Impact of high vacuum annealing temperature on the structural, photoluminescence, and room temperature liquefied petroleum gas sensing of direct current magnetron sputtered CdO films

Abstract

In the present study, CdO nanostructure has been first deposited by direct current (DC) magnetron sputtering and then vacuum annealed at different temperatures. The optimal properties were demonstrated in the film annealed at 875 °C. The X-ray diffraction (XRD) depicted a polycrystalline structure with a cubic system. The fabricated film possesses the lowest crystal size and the highest dislocation density. The field emission scanning electron microscope (FESEM) evinced a porous film with a small grain size. The electron dispersive X-ray (EDX) confirmed the presence of Cd and O elements without any other undesirable chemical elements. The X-ray photoelectron spectroscopy (XPS) analysis ratified the high amount of the oxygen vacancies and defects. The Photoluminescence (PL) analysis manifested that the synthesized films have two main peaks at the visible region, whereas the best film has the highest amount of oxygen vacancies and defects. The film that annealed at 875 °C demonstrated the quick response and recovery times as well as a high sensitivity of (12, 15 s and 83%) towards 500 ppm of the liquefied petroleum gas (LPG) molecules, respectively. In addition, the low limit of detection was calculated and it recorded 21.89 ppm. Moreover, the stability of sensor along 20 days exhibited a little decrease of around 8% of sensitivity. Therefore, this device could be exploited as a nano-electronic sensor in houses and industries.