KR20130020351A - Fabricaion method of high-quality graphen film - Google Patents

Abstract

PURPOSE: A method for forming a graphene thin film and a graphene manufactured by the same method are provided to grow a single crystal metal film easily and inexpensively by growing a single crystal metal film on a single crystal substrate and forming a graphene thin film on a single crystal metal film. CONSTITUTION: A method for forming a graphene thin film includes following steps: A single crystal substrate(10) is prepared. A single crystal metal film(20) is grown on a single crystal substrate. A graphene film(30) is formed on a single crystal metal film. The single crystal substrate is sapphire(α-Al_2O_3). The single crystal metal film is a transition metal. In a single crystal metal film formation step, a thermal evaporation technique and an e-beam evaporation technique are used in order to grow a single crystal metal film.

Description

Formation method of graphene thin film and graphene manufactured by the method {fabricaion method of high-quality graphen film}

The present invention relates to a method for forming a graphene thin film and to graphene prepared by the method, and more particularly, to a method for forming a graphene thin film that is promising as a new material due to its excellent electrical and mechanical properties. It relates to a graphene produced by the method.

Graphene refers to a thin film laminated within about 1 to 5 layers by using a monoatomic layer in which carbon atoms are bonded in a hexagonal honeycomb shape as a basic unit. It is a very promising new material for ultra-fast nano semiconductors, transparent electrode materials, and various sensors because of its high charge mobility of 200,000 cm ² / Vs at room temperature, high mechanical strength, flexibility, and high transmittance to visible light.

M. Taghioskoui published Materials Today 2009, Vol. 12, No. 10 p. Referring to the review of “Trends in graphene research” published in 34-37, the representative methods for obtaining graphene thin film by the existing technology are as follows.

(1) Mechanical exfoliation from graphite.

(2) Graphene is obtained by chemical exfoliation using a redox reaction in a chemical manner.

(3) The silicon carbide (SiC) is heat-treated at a high temperature of 1500 ^° C. or more to sublimate silicon on the silicon carbide surface to form epitaxial graphene on the silicon carbide substrate, leaving only a carbon atom layer.

(4) a raw material gas containing carbon such as CH ₄ , C ₂ H ₄ , C ₂ H ₆ , C ₃ H ₈ , on a transition metal including Ni, Cu, Co, Ru, Pt, and the like; Gases such as H ₂ , Ar, and N ₂ are mixed to form a graphene thin film by chemical vapor deposition at a temperature of approximately 900 to 1000 ^° C.

These existing technologies have their own advantages and disadvantages. In the case of (1), graphene has the best physical properties, but since graphene is obtained in the form of flakes having a size of several tens of μm, it is most disadvantageous for large area and mass production. In case of (2), mass production is possible, but J.K. Wassei and R.B. Kaner et al., Materials Today 2010, Vol. 13, No. 3, p. As pointed out in “Graphene, a promising transparent conductor” in pp. 52-59, the quality of graphene films is very poor. (3) is currently epitaxial graphene, ie large-area single crystals without domain boundaries. The only way to obtain fins, but the price of silicon carbide substrate is very high, which is disadvantageous for practical use.The most advantageous method for large-scale and mass production for commercialization is generally recognized as the chemical vapor deposition method of (4). However, in the case of using chemical vapor deposition, since graphene is deposited using polycrystalline metal, graphene growing on the polycrystalline metal becomes monocrystalline graphene over the entire area due to the nature of the deposition process. It is impossible.

In the prior art, generally, a metal film deposited on an amorphous film such as silicon oxide film (SiO ₂ ) is mainly used, and the metal film grown on the amorphous film has a polycrystalline structure. A good example of this is in J. Hofrichter et al. In 2010 in Nano Letters 10 p. It can be found in the paper “Synthesis of graphene on silicon dioxide by a solid carbon source” published in 36-42, which deposits about 500 nm of Ni on silicon oxide and then forms graphene on it. It was shown that thick domain boundaries were formed along the grain boundary.

Alternatively, graphene may be formed using a metal sheet such as nickel (Ni), copper (Cu), or cobalt (Co). In this case, too, the graphene also has domains and domain boundaries because the metal sheet itself is polycrystalline when not subjected to a special manufacturing process.

