Mechanical properties and Raman spectra of tetrahedral amorphous carbon films with high sp(3) fraction deposited using a filtered cathodic arc

The mechanical and structural properties of the tetrahedral amorphous carbon (ta-C) films deposited by the filtered cathodic Vacuum are technique 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 fractions 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) content. The maximum hardness, Young's modulus, stress critical load and minimum friction coefficient all coincide with the highest sp(3) fraction as determined by electron-energy-loss spectroscopy. All alms are atomically smooth. The Raman spectra of these films when fitted with a skewed 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 ordering of the sp(2) bonded atoms in the ta-C sp(3) matrix.