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

Abstract

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 $7.6\phantom{\rule{0.3em}{0ex}}\mathrm{G}\ensuremath{\Omega}\ifmmode\pm\else\textpm\fi{}10%$ and $460\phantom{\rule{0.3em}{0ex}}\mathrm{M}\ensuremath{\Omega}\ifmmode\pm\else\textpm\fi{}10%$, respectively.