Segregation preparation method of uniform AB stacking few-layer single crystal graphene film

Abstract

The invention relates to the field of preparation of graphene, in particular to a segregation preparation method of a uniform AB stacking few-layer single crystal graphene film, which is suitable for preparing a large-area uniform high-quality AB stacking few-layer single crystal graphene film. A single crystal metal substrate with certain carbon dissolving capacity is adopted, and a few layers of uniformly AB stacked single crystal graphene films are prepared on the surface of the single crystal metal substrate through a three-step method by utilizing the regulation and control effect of temperature on the carbon solubility of the metal substrate. According to the preparation method disclosed by the invention, the dissolution and segregation of carbon of the metal substrate are adjusted by adjusting the staged temperature change in the preparation process, so that a non-uniform multi-layer graphene island-shaped structure is selectively removed, and the uniformity of a few layers of graphene is obviously improved; and a foundation is laid for realizing the application of a few layers of graphene in the fields of new-generation electron, photoelectron and spinning electronic devices and the like.

Description

Technical Field

[0001] The invention relates to the field of graphene preparation, in particular to a method for preparing a uniform AB stacked minority-layer single-crystal graphene film by segregation, which is suitable for preparing a large-area uniform high-quality AB stacked minority-layer single-crystal graphene film. Background Art

[0002] The number of graphene layers and stacking order significantly affect the performance of graphene. Single-layer graphene is a semi-metal, while two-layer graphene in AB stacking has a continuously adjustable band gap when a vertical electric field is applied. Three-layer graphene in AB stacking not only has high carrier mobility but also has the characteristics of long spin relaxation time and weak spin-orbit interaction, which greatly expands its application in the fields of logic devices, optoelectronics and spintronic devices.

[0003] The segregation method has significant advantages such as high controllability, scalability, good repeatability and low cost. The prepared graphene film has high crystallization quality, so it has become a representative method for preparing high-quality minority-layer graphene films. However, the commonly used solid metal foil substrate has a relatively rough surface, which inevitably leads to the formation of uneven multilayer islands and partial crystal domain orientation errors during the segregation growth process, making it difficult to achieve the preparation of AB stacking uniform minority-layer single-crystalline graphene films. Summary of the invention

[0004] The purpose of the present invention is to provide a method for segregation preparation of uniform AB stacked few-layer single-crystalline graphene films, which has the advantages of low cost, excellent controllability, good uniformity, and scalability, and has the potential to further prepare large-area wafer-level AB stacked uniform few-layer single-crystalline graphene films.

[0005] The technical solution of the present invention is:

[0006] A method for preparing a uniform AB-stacked minority-layer single-crystal graphene film by segregation, which adopts a single-crystal metal substrate with a certain carbon solubility, utilizes the regulating effect of temperature on the carbon solubility of the metal substrate, and prepares a uniform AB-stacked minority-layer single-crystal graphene film on the surface of the single-crystal metal substrate through a three-step method; the first step is segregation growth to obtain a high-coverage minority-layer graphene film, which includes an uneven multi-layer island structure; the second step is to increase the growth temperature, and dissolve and remove the uneven multi-layer island area by increasing the carbon solubility of the metal substrate; the third step is to cool the growth again, and use the carbon segregation caused by cooling to fill the defects and gaps in the minority-layer graphene film, and then perform multiple heating-cooling cycles to finally obtain a uniform AB-stacked minority-layer single-crystal graphene film.

[0007] The segregation preparation method of the uniform AB stacked minority-layer single-crystal graphene film, the minority-layer graphene includes graphene with a layer number ranging from 2 to 10 layers, and the multi-layer island specifically refers to an island-structured graphene with a layer number greater than the number of layers of the film in which it is located.

[0008] The method for preparing the segregation of a uniform AB stacked few-layer single-crystal graphene film is applicable to the case where the multi-layer island graphene to be removed is located at the interface between the few-layer graphene film and the metal substrate.

[0009] The segregation preparation method of the uniform AB stacked few-layer single-crystalline graphene film is that the single-crystalline metal substrate adopts a metal with a certain amount of dissolved carbon and a lattice constant that is highly compatible with graphene, including but not limited to metal nickel, iron, cobalt, platinum and alloys formed with other elements, and the graphene film obtained by epitaxial growth on the single-crystalline metal substrate is a few-layer single-crystalline graphene film.

