Extended electron energy loss fine structure analysis of amorphous Al2O3

Publisher Website
Google Scholar
Abstract
Specimens of single-crystal α-Al2O3 in the [0001] orientation have been implanted at—185°C with either 4 × 1016 Alcm−2 and 6×1016O cm−2 or with 4×1016 Fe cm−2. In both cases, amorphous layers were produced which extended from the surface to a depth of approximately 170 nm. Investigation of the response of the amorphous material to post-implantation thermal treatments has revealed significant differences. When annealed for 1 h at 960°C in argon, the material made amorphous by implantation with a stoichiometric ratio of aluminium and oxygen recrystallized into a dual-phase microstructure consisting of γ-Al2O3, a cubic transitional form, and epitactical α-Al2O3. In contrast, when treated under similar conditions, the material made amorphous by implantation with iron recrystallized completely to epitactical α-Al2O3. These differences suggest that fundamental structural and chemical differences exist in the as-implanted state. The analysis of extended energy loss fine structure (EXELFS) in electron energy loss spectra obtained using an analytical electron microscope has been used to investigate these differences. The Al-O interatomic distance measured in the material made amorphous by implantation with a stoichiometric ratio of aluminium and oxygen is 0.170 nm in agreement with the value measured for γ-Al2O3, the form into which it first recrystallizes. Similarly, the Al-O interatomic distance measured for the material made amorphous by implantation with iron is 0.185 nm, which agrees with the value measured for α-Al2O3, the form into which it recrystallizes. The results of the EXELFS analyses confirm the existence of underlying structural differences in amorphous materials.