Temperature-dependence of the optical transitions of spray pyrolysis derived Sn doped Co3O4 thin films

Understanding the temperature dependence of physical properties is essential for optimizing the performance of Co 3 O 4 films, particularly with respect to their optical behavior. Previous studies have shown that Sn doping can influence the physical characteristics of Co 3 O 4 films. In this work, the temperature-dependent optical properties of undoped and 2 mol% Sn doped Co 3 O 4 (SCO) thin films, deposited on glass substrates via the spray pyrolysis technique, are investigated. The temperature effects were investigated using Raman, UV-Vis-IR spectroscopy and in-situ ellipsometry measurements. Raman analysis demonstrated that room temperature to 623 K domain is notably interesting as a stable single-phase range for both samples. Through an exhaustive ellipsometric analysis, including experimental and modeling studies, the evolution with temperature of key optical parameters such as film thickness, dielectric function, absorption coefficient, transition energies and Urbach energies have been successfully determined. The results highlight the influence of the applied heating on the optical responses. Particularly, the electronic transitions were found to decrease as the temperature increases. This dependence was analysed using the well-known Varshni model and the corresponding physical parameters were extracted.