JP2011178644A - Epitaxial growing method of graphene film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a large-scale, uniform and high-quality graphene film and a method for producing the same. <P>SOLUTION: The graphene film 102 is formed on a catalytic thin film by depositing the catalytic thin film 101 on a crystalline substrate 100, heat-treating the catalytic thin film to form a highly-ordered and selectively-oriented crystalline catalytic thin film, heating a gaseous carbon source, and cooling the crystalline catalytic thin film. A catalytic material of the catalytic thin film includes one element or a plurality of elements selected from a group comprising Ni, Pt, Co, Fe, Al, Cr, Cu, Mg, Mn, Rh, Ti, Pd, Ru, Ir and Re, and the thickness of the catalytic thin film lies within a range of about 1 nm to about 2 mm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a graphene film, and more specifically, a large size, uniform, high quality, which is expected to have a wide range of applications from electronics after Moore's Law to ultra-sensitive sensors, actuators, and even transparent electrodes. The present invention relates to a method used for synthesis of a graphene film.

  Graphene is the name given to a single layer of flat carbon atoms packed closely in a two-dimensional (2D) honeycomb lattice, and is the basic building block of all other dimensional graphite materials. Graphene can be rolled into 0D fullerenes and rolled to form 1D nanotubes or stacked to 3D graphite.

Graphene, a sp ² bonded 2D honeycomb lattice, showed abundant unusual properties such as quantum Hall effect and anomalous behavior in quasiparticle bonding. Extremely high carrier mobility and long-range ballistic conduction at room temperature, quantum confinement in nanoribbons, possibility of chemical doping, and high sensitivity to detect single molecule gas. From optoelectronics to sensors and electrodes. The possibility of application over a wide range is expected (see Non-Patent Document 1).

  Several methods for creating graphene films have been proposed. According to the mechanical exfoliation method (see Non-Patent Document 2), only individual, high-quality crystals of the order of micrometers can be produced. This raises questions about the practicality of the method. Epitaxial growth methods on 6H- and 4H-SiC are being actively pursued (see Non-Patent Document 3), but obtaining a large graphene region with a uniform thickness remains a problem ( Non-patent document 3), and SiC single crystal materials used as starting materials in SiC pyrolysis are very expensive. The graphite liquid phase exfoliation method (see Non-Patent Document 4) and the graphene oxide reduction method (see Non-Patent Document 5) can produce a high-yield graphene plate. However, with these two solutions, it is not possible to produce graphene sheets with high quality and controlled layer structure and size.

Graphene film synthesis on transition metal foils or films has been reported. Chemical vapor deposition (CVD) processes require temperatures as high as about 1000 ° C. and a gaseous carbon source (see Non-Patent Document 6). The CVD method generally involves the formation of a Ni or Cu film catalyst layer on a SiO ₂ substrate, or a thick Ni or Cu disk or foil is used as the catalyst layer. The Ni or Cu film formed here is polycrystalline, and thus the synthesized graphene film has structural defects and a mixture of various numbers of graphene layers (see Non-Patent Document 7). See This is the main reason why the graphene film manufactured by the CDV method in this way exhibits lower charge carrier mobility than the graphene film by the mechanical peeling method. Using conventional CVD methods to create graphene with a uniform thickness, macroscopic size and high structural quality is a challenge.

  Therefore, in order to realize the potential application of graphene, there is a need for a new method for producing graphene that is large, uniform and has high structural quality.

  The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention and it is not intended to represent key or essential elements of the invention or to delineate the scope of the invention. Rather, its primary purpose is merely to present one or more concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

  According to at least one aspect of the present invention, a single crystal substrate is prepared, a crystalline catalyst layer is provided on the single crystal substrate, the single crystal substrate provided with the crystalline catalyst layer is processed, and the crystalline material is provided. A method of producing a graphene film is provided that includes forming a graphene film by heating and cooling a gaseous carbon source in the presence of a catalyst layer.

