CO Sensing Behavior of Calcium-Doped ZnO Thin Film: A Study To Address the Cross-Sensitivity of CO in H and CO Environment.

CO, CO, and H are the major pollutants in the environment, which are primarily generated during the combustion of the organic compounds. Development of a smart sensor that could address CO sensing and its cross-sensitivity toward CO and H gases is highly advantageous. In this work, an advanced gas sensor is proposed and developed to address the cross-sensitivity of CO sensing in CO and H environment, which is based on calcium-doped ZnO (Ca_ZnO) thin films. The proposed sensors were successfully synthesized using wet chemical synthesis. We have reported that a 5 atomic weight % calcium-doped ZnO thin film exhibits an efficient sensing performance with a wide range of CO gas concentration (75 000-5000 ppm) at 350 °C. Additionally, mixed gas sensing characteristics have been carried out for various concentrations of CO (500-25 ppm) with CO and H (500-100 ppm) with CO gas at 350 °C. The response (%) was estimated as 53, 83, and 74% for 50 000 ppm CO, 50 000 ppm CO + 500 ppm H, and 50 000 ppm CO + CO gases, respectively. Furthermore, the enhancement of CO sensing was investigated using the Raman spectrum of calcium-doped ZnO thin films. Consequently, the cross-sensitivity of pure and mixed gases has been accomplished using principal component analyses, which shows a distinct cluster formation for each test gas. The proposed gas sensor can be potentially applied to biomass sensing, fuel combustion monitoring, and chemical industries.