Method for rapidly realizing crystallographic orientation imaging in transmission electron microscope

Abstract

The invention discloses a method for rapidly realizing crystallographic orientation imaging in a transmission electron microscope. The method comprises the following steps: collecting conical scanning dark field images of front 8-10 diffraction rings under inclination angles of 3-5 samples through the transmission electron microscope; carrying out drift correction on the dark field images under different sample inclination angles and then carrying out binaryzation on all the dark field images; building an incident electron beam conical scanning model, simulating electron diffraction patterns of any orientation under different sample inclination angles, and building an electron diffraction pattern database; reconstructing a diffraction pattern of each pixel in the dark field image under the same sample inclination angle, and calibrating orientations of all the pixels; and completing orientation calibration of all pixels in combination with data of multiple sample inclination angles. The rapid characterization of the grain orientation is realized based on the transmission electron microscope conical scanning dark field imaging technology and the crystallographic orientation calibration algorithm, and the method is suitable for the crystallographic orientation characterization of the crystal material under the transmission electron microscope.

Description

Technical Field

[0001] The invention belongs to the technical field of material microscopic crystallographic orientation characterization, and in particular relates to a method for rapidly realizing crystallographic orientation imaging in a transmission electron microscope. Background Art

[0002] Materials are the cornerstone of social progress, and crystalline materials play a vital role in today's materials field. For crystalline materials, the orientation of the grains has a crucial impact on the performance of the materials. Therefore, it is necessary to characterize the grain orientation of crystalline materials. Traditional two-dimensional crystallographic orientation characterization methods, such as X-ray Diffraction (XRD) and Electron Backscatter Diffraction (EBSD), have gradually failed to meet the analysis needs of material researchers. In recent years, the development of nanomaterials has put forward higher resolution requirements for two-dimensional crystallographic orientation characterization methods. To this end, foreign scholars have developed the precession electron diffraction (PED) technology in transmission electron microscopy. This technology can weaken the dynamic effect of electron diffraction, and its spatial resolution and angular resolution are about 2-3nm and 1° (Microscopy and Microanalysis 5 (2021), 1102-1112); however, this technology takes 20-40 minutes to collect a 400×400 pixel orientation map (Zeitschrift Fur Kristallographie-Crystalline Materials 225 (2010), 103-109), and it uses a nanobeam, which causes relatively large irradiation damage to the sample. Similarly, the transmission Kikuchi diffraction (TKD) technique can also perform crystallographic orientation calibration on nanomaterials (Journal of Microscopy 245 (2012), 245-251). This technique takes about 40 minutes to collect a complete orientation map (Journal of Microscopy 267 (2017), 318-329). Compared with the EBSD technique, the area of ​​interaction between the transmission electron beam of the TKD technique and the sample is smaller, so the sensitivity of the transmission Kikuchi pattern to crystal defects is reduced. However, when the density of crystal defects in the sample is relatively high, the obtained Kikuchi pattern is still relatively fuzzy, which is not conducive to calibration. Secondly, the transmission Kikuchi pattern is also sensitive to the thickness of the sample. Only when the thickness is appropriate can a clear Kikuchi pattern be obtained.

[0003] In summary, the existing crystallographic orientation characterization techniques can characterize the two-dimensional orientation of nanocrystals, but the application scope of these two-dimensional crystallographic orientation characterization techniques is still relatively limited. Secondly, there is currently no crystallographic orientation characterization technology with a wide range of applications and high spatial resolution in China. Therefore, it is necessary to develop a characterization technology with a small irradiation dose and high spatial resolution that can quickly characterize the crystallographic orientation and geometric morphology of nanomaterials, which will provide important technical support for the research of high-performance nanomaterials. Summary of the invention

[0004] The purpose of the present invention is to provide a system and method for quickly realizing two-dimensional crystallographic orientation imaging in a transmission electron microscope. In a transmission electron microscope equipped with an incident electron beam cone scanning controller, the method for realizing two-dimensional crystallographic orientation imaging of nanomaterials can quickly characterize the two-dimensional crystallographic orientation of nanomaterials with high spatial resolution, and can obtain the two-dimensional crystallographic orientation and morphology information of the nanomaterials.

