A method for preparing graphene by a relatively closed area solid phase method

Abstract

This invention belongs to the field of materials preparation technology, and more specifically, relates to a method for preparing graphene using a relatively closed-region solid-state method. The method involves depositing a carbon source layer and a catalytic metal layer on a substrate to obtain a graphene preparation precursor. This precursor is then either inverted or an inert cap is placed on its surface to form a closed region. Finally, heating and annealing are performed to obtain large-area, high-quality graphene that does not require transfer. Compared to open-region solid-state methods with upright placement or no cap, this relatively closed-region solid-state method yields graphene of better quality, with no metal residue and a wider range of carbon source selection.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of material preparation, and more particularly relates to a method for preparing graphene by a solid phase method in a relatively closed region. BACKGROUND

[0002] Graphene has good electrical and optical properties, such as high carrier mobility (15000 cm 2 V -1 s -1 ) and high transmittance (wavelength range from visible light to near infrared region).

[0003] The most commonly used method for preparing graphene is chemical vapor deposition (CVD), by which a graphene film is grown on a catalytic metal surface, and then a post-growth process is used to etch the catalyst and transfer the graphene to a dielectric substrate (such as SiO2 / Si) for further application, such as assembling functional electronic devices. By chemical vapor deposition, the growth of single-layer or double-layer graphene is achieved on a copper or nickel substrate using methane or ethylene gas as a precursor. However, chemical vapor deposition is limited to the use of gaseous precursors, which makes it difficult to use a wider range of potential other solid precursors.

[0004] In some other methods, graphene can be grown on a substrate of dielectric material by pyrolysis of a polymer on a catalytic metal surface. Depending on the properties of graphene and the needs of electronic devices, graphene is mostly grown on a dielectric surface, such as a silicon dioxide substrate, a quartz glass substrate, a sapphire substrate, etc., and most of the existing methods for growing graphene require a post-growth process, including catalyst etching and graphene substrate transfer, and most of them require high temperature and high pressure, which greatly reduces the preparation efficiency of graphene and increases the growth cost. SUMMARY

[0005] In view of the defects of the prior art, the present application provides a method for preparing graphene by a solid phase method in a relatively closed region, which inverts the carbon source film layer and / or catalytic metal layer prepared by deposition on a substrate on the charging table of an annealing furnace, or covers the surface of the deposited film layer with an inert cover and then places it on the charging table of the annealing furnace, to form a relatively closed region, so as to prepare high-quality single-layer or multi-layer graphene by heat treatment, thereby solving the technical problems that the preparation of graphene by the CVD method of the prior art is limited to the use of flammable and explosive gas precursors, some solid phase methods for preparing graphene require high temperature and high pressure, or the prepared graphene has residual catalytic metal, resulting in poor quality of graphene.

[0006] To achieve the above-mentioned purpose, the present application provides a method for preparing graphene by a solid phase method in a relatively closed region, comprising the following steps:

[0007] (1) depositing a carbon source layer and a catalytic metal layer on a surface-cleaned substrate surface successively or simultaneously to obtain a graphene preparation precursor;

[0008] (2) inverting the graphene preparation precursor on a loading table in an annealing device, and performing a heating annealing process in an oxygen-free or low-oxygen environment; or covering the surface of the carbon source layer and / or the catalytic metal layer of the graphene preparation precursor with an inert cover, and then placing it on a loading table in an annealing device, and performing a heating annealing process in an oxygen-free or low-oxygen environment; the inversion is that when the graphene preparation precursor is placed on the loading table of the annealing device, the substrate is on top and the deposited carbon source layer and / or catalytic metal layer is on the bottom; the substrate, the inert cover and the loading table do not react with the carbon source layer or the catalytic metal layer during the heating annealing process;

[0009] wherein during the heating annealing process, the carbon in the carbon source layer and the metal in the catalytic metal layer form a metastable metal carbide, and then the carbide decomposes to remove the metal therein by evaporation, to obtain single-layer or multi-layer graphene.

[0010] Preferably, step (1) obtains the graphene preparation precursor in any of the following ways:

[0011] (i) depositing a carbon source layer and a catalytic metal layer on a surface-cleaned substrate surface successively to obtain a graphene preparation precursor;

[0012] (ii) depositing a catalytic metal layer and a carbon source layer on a surface-cleaned substrate surface successively to obtain a graphene preparation precursor;

[0013] (iii) depositing a carbon source layer and a catalytic metal layer on a surface-cleaned substrate surface simultaneously to obtain a graphene preparation precursor containing a composite layer of carbon source and catalytic metal.

[0014] Preferably, the carbon source layer is elemental amorphous carbon, amorphous carbon or a hydrocarbon compound, and the catalytic metal in the catalytic metal layer is at least one of nickel, copper or nickel-copper alloy.

[0015] Further preferably, the hydrocarbon compound is a condensed ring aromatic hydrocarbon with a carbon number of 10 to 30.

[0016] Preferably, the thickness of the carbon source layer is in the range of 1 nm to 100 nm; and the thickness of the catalytic metal layer is 1 nm to 1000 nm.

[0017] Further preferably, the thickness of the carbon source layer is in the range of 1 nm to 15 nm; and the thickness of the catalytic metal layer is 50 nm to 200 nm.

[0018] More preferably, the thickness of the carbon source layer is in the range of 2nm to 10nm; and the thickness of the catalytic metal layer is in the range of 40nm to 100nm.

[0019] Preferably, the thickness ratio of the catalytic metal layer to the carbon source layer is in the range of 65:1 to 15, more preferably in the range of 65:2 to 8.

[0020] Preferably, step (1) comprises sequentially depositing a carbon source layer and a catalytic metal layer on a surface-cleaned substrate surface to obtain a graphene preparation precursor; and then performing a heating annealing process of step (2) after performing a patterning process on the catalytic metal layer.

