We report on the structural variation and the concomitant change in the emission characteristics of carbon films with two nano-sized constituents, nanotubes and nanoparticles, induced by the addition of ammonia to the precursor of hot-filament chemical vapor deposition. The increase of the ammonia concentration resulted in a large morphological change due to the change in the relative abundance of two constituents and moreover, a deterioration of carbon layers making up the nanoparticles and nanotubes. The systematic variation of the electron emission accompanying the structural change indicated that the graphitic-sheet quality was one of the important factors that determined the emission from the nano-sized constituents.