Nanostructured ceria thin film for ethanol and trimethylamine sensing

Nanostructured cerium dioxide (CeO2) thin films were deposited on glass substrates at an optimized substrate temperature of 503 K, using spray pyrolysis technique under optimized deposition conditions. An aqueous solution of 0.05 M concentration of Ce(NO3)3·6H2O was used as precursor. The X-ray diffraction (XRD) pattern confirmed the polycrystalline nature of the film with fluorite type face-centered cubic structure. The scanning electron micrographs (SEM) of the annealed films were observed and it was found to be uniform and free from macroscopic defects. An optical energy band gap of 3.63 eV for direct transition was calculated from UV–vis absorbance spectra. Further, the vapour sensing property of annealed CeO2 samples were studied by chemiresistive method for two different volatile organic compounds (VOCs) namely ethanol and trimethylamine at various operating temperatures. Results indicated that the CeO2 thin films changed from n- to p-type character in the presence of ethanol at 323 K till to the maximum temperature studied (400 K) and showed the higher response at 373 K. Conversely, in trimethylamine, the films maintained their n-type character showing appreciable response in the temperature range studied (300–373 K). Therefore, the influence of operating temperature on the selectivity of the CeO2 thin film samples can be effectively used for an efficient food quality assessment.