Plasma nanotexturing of amorphous carbon films by reactive ion etching

Amorphous carbon thin films were grown by magnetron sputtering on crystalline Si and fluorine-doped tin oxide (FTO) substrates and annealed at 600 °C in vacuum. Subsequently, the films were subjected to SF6 plasma nanotexturing processes using different secondary gases such as H2, O2, and Ar. The samples were characterized by profilometry, atomic force microscopy, Raman spectroscopy, FTIR spectroscopy, and contact angle measurement. The samples have shown nanostructured surface patterns that strongly depended on the secondary plasma gas used (H2, O2, or Ar); the films subjected to the SF6 + Ar plasma nanotexturing presented the highest surface roughness. Investigation of the atomic structure indicated that the annealing process is responsible for a significant increase in sp2 hybridization of C. The contact angle measurement results have revealed the hydrophilic to hydrophobic transition owing to the annealing process. In contrast, super hydrophilic behavior was observed after the plasma nanotexturing processes. The increase in both the surface roughness and hydrophilicity of these nanotextured carbon thin films are highly desirable characteristics for their application as counter-electrodes in dye-sensitized solar cells and batteries.