A method for precisely transferring large-area two-dimensional materials

Abstract

The present invention relates to a method for precisely transferring large-area two-dimensional materials. PMMA and a gradient polymer film of two layers of PVA are spin-coated on a fluorophlogopite sheet on which two-dimensional materials are grown; acetone is used to dissolve PMMA at the bottom layer of the polymer film at the edge of the substrate to form a gap, and a method of preheating first, then fixing with 3M tape, and then heating is adopted. Subsequently, it is naturally air-dried, and the two-dimensional materials are transferred onto the target substrate. After the transfer according to the present invention, the morphology of the two-dimensional materials is complete and the surface is clean, alleviating the problems existing in the existing transfer technologies such as damage of two-dimensional materials, great difficulty in the transfer process, and low success rate. It also avoids the problems of easy wrinkling and damage of two-dimensional materials brought about by the traditional water-assisted transfer method. At the same time, it can effectively avoid the residual glue pollution problem caused by the relatively large thickness of PMMA in the traditional water-assisted peeling method. This method can achieve the efficient transfer of large-area two-dimensional materials, and the morphology and structure of the two-dimensional materials after transfer are complete.

Description

Technical Field

[0001] The present invention belongs to the technical field of two-dimensional material applications, and relates to a method for efficiently exfoliating and precisely transferring large-area two-dimensional materials. Background Art

[0002] Since 2004, relevant scholars at the University of Manchester successfully isolated the single-atom layer graphite material - graphene, demonstrating the possibility of the existence of two-dimensional materials at the atomic scale and guiding scholars to open the colorful door of two-dimensional materials. Due to the fact that electrons in two-dimensional materials can only move freely in the nano-scale of two dimensions, two-dimensional materials exhibit unique properties compared to traditional materials, especially attracting extensive attention from researchers in terms of electrical properties. Currently, two-dimensional materials have extremely wide applications in fields such as semiconductor devices and integrated circuits. However, whether studying the basic properties of two-dimensional materials or fabricating optoelectronic devices of two-dimensional materials, etc., it is necessary to transfer two-dimensional materials to specific positions, which requires a fast and efficient two-dimensional material transfer method.

[0003] How to quickly and effectively transfer two-dimensional materials from the growth substrate to the target substrate has become a key issue in the research of two-dimensional material properties and device fabrication processes. Currently, the existing two-dimensional material transfer technologies mainly include mechanical exfoliation method, PDMS dry transfer, chemical etching method, and traditional water-assisted exfoliation method.

[0004] Among them, the mechanical exfoliation method is the earliest method used to handle two-dimensional material transfer. Although this method is simple and fast, it is difficult to guarantee the transfer quality and effect, and the transfer quantity and types are extremely limited. Especially in the case of uneven materials or materials with atomic-level thickness, it is difficult to ensure that the experimental results meet the expected effects, resulting in a large amount of waste of the prepared materials.

[0005] The disadvantage of PDMS dry transfer is that the two-dimensional materials are exfoliated mechanically, which is very easy to break or wrinkle. Moreover, it is difficult for PDMS to completely adhere closely to the growth substrate, resulting in many materials not being completely transferred. The sample quality depends on the flatness of the target substrate and the magnitude of the contact pressure. In actual experiments, it is difficult to control the appropriate contact pressure magnitude for different materials, and it is difficult to achieve the transfer of large-area and low-thickness two-dimensional materials. In addition, the transfer efficiency is low, it is not applicable to most materials grown by chemical vapor deposition methods, and it is not suitable for samples with strong binding force between the substrate and two-dimensional materials, having certain limitations.

[0006] In the chemical etching method, strong acids or strong bases are used to etch metal substrates or SiO2 / Si substrates. On the one hand, some two-dimensional materials themselves may react with strong acids or strong bases, or strong acids or strong bases may modify their surfaces, reducing the quality of two-dimensional materials. They cannot be used as two-dimensional sensitive materials, which greatly limits their application scenarios. It takes a long time, and the phenomenon of damage to two-dimensional materials is likely to occur. Moreover, the etched substrates are difficult to reuse, and the pollution of the etching solvent to the environment is one of the important factors restricting its development.