[0005] The present invention is achieved through the following technical solutions:

[0006] On the one hand, the present invention provides a method for quickly realizing crystallographic orientation imaging in a transmission electron microscope, comprising the following steps: collecting cone scanning dark field images of the first 8 to 10 diffraction rings at 3 to 5 sample inclination angles through a transmission electron microscope; drift correcting the dark field images at different sample inclination angles and binarizing all dark field images; building an incident electron beam cone scanning model, simulating electron diffraction patterns of arbitrary orientation at different sample inclination angles, and constructing an electron diffraction pattern database; reconstructing the diffraction pattern of each pixel in the dark field image at the same sample inclination angle and calibrating the orientation of all pixels; and completing the orientation calibration of all pixels by combining data of multiple sample inclination angles.

[0007] In some embodiments, the scanning dark field image includes: using cone scanning dark field imaging technology to collect dark field images corresponding to the diffraction spots in the first 8 to 10 diffraction rings at 3 to 5 sample inclination angles; such as the dark field image corresponding to the diffraction spots on the face-centered cubic crystal {111} ring to the {420} ring, the incident electron beam on the same diffraction ring rotates around the main optical axis every 2° or 1°, that is, 180 or 360 dark field images are collected on each diffraction ring, and it only takes 3-5 minutes to collect complete data once.

[0008] In some of the embodiments, drift correction of dark field images at different sample inclination angles includes: correcting the drift of bright field images at different sample inclination angles using a feature point method, then correcting the drift of all bright field images at the same sample inclination angle, and indirectly correcting the drift of the dark field image based on the drift value of the bright field image; assuming that the drift values ​​of dark field images within 10 images are approximately linear, one bright field image is collected every 10 dark field images, and then the drift values ​​of the 10 dark field images between every two bright field images are calculated by interpolation and these drift values ​​are applied to the dark field image. When binarizing all dark field images, a machine learning algorithm can be used to binarize all dark field images; specifically, a U-Net network can be used to train a suitable machine learning model and binarize all dark field images.

[0009] In some of the embodiments, constructing an electron diffraction pattern database includes: simulating diffraction patterns of arbitrary orientations and recording the positions of diffraction spots with reference to the principles of incident electron beam conical scanning, reciprocal space, and Ewald sphere. In a specific example, an Ewald sphere is established in reciprocal space according to Bragg's law, wherein the deflection of the incident electron beam means the movement of the center position of the Ewald sphere, and the movement of the center position of the Ewald sphere is calculated according to the deflection of the incident electron beam in real space; secondly, the reciprocal lattice of the initial orientation (Euler angle is (0, 0, 0)) of the material in reciprocal space is calculated according to the crystal structure of the material in real space, such as the lattice type of a face-centered cubic crystal in reciprocal space is body-centered cubic, and the corresponding reciprocal lattice is calculated according to the crystallographic orientation and the tilt angle of the sample; it is generally believed that the reciprocal lattice intersecting with the Ewald sphere The reciprocal lattice points satisfy Bragg diffraction, so it is only necessary to record the position of the reciprocal lattice points that intersect the Ewald sphere and are within the objective aperture. For example, if a diffraction spot is in the first diffraction ring and enters the objective aperture when the incident electron beam rotates 10° around the optical axis, its position is (1, 10). Each time the incident electron beam is deflected, it is necessary to re-search the reciprocal lattice points that intersect the Ewald sphere and record the position of the reciprocal lattice points that enter the objective aperture. By repeating the above process, the diffraction pattern of a material with a specific crystal structure can be simulated under arbitrary crystal orientation and arbitrary sample tilt angle when the incident electron beam is deflected.

[0010] In some embodiments, calibrating the orientation of all pixels at the same sample tilt angle includes: extracting the intensity of the same pixel point in all images at the same sample tilt angle as the basis for crystallographic orientation calibration. Calibrating the orientation of all pixels at the same sample tilt angle includes: using a template matching method to calculate the correlation coefficient between the diffraction pattern and each diffraction pattern in the database, and considering that the orientation corresponding to the diffraction pattern with the highest correlation coefficient is the orientation corresponding to the pixel.

[0011] In some embodiments, the calibration of orientation of all pixels is completed in combination with the data of sample inclination angles, including: first calibrating the data of the first sample inclination angle, retaining the calibration results that meet the conditions, and pixels without signals or whose orientations cannot be accurately determined will participate in the calibration of the second sample inclination angle; calibration of the second sample inclination angle: for pixels with signals but not meeting the conditions, the orientation with a relatively high correlation coefficient screened out during the calibration of the first sample inclination angle is used as the database for the calibration of the second sample inclination angle, and the calibration results that meet the conditions are retained, and pixels without signals or whose orientations cannot be accurately determined will participate in the calibration of the third sample inclination angle; repeating the above process to complete the calibration of the third sample inclination angle. Alternatively, the data under different sample inclination angles are coupled into a whole, and the coupled data is used as the basis for calibrating the orientation to match the simulated database, and the orientation corresponding to the template with the highest correlation coefficient is considered to be the calibration result.