  The treatment may be a treatment selected from the group consisting of heat treatment, polishing treatment and etching treatment.

  Variation in crystal orientation of crystal grains of the crystalline catalyst thin film after the heating step for a predetermined time may be within a range of ± 5 degrees, and the size of the crystal grains may be larger than 1 μm.

The substrate is _{mica, BN, Si, Ge, GeS} , BaF 2, MgF 2, LaF 3, GaF 2, LiF, GaAs, GaP, GaN, InAs, InP, InSb, BaTiO 3, LiNbO 3, LaAlO 3, NdGaO 3 , SrTiO ₃ , SrTiO ₃ , LaAlO ₃ , LiGaO ₂ , LiTaO ₃ , YAlO ₃ , YVO ₄ , ZnO, ZnS, ZnSe, ZnTe, NiO, MgO, TeO ₂ , SiC, and sapphire. It may be a single crystal substrate including a crystal or a combination of a plurality of single crystals.

  The catalyst material of the catalyst layer includes one or more elements selected from the group consisting of Ni, Pt, Co, Fe, Al, Cr, Cu, Mg, Mn, Rh, Ti, Pd, Ru, Ir, and Re. May include.

  The thickness of the catalyst layer may range from about 1 nm to about 2 mm.

  The step of providing the catalyst layer may be performed by deposition, and the single crystal substrate may be maintained in a range of 0 ° C. to 600 ° C. during the deposition.

  The treatment may be a heat treatment that lasts for 1 second to 200 hours at a temperature of 300 ° C. to 1600 ° C.

  The treatment may be a heat treatment performed in a vacuum or an inert atmosphere.

  The gaseous carbon source may be a compound containing 1 to 6 carbon atoms.

  The gaseous carbon source may be one or more compounds selected from the group consisting of ethane, ethylene, ethanol, methanol, acetone, acetylene, propane, propylene, butane, butadiene, pentane and hexane.

  To the accomplishment of the foregoing and related ends, the following description and the annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are just a few of the embodiments in which one or more aspects of the present invention may be used. Other aspects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

  According to the present invention, a large-scale, uniform, and high-quality graphene film can be formed without using expensive materials and complicated processes.

The figure which shows notionally the method of producing the graphene film by the Example of this invention, and transferring it. (A) is a secondary electron image of a graphene film synthesized according to Experimental Example 1, (b) is a C KLL Auger electron map corresponding to (a), (c) is a white sample region and a black sample in (a) Two Auger electron spectra obtained in the region. (A) is a scanning electron microscope image of the graphene film synthesized according to Experimental Example 2, and (b) is two Auger electron spectra obtained in the white sample region and the black sample region in (a). (A) is a scanning electron microscope image of the graphene film synthesized according to Experimental Example 3, and (b) is two Auger electron spectra obtained in the white sample region and the black sample region in (a). The optical microscope image of the graphene film transferred on the SiO ₂ / Si substrate according to Experimental Example 4. Raman spectrum obtained from the sample regions of three of the SiO 2 / _Si graphene film transferred onto the substrate in accordance with Example 4.

  Various embodiments are now more fully described by the drawings and detailed description of the illustrative embodiments. Nevertheless, the invention may be implemented in a variety of forms and is not limited to the specific embodiments described in the drawings and detailed description of these illustrative embodiments.

  Disclosed here is a method for producing a large-scale, uniform and high-quality graphene film. The graphene film produced using this method can be applied to various fields for various applications without any limitation on the shape, size, and thickness of the substrate. Such a substrate is a single crystal. The single crystal is important for forming a highly ordered crystalline catalyst thin film, and hence for producing a graphene film having high structural quality and high performance. In the present application, the crystalline catalyst thin film has a crystal orientation variation within a range of ± 5 degrees (more preferably, the crystal orientation variations of all crystal grains are within a range of ± 5 degrees, and the 99 % Is within the range of ± 2 degrees), and if the size of the crystal grains is larger than 1 μm, it is considered that the order is highly ordered. The use of a single crystal substrate is one of the most important aspects of the present invention. The crystal lattice constant of the catalyst is preferably matched to the lattice constant of the selected substrate. It is also preferred that the crystal lattice constant of the selected catalyst is consistent with the crystal lattice constant of graphene. Preferably, epitaxial growth of the catalyst thin film occurs on the single crystal substrate, and epitaxial formation of the graphene film occurs on the catalyst layer.

