We investigated the influence of processing conditions, nanocrystal/substrate interactions and solvent evaporation rate on the ordering of strongly interacting nanocrystals by synergistically combining electron microscopy and synchrotron-based small-angle X-ray scattering analysis. Spin-cast PbSe nanocrystal films exhibited submicrometer-sized supracrystals with face-centered cubic symmetry and (001)s planes aligned parallel to the substrate. The ordering of drop-cast lead salt nanocrystal films was sensitive to the nature of the substrate and solvent evaporation dynamics. Nanocrystal films drop-cast on rough indium tin oxide substrates were polycrystalline with small grain size and low degree of orientation with respect to the substrate, whereas films drop-cast on flat Si substrates formed highly ordered face-centered cubic supracrystals with close-packed (111)s planes parallel to the substrate. The spatial coherence of nanocrystal films drop-cast in the presence of saturated solvent vapor was significantly improved compared to films drop-cast in a dry environment. Solvent vapor annealing was demonstrated as a postdeposition technique to modify the ordering of nanocrystals in the thin film. Octane vapor significantly improved the long-range order and degree of orientation of initially disordered or polycrystalline nanocrystal assemblies. Exposure to 1,2-ethanedithiol vapor caused partial displacement of surface bound oleic acid ligands and drastically degraded the degree of order in the nanocrystal assembly. © 2009 American Chemical Society.
|Original language||English (US)|
|Number of pages||14|
|State||Published - Sep 3 2009|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: We thank Matthew Oh for assistance with the synthesis of the nanocrystals and Will Baumgardner for assistance with the FTIR measurements. This work was further funded in part by the KAUST-CU Center for Energy and Sustainability. J.J.C. was supported by the NSF IGERT Fellowship Program "Nanoscale Control of Surfaces and interfaces." 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-025180. TEM images were acquired at the Soft Matter CryoTEM Research Unit at the Technical University of Eindhoven in work sponsored by the Joint Solar Programme (JSP) of the Stichting, voor Fundamenteel Onderzoek der Materie FOM, which is supported financially by Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO). The JSP is cofinanced by Gebied Chemische Wetenschappen of the NWO and Stichting Shell Research. SEM images were taken at the Cornell Center for Materials Research.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.