Observation of a true interface state in strained-layer Cu adsorption on Ru(0001)

For coverages up to one monolayer, Cu adsorbs in a pseudomorphic structure on the Ru(0001) surface with a 5% tensile strain. Angle-resolved photoemission near the K point in the surface Brillouin zone reveals a state -1.5 eV below the Fermi level which appears localized in the Cu and outermost Ru layers. This state is confirmed by surface linearized, augmented plane-wave calculations to be the antibonding partner of a pair of Cu(3d)-Ru*4d)--derived interface states.