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The stress distribution in bulk AlN crystals seeded on 6H-SiC was theoretically modeled and also determined experimentally from Raman peak positions. The full width at half maximum of the AlN Raman peaks showed the crystal quality improved as its thickness increased. The theoretical frequency shifts of the E 1 ͑transverse optical͒ mode calculated from model-predicted stress were in good agreement with experimental values taken along the edges of crystal samples. The stress was linearly distributed along the depth of the samples, and changed from compressive at the growing surface to tensile at the interface between AlN and SiC for thickness range of several hundred micrometers. Large tensile stresses, up to 0.6 GPa, were detected in the AlN at the interface. The effects of growth temperature and sample thickness were investigated. It is predicted that the AlN on 6H-SiC must be at least 2 mm thick to prevent it from cracking while cooling down the sample from a growth temperature of 2000°C.

Cereal Chem. 85(4):495-501Nine sorghum cultivars (five inbred lines and four hybrids) were grown in 2006 in three locations (Mount Hope, KS, Halstead, KS, and Plainview, TX) under different irrigation conditions and were evaluated for composition and ethanol fermentation efficiency. The objective was to study, in one growing season, the effects of genotype, growing location, and irrigation on the physical and chemical properties and fermentation efficiencies of grain sorghum. Genotype had a significant effect on chemical composition, physical properties, and ethanol yield. The cultivars showed a large variation in starch (61.0-74.8%), protein (7.56-16.35%), crude fat (2.79-4.77%), crude fiber (0.58-2.57%), ash (1.25-2.26%), kernel weight (20.0-35.9 mg), kernel hardness (49.6-97.5), and kernel size (1.9-2.7 mm) and were the most important factors affecting ethanol fermentation efficiency (87.5-93.9%). Starch and protein contents were significantly affected by growing location but not by irrigation. Environment had a significant effect on ethanol yields. Unexpectedly, irrigation somewhat reduced fermentation efficiency.

The morphology and composition of AlN crystals on 6H-SiC (0001) at the initial stage of crystal growth by sublimation re-condensation technique were investigated by SEM and SAM. Discontinuous AlN coverage occurred after 15 minutes growth. The AlN nuclei size, and growth rate increased as temperature increased or pressure decreased. The SiC substrate decomposed leaving hexagonal hillocks; simultaneously, the AlN nucleated on these SiC hillocks apparently rotated by 15° to 30°. The chemical composition of the substrate and different AlN crystal facets were characterized by SAM. The bare substrate area was stoichiometric SiC with insignificant conversion to silicon nitride, while Si and C preferentially incorporated in the AlN at the initial stages of growth on specific crystal planes.

The present study was undertaken to determine if boron phosphide (BP) crystals could be produced by a simple technique, close-spaced vapor transport (CVST). This technique has proven very successful in achieving very high growth rates for a wide variety of materials including ZnSe, AlN, and SiC. Both silicon (100) and sapphire substrates were used for the CSVT growth. The resulting films were characterized by Raman spectroscopy. Sublimation of BP powder from 1050 to 1450 °C in an argon atmosphere produced a range of deep orange colour, single and polycrystalline BP crystals. The crystal size increased and the crystal density decreased with increasing temperature. Well-faceted crystals were produced at an intermediate temperature of 1200 °C. At temperatures higher then 1450 °C no BP crystals were grown. Only a fibrous mass of fine whiskers, loosely attached to the substrate were produced. The peak position of the Raman LO mode of the BP crystals was shifted to higher wavenumbers than the BP powder source, suggesting that the crystals were compressively strained.