Helium ion implantation in SiAlON: Characterisation of cavity structures using TEM and IBA

Highly swollen nanoporous layers produced in material surfaces by He implan tation are of special interest for applications such as catalysis. Here we investigate whether nanoporous layers can be produced in the covalently bon ded insulating ceramic, SiAlON. The retention of highly swollen porous stru ctures in thinned TEM sections prepared from such hard brittle materials is particularly challenging. We have successfully prepared such sections both parallel to, and perpendicular to, the implanted surface. At intermediate doses the bubble structures are very similar to those found in metals. At h igh helium doses local swellings at depths around the mean projected range of the He ions (similar to 360 nm) are estimated to be well in excess of 20 0%. Bubble structures are stable under heating to temperatures up to 1200 d egrees C. It is found that the highly cavitated layer is buried below a cry stalline overlayer of compact SiAlON. This overlayer is sufficiently compac t to resist the diffusion of gold from a surface layer to the cavities belo w. (C) 2000 Elsevier Science B.V. All rights reserved.