As used herein, the term "graphene film" refers to a graphene or graphene-like substance in the form of a film composed of a carbon skeleton of polycyclic aromatic molecules in which a plurality of carbon atoms are covalently bonded to each other The film is shown. Without wishing to be bound by theory, the covalently bonded carbon atoms form a 6-membered ring as a repeating unit, but can also form 4-membered, 7-membered and / or 8-membered rings. Therefore, in the graphene film, the covalently bonded carbon atoms (usually sp ² bonded carbon) are considered to form a single layer. The graphene film can have various structures, and the structure varies depending on the amount of four-membered ring, five-membered ring, six-membered ring, seven-membered ring and / or eight-membered ring. The graphene film may be composed of a single layer of graphene, may be a bilayer graphene, a few layers (3 to 10 layers), or a multilayer graphene of up to 200 layers.

  The graphene film may be formed according to the method described in FIG. In the method disclosed here, the graphene film 102 is formed by forming the catalyst layer 101 on the single crystal substrate 100 at room temperature or by raising the substrate temperature, and processing the catalyst layer to form highly ordered crystals. The graphene film is formed by heating and cooling the crystalline catalyst layer on the crystalline substrate in the presence of a gaseous carbon source. These processes are performed in a chamber, and are executed while controlling temperature, time, atmosphere and pressure.

Single crystal substrate _{mica, BN, Si, Ge, GeS} , BaF 2, MgF 2, LaF 3, GaF 2, LiF, GaAs, GaP, GaN, InAs, InP, InSb, BaTiO 3, LiNbO 3, LaAlO 3, NdGaO ₃ , SrTiO ₃ , SrTiO ₃ , LaAlO ₃ , LiGaO ₂ , LiTaO ₃ , YAlO ₃ , YVO 4, ZnO, ZnS, ZnSe, ZnTe, NiO, MgO, TeO 2, SiC, and sapphire. May include. Combinations of these elements can also be used. The basic purpose is to epitaxially form a highly ordered catalyst thin film on a substrate. Single crystal substrates are commercially available.

  The catalyst may comprise at least one element selected from the group consisting of Ni, Cu, Pt, Co, Fe, Cr, Mn, Rh, Ti, Pd, Ru, Ir, Al, Mg and Re. Combinations of these elements can also be used. The catalyst layer may be in the form of a thin film or a thick film. The basic principle of selection is to pursue lattice constant matching between the single crystal substrate and the crystalline catalyst.

  The carbon source for producing the graphene film on the catalyst surface may be derived from the contained gaseous carbon compound. The gaseous carbon source may be any compound containing carbon, in particular a compound containing up to 6 carbon atoms, and most particularly a molecule containing up to 2 carbon atoms. Examples of the gaseous carbon source include at least one selected from the group consisting of ethane, ethylene, ethanol, methanol, acetone, acetylene, propane, propylene, butane, butadiene, pentane and hexane.

  The catalyst layer may be in the form of a thin film or a thick film, and may have a wide range of 5 nm to 2 mm, more specifically a thickness in the range of about 10 nm to 700 nm. The catalyst layer can be created by various techniques known in the art such as electron beam deposition, electron gun deposition, sputtering, thermal vacuum deposition and the like. In order to form a highly ordered crystalline catalyst layer, it is preferable to keep the substrate in a heated state. After deposition of the catalyst layer on the single crystal substrate, processing may be required on the catalyst layer to form a high quality crystal layer. This is important in producing high quality graphene films. Examples of treatment of the catalyst layer include, but are not limited to, heat treatment, polishing and etching.

