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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 common scanning modes of atomic force microscopy (AFM). Tap mode probe vibration signal amplitude as a feedback signal, the implementation of real-time detection. At present, there are two methods of analog detection and digital detection. The analog detection method has larger error due to the inherent temperature drift of the analog device. The digital detection method has the advantages of small error but large amount of operation. An improved digital lock-in amplifier (MDLIA) is proposed to detect the tapping mode signal amplitude in real time. The self-made AFM scanning imaging system has both the advantages of smaller error and smaller operation. MDLIA uses a square wave signal of the same frequency and phase as the vibration signal as a reference signal, so that vibration signal amplitude can be detected using only one-channel operation. Firstly, the principle of MDLIA is introduced through theoretical analysis, and then the components and implementation process are introduced. Finally, the computational time-consuming experiment is used to verify the MDLIA’s low computational complexity and fast computing speed. The error comparison experiment shows that the MDLIA error is small, Standard grid scanning experiments verify the stability of MDLIA.