CN117926404A - Preparation method of high-quality uniform few-layer monocrystalline graphene film - Google Patents
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Abstract
The invention relates to the field of a chemical vapor deposition method for preparing graphene, in particular to a preparation method for a high-quality uniform few-layer monocrystalline graphene film, which is suitable for preparing a large-area high-quality uniform few-layer monocrystalline graphene film. A monocrystalline metal substrate with high carbon dissolving quantity is adopted, and a two-step chemical vapor deposition method is adopted to grow a few layers of monocrystalline graphene on the surface of the monocrystalline metal substrate: firstly, growing a few-layer single-crystal graphene film containing a multi-layer graphene island structure, then improving the carbon solubility of a substrate by changing the temperature, selectively dissolving the multi-layer graphene island structure, and finally obtaining the few-layer single-crystal graphene film with uniform layers. According to the invention, the number of layers of the graphene is improved by selectively removing the uneven multilayer structure, so that a few-layer monocrystalline graphene film with uniform wafer level can be prepared, and a foundation is laid for physical property research of few-layer graphene and application in the fields of photoelectric devices, microelectronic devices, electronic transparent films and the like.
Description
Technical Field
The invention relates to the field of a Chemical Vapor Deposition (CVD) method for preparing graphene, in particular to a preparation method for a high-quality uniform few-layer monocrystalline graphene film, which is suitable for preparing a large-area high-quality uniform few-layer monocrystalline graphene film.
Background
The number of layers and stacking of the graphene have great influence on the performance of the graphene, and the graphenes with different layers and stacking modes have completely different energy band structures, so that a plurality of unique properties are brought to the graphenes in the electrical and optical aspects, and the research field and the application space of the graphenes are further expanded. For example: the double-layer graphene of the AB stack and the three-layer graphene of the ABC stack can generate continuously adjustable band gaps under the action of a vertical electric field. In addition, few layers of graphene also exhibit many unique properties in terms of condensed physics, such as: quantum hall effect also has superconductivity, etc.
In the aspect of preparation of graphene, a mechanical stripping method is the earliest method, and the sample prepared by the method has high quality, but has the problems of small sample size and poor controllability. And then the developed sample prepared by the Chemical Vapor Deposition (CVD) method has the characteristics of large size, high quality and good controllability, and is the main method for preparing few layers of graphene at present. However, in the preparation of few-layer graphene at present, it is difficult for a liquid substrate to realize single crystal preparation, whereas a solid substrate typified by copper and its alloy can realize single crystal epitaxy by preparing a single crystal substrate, but since the formation of few-layer graphene islands on these substrates can be not quite different, stable nonuniform multi-layer graphene islands are easily formed. Currently, a method for realizing synchronization of single crystal and uniform layer number is urgently needed.
Disclosure of Invention
The invention aims to provide a preparation method of a high-quality uniform few-layer monocrystalline graphene film, which has the characteristics of simplicity in operation, high controllability, good universality, easiness in large-area expansion and the like, can be used as a method for preparing a large-area high-quality uniform few-layer monocrystalline graphene continuous film, and has the potential of industrialized mass preparation.
The technical scheme of the invention is as follows:
A preparation method of a high-quality uniform few-layer monocrystalline graphene film adopts a monocrystalline metal substrate with high carbon content, and adopts a two-step chemical vapor deposition method to grow few-layer monocrystalline graphene on the surface of the monocrystalline metal substrate: firstly, growing a few-layer single-crystal graphene film containing a multi-layer graphene island structure, then improving the carbon solubility of a substrate by changing the temperature, selectively dissolving the multi-layer graphene island structure, and finally obtaining the few-layer single-crystal graphene film with uniform layers.
According to the preparation method of the high-quality uniform few-layer monocrystalline graphene film, the layers in the nonuniform multilayer structure are more than the uniform few-layer monocrystalline graphene film, and the number of the few-layer monocrystalline graphene film is 2-10; the non-uniform multilayer structure is located at the interface of the minority layer single crystal graphene film and the metal substrate.
The preparation method of the high-quality uniform few-layer monocrystalline graphene film adopts a metal with high carbon solubility and lattice constant matched with graphene as a matrix, and the metal comprises but is not limited to metallic nickel, iron, chromium, cobalt and alloys formed by the metallic nickel, iron, chromium, cobalt and other elements.
The preparation method of the high-quality uniform few-layer monocrystalline graphene film comprises the steps of preparing a monocrystalline metal substrate by adopting a template method or a high-temperature annealing method, wherein: the template method selects a single crystal nonmetallic substrate sapphire (0001), magnesium oxide (111) or spinel (111) which are symmetrically matched as an epitaxial substrate, a layer of film is sequentially deposited on the surface of the nonmetallic substrate by a magnetron sputtering method, the thickness of the film is 100-1000 nm, the single crystal metallic film is obtained by annealing at 1200-1350 ℃ and in a reducing atmosphere, the reducing atmosphere is hydrogen or argon, the flow is 200-500 ml/min, and the annealing time is 1-12 h; the high-temperature annealing method selects commercial metal foil with the thickness of 10-100 mu m, and the single crystal metal film is obtained by annealing at 1350-1500 ℃ in a reducing atmosphere which is hydrogen or argon, the flow is 200-500 ml/min, and the annealing time is 4-24 h.
