Direct observation of sp3 bonding in tetrahedral amorphous carbon using ultraviolet Raman spectroscopy

Abstract

The vibrational modes of the ${\mathrm{sp}}^3$ sites in tetrahedral amorphous carbon (ta-C) thin films are revealed directly using ultraviolet Raman spectroscopy at 244 nm excitation and are shown to produce a Raman peak centered around 1100 ${\mathrm{cm}}^{\mathrm{-1}}$ . In addition, the main Raman peak associated with ${\mathrm{sp}}^2$ vibrational modes is shifted upward in frequency by 100 ${\mathrm{cm}}^{\mathrm{-1}}$ relative to its position in spectra excited at 514 nm. The spectra are interpreted in terms of the bonding in ta-C.