基于原子力显微镜的纳米尺度摩擦力的速度依赖关系

以硅为探针、带有自然氧化物的硅(100)晶面为基底样品,利用原子力显微镜研究了探针扫描速度对于单个微凸体系统中摩擦力的影响.首先,利用热噪声标定法测量出硅悬臂梁的法向弹簧常数和法向灵敏度;然后,利用改进的楔形校准法,通过扫描三角光栅得出侧向灵敏度;最后,测量出扫描区域为15 μm×15 μm、正压力为-5 ～ 10 nN、扫描速度为2.5 ～1 000 μm/s下的摩擦力.实验结果表明,不同速度下摩擦力随正压力的增加呈近似线性增加,服从经典库仑定律.当扫描速度小于40 μm/s时,速度增加所导致的摩擦力的增加不明显;当扫描速度大于40 μm/s时,速度增加则引起摩擦力急剧增加.该结果与热激发的Tomlinson模型的计算结果吻合.

Velocity-dependent nano-scale friction under atomic force-microscope

The effect of the scanning velocity on the friction in a convex system is studied between a Si tip and a naturally oxidized Si(100) substrate by the atomic force microscope(AFM).Firstly,the normal spring constant and the normal sensitivity of the Si cantilever are calibrated by the thermal noise calibration method.Then,the lateral sensitivity is obtained through scanning a triangular grating by the improved wedge calibration method.Finally,the friction-load relation curves with the scan area of 15 μm×15 μm,the normal force of-5～10 nN and the scanning velocity of 2.5～1 000 μm/s are obtained.The experimental results show that with different velocities,the friction increases nearly linearly with the load,which obeys the classical Coulomb law.When the scanning velocity is below 40 μm/s,the increase in the friction is insignificant due to the increase in the velocity.In contrast,when the velocity exceeds 40 μm/s,the friction enhancement becomes significant.The nonlinear correlation between the frictional force and the scanning velocity coincides with the results computed by the thermally-excited Tomlinson model.