一种利用原子力显微镜中的跳跃接触效应定量计算Hamaker常数的方法
A method to quantitatively evaluate Hamaker constant using the jump-into-contact effect in Atomic Force microscopy
摘要：
我们发现，在原子力显微镜（AFM）的悬臂梁的跳跃到接触是由一个固有的不稳定性的AFM悬臂梁的运动。分析是基于一个简单的模型的悬臂梁移动在一个非线性力场。我们表明，跳转到接触距离可以用来找到的悬臂尖与表面的相互作用。在范德华吸引相互作用的特定背景下，这种方法可以实现为测量材料的Hamaker常数的新方法。Hamaker常数是使用悬臂的力常数和尖端曲率半径从悬臂在跳接触处的偏转确定的，所有这些都可以通过测量获得。用不同弹性常数的杠杆对云母解理试样、自然氧化硅片试样和银膜试样进行了实验验证。我们强调，这里描述的方法只适用于表面，具有范德华相互作用的尖端样品相互作用。我们还发现，在跳转到接触的尖端样品分离是简单地与悬臂梁偏转在这一点上，这提供了一种方法来准确地定位表面。
英文摘要：
We find that the jump-into-contact of the cantilever in the atomic force microscope (AFM) is caused by an inherent instability in the motion of the AFM cantilever. The analysis is based on a simple model of the cantilever moving in a nonlinear force field. We show that the jump-into-contact distance can be used to find the interaction of the cantilever tip with the surface. In the specific context of the attractive van der Waals interaction, this method can be realized as a new method of measuring the Hamaker constant for materials. The Hamaker constant is determined from the deflection of the cantilever at the jump-into-contact using the force constant of the cantilever and the tip radius of curvature, all of which can be obtained by measurements. The results have been verified experimentally on a sample of cleaved mica, a sample of Si wafer with natural oxide and a silver film, using a number of cantilevers with different spring constants. We emphasize that the method described here is applicable only to surfaces that have van der Waals interaction as the tip-sample interaction. We also find that the tip to sample separation at the jump-into-contact is simply related to the cantilever deflection at this point, and this provides a method to exactly locate the surface.
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