The carbon nanotubes (CNTs) modified by the carbon particles with diameter of 120-180 nm are prepared by using hydrocarbon ion deposition techniques. Based on the investigation of scanning electron microscopy and transmission electron microscopy, the CNTs are decorated by some nanospheres with size of 120-180 nm randomly, and the full CNTs surface besides the area of nanosphere is coated by the graphene stacks with size of 10-15 nm. The nanospheres are composed of several nanoparticles of graphene stacks and are seamless connected with graphene stacks. The sparse distribution CNTs on Si substrate is crucial for the formation of carbon nanospheres. The formation of carbon nanospheres proceeds through the following three stages: the formation of graphene nanoparticle on CNTs surface and silicon substrate – the migration of active hydrocarbon groups towards the surface of the CNTs deposition zone at high temperature – the formation of carbon nanospheres by the aggregating hydrocarbon active groups.

The field emission (FE) of the carbon nanotubes (CNTs) modified by hydrocarbon ion treatment with an energy of 80 eV has been demonstrated. Compared with untreated CNTs, the turn-on field and the threshold field of the modified CNTs decreased significantly. Scanning electron microscopy and transmission electron microscopy indicate that, after hydrocarbon ion treatment, the CNTs are coated by amorphous carbon layer at 300°C of substrate temperature and nanoparticles of graphene stacks at 700°C. It is considered that both amorphous carbon and stacked graphene coating layer can decrease the effective surface work function of CNTs and thus increase FE.