Microstructure Modulation and Mid-Infrared Optical Properties of VOX Films

This study aims to investigate the effect of annealing time on the phase evolution, microstructure, and mid-infrared laser protection performance of vanadium oxide (VOX) thin films, to provide a simple method for fabricating VOX-based optical limiters with tunable properties, it also provides experimental basis for the design of materials to meet different laser protection requirements (low phase transition threshold or fast response).Methods: VOX thin films were deposited on quartz substrates using a DC magnetron sputtering system using a V₂O₃ target, followed by post-deposition annealing in an argon atmosphere at different durations (5, 15, and 120 minutes).

The crystalline structure, elemental composition, chemical states, and surface morphology of the films were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The optical modulation performance was evaluated by Fourier transform infrared (FTIR) spectroscopy and a self-built optical limiting test system.Results and Discussions: The phase of the VOX films undergoes a significant evolution with increasing annealing time: a mixed phase of V₂O₃ and VO₂ with microcracks after 5 min, a well-crystallized and dense pure VO₂ phase after 15 min, and a mixed phase of VO₂ and sheet structures V₂O₅ after 120 min.