Monochromatic double coloring effect on V2O5 thin films deposited by electron beam

ABSTRACT Electrochromic material is a thin film technology that has a close relationship with environmental sustainability since they can control the light and heat that enter and leave a building. Vanadium oxide films are electrochemically active for lithium and electron co-intercalation, presenting low optical variation in the low energy visible light, which is suitable for application as a passive electrode in the electrochromic devices. The spectral double coloration of vanadium oxide thin film has been investigated but the monochromatic, in particular, for high photons energy, remains poorly explored. To understand the optical behavior of the vanadium oxide films, in high photons energy (E > 2.0 eV), films were opto-electrochemically investigated. The films were electron beam deposited and modified by heat treatment in an inert atmosphere. All samples show crystallographic orientation in a [110] direction, and the charge capacity showed to be dependent on the film conditioning. The charge capacity of the as-grown film is about 6 mC while for the film heat-treated at 100 ºC it is five times higher. The vanadium oxide films showed reversible Li+ intercalation, presenting a double spectral and monochromatic coloration. It was concluded that for low energy photons the small polaron model fully explains the phenomenon of double monochromatic coloration, and, for high-energy, the monochromatic double coloration is due to the crystallographic phase transition.