Growth mechanism and orientation control of well-aligned carbon nanotubes

Carbon nanotube films have been synthesized on nickel coated silicon wafer substrate by hot filament chemical vapor deposition under various conditions in a CH4/H-2 gas mixture. Randomly oriented nanotubes have been obtained with no discharge or with dc glow discharge using the substrate holder as the anode. By initiating a dc glow discharge with the substrate holder as the cathode, well-aligned carbon nanotubes with various orientation angles have been achieved. The nanotubes located far enough from the sample edges are completely vertically aligned, while the nanotubes around the sample edges point away from the sample center and the alignment angle depends on the growth conditions and the distance from the sample edge. The alignment orientation of the nanotubes appears to be determined by the direction of the electric field lines on the sample surface. (C) 2003 Elsevier Science B.V. All rights reserved.