On the other hand, single crystal graphene is considered to be very promising for use in next-generation transistors and sensors, in addition to various transparent electrode applications utilizing high charge mobility and transparency. Therefore, there is an urgent need for a method in which single crystal graphene can be obtained inexpensively in large areas.

Domain boundary means a boundary of domains with different crystal directions in the graphene thin film. If the domain boundary exists in graphene, the direction of crystallization is changed between adjacent domains around this region, and because the carbon layer thickness of the domain boundary is thicker than the thickness of the carbon layer inside the domain, the overall nonuniformity of graphene increases. . Therefore, the physical properties of graphene, including carrier mobility, are greatly reduced compared to the theoretical value. If it is possible to suppress or reduce the domain boundary formation of graphene, the physical properties of graphene will be greatly improved.

It is an object of the present invention to provide a method for obtaining epitaxial graphene without domain boundaries or high-quality graphene thin films where possible suppressing the production of domain boundaries.

When the graphene is formed on the transition metal, the microstructure of the polycrystalline transition metal is transferred to the graphene to form graphene having domains and domain boundaries having different crystal directions. To suppress or minimize the present invention to provide a method for forming a single crystal graphene or graphene having structural properties close to it.

Method of forming a graphene thin film of the present invention, the first step of preparing a single crystal substrate; A second step of growing a single crystal metal film on the single crystal substrate; And a third step of forming a graphene film on the single crystal metal film.

According to a preferred embodiment, the single crystal substrate is an oxide-based single crystal substrate having a sapphire (α-Al ₂ O ₃ ), magnesium oxide (MgO), or perovskite structure.

According to a preferred embodiment, the single crystal metal film is a transition metal, characterized in that the nickel (Ni), copper (Cu), cobalt (Co), ruthenium (Ru) or platinum (Pt).

According to a preferred embodiment, a thermal evaporation technique, an e-beam evaporation technique, a laser ablation, or a sputtering technique is used to grow the single crystal metal film. do.

According to a preferred embodiment, the base pressure of the growth apparatus for growing the single crystal metal film is 1 x 10 ^-7 Torr to 1 x 10 ^-6 Torr.

According to a preferred embodiment, in order to grow the single crystal metal film, the metal film is grown by maintaining the temperature of the single crystal substrate in the range of 100 to 300 ^° C. and the deposition rate in the range of 1 to 20 μs / sec.

According to a preferred embodiment, 1) after the transition metal having a solid solubility to carbon in the second step is grown on the single crystal substrate as a single crystal metal film, and 2) for the growth of graphene in the third step, 5 ^o A device that raises or lowers the substrate temperature at a rate of C / sec or more is used, and a mixture of hydrocarbon gas and carrier gas, which is a raw material gas, is used for 1 minute to 30 in the range of 700 to 1100 ^o C. After the graphene growth is performed for a minute, the graphene thin film is grown on the metal film by rapidly lowering the substrate temperature at a rate of -5 ^o C / sec or more.

Here, the transition metal having solid solubility to carbon is nickel (Ni), cobalt (Co), ruthenium (Ru), or platinum (Pt), and the hydrocarbon gas is methane (CH ₄₎ , acetylene (C ₂ H ₂ ), ethylene (C ₂ H ₄ ), ethane (C ₂ H ₆ ), propene (C ₃ H ₆ ), propane (C ₃ H ₈ ) and mixtures thereof, and The carrier gas is selected from the group consisting of hydrogen (H ₂ ), argon (Ar), nitrogen (N ₂ ) and mixtures thereof.

According to another preferred embodiment, 1) after the transition metal with low solid solubility to carbon in the second step is grown on the single crystal substrate as a single crystal metal film, and 2) for the growth of the graphene in the third step, After mixing a gas (hydrocarbon gas) and a carrier gas (carrier gas) is made over 30 minutes to 5 hours at a deposition temperature of 900 ~ 1000 ^o C. Here, the transition metal having a low solid solubility to carbon is copper (Cu), and the hydrocarbon gas is methane (CH ₄ ), acetylene (C ₂ H ₂ ), ethylene (C ₂ H ₄ ), ethane (C ₂ H ₆ ), propene (C ₃ H ₆ ), propane (C ₃ H ₈ ) and mixtures thereof, wherein the carrier gas is hydrogen (H ₂ ), argon (Ar), nitrogen ( N ₂ ) and mixtures thereof.

