The effect of sputtering-induced disorder on the surface dielectric tensor of Cu(110)

The effect of low-energy sputtering on the surface electronic structure of Cu(110) was studied under room temperature conditions by means of reflection-anisotropy spectroscopy (RAS) at photon energies between 1.6 and 6 eV. Sputtering times varied from 0 to 60 min, and the energy of the Ar+ ions was 500 eV. Spectral changes that depended on fluence in a reproducible manner were observed. We argue that vacancies in the top layer are responsible for some of the strongest changes, at least for short sputtering times. The spectra could be reproduced by local-field calculations where the screened dipole-dipole interaction coefficients between the top layer and the underlying ones were reduced by a factor proportional to the vacancy concentration. Both components of the surface dielectric tensor are calculated. The behaviour of the RAS signal for longer sputtering times is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.