A sample preparation method for in-situ tensile experiment in transmission electron microscopy

Abstract

The invention relates to the technical field of in-situ nanomechanics testing, and discloses a sample preparation method for an in-situ tensile experiment of a transmission electron microscope, comprising the following steps: S1: setting the size of an in-situ tensile sample; S2: placing a sample raw material and a half-divided grid into a focused ion beam system; S3: etching two mutually parallel rectangular grooves on the raw material using an ion beam, so that a rough blank is formed between the two rectangular grooves; S4: trimming the rough blank using an ion beam; S5: cutting the rough blank from the raw material to obtain a semi-finished product, and transferring the semi-finished product to the surface of the half-divided grid; S6: trimming the semi-finished product using an ion beam. By adjusting the shape trimming step and the beam angle and size of the ion beam during trimming, the prepared sample has no gradient phenomenon in the thickness direction, and the sample contour remains smooth and straight; it can be used for sample preparation of superhard materials that are difficult to process, such as diamond. Samples with a large aspect ratio can be prepared.

Description

Technical Field

[0001] The invention relates to the technical field of in-situ nanomechanics testing, in particular to a sample preparation method for an in-situ tensile experiment of a transmission electron microscope. Background Art

[0002] The microstructure of a material affects its macroscopic mechanical properties. Therefore, researchers focus on observing the morphology and behavior of materials at the microscopic and nanoscopic scales to explore the performance and response of materials at the mesoscopic and macroscopic levels. In order to meet this research need, the Transmission Electron Microscope (TEM) has been widely used. With this powerful scientific research tool, researchers can perform a series of operations such as characterization, testing, and loading of samples at the microscopic and nanoscopic scales, which is of great significance for understanding the mechanism of action of materials under multi-field coupling and guiding the design of new materials. In a series of scientific studies using TEM, elastic strain engineering has received widespread attention. It is achieved by controlling the elastic strain of the material to achieve artificial regulation of its mechanical, electrical, thermal, optical and other properties, and with the recoverable characteristics of elastic strain, this performance regulation meets the characteristics of reversibility and controllability.

[0003] At present, there are three main methods for designing and preparing micro-nanoscale samples to achieve elastic strain loading: (1) The sample and the substrate are made as a whole, and the loading of the sample is achieved by loading the whole substrate. (For example, the sample preparation method in the article published in Nature Photonics, Issue 7, pp. 466-472 in 2013). (2) The sample and the substrate are made separately, connected together by welding or bonding, and the loading of the sample is achieved by loading the whole substrate. (For example, the sample preparation method in the article published in Science Advances, Vol. 2, Issue 8, Document No. 1501382 in 2016). (3) Use a focused ion beam (FIB) to make a dog-bone-shaped sample and a loading head, place the sample on a half-split grid, place the half-split grid on the movable end of the TEM sample rod, place the loading head on the fixed end of the TEM sample rod, and directly load the sample through the loading head. (Such as the sample preparation method in the article published in "Science" Volume 371, Issue 6524, Pages 76-78 in 2021). The above methods 1 and 2 are only applicable to samples with low tensile strength. For method 1, it is difficult to achieve a large loading force on the entire substrate. For method 2, the connection between the sample and the substrate is prone to damage before the sample. The above method 3 can be used for in-situ tensile experiments on superhard materials such as diamond, but this method is limited in the size of samples, especially samples with a large aspect ratio, which limits its further development and application. As shown in the attached figureFigure 7 As shown, when the aspect ratio of the diamond sample prepared by this method is greater than 20, it can be observed that the thickness of the sample shows an obvious gradient phenomenon, and the sample contour cannot maintain a smooth straight line. This is because when processing parallel to the ion beam direction, the beam intensity gradually decreases with the increase of processing distance. In particular, for superhard materials such as diamond, the beam intensity at a long distance cannot continue to meet the processing requirements, so it is impossible to prepare samples of superhard materials with a large aspect ratio. However, for ultra-wide bandgap semiconductors such as diamond, the preparation of large aspect ratio samples is very necessary for their application in large-scale integrated circuit chips, optical interconnect communications and other fields. In response to the above problems, this application is proposed. Summary of the invention

[0004] The purpose of the present invention is to provide a sample preparation method for an in-situ tensile experiment of a transmission electron microscope, so as to overcome the problem in the prior art that the processing quality of superhard material samples with a large aspect ratio is difficult to meet the experimental requirements.

