Clean transfer method of two-dimensional material or two-dimensional heterostructure

Abstract

The invention relates to a clean transfer method of a two-dimensional material or a two-dimensional heterostructure, which comprises the following steps: S1, providing a substrate with an oxide layer on the surface, and growing a target material on the surface of the substrate, the target material comprising the two-dimensional material or the two-dimensional heterostructure; s2, determining the position of a target material by using an optical microscope, aligning the transmission electron microscope metal net with the carbon film to a target material area, and dropwise adding a drop near the metal net to enable the drop to spread to a gap between the carbon film and the target material to prepare a substrate adhered with the metal net; s3, carrying out heating treatment; s4, carrying out annealing treatment; s5, corroding the oxide layer on the surface of the substrate to prepare a metal net attached with a target material; and S6, the metal net attached with the target material is subjected to annealing treatment. The method is simple and effective, the use of polymers is avoided, clean transfer of different types of two-dimensional materials or two-dimensional heterostructures can be realized, and the sample preparation and measurement efficiency of transmission physical property measurement is improved.

Description

Technical Field

[0001] The present invention belongs to the field of low-dimensional materials and new materials, and particularly relates to a clean transfer method of two-dimensional materials or two-dimensional heterogeneous structures. Background Art

[0002] Two-dimensional materials (such as graphene) and their artificial heterostructures have become the core system of condensed matter physics and nanodevice research because they exhibit unique electron transport, optical response and interface coupling behaviors. In experimental research, in order to obtain intrinsic physical property information, it is often necessary to transfer the material to a specific substrate such as a transmission electron microscope metal mesh to construct a suspended structure, while in industrial applications, the material needs to be transferred to a functionalized target substrate to achieve device integration. However, the currently widely used polymer-assisted wet transfer process (such as spin coating and etching of supporting layers such as PMMA and PVA) has inherent defects: although high-temperature degumming or organic solvent cleaning can partially remove polymer residues, it will inevitably introduce contamination such as amorphous carbon layers and functional group adsorption on the material surface or at the heterojunction interface. Studies in recent years have shown that such residues will not only significantly degrade the carrier mobility of graphene, but also obscure the intrinsic moiré superlattice effect in the two-dimensional heterojunction, seriously restricting the interpretation of the correlation between basic research and device performance.

[0003] To address the polymer residue issue, researchers have attempted to improve it by optimizing annealing parameters, developing water-soluble polymers, or utilizing the self-supporting properties of two-dimensional materials. However, existing methods face challenges in process compatibility, structural integrity, and cleanliness: low-temperature annealing makes it difficult to completely decompose polymer chains, while high-temperature treatment may induce diffusion contamination of the metal substrate; while some alternative transfer media can reduce organic residues, they face problems such as low transfer success rates or interlayer slippage in heterostructures. Therefore, developing a polymer-free, clean transfer technology suitable for complex heterostructures is of great value in revealing the interfacial physics of two-dimensional materials and promoting their application transformation. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a clean transfer method for two-dimensional materials or two-dimensional heterostructures, which eliminates the introduction of polymer materials from the source, ensures the cleanliness of the target material, and has compatibility with various two-dimensional materials.

[0005] To achieve the above objectives, the present invention provides a method for cleanly transferring a two-dimensional material or a two-dimensional heterostructure, comprising the following steps:

[0006] S1. Providing a substrate with an oxide layer on the surface, on which a target material is grown, wherein the target material comprises a two-dimensional material or a two-dimensional heterostructure;

[0007] S2. Using an optical microscope to confirm the location of the target material on the substrate surface, then aligning the transmission electron microscope metal mesh with the carbon film to the target material area, and adding a drop of the drop agent near the metal mesh, so that the drop agent spreads to the gap between the carbon film and the target material, to obtain a substrate with a metal mesh adhered;

[0008] S3. Placing the substrate with the metal mesh adhered on a heating table for heating treatment, so that the drop agent volatilizes, and the metal mesh and the carbon film are adhered to the surface of the target material;

[0009] S4. Annealing the substrate with the metal mesh adhered to further improve the bonding force between the carbon film and the target material;

[0010] S5. Placing the annealed substrate with the metal mesh adhered in a hydrofluoric acid solution to etch the oxide layer on the surface of the substrate until the metal mesh falls off from the substrate, to obtain a metal mesh with the target material attached;

[0011] S6. Annealing the metal mesh with the target material attached to enhance the bonding force between the metal mesh and the carbon film and the target material, thereby completing the clean transfer of the target material.

