A segregation preparation method of a uniform AB stack few-layer monocrystalline graphene film

Abstract

The present application relates to the field of graphene preparation, in particular to a segregation preparation method of uniform AB-stacked few-layer single-crystal graphene film, which is suitable for preparing large-area uniform high-quality AB-stacked few-layer single-crystal graphene film. A single-crystal metal substrate with a certain carbon solubility is used, and the carbon solubility of the metal substrate is regulated by temperature, and a uniform AB-stacked few-layer single-crystal graphene film is prepared on the surface of the single-crystal metal substrate by a three-step method. The present application regulates the carbon dissolution and segregation of the metal substrate by adjusting the temperature change in the preparation process, and selectively removes the non-uniform multi-layer graphene island structure, which significantly improves the uniformity of the few-layer graphene, and lays a foundation for the application of few-layer graphene in the field of new generation of electronic, optoelectronic and spin electronic devices.

Description

Technical Field

[0001] This invention relates to the field of graphene preparation, specifically to a method for preparing a uniform AB-stacked few-layer single-crystal graphene film with segregation, which is suitable for preparing large-area uniform high-quality AB-stacked few-layer single-crystal graphene films. Background Technology

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

[0003] Segregation has significant advantages such as high controllability, scalability, good repeatability, and low cost. The graphene films prepared by it have high crystal quality, thus becoming a representative method for preparing high-quality few-layer graphene films. However, the commonly used solid metal foil substrate inevitably leads to the formation of uneven multilayer islands and errors in the orientation of some crystal domains during the segregation growth process due to its relatively rough surface, making it difficult to achieve the preparation of uniform few-layer single-crystal graphene films with AB stacking. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a uniform AB-stacked few-layer single-crystal graphene film with segregation. This method has the advantages of low cost, good controllability, good uniformity, and scalability, and has the potential to further prepare large-area wafer-level AB-stacked uniform few-layer single-crystal graphene films.

[0005] The technical solution of this invention is:

[0006] A segregation preparation method for uniformly AB-stacked few-layer monocrystalline graphene films is disclosed. This method utilizes a single-crystal metal substrate with a certain carbon-solubility and leverages the temperature-controlled carbon solubility of the metal substrate to prepare a uniformly AB-stacked few-layer monocrystalline graphene film on the surface of the single-crystal metal substrate via a three-step process. The first step involves segregation growth to obtain a high-coverage few-layer graphene film containing an uneven, multi-layered island structure. The second step involves increasing the growth temperature to dissolve and remove the uneven multi-layered island regions by increasing the carbon solubility of the metal substrate. The third step involves cooling the growth temperature again, utilizing the carbon segregation caused by the cooling to fill defects and voids in the few-layer graphene film. This process is repeated multiple times with heating and cooling cycles to finally obtain a uniformly AB-stacked few-layer monocrystalline graphene film.

[0007] The method for preparing a uniform AB stacked few-layer single-crystal graphene film by segregation, wherein the few-layer graphene includes graphene with 2 to 10 layers, and multi-layer islands specifically refer to island-shaped graphene structures with more layers than the number of layers in the film.

[0008] The method for preparing a uniformly stacked AB-layered single-crystal graphene film with segregation is applicable to cases where the multilayered island-like graphene to be removed is located at the interface between the single-layered graphene film and the metal substrate.

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

[0010] The method for preparing a uniform AB stacked few-layer single-crystal graphene film with segregation involves preparing a single-crystal metal substrate using a high-temperature annealing method. A 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, and the annealing time is 4–8 h.

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

[0012] Stage 1: Using single-crystal metal as the growth substrate, solid, liquid or gaseous carbon sources are used to form a few-layer single-crystal graphene continuous film with a multi-layer graphene island structure through isothermal or cooling segregation.

[0013] Stage 2: Maintaining the growth atmosphere unchanged, the temperature is increased to increase the carbon solubility of the single-crystal metal substrate, dissolving the multilayer graphene islands into the single-crystal metal substrate to obtain a single-crystal graphene film without multilayer graphene islands.

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

[0015] In the segregation preparation method of 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, or polypropylene; the auxiliary carrier gas is one of hydrogen, nitrogen, or argon, or a mixture of hydrogen and nitrogen, or hydrogen and argon, and the carrier gas flow rate is 20-500 ml / min.

