Chen Xinchun, Yin Xuan, Qi Wei, Zhang Chenhui, Choi Junho, Wu Sudong, Wang Rong, Luo Jianbin
State Key Laboratory of Tribology, Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China.
Department of Mechanical Engineering, The University of Tokyo, Tokyo 113-8656, Japan.
Sci Adv. 2020 Mar 27;6(13):eaay1272. doi: 10.1126/sciadv.aay1272. eCollection 2020 Mar.
The origin of instability or even disappearance of the superlubricity state in hydrogenated amorphous carbon (a-C:H) film in the presence of oxygen or water molecules is still controversial. Here, we address this puzzle regarding the tribochemical activities of sliding interfaces at the nanoscale. The results reveal that gaseous oxygen molecules disable the antifriction capacity of a-C:H by surface dehydrogenation of tribo-affected hydrocarbon bonds. In comparison, oxygen incorporation into the hydrocarbon matrix induces the formation of a low-density surface shear band, owing to which the friction state depends on the oxygen content. High friction of a-C:H film in humid environment originates from the "tumor-like" heterogeneous structures as formed in the highly oxidized tribolayer. Notably, an appropriate doping of silicon can completely shield the moisture effect by forming a silica-like tribolayer. These outcomes shed substantial lights upon the roadmap for achieving robust superlubricity of carbon films in a wide range of environments.
在存在氧气或水分子的情况下，氢化非晶碳（a-C:H）薄膜中超润滑状态的不稳定性甚至消失的起源仍然存在争议。在此，我们解决了关于纳米尺度滑动界面摩擦化学活性的这一难题。结果表明，气态氧分子通过对摩擦影响的碳氢键进行表面脱氢，使a-C:H的减摩能力失效。相比之下，氧掺入碳氢基体中会诱导形成低密度表面剪切带，因此摩擦状态取决于氧含量。a-C:H薄膜在潮湿环境中的高摩擦源于高度氧化的摩擦层中形成的“肿瘤状”异质结构。值得注意的是，适当掺杂硅可以通过形成类二氧化硅摩擦层完全屏蔽水分的影响。这些结果为在广泛环境中实现碳膜强大超润滑性的路线图提供了重要启示。
