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

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.