Annealing behavior of Pd/<i>a</i>-Ge bilayer films

Abstract

Solid-state reaction and crystallization in Pd/a-Ge bilayer films of various ratios of thickness (or composition) after annealing have been investigated by transmission electron microscopy. Besides polycrystalline Pd and amorphous Ge, the Pd2Ge phase is formed in as-evaporated films with 54 and 67 at % of Ge. During annealing at 250 °C Pd2Ge and PdGe are formed. During annealing at 350 °C, besides the formation of Pd2Ge and PdGe, crystallization of amorphous Ge takes place, inducing fractal-like structures with a size of about 1 μm. The fractal dimension varies from 1.60 to 1.88, depending on the composition of the films. The fractal formation can be explained by a random successive nucleation model.