The preparation method of the high-quality uniform few-layer monocrystalline graphene film comprises the following steps of:
Stage 1: using single crystal metal as a growth substrate, adopting solid, liquid or gaseous carbon source, and carrying out long-time constant temperature or cooling deposition under the assistance of carrier gas to grow a few layers of single crystal graphene with a multilayer graphene island non-uniform multilayer structure;
Stage 2: maintaining the growth atmosphere unchanged, heating to increase the carbon solubility of the monocrystalline metal substrate, and completely dissolving the multilayer graphene islands into the monocrystalline metal substrate to obtain a monocrystalline graphene film without the multilayer graphene islands;
Stage 3: maintaining the growth atmosphere unchanged, continuing to perform heat preservation and growth for a period of time, and splicing the graphene which is not spliced into a complete film.
In the preparation method of the high-quality uniform few-layer monocrystalline graphene film, in the stage 1, a carbon source is gaseous or liquid hydrocarbon: one or more of methane, ethane, ethylene, acetylene, benzene, toluene, cyclohexane, ethanol, methanol, acetone or carbon monoxide, or a carbon source is 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 the mixed gas of hydrogen, nitrogen and argon, and the flow rate of the carrier gas is 5-500 ml/min.
In the preparation method of the high-quality uniform few-layer monocrystalline graphene film, in the 2 nd stage, graphene spliced into a film with a certain size has good stability and cannot be dissolved into a monocrystalline metal substrate.
According to the preparation method of the high-quality uniform few-layer monocrystalline graphene film, the substrate is monocrystalline metal matched with the graphene in symmetry, and the graphene film obtained through epitaxy of the monocrystalline metal substrate is a few-layer monocrystalline graphene film.
According to the preparation method of the high-quality uniform few-layer monocrystalline graphene film, after the uniform few-layer monocrystalline graphene/monocrystalline metal substrate is protected by the high-molecular polymer, wet transfer is adopted, namely, metal is etched through etching liquid or bubbles are generated by electrolysis of an electrolytic cell to separate graphene from the substrate, then the uniform few-layer monocrystalline graphene film is transferred to a target substrate, and then the high-molecular polymer protection layer is removed by using an organic solvent.
The etching solution is ammonium persulfate aqueous solution, potassium persulfate aqueous solution, hydrochloric acid or ferric chloride aqueous solution, the electrolyte is sodium hydroxide aqueous solution, dilute sulfuric acid or dilute hydrochloric acid, the high-molecular polymer is one or more than two of polymethyl methacrylate, polyethylene, polystyrene and polypropylene, and the organic solvent is one or more than two of ketone, chlorohydrocarbon, halogenated hydrocarbon and aromatic hydrocarbon organic solvents.
The design idea of the invention is as follows:
According to the invention, single crystal metal with high carbon solubility and small lattice mismatch degree with graphene is selected as a matrix, graphene is grown on the surface of the single crystal metal by adopting a chemical vapor deposition method, and the carbon solubility of the substrate is regulated by temperature so as to improve the layer number uniformity of the graphene. The monocrystalline metal substrate is prepared by adopting a monocrystalline non-metal epitaxy method or a metal foil high-temperature annealing method, and the used metal has higher carbon dissolving amount. And (3) growing a few-layer single crystal graphene film containing a large number of multi-layer graphene islands on the surface of the metal substrate by adopting a chemical vapor deposition technology in a layered-island growth mode, and then raising the temperature to improve the carbon dissolution amount of the substrate, so that the multi-layer graphene islands are dissolved into the substrate in a solid solution mode, and the completely uniform few-layer single crystal graphene film is obtained.
The invention has the advantages and beneficial effects that:
1. the method has good layer number controllability, can obtain few-layer graphene samples containing a large number of multi-layer graphene islands by regulating and controlling the substrate components, the growth temperature and the atmosphere, and can realize controllable preparation of 2-10 layers of graphene with completely uniform layer number by dissolving the multi-layer graphene islands into the substrate through heating.
2. According to the invention, the metal substrate is annealed into the monocrystal, so that the minority layer of monocrystal graphene obtained by epitaxy maintains the same orientation, and the controllable preparation of the minority layer of monocrystal graphene is realized.
3. The invention has low requirements on equipment and convenient operation, and is favorable for further industrialized large-area preparation.
Drawings
FIG. 1 is a schematic diagram of an experimental apparatus for desktop magnetron sputtering coating. In the figure, 11 sample trays; 12 blue diamond tablets; 13 target material; 14 magnetron sputtering cathode.
FIG. 2 is an experimental set-up for high temperature reducing atmosphere annealing. In the figure, 21 gas inlet; 22 reaction furnaces; 23 a substrate to be annealed; 24 gas outlet; 25 corundum tube.
Fig. 3 is an experimental apparatus for growing a uniform few-layer single crystal graphene film by CVD. In the figure, 31 gas inlet; a 32 reaction furnace; 33 substrate; 34 gas outlet; 35 quartz tube.
