Method for Evaluating the Quality of Graphene

Abstract

To provide a graphene quality evaluation method, the method allowing real-time evaluation of the quality of continuously-formed graphene by using a confocal laser scanning microscope.SOLUTION: An embodiment of the present invention provides a graphene quality evaluation method by using a confocal laser scanning microscope, and the graphene quality evaluation method includes the steps of: irradiating a graphene layer formed on a catalyst layer with a laser beam; detecting a signal of light reflected from the graphene layer; forming a plane image of the graphene layer by using the detected light signal; and analyzing the contrast ratio between the catalyst layer and graphene in the plane image.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for evaluating the quality of graphene, and more specifically, to a method capable of evaluating in real time the quality of graphene continuously formed using a confocal laser scanning microscope.

Background Art

[0002] Graphene is being utilized in various industrial fields, and technologies for synthesizing high-quality graphene over a large area using chemical vapor deposition (CVD) have been continuously developed. The method for synthesizing graphene using chemical vapor deposition generally involves supplying hydrogen and hydrocarbon gases onto a copper foil heated to a high temperature in a vacuum chamber to grow graphene on the surface of the copper foil. For quality control of graphene formed by chemical vapor deposition, the quality of the synthesized graphene is screened and evaluated.

[0003] Conventionally, after transferring graphene onto a silicon oxide film with a specific thickness, the quality of the graphene was evaluated using an optical microscope or Raman spectrum. The quality evaluation method using an optical microscope directly analyzes the image of graphene on the copper foil. In particular, graphene grown on the copper foil can be analyzed through the dark field (DF) of an optical microscope utilizing Rayleigh light scattering, but this has the limitation that it can only be applied when graphene grows on a copper foil with a large height step. Also, since a DF image is formed by weak scattered light, it takes a somewhat long time, and there is a problem that a sample with graphene formed on the copper foil must be exposed to long-time illumination. On the other hand, the method for evaluating the quality of graphene using Raman spectrum takes an extremely long time and thus was not suitable as a method for evaluating large-area graphene.

[0004] Therefore, in the process of continuously synthesizing graphene over a large area, such as roll to roll, there is a current need for a technique that can evaluate the quality of graphene in real time.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem to be solved by the present invention is to provide a method for evaluating the quality of continuously formed graphene in real time.

[0006] However, the problems to be solved by the present invention are not limited to the problems described above, and other problems not described will be clearly understood by those skilled in the art from the following description.

Means for Solving the Problems

[0007] One embodiment of the present invention is a method for evaluating the quality of graphene using a confocal laser scanning microscope, comprising the steps of irradiating a laser beam onto a graphene layer formed on a catalyst layer, detecting a signal of light reflected from the graphene layer, forming a planar image of the graphene layer using the detected optical signal, and analyzing a contrast ratio between the catalyst layer and graphene in the planar image.

Advantages of the Invention

[0008] The method for evaluating the quality of graphene according to one embodiment of the present invention can evaluate the quality of continuously formed graphene in real time.

[0009] Also, the method for evaluating the quality of graphene according to one embodiment of the present invention can rapidly evaluate the quality of graphene formed over a large area.

[0010] The advantages of the present invention are not limited to the advantages described above, and advantages not described will be clearly understood by those skilled in the art from the present specification and the accompanying drawings.

Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0012] In this specification, when a certain part "includes" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components but can further include other components.

[0013] In this specification, when it is stated that a certain member is "above" another member, this includes not only the case where a certain member is in contact with another member, but also the case where there is still another member between the two members.

[0014] In this specification, the terms "step of ~" and "step of ~" do not mean "step for ~".

[0015] In this specification, the term "graphene layer" refers to a film or sheet formed by graphene in which a plurality of carbon atoms are covalently bonded to each other to form polycyclic aromatic molecules, and the carbon atoms linked by the covalent bonds form a six-membered ring as a basic repeating unit, but may further contain a five-membered ring and / or a seven-membered ring. Therefore, the "graphene layer" appears as a single layer of carbon atoms (usually sp 2 bond). The "graphene layer" can have various structures, and such structures differ depending on the content of five-membered rings and / or seven-membered rings contained in the graphene. The "graphene layer" consists of a single layer of graphene as described above, but several of these can be stacked on each other to form a plurality of layers, and a thickness of up to 100 nm can be formed.

[0016] Hereinafter, with reference to the attached drawings, specific details for implementing the present invention will be described in detail.

[0017] One embodiment of the present invention is a method for evaluating the quality of graphene using a confocal laser scanning microscope, including the steps of irradiating a laser beam onto a graphene layer formed on a catalyst layer, detecting a signal of light reflected from the graphene layer, forming a planar image of the graphene layer using the detected optical signal, and analyzing the contrast ratio between the catalyst layer and the graphene in the planar image. A method for evaluating the quality of graphene is provided.

[0018] The graphene quality evaluation method according to an embodiment of the present invention can evaluate the quality of continuously formed graphene in real time. Further, the graphene quality evaluation method according to an embodiment of the present invention can rapidly evaluate the quality of graphene formed over a large area.

[0019] According to an embodiment of the present invention, the graphene quality evaluation method can evaluate the quality of the graphene using a confocal microscope. Specifically, a confocal laser scanning microscope (CLSM) can be used. Compared with the conventional graphene quality evaluation methods using an optical microscope or Raman spectrum, the graphene quality evaluation method according to an embodiment of the present invention can rapidly evaluate the quality of graphene formed over a large area on the catalyst layer in real time by using a confocal laser scanning microscope. FIG. 1 is a conceptual diagram sequentially showing a method of manufacturing graphene using a roll to roll process. Referring to FIG. 1, the method of manufacturing graphene using a roll to roll process can include a step of synthesizing a graphene layer on a catalyst layer, a step of laminating a flexible substrate on the graphene layer to manufacture a laminate, a step of etching the catalyst layer and transferring the graphene layer to the flexible substrate, a step of patterning the graphene layer transferred to the flexible substrate into a predetermined pattern, and a step of transferring the graphene layer to a base material. The method of manufacturing graphene using the roll to roll process can use the method described in Korean Registered Patent No. 10-1300799. However, the method of manufacturing graphene using the roll to roll process is not limited thereto, and the graphene can also be manufactured by a roll to roll process used in the art.

[0020] At this time, the graphene quality evaluation method according to an embodiment of the present invention is performed during the step of synthesizing a graphene layer on the catalyst layer.

[0021] According to an embodiment of the present invention, a graphene layer can be formed on the catalyst layer. Specifically, graphene can be synthesized on the surface of the catalyst layer by using chemical vapor deposition to form a graphene layer on the surface of the catalyst layer. The method of forming a graphene layer on the catalyst layer can be adopted and used without limitation for the method of synthesizing graphene in the industry. For example, hydrogen gas and a carbon source can be supplied onto a heated catalyst layer to synthesize graphene on the catalyst layer. The carbon source can include at least one of carbon monoxide, carbon dioxide, methane, ethane, ethylene, ethanol, acetylene, propane, butane, butadiene, pentane, pentene, cyclopentadiene, hexane, cyclohexane, benzene, and toluene, but the type of the carbon source is not limited.

