Diamond Formation at Superlubric Sliding Interface.

Until now, all carbons (solids, liquids, and gases) prefer to graphitize at moving mechanical interfaces. The reverse evolution toward diamond is generally not possible at the interfaces due to high activation and kinetic barriers (Diamond can be grown only at pressures of 5-6 GPa and temperatures of 900°C-1400°C). Here, we report diamond formation at superlubric sliding interfaces (coefficient of friction 0.008), breaking this pattern. This is accomplished by the van der Waals encapsulation of carbonaceous wear debris, when sliding Al2O3 balls against MoS2-coated amorphous carbon surfaces. Atomistic simulations reveal the encapsulation to reduce potential energy difference (30%) and accelerate structural relaxation dynamics (2.0 times), which triggers a disproportionation transformation that forms diamond. This study observes diamond formation at mechanical moving interfaces, which opens many possibilities for further basic science studies and for this field of mechanical friction.