Dynamic Charging At Room Temperature Of Au Nanoparticles Prepared By A Micellar Technique

Applying a recently developed micellar technique, ordered arrays of gold nanoparticles with narrow size distributions were deposited onto thin Nb(110) films covered by an ultrathin Al2O3 layer of thickness similar to 1 nm serving as tunneling barrier. Analyzing these particles by scanning tunneling microscopy and spectroscopy at room temperature revealed Coulomb blockade (CB) effects with charging energies in the range 0.2-1.5 eV. Relevant CB parameters of individual nanoparticles, which are clearly separated from their neighbors, could be determined quantitatively by fitting experimentally obtained current-voltage curves to orthodox theory. In this way, an almost linear relation between the total capacitance of the CB system and the particle size is found as expected for a simple free sphere model with an effective dielectric constant. Though the agreement between orthodox theory and experiment in general is satisfying, there are also some significant deviations such as non-Ohmic behavior of the tunneling barriers, a strong dependence of the charging on the lateral position of the tunneling tip with respect to a single particle, and an unexpected heating effect possibly due to the long dwell time of the charge carriers on the islands.