Electrode-oxide semiconductor

The aim of this chapter is to describe and review the interface chemistry and transition theory of the electrode-oxide semiconductor layer in gas sensor operation. Section 3.2 deals with criteria for selecting the metal and semiconductor materials used in the fabrication of gas sensors.The chemistry and... 

Electrodes of semiconductor gas sensors have a function of conductor to an external circuit as a contact material. Contact resistance that is formed in the electrode-oxide semiconductors may in some cases have significant contribution on the response of the sensors. Electrode materials are also utilized as catalyst activators in the sensor operation. In special cases, for electrode materials to operate at high temperature in automotive and aerospace industries, they have to endure at temperature up to 600°C. Therefore, the electrode materials of semiconductor gas sensors are responsible for their sensitivity and selectivity to specific gases. 

The physical understanding of the electrode-oxide semiconductor interfaces are described in this section. Interfaces of this type occur in oxide semiconductor gas sensors and metal-insulator-semiconductors (MIS) devices. When a metal is contacted with oxide, the potential barrier arises from the separation of changes of the metal-oxide interface as well as the metal-semiconductor contacts. 

The first significant step towards understanding the mechanism of the electrode-oxide semiconductor is given in an ideal case contact. Another advance in our understanding of the electrode-oxide semiconductor junction is concerned with contacts with surface states, and interfacial layer and... 

Charge carrier transport in the electrode-oxide semiconductor interfaces... 

FfCURE 13.54 Semiconductor gas sensors (o) tubular, (b) thick film, (e) bulk-type one-electrode sensor where a thin Pt wire spiral is embedded Inside a sintered oxide semiconductor button. ... 

A novel development of the use of ion-selective electrodes is the incorporation of a very thin ion-selective membrane (C) into a modified metal oxide semiconductor field effect transistor (A) which is encased in a non-conducting shield (B) (Fig. 15.4). When the membrane is placed in contact with a test solution containing an appropriate ion, a potential is developed, and this potential affects the current flowing through the transistor between terminals Tt and T2. 

Several demonstrations of this concept have recently been published The first one is based on the pH dependence of redox transitions in oxide semiconductors that are connected with conductivity changes. If the bridging polymer layer in Fig. 6 is WO3 sputtered onto the electrode array or electrochemically deposited Ni(OH)j the transistor amplification is a function of the pH of the... 

This classification is ratfier arbitrary, since different reaction products may form at the same electrode, depending on the reaction conditions. Nonmetallic substances such as oxides, semiconductors, and orgaihc N4 complexes are used as electrode materials as well. 

The ISFET is an electrochemical sensor based on a modification of the metal oxide semiconductor field effect transistor (MOSFET). The metal gate of the MOSFET is replaced by a reference electrode and the gate insulator is exposed to the analyte solution or is coated with an ion-selective membrane as illustrated in Fig. 

Photo)electrochemistry (electrodes, oxide electrodes and semiconductors)... 

Variation of the nature of the gate electrode results in the different types of FET. For example, in the metal oxide semiconductor FET (MOS-FET) palladium/palladium oxide is used as the gate electrode. This catalyti-cally decomposes gases such as hydrogen sulphide or ammonia with the production of hydrogen ions, which pass into the semiconductor layer. An enzyme may be coated on the palladium, e.g. urease, which catalyses the production of ammonia from urea and thus provides a device for the measurement of this substrate. 

TABLE 5- Tbe flat band potential , the iso-electric point pHi, the potential of the conduction band edge aiep) at pH q> for metal oxide semiconductor electrodes in aqueous solutions t, = band gap of metal oxides pH= solution pH at which the flat band potential is measured. [From Morrison, 1980.]... 

This chapter considers photoanodes comprised of metal oxide semiconductors, which are of relatively low cost and relatively greater stability than their non-oxide counterparts. In 1972 Fujishima and Honda [1] first used a crystal wafer of n-type Ti02 (rutile) as a photoanode. A photoelectrochemical cell was constructed for the decomposition of water in which the Ti02 photoanode was connected with a Ft cathode through an external circuit. With illumination of the Ti02 current flowed from the Ft electrode to the... 

This chapter considers photo-electrodes consisting of non-oxide semiconductors, alone and in combination with oxide semiconductors for water splitting. 

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