Hydrogen atom-induced deuterium adatom abstraction has been studied on the Si͑100͒ surface from a desorption point of view. Abstraction of HD as well as collision-induced D 2 desorption are observed on the D/Si͑100͒ surface during H beam exposure at 573 K. For 1 ML D ad precoverage, about 30% of the desorbed D atoms are ejected as collision-induced D 2 desorption at the very beginning of H(g) exposure. It is found that the decay of the HD and D 2 rates are affected by the total coverage, HϩD . The decay rate of the HD rate is much lower in the low coverage regime than in the high coverage regime. The nominal cross section of the former is 2.3Ϯ1.0 Å 2 , while for the latter 7.2Ϯ0.5 Å 2 . The HD rate curves show that the abstraction obeys nearly first-order kinetics towards D coverage, D . On the other hand, the D 2 rate curves show that the collision-induced desorption obeys nearly fourth-order kinetics towards D . Such HD abstraction is also observed on an oxygen-deposited D/Si͑100͒ surface where the oxygen atoms are known to be incorporated between Si atoms. The observed decay rate of the HD rate is extremely low, with a cross section of 1.5Ϯ1.0 Å 2 . The reaction kinetics are well understood by adopting the kinetics model recently proposed by Flowers et al. ͓Surf. Sci. 396, 227 ͑1998͔͒. The abstraction of HD may be due to an Eley-Rideal mechanism rather than to a hot atom mechanism. Collision-induced D 2 desorption may take place upon encounter of two dideuteride species via an isomerization reaction at quasiequilibrium.
Plasma etching of j?-Si3N4, cy-sialon/j?-Si3N4 and a-sialon ceramics were performed with hydrogen glow plasma at 600°C for 10h. The preferential etching of j?-Si3N4 grains was observed. The etching rate of cy-sialon grains and of the grain-boundary glassy phase was distinctly lower than that of B-Si3N4 grains. The size, shape, and distribution of BSi3N4 grains in the a-sialon/&Si3N4 composite ceramics were revealed by the present method. [
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