Reactive high-rate deposition of titanium oxide coatings using electron beam evaporation, spotless arc and dual crucible

• High-rate electron beam evaporation was combined with a spotless arc for plasma-asssisted thin film deposition.
• The spotless arc burns between two molten titanium electrodes.
• TiOx layers were deposited at a very high deposition rate (approximately 50 to 100 nm/s).
• Amorphous as well as anatase-form crystalline TiO2 layers were produced.
• Transparent amorphous layers with a high refractive index (2.4) were produced.

Results of investigations on thin films of titanium oxide are presented in which the layers were deposited at a very high deposition rate of approximately 50–100 nm/s. The high-performance coating process is based upon electron beam evaporation, a dual crucible, and a spotless arc that burns in the metal vapor and reactive gas between the evaporating titanium electrodes that are heated by the electron beam. Electron beam power, arc current and 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 a high refractive index (2.4) could be produced. Amorphous TiO2 coatings were obtained at a substrate temperature below 150 °C while crystalline layers of the anatase form could be deposited at a substrate temperature in the range of 200 to 300 °C. The data regarding the chemical composition of the titanium oxide layers are compared with a mathematical model of reactive vapor deposition. An estimate based on the model shows that the incorporation coefficient of oxygen, which gives its deposit probability in the coating, is approximately 0.25 for stoichiometric TiO2 layers. Possible applications of the PVD process presented are foreseen for large-area optical coating systems and large-scale application of photo-induced effects.