Relationship between strain and the surface electronic structure of Cu(111) films on Ru(0001): Theory and experiment

Abstract

The relationship between strain and surface electronic structure of Cu(111) films grown on Ru(0001) is studied by a combination of tunneling spectroscopy and ab initio theoretical calculations. Experimentally, the relaxation of the 5.5% in-plane lattice mismatch between Ru(0001) and Cu(111) changes layer-by-layer the lateral lattice parameter of the Cu film, while the surface state, that is above the Fermi level for the pseudomorphic monolayer of Cu, shifts down in energy with increasing thickness until it becomes the occupied surface state of Cu(111). The effects due to strain in the Cu films are distinguished from those due to the proximity to the Ru substrate by detailed comparisons with theoretically expanded Cu(111) and Cu/Ru(0001) surfaces. Our ab initio calculations indicate that the observed energy shift must be essentially assigned to the decreasing tensile stress of the deposited film.