One-step preparation of three-dimensional superlattices during nanoparticle synthesis

Superlattices obtained by assembling inorganic nanoparticles are anticipated to constitute a novel class of materials, as they exhibit cooperative physical properties that are not observed in the isolated state of nanoparticles. Moreover, they have been investigated as a model for elucidating molecular crystallization mechanisms or as a visually accessible artificial atomic motif. In many conventional methods for fabricating superlattices, the superlattice structure typically forms as a two-dimensional film on a substrate, and even when three-dimensional superlattices are produced, multiple steps and careful adjustment of conditions are often required. Here, we review previous researches on the direct formation of three-dimensional, free-standing nanoparticle superlattices from molecular precursors through spontaneous self-assembly during nanoparticle growth in synthesis solutions. Although this method is less common than traditional techniques involving solvent evaporation and ligand-mediated assembly, it has been reported to enable the formation of various types of superlattices with a relatively simple procedure, regardless of the material. Additionally, an unusual dynamic transformation of the superlattice due to growth of nanoparticle components has been observed, providing new insights into the behavior of nanoparticle superlattices.