Influence of plasma ion-beam assistance on TiO2 and MgF2 thin films deposited by plasma ion-assisted deposition

Influences of plasma ion-beam assistance on the optical, structural and chemical properties of TiO2 films, MgF2 films and TiO2/MgF2 narrow band-pass filters deposited by conventional e-beam evaporation (CE) and plasma ion-assisted deposition (PIAD), respectively, were investigated. The results show that PIAD for the TiO2 film induces a high refractive index, low extinction coefficient, and smooth surface. Also, PIAD changes the TiO2 film from tensile stress to compressive. In the case of MgF2 film, the results show that the plasma ion-beam assistance exhibits large extinction coefficient, high optical absorption, and smooth surface. High tensile stress in the CE MgF2 film is decreased by PIAD. As an application, a TiO2/MgF2 multilayer filter, consisting of PIAD TiO2 films and CE MgF2 films, has a small total stress and does not exhibit microcracks, while a filter with CE TiO2 films shows many microcracks due to high tensile stress. In conclusion, it is found that the plasma ion-beam assistance for TiO2 films is very useful in achieving stable TiO2/MgF2 multilayer optical coatings due to the dense microstructure, high refractive index, low extinction coefficient, smooth surface, and compressive stress.