Low-Temperature Growth of Carbon Nanotube by Plasma-Enhanced Chemical Vapor Deposition using Nickel Catalyst

Abstract

Carbon nanotubes (CNTs) were grown on silicon (Si) substrates with a native oxide layer using a nickel (Ni) catalyst by the plasma-enhanced chemical vapor deposition method at 550 and 650°C. Multiwall CNTs with a large inside hollow core were observed with samples deposited on Si substrates with a native oxide layer. However, no CNT growth was observed with samples deposited on Si substrates without a native oxide layer due to the formation of Ni-silicide. The native oxide layer was believed to act as the diffusion barrier and to suppress the formation of Ni-silicide. The typical diameter and length of CNTs ranged from about 30 to 100 nm and 2 to 3 µm, respectively. The size of CNTs was more strongly dependent on the thickness of the Ni layer than on the growth temperature. The surface roughness and amount of surface defects decreased with increasing process temperature. We performed a post hydrogen plasma treatment for the purification of raw CNTs. The post hydrogen plasma treatment successfully removed residual graphite particles and/or metallic impurities without significant damage to the CNTs.