How To Control the Crystalline Structure of Supracrystals of 5-nm Silver Nanocrystals

Supracrystals of 5-nm silver nanocrystals are characterized by various structures, ranging from face-centered-cubic (fcc), to hexagonal-close-packed (hcp), to body-centered-cubic (bcc) structures. Here, it is shown that the transition from fcc to hcp is solvent-dependent and attributed to specific stacking processes, depending on the evaporation kinetics. Hence, at a fixed substrate temperature, the most volatile solvents (such as hexane and toluene) favor the growth of fcc superlattices, whereas with solvents that have a higher boiling point (such as octane, decane, and dodecane), hcp supracrystals are produced. In contrast, the formation of bcc structures is shown to be solvent-independent and is attributed to van der Waals attractions. The chain length of the coating agent and the deposition temperature govern the transition from compact (fcc/hcp) to bcc supracrystals. The experimentally phase transitions are interpreted by theoretical approaches.