  Localized surface plasmon resonance (LSPR) excitation of nanostructures and
charge transfer in plasmonic nanocavities plays a central role in nanoscale
optoelectronics and in applications for plasmonic devices. However, the direct
observation of near-filed induced charge transfer has remained as a challenging
experiment. Here we present LSPR-assisted resonant electron tunneling from an
Ag or Au tip to the image potential states of a Ag(111) surface using scanning
tunneling microscopy (STM). The LSPR-assisted tunneling process results in an
incident photon-energy dependent red-shift of the field emission resonances
(FERs) in the gap. Using the precise control of the gap distance in the STM
junction we demonstrate tuning of the relative contribution from the
LSPR-assisted and the normal STM electron tunneling processes. Furthermore, the
FER intensity mapping of local defects on the surface allows assigning
unambiguously the respective FER levels with and without laser excitation.
