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 e xcitation wavelengths were 244, 488, 514 and 633 nm, corresponding to photo n energies of 5.08, 2.54, 2.41 and 1.96 eV, respectively. In the visible Ra man spectra only vibrational modes of sp(2)-bonded carbon (G and D peaks) a re observed, while a wide peak (called the T peak) can be observed at appro ximately 1100 cm(-1) by UV-Raman spectra which is associated with the vibra tional mode of sp(3)-bonded carbon. Both the position and the width of the G peak decrease almost linearly with increasing excitation wavelength, whic h 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 ener gy of 100 eV. The changes of these spectral parameters are discussed and co rrelated with the sp(3) fraction of carbon atoms in the films. (C) 2001 Els evier Science B.V. All rights reserved.