Abstract
Most properties of nanocrystalline materials are shape-dependent, providing their exquisite tunability in optical, mechanical, electronic and catalytic properties. An example of the former is localized surface plasmon resonance (LSPR), the coherent oscillation of conduction electrons in metals that can be excited by the electric field of light; this resonance frequency is highly dependent on both the size and shape of a nanocrystal. An example of the latter is the marked difference in catalytic activity observed for different Pd nanoparticles. Such examples highlight the importance of particle shape in nanocrystalline materials and their practical applications. However, one may ask 'how are nanoshapes created?', 'how does the shape relate to the atomic packing and crystallography of the material?', 'how can we control and characterize the external shape and crystal structure of such small nanocrystals?'. This feature article aims to give the reader an overview of important techniques, concepts and recent advances related to these questions. Nucleation, growth and how seed crystallography influences the final synthesis product are discussed, followed by shape prediction models based on seed crystallography and thermodynamic or kinetic parameters. The crystallographic implications of epitaxy and orientation in multilayered, core-shell nanoparticles are overviewed, and, finally, the development and implications of novel, spatially resolved analysis tools are discussed.
Highlights
Nanocrystalline materials abound in nature and technology, bridging the gap between molecular sized and macroscale objects
Most properties of nanocrystalline materials are shapedependent, providing their exquisite tunability in optical, mechanical, electronic and catalytic properties (Osawa & Kawata, 2001; Bell, 2003; Wiley et al, 2006). An example of the former is localized surface plasmon resonance (LSPR; Liebsch, 1993; Osawa & Kawata, 2001; Haes & Van Duyne 2004; Ozbay, 2006), the coherent oscillation of conduction electrons in metals that can be excited by the electric field of light
Shape and size strongly influence the bandgap of nanosized direct bandgap semiconductors, from the well known CdS, CdSe and CdTe to the more recent core-shell architectures (Brus, 1983; Reiss et al, 2009; Doane & Burda, 2012; Shirasaki et al, 2013). Such examples highlight the importance of particle shape in nanocrystalline materials and their practical applications, where specific properties can be enabled and optimized by tuning the particle shape
Summary
Nanocrystalline materials abound in nature and technology, bridging the gap between molecular sized and macroscale objects. The control and understanding of nanocrystalline shape remains an active area of research with much yet to be learned: we are still asking ourselves ‘how are nanoshapes created?’, ‘how does the shape relate to the atomic packing and crystallography of the material?’, ‘how can we control and characterize the external shape and crystal structure of such small nanocrystals?’ Through this feature article, we will provide the most current answers to these questions and give the reader an overview of important techniques and recent advances in the field, focusing on electron microscopy and diffraction characterization of nanocrystalline materials. Potential applications are reviewed, followed by an overview of future possibilities
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