[0010] The segregation preparation method of the uniform AB stacked few-layer single-crystalline graphene film adopts a high-temperature annealing method to prepare the single-crystalline metal substrate, and annealing commercial polycrystalline metal foil to obtain the single-crystalline metal substrate. The typical annealing temperature is 1000-1200°C, the annealing atmosphere is hydrogen or a mixture of hydrogen and argon, the flow rate is 200-500 ml / min, and the annealing time is 4-8h.

[0011] The segregation preparation method of the uniform AB stacking minority layer single crystal graphene film, the preparation process of the uniform AB stacking minority layer single crystal graphene film is as follows:

[0012] Stage 1: Using single crystal metal as the growth substrate, solid, liquid or gaseous carbon source, and forming a few-layer single crystal graphene continuous film with a multi-layer graphene island structure through constant temperature or cooling segregation;

[0013] Stage 2: Maintaining the growth atmosphere unchanged, raising the temperature to increase the carbon solubility of the single crystal metal substrate, dissolving the multilayer graphene islands into the single crystal metal substrate, and obtaining a single crystal graphene film without multilayer graphene islands;

[0014] Stage 3: Maintaining the growth atmosphere unchanged, cooling down again for segregation, and then performing multiple heating-cooling cycles to splice the incomplete few layers of graphene into a complete film.

[0015] The segregation preparation method of the uniform AB stacked few-layer single-crystal graphene film, in the first stage, the carbon source is a gaseous or liquid hydrocarbon: one or more of methane, ethane, ethylene, acetylene, benzene, toluene, cyclohexane, ethanol, methanol, acetone or carbon monoxide, or the carbon source is a solid carbon source: one or more of amorphous carbon, paraffin, polymethyl methacrylate, polycarbonate, polystyrene, polyethylene, polypropylene; the auxiliary carrier gas is one of hydrogen, nitrogen, argon or a mixture of hydrogen and nitrogen, hydrogen and argon, and the carrier gas flow rate is 20 to 500 ml / min.

[0016] In the segregation preparation method of the uniform AB stacked few-layer single-crystal graphene film, in the second stage, the temperature increase amplitude depends on the dissolved carbon content of the metal substrate and its increase amplitude with temperature. After the temperature is increased, it is necessary to keep warm to ensure that the graphene multilayer islands are fully dissolved into the metal substrate.

[0017] In the segregation preparation method of the uniform AB stacked minority-layer single-crystalline graphene film, in the third stage, the temperature reduction amplitude depends on the proportion of the incomplete area in the minority-layer graphene.

[0018] In the segregation preparation method of the uniform AB stacked minority-layer single-crystalline graphene film, in the third stage, in order to fully dissolve and remove the non-uniform multilayer island structure and reduce the dissolution of the minority-layer graphene during the heating process, usually more than three heating-cooling cycles are required.

[0019] The design concept of the present invention is:

[0020] The present invention selects a single crystal metal with adjustable carbon solubility with temperature and small mismatch with graphene lattice as a matrix, and adopts a segregation method to prepare a few-layer graphene film. For the region of the uneven multilayer island appearing during the growth process, a heating method is adopted to increase the carbon solubility of the metal substrate, so that the multilayer graphene island is dissolved into the matrix to improve the uniformity. However, the heating process also causes dissolution and etching of the few-layer graphene, and it is necessary to repair the etched region in the few-layer graphene by cooling and segregating again. Through multiple heating-cooling cycle treatments, a uniform few-layer single crystal graphene film can be obtained, and this process also promotes the graphene to form the most stable AB stacking structure.

[0021] The advantages and beneficial effects of the present invention are:

[0022] 1. The present invention adjusts the dissolution and segregation of carbon on the metal substrate by adjusting the staged temperature changes during the preparation process, selectively removes the uneven multilayer graphene island structure, and effectively improves the uniformity of the minority layer graphene. In view of the unavoidable uneven multilayer graphene islands in the preparation of minority layers by the segregation method, uniform AB stacked minority layer graphene preparation can be obtained by heating-cooling cycle treatment.

[0023] 2. The present invention adopts a single crystal metal substrate to ensure that the crystal domains of the epitaxially grown graphene thereon are oriented in a consistent manner, thereby achieving controllable preparation of a few layers of single crystal graphene. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is an experimental device for high temperature reducing atmosphere annealing. In the figure, 11 is a gas inlet; 12 is a horizontal reaction furnace; 13 is a substrate to be annealed; 14 is a gas outlet; and 15 is a quartz tube.

