Figure 3. Real time XRD θ−2θ scans of (a) VO₂(B)/STO(001) and (b) VO₂(A)/STO(011) samples as a function of temperature in 0.37 Torr of air. A clear phase change was observed from both samples, indicating that the phases are in close proximity with each other. The phase changes were, however, irreversible upon cooling. It is also worth noting that there are temperature gaps where the XRD peaks are hardly seen before showing up the polycrystalline phases. They are 470–520 °C in (a) and 430–470 °C in (b). We attribute this to the films in metastable state undergoing polycrystallization during the phase transition, even though it is hard to clearly identify due to the suppressed XRD peaks.