The transformation of β-FeSi2 under Ar ion bombardment studied by XPS, AES and Mössbauer spectroscopy

Abstract

Irradiation effects on iron disilicide layers were induced by 3.5 keV argon ion bombardment and studied by XPS, AES and the Mössbauer spectroscopy. The use of these electron spectroscopies enables the investigation of different depth regions of the altered layer. Iron enrichment is found in a surface-near region by surface-sensitive XPS and shown to influence the electronic structure evaluated by factor analysis. For deeper regions a phase transformation of the stoichiometric β-FeSi2 into the iron-depleted α-FeSi2 is proved by non-destructive Mössbauer spectroscopy (CEMS). Applying depth-selective CEMS it turns out that the transformation to α-FeSi2 reaches up to a depth of 25 nm as evaluated by a model calculation. Simulations of preferential sputtering and atomic mixing processes by the TRIDYN Monte Carlo program agree very well with the experimental results. From these simulations, Si preferential recoil implantation appears to trigger the phase transformation for the structurally favoured α-phase under the sputtering conditions used.