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 ($T=2\mathrm{K}$) 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 ($n\ge 5$) exhibit a universal scaling behavior $R\sim \exp [(T_0/T{)}^{\nu }]$ with $\nu =0.65$, and all metallic samples ($n\le 5$) exhibit weaker $R\mathrm{\text{−}}T$ dependencies than bulk gold. We discuss these observations in terms of competitive thermally activated processes and strong, $T$-independent elastic scattering, respectively.