[0016] In the segregation preparation method of uniform AB stacked few-layer single-crystal graphene film, in the second stage, the heating range depends on the amount of carbon dissolved in the metal substrate and its increase with temperature. After heating, 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 uniform AB stacked few-layer single-crystal graphene film, in the third stage, the cooling rate depends on the proportion of incomplete regions in the few-layer graphene.

[0018] In the segregation preparation method of uniform AB stacked few-layer single-crystal 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 few-layer graphene during the heating process, more than three heating-cooling cycles are usually required.

[0019] The design concept of this invention is:

[0020] This invention uses a single-crystal metal substrate with temperature-adjustable carbon solubility and low lattice mismatch with graphene as the matrix, and employs a segregation method to prepare a few-layer graphene film. To address the uneven multilayer island regions that appear during growth, a heating method is used to increase the carbon solubility of the metal substrate, allowing the multilayer graphene islands to dissolve into the substrate and improve uniformity. However, the heating process also causes dissolution and etching of the few-layer graphene, requiring subsequent cooling and segregation to repair the etched areas. Through multiple heating-cooling cycles, a uniform few-layer single-crystal graphene film can be obtained. This process also promotes the formation of the most stable AB stacking structure of graphene.

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

[0022] 1. This invention regulates the dissolution and segregation of carbon in the metal substrate by adjusting the staged temperature changes during the preparation process, selectively removing the non-uniform multilayer graphene island structure and effectively improving the uniformity of few-layer graphene. For the non-uniform multilayer graphene islands that are difficult to avoid in the preparation of few-layer graphene by the segregation method, uniform AB-stacked few-layer graphene can be obtained through a heating-cooling cycle.

[0023] 2. This invention uses a single-crystal metal substrate to ensure that the orientation of the epitaxially grown graphene domains is consistent, thereby achieving controllable preparation of a few-layer single-crystal graphene. Attached Figure Description

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

[0025] Figure 2 This is the experimental setup for electroless plating. In the diagram, 21 is a beaker; 22 is the plating solution; 23 is a DC power supply; 24 is the plating metal; and 25 is the substrate to be plated.

[0026] Figure 3 This is an experimental setup for growing uniform few-layer single-crystal graphene films using the segregation method. In the figure, 31 is the gas inlet; 32 is the horizontal reactor; 33 is the metal substrate; 34 is the gas outlet; and 35 is the quartz tube. Detailed Implementation

[0027] In its specific implementation, this invention provides a method for preparing a uniformly AB-stacked few-layer monocrystalline graphene film with segregation. First, a single-crystal metal substrate is prepared using a high-temperature annealing method. For single-crystal alloys that cannot be obtained through direct annealing, a chemical plating method is used to deposit metals of other compositions onto both sides of the prepared single-crystal metal substrate, followed by prolonged high-temperature annealing to obtain the single-crystal metal substrate. The prepared single-crystal metal substrate is then used for the segregation growth of graphene. After growing a few-layer graphene film with unevenly distributed multilayer islands, multiple heating-cooling cycles are used to remove the multilayer island structure, ultimately obtaining a uniformly AB-stacked few-layer monocrystalline graphene film. The first layer of the monocrystalline graphene film is formed through surface diffusion growth, while the second and subsequent layers rely on the cooling segregation of carbon from the single-crystal metal substrate for growth. The number of graphene layers can be controlled by adjusting the alloy composition and carbon source concentration of the single-crystal metal substrate.

[0028] The present invention will be further described in detail below through embodiments.

