Preparation method of two-dimensional material sample suitable for transmission electron microscope
By combining a three-dimensional moving platform and an optical microscope, and utilizing a vacuum suction pen and plasma-treated TEM grid, the precise and controllable transfer of two-dimensional materials to the TEM grid was achieved. This solved the problems of easy breakage and difficult transfer of two-dimensional materials on the TEM grid, and provided high-quality TEM samples.
Patent Information
- Application Number
- CN202511590464.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-03
- Publication Date
- 2026-03-13
AI Technical Summary
This study demonstrates how to precisely and controllably transfer specific regions of micron-scale two-dimensional materials onto a transmission electron microscope (TEM) grid that is prone to breakage and has extremely small viewing windows, thus solving the problems of easy breakage and difficult transfer of two-dimensional materials during the preparation process.
A method combining a three-dimensional moving platform with real-time observation using an optical microscope was adopted. A plasma-treated TEM grid was picked up by a vacuum suction pen, and two-dimensional materials were precisely transferred onto the TEM grid using van der Waals forces. The contact status was judged by the light transmittance of the grid, thus avoiding damage to the grid and the sample.
This technology enables precise and controllable transfer of two-dimensional materials, improves the transfer success rate, reduces the risk of damage caused by blind spots in operation, and provides high-quality TEM samples, laying the foundation for subsequent electron microscopy research.
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Figure CN121656302A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of two-dimensional material characterization technology, specifically relating to a method for preparing two-dimensional material samples suitable for transmission electron microscopy. Background Technology
[0002] Two-dimensional materials, due to their atomic-level thickness, possess unique phonon and electronic structures. In recent years, especially through the manipulation of interlayer rotation angles in two-dimensional materials, novel physical behaviors have emerged, such as moiré ferroelectricity, moiré phonons, and twisted electronics. These exhibit enormous potential in highly integrated microelectronic devices, potentially replacing traditional silicon-based transistors and further pushing the limits of Moore's Law. While the performance of two-dimensional materials is typically characterized using optical microscopy, atomic force microscopy, and Raman spectroscopy, detailed characterization of electromagnetics, thermals, and mechanics at the sub-micrometer scale, such as interface analysis and corner supercells, often requires transmission electron microscopy (TEM) for precise characterization. Examples include scanning transmission electron microscopy (STEM-EELS) for phonon detection and ptychography for extracting the average thermal vibration amplitude of atoms. Due to the limited penetrating power of electron beams, TEM samples are typically required to be less than 100 nm thick, and techniques such as... Figure 1 (a) The copper mesh shown Figure 1 (b) shows the in-situ chip and other loaded samples, which were characterized by electron microscopy. The support frame of the viewing window in these grids is about 1 μm thick, which is very easy to break during sample preparation. The viewing window of the in-situ chip is only about 50 μm. In addition, the two-dimensional materials are easy to curl and break, which further increases the difficulty of sample transfer.
[0003] Currently, common methods for transferring two-dimensional materials are mainly divided into wet transfer, dry transfer, and transfer in an inert gas environment, such as PMMA wet transfer, PLLA rapid transfer, PVA adsorption transfer, chemical etching transfer, PDMS exfoliation transfer, and vdWs interaction transfer. These methods are generally suitable for transferring two-dimensional materials to relatively rigid substrates, such as silicon wafers. Furthermore, when introducing rotation control and heterojunction interfaces, the prepared two-dimensional materials are typically small (~10 μm). Therefore, transferring two-dimensional materials with specific structures to specific TEM viewing windows is a problem that urgently needs to be solved. Summary of the Invention
[0004] [Technical Issues] The technical problem to be solved by this invention is how to accurately and controllably transfer a specific region of a two-dimensional material at the micrometer scale onto a transmission electron microscope (TEM) grid that is fragile and has a very small viewing window.
[0005] [Technical Solution] To address the above problems, this invention provides a method for preparing two-dimensional material samples suitable for transmission electron microscopy.
[0006] The present invention discloses a method for preparing two-dimensional material samples suitable for transmission electron microscopy, comprising the following steps: Step 1: Place the two-dimensional material sample to be transferred on the stage of the optical microscope; Step 2: Use a vacuum suction pen to pick up the back edge of the plasma-treated TEM mesh, so that the front side of the TEM mesh is facing down and suspended in the air; Step 3: Control the vacuum pen and the TEM grid it has picked up using a three-dimensional moving platform, and move them above the target area of the two-dimensional material within the field of view of the optical microscope; Step 4: Adjust the height of the three-dimensional moving platform and use the optical microscope imaging focus state to determine whether the TEM grid is in contact with the two-dimensional material sample; Step 5: The target region of the two-dimensional material is transferred to the TEM grid through van der Waals adsorption.
