Titanium dioxide (TiO₂) films have versatile applications, which include: ultra-thin film high-k insulators in integrated circuits and surface passivation, as well as biocompatible coatings availing their chemical and thermal resistance. Due to its high refractive index, it is commonly used for antireflection coatings. Moreover, it appears to be a material for effective UV absorption.

This is of special interest for the protection of polymers, which suffer photo-degradation. Thus, thin amorphous films, mainly, consisting of TiO₂ , as discussed in an earlier work [1], were deposited at temperatures of 70°C on films of polycarbonate, polyethylene-terephthalat and on quartz as reference material.

Therefore, a low pressure rf discharge was operated in oxygen, oxygen/nitrogen and oxygen/argon with small admixtures of titanium(IV)isopropoxide (TTIP) at an input power of 200 W for 5 min. By changing the flow rate of oxygen, the oxygen-to-TTIP ratio q was varied for all types of discharges gas mixtures for q = 10 to 45. Besides the variation of the deposition rate (i.e. film thickness), the behaviour of the spectral transmittance of visually transparent films was determined in the range from 200 to 500 nm. Furthermore, the absorptance of films has been derived at characteristic spectral positions of the transmission spectra of the films. Accordingly, the cut-off wavelength of the films was found to be a subject of variation depending on the ratio q for gas mixtures containing nitrogen or argon. But, for mixtures of pure oxygen and TTIP, it appeared to depend on q only slightly. Furthermore, at 310 nm, the spectral absorption coefficient (extinction coefficient x concentration) was 13x10⁶ m^-1 for q = 44 in oxygen/argon and marginally lower for oxygen/nitrogen (12x10⁶ m^-1) as well as for oxygen (11x10⁶ m^-1). However, with decreasing value of q a drastic decrease of the absorption coefficient (toward 8x10⁶ m^-1) was witnessed for the oxygen/TTIP mixture. In contrast, the coefficient decreases only slightly (by 10⁶ m^-1) for nitrogen and argon containing mixtures.

[1] A. Sonnenfeld, R. Hauert, Ph. Rudolf von Rohr, UV Absorptance of Titanium Dioxide Thin Films by Plasma Enhanced Deposition from Mixtures of Oxygen and Titanium-Tetrakis-Isopropoxide, Plasma Processes and Chemistry, DOI: 10.1007/s11090-006-9022-6, online at Springer-Link, 2006