ABSTRACT

The influence of instrumental parameters of an atomic force microscope (AFM) on adhesion forces demands clarification. Adhesion forces between a tipless cantilever and mica were measured in a humid environment to investigate the influence of instrumental parameters. The adhesion force measured repeatedly at a location is relatively stable with excellent reproducibility. The force abnormally decreases by ~10% with dwell time (0 ~ 0.4 s), then remains almost stable (0.4 ~ 10 s). The reason was the dynamic formation process of a liquid bridge. Due to a large driving pressure, the volume of the liquid bridge can increase intensely to the maximum one, which is larger than that in saturation. This leads to the reduction in the bridge by liquid flow, eventually resulting in the decrease. The force increases by a small magnitude with approach velocity and then remains stable. However, it increases logarithmically with retraction velocity and increases with piezo velocity with a concave downward shape in the logarithmic coordinate. The velocity dependence was ascribed to the dynamic enhancement of viscous force and the contact time dependence. The outcomes may help to understand the influence of instrumental parameters, and deepen the understanding of the formation mechanism of a liquid bridge.

摘要

原子力显微镜 (AFM) 的仪器参数对粘附力的影响需要澄清。在潮湿环境中测量无端悬臂和云母之间的粘附力，以研究仪器参数的影响。在一个位置重复测量的粘附力相对稳定，重现性好。随着停留时间（0 ~ 0.4 s），力异常下降约 10%，然后几乎保持稳定（0.4 ~ 10 s）。原因是液桥的动态形成过程。由于驱动压力大，液桥的体积可以剧烈增加至最大，大于饱和时的体积。这导致通过液体流动减少桥，最终导致减少。力随着接近速度增加一个小幅度，然后保持稳定。然而，它随着缩回速度呈对数增加，并随着压电速度增加，在对数坐标中呈向下凹的形状。速度依赖性归因于粘性力的动态增强和接触时间依赖性。研究结果可能有助于理解仪器参数的影响，加深对液桥形成机制的理解。