JP5563500B2 - Synthesis method of graphene and carbon molecular thin film - Google Patents

Description

  The present invention relates to a graphene that is a monolayer sheet in which carbon atoms are two-dimensionally bonded to each other, and a method for synthesizing a carbon molecular thin film having a structure in which the graphene is laminated.

Graphene is a monoatomic layer sheet represented as a honeycomb sheet structure in which six-membered ring structures formed by sp ² bonds of carbon atoms are continuously bonded two-dimensionally. Here, a stack of graphene is referred to as a carbon molecular thin film. In recent years, it has attracted attention for its characteristic properties such as electron / hole mobility and spin transport properties, and is a nanomaterial expected to be applied to devices and the like.

  As a method of synthesizing graphene and a carbon molecular thin film, a method of synthesizing using a metal as a catalyst is widely known. In this method, a gas or the like as a carbon atom supply source is supplied to the catalyst metal, and a graphene and carbon molecule thin film is formed on the surface of the catalyst metal through a decomposition reaction of gas molecules and a graphene structure formation reaction by the combination of carbon atoms. The

  Since graphene has a two-dimensional planar structure, it is considered ideal for the synthesis of graphene with few defects that the metal surface on which graphene is synthesized is flat at the atomic level. Therefore, it is ideal that the metal surface is a metal crystal plane.

  In addition, graphene is considered to have a characteristic structure and physical properties even if it is as small as several tens of nanometers, but when considering application to devices, etc., a uniform range should be as much as possible. It is desirable to make it wide.

  In order to satisfy these requirements, a method of synthesizing uniform graphene and carbon molecular thin films on the surface using a metal single crystal such as iridium (111) serving as a catalyst metal as a substrate has been reported ( For example, refer nonpatent literature 1).

J. Coraux et al., "Growth of graphene on Ir (111)", New Journal of Physics, vol.11, 023006, 2009.

  However, when the above-described metal single crystal is used as the substrate, the production of the metal single crystal substrate is time-consuming and requires, for example, repeated application of high-temperature catalytic metal and high-temperature heating under ultrahigh vacuum. The conditions are severe and the production is very difficult.

For example, in the production of the iridium (111) single-crystal substrate of Non-Patent Document 1 described above, iridium is sputtered onto a substrate heated to 1120 K in a chamber having an ultrahigh vacuum performance of about 1 × 10 ⁻⁵ Pa. Then, by repeating the process of heating at 1570 K, an iridium (111) substrate having a thickness of several hundred nanometers is produced.

  Manufacturing an apparatus that realizes such an ultra-high vacuum / ultra-high temperature processing process requires high technology and a large amount of money, and the number of operators that can be implemented is limited. Further, if a large amount of such a metal single crystal substrate is procured in the market, a cost burden increases.

  The present invention provides a method for synthesizing graphene and carbon molecular thin film that solves the above problems, and using a metal thin film produced by a general film forming method, prepares a metal crystal as a catalyst, It is an object of the present invention to provide a method for easily synthesizing graphene and carbon molecular thin films having a wider uniform region at low cost.

A method for synthesizing graphene and a carbon molecular thin film according to the present invention includes a first step for producing catalyst metal crystal grains and a second step for synthesizing graphene and a carbon molecular thin film. The first step is an inert gas. A step of heating the catalyst metal in a hydrogen gas atmosphere to raise the temperature to a first predetermined temperature, a step of maintaining the first predetermined temperature after the temperature increase for a first predetermined time, And a step of decreasing the temperature at a first predetermined temperature decrease rate that is constant within a range including a temperature range to be rearranged.

Furthermore, the second step includes a step of heating the catalyst metal in an inert gas and hydrogen gas atmosphere to raise the temperature to a second predetermined temperature, and after raising the temperature to the second predetermined temperature, over a second predetermined time. A step of further supplying a carbon source gas, and a step of lowering the temperature at a second predetermined temperature decrease rate that is constant within a range including a temperature range in which the catalyst metal is rearranged from the second predetermined temperature.

Furthermore , by controlling the first and second predetermined temperatures and the first and second predetermined temperature-decreasing speeds, a polycrystalline surface of the catalyst metal is produced, and the average particle size of each crystal grain of the polycrystalline surface In addition, the graphene and the carbon molecular thin film are synthesized on the polycrystalline surface by controlling the crystal grains so that the crystal orientations of the crystal grains are aligned. Thereby, high-quality graphene and carbon molecular thin films with few defects can be obtained.

In the second step, after raising the temperature to the second predetermined temperature, maintaining the second predetermined temperature and further supplying the carbon source gas over a second predetermined time; and exhausting the carbon source gas And a step of lowering the temperature at a second predetermined temperature reduction rate in an inert gas and hydrogen gas atmosphere.

