Structure and method for manufacturing the structure

Abstract

To provide a structure having a dense carbon film. [Solution] A structure comprising a conductive substrate and a carbon film on the surface of the conductive substrate, wherein the carbon film includes an aggregate of carbon nanoparticles, and the carbon nanoparticles are made of amorphous carbon.

Description

[Technical Field]

[0001] This disclosure relates to a structure and a method for manufacturing the structure. [Background technology]

[0002] By forming a carbon deposition film or protective film on the surface of conductive materials such as metals to create a structure, it is possible to improve not only the surface's abrasion resistance, low friction, and corrosion resistance, but also to simultaneously improve insulation and adjust electrical properties such as conductivity. Therefore, carbon deposition films and protective films are expected to have a wide range of applications, including cutting tools, engine parts, medical devices, electronic devices, and industrial piping / storage tanks (Patent Document 1).

[0003] Conventionally, amorphous coatings such as diamond-like carbon (DLC) and glassy carbon have often been formed on surfaces using various physicochemical vapor deposition methods (PVD / CVD), ion plating, and spray coating from gaseous and solution-based carbon sources (Non-Patent Documents 1 and 2). In recent years, coating films made of novel nanocarbons such as graphene, which have excellent properties in terms of electrical conductivity, thermal conductivity, and mechanical strength, have also been investigated (Non-Patent Documents 3 and 4).

[0004] For example, graphene coatings can be formed using conventional CVD methods or related transfer deposition methods (a method in which a graphene film formed on a catalytic surface by CVD is fixed to a polymer, then peeled off and transferred to another target surface). In addition, research examples have been reported of forming graphene oxides from electrophoretic deposition (EPD), which are water-soluble and surface-charged (Non-Patent Literature 5). Compared to conventional CVD methods, which require high temperatures, the input of expensive raw material gases, and relatively complex equipment configurations, electrophoresis can be performed at room temperature and is superior in terms of simplicity of method and conditions, film uniformity, and ease of thickness control, making it an environmentally friendly method that is attracting attention. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2014-136785 [Non-patent literature]

[0006] [Non-Patent Document 1] J. Robertson, Diamond-like amorphous carbon, Materials Science and Engineering: R: Reports, 2002, 37, 129-281. [Non-Patent Document 2] K. Bewilogua and D. Hofmann, History of diamond-like carbon films - From first experiments to world wide applications, Surface & Coatings Technol., 2014, 242, 214-225. [Non-Patent Document 3] G. Cui, et al., A comprehensive review on graphene-based anti-corrosive coatings, Chem. Eng. J., 2019, 373, 104-121. [Non-Patent Document 4] B. Kulyk, et al., A critical review on the production and application of graphene and graphene-based materials in anti-corrosion coatings, Critical Reviews in Solid State and Materials Science, 2022, 47, 309-355. https: / / doi.org / 10.1080 / 10408436.2021.1886046 [Non-Patent Document 5] MA Raza, et al., Corrosion study of electrophoretically deposited graphene oxide coatings on copper metal, Thin Solid Films, 2016, 620, 150-159. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] As mentioned above, Non-Patent Document 5 discloses electrophoresis. However, many ionic carbon sources, such as graphene oxide, have surface properties that cause their surfaces to become negatively charged in water due to the dissociation of oxygen-containing functional groups. Therefore, the inventors focused on the fact that, in principle, electrophoresis using these carbon sources can only be performed as cathode electrophoresis (Anodic EPD, aEPD) in aqueous solution. In cathode electrophoresis, since the matrix metal is located at the positive electrode, it is necessary to take measures to prevent the elution of the matrix metal, such as keeping the operating voltage low, which results in disadvantages such as a narrow range of applications. Cathode electrophoresis is also used in Patent Document 1. On the other hand, if negative electrode electrophoresis (Cathodic EPD, cEPD), in which the matrix metal is located at the negative electrode, can be realized, the above problems in the case of positive electrode film deposition can be solved. Negative electrode electrophoresis offers the advantage of allowing for a wider range of control conditions, such as increasing the voltage. Therefore, we investigated the development of a carbon source with a positively charged surface charge that can be used for negative electrode film deposition.

