Carbon nanotube (CNT) cathode surfaces have been exposed to Ar plasma and the emission characteristics were measured. When a CNT cathode was exposed to Ar plasma for 3 min, the emission characteristics were improved. The emission current increased after an Ar plasma treatment for 3 min by three orders of magnitude from 9.0 x 10(-5) to 3.3 x 10(-1) mA/cn(2) at 4.0 V/mum with a decrease in turn-on voltage from 3.3 to 1.7 V/mum. According to scanning electron microscopy images, entangled CNT bundles were raveled out by Ar plasma treatment. (C) 2004 American Vacuum Society.