A scanning tunneling microscope control system based on ESP32

Abstract

The present invention discloses a scanning tunneling microscope control system based on ESP32, including a main control chip ESP32, a motor stepping module for controlling the movement of a scanning lens, a lens scanning module, a scanning signal acquisition module, a pressure module for applying voltage between a probe and a sample, and a communication module for communicating with a host computer. The main control chip ESP32 has an independently working dual-core system and comes with a scanning signal acquisition module and a communication module. The PWM output function of the main control chip ESP32 outputs different waveforms by changing the duty cycle, and then completes the DAC conversion to control the slow motor through a low-pass filter circuit; IIC communication or SPI communication external high-speed DAC to control the output of the waveform to control the fast motor. The invention replaces the existing scanning tunneling microscope control system, has low cost, small size, and fully utilizes the hardware resources of ESP32. At the same time, the chips used in the main control chip ESP32 and its accompanying filter circuit and amplifier circuit are all domestic chips, avoiding the dilemma of chip dependence on imports.

Description

Technical Field

[0001] The present invention relates to a control system of a scanning tunneling microscope, and in particular to a control system of a scanning tunneling microscope based on ESP32. Background Art

[0002] Scanning tunneling microscopy is an important analysis and characterization method for surface science, biology and materials science. It can observe the arrangement state of single atoms on the surface of materials in real time and characterize the physical and chemical properties related to the surface electronic behavior. Scanning tunneling microscopy characterizes the surface electronic state of the sample through the tunneling current between the probe and the sample, and obtains the surface information of the sample by performing two-dimensional plane scanning. At present, the control system of commercially sold scanning tunneling microscopes is relatively complex, mainly composed of components such as industrial control boards, data acquisition cards and drive circuits. The industrial control board is installed with a real-time operating system and connected to the host PC via Ethernet. The PC is installed with the corresponding software to control the lower computer and the data acquisition card to output the corresponding drive signal and collect the required signal. The system has superior performance and mature technology, and is widely used in scanning tunneling microscope equipment. However, its high cost, large size, insufficient hardware resources and dependence on imported chips limit its use in scientific research. Summary of the invention

[0003] Purpose of the invention: The purpose of the present invention is to solve the problems of high cost, bulky size and reliance on imported chips in the scanning tunneling microscope control system, and to provide a scanning tunneling microscope control system based on ESP32.

[0004] Technical solution: The scanning tunneling microscope control system based on ESP32 described in the present invention includes a main control chip ESP32, a motor stepping module for controlling the movement of the scanning lens, a lens scanning module, a scanning signal acquisition module, a pressure module for applying voltage between the probe and the sample, and a communication module for communicating with a host computer. The main control chip ESP32 has an independently working dual-core system and comes with a scanning signal acquisition module and a communication module.

[0005] Furthermore, the motor stepper module is compatible with a slow motor whose received signal changes slowly and a fast motor whose received signal changes quickly.

[0006] Furthermore, the PWM output function of the main control chip ESP32 outputs different waveforms by changing the duty cycle, and then completes the DAC conversion through a low-pass filter circuit to achieve control of the slow motor; the IIC communication or SPI communication of the main control chip ESP32 uses an external high-speed DAC to control the output of the waveform to achieve control of the fast motor.

[0007] Furthermore, the lens scanning module includes two-dimensional plane scanning imaging of the sample and adjusting the extension or contraction of the scanning lens.

[0008] Furthermore, the two 8-bit DACs of the main control chip ESP32 control the lens scanning module to perform two-dimensional plane scanning imaging by outputting triangular waves, and the image resolution is 256*256; the main control chip ESP32 outputs PWM waveforms with different duty cycles, and then applies different DC voltages to the electrodes inside the scanning lens through low-pass filtering to achieve the extension or shortening of the scanning lens.

[0009] Furthermore, the ADC acquisition module of the main control chip ESP32 includes a voltage signal obtained by processing the current in the tunnel through a pre-amplifier circuit and scaling the signal to 0-3.3V through a proportional circuit to collect the scanning signal, and the sampling rate is 128Hz to 5120Hz.

[0010] Furthermore, the main control chip ESP32 filters the PWM output waveform through a filter circuit to apply voltage between the scanning probe and the sample.

[0011] Furthermore, the main control chip ESP32 communicates with the host computer via WIFI or Bluetooth.

