Nanostructure Phase and interface engineering via controlled Au self-assembly on GaAs(001) surface

We have investigated the temperature-dependent morphology and composition changes occurring during a controlled self-assembling of thin Au film on the Gallium arsenide (001) surface by means of electron microscopy at nano and atomic levels. It has been found that the deposition of 2 ML of Au at a substrate temperature lower than 798 K leads to the formation of pure Au nanoislands. For the deposition at a substrate temperature of about 798 K the nanostructures of stoichiometric AuGa phase grown. In turn, Au deposition at higher substrate temperatures results in the formation of well-shaped octagonal nanostructures composed of AuGa2 alloy with the top edge oriented along [-110] the crystallographic direction of the GaAs(001) surface. We have proved that the temperature-controlled efficiency of Au-induced etching-like of the GaAs substrate follows in the layer-by-layer manner leading to the enrichment of the substrate surface in gallium. The excess Ga together with Au forms liquid droplets which, while cooling the sample to room temperature, crystallize developing crystalline nanostructures of atomically-sharp interfaces with the substrate. The minimal stable cluster of 2 atoms and the activation energy for surface diffusion Ed=0.78eV was determined. We show that by changing the temperature of the self-assembling process one can control the phase, interface and the size of the nanostructures formed.