Effect of thermal oxidation on helium implanted pure iron

The impact of thermal oxidation on Helium (He) implanted pure iron (Fe) was investigated to experimentally evaluate how thermal oxidation influences the diffusion and distribution of He within the material. In case of the sample with the lowest dose (2 × 10¹⁷ ions/cm²), the thinnest oxide layer was observed compared to the non-implanted pure Fe. It is due to He nano bubbles implanted in the material, which hinder the diffusion of Fe ions necessary for forming the oxide layer. For the medium dose sample (5 × 10¹⁷ ions/cm²), the oxide layer was slightly thicker than that of the lowest dose, however it had more porous structure due to the numerous nano He bubbles. In addition, a large bubble region around 150–200 nm depth was generated. The highest dose sample (1 × 10¹⁸ ions/cm²) was observed that the escape of He was accelerated by the large amount of nano He bubbles from within the metal, forming a porous Fe matrix on the top surface and an oxide layer that is very porous but thicker than those of lower doses.