Au/Si nanodroplets towards Si nanowires formation: characterization of the thermal-induced self-organization mechanism

Si nanowires grown by the vapour-liquid-solid technique acquired fundamental relevance in the design of innovative nanostructured devices for electronic and optoelectronic applications. Au clusters deposited on Si are widely used as catalysts of the Si nanowires growth. It has been recognized that the starting Au nanoclusters size distribution strongly influences the final distribution of the Si nanowires and therefore the performances of the nanostructured devices based on them. In the present work we illustrate the formation of Au/Si droplets by the deposition of a thick Au film on Si(100) and annealing at 873K for different times. We focus our attention on the study of the evolution of the droplets size distribution and center-to-center distance distribution as a function of the annealing time at 873K using microscopic techniques such as atomic force microscopy, and scanning electron microscopy. The droplets isothermal-induced self-organization is shown to be a ripening process of hemispherical three dimensional structures limited by the Au surface diffusion. The application of the ripening theory allowed us to calculate the surface diffusion coefficient and all the other parameters needed to describe the entire process.