A microstructural study of transparent metal oxide gas barrier films

The relationship between the microstructure and the water vapour transmissi on rates of aluminium oxide and aluminium coatings deposited by magnetron s puttering on polyethylene terephthalate have been investigated. The gas bar rier properties of the films have been measured as a function of temperatur e and a range of techniques used to characterize the coatings including ato mic force microscopy, which also provided information on the early growth m echanism. It was found that the Al/PET film showed a better water vapour ba rrier than the AlOx/PET although the activation energy for water vapour per meation was the same for both. We propose that the interaction of water wit h the barrier coating plays a significant part in determining the observed gas barrier performance. (C) 1999 Elsevier Science S.A. All rights reserved .