On the role of Fe in the growth of single crystalline heteroepitaxial Au thin films on sapphire

Abstract Thin Au–Fe bilayers were deposited on c-plane sapphire (α-Al2O3) substrates at room temperature employing the electron beam deposition method. The layers were found to be single crystalline (i.e. the grain size was much larger than the film thickness), with a [1 1 1] and [1 1 0] texture for Au and Fe, respectively, and strong heteroepitaxy to the substrate. Au films deposited on sapphire and Au–Fe bilayers deposited on amorphous SiO2 were polycrystalline and exhibited random in-plane orientation of the grains. The effects of Fe and the Fe–sapphire interface on the microstructure of the Au film were investigated and discussed in terms of the orientation relationships, in-plane strain, interface energy and adhesion. The microstructures of annealed and as-deposited films were very similar, indicating that as-deposited films are close to thermodynamic equilibrium in terms of the orientation relationship with the substrate. This is uncommon for non-equilibrium thin film deposition processes, which usually result in a high density of defects in the as-deposited films.