Raman Spectroscopy of $a$-C:H Films Deposited Using Ar $+$ H$_{2}+$ C$_{7}$H$_{8}$ Plasma CVD

We investigated the effects of ion energy on Raman spectra of $a$-C:H films prepared by Ar $+$ H$_{2}+$ C$_{7}$H$_{8}$ plasma CVD. Raman spectra were measured with a laser Raman spectrometer (JASCO NRS-3100). Both the D-peak position and G-peak position shift toward higher wavenumbers as ion energy increases. The intensity ratio of the D-peak and G-peak, $I_{\mathrm{D}}$/$I_{\mathrm{G}}$ increases with increasing the ion energy, indicating that the amount of ring-like \textit{sp}$^{2}$ clusters increases. The H content in $a$-C:H derived from photoluminescence (PL) background decreases with increasing the ion energy. The full width at half maximum of the G-peak, FWHM$_{\mathrm{G}}$ related to the C-C \textit{sp}$^{3}$ content and H content increases with increasing the ion energy to 100 eV, whereas it decreases with increasing further the ion energy to 105 eV. The variation of FWHM$_{\mathrm{G}}$ is consistent with that of mass density. There results indicate that the structure of $a$-C:H films transforms from polymer-like carbon to diamond-like one with increasing the ion energy above the threshold value of $\sim$ 100 eV.