Nitrogen implantation into metals: a numerical model to explain the high temperature shape of the nitrogen depth profile

Abstract

The depth profile of nitrogen implanted in pure iron shows a surface peak whose area increases with the temperature of the sample during the implantation. This surface peak has already been observed by other workers. The nitrogen depth profiles have been measured on a set of iron samples (99.5% purity) implanted with 100 keV N 2 + ions at different doses ( 2 × 10 16−5 × 10 17 ions cm −2 ) and at different temperatures (20–200 °C). In order to explain the shape of the depth profiles and in particular the existence of the surface peak and its dependence on implantation temperature, a numerical model has been developed. This model takes into account preferential sputtering, ion beam mixing, thermal diffusion, radiation-enhanced diffusion (RED), radiation-induced segregation (RIS), secondary phase precipitation and radiolytic decomposition of the precipitates. The surface peak cannot be explained by RED or RIS alone but is the consequence of an enhanced precipitation near the surface of the sample. Samples of copper, molybdenum and nickel have also been investigated in order to confirm that hypothesis and to show that there is a correlation between the presence of the surface peak and the formation energy of the corresponding nitrides. The ion deposition profiles, sputtering yields, ion beam mixing and radiolytic decomposition of the precipitates were calculated with the TRIDYN program.