Method for preparing complete graphene based on wet transfer

Abstract

The invention provides a method for preparing complete graphene based on wet transfer, which comprises the following steps: S1, spin-coating PMMA (Polymethyl Methacrylate) on the surface of graphene on a metal substrate to form a PMMA layer / graphene film / metal substrate sample; s2, etching the metal substrate by using an ammonium persulfate solution, and cleaning to obtain a PMMA layer / graphene film sample; s3, contacting the PMMA layer / graphene film sample with a FeCl2 / FeCl3 mixed solution for a period of time, cleaning, transferring the cleaned PMMA layer / graphene film sample to a target substrate, and drying to form a PMMA layer / graphene film / target substrate sample; s4, the PMMA layer is removed through acetone dissolution, and the graphene film completely attached to the target substrate is obtained. The method provided by the invention is simple and easy to implement, has good repeatability, can effectively improve the integrity of graphene transferred by a wet method, and can be used for transferring a large-area graphene film.

Description

Technical Field

[0001] The present invention belongs to the technical field of two-dimensional material transfer, and particularly relates to a method for preparing integral graphene based on wet transfer. Background Art

[0002] In recent years, the related research on growing graphene by chemical vapor deposition method has been gradually deepened, and the chemical vapor deposition growth process of high-quality graphene has been relatively mature. However, the graphene grown on the metal substrate cannot be directly applied in the fields of microelectronics, etc., but needs to go through a transfer process of transferring the graphene from the metal substrate to the target substrate adapted to the semiconductor process. Therefore, realizing the lossless transfer of graphene is the key to giving full play to the many application advantages of graphene in the fields of microelectronics, etc.

[0003] At present, the transfer processes of graphene are mainly divided into three types: wet etching transfer, bubble transfer, and dry transfer. However, both the bubble transfer and dry transfer methods face the dilemma of being difficult to achieve the complete transfer of graphene, so the wet etching transfer is still the most main method in the current graphene transfer. In the existing research on the wet etching transfer process of graphene, researchers have paid more attention to the improvement of the polymer support layer, while ignoring the impact of the metal etchant itself on the integrity of graphene. Ammonium persulfate solution is a typical metal etchant and has been widely used in the graphene transfer process. However, the residue of ammonium persulfate solution between the graphene and the target substrate will seriously affect the integrity of the transferred graphene. Moreover, it is actually difficult to remove the ammonium persulfate residue adsorbed on the lower surface of graphene only by simple deionized water washing operation.

[0004] Therefore, how to effectively and thoroughly remove the residue of ammonium persulfate solution on the lower surface of graphene has become the key to realizing the complete transfer of graphene and even the application of graphene thin films in the fields of microelectronics, etc. Summary of the Invention

[0005] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a method for preparing integral graphene based on wet transfer, which is used to solve the problem that the residue of ammonium persulfate solution between the graphene and the target substrate in the prior art seriously affects the integrity of the transferred graphene.

[0006] To achieve the above purpose and other related purposes, the present invention provides a method for preparing integral graphene based on wet transfer, and the method includes the following steps:

[0007] S1. Spin-coat PMMA on the surface of graphene on the metal substrate to form a PMMA layer / graphene thin film / metal substrate sample;

[0008] S2. Etch the metal substrate of the PMMA layer / graphene thin film / metal substrate sample with ammonium persulfate solution. After cleaning, a PMMA layer / graphene thin film sample is obtained.

[0009] S3. Bring the PMMA layer / graphene thin film sample into contact with the FeCl2 / FeCl3 mixed solution, and the side of the graphene thin film away from the PMMA layer is in contact with the liquid surface of the FeCl2 / FeCl3 mixed solution. After contacting for a period of time, wash with deionized water, then transfer the washed PMMA layer / graphene thin film sample onto the target substrate and dry it to form a PMMA layer / graphene thin film / target substrate sample.

[0010] S4. Dissolve and remove the PMMA layer of the PMMA layer / graphene thin film / target substrate sample with acetone to obtain a graphene thin film completely attached to the target substrate.

[0011] Preferably, the graphene on the metal substrate in step S1 is grown by chemical vapor deposition.

