Inelastic Low-Energy Electron Diffraction Measurements on Al (111)

Abstract

An experimental study has been made of electrons in the energy range 40–80 eV, inelastically scattered and diffracted from a clean Al(111) surface. The surface is prepared by epitaxial vapor deposition on a Si(111) single-crystal surface in ultrahigh vacuum immediately preceding the measurements. The inelastic electron intensity at a given energy loss and angle is obtained as the energy derivative of the amplified electron current from a Faraday collector having a retarding field analyzer and limited angular acceptance. The energy derivative comes from the digitally computed average of a repeatedly measured difference in dc signal accompanying a fixed increment in retarding field. Using this method inelastic angular and loss profiles at 15° incidence have been obtained in the vicinity of a Bragg maximum of the 00 elastic beam. The profiles show structure related to the surface and volume plasmon momenta by a two-step model of inelastic diffraction. Dispersion data inferred by applying this model to the “loss-before-diffraction” structure are compared with results from other sources. The surface plasmon dispersion obtained from inelastic low energy electron diffraction measurements shows promise as a new means of characterizing solid crystalline surfaces.