A mathematical processing method for defocused element surface distribution diagram

Abstract

The present invention belongs to the field of image processing of electron probe analysis technology, and discloses a mathematical processing method for defocused element surface distribution map. The present invention introduces a mathematical processing method for obtaining a surface distribution map from a standard sample with a flat and clean surface and uniform element distribution, extracting a correction factor from it and applying it to the surface distribution map of the same type of element collected under the same experimental conditions, thereby eliminating the defocus effect. Specifically, the characteristic that the element concentration or counting intensity decreases from the optimal focusing line to the isofocal lines parallel to it on both sides is utilized. By using the element surface distribution map of the standard sample to obtain the corresponding correction factor, the element surface distribution map of the same type collected under the same experimental conditions is corrected, and finally the true state of the element surface distribution map of the sample to be tested is restored. The results show that the element surface distribution image after processing is basically consistent with the image obtained using the sample stage scanning mode.

Description

Technical Field

[0001] The present invention relates to the technical field related to image processing of electron probe analysis technology, and more specifically to a mathematical processing method for a defocused element surface distribution diagram of an electron probe-spectrometer. Background Art

[0002] Since it can intuitively display the two-dimensional distribution of element content on the sample surface, the surface distribution Figure 1 Vertical is one of the main functions of electron probe analysis technology, and has been widely used in research fields such as geology, materials, environment, and paleontology. Both the sample stage scanning and electron beam scanning methods can obtain element surface distribution images. In the former, the electron beam is fixed and the sample stage moves in a plane perpendicular to the electron beam. In the latter, the sample stage is fixed and the electron beam performs a small angle scan in a rectangular area on the sample surface. The characteristic X-ray signal of the element excited by each pixel is then collected by the spectrometer, and finally a rectangular element surface distribution map is generated in which the X-ray signal counting intensity or element concentration varies with position.

[0003] The stage scanning mode is not suitable for element surface distribution mapping at high magnifications because it is easily affected by stage drift. In addition, due to technical and time cost limitations, the image resolution cannot be set too high and the pixel pitch cannot be set too small (≥0.02μm). The electron beam scanning mode avoids the mechanical loss caused by the frequent movement of the stage during the mapping process, and the image resolution and pixel pitch are theoretically unlimited, but are affected by the defocusing effect at magnifications below 2000-3000. The reason is that the angle range of the electron beam deflection during scanning is relatively large, resulting in the X-rays emitted from the edge pixels of the scanning area to the spectroscopic crystal cannot meet the Bragg diffraction conditions, causing the X-ray counting signals collected by the detector to have different degrees of loss compared to the ideal Bragg diffraction conditions. The intuitive manifestation is that the element surface distribution that should have been uniform becomes the element concentration or count value from the optimal focus line (Line of Optimum Focus, referred to as LOOF, here refers to a line connected by the maximum concentration or intensity points, see attached Figure 2 ) to the two sides of the equifocal line (EL, here refers to the same concentration or intensity points connected by a number of parallel lines) gradually decrease, and the greater the deflection angle (or the smaller the magnification), the more significant the defocusing effect. In order to make the element surface distribution image obtained by the electron beam scanning mode at low magnification reflect the true state of the sample itself, it is necessary to develop a mathematical processing method to correct the above defocusing effect. Summary of the invention

[0004] In view of the defocus effect problem existing in the prior art, the purpose of the present invention is to provide a mathematical processing method for obtaining a surface distribution map from a standard sample with a flat, clean surface and uniform element distribution, extracting correction factors from it and applying them to the surface distribution map of the same type of elements collected under the same experimental conditions, thereby eliminating the defocus effect. The results show that the element surface distribution image after processing is basically consistent with the image obtained using the sample stage scanning mode.

[0005] The invention provides a mathematical processing method for a defocused element surface distribution diagram of an electron probe-spectrometer. The real state of the element surface distribution diagram can be restored by correcting the defocusing effect.

