Applied Surface Science, Vol.252, No.9, 3274-3277, 2006
Slow positron beam study of corrosion-related defects in pure iron
Corrosion-related defects of pure iron were investigated by measuring Doppler broadening energy spectra (DBES) of positron annihilation and positron annihilation lifetime (PAL). Defect profiles of the S-parameter from DBES as a function of positron incident energy up to 30 keV (i.e. similar to 1 mu m depth) were analyzed. The DBES data show that S-parameter increases as a function of positron incident energy (mean depth) after corrosion, and the increase in the S-parameter is larger near the surface than in the bulk due to corrosion. Furthermore, information on defect size from PAL data as a function of positron incident energy up to 10 keV (i.e. similar to 0.2 mu m depth) was analyzed. In the two-state trapping model, the lifetime tau(2) = 500 ps is ascribed to annihilation of positrons in voids with a size of the order of nanometer. tau(1), which decreases with depth from the surface to the bulk, is ascribed to the annihilation of positrons in dislocations and three-dimensional vacancy clusters. The corroded samples show a significant increase in tau(1), and the intensity I-2, and near the surface the corroded iron introduces both voids and large-size three-dimensional vacancy clusters. The size of vacancy clusters decreases with depth. (c) 2005 Published by Elsevier B.V.