[0012] Preferably, the metal substrate in step S1 is a metal thin film or a metal foil, and the composition of the metal substrate includes one or a combination of copper, nickel, cobalt, and iron.

[0013] Preferably, the number of layers of the graphene thin film in step S1 is at least monolayer.

[0014] Preferably, the graphene thin film in step S1 is a continuous graphene thin film.

[0015] Preferably, the graphene thin film in step S1 is a discrete domain graphene thin film.

[0016] Preferably, the ammonium persulfate solution in step S2 is an aqueous solution of ammonium persulfate, and the concentration of the ammonium persulfate solution is 0.1 - 3 mol / L.

[0017] Preferably, when the PMMA layer / graphene thin film sample is brought into contact with the FeCl2 / FeCl3 mixed solution in step S3, specifically, the PMMA layer / graphene thin film sample floats on the FeCl2 / FeCl3 mixed solution.

[0018] Preferably, when the PMMA layer / graphene thin film sample is brought into contact with the FeCl2 / FeCl3 mixed solution in step S3, specifically, the PMMA layer / graphene thin film sample is immersed in the FeCl2 / FeCl3 mixed solution.

[0019] Preferably, the FeCl2 / FeCl3 mixed solution in step S3 refers to an aqueous mixed solution of FeCl2 and FeCl3. The concentration of FeCl2 in the FeCl2 / FeCl3 mixed solution is 0.4 - 4 mol / L, and the concentration of FeCl3 in the FeCl2 / FeCl3 mixed solution is 0.4 - 4 mol / L.

[0020] Preferably, the contact time between the side of the graphene film away from the PMMA layer and the FeCl2 / FeCl3 mixed solution in step S3 is 20 - 120 min.

[0021] Preferably, the target substrate in step S3 includes one of a Si / SiO2 substrate and a quartz substrate.

[0022] As described above, the method for preparing integral graphene based on wet transfer of the present invention has the following beneficial effects:

[0023] The method for preparing integral graphene based on wet transfer provided by the present invention is simple and easy to implement, has good repeatability, can effectively improve the integrity of the wet - transferred graphene, and can be used for the transfer of large - area graphene films. Moreover, the method provided by the present invention can effectively treat the residue of ammonium persulfate on the lower surface of graphene caused by wet transfer through a simple chemical reaction, improve the cleanliness of the transferred graphene, and thus improve the integrity of the transferred graphene. Description of the Drawings

[0024] Figure 1 It shows a schematic flow chart of preparing integral graphene based on wet transfer in a specific embodiment of the present invention.

[0025] Figure 2 It shows an optical microscope photograph of the transferred graphene on a Si / SiO2 substrate in Comparative Example 1 of the present invention. Figure 2 a is an optical microscope photograph (magnified 100 times) of the PMMA layer / graphene film / Si / SiO2 substrate sample before removing PMMA. Figure 2 b is an optical microscope photograph (magnified 50 times) of the graphene film / Si / SiO2 substrate sample after removing PMMA.

[0026] Figure 3 It shows an optical microscope photograph of the graphene film / Si / SiO2 substrate prepared in Example 1 of the present invention. Figure 3 a and Figure 3 b are respectively optical microscope photographs of single - layer graphene at magnifications of 100 times and 500 times. Figure 3 c and Figure 3 d are respectively optical microscope photographs of two - layer and more than two - layer graphene at magnifications of 100 times and 500 times.

[0027] Figure 4 Shown is the Raman spectrum of the graphene film / Si / SiO2 substrate prepared in Example 1 of the present invention. 4a shows the Raman spectra at three different positions of monolayer graphene, and 4b shows the Raman spectra at three different positions of bilayer graphene. Detailed implementation manners

[0028] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0029] Based on the prior art in the process of wet etching and transferring graphene, since the residue of ammonium persulfate solution between the graphene and the target substrate will seriously affect the integrity of the transferred graphene, simply relying on the operation of washing with deionized water actually makes it difficult to remove the ammonium persulfate residue adsorbed on the lower surface of the graphene.