[0029] Example 1

[0030] First, a single-crystal metal substrate was prepared using a high-temperature annealing method, and a 40×60mm commercial polycrystalline copper foil was cut as the substrate to be annealed 13. Figure 1As shown, a quartz tube 15 is horizontally inserted into the furnace tube of a horizontal reactor 12 (furnace tube inner diameter 50 mm, central constant temperature zone length 100 mm). The substrate 13 to be annealed is placed in the constant temperature zone inside the quartz tube 15. The two ends of the quartz tube 15 are respectively provided with a gas inlet 11 and a gas outlet 14. The gas inlet 11 consists of two parallel lines that converge into one line extending into the quartz tube 15. Both ends of the quartz tube 15 are sealed with flanges and gaskets. The furnace temperature is maintained at 1020℃. Under a hydrogen reducing atmosphere of 500 ml / min, the annealing time is 4 hours. After annealing, the substrate is removed 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, used as the substrate to be plated 25, is suspended in the electroplating solution 22 within a beaker 21 and connected to the negative terminal of a DC power supply 23 via a wire. The positive terminal of the DC power supply 23 is connected to the plating metal 24 (a 100μm thick nickel sheet with a purity of 99.999wt%). The specific formulation of the electroplating solution 22 is: 140 g nickel sulfate hexahydrate, 4 g nickel chloride hexahydrate, 2 g sodium fluoride, and 15 g boric acid dissolved in 500 ml of deionized water. The nickel plating time is 2 hours, depositing a nickel layer of approximately 3μm thickness on both sides of the substrate 25 to obtain a copper-nickel substrate. After completion, the surface is rinsed 2-3 times with deionized water and quickly dried with a nitrogen gun. The copper-nickel substrate with nickel layers deposited on both sides is then placed in a... Figure 1 In the central region of the horizontal reactor 12 shown, the furnace temperature was set to 1050℃, the atmosphere was 500 ml / min of hydrogen, and the annealing time was 6 h, and a single crystal copper-nickel alloy substrate was successfully prepared.

[0032] like Figure 3 As shown, this invention uses a horizontal reactor 32 (furnace tube inner diameter 22 mm, central constant temperature zone length 100 mm) to grow uniform few-layer single-crystal graphene films. A quartz tube 35 is horizontally inserted into the furnace tube of the horizontal reactor 32. The two ends of the quartz tube 35 are respectively provided with gas inlet 31 and gas outlet 34. The gas inlet 31 consists of three parallel connections that converge into one line 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, pushing the metal substrate 33 (single-crystal copper-nickel alloy substrate) into 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 for uniformly stacked AB layers of single-crystal graphene are as follows:

[0034] 1) The temperature of the horizontal reactor was raised to 1070℃ in an argon atmosphere at a heating rate of 15℃ / min. Once the set temperature was reached, the single-crystal copper-nickel alloy substrate was moved to the central isothermal zone and annealed for 5 minutes in argon (500 mL / min) to remove any adsorbed organic matter or other impurities. Then, annealing was performed in hydrogen (500 mL / min) for another 5 minutes to further clean and smooth the substrate. A mixture of methane, hydrogen, and argon (gas flow rate: methane 0.5 mL / min, hydrogen 50 mL / min, carrier argon 500 mL / min) was introduced to begin carburizing the surface of the single-crystal copper-nickel alloy substrate. After a 20-minute isothermal process, the temperature was lowered to 850℃ at a rate of 5℃ / min while maintaining a constant gas flow rate and held for 20 minutes. This resulted in the growth of a high-coverage two-layer graphene film with a distinctly non-uniform multilayer island structure.

[0035] 2) Keeping the gas flow rate constant, the furnace temperature is raised to 1050℃ at a rate of about 7℃ / min and held for 20min. The carbon solubility of the substrate increases with the increase of temperature, which gradually dissolves the multilayer graphene islands under the two graphene films, improving the uniformity of the two graphene films, but not yet obtaining a completely uniform two-layer graphene film.

[0036] 3) Keeping the gas flow rate constant, continue to cool down to 850°C at a rate of about 7°C / min and hold for 20 min. Then, raise the furnace temperature to 1050°C at a rate of 7°C / min and hold for 20 min. Repeat this cycle 3 times to finally obtain a uniform AB stacked two-layer monocrystalline graphene film with a thickness of 0.34 nm for each layer.

[0037] Example 2

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

[0039] 1) In an argon atmosphere, raise the furnace temperature of the horizontal reactor to 1030°C at a heating rate of 15°C / min. When the furnace temperature reaches the set temperature, push the single crystal copper-nickel alloy substrate to the central constant temperature zone. First, anneal it in argon (500 ml / min) for 5 min to remove any organic matter or other impurities that may be adsorbed on the surface. Then, switch to hydrogen (500 ml / min) for annealing for 5 min to further clean and make the substrate smoother. A mixture of methane, hydrogen, and argon was introduced (gas flow rate: methane 0.5 mL / min, hydrogen 200 mL / min, carrier argon 500 mL / min). After 30 min of incubation, the hydrogen flow rate was switched to 50 mL / min, while the flow rates of methane and argon remained constant. The incubation continued for another 40 min. The initial stage used a high flow rate of hydrogen to slow down the formation of the first graphene layer, which was beneficial for the formation of two or more graphene domains. The flow rate was then adjusted to 50 mL / min, and the growth continued to obtain two graphene layers with high coverage and multi-layered island regions with uneven distribution.