The heat treatment of the catalyst layer on the crystalline substrate may be performed in an argon, helium or hydrogen atmosphere, or in a vacuum up to ultra high vacuum (about 10 ⁻¹² torr). This heat treatment may be performed at a temperature of about 300 ° C. to 1600 ° C. for a period between 1 second and 200 hours. Heating may occur at a rate between about 0.1 ° C./min and about 500 ° C./min. This heat treatment may be performed by resistance heating, radiant heating, induction heating, laser, infrared radiation, microwave, plasma, ultraviolet radiation, surface plasma heating, or similar methods well known in the art.

  By heating the gaseous carbon source at 300 ° C. to 1600 ° C. for a period between 1 second and 200 hours, CVD growth of the graphene film can be achieved. Heating may occur at a rate between about 0.1 ° C./min and about 500 ° C./min. A carrier gas such as argon, helium or hydrogen may be used with a gaseous carbon source while controlling its flow rate.

The cooling process to room temperature may be performed in an inert atmosphere such as argon, or in a vacuum up to ultra high vacuum (about 10 ⁻¹² torr). This cooling may occur at a rate between about 0.1 ° C./min and about 500 ° C./min, or by a natural cooling process by turning off the power.

  The degree of graphene formation can be controlled by adjusting the temperature and time of the heating and cooling process. Furthermore, the success or failure of a large-scale, uniform and high-quality graphene film depends on a smooth crystalline catalyst surface having a large-size terrace portion and a small number of steps. Depending on the crystalline catalyst thin film on the substrate, further heating, cooling treatment and / or pressure. The single crystal substrate functions as a template for epitaxial growth of a high quality crystalline catalyst surface.

  The formation of graphene is due to the gaseous carbon compound being decomposed on the catalyst surface to form single-layer islands, which are further fused into complete single-layer graphene covering the entire surface of the catalyst. Multi-layer graphene up to two layers, several layers, and up to 200 layers can be formed by controlling temperature, growth time and atmosphere. In addition, the process may include supplying argon, helium, or hydrogen with the gaseous carbon compound.

  Furthermore, the graphene film formed on the catalyst surface is separated from the catalyst layer using a suitable method such as solvent treatment and transferred to any other substrate according to its desired application and processed in various ways. can do. Separation of the graphene film from the catalyst surface can be achieved by removing the catalyst layer interposed between the substrate and the synthesized graphene film. This separation is generally accomplished by etching the catalyst using a suitable solvent.

  Further detailed disclosure will be made with reference to the following experimental examples. The following experimental examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[Experimental Example 1]
Synthesis of graphene film on Ni / mica substrate A fresh mica surface was prepared in a clean room.
2. A 100 nm thick Ni film was deposited on a 1 cm × 1 cm mica substrate by electron gun deposition at a deposition rate of 0.1 nm / second under a base pressure of 5.0 × 10 ⁻⁸ torr.
3. A sample of Ni / mica was loaded into a quartz tube furnace and the chamber was evacuated to a base pressure of about 1.0 × 10 ⁻⁷ torr.
4). Ni / mica was treated under a hydrogen atmosphere at 650 ° C. for 15 hours at a pressure of about 5 Pa.
5. The supply of hydrogen was stopped.
6). While circulating a C ₂ H ₄ gaseous carbon source, the temperature was maintained at 650 ° C. for 10 minutes, and the atmosphere was maintained at about 1.0 × 10 ⁻⁵ torr.
7). The supply of gaseous carbon compound was stopped and the system was cooled to room temperature by turning off the power.
8). A graphene film on a Ni / mica substrate was obtained.

