The determining factors for the growth mode of carbon nanotubes in the chemical vapourdeposition process

Abstract

There are two growth modes, tip- and base-growth modes, in carbon nanotube (CNT)synthesis. We have shown that the determining factor for the growth mode is the adhesionforce of the catalytic metal particles to the substrate through a systematic study of thesynthesis in the plasma-enhanced chemical vapour deposition method (PECVD). Theexperiment was further expanded to a series of syntheses on various substrates havingdifferent surface morphologies while using thermal CVD to avoid the plasma bombardmenteffect on the adhesion force. Synthesis on substrates of sapphire, alumina depositedby atomic layer deposition (ALD), and an anodized aluminium oxide (AAO)membrane was carried out. They are similar in chemical stoichiometry, but the surfaceroughnesses are different. Only the CNTs grown on the backside of the AAOmembrane revealed the tip-growth mode regardless of the coating method, kind ofcatalyst, and thickness of the catalytic metal films due to its high roughness.