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.

摘要：电致变色材料（Electrochromic Material）是一类薄膜技术，可调控建筑的进出光热，与环境可持续发展息息相关。氧化钒薄膜（Vanadium Oxide Thin Film）可实现锂离子与电子的共插层脱嵌，在低能可见光区间的光学变化幅度较低，适配作为电致变色器件中的无源电极（Passive Electrode）。目前学界已对氧化钒薄膜的光谱双色变色行为开展研究，但针对高光子能量区间的单色变色现象，相关探索仍较为匮乏。为探明氧化钒薄膜在高光子能量（E＞2.0 eV）区间的光学行为，本研究对薄膜开展了光电化学表征（Opto-electrochemical Characterization）。薄膜通过电子束沉积法制备，并经惰性气氛热处理改性。所有样品均呈现[110]晶向的晶体取向，且电荷容量取决于薄膜的后处理状态。原始生长薄膜的电荷容量约为6毫库仑（mC），经100℃热处理后的薄膜电荷容量则提升至其5倍。氧化钒薄膜具备可逆的锂离子嵌脱行为，可同时实现光谱双色与单色变色。研究结论表明：针对低能光子区间，小极化子模型（Small Polaron Model）可完整解释单色双色变色现象；而在高能区间，单色双色变色行为则源于晶体相变（Crystallographic Phase Transition）。