Spectrally selective energy-saving coatings based on reactively sputtered bismuth oxide thin films

Spectrally selective coatings are multilayer structures that are deposited on glass. These structures consist of a metal/dielectric bi-layer, in which the metal is silver and the dielectric is a wide-bandgap semiconductor with a high refractive index. These layers are typically very thin (> 30 nm), and thus may be etched away if deposited by a sputtering process. This work has two objectives. First, a new design is fabricated that can sustain the sputtering process. Second, a high-refractive-index material (i.e., bismuth oxide) is selected to serve as the dielectric. Bismuth oxide is deposited by reactive direct-current sputtering, and the deposition parameters are optimized to yield films that are suitable for use in spectrally selective coatings. When used in a silver-based multilayer structure, the resulting peak visible transmittance was 68%, and the maximum infrared reflectance was 85%.