Copper clusters on Al2O3/NiAl(1 1 0) studied with STM

The structure of nanosize Cu clusters has been studied with scanning tunnelling microscopy (STM). The clusters were deposited on a thin aluminium oxide film created by oxidation of NiAl(1 1 0). The STM images show that the Cu grows as 3D islands on the Al2O3 film, for the coverages studied (θCu⩽5 ML). For crystalline clusters larger than ∼40 Å, the top facet could be imaged with atomic resolution, revealing a (1 1 1) facet. From the shape of the crystalline clusters information about the Cu surface energies has been extracted and compared to theoretical values. From the height-to-width ratio of the Cu clusters the work of adhesion for Cu on the Al2O3 film could be determined to be 2.8±0.2 J/m2 using theoretical values for the surface energies.