A method for producing integrity graphene based on wet transfer

Abstract

The application provides a method for preparing integrity graphene based on wet transfer, and the method comprises the following steps: S1, spin coating PMMA on a graphene surface on a metal substrate to form a PMMA layer / graphene film / metal substrate sample; S2, etching the metal substrate with an ammonium persulfate solution, and after cleaning, a PMMA layer / graphene film sample is obtained; S3, contacting the PMMA layer / graphene film sample with a mixed solution of FeCl2 and FeCl3 for a period of time, cleaning, then transferring the cleaned PMMA layer / graphene film sample to a target substrate, and drying to form a PMMA layer / graphene film / target substrate sample; and S4, dissolving and removing the PMMA layer with acetone to obtain a graphene film which is completely attached to the target substrate. The method is simple and easy to operate, has good repeatability, can effectively improve the integrity of the graphene transferred by the wet method, and can be used for the transfer of a large-area graphene film.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional material transfer technology, and in particular relates to a method for preparing intact graphene based on wet transfer. Background Technology

[0002] In recent years, research on the growth of graphene using chemical vapor deposition (CVD) has deepened, and the CVD growth process for high-quality graphene has become relatively mature. However, graphene grown on metal substrates cannot be directly applied in fields such as microelectronics; instead, it requires a transfer process to transfer the graphene from the metal substrate to a target substrate adapted for semiconductor processes. Therefore, achieving lossless transfer of graphene is key to realizing its numerous advantages in applications such as microelectronics.

[0003] Currently, graphene transfer processes are mainly divided into three types: wet etching transfer, bubble transfer, and dry transfer. However, both bubble transfer and dry transfer methods face the challenge of achieving complete graphene transfer, so wet etching transfer remains the most prevalent method. In existing research on wet etching transfer of graphene, researchers have focused more on improving the polymer support layer, neglecting the impact of the metal etchant itself on the integrity of the graphene. Ammonium persulfate solution is a typical metal etchant and has been widely used in graphene transfer processes. However, the residue of ammonium persulfate solution between the graphene and the target substrate will severely affect the integrity of the transferred graphene. Moreover, simple deionized water washing alone is insufficient to remove the ammonium persulfate residue adsorbed on the lower surface of the graphene.

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

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for preparing intact graphene based on wet transfer, which solves the problem in the prior art that the residual ammonium persulfate solution between graphene and target substrate seriously affects the integrity of graphene after transfer.

[0006] To achieve the above and other related objectives, the present invention provides a method for preparing intact graphene based on wet transfer, the method comprising the following steps:

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

[0008] S2. Etch the metal substrate of the PMMA layer / graphene film / metal substrate sample with ammonium persulfate solution, and after cleaning, obtain the PMMA layer / graphene film sample.

[0009] S3. The PMMA layer / graphene film sample is brought into contact with a FeCl2 / FeCl3 mixed solution, with the side of the graphene film away from the PMMA layer in contact with the surface of the FeCl2 / FeCl3 mixed solution. After contacting for a period of time, it is washed with deionized water. Then, the cleaned PMMA layer / graphene film sample is transferred to the target substrate and dried to form a PMMA layer / graphene film / target substrate sample.

[0010] 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.

[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 graphene film in step S1 has at least one layer.

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

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

[0016] Preferably, 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.

[0017] Preferably, 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 floats on the FeCl2 / FeCl3 mixed solution.

[0018] Preferably, 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.

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

[0020] Preferably, in step S3, the side of the graphene film away from the PMMA layer is in contact with the FeCl2 / FeCl3 mixed solution for 20 to 120 minutes.

[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 intact graphene based on wet transfer according to the present invention has the following beneficial effects:

[0023] The method for preparing intact graphene based on wet transfer provided by this invention is simple, easy to implement, and highly reproducible. It can effectively improve the integrity of graphene transferred by wet transfer and can be used for the transfer of large-area graphene films. Furthermore, the method provided by this invention can effectively remove the residue of ammonium persulfate on the lower surface of graphene caused by wet transfer through a simple chemical reaction, thereby improving the cleanliness of the transferred graphene and thus improving its integrity. Attached Figure Description

[0024] Figure 1 The diagram shows a process flow diagram for preparing intact graphene based on wet transfer in a specific embodiment of the present invention.