[0030] Refer to Figure 1 , the present invention provides a method for preparing complete graphene based on wet transfer, and this method includes the following steps:

[0031] S1. Spin-coat PMMA on the surface of graphene on the metal substrate to form a PMMA layer / graphene film / metal substrate sample;

[0032] S2. Etch the metal substrate of the PMMA layer / graphene film / metal substrate sample with ammonium persulfate solution, and after washing, obtain a PMMA layer / graphene film sample;

[0033] S3. Contact the PMMA layer / graphene film sample with the FeCl2 / FeCl3 mixed solution, and the side of the graphene film away from the PMMA layer is in contact with the liquid surface of the FeCl2 / FeCl3 mixed solution. After contacting for a period of time, wash with deionized water, and then transfer the washed PMMA layer / graphene film sample to the target substrate and dry it to form a PMMA layer / graphene film / target substrate sample;

[0034] S4. Dissolve and remove the PMMA layer of the PMMA layer / graphene film / target substrate sample with acetone to obtain a graphene film completely attached to the target substrate, which is the graphene film / target substrate.

[0035] Specifically, the method for preparing complete graphene based on wet transfer in the specific embodiments of the present invention is simple and easy to implement, has good repeatability, and can effectively improve the integrity of wet-transferred graphene.

[0036] In addition, in step S2, the step of etching the metal substrate with an ammonium persulfate solution is specifically as follows: the PMMA layer / graphene thin film / metal substrate sample with PMMA spin-coated thereon is floated on the liquid surface of the ammonium persulfate solution, and wait until the metal substrate is etched clean. The side of the metal substrate away from the graphene thin film is in contact with the ammonium persulfate solution, and the side of the PMMA layer / graphene thin film faces upward and is exposed to the air. When dissolving the PMMA layer with acetone in step S4, preferably the dissolution temperature is 56°C.

[0037] As an example, in step S1, the graphene on the metal substrate is grown by chemical vapor deposition.

[0038] Specifically, the specific method of growing graphene on the metal substrate by chemical vapor deposition is not overly restricted here, and the chemical vapor deposition methods commonly used in the prior art are adopted.

[0039] As an example, in step S1, the metal substrate is a metal thin film or a metal foil, and the composition of the metal substrate includes one or a combination of copper, nickel, cobalt, and iron.

[0040] As an example, in step S1, the number of layers of the graphene thin film is at least monolayer.

[0041] As an example, in step S1, the graphene thin film is a continuous graphene thin film.

[0042] As an example, in step S1, the graphene thin film is a discrete domain graphene thin film.

[0043] As an example, in step S2, the ammonium persulfate solution is an aqueous solution of ammonium persulfate, and the concentration of the ammonium persulfate solution is 0.1 - 3 mol / L.

[0044] Specifically, the concentration of the ammonium persulfate solution can include any value within the range such as 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, etc., and can be specifically adjusted according to the actual situation. If a lower concentration of the ammonium persulfate solution is used, the amount of the ammonium persulfate solution needs to be increased to ensure that the metal substrate can be completely etched clean.

[0045] In the specific embodiment of the present invention, the cleaning is to preliminarily clean the ammonium persulfate residue on the lower surface of the graphene thin film with deionized water, and the specific number of cleaning times is not overly restricted here.

[0046] As an example, in step S3, the PMMA layer / graphene thin film sample is in contact with the FeCl2 / FeCl3 mixed solution, specifically, the PMMA layer / graphene thin film sample is floated on the FeCl2 / FeCl3 mixed solution.

[0047] As an example, in step S3, the PMMA layer / graphene film sample is in contact with the FeCl2 / FeCl3 mixed solution. Specifically, the PMMA layer / graphene film sample is immersed in the FeCl2 / FeCl3 mixed solution.

[0048] Specifically, based on the principle of chemical reaction, the ammonium persulfate residue on the lower surface of the graphene film in the wet transfer is consumed, thereby preventing it from decomposing on the lower surface of the graphene to form oxygen bubbles and improving the integrity of the transferred graphene. On the one hand, ferrous ions can undergo an oxidation-reduction reaction with persulfate ions to directly consume persulfate ions. On the other hand, hydrogen peroxide generated by the decomposition of persulfate ions in water will rapidly decompose under the catalysis of ferric ions, thus promoting the decomposition of persulfate ions. Therefore, the ammonium persulfate solution residue after etching will be completely decomposed during the contact with the FeCl2 / FeCl3 mixed solution.