[0012] Furthermore, the PWM waveform and DAC signal output by the main control chip ESP32 for controlling the motor stepping module and the lens scanning module include filtering out the superimposed DC component through a subtraction circuit and amplifying the signal through an amplifier circuit.

[0013] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. Low cost. The main control chip ESP32 is cheap, and the cost of accessories such as superimposed filtering and amplifying circuits is much lower than that of imported controllers; 2. Small size. The main control board and the filtering circuit and the amplifying circuit are integrated together, which greatly reduces the size of the controller; 3. The hardware resources of ESP32 are fully utilized to reduce the waste of resources; 4. The chips used in the main control chip ESP32 and its accompanying filtering circuit and amplifying circuit are all domestic chips, avoiding the dilemma of relying on imported chips. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the framework of the present invention;

[0015] Figure 2 It is a work flow chart of the present invention;

[0016] Figure 3 It is a scanning flow chart of the present invention;

[0017] Figure 4 This is the pinout diagram of the main control chip of the present invention. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0019] like Figure 1-4 The ESP32-based scanning tunneling microscope control system shown in the figure includes a main control chip ESP32, a motor stepping module for controlling the movement of the scanning lens, a lens scanning module, a scanning signal acquisition module, a pressure module for applying voltage between the probe and the sample, and a communication module for communicating with the host computer. The main control chip ESP32 has an independently working dual-core system and comes with a scanning signal acquisition module and a communication module. Core 1 is responsible for processing the signals of the motor stepping module and the lens scanning module, and core 0 is responsible for processing the signals of the pressure module and the communication module.

[0020] The pin assignment of the main control chip ESP32 is shown in Table 1. Among them, the IO25 and IO26 pins are used as 8-bit DAC to output two triangular waves to control the scanning lens to scan the sample in the XY two-dimensional plane. The IO34 pin is used as the ADC input to collect the tunnel current signal. The motor stepper module, the four pins IO12 to IO15 are used to control the signal output of the slow motor; the high-speed control signal output of the fast motor uses an external high-speed DAC module, the IO21 and IO22 pins are used as IIC communication to control the DAC module, and the IO5, IO18, IO19, and IO23 pins are used as SPI communication to control the DAC module. The electrodes inside the scanning lens are controlled by the IO32 pin. The DC bias between the probe and the sample is output using the IO33 pin. The PWM DC reference signal used in the subtraction circuit and the amplifier circuit is output using the IO27 pin.

[0021] Table 1 Pin assignment

[0022] Modules Pin Number IIC IO21, IO22 SPI IO5, IO18, IO19, IO23 DAC IO25, IO26 ADC IO34 PWM (motor module) IO12-IO15 PWM (scanning electrodes inside the lens) IO32 PWM (DC bias) IO33 PWM (DC reference) IO27

[0023] After connecting the circuit, download the program to the main control chip ESP32, such as Figure 2 The workflow diagram of the scanning electron microscope is shown.

[0024] The first step is to connect the main control chip ESP32 to the host PC or mobile phone via WIFI / Bluetooth. In the host computer interface, set the motor step voltage, motor step speed, bias value and other parameters, set the tunnel current threshold to 1V, and run the program button of the motor step module.

[0025] In the second step, the main control chip ESP32 first outputs the set bias value and outputs the PWM DC reference signal; then controls the scanning lens to slowly extend to the longest. In this process, it detects in real time whether the tunnel current reaches the threshold. If it does not reach the threshold, the scanning head is retracted to the shortest, and then the motor is controlled to push the scanning head forward. Then continue to control the scanning head to extend to the longest, detect whether the tunnel current reaches the current, and repeat this cycle until the tunnel current reaches the threshold. At this time, the stepping program ends automatically, the bias and DC reference remain unchanged, and the scanning head extension signal no longer changes, keeping the tunnel current unchanged.

