Single-component atmospheric particle thickness measurement method based on transmission electron microscope image

Abstract

The invention provides a single-component atmospheric particle thickness measurement method based on a transmission electron microscope image. The method comprises the following steps: S1, manufacturing a standard particle reference group, collecting to-be-detected particles in the atmosphere, and obtaining standard particles and TEM images of the to-be-detected particles; s2, analyzing the transmission electron microscope image by adopting ImageJ to obtain a reference gray value; s3, obtaining different particle size gray levels of standard particles, and taking absolute values after removing reference gray values; s4, establishing a function relationship between the standard particle size and a gray absolute value; s5, partitioning the particles to be measured, and calculating absolute values of the particle gray values in the partitions after the reference gray value is removed; and S6, substituting the absolute value of the gray value of the particle in each partition into a function of the standard particle size and the absolute value of the gray value, and calculating to obtain the thickness of the particle in each partition. According to the method, the change of the gray value of the TEM image of the particulate matter is associated with the standard particles with different particle sizes, so that the thickness of the single-component atmospheric particles can be quickly and conveniently obtained.

Description

Technical Field

[0001] The invention relates to the field of environmental aerosols, in particular to a single-component atmospheric particle thickness measurement method based on transmission electron microscope images. Background Art

[0002] The composition of environmental aerosols is complex and diverse. In addition to solid particles, liquid particles, and organic components, there are also some biological bacteria and viruses. The mixed existence of various particles causes pollution to the atmospheric environment. Measuring and analyzing the thickness of single particles in environmental aerosols helps to understand climate change in a timely manner and reduce atmospheric impacts. Single-component atmospheric particles are particles composed of a certain specific component, such as black carbon, sand and dust. Black carbon is a chain polymer of carbon spheres with strong light absorption characteristics. It is an important absorptive aerosol; sand and dust particles are mainly composed of minerals and soil particles. Transmission electron microscopy is often used in atmospheric environmental research to analyze the microscopic morphology of particles. The analysis based on transmission electron microscopy is generally limited to two-dimensional area and circumference, and cannot involve three dimensions. In order to quickly and easily determine the thickness of single-component particles in environmental aerosols and facilitate the optical calculation of aerosol particles, it is necessary to realize the thickness measurement of single-component particles based on transmission electron microscope images.

[0003] The existing methods for analyzing the microscopic morphology of atmospheric particles have obvious deficiencies in the rapid measurement of the thickness of single-component particles. In 2014, Zhou Jinhua et al. from the University of Science and Technology of China proposed a method for measuring particle size based on image grayscale of microscopic imaging. The image of the particle was obtained through a microscope, and a characteristic curve of the equivalent diameter and the true diameter of the particle was established based on the image, which was used to accurately obtain the true diameter of the unknown particle. In 2015, Bai Benfeng et al. from Tsinghua University proposed a method for measuring the particle size of a single nanoparticle. By obtaining the dark field microscope image of the scattered light spot of the nanoparticle, the relationship between the intensity of the scattered light spot and the particle size was established to achieve the measurement of the particle size. In 2021, Chu Huaqiang et al. from Anhui University of Technology proposed a method for measuring the particle size and area of ​​soot particles based on ImageJ. The background of the TEM image of soot particles was removed by Photoshop, making the measurement results of the particle size and area of ​​soot particles more accurate. However, this method cannot measure the thickness of single-component particles through TEM images. Therefore, it is of great significance to develop a method for measuring the thickness of single-component atmospheric particles based on transmission electron microscope images for aerosol environmental analysis. Summary of the invention

[0004] The purpose of the present invention is to provide a method for measuring the thickness of single-component atmospheric particles based on transmission electron microscope images. The method uses transmission electron microscope TEM image analysis technology to construct a grayscale value-particle size-thickness association, and obtains the thickness of single-component atmospheric particles simply and quickly.

[0005] The present invention is achieved in that:

[0006] The present invention samples standard particles and particulate matter in the atmosphere, analyzes transmission electron microscope images, obtains a standard particle size-grayscale absolute value function relationship, divides single-component particles in the atmosphere (particles of the same component), and substitutes the grayscale in each partition into the standard particle size-grayscale absolute value function, thereby calculating the thickness of single-component atmospheric particles. The method of the present invention can conveniently and quickly realize particle thickness detection, and can also perform three-dimensional morphology modeling of the particle surface microstructure.

