Lithium insertion and electrochromism in polycrystalline molybdenum oxide films

In this work, molybdenum oxide thin films were deposited by r.f. reactive sputtering of metallic molybdenum target in an Ar+O2 atmosphere. Thin films with different compositions and crystal structures were obtained by varying the oxygen flow (φ). All samples, with the exception of the MoO2 film, showed an electrochromic behavior, due to the reversible Li+/e− insertion or extraction process. The transmittance change (λ=632.8 nm), for the best sample, was ∼70%. The film having the best optical behavior is mostly formed by the β-MoO3 phase. The composition, optical and mechanical properties were determined and analyzed in as-grown and in Li intercalated films. The local order structure was analyzed by X-ray absorption spectroscopy measurements at the Mo L2,3-edges. The valence band was studied by Photoelectron Spectroscopy.