It had been reported that, under DC plasma conditions, the diffusion of C into Fe was much greater than that obtained under thermal equilibrium conditions. It had been postulated that the exceptionally high C up-take was due to the rapid infusion of C into the surface, from the plasma, and not to an anomalously high diffusion rate in the bulk. The present aim was to determine whether rapid infusion of C, and classical C diffusion rates obtained from high CH4 concentration plasmas, were also observed for the lower C-content (1%CH4) plasmas used in CVD diamond deposition. Experiments were conducted for deposition times of up to 300s under plasma-CVD diamond deposition conditions at a substrate temperature of 950C. The C profile was analyzed by using Auger electron spectroscopy and Rutherford back-scattering spectroscopy. The diffusion coefficient calculated for 950C, from thermodynamic data, was 3.0 x 10−11m2/s. That estimated from Auger electron spectroscopic depth profiles, by using a constant surface concentration solution to Fick’s second law, was found to be 4.2 x 10−10m2/s. Thus, although the C content in the plasma was very low, the diffusion which occurred under plasma conditions at a sample temperature of 950C was equivalent to that expected for thermal diffusion at 1244C.

P.S.Weiser, S.Prawer, D.N.Jamieson, R.R.Manory: Thin Solid Films, 1996, 290-291, 186-9