Femtosecond Dynamics of Electron Localization at Interfaces
N.-H. Ge,
C. M. Wong,
R. L. Lingle Jr.,
*
J. D. McNeill,
K. J. Gaffney,
C. B. Harris
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.
Department of Chemistry, University of California, Berkeley, CA
94720, USA, and Chemical Sciences Division, Lawrence Berkeley National
Laboratory, Berkeley, CA 94720, USA.
*
Present address: Lucent Technologies, Bell Laboratories, 2000 Northeast Expressway, Norcross, GA 30071, USA.
To whom correspondence should be addressed. E-mail:
harris{at}socrates.berkeley.edu