Moreover, after performing a 1st process in multiple times, a 2nd process is performed. At this time, the first predetermined temperature, the first predetermined time, the first predetermined temperature decrease rate, the second predetermined temperature, the second predetermined time, and the second predetermined temperature decrease rate are independent of each other. By controlling this, the crystal grains of the catalyst metal can be produced, and the graphene and the carbon molecular thin film can be synthesized on the crystal plane of the crystal grains. When the first step is repeated a plurality of times, the first predetermined temperature, the first predetermined time, and the first predetermined temperature decrease rate may be controlled independently.

Further, the method for synthesizing graphene and carbon molecular thin film according to the present invention includes a step of heating a catalyst metal in an inert gas and hydrogen gas atmosphere to raise the temperature to a predetermined temperature, and after the temperature increase, for a predetermined time. A step of further supplying a carbon source gas, and a step of lowering the temperature at a predetermined temperature decrease rate that is constant in a range including a temperature range in which the catalyst metal is rearranged, and by controlling the predetermined temperature and the predetermined temperature decrease rate, A polycrystalline surface of the catalyst metal is produced, and the average grain size of each crystal grain of the polycrystalline surface is increased, and the crystal orientation of each crystal grain is controlled to be aligned, so that graphene and Synthesize carbon molecular thin film.

Further, after the temperature rise, the step of maintaining the predetermined temperature and further supplying the carbon raw material gas over a predetermined time; and exhausting the carbon raw material gas at a predetermined temperature decreasing rate in an inert gas and hydrogen gas atmosphere And a step of lowering the temperature.

  According to the present invention described above, a metal crystal serving as a catalyst is prepared using a metal thin film produced by a general film forming method, and graphene and carbon molecular thin films having a wider uniform region are prepared at a low cost. An excellent effect that it can be easily synthesized is obtained.

It is a flowchart which shows the synthesis | combining method of the graphene and carbon molecular thin film which concern on Embodiment 1 of this invention. It is the figure which showed typically the electric furnace used with the synthesis | combining method of the graphene which concerns on Embodiment 1-3 of this invention, and a carbon molecule thin film. It is the time chart which showed the temperature change when temperature-falling a catalyst metal substrate in the synthesis method of the graphene and carbon molecule thin film concerning Embodiments 1-3 of the present invention. As in Embodiments 1 to 3 of the present invention, an atomic force microscope (AFM) image (a) of the surface of the catalytic metal that has undergone the process of controlling to a predetermined temperature-decreasing rate, and the catalytic metal naturally cooled without control It is an AFM image (b) of the surface. It is the result of having analyzed the crystal orientation of the nickel surface after going through temperature rising and temperature falling processes similarly to Embodiments 1-3 of the present invention. Both (a) and (b) have undergone a single temperature rise and fall process, (a) is when the temperature drop rate is controlled, and (b) is a scanning electron microscope when cooled naturally without control. (SEM) image. (A ′) and (b ′) are mapping images obtained by analyzing the crystal orientation of each crystal grain by backscattered electron diffraction (EBSD) with respect to the broken line portions of (a) and (b), respectively. It is the photograph of the transmission electron microscope image (TEM image) which observed the cross section of what was synthesize | combined by the synthesis | combining method of the graphene which concerns on Embodiment 1-3 of this invention, and a carbon molecule thin film. This is an example of observing a crystal grain boundary. It is the photograph of the transmission electron microscope image (TEM image) and electron diffraction image which observed an example of what was synthesize | combined by the synthesis | combining method of the graphene which concerns on Embodiment 1-3 of this invention, and a carbon molecule thin film. These are a TEM image (a) observed from a direction perpendicular to the film, an enlarged image (b) thereof, and an electron diffraction image (c) with respect to a region surrounded by a circle in (a). It is a flowchart which shows the synthesis | combining method of the graphene and carbon molecular thin film which concern on Embodiment 2 of this invention. It is a flowchart which shows the synthesis | combining method of the graphene and carbon molecular thin film which concern on Embodiment 3 of this invention. Similar to Embodiment 3 of the present invention, the AFM image (a) of the nickel surface obtained by repeating the catalytic metal crystal grain preparation step three times, and the amorphous nickel surface before executing the catalytic metal crystal grain preparation step This is an AFM image (b).

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Embodiment 1]
FIG. 1 is a flowchart showing a method for synthesizing graphene and a carbon molecular thin film according to Embodiment 1 of the present invention.

First, a catalytic metal is applied to the substrate. As the substrate, for example, a smooth substrate in which a polished silicon wafer is thermally oxidized to form silicon dioxide (SiO ₂ ) on the surface is used. The substrate is not limited to this, and may be any material that is smooth and made of a material that does not react with the catalyst metal at the graphene synthesis temperature. Other examples include magnesium oxide (MgO) and sapphire (Al ₂ O ₃ ).

  On the substrate, for example, a catalytic metal such as nickel (Ni) is applied to a thickness of 300 nm to produce a catalytic metal substrate. Here, as a method of applying the catalytic metal, a method of applying the metal by melting and evaporating (vapor deposition), a method of applying metal atoms from the target of the catalytic metal by high-speed particles (sputtering method), etc. A general film forming method can be employed.

