The selective ethanol gas sensing performance of CdO1−XZnOX nanocomposite

Abstract

The (CdO)1−XZnOX composite films have been deposited onto the glass substrate by simple and inexpensive chemical bath deposition (CBD) method. In synthesis of composite thin films, 0.1 M Cd (NO3)2 and 0.1 M Zn(NO3)2 were used as a sources of cadmium and zinc ions, respectively. Liquor ammonia was added as complexing agent in precursor solution. The XRD patterns of composite samples revealed distinct peaks of ZnO and CdO, which clearly indicates formation of CdO–ZnO nanocomposites in thin film form. SEM micrographs of (CdO)1−XZnOX samples with x = 0.25 shows nanowire-like morphology grown over the entire glass substrate while the samples with x = 0.75 shows the development of nanoflakes. Spherical granular morphology have been observed for sample with x = 0.50. Elemental compositions of the all deposited films have been confirmed by EDAX. The gas sensing behavior of the pure and composite sensor was systematically investigated for three different test gases such as ethanol, ammonia and hydrogen sulfide. Under optimum operating temperature of 275 °C and 24 ppm ethanol, the CdO–ZnO sensor showed maximum response of 58.69% among other test gases. The response and recovery time of CdO–ZnO sensor for ethanol was found to be 54 and 59 s, respectively. The CdO–ZnO composite sensor showed better response than pure ZnO and CdO sensor, which is attributed n–n heterojunction at intergrain boundaries. In addition, the energy band structure of CdO–ZnO heterojunction and the ethanol sensing mechanism are analyzed. The CdO–ZnO sensor is found to be selective towards ethanol even at lower concentration.