VOLTAGE-ACTIVATED CHARGE MOTION MEASURED BY A MESOSCOPIC 2-TUNNEL-JUNCTION SYSTEM

We present measurements on two serially coupled, small-capacitance tun nel junctions formed using a scanning tunneling microscope and a film composed of isolated metallic islands on an oxidized conducting substr ate. Grains near the current-carrying island serve as mesoscopic charg e traps. This geometry provides a model system in order to understand the effect of charge traps as noise sources in single-electron devices . We measure discontinuous shifts in tunnel current caused by changes in the local electrostatic environment. These shifts depend on the tip height above the sample. The tip is thus a driving force for charge m otion near the device; its electrostatic influence extends over an are a larger than the region of tunneling contact.