Transport Properties of Gold Nanoparticle Arrays at Low Temperatures

We investigated the effects of elastic and inelastic cotunneling on the electronic transport properties of Au monolayers and multilayers. Highly-ordered monolayers of dodecanethiol-ligated Au particles (6nm in diameter)$^{1}$ were assembled onto Si$_{3}$N$_{4}$ substrates with prefabricated electrodes. Multilayers were created by adding layers to the original monolayers$^{2}$. Current-voltage (IV) measurements were performed with 50fA resolution down to 30mK. TEM images were taken posterior to all measurements. We found that transition from inelastic to elastic cotunneling occurred at T$\sim $5K. In the inelastic cotunneling regime, the IV curves were found to be nonlinear for k$_{B}$T $<$ eV/N $<$E$_{C }$ and linear when k$_{B}$T $>$ eV/N where N is the number of grains across the electrode gap. In the elastic regime below 5K, the IV curves were found to be linear for eV/N $<$ (E$_{C}$ $\delta )^{1/2 }$where $\delta $ is the level spacing and E$_{C}$ is the charging energy. As a consequence of cotunneling, Efros-Shklovskii variable-range-hopping-like conduction (VRH) was observed near zero bias. Above T$\sim $ 80-100K, transition from VRH to nearest-neighbor hopping took place.. X.M. Lin, \textit{et.al.}, J. Nanoparticle Res. \textbf{2} 157 (2000). T.B. Tran, \textit{et.al.}, Phys. Rev. Lett. \textbf{95} 076806 (2005),