Transmission electron microscope sample preparation method of two-dimensional heterostructure material

Abstract

The invention discloses a transmission electron microscope sample preparation method of a two-dimensional heterostructure material, which can realize accurate transfer of the two-dimensional heterostructure material to a transmission electron microscope grid, greatly improve the success rate of transmission electron microscope sample preparation, and facilitate rapid finding of the target two-dimensional heterostructure material in a transmission electron microscope test process. And the test efficiency of the transmission electron microscope is greatly improved. The preparation method comprises the following steps: (1) preparing a two-dimensional heterostructure material; (2) preparing a polymer solution; (3) spin-coating a polymer film; (4) picking up the two-dimensional heterostructure material; and (5) transferring the two-dimensional heterostructure material to a transmission electron microscope grid.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of two-dimensional heterostructure materials and transmission electron microscopy characterization, and in particular to a transmission electron microscopy sample preparation method for two-dimensional heterostructure materials, which can accurately transfer micrometer-scale two-dimensional heterostructure materials to a transmission electron microscope grid. Background Art

[0002] Two-dimensional van der Waals heterostructures (hereinafter referred to as two-dimensional heterostructures) are heterostructure materials formed by stacking different two-dimensional materials in a vertical direction through interlayer van der Waals forces. Compared with heterostructure materials prepared by physical or chemical deposition methods, two-dimensional heterostructures are not restricted by lattice mismatch and can freely stack and combine various types of two-dimensional materials, thereby greatly enriching the types and diversity of heterostructure materials. Two-dimensional heterostructures provide an ideal material platform for exploring rich and diverse physical effects and novel physical phenomena. In addition, the structure usually has a unique electronic structure and spin transport properties, which makes it show great application potential in the fields of spin electronics devices, optoelectronics devices, thermoelectric materials, energy storage and conversion, biomedicine and quantum computing.

[0003] Transmission electron microscopy (TEM), also known as transmission electron microscopy, has important applications and significant advantages in the study of the physical properties of two-dimensional heterostructure materials. TEM can provide imaging with extremely high spatial resolution, directly observe the microscopic features of the atomic arrangement, interlayer stacking mode, interlayer angle, interface structure and defects of two-dimensional heterostructure materials, and provide key experimental data for the study of material properties. TEM can also be combined with a variety of analytical techniques, such as selected area electron diffraction (SAED), electron energy loss spectroscopy (EELS), etc., to conduct a comprehensive analysis of the crystal structure, electronic state density, chemical composition, etc. of two-dimensional heterostructure materials. Among them, the Lorentz transmission electron microscope (L-TEM) can observe the nanoscale magnetic domain structure in magnetic materials, including the morphology, distribution and dynamic changes of the magnetic domain, and obtain high-resolution images of the magnetic domain structure. Therefore, L-TEM is a powerful tool for observing topological magnetic domain structures such as skyrmions, anti-skyrmions, diskyrmions, melamines, magnetic bubbles, and vortices in topological magnetic materials.

[0004] When using a transmission electron microscope to study two-dimensional heterostructure materials, preparing high-quality transmission electron microscope samples is a crucial step. The lateral dimensions of two-dimensional heterostructure materials are generally in the micrometer or even nanometer range, the thickness is generally in the nanometer range, and there are some two-dimensional thin film materials around them, which increases the difficulty of accurately transferring two-dimensional heterostructure materials to the transmission electron microscope grid. At present, there are few transmission electron microscope sample preparation methods for two-dimensional heterostructure materials, and there are problems such as low success rate and easy contamination. Traditional wet transfer also uses corrosive liquids such as hydrofluoric acid, which is harmful to the environment or human body. Summary of the invention

[0005] In order to overcome the defects of the prior art, the technical problem to be solved by the present invention is to provide a transmission electron microscopy sample preparation method for two-dimensional heterostructure materials, which can achieve accurate transfer of two-dimensional heterostructure materials to the transmission electron microscope grid and greatly improve the success rate of transmission electron microscope sample preparation. It is also convenient to quickly find the target two-dimensional heterostructure material during the transmission electron microscope test, thereby improving the efficiency of electron microscope testing.

