Self-assembly of charged nanocrystals into strongly electronically coupled all-inorganic supercrystalline solids

Colloidal nanocrystals of different metals, semiconductors, and other functional materials can self-assemble into long-range ordered crystalline phases. However, insulating organic surface ligands prevent the development of collective electronic states in ordered nanocrystal assemblies. Here we report reversible self-assembly of colloidal, charged nanocrystals with conductive inorganic ligands into superlattices exhibiting optical and electronic properties consistent with strong electronic coupling between the constituent nanocrystals. We show that the phase behavior of charge-stabilized nanocrystals can be rationalized and navigated using phase diagrams computed for particles interacting through short range attractive potentials similar to previous reports for globular proteins and PMMA spheres. By finely tuning conditions, the assembly can proceed either via one-step nucleation or non-classical two-step nucleation pathways.  The ability to grow ordered all-inorganic assemblies of strongly coupled nanoscale building blocks, combined with the already available synthesis toolset for engineering nanocrystal size, shape, and functionality, may offer endless possibilities for engineering hierarchical solids.