Method for measuring and correcting deviation of angle measuring table of transmission electron microscope

Abstract

The invention provides a method for measuring and correcting deviation of an angle measuring table of a transmission electron microscope. The method comprises the following steps: S1, acquiring a Ronchigram image, and extracting an accurate coordinate of the center of the image; s2, a plurality of data points are collected based on the polycrystalline FIB sample, and the data comprise alpha and beta tilt angle data corresponding to a plurality of sample crystal grains when the sample crystal grains tilt to a positive axis, so that the reliability and repeatability of data statistics in the calibration process are ensured; s3, calculating corresponding x and y coordinates, namely Pixelx and Pixely, of the crystal grain on the image when the crystal grain tilts to the positive axis; s4, constructing a mathematical model used for describing a geometrical relationship between an actual tilting system and an image acquisition system of the transmission electron microscope; s5, fitting processing and parameter solving are carried out on two groups of data, namely the actually collected alpha and beta tilt angle data and the corresponding Pixelx and Pixely data; step S6, calculating the tilting angle for the electron microscope rotating shaft operation according to the calculation result of the step S5; the method has the advantages of being high in precision, good in stability and high in repeatability.

Description

Technical Field

[0001] The present invention relates to the technical field of electron microscope equipment, and in particular to a method for measuring and correcting the deviation of the goniometer of a transmission electron microscope. Background Art

[0002] At present, the tilting stage of a transmission electron microscope generally adopts a double-tilting axis structure, that is, it includes an α-axis and a β-axis, and the two axes together form a tilting coordinate system (αOβ coordinate system). In this coordinate system, theoretically, any target point in the reciprocal space can be accurately positioned at the diffraction center through tilting operations. However, in the actual imaging and data processing process, there is usually also an observation coordinate system (XOY coordinate system) for image acquisition and display. Ideally, the tilting coordinate system and the observation coordinate system should be strictly aligned to ensure the accurate positioning of the sample during tilting. However, actual detection shows that due to factors such as mechanical manufacturing tolerances, assembly errors, and instrument relocation and reinstallation, there is a certain deviation angle between the two coordinate systems; at the same time, the α-axis and the β-axis may not be strictly orthogonal. Specifically, there is a deviation angle (denoted as γ) between the α-axis and the x-axis in the observation coordinate system, and the angle between the α-axis and the β-axis may also deviate from the ideal orthogonal state (i.e., 90°) (denoted as θ). In actual applications and method designs, it is usually assumed that there is no deviation between the tilting coordinate system and the observation coordinate system, but experiments have shown that this deviation may cause an error of 2-3° when analyzing the tilting results.

[0003] To solve the above problems, the present invention proposes a method for correcting the deviation of the tilting axis of a transmission electron microscope, and its main purpose is to verify and correct the deviation angle between the tilting coordinate system (αOβ) and the image observation coordinate system (XOY), so as to control the final tilting angle error within 0.5°. Summary of the Invention

[0004] The present invention proposes a method for measuring and correcting the deviation of the goniometer of a transmission electron microscope, which can realize the dynamic real-time correction of the deviation of the tilting axis of a transmission electron microscope, and has the advantages of high precision, good stability, and strong repeatability.

[0005] The present invention adopts the following technical solutions.

[0006] A method for measuring and correcting the deviation of the goniometer of a transmission electron microscope includes the following steps;

[0007] Step S1: Collect Ronchigram images and extract the accurate coordinates of the image center;

[0008] Step S2: Collect multiple data points based on a polycrystalline FIB sample, and the data includes the α and β tilting angle data corresponding to multiple sample grains when tilted to the positive axis, so as to ensure the reliability and repeatability of data statistics during the calibration process;

[0009] Step S3: Calculate the corresponding x and y coordinates of the grain on the image when it is tilted to the positive axis, namely Pixelx and Pixely;

[0010] Step S4: Construct a mathematical model to describe the geometric relationship between the actual tilting system and the image acquisition system of the transmission electron microscope;

[0011] Step S5: Perform fitting processing and parameter solving for the two sets of data of the actually collected α and β tilting angle data and the corresponding Pixelx and Pixely data;

[0012] Step S6: Calculate the tilting angle for the operation of the electron microscope rotation axis based on the calculation result of Step S5.

