Chemical semiconductive sensor

Metal oxide semiconductive sensors are an important class of chemical sensors particularly for gaseous sensing. Among the metal oxide semiconductive materials. 

Metal oxide semiconductive sensors are not limited to tin oxide only. Many other metal oxides, such as zinc oxide, tungsten oxide, and others can also be used for chemical and gas sensing. It is understandable that an incorporation of a selective catalyst or a dopant may enhance the selectivity of the MOS sensors. Palladium, platinum, and others have been used as catalytic dopants for these sensors. The processes... 

The first commercial chemical sensor was a gas alarm sensor, which detects inflammable gases and prevents gas accidents. The sensor is simple, portable, and can be easily installed in most places. These features encourage mass production, and thus contribute to the production of an inexpensive device. The base materials for these sensors are mainly tin oxide (Sn02) or zinc oxide (ZnO) semiconductors with type-I detection. When inflammable gases come in contact with the oxides, the electric conductivity changes and this change is used as a sensor output. The variation of the change is proportional to the gas concentration. In a practical semiconductive sensor, noble metals... 

Several kinds of conduction mechanisms are operative in ceramic thermistors, resistors, varistors, and chemical sensors. Negative temperature coefficient (NTC) thermistors make use of the semiconducting properties of heavily doped transition metal oxides such as n-ty e Ti O andp-ty e... 

Chemical modulation of the surface conductivity is the principle of operation of some of the most commercially successful chemical sensors, the high temperature semiconducting oxide sensors. They are known by their brand name Figaro sensors. They are discussed in detail in Section 8.2.2.1. The reason for their commercial success lies in the fact that their performance and cost match exactly the specific practical needs of many applications, particularly those of the automotive industry. They have been described in great detail, from the point of view of both the underlying physics and chemistry (Morrison, 1994 Logothetis, 1987). 

Williams, D.E. (1999) Semiconducting oxides as gas-sensitive resistors, Sensors And Actuators B-Chemical, B57, pp. 1-16. 

Diamondlike Carbon and Hard Carbon-Based Sensors Sensors that are based upon diamond technology include thermistors, pressure and flow sensors, radiation detectors, and surface acoustic wave devices [103]. The relative ease of depositing prepattemed, dielectrically isolated insulating and. semiconducting (boron-doped p type) diamond films has made polycrystalline diamond-based sensors low-cost alternatives to those based on conventional semiconductors. Diamondlike carbon and diamond films synthesized by chemical... 

In this entry, we focus on the discussion of the platform technology for electrochemical sensors, metal oxide semiconductive (MOS) sensors, and piezoelectric based quartz crystal microbalance (QCM) sensors. There are other types of chemical sensors, such as optical sensors, Schottky diode based sensors, calorimetric sensors, field-effect transistor (FET) based sensors, surface acoustic wave sensors, etc. Information of these specific sensors can be found elsewhere and in current journals on sensor technologies. Because of the increasing importance of microfabricated sensors, a brief discussion of microsensors is also given. 

Sensors and other devices were developed on optical fibers by incorporating metallic and semiconducting nanoparticles on the surface of optical fibers. Several ways of forming sensitive and robust chemical sensors based on plasmon resonances of metallic islands and nanoparticles were demonstrated. Development of in-line optical fiber stractmes, involving single mode or multimode optical fibers fused to an arrangement of coreless... 

The outputs of some mixed potential-type chemical sensors correlate with the type of electronic defect (i.e., n-type versus p-type), so the response has been attributed to the semiconducting behavior of the electrode material [314]. LaFeO3, which has been used as a semiconductor-type gas sensor ] 315, 316], has also been used as an electrode with YSZ [255, 263, 317] or NASICON ]317, 318] electrolytes for potentiometric NO, sensors. Strontium (i.e., (La,Sr)FeO3 ]255, 256, 284]) or strontium and cobalt (i.e., (La, Sr)(Co,Fe)O3 ]275, 280, 309]) have been added to LaFeO3 to improve electrode performance. (La,Ca)MnO3 doped with either cobalt or nickel on the manganese site has been used as the electrode for N O, sensors ]319]. The outputs of some NO, sensors with perovskite electrodes are shown in Figure 13.26 ]255, 256, 264, 275, 309, 312]. 

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. 

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