[0021] Preferably, the substrate material is at least one of a silicon oxide / silicon composite layer, sapphire, quartz or glass; and the inert cover material is a silicon wafer, a quartz wafer or sapphire.

[0022] Preferably, step (1) comprises depositing the carbon source layer and the catalytic metal layer by a thin film deposition process, wherein the thin film deposition process is magnetron sputtering, electron beam evaporation or thermal evaporation plating.

[0023] Preferably, the heating annealing process is performed in a vacuum degree of less than or equal to 3x10 -3 torr, at a temperature of 900℃ to 1200℃, and for a time period of 2 to 10 minutes.

[0024] Preferably, a light beam is applied to rapidly heat the carbon source layer and the catalytic metal layer, wherein the light source of the light beam is further preferably an infrared lamp tube, a laser beam or a xenon lamp.

[0025] Preferably, the heating annealing process comprises: heating to a temperature of 500 to 700℃ at a rate of 3 to 6℃ / second, then heating to a temperature of 900 to 1200℃ at a rate of 8 to 12℃ / second, and maintaining the temperature of 900 to 1200℃ for a time period of 2 to 10 minutes.

[0026] In general, the above technical solutions of the present application have the following beneficial effects compared with the prior art:

[0027] (1) The application provides a method for preparing graphene by a relatively closed area solid phase method, which is relative to an open area solid phase method for preparing graphene. A carbon source and a catalytic metal are deposited on a substrate to obtain a graphene preparation precursor, the precursor is inverted on a loading table of an annealing device, the substrate is on the top, and the carbon source thin film layer and the catalytic metal thin film layer are on the bottom, so that a closed area is formed; or after the carbon source layer thin film and the catalytic metal layer thin film are deposited on the substrate, an inert cover is directly covered on the surface of the thin film to form a closed area; then the carbon source and the catalytic metal are heated in an oxygen-free or low-oxygen environment to form graphene on the substrate. The catalytic metal evaporates in the heating process, so that only graphene remains on the substrate. Experiments show that, compared with the open area solid phase method for preparing graphene, that is, after the carbon source layer thin film and the catalytic metal layer thin film are deposited on the substrate, the thin film and the substrate are directly placed in the annealing device vertically, the carbon source thin film and / or the catalytic metal layer thin film are on the top, and the substrate is on the bottom, graphene prepared by heating and annealing to prepare graphene under the same conditions does not contain metal residues, and the quality of the graphene is higher.

[0028] (2) The relatively closed area solid phase method for preparing graphene provided by the application does not need to use flammable and explosive precursors, such as H2 and CH4, and can directly deposit a solid phase carbon source thin film on a substrate by using an existing thin film deposition method. The carbon source can be amorphous carbon with a relatively high melting point or a carbon hydride such as pentacene with a relatively low melting point, the range of the carbon source is larger, and the selection of the carbon source with a low melting point can greatly reduce the energy consumption of graphene preparation.

[0029] (3) The application selects a carbon hydride with a low melting point, such as pentacene with a melting point of only 300℃, and adopts the closed area solid phase method to invert the graphene preparation precursor or cover the inert cover on the surface of the carbon source layer and the catalytic metal layer of the graphene preparation precursor. Inverting or setting the inert cover enables the carbon source layer thin film and the catalytic metal thin film to fully react in a micro area close to the surface of the loading table of the annealing furnace to form a relatively closed area, which can avoid the rapid volatilization of carbon in the carbon source layer, enable the carbon in the carbon source layer to react with the metal in the catalytic metal layer, and generate high-quality graphene.

[0030] (4) In the graphene preparation of the application, the substrate can be a dielectric substrate on which an electronic circuit can be constructed, and a graphene transfer process is not needed to transfer graphene from an intermediate substrate to a final substrate.

[0031] (5) After the carbon source layer and the catalytic metal layer are deposited on the substrate, the catalytic metal layer can be subjected to a patterning treatment, and then annealing is performed to prepare patterned graphene, so as to meet the needs in the scenes of integrated circuits, field effect transistor arrays and printed electronic devices.

[0032] (6) In the process of preparing graphene by the solid phase method, single-layer or multi-layer graphene can be prepared by controlling the thickness ratio of the carbon source layer and the catalytic metal layer to meet different application requirements. The graphene product prepared in the preferred embodiment of the present application has a Raman spectrum indicating that the graphene has a sharp and strong G peak (1582 cm -1 ), a 2D peak (2700 cm -1 ), and a weak D band (1357 cm -1 ). The I 2D / I G ratio is 1.4, indicating that single-layer or double-layer graphene is formed.

[0033] (7) The graphene preparation method provided by the present application is a transfer-free large-area high-quality graphene preparation method based on the closed-area solid phase method. The method has few preparation steps, low cost, and can prepare large-area high-quality graphene. The graphene can be directly grown on a dielectric substrate without transfer, and can be used as a transparent conductor to manufacture electronic devices, or as a transparent electrode to manufacture displays and the like. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a flowchart of the closed-area solid phase method for preparing graphene according to the present application.

[0035] Figure 2 is a schematic diagram of a vacuum annealing device used in some embodiments of the present application.

[0036] Figure 3 is a flowchart of the open-area solid phase method for preparing graphene in a comparative experiment.

[0037] Figure 4 is a Raman spectrum of graphene prepared by the closed-area solid phase method according to Embodiment 1 of the present application.

[0038] Figure 5 is a comparison chart of Raman spectra of graphene prepared by the closed-area solid phase method according to Embodiment 1 of the present application with different precursor thicknesses.

