Optical recognition of atomic steps on surfaces.

Visible and UV light spectra display striking differences in optical reflectivity for the two types of monatomic steps on copper (111) surfaces. Electronic structure calculations trace these differences to the specific contributions of p(axially) and p(radially) local densities of states, parallel and perpendicular to the steps, of the distinctly coordinated corner atoms. The local origin of the spectral reflectance anisotropy is further corroborated by experiments on Cu(111) surfaces with varying step densities. Site specificity of the electronic structure of atoms in low coordinated sites on Cu(111) vicinals is thus revealed by reflectance anisotropy spectroscopy which can thereby detect step atom densities down to 10(13) atoms/cm(2).