Temperature and dose dependences of nitrogen implantation into iron

It has been shown that the depth profile of nitrogen implanted into iron depends strongly on the temperature during and after the implantation. The nitrogen depth profile shows a surface peak which increases with increasing implantation temperature. A systematic study of nitrogen-implanted iron has been performed with different experimental techniques in order to explain this temperature effect.

Pure iron samples have been implanted with 100 keV 15N2+ ions at different doses (5x10¹⁶-5x10¹⁷ ions cm^-2) and at various temperatures (20–200 °C). The specimens were studied by conversion electron Mössbauer spectroscopy in order to measure the relative concentration of iron nitrides such as ε-Fe2N, ε-Fe2N or γ′-Fe4N formed after nitrogen implantation.

These results have been correlated with the nitrogen diffusion process deduced from the nuclear profile taken on the same specimens. The nitrogen surface peak was carefully examined by combining ion scattering spectrometry and secondary ion mass spectrometry with ion beam sputter profiling of the samples. The depth profile of nitrogen clearly shows that nitrogen diffuses towards the surface when the sample is heated during the implantation.