A method for transferring a graphene film

Abstract

The present invention provides a method for transferring a graphene film, comprising the following steps: S1, dissolving rosin in an ethyl acetate organic solvent to obtain a rosin solution, coating the rosin solution on the graphene side of the growth substrate / graphene, and drying to obtain a growth substrate / graphene / rosin composite structure; S2, coating a toughening agent with an appropriate concentration on the rosin layer and then drying to obtain a growth substrate / graphene / rosin / toughening agent composite structure, wherein the toughening agent is syrup; S3, removing the growth substrate in the composite structure obtained in step S2 to obtain a graphene / rosin / toughening agent composite structure; S4, loading the composite structure obtained in step S3 onto a target substrate, drying, and then sequentially removing the toughening agent and rosin to obtain a target substrate / graphene structure. By introducing syrup as a toughening agent, the present invention improves the disadvantage that rosin is brittle and easy to break, and realizes the non-destructive transfer of large-area graphene films such as A4 and A3 sizes.

Description

Technical Field

[0001] The present invention belongs to the field of graphene, and specifically relates to a highly clean and non-destructive transfer of large-size graphene films. Background Art

[0002] Graphene is a honeycomb two-dimensional material composed of carbon atoms bonded in a sp2 hybridization manner. Since its successful preparation in 2004, it has become the most popular two-dimensional new material due to its excellent electrical conductivity, thermal conductivity, and mechanical properties. The research on it involves controllable synthesis, morphology regulation, doping modification, application exploration, and industrialization transformation, etc.

[0003] In the mainstream synthesis methods of graphene, the CVD (Chemical Vapor Deposition) method assembles active carbon substances generated by the cracking of carbon sources into graphene with adjustable number of layers from bottom to top on catalytic substrates such as copper and nickel, and is recognized as a method for preparing high-quality graphene films. Currently, graphene films grown by the CVD method have been widely applied in fields such as information storage, information display, energy devices, and biosensing. However, for specific application examples such as chips for information storage and processing and flexible screens in information display, the CVD graphene films on the growth substrate usually cannot be directly used and need to be transferred to other target substrates, such as silicon wafers and PET, before further use.

[0004] Since CVD graphene films generally have an atomic thickness, in order to prevent film breakage during the transfer process, a suitable transfer support medium needs to be used for transfer. Commonly used transfer media include thermal release tapes, self-adhesive tapes, PMMA, pentacene, etc. However, these transfer media usually have some drawbacks. For example, thermal release tapes and self-adhesive tapes leave difficult-to-remove glue dots after transfer, and the graphene is prone to breakage during the adhesive release and tearing process; PMMA, due to its macromolecular chain structure, is not easily soluble in organic solvents, resulting in its inability to be completely removed from graphene, and it forms sp3 hybridization with graphene, leading to an increase in the defect degree of graphene, affecting the surface flatness and performance of graphene. Although some studies use intermediate layers such as tetrahydrofuran to isolate the direct contact between graphene and PMMA, the subsequent acetone vapor fumigation and cleaning process is too complex and time-consuming; while small molecules such as pentacene have good solubility, but due to their insufficient strength and π-π interaction with graphene, they also cause film breakage and incomplete removal of the transfer medium. In summary, all transfer media face the problems of film breakage after transfer and residue of the transfer medium. Moreover, as the size of the graphene film increases, the transfer difficulty and the film breakage rate after transfer will increase. Therefore, there is less research on the transfer process methods for large-size graphene films such as A4 and A3 currently.

[0005] Therefore, a suitable transfer medium should have sufficient support strength, good solubility in organic solvents, and low adsorption energy. Rosin, a natural organic polymer material, has been shown in related research to have good dissolution ability, sufficient strength, and low adsorption energy, and can be used for the transfer of large-area ultra-clean graphene films. Currently, the largest size of the graphene film transferred using rosin as the transfer medium is 10*10 cm. Although rosin has sufficient strength, it will be found in actual operation that its texture is brittle, and when the film area is too large or there is a slight disturbance during the transfer process, the film will crack and break, resulting in transfer failure. Summary of the Invention

[0006] To solve the above technical problems, based on using rosin as the transfer medium, the present invention prepares a composite transfer medium through a toughening method, achieving the lossless and highly clean transfer of large-area graphene films of A4 and A3 sizes.

