Environmental control by means of a new gas detection principle: gas sensing by metal oxides hetero- junctions

Projektinformationen

GASMOH

ID Finanzhilfevereinbarung: ICA2-CT-2000-10041

Projekt abgeschlossen

Startdatum 1 Dezember 2000

Enddatum 30 November 2003

Finanziert unter

• Programme for research, technological development and demonstration on "Confirming the international role of Community research,1998-2002"

Gesamtkosten

€ 541 928,00

EU-Beitrag

€ 434 194,00

Koordiniert durch

NATIONAL RESEARCH COUNCIL OF ITALY
Italy

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Leistungen

Structural peculiarities of indium and iron oxides/ Synthesis of indium and iron oxides with specific structure and its nanocomposites/ Correlation of gas-sensing properties of indium-iron oxide

Establishment of fine structural peculiarities of indium and iron oxides and their composites: Morphology, dispersity and fine structural features of iron and indium oxides and their composites depending on synthesis conditions and mode of post-treatment have been studied by using XRD, TEM, SEM, IR, DTA/TG and Moessbauer Spectroscopy. A series of important regularities has been established. It was found, that the oxide systems prepared by the elaborated methods differ by low grain size, poor crystallinity and high defectiveness. It provides higher activity of the materials in gas detection and catalysis as compared to other preparation techniques, like thermal decomposition of organic and inorganic precursors, RGTO etc. Synthesis of nanocomposites based on indium and iron oxides: Different modifications of sol-gel technique were applied to obtain binary nanocomposites based on indium and iron oxides. Using of these approaches allows obtaining a series of advanced complex oxide systems of the required chemical and phase composition in form of sols, thin films and powders. Fine structure of the materials can be easily adjusted by varying the synthesis condition and mode of post-treatment. Synthesis of indium and iron oxides with specific structure: A convenient modification of sol-gel technique, which provides the preparation of highly dispersive and defective indium and iron oxides of different structural modification, has been elaborated. The method allows obtaining the oxide materials in form of sols, thin films and powders. Correlation between the structure and gas-sensing properties of indium-iron oxide composites; mechanisms of gas detection: The correlation between the structural peculiarities of the oxide systems and their gas-sensitive properties has been established. The mechanisms of certain gas detections have been suggested, taking into consideration both red-ox and acid-base features of metal oxides. As it was found out, high performance of the studied systems is caused by microheterogeneity of the composites and bi-layer structures. Thus, the functions of receptor and transducer are divided between separate clusters of different oxide phases, which possess unequal activity in red-ox and acid-base interactions.

Deposition of sol-gel heterojunction by 2 or more oxide thin films/ Deposition of thick film sensing layers based on single metal oxides and on hetero-junctions of 2 and more single metal oxides

Deposition of sol-gel heterojunction by 2 or more oxide thin films: Innovative materials based on both single and heterojunction of 2 or more metal oxides were synthesised and deposited on suitable substrates in the form of thin films. The materials were prepared by sol-gel methodology starting from suitable precursors and optimising the right procedure in order to obtain thin film having the required performance for gas sensors. Deposition of thick film sensing layers based on single metal oxides: Deposition of the thick film sensing layers based on single metal oxides has been done by screen-printing on the ceramic alumina substrates. Already pre-treated metal oxides have been used for the deposition. It was shown that the screen-printing technique could be successfully applied for the deposition of the thick film sensing layers based on single metal oxides. This result is planned to be used outside the consortium. Deposition of thick film sensing layers based on hetero-junctions of 2 and more single metal oxides: Deposition of the thick film sensing layers based on hetero-junctions of 2 and more metal oxides have been done by screen-printing on the ceramic (alumina) and Si substrates. Already pre-treated single metal oxides have been used for the preparation of the slurry and for the deposition. It was shown that screen-printing technique can be successfully applied for the deposition of the thick film sensing layers based on hetero junction of 2 and more pre-treated single metal oxides. This result is planned to be used outside the consortium.

Gas-sensing properties of thin- and thick film sensors based on indium and iron oxides

Gas-sensing behaviour of simple indium and iron oxides, their composites and bi-layer structures (indium oxide/iron oxide, indium oxide/indium oxide-iron oxide) have been estimated regarding ozone, nitrogen dioxide, carbon monoxide, methane, methanol and ethanol. For the first time a systematic comprehensive study of gas-sensing properties of thin- and thick film sensors based on indium-iron oxide systems with different chemical and phase composition and widely varied fine structure to a great number of gases was performed. Extremely high response to ozone was demonstrated by bi-layer sample based on gamma-modification of iron oxide. Meanwhile, the composites based on alpha-iron oxide were found to be very sensitive to nitrogen dioxide. Thus, for the first time, the great distinction in oxide sensitivity to ozone and nitrogen dioxide, which are both oxidising agents, was achieved. Iron-indium oxide composites overcome in sensitivity all the previously studied systems based on indium, molybdenum, tin and nikel oxides. Besides, the response of the above mentioned sensors to reducing gases are very small at the temperature range, which is optimal for ozone and nitrogen dioxide detection.

Gas-sensing properties of the corundum-type indium oxide. Measurement technology of simultaneous conductance and work function changes on metal oxide layers

Gas-sensing properties of the corundum-type indium oxide: For the first time, the gas sensing properties of the high-pressure modification of indium oxide (so-called corundum-type or hexagonal In(2)O(3)) have been studied. It was found that thick film sensors based on hexagonal indium oxide show high response to ozone in the air. Measurement technology of simultaneous conductance and work function changes on metal oxide layers: Simultaneous conductance (under constant voltage polarisation) and work function measurements have been performed by a McAllister Kelvin Probe set-up. From the obtained values for CPD (contact potential difference) and conductance under different gaseous atmospheres the changes in work function, band bending and electron affinity can be calculated.

Deposition by sputtering of Al-V mixed oxides hetrojunctions for gas sensing and of p-n and n-n+ heterojunctions for gas sensing

Deposition by sputtering of Al-V mixed oxides hetrojunctions for gas sensing: Thin film sensing layers based on Al-V mixed oxide, as heterojunction obtained via mixing two different separate phases, has been deposited by RF magnetron sputtering over low power Si micromachined substrates as organic vapour sensor. This result is planned to be used outside the consortium. Deposition by sputtering of p-n and n-n+ heterojunctions for gas sensing: p-n and n-n+ heterostructures made by a TiO/In(2)O(3), TiO(2)/In(2)O(3) and TiO/WO(3) heterojunctions were prepared by sputtering over ceramic substrates through layer by layer deposition that produces one heterojunction at the interface between the two films. The sensing properties toward environmental pollutants has been studied. These results are planned to be used outside the consortium.