Remarkably Strong Interparticle Coupling in Two-Dimensional Ensembles of Naked Silver Quantum Dots: The Effect on Optical and Conduction Characteristics

Abstract

Tunable two-dimensional ensembles of naked silver quantum dots have been assembled, using gas-phase deposition techniques, and their conduction and optical characteristics have been measured. With decreasing interparticle separation, the optical properties are found to evolve from particle-like to bulk metal-like. Two conduction mechanisms are found. At relatively large interparticle separations, interparticle tunneling of charge is prominent. At relatively small separations, we propose that resonant charge transport through the quantum dot ensembles occurs. Because the quantum dots are naked, these results provide new insight into particle−particle coupling interactions, specifically, which are much stronger than those observed in the ligated nanoparticle film systems that are typically studied. Tunneling current is observed over remarkably large average interparticle separations (greater than 40 nm), and surface plasmon resonances are shifted more than 1.7 eV as a result of the strong interparticle coupling. Because of stronger coupling, we also find that the ensemble-dependent band gap can be tuned from 0 to ∼5 V over a larger range of interparticle separations than possible in the ligated nanoparticle film systems.