Tribological study of the solid lubricant surface under high vacuum and the sliding mechanism

本计画的重点在于（1）接触表面间的化学交互作用对摩擦系数的贡献，以及（2）设计一种在真空环境下长寿命滑动的表面结构。本课题成功地开展了一系列的研究工作，并得到了该项目的资助。我们研究了宏观金刚石球（直径3 mm）与厚度为1-100 nm的超薄Ag层的摩擦。我们发现在Si（111）衬底上沉积的1-8 nm厚的Ag层的摩擦系数最小。在至少1000个往复循环期间，薄Ag膜通过滑动而不被排除在滑动轨道之外，并且在这些循环期间持续0.01或更小的超低摩擦系数。通过AES、RHEED和SEM等技术对非滑动和滑动表面的精确观察，讨论了原子级薄Ag层超低摩擦现象的可能机理。MoS_2和石墨的超低摩擦与相应的现象被证明是不同的机制，因为Ag原子平面是随机堆积在沉积态Ag层上的，在其上的反复滑动是完全不磨损的，我们认为这是由于Ag原子在室温下以很低的能量沿着Si（111）表面移动的。实验结果表明，通过重构二维Ag微粒，可以在滑动表面上形成自恢复滑动面。

This project is focused on (1) the contribution of chemical interaction between contact surfaces to the coefficient of friction, and (2) designing a surface structure for long-life sliding under vacuum circumstance. This project was carried out successfully and we awe to this grant supported this project.We investigated for the friction of macroscopic diamond sphere (3mm in diameter) sliding with ultra-thin Ag layers between 1-100 nm thick. We found a minimum coefficient of friction on the 1-8 nm-thick Ag layers deposited on Si(111) substrate. The thin Ag films were not excluded out of the sliding track by sliding during at least 1000 reciprocal cycles and the ultra-low coefficient of friction 0.01 or less lasted over these cycles. By our precise observation of the non-slide and slide surfaces in terms of AES, RHEED and SEM techniques, we discussed for the plausible mechanism of the ultra-low friction phenomenon of the atomically thin Ag layers. The ultra-low friction found for MoS_2 and graphite were proved different mechanism with the relevant phenomena, because the Ag atomic planes are a randomly stacked on the as-deposited Ag layers and exactly non-wearing is occurred by iterated sliding on it. We proposed this is due to the Ag atoms are mobile along the Si(111) surface with very low energy even at room temperature. We have reached to a conclusion experimentally that a self-recovering sliding plane can be formed on the slid surfaces by reconstructing two-dimensional Ag fine particles.