Photoelectron Spectroscopy for Structural Characterization of Layered Transition Metal Dichalcogenides

Layered transition metal dichalcogenides (TMDs) exhibit remarkable structural flexibility and electronic tunability, where subtle structural variations, such as defects, self-intercalation, lattice distortion, stacking sequence and phase transitions, can significantly modify their physical properties. However, reliably identifying these structural degrees of freedom remains challenging when changes in stoichiometry or long-range order are minimal. Core-level photoelectron spectroscopy (PES) provides a uniquely sensitive approach to probe the local electronic structure and chemical environment. In this review, we establish a unified framework showing how different structural modulations give rise to distinct spectroscopic signatures governed by initial-state chemical shift and final-state core-hole screening. Vacancy defects and self-intercalation primarily induce core-level shifts of the defective element. Periodic lattice distortion leads to spectral splitting. Inter-layer sliding leads to subtle binding energy variations without new features. The structural phase transitions generate new spectral components with pronounced binding energy shifts. Using representative TMD systems, we demonstrate how core-level PES can identify defect types, quantify self-intercalation, clarify lattice distortion and track stacking arrangements and phase evolution. These capabilities highlight PES as a powerful probe of local structural modulation and many-body electronic responses, providing a direct spectroscopic link between structural variations and electronic properties.