Electrically Conducting Polymeric Nanostructures: Techniques for One-Dimensional Synthesis
Read full article onlineFull Article
As the desire for smaller components heightens, techniques to fabricate materials and building blocks for materials that take advantage of the nanorealm continue to proliferate. Since the discovery of carbon nanotubes in 1991, nanoscale objects fabricated from various compounds with various shapes have emerged. Although many synthetic techniques have surfaced to fabricate materials with nanoscale dimensions, there is a significant need to then arrange these materials into active and useful materials. Because of the requirement of smaller components for microelectronics, electrically conducting polymers have captured interest as materials of which nanoscale objects would be highly desirable.
Since the discovery that polyacetylene can be doped so that the electrical conductivity can be controlled over 11 orders of magnitude, many studies have been carried out to better understand and improve the conductivities and properties of these polymers. Intrinsically conducting polymers have attracted a great deal of interest as potential chemical sensors, single-molecular transistors, electron emitting flat panel displays, and other microelectronic devices. Intrinsically conducting polymers are attractive in many applications as their conductivity can be tuned by chemical manipulation of the polymer backbone, by selection of the dopant, by alteration of the doping degree, or by mixing with a matrix material producing a composite. In addition, conducting polymers offer advantages over metals and other semiconducting materials because of their good mechanical properties, stability, ease of processing, and relatively low price. Because of the desirable properties of intrinsically conducting polymers and the elevated conductivity by molecular alignment, a number of techniques have arisen to synthesize 1-D nanostructures of conducting polymers. In this chapter we will review techniques that are currently available to synthesize 1-D nanoscale structures of electrically conducting polymers both in solution and on surfaces.
As conventional lithographic techniques cannot be applied to produce conducting lines in the sub-100-nm regime, the ability to render high quality 1-D wires of π-conjugated polymers with these dimensions is of great interest. Additionally, as the conductivity of π-conjugated polymers is dictated in part by molecular alignment, and the radius of gyration of polymers is generally in the tens of nanometer range, 1-D nanostrutures of π-conjugated polymer would likely afford elevated conductivities. Although other methods do exist, techniques to fabricate 1-D nanostructures of conducting polymers evolve from the use of templates in the form of either solid materials or arranged molecules. We will begin our discussion with methods to produce 1-D nanostructures of conducting polymers in bulk solution by using “hard” or “soft” templates, and follow with techniques to fabricate 1-D nanostructures directly on surfaces.