The applicability of ultra thin silicon films as interlayers for CVD diamond deposition on steels

In this study, the use of thin Si interlayers (35-150 nm) for promoting diamond deposition onto steel is investigated. The diamond films are deposited by hot filament CVD onto AISI type 316 stainless and high-speed steels. Single stage deposition at substrate temperatures. ranging from as low as 475 to 750 degreesC is found to result only in non-continuous films with low number densities of diamond crystallites. A composite film of diamond and carbides is formed at intermediate temperatures of about 650 degreesC. It is believed that the formation of iron silicide phases at the exposed steel substrate surfaces leads to diffusion barriers for free iron from the steel matrix, so that graphitic soot formation is significantly avoided. Utilizing a two-stage deposition process, the density and uniformity of the deposited diamond films are increased and a nearly continuous cauliflower shaped diamond film is obtained. Micro-Raman spectroscopy, scanning electron microscopy and X-ray diffraction techniques are employed to study the phases, morphology, composition, quality and residual stresses of the grown diamond layers.