Plenary talk - deposition of nanocrystalline TiO2 thin films on poly(ethylene terephthalate) at ≤130°C

It is well known that crystallinity is required for photocatalytic activity in TiO₂ and that the metastable anatase phase usually exhibits photocatalytic activity superior to that of the equilibrium rutile phase. This phase transformation temperature often is observed to occur at ~600°C, although temperatures in the range 400°-1200°C have been observed. Therefore, retention of anatase below 400°C is considered a desirable goal in the processing of TiO₂ thin films. However, most thin-film fabrication methods typically require heating at temperatures in excess of 400°C so as to recrystallise the films. This limitation in high-temperature processing impacts on the potential to retain anatase as well as the types of substrates that can be used to support the thin films. That is, almost no polymers can withstand these temperatures, so ceramics and metals are the alternatives. Therefore, the development of TiO₂ coating methods at low temperatures would make possible the production of flexible light-weight coatings on polymers. The present work was designed to obtain crystalline TiO₂ at temperatures sufficiently low to avoid the anatase → rutile phase transformation and charring/melting of polymeric substrates.