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 specifi c stacking processes, depending on the evaporation kinetics. Hence, at a fi xed 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.
Source : How to control the crystalline structure of supracrystals of 5-nm Ag nanocrystals ?A. Courty, J. Richardi, P.A. Albouy and M.P. Pileni, Chem Mat., 2011, 23, 4186-4192.