  We use simultaneous electronic transport and optical characterization
measurements to reveal new information about electronic and optical processes
in nanoscale junctions fabricated by electromigration. Comparing electronic
tunneling and photocurrents allows us to infer the optical frequency potential
difference produced by the plasmon response of the junction. Together with the
measured tunneling conductance, we can then determine the locally enhanced
electric field within the junction. In similar structures containing molecules,
anti-Stokes and Stokes Raman emission allow us to infer the effective local
vibrational and electronic temperatures as a function of DC current, examining
heating and dissipation on the nanometer scale.