[0039] Figure 6 is a transmittance test chart of graphene prepared by the closed-area solid phase method according to Embodiment 1 of the present application.

[0040] Figure 7 is an atomic force microscope test chart of graphene prepared by the closed-area solid phase method according to Embodiment 1 of the present application.

[0041] Figure 8 is an optical microscope test chart of graphene prepared by the closed-area solid phase method according to Embodiment 1 of the present application.

[0042] Figure 9Raman spectrum (a) and optical microscope image (b) of graphene prepared by the open area solid phase method of Comparative Example 1.

[0043] Figure 10 Schematic diagrams of three different methods of Example 2: (a) open area heat treatment method, (b) surface covering heat treatment method, and (c) closed area heat treatment method.

[0044] Figure 11 Raman characterization results of products of three different heat treatment methods of Example 2: (a) closed area heat treatment, (b) surface covering closed heat treatment, and (c) substrate inverted closed area heat treatment.

[0045] Figure 12 Raman spectrum characterization diagram of graphene prepared by different heat treatment temperatures of Example 3.

[0046] Figure 13 Raman spectrum characterization diagram of graphene prepared by different conditions of Example 4. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0048] The present application provides a method for making graphene thin film. First, a carbon source and a metal catalyst are deposited on a substrate, and the carbon source and the metal catalyst are heated to form graphene on the substrate. During the heating process, carbon in the carbon source and metal in the catalyst form a metastable metal carbide, and then the carbide decomposes so that the metal therein is removed by evaporation, thus leaving only graphene on the substrate. Using the method of the present application, there is no need to use flammable and explosive precursors such as hydrogen (H2) and methane (CH4), and the substrate can use a dielectric substrate, so there is no need for a transfer process to transfer graphene from an intermediate substrate to a final substrate.

[0049] Specifically, the present application provides a method for preparing graphene by a relatively closed area solid phase method, comprising the following steps:

[0050] (1) depositing a carbon source layer and a catalytic metal layer on the surface of a clean substrate surface in sequence or simultaneously to obtain a graphene preparation precursor;

[0051] (2) the graphene preparation precursor is inverted on a loading table in an annealing device, and heated and annealed in an oxygen-free or low-oxygen environment, the inversion being that the substrate is on top and the deposited carbon source layer and / or catalytic metal layer is on bottom, and placed on the loading table in the annealing device; or the surface of the carbon source layer and / or catalytic metal layer of the graphene preparation precursor is covered with an inert cover, and then placed on the loading table in the annealing device, and heated and annealed in an oxygen-free or low-oxygen environment; the substrate, the inert cover and the loading table do not react with or interact with the carbon source layer or the catalytic metal layer during the heating and annealing process; during the heating and annealing process, the carbon in the carbon source layer and the metal in the catalytic metal layer form a metastable metal carbide, and then the carbide decomposes so that the metal therein is removed by evaporation, to obtain single-layer or multi-layer graphene.

[0052] The "deposited carbon source layer and / or catalytic metal layer" and "the carbon source layer and / or catalytic metal layer of the graphene preparation precursor" in the present application, "or" herein means a carbon source layer or a catalytic metal layer alone, and "and" means a composite layer of a carbon source layer and a catalytic metal layer prepared simultaneously on a substrate.

[0053] The annealing device in the present application is an annealing furnace, and the surface material of the loading table in the annealing furnace is an inert material, i.e. a material that does not participate in a reaction or interaction, including but not limited to silicon, silicon dioxide, ceramic, aluminum nitride, etc. The "on top" and "on bottom" in the present application are with respect to the horizontal direction of the horizontal plane of the loading table of the annealing furnace, and when the graphene preparation precursor is inverted, in the vertical direction perpendicular to the horizontal direction, the substrate is above the carbon source layer and / or catalytic metal layer, i.e. "on top", and the carbon source layer and the catalytic metal layer are below the substrate, i.e. "on bottom".

[0054] In some embodiments of the present application, step (1) obtains the graphene preparation precursor in the following ways:

[0055] (i) sequentially depositing a carbon source layer and a catalytic metal layer on a clean surface of a substrate to obtain a graphene preparation precursor;

[0056] (ii) sequentially depositing a catalytic metal layer and a carbon source layer on a clean surface of a substrate to obtain a graphene preparation precursor;

[0057] (iii) simultaneously depositing a carbon source layer and a catalytic metal layer on a clean surface of a substrate to obtain a graphene preparation precursor containing a composite layer of a carbon source and a catalytic metal.

[0058] In some embodiments, the carbon source layer is elemental amorphous carbon, amorphous carbon or hydrocarbon, and the catalytic metal in the catalytic metal layer is at least one of nickel, copper or nickel-copper alloy. The carbon source layer and the catalytic metal layer are deposited by a thin film deposition process, which is a common thin film deposition process including but not limited to magnetron sputtering, electron beam evaporation or thermal evaporation. The hydrocarbon is preferably a condensed ring aromatic hydrocarbon with a carbon number of 10 to 30, and further preferably a condensed ring aromatic hydrocarbon with a melting point of 200-500°C and capable of being prepared by a thin film deposition process, including but not limited to anthracene (chemical formula C 14 H 10 ), biphenyl (chemical formula C 12 H 10 ), tetracene (chemical formula C 18 H 12 ) or pentacene (chemical formula C 22 H 14 ).

[0059] In some embodiments, the thickness of the carbon source layer is in the range of 1 nm to 100 nm, preferably 1-15 nm, and more preferably 2-10 nm; and the thickness of the catalytic metal layer is 1 nm to 1000 nm, preferably 50-200 nm, and more preferably 40-100 nm.

