Structures and properties of nanoparticle thin films formed via a one-step - Exchange-cross-linking - Precipitation route

This paper describes the characterizations of structural and electrochemical properties of nanoparticle thin films derived by a one-step exchange-cross-linking-precipitation route. While there exists a stepwise layer-by-layer construction method, our motivation stems from seeking an alternative and simpler pathway to prepare such thin films as electrode nanomaterials. The model system consisting of thiolate-encapsulated gold nanocrystals and alpha,omega-alkanedithiol cross-linkers was studied. The mixing of these two components in solutions allowed sequential exchanging, cross-linking, and eventual precipitation of the dithiol-cross-linked nanocrystals as thin films on almost any substrates. A series of comparative microscopic, spectroscopic, and electrochemical analyses were performed on thin films derived from nanocrystals of 2- and 5-nm core sizes. The 5-nm particles were fabricated by size and shape evolution of preformed 2-nm particles. The films were specularly reflecting, electronically continuous, and remarkably comparable with stepwise-derived thin films in structural, electronic, and electrochemical properties. The electrochemical data were discussed in terms of thiolate binding and barrier properties of the core-shell structures, which may have potential chemical recognition applications.