Because of their prominent electrical, chemical and mechanical properties, carbon nanotubes (CNT) have been studied to realize their practical application. Recently, there has been considerable concentration on the use of e.g. CNT-based composites or nano-electro-mechanical-systems. Thus, it is still necessary to rationally grow CNT with well defined architectures and performances without a decrease of CNT quality.
In this presentation, we present our recent studies of large scale growth of vertically aligned CNT arrays. We employed atmospheric thermal chemical vapor deposition (CVD), which can independently control the process parameters, so that we can investigate the effect of various factors on final growth features. We used acetylene or ethylene as a carbon feedstock and argon and hydrogen as carrier gases. We mainly investigated the effects of thicknesses of catalyst film or underlayers, flow rate of feedstock, and growth time. After the growth, scanning electron microscopy and transmission electron microscopy were mainly used for structural characterization. A Raman scattering spectroscopy was also used to evaluate CNT quality or estimate CNT diameter distribution. To investigate the effect of substrate surfaces, AFM was used before and after the CVD process.
The CNT grown at 750 C for 15 min using acetylene gas showed the longest CNT array. It is noteworthy that as grown CNT produced clear resonant peaks at the low frequency region of Raman spectra. It is found that CNT length was highly dependent on gas composition, flow rate, and underlayer thicknesses. As a result of growth efforts, we have successfully made highly selective patterned CNT architectures using electron beam lithographic technique. These results can be developed toward practical applications as we mentioned.
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