Experimental hot-electron and photohole lifetimes at metal surfaces - what do we know?

The dynamics of excited electron states at metal surfaces is of considerable relevance for various surface processes. Therefore, intense research activities are presently addressed to its experimental observation 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 unclear. Hole-lifetimes near E-F seem to be masked by rapid dephasing processes due to defect scattering. Hot-electron lifetimes obtained by different groups using different techniques show unexplained discrepancies. Ln particular, if we assume an energy dependence of the energy relaxation according to tau proportional to(E-E-F)(lambda), the presently available database does not yet reveal whether lambda= -1 or -2. (C) 1998 Elsevier Science B.V. All rights reserved.