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 Sn-119 conversion electron Mossbauer spectroscopy (CEMS), x-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM). Sn ion implantation was performed at 80 keV with a fluence of 1x10(16) cm(-2), positioning the peak of the implantation profile in the middle of the SiO2. The annealing treatments were performed in the temperature range 800-1100degreesC 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.