Proceedings of Online school on Fundamentals of Semiconductive Quantum Dots (QDsSCHOOL)
DOI: https://doi.org/10.29363/nanoge.qdsschool.2021.018
Publication date: 30th April 2021
Colloidal nanocrystal superlattices are highly ordered aggregates of particles. Crystals are highly ordered aggregates of atoms. However, nanocrystal superlattices are not conventionally considered crystals. But where does the border lie? Previously, we reported that CsPbBr3 nanocrystal superlattices have a structural perfection comparable with that of epitaxially grown multilayers, which can be considered as full-fledged single-crystals.
In this talk, we will discuss a novel approach to the characterization of periodically stacked colloidal nanocrystals, which was inspired by diffraction experiments on multilayers grown by molecular beam epitaxy. Our method takes advantage of optical interference phenomena arising from the superlattice periodicity, which enrich the profile of Bragg peaks in structural information. By fitting these profiles, collected with a common lab-grade diffractometer, we can extract structural information usually requiring high-end setups such as synchrotrons. Our approach is especially suitable for bidimensional colloidal crystals like nanoplatelets and nanosheets, because they spontaneously assemble into stacked periodic structures thanks to their highly anisotropic shape. However, we expect that our approach can be also extended 2D-layered organic-inorganic materials, which are not considered superlattices but share with them the periodic alternation of different layers.
To demonstrate our approach, we analyzed nanoplatelets of CsPbBr3 and PbS measuring with high precision thickness, interparticle distance and even distortions in their atomic lattice. In addition, we demonstrated that such nanocrystal superlattices reach stacking displacements as small as 0.3-0.5 Å. This is comparable with atomic displacement parameters found in metal-organic bulk crystals, leading to intriguing questions. For example, how different is a stacking of perovskite nanoplatelets from a bulk crystal of a hybrid Ruddlesden-Popper perovskite? Can we study nanocrystal superlattices as they were bulk crystals? In the end, are nanocrystal superlattices a new class of hybrid organic-inorganic bulk crystals?
The work of D.B. was supported by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 794560 (RETAIN). The visit of S.T. to Cornell University was supported by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 691185 (COMPASS). Work on perovskite nanoplatelets was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under contract no. DEAC02-05-CH11231 within the Physical Chemistry of Inorganic Nanostructures Program (KC3103). J.D. acknowledges support by the National Science Foundation Graduate Research Fellowship under DGE 1752814 and by the Kavli NanoScience Institute, University of California, Berkeley through the Philomathia Graduate Student Fellowship. C.G., D.A., and F.S. (IC-CNR) acknowledge support from the PON “R&I” 2014−2020 “Energie per l’Ambiente TARANTO - Tecnologie e processi per l’Abbattimento di inquinanti e la bonifica di siti contaminati con Recupero di mAterie prime e produzioNe di energia TOtally green” - Code: ARS01_00637 (CUP: B86C18000870005).
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