Self-Assembled Superlattices of Size- and Shape-Selected Nanocrystals: Interdigitative and Gear Molecular Assembling Models

Size and shape selected nanocrystals behave as fundamental building blocks that can be used to construct nanocrystal assembled superlattices. This is a new state of materials that has orders in atomistic and nanocrystal length-scales. The nanocrystals are passivated with organic molecules (call thiolates) that not only protect them from coalescing but act as the molecular bonds for forming the superlattice structure. The interparticle distance is adjustable, possibly resulting in tunable electric, optical, and transport properties. In this article, nanocrystal superlattices (NCSs) constructed by truncated octahedral Ag particles are studied to illustrate the bundling and interdigitation of the passivation thiolates in forming the directional molecular bonds in NCSs. The {111}s facets observed in the NCSs suggest the key roles played by the molecular bonding energy in forming the surfaces of NCSs. The formation of twins in the NCSs supports the “gear” assembling model of the nanocrystals. The gear assembling is likely to have higher energy than the interdigitative assembling.