Interplay between surface and electronic structures in epitaxial Ag ultra thin films on Cu(111)

The atomic structure and surface electronic properties of Ag epitaxial ultra-thin films on Cu(111) substrate have been studied by scanning tunneling microscopy (STM) and angle-resolved photoemission (ARPES). In the submonolayer range, Ag films exhibit a surface reconstruction which depends on the preparation temperature. At T=150 K, a 9×9 moiré superstructure is observed resulting from the superposition of Ag and Cu lattices whereas at room temperature a triangular structure is stabilized. Photoemission spectroscopy shows that the surface state energy reflects the morphology and the structure of the Ag films. Below one monolayer, two parabolic dispersions indicate the presence of confined surface states in the Cu terraces and in the Ag islands. The different surface state energies associated with the two Ag layer reconstructions allow to study the irreversible transition from the moiré to the triangular structure.