[0013] The method is used for a tilting stage of a transmission electron microscope with a double-tilting axis structure, including an α-axis and a β-axis, and the two axes jointly form an αOβ tilting coordinate system, and is used to calibrate and correct the deviation angle between the tilting coordinate system αOβ and the image observation coordinate system XOY.

[0014] Specifically, Step S1 is to collect a Ronchigram image, process the image using MATLAB, and extract the accurate coordinates at the center of the current Ronchigram, which is used to provide a reference benchmark for subsequent coordinate system calibration.

[0015] The method of Step S1 is operated when the transmission electron microscope is in a vacuum state.

[0016] Step S2 is used to ensure that the Kikuchi line can be clearly observed and tracked as a marker during the operation. A polycrystalline FIB sample with obvious Kikuchi line characteristics is selected. The sample contains multiple grains and the Kikuchi line can be clearly shown on each grain, so as to facilitate the collection of multiple data points in different regions.

[0017] In Step S2, a polycrystalline FIB sample with mature preparation process, high stability, and capable of meeting the requirements of data repeatability and statistical reliability is used. The selected sample and the data points collected at the sample can form an accurate mapping between the image coordinates and the tilting angle.

[0018] In Step S3, MATLAB is used to process the collected data, and the corresponding x and y coordinates of the grain on the image when it is tilted to the positive axis are calculated to realize the correspondence between the tilting angle and the image coordinates, providing a data basis for establishing a mathematical model.

[0019] In step S4, when establishing the model, the following assumptions are made: there is a deviation angle γ between the α-axis and the x-axis of the observation coordinate system; the angle θ between the β-axis and the α-axis may deviate from the orthogonal state; at the same time, considering the pixel size PixelSize of the image, the established mathematical model is used to describe the geometric relationship between the actual tilting system and the image acquisition system of the transmission electron microscope, which is expressed by the formula as follows:

[0020]

[0021] Step S5 is specifically as follows: The MATLAB software is used to perform fitting processing on two sets of data: one set is the actually collected α and β tilting angle data, and the other set is the corresponding Pixelx and Pixely data; through the mathematical fitting method, the numerical values of the deviation angles γ and θ and the image pixel size PixelSize are accurately calculated and solved, so as to realize the quantitative correction of the tilting axis deviation and pixel calibration of the transmission electron microscope.

[0022] The results show that the average error after correction is 0.28°, which is significantly lower than the empirical value of 2 - 3° before correction.

[0023] Step S6 is specifically as follows: After obtaining the accurate numerical values of γ, θ, and PixelSize, the tilting angle is calculated for any point in the reciprocal space of the area related to the operation of the electron microscope rotation axis, that is, according to the position of the point in the image, the corresponding α and β values required for it to tilt to the central position are calculated, which is used to improve the efficiency and accuracy of the operation of the electron microscope rotation axis.

[0024] After step S6, all the collected and processed data are archived to facilitate subsequent analysis, equipment maintenance, and parameter optimization. According to the long-term usage situation, re-calibration is carried out regularly to maintain the long-term stable and high-precision operation of the system.

[0025] The technical advantages of the present invention are as follows:

[0026] 1. It can calibrate the goniometer and the observation coordinate system, that is: aiming at the problem of the deflection angle error commonly existing between the goniometer and the observation coordinate system in the traditional transmission electron microscope, the present invention provides an innovative calibration method. In the traditional system, due to factors such as mechanical manufacturing tolerances, assembly errors, and relocation and reinstallation, there are often deviations between the goniometer and the observation coordinate system, which directly affect the reliability of data analysis. The present invention accurately measures the deflection angle between the two coordinate systems and uses image processing and mathematical fitting algorithms to realize the automatic correction of this deviation angle, thereby ensuring the strict alignment of the goniometer and the observation coordinate system.

[0027] 2. A method for extracting the center based on Ronchigram images is implemented, that is, by collecting Ronchigram images under vacuum conditions and processing them using MATLAB, the center coordinates of the images are accurately extracted, providing a stable and reliable reference point for subsequent calibration.

