Influence of plasma ion-beam assistance on TiO 2 and MgF 2 thin films deposited by plasma ion-assisted deposition

Abstract

Influences of plasma ion-beam assistance on the optical, structural and chemical properties of TiO 2 films, MgF 2 films and TiO 2/MgF 2 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 TiO 2 film induces a high refractive index, low extinction coefficient, and smooth surface. Also, PIAD changes the TiO 2 film from tensile stress to compressive. In the case of MgF 2 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 MgF 2 film is decreased by PIAD. As an application, a TiO 2/MgF 2 multilayer filter, consisting of PIAD TiO 2 films and CE MgF 2 films, has a small total stress and does not exhibit microcracks, while a filter with CE TiO 2 films shows many microcracks due to high tensile stress. In conclusion, it is found that the plasma ion-beam assistance for TiO 2 films is very useful in achieving stable TiO 2/MgF 2 multilayer optical coatings due to the dense microstructure, high refractive index, low extinction coefficient, smooth surface, and compressive stress.