Optical reflectance anisotropy of the Si/Cu(110) surface alloy.

ABSTRACT

Measurements of the optical reflectance anisotropy (RA) of the Si/Cu(110)-c(2 × 2) surface alloy are reported. Significant changes in the RA response of Cu(110) are observed upon the formation of the surface alloy, and with the growth of one-dimensional (1D) anisotropic Si chains on top of the surface alloy. The transitions between the surface states near the Fermi level (E(F)) at the [Formula see text] symmetry point on the clean Cu(110) surface are no longer observed in RA spectra of 0.3 ML Si coverage. Peaks in RA spectra arising from transitions between surface-modified bands near E(F) at the L point are found to be sensitive to the formation of the surface alloy. The RA response of the c(2 × 2) surface alloy from 3.0 to 5.5 eV is simulated using a simple three-phase derivative model. The addition of an overlayer phase to this model makes it possible to simulate higher coverage Si/Cu RA profiles where 1D Si chains cover the surface alloy. The success of the models, in which discrete phases contribute to the RA response, supports the view that the Si chains grow on top of the intact c(2 × 2) alloy. Depositing between 1.2 and 1.8 ML Si results in no change to the RA spectroscopy signal, indicating that the signal remains sensitive to the covered alloy interface.