  The thickness of the catalyst metal is not limited to the above-described 300 nm, but may be any thickness, but will be described later so that the catalyst metal does not aggregate and the substrate is not exposed through a temperature rising process described later. The predetermined temperature θ11, the holding time T1 at the predetermined temperature θ11, the catalytic metal species, the affinity between the catalytic metal and the substrate, and the like may be selected as appropriate. In addition to nickel (Ni), catalytic metals such as cobalt (Co), iron (Fe), copper (Cu), and other metal species that can act as a synthesis field for graphene can be used and do not react with the substrate. What is necessary is just to select suitably.

  FIG. 2 is a diagram schematically showing the electric furnace 20 used when the catalytic metal substrate 10 is processed. As shown in FIG. 2, the electric furnace 20 includes a sealed container 22 and a heater 24 that heats the sealed container 22, supplies various gases from one end of the sealed container 22, and pumps from the other end of the sealed container 22. The gas can be exhausted by (not shown).

  The process of heating the catalytic metal substrate 10 using this electric furnace 20 is as follows.

  First, the catalytic metal substrate 10 is loaded into the electric furnace, and the temperature is raised to a predetermined temperature (eg, 900 ° C.) in an inert gas (eg, argon gas) and hydrogen gas atmosphere (step S100). ). Thus, after the temperature of the catalytic metal substrate 10 reaches a predetermined temperature, the carbon source gas is further supplied over the predetermined time (step S110). This may be performed in a state where the temperature is maintained at a predetermined temperature. The carbon source gas is a source gas for forming graphene or a carbon molecular thin film on the catalyst metal. Next, the temperature of the catalyst metal substrate 10 is decreased at a predetermined temperature decrease rate (for example, −12.5 ° C./min) (step S120). This temperature decrease may be performed, for example, in an inert gas and hydrogen gas atmosphere after exhausting the gas in the sealed container 22.

  Hereafter, each processing content of step S100-S120 is demonstrated in detail.

  First, the catalytic metal substrate 10 is loaded into the electric furnace, and the temperature is raised to a predetermined temperature (eg, 900 ° C.) in an inert gas and hydrogen gas atmosphere (step S100).

As shown in FIG. 2, the gas inside the sealed container 22 is exhausted by a pump while the catalytic metal substrate 10 is loaded in the sealed container 22, and then the argon gas 180 sccm and the hydrogen gas 20 sccm, which are inert gases, are sealed. The pressure in the sealed container 22 is maintained at about 5 × 10 ⁴ Pa by supplying from one end of the container 22 and exhausting the other end side by a pump.

The pressure in the sealed container 22 may be any pressure from several hundred Pa to around normal pressure (atmospheric pressure), and is about 5 × 10 ⁴ Pa, which is safe in practice and has high vacuum and high pressure resistance. There is no need to use high performance containers. In addition, a low pressure of about 5 × 10 ³ Pa may be used to further enhance gas diffusion and uniformity. Further, the flow rates of argon gas and hydrogen gas are not limited to the above values, and may be set to suitable flow rates in view of the set pressure in the sealed container 22. Hydrogen gas has the effect | action etc. which reduce | restore the oxide of the catalyst metal surface. Argon gas, which is an inert gas, is a carrier gas, and the flow rate may be zero. Note that sccm is a unit of flow rate, and indicates that a fluid at 0 ° C. and 1013 hPa flows 1 cm ³ per minute.

  Under such conditions, the heater 24 is operated, and the catalytic metal substrate 10 is heated at a pace of, for example, 60 ° C./min until reaching the predetermined temperature θ11.

  The predetermined temperature θ11 may be any temperature as long as it is lower than the boiling point of the catalytic metal, the catalytic metal atoms on the surface can be rearranged, and graphene can be synthesized by the treatment described later. The higher the predetermined temperature θ11, the rearrangement of catalytic metal atoms at a deeper position from the surface is possible with a shorter holding time (including zero). For this reason, the predetermined temperature θ11 may be appropriately changed in consideration of the type of catalyst metal, the thickness of the catalyst metal, the holding time, and the like. Further, the rate of temperature increase is not limited to the above-described numerical value of 60 ° C./min, and may be a value that quickly reaches the predetermined temperature θ11.

  Subsequently, after the temperature of the catalytic metal substrate 10 reaches a predetermined temperature, the carbon source gas is further supplied over a predetermined time T11 while maintaining the predetermined temperature (step S110). Specifically, while maintaining the temperature of the catalytic metal substrate 10 at a predetermined temperature θ11, graphene and carbon are added by flowing 10 sccm of methane gas in addition to argon gas and hydrogen gas over a predetermined time T11 (for example, 5 minutes). Supply carbon atoms that will be the constituent material of the molecular thin film. The predetermined time T11 may be the same as the time for holding at the predetermined temperature, or may be shorter than this.

