Local electronic structure of metal particles on metal oxide surfaces: Ni on alumina

Abstract

Ni supported on thin alumina films epitaxially grown on the Re(0001) surface has been studied using scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy (STS). Ni, deposited at 300 K onto the Al₂O₃(111)/Re(0001) surface, forms hemispherical particles with a very narrow size distribution. The transition from layer-by-layer growth to three-dimensional cluster formation has been found to occur at an Ni coverage as low as 0.03 monolayers (ML), indicating a Volmer–Weber growth mode for Ni on Al₂O₃. Upon heating to 900 K, the Ni layer in contact with the Al₂O₃ surface reacts with Al₂O₃ and becomes indistinguishable from the substrate via STM, while Ni in the second and subsequent layers agglomerates. STS was used to study the local electronic structure and to identify the features observed in the STM topographic images.