Three-dimensional atom probe sample and preparation method thereof

Abstract

The invention relates to a preparation method of a three-dimensional atom probe sample, which comprises the following steps: S1, imaging a sample under a scanning electron microscope, and marking an interested area on the surface of the sample; s2, cutting the region to expose the section of the sample; s3, performing ion beam irradiation on the cross section so as to generate bright and dark contrast beneficial to observation on two sides of a crystal boundary in the cross section; s4, according to the position of the contrast, cutting the sample to form a slice sample containing a grain boundary; and S5, annularly cutting the sheet sample to form a needle point sample containing the crystal boundary. According to the preparation method, efficient and accurate positioning is provided, the sample preparation time is effectively shortened, and the sample preparation success rate is increased.

Description

Technical Field

[0001] The invention relates to the technical field of micro-nanoscale material sample preparation, and in particular to a three-dimensional atomic probe sample and a preparation method thereof. Background Art

[0002] At present, the diameter of the tip of the needle used to prepare three-dimensional atom probe samples is less than 100nm. For sample preparation containing alloy interfaces, the interface to be observed must be included in the tip volume. However, for alloy materials with complex phase components, both grain boundary interfaces and phase interfaces are included. These interfaces are difficult to distinguish in scanning electron beam imaging, resulting in uncertainty in the positioning of grain boundaries during the tip preparation process.

[0003] The properties and characteristics of grain boundaries have a significant impact on the performance of alloys. Therefore, an efficient and accurate method is needed to locate and prepare samples containing grain boundaries for further research and application. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a method for preparing a three-dimensional atom probe sample, which can effectively improve the sample preparation efficiency. The preparation method comprises the following steps:

[0005] S1. The sample is imaged under a scanning electron microscope and the area of ​​interest is marked on the sample surface;

[0006] S2, cutting the area to expose a cross section of the sample;

[0007] S3, irradiating the cross section with an ion beam so as to produce a light-dark contrast on both sides of the grain boundary in the cross section that is conducive to observation;

[0008] S4, cutting the sample into a thin slice sample including a grain boundary according to the position of the contrast;

[0009] S5. Cut the thin slice sample in a circular manner to form a needle tip sample including the grain boundary.

[0010] Furthermore, in step S3, the beam current of the ion beam irradiation is 100 pA to 200 pA, and the irradiation duration is not less than 15 seconds.

[0011] Furthermore, the sample is a metal alloy.

[0012] Furthermore, the method also includes a step of cooling the sample when cutting the sample.

[0013] The method for preparing a three-dimensional atom probe sample as claimed in claim 1 is characterized in that in step S1, focused ion beam induced chemical vapor deposition is used to deposit metal in the area of ​​interest to mark the sample surface.

[0014] Furthermore, before step S5, the process also includes transferring and welding the thin slice sample to the sample preparation stage.

[0015] Furthermore, in step S2 and step S4, the cutting method includes: any one of nano-hand cutting and focused ion beam cutting.

[0016] Furthermore, in step S5, a focused ion beam is used to perform annular cutting.

[0017] In addition, the present invention also proposes a three-dimensional atomic probe sample, which is made by adopting the preparation method.

[0018] The preparation method of the present invention provides efficient and precise positioning, effectively improves the preparation efficiency of the needle tip sample containing the interface, and improves the success rate of sample preparation. The needle tip sample prepared by this method is very suitable for three-dimensional atomic probe testing, providing important technical support for alloy microstructure characterization research. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a flow chart of a method for preparing a three-dimensional atom probe sample of the present invention;

[0020] Figure 2 is an electron microscope image of the sample of the present invention after being irradiated by an ion beam;

[0021] Figure 3 This is an electron microscope image of the sample of the present invention welded on a stage;

[0022] Figure 4 This is an electron microscope image of the sample of the present invention after circular cutting. DETAILED DESCRIPTION

[0023] The following is a further detailed description of a three-dimensional atom probe sample and a preparation method thereof proposed by the present invention in conjunction with the accompanying drawings and specific embodiments.

