Chemical vapor deposition preparation method of wrinkle-free uniform single-layer graphene film

Abstract

The invention relates to the field of graphene preparation, in particular to a chemical vapor deposition preparation method of a wrinkle-free uniform single-layer graphene film. The method comprises the following steps: 1, introducing nanoparticles on the surface of a flat metal substrate by adopting a metal substrate with relatively good catalytic capability; and 2, growing graphene to form a graphene-nanoparticle-metal substrate structure, weakening the interfacial stress action between the graphene and the metal substrate by using nanoparticles, inhibiting the formation of wrinkles and the infiltration and precipitation process of a carbon source, and finally obtaining the uniform single-layer graphene film without wrinkles. According to the preparation method, the nano particles with the thermal expansion coefficient smaller than that of the metal substrate and adjustable distribution density are introduced to the surface of the flat metal substrate, the interface stress effect of the metal substrate on graphene and additional carburizing and carbon precipitation are weakened, and therefore wrinkles formed due to mismatching of the thermal expansion coefficients during high-temperature chemical vapor deposition cooling are avoided; and meanwhile, the formation of a non-uniform multi-layer graphene island-shaped structure is avoided.

Description

Technical Field

[0001] This invention relates to the field of chemical vapor deposition (CVD) preparation of graphene, specifically a chemical vapor deposition method for preparing wrinkle-free uniform monolayer graphene films, which is suitable for preparing large-area, wrinkle-free uniform monolayer graphene films. Background Technology

[0002] In the preparation of graphene films using high-temperature chemical vapor deposition (CVD), thermal mismatch between graphene and typical growth substrates inevitably leads to wrinkle formation during cooling. Wrinkles significantly affect the electrical behavior of graphene, such as reducing carrier mobility and causing anisotropic electrical transport behavior. Wrinkle formation is closely related to the interfacial interaction between graphene and the growth substrate; achieving uniform weak coupling at the graphene-substrate interface is an effective way to prepare wrinkle-free graphene. Furthermore, in the process of growing graphene using solid-state metal substrates via CVD, the small difference in formation energy between graphene layers, along with impurities and defects on the metal surface and potential disturbances in the reaction system, can all lead to the formation of inhomogeneous few-layer and multi-layer island formations.

[0003] Patent CN105819429A discloses a method for preparing wrinkle-free graphene. It involves controlling the crystallographic orientation of copper foil (e.g., the (001) crystal plane), growing graphene using CVD, and relying on the flatness of the low-index crystal planes of the copper foil to achieve stepless graphene. After transfer, a wrinkle-free sample is obtained. However, because this method relies on controlling the crystallographic orientation of the copper foil, growing graphene using CVD, and relying on the flatness of the low-index crystal planes of the copper foil to achieve stepless graphene, and obtaining a wrinkle-free sample after transfer, it cannot guarantee the uniformity of the single layer. Patent CN112707389A discloses a method for preparing wrinkle-free graphene films. It involves adjusting the hydrogen partial pressure to induce the formation of additional layer domains in the graphene, weakening the van der Waals forces between the graphene and the substrate, and reducing wrinkles. While the additional layer weakens the interfacial interaction, it disrupts the uniformity of the single layer and cannot solve problems such as substrate impurities and reaction disturbances leading to multilayer island structures. Patent CN114684813A discloses a method for preparing large-area uniform monolayer graphene films, employing a two-step carbon source supply method. First, multilayer graphene is grown using a high carbon source, then selective etching is performed by reducing the carbon source flux, ultimately obtaining a large-area monolayer graphene. However, because the interfacial interaction between graphene and the substrate is not controlled, wrinkles cannot be suppressed at their source. Therefore, achieving rapid growth of large-area, wrinkle-free, uniform monolayer high-quality graphene remains a challenging problem. Summary of the Invention

[0004] The purpose of this invention is to provide a chemical vapor deposition method for preparing wrinkle-free uniform single-layer graphene films, which solves the problems of existing technologies that cannot simultaneously suppress wrinkle formation and multi-layer island structure growth, as well as the problems of poor uniformity, complex process, low growth efficiency, and significant impact on graphene properties during large-area preparation.

