Colloidal synthesis of nanocrystals and nanocrystal superlattices

This paper provides an overview of the synthetic techniques used to prepare colloidal nanocrystals (NCs) of controlled composition, size, shape, and internal structure and the methods for manipulation of these materials into ordered NC assemblies (superlattices). High-temperature solution-phase synthesis (100–300°C) is followed by size-selective separation techniques in the preparation of monodisperse NC samples tunable in size from ∼1 to 15 nm in diameter with <5% standard deviation. Each NC consists of a crystalline inorganic core coordinated by an organic monolayer. These monodisperse NC samples enable systematic studies of structural, electronic, magnetic, and optical properties of materials as a function of size evolution from molecular species (<100 atoms) to bulk solids (>100 000 atoms). We illustrate size-dependent properties for magnetic materials using Co and for semiconducting materials using PbSe. These NC samples are sufficiently uniform in size to self-assemble into close-packed, ordered NC superlattices, also known as colloidal crystals.