[0006] The present invention adopts the following technical solution:

[0007] Step 1: According to the requirements of electron probe detection, prepare optical slices or thin slices of the standard sample and the sample to be detected, and evaporate a 20nm thick carbon film on the surface of the sample;

[0008] Step 2: Select the electron probe instrument, turn it on, and debug the instrument after the beam current stabilizes;

[0009] Step 3: According to the instrument sampling requirements, install the standard sample and the sample to be tested on the sample stage and transfer them to the vacuum sample chamber. Under the same experimental working conditions and configuration parameters, collect element surface distribution images for the standard sample and the sample to be tested respectively. The specific steps are as follows:

[0010] S31: installing the standard sample and the sample to be tested on the sample stage and transferring them to the vacuum sample chamber;

[0011] S32: Setting experimental working conditions;

[0012] S33: Set the experimental configuration parameters;

[0013] S34: Select a surface scanning area for testing;

[0014] S35: Under the same experimental working conditions and configuration parameters, element surface distribution images are collected for the standard sample and the sample to be tested, respectively, to obtain an element surface distribution map of the standard sample and an original element surface distribution map of the sample to be tested;

[0015] Step 4: Process the element surface distribution map (concentration or counting intensity array, such as 512*512) of the standard sample collected in step 3, obtain the correction factor of the specific element under the specific experimental configuration parameters and save it;

[0016] Step 5: Call the correction factor obtained in step 4 to correct and save the original element surface distribution map of the sample to be tested in step 3.

[0017] Preferably, in step 1, the preparation process of the standard sample and the sample to be tested includes cutting, inlaying, rough grinding, fine grinding and polishing, etc., and finally a light sheet or thin sheet of suitable size is made. The specifications of the light sheet do not exceed 20 mm long × 20 mm wide × 10 mm high, and the specifications of the thin sheet are generally 50 mm long × 25 mm wide × 2 mm high.

[0018] Preferably, in step 2, the instrument used is the JXA-8100 electron probe of Japan Electronics Co., Ltd. (Jeol), which is conventionally equipped with a 4-channel spectrometer (it can be upgraded to a fifth spectrometer, see attached Figure 1 ), where the first channel is equipped with TAP and LDE1 spectroscopic crystals, the second channel is equipped with TAP and LDE2 spectroscopic crystals, the third channel is equipped with PETH and LIFH spectroscopic crystals, and the fourth channel is equipped with PETJ and LIF spectroscopic crystals. The Rowland circle radius of the first, second and fourth spectrometers is 140mm, and the Rowland circle radius of the third spectrometer is 110mm. The X-ray detection angles of the four spectrometers are all 40°.

[0019] Preferably, in step 3, the acceleration voltage of the electron probe surface scanning experiment is generally 10-25 kV, the beam current is generally 50-300 nA, and the beam spot is generally set to a focused state, and the beam can be appropriately expanded according to actual needs.

[0020] Preferably, in step 3, the experimental configuration parameters include test elements, spectrometer channel number, spectroscopic crystal, detector, image resolution, and the residence time of the electron beam at each pixel.

[0021] Preferably, in step 3, the element surface distribution map refers to an orthogonal array consisting of a large number of equidistant pixel points in the X and Y directions on the sample, and the value of each pixel point represents the X-ray signal counting intensity of the element collected at that position or the element concentration converted from the intensity. The counting intensity or concentration can be represented by different grayscales or colors.

[0022] Preferably, in step 4, the process of processing the element surface distribution map of the standard sample is as follows:

[0023] S41: Import the elemental surface distribution map of the standard sample and set the spectrometer parameter information (such as the number of spectrometer channels, spectral crystal and crystal arrangement angle, etc.);

[0024] S42: Calculate the average value of the X-ray signal count intensity or element concentration of all pixel points on the optimal focus line and each isofocal line parallel to it, and replace the initial value of all pixel points on each of the above lines with the average value;

[0025] S43: sampling the image in a direction orthogonal to the isofocal line to obtain a distribution profile of the X-ray signal counting intensity or element concentration in the direction;

[0026] S44: Use the Savitzky-Golay filter algorithm to smooth the profile curve and replace the previous average value with the smoothed data;

[0027] S45: Calculate and save the correction factors of all pixels on the isofocal line.

[0028] Preferably, in steps 3-5, the acquisition dates of the element surface distribution map of the sample to be tested and the element surface distribution map of the standard sample do not have to be consistent, that is, after the correction factor of a specific element under specific working conditions and experimental configuration parameters is determined, it can be applied to the processing of the same type of element surface distribution map collected under the same experimental conditions thereafter.

[0029] Compared with the prior art, the advantages of the present invention are:

[0030] 1. This scheme aims to solve the problem that the electron beam scanning surface distribution map of the electron probe-spectrometer is affected by the defocusing effect at low magnification. It utilizes the characteristic that the element concentration or counting intensity decreases from the optimal focusing line to the isofocal lines parallel to it on both sides. By using the element surface distribution map of the standard sample to obtain the corresponding correction factor, the element surface distribution map of the same type collected under the same experimental conditions is corrected, and finally the true state of the element surface distribution map of the sample to be tested is restored.

