Publication date: 3rd July 2020
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.[1]
In this work, we will discuss a novel approach to the characterization of periodic colloidal nanostructures self-assembled on flat substrates. Our method takes advantage of the modulation of the Bragg peaks profile by the superlattice periodicity, which enriches them in structural information. Nanocrystal superlattices are often studied by grazing-incidence scattering techniques, which require dedicated instruments or synchrotron beamlines and the development of complex and sample-tailored fitting programs. Instead, our approach enables to extract as much detailed information with the help of a common lab-grade diffractometer and a straightforward fitting routine imported from epitaxial multilayers research.[2] The versatility of the analysis is demonstrated on a variety of nanocrystal compositions and shapes (CsPbBr3 and PbS, nanocrystals and nanoplatelets) with excellent results.
By using our approach, we could accurately determine all the superlattice structural parameters, track their evolution upon treatment and demonstrate that our colloidal superlattices feature nanocrystal displacements in the range 0.5 – 1.3 Å. This opens to promising and easily accessible perspectives for future research in the field of structural and optoelectronic characterization on those and similar systems, such as the 2D layered perovskites. Furthermore, there is a broad interest in nanocrystal superlattices for applications such as quantum light sources, miniband-based electronics and magnetic mesostructures, and a possible bottleneck in their development is the high demands for their structural investigation. The development of a simple and accessible characterization method can significantly speed up the process of turning those fascinating system into real-life applicable devices.
The work of D.B. was supported by the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 794560 (RETAIN).
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