Compatible microscopic surface scanning system

Abstract

The invention relates to a compatible microscopic surface scanning system, which comprises a microscopic imaging system used for observing and confirming the position of a detected sample; the plane coarse movement displacement table has an X movement direction and a Y movement direction and is used for realizing coarse positioning on the sample and moving the sample to the position below the probe; the Z-axis approaching displacement table and the bracket thereof are used for fixing a signal acquisition circuit and realizing approaching of the probe to the sample; the nanometer displacement table and the controller thereof have movement in the X axis direction, the Y axis direction and the Z axis direction and are used for completing plane scanning in the X direction and the Y direction, and meanwhile the Z axis is used for further controlling the distance between the probe and the surface of the sample within a range of several nanometers after the scanning probe passes through the coarse proximity; the two signal acquisition circuits are respectively used for acquiring AFM signals and STM signals and transmitting the AFM signals and the STM signals to the signal acquisition equipment and the upper computer; and the signal acquisition equipment and the upper computer software are used for reading, processing and storing the signals collected by the signal acquisition circuit. The design scheme of moving the probe in the Z axis and moving the sample in the XYZ two-stage three axes is adopted, two signal acquisition circuits are compatible, the functions of AFM and STM are achieved at the same time through one set of equipment, scanning information of the microscopic surface of the sample is detected in multiple ways, the equipment cost is saved, the detection efficiency is improved, and the detection cost is reduced. And the multi-angle analysis on the microstructure of the sample is enhanced.

Description

Technical Field

[0001] The invention relates to a multifunctional experimental instrument in the field of microscopic surface imaging, and in particular to a compatible microscopic surface scanning system. Background Art

[0002] In the field of microscopic surface imaging, two commonly used techniques are atomic force microscopy (AFM) and scanning tunneling microscopy (STM). AFM uses a high-speed vibrating probe close to a sample. The atomic force influences the probe's vibration characteristics, and changes in the probe's oscillation signal amplitude or frequency can be used to reflect the sample's surface topography. STM uses a probe tip close to the sample surface and measures the tunneling current between the sample and the tip to obtain the sample's surface topography.

[0003] AFM can operate in liquid environments and measure insulating samples, but it often comes into contact with the sample during operation, causing wear on the tip. STM can achieve molecular-scale resolution, is easier to prepare probes, and offers faster imaging speeds. Both have their advantages and share similarities in many structural and control processes, such as sample alignment, scanning, and signal processing. However, these two microscopic surface imaging methods currently require different equipment, increasing instrument acquisition and learning costs. Summary of the Invention

[0004] In view of the shortcomings of the prior art mentioned above, the purpose of the present invention is to propose a compatible microscopic surface scanning system. The present invention realizes the reuse of equipment in sample alignment, coarse position adjustment, probe approach, sample scanning, signal acquisition and processing, and provides two signal acquisition circuits. It can use atomic force or tunneling current to realize scanning and imaging of the microscopic surface of the sample. One instrument can meet the application scenarios of most microscopic surface scanning, reducing the production and purchase cost and learning threshold of the instrument.

[0005] To achieve the above-mentioned objectives, the present invention provides a compatible microscopic surface scanning system. According to an embodiment of the present invention, the device includes a microscopic imaging system for observing and confirming the position of the sample being measured; a planar coarse motion stage with two XY motion directions for coarsely positioning the sample and moving the sample under the probe; a Z-axis approach stage and its bracket for fixing the signal acquisition circuit and enabling the probe to approach the sample; a nanometer displacement stage and its controller with three XYZ axial motions for completing XY plane scanning, while the Z axis is used to further control the distance between the probe and the sample surface within the nanometer range after the scanning probe has undergone coarse approach; two signal acquisition circuits for respectively acquiring AFM and STM signals and transmitting them to the signal acquisition device and host computer; and the signal acquisition device and host computer software for reading, processing, and storing the physical quantities collected by the signal acquisition circuit.

[0006] Furthermore, the microscopic imaging system includes a microscope focus adjustment bracket, a microscope tube, an illumination device, an objective lens connector and objective lenses of various magnifications. The planar coarse motion stage includes two mutually perpendicular linear motion stages that are fastened together. A single linear motion stage is composed of two upper and lower metal plates and a spring, which are pushed by a side feed mechanism to achieve linear sliding of the upper plane relative to the lower plane. The two linear motion stages are stacked vertically to achieve searching and aligning samples on the plane. The Z-axis approach stage and its bracket, the Z-axis approach stage is a single linear motion stage placed longitudinally, which can achieve linear motion of the Z axis under the push of a feed mechanism. The stage bracket is used to fix the approach stage so that the probe is under the objective lens.