[0006] The technical solution of the present invention is: a transmission electron microscopy sample preparation method for two-dimensional heterogeneous structure materials, which comprises the following steps:

[0007] (1) Preparation of two-dimensional heterostructure materials: Different types of two-dimensional thin film materials are prepared by a tape-assisted mechanical exfoliation method. A dry transfer technique based on polydimethylsiloxane / polycarbonate or polydimethylsiloxane / polypropylene carbonate is used to sequentially pick up multiple different two-dimensional thin film materials and stack them vertically to obtain a two-dimensional heterostructure material, and then transfer it to a clean silicon wafer. Subsequently, the silicon wafer containing the two-dimensional heterostructure material is placed in a chloroform solution to clean the polycarbonate film or polypropylene carbonate film on the surface.

[0008] (2) Preparation of polymer solution: Mix the polymer powder and deionized water in a mass ratio of 1:6, and heat and stir until the polymer solution is evenly mixed. The mass ratio of the polymer material powder and deionized water will affect the thickness and viscosity of the spin-coated polymer film.

[0009] (3) Spin coating polymer film: Place the silicon wafer containing the two-dimensional heterostructure material on the turntable of the coating machine, add the polymer solution, set the appropriate spin coating speed, and spin coat a uniform polymer film on the surface of the silicon wafer. The thickness of the polyvinyl alcohol film is mainly related to the high spin speed and the spin coating time. The lower the high spin speed and the shorter the spin coating time, the thicker the polyvinyl alcohol film.

[0010] (4) Picking up the two-dimensional heterostructure material: Immediately remove the silicon wafer with the polymer film spin-coated from the coating machine, and use tweezers to gently peel off the polymer film from the silicon wafer. At this time, the two-dimensional heterostructure material is detached from the surface of the silicon wafer and adheres to the polymer film. The interval between taking it out from the coating machine and peeling off the polyvinyl alcohol film should not be too long to avoid excessive evaporation of water and the polyvinyl alcohol film being too dry, which is not conducive to complete peeling.

[0011] (5) Transferring the two-dimensional heterostructure material to the transmission electron microscope grid: Use tweezers to spread the polymer film with the two-dimensional heterostructure material on the transmission electron microscope grid and fix the polymer film. Then, add a drop of dissolving solution to dissolve the polymer film. Finally, dry the transmission electron microscope grid and store the prepared two-dimensional heterostructure material transmission electron microscope sample in a sample box.

[0012] The present invention can realize the accurate transfer of two-dimensional heterostructure materials to the transmission electron microscope grid, and greatly improves the success rate of transmission electron microscope sample preparation. In addition, the surface of the transmission electron microscope grid loaded with two-dimensional heterostructure materials is relatively clean, with less impurity materials, so it is convenient to quickly find the target two-dimensional heterostructure materials during the transmission electron microscope test process, greatly improving the transmission electron microscope test efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The present invention is a flow chart of a method for preparing samples for transmission electron microscopy of a two-dimensional heterostructure material.

[0014] Figure 2 The process of transferring two-dimensional heterostructure materials to transmission electron microscope grids.

[0015] Figure 3 Optical microscopy image of hexagonal boron nitride film.

[0016] Figure 4 Optical microscopy image of graphene film.

[0017] Figure 5 Optical microscopy image of hexagonal boron nitride / graphene heterostructure material.

[0018] Figure 6 Optical microscopic image of hexagonal boron nitride / graphene heterostructure material transferred onto a transmission electron microscope grid.

[0019] Figure 7 Transmission electron microscope image of hexagonal boron nitride / graphene heterostructure material.

[0020] Figure 8 This is the electron diffraction pattern of the hexagonal boron nitride area.

