In this review we focus on nanocrystal self-assembly, covering the techniques for preparation and characterization of nanocrystal superlattices and other superstructures, the range of building blocks and accessible architectures, factors governing the assembly process, potential applications of ordered nanocrystal solids, and current challenges facing the field. #Xsection 7.7 traces of the section plane serial(8, 9) Self-assembly can also make use of external forces such as electric/magnetic fields or fluid flows, but the term does not extend to serial manipulation of building blocks (e.g., dragging individual particles into position). (1) Following this classification, examples of self-assembled structures include DNA, (2) proteins, (3) lipid vesicles, (4) block copolymer melts, (5) opals, (6, 7) and nanocrystal superlattices. While sufficiently broad to include crystallization of atomic solids, the term is generally reserved for building blocks not linked together via covalent bonds but ordered through weak forces (e.g., van der Waals, hydrogen bonding) or hard-particle (e.g., excluded volume) interactions. Self-assembly is the process by which individual components arrange themselves into an ordered structure. We end with a discussion of the unique optical, magnetic, electronic, and catalytic properties of ordered nanocrystal superlattices, and the coming advances required to make use of this new class of solids. We then explore the unique possibilities offered by leveraging nontraditional surface chemistries and assembly environments to control superlattice structure and produce nonbulk assemblies. We also provide an overview of structural defects in nanocrystal superlattices. We outline the extensive catalog of superlattices prepared to date using hydrocarbon-capped nanocrystals with spherical, polyhedral, rod, plate, and branched inorganic core shapes, as well as those obtained by mixing combinations thereof. We then summarize the theory of nanocrystal interactions and examine fundamental principles governing nanocrystal self-assembly from hard and soft particle perspectives borrowed from the comparatively established fields of micrometer colloids and block copolymer assembly. The introduction provides the reader with a practical overview of nanocrystal synthesis, self-assembly, and superlattice characterization. This process is often driven by both interparticle interactions and the influence of the assembly environment. In this review, we discuss efforts to create next-generation materials via bottom-up organization of nanocrystals with preprogrammed functionality and self-assembly instructions. Recently, the range of accessible inorganic cores and tunable surface chemistries dramatically increased, expanding the set of nanocrystal arrangements experimentally attainable. These Brownian objects readily order into superlattices. Chemical methods developed over the past two decades enable preparation of colloidal nanocrystals with uniform size and shape.
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