Micro-tribological study of metal surfaces using scanning probe microscope

利用扫描探针显微镜（SPM）进行了微摩擦学研究，该显微镜可以测量侧向力和法向力图像。SPM放置在气氛控制装置中，尖端样品周围的相对湿度控制在30%到70%之间。测量也在高纯度水浴中进行。所研究的样品是云母、HOPG和MoS_2的切割表面，以及Ni、Cu和Al的抛光表面。为了讨论吸附水分子和水的毛细凝聚的微摩擦学效应，定量地检测了样品表面法向载荷的侧向力图像。对于云母、HOPG和MoS_2表面，采用与原子尺度形貌相同的方法获得了具有晶格周期性的横向力图像。发现侧向力大小对法向力的依赖关系受尖端和样品周围大气的影响。在低相对湿度（30%）下，原子尺度成像中的侧向力大小几乎与正常载荷无关。在高相对湿度，70%，横向力的大小表现出依赖于在法向载荷。在水中，侧向力的大小大约与正常载荷成正比。对于金属表面，横向力的平均值几乎相同。我们得出结论，由于水的存在而产生的粘附力对横向力有严重的影响。从赫兹分析、弹流润滑和水的毛细凝结等观点出发，揭示了尖端试样的接触机理。

Micro-tribological studies are made using a scanning probe microscope (SPM) which can measure the lateral force as well as the normal force images. The SPM is placed in an atmosphere control apparatus and the relative humidity around the tip-sample is controlled from 30% to 70%. Measurements are also performed in a high purity water bath. Samples investigated are the cleaved surfaces of mica, HOPG and MoS_2, and the polished metal surfaces of Ni, Cu and Al. In order to discuss the micro-tribological effects of adsorbed water molecules and the capillary condensation of water, the lateral force images are examined quantitatively as a function of the normal load on the sample surface. For surfaces of mica, HOPG and MoS_2, lateral force images with the lattice periodicity are obtained in the same manner as atomic scale topography images. The dependence of lateral force magnitude on the normal force is found to be affected by the atmosphere around the tip and the sample. At low relative humidity, 30%, the lateral force magnitude in atomic scale imaging is almost independent of the normal load. At high relative humidity, 70%, the lateral force magnitude exhibits dependence on the normal load. In water, the lateral force magnitude is approximately in proportion to the normal load. For surfaces of metal almost same behavior is obtained in the average value of lateral force. We conclude that the adhesive force due to the presence of water has severe influence upon the lateral force. From discussion on the viewpoints of Hertz analysis, Elasto-Hydrodynamic Lubrication and capillary condensation of water, the contact mechanism of the tip-sample is revealed.