[0007] A method for measuring the thickness of single-component atmospheric particles based on transmission electron microscope images comprises the following steps:

[0008] S1. Prepare standard particles: prepare aqueous solutions of spherical particle samples of different particle sizes, and drop the aqueous solutions of spherical particle samples onto a copper mesh after dilution and ultrasonication; the standard particles are carbon spheres and silica particles;

[0009] S2. Performing a transmission electron microscope test on the standard particles, and obtaining the grayscale absolute value of the standard particles according to the transmission electron microscope image; the grayscale absolute value of the standard particles is obtained by subtracting the grayscale value of the copper mesh carbon film from the grayscale value of the standard particles and taking the absolute value;

[0010] S3. Establishing a rectangular coordinate system according to the standard particle size and the grayscale absolute value, drawing a scatter plot of the standard particle size and its corresponding grayscale absolute value, and obtaining a functional relationship curve between the standard particle size and its corresponding grayscale absolute value by fitting;

[0011] S4. Use an aerosol single particle sampler to collect particles in the air, introduce the airflow containing particles into a heat diffuser, set the heat diffuser to a preset temperature to remove impurities on the surface of the particles, and then make the particles to be tested adhere to the copper mesh;

[0012] S5. Analyze the particles attached to the copper mesh using a transmission electron microscope, identify the black carbon and dust in the particles to be tested, and save the corresponding transmission electron microscope images;

[0013] S6. Partition the transmission electron microscope images of black carbon and dust respectively, and the area size of the partitioned regions is the same as the minimum particle size of standard particles of the same composition;

[0014] S7. Read the gray value of the single-component particles in each partition on the transmission electron microscope image of black carbon and dust, and then subtract the reference gray value of the copper mesh carbon film to obtain the absolute value;

[0015] S8. Substitute the grayscale absolute value of the single-component particles in each partition into the functional relationship between the particle size and the grayscale absolute value of the standard particles of the corresponding component, and calculate the thickness value of the single-component particles in each partition.

[0016] In the above scheme, step S4 can be performed after step S1, that is, on the same copper mesh, standard particles and atmospheric particles to be measured are prepared. The atmospheric particles to be measured usually include black carbon and dust.

[0017] In the above scheme, in step S5, black carbon and dust in the particulate matter are first identified based on the microscopic morphology of the image in the transmission electron microscope image. If black carbon and dust cannot be identified based on the microscopic morphology, they are then identified with the aid of an X-ray spectrometer.

[0018] Preferably, the calculation method of the reference grayscale value of the copper mesh carbon film in steps S2 and S7 is as follows: read the grayscale value distribution of the copper mesh carbon film in the transmission electron microscope image, select several points in the grayscale value distribution of the copper mesh carbon film and average the grayscale values ​​to obtain the reference grayscale value of the copper mesh carbon film.

[0019] Preferably, in step S3, the functional relationship between the standard particle diameter and its corresponding grayscale absolute value is a linear function relationship.

[0020] Preferably, the method further comprises step S9, wherein a 3D drawing tool is used to obtain a three-dimensional model of the surface microstructure of the single-component particles according to the thickness values ​​of the single-component particles in each partition.

[0021] Preferably, the preset temperature in step S4 is 500-600°C.

[0022] The present invention measures the thickness of single-component atmospheric particles based on transmission electron microscope images. When a high-energy electron beam of a transmission electron microscope is used to irradiate particles, the grayscale on the image obtained by the interaction between the electron beam and a substance of the same component reflects the depth, i.e., the thickness, of the electron beam penetrating the substance, and the grayscale is not affected by the morphology of the substance. Therefore, by associating the grayscale value change of the particle TEM image with standard particles of different particle sizes, the thickness of single-component particles can be accurately measured. A three-dimensional morphological model can also be constructed to facilitate optical calculation of aerosol particles, thereby reducing the influence of the image on the thickness measurement of single-component particles, effectively reducing errors in the image processing process, and concretely depicting the three-dimensional morphology. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flow chart of the method of the present invention.

[0024] Figure 2 It is a transmission electron microscope image of the standard granular silicon dioxide and the collected dust in the air in the embodiment of the present invention.

