Microstructure of Au nanoclusters formed in and on SiO(2)

Au nanocrystals dispersed in or on an amorphous SiO2 substrate were formed by a self-organizationprocedure based on sputtering deposition and subsequent annealing.The kinetic mechanisms of the Au nanocrystals self-organization induced by the annealing processeswere studied by transmission electron microscopy. A clear difference between the Au nanocrystals growthin and on SiO2 was found: in either cases the growth process was a ripening mechanism limited by diffusionbut with a different growth rate.On the other hand, high-resolution transmission electron microscopy analyses allowed us to studythe nanocrystals equilibrium shape and internal atomic structure evidencing a strong influence of thesurrounding environment. Quantitative data on the cluster surface free energy were obtained via theinverse Wulff construction. An angular and radial symmetric surface free energy function for nanocrystalsisotropically surrounded (Au nanocrystals in SiO2) was found, determining symmetric nanocrystalsequilibrium shapes. An angular and radial asymmetrical surface free energy function for nanocrystalsanisotropically surrounded (Au nanocrystals on SiO2) was found, determining asymmetrical nanocrystalsequilibrium shapes.