Preparation method of double-layer graphene
By alternately entering hydrogen and carbon source gas under high temperature conditions on the sapphire substrate and growing graphene circulatedly, the problem of poor crystal quality and layer uniformity of graphene is solved, and high-quality bilayer graphene is achieved efficiently, which promotes the development of high-performance graphene devices.
Patent Information
- Application Number
- CN202510584799.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-07
- Publication Date
- 2025-07-25
AI Technical Summary
The prior art has poor crystal quality of directly grown graphene on sapphire substrates and poor uniformity of the double-layer graphene layer number, which limits its application in high-end devices.
Hydrogen and carbon source gas are alternately passed on to the sapphire substrate under high temperature conditions, graphene is grown circulated, and repeated growth and annealing steps are set to control the uniformity of carbon source supply, promote interface structure reorganization, and improve crystallization quality and layer uniformity.
It realizes the rapid growth of high-quality and uniform double-layer graphene on sapphire substrates, improves the generation efficiency and provides the material basis and process path of high-performance graphene devices.
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Figure CN120364683A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of bilayer graphene, and particularly to a preparation method of bilayer graphene. Background Art
[0002] Bilayer graphene is a two-dimensional material stacked by two layers of single-atom-thick graphene. Its unique interlayer coupling and tunable electronic structure have attracted much attention in the research of condensed matter physics and the application of nanodevices. At present, the preparation methods of bilayer graphene mostly rely on chemical vapor deposition (CVD) on metal substrates (such as Cu or Ni) and subsequent transfer processes. This process is not only complex and inefficient, but also prone to introduce pollution, stress and structural defects, which limits its practical application in high-end devices. In order to avoid the adverse effects brought by the transfer, directly growing graphene on a sapphire substrate is regarded as an ideal solution. Among them, the sapphire substrate, due to its excellent thermal stability, electrical insulation and mechanical strength, becomes one of the ideal candidate materials for direct epitaxial growth of graphene. Especially under the application requirements of pursuing high-quality and transfer-free graphene films, the industrial compatibility and low-cost advantages of the sapphire substrate show good application prospects. However, limited by its low catalytic activity, directly growing graphene on its surface faces problems such as high nucleation energy barrier, low carbon source decomposition efficiency and difficulty in layer number control. In particular, the direct growth of high-quality bilayer graphene is more challenging. Summary of the Invention
[0003] Therefore, the technical problem to be solved by the present invention is to overcome the defect of poor crystal quality of directly growing graphene on a sapphire substrate in the prior art, so as to provide a preparation method of bilayer graphene.
[0004] Another technical problem to be solved by the present invention is to overcome the defect of poor layer uniformity of bilayer graphene in the prior art, so as to provide a preparation method of bilayer graphene.
[0005] For this purpose, the present invention provides a preparation method of bilayer graphene, including the following steps: (1) placing the sapphire substrate in a reaction chamber, and heating it to a target temperature of 1390 - 1410 °C under an inert atmosphere; (2) continuously introducing hydrogen, and alternately introducing the carbon source gas 2 - 4 times. Among them, after annealing with hydrogen for 5 - 15 minutes each time, introducing the carbon source gas to deposit and grow graphene on the surface of the sapphire substrate for 20 - 40 minutes; (3) closing the hydrogen and the carbon source gas, and cooling to room temperature under an inert atmosphere.
[0006] Preferably, the target temperature in step (1) is 1400 °C.
[0007] Preferably, the size of the sapphire substrate is 1.5 - 3 inches. The preparation method provided by the present invention has significant advantages in the uniformity between graphene layers grown on a substrate with a large area.
[0008] In some embodiments, in step (2), the carbon source gas is alternately introduced 3 times. After annealing with hydrogen for 10 minutes each time during each alternation, the carbon source gas is introduced to deposit and grow graphene on the surface of the sapphire substrate for 30 minutes.
[0009] In some embodiments, the carbon source gas includes methane.
[0010] In some embodiments, the flow rate of the carbon source gas introduced in step (2) is 80 - 90 sccm.
[0011] In some embodiments, in step (1), the system temperature is raised to the target temperature in a stepwise manner. The specific steps are as follows: the temperature is raised to 1000 - 1100 °C at a heating rate of 10 - 15 °C / min, and then the temperature is raised to the target temperature at a heating rate of 5 - 10 °C / min.