[0007] The present invention provides a method for transferring a graphene film, comprising the following steps:

[0008] S1. Dissolve rosin in an ethyl acetate organic solvent to obtain a rosin solution, coat the rosin solution on the graphene side of the growth substrate / graphene, and dry to obtain a growth substrate / graphene / rosin composite structure;

[0009] S2. Coat a suitable concentration of toughening agent on the rosin layer and dry to obtain a growth substrate / graphene / rosin / toughening agent composite structure, wherein the toughening agent is syrup;

[0010] S3. Remove the growth substrate in the composite structure obtained in step S2 to obtain a graphene / rosin / toughening agent composite structure;

[0011] S4. Load the composite structure obtained in step S3 onto a target substrate, dry, and then remove the toughening agent and rosin in sequence to obtain a target substrate / graphene structure.

[0012] Preferably, the viscosity of the toughening agent, i.e., syrup, is 1100 - 1600 mPa·S. Preferably, the viscosity of the syrup is 1400 - 1500 mPa·S.

[0013] Preferably, the toughening agent is one or more of fructose syrup, glucose syrup, malt syrup, and sucrose syrup;

[0014] And / or, the toughening agent undergoes a caramelization reaction to impart a suitable viscosity.

[0015] Preferably, the concentration of the rosin solution is 20 - 50%.

[0016] Preferably, the concentration of the rosin solution is 40 - 45%.

[0017] Preferably, before coating a toughening agent with a suitable concentration on the rosin layer, it further includes step S11 of pre-etching the side of the growth substrate of the dried growth substrate / graphene / rosin composite structure away from the graphene, so as to remove the defective graphene grown during the chemical vapor deposition growth process and impurity carbon clusters.

[0018] Preferably, the pre-etching treatment is specifically carried out using an etching solution, and the etching solution is a mixed solution of ferric chloride hexahydrate and hydrochloric acid. The concentration of ferric chloride hexahydrate is 0.5 - 2 mol / L, and the concentration of hydrochloric acid is 1.5 - 6 mol / L.

[0019] Preferably, removing the toughening agent in step S4 is specifically as follows: immersing the target substrate / graphene / rosin / toughening agent composite structure in deionized water for soaking to obtain the target substrate / graphene / rosin composite structure.

[0020] Preferably, removing the rosin in step S4 is specifically as follows:

[0021] a. Immerse the target substrate / graphene / rosin composite structure into a cleaning tank filled with acetone solution and slowly rinse it for 0.5 - 2 min, then change to a clean acetone solution and continue to slowly rinse it for 0.5 - 2 min. Repeat the liquid-changing / rinsing step 2 - 4 times;

[0022] b. Rinse it with ethyl valerate solution for 0.5 - 2 min to obtain the target substrate / graphene structure.

[0023] Preferably, this method for transferring the graphene film further includes step S0 of fixing and sealing the edge of the growth substrate / graphene.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] Introducing syrup with a suitable viscosity as a toughening agent improves the disadvantage that rosin is brittle and easy to break, and realizes the lossless transfer of large-area graphene films of A4 and A3 sizes;

[0026] Syrup with a suitable viscosity can provide necessary toughness and strength. The syrup is easily soluble in water and can be quickly and conveniently removed completely without residue after transfer. It forms a composite transfer medium with rosin and synergistically realizes the transfer of large-area ultra-clean graphene films;

[0027] This method is not only applicable to the transfer of large-area graphene to flexible substrates such as PET, but also applicable to the transfer onto rigid substrates such as glass, silicon, silicon / silica, and sapphire;

[0028] It is a simple, efficient, and green process for realizing the clean and lossless transfer of large-area graphene. Description of the Drawings

[0029] Figure 1 SEM characterization diagram of the transferred thin film in Example 1

[0030] Figure 2 AFM characterization diagrams of the thin film before and after transfer in Example 1

[0031] Figure 3 Actual process diagram of the transfer process in Example 1

[0032] Figure 4 Actual effect diagram of Comparative Example 1

[0033] Figure 5 SEM characterization diagram of the transferred thin film in Comparative Example 3

[0034] Figure 6 SEM characterization diagram of the transferred thin film in Comparative Example 4 Specific implementation manners

[0035] The technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0036] The purpose of the present invention is to provide a method for transferring a graphene thin film to achieve lossless and highly clean transfer of large-size graphene thin films such as A4 / A3, including the following steps:

