A method for rapidly growing double-layer graphene single crystals

Abstract

The invention provides a method for rapidly growing a double-layer graphene single crystal, comprising the following steps: step 1, putting a catalyst and a polished copper foil into two quartz boats and placing them in a quartz tube, the outside of the quartz tube is provided with a heating sleeve and a tubular furnace, placing the catalyst in the center of the heating sleeve, placing the copper foil in the center of the tubular furnace, turning on a vacuum pump connected to the quartz tube, heating the heating sleeve and the tubular furnace until the pressure is reduced to a preset pressure; step 2, annealing the copper foil in a vacuum; step 3, introducing hydrogen and carbon dioxide into the quartz tube, and rapidly adjusting the pressure, reacting under the action of the catalyst to generate methane, carbon monoxide and water, methane as a direct carbon source, growing on the copper foil in an oxygen-containing etching component to obtain a double-layer graphene single crystal; step 4, removing the copper foil from the center of the tubular furnace, introducing hydrogen and rapidly cooling it at a set pressure; step 5, taking out the copper foil cooled to room temperature, and transferring the double-layer graphene single crystal on the copper foil to a silicon wafer.

Description

Technical Field

[0001] The invention belongs to the field of two-dimensional material preparation, and in particular relates to a method for rapidly growing a double-layer graphene single crystal. Background Art

[0002] Double-layer graphene is an excellent two-dimensional material that can be used in the field of semiconductor chips. Because there are no grain boundaries in double-layer graphene single crystals to hinder electron transfer, they have a very high electron mobility. However, due to the difficulty of double-layer crystal nucleation, the growth rate of double-layer single crystals is slow, and is currently generally less than 200μm / h. The main reason for the difficulty in nucleation is that graphene growth must be carried out on the catalyst surface. When the surface of the catalytic substrate is covered with a single layer of graphene, the second layer of graphene will be restricted from nucleation.

[0003] There are currently two methods for forming double-layer nuclei: the first is to introduce exogenous nuclei. By introducing double-layer graphene fragments on the single-layer graphene, the second layer of nuclei is formed, but the size of the double-layer graphene single crystal obtained by this growth strategy is small and difficult to control; the second is to use etching components to promote the nucleation of double-layer graphene. Although excessive etching components will reduce the quality of graphene, the appropriate component content can create defects and open carbon diffusion channels to promote nucleation. A higher hydrogen partial pressure can etch the edge of the already formed single-layer graphene and promote the formation of double-layer graphene nuclei, but the nucleation efficiency of hydrogen etching is low. Introducing oxygen on the copper substrate can open the diffusion channel of carbon atoms and promote the diffusion of carbon atoms to the bottom of the single-layer graphene to form a second layer of nuclei. The oxygen content is difficult to control and the total amount of oxygen supply is limited during the growth process, which hinders the industrial application of this method. Summary of the invention

[0004] The present invention is made to solve the above-mentioned problem, and aims to provide a method for rapidly growing a double-layer graphene single crystal.

[0005] The present invention provides a method for rapidly growing a double-layer graphene single crystal, which has the following characteristics and comprises the following steps: Step 1, placing a catalyst and a polished copper foil into two quartz boats respectively and placing them in a quartz tube, wherein a heating jacket and a tubular furnace are respectively provided outside the quartz tube, the catalyst is placed in the center of the heating jacket, the copper foil is placed in the center of the tubular furnace, a vacuum pump connected to the inside of the quartz tube is turned on, and the heating jacket and the tubular furnace are heated until the pressure in the quartz tube is reduced to a preset pressure;

[0006] Step 2, annealing the copper foil in a vacuum atmosphere;

[0007] Step 3, using carbon dioxide as a carbon source and hydrogen as a reducing gas, hydrogen and carbon dioxide are introduced into a quartz tube, and the pressure is rapidly adjusted, carbon dioxide and hydrogen react under the action of a catalyst to generate methane, carbon monoxide and water, and methane is used as a direct carbon source to grow a double-layer graphene single crystal on a copper foil in an oxygen-containing etching component;

[0008] Step 4: After the growth is completed, the copper foil is removed from the center of the tube furnace, and only hydrogen is introduced and the temperature is rapidly reduced in an atmosphere of set pressure;

[0009] Step 5, taking out the copper foil cooled to room temperature, and transferring the double-layer graphene single crystal on the copper foil to the silicon wafer.

