  Efficient generation of charge carriers from a metallic surface is a critical
challenge in a wide variety of applications including vacuum microelectronics
and photo-electrochemical devices. Replacing semiconductors with vacuum/gas as
the medium of electron transport offers superior speed, power, and robustness
to radiation and temperature. We propose a metallic resonant surface combining
optical and electrical excitations of electrons and significantly reducing
powers required using plasmon-induced enhancement of confined electric field.
The properties of the device are modeled using the exact solution of the
time-dependent Schr\"odinger equation at the barrier. Measurement results
exhibit strong agreement with an analytical solution, and allow us to extract
the field enhancement factor at the surface. Significant photocurrents are
observed using combination of W/cm^2 optical power and 10 volts DC excitation
on the surface. The model suggests optical field enhancement of 3 orders of
magnitude at the metal interface due to plasmonic resonance. This simple planar
structure provides valuable evidence on the electron emission mechanisms
involved and it can be used for implementation of semiconductor compatible
vacuum devices.
