Figure 1. Single conducting polymer nanowire grown between platinum electrodes.	Figure 2. Multiple nanowires grown between gold electrodes

Solving the problem of how to incorporate single conducting polymer nanowires into electronic circuits is a current stumbling block in the development of organic nanowire devices such as field effect transistors and ultra-sensitive chemical and biological sensors. One of the current areas of research in our group concerns the development of new bottom-up fabrication techniques that will allow nanowires to be grown within a prefabricated device without the need for nano-manipulation techniques for positioning and making electrical connections to the nanowires post-synthesis. Recently, we have developed a technique that allows single (Fig.1) and multiple (Fig. 2) nanowires to bridge across the gap between two metal contacts. This has been achieved through a combination of highly controlled electrochemical nanowire growth, surface modification to encourage polymerization in site specific areas and focused ion beam milling for nanofabrication of the devices.

Besides studying the nanowires’ intrinsic electrical and morphological properties using low temperature electrical transport measurements, we are also researching their use in chemical and gas sensor applications. Conducting polymers are known to have excellent gas sensing characteristics since they are chemically active, electrically conducting and their (organic) carbon-carbon based nature means they are highly functional – for example sensitivity to specific molecular species such as trinitrotoluene (TNT). In contrast to conventional thin film polymer sensors the small diameter (50nm) and high surface area to volume ratio of the nanowires is known to give significant improvements in response time and sensitivity. To date our measurements on multiple nanowire devices show sensitivity to ammonia gas at levels as low as 0.1ppm. We are currently working to further improve on this through the development of single nanowire field effect transistors (FET’s).

Neil Kemp, Richard Newbury
and Jack Cochrane