Direct Growth of Carbon Nanotubes on Metal Supports by Chemical Vapor Deposition

Abstract

Since their discovery (Iijima, 1991), carbon nanotubes (CNTs) have been attracted much attention due to their excellent mechanical, physical and chemical properties. In the past thirty years, thousands of articles have been published to discuss their growth, properties, and applications. For the CNT growth, there are three main methods: arc discharge, laser ablation and chemical vapour deposition (CVD). Compared with the first two methods, CVD was regarded as the most promising one for industrial application with low cost, although it usually introduces more defects in CNTs during the growth process. Furthermore, CVD is the preferred choice to grow patterned CNTs on substrates for nanoelectronic applications. Typically, nanotubes are grown by CVD on metal catalyst particles or islands that are deposited on top of semiconducting or insulating materials, such as alumina, silicon and silicon oxide. These non-conducting substrates assist in the formation of small islands or nanoparticles of metal catalyst on their surfaces, which is necessary for the CNT growth. However, for many applications, such as displays, cell electrodes, gigascale interconnects, high electrical and thermal conductivities are required, usually needing a conductive substrate to connect with CNTs. Furthermore, minimization of the contact resistance between metal substrate and CNTs is also a major challenge in nanoelectronics. Apart from geometrical factors, contact resistance depends mostly on alignment of Fermi energy levels of CNT and substrate. Since multi-walled CNTs are predominantly metallic (Single-walled CNTs can be adjusted to be metallic by controlling their structure), a metallic substrate to connect with CNTs is expected to have least contact resistance. In order to assemble the CNTs on metal substrate with fine patterned architectures, the obvious and effective way would be to grow CNTs directly on metal substrates. Herein, the current development of direct growth technique and its applications were summarized.