Conducting atomic force microscopy (C-AFM) has been used to compare the nanoscale electron emissions from hydrogen-free (a-C), hydrogenated (a-C:H), and tetrahedral (ta-C) diamond-like carbon films. The current measurements are performed on the locations where the low-resistant surface layers are removed. The measurements show the uniform electron emissions from a-C:H and ta-C films. The inhomogeneous electron emission from the a-C film is primarily due to the conducting graphite clusters inside the film. The analysis of Fowler-Nordheim tunnelling currents indicates the formation of filament-like emission channels inside these films. The implications of film structures for electron field emissions are discussed. (c) 2004 Elsevier B.V. All rights reserved.