In this work, the authors studied electron field emission from well-ordered ZnOx nanoparticles decorated on vertically aligned carbon nanotubes (CNTs). The vertically aligned CNTs are grown by thermal chemical vapor deposition with gravity effect and water-assisted etching at 700 degrees C. ZnOx nanoparticles are then decorated on CNTs by exposing CNTs to evaporated ZnOx vapor under H-2/Ar ambient at different pressures. The effect of process pressure on structural, chemical, and electron field-emission properties of ZnOx decorated on vertically aligned CNTs is characterized. ZnOx nanoparticles are observed to be deposited on top of CNTs. Low pressure (5-20 torr) results in fine ZnOx nanoparticles 5-15 nm in diameter uniformly distributed on the cap of CNTs, whereas high pressure (>100 Torr) results in large ZnOx particles and agglomeration on CNTs. In addition, electron field emission from vertically aligned CNTs is found to be further improved by ZnOx nanoparticle decoration at low pressure, and a low turn-on electric field of similar to 1.5 V/mu m is observed. On the other hand, large ZnOx particles decorated at high pressure result in electron field-emission degradation. The effects of ZnOx nanoparticles on electron field emission from CNTs have been explained based on the Fowler-Nordheim analysis and plausible hypotheses have been proposed. (C) 2008 American Vacuum Society.