[0031] 2. The method of this scheme can give full play to the unique advantages of the electron beam scanning mode in high magnification and high-resolution surface distribution mapping, overcome the defects of sample stage scanning surface distribution mapping, such as sample stage drift, long mapping time, limited image resolution and pixel spacing, and is an effective supplement to the conventional sample stage scanning surface distribution mapping technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the installation layout of the electron probe-spectrometer (JEOL JXA-8100 electron probe, the dotted line indicates the fifth spectrometer that can be expanded and installed);

[0033] Figure 2 Figure a is a typical defocused element surface distribution diagram; Figure b is a simplified diagram of the image processing principle (angle α indicates the direction of LOOF)

[0034] Figure 3 The original and calibrated elemental distribution maps of the quartz single mineral standard sample collected by the first wave spectrometer (electron beam scanning mode, a and b are the original and processed images of silicon element (TAP crystal, x2000); c and d are the original and processed images of oxygen element (LDE1 crystal, x180));

[0035] Figure 4The original and calibrated elemental distribution maps of the forsterite single mineral standard sample collected using the second spectrometer (electron beam scanning mode, a and b are the original and processed images of silicon elements (TAP crystal, x600); c and d are the original and processed images of oxygen elements (LDE2 crystal, x300));

[0036] Figure 5 The original and calibrated elemental distribution maps of diopside (calcium) and iron garnet (iron) single mineral standard samples collected using the third-channel spectrometer (a and b are the original and processed maps of calcium, respectively (PETH crystal, x1000); c and d are the original and processed maps of iron, respectively (LIFH crystal, x600));

[0037] Figure 6 The original and calibrated elemental distribution maps of diopside (calcium) and iron garnet (iron) single mineral standard samples collected using the fourth-channel spectrometer (a and b are the original and processed maps of calcium, respectively (PETJ crystal, x1000); c and d are the original and processed maps of iron, respectively (LIF crystal, x600));

[0038] Figure 7 The following are example diagrams of the present invention applied to the defocused element surface distribution diagram of electron beam surface scanning of typical rock slices (calcium element, fourth channel spectrometer, PETJ crystal, x1000): a is the calcium element surface distribution diagram (grayscale diagram) collected using the electron beam scanning mode; b is the calcium element surface distribution diagram (electron beam scanning mode) represented by pseudo color, and there is obvious attenuation of X-ray signal counting intensity in the upper left corner of the above two figures; c is the calcium element surface distribution diagram (grayscale diagram) after Figure a is processed using the present invention; d is the calcium element surface distribution diagram (grayscale diagram) collected using the sample stage scanning mode. DETAILED DESCRIPTION

[0039] Embodiment 1:

[0040] Step 1: Prepare a light sheet or a thin sheet;

[0041] Select the microbeam analysis standard sample with a larger particle size (recommended particle size ≥ 2mm) and the sample to be tested, and make it into a light sheet or thin slice by inlaying, grinding and polishing. The sample surface is required to be clean and flat. The specification of the light sheet is recommended not to exceed 20mm long × 20mm wide × 10mm high, and the specification of the thin slice is generally 50mm long × 25mm wide × 2mm high. Before testing, evaporate a 20nm thick carbon film on the surface of the sample.

[0042] Step 2: Select the JXA-8100 electron probe from Japan Electronics Corporation, turn it on, and debug the instrument after the beam current stabilizes.

[0043] Step 3: Under the same experimental working conditions and configuration parameters, collect element surface distribution maps for the standard sample and the sample to be tested respectively;

[0044] Specifically:

[0045] 3.1: Install the standard sample and the sample to be tested on the sample stage and transfer them to the vacuum sample chamber.

[0046] 3.2: Set the working conditions: acceleration voltage 15kV, beam current 100nA, and beam spot in focused state.

[0047] 3.3: Set the experimental configuration parameters: select the test element and the corresponding spectrometer channels, spectroscopic crystals, detectors, etc., image resolution 512*512, electron beam residence time at each pixel 60ms, pixel spacing changes with magnification.

[0048] 3.4: Select the surface scanning area for testing.

