Optical and surface properties of LiFePO4 thin films prepared by RF magnetron sputtering

LiFePO4 thin films with thickness values of 65 nm and 70 nm were deposited onto glass substrates by RF magnetron sputtering, using a LiFePO4 target in the argon atmosphere. A comprehensive study of the optical properties was performed and the dispersions of the constants were determined. The transmittance and absorbance spectra were measured in the wavelength range of 400-1000 nm. The films showed optical transmittance over 90% in the visible range. The optical band gap value of the films was evaluated as 3 eV. The refractive index value of the films is 1.63 at lambda = 550 nm. AFM micrographs indicate smooth surface with low values ofroot mean square roughness. Contact angle measurements of several testing liquids were used to characterize each sample in terms of wettability. The films are hydrophilic as observed from contact angle measurements. The surface free energy of the film surfaces and their components ( dispersive and polar) were calculated from the contact angle data using the different theories available in the literature.