Dynamics of excited electrons in metals, thin films and nanostructures

The immense progress in the field of ultrashort pulsed lasers made it possible to study ultrafast dynamics of photoexcited hot electrons in metals by means of a variety of pump-probe techniques. Time-resolved two-photon photoemission has the capability of directly monitoring the dynamics of electrons with specific energy and momentum during the course of the transformation of a nascent (as photoexcited) nonthermal electron distribution to an excited Fermi-Dirac distribution. The main purpose of this investigation was to gain a basic understanding of the dynamics of single excited electrons at a metal surface, particularly in an energy region which is important for surface photochemistry and catalytic model reactions (E-F<E<E-Vac). In these studies, the roles of secondary electrons and transport effects in equal pulse cross-correlation experiments were considered. The results demonstrate the feasibility of studying electron relaxation in noble and transition metals as a function of band structure, spin-polarization, surface morphology and dimensionality. We also present an extension of the common time-resolved two photon photoemission method to higher energies (hv>20 eV, UPS mode) and high lateral resolution (PEEM mode). (C) 2002 Elsevier Science B.V. All rights reserved.