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|Influence of annealing atmosphere on the behavior of titanium implanted sapphire
|Sapphire single crystals with (0 0 0 1) and (0 2 2̄ 1) orientations were implanted at room temperature with several fluences of Ti at 150 keV. For low fluences (up to 1 × 1015 Ti+/cm2) the Ti ions are fully incorporated in Al sites of the lattice and remain stable up to temperatures of the order of 1000 °C as revealed by detailed channeling angular scans. The amorphous state is reached after implantation of 5 × 1016 Ti+/cm2. Annealing in oxidizing atmosphere leads to complete recovery of the amorphous region and the segregation of Ti to the surface. The RBS and TEM pictures show that Ti oxides concentrate at the surface after annealing at 1000 °C. The same annealing in a reducing atmosphere produces a buried layer of Ti precipitates centered at the range of the implanted ions. The damage recovery is hindered by the presence of this layer as shown by the 〈0 0 0 1〉 aligned RBS spectrum. The surface layer becomes polycrystalline as the TEM micrographs reveal. Optical absorption measurements show the presence of a broad band centered at 350 nm for the samples annealed in air. This band is absent in the samples annealed in a reducing atmosphere but the background absorption is much higher compared with the samples annealed on air. Photoluminescence (PL) measurements reveal the presence of an emission band centered around 800 nm.
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