Photoactivated sensitivity of In2O3-ZnO composite films to hydrogen
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Fizică nucleară. Fizică atomică. Fizică moleculară (86)
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ILIN, A., FORSH, Pavel, IKIM, M. I., TRAKHTENBERG, Leonid. Photoactivated sensitivity of In2O3-ZnO composite films to hydrogen. In: Materials Science and Condensed Matter Physics, Ed. 9, 25-28 septembrie 2018, Chișinău. Chișinău, Republica Moldova: Institutul de Fizică Aplicată, 2018, Ediția 9, p. 106.
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Materials Science and Condensed Matter Physics
Ediția 9, 2018
Conferința "International Conference on Materials Science and Condensed Matter Physics"
9, Chișinău, Moldova, 25-28 septembrie 2018

Photoactivated sensitivity of In2O3-ZnO composite films to hydrogen

CZU: 539.12+544

Pag. 106-106

Ilin A.1, Forsh Pavel12, Ikim M. I.3, Trakhtenberg Leonid3
 
1 Lomonosov Moscow State University,
2 National Research Centre "Kurchatov Institute", Moscow,
3 N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences
 
Disponibil în IBN: 17 ianuarie 2019


Rezumat

Composite based on mixed metal oxides is perspective material for gas sensors as it have a higher sensitivity to certain gases than single metal oxide. Particularly composite based on indium and zinc oxides (ZnO-In2O3) shows the higher sensitivity to H2 than indium oxide (In2O3) or zinc oxide (ZnO) alone [1]. However, ZnO-In2O3 exhibits sensitivity only at high temperatures (300-500 °С), which leads to an explosive sensor and a large power consumption. It is possible to reduce the operating temperature to room temperature by illumination, but this effect was investigated only under ultraviolet illumination (UV) for pure In2O3 or ZnO [2, 3]. The decrease in operating temperature under illumination was explained, but the explanation is valid only for ultraviolet illumination and invalid for visible illumination. In addition, proposed explanations of the illumination effect on the sensor response of metal oxides (to both oxidizing and reducing gases) don`t consider that the illumination realizes non-equilibrium condition and the observed effects of gases adsorption on the surface of metal oxides under illumination can be determined by generation-recombination processes of non-equilibrium charge carriers. In this paper we investigated the effect of visible illumination on the sensitivity of ZnO-In2O3 composites to hydrogen at room temperature.  Nanocrystalline composite films were prepared using commercial nanopowders In2O3 and ZnO. The average nanocrystal size of the oxides in the original powder is 50-80 nm. For composite preparing the certain amounts of ZnO and In2O3 were mixed and triturated in an agate mortar with a small amount of distilled water until a homogeneous suspension with pre-determined mass proportion of constituent oxides was obtained. The resulting slurry was screen printed on a dielectric alumina substrate equipped with platinum contacts and a heater. The resulting layer was heated during 3 hours at 120 °C and then annealed in air, the temperature was gradually raising up to 550 °C and was kept at this value until a constant resistance value of the resulting nanocomposite film was obtained.  The possibility of reducing the operating temperature of H2 gas sensor based on ZnO-In2O3 down to room temperature under green illumination is shown. It is found that sensitivity of ZnO-In2O3 composite to H2 nonmonotonically depends on the composite content. The maximum sensitivity to 1000 ppm of H2 is observed for the composite based on 65 wt.% ZnO and 35 wt.% In2O3. We proposed the new mechanism of nanocrystalline ZnO-In2O3 sensor sensitivity to H2 under illumination by green light. The mechanism considers the illumination turns the composite into nonequilibrium state and the photoconductivity of composite change in the H2 atmosphere is largely determined by recombination processes. The recombination processes determine the photoconductivity relaxation time which in turn determines the photoconductivity of the composite. It is shown that the photoconductivity relaxation time is linked with the response of the ZnO-In2O3 composites to H2. The possible recombination mechanisms of non-equilibrium charge carriers in the studied structures are discussed.