High-fluence nitrogen implantation into metals

Nitride ceramics are formed on metal surfaces by high-fluence nitrogen implantation and the mechanical and chemical properties of the surfaces are modified. However, the thickness of the nitride layer is limited by the sputtering effect and the migration of implanted nitrogen towards the surface. In this work, we studied these effects for nitrogen implantation into several kinds of metals (Al, Si, Ti, V, Fe, Co, Ni, Zr, Nb, Mo, Ta and W) by Monte Carlo simulations using the dynamic SASAMAL code in comparison with the experimental results obtained by NRA. The dynamic SASAML code takes into account target alterations which occur under high-fluence implantations, so that dynamic changes in composition, deposited energy, retained probability of the implanted ion, sputtering effects, etc. with fluence can be calculated. For nitrogen implantations into metals, the saturated nitrogen concentration is assumed to equal that of the saturated nitride phase and nitrogen atoms above stoichiometry are assumed to diffuse towards the surface. The depth profiles of nitrogen concentration and the retention of nitrogen obtained by the code agree very well. with the experimental results for 50 keV nitrogen implantations into metals with fluences of 10(17)-10(18) ions cm(-2). The calculated sputtering yields were compared with the semi-empirical values.