The field emission behavior of base-model well-aligned carbon nanotubes (Base-CNTs), curled carbon nanotubes (Curled-CNTs), and tip-model well-aligned CNTs (Tip-CNTs) was examined. The nanotubes were fabricated by means of direct current plasma-enhanced chemical vapor deposition using different ammonia (NH3) Pre-treatment plasma currents. The turn-on electric field values required to obtain a 10-nA current for Base-CNTs, Curled-CNTs, and Tip-CNTs were determined at 3.8, 4.3, and 4.9 V/mu m, respectively. The field enhancement factor of Base-CNTs, calculated from a Fowler-Nordheim plot, was higher than that for the Curled-CNTs and Tip-CNTs. In the presence of a strong electric field, argon ion irradiation permanently straightened the as-grown Curled-CNTs films. The straightening process enhanced the emission properties of the as-grown Curled-CNTs films by decreasing the turn-on field and increasing the total emission current. Thus, morphology parameters of the MWNTs significantly affect the emission properties of CNTs. (c) 2005 Elsevier B.V. All rights reserved.