Individual and collective electronic properties of Ag nanocrystals

We report on the electronic transport properties of individual alkanethiol- passivated Ag nanocrystals and their superlattices. Isolated Ag particles w ith diameters in the range of 2.7-4.8 nm supported by a metallic substrate passivated with an organic layer show a Coulomb gap. Monolayer films of Ag particles exhibit four distinct electronic signatures, two of which have no t been previously reported, depending on their structures. In two-dimension al ordered superlattices of octanethiol-capped 4.8 nm diameter nanocrystals on graphite, the strong interparticle electronic coupling produces metalli c films. A disordered monolayer of dodecanethiol-capped 6.6 nm diameter nan ocrystals exhibits a temperature-dependent differential conductance, which is attributed to the localized states formed by the disorder in the lattice . For two-dimensional ordered superlattices of pentanethiol- and hexanethio l-capped 2.7 nm diameter Ag particles, we find that the films are insulatin g, and individual nanocrystals maintain their individual electronic identit y. Two different types of insulating films have been observed: one with ele ctronically homogeneous nanocrystals in a close-packed lattice and the othe r with sublattices of electronically distinct nanocrystals within a square lattice. We discuss the relationship of the Coulomb blockade and nanocrysta l ordering to the electronic behavior of this class of architectonic materi als.