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Zinc oxide nanopowder was made using an auto-combustion method, and oxygen vacancies were formed using a thermally activated procedure under vacuum treatment. The structural and morphological properties of ZnO1-X samples were determined by using X ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electronic microscope (SEM) characterizations. XRD studies revealed that the ZnO1-X samples had a hexagonal wurtzite structure, with nanoparticle sizes ranging from 40 to 47 nm. The growing quantity of oxygen vacancies was confirmed by XPS tests. SEM images showed a spherical nanometric particle with high porosity especially for ZnO0.90. Optical measurements with spectroscopy UV–Visible revealed that oxygen vacancies increase absorption of the material in the visible region. Also, the photoluminescence properties of the prepared samples were investigated by PL and PLE measurement, which indicate a high presence of oxygen vacancies and other defaults in the structure of ZnO0.90 more than pure zinc oxide. The electrical conductivity proportional to the temperature showed that the conduction process was thermally activated and that the carriers had long-distance mobility. Thus, we found that the conductivity of ZnO0.90 was lower than that of ZnO, which can be explained by the introduction of oxygen vacancies which allows the creation of electron trapping centers localized by the presence of the deep-levels. Spraying an aqueous solution of ZnO1-X nanoparticles over alumina substrates with pre-deposited gold interdigitated electrodes resulted in gas sensors. At ambient temperature and under white light illumination, the manufactured sensors showed excellent sensing responses to 0.5 ppm NO2. The presence of oxygen vacancies improves sensor performance, which the sensor based on ZnO0.90 showed a high response of 76. [ABSTRACT FROM AUTHOR]

ZnO nanoparticles have been prepared by auto-combustion method. Morphological and structural properties of the prepared samples were investigated by SEM, XRD, Raman and XPS characterizations. The XRD diffractogram of the sample indicates that ZnO has a hexagonal wurtzite structure. The crystallites average size, calculated from the Williamson–Hall plot, was 69.3 nm and the estimated by the SEM image (76.86 nm). Raman investigation indicates different modes of atomic displacement which correspond to longitudinal/transversal optical components with different frequencies. These modes are due to the macroscopic electric fields associated with the basic phonon of hexagonal ZnO. The XPS spectra indicate the presence of Zn and O in the structure with a small number of interstitial Zn2+, oxygen vacancies (Vo), and a negligible amount of chemical bonds with carbon (=CO ...), confirmed by FTIR spectroscopy. The UV absorbance and reflectance spectra show a high absorbance with gap energy of 3.17 eV, estimated by Tauc's model. The a.c. electrical spectroscopy can be described by the Jonscher universal power-law. The charge carriers move according to the correlated barrier hopping pattern over the dispersive region. At room temperature, the conductivity of ZnO is high (~ 8 × 10–6 S.m−1) making it promises for gas detection applications. The sensor was prepared by spraying the suspension of ZnO nanopowders on alumina substrates with pre-deposited gold interdigitated electrodes. The sensor responses of NO2, for concentrations of 0.5, 0.75 and 1 ppm, were investigated at room temperature under illumination with different wavelengths. The best response of the sensor was obtained for a concentration of 1 ppm NO2 excited by 400 nm (purple) and 380 nm (UV) wavelengths, which were 91 and 88 with response/recovery times equal to 4/6.7 min and 4.4/3.3 min. Higher responses at the lower wavelength are due to the higher excitation energy which tends to excite more electrons, at the material surface, subsequently participating in the detection mechanism with gas molecules [ABSTRACT FROM AUTHOR]

Pure zinc oxide was prepared by a simple auto-combustion method. The microstructure and morphological proprieties, of the prepared sample, were investigated by XRD, XPS, and SEM characterizations which indicated that the ZnO nanoparticles have a hexagonal wurtzite structure with space group P63mc. The average size estimated by Willams-Hall exhibits to be 61.45 nm which is in good agreement with that estimated by the SEM image (62 nm). The absorbance spectra indicated a high absorbance in the UV range and the gap energy, estimated by Tauc's model, was 3.17 eV. The sensor was prepared by spraying the suspension of ZnO nanopowders on an alumina substrate with pre-deposited gold-interdigitated electrodes. The fabricated sensors exhibited a high response (ΔR/R = 208) and acceptable response/recovery times (5/2.5 min) to 1 ppm of NO2 at low operational temperature (150 °C) in the dark and 50%RH. [ABSTRACT FROM AUTHOR]