[0022] According to an embodiment of the present invention, the catalyst layer can include at least one of Cu, Ni, Co, Fe, Pt, Au, Al, Cr, Mg, Mn, Mo, Rh, Si, Ta, Ti, W, U, V, Zr, Fe, brass, bronze, cupronickel, stainless steel, and Ge. The catalyst layer may be a metal catalyst layer for graphene synthesis, or an appropriate catalyst layer can be selected in consideration of the synthesis conditions of graphene.

[0023] According to an embodiment of the present invention, the catalyst layer is provided as a thin film or a thick film. Specifically, the thickness of the catalyst layer may be 1 nm or more and 1,000 nm or less, 1 nm or more and 500 nm or less, or 1 nm or more and 300 nm or less. Also, the thickness of the catalyst layer may be 1 μm or more and 1,000 μm or less, 1 μm or more and 500 μm or less, 1 μm or more and 100 μm or less, or 1 μm or more and 50 μm or less. Further, the thickness of the catalyst layer may be 1 mm or more and 5 mm or less. However, the thickness of the catalyst layer is not limited, and the thickness of the catalyst layer can be set in consideration of the synthesis conditions of the graphene layer, the use of the graphene layer, and the like.

[0024] According to an embodiment of the present invention, the chemical vapor deposition method is performed at a temperature of 700 °C or higher. Specifically, the chemical vapor deposition method is performed at a temperature of 750 °C or higher, 800 °C or higher, 850 °C or higher, 900 °C or higher, or 1,000 °C or higher. Further, the chemical vapor deposition method is performed at a temperature of 2,000 °C or lower, 1,900 °C or lower, 1,800 °C or lower, 1,700 °C or lower, 1,600 °C or lower, or 1,500 °C or lower. The temperature at which the chemical vapor deposition method is performed can be set according to the type of the substance forming the catalyst layer. Specifically, it can be set in consideration of the melting point of the substance forming the catalyst layer. For example, when forming the catalyst layer using copper, the chemical vapor deposition method is performed at a temperature of 1,000 °C or higher and 1,085 °C or lower. Further, when forming the catalyst layer using nickel, the chemical vapor deposition method is performed at a temperature of 750 °C or higher and 850 °C or lower. Furthermore, when forming the catalyst layer using palladium, the chemical vapor deposition method is performed at a temperature of 950 °C or higher and 1,050 °C or lower.

[0025] When the temperature at which the chemical vapor deposition method is performed is within the above-described range, the graphene layer can be stably formed on the catalyst layer, and the crystallinity of the synthesized graphene can be excellent. That is, by setting the temperature at which the chemical vapor deposition method is performed in consideration of the melting point of the substance used to form the catalyst layer, the graphene layer can be stably formed on the catalyst layer, and the crystallinity of the synthesized graphene can be further improved.

[0026] Also, the temperature at which the chemical vapor deposition (CVD) is performed can be derived by the quality evaluation method of the graphene. For example, the graphene layer can be formed on the catalyst layer while varying the temperature at which the CVD is performed, and the quality of the graphene synthesized according to the temperature at which the CVD is performed can be evaluated using the quality evaluation method of the graphene. Further, using the quality evaluation method of the graphene, it is also possible to derive a suitable CVD execution temperature according to conditions such as the type of the catalyst layer, the thickness of the catalyst layer, the type of the carbonization source, the amount of the carbonization source supplied, and the synthesis time of the graphene. Thereby, before manufacturing the graphene, it is possible to preset an appropriate CVD execution temperature in consideration of conditions such as those adjusted in the manufacturing process of the graphene.

[0027] According to one embodiment of the present invention, the graphene is continuously formed on the catalyst layer in a roll-to-roll process. In order to form the graphene layer by the roll-to-roll process, the catalyst layer is provided in a roll form. Specifically, the catalyst layer is provided in the form of a metal foil having flexibility suitable for use in the roll-to-roll process. For example, the catalyst layer of the wound metal foil can be unwound, and the graphene layer can be formed on the unwound catalyst layer using the chemical vapor deposition method.

[0028] FIG. 2 is a diagram showing a method for evaluating the quality of graphene using a confocal laser scanning microscope according to one embodiment of the present invention. Referring to FIG. 2, the confocal laser scanning microscope may include a light source 10, a beam scanner 20, a relay lens 30, a beam splitter 40, an objective lens 50, a tube lens 60, a camera 70, a collimator 80, and a photodetector 90. However, the configuration included in the confocal laser scanning microscope is not limited to the above-mentioned ones, and the configuration included in the confocal laser scanning microscope used in the art may be additionally included. For example, the confocal laser scanning microscope may further include a filter, a polarizing plate, and the like.

[0029] According to an embodiment of the present invention, a graphene layer formed on a catalyst layer can be irradiated with a laser beam. Referring to FIG. 2, the laser beam emitted from the light source 10 included in the confocal laser scanning microscope is reflected by the beam scanner 20 and irradiated onto the graphene layer GL through the relay lens 30, the first beam splitter 41, and the objective lens 50.

[0030] According to an embodiment of the present invention, the light source 10 is a light source capable of emitting a laser beam, and a laser light source used in the art can be used without limitation. At this time, the light source 10 can adjust the wavelength value of the emitted laser beam. The light emitted from the light source 10 is irradiated onto the beam scanner 20 through the optical fiber 11.

[0031] According to an embodiment of the present invention, the laser beam is irradiated with a wavelength value of 400 nm or more and 550 nm or less. That is, the light source can irradiate a laser beam having a wavelength value of 400 nm or more and 550 nm or less. Specifically, the wavelength value of the laser beam may be 400 nm or more and 545 nm or less, 400 nm or more and 520 nm or less, 400 nm or more and 500 nm or less, or 400 nm or more and 490 nm or less. When the wavelength value of the laser beam is within the above range, the catalyst layer and the graphene can be clearly distinguished in the planar image of the graphene layer described later. Thereby, the contrast ratio between the catalyst layer and the graphene in the planar image can be effectively analyzed.

[0032] According to an embodiment of the present invention, the beam scanner 20 may be configured to scan the surface position of the graphene layer GL on the focal plane of the objective lens 50. The beam scanner 20 can include at least one of a resonant scanning mirror and a galvano mirror. Specifically, the beam scanner 20 can include a galvano mirror. The laser light emitted from the light source 10 is irradiated to different positions on the surface of the graphene layer GL by the beam scanner 20. Specifically, the beam scanner 20 can two-dimensionally scan the graphene layer GL by changing the position of the graphene layer GL where the laser light passing through the objective lens 50 is irradiated.

[0033] Further, the beam scanner 20 can further include a uniaxial scanner capable of axial scanning. By further including the uniaxial scanner, it is also possible to three-dimensionally scan the focal point within the space of the test piece without moving the objective lens. At this time, the additional uniaxial scanner can be realized using electronic or mechanical focus modulation.

[0034] According to an embodiment of the present invention, the laser light reflected by the beam scanner 20 is irradiated to the relay lens 30. The relay lens 30 can include a first relay lens 31 and a second relay lens 32. The relay lens 30 can have a predetermined magnification, and the magnification of the relay lens 30 can be adjusted by adjusting the first and second relay lenses 31, 32.

