  The growth of wafer-scale and uniform monoclinic VO2 film was a challenge if
considering the multivalent vanadium atom and the various phase structures of
VO2 compound. Directly oxidizing metallic vanadium film in oxygen gas seemed to
be an easy way, while the oxidation parameters were extremely sensitive due to
the critical preparation window. Here we proposed a facile thermal oxidation by
water-vapor to produce wafer-scale VO2 films with high quality. Results
indicated that by using the water-vapor oxidant, the temperature window for VO2
growth was greatly broadened. In addition, the obtained wafer-size VO2 film
showed very uniform surface and sharp resistance change. The chemical reaction
routes with water-vapor were calculated, which favored the VO2 film growth. Our
results not only demonstrated that the water-vapor could be used as a modest
oxidizing agent, but also showed the unique advantage for large size VO2 film
preparation.