[0040] 2) Keeping the gas flow rate constant, the furnace temperature is raised to 1050℃ at a rate of about 7℃ / min and held for 10min. The carbon solubility of the substrate increases with the increase of temperature, which gradually dissolves the multilayer graphene islands under the two layers of graphene, improving the uniformity of the two layers of graphene, but a completely uniform two-layer graphene film has not yet been obtained.

[0041] 3) Keep the gas flow rate constant and continue to cool down to 850°C at a rate of about 7°C / min and hold for 30 min. The carbon atoms segregated during the cooling stage can fill the defects and even pores dissolved and etched during the heating process, so that the coverage of a few layers of graphene is close to 100%. Then, raise the furnace temperature to 1050°C at a rate of 7°C / min and hold for 10 min. Repeat this cycle 3 times to finally prepare a uniform AB stacked two-layer monocrystalline graphene film with a thickness of 0.34 nm for each layer of monocrystalline graphene film.

[0042] Example 3

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

[0044] 1) The temperature of the horizontal reactor was raised to 1070℃ in an argon atmosphere at a heating rate of 15℃ / min. When the furnace temperature reached the set temperature, the single-crystal copper-nickel alloy substrate was pushed to the central isothermal zone and annealed in argon (500 ml / min) for 5 min to remove any adsorbed organic matter or other impurities from the surface. Then, it was annealed in hydrogen (500 ml / min) for 5 min to further clean and flatten the substrate. A mixture of methane, hydrogen, and argon was introduced (gas flow rate: methane 0.8 ml / min, hydrogen 50 ml / min, carrier argon 500 ml / min). After holding at this temperature for 30 min, the temperature was lowered to 850℃ at a cooling rate of 5℃ / min while maintaining a constant gas flow rate, and held for 20 min. A three-layer graphene film with high coverage was obtained through segregation growth, but it was accompanied by a significant non-uniform multilayer island structure.

[0045] 2) Keeping the gas flow rate constant, the furnace temperature is raised to 1050℃ at a rate of about 7℃ / min and held for 20min. The carbon solubility of the substrate increases with the increase of temperature. The multilayer graphene islands under the three-layer graphene preferentially dissolve, which improves the uniformity of the three-layer graphene, but a completely uniform three-layer graphene film has not yet been obtained.

[0046] 3) Keep the gas flow rate constant, continue to cool down to 850°C at a rate of about 7°C / min and hold for 20 min. Then raise the furnace temperature to 1050°C at a rate of 7°C / min and hold for 20 min. Repeat this cycle 4 times to finally prepare a uniform AB stacked three-layer single-crystal graphene with a thickness of 0.34 nm for each single-crystal graphene film.

[0047] Example 4

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

[0049] 1) The temperature of the horizontal reactor was raised to 1030°C in an argon atmosphere at a heating rate of 15°C / min. Once the set temperature was reached, the single-crystal copper-nickel alloy substrate was moved to the central isothermal zone and annealed in hydrogen (500 mL / min) for 10 min. This process removed surface contaminants and activated the metal substrate surface, promoting few-layer and multilayer nucleation during growth. A mixture of methane, hydrogen, and argon (gas flow rate: methane 0.5 mL / min, hydrogen adjusted to 50 mL / min, argon carrier gas 500 mL / min) was introduced to begin graphene growth on the single-crystal copper-nickel alloy substrate. After 50 min of isothermal growth, a high-coverage four-layer graphene film and multilayer island regions were obtained.

[0050] 2) Keep the gas flow rate constant and raise the furnace temperature to 1060℃ at a rate of about 7℃ / min and hold for 20min. The carbon solubility of the substrate increases with the increase of temperature. The multilayer graphene islands under the four-layer graphene preferentially dissolve in the matrix, which improves the uniformity of the few-layer graphene.

[0051] 3) Keeping the gas flow rate constant, continue cooling to 850℃ at a rate of about 7℃ / min and hold for 20min. The carbon source released during the cooling process can repair structural defects and ensure the integrity and stability of the few-layer graphene film. Then, raise the furnace temperature to 1050℃ at a rate of 7℃ / min and hold for 20min. Repeat this cycle 6 times to finally prepare a uniform AB stacked four-layer single-crystal graphene with a thickness of 0.34nm for each single-crystal graphene film.

