Temperature and dose dependence of Nitrogen implantation into iron: Experimental results and numerical modelling

It has been shown that the depth profile of nitrogen implanted into iron depends strongly on the temperature of the sample during the implantation. The nitrogen depth profile shows a surface peak which increases with the implantation temperature. A systematic study of nitrogen implanted iron has been performed with different experimental techniques, and a numerical model has been developed in order to explain this temperature effect. Pure iron samples have been implanted with 100 keV15N2+ ions (50 keV atom−1) to different doses (2 × 1016 to 5 × 1017 N cm−2) and at various implantation temperatures (20–200 °C). The specimens were studied by conversion electron Mössbauer spectroscopy in order to measure the relative concentration of iron nitrides (ϵ-Fe2N, ϵ-Fe3N, γ′-Fe4N).

The nitrogen depth profiles were measured with the 15N(p, αγ)12C nuclear resonant reaction (Ep = 429 keV). The numerical model takes into account preferential sputtering, thermal diffusion, radiation enhanced diffusion, secondary phase precipitation and radiolytic decomposition of the precipitates. The nitrogen surface peak is shown to be the consequence of an enhanced precipitation near the surface. Nitrogen implantation in copper, nickel, molybdenum and cobalt show that the existence of that peak is correlated with the formation enthalpy of the corresponding nitride.