Gas Sensor Applications

Temporal response of the cantilever-based sensor to water vapor diluted in is shown in Fig. 11.6. 

Allendorf et al. (2(X)8) established that the energy of molecular adsorption within a porous MOF structure could be transformed into mechanical energy which could be utilized to create a responsive, reversible, and selective sensor. Allendorf et al. (2011) believe that this application is limited only by the development of MOFs with high chemical selectivity and the ability to grow these onto the desired substrate. 

Several recent reviews summarize the gas adsorption isotherms and gas-sensing applications of MOFs (Thomas 2009 Chen et al. 2010a Fang et al. 2010 AUendorf et al. 2011 Keskin and Kizilel 2011 Meek et al. 2011 Shekhah et al. 2011 Khoshaman and Bahreyni 2012 Kreno et al. 2012). Table 11.3 summarizes results of research related to application of MOFs in gas sensors. 

MOF Sensor type/T V 47 ooer Gas tested Characterization References 

ZIF-8-TiOj Optical (reflection) EtOH, MeOH, Maximum sensitivity to Hinterholzinger 

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SILAR-grown ZnO films have been tested for gas sensor applications.29 The ZnO films, doped with tin for this purpose, were grown from a mixture of dilute zinc sulfate, sodium hydroxide, and sodium tin(IV)oxide solutions. The final step, resulting in the oxide film, was treatment of the substrate and film in a nearly boiling water bath. The N02 gas sensing properties were tested for films doped with Al, Cu, Pd, and Sn, but only the film doped with tin exhibited sensitivity toward N02. The sensitivity of the ZnO Sn film was 5% /ppm after rapid photothermal processing (RPP). The best sensitivity was obtained when the tin concentration was 5-10%.29... 

Microhotplates, however, are not only used for metal-oxide-based gas sensor applications. In all cases, in which elevated temperatures are required, or thermal decoupling from the bulk substrate is necessary, microhotplate-like structures can be used with various materials and detector configurations [25]. Examples include polymer-based capacitive sensors [26], pellistors [27-29], GasFETs [30,31], sensors based on changes in thermal conductivity [32], or devices that rely on metal films [33,34]. Only microhotplates for chemoresistive metal-oxide materials will be further detailed here. The relevant design considerations will be addressed. 

S. Moller, J. Lin, and E. Obermeier. Material and Design Considerations for Low-Power Microheater Modules for Gas-Sensor Applications , Sensors and Actuators B25 (1995), 343-346. 

We recently published a chapter in the book Silicon Carbide Recent Major Advances by Choyke et al. [19] that describes SiC gas sensor applications in detail. In this book, we emphasize device properties applications are only briefly reviewed at the end. The device and gas sensing properties of various field-effect chemical gas sensing devices based on SiC are described, and other wide bandgap material devices are reviewed. The detection principle and gas response is explained, and the buried channel SiC-FET device is described in detail. Some special phenomena related to the high-temperature influence of hydrogen at high temperature are also reported. 

Shang et al. (61) used microemulsion polymerization to synthesize MWCNT-PMMA composites for gas sensor applications. Better dispersion, enhanced electrical conductivity and better sensor response was observed for in-situ fabricated composites compared to composites prepared by solution mixing. Ma et al. (62) performed in-situ polymerization of MWCNT-PMMA composites in the presence of an AC electric field to study dispersion and alignment of MWCNT in PMMA matrix induced by the electric field. Experimental evidences from in-situ optical microscopy, Raman spectroscopy, SEM and electrical conductivity showed that both dispersion and alignment qualities were significantly enhanced for oxidized MWCNT compared to pristine MWCNT. 

Shang et al. 2009 (61) MWCNT Purified Microemulsion polymerization CNT Loading levels 1 tol5wt% MWCNT-PMMA composites prepared by microemulsion polymerization at 8 wt% loading showed high sensor responses to different organic vapors such as acetone, toluene, THF, choloroform, acetonitrile, benzene They suggested the use of these composites for gas sensor applications ... 

Leite E. R., Weber I. T., Longo E. and Varela, J. A. A new method to control particle size and particle size distribution of Sn02 nanoparticles for gas sensor applications, Adv. Mater. 12 (2000) pp. 965-968. 

FIGURE 10.30 Scanning electron microscopy (SEM) images of cross section of a commercial optical fiber coated with a NaA zeoUte thick layer (a) total cross section and (b) magnification view of the NaA zeolite layer. (From Lopez, J., Pina, M.P., Coronas, J., Pelayo, J., and Santamaria, J., A novel optical device for gas sensor applications based on zeolitic materials. Books of abstracts of the 1st NanoSpain Workshop, San Sebastian, 2004.)... 

