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 (R_g/R_a) 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.