[0007] Optionally, the TEM mesh includes an in-situ chip and a copper mesh, and the diameter of the viewing window of the TEM mesh is no greater than 50 μm.
[0008] Optionally, the TEM grid is transparent, and its relative position and contact with the two-dimensional material can be observed under the focusing state of an optical microscope; the method to determine whether the TEM grid is in contact with the two-dimensional material sample is to observe whether the image of the edge of the TEM grid in the optical microscope changes from blurry to clear.
[0009] Optionally, the two-dimensional material includes graphene, transition metal chalcogenides, or two-dimensional heterojunction structures composed of them.
[0010] Optionally, before step 5, an isopropanol solution is dropped between the TEM grid and the two-dimensional material to wet the surface of the TEM grid to remove air. After drying, the adsorption and transfer are completed using van der Waals forces.
[0011] Optionally, the two-dimensional material sample to be transferred is prepared on a polymer support layer on a silicon wafer substrate; the polymer support layer is a polymethyl methacrylate (PMMA) and methyl methacrylate (MMA) layer; the solvent is acetone vapor.
[0012] Optionally, after completing step 5, the TEM mesh with the two-dimensional material is placed in a solvent vapor environment to remove the polymer support layer.
[0013] Optionally, the two-dimensional material sample is prepared by mechanical exfoliation using a blue film or PDMS.
[0014] Optionally, after step 5, a verification step is also included: placing the TEM grid under a transmission electron microscope and observing its morphology or obtaining its selected area electron diffraction pattern to confirm that the two-dimensional material has been successfully transferred into the viewing window of the TEM grid.
[0015] [Beneficial Effects] 1. Precise and controllable transfer process: Steps 3 and 4 of this invention utilize the movement precision of the three-dimensional moving platform, combined with real-time observation by an optical microscope, to precisely move the TEM grid directly above the target area of the two-dimensional material. By observing the focusing state of the grid edge in the optical microscope (from blurry to clear), the contact point can be accurately determined, thus achieving precise control of the transfer position and solving the problem that traditional methods are difficult to target specific micro-areas.
[0016] 2. Intuitive operation and high success rate: Step 4 of this invention utilizes the light transmission characteristics of the TEM grid to directly observe changes in the focusing state through an optical microscope to determine the contact status. This method is intuitive and reliable, greatly reducing the risk of grid damage or sample transfer failure due to blind spots in the operation.
[0017] 3. Pretreatment enhances adsorption effect: Step 2 of the present invention effectively improves the surface activity of the TEM grid by plasma treatment, significantly enhances the van der Waals adsorption effect, ensures that the two-dimensional material can be stably and completely adsorbed onto the grid, and improves the transfer success rate and sample quality.
[0018] 4. Achieves non-destructive operation on fragile carriers: Step 2 of this invention uses a vacuum suction pen to pick up the back edge of the carrier, which not only firmly grips the carrier but also completely avoids obstruction, contamination, or mechanical damage to its small front viewing window. It is particularly suitable for processing fragile precision carriers such as in-situ chips with a window diameter of only 50μm.
[0019] 5. Wide applicability and conducive to cutting-edge research: This method can efficiently and cleanly prepare high-quality TEM samples from two-dimensional materials, such as graphene, transition metal chalcogenides, and their heterojunctions and "magic angle" structures, providing a reliable sample basis for subsequent atomic-scale studies of electrical, thermal, mechanical, and magnetic properties using advanced electron microscopy techniques such as STEM-EELS and ptychography. Attached Figure Description
[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0021] Figure 1 This is a schematic diagram of a common electron microscope grid provided by the present invention.
[0022] Figure 2 This is a diagram of the TEM two-dimensional material sample transfer platform provided by the present invention.
[0023] Figure 3 This is a schematic diagram of the in-situ chip two-dimensional sample preparation provided by the present invention.
[0024] Figure 4 This is a schematic diagram illustrating the preparation of the TEM copper mesh sample provided by the present invention.
[0025] Figure 5 This is a schematic diagram of the graphene-encapsulated liquid pool provided by the present invention.
[0026] Figure label: Figure 1 The left side (a) shows a microgrid copper mesh; the right side (b) shows a chip for in-situ heating from a certain company. Detailed Implementation
[0027] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0028] Example 1: This embodiment provides a method for preparing two-dimensional material samples suitable for transmission electron microscopy, including the following steps: Step 1: Place the two-dimensional material sample to be transferred, which is prepared on a polymer support layer on a silicon wafer substrate (the method in this embodiment relies on the surface of this polymer layer and cannot be directly transferred to a bare substrate), on the stage of an optical microscope.
[0029] In this embodiment, the two-dimensional material includes graphene, transition metal chalcogenides, or two-dimensional heterojunction structures composed of them, and the two-dimensional material sample is prepared by mechanical exfoliation using a blue film or PDMS.