[0025] Figure 3 It is a fitting curve diagram of the particle size and grayscale absolute value of the standard granular silicon dioxide in the embodiment of the present invention.

[0026] Figure 4 It is a schematic diagram of dividing the sand and dust in the air collected by the embodiment of the present invention into different zones.

[0027] Figure 5 It is a graph of the thickness test results of several partitions of sand and dust in the air collected by an embodiment of the present invention. DETAILED DESCRIPTION

[0028] Combination Figure 1 The single-component atmospheric particle thickness measurement method based on transmission electron microscope images provided by the present invention specifically comprises the following steps:

[0029] S1. Make standard particles: Prepare different particle sizes D1...D for carbon spheres and silica respectively m (m≥2) carbon sphere aqueous solution sample and silicon dioxide aqueous solution sample, the carbon spheres and silicon dioxide prepared here are all solid spherical structures. Use a pipette to dilute the carbon sphere and silicon dioxide aqueous solution samples, ultrasonically obtain relatively dispersed carbon spheres and silicon dioxide, and then use a pipette to absorb a certain amount of diluted sample solution and drop it on a clean copper mesh to obtain carbon sphere standard particles and silicon dioxide standard particles.

[0030] In a specific embodiment, the standard particles produced in this step can be any one of carbon spheres and silicon dioxide, or both standard particles can be produced.

[0031] S2. Obtain the transmission electron microscope image of the standard particles through a transmission electron microscope, import the transmission electron microscope image of the standard particles into imageJ, convert the RGB image into an 8-bit image for analysis, read the gray value distribution of the copper mesh carbon film in the image, and select some points V1-V n (n≥2) is averaged and the gray value of the carbon film is calculated as a benchmark. Copper mesh carbon film benchmark gray value V L The calculation formula is as follows:

[0032]

[0033] Among them, V L is the reference gray value of the copper mesh carbon film, and selects some points V n Sum and average.

[0034] S3. In the transmission electron microscope (TEM) image of the standard particles, the grayscale at the center of the standard particles corresponds to the length of the thickness and diameter. Take a certain amount of standard particles of different sizes for analysis, and use imageJ to confirm the particle size D1...D of the standard particles in the image. m . Read the gray value C1...C corresponding to the center position of the standard particle on the image m (m≥2) and then remove the reference gray value V L , and obtain different particle sizes D1...D mThe absolute value is taken after the real gray value of the standard particles under the condition is calculated as follows:

[0035] V1...V m =|C1...C m -V L | (2)

[0036] Among them, V1…V m is the absolute value of grayscale of standard particles with different particle sizes, C1…C m is the gray value of the standard particles on the image, V L is the reference grayscale value of copper mesh carbon film.

[0037] S4. According to the different particle sizes of the standard particles and their corresponding grayscale absolute values, a plane rectangular coordinate system is established with different particle sizes of the standard particles D1...D m As the X-axis, the grayscale absolute value V1...V m As the Y axis, draw a scatter plot. In the scatter plot, there is a monotonic trend between different particle sizes and their corresponding grayscale absolute values. Select a certain functional relationship to fit the scatter points, so as to obtain the functional relationship between the grayscale absolute values ​​of different particle sizes of standard particles. The curve formula generated by fitting is as follows:

[0038] y=a+bx (3)

[0039] The functional relationship between the particle size and the absolute value of grayscale can be obtained for both carbon spheres and silicon dioxide standard particles through steps S2 to S4. For standard particles, their particle size and thickness are the same, so the functional relationship between the particle size and the absolute value of grayscale of the obtained standard particles can be converted into the functional relationship between the particle thickness and the absolute value of grayscale.

[0040] S5. Use an aerosol single particle sampler to collect particulate matter in the air. By introducing the airflow containing particulate matter into a heat diffuser, the heat diffuser is set to an appropriate temperature to remove impurities on the surface of black carbon and / or dust, and the particulate matter is collected on a copper mesh with standard particles attached (of course, it is also possible to collect particulate matter on other copper meshes, but the copper mesh for collecting standard particles and the copper mesh for atmospheric sampling need to be placed under an electron microscope at the same time, or at least the operating conditions of the electron microscopes for the two need to be the same). Standard particles of different particle sizes attached to the copper mesh serve as a reference group for the actual collection of particulate matter in the air.

