A method for measuring the thickness of nanoparticles based on high-angle annular dark-field images of a transmission electron microscope

Abstract

The application provides a kind of nanoparticle thickness measurement method based on transmission electron microscopy high-angle annular dark-field image, belongs to the technical field of nanoparticle material.This method includes: the absolute brightness intensity value and thickness value data of standard nanoparticle with same composition and different particle size of the nanoparticle to be measured are collected to construct data set;The standard nanoparticle is regular shape nanoparticle;The relationship function of the absolute brightness intensity value and thickness value of the nanoparticle is established based on the data set;The absolute brightness intensity value of the nanoparticle to be measured is collected by transmission electron microscopy, and the thickness of the nanoparticle to be measured is obtained by the relationship function of the absolute brightness intensity value and thickness value of the nanoparticle.The method effectively avoids the interference of different crystal orientations on the brightness intensity in ordinary transmission mode imaging, and can obtain accurate nanoparticle thickness information.

Description

Technical Field

[0001] This invention relates to the field of nanoparticle materials technology, and in particular to a method for measuring the thickness of nanoparticles based on high-angle annular dark-field images obtained by transmission electron microscopy. Background Technology

[0002] Nanoparticle materials, with their unique properties such as high specific surface area, high surface atomic activity, and quantum size effect, have irreplaceable application value in catalysis, energy, and biomedicine. For example, nanoparticle catalysts can significantly improve catalytic reaction efficiency, quantum dot fluorescent materials drive innovation in high color gamut display technology, and magnetic nanocarriers enable targeted thermotherapy for tumors. However, existing technologies for measuring nanoparticle thickness have limitations: X-ray diffraction has limited resolution, and dynamic light scattering makes it difficult to accurately distinguish nanoparticle morphologies. Given that nanoparticle thickness directly affects key properties such as surface activity and carrier mobility, existing measurement methods are no longer sufficient to meet the requirements for high-precision characterization. Currently, microscopy, with its high-resolution imaging capabilities, can directly obtain morphological information of nanoparticles in real space. Compared to other microscopy techniques such as atomic force microscopy, transmission electron microscopy (TEM) has become an ideal tool for nanoparticle analysis due to its atomic-level resolution, rapid imaging, and simultaneous detection of elemental composition / atomic valence states. However, in TEM, there is still a lack of efficient methods for obtaining thickness information of nanoparticles, especially irregularly shaped nanoparticles.

[0003] Therefore, a method for measuring the thickness of nanoparticles based on transmission electron microscopy images is needed. Summary of the Invention

[0004] In view of this, the present invention provides a method for measuring the thickness of nanoparticles based on high-angle annular dark-field images of transmission electron microscopy. First, the brightness intensity-thickness calibration of regular-shaped nanoparticles with the same composition as the nanoparticles to be measured is performed using transmission electron microscopy image analysis technology. Then, the thickness information of the corresponding point is obtained based on the brightness intensity in the high-angle annular dark-field image of the nanoparticles to be measured.

[0005] Therefore, the present invention provides the following technical solution:

[0006] A method for measuring the thickness of nanoparticles based on high-angle annular dark-field images obtained by transmission electron microscopy includes: A dataset is constructed by collecting absolute brightness intensity and thickness data of standard nanoparticles with the same composition as the nanoparticles to be tested but different particle sizes; the standard nanoparticles are regularly shaped nanoparticles. Based on the aforementioned dataset, a function relating the absolute brightness intensity value to the thickness value of the nanoparticles is established. The absolute brightness intensity value of the nanoparticle under test was acquired by transmission electron microscopy, and the thickness of the nanoparticle under test was obtained by the relationship function between the absolute brightness intensity value and the thickness value.

[0007] Furthermore, the standard nanoparticles include: Electron beams can penetrate crystalline and amorphous solid nanoparticles with a thickness of less than 0.5 mm along the incident direction of the electron beam. ; The standard nanoparticles may have the following shapes: spheres, cubes, and cylinders.

[0008] Furthermore, the acquisition of absolute brightness intensity and thickness data of standard nanoparticles with the same composition as the nanoparticles to be tested but different particle sizes includes: The standard nanoparticle ethanol dispersion solution was prepared, diluted and sonicated, and then dropped onto a grid. A high-angle annular dark field image of the standard nanoparticles was obtained in the scanning transmission mode of a transmission electron microscope. The absolute brightness intensity value of the pixel points in the thickness region to be measured of the standard nanoparticle is obtained based on the high-angle annular dark field image of the standard nanoparticle. The thickness of the standard nanoparticle is calculated at its center using a high-angle annular dark-field image.

