Electrochemical observation of a metal/insulator transition by scanning electrochemical microscopy

We report the novel use of the scanning electrochemical microscope (SECM) to follow the compression of a monolayer of monodisperse silver thiol-capped nanoparticles on a Langmuir trough. SECM allowed the direct electrochemical visualization of the lateral connectivity of the particles in the film at the air/water interface through monitoring the transition from negative feedback (insulating substrate) to positive feedback (conducting substrate) at the Pt SECM tip, with ferrocene methanol (FcMeOH) as the redox mediator, as the interparticle separation decreased by compressing the film. The transition from an insulating to conductive behavior with compression could thus be followed.