Surface state in epitaxial Ag ultrathin films on Cu(111)

Room temperature scanning tunneling spectroscopy (STS) and angle resolved photoemission measurements (AR-PES) have been carried out to study the modification of the Shockley surface state in Ag epitaxial layer grown on Cu(1 1 1). Surface morphology of this system is characterized by Ag islands growing along the step edges of the Cu substrate with the well-known 9 x 9 structure. STS reveals two surface states localized on the Cu terraces and on the Ag islands respectively, whose energy position is nearly coverage independent at least in the submonolayer range. Photoemission experiments corroborate this behavior by evidencing two parabolic dispersive bands. The two spectroscopies indicate a shift (120 meV) of the surface state in Ag islands with respect to its position in thick Ag layers. (C) 2001 Elsevier Science B.V. All rights reserved.