Optical properties of copper and silver in the energy range 2.5–9.0 eV

Abstract

The optical properties of copper and silver bulk crystals with atomically clean surfaces have been determined experimentally and interpreted in terms of ab initio band structure calculations. The dielectric functions are evaluated from spectroscopic ellipsometry data taken in ultrahigh vacuum (UHV) in the spectral range of 2.5--9.0 eV (at room temperature). The data are corrected for surface roughness using results from ex situ atomic force microscopy (AFM). Significant differences of detail in the amplitudes and line shape are attributed to the better surface quality of our samples. Density functional calculations of the dielectric functions of copper and silver are carried out, based on models of the valence bands deduced by fitting to experimental Fermi surface and quasiparticle mass data. Small energy shifts, which take into account many-body effects in the final states of the optical transitions in an extended scissors approximation, are needed to bring the calculated dielectric functions into good agreement with the experimental data. The interband transitions associated with individual features in the dielectric function are identified by comparing the energy derivatives of the measured and calculated dielectric functions.