Here, the carbon source gas that is a constituent material of the graphene and the carbon molecular thin film is not limited to methane gas, but other saturated hydrocarbon gas, unsaturated hydrocarbon gas such as ethylene (C ₂ H ₄ ), ethanol (C ₂ An alcohol vapor gas such as H ₅ OH) may be used.

  Further, the predetermined temperature θ11 may be a temperature at which a gas molecule serving as a carbon supply source decomposes and a reaction in which graphene is formed from carbon atoms by the catalytic action of the catalytic metal proceeds. Therefore, the predetermined temperature θ11 can be appropriately selected depending on the type of gas used and the type of catalytic metal. The time for flowing the methane gas may be at least as long as the amount of carbon capable of forming graphene can be supplied to the catalyst metal, and can be changed as appropriate. In general, the supply amount (flow rate) of the carbon source is considered to affect the number of graphene layers and the like, and may be appropriately changed in view of the desired graphene and the shape of the carbon molecular thin film.

  Next, after the gas in the sealed container 22 is exhausted, the temperature of the catalytic metal substrate 10 is decreased at a predetermined temperature decrease rate (for example, −12.5 ° C./min, etc.) in an atmosphere of argon gas and hydrogen gas (Step 1). S120).

Specifically, first, the methane gas, argon gas, and hydrogen gas in the sealed container 22 are all exhausted once to remove the gas serving as the carbon source, and then argon gas 180 sccm and hydrogen gas 20 sccm are again added to 5 × 10 ^4. It is made to flow under a pressure of Pa (when it is initially set to a low pressure of about 5 × 10 ³ Pa, it is flowed under that pressure). Under such conditions, the temperature of the catalytic metal substrate 10 is cooled from a predetermined temperature θ11 to a predetermined temperature θ12 (for example, 100 to 150 ° C.) at a predetermined temperature decrease rate Δθ1 (for example, 12.5 ° C./min). . Note that the methane gas, the argon gas, and the hydrogen gas may be cooled at a predetermined temperature decrease rate while the methane gas, the argon gas, and the hydrogen gas are allowed to flow without being exhausted once. Further, the methane gas may be stopped in the middle of temperature lowering, and only argon gas and hydrogen gas may be used.

  The predetermined temperature decrease rate Δθ1 is set so that the cooling rate in the initial temperature decrease period, that is, in the region where the temperature is high, is slower than that in the case where the temperature is naturally cooled without stopping and controlling. The temperature range for cooling at a predetermined temperature drop rate may be a range including a temperature range in which the catalyst metal atoms move and rearrange. The temperature lowering rate is not limited to the above value, and may be any temperature cooling rate that promotes the formation of crystal grains, and may be appropriately selected depending on the characteristics of the catalyst metal species. As described above, according to the present embodiment, by controlling the predetermined temperature to be reached, the predetermined time for further supplying the carbon source gas, and the predetermined temperature decrease rate, the crystal such as the grain size as will be described later. It is characterized by controlling the morphology of the grains.

  FIG. 3 shows, in a solid line, the temperature change when the catalytic metal substrate 10 is cooled at a predetermined temperature decrease rate in the method for synthesizing graphene and carbon molecular thin film according to the present embodiment, and naturally without controlling the temperature decrease rate. It is the time chart which showed the temperature change at the time of cooling with the dotted line. The vertical axis indicates the temperature, and the horizontal axis indicates the elapsed time since the start of the temperature decrease. The predetermined temperature decrease rate Δθ1 may be set so that the temperature decrease rate in the relatively high temperature region at the beginning of the temperature decrease is slow and constant, as shown in FIG. 3, as compared with the case where the temperature is naturally cooled without control. .

  The temperature range for cooling at a predetermined temperature decrease rate may be a range including a temperature range in which the catalyst metal atoms move and rearrange. The temperature lowering rate is not limited to the above value, and may be any temperature cooling rate that promotes the formation of crystal grains, and may be appropriately selected depending on the characteristics of the catalyst metal species. Note that, as described above, the temperature before the temperature decrease (predetermined temperature θ11) is such that the gas (carbon raw material gas) molecule serving as the carbon supply source is decomposed and graphene is formed from carbon atoms by the catalytic action of the catalytic metal. At advancing temperature, the metal atoms move and can be rearranged.

  During the temperature lowering process, catalytic metal atoms (nickel atoms) are rearranged and fixed, and nickel crystal grains are formed on the surface. FIG. 4 is an atomic force microscope (AFM) image in which the surface of the catalytic metal substrate is compared with and without controlling the temperature drop rate. FIG. 4A is an AFM image of the catalytic metal substrate obtained by controlling and cooling at a temperature drop rate Δθ1, and FIG. 4B is an AFM image of the catalytic metal substrate obtained by natural cooling without control. It is a statue. From FIG. 4, compared with the case where it cools naturally without controlling to a predetermined temperature-decreasing rate, when the temperature is controlled and the temperature is decreased at a temperature-decreasing rate Δθ1, the crystal grain size of the catalyst metal formed increases. I understand that.

