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

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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.