[0007] Furthermore, the three-axis nanometer stage comprises two perpendicularly fixed linear stages and a Z-axis stage, with the feed mechanism utilizing a piezoelectric crystal to achieve nanometer-scale displacement. The two linear stages are used to scan the sample surface, while the Z-axis stage further controls the probe within nanometers of the sample surface after advancing it from the linear stage. The nanometer stage controller includes three linear DC voltage output channels, which are controlled by host computer software to output DC voltage to the piezoelectric crystal, controlling its expansion and contraction.

[0008] Furthermore, the two signal acquisition circuits have consistent circuit board mounting and interface definitions, are compatible with each other, and can be easily fixed to the Z-axis proximity stage with screws. The atomic force signal acquisition circuit can be fixed to the Z-axis proximity stage, using a high-precision four-channel operational amplifier and an atomic force probe installed to drive the probe to vibrate and amplify the oscillation signal. The tunneling current acquisition circuit can be fixed to the Z-axis proximity stage, using a single-channel operational amplifier and a scanning probe installed to convert the tunneling current signal into a voltage signal and amplify the output.

[0009] Furthermore, the signal acquisition device can output an oscillation signal used to drive the atomic force probe to resonate, collect oscillation signals from the atomic force signal acquisition circuit, and simultaneously collect signals from the tunneling current acquisition circuit. The host computer and control software are used to store and process signals and control the probe's approach and scanning process. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a schematic diagram of the overall three-dimensional structure of a compatible microscopic surface scanning system according to the present invention;

[0011] Figure 2 This is a schematic diagram of the three-dimensional structure of the patented microscopic imaging system of the present invention;

[0012] Figure 3Schematic diagram of the three-axis nano-displacement stage of the present invention;

[0013] Figure 4 This is a schematic diagram of the three-dimensional structure of the planar coarse motion stage of the present invention;

[0014] Figure 5 This is a schematic diagram of the three-dimensional structure of the Z-axis approach translation stage and its bracket;

[0015] Figure 6 This is the schematic diagram of the atomic force signal acquisition circuit of the patent of this invention;

[0016] Figure 7 This is the schematic diagram of the tunneling current acquisition circuit of the present invention; DETAILED DESCRIPTION

[0017] In order for those skilled in the art to better understand the scheme of this application, the technical scheme in this application will be described in detail and completely in conjunction with the drawings in the embodiments of this application. The described embodiments are only embodiments of a part of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of this application. The directional terms mentioned in the embodiments, such as "up", "down", "front", "back", "left", "right", etc., are only reference to the directions of the drawings and are not used to limit the scope of protection of this disclosure.

[0018] This patent provides a compatible microscopic surface scanning system. The present invention comprises a microscopic imaging system 1 for observing and confirming the position of the sample being measured; a planar coarse motion stage 3 with two XY motion directions for coarsely positioning the sample and moving it under the probe; a Z-axis approach stage and its bracket 4 for securing the signal acquisition circuit and enabling the probe to approach the sample; a three-axis nanometer stage 2 and its controller 6 with three XYZ axial motion for completing XY plane scanning. The Z axis is used to further control the distance between the probe and the sample surface to the nanometer range after the scanning probe has undergone coarse approach; two signal acquisition circuits 21 for acquiring AFM and STM signals, respectively, and transmitting them to the signal acquisition device and host computer 5; and the signal acquisition device and host computer software 5 for reading, processing, and storing the physical quantities collected by the signal acquisition circuit.

[0019] See also Figure 2 The microscopic imaging system includes a focus adjustment bracket 7, a camera 8, a microscope tube 9, an illumination device 10, an objective lens connecting bracket 11, and an objective lens 12. By adjusting the focus adjustment bracket 7, the camera 8 can obtain a clear sample image.

[0020] See also Figure 3 The three-axis nanometer displacement stage includes a linear displacement stage 13, a Z-axis displacement stage 14, and a piezoelectric crystal 15. The piezoelectric displacement stage driver 6 is a three-channel voltage output device that connects the output to the piezoelectric crystal 15, causing it to expand and contract according to the output voltage, thereby driving the displacement stage to move in steps of a few nanometers.

[0021] See also Figure 4 , the plane coarse motion displacement stage includes a linear displacement stage 16 and a side feeding mechanism 17.

[0022] See also Figure 5 The Z-axis approach stage and its bracket include a bracket 20, a linear stage 18 vertically fixed to the bracket 20, a feed mechanism 19 for the stage, a signal acquisition circuit 21, and a scanning probe 22. The signal acquisition circuit 21 is fixed to the linear stage 18 by screws and has two replacement options.

