Field emission of carbon nanotubes on anodic aluminum oxide template with controlled tube density

Abstract

The tube number density of aligned carbon nanotubes (CNTs) grown over the nanoporous anodic aluminum oxide (AAO) template can be directly controlled by adjusting the CH4/H-2 feed ratio during the CNT growth. We ascribe the variation of the tube density as a function of the CH4/H-2 feed ratio to the kinetic competition between outgrowth of cobalt-catalyzed CNTs from the AAO pore bottom and deposition of the amorphous carbon (a-C) overlayer on the AAO template. A pore-filling ratio of 18% to 82% for the nanotubes overgrown out of nanopores on the AAO template can be easily achieved by adjusting the CH4/H-2 feed ratio. Enhanced field emission properties of CNTs were obtained by lowering the tube density on AAO. However, at a high CH4 concentration, a-C by-product deposit on the CNT surface can degrade the field emission property due to a high energy barrier and significant potential drop at the emission site. (C) 2005 American Institute of Physics.