[0007] In the traditional water-assisted exfoliation method, PMMA is generally used as the polymer film, and the polymer thin film is usually spin-coated on the surface of two-dimensional materials in one step. The authorized number CN 110954570 A discloses a method for temperature-controlled bubble exfoliation of two-dimensional materials grown on sapphire substrates. This method is an improvement on the traditional water-assisted exfoliation method. The bubbles of the aqueous solution of NH4OH and H2O2 are used to provide traction to separate the two-dimensional material-PMMA film from the sapphire substrate. The advantage of this method is that it uses a solvent-assisted method, does not require etching the substrate, the transfer process is gentle, and it has universality. Its disadvantages are as follows: relying on the support and protection of the polymer film, on the one hand, if the polymer film is spin-coated thickly, although it can ensure the support and protection of the polymer film for two-dimensional materials, the subsequent problem is that it is difficult to completely dissolve and remove the polymer film in the later stage, and it is easy to cause secondary pollution to the materials; on the other hand, if it is spin-coated thinly, it is difficult to play a supporting and protecting role for two-dimensional materials, and two-dimensional materials are prone to breakage under the water tension during the transfer process, resulting in the loss or incompleteness of two-dimensional materials. Therefore, the spin-coating technique and the spin-coating thickness are very important factors. At the same time, there are also certain problems with its use of bubbles for exfoliation. First, it is difficult to generate bubbles at the edge of the substrate by the aqueous solution of NH4OH and H2O2, especially on ultra-thin substrates (5-10um), and the utilization rate and use effect of the generated bubbles are very low; second, during spin-coating, the colloid is easy to coat the edge of the substrate. Unless special treatments such as mechanical edge scraping are used to remove the residual glue at the edge, it is difficult to use the traction of the bubbles to separate PMMA and the substrate. Therefore, the actual operation difficulty is relatively large.

[0008] As is well known, two-dimensional materials, especially the morphology, thickness, etc. of two-dimensional materials, will seriously affect their electrical properties, optical properties and other characteristics. Therefore, it is necessary to avoid phenomena such as breakage and wrinkles of two-dimensional materials during the transfer process to ensure the complete and efficient transfer of the materials. Thus, it can be seen that developing a method for efficient exfoliation and precise transfer of large-area two-dimensional materials is particularly important for the research and application of two-dimensional materials. Summary of the Invention

[0009] Technical Problems to be Solved

[0010] To avoid the deficiencies of the prior art, the present invention proposes a method for efficiently peeling and precisely transferring large-area two-dimensional materials. This method requires few devices, has simple operation steps, easily obtainable transferred materials, and low costs. It can efficiently and stably transfer two-dimensional materials onto a target substrate. After the transfer, the morphology of the two-dimensional materials is complete and the surface is clean, alleviating problems existing in the prior transfer technologies such as damage to two-dimensional materials, great difficulty in the transfer process, and low success rate. It also avoids problems such as easy wrinkling and damage of two-dimensional materials brought about by the traditional water-assisted transfer method. At the same time, it can effectively avoid the residual glue pollution problem caused by the relatively large thickness of PMMA in the traditional water-assisted peeling method. This method can achieve the efficient transfer of large-area two-dimensional materials, and the morphology and structure of the two-dimensional materials after the transfer are complete.

[0011] Technical solution

[0012] A method for precisely transferring large-area two-dimensional materials, characterized by the following steps:

[0013] Step 1: Spin-coat PMMA on a fluorophlogopite sheet growing two-dimensional materials, and form a PMMA polymer film after drying; continue to spin-coat a gradient polymer film of two layers of PVA on the PMMA polymer film, and then dry to form a gradient polymer film containing one layer of PMMA and two layers of PVA;

[0014] Step 2: Wipe the edge of the fluorophlogopite sheet with acetone to dissolve the PMMA at the bottom layer of the polymer film at the edge of the fluorophlogopite sheet, forming a gap;

