Charge transport in weakly coupled CoPt₃ nanocrystal assemblies

We report on charge transport through laterally contacted assemblies of weakly coupled, 10.2-nm-diameter CoPt₃ nanocrystals, where the shortest conducting paths consist of fewer than five nanocrystals. High-resolution electron microscopy reveals that the mean inter-nanocrystal separation can be reduced in situ through the use of mild thermal annealing without melting or sintering the nanocrystals. Devices annealed at 150°C show measured resistances that are several orders of magnitude lower than that for unannealed assemblies, which is attributable to increased inter-nanocrystal tunneling. Variable-temperature dc electrical characterization demonstrates that these devices act as Mott insulators with transport characteristics governed by single-electron charging energies of the electrically isolated nanocrystals. Observed scaling behavior of low-temperature current-voltage characteristics indicates transport through current-carrying networks with dimensionality greater than two dimensions and also reflects the finite geometric disorder in the nanocrystal assembly.