[0028] 3. A multi-data point calibration strategy is implemented, that is, by using a polycrystalline FIB sample to collect α and β data when multiple grains are tilted to the positive axis, and corresponding calculating the pixel coordinates on the image, a systematic calibration starting from multiple angles and multiple data points is achieved, greatly improving the statistical reliability of the data.

[0029] 4. An innovative mathematical model is constructed, that is, the deviation angle γ between the α axis and the x axis of the observation coordinate system, the deviation angle θ between the α axis and the β axis, and the pixel size (PixelSize) parameter of the image are introduced into the model to construct a geometric model that comprehensively reflects the influence of various factors in the actual working environment, providing a theoretical basis for accurate correction.

[0030] 5. Precise calculation for tilting any point to the center can be achieved, that is, after calibration, through the obtained parameters, the rapid calculation of the α and β values required for tilting any point on the image to the center can be realized, thus greatly improving the efficiency and data accuracy of the electron microscope rotation axis operation.

[0031] 6. An automated and high-precision correction technology can be achieved, that is, a new automated correction scheme is provided, which combines image processing and mathematical model fitting to realize the dynamic real-time correction of the deviation of the rotation axis of the transmission electron microscope, with the advantages of high precision, good stability and strong repeatability.

[0032] The advantages of the present invention also lie in:

[0033] 1. High-precision calibration:

[0034] By collecting Ronchigram images and accurately extracting the center of the images using MATLAB, accurate correction of the deviation angles (γ and θ) of the α axis and the β axis and the PixelSize of the image is achieved, effectively reducing the errors in traditional methods.

[0035] 2. Automated operation and real-time correction:

[0036] Built-in data processing and model fitting algorithms can automatically calculate and update correction parameters to achieve real-time correction, reduce human intervention, and improve operation efficiency and data repeatability.

[0037] 3. Multi-data point correction strategy:

[0038] Statistical calibration is carried out using a large amount of grain data to ensure the stability and reliability of the correction results, and to meet the measurement requirements under complex samples and changing environments.

[0039] 4. Precise mapping of pixels and tilting angles:

[0040] Precisely calibrate the tilting angle (unit: mrad) corresponding to each pixel, providing a reliable conversion relationship for subsequent image processing and quantitative analysis, and improving the accuracy of data.

[0041] 5. Improve operation efficiency:

[0042] After calibration, it can quickly calculate the α and β values required for tilting any image point to the center, greatly simplifying the operation process of the electron microscope, saving calibration time, and improving the overall working efficiency of the equipment.

[0043] 6. Strong adaptability and good stability:

[0044] The proposed solution of the present invention takes into account factors such as environmental temperature changes and mechanical wear, ensuring high precision and high stability during long-term use, and is applicable to various high-end transmission electron microscope systems.

[0045] The method of the present invention can be implemented for the following uses:

[0046] 1. Electron microscope calibration

[0047] Used for calibrating the deviation of the tilting axis of a transmission electron microscope, ensuring precise positioning of the sample during multi-angle imaging, and improving the accuracy of image geometric calibration and data reconstruction.

[0048] 2. High-resolution image quantitative analysis

[0049] Provide precise image coordinate and tilting angle conversion support for fields such as materials science, nanotechnology, and semiconductor detection, promoting quantitative analysis and structural analysis.

[0050] 3. Scientific research and industrial inspection

[0051] Applicable to various scientific research laboratories and industrial inspection scenarios, improving the reliability and repeatability of data acquisition of transmission electron microscopes through automatic calibration and parameter fitting.

[0052] 4. Sample positioning and tracking

[0053] Support calculating the required rotation axis adjustment for tilting to the center through any point on the image, realizing fast and precise sample positioning and tracking, and adapting to the operation requirements under dynamic experimental conditions.

