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 (${\mathrm{C}}_{n}{\mathrm{S}}_{2}$) is varied, resistance ($R$) at low temperature ($T=2\text{ }\text{ }\mathrm{K}$) 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 ($n\ensuremath{\ge}5$) exhibit a universal scaling behavior $R\ensuremath{\sim}\mathrm{exp} [({T}_{0}/T{)}^{\ensuremath{\nu}}]$ with $\ensuremath{\nu}=0.65$, and all metallic samples ($n\ensuremath{\le}5$) exhibit weaker $R\mathrm{\text{\ensuremath{-}}}T$ dependencies than bulk gold. We discuss these observations in terms of competitive thermally activated processes and strong, $T$-independent elastic scattering, respectively.