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. 2017 Feb 1:7:41716.
doi: 10.1038/srep41716.

Enhanced Gas Sensing Properties of Spin-coated Na-doped ZnO Nanostructured Films

Mohamed A Basyooni  1   2 , Mohamed Shaban  1 , Adel M El Sayed  3
Affiliations

Enhanced Gas Sensing Properties of Spin-coated Na-doped ZnO Nanostructured Films

Mohamed A Basyooni et al. Sci Rep. .

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.

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Conflict of interest statement

The authors declare no competing financial interests.

Figures

Figure 1
Figure 1
(a) XRD spectra of pure and 2.5% Na-doped ZnO films and (b) EDX spectrum of 2.5% Na-doped ZnO film.
Figure 2
Figure 2
FE-SEM images at two different magnifications for (a,b) pure ZnO and (c,d) for 2.5% Na-doped film.
Figure 3
Figure 3
(a) Transmission (T) and reflectivity (R) spectra and (b) the plots of (αhν)2 & hν to determine Eg values for pure and 2.5% Na-doped ZnO films. The inset shows the absorption spectrum of the films.
Figure 4
Figure 4
(a) The dependence of the absorption index, k, (b) the refractive index, n, (c) the real part and (d) the imaginary part of the dielectric constant of the ZnO and ZnO: 2.5%Na films with wavelength.
Figure 5
Figure 5
I–V characteristics of (a) pure and (b) 2.5% Na – doped ZnO sensors to CO2 and N2.
Figure 6
Figure 6
The dynamic response of (a) pure ZnO and (b) 2.5% Na- doped ZnO sensors with the detection time; (c) The sensor response % as a function of CO2 concentration in sccm unit; and (d) response time (t res) and (e) recovery time (t recov) of pure and 2.5% Na- doped ZnO vs. CO2 concentration in sccm unit.
Figure 7
Figure 7. Schematic diagram of the experimental set-up of the gas sensing system.
See this image and copyright information in PMC

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