Gas sensor operation

Wang HC, Li Y, Yang MJ (2006) Fast response thin film Sn02 gas sensors operating at room temperature. Sens Actu B 119 380-383... 

The original design was developed specifically for sensing of carbon dioxide (Severinghaus, 1965), but the principle on which these gas sensors operate is general. The key element is a small compartment into which the gas can penetrate through a semipermeable membrane (Fig. 6.28). 

Solid-Electrolyte Hydrogen Sensor. Most of solid gas sensors so far developed need high temperature operation because of limited ionic conductivities when the electrolyte is near room temperature. If solid electrolytes with sufficiently large ionic conductivities are available, unique gas sensors operative near room temperature can be fabricated. An example is the following proton conductor hydrogen sensor proposed by our group (10, 11). 

In recent years, gas sensors operating at room temperature are becoming increasingly more important in many fields. These sensors can be used as so called "cordless sensors", because they need no external electric sources to heat the sensor elements. Although electrochemical gas sensors which utilize liquid electrolytes are available to detect inorganic gases, e.g., 02, CO, Cl2, H2S, etc. at room temperature (1-3), they often have time-related problems such as leakage and corrosion. The problems are minimized if solid electrolytes are used in place of liquid electrolytes. 

Hasegawa, I., Tamura, S. and Imanaka, N. (2005) Solid electrolyte nitrogen monoxide gas sensor operating at intermediate temperature range. Sens. Actuators B, 108, 314—18. 

Ihe experiments were performed on an Sn02-based gas sensor operated at 300°C. Investigations were made into the influences of CO and H2 in... 

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... 

Morrison, S., Mechanism of semicondnctor gas sensor operation . Sensor Actual. B, 1987,11,283-7... 

Hieu, N. V., Thuya, L. T. B. and Chien, N. D. (2008) Highly sensitive thin film NH3 gas sensor operating at room temperature based on SnOj/MWCNTs composite , Sens. Actuat. B, 129,888-95. 

Abstract This chapter discusses the use of porous silicon (PSi) for gas sensors. It is of great importance to develop efficient and economically viable gas sensors for different applications. PSi can be nsed as an alternative material for gas sensors, operating at a relatively low temperature, including room temperatnre.The interest in this material is mainly due to its extremely high surface-to-volume ratio, the ease of its formation and its compatibility with modem silicon microelectronics fabrication technologies. A large variety of different sensors made of PSi have been manufactured in recent years, and achievements in this field are reported in this chapter. 

Table 5.2 Parameters of SiNW-based gas sensors operated at room temperature...

The problems of stability and reliability of gas sensors operation remain dominant while designing devices for the sensor market. Devices designed for this market should provide a stable and reproducible signal for a period of at least 2-3 years (typically 17,(XX)-26,(X)0 h of operation). Therefore, sensing materials and conditions of their operation should be selected in consideration of the above-mentioned requirements (Korotcenkov 2007 Korotcenkov and Cho 2011). For example, the organic polymer Nation may retain working capacity in electrochemical gas sensors for a period of up to about 1 year. To achieve this result, however, the Naflon should be wetted by a wick system connected to a reservoir (Pasierb et al. 2004). This means that dry atmosphere does not facilitate a long lifetime for polymer-based electrochemical gas sensors. 

It should be noted that it is impossible to determine the main reason for gas sensor instabilities in a general sense the task is too complicated. In addition, the reasons for instability could depend on the constructive and/or technological features of the sensor fabrication or on temperature effects at the point of use. Therefore, at present there are a great number of approaches, aU of which—in the author s opinion—can be effective in resolving instability problems in gas sensors. According to Korotcenkov and Cho (2011), to attain maximum gas sensor operational stability, it is necessary to stick to the following recommendations. 

Gas sensors operate by binding molecules to the device surface via one of several mechanisms, depending how the surface is modified. If a bulk layer of liquid is placed on the surface, absorption of gaseous material can take place. Alternatively, if the surface is covered with a thin molecular layer one or a few monolayers thick, material will be surface-bound by some combination of physical and chemical interactions. 

Working Principles and Theory. The mechanisms responsible for semiconductor gas-sensor operation can be divided into two classes. The first class involves changes in bulk conductance (transducer function), while the second relies on changes in surface conductance (receptor func-... 

Monkman G (2000) Monomolecular Langmuir-Blodgett films— tomorrow s sensors Sensor Rev 20 127-131 Morrison SR (1987) Mechanism of semiconductor gas sensor operation. Sens Actuators 11 283—287 Moseley PT, Norris JOW, Williams DE (eds) (1991) Techniques and mechanisms in gas sensing. Adam Hilger, Bristol Moskalenko KL, Nadezhdinskii AI, Adamovskaya lA (1996) Human breath trace gas content study by tuneable diode laser spectroscopy. Infrared Phys Technol 37 181-192... 

As was shown before, conventional gas-sensing metal oxides, such as SnO, In Oj, WO3, ZnO, as a rule are used in conductometric gas sensors operated at high temperatures. However, during experiments carried out recently (last decade) it was established that conductometric gas sensors based on these metal oxides can operate at room temperatures as well. Examples of these sensors are presented in Table 2.19. 

Shin W, Imai K, Izu N, Murayama N (2001) Thermoelectric thick-film hydrogen gas sensor operating at room temperature. Jpn J Appl Phys 2 Lett 40 L1232-L1234... 

Strong water vapor influence (see Figs. 3.14 and 3.15c) is one of the main disadvantages of polymer-based gas sensors, because water vapor is the most common interferant for gas sensors operating at room temperature (Buchler and Ryan 1997 James et al. 2005 Pejcic et al. 2007). For example, Kaplan and Braham (1998) showed that an e-nose based on polymer gas sensors lost sensitivity in the presence of water vapor. Therefore, when humidity levels are not compensated for or controlled, it is possible that the humidity is responsible for some successful discriminations. For example, the... 

Miura N, Yamazoe N (1992b) Solid-state gas sensors operating at room temperature. In Colomban P (ed) Chemistry of soUd state materials 2 proton conductors. Cambridge University Press, Cambridge, p 527 Miura N, Kato H, Yamazoe N, Seiyama T (1983) Mixed potential type NO sensor based on stabihzed zirconia. In Proceedings of international meeting of chemical sensors, Fukuoka, Japan. Kodansha/Elsevier, Tokyo/Amsterdam, p233... 

Of course, in the case of gas sensors operated at room temperature we do not have such strong requirements from electrode materials, and therefore other materials, which are not as stable as Pt, can be used. In particular, gold (front and back) electrodes are used in most conventional QCMs. Other electrode materials such as aluminum, copper, silver, chromium, nickel, titanium, tungsten, zinc, as well as carbon and sihcon can also be used in gas sensors (ICM, htq> //www.icmfg.com/crystalsJitml). 

Morrison SR (1987) Mechanism of semiconductor gas sensor operation. Sens Actuators 11 283-287 Moseley PT, Tofield BC (eds) (1987) Solid state gas sensors. Adam HUger, Bristol... 

As it was shown before, optical IR, NDIR, and UV gas sensors need light sources for the excitation of the gas molecules in the wavelength range for the particular gas (see Table 14.4). Of course, for optimal gas sensor operation these light sources should correspond to the following requiranents... 

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