[0009] Further, obtaining the absolute luminance intensity value of the pixels in the thickness region to be measured of the standard nanoparticle based on the high-angle annular dark-field image of the standard nanoparticle includes: Calculate the average brightness intensity value of the carrier support film; The average brightness intensity of the carrier support film is subtracted from the brightness intensity value of each pixel in the high-angle annular dark field image of the standard nanoparticles to obtain the processed high-angle annular dark field image of the standard nanoparticles. The absolute brightness intensity value of the pixels in the thickness region to be measured of the standard nanoparticles is determined by image analysis software based on the processed high-angle annular dark field image of the standard nanoparticles.

[0010] Furthermore, the acquisition of the absolute brightness intensity value of the nanoparticle under test by transmission electron microscopy includes: An ethanol dispersion solution of the nanoparticles to be tested was prepared, diluted and sonicated, and then dropped onto a grid. A high-angle annular dark field image of the nanoparticles to be tested was acquired in the scanning transmission mode of a transmission electron microscope. Calculate the average brightness intensity value of the carrier support film; The average brightness intensity value of the carrier support film is subtracted from the brightness intensity value of each pixel in the high-angle annular dark field image of the nanoparticle under test to obtain the processed high-angle annular dark field image of the nanoparticle under test. The absolute brightness intensity value of the pixels in the thickness region to be measured of the nanoparticle under test is determined by image analysis software based on the processed high-angle annular dark field image of the nanoparticle under test.

[0011] Furthermore, the netting parameters for acquiring the high-angle annular dark field image of the nanoparticle under test are the same as those for acquiring the high-angle annular dark field image of the standard nanoparticle. The imaging parameters for acquiring the high-angle annular dark field image of the nanoparticle under test are the same as those for acquiring the high-angle annular dark field image of the standard nanoparticle.

[0012] Furthermore, the relationship function between the absolute brightness intensity value and the thickness value of the nanoparticles includes: A rectangular coordinate system is established with the thickness at the center of the standard nanoparticle as the y-axis and the absolute brightness intensity of the standard nanoparticle as the x-axis, thus constructing a linear function in one variable.

[0013] Furthermore, the imaging parameters include: Accelerating voltage, condenser aperture size, electron beam current intensity, magnification, camera length, electron beam movement step size, and electron scan dwell time.

[0014] Furthermore, the carrier network parameters include: Supports membrane material, membrane thickness, screen material, and screen mesh count.

[0015] Advantages and positive effects of the present invention: This method obtains the thickness and absolute brightness intensity values ​​of regularly shaped nanoparticles using scanning transmission electron microscopy, and constructs a relationship function between the thickness and absolute brightness intensity values. Then, it uses this relationship function to obtain the thickness information of nanoparticles of arbitrary shapes, effectively avoiding the interference of different crystal orientations on the brightness intensity in the image during ordinary transmission mode imaging, and can obtain accurate nanoparticle thickness information. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart of a method for measuring the thickness of nanoparticles based on high-angle annular dark-field images from a transmission electron microscope.

[0018] Figure 2 This is a high-angle annular dark-field image of the spherical nanoparticles used for calibration in the examples.

[0019] Figure 3 This is a schematic diagram of the method for measuring the brightness intensity value at the center of the particle in the embodiment.

[0020] Figure 4 Based on the example Figure 2 The curve showing the relationship between the absolute brightness intensity value and the thickness value of the obtained spherical particles.

[0021] Figure 5 This is a high-angle annular dark-field image of the nanoparticles under test obtained by scanning transmission electron microscopy in the example.

[0022] Figure 6 This is a schematic diagram of the method for measuring the brightness intensity value at the location where the thickness of the particle to be measured needs to be measured in the embodiment. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0024] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0025] This invention provides a method for measuring the thickness of nanoparticles based on high-angle annular dark-field images obtained by transmission electron microscopy (TEM). First, high-angle annular dark-field images of nanoparticles with the same regular shape as the nanoparticles to be measured are acquired using TEM. Based on these regular shapes, the brightness intensity-thickness function relationship of the corresponding nanoparticle components is obtained. Then, using the same imaging conditions, high-angle annular dark-field images of the nanoparticles to be measured are acquired using TEM. The brightness intensity of the corresponding pixels in these images is then substituted into the brightness intensity-thickness function relationship of the corresponding nanoparticle components obtained in the previous step to calculate the thickness information of the corresponding points of the nanoparticles to be measured.

