Single-Electron Tunnelling at Room Temperature with Adjustable Double-Barrier Junctions

Abstract

Ultrasmall double-barrier junctions with capacitance 10-19-10-18 F were realized in a system consisting of a metallic substrate, an insulating thin organic film, an isolated metal particle, an adjustable tunnelling gap and the tip of a scanning tunnelling microscope (STM). These structures were characterized by STM topography and local current-voltage (I-V) measurements at room temperature. We found clear evidence of Coulomb blockade effects in the I-V characteristics which could readily be explained in terms of simulations based on the semi-classical theory of single-electron tunnelling. The charging energies and resistances derived from our experiments clearly exceed the theoretical limits of thermal energy and resistance quantum required for observing single-electron tunnelling. By varying the STM gap we also verified the dependences of the particle capacitance and of the double-barrier series resistance.