Nucleation of Silicon Nanoparticles in Amorphous Silicon Dioxide Matrices

In this contribution I summarize our research on the formation of nanoparticles embedded in a-SiO2-x matrices. In particular, I focus on the Si diffusion in SiO2-x matrices, and amorphous-to-crystalline phase transition in Si nanoparticles embedded in SiO2-x. I show that Si diffusion can be rationalized in terms of three mechanisms: O-driven (i.e. driven by the change of O-coordination), Si-driven, and bond-swapping (i.e. driven by the change of "local" stoichiometry). The relevance of each of these mechanisms depends on the silicon concentration in the sample and on the temperature. The O-driven mechanism dominates at low Si concentrations, and Si-driven and bond-swapping dominate at higher ones. At higher T the effect is mitigating the difference of contribution among the various mechanisms. Concerning amorphous-to-crystalline phase transition, I show that in small nanoparticles (radius = 1150 degrees C).