[0015] Step 3: Slowly drop ultrapure water into the gap between the polymer film and the edge of the substrate, and use the surface tension of water to separate the polymer film from the fluorophlogopite sheet to obtain a polymer film carrying two-dimensional materials;

[0016] Step 4: After transferring the polymer film carrying two-dimensional materials onto the target substrate and preheating, paste a 3M tape with a hollow border on the polymer film on the surface of the target substrate to fix the polymer film, and continue to heat and dry the target substrate;

[0017] The 3M tape with the hollow border is slightly wider than the polymer film;

[0018] Step 5: Put the dried target substrate into a container, slowly inject ultrapure water along the glass wall until the ultrapure water covers the surface of the target substrate, heat the container and keep it warm to dissolve PVA;

[0019] Remove the target substrate and put it into another container, repeat this step to further dissolve PVA;

[0020] Step 6: Move the target substrate to another container, inject acetone until it covers the target substrate, let it stand for 15 - 30 min to dissolve PMMA, and then slowly suck out the acetone in the petri dish with a syringe;

[0021] The container remains stationary so that the transferred two-dimensional material is not damaged;

[0022] Repeat this step, and then air-dry naturally to transfer the two-dimensional material onto the target substrate.

[0023] In step 1, the PMMA is spin-coated at a low speed of 200 - 1000 rad s -1 Spin-coated for 10 - 30 s, and at a high speed of 1500 - 4500 rad s -1 Spin-coated for 25 - 55 s.

[0024] The concentration of the PMMA is 0.005 - 0.05 g ml -1 .

[0025] After spin-coating the PMMA, drying is to dry the spin-coated fluorophlogopite sheet on a heating table at 50 - 60 °C for 20 - 60 s.

[0026] In step 1, the first layer of PVA is spin-coated at a low speed of 200 - 1000 rad s -1 Spin-coated for 10 - 30 s, and at a high speed of 1500 - 4500 rad s -1 Spin-coated for 25 - 55 s, and the concentration of the first layer of PVA is 0.01 - 0.15 g ml -1 .

[0027] In step 1, the second layer of PVA is spin-coated at a low speed of 200 - 1000 rad s -1 Spin-coated for 10 - 30 s, and at a high speed of 1500 - 4500 rad s -1 Spin-coated for 25 - 55 s, and the concentration of the second layer of PVA is 0.15 - 0.3 g ml -1 .

[0028] After spin-coating the PVA, drying is to continuously dry the fluorophlogopite sheet with the polymer film on a heating table at 45 - 90 °C for 5 - 25 min, and then continuously dry at 90 - 130 °C for 20 - 40 min.

[0029] In step 4, preheating on the target substrate is: placing the target substrate on a heating table and preheating at 50 - 100 °C for 10 - 60 s.

[0030] In step 4, after pasting the 3M tape, continuing to heat the target substrate is: heating and drying at 50 - 100 °C for 10 - 30 min;

[0031] In step 5, heating the container to 60 °C - 80 °C, keeping warm for 20 - 40 min to dissolve the PVA.

[0032] Beneficial effects

[0033] A method for precisely transferring large-area two-dimensional materials proposed by the present invention obtains a gradient polymer film containing one layer of PMMA and two layers of PVA by a three-step spin-coating method. The PMMA is thin and has a uniform thickness. On the one hand, the thin PMMA is convenient for subsequent dissolution, solving the problem of material surface contamination caused by incomplete dissolution due to the relatively thick PMMA. On the other hand, the PMMA with a consistent thickness can fit evenly with the two-dimensional material, which is beneficial to the overall peeling of the two-dimensional material in the later stage. The PVA is spin-coated twice. On the one hand, the PVA is spin-coated more evenly. On the other hand, the two layers of PVA can play an efficient supporting role, and the interface formed between PVA with different concentrations is beneficial to the subsequent dissolution and separation of the film.

