Schottky-barrier formation at nanoscale metal-oxide interfaces

Isolated, nanoscale (5.0–20.0 nm diameter) Cu clusters on a reduced ${\mathrm{TiO}}_2$ (110) surface exhibit the initiation of the Schottky effect. Apparent height changes of isolated clusters occur in scanning tunneling microscopy imaging as bias conditions are changed. This apparent height change is directly related to current flow through the cluster-oxide interface barrier. Further, depletion zones along the substrate surface adjacent to the clusters exhibit the same bias dependence indicating that changes are associated with local band-bending, analogous to that of macroscopic Schottky barriers. Barrier-height variations with cluster size and with applied voltage are quantified. When compared to models of edge effects in finite-sized systems a direct correlation between geometry and barrier formation is made.