Effect of O2 partial pressure and thickness on the gasochromic properties of sputtered V2O5 films

摘要

V2O5 thin films were deposited by reactive DC-diode sputtering technique in a mixed atmosphere of O2/Ar gas at room temperature from a high purity target of 99.99% vanadium. For the investigation, the thickness of the films and the O2/Ar ratio during the sputtering process were the parameters. The sputtering rate of the V2O5 films dramatically decreases with increasing the O2/Ar ratio. By X-ray diffraction it was found that films sputtered with 1% O2/Ar ratio grow preferentially in two orientations: the 200 and the 001 orientation. The increase of the O2/Ar ratio enhances the growth preferentially in the c-axis (001) and strongly decreases the growth in the a-axis (200) direction. The scanning electron microscope pictures confirm these results. In the visible region the optical transmittance is increased with increasing the O2/Ar ratio in the sputter gas. Additionally, the optical band gap is slightly larger for the films sputtered with an O2/Ar ratio higher than 5%. Beyond a thickness of about 220 nm and an O2/Ar ratio of 10% the electrical sheet resistance of the films increases dramatically. During the insertion/extraction of hydrogen ions, the change in the optical transmission was investigated. The gasochromism of the V2O5 films was explained by use of the Infra Red (IR) measurements during the insertion/extraction of hydrogen ions.