[0008] The present disclosure provides a method for manufacturing a structure that can prevent elution of a conductive substrate that may occur in the case of positive electrode electrophoresis. Further, the present disclosure provides a structure having a dense carbon film.

Means for Solving the Problems

[0009] The present disclosure is a structure having a conductive substrate and a carbon film on the surface of the conductive substrate, where the carbon film includes an aggregate of carbon nanoparticles, and the carbon nanoparticles are made of amorphous carbon, and relates to a structure.

[0010] Further, the present disclosure is a method for manufacturing the structure of the present disclosure, where the manufacturing method includes an electrophoresis step of electrophoresing a carbon quantum dot solution, the carbon quantum dots contained in the carbon quantum dot solution have a positive surface charge, and in the electrophoresis step, the conductive substrate is used as a negative electrode, and relates to a method for manufacturing a structure.

Advantages of the Invention

[0011] According to the present disclosure, a method for manufacturing a structure that can prevent elution of a conductive substrate that may occur in the case of positive electrode electrophoresis is provided. Further, according to the present disclosure, a structure having a dense carbon film is provided.

Brief Description of the Drawings

[0012] [Figure 1] Explanatory drawing showing the fluorescence characteristics of the electrophoresis solution. [Figure 2] Explanatory drawing showing the observation results of the A to H structures in FIG. 2. [Figure 3] Explanatory drawing showing the results of EDX analysis of the A to B structures in FIG. 3. [Figure 4] Explanatory drawing showing the fluorescence characteristics of the electrophoresis solution. [Figure 5] Explanatory drawing showing a cross-sectional SEM image of the coating film. [Figure 6] An explanatory diagram showing the results of EDX analysis of the cross-section of the coating film. [Figure 7] This is an explanatory diagram showing the observation results of structures A to D in Figure 7. [Figure 8] An explanatory diagram showing the Raman spectrum of a carbon film. [Figure 9] Figure 9 is an explanatory diagram showing the observation results of structures A to F. [Figure 10] Figure 10 is an explanatory diagram showing the observation results of structures A to F. [Figure 11] An explanatory diagram showing a cross-sectional FIB-SIM image of the coating film. [Figure 12] Figure 12A-B is an explanatory diagram showing the EDX analysis results of the coating film. [Figure 13] An explanatory diagram showing the fluorescence properties of the electrophoresis solution. [Figure 14] This is an explanatory diagram showing the observation results of structures A to D in Figure 14. [Modes for carrying out the invention]

[0013] The embodiments of this disclosure are described in detail below. The descriptions of the constituent elements described below are examples (representative examples) of embodiments of this disclosure, and this disclosure is not limited to these contents unless it exceeds its gist.

[0014] In this disclosure, "X~Y" indicating a range means "X or greater and Y or less". Furthermore, when numerical ranges expressed as "X~Y" or "X or greater and Y or less" are listed in stages (for example, in preferred order), the upper and lower limits of each numerical range can be any combination.

[0015] In this disclosure, phrases such as "one or more selected from the group consisting of X, Y, and Z" mean any of the following: X, Y, Z, a combination of X and Y, a combination of X and Z, a combination of Y and Z, or a combination of X, Y, and Z. Note that if X is a group, multiple selections may be made from X, and the same applies to Y and Z.

[0016] In this disclosure, any mention of "X such as x1, x2, and x3" is merely an example of X, and does not imply that X is limited to x1, x2, and x3.

[0017] As a result of diligent research by the inventors, a specific carbon quantum dot (Carbon Quantum We discovered that a carbon film can be formed on the surface of a conductive substrate such as a metal by using a solution (hereinafter also referred to as CQD) as the electrophoresis solution and going through a negative electrode electrophoresis process involving an electrochemical reaction.