[0035] According to an embodiment of the present invention, the laser light that has passed through the relay lens 30 sequentially passes through the first beam splitter 41 and the objective lens 50 and is irradiated onto the graphene layer GL. Specifically, the object irradiated with the laser light may be a graphene layer GL formed by synthesizing graphene on a part of the surface of the catalyst layer CL. The graphene layer GL may not completely cover the surface of the catalyst layer CL and may expose a part of the catalyst layer CL. That is, the laser light is irradiated onto a composite including the catalyst layer GL and the graphene layer GL formed on a part of the surface of the catalyst layer CL. Specific details regarding this will be described later.

[0036] According to an embodiment of the present invention, the laser light (hereinafter referred to as reflected light) reflected from the graphene layer (for example, the composite) can pass through the objective lens 50 again and flow into the first beam splitter 41. The reflected light that has flowed into the first beam splitter 41 is split into two or more lights, and one of these lights can flow into the tube lens 60.

[0037] According to an embodiment of the present invention, the tube lens 60 can include a pinhole, and the pinhole corresponds to a configuration for forming a confocal point. The pinhole included in the tube lens 60 can be adjusted to be opened or closed.

[0038] According to an embodiment of the present invention, the light that has passed through the tube lens 60 flows into the second beam splitter 42 and is split into two or more lights. Referring to FIG. 2, a part of the light split by the second beam splitter 42 flows into the collimator 80, and another part can also flow into the camera 70. At this time, the camera 70 may be a CCD camera. The collimator 80 can receive the light split by the second beam splitter 42 and convert it into parallel light.

[0039] According to an embodiment of the present invention, it is possible to detect the optical signal of the light reflected from the graphene layer GL. As described above, the light reflected from the graphene layer GL can pass through the objective lens 50, the first beam splitter 41, the tube lens 60, the second beam splitter 42, and the collimator 80 and flow into the photodetector 90. The photodetector 60 can detect the signal of the reflected light. The photodetector 60 can include a photodiode, and a signal can be detected from the incident light using the photodiode. Specifically, the photodiode can detect the intensity of the incident light and convert it into an electric current. A photomultiplier tube can be used as the photodetector 60.

[0040] According to an embodiment of the present invention, a planar image of the graphene layer can be formed using the detected optical signal. The planar image of the graphene layer may be a planar image of the surface of the graphene layer. Specifically, the planar image can include an image of a graphene layer portion formed on a part of the surface of the catalyst layer and an image of a portion of the catalyst layer exposed without graphene synthesis.

[0041] According to an embodiment of the present invention, the detected optical signal can be provided to an image former provided in the confocal laser scanning microscope or provided externally to form a planar image of the graphene layer. The type of the image former is not particularly limited, and any device equipped with software capable of forming an image using an electric current in the art can be used without limitation.

[0042] According to an embodiment of the present invention, the contrast ratio between the catalyst layer and the graphene in the planar image can be analyzed. By a simple method of analyzing the contrast ratio between the catalyst layer and the graphene in the planar image, the quality of the graphene can be analyzed quickly and effectively.

[0043] According to an embodiment of the present invention, the step of analyzing the contrast ratio may include analyzing the gray scale of a predetermined region of the planar image to calculate the contrast ratio between the catalyst layer and the graphene in the region. Specifically, the analysis of the gray scale may be to obtain and analyze a gray scale histogram or a gray scale profile in the region. A predetermined region can be selected from the planar image, and a gray scale histogram or a gray scale profile can be obtained based on the gray scale of the catalyst layer and the graphene in the selected predetermined region. By analyzing the obtained gray scale histogram or gray scale profile, the contrast ratio between the catalyst layer and the graphene can finally be calculated.

[0044] According to an embodiment of the present invention, the gray scale profile can be obtained in the form of a line profile of the gray scale. When using a gray scale histogram to analyze a small-sized region, it may be difficult to distinguish the graphene peak and the catalyst layer peak because the peaks in the gray scale histogram are formed small. In this case, by using a gray scale profile instead of a gray scale histogram, the contrast ratio between the catalyst layer and the graphene in a small-scale region can be effectively analyzed.

[0045] According to an embodiment of the present invention, the method for evaluating the quality of the graphene can evaluate the quality of the graphene continuously formed on the catalyst layer in real time by a roll-to-roll process. Specifically, during the process of continuously forming graphene using a roll-to-roll process to which chemical vapor deposition is applied, the quality of the graphene synthesized in real time can be evaluated.

[0046] According to an embodiment of the present invention, the method for evaluating the quality of the graphene is performed in real time during the continuous formation of the graphene. Specifically, the method for evaluating the quality of the graphene is performed before the graphene layer is completely formed on the catalyst layer. That is, before the synthesized graphene covers the entire surface of the catalyst layer, the graphene layer can be irradiated with laser light to evaluate the quality of the graphene as described above. When the graphene layer is formed on the entire surface of the catalyst layer, only the graphene layer appears in the planar image, so the contrast ratio between the catalyst layer and the graphene cannot be analyzed.

[0047] According to an embodiment of the present invention, laser light can be irradiated onto a graphene layer formed with a coverage rate of the graphene per unit area of the catalyst layer of 30% or more and 99% or less. Specifically, the coverage rate of the graphene layer irradiated with laser light may be 30% or more and 95% or less, 30% or more and 90% or less, 30% or more and 85% or less, 30% or more and 80% or less, 35% or more and 75% or less, 45% or more and 70% or less, 50% or more and 65% or less, 30% or more and 75% or less, or 70% or more and 99% or less.

[0048] The coverage rate of the graphene is calculated by the following formula 1. [Formula 1] Coverage rate (%) = Total area of graphene layer per unit area of catalyst layer / Unit area of catalyst layer

[0049] When laser light is irradiated onto a graphene layer that satisfies the above-described range of the coverage rate of the graphene to obtain a planar image of the graphene layer, the contrast ratio between the catalyst layer and the graphene in the planar image can be effectively analyzed.

[0050] Also, according to one embodiment of the present invention, a graphene layer formed with a coverage rate of the graphene per unit area of the catalyst layer of 0.5% or more and less than 30% can be irradiated with a laser beam. When irradiating a graphene layer with a coverage rate of the graphene satisfying the above-described range with a laser beam to obtain a planar image of the graphene layer, the form of the seed of the graphene layer and / or the form in which the graphene layer grows in the planar image can be effectively analyzed.

[0051] The unit area of the catalyst layer is 10 μm 2 or more and 10,000 μm 2 or less. However, the unit area range of the catalyst layer for deriving the coverage rate of the graphene layer is not limited to the above-described range.

[0052] According to one embodiment of the present invention, the confocal laser scanning microscope can operate without a pinhole. As confirmed from the examples described later, when operating the confocal laser scanning microscope, there was no difference in the obtained planar image between the case where a pinhole is provided and the case where no pinhole is provided. That is, when evaluating the quality of the graphene, the step of setting a pinhole to form a confocal can be omitted. Thereby, the execution time and the difficulty of execution of the graphene quality evaluation method can be effectively reduced.

