Growth Velocity and Direct Length-Sorted Growth of Short Single-Walled Carbon Nanotubes by a Metal-Catalyst-Free Chemical Vapor Deposition Process

We report on the observation of a very low growth velocity of single-walled carbon nanotubes (SWNTs) and consequently the direct length-sorted growth and patterned growth of SWNTs by using a metal-catalyst-free chemical vapor deposition (CVD) process proposed recently by our group, in which SiO2 serves as catalyst. We found that the growth velocity of the SWNTs from SiO2 catalyst is only 8.3 nm/s, which is about 300 times slower than that of the commonly used iron group catalysts (Co as a counterpart catalyst in this study). Such a slow growth velocity renders direct length-sorted growth of SWNTs, especially for short SWNTs with hundreds of nanometers in length. By simply adjusting the growth duration, SWNTs with average lengths of 149, 342, and 483 nm were selectively obtained and SWNTs as short as similar to 20 nm in length can be grown directly, Moreover, comparative studies indicate that the SiO2 catalyst possesses a much longer catalytic active time, showing sharp contrast with the commonly used Co catalyst which quickly loses its catalytic activity. Taking advantage of the very slow growth velocity of the SiO2 catalyst, patterned growth of SWNT networks confined in a narrow region of <5 mu m was also achieved. The short SWNTs may show intriguing physics owing to their finite length effect and are attractive for various practical applications.