[0012] In some embodiments, from step (1) to step (2), an inert atmosphere is continuously introduced into the system. The flow rate of the inert atmosphere is 1000 - 1100 sccm, and the pressure in the reaction chamber is 5000 - 6000 Pa.
[0013] In some embodiments, the inert atmosphere in step (1) and / or step (3) includes argon.
[0014] In some embodiments, in step (3), when cooling to 100 °C, the system pressure is adjusted to atmospheric pressure using an inert atmosphere.
[0015] In some embodiments, step (1) further includes a step of activating the sapphire substrate. The activation step includes a step of introducing hydrogen into the reaction chamber. The flow rate of hydrogen introduced is 200 - 400 sccm, and the time for introducing hydrogen is 8 - 15 minutes.
[0016] In some embodiments, the sapphire substrate undergoes a reaction after pretreatment. The pretreatment steps include successively ultrasonic cleaning the sapphire substrate with acetone, absolute ethanol, and deionized water, and then purging the sapphire substrate with an inert atmosphere.
[0017] The technical solution of the present invention has the following advantages:
[0018] 1. A method for preparing bilayer graphene provided by the present invention includes the following steps: (1) placing a sapphire substrate in a reaction chamber, and under an inert atmosphere, heating to a target temperature of 1390 - 1410 °C; (2) continuously introducing hydrogen and alternately introducing a carbon source gas 2 - 4 times. Among them, after each alternation, hydrogen is annealed for 5 - 15 minutes, and then the carbon source gas is introduced to deposit and grow graphene on the surface of the sapphire substrate for 20 - 40 minutes; (3) closing the hydrogen and the carbon source gas, and cooling to room temperature under an inert atmosphere. The present invention utilizes the fact that a bilayer metastable structure will appear during the nucleation of graphene at a high temperature of 1390 - 1410 °C, which is more conducive to the synchronous epitaxial growth of bilayer graphene; the present invention sets steps of repeated growth and annealing to gradually construct a double-layer structure, enhances the accuracy of carbon source regulation, and can maintain the dynamic stability of the carbon concentration on the surface of the sapphire substrate by introducing the carbon source gas into the system at least 2 - 4 times, inhibits local saturation, reduces the random formation of multi-layer islands, promotes the restructuring of the interface structure by annealing after growth, reduces the accumulation of defects, helps to eliminate the self-limiting phenomenon of early nucleation, makes the carbon source supply more uniform through cyclic growth, the composition of the growth interface is stable, effectively promotes the control of the number of layers of the graphene film and the improvement of continuity, not only improves the crystallization quality and layer uniformity of the bilayer graphene, but also improves the generation efficiency of the bilayer graphene.
[0019] The present invention realizes the rapid growth of bilayer graphene on a sapphire substrate, exhibits excellent repeatability and scale-up potential, and provides a reliable material basis and process path for the development of future high-performance graphene devices.
[0020] 2. A method for preparing bilayer graphene provided by the present invention, in step (2), the carbon source gas is alternately introduced 3 times. Among them, after hydrogen is annealed for 10 minutes each time, the carbon source gas is introduced to deposit and grow graphene on the surface of the sapphire substrate for 30 minutes. The present invention can effectively control the number of layers and thickness of the bilayer graphene by setting the number of times of alternating carbon source introduction, the time of single introduction, and the time of hydrogen annealing.
[0021] 3. A method for preparing bilayer graphene provided by the present invention, in step (1), the system temperature is raised to the target temperature by a stepwise heating method. The specific steps are as follows: the temperature is raised to 1000 - 1100 °C at a heating rate of 10 - 15 °C / min, and then the temperature is raised to the target temperature at a heating rate of 5 - 10 °C / min. The present invention utilizes the stepwise heating method to ensure that the system heating process is uniform and there is no thermal shock.
[0022] 4. The preparation method of the bilayer graphene provided by the present invention further includes a step of activating the sapphire substrate in step (1). The activation step includes a step of introducing hydrogen into the reaction chamber. The flow rate of hydrogen introduced is 200-400 sccm, and the time for introducing hydrogen is 8-15 min. By introducing the pretreatment of the sapphire substrate and optimizing the atmosphere composition, the present invention utilizes the atomic-level step structure formed by the sapphire substrate under the high-temperature condition of the target temperature to effectively guide the orderly nucleation and interfacial combination of carbon species. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.
