Continuous Synthesis of Carbon Nanotubes Using a Plasma-Enhanced Chemical Vapor Deposition System at Atmospheric Pressure

Continuous synthesis of carbon nanotubes (CNTs) without replenishment of catalyst was investigated using a plasma-enhanced chemical vapor deposition system at atmospheric pressure for the first time. CNTs were successfully grown in a continuous manner on an iron-catalyzed substrate up to a height of 750 µm by two cycle of continuous growth. In the first growth step, the height of the CNT forest was 427 µm under the optimum synthesis conditions. The high-density Fe nanoparticles remained on the surface after the first growth step, although the density was slightly reduced. The second growth step was performed after harvesting the grown CNTs mechanically. The height of the CNTs obtained in the second growth step was 320 µm, which is 100 µm shorter than that of the CNTs obtained in the first growth step. By the same procedure, the third growth step was carried out. Unlike the results of the first two growth steps, the CNT forest was sparsely formed with a height of less than 30 µm, suggesting that the catalytic material was used up during the second growth step. The results show that a 20-nm-thick catalytic material was consumed for the growth of CNTs up to a height of 750 µm. This study opens up the possibility of continuous synthesis of CNTs and mass production at low cost for industrial applications.