Growth of carbon nanotubes on metallic substrates using a substrate-shielded microwave plasma-enhanced chemical vapor deposition

Aligned carbon nanotubes (CNTs) were grown with unprecedentedly high growth rates on copper and nickel substrates using a microwave plasma-enhanced chemical vapor deposition system. A simple technique, involving a microwave shield, was used to prevent the reflection of microwaves from the metallic substrates. In the mean time, the shield still allows the growth species to reach the substrate or growing CNTs. There is basically no growth of CNTs when the shield is not used. This is due to the undesirable interaction between the metals and plasma during the growth. On the other hand, such a simple use of microwave shielding leads to the growth of very long aligned CNTs, up to 310 m, and an unprecedentedly high growth rate of 62 mmin. The key factors that contribute to the enhanced growth are discussed. The resulting CNTs, exhibiting very high aspect ratios, also show excellent field emission properties, including a turn-on field (at 10 μAcm ²⁺), a threshold field (at 1 mAcm ²⁺), and a maximum current density (at 2.12 V/μm) of 1.08 V/μm, 1.31 V/μm, 27.9 mAcm ²⁺, respectively.