Analogy Between Atoms in a Nanocrystal and Nanocrystals in a Supracrystal: Is It Real or Just a Highly Probable Speculation?

Nanocrystals and supracrystals are arrangements of highly ordered atoms and nanocrystals, respectively. At the nanometer scale, from face-centered cubic (fcc) tetrahedral subunits, either single fcc nanocrystals such as cubooctahedra and octahedra or decahedral and icosahedral nanocrystals are produced. Such nanocrystals with different shapes are produced by soft chemistry. At the micrometer scale, very surprisingly, supracrystals having shapes similar to those obtained at the nanometer scale are produced. For example, large triangular nanocrystals as well as supracrystals are produced either by soft chemistry, from nanocrystal diffusion on a surface, or by nanocrystal interactions in solution. The morphologies of nanocrystals, supracrystals, and minerals, which are similar at various scales (nm and mm), are pointed out, and an explanation of these similarities is undertaken

How to Predict the Growth Mechanism of Supracrystals from Gold Nanocrystals

Here we report the influence of the nanocrystal size and the solvent on the growth of supracrystal made of gold nanocrystals. These parameters may determine the final morphology of nanocrystals assemblies with either a layer-by-layer growth or a process of nucleation in solution. Experiments supported by simulations demonstrate that supracrystal nucleation is mainly driven by solvent-mediated interactions and not solely by the van der Waals attraction between nanocrystal cores, as widely assumed in the literature

Hierarchy in Au Nanocrystal Ordering in Supracrystals: A Potential Approach to Detect New Physical Properties

Here we describe the morphologies of Au nanocrystals self-assembled in fcc 3D superlattices called supracrystals. The average size of the nanocrystals is either 5 or 7 nm with a very small size distribution (<7%). The coating agents used to stabilize the nanocrystals are dodecanethiol (C₁₂H₂₅–SH), tetradecanethiol (C₁₄H₂₉–SH), and hexadecanethiol (C₁₆H₃₃–SH). The influences of the evaporation time, the volume of the chamber used to evaporate the toluene solvent, and the substrate temperature are studied. For nanocrystals characterized by the same size and coating agent, the supracrystal morphologies markedly change on increasing the evaporation time from 8 to 9 to 25 h whereas a slight change takes place on increasing the chamber volume. The nanocrystals’ ability to self-order in supracrystals decreases upon increasing the chain length of the coating agent from dodecanethiol (C₁₂) to tetradecanethiol (C₁₄) to hexadecanethiol (C₁₆). Decreasing the evaporation rate (25 h) and/or increasing the substrate temperature (50 °C) improves the nanocrystal ordering in fcc supracrystals. A hierarchy in nanocrystal ordering has the following sequence disordered assemblies, supracrystal film sitting on a disordered nanocrystal film, supracrystal films grown layer-by-layer, and finally supracrystals grown in solution with various well-defined shapes