[0024] Figure 1 It is a graph showing the relationship between temperature and time in the preparation method of bilayer graphene in Example 1 of the present invention;
[0025] Figure 2 It is an atomic force microscope image of bilayer graphene in Example 1 of the present invention. Figure 2 In it, Wrinkles represents the slight wrinkles on the bilayer graphene;
[0026] Figure 3 It is a Raman spectrum diagram of bilayer graphene in Example 1 of the present invention;
[0027] Figure 4 It is the optical transmittance of bilayer graphene in the visible light band in Example 1 of the present invention;
[0028] Figure 5 It is a detection diagram of the resistance distribution of the sample in Example 1 of the present invention;
[0029] Figure 6 It is a high-resolution transmission electron microscope image of the sample in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0030] The following embodiments are provided to better further understand the present invention. They are not limited to the best embodiments, and do not limit the content and protection scope of the present invention. Any product obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features that is the same or similar to the present invention falls within the protection scope of the present invention.
[0031] For those without specific experimental procedures or conditions indicated in the examples, the operations or conditions of the conventional experimental procedures described in the literature in this field can be followed. For reagents or instruments without the manufacturer indicated, they are all conventional reagent products that can be obtained through commercial purchase.
[0032] Example 1
[0033] Refer to Figure 1 As shown, this example provides a method for preparing bilayer graphene, and the specific steps and parameters are as follows:
[0034] (1) Pretreatment of sapphire substrate:
[0035] Substrate cleaning: Place the C-plane (0001) sapphire wafer (size 2 inches) substrate in acetone, absolute ethanol, and deionized water in sequence for ultrasonic cleaning. Each ultrasonic cleaning lasts for 10 minutes to remove surface organic substances and particulate pollutants, and then dry it with high-purity nitrogen for standby.
[0036] Chamber pretreatment: Use a clean dust-free cloth and a dust suction device to preliminarily clean the inside of the reaction chamber to remove attached dust particles and residual impurities.
[0037] Atmosphere replacement: Introduce high-purity argon into the reaction chamber for 15 minutes to purge residual air and impurity gases, ensuring the cleanliness and stability of the reaction environment.
[0038] Sample loading: Place the substrate in a graphite carrier and position it in the central area of the chamber of a cold-wall electromagnetic induction heating reaction furnace to ensure the symmetry of the thermal field and close the chamber.
[0039] (2) Activate the sapphire substrate:
[0040] Vacuum pumping and atmosphere backfilling: Turn on the vacuum system, pump the chamber pressure below 5 Pa. After confirming the airtightness is correct, introduce 1000 sccm of argon and slowly backfill to 5000 Pa to establish the initial reaction atmosphere.
[0041] Heating rate control: Start the temperature control system and heat up to 1400 °C according to the preset heating program. The specific preset heating program is: heat up at a rate of 10 °C / min in the range of 20–1000 °C, and heat up at a rate of 5 °C / min in the range of 1000–1400 °C to ensure a uniform heating process without thermal shock.
[0042] High-temperature annealing: After the temperature rises to 1400 °C, introduce hydrogen (300 sccm) and anneal for 10 minutes to clean the substrate surface and activate the reaction interface, which is beneficial for subsequent nucleation and growth.
[0043] (3) Cyclic growth:
[0044] First round of injection: Methane (80 sccm) was introduced for 30 minutes, and then methane was turned off while hydrogen was retained for an additional 10 minutes of annealing;
[0045] Second round of injection: The steps of the first round of injection were repeated once;
[0046] Third round of injection: Methane (80 sccm) was continuously injected for 30 minutes to complete the entire growth stage.
[0047] During the cyclic growth process, argon and hydrogen were continuously introduced into the reaction chamber. During the entire cyclic growth process, the carbon source gas was alternately introduced 3 times.
[0048] (4) Post-treatment:
[0049] Cooling and gas protection: After the graphene growth stage ended, methane, hydrogen, and the heating system were immediately turned off, and the chamber was allowed to cool naturally to room temperature. Argon was continuously introduced during the cooling process to protect the sample and prevent secondary carbon deposition.
[0050] Sample removal: After the temperature dropped below 100 °C, the vacuum system was turned off and the chamber was backfilled with argon to atmospheric pressure. The chamber was opened, and the sapphire substrate was removed to obtain a high-quality, bilayer graphene sample with controllable number of layers.
[0051] The bilayer graphene sample prepared in this example was scanned by atomic force microscopy. For the microscopic morphology image, see Figure 2 , it can be seen that the bilayer graphene prepared in this example has a continuous wavy structure and slight wrinkles, indicating that the film morphology is flat.
