Structure evolution of fluorinated diamond-like carbon films prepared at varying source gas flow ratios

The F-DLC films with high fluorine content were prepared by reactive magnetron sputtering with trifluromethane (CHF3)/argon as source gases and pure graphite as a target. The influence of source gas flow ratios on the film bonding configuration, sp2/sp3 hybridization ratio and optical band gap were investigated by Raman, infrared absorption, UV–VIS spectra and XPS spectra. The results show that the skeleton structures of the samples were aromatic rings with attached fluorine (F-aryl), and the strongest vibration modes in CFx modes were CF2 modes. Some aromatic rings without fluorine attached were found in FTIR spectra of the films, which indicated that incorporation of fluorine atoms may lead to a significant distortion of the aromatic rings symmetry and turn the CC bonds into IR-active. The optical band gaps and C–Fx bonding states stability of the films were affected not only by fluorine content in the films but also by the bonding configuration. The films with high fluorine content and low CC bonding states will have wide optical band gaps.