  FIG. 5 is an example of the result of analyzing the crystal orientation of nickel crystal grains when the temperature drop rate is controlled (a) or not (b) by backscattered electron diffraction (EBSD). . Further, (a ′) in FIG. 5 and (b ′) in FIG. 5 show the crystal of each crystal grain in the region corresponding to the portion surrounded by the broken line in the secondary electron image (SEM image) of the scanning electron microscope. The azimuth is shown by shading. In the same figure, the crystal grains are shown with a higher concentration (blacker) as the crystal plane orientation of the crystal grains becomes (111).

  (A) of FIG. 5 has many parts with a high density | concentration, and this has shown that many parts with crystal plane orientation close | similar to (111) and a large crystal grain have appeared. On the other hand, (b) of FIG. 5 shows that the concentration is high and the wide portion is small, and the high concentration portion is small and dispersed. This means that the crystal plane orientation is close to (111) and there are few large crystal grains. Show. From these observation results, in the case of the catalytic metal substrate controlled to the above-described predetermined temperature drop rate, the crystal plane orientation of the crystal grains of the catalytic metal formed on the surface tends to be aligned with the (111) orientation. I understand. In addition, as the crystal grains become larger, a tendency to align in the (111) orientation is observed.

  Since the lattice constant of the nickel (111) crystal plane is 0.2497 nm and the lattice constant of graphene is 0.246 nm, the compatibility is very good. Graphene synthesized on the nickel (111) crystal plane has a lattice constant. It may be affected by the crystal planes with close numerical values, and it is considered that high-quality uniform single-crystal graphene and carbon molecular thin films are likely to be formed. Therefore, by this method of enlarging the crystal plane of the catalyst metal and aligning the plane orientation of each crystal plane, it is possible to easily obtain graphene and a carbon molecular thin film having a larger uniform region.

  Furthermore, as shown in FIGS. 4 and 5, the catalytic metal surface according to the present invention has a large number of crystal planes. Although the graphene and the carbon molecular thin film formed on each crystal plane are connected in a row, the number of layers tends to change. FIG. 6 is a transmission electron microscope image (TEM image) obtained by observing a state in which the number of graphene layers is greatly changed at a grain boundary portion between crystal grains. In this way, a series of carbon molecular thin films having different shapes and the number of layers can be obtained for each region corresponding to each crystal grain. If each region is separated by a microfabrication technique, only a portion having a desired shape and number of layers can be used.

  In addition, the carbon molecular thin films in which a plurality of graphene layers are formed according to the present invention tend to have a structure in which they are regularly stacked (stacked). FIG. 7A shows a planar TEM image, FIG. 7B shows an enlarged image, and FIG. 7C shows an electron diffraction image. FIG. 7C is an electron diffraction image of a region surrounded by a circle in FIG. In (a) of FIG. 7, the area | region divided by the shape corresponding to each crystal grain can be seen in a continuous carbon molecule thin film. As shown in FIG. 7B, the boundary of each section is considered to appear because the wrinkles of the carbon molecular thin film stand more vertically.

  As shown in FIG. 7 (c), a diffraction image resulting from the six-membered ring unit cell structure of graphene is obtained. If each graphene layer is a turbulent carbon molecular thin film simply stacked at a random rotation angle, it can be predicted that an annular diffraction image will be observed. From the results shown in FIG. It can be seen that the thin film is not a turbulent layer but is stacked. The presence of several components with different rotation angles indicates that there are a plurality of stacked single crystal graphenes in the measurement region.

  When graphene stacks, it exhibits different physical properties than a turbulent layer simply stacked at random rotation angles. As a typical example, the effect on the band structure is known. For example, a carbon molecular thin film (double-layer graphene) stacked in two layers has a band gap that is applied by applying an electric field in a direction perpendicular to the surface. It is formed. By using this band gap, an on / off operation of an ultrafast field effect transistor using bilayer graphene as a channel becomes possible.

  As described above, according to the present invention, it is possible to obtain a homogeneous graphene and carbon molecular thin film having a size corresponding to a crystal grain, and the carbon molecular thin film can be synthesized as a stacking structure. Combining with technology, etc. enables application using the features.

[Embodiment 2]
Next, a method for synthesizing graphene and a carbon molecular thin film according to Embodiment 2 of the present invention will be described. The same components as those described in the first embodiment (electric furnace) are denoted by the same reference numerals and detailed description thereof is omitted. Hereinafter, the difference from Embodiment 1 of the present invention will be mainly described.

  FIG. 8 is a flowchart showing a method of synthesizing graphene and a carbon molecular thin film according to Embodiment 2 of the present invention.

  The process for raising the temperature of the catalytic metal substrate 10 in step S200 is the same as that in step S100 described in the first embodiment, and thus the description thereof is omitted.