Detailed Description
In a specific implementation process, the invention provides a preparation method of a high-quality uniform few-layer monocrystalline graphene film, and monocrystalline metal is selected as a growth substrate. The method comprises the steps of plating high-carbon-solubility metal on the surface of a symmetrical lattice-matched monocrystal nonmetallic substrate uniformly by a magnetron sputtering method, and annealing to obtain a monocrystal metal film, or directly annealing commercial metal foil at high temperature to form a monocrystal. And (3) using the obtained single crystal substrate for CVD growth, obtaining uneven multi-layer graphene at a constant temperature or a cooling stage, and finally obtaining 2-10 layers of single crystal graphene films with even layers by utilizing the characteristic that the carbon solubility of metal increases with the temperature and improving the carbon solubility of the metal substrate through heating to dissolve the uneven multi-layer graphene islands.
The invention is further illustrated by the following examples.
Example 1
First, a single crystal metal substrate is prepared by a magnetron sputtering method. The (0001) plane single crystal sapphire (thickness 0.5mm, single side polishing) was placed in a polishing solution (50 ml of concentrated sulfuric acid, 150ml of phosphoric acid), and chemical polishing was performed at 300 ℃ for 30min to remove the fragments and impurities on the sapphire surface, and then taken out and rinsed with deionized water for 5min.
After the cleaning was completed, as shown in fig. 1, a sapphire sheet 12 was fixed as a substrate on a sample disk 11 and rotated at a speed of 30 rpm along with the sample disk 11, first, an iron target 13 having a purity of 99.95wt% was used as a sputtering source, a cylindrical iron target 13 was mounted in an annular magnetron sputtering anode 14, and after the vacuum chamber pressure was reduced to the order of 10 -5 mbar, 8 ml/min of argon gas was introduced, the sputtering source voltage was set at 600V, the current was set at 200mA, and coating was performed at a speed of 0.65 a/sec. When the thickness of the Fe film reaches 160nm, a power supply is turned off, a nickel target 13 with the purity of 99.99wt% is replaced and used as a sputtering source, a cylindrical nickel target 13 is arranged in an annular magnetron sputtering cathode 14, when the air pressure of a vacuum cavity is reduced to the order of 10 -5 mbar, 8 ml/min of argon is introduced, the voltage of the sputtering source is set to 600V, the current is set to 200mA, film coating is carried out at the speed of 0.78 angstrom/s, and when the thickness of the Ni film reaches 340nm, the power supply is turned off, and a substrate is taken out.
As shown in fig. 2, a horizontal atmospheric reaction furnace 22 (the diameter of the furnace tube is 36 mm, and the length of the reaction zone is 100 mm) is adopted to anneal the substrate, a corundum tube 25 is arranged on the furnace tube of the horizontal atmospheric reaction furnace 22 in a penetrating manner along the horizontal direction, two ends of the corundum tube 25 are sealed by flanges, and a gas inlet 21 and a gas outlet 24 are respectively arranged on the flanges at two ends of the corundum tube 25. The substrate 23 to be annealed is placed in a corundum tube 25 in the central area of a reaction furnace 22, 300 ml/min of hydrogen is introduced, the temperature is raised to 1300 ℃ at the same time, and the temperature is maintained for 2 hours, so that the monocrystalline iron-nickel alloy film substrate is finally obtained.
As shown in FIG. 3, a horizontal reaction furnace 32 (the diameter of the furnace tube is 22 mm, the length of the reaction zone is 20 mm) is adopted to grow a uniform double-layer monocrystalline graphene film, a quartz tube 35 is arranged on the furnace tube of the horizontal reaction furnace 32 in a penetrating manner along the horizontal direction, two ends of the quartz tube 35 are sealed by flanges, a gas inlet 31 and a gas outlet 34 are respectively arranged on the flanges at two ends of the quartz tube 35, and a monocrystalline iron-nickel alloy film substrate 33 is arranged in the quartz tube 35 in the constant temperature zone of the horizontal reaction furnace 32. The specific growth steps of the uniform double-layer monocrystalline graphene are as follows:
1) Heating the horizontal reaction furnace to 1050 ℃ at a speed of 20 ℃/min, switching the atmosphere in the quartz tube 35 to hydrogen (the flow rate is 500 ml/min), placing the monocrystalline iron-nickel alloy film substrate in the central area of the horizontal reaction furnace, maintaining for 5min to remove organic matter residues and oxide layers on the surface of the substrate, introducing mixed gas of methane and hydrogen (the gas flow rates are 3.5 ml/min for methane and 500 ml/min for hydrogen respectively), and starting to grow graphene on the surface of the substrate. After 4h of growth, the surface of the substrate is covered with large-area film-forming double-layer graphene and a large number of multi-layer graphene islands.
2) And (3) keeping the gas flow unchanged, increasing the temperature to 1060 ℃ at a speed of 1 ℃/min, increasing the solubility of the substrate carbon, and dissolving the multi-layer graphene islands on the surface of the double-layer graphene to obtain a uniform single-crystal double-layer graphene film, wherein the thickness of the single-crystal double-layer graphene film is 0.68nm.
