Friction reversed

Graphite is well known as a lubricant material but researchers at the National Institute of Standards and Technology (NIST) have found that graphite can exhibit a negative coefficient of friction if a nanoscopic pencil tip of graphite is tested using atomic force microscopy and varying the amount of oxygen on the surface of a graphene sheet. Team member Zhao Deng found that the adhesive force between the graphene and the stylus became greater than the graphene layer's attraction to the graphite below, reducing the pressure on the stylus made it harder to drag the tip across the surface-a negative differential friction.