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

Surface properties of single crystalline α-Al2O3 were changed by the implantation of high doses of Co ions. Colorless and transparent (0001) and (112̄0) sapphire samples were implanted at room temperature with 150 keV cobalt ions with fluences in the range of 1016 to 5×1017 Co+/cm2. For the highest dose the surface displays a metallic-like behavior after implantation. The absorption spectra reveal the presence of the 200 nm band due to the implantation damage. Annealing in an oxidizing atmosphere promotes the diffusion of Co leading to the formation of a Co–Al–O compound that extends to a depth of 250 nm. This new structure is responsible for the blue and green coloration of the samples, depending on the Co fluence. Annealing in reducing atmosphere produces a Co-rich layer in the first 80 nm of the surface and the samples remain with the dark brown coloration characteristic of the implantation damage.