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 with 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 not been previously reported, depending on their structures. In two-dimensional ordered superlattices of octanethiol-capped 4.8 nm diameter nanocrystals on graphite, the strong interparticle electronic coupling produces metallic films. A disordered monolayer of dodecanethiol-capped 6.6 nm diameter nanocrystals 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 hexanethiol-capped 2.7 nm diameter Ag particles, we find that the films are insulating, and individual nanocrystals maintain their individual electronic identity. Two different types of insulating films have been observed: one with electronically homogeneous nanocrystals in a close-packed lattice and the other with sublattices of electronically distinct nanocrystals within a square lattice. We discuss the relationship of the Coulomb blockade and nanocrystal ordering to the electronic behavior of this class of architectonic materials.