Deformation mechanisms of Si-doped diamond-like carbon films under uniaxial tension conditions

Abstract

Element-doped diamond-like carbon (DLC) films have been fabricated to achieve excellent mechanical properties but their elastic/plastic deformation mechanisms are unclear due to experimental limitations in characterizing the deformation process. This study investigates the deformation mechanisms of Si-doped DLC films by simulating their uniaxial tensile tests. It is found that these films show many strain-localized regions under tensile deformations. The coordination number (CN) of Si atoms in such regions decreases even with a small tensile strain. The sp3-sp2 bonding transition of C atoms also happen in these regions with a large tensile strain. As a result, these regions show highly-degraded structures with weak mechanical strength and can be regarded as the defects in the Si-DLC films. In this case, the tensile forces are mainly undertaken by the networks formed of both sp3C atoms and Si atoms with large CN, and hence such networks can be regarded as backbones of Si-DLC films. Their fracture finally initiates in the strain-localized regions. Furthermore, Si-DLC films with an increased Si content show large fraction of sp3C atoms but still exhibit a decreased strength due to the rapid presence of strain-localized regions.