[0034] Wipe the edge of the substrate with a cotton swab dipped in acetone to dissolve the PMMA at the bottom layer of the polymer film at the edge of the substrate to form a gap, avoiding the secondary damage to the two-dimensional material during the transfer process caused by the traditional mechanical edge scraping method, and greatly improving the transfer efficiency. Slowly drip ultrapure water into the gap between the polymer film and the edge of the substrate using a syringe, and the dripping speed of the ultrapure water can be controlled according to the actual situation, thereby effectively controlling the separation speed of the polymer film from the substrate and the magnitude of the force during separation, ensuring the integrity of the two-dimensional material during the separation process.

[0035] When drying the target substrate carrying the polymer film and the two-dimensional material, first preheat, then fix it with 3M tape, and then heat. The purpose of preheating is, on the one hand, to evaporate the moisture on the upper surface of the polymer film, making the 3M tape fit more tightly with the polymer film; on the other hand, to reduce the moisture between the polymer film and the target substrate, making their fit more tight. At this time, the target substrate is not easy to slide when sticking the tape. Use a hollow 3M tape to fix the edge of the polymer film, reducing the shrinkage and detachment of the polymer film during the heating process, as well as problems such as breakage and wrinkles of the two-dimensional material caused thereby.

[0036] The main innovation points of the present invention are as follows:

[0037] 1. The number of devices used is small, only a spin coater and a heating platform are needed, and the operation steps are simple and convenient;

[0038] 2. A gradient polymer film containing one layer of PMMA and two layers of PVA is obtained by a three-step spin-coating method, effectively controlling the spin-coating thickness, ensuring the supporting role of the film and convenient and effective dissolution, effectively solving the problem of secondary pollution to the material caused by the traditional method, achieving a clean interface, and ensuring the physical and chemical properties of the two-dimensional material;

[0039] 3. The method of the invention effectively reduces problems such as breakage and wrinkles of the two-dimensional material during the transfer process, ensuring the morphology and structural integrity of the two-dimensional material during the transfer process;

[0040] 4. The method of the invention can achieve the high-efficiency transfer of large-area two-dimensional materials with atomic thickness.

[0041] 5. The application field of the inventive method is wide and it can be widely used in the fields of transfer and property detection of two-dimensional materials, preparation of heterojunctions and devices, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 : Optical microscope image of BiOBr two-dimensional material after transfer;

[0043] Figure 2 ; Optical microscope image of WS2 two-dimensional material after transfer;

[0044] Figure 3 : Optical microscope image of BiOI two-dimensional material after transfer; DETAILED DESCRIPTION OF THE INVENTION

[0045] The present invention will be further described below in combination with examples and drawings:

[0046] To achieve the above object, the present invention is realized through the following technical solutions:

[0047] (1) Fix the fluorophlogopite sheet growing with two-dimensional material on the sample stage of the spin coater with double-sided tape, and then drop 0.1 - 0.25 ml of PMMA with a concentration of 0.005 - 0.05 g / ml onto the fluorophlogopite sheet growing with two-dimensional nanosheets, spin coat at a low speed of 200 - 1000 rad / s for 10 - 30 s, and spin coat at a high speed of 1500 - 4500 rad / s for 25 - 55 s to perform the first spin coating; -1 -1 -1

[0048] (2) Dry the spin-coated fluorophlogopite sheet on a heating table at 50 - 60 °C for 20 - 60 s;

[0049] (3) Drop 0.2 - 0.35 ml of PVA with a concentration of 0.01 - 0.15 g / ml onto the fluorophlogopite sheet spin-coated in the first step, spin coat at a low speed of 200 - 1000 rad / s for 10 - 30 s, and spin coat at a high speed of 1500 - 4500 rad / s for 25 - 55 s to perform the second spin coating; -1 -1 -1

[0050] (4) Drop 0.2 - 0.35 ml of PVA with a concentration of 0.15 - 0.3 g / ml onto the fluorophlogopite sheet spin-coated with PVA, spin coat at a low speed of 200 - 1000 rad / s for 10 - 30 s, and spin coat at a high speed of 1500 - 4500 rad / s for 25 - 55 s; -1 -1 -1 ​​​​​​​​Spin coat for 25 - 55 s to perform the third spin coating to form a gradient polymer film containing one layer of PMMA and two layers of PVA;

