Steric Effects Control Dry Friction of H- and F-Terminated Carbon Surfaces.

摘要: A stable passivation of surface dangling bonds underlies the outstanding friction properties diamond and diamond-like carbon (DLC) coatings in boundary lubrication. While hydrogen is simplest termination a bond, fluorine can also be used as monoatomic termination, providing an even higher chemical stability. However, whether under which conditions substitution with beneficial to still open question. Moreover, differences between C-H C-F are responsible for change has not been unequivocally understood yet. In order shed light on this problem, we develop density functional theory-based, nonreactive force field that describes relevant hydrogen- fluorine-terminated DLC tribological interfaces. Molecular dynamics nudged elastic band simulations reveal frictional stress at such interfaces correlates corrugation contact potential energy, thus ruling out significant role mass terminating species friction. Furthermore, energy almost exclusively determined by steric factors, while electrostatic interactions only play minor role. particular, atomically flat surfaces controlled terminations, bond lengths, H F atomic radii. For sliding DLC/DLC interfaces, intrinsic atomic-scale roughness plays additional fluorination decreases incommensurate contacts, it negatively affect performance disordered flat. This work provides general framework understand impact structure generate design rules optimally terminated low-friction systems.