The effect of buffer layer on the thermochromic properties of undoped radio frequency sputtered VO2 thin films

Thermochromic (TC) coatings can find use in a wide range of applications. Vanadium dioxide (VO2) specifically, can be potentially used as a smart window coating, as it presents a metal-to-semiconductor transition close to the room temperature (Tc = 68 °C). This results in low transmission in the infrared (thermal) part of the spectrum, while preserving its transmittance in the visible. In the present work, vanadium dioxide (VO2) thin films with a thickness of ~ 85 nm were prepared by radio frequency sputtering, to investigate the influence of the buffer layer and deposition properties employed, on their thermochromic behavior. The substrates used were uncoated glass and pre-coated glasses with SnO2 or ZnON as buffer layer. The lowest growth temperature applied was 300 °C, yielding TC-VO2, without the necessity of any post-growth treatment. The structure of the VO2 films was studied by X-ray diffraction and temperature-dependent micro Raman techniques, and the transition temperatures were determined through transmittance measurements.