[0052] The results of the examples show that the present invention can significantly improve the uniformity of few-layer graphene and can prepare uniformly stacked AB few-layer single-crystal graphene films, laying the foundation for the application of few-layer graphene in next-generation electronic, optoelectronic and spintronic devices.

Claims

1. A method for preparing a uniformly stacked AB-layered few-layer single-crystal graphene film with segregation, characterized in that: Using a single-crystal metal substrate with a certain carbon solubility, and leveraging the effect of temperature on the carbon solubility of the metal substrate, a three-step method was employed to prepare a uniformly stacked few-layer single-crystal graphene film on the surface of the single-crystal metal substrate. The first step involved segregation growth to obtain a high-coverage few-layer graphene film containing an uneven multi-layer island structure. The second step involved increasing the growth temperature to dissolve and remove the uneven multi-layer island regions by increasing the carbon solubility of the metal substrate. The third step involved cooling growth again, using the carbon segregation caused by the cooling to fill the defects and voids in the few-layer graphene film. This process was repeated multiple times with heating and cooling cycles to finally obtain a uniformly stacked few-layer single-crystal graphene film.

2. The method for preparing a uniformly stacked few-layer single-crystal graphene film according to claim 1, characterized in that, Few-layer graphene includes graphene with 2 to 10 layers, while multi-layer islands specifically refer to island-like graphene structures with more layers than the number of layers in the film.

3. The method for preparing a uniformly stacked few-layer single-crystal graphene film according to claim 1, characterized in that, This method is applicable when the multilayer island-like graphene that needs to be removed is located at the interface between a few layers of graphene film and the metal substrate.

4. The method for preparing a uniformly stacked few-layer single-crystal graphene film 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 nickel, iron, cobalt, platinum and their alloys with other elements. The graphene film obtained by epitaxial growth on the single-crystal metal substrate is a few-layer single-crystal graphene film.

5. The method for preparing a uniformly stacked few-layer single-crystal graphene film according to claim 1, characterized in that, The single-crystal metal substrate is prepared by high-temperature annealing. Commercial polycrystalline metal foil is annealed to obtain the single-crystal metal substrate. The typical annealing temperature is 1000~1200℃, 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 4~8 h.

6. The method for preparing a uniformly stacked few-layer single-crystal graphene film according to any one of claims 1 to 5, characterized in that, The preparation process of uniformly stacked AB few-layer single-crystal graphene films is as follows: Stage 1: Using single-crystal metal as the growth substrate, solid, liquid or gaseous carbon sources are used to form a few-layer single-crystal graphene continuous film with a multi-layer graphene island structure through isothermal or cooling segregation. Stage 2: Maintaining the growth atmosphere unchanged, the temperature is increased to increase the carbon solubility of the single-crystal metal substrate, dissolving the multilayer graphene islands into the single-crystal metal substrate to obtain a single-crystal graphene film without multilayer graphene islands. Stage 3: Maintain the growth atmosphere unchanged, cool down again for segregation, and then perform multiple heating-cooling cycles to splice the incomplete few-layer graphene into a complete film.

7. The method for preparing a uniformly stacked few-layer single-crystal graphene film 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, and cyclohexane, or a solid carbon source: one or more of amorphous carbon, paraffin, polymethyl methacrylate, polycarbonate, polystyrene, polyethylene, and polypropylene; the auxiliary carrier gas is one of hydrogen, nitrogen, and argon, or a mixture of hydrogen and nitrogen, or hydrogen and argon, and the carrier gas flow rate is 20-500 ml / min.

8. The method for preparing a uniformly stacked few-layer single-crystal graphene film according to claim 6, characterized in that, In the second stage, the temperature rise depends on the amount of carbon dissolved in the metal substrate and the rate of increase with temperature. After heating, it is necessary to keep the substrate warm to ensure that the graphene multilayer islands are fully dissolved and incorporated into the metal substrate.

9. The method for preparing a uniformly stacked few-layer single-crystal graphene film according to claim 6, characterized in that, In the third stage, the cooling rate depends on the proportion of incomplete regions in the few-layer graphene.

10. The method for preparing a uniformly stacked few-layer single-crystal graphene film 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, more than three heating-cooling cycles are performed.

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