[0051] (5) Continuously dry the fluorophlogopite sheet spin - coated with the polymer film on a heating stage at 45 - 90 °C for 5 - 25 min, and then continuously dry it at 90 - 130 °C for 20 - 40 min;

[0052] (6) Gently wipe the edge of the fluorophlogopite sheet with a cotton swab dipped in acetone to dissolve the PMMA at the bottom layer of the polymer film at the edge of the fluorophlogopite sheet to form a gap;

[0053] (7) Slowly drip ultrapure water into the gap between the polymer film and the edge of the fluorophlogopite sheet with a syringe, and use the surface tension of water to separate the polymer film from the fluorophlogopite sheet to obtain a polymer film carrying two - dimensional materials;

[0054] (8) Use tweezers to transfer the polymer film carrying two - dimensional materials to a clean target substrate, and place the target substrate on a heating stage to pre - heat at 50 - 100 °C for 10 - 60 s;

[0055] (9) Use a knife to cut out a hollow border on the 3M tape that is slightly wider than the polymer film, and stick it on the polymer film on the surface of the target substrate to fix the polymer film;

[0056] (10) Continue to heat and dry the target substrate at 50 - 100 °C for 10 - 30 min;

[0057] (11) Put the dried target substrate into a clean petri dish, use a syringe to suck up a certain amount of ultrapure water and slowly inject it along the glass wall until the ultrapure water covers the surface of the target substrate, heat the petri dish to 60 °C - 80 °C, and keep it warm for 20 - 40 min to dissolve PVA;

[0058] (12) Move the target substrate in (11) to a new petri dish, and repeat the operation steps in (11) to further dissolve PVA;

[0059] (13) Move the target substrate in (12) to a new petri dish, inject a certain amount of acetone until it covers the target substrate, let it stand for 15 - 30 min to dissolve PMMA, and then slowly suck out the acetone in the petri dish with a syringe (during this process, the petri dish must be kept stationary, otherwise it is easy to damage the transferred two - dimensional material sample).

[0060] Repeat the operation in (13) once, and then air - dry it naturally. Specific embodiments:

[0062] Example 1:

[0063] (1) Fix the fluorophlogopite sheet with BiOBr grown on it to the sample stage of the spin coater using double-sided tape, and then drop 0.15 ml of PMMA with a concentration of 0.03 g / ml onto the fluorophlogopite sheet with two-dimensional nanosheets grown on it. Spin coat at a low speed of 500 rad / s for 15 s and at a high speed of 2000 rad / s for 40 s to perform the first spin coating; -1 -1 -1

[0064] (2) Dry the spin-coated fluorophlogopite sheet on a heating stage at 50 °C for 30 s;

[0065] (3) Drop 0.2 ml of PVA with a concentration of 0.1 g / ml onto the fluorophlogopite sheet spin-coated in the first step. Spin coat at a low speed of 500 rad / s for 15 s and at a high speed of 2000 rad / s for 40 s to perform the second spin coating; -1 -1 -1

[0066] (4) Drop 0.25 ml of PVA with a concentration of 0.2 g / ml onto the fluorophlogopite sheet spin-coated with PVA. Spin coat at a low speed of 500 rad / s for 15 s and at a high speed of 2000 rad / s for 40 s to perform the third spin coating, forming a gradient polymer film containing one layer of PMMA and two layers of PVA; -1 -1 -1

[0067] (5) Continuously dry the fluorophlogopite sheet spin-coated with the polymer film in (4) on a heating stage at 60 °C for 10 min, and then continuously dry it at 110 °C for 20 min;

[0068] (6) Gently wipe the edge of the fluorophlogopite sheet with a cotton swab dipped in acetone to dissolve the PMMA at the bottom layer of the polymer film at the edge of the fluorophlogopite sheet, forming a gap;