[0025] Figure 2 The experimental device of chemical plating is shown in the figure, 21 is a beaker; 22 is a plating solution; 23 is a DC power supply; 24 is a plating metal; 25 is a substrate to be plated.

[0026] Figure 3 This is an experimental device for growing a uniform few-layer single-crystal graphene film by the segregation method. In the figure, 31 is a gas inlet; 32 is a horizontal reactor; 33 is a metal substrate; 34 is a gas outlet; and 35 is a quartz tube. DETAILED DESCRIPTION

[0027] In the specific implementation process, the present invention provides a method for preparing a uniform AB stacked minority layer single crystal graphene film by segregation. First, a single crystal metal substrate is prepared by a high temperature annealing method. For single crystal alloys that cannot be obtained by direct annealing, metals of other components are plated on both sides of the prepared single crystal metal substrate by a chemical plating method, and then the single crystal metal substrate is obtained by long-term high temperature annealing. The prepared single crystal metal substrate is then used for the segregation growth of graphene. After the growth of a minority layer of graphene film with uneven multilayer islands, multiple heating-cooling cycles are used to remove the multilayer island structure, and finally a uniform AB stacked minority layer single crystal graphene film is obtained. Among them, the first layer of the single crystal graphene film is formed by surface diffusion growth, and the second layer and more layers rely on the cooling and segregation of carbon growth on the single crystal metal substrate. The number of graphene layers can be controlled by regulating the alloy composition and carbon source concentration of the single crystal metal substrate.

[0028] Below, the present invention is further described in detail by examples.

[0029] Example 1

[0030] First, a single crystal metal substrate was prepared by high temperature annealing method, and a commercial polycrystalline copper foil of 40×60 mm was cut as the substrate to be annealed 13. Figure 1As shown, a quartz tube 15 is horizontally inserted into a furnace tube of a horizontal reactor 12 (the inner diameter of the furnace tube is 50 mm, and the length of the central constant temperature zone is 100 mm). The substrate 13 to be annealed is placed in the constant temperature zone of the inner cavity of the quartz tube 15. A gas inlet 11 and a gas outlet 14 are respectively provided at both ends of the quartz tube 15. The gas inlet 11 is two-way parallel connection and then converged into one way extending into the quartz tube 15. Both ends of the quartz tube 15 are sealed with flanges and sealing gaskets. The furnace temperature is maintained at 1020°C. In a hydrogen reducing atmosphere of 500 ml / min, the annealing time is 4 hours. After the annealing is completed, it is pushed out from the high temperature zone and cooled to room temperature to obtain a single crystal copper substrate with a thickness of 25 μm.

[0031] like Figure 2 As shown, the prepared single crystal copper substrate is used as the substrate to be plated 25 and is suspended in the electroplating solution 22 in the beaker 21, and is connected to the negative electrode of the DC power supply 23 through a wire. The positive electrode of the DC power supply 23 is connected to the plating metal 24 (a high-purity 99.999wt% nickel sheet with a thickness of 100μm). The specific formula of the electroplating solution 22 is: 140 g of nickel sulfate hexahydrate, 4 g of nickel chloride hexahydrate, 2 g of sodium fluoride, and 15 g of boric acid dissolved in 500ml of deionized water. The nickel plating time is 2h, and a nickel layer with a thickness of about 3μm is deposited on both sides of the substrate to be plated 25 to obtain a copper-nickel substrate. After completion, the surface is rinsed with deionized water 2 to 3 times, and quickly blown dry with a nitrogen gun. The copper-nickel substrate with nickel layers deposited on both sides is placed as shown in the following. Figure 1 The central area of ​​the horizontal reactor 12 shown was set at a furnace temperature of 1050° C., an atmosphere of 500 ml / min of hydrogen, and an annealing time of 6 h, and finally a single crystal copper-nickel alloy substrate was successfully prepared.

[0032] like Figure 3 As shown, the present invention adopts a horizontal reactor 32 (furnace tube inner diameter 22 mm, central constant temperature zone length 100 mm) to grow a uniform few-layer single-crystalline graphene film. A quartz tube 35 is horizontally penetrated through the furnace tube of the horizontal reactor 32. A gas inlet 31 and a gas outlet 34 are respectively provided at both ends of the quartz tube 35. The gas inlet 31 is three-way parallel connection and then converged into one way extending into the quartz tube 35. The three gas inlet ends of the gas inlet 31 correspond to hydrogen, argon, and carbon source methane, respectively, and the metal substrate 33 (single crystal copper-nickel alloy substrate) is pushed to the central constant temperature zone of the horizontal reactor 32 corresponding to the inner cavity of the quartz tube 35.

