Tunable single-electron tunneling behavior of ligand-stabilized gold particles on self-assembled monolayers

A series of heptanethiol-stabilized gold particles with narrowly distributed core sizes ranging from $\sim 1.8$ to $\sim 15$ nm were synthesized and deposited on self-assembled alkanethiol monolayers. The current-voltage characteristics were studied systematically by scanning tunneling microscopy and scanning tunneling spectroscopy, and the results correlate well with the gold core sizes. While equidistant staircases originating from the Coulomb blockade (CB) effect are observed for large particles $(>~4.6$ nm), irregular staircases are observed for small particles (nominal size of 1.8 nm). The latter indicates that both the CB effect and discrete quantum energy levels contribute to the current-voltage spectra. Furthermore, single-electron tunneling behavior are shown to be tunable either by varying the gold particle size or by adjusting the tip-particle distance.