Shape-controlled synthesis of metal nanocrystals
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troduction Materials with at least one dimension of their constituent structures between 1 nm and 100 nm are known as nanomaterials.1 These have received steadily growing interest owing to their unique position as a bridge between atoms and bulk materials, as well as their remarkable properties and important applications. The ability to generate nanomaterials with well-controlled sizes, shapes, compositions, and internal structures (e.g., solid versus hollow) is central to advances in many areas of modern science and technology. Among various types of functional materials, metals deserve our special attention because they represent more than two-thirds of the elements in the periodic table. Essentially, all of them have found extensive use in applications ranging from catalysis to electronics, photonics, information storage, sensing, imaging, medicine, photography, as well as generation, conversion, and storage of energy.2–7 Most of these applications require the use of metals in a finely divided state to maximize the specific surface area, preferably in the form of nanocrystals with well-defined facets. In principle, the size of a nanocrystal determines how the electrons are confined, as well as the surface-to-bulk atomic ratio and the proportions of different types of atoms located
at specific sites of a nanocrystal (e.g., vertex, edge, and face), whereas the shape defines the types of facets on its surface and thus the arrangement of atoms on the faces. The shape and size of a metal nanocrystal not only determine its physicochemical properties but also its relevance for various applications. Considering platinum as an example, it plays a central role in a variety of applications, such as catalytic converters, petroleum refining, and fuel cell technology.8 However, the extremely limited supply of this scarce metal means that we have to maximize performance in these applications by controlling the shape and size of the platinum nanocrystals, so their loading in the catalysts or devices could be substantially reduced to achieve economical and sustainable use of this precious metal. Other good examples are silver and gold; their nanocrystals have fascinating optical properties known as localized surface plasmon resonance (LSPR) and surface-enhanced Raman scattering (SERS).4 Again, both of these properties have a strong dependence on the shape of the nanocrystals.9 These and many other examples clearly demonstrate the importance of shape control to more efficiently utilize metal nanocrystals. The last decade has witnessed the successful synthesis of metal nanocrystals with a variety of shapes, with notable
Younan Xia, Georgia Institute of Technology; [email protected] Xiaohu Xia, Georgia Institute of Technology; [email protected] Yi Wang, Southwest University, China; [email protected] Shuifen Xie, Xiamen University, China; [email protected] DOI: 10.1557/mrs.2013.84
© 2013 Materials Research Society
MRS BULLETIN • VOLUME 38 • APRIL 2013 • www.mrs.org/bulletin
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SHAPE-CONTROLLED SYNTHESIS O
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