Photoemission Studies of the Noble Metals. I. Copper

Abstract

New photoelectric energy-distribution and quantum-yield measurements have been made on carefully prepared clean Cu films in the range of photon energies 4.8-11.6 eV. The energy-distribution curves (EDC's) are found to be rich in structure. They give no evidence that conservation of k provides an important optical selection rule; rather, it appears that the model of nondirect transition suffices to explain the data. [In this model only conservation of energy and the product of the initial and final optical densities of states (ODS) are important in determining the optical transition probability.] By combining our new results with those obtained earlier by Berglund and Spicer from cesiated Cu, an ODS has been constructed for copper over a range of ∼20 eV. Four peaks or shoulders are found in the ODS for the $d$ states, which correlate well in position with structure in the density of states calculated by Mueller and by Snow. These peaks or shoulders are located approximately 2.3, 2.9, 3.7, and 4.5 eV below the Fermi surface. Comparison is also made between the ODS and information on the density of states obtained by x-ray and ion-neutralization studies. Using the ODS, a large number of EDC's are calculated and found to agree well with experiment. In addition, reasonable agreement is found with experiment when the ODS is used to calculate the quantum yield, the electron-electron scattering length, and the imaginary part of the dielectric constant.