[0025] Figure 2 The image shown is an optical microscope photograph of graphene transferred onto a Si / SiO2 substrate, as shown in Comparative Example 1 of this invention. Figure 2 Image a is an optical microscope image (100x magnification) of the PMMA layer / graphene film / Si / SiO2 substrate sample before PMMA removal. Figure 2 b is an optical microscope image (50x magnification) of the graphene film / Si / SiO2 substrate sample after PMMA removal.

[0026] Figure 3 The image shown is an optical microscope photograph of the graphene film / Si / SiO2 substrate prepared in Example 1 of this invention. Figure 3 a and Figure 3 b are optical microscope images of monolayer graphene magnified at 100x and 500x, respectively. Figure 3 c and Figure 3 d are optical microscope images of two or more layers of graphene magnified at 100x and 500x, respectively.

[0027] Figure 4 The images shown are Raman spectra of the graphene film / Si / SiO2 substrate prepared in Example 1 of this invention. 4a is the Raman spectrum of the monolayer graphene at three different positions, and 4b is the Raman spectrum of the bilayer graphene at three different positions. Detailed Implementation

[0028] The following specific examples illustrate the implementation 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 embodiments, 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] In the existing wet etching process for transferring graphene, the residue of ammonium persulfate solution between the graphene and the target substrate will seriously affect the integrity of the transferred graphene. It is actually difficult to remove the ammonium persulfate residue adsorbed on the lower surface of the graphene by simply relying on deionized water cleaning.

[0030] See Figure 1 This invention provides a method for preparing intact graphene based on wet transfer, the method comprising the following steps:

[0031] S1. Spin-coat PMMA onto the graphene surface 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 cleaning, obtain the PMMA layer / graphene film sample.

[0033] S3. The PMMA layer / graphene film sample is brought into contact with a FeCl2 / FeCl3 mixed solution, with the side of the graphene film away from the PMMA layer in contact with the surface of the FeCl2 / FeCl3 mixed solution. After contacting for a period of time, it is washed with deionized water. Then, the cleaned PMMA layer / graphene film sample is transferred to the target substrate and dried to form a PMMA layer / graphene film / target substrate sample.

[0034] S4. Dissolve and remove 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 intact graphene based on wet transfer in the specific embodiments of the present invention is simple, easy to implement, and has good repeatability, and can effectively improve the integrity of wet-transferred graphene.

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

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

[0038] Specifically, the method for growing graphene on a metal substrate using chemical vapor deposition will not be overly restricted here; the commonly used chemical vapor deposition method in existing technologies will be 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, the graphene film in step S1 has at least one layer.

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

[0042] As an example, the graphene film in step S1 is a discrete domain graphene 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 ammonium persulfate solution can be any value within the range of 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. The specific concentration can be adjusted according to the actual situation. If a lower concentration of ammonium persulfate solution is used, the amount of ammonium persulfate solution needs to be increased to ensure that the metal substrate can be completely etched clean.

[0045] In a specific embodiment of the present invention, cleaning is performed by using deionized water to preliminarily clean the ammonium persulfate residue on the lower surface of the graphene film. The specific number of cleaning cycles is not excessively limited here.

[0046] As an example, in step S3, the PMMA layer / graphene film sample is brought into contact with the FeCl2 / FeCl3 mixed solution. Specifically, the PMMA layer / graphene film sample floats on the FeCl2 / FeCl3 mixed solution.

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

[0048] Specifically, through the principle of chemical reaction, the residual ammonium persulfate on the lower surface of the graphene film during wet transfer is consumed, thereby preventing its decomposition on the lower surface of the graphene and the formation of oxygen bubbles, thus improving the integrity of the graphene after transfer. On the one hand, ferrous ions can undergo redox reactions with persulfate ions, directly consuming the persulfate ions; on the other hand, the hydrogen peroxide produced by the decomposition of persulfate ions in water will be rapidly decomposed under the catalysis of ferric ions, thereby promoting the decomposition of persulfate ions. Therefore, the residual ammonium persulfate solution after etching will be completely decomposed during contact with the FeCl2 / FeCl3 mixed solution.

