Figure 2

(a) Temperature dependence of transient reflectivity with the extracted component of coherent phonons (inset) for the VO₂/AlN/Si sample. (b) Temperature-frequency map of the five coherent phonon modes (P1-P5, black circles) with R/R ₀ red-dotted curve from Fig. 1b, simultaneously revealing the structural and electronic states of VO₂ on AlN/Si. (c–e) Representative FFT spectra obtained at different temperatures. Inset of Fig. 2c shows an example of the Lorenzian function fitting of the FFT spectrum taken at 303 K. Inset of Fig. 2d shows the band diagrams for the semiconducting (or insulating) VO₂ with the CDW_M2 and IC_M2 substructures (before IMT) and for the semiconducting (or insulating) CDW_MMP and metallic MC_MMP substructures (after IMT).