Effects of the annealing process on the structure and valence state of vanadium oxide thin films

Abstract V 2 O 5 was used to prepare vanadium oxide films via the sol-gel method. The “ n ” in V 2 O 5 ∙ n H 2 O was determined to be approximately 1.67. After annealing at 390 °C for 4 h, a pure VO 2 (M) phase was obtained and denoted sample Ⅴ. The crystallite sizes of VO 2 (M) in samples Ⅱ, Ⅲ, Ⅳ and Ⅴ were 42, 41, 35 and 24 nm, respectively. The surface morphology of sample Ⅰ was flat; however, many small, dense particles covered the surface of sample Ⅴ. Sample Ⅱ had a layered structure, and samples Ⅲ and Ⅳ consisted of compact grains. The binding energy (BE) differences between the O1s and the V 5+ 2p 3/2 , V 4+ 2p 3/2 , and V 3+ 2p 3/2 core levels were 12.75, 14.0 and 14.7 eV, respectively. For the sample Ⅴ film, the maximum transmittance change at 2500 nm was 39%, the phase transition temperature ( Tc ) was 64.3 °C, and the hysteresis loop width was 12.1 °C.