[0037] S1. Dissolve rosin in an ethyl acetate organic solvent to obtain a rosin solution, coat the rosin solution on the graphene side of the growth substrate / graphene, and dry to obtain a growth substrate / graphene / rosin composite structure;

[0038] S2. Coat a suitable concentration of toughening agent on the rosin layer and dry to obtain a growth substrate / graphene / rosin / toughening agent composite structure, and the toughening agent is syrup;

[0039] S3. Remove the growth substrate in the composite structure obtained in step S2 to obtain a graphene / rosin / toughening agent composite structure;

[0040] S4. Load the composite structure obtained in step S3 onto a target substrate, dry, and then remove the toughening agent and rosin in sequence to obtain a target substrate / graphene structure.

[0041] In an embodiment of the present invention, the rosin solution in step S1 is obtained by dissolving it in an ethyl acetate organic solvent. Specifically, the ethyl acetate organic solution is ethyl lactate, and the concentration of the rosin solution is controlled within 20 - 50%. More preferably, the concentration can be controlled within 40 - 45%. This is because when the concentration is lower than the given range, the film after spraying cannot provide the required support strength and the transfer operation cannot be carried out. While when it is higher than the given range, the dissolution of rosin becomes a problem as its solubility is limited. At this time, the high-concentration rosin solution will show the phenomenon of precipitation and sandification, which is not only unfavorable for spraying operations and clogs the nozzle, but also the film formation after spraying has poor continuity, there is a phenomenon of sand falling on the surface after drying, and the brittleness of the rosin increases after excessive concentration and sandification, resulting in a decrease in the ability to resist external force disturbances.

[0042] In some specific embodiments, when coating the rosin solution on the graphene side of the growth substrate / graphene, the spin coating or spraying method can be selected. Both spin coating and spraying are to make the rosin solution evenly coated on the graphene film. However, since spin coating requires direct contact with the growth substrate / graphene composite structure, the larger the area of this composite structure, the greater the centrifugal force it receives during the operation, and the growth substrate is likely to be stressed and form wrinkles. In this application, the specific coating method can be selected according to the specific size of the growth substrate / graphene composite structure. But for better applicability to the transfer of large-area graphene films, the spraying method is preferably used. Specifically, an appropriate amount of the prepared rosin solution with a certain concentration is poured into a spray gun to spray the graphene film. During the spraying process, it is only necessary to keep the glue layer uniform. The spraying dosage of the rosin solution is approximately 20 ml / sheet.

[0043] In an embodiment of the present invention, the purpose of the drying treatment in step S1 is to volatilize the ethyl acetate solvent in the rosin solution, form a film and provide a certain strength. The drying temperature and time are not limited. For example, the drying temperature can be set at 60 °C and the drying time can be set at 120 min.

[0044] In an embodiment of the present invention, the toughening agent in step S2 is selected from syrup, which is mainly used in the food field as a sweetener, additive, preservative, and moisturizer. The inventors found that syrup has a certain viscosity, has a certain toughness and strength after hardening, and is easily soluble in water. After forming a composite transfer medium with rosin, it can improve the shortcomings of rosin being brittle and fragile, and synergistically realize the transfer of large-area ultra-clean graphene films. The viscosity of the syrup is preferably 1100-1600mPa.S. If the viscosity is too high, the brushing operation of the syrup is not easy to carry out, and the syrup will seriously stick to the brushing tool and the rosin layer. The high-viscosity syrup has poor fluidity, which is not conducive to the realization of uniform film formation. The film layer is highly undulating, which is not conducive to the development of the later scooping step and the perfect fit of the film on the target substrate, resulting in bubbles, breakage and wrinkles. If the viscosity is too low, the syrup will spontaneously gather into small droplets after brushing, and it is impossible to continuously form a film on the surface of the rosin layer, and it cannot provide the necessary strength and toughness, resulting in toughening failure, and it is impossible to achieve large-area lossless transfer. More preferably, the viscosity of the syrup is selected to be 1400-1500mPa.s.

[0045] In some specific embodiments, the toughening agent is one or more of fructose syrup, glucose syrup, maltose syrup, and sucrose syrup. The viscosity of commercially available single syrup or mixed syrup is difficult to meet the requirements of the present invention. It is necessary to mix with deionized water and heat to produce a caramelization reaction to give the syrup a suitable viscosity, thereby ensuring its suitable strength and toughness.

