Deposition of NiVOx thin films by pulse magnetron sputtering with various Ar/O2 ratios

NiVOx thin films were deposited by pulse magnetron sputtering using an alloy target of 8 at%V and 92at%Ni to prevent the ferromagnetic disadvantage that is associated with the use of a pure Ni metallic target. Their surface properties and related electrochromic behaviors were also examined systematically by X-ray diffraction (XRD), X-ray photo-electron spectroscopy (XPS) and scanning electron microscopy. Additionally, the optical density and modulation of the NiVOx films were analyzed using a UV/VIS spectrophotometer (UV–Visible). Electrochromic tests were conducted using an electrochemical analyzer. Experimental results reveal that electrochromic properties heavily depended on the crystalline phase, thickness, chemical composition and microstructure, which were controlled by varying the plasma power and the argon/oxygen ratio. As well as demonstrating that V can significantly reduce the ferromagnetic effect, stabilize the plasma state and produce NiVOx films with a high percentage of Ni2 +, XPS and XRD analyses reveal that Ni2 +, Ni3 +, V4 + and V5 + co-exist in the NiVOx films thus produced non-ideal stoichiometric compounds at an argon/oxygen ratio of three. Hence, films fabricated at Ar/O2 = 3 had the optimal electrochromic properties, with high optical modulation, high optical density and the lowest color memory effect at wavelengths of 400, 550 and 800 nm.

► The morphology of NiVOx film becomes coarser as the Ar/O2 ratio increases.
► Reducing the Ar/O2 ratio transforms the crystalline phase from (111) to (200).
► NiVOx films exhibit coarse surface and comprise non-ideal stoichiometric compounds.
► The optical density of NiVOx films shows potential in electrochromic applications.