Minimization of nano-scale friction force of DLC films with the periodic structiues processed by a femto-seoond laser

众所周知，最佳的表面粗糙度能够减小侧向力。利用扫描探针显微镜(SPM)测量了空气中不同曲率半径的球形针尖在相对湿度控制下的拉力和侧向力。(1)利用扫描探针显微镜在纳米尺度上研究了周期性结构类金刚石(DLC)薄膜的摩擦性能。采用非平衡磁控溅射方法制备了类金刚石薄膜。在烧蚀阈值附近的偏振飞秒激光(τ=40fs，λ=800 nm，F=10 Hz)作用下，在类金刚石薄膜表面形成了周期性结构。用SPM验证了法向荷载和相对湿度对侧向力的影响。我们使用了带有锐化金字塔尖端的氮化硅矩形悬臂梁或球形玻璃尖端。使用锐化的锥体尖端，具有周期性结构的DLC薄膜的侧向力比不具有周期性结构的薄膜的侧向力要大。在低法向载荷和低相对湿度条件下，具有周期性结构的DLC薄膜的侧向力低于无周期性结构的薄膜。(2)对多孔Al_2O_3 Fas和花状Al_2O_3 Fas两种超疏水涂层进行了实验研究。对于曲率半径过小的正弦尖端，侧向力随表面粗糙度的增大而增大。反之，对于曲率半径较大的玻璃球尖端，侧向力几乎不受表面粗糙度的影响，且几乎为恒定值。结果表明，对于纳米尺度的摩擦力控制，表面粗糙度的控制是有效的，利用这种方法可以减小摩擦力。

It is known that the optimum surface roughness is capable of reducing lateral force. The pull-off force and lateral force were measured by using a scanning probe microscope (SPM) with various curvature radius of a spherical tip in air under the relative humidity controlled.(1)The frictional properties of the diamond-like carbon (DLC) films with the periodic structures were investigated in nano-scale using SPM. DLC films were prepared by an unbalanced magnetron sputtering method. The periodic structures have been generated on the surface of DLC films by polarized femto-second laser (τ=40fs, λ=800nm, F=10Hz) of energies nearby ablation threshold. The influence of normal load and relative humidity on the lateral forces was confirmed by the SPM. We used a silicon nitride rectangular cantilever with sharpened pyramidal tip or a spherical glass tip. Using the sharpened pyramidal tip, the lateral force of the DLC film with the periodic structures was higher than that of the film without the periodic structures. On the other hand, the lateral force of the DLC film with the periodic structures was lower than that of the film without the periodic structures using a spherical glass tip at low normal load and low relative humidity.(2)The tests were performed with two kinds of super-water-repellent coating films, which are the porous Al_2O_3+FAS and the flower-like Al_2O_3+FAS. The lateral force increases with the increase in the inclination of surface asperities in case of the SiN tip whose radius of curvature is too small. On the contrary, the lateral force hardly takes the influence of the inclination of surface asperities, and almost becomes constant value with the glass sphere tip whose radius of curvature is big.From these results, it is found that for the control of the friction force in nano-scale, the control of the surface roughness is effective and we can reduce the friction force using this method.