Growth Mechanisms of Horizontally Aligned Carbon Nanotubes by CVD

The selective production of long, horizontally aligned carbon nanotubes (>1mm) or short, randomly oriented carbon nanotubes (<50μm) was achieved in a chemical vapor deposition process by influencing the catalyst pretreatment and reaction conditions. A detailed investigation was undertaken to elucidate the mechanism yielding the two different morphologies. It was found that the duration of the catalytic growth of a nanotube plays a vital role; i.e., the actual growth period of long nanotubes is significantly higher (up to 15 minutes or more) compared to short nanotubes (10 seconds or less). Alignment with the gas flow occurs only when a nanotube reaches a critical length, which suggests that short growth durations limit not only the length of CNTs but also their alignment with the gas flow. Furthermore, it is concluded that differences in the nanoparticle’s catalytic lifetime is the most probable factor determining the extension of growth duration and lengths to obtain long, horizontally aligned CNTs. This work represents a step forward towards the integration of CNTs in electronic applications.