Synthesis, field emission and humidity sensing characteristics of monoclinic VO2 nanostructures

VO 2 (M 1 ) nanostructures were synthesized via hydrothermal and heat-transformation processes using NH 4 VO 3 as source and oxalic acid as reductant. Different morphologies of nanorods, nanoflakes, nanoflowers, and nanospheres were obtained by adjusting the concentration of oxalic acid. Their microstructures were evaluated using X-ray diffraction and scanning and transmission electron microscopies, respectively. FE properties measurement of these nanostructures showed that the hollow nanospheres have best field emission performance with turn-on field of ∼4 V/μm and threshold field of ∼11.4 V/μm. Due to the high surface-to-volume ratio, nanoflowers were chosen to test their humidity sensing properties, demonstrating that the sensor based on VO 2 (M 1 ) nanoflowers have fast response speed with response time of ∼13 s and recovery time of ∼5 s. This indicates that VO 2 (M 1 ) nanostructures are promising candidate materials for the application in high performance humidity sensors.