[0012] Preferably, the substrate in step S1 includes any one of a silicon substrate or a quartz substrate.

[0013] Preferably, the substrate in step S1 can conveniently judge the number of layers, cleanliness, and morphology of the two-dimensional material in the target material.

[0014] Preferably, the oxide layer in step S1 is prepared by a dry oxidation or thermal oxidation process, and has a thickness of 80-350 nanometers.

[0015] More preferably, the substrate in step S1 is attached with an oxide layer prepared by a dry oxidation process, and has a thickness of 290 nanometers.

[0016] Preferably, the metal mesh in step S2 is made of any one of copper, gold, or molybdenum; the carbon film has a thickness of 1-3 nanometers, and includes a microporous carbon film or a non-porous carbon film.

[0017] More preferably, the metal mesh in step S2 is made of molybdenum, and is attached with a microporous carbon film having a thickness of 2 nanometers and a micropore diameter of 2 micrometers.

[0018] Preferably, the drop agent in step S2 includes, but is not limited to, any one of isopropyl alcohol or an isopropyl alcohol / alcohol mixed solution.

[0019] Preferably, the heating temperature of the heating table in step S3 is 50-150°C, and the heating time is 5-20 minutes.

[0020] More preferably, the heating temperature of the heating table in step S3 is 100℃, and the heating time is 10 minutes.

[0021] Preferably, the annealing condition in step S4 is 80-200℃, annealing for 0.5-6 hours, pressure 110-150 Pa, vacuum environment, and the atmosphere includes one or more of argon, nitrogen, and hydrogen.

[0022] More preferably, the annealing condition in step S4 is argon atmosphere, 150℃ annealing for 3 hours, and pressure 110-150 Pa.

[0023] Preferably, the concentration of the hydrofluoric acid solution in step S5 is 1%-40%, and the solvent is deionized water.

[0024] More preferably, the concentration of the hydrofluoric acid solution in step S5 is 20%, and the etching time is 3 minutes.

[0025] Preferably, the annealing condition in step S6 is 80-200℃, annealing for 0.5-6 hours, pressure 110-150 Pa, and vacuum environment, and the atmosphere includes one or more of argon, nitrogen, and hydrogen, to further improve the binding force between the carbon film and the target material and prevent the carbon film from falling off in the subsequent measurement process.

[0026] More preferably, the annealing condition in step S6 is argon atmosphere, 120℃ annealing for 5 hours, and pressure 110-150 Pa, to further improve the binding force between the carbon film and the sample and prevent the carbon film from falling off in the subsequent measurement process.

[0027] The present application overcomes the problem of polymer residue in the transfer process of two-dimensional materials or two-dimensional heterostructures, ensures the cleanliness of the target material surface and interface, provides a clean platform for the physical property research based on two-dimensional materials and their heterostructures, and improves the sample preparation efficiency of two-dimensional suspended structures in transmission property measurement.

[0028] Advantageous effects

[0029] (1) The present application provides a clean transfer method of two-dimensional materials or two-dimensional heterostructures, which realizes clean transfer of two-dimensional materials or two-dimensional heterostructures by van der Waals force contact between the carbon film of the carrier net and the target sample, avoiding the use of polymers.

[0030] (2) The method of the present application is simple and effective, can be adapted to different types of two-dimensional materials or heterostructures, improves the sample preparation and measurement efficiency, and accelerates the development of potential applications. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a flowchart of the clean transfer method of graphene / hexagonal boron nitride heterojunction in Example 1.

[0032] Figure 2 Optical microscope images of the metal molybdenum mesh adhered to the silicon substrate in Example 1 after annealing (a) and the metal molybdenum mesh with graphene / hexagonal boron nitride heterojunction attached after transfer (b). DETAILED DESCRIPTION

[0033] The application will be further described with reference to the following examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, it should be understood that various modifications can be made to the application by those skilled in the art upon reading the teachings of this application, and such modifications are intended to come within the scope of the appended claims.