[0060] In some embodiments, step (1) is performed by sequentially depositing the carbon source layer and the catalytic metal layer on a clean substrate surface to obtain a graphene preparation precursor; and then step (2) is performed by performing a heating annealing process on the catalytic metal layer after being patterned. In this way, graphene with the same pattern as the catalytic metal can be finally formed on the substrate.

[0061] In the heating annealing process, the substrate does not react or interact with the catalytic metal layer or the carbon source layer; the substrate includes but is not limited to at least one of a silicon / silicon oxide composite layer, sapphire, quartz or glass; and the inert cover material includes but is not limited to a flat and high-temperature-resistant material such as a silicon wafer, a quartz wafer, a sapphire wafer or a mica wafer.

[0062] In some embodiments, the heating starts at a vacuum degree of less than or equal to 3x10 -3 torr, and the heating annealing is performed at 900-1200°C, preferably by applying a light beam to rapidly heat the carbon source layer and the catalytic metal layer, and the light source of the light beam includes but is not limited to an infrared lamp, a laser beam or a xenon lamp; and the heating annealing time is 2-10 minutes. The heating annealing process is preferably performed by increasing the temperature to 500-700°C at a rate of 3-6°C / s, then increasing the temperature to 900-1200°C at a rate of 8-12°C / s, and maintaining the temperature at 900-1200°C for 2-10 minutes to obtain the finished product.

[0063] In some embodiments of the present application, inert gas is introduced into the annealing device to clean the device before annealing the graphene precursor. The inert gas can include, but is not limited to, helium, argon, and the like.

[0064] In the present application, the graphene precursor prepared in step (1) is inverted on a loading table in the annealing device, so that the carbon source layer or the catalytic metal layer is in direct contact with the surface of the loading table of the annealing device, or an inert cover is placed on the surface of the carbon source layer and the catalytic metal layer of the graphene precursor, and then the graphene precursor is placed on the loading table in the annealing device, thereby forming a closed area to a certain extent, and the heating and annealing process is performed in the closed area. The surface of the loading table of the annealing device is an inert material that does not react with or interact with the carbon source layer or the catalytic metal layer, including but not limited to ceramic, silicon, aluminum nitride, quartz, sapphire, mica, and the like.

[0065] The graphene prepared by the method of the present application can be used as a transparent conductor to manufacture electronic devices. The graphene can be used as a transparent conductor to manufacture displays, OLEDs, electrodes of field effect tubes, and the like.

[0066] In some embodiments, a thin film deposition technique is used to deposit a carbon source layer on a substrate, for example, an evaporation plating technique. Similarly, an evaporation plating technique is used to deposit a catalytic metal layer on the carbon source layer, for example, nickel, as shown in the flowchart Figure 1 .

[0067] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. Figure 1 is a structural diagram of depositing a thin film on a substrate. First, a clean substrate is prepared, which can be a SiO2 / Si, quartz, sapphire, and quartz glass substrate, or a substrate made of other materials (dielectric material). Then, a carbon source film is deposited on the substrate, for example, the carbon source film can be amorphous carbon with a thickness of 1 nm to 100 nm (in some specific cases, the thickness is between 2 nm and 8 nm), which is deposited on the substrate using a magnetron sputtering plating technique. Then, a catalytic metal film is deposited on the carbon source film, for example, using an evaporation plating technique, with a thickness of 1 nm to 1000 nm (in some cases, the thickness is between 50 nm and 120 nm, or between 50 nm and 95 nm).

[0068] The plated carbon source film and catalytic metal film are heated, for example, as shown in the device diagram Figure 2 In some embodiments, a vacuum rapid annealing device is used. The substrate with the carbon source film and the nickel film is placed in a small annealing furnace, the air pressure in the furnace is reduced to about 20 mTorr using a vacuum pump, and then the temperature in the furnace is rapidly increased to between 900°C and 1000°C, which lasts for about 5-10 min, and then rapidly cooled to room temperature.

[0069] In the rapid thermal process, the sample is inverted in a heating furnace to form a closed area, and the catalytic metal layer film on the upper layer is automatically evaporated, leaving the deposited graphene on the substrate. In the rapid thermal process, the catalytic metal layer film is thermally evaporated, and after the rapid thermal process, the graphene is formed on the substrate.

[0070] The entire rapid thermal process is carried out under low pressure to reduce the influence of oxidation on the catalytic metal film and graphene, and protective gas argon can be introduced to further clean the furnace chamber to exhaust the internal air and reduce oxidation.

[0071] For example, when the carbon source film thickness is 2-10 nm and the catalytic metal film thickness is between 40 nm and 65 nm, uniform high-quality graphene will be formed on the entire substrate after rapid thermal processing, and these graphene includes single-layer, double-layer and multi-layer (three or more layers).

[0072] It is found in experiments that the number of layers of graphene growth is determined by the thickness ratio of the carbon film and the nickel film. In some embodiments, when the thickness of the nickel film is 65 nm and the thickness of the carbon source film is between 2-5 nm, single-layer graphene will be formed. When the thickness of the nickel film is 65 nm and the thickness of the carbon source film is between 5-7 nm, double-layer graphene will be formed. When the thickness of the nickel film is 65 nm and the thickness of the carbon source film is between 7-8 nm, multi-layer graphene will be formed.

[0073] In specific implementations, a catalytic metal layer film can also be deposited on the substrate first, and then a carbon source layer film is deposited on the catalytic metal layer film. Or a carbon source layer film and a nickel film are co-deposited on the substrate. For example, using evaporation plating film technology, carbon source and catalyst metal are co-deposited on the substrate using co-evaporation technology. The catalyst metal nickel can also be replaced by other catalyst metals, such as copper or nickel-copper alloy.