[0026] A method for measuring the thickness of nanoparticles based on high-angle annular dark-field images obtained by scanning transmission electron microscopy includes the following steps: S1. Construct a dataset of absolute brightness intensity and thickness values ​​that are identical in composition to the nanoparticles to be tested but have different particle sizes; 1) Prepare a standard nanoparticle ethanol dispersion solution with the same composition as the nanoparticles to be tested but with a different particle size; Nanoparticles include: crystalline and amorphous solid nanoparticles that can be penetrated by electron beams, with a thickness of less than 0.5 mm along the electron beam incident direction. .

[0027] Nanoparticles are regularly shaped nanoparticles, and the thickness information at the center of the nanoparticle can be deduced from electron micrographs. The regular shape is such as sphere, cube, etc.

[0028] 2) After diluting and sonicating the standard nanoparticle ethanol dispersion solution, drop it onto the grid. Under the scanning transmission mode of a transmission electron microscope, acquire a high-angle annular dark field image of the standard nanoparticle ethanol dispersion solution.

[0029] 3) Process the high-angle annular dark field image to obtain the processed high-angle annular dark field image; The processing involves subtracting the average brightness intensity of the supporting film from the brightness intensity value of each pixel in the high-angle annular dark field image to remove the background brightness intensity.

[0030] 4) Determine the thickness and absolute brightness intensity of the center of the standard nanoparticle based on the processed high-angle annular dark field image.

[0031] S2. Establish a functional relationship curve between the absolute brightness intensity value and the thickness value of standard nanoparticles based on the dataset; A rectangular coordinate system was established with the thickness of the center of the standard nanoparticle as the y-axis and the corresponding absolute brightness intensity as the x-axis. A scatter plot of the absolute brightness intensity value of the center of the standard nanoparticle and the thickness value of the center of the nanoparticle was plotted. The functional relationship curve between the absolute brightness intensity value and the thickness value of the nanoparticle was obtained by fitting.

[0032] The absolute brightness intensity value of the nanoparticles is a linear function of one variable passing through the origin, which is a function of thickness value.

[0033] S3. The absolute brightness intensity value of the nanoparticle under test is acquired by transmission electron microscopy, and the thickness of the nanoparticle under test is obtained by the function of the absolute brightness intensity value and the thickness value.

[0034] 1) Prepare an ethanol dispersion solution of the nanoparticles to be tested, dilute and sonicate it, and then drop the solution onto the carrier grid.

[0035] 2) In the scanning transmission mode of the transmission electron microscope, a high-angle annular dark field image of the nanoparticle under test is acquired.

[0036] 3) Obtain a high-angle annular dark field image of the nanoparticles to be tested after processing.

[0037] The processing involves subtracting the average brightness intensity of the supporting film from the brightness intensity value of each pixel in the high-angle annular dark field image to remove the background brightness intensity.

[0038] 4) Based on the processed high-angle annular dark field image of the nanoparticle to be tested, obtain the absolute brightness intensity value of the pixel corresponding to the thickness region to be measured of the nanoparticle to be tested.

[0039] 5) Substitute the absolute brightness intensity value of the pixel corresponding to the area where the thickness of the nanoparticle to be measured is used into the functional relationship between the absolute brightness intensity value and the thickness value of the nanoparticle to obtain the thickness value of the pixel corresponding to the area where the thickness of the nanoparticle to be measured is required.

[0040] Scanning is performed using a carrier screen with the same parameters, including: supporting membrane material, supporting membrane thickness, carrier screen material, and carrier screen mesh count.

[0041] Each transmission electron microscope (TEM) scan uses the same imaging parameters in the transmission mode. These imaging parameters include: Accelerating voltage, condenser aperture size, electron beam current intensity, magnification, camera length, electron beam movement step size, and electron scan dwell time.

