Study of new surface structures created on sapphire by Co ion implantation

Single crystalline alpha -Al2O3 was implanted with several fluences of Co i ons. Detailed angular scans performed after implantation indicate incorpora tion of the Co ions into substitutional Al sites for fluences up to 1 x 10( 15) cm(-2). For higher fluences a large amount of defects are produced and new compounds start to form in the implanted region. At a fluence of 5 x 10 (17) cm(-2) the samples displayed both metallic conduction and ferromagneti c behaviour. Annealing in an oxidising atmosphere promote the diffusion of Co into the bulk leaving a Go-rich thin layer at the surface and leading to the formation of a Co-Al-O compound that extends to a depth of 250 nm. Aft er this annealing the magnetic behaviour disappears and the samples become insulating. Annealing in a reducing atmosphere produces a Go-rich layer in the topmost 80 nm of the surface without loss of the ferromagnetic behaviou r and the metallic conductivity. (C) 2001 Elsevier Science B.V. All rights reserved.