S. Xu et al., MECHANICAL-PROPERTIES AND RAMAN-SPECTRA OF TETRAHEDRAL AMORPHOUS-CARBON FILMS WITH HIGH SP(3) FRACTION DEPOSITED USING A FILTERED CATHODIC ARC, Philosophical magazine. B. Physics of condensed matter. Statistical mechanics, electronic, optical and magnetic, 76(3), 1997, pp. 351-361
The mechanical and structural properties of the tetrahedral amorphous
carbon (ta-C) films deposited by the filtered cathodic Vacuum are tech
nique on silicon at room temperature have been studied over the carbon
ion energy range 15-200 eV. High (about 80% or higher) sp(3) bond fra
ctions were obtained for almost all ion energies investigated (E > 50
eV), with a maximum of about 87% at about 95 eV. The variations in the
mechanical properties have been correlated to the sp(3) fraction and
show an almost linear dependence on the small variation in sp(3) conte
nt. The maximum hardness, Young's modulus, stress critical load and mi
nimum friction coefficient all coincide with the highest sp(3) fractio
n as determined by electron-energy-loss spectroscopy. All alms are ato
mically smooth. The Raman spectra of these films when fitted with a sk
ewed Lorentzian, a parameter Q, which measures the degree of skewness,
is noticeably dependent on films with sp(2) content below 30% and can
also be used to verify the ion energy corresponding to the maximum sp
(3) content. The change observed in the mechanical properties as well
as the skewness parameter Q is attributed to a change in the local ord
ering of the sp(2) bonded atoms in the ta-C sp(3) matrix.