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Séminaire Zhuoying Chen

Structure Direction of II-VI Semiconductor Quantum Dot Binary Nanoparticle Superlattices by Tuning Radius Ratio


Zhuoying Chen

Cavendish Laboratory
University of Cambridge, UK

Self-assembly is a delightful concept, essentially one in which the complex work of engineering is performed by nature’s own intent. In materials chemistry, we generally desire that self-assembly produce recognizable and reproducible structure of order and periodicity, thus demonstrating that components can be placed in predetermined positions (e.g. on a lattice). Such observations are a prelude to the conviction that functional architectures can be purposely designed in this way.

Nanoparticle superlattices of CdSe and CdTe quantum dots in different structures.

In this talk, I will present some of the latest results on binary nanoparticle superlattices of CdTe and CdSe quantum dots by self-assembly. Such a system is a means to include two discretized, quantum-confined, and complimentary semiconductor units in close proximity, which might exhibit interesting charge transport properties for applications such as solar cells. In a first part, I will discuss some of the important experimental steps required to obtain a superlattice : the synthesis of monodisperse inorganic nanoparticles, and the determination of optimized conditions for the self-assembly process. In a second part, I will discuss the possible origins of the superlattices formation. When tuning the particle effective radius ratio (γeff) in this system, the large variety of structures obtained, among which AlB2, cub-NaZn13, ico-NaZn13, CaCu5, or MgZn2, led us to identify γeff as the key parameter to control the eventual superlattice structure. In an attempt to rationalize the occurrence of a specific structure for a given γeff, we analyzed these experimental results in the light of the well-known space-filling principle. A sticking correlation may indeed be established between the occurrence of a particular structure and the proximity of a local maximum in its space-filling factor for a given γeff. I will finally demonstrate the ability to select specific BNSLs based solely on γeff, highlighting the role of entropy as a dominant driving force for self-assembly at the nanoscale.

 

Reference :

1) Chen, Z. ; O’Brien, S. Structure Direction of II-VI Semiconductor Quantum Dot Binary Nanoparticle Superlattices by Tuning Radius Ratio. ACS Nano 2008, 2, 1219–1229.
2) Chen, Z. ; Moore, J. ; Radtke, G. ; Sirringhaus, H. ; O’Brien, S. Binary Nanoparticle Superlattices in the Semiconductor-Semiconductor System : CdTe and CdSe. J. Am. Chem. Soc. 2007, 129, 5702–15709.
3) Shevchenko, E. V. ; Talapin, D. V. ; Kotov, N. A. ; O’Brien, S. ; Murray, C. B. Structural Diversity in Binary Nanoparticle Superlattices. Nature 2006, 439, 55–59.
4) Redl, F. X. ; Cho, K.-S. ; Murray, C. B. ; O’Brien, S. Three-Dimensional Binary Superlattices of Magnetic Nanocrystals and Semiconductor Quantum Dots. Nature 2003, 423, 968–971.