Direct Observation of Self-Intercalation Driven 2D-to-3D Phase Transition in VSe<sub>2</sub>.

Chen, Jianchu; Zhang, Jianwei; Wang, Kai-Qi; Zeng, Jun; Du, Yuhan; Yuan, Xiang; Qu, Ke; Yang, Zhenzhong et al. · Nano Lett · 2026

basic_science · Level V

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Abstract

Precise control of phase transitions is essential for tuning properties of two-dimensional (2D) materials. Self-intercalation can modulate structural and electronic states in layered systems, yet its microscopic mechanism remains unclear owing to scarce atomic-scale in situ evidence. Using atomic-resolution scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy (EDS), we directly visualize the self-intercalation-driven conversion from the 2D 1T phase to a three-dimensional (3D) self-intercalated phase in VSe<sub>2</sub>. In situ manipulation reveals atomic structural evolution as vanadium ions migrate into van der Waals (vdW) gaps during the 2D-to-3D transition. Density functional theory (DFT) calculations confirm the stability and intrinsic ferromagnetism of the 3D phase. This work establishes a structural evolution model for the 2D-to-3D transition in VSe<sub>2</sub>, elucidates the atomic mechanism of self-intercalation-induced phase transitions in transition metal dichalcogenides (TMDs), and provides a mechanistic foundation for rational phase engineering of low-dimensional magnetic materials.