[0005] The technical solution of this invention is:

[0006] A chemical vapor deposition method for preparing wrinkle-free uniform monolayer graphene films involves using a metal substrate with good catalytic ability. The first step is to introduce nanoparticles onto the surface of a flat metal substrate. The second step is to grow graphene to form a "graphene-nanoparticle-metal substrate" structure. The nanoparticles are used to reduce the interfacial stress between graphene and the metal substrate, suppressing wrinkle formation and carbon source infiltration and precipitation, ultimately obtaining wrinkle-free uniform monolayer graphene films.

[0007] The method for preparing wrinkle-free uniform single-layer graphene film by chemical vapor deposition involves nanoparticles composed of oxides or nitrides. The coefficient of thermal expansion of the nanoparticles is less than that of the metal substrate, the melting point is higher than the growth temperature of graphene by chemical vapor deposition, and the nanoparticles do not dissolve in the metal substrate or react with carbon to form interstitial phases.

[0008] The chemical vapor deposition method for preparing wrinkle-free uniform monolayer graphene films involves introducing nanoparticles through physical deposition, chemical reaction, or solution coating before graphene growth.

[0009] The chemical vapor deposition method for preparing wrinkle-free uniform monolayer graphene films regulates the distribution density of nanoparticles by controlling physical deposition parameters or chemical reaction conditions, thereby controlling the wrinkling behavior of subsequent graphene growth.

[0010] The chemical vapor deposition method for preparing wrinkle-free uniform single-layer graphene films uses a flat-surfaced, catalytically active metal film or metal foil as a metal substrate, including but not limited to metals such as copper, nickel, iron, cobalt, platinum, or alloys formed with other elements.

[0011] The chemical vapor deposition method for preparing wrinkle-free uniform monolayer graphene films employs chemical dissolution or physical etching to remove nanoparticles between graphene and the metal substrate, thereby achieving clean transfer of wrinkle-free uniform monolayer graphene films.

[0012] The method for preparing wrinkle-free uniform monolayer graphene films by chemical vapor deposition, the preparation process of wrinkle-free uniform monolayer graphene films is as follows:

[0013] Stage 1: Introduce nanoparticles onto the surface of a flat metal foil or metal film to form a "nanoparticle-metal substrate" structure. The distribution density of nanoparticles can be controlled by changing the parameters of specific chemical reactions or the conditions of physical methods.

[0014] Stage 2: Introduce an auxiliary carrier gas and use a solid, liquid, or gaseous carbon source to perform isothermal chemical vapor deposition of a single-layer graphene film on a "nanoparticle-metal substrate" structure.

[0015] In the chemical vapor deposition preparation method for wrinkle-free uniform monolayer graphene films, in the first stage, the distribution of nanoparticles is controlled to be dense or sparse by changing the parameters of the specific method for introducing nanoparticles.

[0016] In the chemical vapor deposition method for preparing wrinkle-free uniform monolayer graphene films, in the second 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 wax, 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 20–1000 ml / min.

[0017] The chemical vapor deposition method for preparing wrinkle-free uniform monolayer graphene films involves nanoparticles positioned between graphene and a metal substrate, forming a three-layer structure of "graphene-nanoparticle-metal substrate". The distribution density of the nanoparticles affects the subsequent graphene growth behavior: when the nanoparticles are dense on the metal substrate surface, complete separation of graphene growth from the metal substrate is achieved, resulting in wrinkle-free uniform monolayer graphene; when the nanoparticles are sparse on the metal substrate surface, partial separation of graphene growth from the metal substrate is achieved, resulting in fold-free wrinkle-free uniform monolayer graphene.

[0018] The design concept of this invention is:

[0019] This invention selects a metal thin film or metal foil with high catalytic activity as the growth substrate, and introduces nanoparticles with a smaller coefficient of thermal expansion on its surface to reduce the interfacial stress between the graphene grown on the surface and the metal substrate, reduce the formation of wrinkles, and inhibit the carbon diffusion and carbon precipitation process of the metal substrate, which is beneficial to the preparation of a single-layer graphene film with a uniform structure.