[0010] The method for rapidly growing double-layer graphene single crystals provided by the present invention may also have the following characteristics: wherein the oxygen-containing etching components are carbon dioxide, carbon monoxide and water, and the optimal ratio of the oxygen-containing etching components to methane is 1.2-1.3.

[0011] The method for rapidly growing a double-layer graphene single crystal provided by the present invention may also have the following characteristics: wherein, in step 1, the purity of the copper foil before polishing is 99.9% and the thickness is 30 μm, and the specific process of polishing is as follows: the copper foil is placed in a phosphoric acid aqueous solution with a volume fraction of 75%, the polishing area is 1 cm×3 cm, the voltage is 5 V, the current is 2 A, the polishing time is 1 min, and after polishing, the phosphoric acid aqueous solution is washed with deionized water, and the deionized water is blown dry with a nitrogen gun.

[0012] The method for rapidly growing double-layer graphene single crystals provided by the present invention may also have the following characteristics: wherein the catalyst is Ni / Al2O3, the optimum catalytic temperature of the catalyst is 300°C, and the growth temperature is 1000°C-1055°C.

[0013] The method for rapidly growing double-layer graphene single crystals provided by the present invention may also have the following characteristics: wherein, in step 1, the heating jacket is heated to 300°C, the tubular furnace is heated to 1000°C-1055°C, and the preset pressure is 20mTorr.

[0014] The method for rapidly growing a double-layer graphene single crystal provided by the present invention may also have the following characteristics: wherein, in step 2, the vacuum degree of the vacuum is 20 mTorr, and the duration of the annealing treatment of the copper foil is 10 minutes.

[0015] The method for rapidly growing a double-layer graphene single crystal provided by the present invention may also have the following characteristics: wherein, in step 3, the flow rate of hydrogen is 200 sccm, the flow rate of carbon dioxide is 1.5 sccm, the pressure is adjusted to 1000Pa-1200Pa, and the growth time of the double-layer graphene single crystal on the copper foil is 40 minutes.

[0016] The method for rapidly growing a double-layer graphene single crystal provided by the present invention may also have the following characteristics: wherein, in step 4, the hydrogen flow rate is 100 sccm and the set pressure is 100 Pa.

[0017] The method for rapidly growing a double-layer graphene single crystal provided by the present invention may also have the following characteristics: wherein, in step 5, the specific process of transferring the double-layer graphene single crystal on the copper foil to the silicon wafer is as follows:

[0018] The copper foil on which the double-layer graphene single crystal is grown is cut into copper sheets of 1 cm×1 cm in size, a layer of polymethyl methacrylate solution is spin-coated on the surface of the double-layer graphene single crystal, and after drying in air, the copper foil is placed in an etchant to etch away the copper substrate to obtain a double-layer graphene single crystal film protected by PMMA, and the double-layer graphene single crystal film is transferred to a silicon wafer. When the double-layer graphene single crystal film and the silicon wafer are completely bonded, the PMMA is removed with hot toluene and hot acetone solutions to obtain a double-layer graphene single crystal attached to the silicon wafer.

[0019] The preparation method of the polymethyl methacrylate solution is as follows: 0.6 g of polymethyl methacrylate with a molecular weight of 500,000 is dissolved in 10 mL of anisole and stirred, and a polymethyl methacrylate solution with a mass fraction of 6% is obtained after heating in a water bath at 85° C. for 1 hour. The spin coating speed is 600 r / s-3000 r / s, the time is 6 s at a low speed and 30 s at a high speed, and the etchant is 0.05 mol / L of a pentahydrate copper sulfate hydrochloric acid aqueous solution and 0.20 mol / L of an ammonium persulfate aqueous solution. The pentahydrate copper sulfate hydrochloric acid aqueous solution is passed through The ammonium persulfate aqueous solution was prepared by dissolving 129.84 g of copper sulfate pentahydrate in 50 mL of water and 50 mL of hydrochloric acid solution. The ammonium persulfate aqueous solution was prepared by dissolving 2.28 g of ammonium persulfate in 100 mL of water. The etching process was first etching with copper sulfate pentahydrate hydrochloric acid aqueous solution for 5 minutes, and then etching with ammonium persulfate aqueous solution for 12 hours. The bonding process was heating at 110°C for 1 hour, followed by heating at 150°C for 1 hour. The process of removing PMMA was first soaking in 90°C toluene solution for half an hour, and then soaking in 65°C acetone solution for half an hour.

