Methods for preparing titania coatings by plasma CVD at atmospheric pressure

#The present application is the U.S. counterpart of WO 2004/013376 and claims priority to UK Application No. 0217553.7 filed on Jul. 20, 2002, the entire contents of each of which are hereby incorporated herein by reference.

#Titania is a widely used material in thin film coatings. It has been used, for example, as a hard coating and as a transparent dielectric materials in optical stacks. In recent years the photo-catalytic properties of titania have attracted increasing interest. (e.g Paz & Luo, J. Mat. Res Vol 10, no 11, November 1995). Titania layers have been deposited by many techniques (e.g. evaporation, e-beam, sputtering, sol gel, and CVD).

#Chemical Vapour Deposition (CVD) has been widely used for many years across a wide range of industrial applications, to produce thin film coatings. In such a process a reactive gas mixture is introduced in the coating region, and a source of energy applied to initiate (or accelerate) a chemical reaction, resulting in the growth of a coating on the target substrate.

#The examples below are meant to illustrate scope, and potential, and are not in themselves meant to be limiting.

#Typical Experimental Conditions Applied: Frequency: 10-25 KHz (variable) Power: 100 W to 1 KW. Configuration: parallel plates with either one or both surfaces covered by an dielectric barrier (e.g. glass, ceramic or plastic film or sheet). Electrode gap (as measured from the internal surface whether it be the metal electrode or the dielectric) of varied between approx 1 and 15 mm. Optimum region was between 2 and 6 mm. Power densities: 0.1-10 Watts cm2 (generally 0.5-2 watts cm2) Carrier (i.e. plasma) gas-helium Carrier Gas temperature (delivered)—ambient to approx 50° C. (to ensure precursor volatility) Plasma gas temperature approx 50-100° C. (measured by contact probe) Carrier Gas flow rate 1-2 liters min Titania precursor pre-volatilised (e.g. in a bubbler) and delivered at conc. ranges below 1% and most often in the region of O 0.1%. Oxygen level less than 1% and typically less than 0.1% Photo-catalytic Activity Measurement

#The activity of the films produced has been measured using a series of techniques including stearic acid removal rate, optical scattering reduction, and surface energy measurements. The most commonly applied technique in the literature is stearic acid removal and the experimental procedures are described in a paper by Heller and Paz, J Mat Res vol. 12, no 10, October 1997. In summary, a stearic acid film is deposited on the coating to be tested, and under selected UV irradiation, the reduction in the area of a selected IR peak of stearic acid is monitored as it progressively reduces. In our work we use an FTIR spectrometer to measure this peak.