[0018] <Method for manufacturing the structure> In other words, this disclosure is, A method for manufacturing a structure according to the present disclosure, The manufacturing method includes an electrophoresis step of electrophoresis of a carbon quantum dot solution, The carbon quantum dots contained in the carbon quantum dot solution have a positive surface charge, The present invention relates to a method for manufacturing a structure, wherein the conductive substrate is used as the negative electrode in the electrophoresis step.

[0019] As described above, a specific carbon quantum dot solution refers to a carbon quantum dot solution in which the carbon quantum dots contained in the solution have a positive surface charge. A carbon quantum dot having a positive surface charge means that when the pH of the carbon quantum dot solution is adjusted to 5-6 and the zeta potential of the pH-adjusted carbon quantum dot solution is measured, the zeta potential exceeds 0mV. The zeta potential value may be 5mV or higher, preferably 10mV or higher, and more preferably 15mV or higher. There is no particular upper limit, but it may be, for example, 100mV or lower. That is, the range of the zeta potential value may be greater than 0mV and less than or equal to 100mV, 5mV or more and less than or equal to 100mV, 10mV or more and less than or equal to 100mV, and 15mV or more and less than or equal to 100mV.

[0020] One method for giving carbon quantum dots a positive surface charge is a hydrothermal treatment step in which an aqueous solution containing sugars and one or more selected from the group consisting of organic amines and organic amine salts is hydrothermally treated. That is, it is preferable that the method for producing the structure includes a preparation step for preparing a carbon quantum dot solution. It is even more preferable that the preparation step includes a hydrothermal treatment step. Hereinafter, one or more selected from the group consisting of organic amines and organic amine salts will simply be referred to as organic amines. It is also said that. A hydrothermal treatment process is used to react sugars with organic amines to prepare a carbon quantum dot solution. In other words, carbon quantum dots are the reaction products of sugars and organic amines. The organic amines are preferably organic amine salts. When organic amine salts are used, the resulting carbon quantum dots become more basic. Therefore, they dissociate more easily and become positively charged at around neutral pH.

[0021] Sugars act as a carbon source for carbon quantum dots. The sugars are not particularly limited and include monosaccharides such as glucose and fructose, disaccharides such as sucrose and maltose, and polysaccharides such as starch and glycogen. Among these, disaccharides are preferred, and sucrose is more preferred.

[0022] Organic amines and organic amine salts contain nitrogen atoms in their molecules and therefore act as nitrogen sources for carbon quantum dots. Consequently, carbon quantum dots prepared using organic amines contain nitrogen atoms. As a result, the carbon quantum dots in the solution have a positive surface charge.

[0023] The organic amines are not particularly limited and include, for example, ethyleneamines such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, piperazine, and aminoethylpiperazine; ethanolamines such as monoethanolamine, diethanolamine, and triethanolamine; and amino acids such as aspartic acid, arginine, and glutamine. The organic amine salt is not particularly limited, and examples include carboxylate salts and hydrochloride salts of the above-mentioned organic amines, with hydrochloride salts being preferred. Specifically, ethylenediammonium dichloride is particularly preferred.

[0024] Carbon quantum dots have two emission centers, for example, with excitation center wavelengths of approximately 380 nm (e.g., 370-390 nm) and approximately 340 nm (e.g., 330-350 nm). Furthermore, it is desirable for the emission intensity of the emission center with an excitation center wavelength of approximately 380 nm to be stronger than that of the emission center with an excitation center wavelength of approximately 340 nm, as this results in a better carbon film. The emission centers of carbon quantum dots are obtained by measuring the carbon quantum dot solution using an Aqualog type three-dimensional fluorescence analyzer manufactured by Horiba, Ltd.

[0025] The method for manufacturing the structure includes an electrophoresis step in which a carbon quantum dot solution is electrophoresed. In the electrophoresis step, an external power source, such as a constant current voltage, is connected to the positive and negative electrodes, and the carbon quantum dot solution is electrophoresed. Furthermore, a conductive substrate is used as the negative electrode in the electrophoresis step. As a result, a carbon film can be formed on the surface of the conductive substrate that serves as the negative electrode.

