Transparent heat-mirror films of TiO2/Ag/TiO2 on glass with a visible transmission of 84% (at 0.5 μm) and an infrared reflectivity of 98–99% (at 10 μm) have been fabricated by rf sputtering. Initial tests indicate that the films are thermally stable in air at 200°C and inert to water attack. Because of their excellent optical properties and apparent stability, these transparent heat-mirror films offer great promise for use in solar-thermal power conversion and as transparent thermal insulators.

The electrical and optical properties of rf-sputtered Sn-doped In2O3 (ITO) films have been found to depend strongly on the O2 partial pressure during deposition. For the sputtering conditions used, films with both low electrical resistivity (ρ ∼ 3 × 10−4 Ω cm) and high visible transmission (∼ 90%) were obtained only over a narrow range of O2 pressures, from 3 × 10−5 to 4 × 10−5 Torr. Our results appear to explain the difficulties that have previously been encountered in obtaining high-quality ITO films, and indicate that control of the O2 pressure during deposition is essential for reproducible preparation of such films.

Transparent heat-mirror films, which transmit solar radiation but reflect ir thermal radiation, have potentially important applications in solar/thermal/electric conversion, solar heating, solar photovoltaic conversion, and window insulation. We have used rf sputtering to prepare two types of films: TiO(2)/Ag/TiO(2) and Sn-doped In(2)O(3). To characterize the properties of heat-mirror films for solar-energy collection, we define the parameters alpha(eff), the effective solar absorptivity, and epsilon(eff), the effective ir emissivity. For our Sn-doped In(2)O(3) films, alpha(eff)/epsilon(eff) is comparable to the values of alpha/epsilon reported for the leading selective absorbers. Even higher values of alpha(eff)/epsilon(eff) are obtained for the TiO(2)/Ag/TiO(2) films.