Effects of Deposition Conditions of TiO2 Film and Substrate Prestrain on Film Void Geometries and Optical Properties in TiO2/PET Specimens

Abstract

TiO2/poly(ethylene terephthalate) (PET) specimens with various PET substrate prestrains are prepared to investigate the effect of the deposition conditions of the TiO2 film on the geometries of TiO2 film porosities and the effect of these void geometries on three optical parameters. The response surface methodology is used to express these three geometric parameters and three optical parameters as functions of the substrate prestrain and four deposition parameters. An increase in the O2/Ar flow ratio increases the mean width of voids. The trends of the curved surface of optical transmittance with L* and L*/W* are opposite to those of reflection. The highest transmittance is obtained with the largest L*/W* and the smallest L*. A nonzero flow rate of O2 gas in the deposition process reduces the optical band gap and increases the TiO2 film thickness generally, thus resulting in a reduction in transmittance and an increase in absorption. An increase in the prestrain of the PET substrate decreases the TiO2 film thickness. Both the mean index of refraction (n)mean and the mean extinction coefficient (k)mean due to the provision of the O2 gas are reduced. The n and k parameters for various wavelengths vary in a narrow range.