格子整合系基板へのβ相三酸化モリブデン薄膜の結晶成長とエレクトロクロミック特性

抄録

We have successfully grown monoclinic (β) phase single-crystalline molybdenum trioxide (MoO₃) films on a lattice-matched (LaAlO₃)_0.3-(SrAl_0.5Ta_0.5O₃)_0.7 (LSAT) substrate with a 5-nm-thick WO₃ buffer layer by molecular beam epitaxy (MBE). We investigated the structural changes and electrochromic properties of a 40-nm-thick β-MoO₃ film prepared by proton injection for smart window applications. Proton injection into the film up to 12 mC/cm² resulted in the formation of cubic H_0.99MoO₃ with an associated significant reduction in transmittance in the visible to near-infrared range. The coloration efficiencies at λ = 650 and 1000 nm are ∼32 and ∼65 cm²/C, respectively. Such high values are due to the unique properties of the high-quality β-phase MoO₃ epitaxial thin films. X-ray photoelectron spectroscopy measurements showed that Mo⁵⁺ and Mo⁴⁺ related peaks appeared simultaneously owing to protonation, which may have introduced oxygen vacancies into the molybdenum bronze. Our results provide valuable information for the application of MoO₃-based electrochromic devices.