Graphite holds significant promise as a solid lubricating material for machine operation in ambient conditions. However, the intricacies of its mechanism remain a subject of debate at the nanoscale. In this study, atomic force microscopy (AFM) experiments conducted in ultrahigh vacuum (UHV) conditions provide direct evidence that the adsorption of water molecules significantly compromises friction performance, both on the basal plane and across step edges. This challenges the longstanding belief that the poor lubricating properties of graphite in a vacuum result from the desorption of water molecules. Moreover, the experimental findings put forth a compelling bond passivation hypothesis for graphite lubrication in ambient conditions. The process involves the introduction of defects with dangling bonds on graphite through annealing highly oriented pyrolytic graphite (HOPG) at elevated temperatures ($\ge$$\ge$773 K) in UHV conditions. Subsequently, these dangling bonds are gradually passivated by a small amount of residue atoms or molecules. Consequently, the continuously monitored friction force exhibits an exponential decrease over time following annealing. This study advances a molecular level understanding of low lubrication mechanism for graphite.

石墨作为一种固体润滑材料，对于环境条件下的机器操作具有重要的前景。然而，其机制的复杂性在纳米尺度上仍然是一个争论的话题。在这项研究中，在超高真空 (UHV) 条件下进行的原子力显微镜 (AFM) 实验提供了直接证据，表明水分子的吸附会显着影响基面和跨台阶边缘的摩擦性能。这挑战了长期以来的观点，即石墨在真空中润滑性能较差是由于水分子的解吸造成的。此外，实验结果提出了环境条件下石墨润滑的令人信服的键钝化假说。该过程涉及通过在高温下对高取向热解石墨（HOPG）进行退火，在石墨上引入带有悬挂键的缺陷（$\ge$$\ge$773 K）在特高压条件下。随后，这些悬空键逐渐被少量残留原子或分子钝化。因此，连续监测的摩擦力在退火后随时间呈指数下降。这项研究推进了对石墨低润滑机制的分子水平理解。