Resonant Raman studies of tetrahedral amorphous carbon films

Abstract

Resonant Raman scattering has been used to study the tetrahedral amorphous carbon films deposited by the filtered cathodic vacuum arc technique. The excitation wavelengths were 244, 488, 514 and 633 nm, corresponding to photon energies of 5.08, 2.54, 2.41 and 1.96 eV, respectively. In the visible Raman spectra only vibrational modes of sp2-bonded carbon (G and D peaks) are observed, while a wide peak (called the T peak) can be observed at approximately 1100 cm−1 by UV-Raman spectra which is associated with the vibrational mode of sp3-bonded carbon. Both the position and the width of the G peak decrease almost linearly with increasing excitation wavelength, which is interpreted in terms of the selective ππ* resonant Raman scattering of sp2-bonded carbon clusters with various sizes. The G peak position in the UV-Raman spectra, the T peak position and the intensity ratios of ID/IG and IT/IG all exhibit maximum or minimum values at the carbon ion energy of 100 eV. The changes of these spectral parameters are discussed and correlated with the sp3 fraction of carbon atoms in the films.