This study assessed the influences of fluorine introduced into DLC films on the structural and mechanical properties of the sample. In addition, the effects of the fluorine incorporation on the compressive stress in DLC films were investigated. For this purpose, fluorinated diamond-like carbon (F-DLC) films were deposited on cobalt-chromium-molybdenum substrates using radio-frequency plasma-enhanced chemical vapor. The coatings were examined by Raman scattering (RS), Attenuated total reflectance Fourier transform infrared spectroscopic analysis (ATR-FTIR), and a combination of elastic recoil detection analysis and Rutherford backscattering (ERDA-RBS). Nano-indentation tests were performed to measure hardness. Also, the residual stress of the films was calculated by the Stony equation. The ATR-FTIR analysis revealed that F was present in the amorphous matrix mainly as C-F and C-F2 groups. Based on Raman spectroscopy results, it was determined that F made the DLC films more graphitic. Additionally, it was shown that adding F into the DLC coating resulted in weaker mechanical properties and the F-DLC coating exhibited lower stress than DLC films. These effects were attributed to the replacement of strong C = C by feebler C-F bonds in the F-DLC films. F-doping decreased the hardness of the DLC from 11.5 to 8.8 GPa. In addition, with F addition, the compressive stress of the DLC sample decreased from 1 to 0.7 GPa.

DLC has been attractive as semiconductor materials for solar cell due to its biological friendliness, flexible microstructures, and especially its tunable band gap. In order to fabricate high-efficiency multiband gap solar cell, it is important to control the sp3/ sp2 bonds ratio of DLC film corresponding to optical band gap (Eg). There are many references reporting the relations among the fabrication conditions, Eg, sp3/ sp2, and ID/ IG. However, a more comprehensive database is needed for controllable fabrication. Especially, the quantitative relationship of sp3/ sp2 ratio to Eg of DLC film by PECVD is unclear. In this paper, 36 sets of DLC films were fabricated by RF-PECVD. Characterization methods of XPS, Raman spectroscopy, and IR absorption have been used to determine the sp3/ sp2 ratio of DLC films. UV/visible light absorption method has applied to evaluate Eg. The Eg obtained is in the range 1.45–3.0 eV. Our results agree well with the references. The XPS spectra gives a linear relationship as Eg = − 0.161 (± 0.136) + 26.095 (± 1.704) · {sp3 (XPS)/sp2}, the Raman spectra shows a linear function that Eg = 1.327 (± 0.046) + 0.428 (± 0.036) · (ID/IG), as well as the FTIR analysis demonstrates that Eg = − 0.492 (± 0.093) + 0.464 (± 0.044) · {sp3 (FTIR)/sp2}.