Size-dependent local conductance properties of CdSe nanocrystal ensembles

Applying conductance atomic force microscopy to measure the local current routes in ensembles of CdSe nanocrystallites of diameters in the range of 8-12 nm, we found that the electrical transport takes place through the crystallites themselves rather than along their grain boundaries. Statistical analysis of the current images, in correlation with macroscopic electrical transport measurements, reveals a crossover between two different conduction regimes. The behavior in each regime is found to be governed by the average diameter of the nanocrystals in the ensemble. We interpret the above findings as a transport manifestation of the quantum confinement effect.