Diffusion energy barrier of Au on Bi₂Se₃: theory and experiment

Abstract

The stability and diffusion of ultra-thin thermally deposited Au films on Bi 2 Se 3 was studied using scanning tunneling microscopy and density functional theory calculations. The Au/Bi 2 Se 3 interface is of interest as gold is predicted to provide excellent electrical contact while maintaining the spinpolarized characteristics of the electronic states in Bi 2 Se 3 that make the material attractive for spintronic applications. When deposited at room temperature, Au covers the surface with tightly packed islands of nanometer scale dimension. The surface morphology is stable up to 400 K. At this annealing temperature, Au atoms have sufficient energy to diffuse across the surface and aggregate into larger nanostructures. At 550 K, the Bi 2 Se 3 surface is only sparsely covered, and the Au has formed clusters with length scales 5-10 times larger than the original islands formed at room temperature. Comparison of the experiment and first principle calculation lead to the conclusion that the diffusion energy barrier for Au on Bi 2 Se 3 is as high as 0.47 eV, which is much larger than diffusion barriers on other van der Waals materials.