Voltage-activated charge motion measured by a mesoscopic two-tunnel-junction system

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Abstract
We present measurements on two serially coupled, small-capacitance tunnel junctions formed using a scanning tunneling microscope and a film composed of isolated metallic islands on an oxidized conducting substrate. Grains near the current-carrying island serve as mesoscopic charge 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 motion near the device; its electrostatic influence extends over an area larger than the region of tunneling contact.