In Situ Transmission Electron MicroscopyStudy of Electron Beam-Induced Transformations in Colloidal CesiumLead Halide Perovskite Nanocrystals

摘要

An increasing number of studies have recently reported the rapid degradation of hybrid and all-inorganic lead halide perovskite nanocrystals under electron beam irradiation in the transmission electron microscope, with the formation of nanometer size, high contrast particles. The nature of these nanoparticles and the involved transformations in the perovskite nanocrystals are still a matter of debate. Herein, we have studied the effects of high energy (80/200 keV) electron irradiation on colloidal cesium lead bromide (CsPbBr3) nanocrystals with different shapes and sizes, especially 3 nm thick nanosheets, a morphology that facilitated the analysis of the various ongoing processes. Our results show that the CsPbBr3 nanocrystals undergo a radiolysis process, with electron stimulated desorption of a fraction of bromine atoms and the reduction of a fraction of Pb²⁺ ions to Pb⁰. Subsequently Pb⁰ atoms diffuse and aggregate, giving rise to the high contrast particles, as previously reported by various groups. The diffusion is facilitated by both high temperature and electron beam irradiation. The earlystage Pb nanoparticles are epitaxially bound to the parent CsPbBr3 lattice, and evolve into nonepitaxially bound Pb crystalsupon further irradiation, leading to local amorphization and consequentdismantling of the CsPbBr3 lattice. The comparison amongCsPbBr3 nanocrystals with various shapes and sizes evidencesthat the damage is particularly pronounced at the corners and edgesof the surface, due to a lower diffusion barrier for Pb⁰ on the surface than inside the crystal and the presence of a largerfraction of under-coordinated atoms.