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

[0050] Specifically, the concentration of FeCl2 in the FeCl2 / FeCl3 mixed solution can range from 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, to 4 mol / L, and the concentration of FeCl3 in the FeCl2 / FeCl3 mixed solution can range from 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, to 4 mol / L, etc. Using a lower concentration of FeCl2 / FeCl3 mixed solution will require a longer flotation time to ensure that the ammonium persulfate residue is completely depleted.

[0051] As an example, in step S3, the side of the graphene film away from the PMMA layer is in contact with the FeCl2 / FeCl3 mixed solution for 20 to 120 minutes.

[0052] Specifically, the contact time can be any range of values, such as 20 min, 40 min, 60 min, 80 min, 100 min, 120 min, etc.

[0053] In a specific embodiment of the present invention, cleaning with deionized water is used to remove FeCl2 / FeCl3 residues on the lower surface of the graphene film.

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

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

[0056] Example 1

[0057] This embodiment provides a method for preparing intact graphene based on wet transfer, the method comprising the following steps:

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

[0059] S2. Prepare a 1 mol / L ammonium persulfate solution. Float the PMMA layer / graphene film / metal substrate sample on the surface of the ammonium persulfate solution. Etch the metal substrate. After the etching is complete, take out the PMMA layer / graphene film and float it on the surface of deionized water for cleaning. Repeat the cleaning 5 times to obtain the PMMA layer / graphene film sample.

[0060] S3. Prepare a FeCl2 / FeCl3 mixed solution containing 1 mol / L FeCl2 and 1 mol / L FeCl3. Contact the PMMA layer / graphene film sample with the FeCl2 / FeCl3 mixed solution, with the side of the graphene film away from the PMMA layer in contact with the surface of the FeCl2 / FeCl3 mixed solution. After contact for 30 minutes, take it out and float it again on the surface of deionized water. Repeat the washing 5 times. Then transfer the cleaned PMMA layer / graphene film sample to a Si / SiO2 substrate with an oxide layer thickness of 300 nm. Dry it until the water between the graphene film and the Si / SiO2 substrate is completely evaporated to form a PMMA layer / graphene film / Si / SiO2 substrate sample.

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

[0062] See Figure 3 This is an optical microscope image of the graphene film / Si / SiO2 substrate prepared in Example 1. Figure 3 a and Figure 3 b are optical microscope images of monolayer graphene magnified at 100x and 500x, respectively. Figure 3 c and Figure 3 Image d shows optical microscope images of two or more layers of graphene (graphene films with clearly distinguishable layer counts) at magnifications of 100x and 500x, respectively. As can be seen from the images, the graphene films obtained by this method have a complete and undamaged structure over a large area, indicating that this method can effectively improve the integrity of graphene.

[0063] See Figure 4 The images show the Raman spectra of the graphene film / Si / SiO2 substrate prepared in Example 1. 4a shows the Raman spectra of the monolayer graphene at three different positions, and 4b shows the Raman spectra of the bilayer graphene at three different positions. Figure 4 From a and 4b, we know that it is located at 1580cm. -1 and 2690cm -1 The G and 2D peaks of the nearby graphene clearly show the structure of the graphene; located at 1350 cm⁻¹. -1 The D peak of the nearby graphene is not obvious, which proves that the graphene obtained by transfer has high quality.

[0064] Example 2

[0065] This embodiment provides a method for preparing intact graphene based on wet transfer, the method comprising the following steps:

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

[0067] S2. Prepare a 0.5 mol / L ammonium persulfate solution. Float the PMMA layer / graphene film / metal substrate sample on the surface of the ammonium persulfate solution. Etch the metal substrate. After etching, take out the PMMA layer / graphene film and float it on the surface of deionized water for cleaning. Repeat the cleaning 5 times to obtain the PMMA layer / graphene film sample.

[0068] S3. Prepare a 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, with the side of the graphene film away from the PMMA layer in contact with the surface of the FeCl2 / FeCl3 mixed solution. After contact for 40 minutes, take it out and float it again on the surface of deionized water. Repeat the washing 5 times. Then transfer the cleaned PMMA layer / graphene film sample to a quartz substrate and dry it until the water between the graphene film and the quartz substrate has completely evaporated, forming 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, then remove it to obtain a graphene film completely attached to the quartz substrate, which is the graphene film / quartz substrate.

