  Surface-enhanced Raman spectroscopy (SERS) is enabled by local surface
plasmon resonances (LSPRs) in metallic nanogaps. When SERS is excited by direct
illumination of the nanogap, the background heating of lattice and electrons
can prevent further manipulation of the molecules. To overcome this issue, we
report SERS in electromigrated gold molecular junctions excited remotely:
surface plasmon polaritons (SPPs) are excited at nearby gratings, propagate to
the junction, and couple to the local nanogap plasmon modes. Like direct
excitation, remote excitation of the nanogap can generate both SERS emission
and an open-circuit photovoltage (OCPV). We compare SERS intensity and OCPV in
both direct and remote illumination configurations. SERS spectra obtained by
remote excitation are much more stable than those obtained through direct
excitation when photon count rates are comparable. By statistical analysis of
33 devices, coupling efficiency of remote excitation is calculated to be around
10%, consistent with the simulated energy flow.