[0024] The present invention mainly solves the problem that it is difficult to distinguish between alloy phase interfaces and grain boundaries in alloy samples, resulting in the inability to quickly and accurately locate grain boundaries in scanning electron microscopes. At present, ion beam cutting of alloy samples is mainly used to obtain cross-sectional grain boundary images. The cutting or corrosion of the sample is achieved by focusing the ion beam on the surface of the alloy sample, and the information of the grain boundaries is obtained through imaging technology. Due to the existence of alloy phase interfaces, the identification and positioning of grain boundaries will be interfered with, increasing the complexity and difficulty of the operation. To this end, the present invention proposes a method that can enhance the positioning of grain boundaries during the cutting process, so as to accurately cut and obtain a needle tip sample containing the desired grain boundaries.

[0025] like Figure 1As shown, a method for preparing a three-dimensional atom probe sample proposed by the present invention comprises the following steps:

[0026] S1. The sample is imaged under a scanning electron microscope and the area of ​​interest is marked on the sample surface.

[0027] Marking can be accomplished by chemical vapor deposition of metals. Specifically, focused ion beam induced chemical vapor deposition is used to deposit Pt metal in the area of ​​interest to mark the sample surface. An organic metal precursor gas containing platinum, such as methylcyclopentadienyltrimethylplatinum, is introduced into the interaction area between the ion beam and the sample. Under the action of the ion beam, the precursor gas molecules decompose and platinum atoms are deposited on the sample surface to form a mark.

[0028] S2, cutting the region to expose the cross section of the sample. The cutting can be performed by either nano-hand cutting or focused ion beam cutting. Focused ion beam cutting includes Ga ion cutting technology.

[0029] It should be noted that nano-hand cutting is mainly based on scanning probe microscopy (SPM), such as atomic force microscopy (AFM), which relies on the interaction force between the probe and the atoms on the sample surface (such as van der Waals force, electrostatic force, etc.) to manipulate atoms or nano-scale objects. This technology operates through extremely fine physical contact or close-range interaction, and the focus is on using weak interaction forces to accurately process single atoms or nanoparticles. Ga ion cutting technology is an application of focused ion beam (FIB) technology, which generates a high-energy gallium (Ga) ion beam, bombards the sample surface with the ion beam, and sputters the atoms to achieve cutting.

[0030] S3, irradiate the cross section with an ion beam to produce a light-dark contrast on both sides of the grain boundary in the cross section that is convenient for observation. The irradiation process can be performed with a lower energy. The irradiated sample shows obvious grain boundaries, such as Figure 2 As shown, there is obvious contrast on both sides of the grain boundary indicated by the arrows in the figure.

[0031] The causes of contrast include the following:

[0032] Due to the differences in atomic arrangement and binding energy, the atomic arrangement and atomic spacing of crystal planes with different orientations are different, and the binding energy between atoms is also different. When bombarded by ion beams, crystal plane atoms with high binding energy are more difficult to be sputtered, and the etching rate is slow; crystal planes with low binding energy have a fast etching rate. Therefore, the irradiation energy can be controlled to allow the crystal plane atoms with low binding energy to be sputtered and removed, and the crystal plane atoms with high binding energy to be retained. After a period of irradiation, light and dark contrast will be generated at the grain boundary.

[0033] The different atomic densities result in strong atomic interactions on crystal planes with high atomic density, making it difficult for ion beams to sputter atoms, and a low etching rate. On crystal planes with low atomic density, atomic interactions are weak, making them more easily sputtered by ion beams, and the etching rate is high, thus forming a contrast.

[0034] As well as the electron channel effect, the difference in electron scattering and absorption. When the ion beam bombards the crystal, secondary electrons and other signals will be generated. Crystals with different orientations have different scattering and absorption capabilities for electrons, resulting in different secondary electron yields. Crystal planes with dense atomic arrangement and large atomic number have strong electron scattering and absorption, and low secondary electron yield; crystal planes with loose atomic arrangement and small atomic number are easier for electrons to pass through or produce more secondary electron emission, and the secondary electron yield is high, forming an electron channel contrast.

[0035] As well as the different penetration depths of electrons, the different orientations of crystal planes have an impact on the penetration depth of electrons in the ion beam. Electrons have a shallower penetration depth in some crystal planes, and the signal generated by the interaction with atoms is weaker; while in other crystal planes, the penetration depth is deeper, and the signal generated is stronger, which in turn produces a contrast difference.