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

[0006] A sample preparation method for an in-situ tensile experiment of a transmission electron microscope of the present invention comprises the following steps:

[0007] S1: Set the size of the in-situ tensile sample;

[0008] S2: Place the sample raw material and the half-grid into the focused ion beam system;

[0009] S3: using an ion beam to etch two parallel rectangular grooves on the raw material, so that a rough blank is formed between the two rectangular grooves;

[0010] S4: shape trimming of the rough blank using ion beam;

[0011] S5: Cut the rough blank and the raw material to obtain the semi-finished product, and transfer the semi-finished product to the surface of the half-divided grid;

[0012] S6: Use an ion beam to trim the shape of the semi-finished product so that the trimmed finished product size meets the sample size designed in step S1.

[0013] Furthermore, in step S2, the micro-electromechanical system is also placed in the focused ion beam system;

[0014] The following steps are also included:

[0015] S7: The finished product is assembled onto a MEMS with a preset groove using a tungsten needle, and can then be further used for in-situ tensile experiments using a transmission electron microscope.

[0016] Furthermore, the in-situ tensile sample designed in step S1 includes a gauge length section, a first clamping section symmetrically arranged at two ends of the gauge length section, and a second clamping section arranged at a side of the first clamping section away from the gauge length section.

[0017] Further, the focused ion system described in step S2 is a dual-beam system, which is equipped with an electron beam for observation and an ion beam for material removal and welding; and / or in step S2, the raw material is fixed on a horizontal sample holder, the half-grid is fixed on a 52° sample holder, the micro-electromechanical system is fixed on a 38° sample holder, and the angle between the electron beam direction and the ion beam direction in the focused ion system is 52°.

[0018] Furthermore, the specific steps of step S5 are:

[0019] S51: hollowing out one end and the bottom of the rough blank obtained in step S4 using an ion beam, carrying a tungsten needle to the other end of the rough blank, and welding the tungsten needle and the rough blank;

[0020] S52: Use ion beam to completely cut off the rough blank from the raw material to obtain a semi-finished product;

[0021] S53: transferring the semi-finished product to the surface of the half-divided grid through a tungsten needle, and welding the bottom of the semi-finished product to the surface of the half-divided grid;

[0022] S54: The connection position between the tungsten needle and the semi-finished product is cut off by an ion beam.

[0023] Furthermore, in the step S51, the welding points between the tungsten needle and the rough blank are evenly spaced along the length direction of the rough blank, and the number of welding points is greater than or equal to 5.

[0024] Furthermore, in step S53, the welding points on the bottom of the semi-finished product and the surface of the half-divided grid are evenly distributed along the length direction of the semi-finished product, and the number of welding points is greater than or equal to 7.

[0025] Furthermore, the specific steps of step S6 are:

[0026] S61: trimming the top of the semi-finished product using an ion beam to obtain a first trimmed piece, so that the first trimmed piece meets the length and width dimensions of the pre-designed sample;

[0027] S62: using an ion beam to shape-trim the front surface of the first trimming piece, cutting out a second trimming piece having the same maximum height as the designed sample size, wherein a portion of the bottom structure of one end of the second trimming piece is retained and connected to the first trimming piece;

[0028] S63: carrying the tungsten needle to the part of the structure that still remains connected, welding the tungsten needle and the second trimming piece, and completely cutting off the bottom of the second trimming piece from the first trimming piece by using an ion beam;

[0029] S64: Use an ion beam to further trim the height of the second trimming piece so that the front side of the second trimming piece meets the pre-designed sample size, thereby obtaining a finished product.

