Graphite is known to be a good solid lubricant. The low-friction behavior is commonly ascribed to the low resistance to shear. Using a home-built frictional force microscope that is able to detect forces in three dimensions, we have studied the energy dissipation between a tungsten tip sliding over a graphite surface in dry contact. By measuring atomic-scale friction as a function of the rotational angle between two contacting bodies we show that the origin of the ultra-low friction of graphite lies in the incommensurability between rotated graphite layers, an effect proposed under the name of ‘superlubricity’.

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