Direct quantitative detection of the sp3 bonding in diamond-like carbon films using ultraviolet and visible Raman spectroscopy

The bonding in a series of unhydrogenated amorphous carbon films has been analyzed quantitatively using Raman spectroscopy excited by laser light in both the visible and ultraviolet regions of the spectrum. The asymmetry of the peak near 1550 cm(-1) in the visible Raman spectra is correlated with the percentage of sp(3) bonding in the films. The ultraviolet Raman spectra exhibit two broad Raman peaks at 1650 and 1100 cm(-1), due to sp(2) and sp(3) vibrational modes, respectively. The former is a resonance feature associated with a large proportion of paired sp(2) sites, while the latter is a weighted phonon density-of-states for the distorted random network of sp(3) sites. The position and relative intensity of the two peaks are shown to be strongly correlated with the percentage of sp(3) sites in the films, providing a reliable measure of sp(3) bonding which is both semiquantitative and nondestructive. (C) 2000 American Institute of Physics. [S0021-8979(00)04810-6].