[0026] The inventors surmise that the electrophoresis process using a carbon quantum dot solution containing carbon quantum dots having a positive surface charge involves two electrochemical reactions. That is, the electrophoresis process is thought to include the following first and second steps. The first step is to move the carbon quantum dots onto a conductive substrate by electrostatic attraction, deposit the carbon quantum dots onto the conductive substrate, and allow the carbon quantum dots to undergo an electrochemical reaction. The electrochemical reaction in the first step results in an increase in the negative electrode current. At this time, primary carbon nanoparticles are thought to be obtained. The second step is to allow the carbon quantum dot reactants obtained in the first step to undergo further electrochemical reactions. The electrochemical reaction in the second step results in an increase in the negative electrode current. Furthermore, the increase in the negative electrode current in the second step is greater than the increase in the negative electrode current in the first step, suggesting that a characteristic electrochemical reaction is taking place. At this time, secondary carbon nanoparticles are thought to be obtained. Secondary carbon nanoparticles are aggregates of carbon nanoparticles. This is a combination. Furthermore, aggregates or fusions of secondary carbon nanoparticles can also be considered aggregates of carbon nanoparticles. Through this second step, the carbon quantum dots become carbon nanoparticles made of amorphous carbon, and a carbon film is formed on the surface of the conductive substrate. The carbon film then comes to contain aggregates of carbon nanoparticles. This configuration, in which the carbon film contains aggregates of carbon nanoparticles, is a characteristic configuration obtained by using negative electrode electrophoresis.

[0027] The duration of the first step depends on the concentration of the carbon quantum dot solution used and the voltage during the electrophoresis step, but is preferably, for example, 2 to 3 hours. The duration of the second step depends on the concentration of the carbon quantum dot solution used and the voltage in the electrophoresis step, but is preferably 6 to 48 hours, more preferably 6 to 36 hours, and even more preferably 12 to 36 hours.

[0028] The voltage in the electrophoresis process is not particularly limited, but is preferably 2.5 to 4.5V, more preferably 3.0 to 4.5V, and even more preferably 3.8 to 4.5V.

[0029] In the electrophoresis process, the material used as the positive electrode is not particularly limited, but platinum wire is one example.

[0030] The electrophoresis step may be performed only once or multiple times. Performing it multiple times allows the electrochemical reaction to proceed more rapidly, making it easier to form a dense carbon film. When performing the electrophoresis step multiple times, the number of times is preferably 3 to 7, and more preferably 4 to 6.

[0031] As described above, it is preferable that the method for manufacturing the structure includes a preparation step of preparing a carbon quantum dot solution. Furthermore, it is more preferable that the preparation step includes a hydrothermal treatment step. The sugar content in the aqueous solution at the start of the hydrothermal treatment process is not particularly limited, but may be 2.0 to 15.0% by mass, or 5.0 to 10.0% by mass. The content of organic amines in the aqueous solution at the start of the hydrothermal treatment process is not particularly limited, but may be 0.5 to 5.0% by mass in total, or 1.0 to 3.0% by mass. The amount of sugars per 1 part by mass of organic amines in the aqueous solution at the start of the hydrothermal treatment process is not particularly limited, but is preferably 0.5 to 6.0 parts by mass, and more preferably 2.0 to 6.0 parts by mass.

[0032] The temperature of the hydrothermal treatment process is not particularly limited, but may be between 120 and 220°C, or between 150 and 200°C. The duration of the hydrothermal treatment process is not particularly limited, but may be 0.5 to 2.0 hours or 0.5 to 1.5 hours.

