Optical changes induced by high fluence implantation of Au ions on sapphire

Optical and structural properties of single crystalline α-Al2O3 were changed by the implantation of high doses of Au ions. Colorless transparent (0 0 0 1) and (1 1 2-bar 0) sapphire samples were implanted at room temperature with 160 keV gold ions with fluences up to 1017 Au · cm-2. After implantation amorphization is observed down to 120 nm for the highest doses, with the gold profile centered at 40 nm from the surface. The optical absorption spectra reveal the presence of a band peaking at 560 or 580 nm, depending on the sample orientation and implantation dose. This band is related to the presence of gold colloids. Annealing in an oxidizing atmosphere promotes the full recrystalization of the matrix along with segregation of Au to the surface, in an easily removable layer. Annealing in a reducing atmosphere produces less recrystalization and the redistribution of gold. This shows as a large in-diffusion for the (1 1 2-bar 0)-samples or as a thin Au rich buried layer in (0 0 0 1)-samples. The samples remain with the dark brown coloration characteristic of implantation damage. The sample orientation, the implantation dose and the temperature of annealing in reducing atmosphere produce controllable shifts of the position of the absorption bands in the visible range, thus allowing the control of the colloid system optical properties