Reactive high-rate deposition of titanium oxide coatings using electron beam evaporation, spotless arc and dual crucible
Results of investigations on thin films of titanium oxide are presented in which the layers were deposited at avery high deposition rate of approximately 50-100 nm/s. The high-performance coating process is based uponelectron beam evaporation, a dual crucible, and a spotless arc that burns in themetal vapor and reactive gas betweenthe evaporating titanium electrodes that are heated by the electron beam. Electron beam power, arc currentand oxygen flow rate were varied and the resulting coatings investigated with regard to their composition,optical properties, and microstructure. Even at such high deposition rates, transparent and dense layers with ahigh refractive index (2.4) could be produced. Amorphous TiO2 coatings were obtained at a substrate temperaturebelow 150 °C while crystalline layers of the anatase form could be deposited at a substrate temperature inthe range of 200 to 300 °C. The data regarding the chemical composition of the titanium oxide layers are comparedwith a mathematical model of reactive vapor deposition. An estimate based on the model shows thatthe incorporation coefficient of oxygen, which gives its deposit probability in the coating, is approximately0.25 for stoichiometric TiO2 layers. Possible applications of the PVD process presented are foreseen for largeareaoptical coating systems and large-scale application of photo-induced effects.