[0030] Furthermore, in the step S4, the beam current of the ion beam used to shape trim the rough blank is gradually reduced.

[0031] Furthermore, the beam current of the ion beam subjected to shape trimming in step S61 and / or step S62 and / or step S64 is gradually reduced during the trimming process.

[0032] Beneficial effects of the present invention:

[0033] 1. By adjusting the shape trimming steps and the beam angle and size of the ion beam during trimming, the prepared sample has no gradient in the thickness direction and the sample contour remains smooth and straight, thus avoiding the problem in the traditional sample processing steps that the sample contour cannot remain smooth and straight because the trimming length is too long when the sample is processed parallel to the ion beam direction and the beam intensity gradually decreases with the increase of the processing distance;

[0034] 2. The present invention can be used for sample preparation of superhard materials such as diamond that are difficult to process.

[0035] 3. The present invention can prepare samples with a large aspect ratio for in-situ tensile testing under a transmission electron microscope, and the aspect ratio can reach 20.

[0036] 4. The samples prepared by the present invention can be used in conjunction with various types of micro-electromechanical systems to meet various in-situ experimental requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0038] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0039] Figure 1 This is the front view of the diamond sample used for the in-situ tensile experiment under transmission electron microscope;

[0040] Figure 2A top view of a diamond sample used for in-situ tensile testing using a transmission electron microscope.

[0041] Figure 3 This is a schematic diagram of the structure after the semi-finished product is lifted by the tungsten needle and welded to the surface of the half-load grid;

[0042] Figure 4 is a top view of a first trimming member located on the surface of a half-divided grid;

[0043] Figure 5 The front view of the finished product being lifted by the tungsten needle;

[0044] Figure 6 A process diagram of assembling the finished product lifted by the tungsten needle into the micro-electromechanical system with a preset groove;

[0045] Figure 7 This is the morphology of the high aspect ratio diamond in-situ tensile sample prepared using the currently common focused ion beam sample preparation method, in the thickness direction under a transmission electron microscope. DETAILED DESCRIPTION

[0046] Combine the following Figure 1-6 The present invention is described in detail.

[0047] The present invention discloses a sample preparation method for an in-situ tensile test of a transmission electron microscope. The preparation method can be used for preparing samples of superhard materials, such as diamond, cubic boron nitride, etc. The preparation of a sample of diamond material is taken as an example, and the method comprises the following steps:

[0048] 1. Design the size of the diamond in-situ tensile sample with a large aspect ratio. The main view of the sample used for the in-situ tensile experiment under a transmission electron microscope is as follows: Figure 1 The top view of the sample used for the in-situ tensile test under transmission electron microscopy is shown in Figure 2 As shown, the sample design dimensions of the present invention are marked on Figure 1 and Figure 2 Reference Figure 1 and Figure 2 The diamond in-situ tensile sample comprises a gauge section (3), a first clamping section (2) symmetrically arranged at both ends of the gauge section, and a second clamping section (1) arranged at a side of the first clamping section away from the gauge section; wherein the length, width and height of the second clamping section are 3 μm, 3 μm and 1 μm respectively, the length, width and height of the first clamping section are 2 μm, 1 μm and 1 μm respectively, and the length, width and height of the gauge section are 20 μm, 1 μm and 0.5 μm respectively.

[0049] 2. Fix the diamond material on the horizontal sample holder, fix the half-grid on the 52° sample holder, fix the MEMS on the 38° sample holder, insert all the sample holders into the sample stage of the dual-beam FIB system equipped with electron beam and ion beam, and push them into the sample chamber of the FIB system together. The angle between the electron beam direction and the ion beam direction in the FIB system is 52°.

[0050] 3. Rotate the sample stage so that the ion beam direction is perpendicular to the horizontal sample holder, and use an ion beam with a beam current of 65nA to remove material from the diamond raw material. The removed shape is two parallel rectangular grooves, so that a thin sheet of rough embryo is produced between the two rectangular grooves.