[0074] In other embodiments, the preparation of the carbon source and the metal catalytic layer is the same as described above. The plated carbon source layer film and the catalytic metal layer film are heated, for example, as Figure 2The apparatus diagram shows that a rapid annealing apparatus is used. The substrate with carbon source layer film and catalytic metal layer film is placed in a small annealing furnace, and the sample is placed upside down in the annealing furnace, and the surface of the loading table of the annealing furnace is made of aluminum nitride. The carbon source layer film and the nickel film are fully reacted in the micro area close to the surface of the loading table of the annealing furnace. The air pressure in the furnace is reduced to about 20 mTorr by using a vacuum pump, and then the temperature in the furnace is rapidly increased to between 900 DEG C and 1200 DEG C, and the temperature is maintained for about 2-10 min, and then the temperature is rapidly cooled to room temperature. During the rapid heat treatment process, the upper metal film is automatically evaporated, and the graphene is deposited on the substrate. During the rapid heat treatment process, the metal film is evaporated by heat, and after the rapid heat treatment, the graphene is formed on the substrate. The whole rapid heat treatment process is carried out under low pressure to reduce the influence of oxidation on the metal film and the graphene, and the protective gas argon can be introduced to further clean the furnace cavity to exhaust the internal air and reduce the oxidation.

[0075] In some embodiments, using a photolithography process, large-scale graphene patterns can be directly fabricated on various dielectric substrates such as SiO2 / Si wafers without the need for a graphene transfer process. This can enable the fabrication of graphene-based nanodevices. For example, a comb-shaped graphene pattern can be fabricated by patterning a nickel / carbon source film through a photolithography process followed by rapid thermal treatment. Since standard semiconductor photolithography processes can be used to pattern the graphene film, the above-described techniques for graphene growth can be adapted for graphene. This will enable a wide range of graphene industrial applications, such as the fabrication of transparent electrodes, flat panel displays, solar cells, and other electronic devices.

[0076] The graphene can have high quality and uniformity. For example, single-layer and double-layer graphene can be stably produced on large dielectric wafers. The graphene can have high electrical conductivity. For example, the graphene can have a sheet resistance of less than 100 ohms / square, which is less than graphene produced by some other methods. The graphene can have a low sheet resistance because the graphene has few wrinkles.

[0077] In the closed area solid phase method for preparing graphene according to the present application, different solid carbon sources can be used to grow high-quality graphene with controllable thickness at 900 DEG C-1200 DEG C. In the experiment, a metastable nickel carbide (Ni3C) is formed at the interface of Ni and C. The Ni3C phase starts to decompose at more than 400 DEG C, thereby avoiding residual metal in the product. Using the same experimental apparatus, pristine graphene and doped graphene are grown by the one-step method. Compared with the CVD method, the graphene prepared by this method has the advantages of flexible selection of carbon source, lower required growth temperature, one-step completion, and no need for transfer.

[0078] The document Adv. Mater. 2013, 25, 630-634 proposes a graphene preparation method of open area solid phase method, using amorphous carbon as carbon source, depositing amorphous carbon and nickel metal film on the substrate in turn, directly placing the sample on the loading table of the annealing furnace to anneal at 1100℃, and obtaining single-layer or double-layer graphene. However, when trying to replace the carbon source with a low-melting-point carbon source such as pentacene by using the device, it is found that a large amount of metal remains in the prepared graphene, and single-layer graphene cannot be prepared. This method limits the selection range of the carbon source, and the melting point of amorphous carbon is too high, which requires a very high temperature for the preparation of the carbon source film, resulting in large energy consumption. How to use a low-melting-point carbon source material to prepare high-quality single-layer or multi-layer graphene without metal residues and defects on the basis of reducing the energy consumption of heat treatment is the key technical problem to be solved by the present application.

[0079] In some comparative experiments, the preparation of the carbon source and the catalytic metal layer is the same as described above. The only difference is that the resulting graphene preparation precursor is replaced with a positive, as shown in Figure 3 The flowchart for preparing graphene by open area solid phase method is shown in the figure, that is, the substrate is in contact with the ceramic sheet on the surface of the loading table of the annealing furnace, the carbon source film and the metal catalytic layer film are upward (on the top), and heating and annealing treatment is carried out under the same annealing conditions, which is called open area heat treatment process for preparing graphene. For example, in some comparative examples, 3-5nm thick pentacene and 40-60nm thick nickel are heated at a temperature of 1000℃. The experimental results are characterized by optical microscope and Raman spectrometer. This method can stably obtain 3-5 layers of graphene, but cannot obtain single-layer graphene, and a large amount of catalytic metal remains in the prepared multi-layer graphene. The optical photograph and Raman spectrum results show that the graphene surface has obvious physical defects. The graphene prepared by this method has poor conductivity, low light transmittance and small application potential. It is shown that the graphene prepared by the open area graphene preparation method has low quality.

[0080] The following is an example:

[0081] Example 1

[0082] A relatively closed area solid phase method for preparing graphene, comprising the following steps:

[0083] (1) Selecting an N-type doped silicon wafer as a substrate. The silicon wafer is cleaned using a standard silicon wafer cleaning process (RCA). After drying, the silicon wafer is subjected to secondary cleaning on the surface using a plasma cleaning machine with oxygen as the treatment gas.

[0084] (2) Then, the cleaned silicon wafer is placed in a vacuum evaporation film plating device, and the cabin pressure in the film plating device is reduced to 4×10 -4Next, a 5nm pentacene layer and a 40nm nickel layer are grown sequentially on the silicon wafer.

[0085] (3) Place the silicon wafer on the loading platform in the small annealing furnace, heat it with a 10KW infrared lamp, set the temperature to rise to 600℃ at a rate of 5℃ / second, and then raise the temperature to 1000℃ at a rate of 10℃ / second. Hold the temperature at 1000℃ for two minutes to obtain a graphene sample.