According to another preferred embodiment, 1) a transition metal having solid solubility to carbon is grown on a single crystal substrate as a single crystal metal film in a second step, and then 2) physical vapor deposition is carried out in a third step. deposition to form a carbon film on the single crystal metal film (carbon film), and then in a separate rapid heat treatment apparatus to maintain the temperature of the substrate for 1 to 30 minutes in the range of 700 ~ 1100 ^o C and then -5 ^o C / The graphene film is grown on the metal film by rapidly decreasing the substrate temperature at a rate of sec or more. Here, the transition metal having solid solubility to carbon is nickel (Ni), cobalt (Co), ruthenium (Ru), or platinum (Pt), and the physical vapor deposition method heats a carbon evaporation source with thermal energy. Thermal evaporation method using carbon vapor generated here, electron beam evaporation method using carbon vapor generated by heating the carbon evaporation source, laser ablation method (laser ablation) or carbon target heating the carbon evaporation source with laser Sputtering method.

According to a preferred embodiment, when twin crystal defects occur in the single crystal metal film of the second step, crystal defects are generated only in a direction parallel to the surface of the single crystal metal film, so that the crystal defect is a single crystal metal film. It is not exposed to the surface.

According to a preferred embodiment, after the formation of the graphene thin film, the single crystal metal film is dissolved with ferric chloride (FeCl ₃ ), further comprising the step of obtaining graphene.

By using the concept and method proposed in the present invention, it is possible to grow a single crystal metal film easily and inexpensively, and use it to form high-quality graphene whose domain boundary generation is suppressed. This is much cheaper and simpler than using expensive single crystal metal sheets or subliming SiC at high temperatures to form single crystal graphene.

In addition, since the evaporator, electron beam evaporator, sputter, etc. widely used in the industry can be used to deposit the single crystal metal film, the practicality is also very high.

The high-quality graphene manufactured by the manufacturing method according to the present invention is expected to be applicable to device development of next-generation flexible transistors, flexible sensors, etc., which will replace silicon in the future because there are few domain boundaries acting as defects.

1 is a view showing a state in which a single crystal metal film 20 is deposited on a single crystal substrate 10 and graphene 30 is formed thereon.
FIG. 2 is a part of a picture published in the article "Synthesis of graphene on silicon dioxide by a solid carbon source" published in Nano Letters 10, p.36-42, 2010, formed on a polycrystalline Ni film deposited on a silicon oxide film. Atomic force microscopy image showing the domain boundaries of the pins.
3 to 4 show a state in which a single crystal metal film 20 is deposited on the single crystal substrate 10 and the single crystal substrate.
5 is a photograph of an electron beam evaporator used by the inventors to deposit single crystal Ni and single crystal Cu metal films.
6 is a cross-section transmission electron microscopy diffraction pattern of a single crystal Ni metal film deposited on a sapphire (0001) substrate.
FIG. 7 is a high-resolution cross-sectional TEM image of a single crystal Ni metal film deposited on a sapphire (0001) substrate. FIG.
8 is a cross-sectional transmission electron microscope diffraction pattern of a single crystal Cu metal film deposited on a sapphire (0001) substrate.
9 is a cross-sectional transmission electron microscope bright field image of a single crystal Cu metal film deposited on a sapphire (0001) substrate.
10 is an X-ray diffraction pole figure map of a single crystal Cu metal film deposited on a sapphire (0001) substrate.
Figure 11 is a photograph of the rapid thermal chemical vapor deposition (RTCVD) equipment used by the inventors for graphene deposition.
FIG. 12 is a view illustrating a state in which a specimen 140 enters a hot zone inside the heating element 120 in the deposition tube 110 in which the heating element 120 is mounted.
FIG. 13 is a view showing a state in which the temperature of the specimen 140 is drastically reduced by rapidly moving the specimen 140 to a cool zone outside the heating element 120 using the charging rod 130.
FIG. 14 is a Raman spectrum of a flaw-layer graphene (FLG) deposited by the inventor on a single crystal Ni metal film using the RTCVD apparatus of FIG. 11.
FIG. 15 illustrates a carbon atom 32 when the carbon film 31 deposited on the single crystal metal film 20 using physical vapor deposition is heated to a temperature of 700 to 1100 ^° C. in a rapid thermal anneal apparatus. ) Is a state in which the melted into the single crystal metal film 20.
FIG. 16 illustrates a state in which the carbon atom 32 dissolved in the single crystal metal film 20 precipitates on the surface of the single crystal metal film 20 when the substrate temperature is suddenly lowered in the state of FIG. 15 to form the graphene 30. The figure which shows.