[0069] (7) Slowly drop ultrapure water into the gap at the edge between the polymer film and the fluorophlogopite sheet with a syringe, and use the surface tension of water to separate the polymer film from the fluorophlogopite sheet to obtain a polymer film carrying two-dimensional materials;

[0070] (8) Use tweezers to transfer the polymer film carrying two-dimensional materials to a clean target substrate, and place the target substrate on a heating stage to preheat at 75 °C for 30 s;

[0071] (9) Use a knife to draw a hollow border on the 3M tape that is slightly wider than the polymer film, and stick it on the polymer film on the surface of the target substrate to fix the polymer film;

[0072] (10) Continue to heat and dry the target substrate at 75 °C for 20 min;​​​​​​​​​

[0073] (11) Place the dried target substrate into a clean petri dish, suck up a certain amount of ultrapure water with a syringe and slowly inject it along the glass wall until the ultrapure water covers the surface of the target substrate. Heat the petri dish to 70 °C and keep it warm for 25 min to dissolve the PVA.

[0074] (12) Transfer the target substrate in (11) to a new petri dish and repeat the operation steps in (11) to further dissolve the PVA.

[0075] (13) Transfer the target substrate in (12) to a new petri dish, inject a certain amount of acetone until it covers the target substrate, let it stand for 20 min to dissolve the PMMA, and then slowly suck out the acetone in the petri dish with a syringe (during this process, it is necessary to ensure that the petri dish is stationary, otherwise it is easy to damage the transferred two-dimensional material sample).

[0076] (14) Repeat the operation in (13) once, and then air dry it naturally.

[0077] Example 2:

[0078] (1) Fix the fluorophlogopite sheet with WS2 grown on it on the sample stage of the spin coater with double-sided tape, and then drop 0.5 ml of PMMA with a concentration of 0.05 g / ml onto the fluorophlogopite sheet with two-dimensional nanosheets grown on it, and spin coat at a low speed of 500 rad / s for 20 s and at a high speed of 2000 rad / s for 40 s to perform the first spin coating. -1 of PMMA drop 0.5 ml onto the fluorophlogopite sheet with two-dimensional nanosheets grown on it, spin coat at a low speed of 500 rad / s -1 for 20 s and at a high speed of 2000 rad / s -1 for 40 s to perform the first spin coating.

[0079] (2) Dry the spin-coated fluorophlogopite sheet on the heating table at 50 °C for 30 s.

[0080] (3) Drop 0.25 ml of PVA with a concentration of 0.15 g / ml onto the fluorophlogopite sheet spin-coated in the first step, spin coat at a low speed of 500 rad / s -1 for 20 s and at a high speed of 2000 rad / s -1 for 30 s to perform the second spin coating. -1 Spin coat for 30 s to perform the second spin coating.

[0081] (4) Drop 0.3 ml of PVA with a concentration of 0.25 g / ml onto the fluorophlogopite sheet spin-coated with PVA, spin coat at a low speed of 500 rad / s -1 for 15 s and at a high speed of 2000 rad / s -1 for 25 s to perform the third spin coating to form a gradient polymer film containing one layer of PMMA and two layers of PVA. -1 Spin coat for 25 s to perform the third spin coating to form a gradient polymer film containing one layer of PMMA and two layers of PVA.

[0082] (5) The fluorophlogopite mica sheet spin-coated with the polymer film in (4) is continuously dried on a heating table at 80 °C for 15 min, and then continuously dried at 105 °C for 30 min;

[0083] (6) Gently wipe the edge of the fluorophlogopite mica sheet with a cotton swab dipped in acetone to dissolve the PMMA at the bottom layer of the polymer film at the edge of the fluorophlogopite mica sheet, forming a gap;

[0084] (7) Slowly drip ultrapure water into the gap between the polymer film and the edge of the fluorophlogopite mica sheet with a syringe, and use the surface tension of water to separate the polymer film from the fluorophlogopite mica sheet to obtain a polymer film carrying two-dimensional materials;

[0085] (8) Use tweezers to transfer the polymer film carrying two-dimensional materials to a clean target substrate, and place the target substrate on a heating table to preheat at 75 °C for 20 s;