And (3) dropwise adding an ethyl lactate solution of polymethyl methacrylate (PMMA) (the mass fraction of the polymethyl methacrylate is 4 wt%) onto the surface of graphene, spin-coating a layer of polymethyl methacrylate on the surface of the graphene by a spin-coating method (the spin-coating speed is 2500 rpm, the spin-coating time is 60 seconds, the spin-coating times are 2 times), and placing the spin-coated polymethyl methacrylate/graphene/single crystal iron-nickel alloy film/sapphire on a hot table and drying at 90 ℃ for 10 minutes. After etching iron-nickel alloy on a substrate by using 1mol/L ferric chloride aqueous solution, transferring polymethyl methacrylate/graphene onto a SiO 2/Si substrate (a 300nm thick SiO 2 insulating layer is deposited on the surface of the Si substrate), removing polymethyl methacrylate on the surface of the graphene by using acetone at the temperature of 70 ℃, and then flushing the graphene by using isopropanol and ethanol sequentially, so that successful transfer of the single-crystal double-layer graphene film is finally realized.
Example 2
First, a single crystal metal substrate is prepared by a magnetron sputtering method. The (0001) plane single crystal sapphire (thickness 0.5mm, single side polishing) was placed in a polishing solution (50 ml of concentrated sulfuric acid, 150ml of phosphoric acid), and chemical polishing was performed at 300 ℃ for 30min to remove the fragments and impurities on the sapphire surface, and then taken out and rinsed with deionized water for 5min.
After the cleaning was completed, as shown in fig. 1, a sapphire sheet 12 was fixed as a substrate on a sample disk 11 and rotated at a speed of 30 rpm along with the sample disk 11, first, an iron target 13 having a purity of 99.95wt% was used as a sputtering source, a cylindrical iron target 13 was mounted in an annular magnetron sputtering anode 14, and after the vacuum chamber pressure was reduced to the order of 10 -5 mbar, 8 ml/min of argon gas was introduced, the sputtering source voltage was set at 600V, the current was set at 200mA, and coating was performed at a speed of 0.65 a/sec. When the thickness of the Fe film reaches 160nm, a power supply is turned off, a nickel target 13 with the purity of 99.99wt% is replaced and used as a sputtering source, a cylindrical nickel target 13 is arranged in an annular magnetron sputtering cathode 14, when the air pressure of a vacuum cavity is reduced to the order of 10 -5 mbar, 8 ml/min of argon is introduced, the voltage of the sputtering source is set to 600V, the current is set to 200mA, film coating is carried out at the speed of 0.78 angstrom/s, and when the thickness of the Ni film reaches 340nm, the power supply is turned off, and a substrate is taken out.
As shown in fig. 2, a horizontal atmospheric reaction furnace 22 (the diameter of the furnace tube is 36 mm, and the length of the reaction zone is 100 mm) is adopted to anneal the substrate, a corundum tube 25 is arranged on the furnace tube of the horizontal atmospheric reaction furnace 22 in a penetrating manner along the horizontal direction, two ends of the corundum tube 25 are sealed by flanges, and a gas inlet 21 and a gas outlet 24 are respectively arranged on the flanges at two ends of the corundum tube 25. Placing the substrate in a corundum tube 25 in the central area of the reaction furnace, introducing 300 ml/min of hydrogen, and simultaneously raising the temperature to 1300 ℃ and maintaining for 2 hours to finally obtain the monocrystalline iron-nickel alloy film substrate.
As shown in FIG. 3, a horizontal reaction furnace 32 (the diameter of the furnace tube is 22 mm, the length of the reaction zone is 20 mm) is adopted to grow a uniform three-layer monocrystalline graphene film, a quartz tube 35 is arranged on the furnace tube of the horizontal reaction furnace 32 in a penetrating manner along the horizontal direction, two ends of the quartz tube 35 are sealed by flanges, a gas inlet 31 and a gas outlet 34 are respectively arranged on the flanges at two ends of the quartz tube 35, and a monocrystalline iron-nickel alloy film substrate 33 is arranged in the quartz tube 35 in the constant temperature zone of the horizontal reaction furnace 32. The specific growth steps of the uniform three-layer monocrystalline graphene are as follows:
1) Heating the horizontal reaction furnace to 1050 ℃ at a speed of 20 ℃/min, switching the atmosphere in the quartz tube 35 to hydrogen (the flow rate is 500 ml/min), placing the monocrystalline iron-nickel alloy film substrate in the central area of the horizontal reaction furnace, maintaining for 5min to remove organic matter residues and oxide layers on the surface of the substrate, introducing mixed gas of methane and hydrogen (the gas flow rates are 3.8 ml/min for methane and 500 ml/min for hydrogen respectively), and starting to grow graphene on the surface of the substrate. After 2h of growth, the surface of the substrate is covered with a single-layer graphene and a large number of multi-layer graphene islands.
2) And regulating the flow rate of methane to 4.3 milliliters/min, reducing the temperature to 950 ℃ at a speed of 5 ℃/min, separating carbon from the substrate, and epitaxially forming a second layer and a third layer of graphene between the graphene and the substrate.
3) And (3) keeping the gas flow unchanged, increasing the temperature to 1000 ℃ at a speed of 5 ℃/min, increasing the solubility of the substrate carbon, and dissolving the multi-layer graphene islands on the surface of the three-layer graphene to obtain a uniform single-crystal three-layer graphene film, wherein the thickness of the single-crystal three-layer graphene film is 1.02nm.
