In this paper, we introduce a low-cost, expansible, and compatible measurement and control system for atomic force microscopes (AFM) based on a quartz tuning fork (QTF) self-sensing probe and frequency modulation, which is mainly composed of an embedded control system and a probe system. The embedded control system is based on a dual-core OMAPL138 microprocessor (DSP + ARM) equipped with 16 channels of a 16-bit high-precision general analog-to-digital converter (ADC) and a 16-bit high-precision general digital-to-analog converter (DAC), six channels of an analog-to-digital converter with a second-order anti-aliasing filter, four channels of a direct digital frequency synthesizer (DDS), a digital input and output (DIO) interface, and other peripherals. The uniqueness of the system hardware lies in the design of a high-precision and low-noise digital-analog hybrid lock-in amplifier (LIA), which is used to detect and track the frequency and phase of the QTF probe response signal. In terms of the system software, a software difference frequency detection method based on a digital signal processor (DSP) is implemented to detect the frequency change caused by the force gradient between the tip and the sample, and the relative error of frequency measurement is less than 3%. For the probe system, a self-sensing probe controller, including an automatic gain control (AGC) self-excitation circuit, is designed for a homemade balanced QTF self-sensing probe with a high quality factor (Q value) in an atmospheric environment. We measured the quality factor (Q value) of the balanced QTF self-sensing probes with different lengths of tungsten tips and successfully realized AFM topography imaging with a tungsten-tip QTF probe 3 mm in length. The results show that the QTF-based self-sensing probe and the developed AFM measurement and control system can obtain high quality surface topography scanning images in an atmospheric environment.

中文翻译：

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基于石英音叉自感探头的原子力显微镜测控系统。

在本文中，我们介绍了一种基于石英音叉（QTF）自传感探头和频率调制的低成本、可扩展、兼容的原子力显微镜（AFM）测控系统，该系统主要由嵌入式控制系统和探测系统。嵌入式控制系统基于双核OMAPL138微处理器（DSP+ARM）配备16通道16位高精度通用模数转换器（ADC）和16位高精度通用数字转换器模拟转换器（DAC），六通道带二阶抗混叠滤波器的模数转换器，四通道直接数字频率合成器（DDS），数字输入输出（DIO）接口，以及其他外围设备。系统硬件的独特之处在于设计了高精度、低噪声的数模混合锁相放大器（LIA），用于检测和跟踪QTF探头响应信号的频率和相位。在系统软件方面，实现了基于数字信号处理器（DSP）的软件差频检测方法，检测针尖与样品之间的力梯度引起的频率变化，频率测量的相对误差较小超过 3%。对于探头系统，自感应探头控制器，包括自动增益控制（AGC）自激电路，是为在大气环境中具有高质量因数（Q值）的自制平衡QTF自感应探头而设计的。我们测量了具有不同长度钨针尖的平衡式 QTF 自传感探针的品质因数（Q 值），并成功地实现了长度为 3 mm 的钨针尖 QTF 探针的 AFM 形貌成像。结果表明，基于QTF的自传感探头和研制的AFM测控系统能够在大气环境下获得高质量的地表形貌扫描图像。