Hot plasma chemical vapor deposition of GaN on GaAs(100) substrate

GaN films have been deposited on GaAs(lOO) substrates by a novel growth technique, hot plasma chemical vapor deposition. A radio frequency N plasma source with high power, up to 5 kW, provides an abundance of nitrogen atoms during growth. In addition, strong ultraviolet emissions from the hot plasma irradiate onto the substrate and promote the dissociation of triethylgallium, this results in growth of GaN at very low temperature (even at room temperature). In this paper, we describe the characteristics of hot nitrogen plasma and present the results of the low temperature growth of GaN. In addition, we have investigated the effects of the nitridation of GaAs substrates. Reflection high energy electron diffraction indicates the formation of a surface cubic nitrided layer on the pretreated GaAs. The GaN films grown on fully nitrided GaAs(l00) substrates are of dominantly cubic structures.     

Effect of ion implantation layer on adhesion of DLC film by plasma-based ion implantation and deposition

High adhesive diamond-like carbon (DLC) film on SUS304 was obtained using carbon ion implantation between DLC film and substrate material by plasma-based ion implantation and deposition (PBIID). Implantation of mixed silicon and carbon ions to the substrate resulted in much higher adhesion strength than that of the epoxy resin. Effect of ion implantation on adhesion of DLC film was studied by cross sectional STEM observation and EDS element analysis. Enhancement in adhesive strength by ion implantation of mixed carbon and silicon was ascribed to the formation of the multilayer interface consisting of mixed carbon and silicon ion implanted layer and the amorphous layer of carbon and silicon.     

Serum pyridoxal concentration in children during theophylline therapy for bronchial asthma

This study was designed to investigate the effect of sustained-release theophylline therapy on serum pyridoxal concentration in children with bronchial asthma. Forty-two children with bronchial asthma were divided into two groups according to duration of theophylline administration: The 22 children in group A had been treated with theophylline for less than 4 weeks, whereas the 20 children in group B had been treated for more than 5 weeks. The results obtained from this study were as follows: 1) The serum pyridoxal concentration in group B was significantly lower than that those in group A (p < 0.01). 2) The serum pyridoxal concentration was not significantly correlated with the serum theophylline concentration. These findings suggest that long-term theophylline therapy can depress vitamin B6 status in children with bronchial asthma. Theophylline-induced seizure may be caused by the possible decreased in gamma-aminobutyric acid concentration in the brain as a result of decrease in gamma-aminobutyric acid concentration in the brain as a result of decrease in vitamin B6 status, even if the serum theophylline concentrations are within the therapeutic range.     

Evaluation of apolipoprotein A-I kinetics in rabbits <Emphasis Type="Italic">in vivo</Emphasis> using <Emphasis Type="Italic">in situ</Emphasis> and exogenous radioiodination methods

The kinetics of in vivo clearance of apolipoprotein (apo) A-I radioiodinated by the iodine monochloride (ICI) method of McFarlane [McFarlane, A.S. (1958) Efficient Trace-Labelling of Proteins with Iodine, Nature 182, 53] as modified by Bilheimer and co-workers [Bilheimer, D.W., Eisenberg, S., and Levy, R.I. (1972) The Metabolism of Very Low Density Lipoprotein Proteins. I. Preliminary in vitro and in vivo Observations, Biochim. Biophys. Acta 260, 212–221] and by using the IODO Beads Iodination Reagent were evaluated in rabbits. Both human apoA-I and rabbit HDL radioiodinated by the IODO Beads Iodination Reagent were cleared faster from plasma of rabbits than those radiolabeled by the ICl method. However, the different radiolabeling procedures in the ICl method, i.e., apoA-I radiolabeled either exogenously or in situ as a part of intact HDL, were not associated with a significant difference in the in vivo kinetics of apoA-I in rabbits if apoA-I was prepared by the guanidine HCl method and used fresh. ¹²⁵I-ApoA-I subjected to delipidation and lyophilization was cleared only slightly faster from the plasma of rabbits than fresh ¹²⁵I-apoA-I. We also found that apoA-I separated by the guanidine HCl method and used fresh was cleared faster from the plasma of rabbits when it was injected as free apoA-I without adding serum albumin or after in vitro incubation with rabbit HDL than when injected after reassociation with rabbit plasma. We conclude that the ICl method is a more appropriate radioiodination method for studying the in vivo kinetics of HDL than the IODO Beads Iodination Reagent and that the in vitro incubation conditions before injection are important factors that affect the in vivo kinetics of apo A-I.     

Microstructure of pressureless-sintered Al2O3-24 vol% ZrO2 composite studied by high-resolution electron microscopy

The microstructure of an Al₂O₃-24 vol% ZrO₂ composite prepared by pressureless-sintering was investigated by high-resolution electron microscopy. The composite was formed of homogeneously dispersed ZrO₂ and Al₂O₃ grains with average sizes of 0.3 and 0.5 m, respectively. Most ZrO₂ grains had a monoclinic structure, but a few ZrO₂ embedded in Al₂O₃ grains were a tetragonal structure. At interfaces between ZrO₂ with a lamella-type twin structure and Al₂O₃, microcracks were observed, in addition to strain fields in the Al₂O₃ matrix. Complex twin structures accompanied by dislocations were observed in ZrO₂ with a spherical shape. In in situ observations with electron-beam heating, it was found that a crack propagated along an Al₂O₃/ZrO₂ interface and stopped at the place where a tetragonal ZrO₂ had undergone a structural change to monoclinic ZrO₂.     

High-strain-rate superplasticity in oxide ceramics

Factors limiting the strain rate of superplastic deformation in ceramic materials are discussed on the basis of existing models and experimental results concerning high-temperature plastic deformation, intergranular cavitation and dynamic grain growth. From the discussion, it is indicated that simultaneously fulfilling the following conditions is essential for attaining high-strain-rate superplasticity (HSRS) in ceramic materials: reduction in the initial grain size, enhanced diffusivity, suppressed dynamic grain growth, a homogeneous microstructure and a reduced number of residual defects. In the light of these conditions, explanations are given for HSRS attained in earlier studies on some oxide materials. It is also shown that HSRS can be intentionally attained in doped yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) and composites synthesized from ZrO₂, Al₂O₃ and MgO₂; the tensile ductility of these composites reached 300–2500% at a strain rate of 0.01–1.0 s⁻¹. The postdeformation microstructure indicates that some secondary phases may suppress cavitation damage and thereby enhance HSRS.     

High temperature creep damage in steels and superalloys

The nucleation and growth of cavities was examined in steel bicrystals (Fe-3%-Si, X 8 CrNiNb 16 13) and in the ODS superalloy Inconel MA 754 (Inconel MA 754 (78% Ni; 20% Cr; 0.5% Ti; 0.3% Al; 0.6% Y₂O₃). Cavity density distributions were measured on metallographic sections and on cleaved grain boundaries as a function of time, strain, temperature and stress. Nucleation and growth laws were obtained by evaluating the distributions with appropriate models. For the fcc and bcc bicrystals, it was found that cavities nucleated continuously at sulfide and carbide particles during creep. They grew by grain boundary diffusion. But the growth rate was delayed with increasing creep strain due to cavities which nucleated in the surroundings of existing cavities. For the ODS alloy, however, many round cavities preexisted on quasi-boundaries consisting of the aggregate of coarse oxide and carbide particles. They grew initially by diffusion, but with increasing creep time (cavity size), the growth mechanism switched from growth controlled by grain boundary diffusion to growth controlled by power law creep. Implications for life predictions are discussed.