Research Topic 1: Shape-controlled synthesis of noble-metal and metal-semiconductor hybrid nanocrystals



Part A: Noble-metal nanocrystals


Interest in noble-metal nanocrystals with controlled sizes and shapes has grown steadily because of strong correlations between the size/shape of nanocrystals and chemical, physical, electronic, optical, magnetic, and catalytic properties. The interest has also been enhanced by the technological applications of these nanocrystals in areas ranging from catalysis to sensing, imaging, and biomedical research. For Ag and Au, the applications are mainly based on their localized surface plasmon resonance (LSPR) and surface-enhanced Raman scattering (SERS) properties. In these cases, computational and experimental studies have shown that the shape of a Ag or Au nanocrystal plays the most important role in determining the number, position, and intensity of LSPR peaks, as well as the spectral region for effective SERS detection. For Pd and Pt, the applications are largely in catalysis, and the activity/selectivity has been found to be highly sensitive to the shape and thus facets expressed on the surface. For example, it has been shown that Pt nanocrystals can selectively catalyze different types of reactions depending on the facets, with {100} and {210} facets being most active for reactions involving H2 and CO, respectively. These examples clearly demonstrate the pivotal importance of size and shape control in maximizing the use of noble-metal nanocrystals. The ultimate goal of this research is to synthesize noble-metal nanocrystals with well-defined shapes associated with desired properties for various applications.




[1] Kinetically controlled overgrowth of Ag or Au on Pd nanocrystal seeds: from hybrid dimers to non-concentric and concentric bimetallic nanocrystals
Zhu, C.; Zeng, J. (equal contribution); Tao, J.; Zhu, Y.; Gu, Z. and Xia, Y. J. Am. Chem. Soc. 2012, 134, 15822-15831.

[2] A quantitative analysis of the role played by poly(vinyl pyrrolidone) in seed-mediated growth of Ag nanocrystals
Xia, X.; Zeng, J. (equal contribution); Oetjen L.; Li, Q. and Xia, Y. J. Am. Chem. Soc. 2012, 134, 1793.

[3] Controlling the nucleation and growth of silver on palladium nanocubes by manipulating the reaction kinetics
Zeng, J.; Zhu, C.; Tao, J.; Jin, M.; Zhang, H.; Li, Z.-Y.; Zhu, Y. and Xia, Y. Angew. Chem. Int. Ed. 2012, 51, 2354.

[4] Silver nanocrystals with concave surfaces and their optical and surface-enhanced Raman scattering properties
Xia, X.; Zeng, J. (equal contribution); McDearmon, B.; Zheng, Y.; Li, Q. and Xia, Y. Angew. Chem. Int. Ed. 2011, 50, 12542.

[5] Controlling the shapes of silver nanocrystals with different capping agents
Zeng, J.; Zheng, Y.; Rycenga, M.; Tao, J.; Li, Z.-Y.; Zhang, Q.; Zhu, Y. and Xia, Y. J. Am. Chem. Soc. 2010, 132, 8552-8553.



Part B: Metal-semiconductor hybrid nanocrystals


Hybrid nanostructures that integrate two or more nanoscale components have recently attracted much attention owing to the synergistic properties induced by interactions between these objects. Promising examples of such structures are metal-semiconductor hybrid nanocrystals, in which a metal and its semiconductor counterpart are closely coupled in an effort to produce intriguing behaviors and functionalities far beyond those of their individual counterparts. For example, metal tips on semiconductor nanorods can serve as anchor points for electrical connections or for head-to-end self-assembly into complex structures, while improved charge separation at the metal-semiconductor interface can enhance its photocatalytic activities or modify its nonlinear optical response. Furthermore, addition of semiconductor tips to metal nanocrystals can greatly improve the stability of metal nanocrystals against aging at a high temperature and maneuver the fascinating optical properties of metal nanocrystals known as surface plasmon resonance. As many of their physical and chemical properties are highly dependent on the size, shape, composition, and spatial distribution of each component, the synthetic strategy of such metal-semiconductor hybrid nanonanocrystals has become increasingly important. The ultimate goal of this research is to spatially control the component distribution and thus regulate the symmetry of different types of metal-semiconductor hybrid nanocrystals.




[1] Symmetric and asymmetric Au-AgCdSe hybrid nanorods
Liang, S.; Liu, X.-L.; Yang, Y.-Z.; Wang, Y.-L.; Wang, J.-H.; Yang, Z.-J.; Wang, L.-B.; Jia, S.-F.; Yu, X.-F.*; Zhou, L.; Wang, J.-B.; Zeng, J.*; Wang, Q.-Q.* and Zhang, Z. Nano Lett. 2012, 12, 5281-5286.

[2] Selective sulfuration at the corner sites of a silver nanocrystal and its use in stabilization of the shape
Zeng, J.; Tao, J.; Su, D.; Qin, D. and Xia, Y. Nano Lett. 2011, 11, 3010-3015.

[3] Gold-based hybrid nanocrystals through heterogeneous nucleation and growth
Zeng, J.*; Huang, J.; Liu, C.; Wu, C.; Lin, Y.; Wang, X.*; Zhang, S.; Hou, J. G.* and Xia, Y. Adv. Mater. 2010, 22, 1936-1940 (highlighted on the inside cover).