Optical properties of selectively absorbing r.f. sputtered NiAl₂O₃ composite films

NiAl₂O₃ composite films of various compositions were deposited by planar magnetron-assisted r.f. sputtering. The films were deposited by sputtering hot-pressed NiAl₂O₃ targets of two different compositions. To increase the weight per cent of nickel, additional nickel pellets distributed uniformly on the target were cosputtered along with the target of known composition. Al₂O₃ and SiO₂ were used as antireflecting coatings. The composition of nickel in the films was estimated using energy-dispersive analysis of X-rays and atomic absorption spectroscopy. A molybdenum or nickel backing layer was used as a high reflecting mirror. The optical constants were extracted from the near normal incidence reflectance (R) and transmittance (T). Optical simulations are presented of some specially adjusted spectral profiles and their experimental realization using a two-layer coating consisting of NiAl₂O₃ cermet film and SiO₂ antireflecting film deposited onto a metallic substrate. An absorptance of 0.94 and emittance of 0.07 (at 100 °C) were obtained for a 650 Å NiAl₂O₃ film (fill factor, 0.61), coated with an antireflecting layer of 780 Å SiO₂ or Al₂O₃ on a nickel-backed glass substrate, which was predicted by computer simulation studies. Films deposited on molybdenum coated nickel-plated stainless steel substrates were stable up to 500 °C in air.