On the structure of thin amorphous carbon films

Abstract

Abstract Diamond-like carbon films have been prepared by KrF excimer pulsed-laser deposition at a wavelength of 248 nm, with power densities ranging from 0.05 to 1.85 GW cm−2, in vacuum and in a nitrogen atmosphere. Structural analysis was performed first by Fourier transform infrared spectroscopy, which shows that the films are hydrogen free and become transparent above a threshold power density. The band features indicate that the structure of the films is disordered. Combined visible and ultraviolet (UV) Raman spectroscopies allowed us to enhance the scattering cross-section from sp3-coordinated carbon with respect to the sp2 signals. In visible Raman spectra the D and G peaks are found; in UV Raman spectra, besides the blue-shifted G peak and the T peak, a further peak, not reported before, at about 1400 cm−2 is evident in spectra from films deposited in vacuum at low fluences. An analysis of the evolution of Raman fitting parameters with increasing deposition power density shows that above a threshol...