Upon irradiating thin Fe films (deposited on Si wafers) with swift heavy ions in the energy range of a few MeV/amu, it was observed that the Fe surface oxidized due to residual O in the irradiation chamber, induced by the energy deposited by the ion. These processes were investigated in detail by using Rutherford back-scattering spectrometry and conversion electron Mössbauer spectroscopy. It was found that 2 different types of oxidation process were active; depending upon the electronic energy loss of the incident ions. Irradiation above the track formation threshold SecFe of Fe resulted in diffusion-controlled dissolution of O in the Fe bulk. Below SecFe, but above the track formation threshold of iron oxide, chemical reaction and homogeneous oxide phase formation took place in a surface layer, while almost no O diffusion into the Fe bulk was now observed. These phenomena were explained in terms of the O mobility in the excited ion tracks in Fe and iron oxide. The effective diffusion constant estimated for swift heavy ion induced O diffusion in Fe was larger by a factor of 100 to 1000 than the one reported for thermally activated O diffusion in molten Fe.

Oxygen Diffusion and Oxide Phase Formation in Iron under Swift Heavy Ion Irradiation. T.Roller, W.Bolse: Physical Review B, 2007, 75[5], 054107 (7pp)