[0020] This invention introduces nanoparticles with a lower coefficient of thermal expansion than the metal substrate and an adjustable distribution density onto a flat metal substrate surface to form a "graphene-nanoparticle-metal substrate" structure. The nanoparticles reduce the interfacial stress on the graphene caused by the metal substrate and the additional carburization and carbon precipitation, thereby avoiding wrinkles caused by the mismatch of thermal expansion coefficients during the cooling of high-temperature chemical vapor deposition, and also avoiding the formation of uneven multilayer graphene island structures.

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

[0022] 1. This invention significantly reduces the interfacial stress between graphene and the metal substrate by introducing nanoparticles on the surface of the metal substrate. The morphology of wrinkles can be changed by controlling the distribution density of nanoparticles, thereby avoiding the formation of wrinkles. The method is simple and highly controllable, effectively improving the flatness and uniformity of graphene films.

[0023] 2. This invention uses nanoparticles to block carbon atoms from penetrating into a metal substrate, which can simultaneously suppress the growth of uneven multilayer graphene structures and obtain a uniform single-layer graphene film.

[0024] 3. The method of the present invention has the advantages of simple operation, good repeatability, easy expansion, low cost and good uniformity. It is easy to scale up and realize the rapid growth of large-area uniform single-layer graphene films. It can prepare wrinkle-free uniform single-layer graphene films with wafer-level or larger dimensions.

[0025] 4. The nanoparticles of this invention can be removed by chemical dissolution or physical etching, achieving non-damaging transfer of graphene. Attached Figure Description

[0026] 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 quartz tube; and 15 is the gas outlet.

[0027] Figure 2 This is the experimental setup for electroless plating. In the diagram, 21 is the electrolytic cell; 22 is the plating solution; 23 is the DC power supply; 24 is the substrate to be plated; and 25 is the plating metal.

[0028] Figure 3 This is an experimental setup for growing wrinkle-free, uniform monolayer graphene films using the CVD method. In the figure, 31 is the gas inlet; 32 is the horizontal reactor; 33 is the metal substrate; 34 is the quartz tube; and 35 is the gas outlet.

[0029] Figure 4 This is a schematic diagram of an experimental setup for desktop magnetron sputtering coating. In the diagram, 41 is the metal substrate; 42 is the sample disk; 43 is the target material; and 44 is the magnetron sputtering negative electrode.

[0030] Figure 5The image shows the morphology of the wrinkle-free, uniform monolayer graphene film obtained in Example 1.

[0031] Figure 6 The image shows the morphology of the wrinkle-free, uniform monolayer graphene film obtained in Example 2.

[0032] Figure 7 The image shows the morphology of the wrinkle-free, uniform monolayer graphene film obtained in Example 5. Detailed Implementation

[0033] In its specific implementation, this invention provides a chemical vapor deposition method for preparing a wrinkle-free, uniform monolayer graphene film. First, a clean and flat metal substrate is prepared using a high-temperature annealing method. Then, nanoparticles are introduced onto the flat metal substrate (metal foil or metal film) surface using methods such as physical deposition, chemical reaction, and solution coating. The nanoparticles have a melting point higher than the growth temperature of graphene in chemical vapor deposition and are insoluble in the metal substrate and carbon, or react with it, including but not limited to oxides and nitrides. Subsequently, a CVD growth process of graphene is performed to grow a monolayer graphene film on the "metal substrate-nanoparticle" structure. By controlling the specific parameters of the nanoparticle reaction, the distribution density of the nanoparticles is controlled, thereby controlling the wrinkle behavior of the graphene and avoiding the formation of uneven, multi-layered island structures, thus achieving the successful preparation of a wrinkle-free, uniform monolayer graphene film. The presence of nanoparticles enables partial separation between graphene growth and the metal substrate, significantly reducing wrinkle formation; at the same time, it inhibits the carburization and carbon precipitation process of the metal substrate during graphene growth, and uniform, island-free monolayer graphene is prepared within a fairly wide growth temperature window.

[0034] The present invention will be further described in detail below through embodiments.

