Dopants conductance sensor materials

Anitha G, Subrameuiian E (2003) Dopant induced specificity in sensor behaviour of conducting polyaniline materials with organic solvents. Sens Actuators B Chem 92 49-59... 

A further interesting effect discovered in our laboratories is that the addition of low levels of a second component, or dopant ion, can lead to significant increases in the ionic conductivity [6, 30, 31]. Typically these dopant species, for example, Li, OH , and H" ", are much smaller than the organic ions of the matrix, and since the relaxation times characterizing the motion of these ions are more rapid than those of the bulk matrix itself, these materials may represent a new class of fast ion conductor. The dopant ion effect can be used to design materials for specific applications, for example, Li+ for lithium batteries and H /OH for fuel cells or other specific sensor applications. Finally, we have recently discovered that this dopant effect can also be apphed to molecular plastic crystals such as succinonitrile [32]. Such materials have the added advantage that the ionic conductivity is purely a result of the dopant ions and not of the solvent matrix itself. 

Tin (IV) oxide, Sn02, (rutile-type structure), a well-established n-type semiconductor with a wide band gap ( gap = 3.6 eV at 300 K) also has potential applications as a catalyst support,as transparent conducting electrodes,and as a gas sensor.i This material possesses many advantages, such as (i) high thermodynamic stability in air (at least up to 500 °C), (ii) low cost, and (iii) the possibility of the introduction of catalysts or dopants to enhance the sensitivity or selectivity. ... 

For example, when the PANI-SWCNT sensor was individually exposed to NHj and CO, the sensor resistance increased and decreased, respectively, while the resistance increased for gas mixture (Figure 12.24). This is because the CO (-CO+) can naturally interact with undoped nitrogen atoms in the PANI chains to produce a polaron (-NH. ) thus increasing the conductance, while NHj reacts with the dopant HCl and decrease the doping ability or conductivity for it. Since the absorption response of NH might be faster than that of CO, the resistance increased over the initial value [69]. Firstly absorbed NH gas dominantly reacts with the composite materials, and followed reaction with CO gas cannot probably function properly in the total reaction. 

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