[0020] The method for rapidly growing double-layer graphene single crystals provided by the present invention may also have the following characteristics: among the double-layer graphene single crystals grown, 72%-73% are AB-stacked double-layer graphene single crystals, and 27%-28% are 30° rotated double-layer graphene single crystals. The average size of the double-layer graphene single crystals is 125 μm, and the maximum size exceeds 200 μm. The growth rate of the double-layer graphene single crystals during growth is 300 μm / h.

[0021] Functions and Effects of the Invention

[0022] According to a method for rapidly growing double-layer graphene single crystals involved in the present invention, carbon dioxide is directly catalytically converted into high-quality double-layer graphene single crystals by using carbon dioxide as a carbon source, and the size of the prepared double-layer graphene single crystal reaches 200μm, and the growth rate is 300μm / h. The method of the present invention has simple process and good repeatability, overcomes the shortcomings of difficult nucleation and slow growth of double-layer graphene, and can directly prepare high-quality double-layer graphene with high added value and applied to electronic devices by catalytic carbon neutralization of CO2 gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram of the growth of a double-layer graphene single crystal in an embodiment of the present invention;

[0024] Figure 2 is a flow chart of a method for rapidly growing a double-layer graphene single crystal in an embodiment of the present invention;

[0025] Figure 3 is a structural representation diagram of a double-layer graphene single crystal in an embodiment of the present invention;

[0026] Figure 4 are Raman spectra of single-layer graphene and double-layer graphene single crystals in the embodiments of the present invention;

[0027] Figure 5 is a size distribution diagram of a double-layer graphene single crystal prepared in an embodiment of the present invention;

[0028] Figure 6 is a data set diagram proving that the double-layer graphene single crystal is a single crystal structure in an embodiment of the present invention;

[0029] Figure 7 are optical microscopic images of double-layer graphene at different growth times in an embodiment of the present invention;

[0030] Figure 8 is a graph showing the growth rates of single-layer graphene and double-layer graphene in an embodiment of the present invention;

[0031] Fig. 9is a graph showing the change of the crystal nucleus density of double-layer graphene and multi-layer graphene with the reaction time in the embodiment of the present invention;

[0032] Fig.10 is a gas phase analysis result diagram in an embodiment of the present invention;

[0033] Fig.11 is a Raman spectrum diagram of a single-layer graphene film etched by carbon dioxide at 900° C. and a single-layer graphene film in the region before and after etching in an embodiment of the present invention;

[0034] Fig.12 is an optical microscope image of double-layer graphene under different growth pressures in an embodiment of the present invention;

[0035] Fig.13 is the crystal nucleus density of double-layer graphene and multi-layer graphene under different growth pressures in the embodiments of the present invention;

[0036] Fig.14 is the ratio of oxygen-containing etchant component to methane at different growth pressures in the embodiments of the present invention;

[0037] Fig.15 It is the relationship between the multi-layer graphene core density, the double-layer graphene core density and the ratio of oxygen-containing etching components to methane in the embodiments of the present invention. DETAILED DESCRIPTION

[0038] In order to make the technical means and effects achieved by the present invention easier to understand, the present invention is described in detail below in conjunction with embodiments and drawings.

[0039] <Example>

[0040] Figure 1 It is a schematic diagram of the growth of a double-layer graphene single crystal in an embodiment of the present invention.

[0041] like Figure 1 As shown, 1 is a heating jacket for heating the catalyst, 2 is a tubular furnace, 3 is a quartz tube, 4 is a catalyst, and 5 is a copper foil covered with a double-layer graphene single crystal. Carbon dioxide and hydrogen are introduced into the reaction system, and the carbon dioxide gas is first activated by passing through the first temperature zone, and then grows on the growth substrate in the second temperature zone to obtain a double-layer graphene single crystal.

[0042] Figure 2 It is a flow chart of a method for rapidly growing a double-layer graphene single crystal in an embodiment of the present invention.