[0012] On the other hand, the present invention provides a system for realizing two-dimensional crystallographic orientation imaging in a transmission electron microscope, comprising a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to realize the method for quickly realizing crystallographic orientation imaging in a transmission electron microscope as described in any of the above embodiments.

[0013] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0014] (1) High-quality cone scanning dark field images can be obtained in a transmission electron microscope equipped with an incident electron beam cone scanning controller;

[0015] (2) It only takes 3-5 minutes to collect complete data;

[0016] (3) Combined with machine learning algorithms, it can better segment dark field images;

[0017] (4) Ability to obtain the crystallographic orientation map of materials through high-quality conical scanning dark field images;

[0018] (5) The incident electron beam is a parallel beam and will not cause serious radiation damage to light metals;

[0019] (6) A reasonable method was used to correct the drift of the sample, and the resulting crystallographic orientation map was more accurate with a spatial resolution of up to 1 nm;

[0020] (7) Combining dark field images at multiple sample tilt angles can eliminate the 180° uncertainty of diffraction pattern calibration and avoid dynamic effects;

[0021] (8) The operation process is simple and requires less human intervention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 A schematic flow chart of a method for rapidly implementing crystallographic orientation imaging in a transmission electron microscope provided in some embodiments of the present invention;

[0024] Figure 2 Schematic diagram of the diffraction pattern of a randomly selected pixel in some embodiments of the present invention and the cone scanning diffraction pattern of the corresponding orientation after calibration, wherein (a) is the diffraction pattern reconstructed from the dark field image obtained by actual experimental collection, and (b) is the simulated diffraction pattern of the corresponding orientation after calibration.

[0025] Figure 3 Bright field images and orientation maps are provided in some embodiments of the present invention, wherein (a) is a bright field image when the sample inclination angle is 0 degrees and the incident electron beam is not deflected, and the figure shows the sample coordinate system and grain number, (b) is an orientation map obtained according to the calibration results, colored along the rolling direction (Z) of the sample, and (c) is a schematic diagram of the lattice of the five grains shown in the figure in three-dimensional space and the corresponding Euler angles. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0027] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. used to indicate the orientation or position relationship are based on the orientation or position relationship shown in the accompanying drawings, or are the orientation or position relationship commonly placed when the product of the invention is used. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0028] In addition, if the terms "horizontal" or "vertical" appear in the description of the present invention, it does not mean that the components are required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0029] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] The terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or device that includes a series of steps or modules is not limited to the listed steps or modules, but may optionally include steps or modules that are not listed, or may optionally include other steps or modules that are inherent to these processes, methods, products, or devices.

[0031] On the one hand, see Figure 1 The embodiment of the present invention provides a method for quickly realizing crystallographic orientation imaging in a transmission electron microscope, which mainly includes the following steps:

[0032] S1. Collect conical scanning dark field images of the first 8 to 10 diffraction rings at 3 to 5 sample inclination angles through a transmission electron microscope. In S1, in some examples, the conical scanning dark field imaging technology can be used to collect dark field images corresponding to the diffraction spots in the first 8 to 10 diffraction rings at 3 to 5 sample inclination angles, that is, deflect the incident electron beam so that the diffraction beam passes through the objective lens aperture to form a central dark field image. Specifically, the conical scanning dark field imaging technology is used to collect dark field images corresponding to the diffraction spots on 8 diffraction rings (such as the face-centered cubic crystal {111} ring to {420} ring) at multiple sample inclination angles. The incident electron beam on the same diffraction ring rotates around the main optical axis once every 2° or 1°, that is, 180 or 360 dark field images are collected on each diffraction ring. It takes 3-5 minutes to collect complete data.

[0033] S2. After drift correction of dark field images at different sample inclination angles, all dark field images are binarized. In S2, in some examples, the drift of dark field images can be corrected by interpolation method, and the drift amount of feature points can be determined to correct the image; specifically, the drift of bright field images at different sample inclination angles is first corrected by feature point method, and then the drift of all bright field images at the same sample inclination angle is corrected; assuming that the drift values ​​of dark field images within 10 images are approximately linear, one bright field image is collected every 10 dark field images, and then the drift values ​​of 10 dark field images between every two bright field images are calculated by interpolation method and these drift values ​​are applied to the dark field images. The drift of bright field images is corrected by feature point method, and the drift amount of feature points is determined to correct the image. In S2, in some specific examples, all dark field images can be binarized by machine learning algorithm; specifically, a suitable machine learning model can be trained using U-Net network and all dark field images can be binarized.

