Department of Mechanical Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung 80807, Taiwan.
Micron. 2013 Jan;44:410-8. doi: 10.1016/j.micron.2012.09.007. Epub 2012 Sep 19.
The nanotribology of an alkanethiol self-assembled monolayer (SAM) under tilt contact with a scanning probe tip is studied using molecular dynamics (MD) simulations. The tilt contact is described in terms of the tilt angle and the magnitude of the specimen-tip separation. The effects of tilt angle and magnitude of the specimen-tip separation on the normal force, friction force, friction coefficient, shear strength of the tip-SAM junction, and self-recovery characteristics are evaluated during the scanning probe tip process at a temperature of 300 K. The simulation results clearly show that the magnitudes and periods of the normal force and friction force increase with decreasing magnitude of the specimen-tip separation due to a large change of the tilt angle of the SAM chains during the deformation and recovery stages. For scanning and indentation processes, the effect of the tilt angle of the probe tip on the normal force is more significant than that on the friction force for the SAM. The behaviors of interfacial contact forces, friction coefficient, and shear strength strongly depend on the number of interacting atoms and the contact area, which increases with decreasing magnitude of the specimen-tip separation and increasing tilt angle of the probe tip. The self-recovery of SAM is significantly affected by the magnitude of the specimen-tip separation; the recovery ability of SAM is worse for magnitude of the specimen-tip separation below -0.9 nm with a large tilt angle of the probe tip.
使用分子动力学（MD）模拟研究了烷硫醇自组装单分子层（SAM）在倾斜接触扫描探针尖端时的纳米摩擦学。倾斜接触用倾斜角和标本-尖端分离的大小来描述。在 300 K 温度下，评估了倾斜角和标本-尖端分离的大小对法向力、摩擦力、摩擦系数、尖端-SAM 结的剪切强度以及在扫描探针尖端过程中的自恢复特性的影响。模拟结果清楚地表明，由于 SAM 链在变形和恢复阶段的倾斜角发生了很大的变化，法向力和摩擦力的大小和周期随着标本-尖端分离的大小的减小而增加。对于扫描和压痕过程，对于 SAM，探针尖端的倾斜角对法向力的影响比对摩擦力的影响更显著。界面接触力、摩擦系数和剪切强度的行为强烈依赖于相互作用原子的数量和接触面积，这随着标本-尖端分离的大小的减小和探针尖端的倾斜角的增加而增加。SAM 的自恢复受到标本-尖端分离大小的显著影响；对于具有大探针尖端倾斜角的标本-尖端分离小于-0.9 nm 的情况，SAM 的恢复能力更差。