[0053] According to one embodiment of the present invention, the graphene quality evaluation method can evaluate the crystallinity of the graphene synthesized on the catalyst layer by analyzing the contrast ratio between the catalyst layer and the graphene. The contrast ratio between the catalyst layer and the graphene is affected by the defects of the synthesized graphene. The better the crystallinity of the synthesized graphene, the larger the contrast ratio. Also, the better the crystallinity of the synthesized graphene, the more the carrier mobility of the graphene can be increased. That is, by analyzing the contrast ratio between the catalyst layer and the graphene from the planar image of the graphene layer synthesized on the catalyst layer, the quality of the finally produced graphene can be predicted.

[0054] According to one embodiment of the present invention, the graphene quality evaluation method can further include a step of determining that the graphene layer is formed on the catalyst layer when the contrast ratio between the catalyst layer and the graphene is 1.05 or more. Specifically, when the contrast ratio between the catalyst layer and the graphene is 1.05 or more, it can be confirmed that graphene is formed on the catalyst layer and a graphene layer is produced.

[0055] On the other hand, when the contrast ratio between the catalyst layer and the graphene is 1.10 or more, or 1.15 or more, the quality of the graphene layer can be determined as good. Also, when the contrast ratio between the catalyst layer and the graphene is 1.5 or less, 1.45 or less, 1.4 or less, 1.35 or less, or 1.3 or less, the quality of the graphene layer can be determined as good. As described above, the higher the contrast ratio between the catalyst layer and the graphene, the higher quality graphene should be produced. Therefore, considering the use of the produced graphene and the like, the numerical value of the contrast ratio for determining the produced graphene as good can be changed. For example, depending on the physical properties required by the customer, even when the contrast ratio between the catalyst layer and the graphene is less than 1.05, it can be determined as good.

[0056] According to an embodiment of the present invention, in the process of continuously forming the graphene layer on the catalyst layer, the contrast ratio between the catalyst layer and the graphene is calculated, the carrier mobility of the produced graphene is evaluated, the quality of the graphene corresponding to the contrast ratio is stored in a database, and the numerical value of the contrast ratio for determining the produced graphene as defective can be set by using the constructed database.

[0057] According to an embodiment of the present invention, the method for evaluating the quality of the graphene may further include the step of post-processing the graphene determined to be defective. As described above, in the process of continuously forming the graphene layer on the catalyst layer, the graphene layer portion determined to be defective by calculating the contrast ratio between the catalyst layer and the graphene is post-processable. For example, after recovering the composite portion including the graphene layer portion determined to be defective and excluding it from the continuous process, a new graphene layer can be formed on the graphene layer determined to be defective. Thereby, the graphene layer determined to be defective can be excluded in advance before performing the subsequent process of the roll-to-roll process, and the manufacturing efficiency of the graphene using the roll-to-roll process can be further improved. In addition, since the graphene layer determined to be defective can be recovered in the graphene synthesis step and remanufactured into a good-quality graphene layer, the manufacturing cost of the graphene can be reduced.

[0058] Hereinafter, the present invention will be specifically described with reference to examples in detail. However, the examples according to the present invention can be deformed into various different forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples in this specification are provided to more fully explain the present invention to those with average knowledge in the industry.

[0059] Hereinafter, the present invention will be specifically described with reference to examples in detail.

[0060] Example 1 Graphene was synthesized on a copper foil (purity 99.7%) with a thickness of 25 μm using chemical vapor deposition (CVD). Specifically, a mixed gas of hydrogen and methane gas (H2 5 sccm / CH4 80 sccm) was injected into a quartz tube furnace containing the copper foil, heated to a temperature of 1,000 °C under a pressure of 30 mTorr, and then the copper foil was annealed for 30 minutes in a hydrogen atmosphere to form a graphene layer on the copper foil and produce a test piece for photography. At this time, the injection time of the mixed gas (graphene synthesis time) was about 13 minutes.

[0061] The test piece for photography was excited using an Ar laser with an excitation power of 120 mW, a wavelength value of 514 nm, and a spot size of 1 μm. +

[0062] A planar image of the test piece was obtained using the reflection mode of a confocal laser scanning microscope (Carl Zeiss, LSM710). Specifically, an objective lens with a magnification of x100 (N.A = 1.30) was used, and the test piece was loaded onto a stage covered with a glass microscope slide. The distance between the surface of the test piece and the objective lens was adjusted to compensate for different focal lengths with different chromatic aberrations, the pinhole was opened, and the confocal laser scanning microscope was operated.

[0063] At this time, the surface of the test piece was irradiated with a laser beam having a wavelength value of 405 nm, and the signal of the light reflected from the surface of the test piece was detected to obtain a planar image of the test piece. At this time, a planar image file was extracted and analyzed by ZEN (black edition) and ZEN (blue edition) programs, and additionally analyzed using adobe Photoshop CC2018.

[0064] Example 2 A planar image of the test piece was obtained using the reflection mode of a confocal laser scanning microscope in the same manner as in Example 1, except that the injection time of the mixed gas was set to 10 minutes during the synthesis of the graphene.

[0065] ​ Example 3 In the same manner as in Example 1, a planar image of the test piece was obtained using the reflection mode of a confocal laser scanning microscope.

[0066] Thereafter, a predetermined region was selected from the obtained planar image, and the gray scale in the region was analyzed using LSM 710 ZEN software (Carl Zeiss) to create a gray scale histogram. Thereafter, the contrast ratio between the copper foil and graphene in the region was calculated from the gray scale histogram using the ratio of the peak points of the histogram.

[0067] Example 4 A planar image of the test piece, a gray scale histogram, and a contrast ratio were obtained in the same manner as in Example 3, except that the wavelength value of the laser light irradiated on the surface of the test piece in Example 3 was adjusted to 488 nm.

[0068] Example 5 A planar image of the test piece, a gray scale histogram, and a contrast ratio were obtained in the same manner as in Example 3, except that the wavelength value of the laser light irradiated on the surface of the test piece in Example 3 was adjusted to 543 nm.

[0069] Example 6 A planar image of the test piece was obtained using the reflection mode of a confocal laser scanning microscope in the same manner as in Example 1, except that the synthesis temperature of the graphene in Example 1 was set to 700 °C to produce the test piece for photographing.

[0070] Thereafter, a predetermined region was selected from the obtained planar image, the planar image file was extracted and analyzed using the ZEN (black edition) and ZEN (blue edition) programs, and additionally, the grayscale in the region was analyzed using Adobe Photoshop CC2018 to create a line profile of grayscale (LINE PROFILE OF GRAYSCALE). The ratio between the grayscale at the upper end and the lower end of the peak that appeared in the created line profile of grayscale was calculated to obtain the contrast ratio between copper and graphene in the region.

[0071] Also, using a Renishaw micro-Raman spectroscopy system, the Raman spectrum of the test piece was obtained. From the obtained Raman spectrum, the full width of half maximum (FWHM) of 2D and the intensity ratio of D / G were extracted.