[0046] In the embodiment of the present invention, the purpose of the drying treatment in step S2 is to harden the surface of the syrup to facilitate the subsequent transfer of the graphene film. The drying method, temperature and time are not limited, for example, air drying can be performed at a temperature of room temperature to 40°C.

[0047] In an embodiment of the present invention, the method of removing the growth substrate in step S3 can be selected as etching treatment or chemical stripping. Preferably, etching treatment is adopted, which is specifically as follows: a certain amount of etching solution is poured into an etching container, and the etching solution is selected as a mixture of ferric chloride hexahydrate and hydrochloric acid. Because other etchants such as ammonium persulfate, sodium persulfate, and potassium persulfate are used, bubbles will be generated during the etching process, and the bubbles will gather under the etched film and cannot be completely removed and driven away, resulting in the sealing of bubbles during the later scooping and bonding process, which causes the graphene film to rupture. Therefore, a ferric chloride solution that does not generate bubbles is selected, and the concentration of the ferric chloride hexahydrate is 0.5-2mol / L, and the concentration of the hydrochloric acid is 1.5-6mol / L. Here, the concentration ratio of ferric chloride to hydrochloric acid is controlled at 1:3, because Fe 3+ It is easy to undergo hydrolysis reaction to generate Fe(OH)3, commonly known as rust. The formation of rust will cause Fe 3+The etching process of the redox reaction with the growth substrate is weakened due to the consumption, and rust will remain on the surface of the graphene film as a pollutant and impurity, significantly affecting the performance of the film in later applications. Its hydrolysis equation is Fe 3+ + 3H2O <==> Fe(OH)3 + 3H + , in order to effectively inhibit the occurrence of this hydrolysis process, the molar concentration ratio of ferric chloride to hydrochloric acid is set to 1:3. The concentration of ferric chloride is set to 0.5 - 2 mol / L because when the concentration is too low, the etching time will be prolonged and the etching will be incomplete, resulting in the residue of the growth substrate. When the concentration is too high, due to the too fast etching speed, the probability of film rupture will increase and unnecessary resource waste will be caused. The dosage of the etchant is such that a liquid depth of about 1 cm can be formed in the container. Transfer the growth substrate / graphene / rosin / toughening agent composite structure treated in step S2 to a flat plate, and then obliquely immerse one side of the flat plate into the etching solution so that one side of the growth substrate / graphene / rosin / toughening agent composite structure comes into contact with the etching solution. After contact, slowly withdraw the flat plate so that the growth substrate / graphene / rosin / toughening agent composite structure floats entirely on the etching solution until the growth substrate is completely etched away. Subsequently, drain the etching waste liquid and at the same time add deionized water until the liquid in the container changes from dark green to clear and the pH is neutral. The purpose of the oblique immersion and slow withdrawal is to avoid the generation and retention of bubbles under the growth substrate / graphene / rosin / toughening agent composite structure, which will affect the etching and cause the rupture of the graphene film.

[0048] In the embodiment of the present invention, the target substrate in step S4 can be a flexible substrate such as PET, or a rigid substrate such as glass, silicon, silicon / silicon dioxide, and sapphire.

[0049] The purpose of the drying treatment in step S4 is to remove moisture and increase the bonding strength between the graphene and the target substrate. The specific drying time and temperature are determined according to the product size until the color at the contact interface between the product and the target substrate changes from water cyan to transparent.

[0050] The removal of the toughening agent in step S4 is specifically: Immerse the target substrate / graphene / rosin / toughening agent composite structure in deionized water to obtain the target substrate / graphene / rosin composite structure. This benefits from the water solubility of the syrup as a toughening agent, and it can be removed without residue in deionized water, thus realizing the high-purity transfer of the graphene film.

[0051] The specific method for removing rosin in step S4 is as follows: a. Immerse the target substrate / graphene / rosin composite structure into a cleaning tank filled with acetone solution and slowly rinse it for 0.5 - 2 min. Then, replace it with clean acetone solution and continue to slowly rinse it for 0.5 - 2 min. Repeat the liquid replacement - rinsing step 2 - 4 times; b. Rinse it with ethyl valerate solution for 0.5 - 2 min to obtain the target substrate / graphene structure.