[0086] (9) Use a knife to draw a hollow border slightly wider than the polymer film on the 3M tape, and stick it on the polymer film on the surface of the target substrate to fix the polymer film;

[0087] (10) Continue to heat and dry the target substrate at 75 °C for 20 min;

[0088] (11) Put the dried target substrate into a clean petri dish, suck a certain amount of ultrapure water with a syringe and slowly inject it along the glass wall until the ultrapure water covers the surface of the target substrate, heat the petri dish to 75 °C, and keep it warm for 20 min to dissolve PVA;

[0089] (12) Move the target substrate in (11) to a new petri dish, and repeat the operation steps in (11) to further dissolve PVA;

[0090] (13) Move the target substrate in (12) to a new petri dish, inject a certain amount of acetone until it covers the target substrate, let it stand for 30 min to dissolve PMMA, and then slowly suck out the acetone in the petri dish with a syringe (during this process, the petri dish must be kept stationary, otherwise it is easy to damage the transferred two-dimensional material sample).

[0091] (14) Repeat the operation in (13) once, and then air dry it naturally.

[0092] Example 3:

[0093] (1) Fix the fluorophlogopite mica sheet grown with BiOI on the sample stage of the spin coater with double-sided tape, and then drop 0.2 ml of PMMA with a concentration of 0.05 g ml -1 onto the fluorophlogopite mica sheet grown with two-dimensional nanosheets, spin coat at a low speed of 600 rad s -1 for 15 s, and at a high speed of 2500 rad s-1 Spin coat for 30 s for the first spin coating step;

[0094] (2) Dry the spin-coated fluorophlogopite sheet on a heating stage at 60 °C for 25 s;

[0095] (3) Drop 0.3 ml of PVA with a concentration of 0.15 g / ml onto the fluorophlogopite sheet spin-coated in the first step, and spin coat at a low speed of 600 rad / s for 15 s and then at a high speed of 2500 rad / s for 30 s for the second spin coating step; -1 -1 -1

[0096] (4) Drop 0.25 ml of PVA with a concentration of 0.25 g / ml onto the fluorophlogopite sheet spin-coated with PVA, and spin coat at a low speed of 600 rad / s for 20 s and then at a high speed of 2500 rad / s for 30 s for the third spin coating step to form a gradient polymer film containing one layer of PMMA and two layers of PVA; -1 -1 -1

[0097] (5) Continuously dry the fluorophlogopite sheet spin-coated with the polymer film in (4) on a heating stage at 60 °C for 10 min, and then continuously dry at 100 °C for 40 min;

[0098] (6) Gently wipe the edge of the fluorophlogopite sheet with a cotton swab dipped in acetone to dissolve the PMMA at the bottom layer of the polymer film at the edge of the fluorophlogopite sheet to form a gap;

[0099] (7) Slowly drop ultrapure water into the gap at the edge between the polymer film and the fluorophlogopite sheet with a syringe, and use the surface tension of water to separate the polymer film from the fluorophlogopite sheet to obtain a polymer film carrying two-dimensional materials;

[0100] (8) Transfer the polymer film carrying two-dimensional materials to a clean target substrate with tweezers, and place the target substrate on a heating stage to preheat at 75 °C for 40 s;

[0101] (9) Use a knife to draw a hollow border on the 3M tape that is slightly wider than the polymer film, and stick it on the polymer film on the surface of the target substrate to fix the polymer film;

[0102] (10) Continue to heat and dry the target substrate at 75 °C for 25 min;

[0103] (11) Put the dried target substrate into a clean petri dish, suck a certain amount of ultrapure water with a syringe and slowly inject it along the glass wall until the ultrapure water covers the surface of the target substrate, heat the petri dish to 70 °C and keep it warm for 25 min to dissolve the PVA;

[0104] ​​​​​​(12) Transfer the target substrate in (11) to a new petri dish, and repeat the operation steps in (11) to further dissolve PVA;

[0105] (13) Transfer the target substrate in (12) to a new petri dish, inject a certain amount of acetone until it covers the target substrate, let it stand for 20 min to dissolve PMMA, and then slowly suck out the acetone in the petri dish with a syringe (during this process, it is necessary to ensure that the petri dish is stationary, otherwise it is easy to damage the transferred two-dimensional material sample).