And (3) dropwise adding an ethyl lactate solution of polymethyl methacrylate (PMMA) (the mass fraction of the polymethyl methacrylate is 4 wt%) onto the surface of graphene, spin-coating a layer of polymethyl methacrylate on the surface of the graphene by a spin-coating method (the spin-coating speed is 2500 rpm, the spin-coating time is 60 seconds, the spin-coating times are 2 times), and placing the spin-coated polymethyl methacrylate/graphene/single crystal iron-nickel alloy film/sapphire on a hot table and drying at 90 ℃ for 10 minutes. After etching iron-nickel alloy on a substrate by using 1mol/L ferric chloride aqueous solution, transferring polymethyl methacrylate/graphene to a SiO 2/Si (300 nm thick SiO 2 insulating layer is deposited on the surface of a Si substrate), removing polymethyl methacrylate on the surface of the graphene by using 70 ℃ acetone, and then flushing the graphene by using isopropanol and ethanol in sequence, so that the successful transfer of the monocrystalline three-layer graphene film is finally realized.
Example 3
First, a single crystal metal substrate is prepared by a magnetron sputtering method. The (0001) plane single crystal sapphire (thickness 0.5mm, single side polishing) was placed in a polishing solution (50 ml of concentrated sulfuric acid, 150ml of phosphoric acid), and chemical polishing was performed at 300 ℃ for 30min to remove the fragments and impurities on the sapphire surface, and then taken out and rinsed with deionized water for 5min.
After the cleaning was completed, as shown in fig. 1, a sapphire sheet 12 was fixed as a substrate on a sample disk 11 and rotated at a speed of 30 rpm along with the sample disk 11, first, an iron target 13 having a purity of 99.95wt% was used as a sputtering source, a cylindrical iron target 13 was mounted in an annular magnetron sputtering anode 14, and after the vacuum chamber pressure was reduced to the order of 10 -5 mbar, 8 ml/min of argon gas was introduced, the sputtering source voltage was set at 600V, the current was set at 200mA, and coating was performed at a speed of 0.65 a/sec. When the thickness of the Fe film reaches 160nm, a power supply is turned off, a nickel target 13 with the purity of 99.99wt% is replaced and used as a sputtering source, a cylindrical nickel target 13 is arranged in an annular magnetron sputtering cathode 14, when the air pressure of a vacuum cavity is reduced to the order of 10 -5 mbar, 8 ml/min of argon is introduced, the voltage of the sputtering source is set to 600V, the current is set to 200mA, film coating is carried out at the speed of 0.78 angstrom/s, and when the thickness of the Ni film reaches 340nm, the power supply is turned off, and a substrate is taken out.
As shown in fig. 2, a horizontal atmospheric reaction furnace 22 (the diameter of the furnace tube is 36 mm, and the length of the reaction zone is 100 mm) is adopted to anneal the substrate, a corundum tube 25 is arranged on the furnace tube of the horizontal atmospheric reaction furnace 22 in a penetrating manner along the horizontal direction, two ends of the corundum tube 25 are sealed by flanges, and a gas inlet 21 and a gas outlet 24 are respectively arranged on the flanges at two ends of the corundum tube 25. Placing the substrate in a corundum tube 25 in the central area of the reaction furnace, introducing 300 ml/min of hydrogen, and simultaneously raising the temperature to 1300 ℃ and maintaining for 2 hours to finally obtain the monocrystalline iron-nickel alloy film substrate.
As shown in FIG. 3, a horizontal reaction furnace 32 (the diameter of the furnace tube is 22 mm, the length of the reaction zone is 20 mm) is adopted to grow a uniform three-layer monocrystalline graphene film, a quartz tube 35 is arranged on the furnace tube of the horizontal reaction furnace 32 in a penetrating manner along the horizontal direction, two ends of the quartz tube 35 are sealed by flanges, a gas inlet 31 and a gas outlet 34 are respectively arranged on the flanges at two ends of the quartz tube 35, and a monocrystalline iron-nickel alloy film substrate 33 is arranged in the quartz tube 35 in the constant temperature zone of the horizontal reaction furnace 32. The specific growth steps of the uniform three-layer monocrystalline graphene are as follows:
1) Heating the horizontal reaction furnace to 1025 ℃ at a speed of 20 ℃/min, switching the atmosphere in the quartz tube 35 to hydrogen (the flow rate is 500 ml/min), placing the monocrystalline iron-nickel alloy film substrate in the central area of the horizontal reaction furnace, maintaining for 5min to remove organic matter residues and oxide layers on the surface of the substrate, introducing mixed gas of methane and hydrogen (the gas flow rates are 4.5 ml/min for methane and 500 ml/min for hydrogen respectively), and starting to grow graphene on the surface of the substrate. After 10min of growth, the surface of the substrate is covered with single-layer graphene and a large number of multi-layer graphene islands.
2) And (3) keeping the gas flow unchanged, increasing the temperature to 1050 ℃ at a speed of 5 ℃/min, increasing the solubility of the substrate carbon, and dissolving the multi-layer graphene islands on the surface of the single-layer graphene to obtain the single-layer graphene and 2-3-layer graphene islands.
3) And keeping the gas flow unchanged, and continuing to grow for 20min at 1050 ℃ to obtain uniform three-layer monocrystalline graphene, wherein the thickness of the three-layer monocrystalline graphene is 1.02nm.