[0072] Example 7 Except that the synthesis temperature of the graphene was set to 800 °C in Example 1, the test piece for photographing was manufactured in the same manner as in Example 1.

[0073] Thereafter, in the same manner as in Example 6, a planar image of the test piece, a line profile of grayscale, and a contrast ratio were obtained. Also, in the same manner as in Example 6, a Raman spectrum of the test piece, the full width of half maximum of 2D, and the intensity ratio of D / G were obtained.

[0074] Example 8 The test piece for photographing was manufactured in the same manner as in Example 1.

[0075] Thereafter, in the same manner as in Example 6, a planar image of the test piece, a line profile of grayscale, and a contrast ratio were obtained. Also, in the same manner as in Example 6, a Raman spectrum of the test piece, the full width of half maximum of 2D, and the intensity ratio of D / G were obtained.

[0076] Example 9 A planar image of the test piece was obtained using the reflection mode of a confocal laser scanning microscope in the same manner as in Example 1, except that the pinhole was closed in Example 1.

[0077] Example 10 The test piece for imaging was manufactured in the same manner as in Example 1, except that the injection time of the mixed gas was set to about 12 minutes during the synthesis of the graphene.

[0078] Thereafter, a planar image, a grayscale histogram, and a contrast ratio of the test piece were obtained in the same manner as in Example 3. Also, a Raman spectrum of the test piece was obtained in the same manner as in Example 6.

[0079] Example 11 A graphene layer was formed on a copper foil in the same manner as in Example 1. Thereafter, using an SNTEK RIE etching apparatus, nitrogen plasma was irradiated onto the graphene surface on the copper for 5 seconds in a nitrogen (purity 99.999%) atmosphere of 120 mTorr to dope nitrogen into the graphene layer and manufacture a test piece for imaging.

[0080] Thereafter, a planar image, a grayscale histogram, and a contrast ratio of the test piece were obtained in the same manner as in Example 3, except that the pinhole was opened and the wavelength value of the laser light irradiated onto the surface of the test piece was adjusted to 405 nm. Also, a Raman spectrum of the test piece was obtained in the same manner as in Example 6. Furthermore, an N1s XPS peak was obtained by measuring the short wavelength of aluminum X-ray with a Thermo scientific sigma probe ESCA spectrometer.

[0081] Reference Example 1 An AFM image was obtained in the test piece region divided by the red box in (3) of FIG. 3 below using an AFM (Park system, XE-100 model). At this time, the size of the region divided by the red box was 10×10 μm. 2That is, the AFM (atomic force microscope) was set under the condition that the scanning rate was 0.3 Hz in the non-contact mode.

[0082] Reference Examples 2 to 5 In Example 1, except that a nickel foil was used instead of the copper foil as the catalyst layer and the temperature during graphene synthesis using the chemical vapor deposition method was adjusted to 835 °C, a test piece for photography was manufactured in the same manner as in Example 1.

[0083] Thereafter, except that a laser beam having a wavelength value of 405 nm in Reference Example 2, 488 nm in Reference Example 3, 543 nm in Reference Example 4, and 633 nm in Reference Example 5 was irradiated onto the surface of the test piece, a planar image of the test piece was obtained using the reflection mode of a confocal laser scanning microscope in the same manner as in Example 1.

[0084] Reference Examples 6 to 9 In Example 1, except that a palladium foil was used instead of the copper foil as the catalyst layer and the temperature during graphene synthesis using the chemical vapor deposition method was adjusted to 1,000 °C, a test piece for photography was manufactured in the same manner as in Example 1.

[0085] Thereafter, except that a laser beam having a wavelength value of 405 nm in Reference Example 6, 488 nm in Reference Example 7, 543 nm in Reference Example 8, and 633 nm in Reference Example 9 was irradiated onto the surface of the test piece, a planar image of the test piece was obtained using the reflection mode of a confocal laser scanning microscope in the same manner as in Example 1.

[0086] Comparative Example 1 A test piece for photography was manufactured in the same manner as in Example 1, and a bright-field image of the test piece was obtained using the bright-field mode of an optical microscope (Olympus CX41).

[0087] Comparative Example 2 A test piece for photography was manufactured in the same manner as in Example 1, and a dark-field image of the test piece was obtained using the dark field mode of an optical microscope (Olympus CX41).

[0088] Comparative Example 3 A planar image of the test piece was obtained in the same manner as in Example 1, except that the injection time of the mixed gas was set to 30 minutes and the synthesis time of graphene was adjusted to 30 minutes during the synthesis of graphene in Example 1, using the reflection mode of a confocal laser scanning microscope.

[0089] Comparative Example 4 A planar image, a grayscale histogram, and a contrast ratio of the test piece were obtained in the same manner as in Example 3, except that the wavelength value of the laser light irradiated on the surface of the test piece was adjusted to 633 nm in Example 3.

[0090] Experimental Example 1: Comparison of Planar Images of Graphene Layers FIG. 3 is a diagram showing an image taken using an optical microscope and an image taken using a confocal laser scanning microscope for the same region of a test piece. Specifically, (1) in FIG. 3 is an image of the test piece taken using the bright field mode of an optical microscope according to Comparative Example 1, (2) in FIG. 3 is an image of the test piece taken using the dark field mode of an optical microscope according to Comparative Example 2, and (3) in FIG. 3 is an image obtained using the reflection mode of a confocal laser scanning microscope according to Example 1. The length of the scale bar in (1) to (3) of FIG. 3 corresponds to 10 μm.

[0091] Referring to FIG. 3, it can be seen that it is difficult to distinguish the graphene synthesized with the copper foil of the catalyst layer in the bright field image and the dark field image of the test piece taken using an optical microscope. Referring to (1) in FIG. 3, it can be seen that in the bright field image of the optical microscope, the graphene partially grown on the copper foil is hardly distinguishable from the non-oxidized copper.

[0092] On the one hand, referring to (2) of FIG. 3, in the dark-field image of the optical microscope, the edge portion of graphene is emphasized and appears, and the grain boundary of copper and the protruding surface appear brightly due to Rayleigh scattering, indicating that it is difficult to distinguish between the copper foil and graphene.

[0093] On the other hand, referring to (3) of FIG. 3, in the image obtained using the reflection mode of the confocal laser scanning microscope, the synthesized graphene appears brightly and the copper foil appears darkly, indicating that the distinction is clear.

[0094] That is, in the image taken using the conventional optical microscope for the same test piece, it is difficult to distinguish between the catalyst layer and the synthesized graphene, but it was confirmed that they are clearly distinguishable in the image taken using the confocal laser scanning microscope according to an embodiment of the present invention.

[0095] FIG. 4 is a graph showing an AFM image and a depth gradient in the test piece region demarcated by the red box in (3) of FIG. 3. Specifically, (1) of FIG. 4 is an AFM image in the test piece region demarcated by the red box in (3) of FIG. 3 obtained according to Reference Example 1, and (2) of FIG. 4 is a graph showing the depth gradient of copper and graphene in the portion corresponding to the red dotted line in (1) of FIG. 4.

