Changing of the Interfacial Contacts and Shear Behaviors between a-C Films Caused by Si Doping

We used reactive molecular dynamics (ReaxFF-MD) to simulate the friction and shear behavior of a-C:Si films with varying Si content (0-20 at%). We found that the optimal doping content was 7.2 at%, which had similar friction to the undoped film but had smaller wear and running-in time (40 and 60% of the undoped film, respectively). Compared with the undoped film, the proper amount of Si doping significantly inhibited the formation of all-C bridging chains at the interface and prevented the formation of a large number of all-C and Si-involved bridging chains caused by surface dangling bonds at higher Si contents. Our study revealed the atomic scale mechanism of Si doping on the tribological properties of a-C films.