Directional memory effects in inelastic photoelectron scattering

We have recently shown that photoemission from core levels of adsorbates on surfaces shows strong angular effects attributable to diffraction processes. In order to gain structural information from this anisotropy it is important to separate out variations in the inelastically scattered background. In a study of the Ni {100} surface both clean and with adsorbed Na we find substantial anisotropies in the background which appear to be directly related to the strong anisotropies in the Ni 3d photoemission. The data suggest that inelastic loss processes contributing to the photoemission “tail” involve predominantly small changes in the direction of the electron wave vector k and so allow much of the no-loss directionality to be retained. The implications for the adsorbate measurements are not severe, however, as our experiments also show the Ni 3d emission angular dependence to be insensitive to the presence of an overlayer.