Synthesis of spray pyrolysed transition and rare earth metal oxides (Co3O4, MnO2, WO3, CeO2) thin films and their characterization

Abstract

Semiconducting metal oxide based nano-materials play a very important role in the various fields of sensing materials for gas sensor and bio sensors due to rich physical and chemical stability. In this thesis, Iron (Fe) and Copper (Cu) doped cobalt oxide (Co3O4), manganese dioxide (MnO2), tungsten oxide (WO3) and cerium dioxide (CeO2) nanostructured thin films have been synthesized via spray pyrolysis deposition technique to explore their suitable morphological, structural, optical and electrical properties, pre-requisite for glucose sensing abilities. The presence of low concentration of Fe and Cu (about 4 to 6 at.%) strongly influenced the crystallite size of Co3O4, MnO2, WO3 and CeO2, as analyzed by field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD). Elemental analysis by energy dispersive X-ray spectroscopy (EDX) confirmed the stoichiometry and homogeneity of the films. XRD patterns of the deposited films showed spinel cubic, body centered tetragonal, monoclinic and face centered cubic crystal structure of Co3O4, MnO2, WO3 and CeO2, respectively, which well agrees with the JCPDS data. Crystallite sizes of Co3O4, MnO2, WO3 and CeO2 were obtained 29 nm, 24nm, 13 nm and 15 nm respectively, measured by Scherer relation. Optical band gaps calculated using Tauc relation were found 2.02 eV, 3.81eV, 2.72 eV and 3.44 eV for Co3O4, MnO2, WO3 and CeO2 films respectively and were tuned by Fe and Cu concentration. The dc electrical resistivity was obtained in the order of 104 -cm and confirmed the semiconducting behavior of the films. p-type carrier of Co3O4, MnO2, and n-type carrier of WO3, CeO2 were obtained by Hall Effect measurements. Glucose (C6H12O6) sensing performance of MnO2 and Fe doped MnO2 were carried out using electrical four point probe method. The highest glucose-sensing response was recorded about 29% at 5 minutes for 4 at% Fe: MnO2. The sensing performance of 4 at% Fe: MnO2 was found higher than undoped MnO2 sample under the same glucose concentration. Thus, Fe and Cu dopant is expected to improve the sensing properties of Co3O4, MnO2, WO3 and CeO2, and could be suitable candidate for biosensor developments.