[0086] Raman spectroscopy is the most important way to characterize the quality and number of layers of graphene. The G peak represents the tangential stretching (E) of highly oriented pyrolytic graphite (HOPG). 2g The D-peak can reflect the number of layers, while the D-peak originates from the disordered sp-layers in graphene. 2 Hybridized carbon atoms, exhibiting lattice distortion characteristics, characterize graphene defects. The 2D peak originates from a second-order Raman scattering process. Generally, I0 is used. 2D / I G The ratio represents the number of graphene layers.

[0087] Reference Figure 4 . Figure 4 The Raman spectrum of graphene on a SiO2 / Si substrate (SiO2 at 300 nm) is shown. The Raman spectroscopy reveals a sharp and strong G peak (1582 cm⁻¹). -1 ) and 2D peak (2700cm) -1 ), and accompanied by a weak D band (1357cm) -1 ). I 2D / I G A ratio of 1.4 indicates the formation of single-layer or double-layer graphene.

[0088] Figure 5 The Raman spectra of graphene prepared under the same conditions as in Example 1, using carbon sources or metal catalysts of different thicknesses, on a SiO2 / Si substrate (SiO2 thickness of 300 nm) are shown. First, a series of experiments were conducted at a pentacene thickness of 5 nm–20 nm, a nickel thickness of 40 nm, and a heating temperature of 1000 °C. The results are as follows. Figure 5 As shown in content (a), it can be seen that as the thickness of the pentacene used increases, the graphene thickness at 1340 cm⁻¹ increases. -1 The defect peak (D peak) at the graphene layer is significantly increased, indicating that there are more defects on the graphene layer surface. However, as the thickness of the pentacene layer increases, the 2D peak gradually decreases until it disappears, indicating that the number of graphene layers decreases with decreasing pentacene thickness. When using pentacene of 5 nm or less, the product is monolayer to bilayer graphene; when the pentacene thickness exceeds 10 nm, five-layer or thicker graphene is produced. Then, a series of experiments were conducted with varying nickel layer thickness at a pentacene thickness of 5 nm, and the results are as follows... Figure 5As shown in content (b), it can be seen that the height of the three Raman characteristic peaks D, G, 2D of graphene appears significant difference with the thickness of nickel used. With the increase of the thickness of nickel layer, the D peak at 1357 cm -1 significantly decreases, while the 2D peak at 2700 cm -1 significantly enhances and becomes sharp. In addition, the intensity ratio of G band to D band also represents the sp 2 / sp 3 carbon atom ratio, which further indicates that the graphene prepared using 40 nm nickel has higher sp 2 hybrid carbon layer plane length. With the change of the thickness of nickel from 5 nm to 40 nm, the I 2D / I D of Raman peak changes from 0.28 to 1.53, which indicates that the average thickness of the grown graphene changes from multi-layer (more than 10 layers) to single-layer or double-layer, that is, the graphene with less defects and low layer number can be obtained using 40 nm nickel. In general, using 5 nm and below pentacene and 40 nm and above nickel as precursors can stably obtain single-layer to double-layer graphene, and changing the thickness ratio of pentacene and nickel can adjust the layer number of the obtained graphene.

[0089] Referring to Figure 6 . Figure 6 , a visible light transmittance test diagram of graphene grown on a fused quartz substrate in this embodiment is shown. In the visible light range (380 nm-780 nm wavelength), the transmittance of graphene is between 92% and 95%, which has high transmittance.

[0090] Referring to Figure 7 . Figure 7 , an atomic force microscope characterization diagram of graphene prepared in this embodiment on a SiO2 / Si substrate (SiO2 is 300 nm) is shown. The graphene surface Ra=0.895 nm, Rz=12.164 nm, which has low graphene surface roughness. No obvious wrinkles and boundaries are observed in the rapid thermal treatment graphene. In this method, since the nickel top layer evaporates during the rapid thermal treatment process, there is no stress on the residual graphene during the cooling process, so the formation of wrinkles can be effectively avoided. As a result, the rapid thermal treatment graphene has high conductivity.

[0091] Referring to Figure 8 . Figure 8 , in which the optical micrograph shows the graphene formed on the SiO2 / Si substrate (SiO2 is 300 nm) (the scale in the figure is 50 μm). The low contrast in the optical micrograph provides evidence for the uniformity of the rapid thermal treatment graphene.

[0092] The nickel film automatically evaporates during rapid thermal annealing, which has two advantages: (1) it eliminates the process of catalyst etching and graphene transfer after growth; (2) it limits the formation of wrinkles in graphene caused by different coefficients of thermal expansion. The evaporation temperature of nickel is 2913℃, which is much higher than the rapid thermal annealing temperature of 1000℃. Metastable nickel carbide (Ni3C) will form at the Ni-C interface. Simple evaporation of nickel requires 2913℃, while the Ni3C phase will begin to decompose above 400℃, which greatly reduces the temperature required for nickel volatilization and avoids the presence of residual catalytic metal in the product.

[0093] Comparative Example 1

[0094] Other conditions are the same as in Example 1, except that the following is used: Figure 3 The diagram shows a process for preparing graphene using the open-region solid-state method. The prepared graphene precursor is placed directly on the loading platform of the annealing furnace, with the catalytic metal layer on top and the substrate on the bottom. The substrate is in contact with the surface of the aluminum nitride substrate on the loading platform.