[0021] Fig. 9 This is the electron diffraction pattern of the hexagonal boron nitride / graphene heterostructure region. DETAILED DESCRIPTION

[0022] At present, there are relatively few methods for preparing samples for transmission electron microscopy of two-dimensional heterostructure materials. The transmission electron microscopy sample preparation method based on traditional wet transfer has problems such as difficulty in accurately transferring a specific two-dimensional heterostructure material, low success rate, and easy contamination of the interface of the heterostructure. In addition, corrosive liquids such as hydrofluoric acid used in the transfer process are harmful to the environment or human body.

[0023] The electron microscope sample preparation method of the present invention uses a polymer as a transfer medium to accurately transfer a specific two-dimensional heterostructure material at a micrometer scale to a transmission electron microscope grid. In the process of transferring the two-dimensional heterostructure material to the transmission electron microscope grid, the polyvinyl alcohol used is a non-toxic and water-soluble polymer that dissolves quickly in water, and the film can be dissolved cleanly by dropping deionized water. Therefore, the present invention uses a polyvinyl alcohol film to assist in the transfer of the two-dimensional heterostructure material, which not only has a high success rate and high safety, but also the interface and surface of the two-dimensional heterostructure are not easily contaminated.

[0024] like Figure 1 , Figure 2 As shown, the transmission electron microscope sample preparation method of the two-dimensional heterostructure material comprises the following steps:

[0025] (1) Preparation of two-dimensional heterostructure materials: Different types of two-dimensional thin film materials are prepared by a tape-assisted mechanical exfoliation method. A dry transfer technique based on polydimethylsiloxane / polycarbonate or polydimethylsiloxane / polypropylene carbonate is used to sequentially pick up multiple different two-dimensional thin film materials and stack them vertically to obtain a two-dimensional heterostructure material, and then transfer it to a clean silicon wafer. Subsequently, the silicon wafer containing the two-dimensional heterostructure material is placed in a chloroform solution to clean the polycarbonate film or polypropylene carbonate film on the surface.

[0026] (2) Preparation of polymer solution: Mix the polymer material powder and deionized water in a mass ratio of 1:

[0027] 6. Mix, heat and stir until the polymer solution is evenly mixed;

[0028] (3) Spin coating a polymer film: Place the silicon wafer containing the two-dimensional heterostructure material on the turntable of a coating machine, drop the polymer solution, set a suitable spin coating rate, and spin coat a uniform polymer film on the surface of the silicon wafer;

[0029] (4) Picking up the two-dimensional heterostructure material: Immediately remove the silicon wafer with the polymer film spin-coated from the coating machine, and gently peel the polymer film off the silicon wafer with tweezers. At this time, the two-dimensional heterostructure material detaches from the surface of the silicon wafer and adheres to the polymer film;

[0030] (5) Transferring the two-dimensional heterostructure material to the transmission electron microscope grid: Use tweezers to spread the polymer film with the two-dimensional heterostructure material on the transmission electron microscope grid and fix the polymer film. Then, add a dissolving solution to dissolve the polymer film. Dry the transmission electron microscope grid. Finally, store the prepared two-dimensional heterostructure material transmission electron microscope sample in a sample box (e.g., Figure 6 shown).

[0031] The present invention can realize the accurate transfer of two-dimensional heterostructure materials to the transmission electron microscope grid, and greatly improves the success rate of transmission electron microscope sample preparation. In addition, the surface of the transmission electron microscope grid loaded with two-dimensional heterostructure materials is relatively clean, with less impurity materials, so it is convenient to quickly find the target two-dimensional heterostructure materials during the transmission electron microscope test process, greatly improving the transmission electron microscope test efficiency.

[0032] Preferably, in step (1), the two-dimensional heterostructure material is a hexagonal boron nitride / graphene heterostructure material (such as Figure 5 As shown), a tape-assisted mechanical stripping method is used to obtain two-dimensional thin film materials of hexagonal boron nitride and graphene with nanometer thickness on SiO2 / Si substrate, and then two suitable two-dimensional thin film materials are observed and screened out on an optical microscope; on a transfer platform equipped with an optical microscope, a transfer method based on polydimethylsiloxane / polycarbonate or polydimethylsiloxane / polypropylene carbonate is used to stamp and pick up hexagonal boron nitride films (as shown Figure 3 ) and graphene film (as shown Figure 4 As shown), vertically stack the two-dimensional heterostructure materials, and heat release them onto a clean silicon wafer; put the silicon wafer loaded with the hexagonal boron nitride / graphene heterostructure material into a chloroform solution and soak it for 10 minutes to completely dissolve the polycarbonate film or polypropylene carbonate film on the surface of the two-dimensional heterostructure material.