[0043] like Figure 2 As shown, a method for rapidly growing a double-layer graphene single crystal in this embodiment includes the following steps:

[0044] Step 1, put the catalyst and the polished copper foil into two quartz boats respectively and place them in a quartz tube, the outside of the quartz tube is provided with a heating jacket and a tubular furnace respectively, the catalyst is placed in the center of the heating jacket, the copper foil is placed in the center of the tubular furnace, the vacuum pump connected to the inside of the quartz tube is turned on, and the heating jacket and the tubular furnace are heated, the heating jacket is heated to 300°C, and the tubular furnace is heated to 1000-1055°C, until the pressure in the quartz tube is reduced to 20mTorr. In this process, the gas components adsorbed on the catalyst gradually evaporate during the heating process.

[0045] In step 1, the purity of the copper foil before polishing is 99.9% and the thickness is 30 μm. The specific process of polishing is as follows: the copper foil is placed in a phosphoric acid aqueous solution with a volume fraction of 75%, the polishing area is 1 cm×3 cm, the voltage is 5 V, the current is 2 A, and the polishing time is 1 min. After polishing, the phosphoric acid aqueous solution is washed with deionized water and the deionized water is blown dry with a nitrogen gun.

[0046] The catalyst is Ni / Al2O3, the optimum catalytic temperature of the catalyst is 300°C, and the growth temperature is 1000°C-1055°C.

[0047] Step 2: Place the copper foil in the center of the tube furnace and anneal the copper foil for 10 minutes in a vacuum background atmosphere of 20 mTorr.

[0048] Step 3, using carbon dioxide as a carbon source and hydrogen as a reducing gas, 200 sccm of hydrogen and 1.5 sccm of carbon dioxide are introduced into a quartz tube, and the pressure is quickly adjusted to 1000Pa-1200Pa. Carbon dioxide and hydrogen react under the action of a catalyst to generate methane, carbon monoxide and water. Methane is used as a direct carbon source to grow a double-layer graphene single crystal on a copper foil in an oxygen-containing etching component, and the growth time is 40 minutes.

[0049] The oxygen-containing etching components are carbon dioxide, carbon monoxide and water, and the optimal ratio of the oxygen-containing etching components to methane is 1.2-1.3.

[0050] Step 4: After the growth is completed, the copper foil is removed from the center of the tube furnace, and only 100 sccm of hydrogen is introduced and the temperature is rapidly lowered in an atmosphere with a system pressure of 100 Pa.

[0051] Step 5, taking out the copper foil cooled to room temperature, and transferring the double-layer graphene single crystal on the copper foil to the silicon wafer.

[0052] In step 5, the specific process of transferring the double-layer graphene single crystal on the copper foil to the silicon wafer is as follows:

[0053] The copper foil on which the double-layer graphene single crystal is grown is cut into copper sheets of 1 cm×1 cm in size, a layer of polymethyl methacrylate solution is spin-coated on the surface of the double-layer graphene single crystal, and after drying in air, the copper foil is placed in an etchant to etch away the copper substrate to obtain a double-layer graphene single crystal film protected by PMMA, and the double-layer graphene single crystal film is transferred to a silicon wafer. When the double-layer graphene single crystal film and the silicon wafer are completely bonded, the PMMA is removed with hot toluene and hot acetone solutions to obtain a double-layer graphene single crystal attached to the silicon wafer.

[0054] The preparation method of the polymethyl methacrylate solution is as follows: 0.6 g of polymethyl methacrylate with a molecular weight of 500,000 is dissolved in 10 mL of anisole and stirred, and then heated in a water bath at 85° C. for 1 hour to obtain a polymethyl methacrylate solution with a mass fraction of 6%.

[0055] The spin coating speed is 600r / s-3000r / s, the time is 6s at low speed and 30s at high speed.

[0056] The etchant is a 0.05 mol / L aqueous solution of copper sulfate pentahydrate hydrochloric acid and a 0.20 mol / L aqueous solution of ammonium persulfate. The aqueous solution of copper sulfate pentahydrate hydrochloric acid is prepared by dissolving 129.84 g of copper sulfate pentahydrate in 50 mL of water and 50 mL of hydrochloric acid solution. The aqueous solution of ammonium persulfate is prepared by dissolving 2.28 g of ammonium persulfate in 100 mL of water. The etching process is to etch with the aqueous solution of copper sulfate pentahydrate hydrochloric acid for 5 minutes and then etch with the aqueous solution of ammonium persulfate for 12 hours.

[0057] The bonding process is to heat at 110℃ for 1 hour, followed by heating at 150℃ for 1 hour.

[0058] The process of removing PMMA is to first soak it in a 90°C toluene solution for half an hour, and then soak it in a 65°C acetone solution for half an hour.