The method proposed in the present invention uses an oxide single crystal substrate such as sapphire, MgO, or an oxide single crystal substrate having a perovskite structure such as SrTiO ₃ , LaAlO _3, and the like. Epitaxial metal films such as Ni, Cu, Co, Ru, and Pt are deposited by e-beam evaporation, sputtering, and the like, and graphene is formed thereon to form the metal film. It is to suppress the domain boundary generation of graphene due to the polycrystalline structure. That is, the key concept is to deposit a single crystal metal film thereon using a single crystal substrate.

Growth of a single crystal metal film using a single crystal substrate has been studied in the surface science field. For example, I.V. Malikov et al. Reported in 519 Thin Solid Films, p. In the paper published in 527-535, “Epitaxial Ni films for ballistic ferromagnetic nanostructures,” Ni was reported to grow on a sapphire substrate in a single crystal state by laser ablation. Also J.M. Purswani et al. Have grown a Cu single crystal film on a MgO substrate by sputtering in a paper published in 2006, published in Thin Solid Films, Vol. 515, p. 1166-1170, "Growth of epitaxial Cu on MgO (001) by magnetron sputter deposition."

However, in all these cases, the base pressure of the deposition apparatus used to deposit the metal film was in the ultra-high vacuum range of 1 x 10 ^-10 to 1 x 10 ^-9 Torr, and the single crystal metal film growth itself was the research goal. In general, it is widely recognized that such ultra-high vacuum devices are essential for obtaining a single crystal thin film to keep the surface state clean before deposition. However, in the present invention, contrary to conventional wisdom, even if a general vacuum equipment with a base pressure of 1 x 10 ^-7 to 1 x 10 ^-6 Torr is used, it is actually proved that sufficient single crystal Ni and Cu thin films can be obtained by applying appropriate process conditions. The difference is that the single crystal metal film thus obtained can be applied to graphene growth in which domain boundary formation is suppressed.

Ultra-high vacuum equipment is very difficult to apply to mass production in the actual industrial field in terms of price, maintenance and operation of the equipment. However, general vacuum equipments with base pressures of 1 x 10 ^-7 to 1 x 10 ^-6 Torr, for example electron beam evaporators or sputters, are already widely used in industrial fields, including the semiconductor industry, and are highly practical and easy to maintain. It is mass-produced and the process cost is low.

In addition, according to the present invention, since a relatively inexpensive single crystal substrate such as sapphire is used, single crystal metal can be obtained relatively inexpensively. For example, a commercially available 10 mm x 10 mm single crystal Cu sheet is about 300,000 won, whereas a 2 inch diameter sapphire substrate has a market price of about 50,000 won (as of February 2011). Considering the cost of the single crystal metal film deposition process, it is possible to prepare a single crystal metal substrate required to form high quality graphene at a much lower cost. After the graphene is formed, the metal film is melted with a solution such as FeCl ₃ and the graphene is transferred to a third substrate. Then, the single crystal substrate used for depositing the metal film can be reused.

In order to help the understanding of the concepts presented in the present invention, specific examples and actual experimental results obtained by the present inventors are described in detail below. However, this is only one way to actually implement the core concept proposed in the present invention, which is not limited by the core concept of the present invention.

Example 1

First step: preparing a single crystal substrate

A single crystal substrate 10 is prepared as shown in FIG. 3. The single crystal substrate 10 should be a single crystal of the entire substrate, preferably a metal to be deposited thereon and a material that is thermally and chemically stable. The single crystal substrate that satisfies these conditions may be a sapphire (α-Al ₂ O ₃ ) substrate or a magnesium oxide (MgO) substrate or an oxide substrate having a perovskite structure such as SrTiO ₃ or LaAlO ₃ . This is appropriate.

The single crystal substrate is an acid such as hydrochloric acid (HCl), nitric acid (HNO ₃ ), sulfuric acid (H ₂ SO ₄ ), or a base such as ammonium hydroxide (NH ₄ OH) or ammonium fluoride (NH ₄ F), or acetone, Cleaning is performed using an organic solvent such as isopropyl alcohol or methanol. After washing, wash with deionized water, dry the water and immediately put it into the device for metal deposition.

