Inert gas admixtures in PECVD of titanium dioxide thin films on polymers - Influence on the UV absorptance of the films

Abstract

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 α310= 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, α310 increased by 2 μm-1 for gas mixtures with Ar or N2. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.