[0042] Example 1 Combination Figure 1 This invention provides a method for measuring the thickness of nanoparticles based on high-angle annular dark-field images obtained by scanning transmission electron microscopy, comprising the following steps: S1. Prepare a standard nanoparticle ethanol dispersion solution of standard regular-shaped nanoparticles with different particle sizes, dilute and sonicate the solution, and then drop it onto a carrier grid.

[0043] In this embodiment, the nanoparticles to be tested are The bimetallic nanoparticles are spherical in shape; the carrier mesh and the supporting film are a copper carrier mesh and an ultrathin carbon film, respectively.

[0044] S2. In the scanning transmission mode of a transmission electron microscope, acquire a high-angle annular dark-field image of the standard nanoparticles.

[0045] S3. Import the image obtained in step S2 into image analysis software. Select n (n≥5) pixels corresponding to the ultrathin carbon film, measure the brightness intensity values ​​of these n pixels, and average them. This average value is the average brightness intensity value of the ultrathin carbon film. The formula for calculating the average brightness intensity value of the ultrathin carbon film is as follows:

[0046] in, This represents the average brightness intensity value of the ultrathin carbon film. This represents the brightness intensity value of the pixel corresponding to the nth ultrathin carbon film.

[0047] Subtracting the average brightness intensity of the support film from the brightness intensity value of each pixel in the image obtained in S2 yields a high-angle annular dark-field image of the nanoparticles with background brightness removed using a scanning transmission electron microscope.

[0048] In this embodiment, the image analysis software is DigitalMicrograph (version number: 3.41.2984.1), and the pixels corresponding to the ultrathin carbon film are randomly selected.

[0049] S4. Randomly select from the high-angle annular dark field image after removing the background brightness intensity. ( ≥5) different nanoparticles, and obtain the thickness value corresponding to their center pixel. and absolute luminance intensity value .

[0050] In this embodiment, the nanoparticles are spherical, so the thickness value corresponding to the center pixel of the nanoparticle is the particle size. The brightness intensity value of the center pixel is obtained by measuring the brightness value corresponding to the center point of the nanoparticle from the brightness intensity distribution map of the nanoparticle center point.

[0051] S5. Establish a rectangular coordinate system based on the absolute brightness intensity value of the nanoparticles obtained in step S4 and the center thickness value of the nanoparticles obtained in step S2, and use different thickness values ​​of standard spherical nanoparticles as the coordinates. As Axis, absolute luminance intensity value As Plot a scatter plot along the axis. Fit a specific function to the scatter plot to obtain the curve showing the relationship between the absolute brightness intensity and thickness of the nanoparticles. The formula for the fitted curve is as follows:

[0052] S6. Prepare an ethanol dispersion solution of the nanoparticles to be tested, dilute and sonicate it, and then drop the solution onto an ultrathin carbon film copper grid with the same parameters as in step S1.

[0053] S7. In the scanning transmission mode of the transmission electron microscope, using the same instrument parameters as in step S2, acquire a high-angle annular dark-field image of the nanoparticles to be tested using the scanning transmission electron microscope.

[0054] S8. Obtain a high-angle annular dark-field image of the nanoparticles under test after removing the background brightness intensity: Import the image obtained in step S7 into the image analysis software. Then select... ( ≥5) pixels corresponding to ultrathin carbon films, measuring this The average brightness intensity value of the ultra-thin carbon film is obtained by averaging the brightness intensity values ​​of each pixel. The formula for calculating the average brightness intensity value of the ultra-thin carbon film is as follows:

[0055] in, This represents the average brightness intensity value of the ultrathin carbon film. For the corresponding number The brightness intensity value of each pixel corresponding to an ultra-thin carbon film.

[0056] By subtracting the average brightness intensity of the support film from the brightness intensity value of each pixel in the image acquired in S7, a high-angle annular dark-field image of the nanoparticle under test with background brightness intensity removed can be obtained.

[0057] In this embodiment, the pixels corresponding to the ultrathin carbon film are randomly selected.

[0058] S9. In the high-angle annular dark-field image of the nanoparticles to be tested obtained in step S8 after removing the background brightness intensity, measure the absolute brightness intensity value of the corresponding pixel in the area to be tested. .

[0059] In this embodiment, the number of pixels selected in the test area can be multiple.