[0059] Figure 3 It is a structural representation diagram of a double-layer graphene single crystal in an embodiment of the present invention.

[0060] Figure 3 (a) is an optical microscope image of double-layer graphene (scale bar: 50 μm); (b) is a mapping analysis of the half-width of the Raman 2D peak of double-layer graphene; (c) is a mapping analysis of the ratio of the Raman 2D peak intensity to the G peak intensity of double-layer graphene.

[0061] like Figure 3 As shown, the half-peak width of the 2D peak and the intensity ratio of the 2D peak to the G peak are 55–65 cm -1 and 0.7-0.8, which is consistent with the properties of AB stacked bilayer graphene, and its mapping diagram has a uniform distribution ( Figure 3(b)(c)), proving that the entire double-layer graphene single crystal has the same thickness and stacking pattern.

[0062] Figure 4 3 are Raman spectra of single-layer graphene and double-layer graphene single crystals in the embodiments of the present invention.

[0063] Figure 4 (a) and (b) are the Raman spectra of single-layer graphene and double-layer graphene single crystals, respectively.

[0064] like Figure 4 As shown, no D peak is observed in the Raman peaks of the monolayer region and the bilayer region, indicating that graphene has a defect-free atomic arrangement.

[0065] Through optical microscopy and SAED statistics, it was found that 72%-73% of the double-layer graphene single crystals were in AB stacking mode, and the rest were double-layer graphene single crystals rotated by 30°.

[0066] Figure 5 3 is a size distribution diagram of the double-layer graphene single crystal prepared in the embodiment of the present invention.

[0067] like Figure 5 As shown, the average size of the double-layer graphene single crystal is 125 μm, and the maximum size exceeds 200 μm.

[0068] In this example, in order to prove the single crystal structure, a double-layer graphene single crystal attached to a silicon wafer was transferred to a TEMgrid. The specific process is as follows:

[0069] Select a double-layer graphene single crystal sample transferred to a silicon wafer, select the area that needs to be transferred to the TEMgrid for further observation under an optical microscope, spin-coat a layer of PMMA film on the sample, dry it in the air, place it in an etchant to etch away the silicon substrate, and obtain a double-layer graphene single crystal film protected by PMMA, and transfer the film to the TEMgrid. When the film and TEMgrid are completely bonded, use hot acetone solution to remove the PMMA solution to obtain a double-layer graphene single crystal attached to the TEMgrid.

[0070] The spin coating speed is 600-3000 r / s, the time is 6s at low speed and 30s at high speed; the etchant is 15.44mmol / LBOE solution (8g ammonium fluoride dissolved in 2mL hydrogen fluoride and 12mL water); the etching time is 24h; the bonding process is heated at 70°C for 10min;

[0071] The process of removing PMMA is to use a dropper to absorb 10mL of hot acetone at 65℃ and drip it on the edge of the TEMgrid placed on the filter paper at a rate of one drop per second. The droplet infiltrates from the edge to the entire TEMgrid surface and transfers the dissolved PMMA to the filter paper.

[0072] Figure 6 It is a data set diagram proving that the double-layer graphene single crystal is a single crystal structure in the embodiment of the present invention.

[0073] Figure 6 (a) is the region where the double-layer graphene single crystal domains have the same orientation; (b) is the overlap of the selected electron diffraction patterns in this region; (c) is the electron diffraction patterns at different positions. The relative strength of the crystal planes.

[0074] like Figure 6 As shown, it was found that within the 20μm×30μm area on the TEMgrid ( Figure 6 (a)), the selected area electron diffraction patterns of graphene can be well overlapped ( Figure 6 (b)), and they all conform to the properties of AB stacked bilayer graphene, that is, and The strength of the crystal face is and Half of the crystal face ( Figure 6 (c)), demonstrating that the domain orientations in the crystal are consistent.

[0075] Figure 7 1 is an optical microscope image of double-layer graphene at different growth times in an embodiment of the present invention.

[0076] Figure 7 (a), (b), (c), and (d) are optical microscopic images at 5 min, 10 min, 20 min, and 40 min, respectively (scale bar: 100 μm).

[0077] like Figure 7 As shown, under the same pressure (1200Pa) and the same gas source ratio (hydrogen: carbon dioxide = 200:1.5), as the reaction proceeds, double-layer graphene nucleates at 10 minutes, and single-layer graphene grows into a continuous film at 40 minutes.

