The growth of nanocrystal superlattices of 5 nm single domain Au nanocrystals at an air–toluene interface induces formation of well-defined thin films (300–400 nm) with large coherence lengths. High-resolution electron microscopy showed that polyhedral holes (negative supracrystal) were formed on the nanocrystal superlattice surface. Formation of negative supracrystals is attributed to inclusion in the superlattice of organic molecules (dodecanethiol), which are present in concentrated zones at the air–toluene interface. The coexistence of two supracrystalline structures (bcc/fcc) is attributed to diffusion of dodecanethiol molecules resulting in a Bain deformation of the nanocrystal array.

A colloidal solution of 5 nm Au tetradecanethiol-coated nanoparticles is synthesized. After fast evaporation of one drop, ordered monolayers both composed of single domain and polycrystalline nanocrystals are obtained. On increasing the amount of materials and the evaporation time, nanocrystal films with irregular outlines are produced together with close-packed 3D superlattices exhibiting a truncated-tetrahedral shape. Using low-frequency micro-Raman scattering spectroscopy and electron microscopy the building block nanocrystallinity is characterized. Spontaneous nanocrystallinity segregation is revealed: the truncated-tetrahedral supracrystals are shown to mainly contain single domain building blocks while the supracrystalline films are composed of a mixture of single domain and polycrystalline nanocrystals. This observation points out the correlation between the nanocrystallinity segregation involved in the growth of the nanocrystal superlattices and their morphology.