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

V2O5 thin films were deposited by reactive DC-diode sputtering technique in a mixed atmosphere of O-2/Ar gas at room temperature from a high purity target of 99.99% vanadium. For the investigation, the thickness of the films and the O-2/Ar ratio during the sputtering process were the parameters. The sputtering rate of the V2O5 films dramatically decreases with increasing the O-2/Ar ratio. By X-ray diffraction it was found that films sputtered with 1% O-2/Ar ratio grow preferentially in two orientations: the 200 and the 001 orientation. The increase of the O-2/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 O-2/Ar ratio in the sputter gas. Additionally, the optical band gap is slightly larger for the films sputtered with an O-2/Ar ratio higher than 5%. Beyond a thickness of about 220 nm and an O-2/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.