COULOMB-BLOCKADE SPECTROSCOPY OF GOLD PARTICLES IMAGED WITH SCANNING-TUNNELING-MICROSCOPY

We have measured Coulomb-blockade effects in a two-tunnel-junction structure formed with a scanning-tunneling-microscope (STM) tip and samples composed of gold particles deposited onto a partially oxidized aluminum-base-layer film. Clear topographic images of the particles are routinely taken with the STM and well-defined Coulomb-blockade and staircase current-voltage (I-V) characteristics of the imaged particles are obtained. The variable nature of the tip-particle junction is used to measure the changes in the I-V characteristic as the tip-particle separation is changed. Using a semiclassical theory for the Coulomb blockade in serially coupled junctions, the tip-particle and particle-base-layer junction parameters are uniquely determined. These parameters vary as expected due to the changing tip-particle separation and are consistent with the geometric information obtained in the images. In addition, when the tip-particle separation is made small, a smearing of the Coulomb staircase occurs that is not described by the semiclassical theory.