[0041] This step can be performed in parallel with step S1, that is, before calculating the functional relationship between the thickness and grayscale value of the standard particles, the standard particles and the atmospheric particles to be tested can be collected on the copper mesh. On the same copper mesh, the standard particles serve as a reference group.

[0042] S6. Use a transmission electron microscope to analyze the particles attached to the copper mesh. Select the electron microscope to observe the particles in the field of view. First, the carbon balls and silica standard particles can be identified by their morphology. Secondly, the collected particles are classified. If the collected black carbon and dust can be identified by their morphology, the corresponding transmission electron microscope image can be directly saved; otherwise, the sample needs to be subjected to an X-ray energy spectrum analyzer, and the collected black carbon and dust can be further identified by the X-ray energy spectrum analysis results, and finally the corresponding transmission electron microscope image is saved.

[0043] S7. Partition the black carbon and dust in the TEM image separately. This partition is usually random uniform partitioning, that is, a whole regular area including the particles to be measured is divided into several small uniform areas. The more and smaller the number of blocks, the higher the accuracy of the final measurement. The uniform partitioning mentioned here refers to the uniform partitioning of a regular area including black carbon or dust, such as Figure 5 As shown in the figure, after partitioning, there are complete uniform partitions inside the particles to be tested (black carbon or dust), but there may be incomplete uniform partitions at the boundary line of the particles to be tested. The complete uniform partitions mentioned here are Figure 5 The partitions shown in C and D are as follows; while the partitions A, B, and E are incomplete uniform partitions.

[0044] S8. Continue to analyze the TEM images of dust and black carbon particles collected in the air on the copper mesh through imageJ, read the gray value of the single component particles (dust or black carbon) in each partition (the gray value can be the gray value at the center of the partition), and remove the copper mesh carbon film reference gray value V L , and then take the absolute value to obtain the absolute value of the grayscale of single-component particles (sand or black carbon) in each partition.

[0045] S9. According to the functional relationship between the different particle sizes of the standard particles and their corresponding grayscale absolute values ​​in step S4, the grayscale absolute value distribution of the single-component particles collected from the air is analyzed and read from the TEM image in step S8, and the grayscale absolute value of the single-component particles of sand or black carbon in each partition is substituted into the function of the particle size and grayscale absolute value of the standard particles of silica or carbon balls, and the thickness distribution of the single-component particles of sand and black carbon in each partition is calculated, thereby realizing the single-component atmospheric particle thickness measurement based on TEM images.

[0046] When the present invention collects particles in the air, most of the collected particles are irregular in shape, which leads to inconsistency in the grayscale value of the projected area and uneven thickness distribution. The present invention uses the particle size-grayscale absolute value correspondence method to accurately measure the thickness distribution of irregular particles, and then calculate the volume of irregular particles.

[0047] Based on the thickness information of different parts of the particles, the 3D morphology model of the single-component particles can be further constructed using 3D drawing tools. Figure 5 , Figure 5 The divided areas are uniform square blocks, and the single-component particles are irregular in shape. Therefore, there are irregular blocks (such as blocks A, B, and E) at the boundary of the single-component particles, and the interior is a complete square block (such as blocks C and D). When the area of ​​a block inside the single-component particle is greater than 50% of the area of ​​a single square block, this block is considered in the three-dimensional modeling process. The surface structure of the constructed morphological model is affected by the size of the block division. The smaller the block, the more accurately it can reproduce the surface microstructure of the particle, which is convenient for later optical calculations.

[0048] The single-component atmospheric particle thickness measurement method based on transmission electron microscope image provided by the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The described embodiment is only one embodiment of the present invention.

