Three-dimensional atom probe data reconstruction method suitable for aspheric tip sample

Abstract

The invention relates to the technical field of material characterization, in particular to a three-dimensional atom probe data reconstruction method suitable for an aspheric needle tip sample, and overcomes the limitation of a three-dimensional reconstruction method based on spherical hypothesis in processing needle tip samples in complex shapes. Through observation and fitting of dynamic morphology evolution of a multi-phase material in a laser pulse excitation mode in an experiment process, accurate reconstruction of an aspheric needle tip sample is realized, and the accuracy degree of subsequent sample microstructure morphology and component information analysis is improved. According to the optimized three-dimensional reconstruction method, the precision of three-dimensional atom probe data reconstruction can be effectively improved, and the analysis precision of morphology, components and the like of microstructures such as a GP region and a grain boundary in a material is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of material characterization, and particularly to a three-dimensional atomic probe data reconstruction method applicable to aspherical tip samples. Background Art

[0002] The three-dimensional atomic probe is currently the only ultra-precise analytical instrument that can detect and obtain the three-dimensional spatial distribution of all elements atom by atom, and has important applications in the characterization of the fine structure of materials and the quantification of chemical components. The sample analyzed by the three-dimensional atomic probe is a needle-shaped sample with a tip diameter of about 100 nm. The basic principle of obtaining the real position (xs, ys, zs) information of atoms in the needle tip sample is based on the excitation of atoms under the action of an electric field, and the position (XD, YD) and arrival sequence (ND) of the atoms flying to the position-sensitive detector under the action of an external electric field are traced back. This tracing process is the three-dimensional reconstruction of the three-dimensional atomic probe data, and its reconstruction accuracy directly determines the accuracy of subsequent data analysis.

[0003] Existing three-dimensional atomic probe data three-dimensional reconstruction algorithms all assume that the tip of the needle tip sample is always spherical during the entire test process. However, during the test of the sample, its tip morphology often deviates from this assumption. Since the current mainstream three-dimensional atomic probe equipment uses unilateral laser pulse-induced atomic excitation, it inevitably causes more significant excitation on the laser-facing side of the sample than on the back laser side, resulting in the deviation of the tip morphology of the sample from the hemispherical assumption; in addition, for multiphase materials, due to the different excitation difficulties of different phases, the surface excitation is uneven, resulting in the evolution of the sample tip into an irregular morphology. For the above situations, the three-dimensional reconstruction images obtained by using the algorithm based on the spherical assumption often have local distortions, which affect the accuracy of subsequent analysis of the microstructure morphology and composition information of the sample.

[0004] Therefore, there is an urgent need for an innovative method to achieve accurate three-dimensional reconstruction of aspherical tip samples, which will have important practical value for material research. Summary of the Invention

[0005] The present invention provides a three-dimensional atomic probe data reconstruction method applicable to aspherical tip samples to solve the problems raised in the above background art.

[0006] To achieve the above object, the present invention provides the following technical solutions: A three-dimensional atomic probe data reconstruction method applicable to aspherical tip samples includes the following steps: Step 1: Coaxial scribing marking: Use a focused ion beam to scribe marks at a certain depth on the side of the aspherical tip sample to provide an angular and horizontal position reference for photographing the aspherical tip sample at different angles; Step 2: Obtaining the initial morphology: Take the morphology photos of the aspherical tip sample at different angles at the top before the three-dimensional atom probe experiment, extract the edge points and reconstruct the three-dimensional model of the sample top surface; Step 3: Obtaining the morphology at different experimental stages: Take the morphology photos of the aspherical tip sample at different angles at the top at different experimental stages of the three-dimensional atom probe, extract the edge points and reconstruct the three-dimensional model of the sample top surface; Step 4: Fitting the tip top surface: Fit the tip top surfaces before the experiment and at different experimental stages to obtain the three-dimensional mathematical model S n (x ni , y ni , z ni ) of the tip top morphology at different experimental stages; Step 5: Obtaining the dynamic depth compensation variable: Compare the three-dimensional mathematical model S n (x ni , y ni , z ni ) of the tip top morphology at different experimental stages with the corresponding spherical surface model of the curvature radius, calculate the difference between the two, and obtain the dynamic depth compensation variable ε(x ni , y ni , d ni , y ni , d ni ) corresponding to the positions; Step 6: Three-dimensional atom probe data reconstruction: Compensate the depth of the position of the ions in the sample through the dynamic depth compensation variable ε(x ni , y ni , d ni ) to establish the three-dimensional reconstruction of the true morphology of the aspherical tip sample.

