CFx thin solid films deposited by high power impulse magnetron sputtering: Synthesis and characterization

Fluorine containing amorphous carbon films (CF_x, 0.16 ≤ x ≤ 0.35) have been synthesized by reactive high power impulse magnetron sputtering (HiPIMS) in an Ar/CF₄ atmosphere. The fluorine content of the films was controlled by varying the CF₄ partial pressure from 0 mPa to 110 mPa at a constant deposition pressure of 400 mPa and a substrate temperature of 110 °C. The films were characterized regarding their composition, chemical bonding and microstructure as well as mechanical properties by applying elastic recoil detection analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and nanoindentation. First-principles calculations were carried out to predict and explain F-containing carbon thin film synthesis and properties. By geometry optimizations and cohesive energy calculations the relative stability of precursor species including C₂, F₂ and radicals, resulting from dissociation of CF₄, were established. Furthermore, structural defects, arising from the incorporation of F atoms in a graphene-like network, were evaluated. All as-deposited CF_x films are amorphous. Results from X-ray photoelectron spectroscopy and Raman spectroscopy indicate a graphitic nature of CF_x films with x ≤ 0.23 and a polymeric structure for films with x ≥ 0.26. Nanoindentation reveals hardnesses between ~ 1 GPa and ~ 16 GPa and an elastic recovery of up to 98%.