a substantial effect on the band structure and electron behavior. Unfortunately, over past few years, most perovskite optoelectronic devices focus on polycrystalline perovskite thin-films, [10][11][12][13] and can only get the average surface-related optoelectronic properties of polycrystalline particles. The random arrangement of surface orientation in polycrystalline perovskite thin films seriously affects the carrier transportability and limits the microscopic photovoltaic performance. [14][15][16] Instead, a single-crystal-basedperovskite device can not only effectively improve photovoltaic performances due to their lower trap-state density and ultralong carrier diffusion lengths, [17][18][19] but also provide great opportunity for tailing the surface-determined optical and electronic properties. [17][18][19][20][21] However, it is still a great challenge to engineer the anisotropic surface of halide perovskite single crystals due to their ionic nature and fast crystallization during their regular solution-based growth, [22][23][24] and it is extremely difficult to quantify the surface-dependent optoelectronic properties as well as the underlying anisotropy mechanism.Herein, we report a one-step atmospheric-pressure chemical vapor deposition (APCVD) method for fabricating uniform perovskite CsPbBr 3 cube and tetrahedron single-crystals with precise control of ( 100) and ( 111) surface anisotropy, respectively (Figure S1, Supporting Information, see Methods in the Supporting Information for more synthesis details). The single-crystal-based optoelectronic devices demonstrated that the preferred (100) surface engineering of CsPbBr 3 singlecrystals enables a lowest surface bandgap energy of 2.33 eV, long carrier lifetime of 8.68 ns and high-rate carrier mobility up to 241 µm 2 V -1 s -1 , whereas the polar (111) surface induces ≈0.16 eV upward surface band bending and ultrahigh charged surface defect density of 1.49 × 10 15 cm -3 . Our results pave an ideal way to optimize the performance of halide-perovskitebased optoelectronic and/or catalysis devices by anisotropic surface engineering. Results and DiscussionScanning electron microscopy (SEM) images (Figure 1A-D) and optical microscopy images (Figures S2 and S3, Supporting Information) show that CsPbBr 3 cubes and tetrahedrons are uniform in size (≈4 µm) and monodispersed on the surface of the SiO 2 /Si substrate. The elemental distribution of Cs, Pb and Br was characterized using scanningelectron microscopy-energydispersive X-ray spectroscopy (SEM-EDS) elemental mapping, Engineering surface structure can precisely and effectively tune the optoelectronic properties of halide perovskites, but are incredibly challenging. Herein, the design and fabrication of uniform all-inorganic CsPbBr 3 cubic/tetrahedral single-crystals are reported with precise control of the ( 100) and ( 111) surface anisotropy, respectively. By combining with theoretical calculations, it is demonstrated that the preferred (100) surface engineering of the CsPbBr 3 single-crystals enables a lo...

A deep understanding of the fine structure at the atomic scale of halide perovskite materials has been limited by their sensitivity to the electron beam that is widely used for structural characterization. The sensitivity of a γ-CsPbIBr 2 perovskite thin film under electron beam irradiation is revealed by scanning transmission electron microscopy (STEM) through a universal large-range electron dose measurement, which is based on discrete single-electron events in the STEM mode. Our research indicates that the γ-CsPbIBr 2 thin film undergoes structural changes with increasing electron overall dose (e − •Å −2 ) rather than dose rate (e − •Å −2 •s −1 ), which suggests that overall dose is the key operative parameter. The electron beam-induced structural evolution of γ-CsPbIBr 2 is monitored by fine control of the electron beam dose, together with the analysis of high-resolution (S)TEM, diffraction, and energy-dispersive X-ray spectroscopy. Our results show that the γ-CsPbIBr 2 phase first forms an intermediate phase [e.g., CsPb (1−x) (IBr) (3−y) ] with a superstructure of ordered vacancies in the pristine unit cell, while a fraction of Pb 2+ is reduced to Pb 0 . As the electron dose increases, Pb nanoparticles precipitate, while the remaining framework forms the Cs 2 IBr phase, accompanied by some amorphization. This work provides guidelines to minimize electron beam irradiation artifacts for atomic-resolution imaging on CsPbIBr 2 thin films.

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Safety is a primary concern for the civil aviation industry. Airlines record high-frequency but potentially low-severity unsafe events, i.e., incidents, in their reports. Over the past few decades, civil aviation security practitioners have made efforts to analyze these issues. The information in incident reports is valuable for risk analysis. However, incident reports were inefficiently utilized due to incoherence, large volume, and poor structure. In this study, we proposed a technical scheme to intelligently classify and extract risk factors from Chinese civil aviation incident reports. Firstly, we adopted machine learning classifiers and vectorization strategies to classify incident reports into 11 categories. Grid search was used to adjust the parameters of the classifier. In the preliminary experiment, the combination of the extreme gradient boosting (XGBoost) classifier and the occurrence position (OC-POS) vectorization strategy outperformed with an 0.85 weighted F1-score. In addition, we designed a rule-based system to identify the factors related to the occurrence of incidents from 25 empirical causes, which included equipment, human, environment, and organizational causes. For cause identification, we used rules obtained through manual analysis with keywords and discourse. F1-score above 0.90 was obtained on the test set using the causes identification model derived from the training set. The proposed system permits insights into unsafe factors in aviation incidents and prevents reoccurrence. Future works can proceed on this study, such as exploring the causal relationship between causes and incidents.

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