XRM2024 - Thu02A - "Beam Damage and Mitigation in Metal Halide Perovskites under High Brilliance X-ray Photon Sources"

Metal halide perovskites (MHP) suffer from photo-structural-chemical instabilities whose intricacy requires state-of-the-art tools to investigate their properties under various conditions.¹ This study addresses the damage caused by focused X-ray beams on MHP through a correlative multi-technique approach: chemical variations of the metallic part and halides were monitored via nano x-ray fluorescence maps at CARNAÚBA beamline² while the organic part was tracked by µ-Fourier transform infrared spectroscopy at IMBUIA beamline, both at LNLS synchrotron. The damage after high-dose irradiation is noticeable in many ways: the ejection of iodine and organic components, whose relative amount is reduced; the formation of an excavated area modifying the sample morphology; and an altered optical reflectivity indicating an optically inactive layer. The damage mechanism combines radiolysis and sputtering processes. Interestingly, the bulk underneath the excavated area keeps the initial halide proportion demonstrated by a stable photoluminescence emission energy. We also show that controlling the beam dose and environment is an excellent strategy to mitigate the dose harm. Hence, we combined a controlled X-ray dose with an inert N₂ atmosphere to certify the conditions to probe MHP properties while mitigating damage efficiently. Finally, we applied optimized conditions in an X-ray ptychography experiment, reaching a 15-nm spatial resolution, an outcome that has never been attained in this class of materials.

Ptychography in phase contrast (14 nm pixel size @10 keV) reveals morphological aspects not visible in traditional scanning transmission (STXM) maps. In addition, thanks to the XRF maps, we correlate the grain boundary regions to a higher concentration of iodine in the outer regions of the grain and a lower electronic density, as highlighted by the phase advances. (Fig. 1) The possibility of measuring in fly-scan mode and N₂ atmosphere³ was essential to mitigate eventual sample damages that are typically the main limiting factor to applying the CDI in such samples. Our multispectral images of MHP are a pivotal step in developing and applying the technique in beam-sensitive samples for high-resolution imaging, especially in the case of heterogeneous and hierarchical functional materials in which the multiscale properties determine final device performances.

References:

[1] da Silva, Francisco MC, et al. "Disentangling X‐ray and sunlight irradiation effects under a controllable atmosphere in metal halide perovskites." Solar RRL 7.1 (2023): 2200898.
[2] Tolentino, Hélio CN, et al. "The CARNAÚBA X-ray nanospectroscopy beamline at the Sirius-LNLS synchrotron light source: Developments, commissioning, and first science at the TARUMÃ station." Journal of Electron Spectroscopy and Related Phenomena 266 (2023): 147340.
[3] Lena, F. R., et al. "Commissioning of the cryogenic sample environment for the TARUMÃ station at the CARNAÚBA beamline at Sirius/LNLS." Journal of Physics: Conference Series. Vol. 2380. No. 1. IOP Publishing, 2022.