[0049] As an example, the FeCl2 / FeCl3 mixed solution in step S3 refers to an aqueous mixed solution of FeCl2 and FeCl3. The concentration of FeCl2 in the FeCl2 / FeCl3 mixed solution is 0.4 - 4 mol / L, and the concentration of FeCl3 in the FeCl2 / FeCl3 mixed solution is 0.4 - 4 mol / L.

[0050] Specifically, the concentration of FeCl2 in the FeCl2 / FeCl3 mixed solution can include any value within the range such as 0.4 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, etc. The concentration of FeCl3 in the FeCl2 / FeCl3 mixed solution can include any value within the range such as 0.4 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, etc. If a FeCl2 / FeCl3 mixed solution with a lower concentration is used, a longer floating time will be required to ensure that the ammonium persulfate residue is completely depleted.

[0051] As an example, the contact time between the side of the graphene film away from the PMMA layer and the FeCl2 / FeCl3 mixed solution in step S3 is 20 - 120 min.

[0052] Specifically, the contact time can include any value within the range such as 20 min, 40 min, 60 min, 80 min, 100 min, 120 min, etc.

[0053] In a specific embodiment of the present invention, washing with deionized water is to wash away the FeCl2 / FeCl3 residue on the lower surface of the graphene film.

[0054] As an example, in step S3, the target substrate includes one of a Si / SiO2 substrate and a quartz substrate.

[0055] To better understand the method for preparing integral graphene based on wet transfer in the present invention, the method for preparing integral graphene based on wet transfer in the present invention will be described below with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0056] Example 1

[0057] This example provides a method for preparing integral graphene based on wet transfer, and the method includes the following steps:

[0058] S1. Prepare a graphene sample grown by chemical vapor deposition on a metal substrate, and use a spin coater to spin-coat PMMA on the surface of the graphene on the metal substrate at a rotation speed of 2000 r / min to form a PMMA layer / graphene thin film / metal substrate sample.

[0059] S2. Prepare an ammonium persulfate solution with a concentration of 1 mol / L, float the PMMA layer / graphene thin film / metal substrate sample on the liquid surface of the ammonium persulfate solution to etch the metal substrate. After etching is complete, fish out the PMMA layer / graphene thin film and float it on the liquid surface of deionized water for cleaning, and repeat the cleaning 5 times to obtain a PMMA layer / graphene thin film sample.

[0060] S3. Prepare an FeCl2 / FeCl3 mixed solution containing 1 mol / L FeCl2 and 1 mol / L FeCl3, bring the PMMA layer / graphene thin film sample into contact with the FeCl2 / FeCl3 mixed solution, and make the side of the graphene thin film away from the PMMA layer in contact with the liquid surface of the FeCl2 / FeCl3 mixed solution. After contacting for 30 min, fish out and float it on the liquid surface of deionized water again, and repeat the cleaning 5 times. Then transfer the cleaned PMMA layer / graphene thin film sample to a Si / SiO2 substrate with an oxide layer thickness of 300 nm, and dry it until the water between the graphene thin film and the Si / SiO2 substrate completely evaporates to form a PMMA layer / graphene thin film / Si / SiO2 substrate sample.

[0061] S4. Immerse the PMMA layer / graphene thin film / Si / SiO2 substrate sample in acetone at 56 °C for 1 h, take it out, and obtain a graphene thin film completely attached to the Si / SiO2 substrate, which is the graphene thin film / Si / SiO2 substrate.

[0062] Refer to Figure 3 is an optical microscope photograph of the graphene thin film / Si / SiO2 substrate prepared in Example 1.Figure 3 a and Figure 3 b are optical microscope photos of single-layer graphene at magnifications of 100 times and 500 times respectively, Figure 3 c and Figure 3 d are optical microscope photos of bilayer and more than bilayer graphene (graphene films with distinguishable number of layers) at magnifications of 100 times and 500 times respectively; It can be seen from the figure that the graphene films transferred by this method are structurally intact and undamaged in a large area, indicating that this method can effectively improve the integrity of graphene.

