NO₂ Gas Sensing Performance of a VO₂(B) Ultrathin Vertical Nanosheet Array: Experimental and DFT Investigation

A VO₂(B) ultrathin vertical nanosheet array was prepared by the hydrothermal method. The influence of the concentration of oxalic acid on the crystal structure and room-temperature NO₂ sensing performance was studied. The morphology and crystal structure of the nanosheets were characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Room-temperature gas sensing measurements of this structure to NO₂ with a concentration span from 0.5 to 5 ppm were carried out. The experimental results showed that the thickness of the vertical VO₂(B) nanosheet was lower than 20 nm and close to the 2 times Debye length of VO₂(B). The response of the sensor based on this structure to 5 ppm NO₂ was up to 2.03, and the detection limit was 20 ppb. Its high response performance was due to the fact that the target gas could completely control the entire conductive path by forming depletion layers on the surface of VO₂(B) nanosheets. Density functional theory was used to analyze the adsorption of NO₂ on the VO₂(B) surface. It is found that the band gap of VO₂(B) becomes narrower and the Fermi level moves to the valence band after NO₂ adsorption, and the density of states near the Fermi level increases significantly. This ultrathin vertical nanosheet array structure can make VO₂(B) detect NO₂ with high sensitivity at room temperature and therefore has potential applications in the field of low-power-consumption gas sensors.