Sensing semiconducting metal oxide

The sensing action by metal oxides depends on several factors such as grain size (available surface area) and surface states as well as the efficiency with which the test gas molecules adsorb on the surface [25-27]. The sensing mechanism of n-type semiconducting metal oxides involves... 

Heterogeneous layers based on semiconducting metal oxides are known to show gas-sensing features different as compared to single oxides [1,2], The mentioned synergetic phenomenon can be provided by two effects i) the presence of active centers with diverse adsorption and catalytic behavior ii) the efficient separation of the sensor functions, receptor and transducer, between different oxide phases. 

Compact chemical sensors can be broadly classified as being based on electronic or optical readout mechanisms [28]. The electronic sensor types would include resistive, capacitive, surface acoustic wave (SAW), electrochemical, and mass (e.g., quartz crystal microbalance (QCM) and microelectromechanical systems (MEMSs)). Chemical specificity of most sensors relies critically on the materials designed either as part of the sensor readout itself (e.g., semiconducting metal oxides, nanoparticle films, or polymers in resistive sensors) or on a chemically sensitive coating (e.g., polymers used in MEMS, QCM, and SAW sensors). This review will focus on the mechanism of sensing in conductivity based chemical sensors that contain a semiconducting thin film of a phthalocyanine or metal phthalocyanine sensing layer. 

In the next section, a variety of solid state environment gases sensors (NO,, CO2, CO, SO2, O2, etc.) are reviewed, and attention is also paid to semiconducting metal oxide type. Also discussed are the extension of the operating temperature to the near-human temperature regimes and better sensing properties derived from the nanostructured semiconducting metal oxide gas sensors. 

Conduction mechanism in semiconducting metal oxide sensing films impact on transduction... 

Key words semiconducting metal oxide (SMOX), sensing and transduction of SMOXs, p- and n-type MOXs, conduction mechanism, modelling, measurements taken in working conditions. 

General discussion about sensing with semiconducting metal oxide gas sensors... 

Sensing and transduction for p- and n-type semiconducting metal oxides... 

Barsan, N., Simion, C., Heine,T., Pokhrel, S. and Weimar, U. (2010) Modehng of sensing and transduction for p-type semiconducting metal oxide based gas sensors . Journal of Electroceramics, 25(1), 11-19, DOI 10.1007/sl0832-009-9583-x... 

Resistive gas sensors are based upon monitoring a change in the electrical conductivity of a sensing material (primarily, non-stoichiometric semiconducting metal oxides like Sn02, WO3, ZnO and Ti02) at high temperature... 

Modem solid-state (resistive) gas sensors are generally based on wide-band-gap semiconducting metal oxide sensing materials. Resistive gas sensors available in the market (e.g. TGS 812, Figaro Engineering) generally use... 

Fig. 15.4 Principle of the optical gas-sensing effect, (a) Schematic iiiustration of goid nanoparticles embedded in the volume and on the surface of a semiconducting metal oxide layer with refractive index n. (b) Shift of the absorption peak of a single gold nanocluster (75 nm in diameter) by a variation of the refractive index of the surrounding medium at exposure to a reducing or oxidizing gas (Reprinted with permission from Schleunitz et ai. 2007, Copyright 2007...

Metal oxides fonn the class of materials which has seen the widest application in gas sensors (Park and Akbar 2003 Korotcenkov 2007a, b). As can be seen in Table 2.1 and Fig. 2.1, they can be used in every type of gas sensor. For example, in conductometric sensors, semiconducting metal oxides are typically used as gas-sensing materials that change their electrical resistance upon exposure to oxidizing or reducing gases. 

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