Quasilocalized hopping in molecularly linked Au nanoparticle arrays near the metal-insulator transition

Abstract

We have investigated the temperature dependence of the conductance of 1,4-butane dithiol linked Au nanoparticle films from $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. At low temperatures $(T<10\phantom{\rule{0.3em}{0ex}}\mathrm{K})$, conductance becomes independent of temperature and exhibits strong nonlinearity with voltage, which we attribute to tunneling. At higher temperatures $(T>20\phantom{\rule{0.3em}{0ex}}\mathrm{K})$, the conductance behaves as $g\ensuremath{\propto}\mathrm{exp}[\ensuremath{-}{({T}_{0}∕T)}^{1∕2}]$. Qualitatively, this is consistent with an Efros-Shklovskii variable range hopping model based on a competition between Coulombic and intercluster tunneling processes. However, we find that hopping distances are too large ($62--720\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ at $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$) to be consistent with tunneling between clusters and tend to scale with cluster size. We propose a modified, ``quasilocalized hopping'' model based on competition between single-electron cluster charging and intracluster electron backscattering to explain this temperature dependence.