The determining factors for the growth mode of carbon namotubes in the chemical vapour deposition process

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 adhesion force of the catalytic metal particles to the substrate through a systematic study of the synthesis in the plasma-enhanced chemical vapour deposition method (PECVD). The experiment was further expanded to a series of syntheses on various substrates having different surface morphologies while using thermal CVD to avoid the plasma bombardment effect on the adhesion force. Synthesis on substrates of sapphire, alumina deposited by atomic layer deposition (ALD), and an anodized aluminium oxide (AAO) membrane was carried out. They are similar in chemical stoichiometry, but the surface roughnesses are different. Only the CNTs grown on the backside of the AAO membrane revealed the tip-growth mode regardless of the coating method, kind of catalyst, and thickness of the catalytic metal films due to its high roughness.