[0049] Figure 3 (a and c) to Figure 6 (a and c) are the original element distribution maps of single mineral standard samples collected in electron beam scanning mode. Figure 7 a is the original element surface distribution map of the sample to be tested collected in the electron beam scanning mode. It can be seen that it is affected by the defocusing effect at a magnification lower than 2000-3000. Figure 7 d is the original element surface distribution map of the sample to be tested collected in the sample stage scanning mode. When the influence of the sample stage drift is not considered, it reflects the actual surface distribution state of the elements.

[0050] Step 4: Process the original elemental distribution map of the standard sample collected in step 3, obtain the correction factor of the specific element under specific experimental working conditions and configuration parameters and save it. Correction factor calculation formula: f = I i / I0,I i is the X-ray counting intensity of each pixel, and I0 is the maximum X-ray counting intensity.

[0051] Step 5: Call the correction factor obtained in step 4 to correct and save the original element surface distribution map of the sample to be tested.

[0052] Figure 3 (b and d) to Figure 6 (b and d) are the element distribution maps of the single mineral standard sample after correction. It can be seen that the elements are evenly distributed, indicating that the defocus effect at the edge of the image has been corrected; Figure 7 c is the element surface distribution map of the sample to be tested after correction, which is different from the element surface distribution map collected in the sample stage scanning mode ( Figure 7d) are basically the same, indicating that the present invention has a good practical effect in eliminating the defocusing effect. In addition, for the same particle, Figure 7 d is better than Figure 7 The size shown in c is slightly larger, indicating that the particle shape in the surface scanning image is slightly distorted due to the drift of the sample stage, while this problem does not exist in the element surface distribution map obtained using the electron beam scanning mode.

[0053] The above-described embodiments are only preferred embodiments of the present invention, and the embodiments are not intended to limit the scope of patent protection of the present invention. Therefore, any equivalent structural changes made using the contents of the description and drawings of the present invention should also be included in the scope of protection of the present invention.

Claims

1. A mathematical processing method for a defocused element surface distribution diagram, characterized in that: The steps include: Step 1: Prepare the standard sample and the sample to be tested into a light sheet or a thin sheet, and evaporate a layer of carbon film on the surface of the sample; Step 2: Select the electron probe instrument, turn it on, and debug the instrument after the beam current stabilizes; Step 3: Element surface distribution image acquisition: S31: installing the standard sample and the sample to be tested on the sample stage and transferring them to the vacuum sample chamber; S32: Setting experimental working conditions; S33: Set the experimental configuration parameters; S34: Select a surface scanning area for testing; S35: Under the same experimental working conditions and configuration parameters, element surface distribution images are collected for the standard sample and the sample to be tested, respectively, to obtain an element surface distribution map of the standard sample and an original element surface distribution map of the sample to be tested; Step 4: Process the element surface distribution map of the standard sample collected in step 3, obtain the correction factor of the element under the experimental configuration parameters and save it: S41: Import the element surface distribution map of the standard sample and set the spectrometer parameter information; S42: Calculate the average value of the X-ray signal count intensity or element concentration of all pixel points on the optimal focus line and each isofocal line parallel to it, and replace the initial value of all pixel points on each of the above lines with the average value; S43: sampling the image in a direction orthogonal to the isofocal line to obtain a distribution profile of the X-ray signal counting intensity or element concentration in the direction; S44: Smooth the profile curve and replace the previous average value with the smoothed data; S45: Calculate and save the correction factors of all pixels on the isofocal line; Step 5: Call the correction factor obtained in step 4 to correct and save the original element surface distribution map of the sample to be tested in step 3.

2. The mathematical processing method of a defocused element surface distribution diagram according to claim 1, characterized in that: In step 2, the instrument used is the JXA-8100 electron probe produced by Japan Electronics Corporation.

3. The mathematical processing method of a defocused element surface distribution diagram according to claim 1, characterized in that: In step 3-S33, the experimental configuration parameters include the test element, the number of spectrometer channels, the spectroscopic crystal, the detector, the image resolution, and the residence time of the electron beam at each pixel.

4. The mathematical processing method of the defocused element surface distribution diagram according to claim 1, characterized in that: In step 4-S41, the spectrometer parameter information includes the number of spectrometer channels, the spectroscopic crystals and the crystal arrangement angles.

5. The mathematical processing method of the defocused element surface distribution diagram according to claim 1, characterized in that: In step 4-S44, the profile curve is smoothed using a Savitzky-Golay filtering algorithm.

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