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研制了以石英音叉探针作为力传感器的频率调制原子力显微镜(FM-AFM)。利用石英音叉具有压电特性且品质因数高的特点,采用正反馈回路控制石英音叉自激振动于实时共振频率处,通过反馈回路中设置自动增益控制环节控制石英音叉振幅恒定;以简单的标定方法,由流经石英音叉的电流定量计算出石英音叉探针的振动幅度;设计了基于现场可编程逻辑门阵列(FPGA)芯片的数字锁相环算法,实现了对石英音叉共振频率的数字化解调。结合实验室自制的AFM控制器,实现了频率调制成像功能,得到了多种样品的清晰图像。
A frequency modulated atomic force microscope (FM-AFM) with a quartz tuning fork probe as a force sensor was developed. Quartz tuning fork with piezoelectric characteristics and high quality factor characteristics, the use of positive feedback loop control the quartz tuning fork self-excited vibration in the real-time resonant frequency through the feedback loop to set the automatic gain control of quartz tuning fork constant amplitude; a simple calibration method , The vibration amplitude of the quartz tuning fork probe is quantitatively calculated from the current flowing through the quartz tuning fork. A digital phase-locked loop algorithm based on field programmable gate array (FPGA) chip is designed to digitally demodulate the resonant frequency of the quartz tuning fork . Combined with the laboratory-made AFM controller, the function of frequency modulation and imaging was realized, and a clear image of a variety of samples was obtained.