Berlin 2008 – scientific programme

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DS: Fachverband Dünne Schichten

DS 16: Functional Oxides

DS 16.5: Invited Talk

Tuesday, February 26, 2008, 18:30–19:00, H 2032

Semiconducting metal oxides for gas sensors — •Tilman Sauerwald and Thorsten Wagner — Institut für Angewandte Physik, Justus Liebig Universität Giessen, Germany

Gas sensors based on semiconducting metal oxides like SnO_2−x, WO_3−x and Ga₂O_3−x are useful devices for the detection of hydrocarbons e.g. solvents. The sensor effect is based on a change in conductivity of the material caused by chemical reactions on the surface. In ambient air the surface of the metal oxide is covered by adsorbed, negatively charged oxygen. This leads to a depletion of electrons close to the surface (typically ∼10 nm). In granular films (commonly used) the conductivity is determined by the resulting surface barrier. For optimal sensing properties the structural size has to be comparable to the size of the depletion layer. Such structures can be obtained by a classical sol-gel process but they are not thermally stable. Methods utilizing selfassembly processes like endo- and exotemplating produce highly ordered nanostructures with enhanced stability. The reactivity of the metal oxide surface depends on different properties such as the acidity/basicity or the coverage with surface oxygen. Different surface acidity can be obtained by using different metal oxides and surface additives, this can be used for selective detection of solvents. The coverage with surface oxygen can be modulated by the modulation of the density of bulk donors by electrochemical polarisation of the sensor film