Effect of the bottom layer thickness on the structural and optical phase transition properties of V2O5/V/V2O5 thin films

Vanadium dioxide (VO2 (M)) is an intelligence material that undergoes a phase transformation that can be tuned. This material has the potential to be used as an energy-efficient coating. Scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and optical transmittance measurements were used to characterise the multi-layered thin films with a varying bottom layer thickness. Surface morphology reveals irregular shapes, boundary layers, and porous at the nanoscale, and the presence of tiny cracks. For all samples, the root means square (RMS) roughness reveals a smooth film surface. The formation of polycrystalline VO2 (M) thin films is confirmed by XRD patterns. Switching thermochromic properties are demonstrated by temperature-dependent of optical transmittance measurements. Transmittance increases significantly in the infrared region when compared to the visible region. The transmittance in the UV (ultra-violent) ranges between 15 and 25%, while the transmittance in the NIR (near infrared region) ranges between 5 and 40%, depending on the thickness of the bottom layer. We also reduced the phase transition temperature from 48 to 50 °C when compared to pure VO2 (∼68 °C), this reduction in phase transition is attributed to the distinction of nanostructured in VO2. This research could help to advance the use of smart window coatings in the real world.