Impedance Spectroscopy of Ionic Ligand-Modulated Charge Transport of Gold Nanoparticle Films

Assembled monolayer-protected nanoparticles (NPs) possess unique electrical properties that are determined by the coupled effects of their nano-sized electroactive inorganic cores that are capable of donating and accepting electrons and the organic shells. Core and ligand engineering for NP conductance modulation has been extensively explored; however, most studies focus on electron transport and not the interplay between the ion and electron transport processes. It is demonstrated here that electronic- and ionic-conducting properties of nanoparticle assemblies can be controlled by engineering the charge and flexibility of the ligand shell. By using impedance spectroscopy, the electronic, mixed ionic and electronic, and responsive conductance of the nanoparticle film and structure-function correlation are systematically investigated, and this correlation is used to provide a prototype volatile gas sensor based on the combined ionic and electronic conductance behavior of ionic ligand-functionalized gold NPs.