Investigation of structural, morphological and electrical properties of APCVD vanadium oxide thin films

Vanadium oxide films were chemically vapor deposited (CVD) on oxidized Si substrates covered with CVD tungsten (W) thin films and on glass substrates covered with indium tin oxide (ITO) films, using vanadium(V) oxy-tri-isopropoxide (C9H21O4V) vapors. X-ray diffraction (XRD) measurements showed that the deposited films were composed of a mixture of vanadium oxides; the composition was determined mainly by the deposition temperature and less by the precursor temperature. At temperatures up to 450 °C the films were mostly composed by monoclinic VO2. Other peaks corresponding to various vanadium oxides were also observed. X-ray microanalysis confirmed the composition of the films. The surface morphology was studied with atomic force microscopy (AFM) and scanning electron microscopy (SEM). These measurements revealed that the morphology strongly depends on the used substrate and the deposition conditions. The well-known metal-insulator transition was observed near 75 °C for films mostly composed by monoclinic VO2. Films deposited at 450 °C exhibited two transitions one near 50 °C and the other near 60 °C possibly related to the presence of other vanadium phases or of important stresses in them. Finally, the vanadium oxide thin films exhibited significant sensory capabilities decreasing their resistance in the presence of hydrogen gas with response times in the order of a few seconds and working temperature at 40 °C. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)