Spectroscopic ellipsometry and Raman study of fluorinated nanocrystalline carbon thin films

Using spectroscopic ellipsometry and Raman spectroscopy, we measured the ps eudodielectric function and the phonon frequencies of fluorinated nanocryst alline carbon (nc-C:F) thin films grown on silicon substrate at varying gro wth temperature and gas flux ratio of CH4 and CF4. Utilizing the Tauc-Loren tzian formula, we performed multilayer analysis to estimate the dielectric function of the fluorinated nanocrystalline carbon thin films. We also adop ted Gaussian-like density-of-states model proposed by Demichelis [Phys. Rev . B 45, 14364 (1992)] and estimated the amplitude A, the transition energy E-pi, and the broadening sigma (pi) of pi --> pi* transitions. Based on thi s model, we explained the change of the optical gap and the refractive inde x in terms of the change of the amplitude A rather than the shift of transi tion energy E-pi of pi --> pi* transitions. Raman and ellipsometric study s uggested that the average size of nanocrystallites in the fluorinated carbo n thin films was smaller than that of amorphous hydrogenated carbon films s tudied by Hong [Thin Solid Films 352, 41 (1999)]. (C) 2001 American Institu te of Physics.