A method for preparing hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction

Abstract

The invention provides a method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction, which comprises laminating a third sublayer of a hexagonal boron nitride material with a first PMMA material layer through a first intermediate substrate, laminating a sixth sublayer of a graphene material with a third sublayer through a second intermediate substrate, and then laminating a ninth sublayer of the hexagonal boron nitride material with a sixth sublayer through a third intermediate substrate, finally transferring the ninth sublayer, the sixth sublayer, the third sublayer and the first PMMA material layer to a target substrate, and removing the first PMMA material layer, thereby transferring the hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction to the target substrate. The preparation process can avoid contamination of impurities such as PMMA between the interface of the graphene material and the hexagonal boron nitride material, and further improves the film-forming quality of the hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction after transfer.

Description

Technical Field

[0001] The invention relates to the technical field of heterojunction materials, and in particular to a method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction. Background Art

[0002] Since its discovery, graphene has been widely studied due to its excellent performance. Its ultra-high carrier mobility and high saturation rate make graphene have great application potential in the field of high-speed radio frequency. Hexagonal boron nitride has a similar structure to graphene and has a high degree of matching. Using hexagonal boron nitride (h-BN) as the substrate of graphene can greatly improve the carrier mobility of graphene, and the moiré superlattice formed by the vertical heterojunction composed of hexagonal boron nitride and graphene can show novel physical properties. At present, the traditional transfer process mainly uses mechanically exfoliated graphene and hexagonal boron nitride microflakes to prepare high-quality graphene / hexagonal boron nitride heterojunctions with arbitrary stacking structures through transfer and superposition methods, but this will cause the transferred film to be prone to wrinkling and cracking, and there are other contaminants, which seriously damage the performance of the sample. Summary of the invention

[0003] The purpose of the present invention is to provide a method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction, so as to overcome the technical problem of residual PMMA between layers when preparing a vertical stacking heterojunction by wet transfer in the prior art.

[0004] In order to solve the above technical problems, the present invention first provides a method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction, comprising the following steps:

[0005] S10, forming a first PMMA material layer on the first intermediate substrate, the first intermediate substrate comprising a first sublayer, a second sublayer and a third sublayer stacked from bottom to top, the third sublayer is in contact with the first PMMA material layer, the first sublayer and the third sublayer are both hexagonal boron nitride, and the second sublayer is copper;

[0006] S20, performing an etching process on the first intermediate substrate to completely remove the first sublayer and the second sublayer;

[0007] S30, transferring the third sublayer and the first PMMA material layer onto a second intermediate substrate, wherein the second intermediate substrate comprises a fourth sublayer, a fifth sublayer and a sixth sublayer stacked from bottom to top, the third sublayer is in contact with the sixth sublayer, the fourth sublayer and the sixth sublayer are both graphene, and the fifth sublayer is copper;

[0008] S40, performing an etching process on the second intermediate substrate to completely remove the fourth sublayer and the fifth sublayer;

[0009] S50, transferring the sixth sublayer, the third sublayer, and the first PMMA material layer onto a third intermediate substrate, wherein the third intermediate substrate comprises a seventh sublayer, an eighth sublayer, and a ninth sublayer stacked from bottom to top, wherein the ninth sublayer contacts the sixth sublayer, the seventh sublayer and the ninth sublayer are both hexagonal boron nitride, and the eighth sublayer is copper;

[0010] S60, performing an etching process on the third intermediate substrate to completely remove the seventh sublayer and the eighth sublayer;

[0011] S70, transferring the ninth sub-layer, the sixth sub-layer, the third sub-layer and the first PMMA material layer onto the target substrate, and removing the first PMMA material layer.

[0012] Preferably, in step S10, step S30 and step S50, the first intermediate substrate, the second intermediate substrate and the third intermediate substrate are all prepared by a chemical vapor deposition process.

[0013] Preferably, in step S10, the step of forming a first PMMA material layer on the first intermediate substrate specifically includes:

[0014] S101, coating a PMMA solution on the third sub-layer;

[0015] S102, baking the PMMA solution to form a first PMMA material layer after curing;

[0016] The baking temperature is 80° C. to 150° C., and the baking time is 1 min to 5 min.