  Next, the temperature of the catalytic metal substrate 10 is held at a predetermined temperature θ21 for a predetermined time T21 (step S210). In the first embodiment, after the catalyst metal substrate 10 is heated until the temperature reaches the predetermined temperature θ11, the methane gas is added to the argon gas and the hydrogen gas over a predetermined time T11 (step S110 in FIG. 1). In the second embodiment, after the catalyst metal substrate 10 is heated to a predetermined temperature θ21 (for example, 900 ° C. or the like), the argon gas and the hydrogen gas are supplied without flowing the methane gas 110 for a predetermined time T21. The temperature of the catalytic metal substrate 10 is maintained at the predetermined temperature θ21 over (for example, 0 to 60 minutes) (step S210). This treatment is performed to promote the formation of catalyst metal crystal grains. The lower the predetermined temperature θ21, the longer the time may be set. Conversely, if the predetermined temperature θ21 is sufficiently high, the predetermined time T21 may be zero.

  Thereafter, the temperature of the catalytic metal substrate 10 is controlled from a predetermined temperature θ21 to a predetermined temperature θ22 (for example, 100 to 150 ° C., etc.) at a predetermined temperature decrease rate Δθ21 (for example, −12.5 ° C./min, etc.). Step S220). The predetermined temperature θ22 may be a low temperature that prevents the metal atoms of the catalyst metal from moving and rearranging.

  As described above, in the second embodiment, there is provided a catalyst metal crystal grain preparation step for forming catalyst metal crystal grains in the catalyst metal layer in advance through a temperature rising and temperature lowering process without supplying methane gas. For this reason, the size of the crystal grains obtained as a result of the graphene and carbon molecular thin film synthesis step is larger than that of the graphene synthesis by one heating / holding / cooling process as in Example 1. The crystal grain which has is formed. For this reason, homogeneous graphene corresponding to a large crystal plane can be synthesized more easily.

  Further, when nickel of the metal catalyst is applied to the substrate, the nickel is in an amorphous state, and when the catalyst metal crystal grain preparation step is not provided in advance as in the first embodiment, the nickel is crystallized from the amorphous state. In parallel with this process, the synthesis of graphene proceeds. For this reason, it is considered that if the crystal plane is not well formed on the catalytic metal surface due to the progress of the reaction process, graphene cannot be formed or the quality is likely to deteriorate. On the other hand, in Embodiment 2, since the catalyst metal surface is already in a state where crystal grains are already aligned in the catalyst metal crystal grain preparation step, the reaction of carbon atoms is considered to proceed more smoothly, and there are few defects. It is easy to obtain high quality graphene.

  After reaching the predetermined temperature θ22, the catalytic metal substrate 10 is again heated to a predetermined temperature θ23 (for example, 900 ° C.) (step S230). There may be a period of time before the start of temperature increase (for example, 10 minutes).

  Next, as in step S110 of FIG. 1 described in the first embodiment, the temperature of the catalytic metal substrate 10 is maintained at a predetermined temperature θ23 (for example, 900 ° C.), for a predetermined time T22 (for example, 5 minutes). Then, methane gas (for example, 10 sccm) is added to the argon gas and hydrogen gas to flow (step S240), the gas in the sealed container 22 is exhausted, and a predetermined temperature decrease rate Δθ24 (for example, under argon gas and hydrogen gas atmosphere) The temperature of the catalyst metal substrate 10 is taken out from the sealed container 22 after the temperature is lowered to a predetermined temperature θ24 (for example, 100 to 150 ° C.) at a pace of −12.5 ° C./min) (step S250). The predetermined time T22 may be the same as the time for maintaining the predetermined temperature θ23, or may be shorter than that. Alternatively, the temperature in the sealed container 22 may be lowered while flowing methane gas, argon gas, and hydrogen gas as they are without exhausting all of the gas in the sealed container 22 once. Further, the methane gas may be stopped in the middle of temperature lowering, and only argon gas and hydrogen gas may be used.

  Through such treatment, the graphene and carbon molecular thin film according to the present embodiment formed on the crystal grains of the catalyst metal can be obtained. By dividing into the first stage of forming crystal grains in the catalyst metal layer and the second stage of forming graphene and carbon molecular thin films, the expansion of the catalyst metal crystal grains is further promoted. It is easy to reduce the defects of the graphene and carbon molecular thin films formed thereon and to enlarge the uniform region.

  In the above-described second embodiment, the catalyst metal crystal grain preparation process in steps S200 to S220 and the graphene and carbon molecular thin film synthesis process in steps S230 to S250 are performed at predetermined temperatures θ21 and θ23 at the time of temperature increase and at the time of temperature decrease. The predetermined temperatures θ22 and θ24, the predetermined holding times T21 and T22, and the predetermined temperature decrease rates Δθ22 and Δθ24 do not necessarily have the same value, and can be changed as appropriate. In the catalyst metal crystal grain preparation step of steps S200 to S220, a temperature and a holding time that can move and rearrange the atoms of the catalyst metal may be selected, and the graphene and carbon molecular thin film of steps S230 to S250 may be selected. In the synthesis step, a temperature and a holding time that can synthesize graphene and the carbon molecular thin film may be selected. The temperature lowering rate may be any temperature decreasing rate that promotes the formation of crystal grains, and may be appropriately selected depending on the characteristics of the catalyst metal species and the like, and may be appropriately controlled independently in each step.

