In situ study of the formation mechanism of two-dimensional superlattices from PbSe nanocrystals
Jaco J. Geuchies (Universiteit Utrecht, European Synchrotron Radiation Facility)
Carlo Van Overbeek (Universiteit Utrecht)
Wiel H. Evers (Kavli institute of nanoscience Delft, TU Delft - ChemE/Opto-electronic Materials)
Bart Goris (Universiteit Antwerpen)
Annick De Backer (Universiteit Antwerpen)
Anjan P. Gantapara (Universiteit Utrecht)
Freddy T. Rabouw (Universiteit Utrecht)
Jan Hilhorst (European Synchrotron Radiation Facility)
Joep L. Peters (Universiteit Utrecht)
Oleg Konovalov (European Synchrotron Radiation Facility)
Andrei V. Petukhov (Eindhoven University of Technology)
Marjolein Dijkstra (Universiteit Utrecht)
Laurens D A Siebbeles (TU Delft - ChemE/Opto-electronic Materials)
Sandra Van Aert (Universiteit Antwerpen)
Sara Bals (Universiteit Antwerpen)
Daniel Vanmaekelbergh (Universiteit Utrecht)
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Abstract
Oriented attachment of PbSe nanocubes can result in the formation of two-dimensional (2D) superstructures with long-range nanoscale and atomic order. This questions the applicability of classic models in which the superlattice grows by first forming a nucleus, followed by sequential irreversible attachment of nanocrystals, 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.