Response gas sensors

Example polymers in fast-response gas sensors References... 

R. Rojas and N. J. Pinto, Using electrospinning for the fabrication of rapid response gas sensors based on conducting polymer nanowires. Sens. J., IEEE, 8, 951-953 (2008). 

Yu Q, Wang K, Luan C, Geng Y, Lian G, Cui D (2011) A dual-functional highly responsive gas sensors fabricated from Sn02 porous nanosolid. Sens Actuators B 159 271-276... 

Lantto, V., P. Romppainen, and S. Leppiivuori. Response Studies of Some Semiconductor Gas Sensors under Different Experimental Conditions. Sensors Actuators 15 (1988), pp.. 347-357. 

The experimental studies of the surface properties of monocrystals of oxides of various metals recently conducted at well-controlled conditions [32, 210] enable one to proceed with detailed analysis of separate effects of various factors on characteristics of semiconductor gas sensors. In this direction numerous interesting results have been obtained regarding the fact of various electrophysical characteristics of monocrystalline adsorbents on the value of adsorption-related response. Among these characteristics there are crystallographic orientation of facets [211], availability of structural defects, the disorder in stoichiometry [32], application of metal additives, etc. These results are very useful while manufacturing sensors for specific gases with required characteristics. 

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

To define a feature extraction procedure it is necessary to consider that the output signal of a chemical sensor follows the variation of the concentration of gases at which it is exposed with a certain dynamics. The nontrivial handling of gas samples complicates the investigation of the dynamics of the sensor response. Generally, sensor response models based on the assumption of a very rapid concentration transition from two steady states results in exponential behaviour. 

Some bead materials possess porous structure and, therefore, have very high surface to volume ratio. The examples include silica-gel, controlled pore glass, and zeolite beads. These inorganic materials are made use of to design gas sensors. Indicators are usually adsorbed on the surface and the beads are then dispersed in a permeation-selective membrane (usually silicone rubbers). Such sensors possess high sensitivity to oxygen and a fast response in the gas phase but can be rather slow in the aqueous phase since the gas contained in the pores needs to be exchanged. Porous polymeric materials are rarer and have not been used so far in optical nanosensors. 

Fig. 10.8 Dynamic response of meso PS gas sensors of different porosities to low concentrations of N02. Measurements were per-...

It is well established, that the poor selectivity of tin-oxide sensors can partly be overcome by adding catalysts to the sensitive layer. Most common additives are noble metals like gold (Au), platinum (Pt) or palladium (Pd). They can be mixed with the tin oxide during paste formation before deposition. The influence of dopants on the gas sensor response is still subject to debates. The two most established mechanisms are the spill-over and the Fermi-level mechanism [82]. 

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... 

R.E. Cavicchi, J.S. Suehle, K.G. Kreider, M. Gaitan, and P. Chaparala. Optimized temperature-pulse sequences for the enhancement of chemically specific response patterns from micro-hotplate gas sensors , Sensors and Actuators B33 (1996), 142-146. 

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. 

Nakshima et al. have fabricated p-n junction devices by employing A1 implantation to yield a p-doped layer in n-type 6H-SiC [66]. A Pt layer on top of the p-type ohmic contact (PtSi) provided both protection and a catalytic metal contact to create a chemical gas sensor device. A response (30 and 60 mV, respectively) was obtained to both 50 ppm and 100 ppm of ammonia in nitrogen at 500°C. 

It is possible to influence both the position of the base line and the size of the gas response by the application of a negative potential on the substrate [97, 98]. The drain current-voltage characteristics of a chemical gas sensor based on an... 

Chemical gas sensors are characterized by properties such as sensitivity and selectivity, which has been discussed in Section 2.2. Properties like speed of response and long-term stability are of crucial importance for applications such as combustion control in car exhausts or flue gases from boilers. 

Aishima, T. (1991) Aroma discrimination by pattern recognition analysis of responses from semiconductor gas sensor array. J. Agric. Food Chem. 39 752-756. 

Linearity of Response and Reaction Products. The response vs. concentration curves obtained for CO, NO and NO2 gas sensor cells are depicted in Figures 5, 6 and 7 respectively. In all instances good linearity over the range studied was observed between current and partial pressure of each of the above gases (as depicted by equation (k)). The proportionality constants, K, with standard de-... 

Other, secondary effects skew the response of the piezoelectric sensor when it is used as a gas sensor. These can be described phenomenologically as the hydrostatic effect (p), the frictional effect (x), and the sorption effect (m) ... 

One could immobilize the urease layer on top of a Severinghaus electrode for CO2 or NH3 (Section 6.3.2) and use the device as an enzymatic-potentiometric gas sensor. The primary disadvantage of such an arrangement would be its slow response time. A more direct way is through the detection of the ionic species resulting from the hydrolysis of ammonia and carbon dioxide. 

Severinghaus electrodes have found wide application in clinical analysis. It is pertinent to mention here that the general principle of permeation of the gas through a hydrophobic membrane followed by its detection (with or without its solvolysis) has been used with different types of internal sensors, for example, optical, ampero-metric, conductimetric, or a mass sensor. The choice of the internal sensing element depends on the circumstances of the application in which the gas sensor would be used, such as the required time response, selectivity considerations, complexity of instrumentation, and so on. 

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