[0054] 5. Equipment maintenance and performance optimization

[0055] Monitor the equipment status and tilting axis deviation through regular calibration and data feedback, assist in equipment maintenance and performance optimization, extend the service life of the instrument, and reduce maintenance costs. Description of the drawings

[0056] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0057] Attached Figure 1 is a schematic diagram of the deviation between αOβ and the XOY coordinate system;

[0058] Attached Figure 2 is a schematic diagram of extracting the central coordinates of the Ronchigram in step S1;

[0059] Attached Figure 3 is a schematic diagram of the data acquisition process in step S2;

[0060] Attached Figure 4 is a schematic diagram of obtaining the PixelX and PixelY coordinates in step S3;

[0061] Attached Figure 5 is a schematic diagram of the fitting result and error calculation in step S5. Specific embodiments

[0062] As shown in the figure, a method for measuring and correcting the deviation of a transmission electron microscope goniometer includes the following steps;

[0063] Step S1: Collect a Ronchigram image and extract the accurate coordinates of the center of the image;

[0064] Step S2: Based on a polycrystalline FIB sample, collect multiple data points, and the data includes the α and β tilt angle data corresponding to multiple sample grains when tilted to the positive axis to ensure the reliability and repeatability of data statistics during the calibration process;

[0065] Step S3: Calculate the corresponding x and y coordinates of the grain on the image when tilted to the positive axis, that is, Pixelx and Pixely;

[0066] Step S4: Construct a mathematical model for describing the geometric relationship between the actual tilt system and the image acquisition system of the transmission electron microscope;

[0067] Step S5: Perform fitting processing and solve parameters for the two sets of data of the actually collected α and β tilt angle data and the corresponding Pixelx and Pixely data;

[0068] Step S6: Calculate the tilt angle for the operation of the electron microscope rotation axis based on the calculation result of step S5.

[0069] The method is used for a transmission electron microscope goniometer with a double tilt axis structure, including an α axis and a β axis, and the two axes together form an αOβ tilt coordinate system, and is used to calibrate and correct the deviation angle between the tilt coordinate system αOβ and the image observation coordinate system XOY.

[0070] Step S1 specifically involves collecting Ronchigram images, processing the images using MATLAB, and extracting the precise coordinates at the center of the current Ronchigram, which provides a reference benchmark for subsequent coordinate system calibration.

[0071] The method of Step S1 is operated when the transmission electron microscope is in a vacuum state.

[0072] Step S2 is used to ensure that the Kiku Line can be clearly observed and tracked as a marker during the operation. A polycrystalline FIB sample with obvious Kiku Line characteristics is selected. This sample contains multiple grains and the Kiku Line can be clearly displayed on each grain, facilitating the collection of multiple data points in different regions.

[0073] In Step S2, a polycrystalline FIB sample with a mature preparation process, high stability, and capable of meeting the requirements of data repeatability and statistical reliability is adopted. The selected sample and the data points collected at the sample location can form an accurate mapping between the image coordinates and the tilt angle.

[0074] In Step S3, MATLAB is used to process the collected data, and calculate the corresponding x and y coordinates of the grains on the image when tilted to the positive axis, so as to realize the correspondence between the tilt angle and the image coordinates, providing a data basis for establishing a mathematical model.

[0075] In Step S4, when establishing the model, the following assumptions are made: there is a deviation angle γ between the α-axis and the x-axis of the observation coordinate system; the angle θ between the β-axis and the α-axis may deviate from the orthogonal state; at the same time, considering the pixel size PixelSize of the image, the established mathematical model is used to describe the geometric relationship between the actual tilt system and the image acquisition system of the transmission electron microscope, and is expressed by the formula:

[0076]

[0077] Step S5 specifically involves using MATLAB software to perform fitting processing on two sets of data: one set is the actually collected α and β tilt angle data, and the other set is the corresponding Pixelx and Pixely data; through mathematical fitting methods, the values of the deviation angles γ and θ and the image pixel size PixelSize are accurately calculated and solved, thus realizing the quantitative correction of the tilt axis deviation and pixel calibration of the transmission electron microscope.

[0078] The results show that the average error after correction is 0.28°, which is significantly lower than the empirical value of 2 - 3° before correction.

[0079] Specifically, in step S6, after obtaining the accurate values of γ, θ, and PixelSize, the tilting angle is calculated for any point in the reciprocal space of the area related to the electron microscope rotation axis operation. That is, according to the position of this point in the image, the corresponding α and β values required for it to be tilted to the central position are calculated, which is used to improve the efficiency and accuracy of the electron microscope rotation axis operation.