[0017] Preferably, in step S20, the first intermediate substrate is etched with a ferric chloride solution; in step S40, the second intermediate substrate is etched with a ferric chloride solution; in step S60, the third intermediate substrate is etched with a ferric chloride solution.

[0018] Preferably, after step S30, the method further includes: forming a second PMMA material layer on the first PMMA material layer.

[0019] Preferably, after step S50, the method further includes: forming a third PMMA material layer on the second PMMA material layer.

[0020] Preferably, in step S50, the first PMMA material layer, the second PMMA material layer and the third PMMA material layer are removed respectively using an acetone solution.

[0021] Preferably, after step S50, the method further includes: ultrasonically cleaning the target substrate using acetone, alcohol, and deionized water respectively under a nitrogen atmosphere.

[0022] Preferably, in step S50, the target substrate includes a Si material layer and a SiO2 material layer stacked from bottom to top.

[0023] Preferably, in step S10, step S30 and step S50, the first intermediate substrate, the second intermediate substrate and the third intermediate substrate are all bonded to the PET plastic substrate to prevent PMMA material from entering the back side of the intermediate substrates.

[0024] The beneficial effects of the present invention are as follows: Different from the prior art, the present invention provides a method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction, comprising the following steps: first, forming a first PMMA material layer on a first intermediate substrate, and etching the first intermediate substrate to completely remove the first sublayer and the second sublayer; second, transferring the third sublayer and the first PMMA material layer to the second intermediate substrate, and etching the second intermediate substrate to completely remove the fourth sublayer and the fifth sublayer; third, transferring the sixth sublayer, the third sublayer, and the first PMMA material layer to the third intermediate substrate, and etching the third intermediate substrate to completely remove the seventh sublayer and the eighth sublayer; finally, transferring the ninth sublayer, the sixth sublayer, the third sublayer, and the first PMMA material layer to the target substrate, and removing the first PMMA material layer; The present invention firstly bonds the third sublayer of the hexagonal boron nitride material to the first PMMA material layer through the first intermediate substrate, then bonds the sixth sublayer of the graphene material to the third sublayer through the second intermediate substrate, then bonds the ninth sublayer of the hexagonal boron nitride material to the sixth sublayer through the third intermediate substrate, and finally transfers the ninth sublayer, the sixth sublayer, the third sublayer and the first PMMA material layer to the target substrate, and removes the first PMMA material layer, thereby transferring the hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction to the target substrate. In the above preparation process, the graphene material and the hexagonal boron nitride material are directly bonded through the first intermediate substrate, the second intermediate substrate and the third intermediate substrate, thereby avoiding contamination of impurities such as PMMA at the interface between the graphene material and the hexagonal boron nitride material, and further improving the film formation quality of the hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction after transfer. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A flow chart for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction provided by the present invention;

[0026] Figure 2A-2G A schematic structural diagram of the preparation of a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction provided by the present invention;

[0027] Figure 3This is an optical micrograph of hexagonal boron nitride / graphene / hexagonal boron nitride after being transferred to a target substrate in the preparation method provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] In order to solve the above technical problems, the present invention first provides a method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction. Figures 1 to 2G , Figure 1 A flow chart for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction provided by the present invention; Figure 2A-2G A schematic structural diagram of a method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction provided by the present invention.

[0030] The preparation of the above-mentioned hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction comprises the following steps:

[0031] S10, a first PMMA material layer 31 is formed on the first intermediate substrate 20, the first intermediate substrate 20 includes a first sublayer 201, a second sublayer 202 and a third sublayer 203 stacked from bottom to top, the third sublayer 203 is in contact with the first PMMA material layer 31, the first sublayer 201 and the third sublayer 203 are both hexagonal boron nitride, and the second sublayer 202 is copper.

[0032] Specifically, step S10 also includes:

[0033] The first intermediate substrate 20 is adhered to the first PET plastic substrate 10 by a sealing tape, and a first PMMA material layer 31 is formed on the first intermediate substrate 20. Figure 2A As shown; wherein, the first intermediate substrate 20 is prepared by a chemical vapor deposition process, and the first PMMA material layer 31 is prepared by a coating process.

