SAM investigations of temperature programmed surface segregation of impurities in α-iron

The time development of the surface concentration of impurities such as sulphur and nitrogen in high-purity polycrystalline α-iron samples has been investigated by means of Auger Electron Spectroscopy (AES) and Scanning Auger Microscopy (SAM) during linearly increasing the temperature from about 100 to 850°C. The subsequent segregation of N and S revealed strong differences in the segregation kinetics of these elements — especially with respect to the contribution of the dominating transport mechanism (grain boundary diffusion and bulk diffusion). Calculating the effective diffusion coefficient of S from two subsequent segregation runs, strongly differing values were found. An interpretation of the change in the diffusion properties of sulphur is given based on SIMS (Secondary Ion Mass Spectroscopy) investigations performed before and after the thermal treatment.