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 degreesC 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.