[0096] Referring to FIG. 4, the morphology of the surface of the test piece and the depth gradient in that portion can be carefully confirmed using AFM. Also, referring to (3) of FIG. 3, the morphology of the partially grown graphene can be roughly confirmed from the image obtained using the reflection mode of the confocal laser scanning microscope, and it was confirmed that this is similar to the morphology of the surface of the test piece in the AFM image shown in FIG. 4.

[0097] Experimental Example 2: Analysis of Planar Images of Graphene Layers According to Graphene Synthesis Time FIG. 5 is a diagram showing images taken using a confocal laser scanning microscope of test pieces manufactured with different graphene synthesis times. Specifically, (1) in FIG. 5 is an image obtained using the reflection mode of a confocal laser scanning microscope for a test piece in which the graphene synthesis time was adjusted to 10 minutes according to Example 2, (2) in FIG. 5 is an image obtained using the reflection mode of a confocal laser scanning microscope for a test piece in which the graphene synthesis time was adjusted to 13 minutes according to Example 1, and (3) in FIG. 5 is an image obtained using the reflection mode of a confocal laser scanning microscope for a test piece in which the graphene synthesis time was adjusted to 30 minutes according to Comparative Example 3. The length of the scale bar in (1) to (3) of FIG. 5 corresponds to 10 μm.

[0098] Referring to FIG. 5, it can be seen that as the graphene synthesis time increases, the area of graphene covering the surface of the copper foil increases. Referring to (1) in FIG. 5, in the case of Example 2, it was confirmed that graphene appeared brightly, the copper foil appeared darkly, and the contrast was clear. Also, referring to (2) in FIG. 5, in the case of Example 1, although graphene was synthesized on many parts of the copper foil surface, it was confirmed that the contrast between the darkly appearing copper foil and the brightly appearing graphene was possible. In contrast, referring to (3) in FIG. 5, in the case of Comparative Example 3 where the graphene synthesis time was 30 minutes, it was confirmed that graphene was synthesized over the entire surface of the copper foil and the contrast between the copper foil and graphene was impossible.

[0099] Experimental Example 3: Analysis of Contrast Ratio between Catalyst Layer and Graphene According to Wavelength Value of Laser Light FIG. 6 is a diagram showing a planar image of a test piece taken by a confocal laser scanning microscope with different wavelength values of the laser light irradiated to the test piece and a grayscale histogram obtained thereby. The length of the scale bar in the CLSM image of FIG. 6 corresponds to 10 μm.

[0100] Specifically, FIG. 6 shows the planar images (CLSM IMAGE) of the test pieces obtained in Examples 3 to 5 and Comparative Example 4, in which the wavelength values of the laser light irradiated to the same test piece were varied. Further, FIG. 6 shows the grayscale histograms (GRAYSCALE HISTOGRAM) created by analyzing the grayscale in the regions indicated by the red boxes in the respective planar images. In the grayscale histogram, the black Gaussian curve corresponds to copper, and the red Gaussian curve corresponds to graphene.

[0101] Referring to FIG. 6, it can be confirmed that the contrast ratios between copper and graphene in the planar images obtained according to the wavelength values of the laser light irradiated to the same test piece are different. Specifically, in the case of Comparative Example 4 where the wavelength value of the laser light irradiated to the test piece is 633 nm, copper and graphene are not distinguishable in the planar image, and it was confirmed that the Gaussian curve of copper and the Gaussian curve of graphene overlap also on the grayscale histogram.

[0102] On the other hand, in the case of Examples 3 to 5 where the wavelength value of the laser light irradiated to the test piece satisfies the range of 400 nm or more and 550 nm or less, copper and graphene are distinguishable in the planar image, and it can be confirmed that the Gaussian curve of copper and the Gaussian curve of graphene are also distinguishable on the grayscale histogram. In particular, it was confirmed that copper and graphene are more clearly distinguishable in Examples 3 and 4, and that copper and graphene are most clearly distinguishable in Example 3.

[0103] FIG. 7 is a graph showing the contrast ratios between copper and graphene calculated in Examples 3 to 5 and Comparative Example 4 and the contrast ratios calculated by applying the theory. Specifically, FIG. 7 shows the values of the contrast ratios between copper and graphene calculated based on the grayscale histograms shown in FIG. 6. Further, FIG. 7 also shows the contrast ratio values between copper and graphene theoretically calculated according to the wavelength value of the laser irradiated to the test piece.

[0104] Referring to FIG. 7, it was confirmed that the contrast ratio of copper to graphene in Example 3 was 1.260, the contrast ratio of copper to graphene in Example 4 was 1.116, the contrast ratio of copper to graphene in Example 5 was 1.057, and the contrast ratio of copper to graphene in Comparative Example 4 was 1.025.

[0105] That is, in Examples 3 to 5 where the wavelength value range of the laser irradiated to the test piece is adjusted to 400 nm or more and 550 nm or less according to an embodiment of the present invention, the contrast ratio of copper, which is the catalyst layer, to graphene is 1.05 or more, and it can be seen that the quality of graphene formed on the catalyst layer can be effectively evaluated. On the other hand, in the case of Comparative Example 4 where the wavelength value of the laser irradiated to the test piece is 633 nm, it was confirmed that the contrast ratio of copper to graphene is less than 1.05 and it is difficult to separately analyze copper and graphene.

[0106] The theoretical contrast ratio values of copper and graphene shown in FIG. 7 were calculated by the following method.

[0107] FIG. 8 is a diagram schematically showing the conditions set for calculating the theoretical contrast ratio values of graphene and copper.

[0108] As shown in FIG. 8, in order to calculate the theoretical contrast ratio values of graphene and copper, the copper and graphene layers were assumed to be independent layers. The Fresnel’s interference formula was applied to calculate the optical contrast ratio of copper and graphene.

[0109]

Equation

[0110] Also, when the wavelength of the laser light irradiated on the test piece is 405 nm, the refractive index of copper is set to 1.3009 + i2.1595, when the wavelength of the laser light is 488 nm, the refractive index of copper is set to 1.2297 + i2.5379, when the wavelength of the laser light is 543 nm, the refractive index of copper is set to 1.0523 + i2.5833, and when the wavelength of the laser light is 633 nm, the refractive index of copper is set to 0.26965 + i3.4106.

[0111]

Number

[0112] At wavelengths less than 400 nm, strong carrier-carrier interactions result in Van Hove singularities in the electronic joint density. Therefore, the approximation is only applicable in the visible spectrum (E < 3.1 eV) or below.

[0113] When the electronic temperature value is lower than the chemical potential (e.g., T / μ → 0), due to intraband and interband contributions, the optical conductivity is similar to Drude (σ = σ intraband +σ interband ). σ intraband and σ interband are as follows.

[0114]

Equation

Equation

[0115]

Equation

Equation

Equation

[0116] FIG. 9 is a graph showing the optical conductivity of graphene calculated by Equation 4 and Equation 5. Specifically, FIG. 9 shows the value of the actual optical conductivity of graphene synthesized on copper calculated by Equation 4 and the value of the virtual optical conductivity of graphene synthesized on copper calculated by Equation 5 when irradiated with laser light having a wavelength value of 405 nm to 633 nm.

