Alexander Gurlo

Mechanism of O3 and NO2 detection and selectivity of In2O3 sensors

Abstract The gas-sensitive properties of the sol–gel prepared In 2 O 3 , In 2 O 3 –NiO, and In 2 O 3 –MoO 3 thin film sensors at the detection of NO 2 and O 3 were investigated. The differences in the mechanisms of interaction between the oxide surface and O 3 and NO 2 molecules are discussed. The activity and selectivity of oxides substantially depend on the metal–oxygen binding energy in the oxide lattice. The introduction of dopants into In 2 O 3 , which increases the metal–oxygen binding energy as well as creates adsorption centers with the high affinity to oxygen (Mo 5+ ), leads to the shift of NO 2 detection temperature at In 2 O 3 -sensors to the high temperature range. In the case of nonstoichiometric In 2 O 3 films, the optimal ozone detection temperature is low. The observed differences of the interaction between NO 2 and O 3 and the oxide surfaces can be used for measuring the properties of oxide sensor regarding these gases.

Sol-gel prepared In2O3 thin films

Abstract Semiconductor sensors based on nanocrystalline In 2 O 3 thin films, which were prepared by a sol-gel method, showed high sensitivity to NO 2 . In 2 O 3 sensing layers were obtained by calcination of In(OH) 3 sol which was stabilized with nitric acid. These films were investigated in respect to their non-stoichiometry. The effect of annealing in air and in reducing atmosphere was studied by X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR). In XPS core level spectra taken upon heating in vacuo (620 K) an increase in the full width at half-maximum (FWHM) values of the In 3d doublet and a decrease in the oxygen to indium ratio ( n o / n In ) is found. ESR measurements show the presence of electronic and ‘hole’ centers (F-centers, In 2 ) in the sol-gel In 2 O 3 used for the preparation of the sensing layers. Their concentration is increased markedly by heating in vacuum (620 K) and in H 2 (470 K, H 2 under flow conditions). So the combined ESR and XPS investigation suggests the formation of non-stoichiometric In 2 O 3− x upon annealing of stabilized sols and gives evidence for the presence of electronic and hole centers in the sensitive layers.

Corundum-type indium (III) oxide: formation under ambient conditions in Fe2O3–In2O3 system

Abstract The influence of the iron doping on the structural transformations in In 2 O 3 has been studied. The samples were prepared by the sol–gel technique via coprecipitation from the solution of In(III) and Fe(II) salts. For the first time, the formation of corundum-type In 2 O 3 under ambient conditions in iron-doped In 2 O 3 samples was observed.

Properties of indium oxide semiconducting sensors deposited by different techniques

Semiconducting In2O3 gas sensors have been fabricated by two different deposition techniques, i.e., spin-coating and screen-printing. In both cases the same starting material – sol-gel-prepared cubic In2O3 – was used for the deposition in order to ensure a better comparability of the different sensing layers. The morphology of the layers has been characterized using scanning electron microscopy (SEM) technique. The layers deposited by different methods show similar grain size and porosity. Furthermore, Dc electrical tests have been performed to analyze the sensing properties of the different gas sensors. Reducing gases (CO and propanal) as well as oxidizing gases (NO2 and ozone) were used as test gases in the background of dry and humidified synthetic air. All measurements were performed at several temperatures. It was found that the spin-coated and screen-printed layers show different sensing properties, i.e., screen-printed sensors showed higher sensor signals than spin-coated sensors for CO, propanal, and NO2. The most striking differences appeared in the detection of ozone. In this case, spin-coated sensors showed a higher performance than screen-printed sensors. Higher ozone concentrations led to saturation effects for the latter.

Flame spray synthesis of tin oxide nanoparticles for gas sensing

Tin oxide nanoparticles for gas sensing application have been synthesized with an aerosol method. The particles were manufactured with the versatile Flame spray Pyrolysis (FSP) method producing highly crystalline powders with closely controlled a primary particle and crystallite size of 10 nm and 17 nm. The single crystalline particles were only slightly aggregated and directly used for thick film sensor deposition by drop coating and screen printing.The flame made SnO 2 nanoparticles showed high and rapidresponse to reducing gases such as propanal and CO.