[0034] S3. Build a cone scanning model of the incident electron beam, simulate the electron diffraction patterns of arbitrary orientations under different sample inclination angles, and construct an electron diffraction pattern database. In S3, more than 520,000 oriented diffraction patterns are simulated and the positions of the diffraction spots are recorded according to the principles of cone scanning of the incident electron beam, reciprocal space and Ewald sphere. In a specific example, an Ewald sphere is established in the reciprocal space according to Bragg's law, in which the deflection of the incident electron beam means the movement of the center position of the Ewald sphere, and the movement of the center position of the Ewald sphere is calculated according to the deflection of the incident electron beam in the real space; secondly, the reciprocal lattice of the initial orientation (Euler angle is (0, 0, 0)) in the reciprocal space is calculated according to the crystal structure of the material in the real space, such as the lattice type of the face-centered cubic crystal in the reciprocal space is body-centered cubic, and the corresponding reciprocal lattice is calculated according to the crystallographic orientation and the inclination angle of the sample; it is generally believed that the reciprocal lattice intersecting with the Ewald sphere The reciprocal lattice points satisfy Bragg diffraction, so it is only necessary to record the position of the reciprocal lattice points that intersect the Ewald sphere and are within the objective aperture. For example, if a diffraction spot is in the first diffraction ring and enters the objective aperture when the incident electron beam rotates 10° around the optical axis, its position is (1, 10). Each time the incident electron beam is deflected, it is necessary to re-search the reciprocal lattice points that intersect the Ewald sphere and record the position of the reciprocal lattice points that enter the objective aperture. By repeating the above process, the diffraction pattern of a material with a specific crystal structure can be simulated under arbitrary crystal orientation and arbitrary sample tilt angle when the incident electron beam is deflected.

[0035] S4, reconstruct the diffraction pattern of each pixel in the dark field image at the same sample inclination angle and calibrate the orientation of all pixels with signals. In S4, the intensity of the same pixel point in all images at the same sample inclination angle is extracted as the basis for crystallographic orientation calibration, and then these intensity values ​​are expressed in the form of a diffraction pattern. Calibration of the orientation of all pixels at the same sample inclination angle may specifically include: using a two-dimensional correlation coefficient function or a cosine similarity function to calculate the correlation coefficient between the diffraction pattern extracted from S4 and each diffraction pattern in the database, and considering that the orientation corresponding to the diffraction pattern with the highest correlation coefficient is the orientation corresponding to the pixel, and the pixel with the maximum correlation coefficient lower than a certain value is considered to have no corresponding orientation; specifically, using a two-dimensional correlation coefficient function or a cosine similarity function to calculate the correlation coefficient between the reconstructed diffraction data matrix and each matrix in the simulated database. Please refer to Figure 2 , is the diffraction pattern of a randomly selected pixel and the cone scanning diffraction pattern of the corresponding orientation after calibration. The two-dimensional correlation coefficient function is as follows:

[0036]

[0037] Where A and B are the experimental diffraction pattern matrix and the simulated database matrix, respectively. The sizes of these two matrices are the same as m×n. and are the means of matrices A and B respectively.

[0038] The cosine similarity function is as follows:

[0039]

[0040] Where C and D are the vectorized results of matrices A and B respectively, and |C| and |D| are the norms of vectors C and D.

[0041] S5. Combine the orientation data of different sample inclination angles to complete the orientation calibration of all pixels. Under a single sample inclination angle, some grains have fewer Bragg diffraction times or no Bragg diffraction with considerable intensity, which is not enough to calibrate the correct orientation. Therefore, the data of the first sample inclination angle is calibrated first, and the calibration results that meet the conditions are retained. Pixels with no signal or unable to accurately determine the orientation will participate in the calibration of the second sample inclination angle; calibration of the second sample inclination angle: for pixels with signals but not meeting the conditions, the orientation with a relatively high correlation coefficient screened out during the calibration of the first sample inclination angle is used as the database for the calibration of the second sample inclination angle, and the calibration results that meet the conditions are retained. Pixels with no signal or unable to accurately determine the orientation will participate in the calibration of the third sample inclination angle; repeat the above process to complete the calibration of the third sample inclination angle. Alternatively, the data under different sample inclination angles are coupled into a whole, and the coupled data is used as the basis for calibrating the orientation to match the simulated database, and the orientation corresponding to the template with the highest correlation coefficient is considered to be the calibration result. Combining data from multiple sample tilt angles ensures that the orientation of all grains in the same area can be correctly calibrated, while also eliminating the 180° uncertainty in crystal orientation.

