Abstract
In this report, the structures, morphologies, optical, electrical and gas sensing properties of ZnO and ZnO: Na spin-coated films are studied. X-ray diffraction (XRD) results reveal that the films are of a single phase wurtzite ZnO with a preferential orientation along (002) direction parallel to c-axis. Na doping reduces the crystalline quality of the films. The plane surface of ZnO film turned to be wrinkle net-work structure after doping. The reflectance and the optical band gap of the ZnO film decreased after Na doping. The wrinkle net-work nanostructured Na-doped film shows an unusually sensitivity, 81.9% @ 50 sccm, for CO2 gas at room temperature compared to 1.0% for the pure ZnO film. The signals to noise ratio (SNR) and detection limit of Na-doped ZnO sensor are 0.24 and 0.42 sccm, respectively. These enhanced sensing properties are ascribed to high surface-to-volume ratio, hoping effect, and the increase of O- vacancies density according to Kroger VinK effect. The response time increased from 179 to 240 s by the incorporation of Na atoms @50 sccm. This response time increased as the CO2 concentration increased. The recovery time is increased from 122 to 472 s by the incorporation of Na atoms @50 sccm.
Highlights
Carbon dioxide (CO2) sensors play an important role in monitoring and controlling indoor air quality
Na atoms may be substituted Zn atoms or incorporated into interstitial sites in the zinc oxide (ZnO) lattice[26]. This implies that the precursors have been completely converted into ZnO phase, and Na doping did not alter the hexagonal structure of the ZnO lattice
Li et al showed a marginal shift of the characteristic peaks ((100), (002) and (101)) of chemically prepared ZnO nanoparticles toward lower diffraction angle after doping with Gd, Er, and Li37
Summary
Comparable results were accounted for the hydrothermally produced Na-doped ZnO films and nanowires[27,30] This may be ascribed to the values of surface free energy (SFE) of (002), (110) and (100) plans. This EDX spectrum clearly confirms the presence of Zn O, and Na peaks. The T and R plots of the two films showed interference patterns at various λ This phenomenon was reported in the transmittance spectra of (Mg, Ga) and (Al, Ga) - co-doped ZnO films that fabricated by dip coating technique[46,47].
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