VOₓ Thin Films Deposited by Reactive Sputtering: Characterization and Electrochemical Performance

The increasing demand for compact, flexible, and transparent energy storage devices has stimulated intensive research on advanced electrode materials. Transition metal oxides are among the most promising candidates, with vanadium oxide (VOₓ) attracting particular interest due to its wide range of accessible oxidation states and ability to form non-stoichiometric phases. In this work, VOₓ thin films were prepared on ITO-coated glass substrates by DC reactive sputtering under different oxygen pressures, without applying external heating. Structural and optical characterization by SEM and UV-Vis spectroscopy confirmed the formation of smooth, uniform films with a thickness of about 100 nm and no detectable porosity. XPS analysis revealed that varying the oxygen pressure during deposition allows manipulation of the vanadium oxidation states, thereby tuning the electronic structure of the films. This adjustment in oxidation states directly influenced their electrochemical response. Electrochemical testing in 1 M Na₂SO₄ revealed excellent capacitive behavior: cyclic voltammetry showed a volumetric capacitance of 143 F/cm³ at 50 mV/s, while galvanostatic charge–discharge experiments demonstrated stable cycling at 1 mA/cm². These findings highlight reactive sputtering as a scalable method to produce VOₓ thin films with controlled structural and electronic properties. The observed correlation between oxidation state distribution and electrochemical behavior underscores their strong potential as electrodes for supercapacitor applications.