Preparation, properties and optical applications of thin films of titanium dioxide

Abstract

The paper presents data on the optical properties, structure and oxidation of evaporated titanium films and discusses the structure, properties, and applications of titanium dioxide coatings prepared by heat oxidation of vacuum deposited titanium and by decomposition of titanium tetrachloride with atmospheric water vapour. It is shown that the rate of deposition and the pressure in the evaporation unit influence greatly the structure and optical properties of evaporated titanium films and of titanium dioxide coatings prepared by heat oxidation of evaporated titanium. Pure titanium films can only be deposited by fast evaporation at good vacuum. Slow evaporation at poor vacuum results in TiOTiN films with cubic structure. The oxidation of pure titanium films in air at 400° to 450°C results in titanium dioxide films with rutile structure and high n-values while ‘poorly deposited titanium films’ oxidise at the same temperature to titanium dioxide films with anatase structure and much lower n-values. Rutile is especially suitable as a top film in multilayer combinations. Titanium dioxide films produced by fuming titanium tetrachloride onto hot glass are amorphous if the glass temperature is kept below 280°C and consist of anatase at higher temperatures. An anodic method for applying reflectance-increasing films pairs of aluminium oxide and titanium dioxide on aluminium mirrors is described.