By conventional reactive evaporation techniques, films with a certain deviation from stochiometric composition and, therefore, increased absorptance and dielectric losses were obtained. By ionization of the residual gas a considerable increase of reactivity has been achieved. The construction of a discharge tube with a region of high current density for ionization is described. The tube was arranged inside a bell jar. The ionized gas emerged from a nozzle in the wall of the tube directly into the high vacuum region. Production parameters for SiO2, SiOxNy, and TiO2 films were evaluated. On unheated substrates SiO2 films, which are practically free of absorptance down to 190 nm, and TiO2 films with refractive indices up to 2.3, were obtained.
W. Heitmann, "Reactive Evaporation in Ionized Gases," Appl. Opt. 10, 2414-2418 (1971)