Structural and mechanical properties of diamond-like carbon films deposited by direct current magnetron sputtering

Abstract

The microstructure, morphology, and mechanical properties of diamond-like carbon (DLC) films deposited by direct current magnetron sputtering were investigated for microelectromechanical systems applications. Film properties were found to vary markedly with the ion energy (Eion) and ion-to-carbon flux ratio (Jion/JC). Cross-sectional high-resolution transmission electron microscopy revealed an amorphous microstructure. However, the presence of nanometer-sized domains at Eion∼85 eV was detected. Film stresses, σ, which were compressive in all cases, ranged from 0.5 to 3.5 GPa and depended on the flux ratio as well as ion energy. The hardness (H), Young’s moduli (ε), and elastic recovery (R) increased with Eion to maximum values of H=27 GPa, ε=250 GPa, and R=68% at Eion=85 eV and Jion/JC=4.4. However, near edge x-ray absorption fine structure and electron energy-loss spectrum analysis showed that the sp2/sp3 content of the films does not change with Eion or Jion/JC. The measured change in mechanical properties without a corresponding change in sp2/sp3 ratio is not consistent with any previously published models. We suggest that, in the ranges 5 eV ⩽Eion⩽85 eV and 1.1 ⩽Jion/JC⩽6.8, the presence of defective graphite formed by subplanted C and Ar atoms has the dominant influence on the mechanical properties of DLC films.