Prospects of conducting polymers in molecular electronics

Molecular electronics (ME) is rapidly evolving from physics, chemistry, biology, electronics and information technology. This is because the present-day advanced silicon chip can store about 16 million bytes of information within an area less than 1 cm(2). Organic materials such as proteins, pigments and conducting polymers (CPs) have been considered as alternatives for carrying out the same functions that are presently being performed by semiconductor silicon. Among these, CPs have demanded the maximum attention. These ME materials differ from conventional polymers by having a delocalized electronic structure that can accommodate charge carriers such as electrons and holes. Besides, these conjugated electronic materials exhibit Peierl's instabilities due to built-in highly anisotropic interactions. It has been proposed that electrical conduction in CPs occurs via non-linear (or topological) defects (solitons/polarons) generated either during polymerization or as a consequence of doping. Solitons and polarons have recently been shown to have implications in the technical development of ME devices. CPs such as polypyrroles, polythiophenes and polyanilines have been projected for applications for a wide range of ME devices. One of the main reasons for such a wide-spread interest is due to the reported observation that these interesting electronic materials exhibit full range of properties from insulator to superconductor depending upon chemical modification. CPs have been found to have applications as optical, electronic, drug-delivery, memory and biosensing devices. The major challenge confronting the material scientists including chemists and physicists is how do the properties of these electronic materials differ from those of conventional semiconductors. Another advantage lies in the fact that these materials possess specific advantages such as high packing density, possibility of controlling shape and electronic properties by chemical modification. Our group has been actively working towards the application of CPs to Schottky diodes, metal-insulator-semiconductor devices and biosensors for the past about 10 years. This paper is a review of some of the results obtained at our laboratory in the area of CP ME. (C) 2002 Elsevier Science B.V. All rights reserved.