title: Femtosecond dynamics of electron localization at interfaces
abstract: The dynamics of two-dimensional small-polaron formation at ultrathin alkane layers on a silver(111) surface have been studied with femtosecond time- and angle-resolved two-photon photoemission spectroscopy. Optical excitation creates interfacial electrons in quasi-free states for motion parallel to the interface. These initially delocalized electrons self-trap as small polarons in a localized state within a few hundred femtoseconds. The localized electrons then decay back to the metal within picoseconds by tunneling through the adlayer potential barrier. The energy dependence of the self-trapping rate has been measured and modeled with a theory analogous to electron transfer theory. This analysis determines the inter- and intramolecular vibrational modes of the overlayer responsible for self-trapping as well as the relaxation energy of the overlayer molecular lattice. These results for a model interface contribute to the fundamental picture of electron behavior in weakly bonded solids and can lead to better understanding of carrier dynamics in many different systems, including organic light-emitting diodes.
authors.affiliation: Department of Chemistry, University of California, Berkeley, CA 94720, USA, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.initials: N
authors.lastname: Ge
authors.initials: CM
authors.lastname: Wong
authors.initials: RL
authors.lastname: Lingle
authors.initials: JD
authors.lastname: McNeill
authors.initials: KJ
authors.lastname: Gaffney
authors.initials: CB
authors.lastname: Harris