Fukuma Takeshi, Yoshioka Shunsuke, Asakawa Hitoshi
Frontier Science Organization, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan.
Rev Sci Instrum. 2011 Jul;82(7):073707. doi: 10.1063/1.3608447.
We have developed a wideband phase-locked loop (PLL) circuit with real-time phase correction for high-speed and accurate force measurements by frequency modulation atomic force microscopy (FM-AFM) in liquid. A high-speed operation of FM-AFM requires the use of a high frequency cantilever which, however, increases frequency-dependent phase delay caused by the signal delay within the cantilever excitation loop. Such phase delay leads to an error in the force measurements by FM-AFM especially with a low Q factor. Here, we present a method to compensate this phase delay in real time. Combined with a wideband PLL using a subtraction-based phase comparator, the method allows to perform an accurate and high-speed force measurement by FM-AFM. We demonstrate the improved performance by applying the developed PLL to three-dimensional force measurements at a mica/water interface.
我们开发了一种宽带锁相环（PLL）电路，用于在液体中通过调频原子力显微镜（FM-AFM）进行高速且精确的力测量，并具有实时相位校正功能。FM-AFM的高速运行需要使用高频悬臂梁，然而，这会增加由悬臂梁激励回路内的信号延迟引起的频率相关相位延迟。这种相位延迟会导致FM-AFM力测量出现误差，尤其是在低品质因数的情况下。在此，我们提出一种实时补偿这种相位延迟的方法。结合使用基于减法的相位比较器的宽带PLL，该方法能够通过FM-AFM进行精确且高速的力测量。我们通过将所开发的PLL应用于云母/水界面的三维力测量来证明其性能的提升。
