Metal Oxides: Nanostructured Metal Oxides for Gas Sensing Applications

Metal oxide sensors have been extensively developed over fifty years for the detection of toxic and inflammable gases. Progress in gas sensor technology has been possible due to the recognition that performance is closely related to grain size: crystallite sizes in the ~10 nm range produce optimal sensing characteristics. The basic principles of the sensing mechanism are outlined for the cases of oxidizing and reducing gases. Changes in the electrical conductance occur due to physicochemical reactions with gas molecules adsorbed on the surface and these can be directly correlated with gas concentration. While tin dioxide is the most widely employed material for gas sensor applications, because it is sensitive to virtually all gases of interest, various other semiconducting metal oxides have been studied in an effort to increase the sensitivity and selectivity to specific gases. Effects due to interferences between different gases can to a large extent be eliminated by appropriate selection of the sensor operating temperature. Available synthesis methods for the production of metal oxide films are reviewed and the effectiveness of different metal oxides for detecting low concentrations of various gases is compared. Gas sensors can be constructed using either thick film or thin film technology. While the thick film type has the advantage of more robust construction, the thin film type offers better compatibility with standard microelectronic processing techniques. The influence of deposition conditions on the microstructure, electrical properties and sensing behavior of metal oxide films are considered in detail and the effect of the addition of noble metal dopants to increase sensitivity and selectivity is discussed. Advances in device miniaturization are described that enable fabrication of integrated solid state sensor arrays on a single silicon chip. Further improvements in sensor performance may be possible by the use of novel low dimensional metal oxide architectures, such as nanowires and nanobands, which provide increased surface area for adsorption reactions and can also lead to quantum confinement effects that cause modification of the electronic band structure of the metal oxide semiconductor.

RICKERBY David; 

2016-03-02

CRC Press

JRC96953

978-1-4665-8034-3,   

https://www.crcpress.com/CRC-Concise-Encyclopedia-of-Nanotechnology/Kharisov-Kharissova-OrtizMendez/9781466580343,    https://publications.jrc.ec.europa.eu/repository/handle/JRC96953,