[0051] 4. Use an ion beam to trim the shape of the rough embryo, and the beam current size gradually decreases from 21nA to 5nA. The final length, width and height of the rough embryo are 50μm, 5μm and 10μm respectively.

[0052] 5. Rotate the sample stage to make the electron beam direction perpendicular to the horizontal sample holder. Use an ion beam with a beam current of 3nA to hollow out one end and the bottom of the rough blank. Insert a tungsten needle. Carry the tungsten needle to the other end of the rough blank. Insert a platinum needle. Use the platinum deposition method to weld the tungsten needle and the rough blank.

[0053] 6. Use an ion beam with a beam current of 3nA to completely cut off the rough blank and the raw material. Finally, the length, width and height of the semi-finished product lifted by the tungsten needle are 35μm, 5μm and 5μm respectively. The semi-finished product is a diamond block. It should be noted that the welding points between the tungsten needle and the semi-finished product should be evenly distributed along the length direction, and the number of welding points should be no less than 5, otherwise the tungsten needle and the semi-finished product cannot be completely fixed after the connection is cut off.

[0054] 7. Rotate the sample stage to make the electron beam direction level with the 52° sample holder, transfer the semi-finished product lifted by the tungsten needle to the surface of the half-grid, and weld the bottom of the semi-finished product to the surface of the half-grid by depositing platinum. The treatment results are as follows: Figure 3 shown.

[0055] 8. Cut off the connection between the tungsten needle and the semi-finished product with an ion beam with a beam current of 3nA, and retract the tungsten needle and the platinum needle. It should be noted that the welding points on the bottom of the semi-finished product and the surface of the half-grid should be evenly distributed along the length direction, and the number of welding points should be no less than 7, otherwise the semi-finished product and the half-grid cannot be completely fixed after the tungsten needle is cut off.

[0056] 9. Rotate the sample stage to make the ion beam direction level with the 52° sample holder, use the ion beam to trim the top of the semi-finished product, and gradually reduce the beam current from 1nA to 80pA to obtain the first trimmed piece. Make the top of the first trimmed piece meet the pre-designed sample size diagram, that is, the length and width of the first clamping section area are 3μm and 3μm respectively, the length and width of the second clamping section area are 2μm and 1μm respectively, and the length and width of the gauge section area are 20μm and 1μm respectively. The trimming results are as shown in the present invention. Figure 4 shown.

[0057] 10. Rotate the sample stage so that the direction of the ion beam is perpendicular to the 52° sample holder, and use the ion beam to shape the front of the first trimming piece. The beam current gradually decreases from 1nA to 80pA, and a second trimming piece with a height of 1μm is cut out, but it cannot be completely cut off. One side clamping section of the second trimming piece is still connected to the bottom first trimming piece.

[0058] 11. Insert the tungsten needle and carry it to the clamping section that is still connected. Insert the platinum needle and weld the tungsten needle and the second trimming piece by depositing platinum. Use an ion beam with a beam current of 3nA to completely cut off the bottom of the second trimming piece from the first trimming piece.

[0059] 12. Use ion beam to further trim the height of the second trimming piece. The beam current is gradually reduced from 1nA to 80pA to obtain a finished product. The front of the finished product meets the pre-designed sample size diagram, that is, the height of the first and second clamping sections is 1μm, and the height of the gauge section is 0.5μm. The trimming results are as follows: Figure 5 shown.

[0060] 13. Rotate the sample stage to make the electron beam direction perpendicular to the 38° sample holder, and use a tungsten needle to assemble the finished product with trimmed dimensions onto the MEMS with the preset groove. The assembly process is as follows: Figure 6 As shown. After the sample is embedded, the connection between the tungsten needle and the finished product is cut off by an ion beam with a beam current of 3nA. The clamping section of the finished product is welded to the groove of the micro-electromechanical system by using a platinum deposition method, the tungsten needle and the platinum needle are retracted, the sample compartment of the FIB system is opened, and the micro-electromechanical system assembled with the finished product is taken out. The sample prepared by the present invention can be further used for in-situ tensile experiments of TEM.