Metal deposition apparatus evaporator heat (thermal evaporator), or an electron beam evaporation apparatus, a sputtering, and a typical general-purpose equipment, base pressure of 1 x 10 ^-6 Torr or less when it is appropriate (more preferably 1 x 10 as described above ^{- 7} Torr ～ 1 x 10 ^-6 Torr). Immediately after charging, the deposition apparatus is pumped and waited until the base pressure is reached.

Second Step: Deposition of Single Crystal Metal Film

When the base pressure is reached, the single crystal metal film 20 is deposited on the single crystal substrate 10 as shown in FIG. 4. The single crystal metal film 20 is preferably nickel (Ni), copper (Cu), cobalt (Co), ruthenium (Ru), platinum (Pt), and the like, which are commonly used for forming graphene. It is not limited to metals alone.

In the case of using the thermal evaporation method or the electron beam evaporation method, the transition metal is heated by thermal energy or an electron beam so that the metal vapor generated therefrom is deposited on the single crystal substrate 10. In the case of sputtering, an inert gas such as argon (Ar) is ionized and incident on the target made of the transition metal material so that ions of the transition metal protrude from the target surface and are deposited on the single crystal substrate 10.

For reference, FIG. 5 is a photograph of an electron beam evaporator used by the present inventors to deposit nickel (Ni) and copper (Cu) single crystal metal films, and the attainable base pressure is ˜5 × 10 ⁻⁷ Torr and nickel (Ni) and copper General purpose used to deposit various materials such as aluminum (Al), gold (Au), silver (Ag), cobalt (Co), titanium (Ti), iron (Fe), carbon (C) as well as (Cu) It is equipment.

In order to deposit the single crystal metal film, the surface temperature of the single crystal substrate 10 is preferably maintained at 100 to 300 ^° C., and the deposition rate is preferably in the range of 1 to 20 μs / sec.

In addition, it is preferable to proceed as low as possible the base pressure, and to deposit the vapor and other impurities adsorbed on the inner wall of the reactor by heating the inner wall of the reactor before depositing the single crystal metal film, or to deposit the metal in the absence of the specimen. It is desirable to deposit the material of the membrane on the inner wall of the reactor in advance to minimize the outgassing of other impurities.

The thickness of the metal to be deposited is in the range of 1000 to 5000 mm 3.

There are several methods for determining whether the deposited metal film is in a single crystal state, such as X-ray diffraction and transmission electron microscopy.

FIG. 6 is a cross-sectional transmission electron microscope diffraction pattern of a Ni single crystal film of about 2000 mW deposited by the inventor on the (0001) sapphire substrate using the electron beam evaporator of FIG. 5, wherein spots of the sapphire single crystal substrate and the Ni single crystal film are mixed. Is observed. Since no ring is observed in the diffraction pattern, there is clear evidence that Ni was deposited in a single crystal state.

FIG. 7 is a photograph of the Ni single crystal film of FIG. 6 analyzed by a high-resolution transmission electron microscope (high-resolution TEM), where twins are most frequently observed in nickel (Ni) and copper (Cu). This is consistent with the result that twin spots are observed in the diffraction pattern of FIG. 6. From FIG. 6, the crystallographic relationship between the nickel (Ni) single crystal film and the sapphire substrate could be analyzed, as follows.

Al ₂ O ₃ (0001) || Ni (111): The (0001) plane of the sapphire substrate and the (111) plane of Ni are parallel to each other

Al ₂ O ₃ [2110] || Ni (211): The [2110] direction of the sapphire substrate and the (211) direction of Ni are parallel to each other

FIG. 8 is a cross-sectional transmission electron microscope diffraction pattern of a Cu single crystal film having a thickness of ˜5000 mm 3 deposited on the sapphire substrate by the electron beam evaporation method, and shows a pattern similar to that of FIG. 6.

FIG. 9 is a cross-sectional transmission electron microscope bright field image of a Cu single crystal film, in which a plurality of twins were found as well as nickel (Ni), but twins were formed only on a copper (Cu) (111) plane which was unusually parallel to a sapphire substrate. It became.

