Tunneling resistance of double-barrier tunneling structures with an alkanethiol-protected Au nanoparticle

Coulomb staircases in double-barrier tunneling junctions consisting of a scanning-probe-vacuum-gap-alkanethiol-protected Au nanoparticle/Au (111) electrode have been measured as a function of the set point current of scanning tunneling spectroscopy. The tunneling resistances of the scanning probe-Au core of a nanoparticle (R-1) and the Au core-Au (111) electrode (R-2) are evaluated by fitting a theoretical Coulomb staircase into the experimental tunneling current-voltage characteristics measured by scanning tunneling spectroscopy. When a vacuum gap exists between the scanning probe and alkanethiol Au nanoparticles, R-1 is inversely proportional to the set point current. On the contrary, in the case of R-1 < R-2, the top of the tip of the scanning probe tends to penetrate the octanethiol-protecting molecule of an Au nanoparticle. R-2 is found to be independent of the set point current, and R-2 of octanethiol- and hexanethiol-protected Au nanoparticles are evaluated as 7.6 G Omega +/- 10% and 460 M Omega +/- 10%, respectively.