[0033] Preferably, in step (1), a silicon wafer having an oxide layer with a thickness of 285 to 300 nm is used.

[0034] Preferably, in step (2), 4 g of polyvinyl alcohol powder is weighed and mixed with 24 ml of deionized water in a beaker at a mass ratio of 1:6. The beaker is then placed on a magnetic stirring device and heated and stirred for 30 minutes until the polyvinyl alcohol solution is evenly mixed. The mixture is then left to stand for a while until the bubbles disappear.

[0035] Preferably, in the step (3), a silicon wafer loaded with hexagonal boron nitride / graphene heterostructure material is placed on a turntable of a coating machine, 1 to 2 drops of polyvinyl alcohol solution are added to the silicon wafer, and the coating machine is set to spin-coat at a low speed of 1000 r / min for 5 seconds, and then at a high speed of 2200 r / min for 60 seconds. After completion, a polyvinyl alcohol film of a certain thickness is spin-coated on the surface of the silicon wafer.

[0036] Preferably, in step (4), the silicon wafer on which the polyvinyl alcohol film is spin-coated is immediately taken out from the coating machine, and the polyvinyl alcohol film is gently peeled off from the silicon wafer with tweezers, at which time the hexagonal boron nitride / graphene heterostructure material is separated from the surface of the silicon wafer and adhered to the polyvinyl alcohol film. The polyvinyl alcohol film is used as a transfer medium to pick up the hexagonal boron nitride / graphene heterostructure material from the silicon wafer.

[0037] Preferably, in step (5), the polyvinyl alcohol film with hexagonal boron nitride / graphene heterostructure material adhered thereto is spread on a transmission electron microscope grid with tweezers, and the polyvinyl alcohol film is fixed, and then deionized water is added to dissolve the polyvinyl alcohol film. An optical microscope is used to observe whether the polyvinyl alcohol film is completely dissolved. If there is residue on the transmission electron microscope grid, deionized water is repeatedly added until the transmission electron microscope grid and the surface of the two-dimensional heterostructure material are clean. The transmission electron microscope grid loaded with hexagonal boron nitride / graphene heterostructure material is dried and finally stored in a sample box.

[0038] Figure 7 Transmission electron microscope image of hexagonal boron nitride / graphene heterostructure material. Figure 8 This is the electron diffraction pattern of the hexagonal boron nitride area. Fig. 9 This is the electron diffraction pattern of the hexagonal boron nitride / graphene heterostructure region.

[0039] Preferably, in step (2), the polymer solution may also be a polycarbonate solution, and 1.2333 g of polycarbonate particles are mixed with 20 ml of chloroform solution, heated and stirred until the solution is completely mixed to prepare a polycarbonate solution with a mass fraction of 4%.

[0040] Preferably, in step (5), the dissolving liquid can be replaced with NN dimethylformamide, which dissolves the polycarbonate film.

