title: 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 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 increases, showing a maximum under an ion fluence of 1 × 10(16) ions/cm(2). 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 Sn(2+/)Sn(4+) 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.
authors.affiliation: Division of Materials Science and Engineering, Hanyang University , Seoul 133-791, Republic of Korea.
authors.forename: Yong Jung
authors.initials: YJ
authors.lastname: Kwon
authors.affiliation: Division of Materials Science and Engineering, Hanyang University , Seoul 133-791, Republic of Korea.
authors.forename: Sung Yong
authors.initials: SY
authors.lastname: Kang
authors.affiliation: Entropic Interface Group, Singapore University of Technology & Design , Singapore 487372, Singapore.
authors.forename: Ping
authors.initials: P
authors.lastname: Wu
authors.affiliation: Entropic Interface Group, Singapore University of Technology & Design , Singapore 487372, Singapore.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Peng
authors.affiliation: Department of Materials Science and Engineering, Inha University , Incheon 402-751, Republic of Korea.
authors.forename: Sang Sub
authors.initials: SS
authors.lastname: Kim
authors.affiliation: Division of Materials Science and Engineering, Hanyang University , Seoul 133-791, Republic of Korea.
authors.forename: Hyoun Woo
authors.initials: HW
authors.lastname: Kim
keywords: NO2; SnO2; gas sensor; ion-beam irradiation; nanowires