Formation and structure of Sn and Sb nanoclusters in thin SiO2 films

We investigated the formation mechanism of Sn and Sb nanoclusters in thin SiO2 films by X-ray absorption spectroscopy (XAS). Sn and Sb nanoclusters have been formed in 85 and 22 nm thick SiO2 layers, respectively, by 80 keV/l X loll cm(-2) Sn and 10 keV/5 x 10(15) cm(-2) Sb ion implantation followed by thermal treatments. XAS analyses provided unique information on the local environment of Sn and Sb ions in SiO2 with respect to different annealing conditions. Sn and Sb atoms are mainly coordinated with oxygen in the as-implanted samples. Annealing at different temperatures (800-1100 degreesC) and in different atmospheres (N-2 or Ar + 7%H-2) leads to the formation of metallic clusters or oxidized ones. Even when the metallic phase is detected, a fraction of Sn or Sb atoms still remains dissolved in the matrix or forms small oxide clusters. Annealings at high temperature (1100 degreesC) for a short time (30 s) or in Ar + 7%H-2 atmosphere (even if at lower temperature) are more effective for the formation of metallic clusters and for reducing the oxidized atom percentage in the matrix