The relationship between field-emission characteristics and defects measured by Raman scattering for printed carbon-nanotube cathodes treated by plasma and laser was investigated. The Raman intensity ratio of the D to G bands (I-D/I-G) was 0.71 in the case of an untreated sample. With laser irradiation, the I-D/I-G ratio increased to 0.76, which resulted in the increase of the emission-current density. Moreover, with the plasma and additional laser treatment, the I-D/I-G ratio further increased to 1.15, which resulted in the much higher increase of the emission current density. This result indicates that the induced defects, acting as emission sites, together with the improved field-enhancement factor by the surface treatment, play important roles for increasing the field-emission current density. (c) 2008 American Vacuum Society.