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

Fluorine containing amorphous carbon films (CFx, 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 CFx films are amorphous. Results from X-ray photoelectron spectroscopy and Raman spectroscopy indicate a graphitic nature of CFx 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%.