Abstract
Oriented attachment of PbSe nanocubes can result in the formation of two-dimensional (2D) superstructures with long-range nanoscale and atomic order1,2. This questions the applicability of classic models in which the superlattice grows by first forming a nucleus, followed by sequential irreversible attachment of nanocrystals3,4, as one misaligned attachment would disrupt the 2D order beyond repair. Here, we demonstrate the formation mechanism of 2D PbSe superstructures with square geometry by using in situ grazing-incidence X-ray scattering (small angle and wide angle), ex situ electron microscopy, and Monte Carlo simulations. We observed nanocrystal adsorption at the liquid/gas interface, followed by the formation of a hexagonal nanocrystal monolayer. The hexagonal geometry transforms gradually through a pseudo-hexagonal phase into a phase with square order, driven by attractive interactions between the {100} planes perpendicular to the liquid substrate, which maximize facet-to-facet overlap. The nanocrystals then attach atomically via a necking process, resulting in 2D square superlattices.
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Acknowledgements
This research is part of the programme ‘Designing Dirac Carriers in semiconductor honeycomb superlattices (DDC13),’ which is supported by the Foundation for Fundamental Research on Matter (FOM), which is part of the Dutch Research Council (NWO). J.J.G. acknowledges funding from the Debye and ESRF Graduate Programs. The authors gratefully acknowledge funding from the Research Foundation Flanders (G.036915 G.037413 and funding of postdoctoral grants to B.G. and A.d.B). S.B. acknowledges the European Research Council, ERC grant No 335078—Colouratom. The authors gratefully acknowledge I. Swart and M. van Huis for fruitful discussions. We acknowledge funding from NWO-CW TOPPUNT ‘Superficial Superstructures’. The X-ray scattering measurements were performed at the ID10 beamline at ESRF under proposal numbers SC-4125 and SC-3786. The authors thank G. L. Destri and F. Zontone for their support during the experiments.
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J.J.G., C.v.O., F.T.R., J.H. and J.L.P. performed the in situ GISAXS/WAXS experiments under supervision of O.K. and A.V.P. J.J.G. and C.v.O. analysed the GISAXS/WAXS data. The TEM data were collected by C.v.O., W.H.E., J.J.G. and J.L.P. HAADF-STEM and atomic reconstructions were performed by B.G., A.d.B., S.v.A. and S.B. A.P.G. and M.D. performed the Monte Carlo simulations. J.J.G. and C.v.O. wrote the manuscript under supervision of O.K., A.V.P., M.D., S.B., L.D.A.S. and D.V. D.V. supervised the whole project. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.
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Geuchies, J., van Overbeek, C., Evers, W. et al. In situ study of the formation mechanism of two-dimensional superlattices from PbSe nanocrystals. Nature Mater 15, 1248–1254 (2016). https://doi.org/10.1038/nmat4746
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DOI: https://doi.org/10.1038/nmat4746
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