[0034] In the embodiment of the present invention, the first PET plastic substrate 10 is used to prevent the PMMA material in the subsequent steps from entering the back side of the first intermediate substrate 20 .

[0035] Furthermore, the step of forming the first PMMA material layer 31 on the first intermediate substrate 20 specifically includes:

[0036] S101, coating a PMMA solution on the third sub-layer 203;

[0037] S102, baking the PMMA solution to form a first PMMA material layer 31 after solidification;

[0038] The baking temperature is 80° C. to 150° C., and the baking time is 1 min to 5 min.

[0039] S20 , performing an etching process on the first intermediate substrate 20 to completely remove the first sub-layer 201 and the second sub-layer 202 .

[0040] Specifically, step S20 also includes:

[0041] First, the sealing tape between the first intermediate substrate 20 and the first PET plastic substrate 10 is cut off with scissors to separate the first sublayer 201 from the first PET plastic substrate 10; then, the first intermediate substrate 20 is etched to completely remove the first sublayer 201 and the second sublayer 202. Figure 2B As shown; wherein, the first intermediate substrate 20 is etched using a ferric chloride solution.

[0042] S30, transferring the third sublayer 203 and the first PMMA material layer 31 onto the second intermediate substrate 50 together, the second intermediate substrate 50 includes a fourth sublayer 501, a fifth sublayer 502 and a sixth sublayer 503 stacked from bottom to top, the third sublayer 203 is in contact with the sixth sublayer 503, the fourth sublayer 501 and the sixth sublayer 503 are both graphene, and the fifth sublayer 502 is copper.

[0043] Specifically, step S30 also includes:

[0044] The third sublayer 203 and the first PMMA material layer 31 are transferred together onto the second intermediate substrate 50 , wherein the second intermediate substrate 50 is adhered to the second PET plastic substrate 40 by a sealing tape, and the second intermediate substrate 50 is prepared by a chemical vapor deposition process.

[0045] In the embodiment of the present invention, the second PET plastic substrate 40 is used to prevent the PMMA material in the subsequent steps from entering the back side of the second intermediate substrate 50 .

[0046] Furthermore, after step S30, the method further includes: forming a second PMMA material layer 32 on the first PMMA material layer 31, such as Figure 2CAs shown; wherein, the first PMMA material layer 31 is used to protect the third sublayer 203; the second PMMA material layer 32 is coated again because the area of ​​the second intermediate substrate 50 is larger than that of PMMA / h-BN, and coating the second PMMA material layer 32 can prevent water from entering between h-BN and graphene during the subsequent cleaning process, resulting in water ingress or shedding of the interface between graphene and h-BN during the subsequent etching of the copper substrate.

[0047] S40 , performing an etching process on the second intermediate substrate 50 to completely remove the fourth sub-layer 501 and the fifth sub-layer 502 .

[0048] Specifically, step S40 also includes:

[0049] First, the sealing tape between the second intermediate substrate 50 and the second PET plastic substrate 40 is cut off with scissors to separate the fourth sublayer 501 from the second PET plastic substrate 40; then, the second intermediate substrate 50 is etched with a ferric chloride solution to completely remove the fourth sublayer 501 and the fifth sublayer 502. Figure 2D shown.

[0050] S50, the sixth sublayer 503, the third sublayer 203, and the first PMMA material layer 31 are transferred together onto the third intermediate substrate 60, the third intermediate substrate 60 includes the seventh sublayer 601, the eighth sublayer 602, and the ninth sublayer 603 stacked from bottom to top, the ninth sublayer 603 is in contact with the sixth sublayer 503, the seventh sublayer 601 and the ninth sublayer 603 are both hexagonal boron nitride, and the eighth sublayer 602 is copper.

