Anna Scheid (Stuttgart / DE), Yi Wang (Nanjing / CN), Mina Jung (Stuttgart / DE), Tobias Heil (Stuttgart / DE), Davide Moia (Stuttgart / DE), Joachim Maier (Stuttgart / DE), Peter A. van Aken (Stuttgart / DE)
Abstract text (incl. figure legends and references)
Halide perovskites have remarkable electronic properties that make them promising for applications in photovoltaics and optoelectronics. Despite the latest advances in performance optimization and low-cost manufacturing, halide perovskites still face significant challenges with chemical instability. In this context, a great interest has emerged in the chemistry and perovskite community to comprehend the chemical (in)stability and to develop engineering strategies for improving the robustness of perovskite devices [1].
To date, the sensitivity of halide perovskites to the electron beam limits a deeper understanding of the fine structure at the atomic level, which would provide valuable guidance for the optimization of the device performance. Under irradiation, the atomic structure of all-inorganic halide perovskites is disrupted by electron-beam-induced stimulated desorption of halide species. Due to this sensitivity, many of the conventional investigation techniques often utilized for optoelectronic materials, such as bright-field and dark-field scanning transmission electron microscopy (STEM) or spectroscopic methods, are not an option for atomic-scale characterization [2, 3].
In this study, we demonstrate that ptychographic phase reconstructions from 4D-STEM datasets offer great potential to fill this gap for atomic structure investigations with low electron-dose exposure. Recent progress in the development of direct electron cameras (DECs) allows for the acquisition of low-dose, sparse binary diffraction patterns at high frame rates. Specific sample information, such as high-angle scattering to generate synthetic dark-field images or the bright-field disc necessary for phase reconstructions, can be extracted in post-processing steps. With Single-Sideband (SSB) and Wigner-Distribution-Deconvolution (WDD) algorithms, it is possible to reconstruct the electrostatic potential of the sample and thereby obtain high signal-to-noise ratio (SNR) images with a strong phase contrast for all atomic species [4, 5]. The superior dose-efficiency of ptychography with improved SNR allows visualization of fine structural details, invisible in synthetic dark-field images, computed from the same dataset. Atomically resolved phase images of three all-inorganic halide perovskites, CsPbBr3, CsPbIBr2, and CsPbI3, are presented with a resolution down to the aperture-constrained diffraction limit. In addition, we show that even for slightly thicker samples, low-dose ptychographic reconstructions give a representation of the atomic structure [6].
References
[1] T. A. Berhe et al., Energy Environ. Sci., 9, 2 (2016).
[2] X.-G. Zhou et al., J. Phys. Chem. C, 125, 19 (2021).
[3] S. Chen et al., Journal of Applied Physics. 128, 1 (2020).
[4] C. M. O'Leary et al., Appl. Phys. Lett. 116, 12 (2020).
[5] J.M. Rodenburg et al.,Phil. Trans. R. Soc. Lond. A. 339, 1655 (1992).
[6] This work is received funding the European Union's Horizon 2020 research and innovation programme under grant agreement No. 823717 – ESTEEM3.
Figure 1. Synthetic LAADF and phase-reconstructed atomic structure images from 4D-STEM datasets. (a)-(c) CsPbBr3, acquired under conventional STEM imaging conditions. (d)-(f) CsPbIBr2, acquired under low dose conditions with an average dose of ~4070 e-/Å2. The inset shows structural overlays of possible crystallographic directions, indistinguishable in the LAADF image. (g)-(i) CsPbI3, acquired with an average dose of ~3540 e-/Å2.