[0023] See also Figure 6 , atomic force signal acquisition circuit schematic, this embodiment uses the AD8513 four-channel precision JFET amplifier, which has low offset voltage, low input bias current, low input voltage noise and low input current noise characteristics. The INPUT terminal should be connected to an external signal generator, which provides a 50-200mV drive signal according to the resonant frequency of the atomic force probe. Through the first amplifier circuit U1.1, the drive signal will be reduced by 10 times and provided to the probe X1 as a driving source to drive its resonance. The second amplifier circuit realizes the parasitic capacitance compensation of the circuit through VR1. As the probe gradually approaches the sample, its needle tip is subject to the restraining effect of the sample's atomic force, and the amplitude will decrease. After being amplified by the last two stages of amplifier circuits, it is output to the external signal acquisition device through the OUTPUT terminal. This signal can reflect the protrusions and depressions of the sample's surface morphology.

[0024] See also Figure 7 Schematic diagram of the tunneling current acquisition circuit. This embodiment uses the OPA627 precision operational amplifier. The circuit's INPUT terminal is connected to a scanning probe. When the probe approaches the sample surface, a tunneling current is generated. This current is converted into a voltage signal by the amplifier circuit and amplified. The voltage is then output from the OUTPUT terminal to an external signal acquisition device, reflecting the sample's surface topography.

[0025] It is important to note that:

[0026] The aforementioned microscopic image acquisition device includes a microscopic imaging system and a camera. The microscopic imaging system can be a conventional optical microscope, a metallographic microscope, or other microscopes that use visible light to perform microscopic imaging. The camera can be a CCD or CMOS camera.

[0027] In this embodiment of the three-axis nanometer displacement stage, the feed mechanism is replaced with a piezoelectric crystal to achieve nanometer-scale displacement. In other embodiments of the present invention, piezoelectric, electromagnetic, or piezoelectric inertial displacement stages can be used to achieve the same function.

[0028] The above-mentioned planar coarse motion stage can be driven manually or electrically to achieve preliminary alignment between the probe and the sample under the microscope.

[0029] The aforementioned Z-axis approach stage can be driven electrically or manually, but generally adopts an electrically controlled automatic mode. In this embodiment, a linear stepper motor is used. During the probe approach, the collected signal is continuously detected to determine whether the approach is in place. When the collected amplitude signal or tunneling current signal reaches a certain threshold, the probe is very close to the sample surface, and the approach should be stopped promptly to prevent damage caused by hard contact between the probe and the sample.

[0030] The signal acquisition circuit described above uses a different chip model in this embodiment. Improvements based on the principles of this circuit using other op amp chips with the same parameters should be considered other embodiments of the present invention. Regarding the signal acquisition device, this embodiment uses a multifunctional lock-in amplifier with signal output, amplitude detection, and voltage detection capabilities. Other embodiments of the present invention may also utilize devices capable of detecting and acquiring voltage amplitude signals, such as signal generators, benchtop voltmeters, or oscilloscopes.

[0031] The specific working steps of this invention are as follows:

[0032] Atomic force microscope working mode. Fix the atomic force signal acquisition circuit to the Z-axis approach stage 4 with screws. Adjust the fixed position of the Z-axis approach stage bracket 20 so that the probe is located under the objective lens and ensure that it is away from the sample surface. Execute the host computer program, and the signal acquisition device 5 outputs a sinusoidal signal with a fixed amplitude according to the set frequency step and range, and collects the output signal amplitude, draws the frequency response curve, and determines the resonant frequency of the probe. Set the output of the signal acquisition device 5 to the resonant frequency and fix the output amplitude, generally 100mV. At this time, the atomic force probe is in a resonant state, and record the output amplitude of the atomic force signal acquisition circuit at this time.

[0033] Mount the sample. First, secure the sample to be measured on the nano-stage 2. Adjust the bracket 7 of the microscopic imaging system 1 so that the camera 8 obtains a clear, magnified image. Adjust the feed mechanism 17 of the coarse motion stage 3 to locate the sample and bring it under the objective lens. At this point, the sample is also under the probe. Adjust the feed mechanism 17 to determine the scanning starting point.

[0034] The scanning probe approaches. Start the upper computer approach program, and the feed mechanism 19 of the Z-axis approach stage 4 pushes the stage circuit and the probe to gradually descend. The approach step length is 0.1-1μm, which can be set in the upper computer program. During this process, the amplitude signal output by the circuit is continuously detected. When it is detected that the amplitude signal is less than 90% of the previously recorded amplitude signal away from the sample surface, the approach is changed to 0.1μm step length. When it is less than 80% of the amplitude signal away from the sample surface, the approach is stopped. The nanometer stage is controlled by the upper computer to generate three fluctuations within 1-50nm. If the amplitude signal output by the circuit is observed and there is a related fluctuation change, it proves that the atomic force can be detected.

