The self-assembly of colloidal nanocrystals into ordered superstructures depends critically on the shape of the nanocrystal building blocks. We investigated the self-assembly of cubic PbSe nanocrystals from colloidal suspensions in real-time using in situ synchrotron-based X-ray scattering. We combined small-angle and wide-angle scattering to investigate the translational ordering of nanocrystals and their orientational ordering in the lattice sites, respectively. We found that cubic PbSe nanocrystals assembled into a face-up (i.e., 〈100〉 normal to the interface) configuration at the liquid/substrate interface whereas nanocubes at the liquid/air interface assume a corner-up (i.e., 〈111〉 normal to the interface) configuration. The latter nanocrystal superlattice displays polymorphism as a function inter-NC separation distance. We explain the observed superlattice structure polymorphs in terms of the interactions directing the self-assembly. Insights into the directed self-assembly of superlattices gained from this study have important implication on the future development of nanocrystals as building blocks in artificial solids. © 2012 American Chemical Society.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): KUS-C1-018-02
Acknowledgements: We thank Don Koch, Fernando Escobedo, Paul Steen, Terry Bigionie, and Sol Gruner for stimulating discussions. We thank Lena Kourkoutis-Fitting for assistance with the high-resolution TEM microscopy. J.J.C. was supported by the NSF IGERT Fellowship Program on "Nanoscale Control of Surfaces and Interfaces," administered by Cornell's MRSEC. K.B. was supported by NSF-DMR-1056943. W.B. was supported by the KAUST-CU Center for Energy and Sustainability. GISAXS measurements were conducted at the Cornell High Energy Synchrotron Source (CHESS), which is supported by the National Science Foundation and the National Institutes of Health/National Institute of General Medical Sciences under NSF award DMR-0225180. This publication is based on work supported in part by Award No. KUS-C1-018-02, made by King Abdullah University of Science and Technology (KAUST).
This publication acknowledges KAUST support, but has no KAUST affiliated authors.