Characterizing buried nano-interfaces in nanocrystal solids at the atomistic level: a coupled theoretical-experimental approach

The properties of nanomaterials, e.g. nanocrystal (NC)-solids, are dominated by their large surface to volume ratio. Detailed knowledge of the nanoscale interfacial chemistry is required to enable rational device design. By combining electronic structure calculations of surfaces with experiments and first principles molecular dynamics, we investigate fully inorganic NC-solids obtained by chemical solution processing of InAs NCs capped with Sn2S6 ligands. Contrary to organic ligands, which are adsorbed as intact structural units on the NC surface, we find inorganic ligands to dissociate on the NC surface, forming first a surface passivation layer and then a matrix around the NCs with complex structural details depending on the synthesis conditions. Thus the ligands and the matrix form an integral part of the NC-solid, with the NCs not having the same identity as when they are isolated or capped by organic ligands. We also find important atomistic details, such as a sulfur subsurface layer formed below the NC surface and a sulfur chain network inside the matrix, which determine the composite electronic properties and are expected to at least partially explain current experimental observations in InAs nanocrystal solids formed from sulfide-based inorganic ligands.