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Role of Surface Hydrogen Bonds in Determining the Friction Behaviors of Hydrogenated Diamond-like Carbon Films

Friction behaviors of hydrogenated diamond-like carbon (H-DLC) films are investigated on a ball-on-disk type tribometer in dry N2 and dry vacuum. The result shows that the friction behaviors of the H-DLC films are very sensitive to the testing environment, the H-DLC films exhibit a very low friction coefficient of 0.016 in dry N2, and similarly in an inert gas the friction coefficient increases to about 0.063 in dry vacuum. Combining the testing conditions, friction results, SEM and XPS investigation, it is concluded that the friction behaviors of the hydrogenated DLC films are associated with surface hydrogen of the H-DLC films and are dictated by whether or not hydrogen bonds are formed between the transfer films/H-DLC films at the sliding interface. A hydrogen-induced hydrogen bond model is proposed to interpret the friction behaviors of hydrogenated DLC films in different environments.