Local structure of Sn implanted in thin SiO2 films

The formation and the structural properties of Sn nanocrystals produced by ion implantation in thin SiO2 films was investigated by 119Sn conversion electron Moessbauer spectroscopy (CEMS), x-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM). Sn ion implantation was performed at 80 keV with a fluence of 1x1016 cm2, positioning the peak of the implantation profile in the middle of the SiO2. The annealing treatments were performed in the temperature range 800–1100 °C by rapid thermal processing. CEMS and XAS provided unique information on the local atomic and electronic environment of Sn in SiO2 allowing a detailed investigation of the effect of different annealing conditions. In the as-implanted state all Sn ions are oxidized (with both Sn2+ and Sn4+ oxidation states present), while annealing induces the formation of beta-Sn nanoclusters. TEM showed that cluster sizes are in the range 7–17 nm. For clusters with average diameter ,10 nm, XAS detected a reduction in coordination number and interatomic distances. Both XAS and CEMS indicate an increase in the static disorder in the metallic clusters. The investigated annealing treatments do not lead to a complete precipitation of Sn atoms in the metallic phase, leaving a fraction of them oxidized.