Optical, chemical and protective properties of thin films produced by ion-assisted deposition

Abstract

Magnetooptical data storage materials, such as terbium-iron-cobalt (TbFeCo) alloys are susceptible to pinhole formation, as well as oxidation, particularly of the TB component. Previous studies have shown that oxide overlayers or substrates can be directly reduced by the terbium component. Ultra-thin, partially oxidized samarium films (nominally 5-10 nm) were found to serve as a suitable barrier layer between the TbFeCO film and Al₂O₃ overlayers. Furthermore, the interfacial Sm layer was found to increase the coercivity of the TbFeCo film by nearly a factor of two without degrading the magnetooptic figure of merit or significantly changing its curie point. Ion-assisted deposition (IAD) has been used to alter and improve the protective barrier properties of dielectric materials such as alumina (Al₂O₃) and zirconia (ZrO₂). In particular, pinhole formation in iron films (in lieu of TbFeCo) protected by alumina or zirconia films was greatly affected by the use of ion assisted deposition. In the case of the alumina overlayers, any bombardment was found to improve the protection afforded to underlying iron when the samples were exposed to warm, humid environments. Increasing the intensity of the ion bombardment further improved the quality of the alumina overlayers. The protective properties of zirconia films were excellent when deposited without IAD, but were much more sensitive to the choice of ion bombardment and oxide deposition parameters. Reactive ion-assisted deposition of zirconium oxyfluoride was studied as a potential method for fabricating laterally-graded index profiles in planar waveguides for use in integrated optical devices. For some applications, index changes in excess of 0.2 are required, such as a proposed technique for chromatic aberation compensation of focusing grating couplers. We found waveguide losses in evaporated ZrF₄ films of 5.5 dB/cm at 632.8 nm, and refractive index changes in O₂⁺ bombarded films of 0.23.