[0049] A standard particle reference group is prepared. The standard particles prepared in this embodiment are standard silica particles. Silica spheres of different particle sizes within the range of 115-130nm are selected to make a silica solution. The silica solution is diluted and ultrasonicated using a pipette, and then dropped onto a copper mesh to obtain standard silica particles. An aerosol single particle sampler is used to collect particulate matter from sandstorms in the north. The airflow containing particulate matter is introduced into a heat diffuser with the temperature of the heat diffuser set to 550°C. After removing impurities on the surface of black carbon or dust, the particulate matter is collected on a copper mesh with standard particles attached. Under a transmission electron microscope, the sand and dust are mainly composed of minerals and soil particles, showing an irregular, porous structure. The particles are large and have a rough surface, with different shapes and sizes, such as Figure 2 As shown, from Figure 2 The standard particles and dust particles can be identified. Save the transmission electron microscope image and use imageJ software to convert the RGB image into an 8-bit image. Select ten points in the gray value distribution of the copper mesh carbon film and calculate the copper mesh carbon film reference gray value V by formula (1): L The silica standard particles were analyzed and measured using imageJ software. Figure 2The particle sizes of the five available silica standard particles are obtained (there are two overlapping standard particles in the figure, which are not considered here because they overlap each other), and the central grayscale value of the silica standard particles is read. The grayscale value range is generally 0-255, and the grayscale absolute value of the silica standard particles is calculated by formula (2). According to the measurement results that the grayscale absolute value range of the silica standard particle image at a particle size of 115-130nm is 61.6-89.6, the functional relationship between the silica standard particle size and its corresponding grayscale absolute value is obtained by formula (3). At this time, the linear fitting equation is y=0.59569x+0.57402, as shown in Figure 3 Continue to analyze the dust collected in the air through imageJ (the particles to be tested in this embodiment are only dust), and include Figure 2 A square area including the dust in the middle is randomly and evenly divided into multiple areas for processing. The processing results are as follows Figure 4 After reading the grayscale values ​​in each dust partition, remove the reference grayscale value V L (i.e. 136.6) and take the absolute value to obtain the grayscale absolute value of different dust partitions. Substitute the grayscale absolute value of each partition into the particle size-grayscale absolute value function of the silica standard particle to calculate the thickness of each partition. Figure 5 As shown in the figure, the thickness of the five partitions of dust A, B, C, D, and E are 83.41nm, 112.35nm, 108.75nm, 118.54nm, and 90.87nm, respectively. The thickness of the dust particles that occupy more than 50% of the area of ​​the complete block in the partition map is obtained in turn, and a three-dimensional morphological model is constructed according to the different thicknesses of different partitions of the dust using a 3D drawing tool. The modeling uses cubes of different heights to represent the thickness of the block. Since the dust exists in hollow and solid states, the solid part of the dust is randomly distributed within the thickness range, so the number and distribution of the solid part cannot be determined. Therefore, a variety of three-dimensional morphological models of different shapes can be constructed. The surface structure of the morphological model is affected by the size of the block division. The smaller the block, the more accurately the surface microstructure of the particle can be reproduced, thereby facilitating the optical calculation of aerosol particles based on the surface microstructure model.

[0050] Ultimately, it will be possible to measure the thickness of single-component atmospheric particles based on TEM images, characterize the thickness of different regions in single atmospheric particles, and deepen the understanding of the microstructure of single-component particles.

Claims

1. A method for measuring the thickness of single-component atmospheric particles based on transmission electron microscope images, characterized in that: The steps include: S1. Prepare standard particles: prepare aqueous solutions of spherical particle samples of different particle sizes, and drop the aqueous solutions of spherical particle samples onto a copper mesh after dilution and ultrasonication; the standard particles are carbon spheres and silica particles; S2. Performing a transmission electron microscope test on the standard particles, and obtaining the grayscale absolute value of the standard particles according to the transmission electron microscope image; the grayscale absolute value of the standard particles is obtained by subtracting the grayscale value of the copper mesh carbon film from the grayscale value of the standard particles and taking the absolute value; S3. Establishing a rectangular coordinate system according to the standard particle size and the grayscale absolute value, drawing a scatter plot of the standard particle size and its corresponding grayscale absolute value, and obtaining a functional relationship curve between the standard particle size and its corresponding grayscale absolute value by fitting; S4. Use an aerosol single particle sampler to collect particles in the air, introduce the airflow containing particles into a heat diffuser, set the heat diffuser to a preset temperature to remove impurities on the surface of the particles, and then make the particles to be tested adhere to the copper mesh; S5. Analyze the particles attached to the copper mesh using a transmission electron microscope, identify black carbon and dust in the particles, and save the corresponding transmission electron microscope images; S6. Partition the transmission electron microscope images of black carbon and dust separately; S7. Read the gray value of the single-component particles in each partition on the transmission electron microscope image of black carbon and dust, and then subtract the reference gray value of the copper mesh carbon film to obtain the absolute value; S8. Substitute the grayscale absolute value of the single-component particles in each partition into the functional relationship between the particle size and the grayscale absolute value of the standard particles of the corresponding component, and calculate the thickness value of the single-component particles in each partition.