[0052] In some specific embodiments, the method for transferring the graphene film further includes step S0 of fixing and sealing the growth substrate / graphene, specifically: Take a glass sheet with a slightly larger area, place the growth substrate / graphene composite structure flat on it, and then use tape to fix and seal the periphery of the growth substrate / graphene composite structure and press it firmly to prevent the film from wrinkling and bending, and prevent rosin solution from leaking under the growth substrate / graphene composite structure during the rosin solution coating process, which may affect the removal of the growth substrate in the later stage.

[0053] The inventor further found that during the CVD graphene growth process, incomplete graphene and impurity carbon clusters will grow on the back of the growth substrate. The existence of these impurities will significantly reduce the cleanliness of the finally transferred graphene film and significantly increase the surface roughness, thus affecting the actual application of the film. For example, when applied to the flexible display field, the residual contaminants in the graphene film will significantly increase the leakage current of the film, resulting in short - circuit phenomena and device failure. Therefore, in some specific embodiments, before coating a toughening agent with an appropriate concentration on the rosin layer, it further includes step S11 of pre - etching the side of the growth substrate / graphene / rosin composite structure where the growth substrate is away from the graphene, so as to remove the incomplete graphene and impurity carbon clusters grown during the chemical vapor deposition growth process. The pre - etching treatment refers to treating with an etching solution, and the etching solution is a mixed solution of ferric chloride hexahydrate and hydrochloric acid. The concentration of ferric chloride hexahydrate is 0.5 - 2 mol / L, and the concentration of hydrochloric acid is 1.5 - 6 mol / L. More specifically, the specific steps of pre - etching are: Place the growth substrate / graphene / rosin composite structure processed in step S1 on a glass plate with the rosin layer facing down, and press it around with a pressing strip. The height of the pressing strip is about 3 mm to create an enclosed space. Then, pour an appropriate amount of etching solution for etching. After etching for 0.5 - 2 min, pour out the etching solution and rinse it clean with deionized water. During the pre - etching process, only a part of the bottom layer of the growth substrate is removed, rather than etching the entire growth substrate.

[0054] The following further illustrates the content of the present invention with specific embodiments, but it should not be construed as a limitation to the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well - known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field. Example 1

[0055] This example provides a method for transferring a graphene film, which includes the following steps:

[0056] S0. Take a high-borosilicate glass sheet with a slightly larger area, place the A4-sized copper-based graphene film flat on it, and then fix and seal the edges along the four sides of the film with PET tape and press it firmly.

[0057] S1. Weigh ethyl lactate and rosin blocks to prepare a rosin solution with a concentration of 42%wt. Then take 20 ml and pour it into a spray gun, and spray the graphene film evenly. After spraying, transfer it to a blast drying oven and dry it at 60 °C for 120 min to obtain a copper / graphene / rosin composite structure;

[0058] S11. After removing the copper / graphene / rosin composite structure processed in step S1, place it with the rosin layer facing down on another glass plate, press the four sides with a pressing strip to create an enclosed space, and then pour in an etching solution of ferric chloride with a concentration of 1 mol / L until a liquid layer with a depth of 2 mm is formed. After etching for 1 min, pour out the etching solution and rinse it clean with deionized water. Then transfer it to an oven and dry it at 70 °C until the water stains on the back are dry;

[0059] S2. Weigh 90 g of malt syrup, 30 g of sucrose and 120 ml of deionized water in a beaker, stir and heat at 250 °C for 20 min for a caramelization reaction to prepare a mixed sugar solution. The viscosity of the mixed sugar solution is 1429 mPa·S. Take out the film processed in step S11, turn it over so that its front side is facing up, then take 20 ml of the mixed sugar solution and pour it on the film and gently brush it evenly with a soft brush. Then dry it with forced air at 40 °C until the surface sugar solution hardens to obtain a copper / graphene / rosin / toughening agent composite structure;

[0060] S3. Pour the pre-prepared ferric chloride solution with a concentration of 1 mol / L into an etching container to form a liquid level depth of 1 cm. Then transfer the copper / graphene / rosin / toughening agent composite structure processed in step S2 to a flat plate, and then immerse one side of the flat plate obliquely into the etching solution so that one side of the copper / graphene / rosin / toughening agent composite structure comes into contact with the etching solution. After contact, slowly withdraw the flat plate so that the whole film floats on the etching solution until the copper substrate is completely etched away. Then drain the etching waste liquid, and at the same time add deionized water until the liquid in the container changes from dark green to clear and the pH is neutral to obtain a graphene / rosin / toughening agent composite structure.