[0026] Step 3: When the tunnel current reaches the set threshold, it means that the needle tip has approached the sample surface. Click the scanning program button to start scanning. The scanning program flow chart is as follows: Figure 4 As shown. First, the IO25 and IO26 pins of the two DACs output 0X00 to control the scanning lens to reset in the X and Y directions. Then enter the small loop 1: the tunnel current signal amplified by the pre-amplifier circuit is collected through the IO34 pin of the ADC and stored in the first bit of the Buf_X1 array, which has a total of 256 elements; then the IO25 pin output of the DAC plus 1 controls the movement of the scanning lens in the X direction, and determines whether the DAC output exceeds OXFF. If not, the amplified tunnel signal is collected through the IO34 pin of the ADC and stored in the next bit of the Buf_X1 array. If yes, the content of the Buf_X1 array is uploaded to the host computer via WIFI or Bluetooth; after receiving this group of data, the host computer draws the image in real time. Each time a group of data is received, a line of image data is updated until all the data is uploaded. The size of each image is 256*256. Entering small loop 2: DAC output decreases gradually to control the scanning lens to move in the X direction, and the tunnel current signal amplified by the pre-amplifier circuit is collected through the IO34 pin of the ADC, and the collected data is saved in the Buf_X2 array. The data in the Buf_X2 array is transmitted to the host computer through WIFI or Bluetooth. After receiving this group of data, the host computer draws another image in real time. Each time a group of data is received, a line of image data is updated until all the data is uploaded. The size of each image is 256*256. The image obtained by increasing the voltage in the X direction of the scanning tube in turn according to the data uploaded by Buf_X1 is completed, and the image obtained by decreasing the voltage in the X direction of the scanning tube in turn according to the data uploaded by Buf_X2 is completed. After completing small loops 1 and 2, the scanning lens returns to the origin. At this time, the IO26 pin output of the DAC is increased by 1 to control the scanning lens to move in the Y direction, and it is judged whether the DAC output exceeds OXFF. If not, the amplified tunnel signal is continued to be collected through the IO34 pin of the ADC, and small loops 1 and 2 are repeated; if it is, it indicates that the sample scan is completed, and the scanning lens is reset to wait for the next scan instruction.

Claims

1. A scanning tunneling microscope control system based on ESP32, characterized in that It includes a main control chip ESP32, a motor stepping module for controlling the movement of the scanning lens, a lens scanning module, a scanning signal acquisition module, a pressure module for applying voltage between the probe and the sample, and a communication module for communicating with the host computer; the main control chip ESP32 has an independently working dual-core system and comes with a scanning signal acquisition module and a communication module; the motor stepping module is compatible with a slow motor with a slow receiving signal change and a fast motor with a fast receiving signal change; the IIC communication or SPI communication of the main control chip ESP32 uses an external high-speed DAC to control the output of the waveform to achieve control of the fast motor; the PWM output function of the main control chip ESP32 outputs different waveforms by changing the duty cycle, and then completes the DAC conversion through a low-pass filter circuit, thereby achieving The present invention controls the slow motor; the two 8-bit DACs of the main control chip ESP32 control the lens scanning module to perform two-dimensional plane scanning imaging by outputting triangular waves, and the PWM output function of the main control chip ESP32 applies different DC voltages to the electrodes in the scanning lens through low-pass filtering to achieve the extension or shortening of the scanning lens; the ADC acquisition module of the main control chip ESP32 obtains the voltage signal through the pre-amplifier circuit and collects the scanning current signal in the tunnel after scaling the signal through the proportional circuit; the PWM output function of the main control chip ESP32 applies voltage between the scanning probe and the sample through the filter circuit; the PWM output function of the main control chip ESP32 provides a PWM DC reference signal to the subtraction circuit and the amplifier circuit.

2. The scanning tunneling microscope control system based on ESP32 according to claim 1, characterized in that: The lens scanning module includes two-dimensional plane scanning imaging of the sample and adjusting the extension or contraction of the scanning lens.

3. The scanning tunneling microscope control system based on ESP32 according to claim 2, characterized in that: The image resolution of the two-dimensional plane scanning imaging is 256*256.

4. The scanning tunneling microscope control system based on ESP32 according to claim 1, characterized in that: The ADC acquisition module of the main control chip ESP32 scales the signal to 0-3.3V through a proportional circuit.

5. The scanning tunneling microscope control system based on ESP32 according to claim 1, characterized in that The main control chip ESP32 communicates with the host computer via WIFI or Bluetooth.

6. The scanning tunneling microscope control system based on ESP32 according to claim 1, characterized in that The PWM waveform and DAC signal output by the main control chip ESP32 for controlling the motor stepping module and the lens scanning module include filtering out the superimposed DC component through a subtraction circuit and amplifying the signal through an amplifier circuit.

Images