And (3) dropwise adding an ethyl lactate solution of polymethyl methacrylate (PMMA) (the mass fraction of the polymethyl methacrylate is 4 wt%) onto the surface of graphene, spin-coating a layer of polymethyl methacrylate on the surface of the graphene by a spin-coating method (the spin-coating speed is 2500 rpm, the spin-coating time is 60 seconds, the spin-coating times are 2 times), and placing the spin-coated polymethyl methacrylate/graphene/single crystal iron-nickel alloy film/sapphire on a hot table and drying at 90 ℃ for 10 minutes. After etching iron-nickel alloy on a substrate by using 1mol/L ferric chloride aqueous solution, transferring polymethyl methacrylate/graphene onto a SiO 2/Si substrate (a 300nm thick SiO 2 insulating layer is deposited on the surface of the Si substrate), removing polymethyl methacrylate on the surface of the graphene by using acetone at the temperature of 70 ℃, and then flushing the graphene by using isopropanol and ethanol sequentially, so that the successful transfer of the monocrystalline three-layer graphene film is finally realized.
Example 4
Commercial iron-nickel alloy foil (trade name: 4J50, ni content: 50wt%, thickness: 100 μm) was put into acetone, deionized water, isopropanol, and subjected to ultrasonic cleaning for 40min, respectively. After the cleaning is completed, the horizontal reaction furnace 22 shown in fig. 2 (the diameter of the furnace tube is 36 mm, and the length of the reaction zone is 100 mm) is used for annealing, a corundum tube 25 is arranged on the furnace tube of the horizontal normal pressure reaction furnace 22 in a penetrating manner along the horizontal direction, two ends of the corundum tube 25 are sealed by flanges, and a gas inlet 21 and a gas outlet 24 are respectively arranged on the flanges at two ends of the corundum tube 25. The alloy foil is placed in a corundum tube 25 in the central area of a horizontal reaction furnace 22, 300 ml/min of hydrogen is introduced, the temperature is raised to 1400 ℃ to start annealing, the temperature is reduced after 6 hours, and the alloy foil is taken out, so that the iron-nickel alloy foil with the face-centered cubic phase (111) face is obtained.
As shown in FIG. 3, a horizontal reaction furnace 32 (the diameter of the furnace tube is 22 mm, the length of the reaction zone is 20 mm) is adopted to grow a uniform double-layer monocrystalline graphene film, a quartz tube 35 is arranged on the furnace tube of the horizontal reaction furnace 32 in a penetrating manner along the horizontal direction, two ends of the quartz tube 35 are sealed by flanges, a gas inlet 31 and a gas outlet 34 are respectively arranged on the flanges at two ends of the quartz tube 35, and a monocrystalline iron-nickel alloy film substrate 33 is arranged in the quartz tube 35 in the constant temperature zone of the horizontal reaction furnace 32. The specific growth steps of the uniform double-layer monocrystalline graphene are as follows:
1) The horizontal reaction furnace was heated to 1050 ℃ at a rate of 20 ℃/min, the atmosphere in the quartz tube 35 was switched to hydrogen (flow 500 ml/min), a single crystal iron-nickel alloy foil substrate was placed in the central region of the horizontal reaction furnace, and the substrate was maintained for 5min to remove organic residue and oxide layer on the surface of the substrate, and mixed gas of methane and hydrogen (gas flow rates were methane 1.95 ml/min and hydrogen 200 ml/min, respectively) was introduced to start graphene growth on the surface of the substrate. After 20min of growth, the surface of the substrate is covered with single-layer graphene.
2) 200 Ml/min argon is introduced, the argon is used for promoting the carbon dissolved in the substrate to be separated out at the interface of the single-layer graphene and the substrate, and methane decomposition is promoted by the existence of the argon, so that the flow of methane is required to be regulated to 1 ml/min, the furnace temperature is reduced to 1030 ℃ at a speed of 2 ℃/min, the carbon is separated out from the substrate, and a second layer of graphene is epitaxially formed between the graphene and the substrate.
3) And (3) keeping the gas flow unchanged, increasing the temperature to 1035 ℃ at a speed of 1 ℃/min, increasing the solubility of the substrate carbon, and dissolving the multi-layer graphene islands on the surface of the double-layer graphene to obtain a uniform single-crystal double-layer graphene film, wherein the thickness of the single-crystal double-layer graphene film is 0.68nm.
And (3) dropwise adding an ethyl lactate solution of polymethyl methacrylate (PMMA) (the mass fraction of the polymethyl methacrylate is 4 wt%) onto the surface of the graphene, spin-coating a layer of polymethyl methacrylate on the surface of the graphene by a spin-coating method (the spin-coating rotating speed is 2500 rpm, the spin-coating time is 60 seconds, the spin-coating times are 2 times), and placing the spin-coated polymethyl methacrylate/double-layer graphene/iron-nickel alloy foil on a hot table and drying at 90 ℃ for 10 minutes. And (3) placing the polymethyl methacrylate/double-layer graphene/iron-nickel alloy foil serving as a cathode in a 1mol/L NaOH electrolyte, adopting a platinum electrode as an anode, transferring the polymethyl methacrylate/double-layer graphene film onto a SiO 2/Si substrate (the SiO 2 insulating layer with the thickness of 300nm is deposited on the surface of the Si substrate) by adopting an electrochemical bubbling method, removing the polymethyl methacrylate on the surface of the graphene by using acetone at the temperature of 70 ℃, and then flushing the graphene by using isopropanol and ethanol sequentially, so that the successful transfer of the single-crystal double-layer graphene is finally realized.
