Controlled Synthesis and Flexible Self-Assembly of Monodisperse Au@Semiconductor Core/Shell Hetero-Nanocrystals into Diverse Superstructures

Monodisperse nonepitaxially grown Au@MX (MX = Ag2S, ZnS, or CdS) core/shell hetero-nanocrystals (HNCs) with controlled crystallinity, composition, anisotropically shaped Au cores but isotropic overall morphologies were successfully prepared. By using C18 acid/alkali co-capping surface ligands, the as-prepared Au@MX HNCs can self assemble into large-scale two-dimensional monolayer and three-dimensional multilayer superlattices (SLs) on both flexible (graphene) and rigid (Si wafer or glass) substrates. Moreover, unprecedented binary nanocrystal SLs can be achieved through synergistic self-assembly of Au@MX HNCs together with Au NCs (or CdS NCs) into different intricate patterns. Experimental evidence and finite-element method theoretical simulations indicate that the Au@CdS HNC SL film taking up a closest-packing mode has a rate of photocurrent generation much higher than that of its disordered assembled counterpart, probably because of the enhanced plasmon-exciton coupling permitted by the large-scale ordered nanopatterning.