Superlubricity of nanometer-thick Ag, Au films and the two dimensional structure of the slid surface - Study for designing a slide surface which works in space circumstance

本工作的第一个目标是设计一个在真空环境下工作的滑动表面。我们对沉积在硅上的纳米银层进行了滑动实验和分析，观察了滑动表面的结构和特性。用俄歇电子能谱（AES）、反射高能电子衍射（RHEED）、隧道电子显微镜（STM）原位和同步辐射轨道X射线衍射（SOR-XD）非原位研究了Ag的晶体取向和滑动表面的晶体学分析。这些结果揭示了单原子层在滑动表面上的叠加，为理解超润滑机理提供了有用的信息。结果表明：（1）在沉积Ag多晶薄膜时，Ag（111）晶面已朝向任意方向。期间 ...更多信息 在其上反复往复滑动，Ag（111）滑动面平行于滑动面取向。银微晶也增长了10倍的大小，并在室温下再结晶，在滑动过程中，和C平面被堆叠层平行于Si滑动方向，这是由STM和SOR-XD观察证明。Ag微晶导电，好像Ag膜形成液体层，但堆叠的Ag层看起来完整的晶体没有任何非晶部分。近二维的Ag金属薄膜被证明具有与室温一样低的熔点。所观察到的超润滑性被理解为由于Ag原子沿着Si（111）表面和Ag nm厚层上的原子迁移率。（2）Ag原子具有移动的性，表现出超强的润滑作用。因此，在滑动表面上没有发现磨损颗粒，这些磨损颗粒可能是由于原子的迁移而在表面上重新形成的层结构。银膜没有被排除或剥落的滑动从滑动轨道，超过1000个循环的往复滑动。（3）由于试验是在真空条件下进行的，因此所得结果也适用于空间滑动面。测试样本是干净的，测试结果是可再现的，表面上没有任何污染物。结果适用于半导体生产的洁净室机器和使用非油润滑剂的纺织品。（4）研究结果为进一步认识超润滑机理提供了重要的理论基础，并指出了接触表面间的化学相互作用是降低摩擦的最重要因素。少

First objective of this work was designing a slide surface which works in a vacuum circumstance. We carried out sliding experiments and analyses of nanometer-thick Ag layers which was deposited on Si, and observed surface structures and characteristics of the slid surfaces. As a result, super lubricity (coefficient of friction : 0.007 at the minimum) was found on it.Crystal orientation of Ag and crystallographic analyses of the slid surface in ultrahigh vacuum were studied using Auger electron spectroscopy (AES), reflection high energy electron diffraction (RHEED), tunneling electron microscopy (STM), in-situ, and by synclotron orbital radiated X-ray diffraction (SOR-XD), ex-situ. These results revealed that the single atomic layers stack on the slid surfaces, and provided useful information to understand the mechanism of super lubricity. The results were summarized as follows,(1)If the polycrystalline film of Ag were deposited, Ag(111) planes have faced to random direction. During the … More reciprocal and repeated sliding cycles on it, Ag (111) sliding plane orientated parallel to the sliding plane. Ag crystallites also have grown 10 times in size and recrystallized at room temperature, during sliding, and C planes were stacked layer by layer parallel to the Si sliding direction, as was proved by STM and SOR-XD observations. Ag crystallites conducted, as if Ag films formed liquid layer, but the stacked Ag layers looked complete crystals without any amorphous fractions. Nearly two dimensional film of Ag metal were proved to have a melting point, as low as the room temperature. The observed superlubricity was understood due to the atomic mobility of Ag atoms along the Si(111) surface and on the Ag nm-thick layers.(2)The Ag atoms were mobile and showed super lubricant function. On the slid surface, therefore, no worn particles were found. The worn particles were supposedly reformed layer structure on the surfaces due to the mobility of the atoms. Ag films were not excluded out or exfoliated by sliding from the sliding tracks, over 1000 cycles of reciprocal sliding.(3)The results may applicable for sliding surface in space, because the experiments were carried out under ultrahigh vacuum. The test specimens were clean that the test results were reproducible without any contaminants on the surfaces. The results were applicable to clean room machines for semiconductor production, and textile products which use non-oil lubricants.(4)The results provided very important and fundamental understandings of super lubrication, and chemical interaction between contact surfaces as the most important factor to reduce friction. Less