[0034] Example 1

[0035] The flow chart of the clean transfer method of graphene / hexagonal boron nitride heterojunction in this example is shown in FIG. 1, which includes the following steps: Figure 1

[0036] S1. Providing a silicon substrate with a 290 nm thick oxide layer on the surface, and growing graphene / hexagonal boron nitride heterojunction on the surface of the silicon substrate;

[0037] S2. Using an optical microscope to confirm the position of the graphene / hexagonal boron nitride heterojunction on the surface of the silicon substrate, then aligning a transmission electron microscope metal molybdenum mesh with a microporous carbon film (pore size 2 microns, thickness 2 nanometers) to the heterojunction area, and adding isopropyl alcohol droplets near the metal molybdenum mesh to spread to the gap between the microporous carbon film and the heterojunction, to obtain a silicon substrate with a metal mesh adhered to it;

[0038] S3. Placing the silicon substrate with the metal molybdenum mesh adhered to it on a heating stage for heating treatment, with heating conditions of 100°C for 10 minutes;

[0039] S4. Annealing the silicon substrate with the metal molybdenum mesh adhered to it, with annealing conditions of an argon atmosphere, 150°C for 3 hours, and a pressure of 110-150 Pa. The optical microscope image of the silicon substrate with the metal molybdenum mesh adhered to it after annealing is shown in FIG. 2(a). It can be seen that the carbon film of the metal molybdenum mesh is aligned and adhered to the graphene / hexagonal boron nitride heterojunction area through the holes of the metal molybdenum mesh; Figure 2

[0040] S5. Placing the annealed silicon substrate in a 20% hydrofluoric acid solution for 3 minutes to etch the oxide layer on the surface of the silicon substrate, to obtain a metal molybdenum mesh with graphene / hexagonal boron nitride heterojunction attached to it;

[0041] ​​S6. The metal molybdenum net attached with graphene / hexagonal boron nitride heterojunction is annealed, the annealing condition is argon atmosphere, 120℃ annealing for 5 hours, the pressure is 110-150 Pa, the clean transfer of two-dimensional heterojunction is completed, the optical microscope picture of the metal molybdenum net attached with graphene / hexagonal boron nitride heterojunction after transfer is as shown in Figure 2 (b) shown, the graphene / hexagonal boron nitride heterojunction is completely transferred to the carbon film of the metal molybdenum net, the different colors of the heterojunction area represent that the hexagonal boron nitride has different thicknesses.

Claims

1. A method for clean transfer of a two-dimensional material or a two-dimensional heterostructure, comprising the following steps: S1. providing a substrate with an oxide layer on the surface, and a target material grown on the surface of the substrate, wherein the target material comprises a two-dimensional material or a two-dimensional heterostructure; S2. confirming the position of the target material on the surface of the substrate using an optical microscope, and then aligning a transmission electron microscope metal grid with a carbon film to the target material region, and dropping a droplet near the metal grid, so that the droplet spreads to the gap between the carbon film and the target material, to obtain a substrate with the metal grid adhered thereto; S3. placing the substrate with the metal grid adhered thereto on a heating stage for heating treatment; S4. annealing the substrate with the metal grid adhered thereto; S5. placing the annealed substrate with the metal grid adhered thereto in a hydrofluoric acid solution to etch the oxide layer on the surface of the substrate until the metal grid falls off from the substrate, to obtain a metal grid with the target material adhered thereto; S6. annealing the metal grid with the target material adhered thereto, to complete the clean transfer of the target material.

2. The method according to claim 1, wherein The substrate in step S1 comprises any one of a silicon substrate or a quartz substrate.

3. The method according to claim 1, wherein The oxide layer in step S1 is prepared by a dry oxidation or thermal oxidation process, and has a thickness of 80-350 nm. 4.The method of claim 1, wherein The metal grid in step S2 is made of any one of copper, gold or molybdenum; the carbon film has a thickness of 1-3 nm, and comprises a microporous carbon film or a non-porous carbon film. 5.The method of claim 1, wherein The droplet in step S2 comprises any one of isopropyl alcohol or a mixed solution of isopropyl alcohol / alcohol. 6.The method of claim 1, wherein, The heating temperature of the heating stage in step S3 is 50-150℃, and the heating time is 5-20 minutes.

7. The method according to claim 1, wherein The annealing conditions in steps S4 and S6 are 80-200℃, annealing for 0.5-6 hours, a pressure of 110-150 Pa, a vacuum environment, and an atmosphere comprising any one or more of argon, nitrogen and hydrogen. 8.The method of claim 1, wherein, The concentration of the hydrofluoric acid solution in step S5 is 1%-40%, and the solvent is deionized water.

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