[Embodiment 3]
Next, a method for synthesizing graphene and a carbon molecular thin film according to Embodiment 3 of the present invention will be described. Note that the same components as those described in the first embodiment are denoted by the same reference numerals and detailed description thereof is omitted.

  FIG. 9 is a flowchart showing a method of synthesizing graphene and a carbon molecular thin film according to Embodiment 3 of the present invention. Hereinafter, the difference from the first and second embodiments of the present invention will be mainly described.

  Step S300 is a process of forming catalyst metal crystal grains in the catalyst metal layer, and the specific process is as follows. The catalyst metal substrate 10 described in the second embodiment is heated to a predetermined temperature θ21 (see FIG. 8 (step S200), the catalyst metal substrate 10 is held at the predetermined temperature θ21 for a predetermined time T21 (step S210 in FIG. 8), and then cooled at a predetermined temperature decrease rate Δθ21 until the predetermined temperature θ22 is reached (step in FIG. 8). A series of catalytic metal crystal grain production steps S220) are performed a plurality of times (for example, three times). By doing in this way, the average particle diameter of the crystal grain formed in a catalyst metal layer can be increased, and a crystal orientation can be aligned.

  FIG. 10 shows the observation image (FIG. 10A) of the nickel surface on which a larger crystal plane is formed by performing the catalytic metal crystal grain preparation process three times before the catalytic metal crystal grain preparation process. It is shown together with a surface image in a fixed state (FIG. 10B).

  In addition, the arrival temperature and the holding time of each of the catalyst metal crystal grain preparation processes of the plurality of times are not limited to the same, and the arrival temperature and the holding time of the catalyst metal crystal grain preparation process and the graphene and carbon molecule thin film synthesis process are also the same. It is not limited to the same. In the catalyst metal crystal grain preparation step, a temperature and a time at which the catalyst metal atoms can be moved and rearranged may be appropriately selected. In the graphene and carbon molecular thin film synthesis step, the temperature and time at which the graphene synthesis reaction proceeds. May be selected as appropriate. The temperature lowering rate may be any temperature decreasing rate that promotes the formation of crystal grains, and may be appropriately selected depending on the characteristics of the catalyst metal species and the like, and may be appropriately controlled independently in each step.

  Further, in the present invention, the catalyst metal crystal grain preparation process is performed a plurality of times, once the temperature is lowered to a temperature sufficient to eliminate the movement of metal atoms. By doing so, the temperature remains high for a long time without lowering the temperature. Compared with the case where it does, the crystal grain diameter of the catalyst metal is increased more efficiently.

  Subsequently, similar to the processing in steps S230 to S250 of FIG. 8 described in the second embodiment, the catalytic metal substrate 10 is heated to the predetermined temperature θ23 (step S310), and the temperature of the catalytic metal substrate 10 is set to the predetermined temperature. Methane gas (for example, 10 sccm) is added to the argon gas and hydrogen gas for a predetermined time T22 (for example, 5 minutes) while maintaining θ23 (for example, 900 ° C.) (step S320), and then the sealed container 22 After exhausting the gas in the atmosphere, the temperature is set to a predetermined temperature θ24 (for example, 100 to 150 ° C.) at a predetermined temperature decrease rate Δθ24 (for example, −12.5 ° C./min) in an atmosphere of argon gas and hydrogen gas. (Step S330). Through such treatment, graphene and a carbon molecular thin film can be obtained on the crystal plane of the crystal grains on the surface of the catalyst metal layer. The temperature may be lowered in an atmosphere of methane gas, argon gas, or hydrogen gas without exhausting the gas in the sealed container 22.

  It is also possible to control the particle size of the metal crystal grains by controlling the number of catalyst metal crystal grain production steps. By controlling the particle size of the metal crystal grains in this way, the shape of the graphene and the carbon molecular thin film and the size of the uniform crystal region with different number of layers can be easily controlled. It is possible to obtain the graphene and carbon molecular thin film.

[Modification]
In addition, the catalyst metal board | substrate in Embodiment 1-3 mentioned above may use the catalyst metal self-supporting board | substrate, without apply | coating a catalyst metal. Further, in the process of flowing methane gas as a carbon raw material, the temperature may be controlled to a plurality of temperatures in stages, and the methane gas may be flowed at a certain stage. For example, the temperature may be raised to 950 ° C., held for a predetermined time, then lowered to 900 ° C., and stepwise temperature control may be performed in which methane gas is allowed to flow while holding for a predetermined time. Further, a zone heated to a temperature at which the carbon source gas is decomposed may be provided further upstream of the zone for heating the catalytic metal substrate.

[Embodiment 4]
When using the graphene and the carbon molecular thin film synthesized by the synthesis method according to the first to third embodiments, they can be peeled and used as follows.

