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

V2O5 was used to prepare vanadium oxide films via the sol-gel method. The n in V(2)O(5)nH(2)O was determined to be approximately 1.67. After annealing at 390 degrees C for 4 h, a pure VO2 (M) phase was obtained and denoted sample V. The crystallite sizes of VO2 (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 Ols and the V5+ 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 degrees C, and the hysteresis loop width was 12.1 degrees C.