Effect of ion bombardment on microstructures of carbon nanotubes grown by electron cyclotron resonance chemical vapor deposition at low temperatures

Abstract

Vertically aligned multi walled carbon nanotubes (MWNTs) were synthesized by electron cyclotron resonance chemical vapor deposition on Ni-coated glass substrates at temperatures as low as 400degreesC. Negative self-biases were applied to the substrates by radio-frequency (RF) plasma for ion bombardment of the growing surface. It was observed that ion bombardment by RF biasing to the substrates had a great effect upon the growth of carbon nanotubes and their morphologies. High-resolution transmission electron microscopy revealed that the degree of ordering of graphene layers in the synthesized nanotubes increased with RF bias. Raman spectroscopic analyses indicated that the shortening of C-C bonds within the graphene layers of the MWNTs occurred at larger negative biases, which seemed to result from removal of bonded hydrogen from the MWNTs by ion bombardment.