Effects of environmental molecular characteristics and gas–surface interaction on friction behaviour of diamond-like carbon films

The superlow friction behaviours of diamond-like carbon (DLC) films in three different inert environments (dry N2, CO2 and Ar gas) were investigated and compared. The friction of the DLC films in dry N2 and CO2 was superior to that in dry Ar, and was dependent on the environmental exposure time. The possible reason is that N2 and CO2 have the same molecular characteristic of lone pair electrons at both sides of the molecules, while Ar has no lone pair electrons. And a special gas–surface interaction due to π orbital–lone pair electrons interactions is present at the sliding interfaces of DLC films in dry CO2 and N2. A friction model in relation to environmental molecular characteristics and gas–surface interactions was proposed to explain the friction behaviours of DLC films.