2. The single-component atmospheric particle thickness measurement method based on transmission electron microscope images according to claim 1 is characterized in that: The calculation method of the copper mesh carbon film reference grayscale value in steps S2 and S7 is as follows: read the grayscale value distribution of the copper mesh carbon film in the transmission electron microscope image, select several points in the grayscale value distribution of the copper mesh carbon film and average the grayscale values ​​to obtain the copper mesh carbon film reference grayscale value.

3. The single-component atmospheric particle thickness measurement method based on transmission electron microscope images according to claim 1 is characterized in that: In step S3, the functional relationship between the standard particle diameter and its corresponding grayscale absolute value is a linear function relationship.

4. The single-component atmospheric particle thickness measurement method based on transmission electron microscope images according to claim 1 is characterized in that: The method further includes step S9, wherein a 3D drawing tool is used to obtain a three-dimensional model of the surface microstructure of the single-component particles according to the thickness values ​​of the single-component particles in each partition.

5. The single-component atmospheric particle thickness measurement method based on transmission electron microscope images according to claim 1 is characterized in that: The preset temperature in step S4 is 500-600°C.

6. A method for measuring the thickness of single-component atmospheric particles based on transmission electron microscope images, characterized in that: The steps include: S1. Prepare standard particles and particles to be tested: prepare aqueous solutions of spherical particle samples of different particle sizes, and drip the aqueous solutions of spherical particle samples onto a copper mesh after dilution and ultrasonication; the standard particles are carbon spheres and silica particles; use an aerosol single particle sampler to collect particles in the air, introduce the airflow containing particles into a heat diffuser, set the heat diffuser to a preset temperature to remove impurities on the surface of the particles, and then attach the particles to be tested to the copper mesh with standard particles; S2. Perform transmission electron microscopy test on the standard particles and the particles to be tested on the copper mesh; S3. Obtaining the absolute value of the grayscale of the standard particles according to the transmission electron microscope image of the standard particles; the absolute value of the grayscale of the standard particles is obtained by subtracting the absolute value of the grayscale value of the copper mesh carbon film reference from the grayscale value of the standard particles; S4. Establishing a rectangular coordinate system according to the standard particle size and the grayscale absolute value, drawing a scatter plot of the standard particle size and its corresponding grayscale absolute value, and obtaining a functional relationship curve between the standard particle size and its corresponding grayscale absolute value by fitting; S5. Analyze the particles attached to the copper mesh using a transmission electron microscope, identify black carbon and dust in the particles, and save the corresponding transmission electron microscope images; S6. Partition the transmission electron microscope images of black carbon and dust separately; S7. Read the gray value of the single-component particles in each partition on the transmission electron microscope image of black carbon and dust, and then subtract the reference gray value of the copper mesh carbon film to obtain the absolute value; S8. Substitute the grayscale absolute value of the single-component particles in each partition into the functional relationship between the particle size and the grayscale absolute value of the standard particles of the corresponding component, and calculate the thickness value of the single-component particles in each partition.

7. The single-component atmospheric particle thickness measurement method based on transmission electron microscope images according to claim 6 is characterized in that: The calculation method of the copper mesh carbon film reference grayscale value in steps S3 and S7 is as follows: read the grayscale value distribution of the copper mesh carbon film in the transmission electron microscope image, select several points in the grayscale value distribution of the copper mesh carbon film and average the grayscale values ​​to obtain the copper mesh carbon film reference grayscale value.

8. The single-component atmospheric particle thickness measurement method based on transmission electron microscope images according to claim 6 is characterized in that: In step S4, the functional relationship between the standard particle diameter and its corresponding grayscale absolute value is a linear function relationship.

9. The single-component atmospheric particle thickness measurement method based on transmission electron microscope images according to claim 6 is characterized in that: The method further includes step S9, wherein a 3D drawing tool is used to obtain a three-dimensional model of the surface microstructure of the single-component particles according to the thickness values ​​of the single-component particles in each partition.

10. The single-component atmospheric particle thickness measurement method based on transmission electron microscope images according to claim 6 is characterized in that: The preset temperature in step S1 is 500-600°C.

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