Influence of film thickness on structural and optical-switching properties of vanadium pentoxide films

Vanadium oxide films were deposited at different sputtering times on sapphire substrates by radio frequency reactive magnetron sputtering. The effects of thickness on the surface structural, morphology and optical-switching properties of the films were studied comprehensively. X-ray diffraction results show that all the prepared films are polycrystalline vanadium pentoxide films (V2O5) on (001) preferred orientation. Both root-mean-square roughness and average surface grain size decrease with the increase of thickness. With the thickness reduction, the closing time decreases first and then increases at the turning point of 350 nm, and the maximum and the minimum are 2.7 ms at 600 nm and 1.7 ms at 350 nm, respectively. The recovery time decreases rapidly with the reduction of the film, which varies from 40 ms at 600 nm to 27 ms at 150 nm. More concerning, the dynamic range of transmittance varies greatly from thickness, and the transmittance ratio before and after the phase transition covers from 3.75 at 150 nm to the maximum of 7.3 at 600 nm under a continuous probe light of 1064 nm.