Probing the low friction mechanism of hydrogen-free DLC film in oxygen and nitrogen environments by first-principles calculations and molecular dynamics simulation

We try to compare the interfacial bonding behavior of hydrogen-free DLC films in nitrogen or nitrogen atoms environment by first principle calculation and molecular dynamics (MD) simulation, so as to provide an atomic view of the friction behavior in oxygen and nitrogen environments. The results show that hydrogen-free DLC films will form Csingle bondN bonds and Csingle bondO bonds when the coverage of nitrogen or oxygen is not higher than 0.75, but will be completely passivated when the coverage of nitrogen or oxygen is higher than 0.75. The lower Csingle bondO bond strength and higher repulsion force at the friction interface of DLC films in oxygen atmosphere suggest that the friction coefficient is less than that in nitrogen environment. Moreover, the results of molecular dynamics simulation further show that a lower friction of DLC film in the oxygen atmosphere may be due to the smoother friction interface and less interfacial bonds.