Controlled Vapor-Phase Synthesis of VSe2 via Selenium-Driven Gradual Transformation of Single-Crystalline V2O5 Nanosheets

We report a gas-phase precursor modulation strategy for the controlled synthesis of 1T-phase vanadium diselenide (VSe₂) from vanadium pentoxide (V₂O₅) nanosheets by systematically adjusting the vapor pressure of selenium. By controlling the selenium vapor pressure, selenium-free vapor transport of vanadium dioxide led to the spontaneous oxidation and formation of tens-of-micrometer-sized rectangular V₂O₅ crystals, while moderate selenium introduction produced intermediate oxygen-rich phases with trapezoidal crystal facets, and a highly selenium-rich environment yielded trigonal VSe₂ crystals. Raman scattering measurements confirmed the stepwise transformation from V₂O₅ to VSe₂, and atomic force microscopy revealed well-defined layered morphologies and distinct conformation within an atomically thin regime. Additionally, high-resolution transmission electron microscopy validated the orthorhombic and trigonal crystal structures of V₂O₅ and VSe₂, respectively. This work demonstrates the versatility of fine-tuned vapor-phase growth conditions in vanadium-based layered compounds, providing useful platforms to optimize structural composition with atomic precision.