[0033] The specific growth steps of uniform AB stacking two layers of single-crystalline graphene are as follows:

[0034] 1) In an argon atmosphere, the temperature of the horizontal reactor is raised to 1070°C at a heating rate of 15°C / min. When the furnace temperature reaches the set temperature, the single crystal copper-nickel alloy substrate is pushed to the central constant temperature zone, first annealed in argon (500 ml / min) for 5 min to remove organic impurities that may be adsorbed on the surface, and then switched to hydrogen (500 ml / min) for annealing for 5 min to further clean and make the substrate flatter. A mixed gas of methane, hydrogen and argon (gas flow rate: methane 0.5 ml / min, hydrogen 50 ml / min, carrier gas argon 500 ml / min) is introduced to start carburizing the surface of the single crystal copper-nickel alloy substrate. After a 20-min constant temperature process, the gas flow rate is kept unchanged, and the temperature is reduced to 850°C at a cooling rate of 5°C / min and kept for 20 min. A two-layer graphene film with high coverage is obtained by segregation growth, but it contains an obvious non-uniform multilayer island structure.

[0035] 2) Keeping the gas flow rate unchanged, the furnace temperature was raised to 1050°C at a rate of about 7°C / min and kept warm for 20 min. The carbon solubility of the substrate increased with the increase of temperature, and the multi-layer graphene islands under the two-layer graphene film were gradually dissolved, thereby improving the uniformity of the two graphene films. However, a completely uniform two-layer graphene film has not yet been obtained.

[0036] 3) Keeping the gas flow rate unchanged, continue to cool down to 850°C at a rate of about 7°C / min and keep it at that temperature for 20 min, then increase the furnace temperature to 1050°C at a rate of 7°C / min and keep it at that temperature for 20 min, and repeat this cycle for 3 times to finally obtain a uniform AB stacked two-layer single-crystalline graphene film with a thickness of 0.34 nm for each layer of the single-crystalline graphene film.

[0037] Example 2

[0038] The difference from Example 1 is that the specific growth steps of AB stacked two layers of single-crystal graphene are as follows:

[0039] 1) In an argon atmosphere, the temperature of the horizontal reactor was raised to 1030°C at a heating rate of 15°C / min. When the furnace temperature reached the set temperature, the single crystal copper-nickel alloy substrate was pushed to the central constant temperature zone and annealed in argon (500 ml / min) for 5 min to remove impurities such as organic matter that may be adsorbed on the surface, and then switched to hydrogen (500 ml / min) for annealing for 5 min to further clean and make the substrate flatter. A mixed gas of methane, hydrogen and argon (gas flow rate: methane 0.5 ml / min, hydrogen 200 ml / min, carrier gas argon 500 ml / min) was introduced. After 30 minutes of heat preservation growth, the flow rate of hydrogen was switched to 50 ml / min, and the flow rates of methane and argon remained unchanged. The constant temperature growth was continued for 40 minutes. In the initial stage, a large flow of hydrogen was used to slow down the film formation speed of the first layer of graphene and to facilitate the formation of two-layer and multi-layer graphene domains. Thereafter, the flow rate was adjusted to 50 ml / min, and the growth was continued to obtain two-layer graphene with a higher coverage and multi-layer island areas with uneven distribution.

[0040] 2) Keeping the gas flow rate unchanged, the furnace temperature was raised to 1050°C at a rate of about 7°C / min and kept warm for 10 min. The carbon solubility of the substrate increased with the increase in temperature, and the multi-layer graphene islands under the two-layer graphene were gradually dissolved, thereby improving the uniformity of the two-layer graphene. However, a completely uniform two-layer graphene film has not yet been obtained.

[0041] 3) Keeping the gas flow rate unchanged, continue to cool down to 850°C at a rate of about 7°C / min and keep it warm for 30 min. The carbon atoms segregated during the cooling stage can fill the defects and even holes dissolved and etched during the heating process, so that the coverage of a few layers of graphene is close to 100%. Then, the furnace temperature is increased to 1050°C at a rate of 7°C / min and kept warm for 10 min. This cycle is repeated 3 times to finally prepare a uniform AB stacked two-layer single-crystalline graphene film with a thickness of 0.34 nm for each layer of single-crystalline graphene film.

