4. Recent Trends in the Processing and Applications of Carbon Nanotubes and C-MEMS-Based Carbon Nanowires

In this chapter, we review the processing of carbon nanotubes from the first reported work to the present and cover a myriad of CNT applications. For CNT processing, the three most used techniques, i.e., arc discharge, laser ablation, and chemical vapor deposition for both multiwall and single-wall CNTs are detailed. We will learn that these fabrication techniques often need to be adapted to serve a specific application. We analyze processing techniques for CNT application in gas sensors, biosensors, optical sensors, supercapacitors, micro-/nanoelectronics, and in nanoelectromechanical systems. Since the poor adhesion between CNTs and substrates often limits their application, we also survey the work of researchers who developed surface modification techniques. Although CNT research is quite a mature field, it still faces major challenges, including making ohmic contacts, selecting for a precise tube diameter and a precise tube length as well as problems with nanotube positioning accuracy. This explains why the large-scale manufacture of CNT devices remains a daunting task. Due to these limitations in the use of CNTs in a manufacturing environment, we propose an alternative, i.e., C-MEMS or carbon-MEMS. A common C-MEMS fabrication process starts with photolithography of a high-carbon content photosensitive polymer precursor and it is followed by carbonization, also called pyrolysis, of the patterned polymer. Carbon nanowires (CNWs), fabricated by electrospinning of suspended polymer nanowires and photolithography of the contact pads for the suspended wires to attach too and the subsequent pyrolysis of this hybrid construct, have the potential of alleviating some of the aforementioned problems with CNTs. We review the C-MEMS fabrication process of CNWs in detail, compare their properties with CNTs, and discuss their various applications in this chapter.