Surface roughness evolution and growth mechanism of carbon films from hyperthermal species

The roughness evolution of carbon films deposited from hyperthermal species was investigated by AFM. 10 eV C deposition at normal incidence angle starts with formation of 10 nm high islands followed by continuous, sp2 rich films at larger doses with essentially the same feature height and film roughness. 40 eV C deposition at normal incidence angle (0°) forms sp3 rich, atomically smooth films, which become sp2 rich and rough at oblique angles (≥ 60°). The limitations of currently available molecular dynamic simulations prevent their use to describe the island formation during 10 eV C bombardment. Dedicated calculations probing the effect of incidence angle on 40 eV C deposition exhibit similar trends to the experimental data i.e. decrease of the sp3 fraction and increase of the roughness with increasing incidence angle. The results are in accord with the “subplantation” scheme, linking roughness and sp2 bonding to surface entrapment. Implications on recent works discussing growth mechanisms or surface smoothening are given.