Si doping enhances the thermal stability of diamond-like carbon through reductions in carbon-carbon bond length disorder

Low thermal stability is a major limitation of diamond-like carbon (DLC) films, especially amorphous hydrogenated carbon (a-C:H) films, inhibiting their use in several applications. Adding silicon and oxygen to a-C:H increases thermal stability, but mechanisms for this increase are unknown. Reactive molecular dynamics (MD) simulations using the ReaxFF potential were performed on undoped a-C:H and a-C:H containing Si and O (a-C:H:Si:O). As in experiments, the simulated a-C:H:Si:O demonstrated increased thermal stability compared to a-C:H. Atomistic thermal degradation pathways were examined to understand the origins of the enhanced thermal stability of a-C:H:Si:O compared to a-C:H. The primary thermal degradation pathway in undoped a-C:H was the breaking of tensile strained C-C bonds resulting in a transformation of sp(3) to sp(2)-hybridized carbon. The presence of Si suppresses this mechanism by decreasing the frequency of occurrence of highly strained C-C bonds in the unannealed structure. This is due to the longer C-Si equilibrium bond length compared to C-C bonds, which allows the Si-doped films to accommodate higher structural disorder. (C) 2018 Elsevier Ltd. All rights reserved.