  FIG. 2 shows the measurement results of graphene obtained in Experimental Example 1. FIG. 2A is a secondary electron image obtained using Auger electron spectroscopy of this graphene. 2 (b) is a C KLL Auger electron map corresponding to FIG. 2 (a), and FIG. 2 (c) is two Auger electron spectra obtained in the white and black sample regions in FIG. 2 (a). Indicates. These results indicate that the graphene film is uniform.

[Experiment 2]
Synthesis of graphene film on Ni / mica substrate A fresh mica surface was prepared in a clean room.
2. By electron gun deposition, a 100 nm thick Ni film was deposited on a 2 cm × 2 cm mica substrate at a deposition rate of 0.1 nm / second under a base pressure of 5.0 × 10 ⁻⁸ torr.
3. A sample of Ni / mica was loaded into a quartz tube furnace and the chamber was evacuated to a base pressure of about 1.0 × 10 ⁻⁷ torr.
4). Ni / mica was treated under a hydrogen atmosphere at 750 ° C. for 15 hours at a pressure of about 5 Pa.
5. The supply of hydrogen was stopped and the temperature was lowered to 650 ° C.
6). While circulating the C ₂ H ₄ gaseous carbon compound, the temperature was maintained at 650 ° C. for 10 minutes, and the atmosphere was maintained at about 1.0 × 10 ⁻⁵ torr.
7). The supply of gaseous carbon compound was stopped and the system was cooled to room temperature by turning off the power.

  FIG. 3 shows the measurement results of graphene obtained in Experimental Example 2. FIG. 3A is a secondary electron image obtained using Auger electron spectroscopy of this graphene. FIG. 3 (b) shows two Auger electron spectra obtained in the white and black sample regions in FIG. 3 (a). These results indicate that the graphene film is uniform.

[Experiment 3]
Synthesis of graphene film on Ni / mica substrate A fresh surface of mica was prepared using scotch tape in a clean room.
2. A 100 nm thick Ni film was deposited on a 1 cm × 1 cm mica substrate by electron gun deposition at a deposition rate of 0.1 nm / second under a base pressure of 5.0 × 10 ⁻⁸ torr.
3. A sample of Ni / mica was loaded into a quartz tube furnace and the chamber was evacuated to a base pressure of about 1.0 × 10 ⁻⁷ torr.
4). Ni / mica was treated at 950 ° C. for 10 hours.
5. The temperature was lowered to 600 ° C. and kept for 10 minutes while circulating the C ₂ H ₄ gaseous carbon compound, and the atmosphere was maintained at about 1.0 × 10 ⁻⁵ torr.
6). The supply of gaseous carbon compound was stopped and the system was cooled to room temperature by turning off the power.

  FIG. 4 shows the measurement results of graphene obtained in Experimental Example 3. FIG. 4A is a secondary electron image obtained using Auger electron spectroscopy of this graphene. FIG. 4 (b) shows two Auger electron spectra obtained in the white and black sample regions in FIG. 4 (a). These results indicate that the graphene film is uniform.

[Experimental Example 4]
Transfer of graphene film synthesized on Ni / mica substrate to another substrate Poly (methyl methacrylate) (2% anisole solution of PMMA) was spin-coated to a thickness of 300 nm on a graphene film synthesized on Ni / mica according to Experimental Example 1.
2. PMMA-coated graphene samples were baked in air at 180 ° C. for 5 minutes.
3. The Ni layer interposed between the graphene film and the mica substrate was etched using FeCl ₃ (1M). That is, the graphene sample covered with the PMMA film was immersed in a 1M FeCl ₃ solution. After a few minutes, the Ni film was removed, so that the PMMA + graphene film separated from the mica and floated on the etching solution surface.
4). PMMA + graphene was transferred manually onto a Si substrate coated with a 300 nm thick SiO ₂ coating (hereinafter referred to as a 300 nm thick SiO ₂ / Si substrate).
5. After placing PMMA + graphene on the target 300 nm thick SiO ₂ / Si, the PMMA film was dissolved and removed with acetone.
6. A graphene film on 300 nm thick SiO ₂ / Si was obtained.

