UV absorption of coherent and nano-porous titanium oxide films obtained by PECVD

Polymeric materials suffer from chain degradation due to the absorption of ultraviolet (UV) light. Nevertheless, many polymers show excellent optical transmission properties in the visible range and are suitable replacements for glass. Coating of polymers with a thin film of TiO2 by means of PECVD is a typical method to prevent this shortcoming of some polymer materials. This work characterizes optically and morphologically the deposited nano- structured films of TiO2 on PET and samples of quartz glass synthesized via low pressure radio frequency plasma enhanced chemical vapor deposition reactor. A mixture of oxygen, argon and (titanium (IV) isopropoxide) TTIP was utilized. The variation of different process parameters such as the concentration of TTIP (CTTIP) and reactor pressure was investigated. The thickness of deposited films and consequently their deposition rate were determined by means of Ellipsometry. The deposition rate of the film was found to increase linearly with CTTIP while it decreased as a function of the pressure. Besides the film growth rate, the spectral behavior of the transmittance of visually transparent films was determined in the range from 200 to 900 nm by UV-Vis spectrometry. Accordingly, the film spectrum was found to vary with the thickness of deposited film independent of the manner of variable parameter. On the other hand, the reduction in the spectral absorption coefficient with increasing film thickness illustrates the presence of porous deposited films constructed from a combination of TiO2 particles and nano-voids. Furthermore, light scattering by small nano-particles with assuming single spheres is discussed and an overview of the literature research is introduced, Mie theory was identified as the most convenient solution for evaluating the intensity and efficiency factors of scattered light by such particles.