Lopez J, Pina MP, Coronas J, Pelayo J, and Santamaria J. A novel optical device for gas sensor applications based on zeolite materials. Books of abstracts of the 1st NanoSpain Workshop, San Sebastian, 2004. 

Shimizu, Y. Jono, A. Hyodo, T. Egashira, M., Preparation of large mesoporous Sn02 powder for gas sensor application, Sens. Actuators B 2005,108, 56-61... 

Molecular Interactions Between Alcohols and Metal Phthalocyanine Thin Films for Optical Gas Sensor Applications... 

Another important NOj sensors using metal phthalocyanines are SAW gas sensors. SAW devices are attractive for gas sensor applications because of their high sensitivity and reliability, so that NO sensors using SAW devices with metal phthalocyanines have been extensively studied by many researchers. Nieuwenhuizen et al. of Prins Maurits Laboratory TNO, Netherlands, have actively studied on the SAW gas sensors and as an example of the researches they reported the response of SAW gas sensors for NOj, in which different metal phthalocyanines were deposited on one delay-line of a dual delay-line oscillator[16]. Fig. 7 indicates the response of the sensors as a fimction of NOj concentration at 150°C. The response is defined as frequency differences divided by the thickness of a phthalocyanine layer. As shown in the Figure. Co phthalocyanine is most sensitive to NOj, followed by Cu phthalocyanine and... 

Verification of ultrasensitive gas sensors New frontiers of gas sensor applications often demand that they cope with reducing gases at sub-ppm levels. It is necessary, first, to prove that such high-sensitive sensors can be devised. 

Cerdd, I, Arbiol, I, Dezanneau, G., Diaz, R. and Morante, J. R. (2002), Perovskite-type BaSnOs powders for high temperature gas sensor applications. Sensors and Actuators B, 84,21-2. 

Foucaran, A., Pascal-Delannoy, F, Giani, A., Sackda, A., Combette, P. and Boyer, A. Porous silicon layers used for gas sensor applications , (1997) Thin Solid Films, 297,317-20. 

Michel, H. J., Leiste, H. and Halbritter, J. (1995) Structural and electrical characterization of PVD-deposited Sn02 films for gas-sensor application. Sensors and Actuators B Chemical 25,568-72. 

D. Avramov, M. Rapp, A. Voigt, U. Stahl, M. Dirschka, Comparative studies on polymer coated SAW and STW resonators for chemical gas sensor applications, in Proceedings o/rlte/EEEFCS (2000), pp. 58-65... 

Foucaran A, Pascal-Delaimoy F, Giani A, Sackda A, Combette P, Boyer A (1997) Porous silicon layers used for gas sensor applications. Thin Solid Films 297 317-320 Foucaran A, Sorli B, Garcia M, Pascal-Delannoy F, Giani A, Boyer A (2000) Porous silicon layer coupled with thermoelectric cooler a humidity sensor. Sens Actuator A 79 189-193 Gabouze N, Belhousse S, Cheraga H (2005) CHx - Porous silicon structures for gas sensing applications. Phys Stat Solid C 2(9) 3449-3452... 

Massera E, Nasti I, Quercia L, Rea I, Di Franeia G (2004) Improvement of stability and reeoveiy time in porous-silieon-based N02 sensor. Sens Actuator B 102 195-197 Mizsei J (2007) Gas sensor applications of porous Si layers. Thin Solid Films 515 8310-8315 (Review)... 

Strathman H (2011) Introduction to membrane science and technology. Whey VCH, Weinheim Taliercio T et al (1995) Realization of porous sihcon membranes for gas sensor application. Thin... 

A brief analysis of results obtained indicates that CNTs are really promising materials for gas sensor applications (Li et al. 2008 Kalcher et al. 2009 Bondavalli et al. 2009). However, similar to other sensing materials, CNTs have disadvantages as well. Technological difficulties related to sensor fabrication, bad reproducibility, slow response, and low selectivity are the main shortcomings of these devices (Fam et al. 2011). These shortcomings are subject to the following conditions (Bondavalli et al. 2009). 

It must be noted that CNTs are promising material for preparing various composites, which can also be used for gas sensor design. Types of composites formed using CNTs according to their chemical composition and structures are summarized in Fig. 1.14. Features of CNT/polymer composites, which have the most evident advantages for gas sensor application, will be discussed in Chap. 13 (Vol. 2). It was established that polymer/CNT composites combine the unique properties of nanotubes with the ease of processability of polymers. Moreover, for design multifunctional materials based on CNT/polymer composites, a very low fraction content of CNT is required. 

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