[0063] Refer to Figure 4 is the Raman spectrum of the graphene film / Si / SiO2 substrate prepared in Example 1. 4a is the Raman spectra of three different positions of single-layer graphene, and 4b is the Raman spectra of three different positions of bilayer graphene; From Figure 4 a and 4b, it can be seen that the G peak and 2D peak of graphene near 1580 cm -1 and 2690 cm -1 clearly show the structure of graphene; the D peak of graphene near 1350 cm -1 is not obvious, which proves that the transferred graphene has high quality.

[0064] Example 2

[0065] This example provides a method for preparing integral graphene based on wet transfer, and this method includes the following steps:

[0066] S1. Prepare a graphene sample grown by chemical vapor deposition on a metal substrate, and use a spin coater to spin coat PMMA on the surface of graphene on the metal substrate at a speed of 1500 r / min to form a PMMA layer / graphene film / metal substrate sample;

[0067] S2. Prepare an ammonium persulfate solution with a concentration of 0.5 mol / L, float the PMMA layer / graphene film / metal substrate sample on the liquid surface of the ammonium persulfate solution to etch the metal substrate. After the etching is complete, fish out the PMMA layer / graphene film and re-float it on the liquid surface of deionized water for cleaning, and repeat the cleaning 5 times to obtain a PMMA layer / graphene film sample;

[0068] S3. Prepare an FeCl2 / FeCl3 mixed solution containing 1.5 mol / L FeCl2 and 0.6 mol / L FeCl3. Contact the PMMA layer / graphene film sample with the FeCl2 / FeCl3 mixed solution, and make the side of the graphene film away from the PMMA layer contact with the liquid surface of the FeCl2 / FeCl3 mixed solution. After 40 minutes of contact, fish it out and re-float it on the deionized water liquid surface, and repeat the cleaning 5 times. Then transfer the cleaned PMMA layer / graphene film sample onto a quartz substrate, and dry it until the water between the graphene film and the quartz substrate completely evaporates to form a PMMA layer / graphene film / quartz substrate sample;

[0069] S4. Immerse the PMMA layer / graphene film / quartz substrate sample in acetone at 56 °C for 1 hour, take it out, and obtain a graphene film completely attached to the quartz substrate, which is the graphene film / quartz substrate.

[0070] In this example, the transferred graphene film is structurally intact and unbroken in a large area, and is close to the integrity of the graphene prepared by transfer in Example 1.

[0071] Comparative Example 1

[0072] This comparative example provides a method for wet-transferring graphene commonly used in the prior art, and the specific steps are as follows:

[0073] Prepare a graphene sample grown by chemical vapor deposition on a metal substrate, and use a spin coater to spin-coat PMMA at a speed of 2000 r / min to obtain a PMMA layer / graphene film / metal substrate;

[0074] Prepare an ammonium persulfate solution with a concentration of 1 mol / L. Float the PMMA layer / graphene film / metal substrate on the liquid surface of the ammonium persulfate solution and wait until the metal substrate is completely etched. Fish out the obtained PMMA layer / graphene film and re-float it on the deionized water liquid surface, and repeat 5 times to obtain a PMMA layer / graphene film sample;

[0075] Then use a Si / SiO2 substrate with an oxide layer thickness of 300 nm to fish out the PMMA layer / graphene film sample, and dry it until the water between the graphene film and the Si / SiO2 substrate completely evaporates to form a PMMA layer / graphene film / Si / SiO2 substrate sample;

[0076] Immerse the PMMA layer / graphene film / Si / SiO2 substrate sample in acetone at 56 °C for 1 hour, take it out, and the transfer of graphene is completed to obtain a graphene film / Si / SiO2 substrate sample.

[0077] Refer to Figure 2Optical microscope photograph of the transferred graphene on the Si / SiO2 substrate for Comparative Example 1. Figure 2 a is the optical microscope photograph (magnified 100 times) of the PMMA layer / graphene thin film / Si / SiO2 substrate sample before removing PMMA. Figure 2 b is the optical microscope photograph (magnified 50 times) of the graphene thin film / Si / SiO2 substrate sample after removing PMMA. As can be seen from Figure 2 a, before removing PMMA, oxygen bubbles are generated by the reaction of the ammonium persulfate solution remaining between the graphene thin film and the Si / SiO2 substrate. From Figure 2 b, it can be seen that the graphene near the bubbles forms damage after removing PMMA.

