Investigation of angular selective optical properties of silver titanium oxide cermet thin films

Thin films of silver-titanium oxide cermet were prepared with angular and spectral selectivity of optical transmittance. Titanium oxide was deposited reactively by d.c. magnetron sputtering and in a filtered cathodic are system. Metallic silver was co-deposited by thermal evaporation. Deposition parameters were varied to get optimum angular selective properties. The films have inclined columnar microstructure as studied by atomic force microscopy. The study of optical properties shows that the filtered are film performs better than the sputtered film. Unlike most of the angular selective films reported to date, the angular selectivity of this film is large in the near infrared region. Spectral switching of the preferred transmission direction at a particular visible wavelength was observed resulting in 'reverse angular selectivity', where for visible radiation the high transmission direction of incidence lies on the opposite side of the normal to that in the near infra-red range. The angle of incidence dependence of solar and luminous transmittance of each film was analyzed. (C) 1998 Elsevier Science S.A. All rights reserved.