FIG. 10 is an X-ray diffraction pole figure map of the Cu single crystal film, and it can be seen that the Cu (200) peak has 3-fold symmetry. If twins were not produced only in a direction parallel to the Cu metal film surface, Cu (200) peak would have 6-fold symmetry due to twin formation. The formation of twins only with Cu (111) planes parallel to the sapphire substrate is thought to be very advantageous for high-quality graphene growth, because when twins are produced with (111) planes that are not parallel to the substrate This is because a twin boundary is formed at the site where the Cu surface and the twin meet, which is likely to influence the domain formation of graphene having different crystal directions.

The crystallographic relationship between the Cu single crystal film and the sapphire substrate was the same as that of nickel (Ni). In other words, it was analyzed as follows.

Al ₂ O ₃ (0001) || Cu (111): The (0001) plane of the sapphire substrate and the (111) plane of Cu are parallel to each other

Al ₂ O ₃ [2110] || Cu (211): The [2110] direction of the sapphire substrate and the (211) direction of Cu are parallel to each other

As described above, the present inventors proved that it is possible to grow a single crystal metal film without selecting an appropriate single crystal substrate and depositing a metal film under optimized process conditions without using ultra-high vacuum deposition equipment.

Third step: graphene thin film formation step-chemical vapor deposition

After the deposition of the single crystal metal film 20 on the single crystal substrate 10 is completed, the graphene deposition is carried out by loading into the graphene chemical vapor deposition equipment immediately, and the graphene thin film 30 on the single crystal metal film 20 as shown in FIG. Form.

Chemical vapor deposition of graphene is based on the raw materials of methane (CH ₄₎ , acetylene (C ₂ H ₂ ), ethylene (C ₂ H ₄ ), ethane (C ₂ H ₆ ), propene (C ₃ H ₆ ), propane Hydrocarbon gas such as (C ₃ H ₈ ) and a carrier gas such as hydrogen (H ₂ ), argon (Ar), N ₂ (nitrogen) are mixed and in the range of 700 to 1100 ^o C Conduct.

At this time, the characteristics required for the chemical vapor deposition apparatus vary depending on the type of metal film.

1) The first method is to use a rapid thermal anneal type chemical vapor deposition system capable of rapid temperature rise and temperature drop.

In the case of metals with solid solubility of carbon such as nickel (Ni), cobalt (Co), ruthenium (Ru), and platinum (Pt), the carbon atoms are dissolved in the metal film once, and the temperature is reduced to the substrate surface. It is well known that graphene is formed by the precipitation of carbon.

In order to form graphene by precipitation, graphene is formed only after the deposition is completed and the temperature can be rapidly dropped at a rate of at least -5 ^o C / sec or more. Typical devices having such characteristics are halogen lamps. There is a rapid thermal chemical vapor deposition (RTCVD), a rapid thermal anneal chemical vapor deposition apparatus capable of rapid temperature rise and temperature drop.

For reference, FIG. 11 is a photograph of an RTCVD apparatus manufactured by the present inventors, and chemical vapor deposition is performed by mixing C ₂ H ₄ , H ₂ , and Ar. Using a halogen lamp, it is possible to raise the temperature up to a maximum temperature of 950 ^o C, and the temperature increase rate and the temperature decrease rate can be obtained up to ~ 15 ^o C / sec.

When the halogen lamp is not used, as shown in FIGS. 12 and 13, the single crystal substrate 140 is loaded in the hot zone inside the heating element 120 using a loading rod 130 inside the tube 110. There is also a method using a chemical vapor deposition apparatus having a function to move quickly to the cool zone (outside the heating element).

2) Secondly, using a chemical vapor deposition apparatus using a conventional furnace (furnace).

For metals such as Cu where solid solubility of carbon is close to zero and graphene is deposited only through surface reactions, rapid temperature rise and rapid temperature drop functions are not required. On the other hand, traditional chemical vapor deposition using furnaces is more suitable, since long deposition times of more than 30 minutes to 5 hours at deposition temperatures of 900 to 1000 ^o C are generally required.

In the present invention, a few-layer graphene (FLG) consisting of about five layers of carbon layers was successfully deposited on a Ni single crystal film grown on a sapphire substrate using the RTCVD apparatus of FIG. 11.

