The low-temperature degradation of zirconia (ZrO 2 ) that was doped with 3 mol% yttria (Y 2 O 3 ) (3Y-TZP) was prevented by the heat treatment of sintered specimens in nitrogen. The heat treatment of sintered specimens resulted in a surface layer that was stabilized by nitrogen ions, whereas the interior was only slightly affected by the heat treatment. X-ray diffractometry and transmission electron microscopy analyses revealed that the stabilized surface layer consisted of cubic grains with tetragonal precipitates. Although the presence of the surface layer decreased the strength of the sintered 3Y-TZP, the strength of nitrified specimens was maintained when low-temperature annealing was applied.
We examined the possibility of employing the surface treatment of sapphire using reactive ion beam (RIB) pretreatment as an alternative process for GaN growth in metalorganic chemical vapor deposition (MOCVD). As a result of the RIB treatment, etching of the sapphire surface and the formation of a very thin, disordered AlON layer was observed which was partially crystallized during the main growth of GaN. Reduction in both dislocation density and lattice strain of GaN on RIB treated sapphire was obtained. Partial crystallization in the RIB layer promoted two-dimensional growth on the crystallized regions and relieved the misfit strain through relaxation of the disordered RIB layer. The optical properties of the GaN films could be optimized by the proper choice of the ion beam energy. The present results clearly show that RIB pretreatment of the sapphire surface can be used to improve the properties of GaN films grown by MOCVD.
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