Near room temperature tunability of thermochromic VO2 thin films prepared via thermal oxidation method, influence of CO2:N2 gas flux ratios

In this study, we have investigated the thermochromic characterizations of VO2 thin films synthesized by the thermal oxidation method. The oxidation process of a DC sputtered metallic vanadium layer on glass substrates, at 450 degrees C for 1 h, was carried out in the presence of CO2:N-2 gases with different flux ratios of 30:70, 40:60, 50:50, 60:40, and 70:30, respectively. Using CO2, as the oxidizing gas, provides an easy control route for obtaining the VO2 phase among various vanadium oxide phases. The layers were characterized by FESEM, XRD & Raman spectra, sheet resistance vs. temperature (20-120 degrees C), and UV-Vis-NIR spectra at 25 and 90 degrees C. The XRD and Raman spectra confirmed all prepared layers have a VO2 polycrystalline structure in monoclinic phase. We found among the studied samples CN30-70 and CN50-50 having desirable optical characteristics of peak visible transmittance of about 55%, with low transition temperatures (T-cr) of similar to 42 and 31 degrees C, and also relatively high amounts of Delta T-1700nm, Delta T-sol and T-lum,T-av are good candidates for thermochromic smart windows, both from optical properties and economical fabrication method points of view.