期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 132, 期 34, 页码 11967-11977出版社
AMER CHEMICAL SOC
DOI: 10.1021/ja103083q
关键词
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资金
- NSF [DMR-0213745]
- David and Lucile Packard Foundation
- Austrian Nanoinitiative
- U.S Department of Energy [DE-AC02-06CH11357]
We studied the effect of temperature on self-assembly of monodisperse colloidal nanocrystals into single-component and binary superlattices. Temperature, which serves as a weighting factor for the internal energy (U) and entropy (S) contributions to the Helmholtz free energy F= U - TS, allows tailoring relative weights of the interparticle interactions and free-volume entropy during the formation of nanocrystal superlattices. Temperature also provides a convenient tool for directing self-assembly of nanocrystals toward desired superlattice structures. We found that temperature strongly affects the structures of binary superlattices self-assembled from the mixtures of CdSe + PbS nanocrystals and PbSe + Pd nanocrystals. In the former case, small Hamaker constants for CdSe and PbS nanocrystals led to a relatively simple phase diagram, including only high-density NaZn13-, AlB2-, and NaCl-type binary superlattices. In contrast, binary superlattices self-assembled at different temperatures from PbSe and Pd nanocrystals showed a number of low-density complex phases stabilized by strong local van der Waals interactions between Pd nanocrystals. The structural diversity of nanoparticle superlattices is shown to be a result of the cooperative effect of the entropy-driven crystallization and the interparticle interactions. Both Delta U and T Delta S terms associated with the superlattice formation should be of the same order of magnitude, with vertical bar Delta U vertical bar < vertical bar T Delta S vertical bar for the assembly of CdSe and PbS nanocrystals and vertical bar Delta U vertical bar > vertical bar T Delta S vertical bar for the PbSe and Pd nanocrystals.
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