**Part 3**

**Electrical Chemical Sensor** 

212 Advances in Chemical Sensors

Zhao Z., Liu X., Chen W., Li T. (2011). *Carbon nanotubes humidity sensor based on high testing* 

Zhou X., Park Y., Huang S., Liu J., McEuen P.L. (2005). Band structure, phonon scattering,

and the performance limit of single-walled carbon nanotube transistors, Phys.Rev

*frequencies,* Sensors and Actuators A Vol. 168, pp.10–13.

Lett Vol. 95, pp.146805.

**10** 

*Russia* 

**Polymer Thin Film Chemical Sensors** 

Polymer and other organic thin films and multilayers are important for a wide range of applications, including electronics, optoelectronics and sensors. Most modern chemical sensors use semiconducting and conducting polymers because they offer cheap technology, mechanical and size advantages (Gerard et al., 2002; Hangarter et al., 2010; McQuade et al., 2000). They can form selective layers in which the interaction between the analyte substance and the polymer leads to change of a such physical parameter as conductivity. Also they can be used in devices that form circuit elements such as transistors (Dimitrakopoulos & Malenfant, 2002; Qiu et al., 2009). The widespread literature dealing with various applications of these polymers can be divided into two groups: polymers in electronic devices on the one hand (Angelopoulos, 2001) and polymers in chemical sensors based on various transduction mechanisms on the other (Bailey & Persaud, 2001). The sensor applications take advantage of the physical changes that take place in the polymers when they are exposed to various chemicals. This property has its origin in the molecular and macroscopic structure of polymers. In this paper we shall discuss only sensors based on changing of electronic

properties of polymers resulting from their interaction with different chemical agents.

Semiconducting and conducting polymers can be used as the selective layer in sensors or as the transducer itself. For example, change of polymer conductance on exposure to a gas is the sensing mechanism in a chemiresistor. They are relatively easily and inexpensively fabricated. The interaction between organic semiconductor and electrically neutral gas is used as the transduction principle in field-effect transistor (FET) sensors during two last

There are many different formats of chemically sensitive FETs both for gas and liquid applications (Gaponik et al., 1997). In FETs the current magnitude flowing through the polymer is modulated by the interaction with the analyte. The response may depend on both the conductivity and the work function of the polymer*.* It is difficult to separate influence of the various forms of modulation. For example, in (Polk et al., 2002) localized energy states can

FETs, fabricated with single-walled carbon nanotubes, have been found (Collins et al., 2000) to be sensitive to various gases – for example, oxygen, nitrogen dioxide, ammonia, etc. FETs of this type can operate as gas sensors (Qi et al., 2003) on account of their high sensitivity,

affect the value of the work function but do not affect the conductivity of the polymer.

their fast response time, and their compatibility with dense-array fabrications.

**1. Introduction** 

decades (Josowicz & Janata, 1986).

Renat Salikhov1 and Aleksey Lachinov2

*2Institute of Molecule and Crystal Physics, URC RAS,* 

*1Bashkir State Pedagogical University,* 