14 shows Raman spectra of FLG specimens. The RTCVD process temperature applied to the FLG specimen of FIG. 14 was 900 ^o C. After the deposition was completed, the temperature drop rate was about -10 ^o C / sec up to 700 ^o C and then slowly at a rate of -5 ^o C / sec. Went down. For comparison, after growing graphene under the same deposition conditions as the Ni polycrystalline film grown on the silicon oxide film, the graphene on the Ni polycrystalline film had a non-uniform thickness of graphene depending on the site, but the Ni single crystal was grown on the sapphire substrate. A uniform thickness of FLG was grown on the film. This is because, as the inventors of the present invention, FLG having multiple domains was grown on a Ni polycrystalline film, whereas single crystal graphene having a single domain was formed on a Ni single crystal film.

Example 2

When a metal with solid solubility, such as nickel (Ni), cobalt (Co), ruthenium (Ru), and platinum (Pt), is used to form graphene, the physical vapor deposition method is as follows. Graphene may be formed through a carbon film deposition and a rapid heat treatment process using depositin).

First step: preparing a single crystal substrate

Same as Example 1.

Second Step: Deposition of Single Crystal Metal Film

Single crystal metal film deposition was carried out in the same manner as in Example 1.

Third Step: Graphene Thin Film Formation Step-Physical Vapor Deposition

Rapidly test specimens by physically depositing carbon films without using chemical vapor deposition to form graphene after metal film deposition, such as evaporators, electron beam evaporators, sputters, laser ablation devices, etc. Move it.

Depending on the device used, metal film deposition and carbon film deposition may be performed continuously in the same device without breaking the vacuum.

In the case of evaporation or electron beam evaporation, carbon film deposition uses carbon vapor generated by heating carbon evaporation source in pellet or granule form with heat energy or electron beam. In this case, deposition is performed by heating the carbon evaporation source with a laser. In the case of sputtering, vapor deposition is performed using a carbon target. When the carbon film is deposited by the physical vapor deposition method as described above, the single crystal substrate 10 on which the single crystal metal film 20 is deposited does not need to be heated to a high temperature, and may be at room temperature or at a substrate temperature of less than 300 ^° C. It is preferable to proceed. In such a temperature range, the deposited carbon film is generally an amorphous carbon film. The thickness of the carbon film to be deposited will vary depending on the thickness of the single crystal metal film 20, but it is generally preferred to be in the range of 10 to 100 kPa.

Specimens deposited with carbon film are loaded into a device capable of rapid heat treatment and maintained at a constant temperature for 30 seconds to 5 minutes in the range of 700 to 1100 ^o C. At this time, the heat treatment atmosphere is preferably maintained in a vacuum state of less than 1 x 10 ^-6 Torr or inert gas such as Ar to N ₂ to remove the possibility of oxidation of the specimen by residual oxygen.

FIG. 15 is a schematic view showing a state in which some carbon atoms 32 constituting the carbon film 31 are melted into the single crystal metal film 20 and some remain on the surface at a heat treatment temperature.

When the substrate temperature drops after the heat treatment, the carbon solubility of the single crystal metal film 20 is drastically reduced, and thus, the carbon atoms 32 begin to precipitate on the surface of the metal film. Is formed. The appropriate cooling rate will vary depending on the thickness of the metal film, the carbon solubility of the metal, and the detailed conditions of the rapid heat treatment process, but generally the optimum conditions can be found in the range of -5 to -15 ^o C / sec.

10: single crystal substrate
20: single crystal metal film
30: graphene
31: monolayer
32: carbon atom
110: deposition tube
120: heating element
130: charging rod
140: Psalms

Claims (31)

