Ultrafast electron dynamics at surfaces probed by resonant Auger spectroscopy

Ultrafast charge transfer processes from adsorbates to substrates are belie ved to occur on the timescale of (sub)-femtoseconds. In this paper we prese nt experimental evidence for resonant tunneling of electrons at surfaces in the time regime ranging from <1 to similar to 50 fs. The technique used to measure these ultrafast processes is based on high-resolution spectroscopy of the decay of core-excited states. We use the natural lifetime of the co re-excited states, which is on the order of a few femtoseconds for the syst ems investigated, as an internal clock of the adsorbate systems, (C) 2000 E lsevier Science B.V. All rights reserved.