[0007] Preferably, take the morphology photos of the aspherical tip sample at different angles at the top before the three-dimensional atom probe experiment and at different experimental stages through a scanning electron microscope or a transmission electron microscope, and perform three-dimensional model reconstruction.

[0008] Preferably, use Delaunay triangulation to fit the tip top surfaces before the experiment and at different experimental stages to obtain the three-dimensional mathematical model S n of the tip top morphology at different experimental stages.

[0009] Preferably, based on the three-dimensional atom probe spherical model, convert the ion capture positions (X D , Y D ) and arrival order (N D ) collected by the ion detector into the position S s (x s , y s , z s), based on the linear relationship between the depth compensation variable and depth in two adjacent fittings, calculate the corresponding depth z s of the dynamic depth compensation variable ε(x s , y s , d s ), and compensate z s according to z s +d s to establish the three-dimensional reconstruction of the true morphology of the aspherical tip sample.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: A three-dimensional atom probe data reconstruction method applicable to an aspherical tip sample provided by the present invention overcomes the limitations of the three-dimensional reconstruction method based on the spherical surface assumption when dealing with a tip sample with a complex shape. Through the observation and fitting of the dynamic morphology evolution of the laser pulse excitation mode and the multiphase material during the experiment, the accurate reconstruction of the aspherical tip sample is realized, and the accuracy of the subsequent analysis of the microstructure morphology and composition information of the sample is improved. By scribing marks on the side of the tip sample, an accurate angle reference is provided, and this step improves the consistency and reliability of image capture at different experimental stages; by collecting the morphology of the sample at different experimental stages, the morphology changes of the sample during the experiment can be comprehensively reflected, so as to realize the dynamic acquisition of the depth compensation variable and the accurate reconstruction of the tip morphology; the Delaunay triangulation method is used for the surface fitting of the tip top, which can effectively process complex surface features and improve the accuracy and efficiency of fitting; by calculating the dynamic depth compensation variable, the morphology data of the sample can be adjusted in real time, thereby reducing the measurement error caused by the irregular shape and enhancing the accuracy of the reconstruction result. The optimized three-dimensional reconstruction method of the present invention can effectively improve the accuracy of three-dimensional atom probe data reconstruction, and significantly improve the analysis accuracy of the morphology, composition, etc. of microstructures such as GP zones and grain boundaries in the material. Description of the Drawings

[0011] Figure 1 is a flowchart of a three-dimensional atom probe data reconstruction method applicable to an aspherical tip sample provided by the present invention; Figure 2 is a three-dimensional atom probe data reconstruction diagram of the aluminum alloy aspherical tip sample in Embodiment 1 of the present invention; Figure 3 is a three-dimensional atom probe data reconstruction diagram of the aspherical tip sample of steel material in Embodiment 2 of the present invention. Detailed Embodiments

[0012] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0013] Figure 1 It is a flowchart of a three-dimensional atomic probe data reconstruction method applicable to aspherical tip samples. An embodiment of the present invention provides a three-dimensional atomic probe data reconstruction method applicable to aspherical tip samples, as Figure 1 shown, including the following steps: Step 1: Coaxial scribing marking: Use a focused ion beam to scribe and mark a certain depth on the side of the aspherical tip sample to provide an angle and horizontal position reference for taking pictures of the aspherical tip sample at different angles; Step 2: Initial morphology acquisition: Take morphology photos of the top of the aspherical tip sample at different angles before the three-dimensional atomic probe experiment, extract the edge points, and reconstruct the three-dimensional model of the top surface of the sample; Step 3: Morphology acquisition at different experimental stages: Take morphology photos of the top of the aspherical tip sample at different angles at different experimental stages of the three-dimensional atomic probe, extract the edge points, and reconstruct the three-dimensional model of the top surface of the sample; Step 4: Fitting of the tip top surface: Fit the surfaces of the tip top before the experiment and at different experimental stages to obtain the three-dimensional mathematical model S n (x ni , y ni , z ni ) of the tip top morphology at different experimental stages; Step 5: Obtaining the dynamic depth compensation variable: Compare the three-dimensional mathematical model S n (x ni , y ni , z ni ) of the tip top morphology at different experimental stages with the corresponding spherical surface model of the curvature radius, calculate the difference between the two, and obtain the dynamic depth compensation variable ε (x ni , y ni positions corresponding to the dynamic depth compensation variable ε (x ni , y ni , d ni ); Step 6: Three-dimensional atomic probe data reconstruction: Compensate the depth of the position of the ion in the sample through the dynamic depth compensation variable ε (x ni , y ni , d ni ) to establish a three-dimensional reconstruction of the true morphology of the aspherical tip sample.

