Gas sensors performance

The model sensitive layer, which will be used for gas sensor performance tests throughout this book, was Sn02 that has been doped with 0.2 wt % Pd. The minute Pd-content leads to a better sensitivity to carbon monoxide. The larger response is a consequence of the increased reaction rate. For the sensor arrays in Chap. 6, two additional materials have been prepared. Pure tin oxide shows a good sensor response... 

Tulliani, J. M. Moggi, P., Development of a porous layer catalytically activated for improving gas sensor performances, Ceram. Int. 2007, 22, 1199-1203... 

Dieguez A, Vila A, Cabot A, Romano-Rodriguez A, Morante JR, Kappler J, Barsan N, Weimar U, Gopel W (2000) Influence on the gas sensor performances of the metal chemiceil states introduced by impregnation of calcinated SnO sol-gel nanocrystals. Sens Actudors B 68 94—99... 

Sensor performance for different applications is defined by various features of the ceramic. For example, the electrical output of most pressure sensors is dependent on the bulk piezoelectric properties of a PZT ceramic. Oxygen gas sensor performance is defined by the conductivity behavior of Zr02 ceramics, which is in turn dependent on the oxygen vacancy content of the material. The performance of still other sensors, for example, ceramic thermistors, is dependent on the grain boundary characteristics of doped BaTi03 ceramics. For humidity sensors based on NiO/ZnO, the p—n junction characteristics of the interface define sensor performance. 

Andio MA, Browning PN, Morris PA, Akbar SA (2012) Comparison of gas sensor performance of Sn02 nano-structures on microhotplate platforms. Sens Actuators B 165 13-18... 

Agnew J (1973) Thick film technology fundamentals and applications in microelectronics. Hayden, RocheUe Park, NJ Bakrania SD, Wooldridge MS (2009) The effects of two thick film deposition methods on tin dioxide gas sensor performance. Sensors 9 6853-6868... 

Applicability of Semiconductor Gas Sensors Research into the applications of this type of sensor has mainly been concerned with measuring carbon monoxide concentration in flue gases. Tests show that sensors follow the concentration of carbon monoxide in the flue gas. Improvement in sensor performance has resulted with the introduction of a catalytic additive (palladium or... 

Titanium dioxide supported gold catalysts exhibit excellent activity for CO oxidation even at temperatures as low as 90 K [1]. The key is the high dispersion of the nanostructured gold particles over the semiconducting Ti02 support. The potential applications of ambient temperature CO oxidation catalysts include air purifier, gas sensor and fuel cell [2]. This work investigates the effects of ozone pretreatment on the performance of Au/Ti02 for CO oxidation. 

Martin R.C., Malin S.F., Bartnik D.J., Schilling A.M., Furlong S.C., Performance and use of paracorporeal fiber optic blood gas sensors, Proc. SPIE 2131 426 (1994). 

The thermal conductivity of methane is about twice as high as that of any other flammable compound of natural gas. Sensors for determining the methane number use this effect, and the principle is already in use for gas engines [2], as their performance depends heavily on the methane number. 

With the introduction of modern electronics, inexpensive computers, and new materials there is a resurgence of voltammetric techniques in various branches of science as evident in hundreds of new publications. Now, voltammetry can be performed with a nano-electrode for the detection of single molecular events [1], similar electrodes can be used to monitor the activity of neurotransmitter in a single living cell in subnanoliter volume electrochemical cell [2], measurement of fast electron transfer kinetics, trace metal analysis, etc. Voltammetric sensors are now commonplace in gas sensors (home CO sensor), biomedical sensors (blood glucose meter), and detectors for liquid chromatography. Voltammetric sensors appear to be an ideal candidate for miniaturization and mass production. This is evident in the development of lab-on-chip... 

Zuppa et al.60 have used SOMs in the assessment of data from an electronic nose. Six chemicals—water, propanol, acetone, acetonitrile, butanol, and methanol—were presented at varying concentrations to a 32-element conducting polymer gas sensor array. The output was used to train a group of SOMs, rather than a single SOM, to avoid the problems of parameter drift. One SOM was associated with each vapor, and with suitable use of smoothing filters, the SOM array was found to perform effectively. 

