Effect of a CdSe Layer on the Thermo- and Photochromic Properties of MoO3 Thin Films Deposited by Physical Vapor Deposition

The influence of a cadmium selenide (CdSe) layer on the thermochromic and photochromic properties of molybdenum trioxide (MoO3) thin films was studied. The films were deposited on glass substrates by thermal evaporation in vacuum using two different bilayer configurations, namely, substrate/MoO3/CdSe (SMC) and substrate/CdSe/MoO3 (SCM). The film thicknesses for the MoO3 and CdSe layers were ca. 250 and 20 nm, respectively. The thermochromic effect was evaluated in the annealing temperature range from 25 to 225 C, in the presence of air. The characteristic optical absorption band attributed to the color center formation, centered at 820 nm, indicated enhanced thermo- and photochromic effects for both bilayer systems relative to monolayer MoO3 thin films. For the thermochromic effect, this improvement was more pronounced when CdSe was the upper layer, i.e., for the SMC system. Regarding the photochromic effect, the films were irradiated with UV light for several exposure times within the lapse of 30?180 min. While both bilayer systems presented better photochromic response than pure MoO3 thin films, the SCM system exhibited better photochromic response. These results are explained in terms of the optical, structural, and surface chemistry properties of the films.