Preface to the Chemistry of Materials Special Issue: Synthetic and Mechanistic Advances in Nanocrystal Growth

T he preparation, properties, and applications of nanocryst- als have figured prominently in Chemistry of Materials for many years.This special issue recognizes the dramatic advances in the nanocrystal field over the past decade, particularly in synthetic methods, the understanding of growth mechanisms, and the optimization of optical and other physical properties.Emphasis is given here to the rational control of nanocrystal morphology, size, phase, and composition; mechanistic studies establishing chemical and crystal-growth pathways; and detailed understanding and control of surface and core structure.Although a majority of the review and research articles address semiconductor nanocrystals, several covering metallic and ceramic nanocrystals are also included.Synthetic control is advanced by a developing comprehension of precursor-conversion chemistry, the roles of adventitious impurities, the factors influencing nucleation, and the various pathways by which nanocrystals grow.These mechanistic considerations are separately addressed for semiconductor nanocrystals in reviews from Sowers, Swartz, and Krauss and by Cossairt, Liu, Owen, and co-workers.Sabyrov, Burrows, and Penn and DiSalvo and co-workers provide separate studies showing that aggregation and coalescence contribute extensively to nanoparticle growth for TiO 2 and PtFe, respectively.Han and co-workers present a geometricalselection model for the growth of aligned ZnO nanowire arrays.Nanocrystal surface ligation and structure strongly influence optical properties and charge-transfer characteristics, but until recently remained poorly characterized.Weiss and co-workers review the determination of surface-ligand structure and composition by a variety of spectroscopic methods.Hens and Martins provide an NMR toolbox for characterizing nanocrystal-surface chemistry.Many properties of nanocrystals, including optical properties, are strongly affected by internal (core) structures and heterostructures.Sarma and co-workers review the use of Xray photoelectron spectroscopy for determining core structure.A review by Hollingsworth describes the suppression of blinking and Auger recombination by nanocrystal heterostructuring.Shen and Qiangbin Wang review the rational tuning of sulfide-nanocrystal optical properties by alloying, doping, and heterostructuring.Xiaodong Wang and co-workers provide a study of Pt-Sn core-shell and alloy nanoparticles.The challenge of nanocrystal doping has recently been undertaken.Buonsanti and Milliron review the chemistry of doped colloidal nanocrystals.Norris and co-workers review the techniques used to characterize and image atomic impurities in semiconductor nanostructures.Anisotropic gold nanocrystals have contributed extensively to the development of colloidal nanoscience.Lohse and Murphy detail the history of gold-nanorod synthesis.Vigderman and Zubarev and Xuefei Wang and co-workers separately explore the interplay of synthesis and the longitudinal surface-plasmon resonance in gold nanorods.Wei and co-workers study halide ions as shape-directing agents for anisotropic gold nanocrystals.