Clarification of conditions for ultra-low friction

在低载荷条件下，不同金属对的摩擦系数由每种金属材料之间原子间距离的差异决定。在这里，八种类型的金属引脚与覆盖有天然氧化膜的Si（111）衬底摩擦。结果表明，当金属的原子间距离接近SiO_2的原子间距离时，摩擦系数增大。Ag/Cu/Ni对和Au/Pt/Si对之间也存在类似的关系（100）。Au（111）和Si（111）的组合表现出明显的摩擦各向异性，证实了上述由晶体结构相互作用决定的关系。

The friction coefficients of different metal pairs are determined by the difference in the interatomic distance between each metal material under low load conditions. Here, eight types of metal pins were rubbed against Si(111) substrates that were covered with a native oxide film. Results showed that the friction coefficient increased when the interatomic distance of the metal approached the interatomic distance of SiO_2. A similar relationship was found between pairs of Ag/Cu/Ni and Au/Pt/Si(100). The combination of Au(111) and Si(111) exhibited clear friction anisotropy, which confirmed the above-mentioned relationship that was determined by interaction between the crystal structures.