Ion beam processing of sapphire single crystals

Abstract

Ion implantation is a well established and widely used technique to change selectively the near surface properties of materials and particularly insulators. In this work we review the implantation of α-Al2O3 with different ions (transition and noble metals) to study the microscopic processes associated with the formation of the new nanostructures. The formation of nanoclusters is observed for implantation fluences above 5 × 1016 cm− 2 of metals in sapphire at room temperature. The clustering process starts to occur during the implantation with e.g. 1–3 nm precipitates being observed in Fe-implanted samples. After annealing in a vacuum the small precipitates coalesce into larger ones following an Ostwald ripening mechanism. In the case of Fe, Co and Ti fluences above 1 × 1017 cm− 2 create a nearly continuous distribution of metallic precipitates parallel to the c plane and surrounded by two regions containing smaller precipitates with the same orientation. The Fe and Co precipitates crystallize in phases oriented with the matrix as demonstrated by detailed multi-axial channeling and XRD analyses. Optical absorption measurements reveal a UV/blue region damage-related absorption band along with the plasmon resonance absorption band in the visible range, e.g. for gold an absorption band appears at 550 nm due to the presence of gold nanoprecipitates. The influence of annealing atmosphere on the development of the new structures will be also addressed.