[0095] In the Raman spectrum image of the prepared graphene (content 9a), the three characteristic peaks of graphene, D peak (1350 cm⁻¹), can be clearly seen. -1 ), G peak (1580cm) -1 ) and 2D peak (2680cm) -1 ), and also the G* peak (2450 cm⁻¹), a defect peak of graphene. -1 Therefore, the experiment successfully grew graphene. As is well known, I... 2D / I G The ratio decreases with increasing graphene layer number, as shown in Figure I. 2D / I G The value is less than 0.8, therefore the product can be identified as multilayer graphene with more than three layers. Because I 2D / I G The ratio is less than 1, and graphene has a very high G*. Therefore, it can be determined that graphene has a large number of surface defects, such as dislocations, breaks, and surface inhomogeneities. (Optical microscope image) Figure 9 As shown in content (b), a large number of metal particles uniformly attached to the substrate surface remain on the substrate surface. The diameter of the metal particles is between 1 and 3 μm. It is preliminarily judged that the unremoved metal particles have a negative impact on the formation of graphene.

[0096] Adopting such Figure 3 When preparing graphene using the open-region solid-state method, the carbon source pentanebenzene, with a melting point of around 300°C, evaporates too quickly and cannot react with the catalytic metal in time to form carbides, resulting in a large amount of metal residue and poor quality graphene.

[0097] Example 2

[0098] A method for preparing graphene by a closed area solid phase method, comprising the following steps:

[0099] (1) Selecting an N-type doped silicon wafer as a substrate. The silicon wafer is cleaned by using a standard silicon wafer cleaning process (RCA). After drying, the silicon wafer is subjected to secondary cleaning on the surface by using a plasma cleaning machine with oxygen as the processing gas.

[0100] (2) Then, the cleaned silicon wafer is placed in a vacuum evaporation film coating device, and the cabin pressure is reduced to 4x10 -4 Then, 5 nm pentacene and 40 nm metal nickel layers are sequentially grown on the silicon wafer.

[0101] (3) When the graphene preparation precursor is placed in an annealing furnace, there are three ways of placement, as shown in the following: Figure 10 (a) open area heat treatment by placing the precursor right side up, (b) surface covering heat treatment by placing the precursor right side up while covering the surface with a silicon wafer, and (c) closed area heat treatment by placing the precursor upside down. The three groups of samples all use 5 nm pentacene / 40 nm nickel as the precursor, use a 10 KW infrared lamp tube for heating, set the temperature to rise at a speed of 5 ℃ / second to 600 ℃, then rise at a speed of 10 ℃ / second to 1000 ℃, and perform 1000 ℃ heat treatment for 10 minutes. Then, the product quality is characterized by using a Raman spectrum.

[0102] The experimental results are shown in the following: Figure 11 From the Raman spectrum characterization of the products of the three methods, it can be seen that the graphene 2D peak obtained by the open area heat treatment in content (a) is weak and has a wide half-width, and also has a very high D peak. This indicates that in the open heat treatment, the carbon-carbon double bond in the graphite layer is destroyed, and part of the sp 2 hybrid carbon atoms are converted into sp 3 hybrid, resulting in a large number of defects. The higher I D / I G and lower I 2D / I G values indicate that the generated graphene has obvious defects and has a higher number of layers. The Raman results of the products obtained by the two closed area heating methods show higher I 2D / I G values and lower I D / I G values, which indicates that the product is few-layer or single-layer graphene, and the lattice is relatively complete. Generally, there are three stacking modes between the layers of multi-layer graphene, and the 2D peaks of AA-stacked and Berner AB-stacked multi-layer graphene are uniformly symmetrical without shoulder peaks. From the Raman spectrum of the product obtained by the closed area heat treatment in content (c), it can be seen that the 2D peak is uniform and symmetrical without shoulder peaks, which indicates that the product is few-layer or single-layer graphene. Figure 11 content (b) and Figure 11Content (c) can be seen that the growth of graphene 2D peak is a single uniform symmetric Raman peak, so it can be judged that the stacking way is AA stacking or AB stacking. Among them, as Figure 11 Content (c), the graphene I obtained by the method of substrate inversion heating 2D / I G > = 1, that is, the graphene formed is double-layer or single-layer, and the quality is higher than Figure 11 Content (b) shows the graphene obtained by the method of surface coverage heating.

[0103] Example 3

[0104] A method for preparing graphene by a relatively closed area solid phase method, comprising the following steps:

[0105] (1) Selecting an N-type doped silicon wafer as a substrate. The silicon wafer is cleaned using a standard silicon wafer process (RCA). After drying the cleaned silicon wafer, the surface of the silicon wafer is secondarily cleaned using a plasma cleaning machine with oxygen as the treatment gas.

[0106] (2) Then, the cleaned silicon wafer is placed in a vacuum evaporation film plating device, and the cabin pressure in the film plating device is reduced to 4×10 -4 Next, 5nm pentacene and 40nm metal nickel layer are grown on the silicon wafer.

[0107] (3) The silicon wafer is placed on a loading table in a small annealing furnace, and heated using a 10KW infrared lamp tube with a heating rate of 5℃ / s, and heated to 400℃, 600℃, 800℃, and 1000℃, respectively. The heat treatment time is 10 minutes, and the graphene sample is obtained.

[0108] Figure 12 The Raman spectrum of graphene grown at different temperatures is given. In the figure, it can be easily distinguished that only in the case of heating at 1000℃, the D, G, and 2D three Raman peaks of graphene can be found, and in the case of heating below 1000℃, there is no obvious Raman peak. This shows that the reaction of pentacene and nickel in the closed area heating is also carried out at 1000℃ and above. Too high temperature will cause the evaporation loss of the catalytic metal, and the appropriate temperature range is 900-1200℃.

[0109] Example 4

[0110] A method for preparing graphene by a relatively closed area solid phase method, comprising the following steps:

[0111] (1) Selecting an N-type doped silicon wafer as a substrate. The silicon wafer is cleaned using a standard silicon wafer process (RCA). After drying the cleaned silicon wafer, the surface of the silicon wafer is secondarily cleaned using a plasma cleaning machine with oxygen as the treatment gas.