[0035] Example 1

[0036] First, high-temperature annealing was used to remove contaminants from the surface of the metal substrate. A 40×60mm commercial polycrystalline copper foil was cut as the substrate to be annealed (13). Figure 1 As shown, a quartz tube 14 is inserted horizontally 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 14. The two ends of the quartz tube 14 are respectively provided with a gas inlet 11 and a gas outlet 15. Both ends of the quartz tube 14 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 1 hour. After annealing, the substrate is removed from the high temperature zone and cooled to room temperature to obtain a flat copper foil substrate with a thickness of 25 μm.

[0037] like Figure 2As shown, the prepared flat copper foil substrate, used as the substrate to be plated 24, is suspended in the electroplating solution 22 within the electrolytic cell 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 25 (a 100μm thick nickel sheet with a purity of 99.999wt%), which is suspended in the electroplating solution 22 within the electrolytic cell 21. The specific formulation of the electroplating solution 22 is: 140g nickel sulfate hexahydrate, 4g nickel chloride hexahydrate, 2g sodium fluoride, and 15g boric acid dissolved in 500ml of deionized water. The nickel plating time is 2 hours, depositing a nickel layer of approximately 3μm thickness on both sides of the substrate to be plated 24 to obtain a copper-nickel alloy substrate. After completion, the surface is rinsed three times with deionized water and quickly dried with a nitrogen gun. The copper-nickel alloy substrate with nickel layers deposited on both sides is placed as follows... Figure 1 In the central region of the horizontal reactor 12 shown, the furnace tubes are made of quartz. The furnace temperature is set at 1050℃, the atmosphere is hydrogen at 500 ml / min, and the annealing time is 4 hours. A copper-nickel alloy substrate with dissolved trace amounts of silicon atoms was successfully prepared. The trace silicon originated from the 4-6 hour high-temperature annealing at 1050℃ in the quartz tube during the preparation of the single-crystal copper-nickel alloy foil, which may have resulted in the dissolution of trace amounts of silicon. The silicon content in the copper-nickel alloy substrate is approximately 2 at%.

[0038] 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 a wrinkle-free, uniform single-layer graphene film. A quartz tube 34 is inserted horizontally through the furnace tube of the horizontal reactor 32. The two ends of the quartz tube 34 are respectively provided with a gas inlet 31 and a gas outlet 35. The gas inlet 31 consists of three parallel connections that converge into one line extending into the quartz tube 34. The three gas inlets of the gas inlet 31 correspond to hydrogen, argon, and carbon source methane, respectively, pushing the metal substrate 33 into the central constant temperature zone of the horizontal reactor 32 corresponding to the inner cavity of the quartz tube 34.

[0039] The specific growth steps for a wrinkle-free, uniform monolayer graphene film are as follows:

[0040] 1) The temperature of the horizontal reactor is raised to 900°C in an argon atmosphere at a heating rate of 15°C / min. When the furnace temperature reaches the set temperature, the copper-nickel alloy substrate is pushed to the central constant temperature zone. Since the argon contains trace amounts of oxygen (the oxygen content in the argon is 10-50 ppm), it reacts with the silicon atoms in the copper-nickel alloy substrate. After pre-annealing in an argon atmosphere (500 ml / min) for 10 min, densely distributed silicon oxide nanoparticles can be introduced on the surface of the metal substrate.

[0041] 2) A mixture of methane, hydrogen, and argon gas (gas flow rate: methane 0.5 mL / min, hydrogen 50 mL / min, argon 500 mL / min) was introduced to begin graphene growth on the copper-nickel alloy substrate. After 10 minutes of isothermal growth, a three-layer structure of "graphene-silicon oxide nanoparticles-metal substrate" was formed, resulting in a wrinkle-free, uniform single-layer graphene film without obvious uneven multilayer island structures. Figure 5 ).