[0052] The bilayer graphene sample prepared in this example was characterized by Raman spectroscopy. The results are shown in Figure 3 , it can be seen that the intensity ratio of the D peak to the G peak is extremely low, indicating excellent crystal quality and extremely low defect density. The ratio of the 2D peak to the D peak further confirms the bilayer characteristics of the film.
[0053] The optical transmittance of the bilayer graphene sample prepared in this example was measured in the visible light band of 250 - 800 nm. The results are shown in Figure 4 , it can be seen that the bilayer graphene prepared in this example has excellent optical transmittance in the visible light band, and the average transmittance is close to 95%, which is in line with the theoretical light absorption rate of bilayer graphene.
[0054] The resistance distribution of the bilayer graphene sample taken out in this example was detected. The results are shown in Figure 5 , it can be seen that the surface resistance of the sample is mainly concentrated in the range of 1000 - 1500 Ω / sq, showing good electrical conductivity uniformity, which proves that the bilayer graphene prepared in this example has good uniformity. Further, the sample was scanned by high-resolution transmission electron microscopy (HRTEM). The results are shown in Figure 6, it can be seen that graphene forms a continuous and tightly adherent bilayer structure on the surface of the sapphire substrate, with a clear interface and no obvious cracks or folds on the surface.
[0055] Example 2
[0056] This example provides a method for preparing bilayer graphene. The specific steps and parameters are the same as those in Example 1, except that in step (3), the second round of implantation is not set, that is, after the first round of implantation, the third round of implantation is directly carried out, and during the cyclic growth, the carbon source gas is alternately introduced 2 times.
[0057] Example 3
[0058] This example provides a method for preparing bilayer graphene. The specific steps and parameters are the same as those in Example 1, except that in the second round of implantation in step (3), the steps of the first round of implantation are repeated twice, and during the cyclic growth, the carbon source gas is alternately introduced 4 times.
[0059] Example 4
[0060] This example provides a method for preparing bilayer graphene. The specific steps and parameters are as follows:
[0061] (1) Pretreatment of sapphire substrate:
[0062] Substrate cleaning: The C-plane (0001) sapphire wafer (size 2 inches) substrate is successively placed in acetone, absolute ethanol and deionized water for ultrasonic cleaning, and each ultrasonic cleaning lasts for 10 minutes to remove surface organic matters and particulate pollutants, and then it is dried with high-purity nitrogen and reserved.
[0063] Chamber pretreatment: The inside of the reaction chamber is preliminarily cleaned with a clean dust-free cloth and a dust suction device to remove the attached dust particles and residual impurities.
[0064] Atmosphere replacement: High-purity argon gas is introduced into the reaction chamber for 15 minutes to purge the residual air and impurity gases to ensure the cleanliness and stability of the reaction environment.
[0065] Sample loading: The substrate is placed in a graphite carrier and positioned in the central area of the cavity of the cold-wall electromagnetic induction heating reaction furnace to ensure the symmetry of the thermal field and then the cavity is closed.
[0066] (2) Activation of sapphire substrate:
[0067] Vacuum pumping and atmosphere backfilling: The vacuum system is turned on, and the pressure in the chamber is pumped to below 5 Pa. After confirming that the airtightness is correct, 1100 sccm of argon gas is introduced slowly to backfill to 6000 Pa to establish the initial reaction atmosphere.
[0068] Temperature rise control: Start the temperature control system and heat up to the target temperature of 1410°C according to the preset temperature rise program. The specific preset temperature rise program is as follows: In the stage of 20–1100°C, heat up at a rate of 15°C / min, and in the stage of 1100–1410°C, heat up to the target temperature at a rate of 10°C / min to ensure a uniform heating process without thermal shock.
[0069] High-temperature annealing: After the temperature rises to 1410°C, introduce hydrogen (200 sccm) and anneal for 15 minutes to clean the substrate surface and activate the reaction interface, which is beneficial to subsequent nucleation and growth.
[0070] (3) Cyclic growth:
[0071] The first round of injection: Introduce methane (90 sccm) for 20 minutes, and then close the methane and continue annealing with hydrogen for 5 minutes;
[0072] The second round of injection: Introduce methane (90 sccm) for 20 minutes, and then close the methane and continue annealing with hydrogen for 5 minutes;
[0073] The third round of injection: Continue to inject methane (90 sccm) for 20 minutes to complete the entire growth stage.
[0074] During the cyclic growth process, argon and hydrogen are continuously introduced into the reaction chamber.