  The catalytic metal substrate on which the graphene and the carbon molecular thin film are synthesized is immersed in an acid aqueous solution (for example, dilute hydrochloric acid in which hydrochloric acid and water are mixed at a ratio of 1: 3). In the case where the catalyst metal is applied to a smooth substrate with a thickness of 300 nanometers, for example, after a while, the catalyst metal layer synthesized with graphene and the carbon molecular thin film is detached from the smooth substrate and floats on the aqueous solution surface. Come.

  In such a state where the graphene and the carbon molecular thin film are separated and then floated, an arbitrary substrate (for example, a glass substrate) to which the graphene and the carbon molecular thin film are transferred is placed in an acid aqueous solution, and the catalyst metal layer in which the graphene and the carbon molecular thin film are synthesized. Place below. Eventually, the catalytic metal is etched by the acid, and only the graphene and carbon molecular thin film layers float on the acid aqueous solution surface. The acid component can be washed away by repeatedly taking out the aqueous solution of the acid by suction and adding water instead.

  When the acid component is washed away and becomes sufficiently neutral as described above, water is sucked out and the graphene and the carbon molecular thin film are landed on the arbitrary substrate and dried. By doing in this way, it becomes possible to peel and utilize a graphene and a carbon molecule thin film from a catalyst metal. By matching the size of the container containing the aqueous solution with an arbitrary substrate to be transferred, if left unattended, water can be evaporated and transfer can be completed as it is.

  According to the method for producing graphene and carbon molecular thin film according to the present invention described above, a catalyst metal can be produced by a simple method using a catalyst metal in an amorphous state that can be prepared by a general metal coating method and is easily available. By controlling the size of the crystal grains of the layer, high-quality graphene and carbon molecular thin films having a wide uniform region on the crystal plane can be synthesized at a low cost.

  The present invention is not limited to the embodiment described above, and many variations and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious.

  The present invention can be used in the manufacturing industry of graphene and carbon molecular thin films.

  DESCRIPTION OF SYMBOLS 10 ... Catalytic metal substrate, 20 ... Electric furnace, 22 ... Sealed container, 24 ... Heater.

Claims (5)

It consists of a first step of producing catalyst metal crystal grains and a second step of synthesizing graphene and a carbon molecular thin film,
The first step is
Heating the catalyst metal under an inert gas and hydrogen gas atmosphere to raise the temperature to a first predetermined temperature;
Holding the first predetermined temperature for a first predetermined time after the temperature rise;
Lowering the temperature at a first predetermined temperature-decreasing rate that is constant in a range including a temperature range in which the catalytic metal is rearranged .
The second step is
Heating the catalyst metal under an inert gas and hydrogen gas atmosphere to raise the temperature to a second predetermined temperature;
A step of further supplying a carbon source gas over a second predetermined time after raising the temperature to the second predetermined temperature;
From the second predetermined temperature, see contains a step of cooling at a second predetermined descending rate of temperature becomes constant in a range including the temperature range in which the catalytic metal is rearranged,
By controlling the first and second predetermined temperatures and the first and second predetermined temperature-decreasing rates, a polycrystalline plane of the catalyst metal is produced, and each crystal grain of the polycrystalline plane is formed. A method of synthesizing graphene and a carbon molecular thin film , wherein the graphene and the carbon molecular thin film are synthesized on the polycrystal surface by increasing the average grain size and controlling the crystal grains in a direction in which the crystal orientations are aligned . In the second step,
Maintaining the second predetermined temperature after raising the temperature to the second predetermined temperature, and further supplying a carbon source gas over the second predetermined time;
And exhausting the carbon source gas, an inert gas and hydrogen gas atmosphere, a step of cooling by the second predetermined descending rate of temperature
The method for synthesizing graphene and carbon molecular thin film according to claim 1, comprising : Wherein the first step after executing a plurality of times, graphene and synthesis of carbon molecules thin film according to claim 1 or 2, characterized in performing said second step. Heating the catalyst metal in an inert gas and hydrogen gas atmosphere and raising the temperature to a predetermined temperature;
A step of further supplying a carbon source gas over a predetermined time after the temperature rise;
A step of lowering the temperature from the predetermined temperature at a constant temperature lowering rate within a range including a temperature range in which the catalytic metal is rearranged .
By controlling the predetermined temperature and the predetermined temperature-decreasing rate, a polycrystalline surface of the catalytic metal is produced, and the average grain size of each crystal grain of the polycrystalline surface is increased, and the crystal orientation of each crystal grain The graphene and carbon molecular thin films are synthesized on the polycrystalline surface.
A method for synthesizing graphene and a carbon molecular thin film. Maintaining the predetermined temperature after the temperature rise, and further supplying a carbon source gas over the predetermined time;
Exhausting the carbon source gas and lowering the temperature at the predetermined temperature lowering rate in an inert gas and hydrogen gas atmosphere; and
The method for synthesizing graphene and carbon molecular thin film according to claim 4 , comprising :