[0042] On the other hand, an embodiment of the present invention provides a system for rapidly realizing crystallographic orientation imaging in a transmission electron microscope, comprising a memory and a processor, wherein a computer program is stored in the memory, and the processor executes the computer program to implement any one of the methods for rapidly realizing crystallographic orientation imaging in a transmission electron microscope of the above-mentioned embodiments.

[0043] This embodiment also provides a computer storage medium on which a computer program is stored. The computer program is loaded by a processing module to implement any of the methods for rapidly implementing crystallographic orientation imaging in a transmission electron microscope in the above embodiments.

[0044] The above description is only a preferred embodiment of the present invention and does not constitute any limitation to the present invention. Any simple modification or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for rapidly realizing crystallographic orientation imaging in a transmission electron microscope, characterized in that: The following steps are involved: Conical scanning dark field images of the first 8 to 10 diffraction rings at 3 to 5 sample tilt angles were collected by transmission electron microscopy; After drift correction of dark field images at different sample inclination angles, all dark field images were binarized; Build a cone scanning model of the incident electron beam, simulate the electron diffraction patterns of arbitrary orientations at different sample inclination angles, and construct an electron diffraction pattern database; Reconstruct the diffraction pattern of each pixel in the dark field image at the same sample tilt angle and calibrate the orientation of all pixels with signals; The orientation calibration of all pixels is completed by combining the sample inclination data.

2. The method for rapidly realizing crystallographic orientation imaging in a transmission electron microscope according to claim 1, characterized in that: The scanning dark field image includes: using cone scanning dark field imaging technology to collect dark field images corresponding to the diffraction spots in the first 8 to 10 diffraction rings at 3 to 5 sample inclination angles.

3. The method for rapidly realizing crystallographic orientation imaging in a transmission electron microscope according to claim 1, characterized in that: The drift correction of the dark field image at different sample inclination angles includes: using the characteristic point method to correct the drift of the bright field image at different sample inclination angles, then correcting the drift of all bright field images at the same sample inclination angle, and indirectly correcting the drift of the dark field image based on the drift value of the bright field image.

4. The method for rapidly realizing crystallographic orientation imaging in a transmission electron microscope according to claim 1, characterized in that: The diffraction pattern of arbitrary orientation is simulated and the position of the diffraction spot is recorded according to the principles of incident electron beam cone scanning, reciprocal space and Ewald sphere.

5. The method for rapidly realizing crystallographic orientation imaging in a transmission electron microscope according to claim 1, characterized in that: Reconstructing the diffraction pattern of each pixel in the dark field image includes: extracting the intensity of the same pixel point in all images of the same sample inclination angle as the basis for crystallographic orientation calibration; calibrating the orientation of all pixels at the same sample inclination angle includes: using the template matching method to calculate the correlation coefficient between the diffraction pattern and each diffraction pattern in the database, and considering that the orientation corresponding to the diffraction pattern with the highest correlation coefficient is the orientation corresponding to the pixel.

6. The method for rapidly realizing crystallographic orientation imaging in a transmission electron microscope according to claim 1, characterized in that: The calibration of orientation of all pixels is completed in combination with the data of sample inclination angles, including: first calibrating the data of the first sample inclination angle, retaining the calibration results that meet the conditions, and pixels without signals or whose orientations cannot be accurately determined will participate in the calibration of the second sample inclination angle; calibration of the second sample inclination angle: for pixels with signals but not meeting the conditions, the orientations with relatively high correlation coefficients screened out during the calibration of the first sample inclination angle are used as the database for the calibration of the second sample inclination angle, and retaining the calibration results that meet the conditions, and pixels without signals or whose orientations cannot be accurately determined will participate in the calibration of the third sample inclination angle; repeating the above process to complete the calibration of the third sample inclination angle; Alternatively, the data at different sample inclination angles are coupled into a whole, and the coupled data are used as the basis for calibrating the orientation to match with the simulated database, and the orientation corresponding to the template with the highest correlation coefficient is considered to be the calibration result.

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