FIG. 5 is an optical microscope image of a graphene film transferred from Ni / mica onto a 300 nm thick SiO ₂ / Si substrate in Experimental Example 4, and is a large-scale and uniform single-layer graphene (“Graphene other than the lower left corner and the upper right corner”). (region labeled “film”), together with PMMA residue (region labeled “Resistresidue” in the upper right corner), and bare SiO ₂ surface (region labeled “SiO ₂ ” in the lower left corner) .

  Although the present invention has been described in terms of specific implementations only, those skilled in the art who have read and understood the specification and the exemplary embodiments will envision equivalent changes and modifications. The present invention includes all such modifications and changes and is limited only by the scope of the following claims. Furthermore, while specific features or aspects of the invention may have been disclosed in connection with only one of several implementations, such features or aspects may be disclosed for any given or specific application. If desired or convenient for that purpose, it may be combined with one or more other features or aspects of other implementations.

  What is disclosed here is a method for manufacturing a large-scale, uniform, high-quality and transferable graphene film. One skilled in the art will appreciate that such graphene films can be efficiently applied to various applications such as optoelectronic devices, sensors, electrodes, and hydrogen storage media.

100 single crystal substrate 101 catalyst layer 102 graphene film

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Claims (11)

A graphene film manufacturing method including the following steps.
(A) A single crystal substrate is prepared.
(B) A crystalline catalyst layer is provided on the single crystal substrate.
(C) The single crystal substrate provided with the crystalline catalyst layer is processed.
(D) A graphene film is formed by heating and cooling the gaseous carbon source in the presence of the crystalline catalyst layer.   The method of claim 1, wherein the treatment is a treatment selected from the group consisting of heat treatment, polishing treatment and etching treatment.   The variation in crystal orientation of crystal grains of the crystalline catalyst thin film after the heating step for a predetermined time is within a range of ± 5 degrees, and the size of the crystal grains is larger than 1 μm. The method described in 1. The substrate is _{mica, BN, Si, Ge, GeS} , BaF 2, MgF 2, LaF 3, GaF 2, LiF, GaAs, GaP, GaN, InAs, InP, InSb, BaTiO 3, LiNbO 3, LaAlO 3, NdGaO 3 , SrTiO ₃ , SrTiO ₃ , LaAlO ₃ , LiGaO ₂ , LiTaO ₃ , YAlO ₃ , YVO ₄ , ZnO, ZnS, ZnSe, ZnTe, NiO, MgO, TeO ₂ , SiC, and sapphire. The method according to claim 1, wherein the method is a single crystal substrate including a crystal or a combination of a plurality of single crystals.   The catalyst material of the catalyst layer includes one or more elements selected from the group consisting of Ni, Pt, Co, Fe, Al, Cr, Cu, Mg, Mn, Rh, Ti, Pd, Ru, Ir, and Re. The method for producing a graphene film according to any one of claims 1 to 4, further comprising:   The method according to any one of claims 1 to 5, wherein the thickness of the catalyst layer ranges from about 1 nm to about 2 mm.   The method according to claim 1, wherein the step of providing the catalyst layer is performed by deposition, and the single crystal substrate is maintained in a range of 0 ° C. to 600 ° C. during the deposition.   The method according to any one of claims 2 to 7, wherein the treatment is a heat treatment continued at a temperature of 300 ° C to 1600 ° C for 1 second to 200 hours.   The method according to claim 2, wherein the treatment is a heat treatment performed in a vacuum or an inert atmosphere.   The method according to any one of claims 1 to 9, wherein the gaseous carbon source is a compound containing 1 to 6 carbon atoms.   11. The gaseous carbon source is one or more compounds selected from the group consisting of ethane, ethylene, ethanol, methanol, acetone, acetylene, propane, propylene, butane, butadiene, pentane and hexane. the method of.