Example 5
First, a single crystal metal substrate is prepared by a magnetron sputtering method. The (0001) plane single crystal sapphire (thickness 0.5mm, single side polishing) was placed in a polishing solution (50 ml of concentrated sulfuric acid, 150ml of phosphoric acid), and chemical polishing was performed at 300 ℃ for 30min to remove the fragments and impurities on the sapphire surface, and then taken out and rinsed with deionized water for 5min.
After the cleaning was completed, as shown in fig. 1, a sapphire sheet 12 (fixed on a sample disk 11 and rotated at a speed of 30 rpm with the sample disk 11, first, a chromium target 13 having a purity of 99.95wt% was set as a sputtering source, a cylindrical chromium target 13 was set in an annular magnetron sputtering anode 14, an argon gas of 8 ml/min was introduced when the vacuum chamber pressure was reduced to the order of 10 -5 mbar, the sputtering source voltage was set to 600V, the current was set to 200mA, and a film was formed at a speed of 0.72 a/sec, when the Cr film thickness reached 185nm, the power was turned off, a nickel target 13 having a purity of 99.99wt% was replaced as a sputtering source, the cylindrical nickel target 13 was set in the annular magnetron sputtering anode 14, an argon gas of the order of 10 -5 mbar was introduced when the vacuum chamber pressure was reduced, the sputtering source voltage was set to 600V, the current was set to 200mA, a film was formed at a speed of 0.78 a/sec, and when the Ni film thickness reached nm, the power was turned off, and the substrate was taken out.
As shown in fig. 2, a horizontal atmospheric reaction furnace 22 (the diameter of the furnace tube is 36 mm, and the length of the reaction zone is 100 mm) is adopted to anneal the substrate, a corundum tube 25 is arranged on the furnace tube of the horizontal atmospheric reaction furnace 22 in a penetrating manner along the horizontal direction, two ends of the corundum tube 25 are sealed by flanges, and a gas inlet 21 and a gas outlet 24 are respectively arranged on the flanges at two ends of the corundum tube 25. The substrate was placed in a corundum tube 25 in the central region of the reactor, 300 ml/min of hydrogen was introduced, and the temperature was raised to 1300 c for 2 hours, to finally obtain a single crystal nichrome film substrate as shown in fig. 3.
As shown in FIG. 3, a horizontal reaction furnace 32 (the diameter of the furnace tube is 22 mm, the length of the reaction zone is 20 mm) is adopted to grow a uniform double-layer monocrystalline graphene film, a quartz tube 35 is arranged on the furnace tube of the horizontal reaction furnace 32 in a penetrating manner in the horizontal direction, two ends of the quartz tube 35 are sealed by flanges, a gas inlet 31 and a gas outlet 34 are respectively arranged on the flanges at two ends of the quartz tube 35, and a monocrystalline nichrome film substrate 33 is arranged in the quartz tube 35 in the constant temperature zone of the horizontal reaction furnace 32. The specific growth steps of the uniform double-layer monocrystalline graphene are as follows:
1) The horizontal reaction furnace was heated to 1050 ℃ at a rate of 20 ℃/min, the atmosphere in the quartz tube 35 was switched to hydrogen (flow 500 ml/min), the single crystal nichrome film substrate was placed in the central region of the horizontal reaction furnace, and the substrate was maintained for 5min to remove the organic residue and oxide layer on the surface of the substrate, and mixed gas of methane and hydrogen (gas flow rates were 3.2 ml/min for methane and 500 ml/min for hydrogen, respectively) was introduced to start the growth of graphene on the surface of the substrate. After 4h of growth, the surface of the substrate is covered with large-area film-forming double-layer graphene and a large number of multi-layer graphene islands.
2) And (3) keeping the gas flow unchanged, increasing the temperature to 1060 ℃ at a speed of 1 ℃/min, increasing the solubility of the substrate carbon, and dissolving the multi-layer graphene islands on the surface of the double-layer graphene to obtain a uniform single-crystal double-layer graphene film, wherein the thickness of the single-crystal double-layer graphene film is 0.68nm.
And (3) dropwise adding an ethyl lactate solution of polymethyl methacrylate (PMMA) (the mass fraction of the polymethyl methacrylate is 4 wt%) onto the surface of graphene, spin-coating a layer of polymethyl methacrylate on the surface of the graphene by a spin-coating method (the spin-coating speed is 2500 rpm, the spin-coating time is 60 seconds, the spin-coating times are 2 times), and placing the spin-coated polymethyl methacrylate/graphene/nickel chromium film/sapphire on a hot table and drying at 90 ℃ for 10 minutes. After etching nickel-chromium alloy on a substrate by using 1mol/L ferric chloride aqueous solution, transferring polymethyl methacrylate/graphene onto a SiO 2/Si substrate (a 300nm thick SiO 2 insulating layer is deposited on the surface of the Si substrate), removing polymethyl methacrylate on the surface of the graphene by using acetone at the temperature of 70 ℃, and then flushing the graphene by using isopropanol and ethanol sequentially, so that successful transfer of the single-crystal double-layer graphene film is finally realized.