The model analytes, which were used to show the sensor performance of the microsystems include carbon monoxide, CO, and methane, CH4. The sensor microsystems were designed for practical applications, such as environmental monitoring, industrial safety applications or household surveillance, which implies that oxygen and water vapors are present under normal operating conditions. In the following, a brief overview of the relevant gas sensor mechanisms focused on nano crystalline tin-oxide thick-film layers will be given. 

The doping-induced effects on the gas sensing performance of nano crystalline tin oxide include, first and foremost, a conductivity decrease in clean air by one to three orders of magnitudes, and, secondly, a shift of the optimal sensor working temperature from higher to lower temperatures. 

The microhotplate was coated with a thick-film tin-oxide droplet as described in Sect. 4.1.2. To characterize the chemical-sensor performance, the chip was exposed to CO concentrations from 5 to 50 ppm in humidified air at 40% relative humidity (23.4 °C water vaporization temperature) (see Sect. 5.1.8 for a description of the gas test measurement setup). 

N. Barsan, J.R. Stetter, M. Findlay, and W. Gopel. High performance gas sensing of CO Comparative tests for semiconducting (Sn02-based) and for amperometric gas sensors . Analytical Chemistry 71 (1999), 2512-2517. 

I. Simon, N. Barsan, M. Bauer, and U. Weimar. Micromachined metal oxide gas sensors opportunities to improve sensor performance . Sensors and Actuators B73 (2001), 1-26. 

J. Kappler. Characterisation of high-performance Sn02 gas-sensors for CO detection by in situ techniques, Ph.D. thesis. University of Tubingen, Shaker-Verlag, Germany (2001). 

For example, porphyrins have been proposed as active elements in gas-sensor devices. This field has become one of the fastest growing areas in both research and commercial respects. Several authors have proposed the use of some organic materials, e.g., phthalocyanine and porphyrin derivatives (15-18) to improve the device s performance characteristics, such as low operating temperature, selectivity, and so on. 

Schottky-Barrier Diode and Metal-Oxide-Semiconductor Capacitor Gas Sensors Comparison and Performance... 

In this review the basis for the chemical sensitivity of these devices will be explored and the various device structures used for these sensors will be discussed. A survey of the performance of the diode-type and capacitor-type structures will be presented and a comparison of characteristics of these two classes of solid state gas sensors will be given. 

In this manner, a nearly universal and very nonselective detector is created that is a compromise between widespread response and high selectivity. For example, the photoionization detector (PID) can detect part-per-billion levels of benzene but cannot detect methane. Conversely, the flame ionization detector (FID) can detect part-per-billion levels of methane but does not detect chlorinated compounds like CCl very effectively. By combining the filament and electrochemical sensor, all of these chemicals can be detected but only at part-per-million levels and above. Because most chemical vapors have toxic exposure limits above 1 ppm (a few such as hydrazines have limits below 1 ppm), this sensitivity is adequate for the initial applications. Several cases of electrochemical sensors being used at the sub-part-per-million level have been reported (3, 16). The filament and electrochemical sensor form the basic gas sensor required for detecting a wide variety of chemicals in air, but with little or no selectivity. The next step is to use an array of such sensors in a variety of ways (modes) to obtain the information required to perform the qualitative analysis of an unknown airborne chemical. 

Both mechanisms explain the decrease of the resistance with the formation of a rooted or an isolated hydroxyl group out of an O2" of the lattice. In both cases it is assumed that the bonding to the Sn does not contribute to the concentration of free charge carriers, which implies that not all the surface tin atoms are in oxidation state +4 because otherwise the formation of the Sn—OH bond would need an electron from the conduction band. This assumption is reasonable because tin has two stable oxidation states, +2 and +4, and the most stable surface of tin dioxide, (110), can easily be conditioned to show atoms with both oxidation states. Furthermore it is known that defects like vacancies are an essential factor for the performance of Sn02 gas sensors and it probably is not realistic to base a mechanism on the situation on a perfect surface. Emiroglu et al. (2001) and Harbeck et al. (2003) proved the formation of rooted and isolated hydroxyl group on the Sn02 surface in the presence of water, so the final result is clear even if the exact mechanism still allows for speculation. 

When working with sensors, one of the most important issues is cross-sensitivity. Due to the sensing principle, this notably affects metal oxide gas sensors, especially in the case of measurements performed in real life conditions. To prove real life feasibility, it is necessary to keep as close as possible to the real life conditions of the application. In the present case, the real life conditions are mainly represented by the use of ambient air as a carrier gas, but also by the chosen experimental set up. 

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