Thermal behaviour of ultra-thin Co overlayers on rutile TiO2(1Â 0Â 0) surface

Thermal behaviour of ultra-thin Co overlayers on rutile TiO2(1 0 0) surface has been studied by in situ X-ray photoelectron spectroscopy (XPS). Metal Co overlayers of about 30 Å have been deposited at room temperature on rutile TiO2(1 0 0) surfaces, followed by annealing to different temperatures. It was found that the interfacial reaction between the Co overlayers and TiO2(1 0 0) surfaces occurred upon annealing to temperatures above 400 °C. Above these temperatures, all metallic Co atoms were oxidized into the Co2+ state, while some Ti4+ were reduced to Ti3+ with increasing temperature. Ex situ surface morphology studies by atomic force microscopy (AFM) suggest that thermal annealing resulted in the agglomeration of the metal film deposited at room temperature and the formation of islands. Annealing to higher temperature led to the dissociation of the small Co islands due to Co oxidation while the larger islands remained and grew continuously. Two types of island nanostructures were observed by ex situ high-resolution transmission electron microscopy (HRTEM).