[0036] And due to the redeposition and shielding effects, the redeposition process is non-uniform. During the ion beam etching process, some of the sputtered atoms will be redeposited on the sample surface. Crystal surfaces with different orientations have different adsorption and capture capabilities for redeposited atoms, resulting in uneven distribution of redeposited atoms on the surface and contrast differences.

[0037] As well as the influence of shielding effect, during ion beam irradiation etching, grains or regions with different orientations in the crystal may shield each other. The ion beam has a weaker etching effect on the shielded area, while the etching rate of the unshielded area is faster, thus generating contrast at the interface.

[0038] In summary, due to the differences in energy, physical and chemical properties of atoms on different crystal planes, light and dark contrast is generated on both sides of the grain boundary under the scanning electron microscope under the same irradiation conditions, which facilitates observation. The optional irradiation conditions of this embodiment are: the beam current of the ion beam irradiation is 100pA to 200pA, and the irradiation duration is not less than 15 seconds.

[0039] S4. Cut the sample to form a thin slice sample containing grain boundaries according to the location of the contrast. Cutting can be done by either nano-hand cutting or focused ion beam cutting. Since the sample is an alloy material, the cutting process will cause heat to rise, and the sample needs to be cooled during the cutting process.

[0040] S5. Cut the thin slice sample in a circular manner to form a needle tip sample including the grain boundary.

[0041] Before circular cutting, the thin slice sample needs to be transferred and welded to the sample preparation stage. Welding can be done by focused ion beam induced chemical vapor deposition, depositing Pt at the contact position between the needle tip sample and the stage, and welding the sample and the tip of the stage together. Figure 3 As shown, circular cutting can be completed using a focused ion beam, and the sample after circular cutting can be seen in Figure 4 .

[0042] In addition, the present invention also proposes a three-dimensional atom probe sample, which is made by the above-mentioned preparation method. The sample has a grain boundary which is irradiated by an ion beam during the preparation process to produce a light-dark contrast, and finally forms a needle tip containing the grain boundary.

[0043] In summary, by using focused ion beam irradiation to corrode the cross section of the alloy sample, the grain boundary can be accurately positioned and imaged. By eliminating the interference of the alloy phase interface on the grain boundary identification and positioning, the complexity and difficulty of the operation are reduced, and the work efficiency is improved. Finally, this method can quickly and effectively locate the grain boundary and prepare samples, greatly improving the success rate of positioning and sample preparation, and providing important technical support for the characterization of alloy microstructures. This method is particularly suitable for preparing needle tip samples for three-dimensional atomic probe testing.

[0044] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A method for preparing a three-dimensional atom probe sample, characterized in that: The following steps are involved: S1. The sample is imaged under a scanning electron microscope and the area of ​​interest is marked on the sample surface; S2, cutting the area to expose a cross section of the sample; S3, irradiating the cross section with an ion beam so as to produce a light-dark contrast on both sides of the grain boundary in the cross section that is conducive to observation; S4, cutting the sample into a thin slice sample including a grain boundary according to the position of the contrast; S5. Cut the thin slice sample in a circular manner to form a needle tip sample including the grain boundary.

2. The method for preparing a three-dimensional atom probe sample according to claim 1, wherein: The beam current of the ion beam irradiation in step S3 is 100 pA to 200 pA, and the irradiation duration is not less than 15 seconds.

3. The method for preparing a three-dimensional atom probe sample according to claim 1, characterized in that: The sample is a metal alloy.

4. The method for preparing a three-dimensional atom probe sample according to claim 3, characterized in that: Also included is the step of cooling the sample while cutting the sample.

5. The method for preparing a three-dimensional atom probe sample according to claim 1, characterized in that: In step S1, focused ion beam induced chemical vapor deposition is used to deposit metal in the region of interest to mark the sample surface.

6. The method for preparing a three-dimensional atom probe sample according to claim 1, wherein: Before step S5, the process also includes transferring and welding the thin slice sample to the sample preparation stage.

7. The method for preparing a three-dimensional atom probe sample according to claim 1, characterized in that: In step S2 and step S4, the cutting method includes: any one of nano-hand cutting and focused ion beam cutting.

8. The method for preparing a three-dimensional atom probe sample according to claim 1, wherein: In step S5, a focused ion beam is used to perform annular cutting.

9. A three-dimensional atom probe sample, characterized in that: The method is as described in any one of claims 1 to 7.

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