  We present a quantum-mechanical model for surface-assisted carrier excitation
by optical fields in plasmonic nanostructures of arbitrary shape. We derive an
explicit expression, in terms of local fields inside the metal structure, for
surface absorbed power and surface scattering rate that determine the
enhancement of carrier excitation efficiency near the metal-dielectric
interface. We show that surface scattering is highly sensitive to the local
field polarization, and can be incorporated into metal dielectric function
along with phonon and impurity scattering. We also show that the obtained
surface scattering rate describes surface-assisted plasmon decay (Landau
damping) in nanostructures larger than the nonlocality scale. Our model can be
used for calculations of plasmon-assisted hot carrier generation rates in
photovoltaics and photochemistry applications.
