EXPERIMENTAL HOT-ELECTRON AND PHOTOHOLE LIFETIMES AT METAL-SURFACES -WHAT DO WE KNOW

The dynamics of excited electron states at metal surfaces is of consid erable relevance for various surface processes. Therefore, intense res earch activities are presently addressed to its experimental observati on and to a more quantitative theoretical understanding. We present a compilation of some recent experimental results obtained by different groups using various one- or two-photon photoelectron spectroscopies, in both the energy-resolved and the time-resolved regime. An excellent agreement is found for data referring to an s,p-like Shockley surface state located 0.4 eV below E-F on Cu( I 1 1), when results of various techniques are compared. However, in general, the situation is unclea r. Hole-lifetimes near E-F seem to be masked by rapid dephasing proces ses due to defect scattering. Hot-electron lifetimes obtained by diffe rent groups using different techniques show unexplained discrepancies. Ln particular, if we assume an energy dependence of the energy relaxa tion according to tau proportional to(E-E-F)(lambda), the presently av ailable database does not yet reveal whether lambda= -1 or -2. (C) 199 8 Elsevier Science B.V. All rights reserved.