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.