THE EFFECT OF POSTIMPLANTATION ANNEALING ON THE MICROSTRUCTURE OF AL2O3 IMPLANTED WITH IRON AT - 185-DEGREES-C

Analytical electron microscopy and Rutherford backscattering spectrometry have been used to investigate the effect of post-implantation annealing on the microstructure of Al2O3 implanted with iron at -185-degrees-C. By varying the implantation dose, annealing temperature, and annealing environment it has been possible to investigate the Fe2O3-Al2O3 and Fe-Al2O3 phase relationships. It was found that the as-implanted amorphous surface layer crystallizes according to a two-stage process. The amorphous layer first transforms to gamma-Al2O3 and then epitactical regrowth of alpha-Al2O3 follows. The redistribution of Fe during annealing is related to the Al2O3 phase present and is dependent on the annealing environment, O2 or 96% Ar-4% H2. The microstructure which develops during annealing at 1100-degrees-C in oxygen depends on the implantation dose (Fe concentration). Results show that as the dose increases the solubility limit of Fe2O3 in Al2O3 is exceeded and the excess Fe precipitates in the form of Fe2O3. During annealing at 1100-degrees-C in a reducing environment the majority of the Fe is driven towards the surface and precipitated as alpha-Fe. The observed phase transformations are in good agreement with the Fe2O3-Al2O3 phase diagram.