The authors measured the field emission (FE) and secondary-electron emission (SEE) of carbon nanotubes (CNTs) after coating with wide-band-gap materials, such as MOO and CsI. The FE was increased successively after MgO coating and subsequent CsI coating for both single-walled and multiwalled CNTs. SEE also showed the same increase after monolayer and double-layer coating. The field-enhancement factor, beta, was calculated from the Fowler-Nordheim equation of FE results, and SEE yield, delta, was measured directly from the SEE measurements, for both monolayer- and double-layer-coated nanotubes. Both values showed similar trends that may be described as follows: (1) The trend for the double-layer-coated CNTs was higher than that for the mono layer-coated CNTs. (2) The trend for the single-walled CNTs was higher than that for the multiwalled CNTs. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3093886]