Reversible Metal-Insulator Transition in Ordered Metal Nanocrystal Monolayers Observed by Impedance Spectroscopy

Low frequency impedance spectroscopy was applied on a Langmuir monolayer of alkylthiol passivated 35 A diameter silver quantum dots, as a function of interparticle separation distance. As interparticle spacing decreases below 30% of particle diameter, a reduction in interparticle charge tunneling time is observed. On further compression, the complex impedance of the films undergoes a transition from a parallel RC equivalent circuit to an inductive circuit. Optical reflectance changes in the films are consistent with the deduced metal-insulator transition.