Shape-controlled synthesis of metal nanocrystals

Mrs Bulletin, Volume 38, April 2013
Shape-controlled synthesis of metal nanocrystals
Younan Xia, Georgia Institute of Technology ; younan.xia@bme.gatech.edu
Xiaohu Xia, Georgia Institute of Technology ; xiaohu.xia@bme.gatech.edu
Yi Wang, Southwest University , China ; yi.wang@bme.gatech.edu
Shuifen Xie, Xiamen University , China ; shuifen.xie@bme.gatech.edu
This article is based on the Symposium X: Frontiers of Materials Research lecture titled “Simple Chemistry for Complex Nanomaterials” presented by Younan Xia on April 11, 2012, at the MRS Spring Meeting in San Francisco, Calif.
Abstract
The ability to control the shape of metal nanocrystals is central to advances in many areas of modern science and technology, including catalysis, plasmonics, electronics, and biomedicine. This article provides a brief overview of our recent efforts toward the development of solution-phase methods for shape-controlled synthesis of metal nanocrystals.
While the synthetic methods only involve simple redox reactions, we have been working diligently to understand the complex nucleation and growth mechanisms leading to the formation of metal nanocrystals with desired shapes and related properties. We hope this review will inspire new ideas and concepts in the general area of nanomaterial synthesis, expand our ability to engineer the properties of metals for various applications, and contribute to the realization of sustainable use for some of the scarcest materials.
Introduction
The last decade has witnessed the successful synthesis of metal nanocrystals with a variety of shapes, with notable examples including a sphere; spheroid; cube; cuboctahedron; octahedron; tetrahedron; right bipyramid; decahedron; icosahedron; thin plate with a triangular, hexagonal, or circular profi le; and rod or wire with a circular, square, rectangular, pentagonal, or octagonal cross-section. 10 Our research has mainly focused on solution-phase methods because they are inherently more powerful and versatile (at the same time, more complicated) than vapor-phase methods for generating metal nanocrystals with different shapes. Although the fi rst documented solutionphase synthesis of metal nanocrystals can be traced back to work by Faraday more than 150 years ago on gold colloids, only within the last decade have solution-phase methods blossomed and become a powerful route to the synthesis of metal nanocrystals with the quality, quantity, and reproducibility required for a meaningful study of their shape-property relationships and exploration of their applications. Interestingly, the chemical reactions involved in the synthesis of metal nanocrystals are often very simple, and most of them can be easily found in standard textbooks. In contrast, controlling the assembly of metal atoms into nanocrystals with specifi c shapes is still in a rudimentary stage, as it typically involves nucleation and growth steps, which are still too complicated to be fully understood. 
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