Metal–Oxide Interactions on Copper-Segregated and Copper-Deposited TiO2 Rutile (001) Surfaces

Scanning tunneling microscopy and spectroscopy are used to study local electronic variations across a surface containing one monolayer of copper on TiO₂ rutile (001). The interactions that occur at the metal–oxide interface when the sources of the copper are segregation from the bulk and ultra-high-vacuum deposition are compared by characterizing the associated surface morphologies and electronic properties. The morphologies of these surfaces are similar in that the copper forms clusters; they are dissimilar in that copper features exist on two size scales on the segregated surface, whereas the deposited copper clusters are uniform in size and are aggregated. The electronic properties of the two surfaces also are found to differ: the copper-segregated surface is insulating, whereas the copper-deposited surface is conductive. The electronic properties are discussed in terms of the effects of surface-charge and ionic-charge concentration gradients.