[0078] Figure 8 It is a graph showing the growth rates of single-layer graphene and double-layer graphene in an embodiment of the present invention.

[0079] Figure 8 (a) and (b) are the growth rate diagrams of single-layer graphene and double-layer graphene, respectively.

[0080] like Figure 8As shown in Figure 2, the growth rate of single-layer graphene reaches 1200μm / h, and the growth rate of double-layer graphene reaches 300μm / h. This is the highest growth rate of double-layer graphene single crystal so far.

[0081] Fig. 9 Graph showing the change in the crystal nucleus density of double-layer graphene and multi-layer graphene with reaction time in an embodiment of the present invention.

[0082] like Fig. 9 As shown, as the reaction proceeds, the double-layer graphene is transformed into multi-layer graphene nuclei, and the ratio of the double-layer graphene nucleus density to the multi-layer graphene nucleus density continues to decrease.

[0083] In this embodiment, the growth mechanism of double-layer graphene is also studied, as follows:

[0084] The conversion of carbon dioxide into graphene involves many complex processes, such as the deoxygenation and hydrogenation of carbon dioxide. In this embodiment, the components of the reaction system are further analyzed by a hydrogen flame ionization detector (FID) and a thermal conductivity detector (TCD) of a gas chromatograph (GC). Fig.10 It is a graph showing the gas phase analysis result in an example of the present invention.

[0085] Fig.10 (a) is the hydrogen content detected by TCD; (b) is the carbon dioxide, methane and carbon monoxide content detected by FID.

[0086] like Fig.10 As shown, the gas phase analysis results show that the gas components of the reaction system are: hydrogen, carbon dioxide, carbon monoxide, methane and water (water is calculated from the reaction equation of deoxygenation and hydrogenation of carbon dioxide).

[0087] Then, experiments were carried out in the reaction system under different growth atmospheres, as follows:

[0088] 1) In this reaction system, 200 sccm of hydrogen and 1.5 sccm of carbon dioxide were introduced. In the process without catalyst pre-activation, the reaction pressure was 1200 Pa. After 40 minutes of growth, no graphene was generated. No methane was detected in the gas phase components of this process, indicating that methane is the direct carbon source for the growth of double-layer graphene single crystals.

[0089] 2) In this system, 200 sccm of hydrogen and 1.5 sccm of methane were introduced, the reaction pressure was 1200 Pa, and after 40 minutes of growth, only single-layer graphene grew, indicating that oxygen-containing etching components are crucial for the growth of double-layer graphene.

[0090] 3) A single layer of graphene was grown on the copper foil using the traditional method in advance, and the copper foil covered with the single layer of graphene was placed in a quartz tube. After the vacuum of the system was reduced to 20 mTorr, only 1.5 sccm of carbon dioxide was introduced, and the single layer of graphene was etched at 900°C for 1 minute.

[0091] Fig.11 It is a Raman spectrum diagram of a single-layer graphene film etched by carbon dioxide at 900° C. and a single-layer graphene film in the region before and after etching in an embodiment of the present invention.

[0092] Fig.11 (a) and (b) are the Raman spectra of the single-layer graphene film etched by carbon dioxide at 900°C in region 1 and the single-layer graphene film in region 1 before and after etching, respectively.

[0093] like Fig.11 As shown, at this time, defects have been generated on the graphene film. D peaks are observed through Raman spectroscopy. Therefore, it is obtained that the oxygen-containing etching component can etch defects on the single-layer graphene, which serves as the nucleation center of the double-layer graphene.

[0094] The key factors for growing double-layer graphene were further studied by adjusting the total pressure of the reaction system. The ratio of oxygen-containing etching components and methane was changed by adjusting the total pressure. The specific process is as follows:

[0095] 1) Control the hydrogen flow rate to 200 sccm, the carbon dioxide flow rate to 1.5 sccm, and adjust the pressure. Fig.12 is an optical microscope image of double-layer graphene under different growth pressures in an embodiment of the present invention, Fig.13 is the crystal nucleus density of double-layer graphene and multi-layer graphene under different growth pressures in the embodiments of the present invention.

[0096] Fig.12 (a), (b), (c), and (d) are optical microscope images of double-layer graphene grown at 800Pa, 1000Pa, 1200Pa, and 1500Pa for 40min, respectively.