[0117] Using Equation 4 and Equation 5, the reflection contrast ratio between graphene synthesized on copper and copper was calculated. When the wavelength of the laser light irradiated on the test piece is 405 nm, the contrast ratio between graphene and copper is calculated to be 1.447. When the wavelength of the laser light is 488 nm, the contrast ratio is calculated to be 1.326. When the wavelength of the laser light is 543 nm, the contrast ratio is calculated to be 1.277. When the wavelength of the laser light is 633 nm, the contrast ratio is calculated to be 1.043.

[0118] As shown in FIG. 7, since the tendency of the contrast ratio between copper and graphene calculated by applying the theory is similar to the tendency of the actual contrast ratio measured in Examples 3 to 5 and Comparative Example 4, it was confirmed that the contrast ratio value between copper and graphene calculated by applying the theory is reasonable.

[0119] On the other hand, referring to FIG. 7, it was confirmed that there is a slight difference between the contrast ratio measured in Examples 3 to 5 and the contrast ratio calculated by applying the theory. This is judged to be due to the generation of some atomic defects and tensile strain in the synthesized graphene due to the different thermal expansion coefficients of graphene and copper, resulting in an optical conductivity lower than the ideal value.

[0120] Experimental Example 4: Analysis of Contrast Ratio and Carrier Mobility of Graphene According to Graphene Synthesis Temperature Figure 10 is a diagram showing a planar image of a test piece photographed by a confocal laser scanning microscope for graphene produced with different synthesis temperatures and a grayscale line profile obtained thereby.

[0121] Specifically, Figure 10 shows planar images of test pieces photographed by a confocal laser scanning microscope for graphene produced in Example 6 where the synthesis temperature of graphene is 700 °C, Example 7 where the synthesis temperature of graphene is 800 °C, and Example 8 where the synthesis temperature of graphene is 1,000 °C. Further, Figure 10 shows a grayscale line profile (LINE PROFILE OF GRAYSCALE) created by analyzing the grayscale in the region indicated by the red box in each planar image.

[0122] Referring to Figure 10, the ratio of the grayscale at the upper end to the grayscale at the lower end of the peak appearing in the grayscale line profiles of Example 6, Example 7, and Example 8 was calculated to obtain the contrast ratio between copper and graphene in the region. At this time, the upper end and the lower end of the peak are pointed in an inverted triangle in the grayscale line profile of Figure 10.

[0123] Referring to Figure 10, the contrast ratio between copper, which is the catalyst layer in Example 6, and graphene was 1.10, the contrast ratio in Example 7 was 1.24, and the contrast ratio in Example 8 was 1.28. It was confirmed that the contrast ratio between copper and graphene increases as the synthesis temperature of graphene increases. In particular, it was confirmed that when the synthesis temperature of graphene is 800 °C or higher, the contrast ratio between copper and graphene is 1.20 or higher.

[0124] Figure 11 is a graph showing the Raman spectra, full-width at half-maximum, and D / G intensity ratio of graphene produced in Example 6, Example 7, and Example 8 of the present invention. Specifically, (1) in Figure 11 shows the Raman spectra of graphene produced in Example 6 where the synthesis temperature of graphene is 700 °C, Example 7 where the synthesis temperature of graphene is 800 °C, and Example 8 where the synthesis temperature of graphene is 1,000 °C. (2) in Figure 11 shows the full-width at half-maximum of 2D and D / G of graphene extracted from the Raman spectra obtained in Example 6, Example 7, and Example 8.

[0125] Referring to Figure 11, it was confirmed that as the synthesis temperature of graphene increases, the full-width at half-maximum of 2D and the D / G intensity ratio of graphene decrease.

[0126] The carrier mobility of the synthesized graphene is closely related to the full-width at half-maximum of 2D, and it has been verified that it can be estimated by an empirical formula as a function of the full-width at half-maximum of 2D (Robinson, J.A.; Wetherington, M.; Tedesco, J.L.; Campbell, P.M.; Weng, X.; Stitt, J.; Fanton, M.A.; Frantz, E.; Snyder, D.; VanMil, B.L. Correlating Raman spectral signatures with carrier mobility in epitaxial graphene: a guide to achieving high mobility on the wafer scale. Nano letters 2009, 9, 2873 - 2876).

[0127] Using this, the carrier mobility of graphene was calculated from the full-width at half-maximum of 2D for each of the graphene produced in Example 6, Example 7, and Example 8. The carrier mobility of the graphene produced in Example 6 is 357 cm 2 / Vs, and the carrier mobility of the graphene produced in Example 7 is 619 cm 2 / Vs, and the carrier mobility of the graphene produced in Example 8 was 8,105 cm 2 / Vs. It was confirmed that as the synthesis temperature of graphene increased, the carrier mobility of the produced graphene increased. In particular, it can be seen that the graphene of Example 8 synthesized at a temperature of 1,000 °C has the best carrier mobility.

[0128] Figure 12 is a diagram showing the contrast ratio between graphene and copper and the carrier mobility of graphene in the test pieces produced in Example 6, Example 7, and Example 8 of the present invention.

[0129] Referring to Figure 12, it was confirmed that as the synthesis temperature of graphene increased, the contrast ratio between copper and graphene and the carrier mobility of graphene in the test piece increased. In particular, when the contrast ratio increased, it was confirmed that the carrier mobility also tended to increase. From this, it can be seen that the carrier mobility of the produced graphene can be evaluated by calculating the contrast ratio of the graphene produced on the catalyst layer.

[0130] Experimental Example 5: Analysis of Planar Images with or without Pinhole of Confocal Laser Scanning Microscope Figure 13 is a diagram showing images taken using a confocal laser scanning microscope according to Example 1 and Example 9 of the present invention. Specifically, Figure 13 shows a planar image of the test piece obtained in Example 9 in which the confocal laser scanning microscope was operated with the pinhole closed, and a planar image of the test piece obtained in Example 1 in which the confocal laser scanning microscope was operated with the pinhole open. At this time, the planar image according to Example 3 shown in Figure 6 corresponds to an enlarged portion of the planar image according to Example 1 shown in Figure 13.

[0131] Referring to Fig. 13, when irradiating the same test piece with laser light having the same wavelength value (405 nm), it was confirmed that the planar image obtained in Example 1 and the planar image obtained in Example 9 were at substantially the same level. That is, it can be seen that when irradiating the same test piece with laser light having the same wavelength value regardless of the opening and closing of the pinhole, a planar image of the test piece at the same level can be obtained.

[0132] Therefore, it can be seen that the method for evaluating the quality of graphene according to an embodiment of the present invention can omit the step of setting the pinhole, and can effectively reduce the time and difficulty of evaluating the quality of graphene.

[0133] Fig. 14 is a diagram showing images taken using a confocal laser scanning microscope according to Example 4, Example 5 and Comparative Example 4 of the present invention. At this time, each of the planar images according to Example 4, Example 5, and Comparative Example 4 shown in Fig. 6 corresponds to an enlarged portion of each of the planar images according to Example 4, Example 5, and Comparative Example 4 shown in Fig. 14.

