Effect of a CdS interlayer in thermochromism and photochromism of MoO3 thin films

Thin films of molybdenum oxide (MoO3) were prepared by thermal evaporation of MoO3 powder on glass substrates. We used a thin cadmium sulfide (CdS) interlayer between the glass substrate and the oxide film. The semiconductor CdS film was synthesized using the chemical bath deposition technique. The glass/MoO3 and glass/CdS/MoO3 films were illuminated with light from a 100 W tungsten lamp at times of 45-180 min in order to study the photochromic sensitivity of the films. The films were also thermal annealed at temperatures ranging from 100 to 225 degrees C to study the thermochromic properties. The X-ray diffraction studies show that the CdS films were polycrystalline and the oxide films were amorphous. Optical absorption shows the presence of an absorption band centered around 850 nm. This band is due to the color centers formation. The color centers concentrations were calculated by means of the Smakula's equation. The thin oxide films evaporated over the CdS film have better photochromic and thermochromic properties than the oxide films without the CdS. (C) 1999 Elsevier Science S.A. All rights reserved.