Anomalous temperature-dependent friction in diamond-like carbon

Due to the 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. Wherein, 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 300 to 100 K by reciprocally scanning a DLC coated atomic force microscopy (AFM) tip against a DLC substrate in ultra-high vacuum (UHV) conditions. The results reveal a remarkable monotonical temperature dependence of frictional behavior, which remains robust under varying normal loads and sliding velocities. Specially, the overall friction force raises as temperature decreases, with a distinct friction peak at Tmax = 215 ± 10 K. While a logarithmic dependence of friction on velocity is observed at temperatures far from Tmax, friction becomes nearly velocity-independent in the vicinity of Tmax. This non-monotonically temperature dependence of friction beyond conventional thermally activated framework is well interpreted involving 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.