Abstract
Raman spectra of diamond-like carbon (DLC) films prepared using bipolar-type plasma based ion implantation (PBII) are measured and the peak separation is carried out by curve fitting of the spectra using Gaussian, Mixed, Lorenzian and Breit-Wigner-Fano (BWF) functions. The effects of the fitting functions on the intensity ratio of the disorder (D) peak to graphite (G) peak (ID/IG) and their peak positions are examined. Furthermore, the changes of these values are examined as a function of negative pulsed voltages to clarify the differences between functions. The mean square of residuals is used as an indication of the fitting degree. Results show that the Gaussian function yields the best fitting result among these four functions. The ID/IG values depend strongly on the fitting functions. However, G peak positions exhibit less dependence on the fitting function. The tendencies of their changes as a function of negative pulsed voltages show similarity. These results suggest that a qualitatively similar explanation for structural changes of DLC films can be given, notwithstanding their different functions. The D peak position obtained using the Gaussian function is higher than that obtained using other functions, which implies that the Gaussian function overestimates the D peak intensity, possibly because it ignores another small shoulder peak around 1200 cm−1. The possibility of the presence of the other two peaks is also suggested by the peaks in residuals.
