Single films and heat mirrors produced by plasma ion assisted deposition

Single TiO2, MgF2, Ag and TiN thin films and heat mirrors are produced by plasma ion assisted deposition (PIAD) in a vacuum system (Leybold APS 904). Experimental results for the optical properties, stress and topography are reported. The obtained refractive indices at wavelength 550 nm of both TiO2 and MgF2 thin films deposited by PIAD are 2.40 +/- 0.02 and 1.40 +/- 0.02, respectively, and the packing densities are unity within errors of measurement. Both thin films after deposition are not fully crystallized and crystallize during heating at temperatures of 250 to 350 degrees C. The thickness needed for large-scale coalescence of silver thin films is found to be about 9 nm for the films deposited by PIAD. In all cases the oxide-metal-oxide mirrors undergo chemical and physical changes due to the silver layer. To improve the mirror performance very thin (less than 2 nm) Cu block layers are used to protect silver against oxidation. Heat mirrors comprising TiO, and MgF, films, in which the silver layer between MgF2 (with thickness more than 10 nm) is not surrounded by oxide layers, have transmittance which is higher than 75% in the visible region and less than 10% at wavelengths longer than 1000 nm and passed environmental tests. Best durability is observed for TiO2/TiN/TiO2 heat mirrors although they do not have the spectral performance of metal-based heat mirrors in terms of transmittance in the visible and infrared regions. (C) 1997 Elsevier Science B.V.