Mechanical properties and Raman spectra of tetrahedral amorphous carbon films with high sp³ fraction deposited using a filtered cathodic arc

Abstract

Abstract The mechanical and structural properties of the tetrahedral amorphous carbon (ta-C) films deposited by the filtered cathodic vacuum arc technique on silicon at room temperature have been studied over the carbon ion energy range 15–200 eV. High (about 80% or higher) sp3 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 sp3 fraction and show an almost linear dependence on the small variation in sp3 content. The maximum hardness, Young's modulus, stress critical load and minimum friction coefficient all coincide with the highest sp3 fraction as determined by electron-energy-loss spectroscopy. All films 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 sp2 content below 30% and can also be used to verify the ion energy corresponding to the maximum sp3 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 sp2 bonded atoms in the ta-C sp3 matrix.