Oriented Coassembly of Covellite Nanodisks and Graphene Oxide into Lamellar Plasmonic Superlattices

Large-scale assemblies of shaped nanocrystals have the potential to support a number of unique materials properties derived from the innate properties of nanoscale components, such as anisotropic charge transport behavior, collective optical phenomena, and selective surface adsorption. We demonstrate that colloidal covellite (CuS) nanodisks can be coassembled with oleylamine-functionalized graphene oxide (GO) to form lamellar, micron-thick films comprised of bilayered <10 nm lamellar subunits consisting of alternating monolayers of each component. Electron microscopy and small-angle X-ray scattering (SAXS) show that the CuS nanodisks orient with the basal CuS {001} plane parallel to the underlying substrate. Parameters affecting assembly such as GO concentration and colloidal stability are used to tune interlayer spacing and superlattice structure. The resulting superstructure is a multilayer stack of optically isolated CuS nanodisks monolayers where out-of-plane plasmonic coupling is significantly inhibited, as characterized by optical reflection measurements. Furthermore, we examine the out-of-plane conductivity on reduced CuS/GO films using a hanging mercury drop electrode as a function of postfabrication treatment with ascorbic acid.