Pattern evolution of crystalline Ge aggregates during annealing of an Al/Ge bilayer film deposited on a SiO2 substrate

When an Al/Ge bilayer film deposited on a SiO2 substrate is annealed at 373-398 K, Ge atoms diffuse out from the inner amorphous Ge layer and spread over the Free surface of the outer Al layer to form crystalline Ge aggregates exhibiting complex substructures. Scanning electron microscopy observations indicate that the activation energy for the pattern evolution of Ge aggregates on the free surface because of annealing is 1.56 eV which is about half the activation energy for crystallization of amorphous Ge.