Anomalous temperature-dependent friction in diamond-like carbon

Due to their outstanding tribological and wear properties at cryogenic temperatures, diamond-like carbon (DLC) materials are widely used in fields such as deep space exploration and superconducting magnets. The temperature-dependent frictional behavior of DLC is expected to follow the conventional thermally activated process. In this article, the frictional properties of DLC are scrutinized in the temperature range of 100−300 K by reciprocally scanning a DLC-coated atomic force microscopy (AFM) tip against a DLC substrate in ultrahigh vacuum (UHV) conditions. The results reveal a remarkable monotonic temperature dependence of frictional behavior, which remains robust under varying normal loads and sliding velocities. Specifically, the overall friction force increases as the temperature decreases, with a distinct friction peak at T_max = 215±10 K. While a logarithmic dependence of friction on velocity is observed at temperatures far from T_max, friction becomes nearly velocity-independent in the vicinity of T_max. This nonmonotonic temperature dependence of friction beyond the conventional thermally activated framework is well interpreted to involve the formation/rupture of interfacial bonds. This work provides new insights into the interfacial bonding mechanisms affecting the tribological properties of DLC materials at cryogenic temperatures.