Metal to insulator transition in films of molecularly linked gold nanoparticles

We report a metal to insulator transition (MIT) in disordered films of molecularly linked gold nanoparticles (NPs). As the number of carbons (n) of alkanedithiol linker molecules (CnS2) is varied, resistance (R) at low temperature (T=2 K) and at 200 K, as well as trends in R vs T data at intermediate temperatures, all point to an MIT occurring at n=5. We describe these results in a context of a Mott-Hubbard MIT. We find that all insulating samples (n >= 5) exhibit a universal scaling behavior R similar to exp[(T-0/T)(nu)] with nu=0.65, and all metallic samples (n <= 5) exhibit weaker R-T dependencies than bulk gold. We discuss these observations in terms of competitive thermally activated processes and strong, T-independent elastic scattering, respectively.