AFM针尖压入测量中的非线性效应

根据AFM(Atomic-Force Microscope 原子力显微镜)实验得到的典型压入曲线给出了一种标定电压-挠度转化系数的方法.对压入曲线进行常规的数据处理,结果显示在起始段和末段各有5nm左右的名义压入深度.然而,有限元计算结果表明上述名义压入深度并非真正的针尖压入样品的深度.通过悬臂梁响应、光线传播、四象限接收器等几个方面的非线性效应分析,得到了实验中各部分非线性效应对实验结果的影响方式和误差范围,从而发现压入实验中四象限接收器上光斑相对移动引起的非线性效应是造成错误判读压入深度的重要原因.最后,对如何减小测量误差和如何在一定误差范围内得到可靠的实验结果给出了一些建议.

The Nonlinear Effect in Indentation Measurement of AFM

Method for calibrating conversion coefficient between the voltage and cantilever deflection is introduced in this paper based on AFM (Atomic-Force Microscope) experiment. Conventional date processing of pressure curve shows that there is a five-nanometer nominal indentation depth at the pressure curve initial and final part, respectively. However, finite element calculation shows that the nominal indentation is not a real indentation depth on sample. By analyzing cantilever response, optical design and the Position Sensitive Detector (PSD), the mode of nonlinear effect on experimental results and their error scope of each part were obtained. It shows that Position Sensitive Detector's nonlinear effect caused by light spot relative displacement is the important reason of indentation misreading of experiment data curve. Finally, some suggestions about how to reduce measurement error and get reliable results within a certain error scope are proposed.