The results of the examples show that the invention can be used for preparing a wafer-level uniform few-layer monocrystalline graphene film, and lays a foundation for physical property research of few-layer graphene and application in the fields of photoelectric devices, microelectronic devices, electronic transparent films and the like.
Claims (10)
1. A preparation method of a high-quality uniform few-layer monocrystalline graphene film is characterized in that a monocrystalline metal substrate with high carbon content is adopted, and a two-step chemical vapor deposition method is adopted to grow few-layer monocrystalline graphene on the surface of the monocrystalline metal substrate: firstly, growing a few-layer single-crystal graphene film containing a multi-layer graphene island structure, then improving the carbon solubility of a substrate by changing the temperature, selectively dissolving the multi-layer graphene island structure, and finally obtaining the few-layer single-crystal graphene film with uniform layers.
2. The method for preparing a high-quality uniform few-layer single crystal graphene film according to claim 1, wherein the layers in the non-uniform multilayer structure are more than the uniform few-layer single crystal graphene film, and the number of the few-layer single crystal graphene film is 2-10; the non-uniform multilayer structure is located at the interface of the minority layer single crystal graphene film and the metal substrate.
3. The method for preparing a high quality uniform few layer single crystal graphene film according to claim 1, wherein the single crystal metal substrate uses a metal with high carbon solubility and lattice constant matched with graphene as a matrix, including but not limited to nickel, iron, chromium, cobalt and alloys thereof with other elements.
4. The method for preparing a high-quality uniform few-layer monocrystalline graphene film according to claim 1, wherein the preparation of the monocrystalline metal substrate is implemented by a template method or a high-temperature annealing method, wherein: the template method selects a single crystal nonmetallic substrate sapphire (0001), magnesium oxide (111) or spinel (111) which are symmetrically matched as an epitaxial substrate, a layer of film is sequentially deposited on the surface of the nonmetallic substrate by a magnetron sputtering method, the thickness of the film is 100-1000 nm, the single crystal metallic film is obtained by annealing at 1200-1350 ℃ and in a reducing atmosphere, the reducing atmosphere is hydrogen or argon, the flow is 200-500 ml/min, and the annealing time is 1-12 h; the high-temperature annealing method selects commercial metal foil with the thickness of 10-100 mu m, and the single crystal metal film is obtained by annealing at 1350-1500 ℃ in a reducing atmosphere which is hydrogen or argon, the flow is 200-500 ml/min, and the annealing time is 4-24 h.
5. The method for producing a high-quality uniform few-layer single crystal graphene film according to any one of claims 1 to 4, wherein the production process of the high-quality uniform few-layer single crystal graphene film is as follows:
Stage 1: using single crystal metal as a growth substrate, adopting solid, liquid or gaseous carbon source, and carrying out long-time constant temperature or cooling deposition under the assistance of carrier gas to grow a few layers of single crystal graphene with a multilayer graphene island non-uniform multilayer structure;
Stage 2: maintaining the growth atmosphere unchanged, heating to increase the carbon solubility of the monocrystalline metal substrate, and completely dissolving the multilayer graphene islands into the monocrystalline metal substrate to obtain a monocrystalline graphene film without the multilayer graphene islands;
Stage 3: maintaining the growth atmosphere unchanged, continuing to perform heat preservation and growth for a period of time, and splicing the graphene which is not spliced into a complete film.
6. The method for producing a high-quality uniform few-layer single crystal graphene film according to claim 5, wherein in stage 1, 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 a carbon source is 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 the mixed gas of hydrogen, nitrogen and argon, and the flow rate of the carrier gas is 5-500 ml/min.
7. The method for preparing a high-quality uniform few-layer single-crystal graphene film according to claim 5, wherein in the 2 nd stage, graphene spliced into a film with a certain size has good stability and cannot be dissolved into a single-crystal metal substrate.
8. The method for preparing a high-quality uniform few-layer monocrystalline graphene film according to claim 5, wherein the substrate is monocrystalline metal matched with graphene symmetry, and the graphene film obtained by epitaxy of the monocrystalline metal substrate is a few-layer monocrystalline graphene film.
9. The method for preparing a high-quality uniform few-layer monocrystalline graphene film according to claim 5, wherein after the uniform few-layer monocrystalline graphene/monocrystalline metal substrate is protected by a high-molecular polymer, wet transfer is adopted, namely, graphene is separated from the substrate by etching metal through etching liquid or generating bubbles by electrolysis of an electrolytic cell, then the uniform few-layer monocrystalline graphene film is transferred to a target substrate, and then the high-molecular polymer protective layer is removed by using an organic solvent.
10. The method for preparing a high-quality uniform few-layer monocrystalline graphene film according to claim 9, wherein the etching solution is ammonium persulfate aqueous solution, potassium persulfate aqueous solution, hydrochloric acid or ferric chloride aqueous solution, the electrolyte is sodium hydroxide aqueous solution, dilute sulfuric acid or dilute hydrochloric acid, the high-molecular polymer is one or more than two of polymethyl methacrylate, polyethylene, polystyrene and polypropylene, and the organic solvent is one or more than two of ketone, chlorinated hydrocarbon, halogenated hydrocarbon and aromatic hydrocarbon organic solvents.
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