[0097] like Fig.12 and Fig.13 As shown in the figure, when the total pressure is 800Pa, only single-layer graphene is generated. As the pressure increases, the density of double-layer graphene nuclei presents a volcano graph curve with a peak at 1200Pa. The density of multi-layer graphene nuclei gradually increases. Similar experimental phenomena can also be observed when the carbon dioxide flow rate is 1sccm and 2sccm.

[0098] Fig.14 is the ratio of oxygen-containing etching components to methane at different growth pressures in the embodiments of the present invention.

[0099] like Fig.14 As shown, through gas chromatography detection, it was found that the ratio of oxygen-containing etching components and methane decreased with increasing total pressure.

[0100] Fig.15 It is the relationship between the multi-layer graphene core density, the double-layer graphene core density and the ratio of oxygen-containing etching components to methane in the embodiments of the present invention.

[0101] Fig.15 (a) is the relationship between the crystal core density of multilayer graphene and the ratio of oxygen-containing etching components to methane; (b) is the relationship between the crystal core density of double-layer graphene and the ratio of oxygen-containing etching components to methane.

[0102] like Fig.15 As shown, with the increase of the proportion of oxygen-containing etching components and methane, the density of multilayer graphene nuclei gradually decreases, and the density of double-layer graphene nuclei first increases and then decreases.

[0103] In summary, the oxygen-containing etching component will etch defects on the single-layer graphene to form the nucleation center of the double-layer graphene nucleus or the multi-layer graphene nucleus, and the nucleation selectivity of the double-layer graphene and multi-layer graphene is determined by the ratio of the oxygen-containing etching component and methane. High methane concentration will promote the generation of multi-layer nuclei, and the oxygen-containing etching component will etch the multi-layer graphene nucleus and inhibit the transformation of double-layer graphene to multi-layer graphene. However, if the content of the oxygen-containing etching component is further increased, the double-layer graphene will be etched and disappear.

[0104] Therefore, different chemical vapor deposition systems have their optimal growth pressure ranges. The optimal growth pressure range in the 1-inch tube furnace used in this embodiment is 1000Pa-1200Pa, and the optimal ratio of oxygen-containing etching components (carbon dioxide, carbon monoxide, water) to methane is 1.2-1.3. In this growth window, the size of the double-layer graphene single crystal is the largest, and the ratio of double-layer graphene to multi-layer graphene is the highest.

[0105] Functions and Effects of the Embodiments

[0106] According to a method for rapidly growing a double-layer graphene single crystal involved in this embodiment, carbon dioxide is directly catalytically converted into a high-quality double-layer graphene single crystal by using carbon dioxide as a carbon source, and the size of the prepared double-layer graphene single crystal reaches 200μm, and the growth rate is 300μm / h. The method of this embodiment is simple in process and has good repeatability, and overcomes the shortcomings of the difficulty of nucleation and slow growth of double-layer graphene. CO2 gas can be directly prepared into high-quality double-layer graphene with high added value and applied to electronic devices through catalytic carbon neutralization.

[0107] The above-mentioned embodiments are preferred examples of the present invention and are not intended to limit the protection scope of the present invention.

Claims

1. A method for rapidly growing a double-layer graphene single crystal, characterized in that: The following steps are involved: Step 1, placing the catalyst and the polished copper foil in two quartz boats respectively and placing them in a quartz tube, the outside of the quartz tube is respectively provided with a heating jacket and a tubular furnace, placing the catalyst in the center of the heating jacket, placing the copper foil in the center of the tubular furnace, turning on the vacuum pump connected to the inside of the quartz tube, and heating the heating jacket and the tubular furnace until the pressure in the quartz tube drops to a preset pressure; Step 2, annealing the copper foil in a vacuum atmosphere; Step 3, using carbon dioxide as a carbon source and hydrogen as a reducing gas, introducing hydrogen and carbon dioxide into the quartz tube, and rapidly adjusting the pressure, wherein the carbon dioxide and the hydrogen react under the action of the catalyst to generate methane, carbon monoxide and water, and the methane is used as a direct carbon source to grow a double-layer graphene single crystal on the copper foil in an oxygen-containing etching component; Step 4, after the growth is completed, the copper foil is removed from the center of the tube furnace, only hydrogen is introduced, and the temperature is rapidly lowered in an atmosphere of set pressure; Step 5, taking out the copper foil cooled to room temperature, and transferring the double-layer graphene single crystal on the copper foil to a silicon wafer, Wherein, the oxygen-containing etching component is carbon dioxide, carbon monoxide and water, and the ratio of the oxygen-containing etching component to the methane is 1.2-1.3, The catalyst is Ni / Al2O3, the catalytic temperature of the catalyst is 300°C, and the growth temperature is 1000°C-1055°C. In step 3, the flow rate of hydrogen is 200 sccm, the flow rate of carbon dioxide is 1.5 sccm, the pressure is adjusted to 1000 Pa-1200 Pa, and the growth time of the double-layer graphene single crystal on the copper foil is 40 minutes. In step 4, the hydrogen flow rate is 100 sccm and the set pressure is 100 Pa.

