Alignment Characteristic and Mechanism of Carbon Nanotubes Synthesized by Hot Filament Chemical Vapor Deposition in a CH_4/H_2 Plasma

摘要

Carbon nanotube films have been synthesized on nickel coated silicon wafer substrate using hot filament chemical vapor deposition under various bias and discharge conditions in a CH_4/H_2 gas mixture. Growth of carbon nanotubes aligned at different angles with respect to the substrate normal has been achieved by applying a negative bias to the substrate holder and initiating a DC plasma discharge between filament and substrate. The nanotubes located far enough from the substrate edges are completely vertically aligned, while the nanotubes around the sample edges are pointing away from the sample center and the alignment angle depends on the distance between the nanotube location and the sample edge. The orientation of the nanotubes appears to be determined by the direction of the electric field lines on the surface of the substrate. Only randomly oriented nanotubes can be obtained when no bias or a positive bias was applied to the substrate holder. The results suggest that the bombardment of ions is the determining factor in the alignment of CNTs.