[0070] The graphene film obtained by transfer in this embodiment has a complete and undamaged structure over a large area, which is close to the integrity of the graphene prepared by transfer in Example 1.

[0071] Comparative Example 1

[0072] This comparative example provides a commonly used wet transfer method for graphene 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 spin coat PMMA at a speed of 2000 r / min using a spin coater to obtain a PMMA layer / graphene film / metal substrate.

[0074] Prepare a 1 mol / L ammonium persulfate solution, float the PMMA layer / graphene film / metal substrate on the surface of the ammonium persulfate solution, wait for the metal substrate to be completely etched clean, take out the obtained PMMA layer / graphene film and float it again on the surface of deionized water, repeat 5 times to obtain PMMA layer / graphene film sample.

[0075] Then, a PMMA layer / graphene film sample was retrieved from a Si / SiO2 substrate with an oxide layer thickness of 300 nm. After drying until the water between the graphene film and the Si / SiO2 substrate was completely evaporated, a PMMA layer / graphene film / Si / SiO2 substrate sample was formed.

[0076] The PMMA layer / graphene film / Si / SiO2 substrate sample was immersed in acetone at 56°C for 1 hour and then removed, thus completing the transfer of graphene and obtaining the graphene film / Si / SiO2 substrate sample.

[0077] See Figure 2This is an optical microscope image of Comparative Example 1 after graphene was transferred onto a Si / SiO2 substrate. Figure 2 Image a is an optical microscope image (100x magnification) of the PMMA layer / graphene film / Si / SiO2 substrate sample before PMMA removal. Figure 2 b is an optical microscope image (50x magnification) of the graphene film / Si / SiO2 substrate sample after PMMA removal. Figure 2 As can be seen from a, before the PMMA was removed, the ammonium persulfate solution remaining between the graphene film and the Si / SiO2 substrate reacted to generate oxygen bubbles. Figure 2 As can be seen in b, the graphene near the bubble is damaged after the PMMA is removed.

[0078] In summary, the method for preparing intact graphene based on wet transfer provided by this invention is simple, easy to implement, and highly reproducible. It effectively improves the integrity of graphene transferred by wet transfer and can be used for the transfer of large-area graphene films. Furthermore, the method provided by this invention can effectively remove the ammonium persulfate residue on the lower surface of the graphene caused by wet transfer through a simple chemical reaction, improving the cleanliness of the transferred graphene and thus enhancing its integrity. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and has high industrial application value.

[0079] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing intact graphene based on wet transfer, characterized in that, The method includes the following steps: S1. Spin-coat PMMA onto the graphene surface on 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 ammonium persulfate solution, and after cleaning, obtain the PMMA layer / graphene film sample. S3. The PMMA layer / graphene film sample is brought into contact with a FeCl2 / FeCl3 mixed solution, with the side of the graphene film away from the PMMA layer in contact with the surface of the FeCl2 / FeCl3 mixed solution. After contact for a period of time, it is washed with deionized water. Then, the cleaned PMMA layer / graphene film sample is transferred to the target substrate and dried to form a PMMA layer / graphene film / target substrate sample. The PMMA layer / graphene film sample floats in the FeCl2 / FeCl3 mixed solution. The FeCl2 / FeCl3 mixed solution is an aqueous solution of FeCl2 and FeCl3, with a FeCl2 concentration of 0.4~4 mol / L and a FeCl3 concentration of 0.4~4 mol / L. 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 intact graphene based on wet transfer according to claim 1, characterized in that: The graphene on the metal substrate mentioned in step S1 is grown by chemical vapor deposition.

3. The method for preparing intact graphene based on wet transfer according to claim 1, characterized in that: The metal substrate mentioned 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.

4. The method for preparing intact graphene based on wet transfer according to claim 1, characterized in that: Step S1 includes one or a combination of the following conditions: The graphene film has at least one layer. The graphene film is a continuous graphene film. The graphene film is a discrete domain graphene film.

5. The method for preparing intact graphene based on wet transfer according to claim 1, characterized in that: 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 intact graphene based on wet transfer according to claim 1, characterized in that: In step S3, the side of the graphene film away from the PMMA layer is in contact with the FeCl2 / FeCl3 mixed solution for 20 to 120 minutes.

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

Images