Photoemission loss spectra of metals with emergence parallel to the surface

Abstract

A theory is presented for the energy loss spectra of photoelectrons emitted from atoms located outside a metal sample at a distance z 0 from the surface. These electrons travelling along trajectories parallel to the surface, loss energy mostly by surface plasmon excitation, the losses by bulk plasmon or pair excitations being negligible. The intensity of losses by surface plasmon excitations is found to be proportional to the logarithm of the length l of the trip of the photoelectrons along the surface, a length which extends from the emitting atom to the surface edge. But this intensity does not depend on the distance z 0 as long as z 0/ l small. Considering only the high energy photoemission where the initial energy ϵ 0 of the electrons is much larger than the surface plasmon energy ω s , we find that these l-dependent losses only occur when the angle of emergence is smaller than (ω s/ϵ 0) 1 2 and peak strongly when this angle is smaller than ω s /2 ϵ 0. An experiment with appropriate parameters is proposed to verify the principal results of our theory. Further investigation will yield interesting information on the surface plasmon structure, e.g. the dispersion rule.