[0080] After step S6, all the collected and processed data are archived for subsequent analysis, equipment maintenance, and parameter optimization. According to the long-term usage situation, re-calibration is performed regularly to maintain the long-term stability and high-precision operation of the system.

[0081] Embodiment:

[0082] The usage process of this example is as follows:

[0083] 1. Ronchigram Image Acquisition and Center Positioning

[0084] In a vacuum environment, a transmission electron microscope is used to acquire Ronchigram images. The collected Ronchigram images are processed using the supporting MATLAB program to automatically extract the accurate coordinates of the image center, which serves as the reference point for subsequent calibration.

[0085] 2. Data Acquisition and Recording

[0086] Taking a polycrystalline FIB sample as the experimental object, the operator tilts multiple grains to the positive axis position and records the α and β tilting angle data corresponding to each grain.

[0087] Sample Selection Criteria:

[0088] To ensure that the Kiku Line can be clearly observed and tracked as a marker in the experiment, the present invention selects a polycrystalline FIB sample with obvious Kiku Line characteristics. This sample contains multiple grains, and the Kiku Line can be clearly shown on each grain, facilitating the selection of multiple data points for collection in different regions. In addition, the preparation process of the polycrystalline FIB sample is mature and has high stability, which can meet the requirements for data repeatability and statistical reliability, so it becomes an ideal experimental object.

[0089] Data Point Selection Criteria:

[0090] In order to clearly calculate the x and y coordinates of the corresponding α and β tilting axes on the image in the subsequent steps, the present invention selects the Kiku pole as the key reference point. The specific method is as follows: record the α and β tilting angle data when the Kiku pole is tilted to the positive axis, and calculate the corresponding x and y coordinates in the image based on this. The selected data points should be obvious and easily recognizable feature points to ensure the accuracy of the data and provide reliable basic data for subsequent mathematical fitting.

[0091] Selection Criteria and Relevance to the Solution of This Example

[0092] The selection of samples and determination of data points are directly related to the precise mapping between image coordinates and tilt angles in the calibration scheme. Selecting a polycrystalline FIB sample with clear Kikuchi line markings not only facilitates the determination of multiple representative feature points in each grain but also ensures comprehensive data acquisition during tilting. The strategy of using the Kikuchi pole as a reference point helps accurately calculate the correspondence between the α and β tilt angles and image coordinates, providing a solid data foundation for mathematical fitting and subsequent correction. Overall, these selection criteria ensure the statistical reliability and repeatability of data during calibration and are organically unified with the calibration scheme of the present invention, thereby achieving high-precision quantitative correction of the tilt axis deviation and pixel calibration of the transmission electron microscope.

[0093] 3. Image Data Processing and Conversion

[0094] Use MATLAB to process the collected image data and calculate the precise position of the grains in the observation coordinate system (XOY). Match the collected tilt angle data with the corresponding pixel coordinates to provide data support for the construction of subsequent mathematical models.

[0095] 4. Mathematical Model Construction and Parameter Fitting

[0096] Construct a mathematical model, assuming there is a deviation angle γ between the α axis and the x axis, and a deviation angle θ between the α axis and the β axis. At the same time, introduce the pixel size (PixelSize) parameter of the image. Use MATLAB for data fitting, substitute the actually collected α and β tilt angles and the corresponding pixelx and pixely data into the model, and solve for the accurate values of γ, θ, and PixelSize.

[0097] 5. Calculation of Tilt Values for Any Point and Correction Application

[0098] Use the fitted γ, θ, and PixelSize parameters to calculate the α and β values required for tilting any point on the image to the center position. Adjust the rotation axis of the transmission electron microscope according to the calculation results for automatic correction to ensure accurate sample positioning.

[0099] 6. Data Archiving and Subsequent Optimization

[0100] Archive all the collected and processed data for subsequent analysis, equipment maintenance, and parameter optimization. According to the long-term usage situation, perform re-calibration regularly to maintain the long-term stability and high-precision operation of the system.

