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

We have investigated the temperature dependence of the conductance of 1,4-butane dithiol linked Au nanoparticle films from 2 K to 300 K. At low temperatures (T<10 K), conductance becomes independent of temperature and exhibits strong nonlinearity with voltage, which we attribute to tunneling. At higher temperatures (T>20 K), the conductance behaves as g∝exp[−(T₀∕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 nm at 100 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.