[0075] (4) Post-treatment:
[0076] Cooling and gas protection: After the graphene growth stage ends, immediately close the methane, hydrogen, and heating system, and let the chamber cool naturally to room temperature. During the cooling process, argon is continuously introduced to protect the sample and prevent secondary carbon deposition.
[0077] Sample removal: After the temperature drops below 100°C, turn off the vacuum system and backfill with argon to atmospheric pressure, open the chamber, and take out the sapphire substrate to obtain a high-quality, bilayer graphene sample with controllable number of layers.
[0078] Example 5
[0079] This example provides a method for preparing bilayer graphene, and the specific steps and parameters are as follows:
[0080] (1) Sapphire substrate pretreatment:
[0081] Substrate cleaning: Place the C-plane (0001) sapphire wafer (with a size of 2 inches) substrate in acetone, absolute ethanol, and deionized water in sequence for ultrasonic cleaning. Each ultrasonic cleaning lasts for 10 minutes to remove surface organic substances and particulate pollutants, and then dry it with high-purity nitrogen for standby.
[0082] Cavity pretreatment: Use a clean dust-free cloth and a dust suction device to preliminarily clean the inside of the reaction cavity to remove attached dust particles and residual impurities.
[0083] Atmosphere replacement: Continuously introduce high-purity argon into the reaction cavity for 15 minutes to purge residual air and impurity gases, ensuring the cleanliness and stability of the reaction environment.
[0084] Sample loading: Place the substrate in a graphite carrier and position it in the central area of the cavity of the cold-wall electromagnetic induction heating reaction furnace to ensure the symmetry of the thermal field and close the cavity.
[0085] (2) Activate the sapphire substrate:
[0086] Vacuum pumping and atmosphere backfilling: Turn on the vacuum system, pump the cavity pressure below 5 Pa, and after confirming the airtightness is correct, slowly backfill with 1000 sccm of argon to 5000 Pa to establish the initial reaction atmosphere.
[0087] Heating rate control: Start the temperature control system and heat up to 1390 °C according to the preset heating program. The specific preset heating program is as follows: heat up at a rate of 10 °C / min in the range of 20–1100 °C, and heat up at a rate of 5 °C / min in the range of 1100–1390 °C to ensure a uniform heating process without thermal shock.
[0088] High-temperature annealing: After the temperature reaches 1390 °C, introduce hydrogen (400 sccm) and anneal for 8 minutes to clean the substrate surface and activate the reaction interface, which is beneficial for subsequent nucleation and growth.
[0089] (3) Cyclic growth:
[0090] First-round injection: Introduce methane (80 sccm) for 40 minutes, then close the methane and continue annealing with hydrogen for 15 minutes;
[0091] Second-round injection: Introduce methane (80 sccm) for 40 minutes, then close the methane and continue annealing with hydrogen for 15 minutes;
[0092] Third-round injection: Continue to inject methane (80 sccm) for 40 minutes to complete the entire growth stage.
[0093] During the cyclic growth process, argon and hydrogen are continuously introduced into the reaction chamber.
[0094] (4) Post-treatment:
[0095] Cooling and gas protection: After the graphene growth stage is completed, immediately turn off the methane, hydrogen, and heating system, and let the cavity cool naturally to room temperature. Continuously introduce argon during the cooling process to protect the sample and prevent secondary carbon deposition.
[0096] Sample extraction: After the temperature drops below 100°C, turn off the vacuum system and backfill it with argon to atmospheric pressure. Open the chamber and take out the sapphire substrate to obtain a high-quality bilayer graphene sample with controllable number of layers.
[0097] Comparative Example 1
[0098] This comparative example provides a method for preparing bilayer graphene. The specific steps and parameters are the same as those in Example 1, except that in step (2), it is heated to 1350°C according to a preset heating program.
[0099] Comparative Example 2
[0100] This comparative example provides a method for preparing bilayer graphene. The specific steps and parameters are the same as those in Example 1, except that in step (2), it is heated to 1450°C according to a preset heating program.
[0101] Comparative Example 3
[0102] This comparative example provides a method for preparing bilayer graphene. The specific steps and parameters are the same as those in Example 1, except that in step (3), the second round of injection and the third round of injection are not set, and during the cyclic growth process, the number of times of introducing the carbon source is 1 time.
