Toward low friction in high vacuum for hydrogenated diamondlike carbon by tailoring sliding interface.

The high friction of diamondlike carbon (DLC) films in vacuum impedes achieving their application in space environment. Here we show that the vacuum friction coefficients can be lowered below 0.1 by avoiding formation of carbonaceous transfer layers on the counterfaces. First-principles calculations reveal that the low friction coefficients stem from intrinsically weak-interacting sliding interfaces. Conversely, formation of transfer layers and carbonaceous sliding interfaces thus established are invalid for friction reduction for DLC in vacuum. The mating materials are thus highlighted for their crucial roles in transfer-layer formation.