We characterize the dynamic growth rate behavior of a carbon nanotube (CNT) forest grown by means of optical interference phenomena. The CNT growth rate increased with an increase in CNT length at the initial stage and became stabilized after the CNT length was about 2 µm. Then the growth rate started to decelerate, passing the critical growth length in an almost linear manner. The termination length of the carbon nanotube was also precisely estimated by fitting the data of growth rate of carbon nanotubes to time. It was found that the CNTs show a transition from straight to curly nanotubes that is related to the decrease in the growth rate. The use of an in situ optical monitoring method has made possible the delicate length control of carbon nanotubes independent of the growth rate.
Regular arrays of freestanding single carbon nanotubes (CNTs) were prepared on Ni dot arrays by dc plasma-enhanced chemical vapour deposition. The size of the Ni dot was reduced for single CNT growth by means of conventional photolithography and a lateral wet-etch process. The vertical alignment of a single CNT was directly dependent on the location of the catalyst metals. Using this method, well-separated and well-defined regular arrays of freestanding CNTs can be fabricated and the process can be scaled up at a lower cost than electron beam lithography, which is encouraging for applications in field emitters and nanoelectrodes.
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