The initial stages of Cugrowth (up to 20 Å) on ordered Al2O3ultrathin films (∼20 Å thick) synthesized on a Re(0001) substrate are studied by low‐energy ion scattering (LEIS) and x‐ray photoelectron spectroscopy(XPS). LEIS results indicate that Cugrows as three‐dimensional clusters on the Al2O3films at both 80 and 300 K. XPS results show decreases in the Cu 2p 3/2 binding energy and increases in the CuL 3 M 4,5 M 4,5 kinetic energy as a function of coverage. Analysis of these results indicates that Cu is not oxidized at the interface. For the coverage‐dependent shifts in the Cu 2p 3/2 peaks, the initial‐state and final‐state contributions and their relation to Cu cluster size are discussed.