Superior room-temperature sensing of toxic NH3 gas by La2O3-doped CdO thin film sensors

Gas sensitivity has been improved and stabilized when metal oxides are doped with rare earth elements. In this manuscript, we present an Al/La₂O₃:CdO/glass active device that detects ammonia gas to enhance the functionality of lanthanum oxide in a gas sensor made of cadmium oxides. The pulsed laser deposition method, using a laser energy of 300 mJ and a pulse rate of 250 pulses, was used to create thin films of cadmium oxide (CdO) mixed with 3 wt% and 6 wt% of lanthanum oxide (La₂O₃). We used a field emission scanning electron microscope (FESEM), an atomic force microscope, X-ray diffraction (XRD), and ultraviolet–visible spectroscopy to study the structure and optical properties of the films. The XRD pattern shows the cubic structure and polycrystalline nature of the films, with the intensity of the diffraction peaks increasing with increasing doping ratios and some secondary phases present. The FESEM image shows that the films have a nanostructure and nanoflower-like shapes. The optical bandgap value goes up from 2 to 2.75 eV for the films made with more La₂O₃ doping. The CdO doped with the mentioned rare element was used as a sensor for the toxic gas ammonia (NH₃). Sensitivity, response, and recovery time were studied using different concentrations of lanthanum oxide at room temperature, and then the best value of the sensor was chosen, and the operating temperatures were changed to 75 and 125 °C as a comparison. The best device for NH₃ gas sensitivity was CdO doped with 6% La₂O₃, which revealed a sensitivity of 178.2% at 125 °C. We also studied the stability of ammonia gas sensing in terms of long-term stability and repeatability. The results demonstrate that the sensor retained more than 93% of its initial response over 60 days, showing good long-term stability.