Complex metallic surface phases in the Al/Cu(111) system: An experimental and computational study

The growth of complex intermetallics as surface alloys is investigated by annealing Al thin films deposited on Cu(111) substrate in ultrahigh vacuum. Already at room temperature, the large lattice mismatch between Al and Cu results in interfacial intermixing. Upon annealing, various phases are formed by diffusion depending on the thickness of the Al films and the annealing temperature. The surface structures are characterized by scanning tunneling microscopy, low-energy electron diffraction, and x-ray photoelectron spectroscopy. Three different superlattice phases are identified as well as the complex Hume-Rothery gamma-Al4Cu9 phase. The epitaxial relationships between the surface phases and the Cu(111) substrate are determined. We further investigate the electronic structure of the gamma phase by density functional calculations. Experimental valence bands are compared to calculated density of states and simulated STM images are used to identify possible bulk planes appearing as surface termination.