Synthesis of Aligned Arrays of Millimeter Long, Straight Multi-Walled Carbon Nanotubes

The unique electrical and mechanical properties of carbon nanotubes (CNTs) have motivated rapid progress in nanotube synthesis and electronics in the past few years [1]. Many significant initial steps have been taken. For example, simple circuits based on MWNTs have recently been demonstrated [2-4]. However, large-scale integration on a level comparable to current microelectronics, although in principle achievable, is still an elusive goal. In this work, we take a step closer to this goal by demonstrating the controlled growth of millimeter long, straight arrays of MWNTs via mechanothermal. Currently, three general methods exist for the synthesis of SWNTs [5] Arc discharge, laser ablation, and CVD. CVD has the advantage that the catalyst structures that initiate growth can be defined lithographically, initially demonstrated by Kong et al., [6] a significant first step toward large-scale integration of nanosystems. Kong et al. used methane as the feedstock and showed that high-quality SWNTs of length about 10 μm could be grown on Si wafers; the orientation of the nanotubes was not controlled. Subsequent work by the same group showed that with use of a combination of methane, ethylene, and H2 as the feedstock, SWNTs up to 600 μm in length could be synthesized. These were also randomly oriented and contained about 10 loops along their length, i.e., were not straight but rather curly. Using the same growth recipe of methane, ethylene, and Ar feedstock CVD, the Fuhrer group recently synthesized and electrically contacted a single 300 μm long, straight SWNT [7]. Recently, the Liu group has demonstrated outstanding results in the synthesis of arrays of long SWNTs [8-12]. They developed a technique based on mechanical activation and heat-treatment (mechanothermal). Using this technique and graphite as the feedstock, they demonstrated the growth of arrays of MWNTs as large as several millimeters. In this work, we demonstrate the growth of arrays of ultra-high long, straight multi-walled nanotubes fabricated using a planetary mill and controlled furnace with graphite and Ar as the feedstock