Elucidating the structure and chemical state of Co growth on the ZnO(101̄0) surface

This study elucidates the epitaxial growth structure and chemical state of Co on the ZnO(101̄0) surface by using scanning tunneling microscopy, reflection high-energy electron diffraction, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy. The well-ordered cobalt oxide (CoO _x)(2 × 1) structure is formed at 0.5 ML Co coverage. Increasing the Co coverage from 0.7 to 1 ML allows for the surface characterization by the Co stripe structure, while the Co metallic clusters are clearly developed above 3 ML Co coverage. Coverage-dependent measurements of the Co chemical state indicate that the initial Co mixed oxidation and metallic state exists at submonolayer and gradually transfers to a metallic Co-dominated state. The results also suggest that the initial growth mode is two-dimensional-like and bridged to three-dimensional at higher Co coverages.