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

这项工作的第一个目标是设计一种在真空环境中工作的滑动面。对沉积在硅上的纳米厚的银层进行了滑动实验和分析，观察了滑动表面的表面结构和特征。利用俄歇电子能谱、反射高能电子衍射、隧道电子显微镜、原位和同步辐射X-射线衍射仪对超高真空中银的晶体取向和滑动表面的晶体结构进行了研究。这些结果揭示了单原子层在滑动表面上的堆积，为理解超润滑性的机理提供了有用的信息。主要研究结果如下：(1)如果沉积了银多晶薄膜，则银(111)晶面的取向是随机的。在…期间Ag(111)滑动面与滑动面平行，且有更多的往复滑动循环。STM和SOR-XD观察表明，在滑动过程中，Ag微晶尺寸增大了10倍，并在室温下再结晶，C面沿Si滑移方向层层堆积。Ag微晶形成，好像Ag膜形成了液态层，但堆积的Ag层看起来像是完整的晶体，没有任何无定形成分。近二维银金属薄膜被证明有一个熔点，低至室温。观察到的超润滑性是由于Ag原子沿Si(111)表面和Ag nm厚的层上的原子迁移率所致。(2)Ag原子是可移动的，表现出超级润滑性。因此，在滑动表面上，没有发现磨损颗粒。由于原子的移动性，磨损的颗粒可能在表面形成了层状结构。在1000多次往复滑动过程中，银膜没有从滑轨上滑脱或剥落。(3)由于实验是在超高真空下进行的，因此这一结果可能适用于空间滑动面。测试样品是干净的，测试结果是可重复性的，表面没有任何污染物。研究结果适用于半导体生产的洁净室机械，以及使用非油润滑剂的纺织产品。(4)研究结果对超强润滑以及接触表面之间的化学相互作用作为减摩最重要的因素提供了非常重要和基本的认识。较少

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