Zinc influence on nanostructured tin oxide (SnO2) films as ammonia sensor at room temperature

We report the fabrication of Zn defect-influenced SnO2 sensor operating at room temperature. The films for the sensor were prepared by automatic nebulizer spray pyrolysis under a no-vacuum environment. Four different films were prepared with different Zn doping concentrations; 0 at.%, 1 at.% 3 at.% and 5 at.%. The X-ray diffraction analysis showed a tetragonal rutile structure with polycrystalline behavior for all films. The crystallinity was suppressed by Zn doping due to the influence of extrinsic donor defects. When increasing the Zn doping level, the bandgap is increased owing to the observed blue shift in the optical transmittance. The photo-luminescence (PL) spectra of films show a UV emission at 361 nm which reveals near band edge (NBE) emission. And also, the intensity of the NBE emission decreases with an increase in Zn content due to the creation of defect states near the conduction band. The green emission intensity starts to increase with Zn doping indicates the excess oxygen vacancies (Vo) and/or oxygen interstitials in the host structure. These defects play a major role in controlling the interaction between the sensor surface and ammonia (NH3) molecules. NH3 gas sensing studies were carried out at room temperature for all the prepared films. A maximum sensitivity of 121% was exhibited by SnO2 sensor prepared by 3 at.% substitution of Zn. The maximum sensitivity is attributed to the presence of increased defects on the film surface. In addition, Zn doped SnO2 sensors exhibited fast response and recovery times when compared with the undoped sensor. The optimum sensor (3 at.% of Zn) exhibited good repeatability and reproducibility of sensor performance. The aging effect on the sensing behavior showed the maintenance of stability above 90% for the aged film (100 days) when compared with the fresh film.

Automated summary

The fabrication and performance of the Zn-defect-influenced SnO2 sensor at room temperature were studied. The Zn doping suppressed the crystallinity, increased the bandgap, and altered the luminescence and defect density, leading to enhanced sensitivity in NH3 gas sensing.