[0042] 3) A polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA 4 wt%) was dropped onto the surface of the "graphene-silica nanoparticle-metal substrate". A PMMA film was then spin-coated at 2500 rpm and cured on a 100°C hot plate for 10 minutes. The metal substrate was removed using copper etchants (e.g., ferric chloride) and nickel etchants (e.g., hydrochloric acid). The PMMA / graphene sample was then floated in a 4 mol / L sodium hydroxide aqueous solution and treated at 70°C for 2 hours to etch away any remaining silica nanoparticles at the interface. This transferred the monolayer graphene film to the SiO2 / Si substrate. The PMMA was then dissolved in acetone at room temperature, resulting in a clean, wrinkle-free, uniform monolayer graphene film.

[0043] Example 2

[0044] The specific growth steps for a uniform monolayer graphene film without folds or wrinkles are as follows:

[0045] 1) In an argon atmosphere, the furnace 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 copper-nickel alloy substrate is pushed to the central constant temperature zone and pre-annealed in argon (500 ml / min) for 10 min to introduce sparsely distributed silicon oxide nanoparticles on the surface of the metal substrate.

[0046] 2) A mixture of methane, hydrogen, and argon gas was introduced (gas flow rate: methane 0.5 mL / min, hydrogen 50 mL / min, argon 500 mL / min) to begin graphene growth on the copper-nickel alloy substrate. After 10 minutes of isothermal growth, a three-layer structure of "graphene-silicon oxide nanoparticles-metal substrate" was formed, resulting in a uniform, foldless, wrinkle-free monolayer graphene film without obvious non-uniform multilayer island structures. Figure 6 ).

[0047] Example 3

[0048] The difference from Example 1 is as follows:

[0049] like Figure 4As shown, a copper-nickel metal substrate is prepared by magnetron sputtering. A metal substrate 41 (metal foil) is fixed to the bottom surface of a sample disk 42 and rotates with the sample disk 42 at a speed of 30 r / min. A nickel target 43 with a purity of 99.999 wt% is used as the sputtering source, and the target 43 is mounted on a magnetron sputtering negative electrode 44. The vacuum chamber pressure for magnetron sputtering is reduced to 10... -5 Using argon gas at a flow rate of 8 mL / min on the order of mbar, the sputtering source voltage was set to 600V, the current to 220mA, and the deposition rate was 0.5 Å / s. When the nickel film thickness reached 3 μm, the power was turned off, and the metal substrate was removed. The nickel-plated copper-nickel alloy substrate was then placed in a... Figure 1 In the central region of the horizontal reactor 12 shown, the furnace tubes are made of quartz. The furnace temperature is set at 1050℃, the atmosphere is hydrogen at 500 ml / min, and the annealing time is 4 hours. A copper-nickel alloy substrate with dissolved trace amounts of silicon atoms was successfully prepared. The trace silicon originated from the 4-6 hour high-temperature annealing at 1050℃ in the quartz tube during the preparation of the single-crystal copper-nickel alloy foil, which may have resulted in the dissolution of trace amounts of silicon. The silicon content in the copper-nickel alloy substrate is approximately 2 at%.

[0050] The specific growth steps for a wrinkle-free, uniform monolayer graphene film are as follows:

[0051] 1) In an argon atmosphere, the furnace temperature of the horizontal reactor is raised to 930°C at a heating rate of 15°C / min. When the furnace temperature reaches the set temperature, the copper-nickel alloy substrate is pushed to the central constant temperature zone and pre-annealed in argon (500 ml / min) for 10 min to introduce densely distributed silicon oxide nanoparticles on the surface of the metal substrate.

[0052] 2) A mixture of methane, hydrogen, and argon gas (gas flow rates: methane 0.5 mL / min, hydrogen 50 mL / min, argon 500 mL / min) was introduced to begin graphene growth on the copper-nickel alloy substrate. After 10 minutes of isothermal growth, a three-layer structure of "graphene-silicon oxide nanoparticles-metal substrate" was formed, resulting in a wrinkle-free, uniform single-layer graphene film without obvious uneven multilayer island structures.

[0053] Example 4

[0054] The difference from Example 1 is as follows:

[0055] First, high-temperature annealing was used to remove contaminants from the surface of commercial polycrystalline copper foil substrates, resulting in polycrystalline copper foil with a smooth surface. Nano-silica was dispersed in a polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA 4 wt%, nano-silica 3 wt%), and spin-coated onto the copper foil substrate surface at 2000 r / min. The metal substrate coated with silica nanoparticles was then placed on a 100℃ hot plate for curing for 10 min. Unwanted PMMA on the metal substrate was removed by combustion in a tube furnace at 350℃ in an air atmosphere.

