Effects of Process Conditions on the Morphology of Coating Layer Fabricated on the Surface of Carbon Nanotubes via an In-flight Coating Method

Carbon nanotubes (CNTs) coated with other materials are expected to be useful in many applications. The performance of coated CNTs is known to depend on the morphology of the coating layers. In this study, the effects of the conditions of a gas-phase method of coating via plasma-enhanced chemical vapor deposition on the surface of CNTs suspended in gas on the morphology of CNTs are investigated. An increase in the concentration of the precursor for the coating material is found to enhance the formation of coating layers consisting of particulate materials. An increase in the pressure of the plasma reaction zone also leads to a thicker particulate coating layer. In contrast, dense and continuous coating layers are obtained when the plasma reaction is given a longer time. The thickness of such layers tends to increase with time. The difference in the morphologies is considered to be due to the frequency of nuclei formation, and the rate and time allowed for the growth of these nuclei. Each of the morphologies observed here is interesting from the viewpoint of various applications; therefore, the findings from this study will provide useful information on techniques for controlling the morphology of coatings.