[0030] Step 2: Use a vacuum suction pen to pick up the back edge of the plasma-treated TEM screen, so that the front side of the TEM screen is facing down and suspended in the air.
[0031] In this embodiment, the TEM mesh includes an in-situ chip and a copper mesh. The diameter of the viewing window of the TEM mesh is no greater than 50 μm, and the TEM mesh is transparent, so that its relative position and contact with the two-dimensional material can be observed under the focusing state of an optical microscope. The copper mesh is a circle with a diameter of 3 mm, with circular holes of about 30 μm in diameter arranged inside, and a micropore array of 0.25~3 μm is formed by a carbon skeleton.
[0032] This embodiment uses an electric vacuum suction pen with adjustable suction power from 0-12000 Pa via a knob, such as the commercially available Sipot DOUBLE TYPE 12000 suction pen. In this embodiment, the plasma treatment of the TEM mesh aims to clean the mesh surface and improve its hydrophilicity, thereby enhancing the van der Waals adhesion between the two-dimensional material and the mesh, significantly improving the transfer success rate. A preferred plasma treatment process parameter is: using pure argon (Ar) as the process gas, controlling the gas flow rate at 30 sccm (standard milliliters per minute), the treatment power at 10 W, the treatment time at 15 seconds, and maintaining the chamber pressure at 50 Pa during the treatment process. This parameter combination effectively activates the mesh surface while ensuring that the delicate structure of the TEM mesh is not damaged due to excessive energy. Experiments show that using this specific parameter treatment can improve the transfer success rate of two-dimensional materials by more than 50% compared to the case without any plasma treatment.
[0033] Step 3: Control the vacuum suction pen and the TEM grid being sucked up by the three-dimensional moving platform, and move them above the target area of the two-dimensional material within the field of view of the optical microscope.
[0034] In this embodiment, a three-dimensional moving platform with micron-level displacement accuracy is used to precisely move the TEM grid above the target area of the two-dimensional material. This accuracy ensures reliable contact within the optical microscope's field of view by adjusting the height and focus, avoiding positioning errors or sample damage caused by insufficient platform accuracy.
[0035] Step 4: By adjusting the height of the three-dimensional moving platform and using the optical microscope to observe whether the image of the TEM grid edge in the optical microscope changes from blurry to clear, we can determine whether the TEM grid is in contact with the two-dimensional material sample.
[0036] Step 5: Isopropanol solution is dropped between the TEM grid and the two-dimensional material to wet the surface of the TEM grid and remove air. After drying, the target area of the two-dimensional material is transferred to the TEM grid through van der Waals adsorption. The TEM grid with the two-dimensional material is then placed in a solvent vapor environment to remove the polymer support layer. The polymer support layer consists of polymethyl methacrylate (PMMA) and methyl methacrylate (MMA) layers, and the solvent is acetone vapor.
[0037] In this embodiment, the acetone vapor treatment conditions are as follows: the volume ratio of acetone vapor to air is approximately 1:1, and the treatment time is approximately 2 hours. Under these optimized conditions, it is ensured that the methyl methacrylate (MMA) and polymethyl methacrylate (PMMA) support layers are fully and thoroughly decomposed and removed, avoiding organic residues caused by insufficient treatment time, thereby guaranteeing the cleanliness and stability of the transferred two-dimensional material. Under these conditions, the structure and properties of the two-dimensional material itself are not affected.
[0038] Due to the contrast limitations of two-dimensional materials and their supporting meshes under optical microscopes, it is difficult to definitively determine whether the two-dimensional material has been accurately and completely transferred to the viewing window of the TEM mesh using only optical microscopes. Therefore, it is necessary to place the prepared sample under a transmission electron microscope (TEM) to verify whether the transfer was successful: by observing the morphology and structure of the material through the high-resolution imaging mode of the TEM, or by obtaining the selected area electron diffraction (SAED) pattern of the sample and analyzing its crystal structure, it is possible to clearly and reliably verify that the target region of the two-dimensional material has been successfully transferred to the predetermined position.
[0039] Platforms used for transferring two-dimensional materials, such as Figure 2 As shown.
[0040] Example 2 See Figure 3 In this embodiment, a single-layer structure of graphene was separated from high-purity directionally grown graphite using a blue film (polymer adhesive) through mechanical exfoliation. This structure was then attached to a Si / SiO2 surface spin-coated with PMMA and MMA. The surface was heated to 80°C and held for 2 minutes. After cooling, the blue film was peeled off to obtain a Si / SiO2 / PMMA / MMA / Graphene multilayer structure. Raman spectroscopy characterization revealed obvious G peaks and 2D peaks.
[0041] A three-dimensional moving platform was used under an optical microscope to move the visible window of the plasma-treated in-situ chip above the graphene, and the height was determined by focusing to ensure a tight fit between the two. Finally, the Si / SiO2 / PMMA / MMA / Graphene / in-situ chip multilayer structure was moved to acetone vapor to decompose MMA and PMMA, thus transferring a specific area to the visible area of the in-situ chip.