[0056] The specific growth steps for a wrinkle-free, uniform monolayer graphene film are as follows:

[0057] 1) In an argon atmosphere, the furnace temperature of the horizontal reactor is raised to 950°C at a heating rate of 15°C / min. When the furnace temperature reaches the set temperature, the copper foil substrate with dispersed silicon oxide nanoparticles is pushed to the central constant temperature zone.

[0058] 2) A mixture of methane, hydrogen, and argon gas (gas flow rates: methane 0.5 mL / min, hydrogen 50 mL / min, argon 500 mL / min) was introduced to begin graphene growth on the copper foil substrate. After 10 minutes of isothermal growth, a three-layer structure of "graphene-silicon oxide nanoparticles-metal substrate" was formed, resulting in a wrinkle-free, uniform single-layer graphene film without obvious uneven multilayer island structures.

[0059] 3) A polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA 4 wt%) was dropped onto the surface of the "graphene-silica nanoparticle-metal substrate". A PMMA film was then spin-coated at 2500 rpm and cured on a 100°C hot plate for 10 minutes. The metal substrate was removed using a copper etchant (e.g., ferric chloride). The PMMA / graphene sample was then floated in a 4 mol / L sodium hydroxide aqueous solution and treated at 70°C for 2 hours to etch away any remaining silica nanoparticles at the interface, transferring the monolayer graphene film to the SiO2 / Si substrate. The PMMA was then dissolved in acetone at room temperature, resulting in a clean transfer of a wrinkle-free, uniform monolayer graphene film.

[0060] Example 5

[0061] The difference from Example 1 is as follows:

[0062] First, high-temperature annealing was used to remove contaminants from the surface of a commercial polycrystalline copper foil substrate, resulting in a polycrystalline copper foil with a smooth surface. A nano-alumina dispersion was then spin-coated onto the copper foil substrate surface at 2000 r / min. The metal substrate coated with alumina nanoparticles was then baked on a 100℃ hot plate for 2 hours to remove residual moisture, yielding a metal copper foil substrate with uniformly dispersed alumina nanoparticles.

[0063] The specific growth steps for a wrinkle-free, uniform monolayer graphene film are as follows:

[0064] 1) In an argon atmosphere, raise the furnace temperature of the horizontal reactor to 1000°C at a heating rate of 15°C / min. When the furnace temperature reaches the set temperature, push the metal substrate to the central constant temperature zone.

[0065] 2) A mixture of methane, hydrogen, and argon gas was introduced (gas flow rate: methane 0.5 mL / min, hydrogen 50 mL / min, argon 500 mL / min) to begin graphene growth on the metal substrate surface. After 10 minutes of isothermal growth, a three-layer structure of "graphene-alumina nanoparticles-metal substrate" was formed, resulting in a wrinkle-free, uniform monolayer graphene film without obvious uneven multilayer island structures. Figure 7 ).

[0066] 3) A polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA 4 wt%) was dropped onto the surface of the "graphene-alumina nanoparticle-metal substrate". A PMMA film was then spin-coated at 2500 rpm and cured on a 100°C hot plate for 10 minutes. The metal substrate was removed using a copper etchant (e.g., ferric chloride). The PMMA / graphene sample was then floated in 1 mol / L hydrochloric acid and treated at 60°C for 2 hours to etch away any remaining alumina nanoparticles at the interface, transferring the monolayer graphene film onto the SiO2 / Si substrate. The PMMA was then dissolved in acetone at room temperature, resulting in a clean transfer of a wrinkle-free, uniform monolayer graphene film.

[0067] The results of the embodiments demonstrate that by introducing nanoparticles with a smaller coefficient of thermal expansion at the interface between graphene and the metal substrate, this invention can simultaneously suppress wrinkles and non-uniform multilayer island structures, successfully achieving the preparation of wrinkle-free uniform monolayer graphene films. This invention provides a simple and efficient method for the preparation of large-area uniform monolayer graphene films, promotes the application of graphene in devices, and provides an effective approach for achieving low-cost, high-yield preparation of large-area uniform monolayer wrinkle-free graphene films.

