  A setup for studying the influence of external electric fields on dynamic
surface processes is described. Spatially-extended homogeneous electric fields
are realized by applying a DC voltage in between a planar electrode and a
metallic substrate, which are separated by a narrow vacuum gap. The functional
capability of the device is demonstrated by recording the field-emission
characteristic as a function of the applied field up to 2.3 V/nm, revealing
proper Fowler-Nordheim tunneling behavior.
