Growing anisotropic crystals at the nanoscale

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Science  16 Jun 2017:
Vol. 356, Issue 6343, pp. 1120-1121
DOI: 10.1126/science.aam8774

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Technological prospects of metal nanoparticles (NPs) have stimulated intense research activities into their growth mechanisms to predict shape, size, and crystallinity. Of high interest are low-symmetry nanocrystals (NCs), which exhibit high-energy facets that are relevant in catalysis or plasmonic properties that are attractive for applications in areas such as biomedicine. Rodlike shapes are in principle most challenging because the high-symmetry face-centered cubic lattice of the metals of interest, such as gold, tends to form high-symmetry, compact NCs. To promote shape anisotropy, nucleation and growth are usually separated in the so-called seed-mediated growth, in which a metal precursor is reduced on preformed seeds in the presence of shape-directing additives. The growth of nanorods is a nonequilibrium process and remains poorly understood, which accounts for their limited reproducibility and yield. The required control over the crystal habit of the seeds and the effect of additives will necessitate insights from theoretical modeling as well as characterization, especially by state-of-the-art transmission electron microscopy (TEM).