Resonant Raman studies of tetrahedral amorphous carbon films

Resonant Raman scattering has been used to study the tetrahedral amorphous carbon films deposited by the filtered cathodic vacuum are 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 sp(2)-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 sp(3)-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 pi-pi* resonant Raman scattering of sp(2)-bonded carbon dusters with various sizes. The G peak position in the UV-Raman spectra, the T peak position and the intensity ratios of I-D/I-G and I-T/I-G 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 sp(3) fraction of carbon atoms in the films. (C) 2001 Elsevier Science B.V. All rights reserved.