[0134] Experimental Example 6: Analysis of Nitrogen-Doped Graphene Layers Fig. 15 is a diagram showing images taken using a confocal laser scanning microscope of the test pieces according to Example 10 and Example 11 of the present invention. The length of the scale bar in Fig. 15 corresponds to 10 μm.

[0135] Fig. 16 is a diagram showing the grayscale histogram, a graph showing the contrast ratio, and a Raman spectrum of the test pieces according to Example 10 and Example 11 of the present invention. Specifically, (1) in Fig. 16 shows the grayscale histogram of the graphene of Example 10 and the nitrogen-doped graphene of Example 11, (2) in Fig. 16 shows the contrast ratio of the graphene of Example 10 and the nitrogen-doped graphene of Example 11 with copper, and (3) in Fig. 16 shows the Raman spectra of the graphene of Example 10 and the nitrogen-doped graphene of Example 11.

[0136] Referring to FIG. 15, it was confirmed that the nitrogen-doped graphene appears bright, the copper appears dark, and the contrast between the nitrogen-doped graphene and the copper is clear.

[0137] Also, referring to FIG. 16, it was confirmed that a grayscale histogram and a contrast ratio of copper can also be obtained for the nitrogen-doped graphene. Referring to (1) and (2) of FIG. 16, the contrast ratio of the nitrogen-doped graphene (Example 11) is 1.133, and the contrast ratio of the undoped graphene (Example 10) is 1.248. Although the contrast ratio decreases slightly, it can be seen that the quality of the graphene can be confirmed.

[0138] FIG. 17 is a diagram showing the N1s XPS peak of the nitrogen-doped graphene according to Example 11 of the present invention. Specifically, (1) of FIG. 17 shows the N1s XPS peak of the nitrogen-doped graphene according to Example 11, and (2) of FIG. 17 schematically shows the shape of the nitrogen-doped graphene according to Example 11.

[0139] Referring to FIG. 17, in the case of the nitrogen-doped graphene according to Example 11, it can be confirmed that the sp 2 bond of the graphene was cleaved by plasma nitrogen doping, and each of Graphitic nitrogen, Pyrrolic nitrogen, and Pyridinic nitrogen was doped.

[0140] Experimental Example 7: Analysis of Planar Images According to Type of Catalyst Layer FIG. 18 is a diagram showing the Raman spectra of the graphene produced in Reference Example 2 and Reference Example 6. Referring to FIG. 18, it can be confirmed that the 2D / G peak of the graphene grown on nickel (Reference Example 2) and the graphene grown on palladium (Reference Example 6) is less than 2.

[0141] FIG. 19 is a diagram showing a planar image of a test piece photographed by a confocal laser scanning microscope for the graphene produced in Reference Examples 2 to 5, and FIG. 20 is a diagram showing a planar image of a test piece photographed by a confocal laser scanning microscope for the graphene produced in Reference Examples 6 to 9.

[0142] Referring to FIG. 19, in the images of Reference Examples 2 to 5 obtained using the reflection mode of the confocal laser scanning microscope, it can be seen that the synthesized graphene appears dark, nickel appears bright, and the distinction is clear. It is confirmed that the contrast between graphene and nickel is not greatly affected by the wavelength value of the laser light irradiated on the surface of the test piece, but it is confirmed that the contrast is the clearest at a wavelength of 543 nm.

[0143] Also, referring to FIG. 20, similar to Reference Examples 2 to 5, in the images of Reference Examples 6 to 9 obtained using the reflection mode of the confocal laser scanning microscope, it can be seen that the synthesized graphene appears dark, palladium appears bright, and the distinction is clear.

[0144] On the other hand, when compared with the planar image of Example 1 in which the synthesized graphene appears bright and copper appears dark, it is judged that the graphene synthesized in Reference Examples 2 to 9 appears dark and the metal appears bright due to the difference in the thickness and crystallinity of the multilayer graphene and the optical properties of the metal.

[0145] That is, it can be seen that the method for evaluating the quality of graphene according to an embodiment of the present invention can evaluate the quality of graphene formed on various types of metal layers.

[0146] Simulation The optical conductivity of the graphene is derived from the tight-binding approximation. The carriers of graphene are expressed by the (2 + 1)-dimensional relativistic massless Dirac equation. The Dirac Hamiltonian equation is H = V F σα p α provides the energy spectrum of the carrier charge in an electron (m = 0) and the

Number

Number

Number

Number

[0147] Using the Kubo formula, the effective conductivity of graphene composed of intraband and interband contributions can be obtained (σ(ω) = σ intraband (ω) + σ interband (ω)). Here, σ intraband (ω) is

Number

Number

[0148] When graphene is between medium 1 (air) and medium 2 (copper), the boundary conditions of the Maxwell equations at z = 0 are as follows.

Number

Number

Number

Number

[0149] Furthermore, the following relationships can be derived.

Number

[0150] The magnetic field is perpendicular to the plane of incidence. By applying the continuity equation in momentum space, the following relationships can be derived.

Number

[0151] Since the magnetic permeability is 0, the following transmission coefficient (t p ) and reflection coefficient (r p ) can be obtained.

Equation

[0152] Without graphene, the coefficients lead to general results. Finally, the following reflectance (R p ) and transmittance (T p ) can be obtained as functions of wavelength and chemical potential.

Equation

Explanation of Symbols

[0153] 10: Light source 11: Optical fiber 20: Beam scanner 30: Relay lens 31: First relay lens 32: Second relay lens 40: Beam splitter 41: First beam splitter 42: Second beam splitter 50: Objective lens 60: Tube lens 70: Camera 80: Collimator 90: Photodetector CL: Catalyst layer GL: Graphene layer

Claims

1. A method for evaluating the quality of graphene using a confocal laser scanning microscope, comprising: irradiating a graphene layer formed on a copper foil as a catalyst layer with a laser beam; detecting a signal of light reflected from the graphene layer; forming a planar image of the graphene layer using the detected optical signal; analyzing a contrast ratio between the catalyst layer and graphene in the planar image; and the method for evaluating the quality of graphene is performed in real time during continuous formation of the graphene; the laser beam is irradiated with a wavelength value of 400 nm or more and 490 nm or less; the confocal laser scanning microscope operates without a pinhole; the method for evaluating the quality of graphene further comprises determining that the quality of the graphene layer is good when the contrast ratio between the catalyst layer and the graphene is 1.10 or more.

2. The method for evaluating the quality of graphene according to claim 1, wherein the graphene is formed on the catalyst layer by chemical vapor deposition.

3. The method for evaluating the quality of graphene according to claim 1, wherein the graphene is continuously formed on the catalyst layer by a roll-to-roll process.

4. The step of analyzing the contrast ratio comprises: analyzing the gray scale of a predetermined region of the planar image; and calculating a contrast ratio between the catalyst layer and the graphene in the region.

5. The analysis of the gray scale comprises: obtaining and analyzing a gray scale histogram or a gray scale profile in the region.

6. The method for evaluating the quality of graphene according to claim 2, wherein the chemical vapor deposition is performed at a temperature of 700 °C or higher.

Images