Analysis of substrate type and thickness influence on wettability of Nb2O5 thin films

For the purpose of this paper Nb₂O₅ thin films were manufactured by microwave-assisted reactive magnetron sputtering. Nb₂O₅ thin films with different thickness were deposited on standard microscope slides, SiO₂ and silicon substrates. Wettability and optical properties of manufactured coatings were investigated. Knowledge of the macroscopic contact angle for materials allows to predict whether a liquid droplet will bead up on or spread out over a solid surface. In this paper contact angle, critical surface tension and surface free energy of Nb₂O₅ thin films with thickness of 565, 300, 200, 100 and 50 nm were investigated. Measurements of surface free energy and contact angle was carried out with a computer controlled goniometer system with water, ethylene glycol and diiodomethane. Contact angle measurements were performed according to the sessile drop method. The results have shown that all manufactured Nb₂O₅ thin films had the water contact angle of about 90 degrees. There was no difference in wettability for thin films with different thickness and deposited on different substrates. Also optical properties of deposited thin films were compared. Transmittance spectra of Nb₂O₅ thin films were measured using Hitachi U-3501 spectrophotometer. Based on transmittance and reflectance spectra, measured with the aid of Aquila nkd-8000 instrumentation, thickness, refractive index and extinction coefficient of Nb₂O₅ thin films were calculated using Drude - Lorentz model. Transparency in visible light range of deposited thin films varied from about 70 % up to 80 %. Refractive index and extinction coefficient were 2.32 and 4.55×10^-5, respectively.