[0051] Specifically, step S50 also includes:

[0052] The sixth sub-layer 503, the third sub-layer 203, the first PMMA material layer 31 and the second PMMA material layer 32 are transferred to the third intermediate substrate 60. Figure 2E As shown; wherein the third intermediate substrate 60 includes a seventh sublayer 601, an eighth sublayer 602 and a ninth sublayer 603 stacked from bottom to top, the ninth sublayer 603 is in contact with the sixth sublayer 503, the seventh sublayer 601 and the ninth sublayer 603 are both hexagonal boron nitride, and the eighth sublayer 602 is copper;

[0053] Specifically, the third intermediate substrate 60 is adhered to the third PET plastic substrate 70 by means of a sealing tape, and the third PET plastic substrate 70 is used to prevent the PMMA material in subsequent steps from entering the back side of the third intermediate substrate 60 .

[0054] S60 , performing an etching process on the third intermediate substrate 60 to completely remove the seventh sub-layer 601 and the eighth sub-layer 602 .

[0055] Specifically, step S60 further includes:

[0056] First, the sealing tape between the third intermediate substrate 60 and the third PET plastic substrate 70 is cut off with scissors to separate the seventh sublayer 601 from the third PET plastic substrate 70; then, the third intermediate substrate 60 is etched with a ferric chloride solution to completely remove the seventh sublayer 601 and the eighth sublayer 602; a third PMMA material layer 33 is formed on the second PMMA material layer 32, as shown in FIG. Figure 2F shown.

[0057] S70 , transferring the ninth sub-layer 603 , the sixth sub-layer 503 , the third sub-layer 203 and the first PMMA material layer 31 onto the target substrate 80 , and removing the first PMMA material layer 31 .

[0058] Specifically, step S70 further includes:

[0059] The ninth sublayer 603, the sixth sublayer 503, the third sublayer 203, the first PMMA material layer 31, the second PMMA material layer 32, and the third PMMA material layer 33 are transferred to the target substrate 80, and the first PMMA material layer 31, the second PMMA material layer 32, and the third PMMA material layer 33 are removed, and finally the hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction is transferred to the target substrate 80, as shown in FIG. Figure 2G shown.

[0060] Preferably, in step S70, the first PMMA material layer 31, the second PMMA material layer 32 and the third PMMA material layer 33 are removed respectively using an acetone solution.

[0061] Preferably, after step S70, the method further includes: ultrasonically cleaning the target substrate 80 with acetone, alcohol, and deionized water for 5 minutes respectively and drying it with nitrogen.

[0062] Preferably, in step S70, the target substrate 80 includes a Si material layer and a SiO 2 material layer stacked from bottom to top.

[0063] The technical solution of the present invention is now further described in conjunction with specific embodiments.

[0064] Example:

[0065] The preparation of the graphene / hexagonal boron nitride heterojunction provided in this embodiment specifically includes the following steps (taking h-BN / Graphene / h-BN / SiO2 / Si as an example):

[0066] Step 1 (edge ​​sealing): Cut a 1 cm×1 cm piece of h-BN / Cu / h-BN (hexagonal boron nitride / copper / hexagonal boron nitride, the first intermediate substrate 20) and fix its four edges on a plastic substrate made of PET material with polyimide tape. PET is slightly larger than h-BN / Cu / h-BN.

[0067] Step 2 (glue coating): Use a glue spreader to coat a layer of PMMA (mass concentration 4%) on the surface of h-BN / Cu / h-BN / PET, and then bake on a hot plate at 100°C for 1 min to solidify it;

[0068] Step 3 (etching): PMMA / h-BN / Cu / h-BN (placed in ferric chloride solution for 5 min, rinsed the h-BN on the back of the copper foil with deionized water several times, and then placed it in the etching solution for 1-2 hours until the copper substrate was completely etched to form PMMA / h-BN;

[0069] Step 4 (rinsing): transfer PMMA / h-BN into deionized water using a glass slide and rinse repeatedly to clean the residual ferric chloride solution on the surface of h-BN;

[0070] Step 5 (first transfer): Cut a 1.5 cm×1.5 cm piece of Graphene / Cu / Graphene (graphene / copper / graphene, second intermediate substrate 50), and fix its four sides on PET with polyimide tape, use Graphene / Cu / Graphene / PET as a substrate to transfer PMMA / h-BN to its surface, and place PMMA / h-BN / Graphene / Cu / Graphene / PET on filter paper to let it dry naturally;