[0061] In the above steps, in addition to the platinum deposition method, carbon deposition can also be used to achieve welding.

[0062] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology in this field to understand the content of the present invention and implement it, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A sample preparation method for in-situ tensile experiment in transmission electron microscopy, Features: The following steps are involved: S1: Set the size of the in-situ tensile sample; S2: placing the sample raw material and the half-grid into the focused ion beam system, the sample raw material is diamond; S3: using an ion beam to etch two parallel rectangular grooves on the raw material, so that a rough blank is formed between the two rectangular grooves; S4: shape trimming of the rough blank using ion beam; S5: Cut the rough blank and the raw material to obtain the semi-finished product, and transfer the semi-finished product to the surface of the half-divided grid; S6: Using an ion beam to shape-trim the semi-finished product so that the trimmed finished product size meets the sample size designed in step S1; In the step S4, the beam current of the ion beam used to shape the rough blank is gradually reduced; The specific steps of step S5 are: S51: hollowing out one end and the bottom of the rough blank obtained in step S4 using an ion beam, carrying a tungsten needle to the other end of the rough blank, and welding the tungsten needle and the rough blank; S52: Use ion beam to completely cut off the rough blank from the raw material to obtain a semi-finished product; S53: transferring the semi-finished product to the surface of the half-divided grid through a tungsten needle, and welding the bottom of the semi-finished product to the surface of the half-divided grid; S54: Cutting off the connection between the tungsten needle and the semi-finished product by using an ion beam; In the step S51, the welding points between the tungsten needle and the rough blank are evenly spaced along the length direction of the rough blank, and the number of welding points is greater than or equal to 5; In step S53, the welding points on the bottom of the semi-finished product and the surface of the half-split grid are evenly distributed along the length direction of the semi-finished product, and the number of welding points is greater than or equal to 7; The specific steps of step S6 are: S61: trimming the top of the semi-finished product using an ion beam to obtain a first trimmed piece, so that the first trimmed piece meets the length and width dimensions of the pre-designed sample; S62: using an ion beam to shape-trim the front surface of the first trimming piece, cutting out a second trimming piece having the same maximum height as the designed sample size, wherein a portion of the bottom structure of one end of the second trimming piece is retained and connected to the first trimming piece; S63: carrying the tungsten needle to the part of the structure that still remains connected, welding the tungsten needle and the second trimming piece, and completely cutting off the bottom of the second trimming piece from the first trimming piece by using an ion beam; S64: Use an ion beam to further trim the height of the second trimming piece so that the front side of the second trimming piece meets the pre-designed sample size to obtain a finished product; the beam current of the ion beam used for shape trimming in step S61 and / or step S62 and / or step S64 is gradually reduced during the trimming process.

2. A sample preparation method for in-situ tensile experiment of a transmission electron microscope according to claim 1, Features: In the step S2, the micro-electromechanical system is also placed in the focused ion beam system; The following steps are also included: S7: The finished product is assembled onto a MEMS with a preset groove using a tungsten needle, and can then be further used for in-situ tensile experiments using a transmission electron microscope.

3. A sample preparation method for in-situ tensile experiment of a transmission electron microscope according to claim 2, Features: The in-situ tensile sample designed in step S1 includes a gauge length section, a first clamping section symmetrically arranged at two ends of the gauge length section, and a second clamping section arranged at a side of the first clamping section away from the gauge length section.

4. A sample preparation method for in-situ tensile experiment of a transmission electron microscope according to claim 3, Features: The focused ion beam system described in step S2 is a dual-beam system, which is equipped with an electron beam for observation and an ion beam for material removal and welding; and / or in step S2, the raw material is fixed on a horizontal sample holder, the half-grid is fixed on a 52° sample holder, the micro-electromechanical system is fixed on a 38° sample holder, and the angle between the electron beam direction and the ion beam direction in the focused ion system is 52°.

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