Systematic variation of the Raman spectra of DLC films as a function of sp(2):sp(3) composition

We report the Raman spectra of a set of hydrogen-free diamond-like carbon (DLC) films prepared under conditions that result in different types of carbon bonding and for which the sp(2):sp(3) content was independently determined by electron energy loss spectroscopy. The films were prepared using a mass selected C+ ion beam deposition system covering the ion energy range 10 eV to 20 keV. Previous measurements have shown that the sp(2) component of the films decreases as the ion energy is increased from about 10 to 300 eV. For films made with ion energies in excess of 1 keV, the sp(2) component increases with increasing ion energy. The Raman spectra of these films show a broad asymmetric peak which narrows with decreasing sp(2) content. The spectra were fitted with a single skewed lorentzian peak described by the Breit-Wigner-Fano lineshape. The data presented may serve as a reference for DLC characterization. In particular, the parameters from the fits show a strong dependence on the sp(2) component of the films which may be used to identify unambiguously (hydrogen-free) DLC films of low sp(2) content (i.e. very ''diamond-like'' films).