[0078] In summary, the method for preparing integral graphene based on wet transfer provided by the present invention is simple and easy to implement, has good repeatability, can effectively improve the integrity of the wet-transferred graphene, and can be used for the transfer of large-area graphene thin films; moreover, the method provided by the present invention can effectively treat the residue of ammonium persulfate on the lower surface of graphene caused by wet transfer through a simple chemical reaction, improve the cleanliness of the transferred graphene, and thus improve the integrity of the transferred graphene. Therefore, the present invention effectively overcomes various disadvantages in the prior art and has high industrial utilization value.

[0079] The above embodiments are only illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing complete graphene based on wet transfer, characterized in that, The method includes the following steps: S1. Spin-coat PMMA on the graphene surface of the metal substrate to form a PMMA layer / graphene film / metal substrate sample; S2. Etch the metal substrate of the PMMA layer / graphene film / metal substrate sample with an ammonium persulfate solution, and after cleaning, obtain a PMMA layer / graphene film sample; S3. Contact the PMMA layer / graphene film sample with an FeCl2 / FeCl3 mixed solution, and the side of the graphene film away from the PMMA layer is in contact with the liquid surface of the FeCl2 / FeCl3 mixed solution. After contacting for a period of time, wash with deionized water, and then transfer the cleaned PMMA layer / graphene film sample to a target substrate and dry it to form a PMMA layer / graphene film / target substrate sample; S4. Dissolve and remove the PMMA layer of the PMMA layer / graphene film / target substrate sample with acetone to obtain a graphene film completely attached to the target substrate.

2. The method for preparing integral graphene based on wet transfer according to claim 1, wherein: The graphene on the metal substrate in step S1 is grown by chemical vapor deposition.

3. The method for preparing integral graphene based on wet transfer according to claim 1, wherein: The metal substrate in step S1 is a metal film or a metal foil, and the composition of the metal substrate includes one or a combination of copper, nickel, cobalt, and iron.

4. The method for preparing integral graphene based on wet transfer according to claim 1, wherein: Step S1 includes one or a combination of the following conditions: The number of layers of the graphene film is at least a single layer; The graphene film is a continuous graphene film; The graphene film is a discrete domain graphene film.

5. The method for preparing integral graphene based on wet transfer according to claim 1, wherein: In step S2, the ammonium persulfate solution is an aqueous solution of ammonium persulfate, and the concentration of the ammonium persulfate solution is 0.1 - 3 mol / L.

6. The method for preparing integral graphene based on wet transfer according to claim 1, wherein: In step S3, when the PMMA layer / graphene film sample is in contact with the FeCl2 / FeCl3 mixed solution, specifically, the PMMA layer / graphene film sample floats on the FeCl2 / FeCl3 mixed solution.

7. The method for preparing integral graphene based on wet transfer according to claim 1, wherein: In step S3, when the PMMA layer / graphene film sample is in contact with the FeCl2 / FeCl3 mixed solution, specifically, the PMMA layer / graphene film sample is immersed in the FeCl2 / FeCl3 mixed solution.

8. The method for preparing integral graphene based on wet transfer according to claim 1, wherein: In step S3, the FeCl2 / FeCl3 mixed solution refers to a mixed aqueous solution of FeCl2 and FeCl3. In the FeCl2 / FeCl3 mixed solution, the concentration of FeCl2 is 0.4 - 4 mol / L, and in the FeCl2 / FeCl3 mixed solution, the concentration of FeCl3 is 0.4 - 4 mol / L.

9. The method for preparing integral graphene based on wet transfer according to claim 1, wherein: In step S3, the contact time between the side of the graphene film away from the PMMA layer and the FeCl2 / FeCl3 mixed solution is 20 - 120 min.

10. The method for preparing integral graphene based on wet transfer according to claim 1, characterized in that: The target substrate in step S3 includes one of a Si / SiO2 substrate and a quartz substrate.

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