[0103] Comparative Example 4
[0104] This comparative example provides a method for preparing bilayer graphene. The specific steps and parameters are the same as those in Example 1, except that in the second round of injection in step (3), the steps of the first round of injection are repeated three times, and during the cyclic growth, the carbon source gas is alternately introduced 5 times.
[0105] Experimental Example
[0106] Perform Raman spectroscopy characterization on the bilayer graphene samples prepared in Examples 1-5 and Comparative Examples 1-4, and measure the ratio I D / I G of the intensity of the D peak and the intensity of the G peak, and the results are shown in Table 1.
[0107] Table 1 Ratio of the intensity of the D peak and the intensity of the G peak of the bilayer graphene sample
[0108] <![CDATA[I D / I G > <![CDATA[I D / I G > Example 1 0.08 Comparative Example 1 0.16 Example 2 0.09 Comparative Example 2 0.12 Example 3 0.1 Comparative Example 3 0.28 Example 4 0.09 Comparative Example 4 0.32 Example 5 0.09
[0109] According to the data in Table 1, compared with Comparative Examples 1-4, among which the target temperature of Comparative Example 1 is 1350 °C, the target temperature of Comparative Example 2 is 1450 °C, the number of carbon source introductions during the cyclic growth process of Comparative Example 3 is 1 time, and the number of alternating carbon source introductions during the cyclic growth process of Comparative Example 4 is 5 times, the ratio of the D peak intensity to the G peak intensity of the prepared graphene material is greater than 0.16, and the quality of the graphene material is poor. However, the ratio of the D peak intensity to the G peak intensity of the bilayer graphene prepared in Examples 1-5 of the present invention is less than or equal to 0.1, and the quality of the bilayer graphene is good.
[0110] Obviously, the above examples are only for clear illustration and not a limitation on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.
Claims
1. A preparation method of bilayer graphene, characterized in that, It includes the following steps: (1) Place the sapphire substrate in the reaction chamber, and under an inert atmosphere, heat it up to the target temperature of 1390 - 1410 °C; (2) Continuously introduce hydrogen, and alternately introduce the carbon source gas 2 - 4 times. Among them, after each alternation, anneal with hydrogen for 5 - 15 min, and then introduce the carbon source gas to deposit and grow graphene on the surface of the sapphire substrate for 20 - 40 min; (3) Turn off the hydrogen and the carbon source gas, and cool it to room temperature under an inert atmosphere.
2. The preparation method of bilayer graphene according to claim 1, wherein, The target temperature in step (1) is 1400 °C.
3. The preparation method of bilayer graphene according to claim 1, characterized in that, In step (2), alternately introduce the carbon source gas 3 times. Among them, after annealing with hydrogen for 10 min each time, introduce the carbon source gas to deposit and grow graphene on the surface of the sapphire substrate for 30 min.
4. The preparation method of bilayer graphene according to claim 1, wherein The carbon source gas includes methane.
5. The preparation method of bilayer graphene according to claim 1, characterized in that, The flow rate of the carbon source gas introduced in step (2) is 80 - 90 sccm.
6. The preparation method of bilayer graphene according to claim 1, characterized in that, In step (1), the system temperature is raised to the target temperature in a step - by - step heating manner. The specific steps are as follows: raise the temperature to 1000 - 1100 °C at a heating rate of 10 - 15 °C / min, and then raise the temperature to the target temperature at a heating rate of 5 - 10 °C / min.
7. The preparation method of bilayer graphene according to claim 1, wherein, From step (1) to step (2), continuously introduce an inert atmosphere into the system. The flow rate of the inert atmosphere is 1000 - 1100 sccm, and the pressure of the reaction chamber is 5000 - 6000 Pa.
8. The preparation method of bilayer graphene according to claim 1, characterized in that, The inert atmosphere in step (1) and / or step (3) includes argon.
9. The preparation method of bilayer graphene according to any one of claims 1-8, characterized in that, In step (3), when cooling to 100 °C, use the inert atmosphere to adjust the system pressure to atmospheric pressure; Step (1) also includes a step of activating the sapphire substrate. The activation step includes a step of introducing hydrogen into the reaction cavity. The flow rate of hydrogen introduced is 200 - 400 sccm, and the time for introducing hydrogen is 8 - 15 min.
10. The preparation method of bilayer graphene according to any one of claims 1-8, characterized in that, In step (1), the sapphire substrate undergoes reaction after pretreatment. The pretreatment steps include successively ultrasonic cleaning the sapphire substrate with acetone, absolute ethanol, and deionized water, and then purging the sapphire substrate with an inert atmosphere.