Open STM: A low-cost scanning tunneling microscope with a fast approach method

In this paper, we have designed a low-cost scanning tunneling microscope (STM) priced at 300 USD or 2000 CNY. This microscope is suitable for educational purposes and low-demand research imaging at the nanometer level. This microscope's motion components and scanner are controlled using piezoelectric materials, avoiding the thermal drift associated with traditional motor control. Our tip approach algorithm, which considers the capacitance and friction characteristics during piezoelectric slider movement, has reduced the time required for sample loading to establish tunneling current to approximately 1 minute. The dimensions of the microscope body are 45×45×31.5mm(W ×L×H), and the control voltage does not exceed 15V, ensuring the safety of operators with limited experience. In the performance verification, we performed a scanning tunneling scan on a Highly Oriented Pyrolytic Graphite(HOPG) sample with bias voltages of 50mV and 60mV, resulting in clear observations of the atomic features of HOPG in the STM pattern. • 3D Models The STM body is predominantly manufactured through CNC machining of aluminum blocks. A total of 7 components need to be machined. We provide the original Solidworks design and STEP files for manufacturing in this folder. Drill information is documented in the corresponding PDF files. • PCB The STM includes eight PCBs, three utilized for the microscope's control unit, one for the pre-amplifier, and four for circuitry interconnection. The PCBs were designed using EasyEDA(Or JLC EDA in China), and this folder includes project files, schematics, and Gerber files for PCB manufacturing. • HardwareCode The central controller for the circuit control section employs the ESP32-WROOM-32E-N8 microcontroller module. This folder contains the microcontroller firmware and source code (written using the ESP-IDF framework with PlatformIO). • PythonScript This folder includes supervisory software written in Python. Install the libraries(with specific versions) and launch the software by running “launch.bat” or via the command line “python main.py”. All software source code(/PythonScript) is licensed under GPLv3. (https://www.gnu.org/licenses/gpl-3.0.en.html) Everything else is licensed under CC-BY-SA-4.0. (https://creativecommons.org/licenses/by-sa/4.0)本文设计了一款低成本扫描隧道显微镜（scanning tunneling microscope, STM），造价仅300美元或2000元人民币。该显微镜适用于教学用途以及低需求的纳米级成像研究。其运动组件与扫描器均采用压电材料驱动，规避了传统电机控制方案固有的热漂移问题。本文提出的针尖趋近算法，充分考虑了压电滑块运动过程中的电容与摩擦特性，将完成样品加载并建立隧道电流所需的时间缩短至约1分钟。显微镜机身尺寸为45×45×31.5mm（宽×长×高），控制电压不超过15V，可为经验有限的操作人员提供安全保障。在性能验证环节，我们对高定向热解石墨（Highly Oriented Pyrolytic Graphite, HOPG）样品施加50mV与60mV的偏置电压进行扫描隧道成像，最终在STM图像中清晰观测到了HOPG的原子级特征。 • 三维模型 STM机身主要通过铝合金块数控加工（CNC machining）制成，共需加工7个部件。本文件夹提供了用于制造的原始SolidWorks设计文件与STEP格式文件，钻孔参数详见对应PDF文档。 • 印刷电路板（Printed Circuit Board, PCB） 本STM共包含8块印刷电路板：3块用于显微镜控制单元，1块用于前置放大器，剩余4块用于电路互连。PCB采用EasyEDA（国内亦称JLC EDA）设计，本文件夹包含用于PCB制造的项目文件、原理图与Gerber文件。 • 硬件代码 电路控制部分的中央控制器采用ESP32-WROOM-32E-N8微控制器模块。本文件夹包含基于ESP-IDF框架结合PlatformIO开发的微控制器固件与源代码。 • Python脚本 本文件夹包含基于Python编写的监控软件。需安装指定版本的依赖库后，通过运行"launch.bat"或命令行执行"python main.py"即可启动软件。 所有软件源代码（/PythonScript目录下）均采用GPLv3协议授权（https://www.gnu.org/licenses/gpl-3.0.en.html）。其余所有内容均采用CC-BY-SA-4.0协议授权（https://creativecommons.org/licenses/by-sa/4.0）。