Claims

1. A method for preparing a wrinkle-free, uniform single-layer graphene film by chemical vapor deposition, characterized in that: Using a metal substrate with good catalytic ability, the first step is to introduce nanoparticles on the flat surface of the metal substrate; the second step is to grow graphene to form a "graphene-nanoparticle-metal substrate" structure. The nanoparticles are used to reduce the interfacial stress between graphene and the metal substrate, suppress the formation of wrinkles and the carbon source infiltration and precipitation process, and finally obtain a wrinkle-free uniform monolayer graphene film.

2. The method for preparing a wrinkle-free, uniform monolayer graphene film by chemical vapor deposition according to claim 1, characterized in that, The nanoparticles are composed of oxides or nitrides. The coefficient of thermal expansion of the nanoparticles is smaller than that of the metal substrate, the melting point is higher than that of graphene grown by chemical vapor deposition, and they do not dissolve in the metal substrate or react with carbon to form interstitial phases.

3. The method for preparing a wrinkle-free, uniform monolayer graphene film by chemical vapor deposition according to claim 1, characterized in that, Before graphene growth, nanoparticles are introduced through physical deposition, chemical reaction, or solution coating methods.

4. The method for preparing a wrinkle-free, uniform monolayer graphene film by chemical vapor deposition according to claim 1, characterized in that, By adjusting the distribution density of nanoparticles through regulating physical deposition parameters or chemical reaction conditions, the wrinkling behavior of subsequent graphene growth can be controlled.

5. The method for preparing a wrinkle-free, uniform monolayer graphene film by chemical vapor deposition according to claim 1, characterized in that, A flat, catalytically active metal film or foil is used as the metal substrate, including but not limited to metals such as copper, nickel, iron, cobalt, platinum, or alloys formed with other elements.

6. The method for preparing a wrinkle-free, uniform monolayer graphene film by chemical vapor deposition according to claim 1, characterized in that, By employing chemical dissolution or physical etching methods to remove nanoparticles between graphene and the metal substrate, a clean transfer of wrinkle-free, uniform monolayer graphene films can be achieved.

7. A method for preparing a wrinkle-free, uniform monolayer graphene film by chemical vapor deposition according to any one of claims 1 to 6, characterized in that, The preparation process of wrinkle-free uniform monolayer graphene film is as follows: Stage 1: Introduce nanoparticles onto the surface of a flat metal foil or metal film to form a "nanoparticle-metal substrate" structure. The distribution density of nanoparticles can be controlled by changing the parameters of specific chemical reactions or the conditions of physical methods. Stage 2: Introduce an auxiliary carrier gas and use a solid, liquid, or gaseous carbon source to perform isothermal chemical vapor deposition of a single-layer graphene film on a "nanoparticle-metal substrate" structure.

8. The method for preparing a wrinkle-free, uniform monolayer graphene film by chemical vapor deposition according to claim 7, characterized in that, In the first stage, the distribution of nanoparticles is controlled to be either dense or sparse by changing the parameters of the specific method of introducing nanoparticles.

9. The method for preparing a wrinkle-free, uniform monolayer graphene film by chemical vapor deposition according to claim 7, characterized in that, In the second 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 20–1000 ml / min.

10. The method for preparing a wrinkle-free, uniform monolayer graphene film by chemical vapor deposition according to claim 7, characterized in that, Nanoparticles are located between graphene and the metal substrate, forming a three-layer structure of "graphene-nanoparticle-metal substrate". The distribution density of nanoparticles affects the subsequent graphene growth behavior: when nanoparticles are dense on the surface of the metal substrate, graphene growth is completely separated from the metal substrate, resulting in wrinkle-free uniform monolayer graphene; when nanoparticles are sparse on the surface of the metal substrate, graphene growth is partially separated from the metal substrate, resulting in fold-free wrinkle-free uniform monolayer graphene.

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