Exploration of ZrO2-shelled nanowires for chemiresistive detection of NO2 gas

We present novel research devoted to the synthesis of SnO2-ZrO2 core-shell nanowires (C-S NWs) and investigation of their NO2 gas sensing properties. ZrO2 shell layer was deposited on networked SnO2 NWs. The ZrO2 shell thickness was varied using four different numbers of atomic layer deposition (ALD) cycles (50, 100, 150 and 200). Structural, morphological and chemical composition of the synthesized products were confirmed by different characterization techniques. The gas sensors showed an optimal sensing temperature at a relatively low temperature (≤ 150 °C). NO2 sensing results showed a strong dependence of response on the thickness of the ZrO2 shell, or equivalently the number of ALD cycles of ZrO2. The optimal sensor with a ZrO2 shell deposited at 150 ALD cycles (24.1 nm thick) exhibited a high response of (Rg/Ra) 24.7–10 ppm NO2 gas and revealed a good selectivity to NO2 gas. Also, with an increase in the thickness of the ZrO2 shell, the negative influence of humidity on the sensor response to NO2 was significantly decreased. The sensing mechanism involves NO2 removing electrons from the ZrO2 shell. The dependence of responses to shell thickness was explained based on two different regimes, i.e., the surface-electron-limiting regime and adsorbing species-limiting regime. The results obtained in this study can be used for further exploration of the sensing properties of ZrO2 as a novel shell material.