Photoemission Studies of Copper and Silver: Theory

Abstract

Theoretical expressions are derived for the quantum yield and for the energy distribution of photoelectrons assuming bulk photoemission from a solid. The effects of electrons which escape without inelastic scattering after optical excitation, and of those electrons which escape after one inelastic-scattering event, are considered. The expressions relate optical transition probabilities, optical constants, and mean free paths for inelastic scattering in a solid to quantities which can be measured in photoemission experiments. Examples of photoemission data are interpreted to show how the contribution of once-scattered electrons can be separated from the contribution of those electrons which have not suGered an inelastic-scattering event before escaping. The contribution to photoemission of those electrons which have not been scattered is analyzed to show the way in which direct and nondirect optical transitions can be identi6ed and the way in which the density of states in a solid can be determined. The contribution of once-scattered electrons to photoemission is analyzed to show the way in which the nature and strength of inelastic-scattering mechanisms can be determined. The effects of electron-electron scattering, scattering by plasmon creation, and the Auger process are described, and methods of obtaining mean free paths and other scattering parameters are suggested.

Reduction of Intrinsic Electron Emittance from Photocathodes Using Ordered Crystalline Surfaces

“…For polycrystalline cathodes with disordered surfaces, normally used in photoinjectors, the transverse momentum can be calculated within the 3-step photoemission picture [9] as shown by Dowell and Schmerge [10]. This model assumes an isotropic distribution of electron trajectories, a free electron dispersion relation within the material and zero lattice temperature.…”

Surface and bulk contribution to Cu(111) quantum efficiency

“…The predicted total yield, obtained by integrating this quantity over all the possible |i and |f , is supposed to be isotropic for regular systems like noble metals bulk bands, and proportional to |A| 2 inside the sample. As such, in the three step model [10], the only dependence of the yield on the incidence light is expected to be the total absorbed energy. This is proportional to the incident light intensity and to (1−R(θ)), where R(θ) is the reflectivity calculated from the Fresnel laws [14].…”

“…Cu(111) was chosen as a sample due to its robust nature and its well known and experimentally verified band structure [5][6][7]: this allows us, through tuning the incident photon energy hν, to control the relative proportions of surface and bulk electrons emitted. As expected [8,9], the three step model [10], which predicts a QE proportional to the absorbed part (1 − R(θ)) of the incident photon energy, needs to be corrected to account for the more effective emission from the electric-field component perpendicular to the sample's surface. Since the intensity of this behavior, known as the vectorial photoelectric effect, increases with the surface sensitivity of the emission process, it is directly related to the well-known surface photoelectric effect [11][12][13], due to the variation at the sample surface of the perpendicular component A ⊥ of the light electromagnetic potential.…”

A New Spin on Photoemission Spectroscopy

“…This was first shown by Berglund and Spicer in 1964 when they identified the 3d DOS in Ag and Cu. 43,44,45 The electronic states in dispersive valence bands are well defined in both energy and momentum. Because momentum is conserved in optical excitation during the photoemission process, one can consider attempting to measure both the binding energy and momentum, or k vector, of the electronic states in the valence bands.…”