Au nanocrystal superlattices: nanocrystallinity, vicinal surfaces, and growth processes

Abstract

Vicinal Au supracrystal surfaces were prepared from Au_single single domain nanocrystals (NCs), whereas by replacing Au_single with their polycrystalline counterparts common low-energy supracrystal surfaces were produced. By analogy to atomic crystalline surfaces, we propose a mechanism to explain the formation of such unexpected supracrystal vicinal surfaces, composed of only Au_single NCs which are non-compact (bct structure) with a coherent alignment of the atomic planes oriented along the [111] superlattice axis and a slight tilt configuration (8.1°) of NCs. In the presence of Co(ε) NCs, these Au_single supracrystals lose both the slightly tilted configuration of NCs and their orientational order leading to a superlattice transition from bct to fcc. In contrast, supracrystals of Au_poly NCs are insensitive to the presence of Co(ε) NCs. These intriguing structural changes obtained with Au_single compared to Au_poly supracrystals in the absence and presence of Co(ε) NCs could explain the formation of vicinal surfaces. Note that the solvent used to disperse the nanocrystals plays a key role in the formation of supracrystal vicinal surfaces. Here, a new analogy between supracrystals and atomic crystals is presented.