2. The method for rapidly growing a double-layer graphene single crystal according to claim 1, characterized in that: in, In the step 1, the purity of the copper foil before the polishing treatment is 99.9% and the thickness is 30 μm. The specific process of the polishing treatment is as follows: the copper foil is placed in a phosphoric acid aqueous solution with a volume fraction of 75%, the polishing area is 1 cm×3 cm, the voltage is 5 V, the current is 2 A, the polishing time is 1 min, and after polishing, the phosphoric acid aqueous solution is washed with deionized water, and the deionized water is blown dry with a nitrogen gun.

3. The method for rapidly growing a double-layer graphene single crystal according to claim 1, characterized in that: in, In the step 1, the heating jacket is heated to 300° C., the tube furnace is heated to 1000° C.-1055° C., and the preset pressure is 20 mTorr.

4. The method for rapidly growing a double-layer graphene single crystal according to claim 1, characterized in that: in, In step 2, the vacuum degree of the vacuum is 20 mTorr, The copper foil is annealed for 10 minutes.

5. The method for rapidly growing a double-layer graphene single crystal according to claim 1, characterized in that: in, In step 5, the specific process of transferring the double-layer graphene single crystal on the copper foil to the silicon wafer is as follows: The copper foil on which the double-layer graphene single crystal is grown is cut into a copper sheet of 1 cm×1 cm in size, a layer of polymethyl methacrylate solution is spin-coated on the surface of the double-layer graphene single crystal, and after drying in air, the copper foil is placed in an etchant to etch away the copper substrate to obtain a double-layer graphene single crystal film protected by PMMA, and the double-layer graphene single crystal film is transferred to a silicon wafer. When the double-layer graphene single crystal film and the silicon wafer are completely bonded, the PMMA is removed by using hot toluene and hot acetone solutions to obtain the double-layer graphene single crystal attached to the silicon wafer. The preparation method of the polymethyl methacrylate solution is as follows: 0.6 g of polymethyl methacrylate with a molecular weight of 500,000 is dissolved in 10 mL of anisole and stirred, and then heated in a water bath at 85° C. for 1 hour to obtain a polymethyl methacrylate solution with a mass fraction of 6%. The spin coating speed is 600r / s-3000r / s, the time is 6s at low speed and 30s at high speed. The etchant is a 0.05 mol / L aqueous solution of copper sulfate pentahydrate hydrochloric acid and a 0.20 mol / L aqueous solution of ammonium persulfate. The aqueous solution of copper sulfate pentahydrate hydrochloric acid is prepared by dissolving 129.84 g of copper sulfate pentahydrate in 50 mL of water and 50 mL of hydrochloric acid solution. The aqueous solution of ammonium persulfate is prepared by dissolving 2.28 g of ammonium persulfate in 100 mL of water. The etching process is to etch with the aqueous solution of copper sulfate pentahydrate hydrochloric acid for 5 minutes and then etch with the aqueous solution of ammonium persulfate for 12 hours. The bonding process is heating at 110°C for 1 hour, followed by heating at 150°C for 1 hour. The process of removing PMMA is to first soak it in a 90° C. toluene solution for half an hour, and then soak it in a 65° C. acetone solution for half an hour.

6. The method for rapidly growing a double-layer graphene single crystal according to claim 1, characterized in that: in, Among the double-layer graphene single crystals grown, 72%-73% are AB-stacked double-layer graphene single crystals, and 27%-28% are 30° rotated double-layer graphene single crystals. The average size of the double-layer graphene single crystal is 125 μm, the maximum size exceeds 200 μm, and the growth rate of the double-layer graphene single crystal during growth is 300 μm / h.

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