[0060] S10. Obtain the absolute brightness intensity value of the pixel corresponding to the thickness region to be measured of the nanoparticle obtained in step S9. Substitute these values ​​into the functional relationship between the absolute brightness intensity value and the thickness value of the nanoparticles obtained in step S5 to obtain the thickness value corresponding to the pixel to be tested.

[0061] In this embodiment, the brightness intensity value of the pixel to be measured is obtained by measuring the corresponding value of the point to be measured on the brightness envelope line of the brightness intensity distribution map of the pixel to be measured.

[0062] Example 2 1. Preparation of standards with different particle sizes A standard ethanol dispersion of bimetallic spherical nanoparticles was diluted and sonicated before being dropped onto an ultrathin carbon film copper grid.

[0063] 2. Obtain standard samples in the scanning transmission mode of a transmission electron microscope. High-angle annular dark-field image of bimetallic spherical nanoparticles obtained by scanning transmission electron microscopy; corresponding parameters: accelerating voltage 300kV, probe current 20pA, camera length 195.0mm, resolution 2048px×2048px, single-pixel acquisition time 15 seconds. s, semi-convergence angle 9.8 mrad, collection angle 40-200 mrad.

[0064] 3. Import the image into DigitalMicrograph electron microscopy image analysis software, and randomly select 9 pixels in the ultrathin carbon film area of ​​the image, and measure their brightness intensity values, which are: 1150572, 1144547, 1144660, 1146955, 1151657, 1150883, 1150238, 1147684, and 1146834. The average value is 1148226.

[0065] 4. Subtract the average brightness value of the background from the brightness value of each pixel in the image to obtain a high-angle annular dark-field image of the nanoparticles with the background brightness intensity removed, such as... Figure 2 As shown.

[0066] 5. In Figure 2 Ten were randomly selected from the middle. Bimetallic spherical nanoparticles were used to measure the nanoparticle size and the brightness intensity of the central pixel.

[0067] The nanoparticle sizes are 8.73nm, 8.38nm, 7.08nm, 9.88nm, 9.29nm, 11.4nm, 9.26nm, 8.83nm, 10.14nm, and 7.9nm, which represent the thickness values ​​corresponding to the center pixels of these 10 spherical nanoparticles. The absolute luminance intensity values ​​are 24000, 25000, 21750, 25250, 24250, 30500, 25500, 27000, 26500, and 23750, respectively. A schematic diagram of the measurement method is shown below. Figure 3 As shown.

[0068] 6. Draw standards based on the above 10 sets of data. A scatter plot of the absolute brightness intensity values ​​versus thickness values ​​of bimetallic spherical nanoparticles was generated, and a linear fit was performed. The resulting fitting equation is as follows: I = 2,769.12·D This equation is the standard. The curve showing the functional relationship between the absolute brightness intensity value and the thickness value of bimetallic spherical nanoparticles, as shown in the figure. Figure 4 As shown.

[0069] 7. Preparation of the test sample / An ethanol dispersion solution of irregularly shaped nanoparticles was diluted and sonicated, then dropped onto an ultrathin carbon film copper grid with the same parameters. High-angle annular dark-field images of the Cu3Pd / Cu2O irregularly shaped nanoparticle sample were acquired using the same parameters in scanning transmission electron microscopy (STEM) mode.

[0070] 8. Import the image into DigitalMicrograph electron microscopy image analysis software, and randomly select 9 pixels in the ultrathin carbon film area of ​​the image, and measure their brightness intensity values, which are 1147895, 1147469, 1146403, 1148541, 1153917, 1150575, 1147686, 1148113, and 1147744. The average brightness value is 1148705.

[0071] 9. Subtract the average brightness value of the background from the brightness value of each pixel in the image to obtain a high-angle annular dark-field image of the irregularly shaped Cu3Pd / Cu2O nanoparticle sample after removing the background brightness intensity, such as... Figure 5 As shown. The brighter "head" region of the tadpole-shaped nanoparticles in this sample is Cu3Pd, as determined by measurement. Figure 5 The brighter "heads" of the medium-sized nanoparticles correspond to the absolute luminance intensity values ​​of the pixels being measured. A schematic diagram of the measurement method is shown below. Figure 6 As shown, the absolute luminance intensity value of the point to be measured is 41000.

