Influence of the reconstruction in Ag/Cu(111) on the surface electronic structure: Quantitative analysis of the induced band gap

In this work we present high-resolution angle resolved ultraviolet photoelectron spectroscopy on the system Ag/Cu(111). For 1 ML Ag one obtains the well-known quasicommensurate triangular reconstruction for which we observe the opening of a band gap in the Shockley state at a parallel momentum of k(parallel to)approximate to 0.151 angstrom(-1) as a consequence of a Bragg reflection at the new zone boundaries of the supercell. The position of the zone boundaries in k space corresponds to a hexagonal supercell with an extension of 9.4 times the interatomic distance of the Cu(111) surface. We present a quantitative analysis of the position and width of the band gap and discuss the modified shape of the Shockley-state Fermi surface. The reduced surface Brillouin zone can also be observed for the 2 ML system. Here the Shockley state is shifted further towards the Fermi level and, consequently, the gap lies in the region of the unoccupied electronic states clearly above the Fermi level. Our results are in contradiction to previous studies.