[0061] S4. Cut the PET into appropriate sizes, then immerse it into an etching container to fish out the graphene / rosin / toughener composite structure obtained in step S3. After fishing out, place it vertically in a blast drying oven and dry it at 60 °C for 5 hours until the color at the contact interface between the film and the target substrate changes from water cyan to transparent. Then take out the dried graphene / rosin / toughener composite structure, place it face down in deionized water and soak for 10 min to remove the sugar layer, changing the water twice during this period. Subsequently, take it out and dry it at 60 °C until the water stains on the film surface are dry. After drying, immerse the film into a cleaning tank filled with acetone and gently wash it for 1 min, then change to clean acetone and continue to gently wash it for 1 min. Repeat the washing-liquid changing process 3 times, and finally wash it with ethyl valerate for 1 min.

[0062] Perform SEM characterization on the transferred PET-based graphene film. The results are as shown in the appendix Figure 1 It can be seen that the surface of the transferred graphene film is complete, without obvious microscale damage, and there are no metal particles and residues of the transfer medium on the surface;

[0063] Perform AFM characterization on the graphene film before and after transfer. The results are as shown in the appendix Figure 2 It shows that its root mean square roughness Rq is 14.8 nm and the average roughness Ra is 12.2 nm. When graphene grows on the copper foil surface, it replicates the morphology of the copper foil; after transfer, due to the relatively flat target substrate, the root mean square roughness Rq of the transferred film is 4.37 nm and the average roughness Ra is 3.02 nm. The results are better than those of the films transferred using PMMA as the transfer medium reported in the academic SCI literature "Defects Produced during Wet Transfer Affect the Electrical Properties of Graphene", "Ultraclean transfer of CVD-grown graphene and its application to flexible organic photovoltaic cells", and "Robust graphene wet transfer process through low molecular weight polymethylmethacrylate".

[0064] The transfer process of the graphene film provided in this example is as shown in the appendix Figure 3 Finally, a large-size target substrate graphene film that is flat and without damage is obtained. Comparative Example 1

[0065] Compared with Example 1, the process of coating the toughener in step S2 was not carried out, and the other steps were the same. The actual effects are as shown in the appendixFigure 4 As shown, the film is brittle and easy to break, unable to handle the transfer of large-size graphene films, and is only applicable to sizes ≤ 10 * 10 cm. Comparative Example 2

[0066] Compared with Example 1, the viscosities of the mixed sugar solutions in step S2 are 965 mPa·s respectively, and the other preparation steps are the same. The final result is that the concentration of the sugar solution is too low, and most of it is water. After brushing, the film-forming property of the sugar solution on the surface of the rosin layer is very poor, and it will aggregate into small droplets and cannot form a continuous film, resulting in the failure of toughening and the inability to carry out subsequent transfer work. Comparative Example 3

[0067] Compared with Example 1, the viscosities of the mixed sugar solutions in step S2 are 1839 mPa·s respectively, and the other preparation steps are the same. The final result is that the transfer fails. Due to the too high concentration and viscosity, it is difficult for the brush to move smoothly on the surface of the rosin layer during brushing. Slightly exerting force will cause the film to wrinkle and the rosin layer to break. In addition, the film-forming uniformity is not good, with uneven thickness, resulting in the failure of the later fishing work and the inability to fit flat on the surface of the PET substrate, and the graphene film folds and breaks, as Figure 5 shown. Comparative Example 4

[0068] Compared with Example 1, PMMA is selected as the toughening agent in step S2, and the method of removing PMMA is also changed to soaking in acetone solution for 30 min, and the other steps remain unchanged. From Figure 6 the SEM characterization diagram, it can be seen that there is obvious residue of the transfer medium PMMA on the surface of the graphene film of the target substrate finally obtained, and due to the long-term continuous soaking in acetone, the PET substrate has obvious swelling damage. Comparative Example 5

[0069] Compared with Example 1, the pre-etching treatment in step S11 is not carried out, and the other steps are the same. The final result is that obvious contrast difference dull areas can be seen in the transferred PET-based graphene film by naked eye observation, which come from the residual damaged graphene, amorphous carbon and etchant residues adsorbed and coated by amorphous carbon on the back. Comparative Example 6

