Unraveling Diverse Stacking Sequence in CVD-Grown WSe₂ Multilayers via Electron Diffraction Polarity

The transition from two-dimensional (2D) to three-dimensional (3D) layered systems has significantly expanded the research landscape for functional materials. Among these, polar layered materials with noncentrosymmetry, such as 3R-MoS₂, 3R-WSe₂, and In₂Se₃, are particularly intriguing due to their inherent structural asymmetry, which leads to exceptional properties, such as ferroelectricity, piezoelectricity, and nonlinear optical responses. However, precisely determining the layer-by-layer stacking sequence in multilayer polar materials remains a significant challenge. To address this challenge, we present a methodology that determines stacking sequences through an integrated analysis of multiple scattering signatures from the layered atomic arrangement, particularly the electron diffraction polarity arising from structural asymmetry. We demonstrate its capability in chemical vapor deposition (CVD)-grown WSe₂ multilayers, a representative transition metal dichalcogenides (TMDs) with polar noncentrosymmetric stacking and sliding ferroelectricity, accurately identifying diverse stacking scenarios, such as mixed antiparallel and parallel arrangements and complicated structure, such as spiral with stacking faults. Comprehensive validation and comparative analysis by transmission electron microscopy (TEM), Kelvin probe force microscopy (KPFM), and low-frequency Raman spectroscopy confirm the reliability of this diffraction polarity-based technique and its ability to correlate stacking sequence with material properties. This methodology is broadly applicable to layered materials with intrinsically broken inversion symmetry, enabling automatic stacking determination and extending to complex architectures, such as twisted or heterostructural moiré systems. Our method provides a critical tool for probing polar layered materials, which are promising candidates for ferroelectricity, optoelectronics, and spintronics.