Identification of surface optical photoemission (div Ā ≠ 0) from silver: The significance of high index faces

The spectral and crystallographic dependence of the photoyield Y p for p-polarized light has been measured on a cylindrical silver single crystal. In particular on high index faces, the effect of varying not only the polar but also the azimuthal angle of incidence was used to determine the character of the contributing electron excitation processes. A drastic decrease of the observed azimuthal asymmetry towards energies below the volume plasma frequency has been found. The experimental features support the conclusion that nonlocal electron excitations are dominant in the energy range below 3.8 eV.