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

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.

Structural, Topography, and Optical Properties of Ba‐Doped Mn3O4 Thin Films for Ammonia Gas Sensing Application

“…The band gap of the sprayed films is calculated using Tauc's relation using the following equation: where α , B , and Eg are the absorption coefficient, proportionality constant, and optical band gap; respectively, the absorption coefficient is calculated by the following equation: where A and t are the absorbance and thickness, respectively, Figure shows the band gap of pure and Ba‐doped Mn 3 O 4 thin films, the values fairly agree with the work reported in literature . It is found that band gap varies as Ba concentration increases reaching a minimum value 2.85 eV in Mn 3 O 4 :Ba1% thin films, the reduction in band gap may be due to the increase in RMS roughness and crystallite size as reported earlier, it is also observed band gap decreases with the increase in unit cell volume as well as bond lengths of (Mn 2+ O) and (Mn 3+ O) in tetrahedral and octahedral sites; respectively (see Table ) as Ba concentration increases, this behavior agrees with the findings reported in literature …”

Polyvinyl Alcohol/Polypyrrole/Molecularly Imprinted Polymer Nanocomposite as Highly Selective Chemiresistor Sensor for 2,4‐DNT Vapor Recognition

“…The lowest detectable concentration of explosive is restricted by the fabricated setup and depending on the value of noise. The sensor noise is computed from the recorded changes in the relative resistance of the baseline via the root‐mean‐square deviation or rms . …”

UV-activated ZnO films on a flexible substrate for room temperature O2 and H2O sensing

“…For example, Shaban used Na-doped ZnO nanostructures for enhanced CO 2 detection, and Saraswathi demonstrated that DC magnetron sputtered films of polycrystalline ZnO can be used for highly sensitive humidity sensors 6, 7 . Although the environmental effects on the electrical properties of ZnO films are well studied, the response mechanisms are still not fully understood.…”