[0035] Surface topography scanning. Determine the scanning range and number of scanning points. The software will automatically calculate the voltage output step size and then start the host computer scanning program. The scanning process collects the amplitude signal at each point to represent the sample's height and height fluctuations at that point and stores it locally. This data can be easily imported into common scanning data processing software to obtain the sample surface topography.

[0036] After scanning is completed, the needle retraction procedure will be automatically executed. The feed mechanism 19 of the Z-axis approach stage 4 pushes the stage circuit and the probe to gradually rise away from the sample surface, and the three-axis nanometer stage will return to the scanning starting point.

[0037] Scanning tunneling microscope operating mode. Secure the tunneling current acquisition circuit to the Z-axis approach stage 4 with screws. Adjust the fixed position of the Z-axis approach stage bracket 20 so that the probe is below the objective lens and away from the sample surface. Install and secure the sample.

[0038] The scanning probe approaches. The host computer's approach program is activated, and the feed mechanism 19 of the Z-axis approach stage 4 gradually lowers the stage circuit and probe. The approach distance is 0.1-1 μm and can be set in the host computer program. During this process, the circuit output signal is continuously monitored. When a tunneling current is detected, that is, when a voltage is detected at the circuit output, the approach is stopped. At this time, the nanometer stage is controlled to fluctuate within a range of a few nanometers or tens of nanometers to observe whether the tunneling current signal changes with the fluctuation of the stage. If a relevant change trend is observed, the approach is completed. If no signal change is observed, the nanometer stage is pushed upward and the fluctuation test is repeated.

[0039] Surface topography scanning. Once the scanning range and number of scanning points are determined, the software will automatically calculate the voltage output step size and initiate the host computer scanning process. During the scanning process, the amplitude signal at each point is collected to determine the sample's height and height, and stored locally. This data can be easily imported into common scanning data processing software to generate a surface topography image. After the scan is complete, the needle removal process is automatically executed.

[0040] The above are only preferred embodiments of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A compatible microscopic surface scanning system, characterized in that: It includes a microscopic imaging system; a planar coarse motion translation stage; a Z-axis approximate translation stage and its bracket; a three-axis nano-translation stage; a nano-translation stage controller; an atomic force signal acquisition circuit; a tunneling current acquisition circuit; a signal acquisition device; a host computer and control software.

2. A compatible microscopic surface scanning system according to claim 1, characterized in that: The microscopic imaging system comprises a microscope focus adjustment bracket, a microscope tube, an illumination device, an objective lens connector and objective lenses with various magnifications.

3. The compatible microscopic surface scanning system according to claim 1, characterized in that: The planar coarse motion stage comprises two fixed, perpendicular linear stages. A single linear stage is composed of two upper and lower metal plates and a spring, and is pushed by a side feed mechanism to achieve linear sliding of the upper plane relative to the lower plane.

4. The compatible microscopic surface scanning system according to claim 1, characterized in that: The Z-axis approach stage and its bracket. The Z-axis approach stage is a single linear stage placed longitudinally, which can achieve linear motion along the Z axis when driven by a feed mechanism. The stage bracket is used to secure the approach stage so that the probe is under the objective lens.

5. The compatible microscopic surface scanning system according to claim 1, characterized in that: The three-axis nano-displacement stage includes two linear displacement stages fastened perpendicularly to each other and a Z-axis displacement stage, wherein the feeding mechanism uses a piezoelectric crystal to achieve nano-level displacement.

6. The compatible microscopic surface scanning system according to claim 1, characterized in that: The nano-displacement stage controller includes three linear DC voltage output channels, which are controlled by host computer software to output DC voltage to the piezoelectric crystal to control the expansion and contraction of the crystal.

7. The compatible microscopic surface scanning system according to claim 1, characterized in that: The atomic force signal acquisition circuit can be fixed on the Z-axis proximity displacement stage, using a high-precision four-channel operational amplifier, and installed with an atomic force probe to drive the probe to vibrate and collect oscillation signals.

8. The compatible microscopic surface scanning system according to claim 1, characterized in that: The tunneling current acquisition circuit can be fixed on a Z-axis proximity stage, use a single-channel operational amplifier, install a scanning probe, convert the tunneling current signal into a voltage signal, and amplify the output.

9. The compatible microscopic surface scanning system according to claim 1, characterized in that: The signal acquisition device can output an oscillation signal for driving the atomic force probe to resonate, and collect an oscillation amplitude signal from the atomic force signal acquisition circuit; and can also collect a voltage signal from the tunneling current acquisition circuit.

10. The compatible microscopic surface scanning system according to claim 1, characterized in that: The host computer and control software are used to store and process signals and control the probe approach and scanning process.

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