[0042] Example 3

[0043] The difference from Example 1 is that the specific growth steps of the AB stacked three-layer single-crystal graphene are as follows:

[0044] 1) In an argon atmosphere, the temperature of the horizontal reactor was raised to 1070°C at a heating rate of 15°C / min. When the furnace temperature reached the set temperature, the single crystal copper-nickel alloy substrate was pushed to the central constant temperature zone, and annealed in argon (500 ml / min) for 5 min to remove organic impurities that may be adsorbed on the surface, and then switched to hydrogen (500 ml / min) for annealing for 5 min to further clean and make the substrate flatter. A mixed gas of methane, hydrogen and argon (gas flow rate: methane 0.8 ml / min, hydrogen 50 ml / min, carrier gas argon 500 ml / min) was introduced, and after keeping the temperature for 30 min, the gas flow rate was kept unchanged, and the temperature was reduced to 850°C at a cooling rate of 5°C / min and kept for 20 min. A three-layer graphene film with a high coverage was obtained through segregation growth, but it was accompanied by an obvious uneven multilayer island structure.

[0045] 2) Keeping the gas flow rate unchanged, the furnace temperature was raised to 1050°C at a rate of about 7°C / min and kept warm for 20 min. The carbon solubility of the substrate increased with increasing temperature, and the multi-layer graphene islands under the three-layer graphene were preferentially dissolved, thereby improving the uniformity of the three-layer graphene. However, a completely uniform three-layer graphene film has not yet been obtained.

[0046] 3) Keeping the gas flow rate unchanged, continue to cool down to 850°C at a rate of about 7°C / min and keep it at that temperature for 20 min, then increase the furnace temperature to 1050°C at a rate of 7°C / min and keep it at that temperature for 20 min, repeat this cycle 4 times, and finally prepare a uniform AB stacked three-layer single-crystalline graphene, and the thickness of each layer of the single-crystalline graphene film is 0.34 nm.

[0047] Example 4

[0048] The difference from Example 1 is that the specific growth steps of the AB stacked four-layer single-crystal graphene are as follows:

[0049] 1) In an argon atmosphere, the temperature of the horizontal reactor is raised to 1030°C at a heating rate of 15°C / min. When the furnace temperature reaches the set temperature, the single crystal copper-nickel alloy substrate is pushed to the central constant temperature zone and switched to hydrogen (500 ml / min) for annealing for 10 min. On the one hand, the surface pollutants are removed, and on the other hand, the hydrogen pre-annealing can activate the surface of the metal substrate and promote the nucleation of a few layers and multiple layers during the growth process. A mixed gas of methane, hydrogen and argon (gas flow rate: methane 0.5 ml / min, hydrogen adjusted to 50 ml / min, carrier gas argon 500 ml / min) is introduced to start growing graphene on the surface of the single crystal copper-nickel alloy substrate. After 50 minutes of constant temperature growth, a four-layer graphene film with high coverage and a multilayer island area are obtained.

[0050] 2) Keeping the gas flow rate unchanged, the furnace temperature was raised to 1060°C at a rate of about 7°C / min and kept warm for 20 min. The carbon solubility of the substrate increased with increasing temperature, and the multi-layer graphene islands under the four-layer graphene were preferentially dissolved in the matrix, thereby improving the uniformity of the few-layer graphene.

[0051] 3) Keeping the gas flow rate unchanged, continue to cool down to 850°C at a rate of about 7°C / min and keep it warm for 20 min. The carbon source precipitated during the cooling process can repair structural defects and ensure the integrity and stability of the few-layer graphene film. Then, the furnace temperature is increased to 1050°C at a rate of 7°C / min and kept warm for 20 min. This cycle is repeated 6 times to finally prepare uniform AB-stacked four-layer single-crystalline graphene, and the thickness of each single-crystalline graphene film is 0.34 nm.

[0052] The results of the embodiments show that the present invention can significantly improve the uniformity of a few-layer graphene and can prepare a few-layer single-crystalline graphene film with uniform AB stacking, laying a foundation for the application of a few-layer graphene in the fields of new generation electronics, optoelectronics and spintronic devices.