Claims

1. A method for measuring and correcting the deviation of a transmission electron microscope goniometer, characterized in that: Including the following steps; Step S1, collect Ronchigram images and extract the precise coordinates of the image center; Step S2, collect multiple data points based on a polycrystalline FIB sample, the data including the α and β tilt angle data corresponding to multiple sample grains when tilted to the positive axis, to ensure the reliability and repeatability of data statistics during the calibration process; Step S3, calculate the corresponding x and y coordinates on the image when the grain is tilted to the positive axis, namely Pixelx, Pixely; Step S4, construct a mathematical model for describing the geometric relationship between the actual tilt system and the image acquisition system of the transmission electron microscope; Step S5, perform fitting processing and solve parameters for the two sets of data of the actually collected α and β tilt angle data and the corresponding Pixelx, Pixely data; Step S6, calculate the tilt angle for the electron microscope rotation axis operation based on the calculation result of Step S5.

2. A method for measuring and correcting the deviation of the goniometer of a transmission electron microscope according to claim 1, characterized in that: The method is used for a tilt stage of a transmission electron microscope with a double tilt axis structure, including an α axis and a β axis, and the two axes jointly form an αOβ tilt coordinate system, for calibrating and correcting the deviation angle between the tilt coordinate system αOβ and the image observation coordinate system XOY.

3. A method for measuring and correcting the deviation of the goniometer of a transmission electron microscope according to claim 2, characterized in that: Specifically, in Step S1, by collecting Ronchigram images, use MATLAB to process the images and extract the precise coordinates at the center of the current Ronchigram; it is used to provide a reference benchmark for subsequent coordinate system calibration.

4. A method for measuring and correcting the deviation of the goniometer of a transmission electron microscope according to claim 3, characterized in that: The method of Step S1 is operated when the transmission electron microscope is in a vacuum state.

5. A method for measuring and correcting the deviation of the goniometer of a transmission electron microscope according to claim 2, characterized in that: Step S2 is used to ensure that the Kikuchi line (Kiku Line) can be clearly observed and tracked as a marker during the operation. Select a polycrystalline FIB sample with obvious Kikuchi line characteristics. The sample contains multiple grains and the Kikuchi line can be clearly displayed on each grain, so as to facilitate the collection of multiple data points in different regions.

6. A method for measuring and correcting the deviation of the goniometer of a transmission electron microscope according to claim 5, characterized in that: In Step S2, a polycrystalline FIB sample with mature preparation technology, high stability, and capable of meeting the requirements of data repeatability and statistical reliability is used. The selected sample and the data points collected at the sample can form an accurate mapping between the image coordinates and the tilt angle.

7. A method for measuring and correcting the deviation of the goniometer of a transmission electron microscope according to claim 2, characterized in that: In Step S3, use MATLAB to process the collected data and calculate the corresponding x and y coordinates on the image when the grain is tilted to the positive axis, so as to realize the correspondence between the tilt angle and the image coordinates and provide a data basis for establishing a mathematical model.

8. A method for measuring and correcting the deviation of the goniometer of a transmission electron microscope according to claim 2, characterized in that: In Step S4, when establishing the model, assume that: there is a deviation angle γ between the α axis and the x axis of the observation coordinate system; the included angle θ between the β axis and the α axis may deviate from the orthogonal state; at the same time, consider the pixel size PixelSize of the image. The established mathematical model is used to describe the geometric relationship between the actual tilt system and the image acquisition system of the transmission electron microscope, and is expressed by the formula as:

9. A method for measuring and correcting the deviation of a goniometer of a transmission electron microscope according to claim 2, characterized in that: Step S5 specifically is as follows: Use MATLAB software to perform fitting processing on two sets of data: one set is the actually collected α and β tilt angle data, and the other set is the corresponding Pixelx and Pixely data; through mathematical fitting methods, accurately calculate and solve the values of the deviation angles γ and θ and the image pixel size PixelSize, so as to realize the quantitative correction of the tilt axis deviation and pixel calibration of the transmission electron microscope.

10. A method for measuring and correcting the deviation of the goniometer of a transmission electron microscope according to claim 9, characterized in that: Step S6 specifically is as follows. After obtaining the accurate values of γ, θ, and PixelSize, calculate the tilt angle for any point in the reciprocal space of the area related to the electron microscope rotation axis operation, that is, calculate the corresponding α and β values required for it to tilt to the central position according to its position in the image, which is used to improve the efficiency and accuracy of the electron microscope rotation axis operation.

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