Structure evolution from nanocolumns to nanoporous of nitrogen doped amorphous carbon films deposited by magnetron sputtering

Different nitrogen doped amorphous carbon (CNx) films were obtained by magnetron sputtering of carbon target in argon and nitrogen atmosphere at the increasing negative bias voltages from 0 to 150 V. The films structures have experienced great change, from the novel column to nanoporous structure at the bias voltage of 0 V to the porous structure at 150 V. The proposed growth process was that the CNx nuclei grew at 0 V acted as the “seeds” for the growth of the nanocolumns, and ion etching effects at 150 V induced the formation of nanoporous structures. Furthermore, a comparison study showed that the field emission properties of the CNx films were related with the introduction of the nitrogen atoms, the size and concentration of sp² C clusters and the surface roughness. The films with rougher surface have lower threshold field.