutes
20040120951 NASA Marshall Space Flight Center, Huntsville, AL, USA
Bridgman Growth of Germanium Crystals in a Rotating Magnetic Field
Volz, M. P.; Walker, J. S.; Schweizer, M.; Cobb, S. D.; Szofran, F. R.; [2004]; 1 pp.; In English; International Conference on
Crystal Growth 14, 9-13 Aug. 2004, Grenoble, France; No Copyright; Avail: Other Sources; Abstract Only
A series of (100)-oriented gallium-doped germanium crystals have been grown by the Bridgman method and under the
influence of a rotating magnetic field (RMF). Time-dependent flow instabilities occur when the critical magnetic Taylor
number (Tm(sup c) is exceeded, and this can be observed by noting the appearance of striations in the grown crystals. The
experimental data indicate that Tm(sup c) increases as the aspect ratio of the melt decreases. Modeling calculations predicting
Tm(sup c) as a function of aspect ratio are in reasonable agreement with the experimental data. The RMF has a marked affect
on the interface shape, changing it from concave to nearly flat as the RMF strength is increased. Also, by pulsing the RMF
on and off, it is shown that intentional interface demarcations can be introduced.
Author
Bridgman Method; Crystal Growth; Germanium; Magnetic Fields
20040120994 NASA Glenn Research Center, Cleveland, OH, USA
Lateral Movement of Screw Dislocations During Homoepitaxial Growth and Devices Yielded Therefrom Free of the
Detrimental Effects of Screw Dislocations
Neudeck, Philip G., Inventor; Powell, J. Anthony, Inventor; August 31, 2004; 37 pp.; In English; Original contains black and
white illustrations
Patent Info.: Filed 10 Oct. 2002; US-Patent-6,783,592; US-Patent-Appl-SN-268749; NASA-Case-LEW-17237-1; No
Copyright; Avail: CASI; A03, Hardcopy
The present invention is related to a method that enables and improves wide bandgap homoepitaxial layers to be grown
on axis single crystal substrates, particularly SiC. The lateral positions of the screw dislocations in epitaxial layers are
predetermined instead of random, which allows devices to be reproducibly patterned to avoid performance degrading crystal
defects normally created by screw dislocations.
Official Gazette of the U.S. Patent and Trademark Office
Crystal Growth; Epitaxy; Screw Dislocations; Single Crystals
20040121079 NASA Marshall Space Flight Center, Huntsville, AL, USA
Synchrotron X-ray Microdiffraction Analysis of Proton Irradiated Polycrystalline Diamond Films
Newton, R. I.; Davidson, J. L.; Ice, G. E.; Liu, W.; July 26, 2004; 8 pp.; In English; Original contains black and white
illustrations
Contract(s)/Grant(s): DE-AC05-00OR-22725; DE-FG02-91ER-45439; DE-AC05-00OR-22725; W-31-09-eng-38; Copyright;
Avail: CASI; A02, Hardcopy
X-ray microdiffraction is a non-destructive technique that allows for depth-resolved, strain measurements with
sub-micron spatial resolution. These capabilities make this technique promising for understanding the mechanical properties
of MicroElectroMechanical Systems (MEMS). This investigation examined the local strain induced by irradiating a
polycrystalline diamond thin film with a dose of 2x10(exp 17) H(+)per square centimeter protons. Preliminary results indicate
that a measurable strain, on the order of 10(exp -3), was introduced into the film near the End of Range (EOR) region of the
protons.
Author
Synchrotrons; X Ray Diffraction; Protons; Irradiation; Polycrystals; Diamond Films
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