[0041] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing samples of two-dimensional heterostructure materials under transmission electron microscopy, characterized in that: It includes the following steps: (1) Preparation of two-dimensional heterostructure materials: Different types of two-dimensional thin film materials were prepared by tape-assisted mechanical exfoliation, using dry transfer technology based on polydimethylsiloxane / polycarbonate or polydimethylsiloxane / polypropylene carbonate. Pick up multiple different two-dimensional thin film materials in sequence and stack them vertically to obtain a two-dimensional heterostructure material, and transfer it to a clean silicon wafer. Then, put the silicon wafer containing the two-dimensional heterostructure material into a chloroform solution to clean the polycarbonate film or polypropylene carbonate film on the surface. (2) Preparation of polymer solution: Mix the polymer material powder and deionized water in a mass ratio of 1: 6 Mix, heat and stir until the solution is evenly mixed; (3) Spin coating a polymer film: Place the silicon wafer containing the two-dimensional heterostructure material on the turntable of a coating machine, drop the polymer solution, set a suitable spin coating rate, and spin coat a uniform polymer film on the surface of the silicon wafer; (4) Picking up the two-dimensional heterostructure material: Immediately remove the silicon wafer with the polymer film spin-coated from the coating machine, and gently peel the polymer film off the silicon wafer with tweezers. At this time, the two-dimensional heterostructure material detaches from the surface of the silicon wafer and adheres to the polymer film; (5) Transferring the two-dimensional heterostructure material to the transmission electron microscope grid: Use tweezers to spread the polymer film with the two-dimensional heterostructure material on the transmission electron microscope grid and fix the polymer film. Then, add a drop of dissolving solution to dissolve the polymer film. Dry the transmission electron microscope grid loaded with the two-dimensional heterostructure material. Finally, store the transmission electron microscope sample of the two-dimensional heterostructure material in a sample box.

2. The transmission electron microscopy sample preparation method of the two-dimensional heterostructure material according to claim 1, characterized in that: In the step (1), the two-dimensional heterostructure material is a hexagonal boron nitride / graphene heterostructure material, which is vertically stacked by dry transfer technology and finally transferred to a clean silicon wafer.

3. The transmission electron microscopy sample preparation method of the two-dimensional heterostructure material according to claim 2, characterized in that: In the step (1), a silicon wafer having an oxide layer with a thickness of 285 to 300 nm is used.

4. The method for preparing samples for transmission electron microscopy of a two-dimensional heterostructure material according to claim 1, characterized in that: In the step (2), the polymer is polyvinyl alcohol. 4 g of polyvinyl alcohol powder is weighed and mixed with 24 ml of deionized water in a beaker at a mass ratio of 1:

6. The beaker is then placed on a magnetic stirring device and heated and stirred for 30 minutes until the polyvinyl alcohol solution is evenly mixed. The mixture is then left to stand for a while until the bubbles disappear.

5. The method for preparing samples for transmission electron microscopy of a two-dimensional heterostructure material according to claim 1, characterized in that: In the step (3), a silicon wafer loaded with hexagonal boron nitride / graphene heterostructure material is placed on a turntable of a coating machine, 1 to 2 drops of polyvinyl alcohol solution are added to the silicon wafer, and the coating machine is set to first spin-coat at a low speed of 1000 r / min to 1500 r / min for 5 seconds, and then spin-coat at a high speed of 2000-3000 r / min for 60 seconds. After completion, a polyvinyl alcohol film is spin-coated on the surface of the silicon wafer.

6. The method for preparing samples for transmission electron microscopy of a two-dimensional heterostructure material according to claim 1, characterized in that: In the step (4), the polyvinyl alcohol film is used as a transfer medium to pick up the hexagonal boron nitride / graphene heterostructure material.

7. The method for preparing samples for transmission electron microscopy of a two-dimensional heterostructure material according to claim 1, characterized in that: In the step (5), the dissolving liquid is deionized water, and an optical microscope is used to observe whether the polyvinyl alcohol film is completely dissolved. If there is residue on the transmission electron microscope grid, deionized water is repeatedly added until the surface of the transmission electron microscope grid and the hexagonal boron nitride / graphene heterostructure material is clean.

8. The method for preparing samples for transmission electron microscopy of a two-dimensional heterostructure material according to claim 1, characterized in that: In the step (2), the polymer solution is a polycarbonate solution, and 1.2333 g of polycarbonate particles are mixed with 20 ml of chloroform solution, heated and stirred until the solution is completely mixed to prepare a polycarbonate solution with a mass fraction of 4%.

9. The method for preparing samples for transmission electron microscopy of a two-dimensional heterostructure material according to claim 8, characterized in that: In the step (5), the dissolving liquid is NN dimethylformamide, which dissolves the polycarbonate film.

Images