Transparent nano composite PVA–TiO2 and PMMA–TiO2 thin films: Optical and dielectric properties

Transparent nano composite PVA–TiO2 and PMMA–TiO2 thin films were prepared by an easy and cost effective dip coating method. Al/PVA–TiO2/Al and Al/PMMA–TiO2/Al sandwich structures were prepared to study the dielectric behavior. The presence of metal–oxide (Ti–O) bond in the prepared films was confirmed by Fourier transform infrared spectroscopy. X-ray diffraction pattern indicated that the prepared films were predominantly amorphous in nature. Scanning electron micrographs showed cluster of TiO2 nanoparticles distributed over the film surface and also there were no cracks and pin holes on the surface. The transmittance of the films was above 80% in the visible region and the optical band gap was estimated to be about 3.77 eV and 3.78 eV respectively for PVA–TiO2 and PMMA–TiO2 films by using Tauc's plot. The determined refractive index (n) values were between 1.6 and 2.3. High value of dielectric constant (ɛ′ = 24.6 and ɛ′ = 26.8) was obtained for the prepared composite films. The conduction in the composite films was found to be due to electrons. The observed amorphous structure, good optical properties and dielectric behavior of the prepared nano composite thin films indicated that these films could be used in opto-electronic devices and in thin film transistors.