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

D.M. Smilgies,Ruipeng Liand M. P. Pileni Nanoscale, 2018, DOI: 10.1039/C8NR04606A

Vicinal Au supracrystal surfaces were prepared  from Au_singlesingle domain nanocrystals (NCs) whereas by replacing Au_singleby their polycrystalline counterparts common low-energy supracrystal surfaces are produced.  By analogy to atomic crystalline surfaces, we propose a mechanism to explain formation of such unexpected supracrystal vicinal surfaces, composed of only Au_singleNCs are non-compact (bctstructure) with coherent alignment of the atomic planes oriented along the [111] superlattice axis and a slight tilt configuration  (8.1°) of NCs.  In presence of Co() NCs, these Au_singlesupracrystals loose both the slightly tilted configuration of NCs and their orientational order leading to a superlattice transition from bctto fcc. In contrast, supracrystals of Au_polyNCs are unsensitive to the presence of Co() NCs. These intriguing structural changes obtained with Au_singlecompared to Au_polysupracrystals in absence and presence of Co() NCs could explain the formation of vicinal surfaces. Note, the solvent used to disperse the nanocrystals plays a key parameter in the formation of supracrystal vicinal surfaces. Here a new analogy between supracrystals and atomic crystals is presented.