Glossary

Activation energy Describes the amount of energy required for a given thermodynamical process.

Condensation A chemical reaction, which involves elimination of water as a product.

Dip-coating A thin film deposition process using sol-gel precursors, which involves dipping the substrate vertically into the solution (or sol) and then withdrawing it with definite speed under controlled atmosphere. Hydrolysis A chemical reaction, which involves the reaction between metal alkoxide and water. Nanocrystalline Tiny crystalline particles of size in the nanometer range. (1 nm = 10-9 m).

Precursor A starting chemical for a conducting a given chemical reaction.

Receptor function It is related to the ability of the sensor surface to chemically react with the gas to be detected. Recovery time It is the total time taken by the thin film sensor element to regain its 90% of its original electrical resistance in air, when the surrounding controlled atmosphere containing the reducing gas is replaced by pure air. Response time It is the total time taken by the thin film sensor element to reduce its electrical resistance, in the presence of a reducing gas, by 90% of its original resistance in air.

Sensitivity It is defined as the ratio of the electrical resistance of the thin film sensor element in the presence of air to that in the presence of the atmosphere containing the reducing gas.

Sol-gel Wet chemical process involving the hydrolysis and the condensation reactions as a result of chemical reaction between water and metal alkoxide in an alcoholic solvent. Space charge layer Electron depletion region formed on the surface of semiconductor oxide particle as result of chemisorption of the oxygen-ions (O- and O- ions). Spin-coating A thin film deposition process using sol-gel precursors, which involves dropping few drops of the sol on the substrate surface, which is subsequently rotated along the vertical axis with definite speed for specific amount of time to form a thin film adherent to the substrate surface. Transducer function It is related to the ability of the sensor element to conduct the electrons generated due to the chemical reaction between the sensor surface and the reducing gas to be detected.

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