R. Dhahri

ZnO:Ca nanopowders with enhanced CO2 sensing properties

Calcium doped ZnO (CZO) nanopowders with [Ca]/[Zn] atomic ratios of 0, 0.01, 0.03 and 0.05 were prepared via a sol-gel route and characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy (FT-IR). Characterization data showed that undoped and Ca-doped ZnO samples have a hexagonal wurtzite structure with a slight distortion of the ZnO lattice and no extra secondary phases, suggesting the substitution of Ca ions in the ZnO structure.Chemo-resistive devices based on a thick layer of the synthesized CZO nanoparticles were fabricated and their electrical and sensing properties towards CO2 were investigated. Sensing tests have demonstrated that Ca loading is the key factor in modulating the electrical properties and strongly improving the response of ZnO matrix towards CO2. An increased CO2 adsorption with Ca loading has been also evidenced by FT-IR, providing the basis for the formulation of a plausible mechanism for CO2 sensing operating on these sensors.

Gas sensing properties of Al-doped ZnO for UV-activated CO detection

Al-doped ZnO (AZO) samples were prepared using a modified sol–gel route and charaterized by means of trasmission electron microscopy, x-ray diffraction and photoluminescence analysis. Resistive planar devices based on thick films of AZO deposited on interdigitated alumina substrates were fabricated and investigated as UV light activated CO sensors. CO sensing tests were performed in both dark and illumination condition by exposing the samples to UV radiation (λ = 400 nm).Under UV light, Al-doped ZnO gas sensors operated at lower temperature than in dark. Furthermore, by photoactivation we also promoted CO sensitivity and made signal recovery of AZO sensors faster. Results demonstrate that Al-doped ZnO might be a promising sensing material for the detection of CO under UV illumination.

Excellent CO gas sensor based on Ga-doped ZnO nanoparticles

AbstractSol–gel technique was utilized to prepare pure and Ga-doped ZnO nanopowders. To investigate the morphological and microstructural properties, transmission electron microscopy analysis and X-ray powder diffraction have been used. From microstructure analysis we showed that pure and Ga-doped ZnO nanoparticles were polycrystalline, and exhibited hexagonal wurtzite structure. Chemoresistive devices consisting of a thick layer of synthesized nanoparticles on interdigitated alumina substrates have been fabricated and their electrical and sensing characteristics were investigated. The sensor performances of the samples for carbon monoxide (CO) were reported. The results indicated that doped sensor exhibited higher response and quick response/recovery dynamics compared to a ZnO-based sensor. These interesting sensing properties were discussed on the basis of the characterization data were reported.

Optical, electrical and sensing properties of ZnO nanoparticles synthesized by sol-gel technique

Optical, electrical and sensing properties of ZnO nanoparticles, prepared by sol-gel process and subsequent dried in supercritical conditions, are presented. To investigate the morphological and microstructural properties, transmission electron microscopy (TEM), X-ray powder diffraction (XRD), UV-visible spectroscopy and photoluminescence (PL) spectroscopy analysis have been used. From microstructure analysis we showed that pure ZnO nanoparticles were polycrystallines and exhibited the hexagonal wurtzite structure. Chemoresistive sensor consisting of a thick layer of ZnO nanoparticles annealed at 400 °C for 2h in air on interdigitated alumina substrate has been fabricated and its electrical and sensing characteristics were investigated. The sensor performances towards carbon monoxide (CO) with and without UV illumination were reported. An increase of sensitivity, along a reduction of ZnO thick film resistance, was observed when the sensor operates under UV irradiation.

Development of doped ZnO nanoparticles for gas sensing application

In this study sol-gel technique was used to prepare Al-, V- and In-doped ZnO. The morphology and microstructure of samples synthesized was characterized by means of different techniques such as X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM). The characterization results indicated that all as-prepared doped samples maintains the same morphology and microstructure of pure ZnO, being composed of nanoparticles having the hexagonal wurtzite structure of zinc oxide. These characteristics were observed also after thermal treatment. However, with incorporation of dopants, the sensing properties were deeply changed. Results of sensing tests have shown as it is possible to decrease the operating temperature compared to pure ZnO-based sensor and obtain sensors with a higher sensitivity and improved selectivity to the target gas by choosing the more appropriate dopant.