Oxygen-Participated Interfacial Behaviors and Bonding Mechanisms of Amorphous Carbon Films in Friction by First-Principles and Molecular Dynamics

Amorphous carbon (a-C) has gained extensive applications due to its superlubricity characteristics. In practical applications, oxygen is inevitably introduced into the sliding interface which undergoes complex interfacial reactions, leading to distinct friction mechanisms. Herein, the oxygen-participated interfacial behaviors and bonding mechanisms of a-C were investigated through a combination of molecular dynamics (MD) simulations and first-principles calculations. It is found that a-C films in the oxygen-containing environment exhibit more stability and lower friction through the established reactive MD simulations. More analysis of the interfacial behavior indicates that oxygen atoms are incorporated into the friction interface under shear. It reduces interfacial physical adhesion and atomic accumulation while effectively suppressing C-C bond formation between friction counterparts, thereby inducing chemical passivation. These mechanisms collectively enhance the structural stability of the a-C film interface, thereby facilitating ultralow friction. First-principles calculations further confirm that oxygen atoms form bonds primarily via carbonyl (C═O) and ether (C-O-C) groups. Structural optimization and differential electron density analysis demonstrated their high bond strength. They help maintain structural integrity and interfacial stability during friction while also increasing interlayer spacing, ultimately leading to effective friction reduction. This work enhances the understanding of interfacial friction-reduction mechanisms in oxygen-containing a-C and informs the design of amorphous carbon films and advancements in tribological applications.