[0014] In one embodiment of the present invention, the depth of the scribing mark on the side surface of the spherical tip sample in step 1 is 1-5 µm from the top end.

[0015] In one embodiment of the present invention, before the three-dimensional atom probe experiment and at different experimental stages, topographic photos of the aspherical tip sample at different angles are taken by a scanning electron microscope or a transmission electron microscope, and three-dimensional model reconstruction is performed.

[0016] In one embodiment of the present invention, Delaunay triangulation is used to fit the surface of the tip top before the experiment and at different experimental stages, and a three-dimensional mathematical model S of the tip top topography at different experimental stages is obtained. n 。

[0017] Furthermore, in one embodiment of the present invention, based on the three-dimensional atom probe spherical model, the ion capture positions (X D , Y D ) and arrival order (N D ) collected by the ion detector are converted into the position S s (x s , y s , z s ) of the ions in the sample. Based on the linear relationship between the depth compensation variable and the depth in two adjacent fittings, the dynamic depth compensation variable ε (x s , y s , d s ) corresponding to the depth z s is calculated, and z s is compensated according to z s + d s , thereby establishing a three-dimensional reconstruction of the true topography of the aspherical tip sample. Example

[0018] Taking the three-dimensional atom probe data reconstruction of a 2024 aluminum alloy aspherical tip sample as an example, the tip sample for the three-dimensional atom probe experiment is prepared by electrolytic polishing, and the initial topography of its tip top is irregular; after the three-dimensional atom probe test, the shape of the tip top is basically spherical. The reconstruction method is as follows: Step (1): Use a focused ion beam to scribe a mark at a depth of 3 µm on the side surface of the tip sample to provide an angle reference for shooting and ensure the accuracy and consistency of subsequent image acquisition; Step (2): Load the tip sample obtained in step (1) into a scanning electron microscope device, take images of the tip top of the tip sample at angles from 0 to 360° with an angle interval of 30°, extract the edge points and reconstruct the three-dimensional model to form the topography data of the initial sample; Step (3): Load the tip sample obtained in step (2) into a three-dimensional atom probe device for data acquisition. After collecting 10 million data points in the voltage pulse mode, take out the tip and reload it into the scanning electron microscope. Take images of the top of the tip sample at angles from 0 to 360°, with an angular interval of 30°. Extract the edge points and reconstruct the model to obtain the morphological information at different stages. Step (4): Fit the tips of the initial and different experimental stages obtained in steps (2) and (3) using the Delaunay triangulation method to obtain the three-dimensional mathematical model of the tip morphology before and after the experiment. Step (5): Compare the three-dimensional mathematical models at different stages obtained in step (4) with the corresponding spherical equation of the curvature radius, calculate the difference between the two, and obtain the dynamic depth compensation variable ε(x, y, d). Step (6): Use the dynamic compensation variable ε(x, y, d) obtained in step (5) to sequentially correct the atomic positions (x s 、y s 、z s ) in the sample obtained through the spherical model, and finally realize the three-dimensional reconstruction of the true morphology of the aspherical tip sample.

[0019] Figure 2 This is the three-dimensional atom probe data reconstruction diagram of the aspherical tip sample of aluminum alloy in Example 1 of the present invention. As Figure 2 shown, the initial morphology of the three-dimensional atom probe reconstruction data obtained in step (6) of this example is basically the same as the initial morphology of the original sample obtained by the scanning electron microscope, indicating that this method can achieve high-precision reconstruction of the three-dimensional atom probe data of the aluminum alloy aspherical tip sample. Example

