Growth of Au clusters on armorphous Al2O3:: Evidence of cluster mobility above a critical size

We study the 3D growth of clusters during the deposition of Au atoms on amorphous Al2O3. BY comparing transmission electron microscopy images of the growth with Monte Carlo simulations, we show that nucleation takes place on substrate defects, but that further stages of growth imply that clusters leave the defects after they have reached a given critical size, and diffuse. An interesting consequence of this property is that, in contrast to intuition, and in a certain range of size, larger clusters are more mobile than smaller ones in this system.