Electron cotunneling transport in gold nanocrystal arrays

We describe current-voltage characteristics I(V) of alkyl-ligated gold nanocrystals $\sim 5 nm$ arrays in long screening length limit. Arrays with different alkyl ligand lengths have been prepared to tune the electronic tunnel coupling between the nanocrystals. For long ligands, electronic diffusion occurs through sequential tunneling and follows activated laws, as function of temperature $\sigma \propto e^{-T_0/T}$ and as function of electric field $I \propto e^{-\mathcal{E}_0/\mathcal{E}}$. For better conducting arrays, i.e. with small ligands, the transport properties crossover to the cotunneling regime and follows Efros-Shklovskii laws as function of temperature $\sigma \propto e^{-(T_{ES}/T)^{1/2}}$ and as function of electric field $I \propto e^{-(\mathcal{E}_{ES}/\mathcal{E})^{1/2}}$. The data shows that electronic transport in nanocrystal arrays can be tuned from the sequential tunneling to the cotunneling regime by increasing the tunnel barrier transparency.