[0072] 10. Substitute the absolute brightness intensity value of the point to be measured into the functional relationship between the absolute brightness intensity value and the thickness value of the standard Cu3Pd bimetallic spherical nanoparticle, I=2,769.12·D, and the thickness of the point can be obtained as 14.81nm.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for measuring the thickness of nanoparticles based on high-angle annular dark-field images from transmission electron microscopy, characterized in that, include: A dataset is constructed by collecting absolute brightness intensity and thickness data of standard nanoparticles with the same composition as the nanoparticles to be tested but different particle sizes; the standard nanoparticles are regularly shaped nanoparticles. Based on the aforementioned dataset, a function relating the absolute brightness intensity value to the thickness value of the nanoparticles is established. The absolute brightness intensity value of the nanoparticle under test was acquired by transmission electron microscopy, and the thickness of the nanoparticle under test was obtained by the relationship function between the absolute brightness intensity value and the thickness value.

2. The method according to claim 1, characterized in that, The standard nanoparticles include: Electron beams can penetrate crystalline and amorphous solid nanoparticles with a thickness of less than 0.5 mm along the incident direction of the electron beam. ; The standard nanoparticles may have the following shapes: spheres, cubes, and cylinders.

3. The method according to claim 1, characterized in that, The absolute brightness intensity and thickness data of standard nanoparticles with the same composition as the nanoparticles to be tested but different particle sizes are collected, including: The standard nanoparticle ethanol dispersion solution was prepared, diluted and sonicated, and then dropped onto a grid. A high-angle annular dark field image of the standard nanoparticles was obtained in the scanning transmission mode of a transmission electron microscope. The absolute brightness intensity value of the pixel points in the thickness region to be measured of the standard nanoparticle is obtained based on the high-angle annular dark field image of the standard nanoparticle. The thickness of the standard nanoparticle is calculated at its center using a high-angle annular dark-field image.

4. The method according to claim 3, characterized in that, The process of obtaining the absolute luminance intensity value of the pixels in the thickness region to be measured of the standard nanoparticle based on the high-angle annular dark field image of the standard nanoparticle includes: Calculate the average brightness intensity value of the carrier support film; The average brightness intensity of the carrier support film is subtracted from the brightness intensity value of each pixel in the high-angle annular dark field image of the standard nanoparticles to obtain the processed high-angle annular dark field image of the standard nanoparticles. The absolute brightness intensity value of the pixels in the thickness region to be measured of the standard nanoparticles is determined by image analysis software based on the processed high-angle annular dark field image of the standard nanoparticles.

5. The method according to claim 3, characterized in that, The acquisition of the absolute brightness intensity value of the nanoparticles under test by transmission electron microscopy includes: An ethanol dispersion solution of the nanoparticles to be tested was prepared, diluted and sonicated, and then dropped onto a grid. A high-angle annular dark field image of the nanoparticles to be tested was acquired in the scanning transmission mode of a transmission electron microscope. Calculate the average brightness intensity value of the carrier support film; The average brightness intensity value of the carrier support film is subtracted from the brightness intensity value of each pixel in the high-angle annular dark field image of the nanoparticle under test to obtain the processed high-angle annular dark field image of the nanoparticle under test. The absolute brightness intensity value of the pixels in the thickness region to be measured of the nanoparticle under test is determined by image analysis software based on the processed high-angle annular dark field image of the nanoparticle under test.

6. The method according to claim 5, characterized in that, The netting parameters for acquiring the high-angle annular dark field image of the nanoparticle under test are the same as those for acquiring the high-angle annular dark field image of the standard nanoparticle. The imaging parameters for acquiring the high-angle annular dark field image of the nanoparticle under test are the same as those for acquiring the high-angle annular dark field image of the standard nanoparticle.

7. The method according to claim 1, characterized in that, The relationship function between the absolute brightness intensity value and the thickness value of the nanoparticles includes: A rectangular coordinate system is established with the thickness at the center of the standard nanoparticle as the y-axis and the absolute brightness intensity of the standard nanoparticle as the x-axis, thus constructing a linear function in one variable.

8. The method according to claim 6, characterized in that, The imaging parameters include: Accelerating voltage, condenser aperture size, electron beam current intensity, magnification, camera length, electron beam movement step size, and electron scan dwell time.

9. The method according to claim 6, characterized in that, The carrier network parameters include: Supports membrane material, membrane thickness, screen material, and screen mesh count.

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