Inert Gas Admixtures in PECVD of Titanium Dioxide Thin Films on Polymers—Influence on the UV Absorptance of the Films

A low pressure radio frequency discharge (200 W for 5 min) was operated in oxygen, nitrogen/oxygen and argon/oxygen with small admixtures of titanium(IV)isopropoxide (TTIP). By means of the O2-flow, the O2-to-TTIP ratio q was varied in all the gas mixtures. Besides the growth rate, the absorptance of films deposited was determined in the range of 200–500 nm. Accordingly, their cut-off wavelength increased with q for mixtures containing N2 or Ar, while it was unaffected for O2/TTIP mixtures. At 310 nm, the absorption coefficient was a310 = 13 µm−1 for q ≈ 44 in Ar/O2/TTIP and marginally lower in N2/O2/TTIP as well as O2/TTIP. But, for decreasing q, a drastic decrease in a310 ≈ 8 µm−1 was witnessed for O2/TTIP mixtures. In contrast, a310 increased by 2 µm−1 for gas mixtures with Ar or N2.