基于改进型DLIA的AFM探针高速振幅检测

High Speed Amplitude Measurement of AFM Probe Vibration Based on Modified Digital Lock-in Amplifiers

轻敲模式是原子力显微镜(AFM)最为常见的扫描模式之一。轻敲模式以探针振动信号幅值作为反馈信号,实行实时检测。目前,有模拟检测和数字检测两种检测方法,模拟检测方法由于模拟器件固有的温漂导致误差较大,数字检测方法误差小但运算量较大。提出了一种实时检测轻敲模式信号振幅的改进型数字锁相放大器(MDLIA),在自制的AFM扫描成像系统中同时具备误差较小和运算量较小两个优点。MDLIA使用与振动信号同频同相的方波信号作为参考信号,因此仅采用单通道运算即可检测振动信号幅值。首先通过理论分析介绍了MDLIA的原理,然后介绍各组成部分及实现过程,最后通过运算耗时实验验证MDLIA运算量小且运算速度快的特点,并通过误差对比实验证明MDLIA误差较小,同时通过标准栅格扫描实验验证MDLIA的稳定性。

Tapping mode is one of the most commonly used scan modes in atomic force microscope （AFM）. The amplitude of probe vibration signal as feedback signal in tapping mode scan is mea- sured in real time. Currently, there are two kinds of measurement methods, including analog measurement and digital measurement. The analog measurement method has larger error because of intrinsic thermal drift of analog devices, and the digital measurement method realizes less error but has larger calculation. A modified digital lock-in amplifier （MDLIA） for real-time amplitude measurement in tapping model was presented. There are two advantages of less error and less cal- culation in the custom-built AFM scanning image system. The square wave signal with the same frequency and phase as the vibration signal was used as the reference signal in the MDLIA, there- fore the vibration signal amplitude was measured by the one-channel calculation. Firstly, the principle of the MDLIA was introduced by the theoretically analysis, then all components and im- plementation processes were introduced. Finally, the MDLIA was validated through three kindsof experiments. The less calculation and higher speed of the MDLIA were validated by calculation time consumption experiments, the less error of the MDLIA was validated by error comparison experiments, and the stability of the MDLIA was validated by standard grating scan experiments.