Phase transition induced Raman enhancement on vanadium dioxide (VO₂) nanosheets

Semiconductor materials such as transition metal oxides and dichalcogenides have been increasingly explored as promising surface enhanced Raman scattering (SERS) platforms. This work demonstrates, for the first time, that VO₂ nanosheet materials can be another SERS-active platform for molecule detection based on the chemical enhancement mechanism. A systematic study of the phase transition induced Raman enhancement on VO₂ nanosheets reveals that increase in the crystal symmetry from VO₂(B) to VO₂(M) and to VO₂(R) results in a dramatic decline in the enhancement ability of the probe molecules. On defect-rich VO₂(B) nanosheets, a detection limit as low as 10⁻⁷ M can be reached for various dye molecules, confirming VO₂ nanosheets as another kind of effective SERS-active semiconductor metal oxide. This study strongly indicates that a synergetic strategy of low-dimension and low-symmetry may be a new avenue for the design of highly efficient metal oxide-based semiconductor SERS substrates.