Claims

1. A method for preparing a uniform AB stacked few-layer single-crystal graphene film by segregation, characterized in that: A single crystal metal substrate with a certain carbon solubility is used, and the temperature is used to regulate the carbon solubility of the metal substrate. A few-layer single-crystalline graphene film with uniform AB stacking is prepared on the surface of the single crystal metal substrate through a three-step method. The first step is segregation growth to obtain a high-coverage few-layer graphene film, which contains an uneven multi-layer island structure. The second step is to increase the growth temperature and dissolve and remove the uneven multi-layer island area by increasing the carbon solubility of the metal substrate. The third step is to cool the growth again and use the carbon segregation caused by cooling to fill the defects and gaps in the few-layer graphene film. After that, multiple heating-cooling cycles are performed to finally obtain a few-layer single-crystalline graphene film with uniform AB stacking.

2. The method for preparing the uniform AB stacked minority-layer single-crystal graphene film by segregation according to claim 1, characterized in that: Few-layer graphene includes graphene with a layer number ranging from 2 to 10 layers, and multi-layer island specifically refers to island-structured graphene with a layer number greater than the number of layers of the film in which it is located.

3. The method for preparing the uniform AB stacked minority-layer single-crystal graphene film by segregation according to claim 1, characterized in that: This method is applicable to the case where the multilayer island graphene to be removed is located at the interface between a few-layer graphene film and a metal substrate.

4. The method for preparing the uniform AB stacked minority-layer single-crystal graphene film by segregation according to claim 1, characterized in that: The single crystal metal substrate uses a metal with a certain amount of dissolved carbon and a lattice constant that is highly compatible with graphene, including but not limited to metal nickel, iron, cobalt, platinum and alloys formed with other elements. The graphene film obtained by epitaxial growth of the single crystal metal substrate is a few-layer single crystal graphene film.

5. The method for preparing the uniform AB stacked minority-layer single-crystal graphene film by segregation according to claim 1, characterized in that: The single crystal metal substrate is prepared by high temperature annealing method. Commercial polycrystalline metal foil is annealed to obtain a single crystal metal substrate. The typical annealing temperature is 1000-1200°C. The annealing atmosphere is hydrogen or a mixture of hydrogen and argon. The flow rate is 200-500 ml / min. The annealing time is 4-8h.

6. The method for preparing a uniform AB stacked minority-layer single-crystal graphene film by segregation according to any one of claims 1 to 5, characterized in that: The preparation process of uniform AB stacking few-layer single-crystalline graphene film is as follows: Stage 1: Using single crystal metal as the growth substrate, solid, liquid or gaseous carbon source, and forming a few-layer single crystal graphene continuous film with a multi-layer graphene island structure through constant temperature or cooling segregation; Stage 2: Maintaining the growth atmosphere unchanged, raising the temperature to increase the carbon solubility of the single crystal metal substrate, dissolving the multilayer graphene islands into the single crystal metal substrate, and obtaining a single crystal graphene film without multilayer graphene islands; Stage 3: Maintaining the growth atmosphere unchanged, cooling down again for segregation, and then performing multiple heating-cooling cycles to splice the incomplete few layers of graphene into a complete film.

7. The method for preparing the uniform AB stacked minority-layer single-crystal graphene film by segregation according to claim 6, characterized in that: In the first stage, the carbon source is a gaseous or liquid hydrocarbon: one or more of methane, ethane, ethylene, acetylene, benzene, toluene, cyclohexane, ethanol, methanol, acetone or carbon monoxide, or the carbon source is a solid carbon source: one or more of amorphous carbon, paraffin, polymethyl methacrylate, polycarbonate, polystyrene, polyethylene, polypropylene; the auxiliary carrier gas is one of hydrogen, nitrogen, argon or a mixture of hydrogen and nitrogen, hydrogen and argon, and the carrier gas flow rate is 20 to 500 ml / min.

8. The method for preparing the uniform AB stacked minority-layer single-crystal graphene film by segregation according to claim 6, characterized in that: In the second stage, the temperature increase depends on the amount of carbon dissolved in the metal substrate and its increase with temperature. After the temperature is increased, it is necessary to keep warm to ensure that the graphene multilayer islands are fully dissolved into the metal substrate.

9. The method for preparing the uniform AB stacked minority-layer single-crystal graphene film by segregation according to claim 6, characterized in that: In the third stage, the extent of the cooling depends on the proportion of incomplete regions in the few-layer graphene.

10. The method for preparing a uniform AB stacked minority-layer single-crystal graphene film by segregation according to claim 6, characterized in that: In the third stage, in order to fully dissolve and remove the uneven multilayer island structure and reduce the dissolution of a few layers of graphene during the heating process, usually more than three heating-cooling cycles are required.

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