Selective Improvement of NO₂ Gas Sensing Behavior in SnO₂ Nanowires by Ion-Beam Irradiation

Abstract

We irradiated SnO₂ nanowires with He ions (45 MeV) with different ion fluences. Structure and morphology of the SnO₂ nanowires did not undergo noticeable changes upon ion-beam irradiation. Chemical so, equilibrium in SnO₂/gas systems was calculated from thermodynamic principles, which were used to study the sensing selectivity of the tested gases, demonstrating the selective sensitivity of the SnO₂ surface to NO₂ gas. Being different from other gases, including H₂, ethanol, acetone, SO₂, and NH₃, the sensor response to NO₂ gas significantly increases as the ion fluence Acetone increases, showing a maximum under an ion fluence of 1 X 10¹⁶ ions/cm². Photoluminescence analysis shows that the relative intensity of the peak at 2.1 eV to the peak at 2.5 eV increases upon ion-beam irradiation, suggesting that structural defects and/or tin interstitials have been generated. X-ray photoelectron spectroscopy indicated that the ionic ratio of Sn²⁺/Sn⁴⁺ increases by the ion-beam irradiation, supporting the formation of surface Sn interstitials. Using thermodynamic calculations, we explained the observed selective sensing behavior. A molecular level model was also established for the adsorption of NO₂ on ion-irradiated SnO₂ (110) surfaces. We propose that the adsorption of NO₂-related species is considerably enhanced by the generation of surface defects that are comprised of Sn interstitials.