[0071] Step 6 (repeat step 2 to step 4): repeat the above-mentioned coating, etching and rinsing process on the dried PMMA / h-BN / Graphene / Cu / Graphene / PET to obtain PMMA / PMMA / h-BN / Graphene;

[0072] Step 7 (second transfer): cut a 2 cm×2 cm piece of h-BN / Cu / h-BN (hexagonal boron nitride / copper / hexagonal boron nitride, the third intermediate substrate 60), and fix its four sides on PET with polyimide tape, use h-BN / Cu / h-BN / PET as a substrate to transfer PMMA / PMMA / h-BN / Graphene to its surface, and place PMMA / PMMA / h-BN / Graphene / h-BN / Cu / h-BN / PET on filter paper to let it dry naturally;

[0073] Step 8 (repeat steps 2 to 4): repeat the above-mentioned coating, etching, and rinsing processes on the dried PMMA / PMMA / PMMA / h-BN / Graphene / h-BN / Cu / h-BN / PET to obtain PMMA / PMMA / PMMA / h-BN / Graphene / h-BN;

[0074] Step 9 (third transfer): cut a piece of SiO2 / Si target substrate 80 slightly larger than 2 cm×2 cm, transfer PMMA / PMMA / PMMA / h-BN / Graphene / h-BN to the SiO2 / Si substrate, and place it on filter paper to dry naturally;

[0075] Step 10 (removing PMMA material): Place PMMA / PMMA / PMMA / h-BN / Graphene / h-BN / SiO2 / Si in a 40°C acetone solution. After 20 minutes, place h-BN / Graphene / h-BN / SiO2 / Si in new acetone to further remove PMMA residues on the h-BN surface. Finally, rinse h-BN / Graphene / h-BN / SiO2 / Si with acetone and isopropanol and blow dry its surface with nitrogen.

[0076] See also Figure 3 , Figure 3 An optical micrograph of a graphene / hexagonal boron nitride heterojunction after being transferred to a target substrate 80 in the preparation of a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction provided in an embodiment of the present invention. Figure 3 It can be seen that the h-BN / Graphene / h-BN heterojunction is successfully transferred to the target substrate 80 .

[0077] In the embodiment of the present invention, the preparation method of the hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction provided by the present invention is not limited to the preparation of H-BN / graphen / h-BN heterojunction structure. In principle, any vertically stacked structure of H-BN / graphen heterojunction and other two-dimensional material heterojunctions can be prepared, which will not be repeated here.

[0078] In summary, the present invention provides a method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction, comprising the following steps: first, forming a first PMMA material layer 31 on a first intermediate substrate 20, and etching the first intermediate substrate 20 to completely remove the first sublayer 201 and the second sublayer 202; second, transferring the third sublayer 203 and the first PMMA material layer 31 to a second intermediate substrate 50, and etching the second intermediate substrate 50 to completely remove the first sublayer 201 and the second sublayer 202; In addition to the fourth sublayer 501 and the fifth sublayer 502, the sixth sublayer 503, the third sublayer 203, and the first PMMA material layer 31 are transferred to the third intermediate substrate 60, and the third intermediate substrate 60 is etched to completely remove the seventh sublayer 601 and the eighth sublayer 602. Finally, the ninth sublayer 603, the sixth sublayer 503, the third sublayer 203, and the first PMMA material layer 31 are transferred to the target substrate 80, and the first PMMA material layer 31 is removed. The invention firstly laminates the third sublayer 203 of the hexagonal boron nitride material with the first PMMA material layer 31 through the first intermediate substrate 20, then laminates the sixth sublayer 503 of the graphene material with the third sublayer 203 through the second intermediate substrate 50, and then laminates the ninth sublayer 603 of the hexagonal boron nitride material with the sixth sublayer 503 through the third intermediate substrate 60, and finally transfers the ninth sublayer 603, the sixth sublayer 503, the third sublayer 203 and the first PMMA material layer 31 to the target substrate 80. , and remove the first PMMA material layer 31, thereby transferring the hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction to the target substrate 80. In the above preparation process, the graphene material and the hexagonal boron nitride material are directly bonded through the first intermediate substrate 20, the second intermediate substrate 50 and the third intermediate substrate 60, thereby avoiding the contamination of PMMA and other impurities at the interface between the graphene material and the hexagonal boron nitride material, and further improving the film quality of the hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction after transfer.