[0112] (2) Using a magnetron sputtering device to grow amorphous carbon and metal nickel layers of different thicknesses on a cleaned silicon wafer to obtain a graphene preparation precursor, a total of 6 groups of experiments, the first group: the thickness of the first group of carbon is 5 nm, and the thickness of nickel is 60 nm; groups 2-3: the thickness of the carbon is fixed at 8 nm, and the thickness of nickel is 60 nm and 80 nm, respectively; groups 4-6: the thickness of the carbon is fixed at 12 nm, and the thickness of nickel is 60 nm, 80 nm, and 100 nm, respectively.

[0113] (3) The graphene preparation precursor is placed upside down on the loading table in a small annealing furnace, a 10KW infrared lamp tube is used for heating, the temperature is set to rise to 600°C at a rate of 5°C / s, then the temperature is set to rise to 1000°C at a rate of 10°C / s, and a 1000°C heat treatment is performed for 5 minutes, then the product quality is characterized using a Raman spectrum.

[0114] Figure 13 The Raman spectra of graphene prepared using amorphous carbon and metal nickel of different thicknesses are given. As can be seen from the figure, the thickness of the first group of carbon is 5 nm, and the thickness of nickel is 60 nm, according to the ratio of I 2D / I G =1.46, it can be seen that single-layer graphene is generated; groups 2-3: the thickness of the carbon is fixed at 8 nm, and the thickness of nickel is 60 nm and 80 nm, respectively, according to the ratio of I 2D / I G , it can be seen that double-layer and few-layer graphene is generated; groups 4-6: the thickness of the carbon is fixed at 12 nm, and the thickness of nickel is 60 nm, 80 nm, and 100 nm, respectively, it can be seen that as the thickness of nickel increases, I 2D / I G remains basically unchanged, and double-layer graphene is generated.

[0115] Those skilled in the art will readily understand that the above description is only of the preferred embodiments of the present application and is not intended to limit the present application, and any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method of producing graphene by a relative closed area solid phase method, characterized in that, The method comprises the following steps: (1) depositing a carbon source layer and a catalytic metal layer on a surface-cleaned substrate surface in sequence or simultaneously to obtain a graphene preparation precursor; the carbon source layer is elemental amorphous carbon, amorphous carbon or a hydrocarbon compound, and the catalytic metal in the catalytic metal layer is at least one of nickel, copper or nickel-copper alloy; wherein the hydrocarbon compound is a condensed ring aromatic hydrocarbon with a carbon number of 10-30; (2) inverting the graphene preparation precursor on a loading table in an annealing device and performing heating annealing treatment in an oxygen-free or low-oxygen environment; or covering the surface of the carbon source layer and / or the catalytic metal layer of the graphene preparation precursor with an inert cover, and then placing it on a loading table in an annealing device and performing heating annealing treatment in an oxygen-free or low-oxygen environment; the inversion means that when the graphene preparation precursor is placed on the loading table of the annealing device, the substrate is on top and the deposited carbon source layer and / or catalytic metal layer is on the bottom; the substrate, the inert cover and the loading table do not react with the carbon source layer or the catalytic metal layer during the heating annealing process; wherein during the heating annealing process, the carbon in the carbon source layer and the metal in the catalytic metal layer form a metastable metal carbide, and then the carbide decomposes to remove the metal therein by evaporation to obtain single-layer or multi-layer graphene; the inversion or the inert cover allows the carbon source layer and the catalytic metal layer to fully react in the micro area close to the surface of the loading table of the annealing furnace to form a relatively closed area, which can prevent the carbon in the carbon source layer from rapidly evaporating, so that the carbon in the carbon source layer reacts with the metal in the catalytic metal layer to generate high-quality graphene and avoid metal residues.

2. The method of claim 1, wherein, Step (1) obtains the graphene preparation precursor in the following ways: (i) sequentially depositing a carbon source layer and a catalytic metal layer on a surface-cleaned substrate surface to obtain a graphene preparation precursor; (ii) sequentially depositing a catalytic metal layer and a carbon source layer on a surface-cleaned substrate surface to obtain a graphene preparation precursor; (iii) simultaneously depositing a carbon source layer and a catalytic metal layer on a surface-cleaned substrate surface to obtain a graphene preparation precursor containing a composite layer of carbon source and catalytic metal.

3. The method of claim 1, wherein, The thickness of the carbon source layer is in the range of 1 nm to 100 nm; the thickness of the catalytic metal layer is 1 nm to 1000 nm.

4. The method of claim 3, wherein, The thickness ratio of the catalytic metal layer to the carbon source layer is 65:1~15.

5. The method of claim 1, wherein, Step (1) sequentially deposits a carbon source layer and a catalytic metal layer on a surface-cleaned substrate surface to obtain a graphene preparation precursor; then performs a patterning treatment on the catalytic metal layer before performing the heating annealing treatment of step (2).

6. The method of claim 1, wherein, Step (1) deposits the carbon source layer and the catalytic metal layer by a thin film deposition process, and the thin film deposition process is magnetron sputtering, electron beam evaporation or thermal evaporation plating.

7. The method of claim 1, wherein, The heating annealing is performed at 900 to 1200 °C, starting from a vacuum of less than or equal to 3 x 10 -3 tort, for a time of 2 to 10 minutes.

8. The method of claim 1, wherein, The heating annealing process is: heating to 500-700 ℃ at a rate of 3-6 ℃ / s, then heating to 900-1200 ℃ at a rate of 8-12 ℃ / s, and maintaining at 900-1200 ℃ for 2-10 minutes.

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