Effects of steps and ordered defects on Cu(110) surface states

The effects of steps and ordered defects on the surface states supported by Cu(110) terraces are investigated by a combination of reflection anisotropy spectroscopy (RAS) and scanning tunneling microscopy (STM). For several vicinal (110)-type surfaces, we measure the 2.1-eV RAS peak arising from transitions between surface states. A Poelsema-Comsa scattering model is used to relate the intensity of this RAS signal to the surface morphology (the distributions of terrace widths and step-edge roughness) observed by STM, providing a measure of the ability of the surface defects to scatter the Shockley-type surface state. A scattering cross section of area equivalent to 20 unit cells is obtained-a value consistent with previous results obtained from other types of defect for the Cu(110) surface. We find that the Poelsema-Comsa scattering model, originally developed for random distributions of defects, is also applicable to the modeling of RAS intensities of surfaces with ordered and partially ordered defects: specifically steps. Our results highlight the growing importance of the Poelsema-Comsa methodology in combination with RAS data for extracting topographic information associated with surface defects, particularly from surfaces in hostile environments, where RAS can access as a real-time in situ probe.