In the graphene thin film formation method,
Preparing a single crystal substrate;
A second step of growing a single crystal metal film on the single crystal substrate; And
And a third step of forming a graphene film on the single crystal metal film. The method of claim 1,
The single crystal substrate is characterized in that the sapphire (α-Al ₂ O ₃ ). The method of claim 1,
The single crystal substrate is characterized in that the magnesium oxide (MgO). The method of claim 1,
The single crystal substrate is characterized in that the oxide-based single crystal substrate having a perovskite (perovskite) structure. The method of claim 1,
The single crystal metal film is a transition metal. The method of claim 1,
And said single crystal metal film is nickel (Ni). The method of claim 1,
The single crystal metal film is characterized in that the copper (Cu). The method of claim 1,
The single crystal metal film is characterized in that the cobalt (Co). The method of claim 1,
And said single crystal metal film is ruthenium (Ru). The method of claim 1,
The single crystal metal film is platinum (Pt). The method of claim 1,
In the second step, a thermal evaporation technique or an e-beam evaporation technique is used to grow a single crystal metal film. The method of claim 1,
In the second step, a sputtering technique is used to grow a single crystal metal film. 13. The method according to claim 11 or 12,
And a base pressure of the growth device for growing the single crystal metal film is 1 x 10 ^-7 Torr to 1 x 10 ^-6 Torr. 13. The method according to claim 11 or 12,
And growing the metal film by maintaining a temperature of the single crystal substrate in a range of 100 to 300 ^° C. and a deposition rate of 1 to 20 mW / sec to grow the single crystal metal film. The method of claim 1,
1) In the second step, after the transition metal having solid solubility to carbon is grown on the single crystal substrate as a single crystal metal film,
2) In order to grow the graphene in the third stage, a device capable of raising or lowering the substrate temperature at a rate of 5 ^o C / sec or more is used, and a hydrocarbon gas and a carrier gas, which are raw materials, are used. After mixing and growing graphene for a period of 1 to 30 minutes in the range of 700 to 1100 ^o C, the graphene thin film is grown on the metal film by rapidly decreasing the substrate temperature at a rate of -5 ^o C / sec or more. How to. 16. The method of claim 15,
The transition metal with solid solubility to carbon is nickel (Ni), cobalt (Co), ruthenium (Ru), or platinum (Pt). 16. The method of claim 15,
The hydrocarbon gas is methane (CH ₄₎ , acetylene (C ₂ H ₂ ), ethylene (C ₂ H ₄ ), ethane (C ₂ H ₆ ), propene (C ₃ H ₆ ), propane (C ₃ H ₈ ) And a mixture thereof. 16. The method of claim 15,
The carrier gas is selected from the group consisting of hydrogen (H ₂ ), argon (Ar), nitrogen (N ₂ ) and mixtures thereof. The method of claim 1,
1) In the second step, after the transition metal having low solid solubility to carbon is grown on the single crystal substrate as a single crystal metal film,
2) In order to grow the graphene in the third step, the mixture of hydrocarbon gas and carrier gas, which is a raw material gas, is carried out over 30 minutes to 5 hours at a deposition temperature of 900 to 1000 ^o C. How to feature. 20. The method of claim 19,
The transition metal having a low solid solubility to carbon is copper (Cu). 20. The method of claim 19,
The hydrocarbon gas is methane (CH ₄₎ , acetylene (C ₂ H ₂ ), ethylene (C ₂ H ₄ ), ethane (C ₂ H ₆ ), propene (C ₃ H ₆ ), propane (C ₃ H ₈ ) And a mixture thereof. 20. The method of claim 19,
The carrier gas is selected from the group consisting of hydrogen (H ₂ ), argon (Ar), nitrogen (N ₂ ) and mixtures thereof. The method of claim 1,
1) In the second step, after the transition metal having solid solubility to carbon is grown on the single crystal substrate as a single crystal metal film,
2) In the third step, after forming a carbon film (carbon film) on the single crystal metal film by physical vapor deposition (physical vapor deposition), the temperature of the substrate in a separate rapid heat treatment apparatus in the range of 700 ~ 1100 ^o C ~ 1 minute ~ A method of growing a graphene thin film on a metal film by maintaining the temperature for 30 minutes and then rapidly decreasing the substrate temperature at a rate of -5 ^o C / sec or more. 24. The method of claim 23,
The transition metal with solid solubility to carbon is nickel (Ni), cobalt (Co), ruthenium (Ru), or platinum (Pt). 24. The method of claim 23,
The physical vapor deposition method is a heat evaporation method using the carbon vapor generated by heating the carbon evaporation source with thermal energy. 24. The method of claim 23,
The physical vapor deposition method is an electron beam evaporation method using carbon vapor generated by heating the carbon evaporation source with electron beam energy. 24. The method of claim 23,
The physical vapor deposition method is a laser ablation method for heating a carbon evaporation source with a laser. 24. The method of claim 23,
The physical vapor deposition method is a sputtering method using a carbon target. The method of claim 1,
When twin crystal defects occur in the single crystal metal film of the second stage, crystal defects are generated only in a direction parallel to the surface of the single crystal metal film so that the crystal defects are not exposed to the surface of the single crystal metal film. How to feature. The method of claim 1,
And after forming the graphene thin film, dissolving the single crystal metal film with ferric chloride (FeCl ₃ ) to obtain graphene. Graphene obtained by the method of any one of claims 1 to 30.

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