Noble metals, semiconductor sensors

Similar to the case of H-atoms the results obtained fully confirm the validity of expression v = 9Iz, where 9 is the degree of ionization depending on adsorbate, adsorbent, and the temperature. This means that ZnO films (it is also correct both for a CdO layer, and for other chemically stable semiconductor oxides) may be used as very sensitive miniature sensors to determine intensity of atom flow for detected noble metals Ag and Pd (see Table 3.2). If the sensitivity of the measuring equipment is brought up to one can measure atom flows equal to... 

Noble metal additives such as Pt, Pd, or Ag, are often added to metal oxide semiconductor sensor materials to enhance sensor response to a particular gas or class of gases [35]. Other metals, namely Be, Mg, Ca, Sr, Ba, have been used with tin oxide to enhance performance of an alcohol selective sensor [36], for example. Commercially produced metal oxide sensors may customarily use one or more of the above catalysts. 

The electrodeposition of nanostructured materials from LLC phases is not restricted to noble metals, but can be extended into the field of semiconductors [69]. Mesoporous regular semiconductors have great potential for applications in optical sensors and solar cells. The successful electrodeposition of selenium was demonstrated by Nandhakumar et al., who subjected a hexagonally struc-... 

In the field of SMOX-based gas sensors, by far the most studied material is the n-type Sn02. Moreover, most of the commercial sensors marketed today are based on it, generally in combination with noble metal additives (Ihokura and Watson, 1994 Williams, 1999). The other material used in commercial sensors in applications involving the detection of oxidizing gases is WO3, which is also an n-type semiconductor. This is intriguing, because since... 

Abstract A brief overview is given for a variety of sensors for the detection of chemical warfare agents (CWA) semiconductor thick- or thin-fihn gas sensors with oxide and noble metal additives, surface acoustic wave (SAW) sensors with a polymer membrane, and an ion mobility sensor (IMS). This is followed by discussion on the preparation methods for the sensing materials employed in semiconducting devices, and SAW sensors are introduced.The chapter closes with the results and observations from the examination and study of these devices. 

In 1967 both Shaver [24] and Loh [25] described effects achievable with oxide semiconductors modified by the addition of noble metals (e.g.. Pt, Pd, Ir, Rh), and since that time the sensitivity and selectivity of semiconductor sensing devices has been significantly enhanced. Intense efforts in this direction, coupled with the further addition of metal oxides [26]-[28], resulted in widespread application of semiconductor gas sensors beginning in the 1970s. 

The WE, typically a cathode, is generally where the reaction of interest occurs. Typical WEs (see Chapters 5 and 6) include the noble metals (especially gold and platinum), carbon (including pyrolytic carbon, glassy carbon, carbon paste, nanotubes, and vapor-deposited diamond), liquid metals (mercury and its amalgams), and semiconductors (indium-tin oxide. Si, see Chapter 9). WEs can be chemically modified (see Chapter 8) in order to increase their sensitivities toward specific species (i.e., become chemical sensors) or to decrease the potential required to drive a particular reaction (i.e., catalysis). 

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... 

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