Local structure analysis of DLC films using soft X-ray absorption spectroscopy

We measured C K-edge X-ray absorption near edge structure of DLC films with different fabrication conditions to investigate the relationship between fabrication conditions and local structure. By applying the method of calculating the ratio of sp² and sp³ carbons from the π^*/ σ^* peak intensity ratio of C K-edge XANES, it was possible to quantitatively evaluate the ratio of sp² carbons in DLC. The ratio of sp² carbon determined by this method agreed well with the ratio of sp² carbon determined by refractive index. In addition, the relationship between the width of the π^* peak and the graphitic layer size was discussed quantitatively by taking the difference spectrum with HOPG. From the comparison between the measured and calculated XANES spectra of graphitic layer models, it was found that the graphitic layer size was smaller for O-DLC and Ar-DLC, whose surfaces were roughened with oxygen or argon after film formation, than for other DLC. It was also found that the peaks found in H-DLC prepared by adding hydrogen during film formation were attributed to peaks derived from sp³ carbons, such as alkane molecules, which is consistent with the results of other methods that H-DLC contains more polymer-like components than others. (author)