ZnOx-decorated vertically aligned carbon nanotubes prepared by vapor phase transport technique

In this work, vapor phase transport technique for well ordered ZnO_x nanoparticles decoration on vertically aligned carbon nanotubes (CNTs) is developed. Vertically aligned CNTs are grown by thermal chemical vapor deposition (CVD) with gravity effect and water assisted etching at 700 degC. Vertically aligned CNTs of 8-15 nm in diameter and ~80 mum long are achieved with low defects and catalyst residues. ZnO_x is then decorated on CNTs by exposing CNTs to evaporated ZnO_x vapor under H₂/Ar ambient at different pressures. The effect of process pressure on structural, chemical and electron field emission properties of ZnO_x decorated vertically aligned CNTs are characterized. Zn nanoparticles are observed to be deposited on top of CNTs. Low pressure (5-20 Torr) results in fine ZnO_x nanoparticles of 5-15 nm in diameter uniformly distributed on the cap of CNTs while high pressure (Gt100 Torr) result in large ZnO_x particles and agglomeration on CNTs. In addition, electron field emission from vertically aligned CNTs is found to be further improved by ZnO₂ nanoparticle decoration at low pressure and low turn-on electric field of ~1.5 V/Wm is observed. On the other hand, large ZnO_x particles decorated at high pressure result in electron field emission degradation.