[0042] Example 3 See Figure 4 In this embodiment, a copper mesh with plasma treatment and facing down is placed on a substrate loaded with two-dimensional material over a large area using an optical microscope. Isopropanol is added to remove the air between the two-dimensional material and the copper mesh. After drying, the two-dimensional material on the substrate is transferred to the copper mesh through van der Waals adsorption.
[0043] Example 4 See Figure 5 In this embodiment, graphene is prepared by chemical vapor deposition (CVD) and then transferred onto a copper grid using a conventional wet transfer method with the aid of PMMA. Following this method, a copper grid loaded with graphene is obtained. Droplets containing the target sample are aspirated through a capillary with an inner diameter of 0.5 μm. Using a three-dimensional moving platform and an optical microscope, the droplets are then dropped onto the graphene-loaded copper grid. Figure 5 As shown. A vacuum pen can then be used to pick up the back of another copper mesh and place it above the droplet. Through van der Waals adsorption, the droplet is encapsulated between the two layers of graphene, forming a liquid pool. This invention can provide a liquid phase environment for the sample to be tested. Compared with traditional commercial liquid chromatography chips, sample preparation is simpler, and the use of graphene encapsulation can significantly improve resolution.
[0044] The method provided by this invention combines a three-dimensional moving platform with real-time optical microscopy to achieve accurate alignment of the TEM grid with the target area of the two-dimensional material. Utilizing the light transmission characteristics of the grid, contact is intuitively judged by the "edge becoming clearer from blurry," significantly improving the success rate and avoiding blind spots in operation. The vacuum suction pen only clamps the back edge of the grid, ensuring no obstruction, contamination, or contact with the vulnerable window ≤50 μm on the front side throughout the process, guaranteeing non-destructive operation. It can be widely applied to the preparation of high-quality TEM samples such as graphene, transition metal chalcogenides and their heterojunctions, and "magic angle" structures, providing a reliable sample basis for subsequent atomic-scale electrical, thermal, mechanical, and magnetic studies such as STEM-EELS and ptychography.
[0045] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.
Claims
1. A method for preparing two-dimensional material samples suitable for transmission electron microscopy, characterized in that, Includes the following steps: Step 1: Place the two-dimensional material sample to be transferred on the stage of the optical microscope; Step 2: Use a vacuum suction pen to pick up the back edge of the plasma-treated TEM mesh, so that the front side of the TEM mesh is facing down and suspended in the air; Step 3: Control the vacuum pen and the TEM grid it has picked up using a three-dimensional moving platform, and move them above the target area of the two-dimensional material within the field of view of the optical microscope; Step 4: Adjust the height of the three-dimensional moving platform and use the optical microscope imaging focus state to determine whether the TEM grid is in contact with the two-dimensional material sample; Step 5: The target region of the two-dimensional material is transferred to the TEM grid through van der Waals adsorption.
2. The method as described in claim 1, characterized in that, The TEM mesh includes an in-situ chip and a copper mesh, and the diameter of the visible window of the TEM mesh is no greater than 50 μm.
3. The method as described in claim 1, characterized in that, The TEM grid is transparent, and its relative position and contact with the two-dimensional material can be observed under the focusing state of an optical microscope. The method to determine whether the TEM grid is in contact with the two-dimensional material sample is to observe whether the image of the edge of the TEM grid in the optical microscope changes from blurry to clear.
4. The method as described in claim 1, characterized in that, The two-dimensional material includes graphene, transition metal chalcogenides, or two-dimensional heterojunction structures composed of them.
5. The method as described in claim 1, characterized in that, Before step 5, an isopropanol solution is dropped between the TEM grid and the two-dimensional material to wet the surface of the TEM grid to remove air. After drying, the adsorption and transfer are completed using van der Waals forces.
6. The method as described in claim 1, characterized in that, The two-dimensional material sample to be transferred is prepared on a polymer support layer on a silicon wafer substrate; the polymer support layer is a polymethyl methacrylate (PMMA) and methyl methacrylate (MMA) layer; the solvent is acetone vapor.
7. The method as described in claim 6, characterized in that, After completing step 5, the TEM mesh with the two-dimensional material is placed in a solvent vapor environment to remove the polymer support layer.
8. The method as described in claim 6, characterized in that, The two-dimensional material sample was prepared by mechanical exfoliation using a blue film or PDMS.
9. The method as described in claim 1, characterized in that, Following step 5, a verification step is also included: placing the TEM grid under a transmission electron microscope and observing its morphology or obtaining its selected area electron diffraction pattern to confirm that the two-dimensional material has been successfully transferred into the viewing window of the TEM grid.