[0079] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For matters that are not described in detail in some embodiments, reference may be made to the description in other embodiments.

[0080] The above embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction, characterized in that: The following steps are involved: S10, forming a first PMMA material layer on a first intermediate substrate, wherein the first intermediate substrate comprises a first sublayer, a second sublayer and a third sublayer stacked from bottom to top, the third sublayer is in contact with the first PMMA material layer, the first sublayer and the third sublayer are both hexagonal boron nitride, and the second sublayer is copper; S20, performing an etching process on the first intermediate substrate to completely remove the first sublayer and the second sublayer; S30, transferring the third sublayer and the first PMMA material layer onto a second intermediate substrate, wherein the second intermediate substrate comprises a fourth sublayer, a fifth sublayer and a sixth sublayer stacked from bottom to top, the third sublayer is in contact with the sixth sublayer, the fourth sublayer and the sixth sublayer are both graphene, and the fifth sublayer is copper; S40, performing an etching process on the second intermediate substrate to completely remove the fourth sublayer and the fifth sublayer; S50, transferring the sixth sublayer, the third sublayer, and the first PMMA material layer onto a third intermediate substrate, wherein the third intermediate substrate comprises a seventh sublayer, an eighth sublayer, and a ninth sublayer stacked from bottom to top, wherein the ninth sublayer is in contact with the sixth sublayer, the seventh sublayer and the ninth sublayer are both hexagonal boron nitride, and the eighth sublayer is copper; S60, performing an etching process on the third intermediate substrate to completely remove the seventh sublayer and the eighth sublayer; S70, transferring the ninth sub-layer, the sixth sub-layer, the third sub-layer and the first PMMA material layer onto a target substrate, and removing the first PMMA material layer.

2. The method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction according to claim 1, characterized in that: In the step S10, the step S30 and the step S50, the first intermediate substrate, the second intermediate substrate and the third intermediate substrate are all prepared by a chemical vapor deposition process.

3. The method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction according to claim 1, characterized in that: In the step S10, the step of forming the first PMMA material layer on the first intermediate substrate specifically includes: S101, coating a PMMA solution on the third sub-layer; S102, baking the PMMA solution to form the first PMMA material layer after curing; The baking temperature is 80°C to 150°C, and the baking time is 1 min to 5 min.

4. The method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction according to claim 1, characterized in that: In the step S20, the first intermediate substrate is etched with a ferric chloride solution; in the step S40, the second intermediate substrate is etched with a ferric chloride solution; in the step S60, the third intermediate substrate is etched with a ferric chloride solution.

5. The method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction according to claim 1, characterized in that: After step S30, the method further includes: forming a second PMMA material layer on the first PMMA material layer.

6. The method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction according to claim 5, characterized in that: After step S50, the method further includes: forming a third PMMA material layer on the second PMMA material layer.

7. The method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction according to claim 6, characterized in that: In the step S50, the first PMMA material layer, the second PMMA material layer and the third PMMA material layer are removed respectively using an acetone solution.

8. The method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction according to claim 7, characterized in that: After the step S50, the method further includes: ultrasonically cleaning the target substrate using acetone, alcohol, and deionized water respectively in a nitrogen atmosphere.

9. The method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction according to claim 1, characterized in that: In the step S50, the target substrate includes a Si material layer and a SiO2 material layer stacked from bottom to top.

10. The method for preparing a hexagonal boron nitride / graphene / hexagonal boron nitride heterojunction according to claim 1, characterized in that: In the step S10, the step S30 and the step S50, the first intermediate substrate, the second intermediate substrate and the third intermediate substrate are all bonded and connected to the PET plastic substrate.

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