[0020] Taking the three-dimensional atom probe data reconstruction of the aspherical tip sample of martensitic steel material as an example, a tip sample for three-dimensional atom probe experiment is prepared by focused ion beam. The initial morphology of its tip top is irregular; after performing the three-dimensional atom probe test on it, the shape of the tip top is basically spherical. The reconstruction method is as follows: Step (1): Perform a scribing mark on the side of the tip sample at a depth of 1 µm from the top to provide an angular reference for shooting, ensuring the accuracy and consistency of subsequent image acquisition. Step (2): Load the tip sample obtained in step (1) into a transmission electron microscope device, take images of the tip sample top at angles from 0 to 180°, with an angular interval of 20°, extract the edge points and reconstruct the three-dimensional model to form the morphological data of the initial sample. Step (3): Load the tip sample obtained in step (2) into a three-dimensional atom probe device for data acquisition. After collecting 50 million data points in the laser pulse mode, take out the tip and reload it into the transmission electron microscope. Take images of the top of the tip sample at angles from 0° to 180° with an angular interval of 20°. Extract the edge points and reconstruct the model to obtain the morphological information at different stages; Step (4): Fit the tips of the initial and different experimental stages obtained in steps (2) and (3) using the Delaunay triangulation method to obtain the three-dimensional mathematical model of the tip morphology before and after the experiment; Step (5): Compare the three-dimensional mathematical models at different stages obtained in step (4) with the corresponding spherical equation of the radius of curvature, calculate the difference between the two, and obtain the dynamic depth compensation variable ε(x, y, d); Step (6): Use the dynamic compensation variable ε(x, y, d) obtained in step (5) to sequentially correct the atomic positions (x s , y s , z s ) in the sample obtained through the spherical model, and finally realize the three-dimensional reconstruction of the true morphology of the aspherical tip sample.

[0021] Figure 3 This is the three-dimensional atom probe data reconstruction diagram of the aspherical tip sample for steel materials in Example 2 of the present invention. As Figure 3 shown, the initial morphology of the three-dimensional atom probe reconstruction data obtained in step (6) of this embodiment is basically the same as the initial morphology of the original sample obtained by the scanning electron microscope, indicating that this method can achieve high-precision reconstruction of the three-dimensional atom probe data of the aspherical tip sample of steel materials.

[0022] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A three-dimensional atom probe data reconstruction method suitable for non-spherical needle tip samples, characterized in that: The following steps are involved: Step 1: Coaxial line marking: Use the focused ion beam to mark the side of the aspheric needle tip sample at a certain depth to provide an angle and horizontal position reference for shooting the aspheric needle tip sample at different angles; Step 2: Initial morphology acquisition: Take morphological photos of the top of the aspheric needle tip sample at different angles before the 3D atom probe experiment, extract edge points and reconstruct the 3D model of the top surface of the sample; Step 3: Acquisition of morphology at different experimental stages: Take morphology photos of the top of the aspheric tip sample at different angles at different experimental stages of the three-dimensional atom probe, extract edge points and reconstruct a three-dimensional model of the curved surface at the top of the sample; Step 4: Needle tip top surface fitting: Fit the tip top surface before the experiment and at different experimental stages to obtain a three-dimensional mathematical model S of the tip top morphology at different experimental stages. n (x ni ,y ni ,z ni ); Step 5: Obtain dynamic depth compensation variables: The three-dimensional mathematical model S of the tip morphology at different experimental stages n (x ni ,y ni ,z ni ) is compared with the corresponding curvature radius spherical model, and the difference between the two is calculated to obtain the x at different experimental stages. ni ,y ni The dynamic depth compensation variable ε(x ni ,y ni d ni ); Step 6: 3D Atom Probe Data Reconstruction: Dynamic Depth Compensation Variable ε(x ni ,y ni d ni ) compensates for the depth of the ion’s position in the sample, thereby establishing a three-dimensional reconstruction of the true morphology of the aspheric tip sample.

2. A three-dimensional atom probe data reconstruction method suitable for non-spherical needle tip samples according to claim 1, characterized in that: The three-dimensional atomic probe is used to take morphological photos of the top of the aspheric needle tip sample at different angles before the experiment and at different experimental stages by scanning electron microscopy or transmission electron microscopy, and a three-dimensional model is reconstructed.

3. A three-dimensional atom probe data reconstruction method suitable for non-spherical needle tip samples according to claim 1, characterized in that: Delaunay triangulation was used to fit the tip surface before and at different experimental stages to obtain the three-dimensional mathematical model S of the tip morphology at different experimental stages. n .

4. A three-dimensional atom probe data reconstruction method suitable for non-spherical needle tip samples according to claim 1, characterized in that: The ion trapping position (X) collected by the ion detector is calculated based on the three-dimensional atom probe spherical model. D , Y D ) and arrival order (N D ) is converted into the position S of the ion in the sample s (x s ,y s 、z s ), based on the linear relationship between the depth compensation variable and the depth in two adjacent fittings, the corresponding depth z is calculated s The dynamic depth compensation variable ε(x s ,y s ,d s ), and for z s According to z s +d s Compensation is performed to establish a three-dimensional reconstruction of the true morphology of the aspheric tip sample.

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