[0106] Repeat the operation in (13) once, and then air dry naturally.

Claims

1. A method for precisely transferring large-area two-dimensional materials, characterized in that The steps are as follows: Step 1: Spin-coat PMMA on the fluorophlogopite sheet growing with two-dimensional materials, and dry it to form a PMMA polymer film; continue to spin-coat two layers of PVA gradient polymer film on the PMMA polymer film, and then dry it to form a gradient polymer film containing one layer of PMMA and two layers of PVA; Step 2: Wipe the edge of the fluorophlogopite sheet with acetone to dissolve the PMMA at the bottom layer of the polymer film at the edge of the fluorophlogopite sheet, forming a gap; Step 3: Slowly drop ultrapure water into the gap at the edge of the polymer film and the substrate, and use the surface tension of water to separate the polymer film from the fluorophlogopite sheet to obtain the polymer film carrying two-dimensional materials; Step 4: After transferring the polymer film carrying two-dimensional materials to the target substrate and preheating it, paste a 3M tape with a hollow border on the polymer film on the surface of the target substrate to fix the polymer film, and continue to heat and dry the target substrate; The 3M tape with the hollow border is wider than the polymer film; Step 5: Put the dried target substrate into a container, inject ultrapure water and slowly pour it along the glass wall until the ultrapure water covers the surface of the target substrate, heat the container and keep it warm to dissolve PVA; Take out the target substrate and put it into another container, repeat this step to further dissolve PVA; Step 6: Move the target substrate to another container, inject acetone until it covers the target substrate, let it stand for 15 - 30 min to dissolve PMMA, and then slowly suck out the acetone in the petri dish with a syringe; The container remains stationary so that the transferred two-dimensional materials are not damaged; Repeat this step, and then air-dry it to transfer the two-dimensional materials to the target substrate; The concentration of the PMMA is 0.005 - 0.05 g / ml -1 ; In the step 1, the first layer of PVA is spin-coated at a low speed of 200 - 1000 rad s -1 for 10 - 30 s, and then at a high speed of 1500 - 4500 rad s -1 for 25 - 55 s. The concentration of the first layer of PVA is 0.01 - 0.15 g ml -1 ; In the step 1, the second layer of PVA is spin-coated at a low speed of 200 - 1000 rad s -1 for 10 - 30 s, and then at a high speed of 1500 - 4500 rad s -1 for 25 - 55 s. The concentration of the second layer of PVA is 0.15 - 0.3 g ml -1 ; The preheating on the target substrate in Step 4 is: place the target substrate on a heating table and preheat it at 50 - 100 °C for 10 - 60 s; In Step 5, heat the container to 60 °C - 80 °C and keep it warm for 20 - 40 min to dissolve PVA.

2. The method for precisely transferring large-area two-dimensional materials according to claim 1, wherein: In the said step 1, the PMMA is spin-coated at a low speed of 200 - 1000 rad s -1 for 10 - 30 s, and then at a high speed of 1500 - 4500 rad s -1 for 25 - 55 s.

3. The method for precisely transferring a large-area two-dimensional material according to claim 1, characterized in that: The drying after spin-coating PMMA is to dry the spin-coated fluorophlogopite sheet on a heating table at 50 - 60 °C for 20 - 60 s.

4. The method for precisely transferring a large-area two-dimensional material according to claim 1, wherein: The drying of spin-coated PVA is to continuously dry the fluorophlogopite sheet with the polymer film on a heating table at 45 - 90 °C for 5 - 25 min, and then continuously dry it at 90 - 130 °C for 20 - 40 min.

5. The method for precisely transferring large-area two-dimensional materials according to claim 1, characterized in that: The continued heating of the target substrate after pasting the 3M tape in Step 4 is: heat and dry it at 50 - 100 °C for 10 - 30 min.

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