[0070] Compared with Example 1, the concentration of the rosin solution in step S1 is 15%, and the other preparation steps are the same. The final result is that the transfer fails. The low-concentration rosin cannot provide the due strength to support the graphene, resulting in rupture during the etching process, and the etchant infiltrates into the sugar layer from the ruptured rosin layer, and part of the sugar layer is dissolved and damaged. Comparative Example 7

[0071] Compared with Example 1, the concentration of the rosin solution in step S1 is 52%, and the other preparation steps are the same. The final result is that the dissolution of the rosin solution becomes a problem. At this concentration, the color of the rosin solution is yellowish-white, and sandy particles can be seen with the naked eye inside. During spraying, the nozzle is blocked, and many sandy particles remain on the film surface after film formation and drying. They are easy to fall off when gently touched, and the whole film is brittle, resulting in transfer failure.

[0072] In this article, specific examples are used to elaborate on the principles and implementation methods of the present invention. The descriptions of the above examples are only used to help understand the method and its core idea of the present invention. The above are only the preferred implementation methods of the present invention. It should be noted that due to the limited nature of written expression and the objectively infinite specific structures, for those of ordinary skill in the art in this technical field, without departing from the principles of the present invention, several improvements, refinements or changes can be made, or the above technical features can be combined in an appropriate manner; these improvements, refinements, changes or combinations, or directly applying the concept and technical solution of the invention to other occasions without improvement, should all be regarded as the protection scope of the present invention.

Claims

1. A method for transferring a graphene film, characterized in that, It includes the following steps: S1. Dissolve rosin in ethyl acetate organic solvent to obtain a rosin solution, coat the rosin solution on the graphene side of the growth substrate / graphene, and dry it to obtain a growth substrate / graphene / rosin composite structure, where the concentration of the rosin solution is 20-45%; S11. Perform pre-etching treatment on the side of the growth substrate of the dried growth substrate / graphene / rosin composite structure away from graphene, so as to remove the defective graphene and impurity carbon clusters grown during the chemical vapor deposition growth process; S2. Coat a toughening agent with an appropriate concentration on the rosin layer and dry it to obtain a growth substrate / graphene / rosin / toughening agent composite structure, where the toughening agent is syrup, and the viscosity of the syrup is 1100-1600 mPa·S; S3. Remove the growth substrate in the composite structure obtained in step S2 to obtain a graphene / rosin / toughening agent composite structure; S4. Load the composite structure obtained in step S3 onto a target substrate, and after drying, remove the toughening agent and rosin in sequence to obtain a target substrate / graphene structure.

2. A transfer method of the graphene film as described in claim 1, characterized in that, The viscosity of the syrup is 1400-1500 mPa·S.

3. A method for transferring a graphene film as described in claim 2, characterized in that, The toughening agent is one or more of fructose syrup, glucose syrup, malt syrup, and sucrose syrup.

4. A method for transferring a graphene film as described in claim 2, characterized in that, The toughening agent undergoes a caramelization reaction to impart an appropriate viscosity.

5. A method for transferring a graphene film as described in claim 1, characterized in that, The concentration of the rosin solution is 40-45%.

6. A method for transferring a graphene film as described in claim 1, characterized in that, The pre-etching treatment is specifically to use an etching solution for treatment. The etching solution is a mixed solution of ferric chloride hexahydrate and hydrochloric acid, where the concentration of ferric chloride hexahydrate is 0.5-2 mol / L and the concentration of hydrochloric acid is 1.5-6 mol / L.

7. A method for transferring a graphene film as described in claim 1, characterized in that, The removal of the toughening agent in step S4 is specifically: Immerse the target substrate / graphene / rosin / toughening agent composite structure in deionized water to obtain a target substrate / graphene / rosin composite structure.

8. A method for transferring a graphene film as described in claim 1, characterized in that, The removal of rosin in step S4 is specifically: a. Immerse the target substrate / graphene / rosin composite structure in a cleaning tank filled with acetone solution and slowly rinse it for 0.5-2 min, then replace it with clean acetone solution and continue to slowly rinse it for 0.5-2 min, and repeat the liquid replacement-rinsing step 2-4 times; b. Rinse it with ethyl valerate solution for 0.5-2 min to obtain a target substrate / graphene structure.

9. A method for transferring a graphene film as described in claim 1, characterized in that, It also includes step S0, fixing and sealing the edge of the growth substrate / graphene.

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