[0033] The preparation step preferably includes a removal step to remove molecules with a molecular weight of 3500 or more from the aqueous solution obtained in the hydrothermal treatment step. By removing molecules with a molecular weight of 3500 or more, the resulting carbon quantum dots become more uniform, making it easier to obtain a denser carbon film. The method for removing molecules with a molecular weight of 3500 or more is not particularly limited as long as it can be done, but one example is to dialysis the aqueous solution obtained in the hydrothermal treatment step. For example, molecules with a molecular weight of 3500 or more can be removed by placing the aqueous solution obtained in the hydrothermal treatment step into a dialysis cellulose tube such as a visking tube (dialysis cellulose tube, fractional molecular weight approximately 3500, purchased from: AS ONE Corporation), and dialysis the dialysis cellulose tube in ion-exchanged water to obtain an extramembrane solution. The dialysis time is not particularly limited, but may be, for example, 12 to 48 hours, or 18 to 30 hours. That's fine.

[0034] <Structure> The structure of this disclosure is A structure comprising a conductive substrate and a carbon film on the surface of the conductive substrate, The carbon film comprises an aggregate of carbon nanoparticles, The carbon nanoparticles are a structure made of amorphous carbon. The structure of this disclosure can be obtained by the manufacturing method described above.

[0035] As described above, the structure has a conductive substrate. The conductive substrate is not particularly limited as long as it is conductive, and examples include known metal substrates such as copper substrates or conductive glass. Among these, copper substrates are preferred. The shape of the conductive substrate is not particularly limited, and known shapes such as cylindrical or flat plates can be used, but a flat plate shape is preferred.

[0036] The structure has a carbon film on the surface of a conductive substrate. In other words, the structure can be described as a laminate having a conductive substrate and a carbon film on the surface of the conductive substrate. The carbon film also contains aggregates of carbon nanoparticles. The inclusion of aggregates of carbon nanoparticles makes the carbon film denser. It is preferable that the carbon film consists of aggregates of carbon nanoparticles. Furthermore, it is preferable that the carbon film consists of amorphous carbon. Carbon nanoparticles are carbon particles with a number-average particle size on the order of nanometers. The shape of carbon nanoparticles is not particularly limited, but spherical particles are preferred. The spherical particles of this disclosure include particles that are perfectly spherical and particles that are approximately spherical.

[0037] For example, the number-average particle diameter of carbon nanoparticles may be less than 200 nm, and preferably less than 100 nm. The lower limit of the number-average particle diameter of carbon nanoparticles is not particularly limited and may be 10 nm or more. For example, the number-average particle diameter of carbon nanoparticles may be 10 nm or more and less than 200 nm, or 10 nm or more and less than 100 nm. The number-average particle diameter of carbon nanoparticles can be increased by increasing the voltage in the electrophoresis process or increasing the time of the electrophoresis process, and can be decreased by decreasing the voltage in the electrophoresis process or decreasing the time of the electrophoresis process. The number-average particle size of carbon nanoparticles can be obtained by measuring the carbon film using a scanning electron microscope (SEM). Specifically, the measurement is performed using the following procedure. A carbon film is observed using a Hitachi S-4300 type FE-SEM instrument at an acceleration voltage of 3kV and a magnification of 30,000x. The maximum diameter of 100 or more particles is measured from the obtained SEM images, and the arithmetic mean of the obtained maximum diameters is taken as the number-average particle diameter of the carbon nanoparticles.

[0038] Carbon nanoparticles consist of amorphous carbon. Amorphous carbon is a carbon material that exhibits only a broad diffraction pattern in X-ray diffraction. Because amorphous carbon is chemically inert, a carbon film containing aggregates of amorphous carbon nanoparticles can protect the surface of a conductive substrate.

[0039] When the carbon film of the structure was measured using Raman spectroscopy with an excitation wavelength of 532 nm and a Raman spectrum was obtained, the Raman spectrum showed 1587 cm⁻¹. -1 Nearby (for example, 1560-1620cm) -1 (Within the range) G band, 1408cm -1 Nearby (for example, 1380-1440cm) -1 It is preferable to observe a D band (within the range), a 2D band corresponding to the D band, a 2G band corresponding to the G band, and a D+G band corresponding to both the D and G bands. The 2D band is a band of harmonics of the D band, the 2G band is a band of harmonics of the G band, and the D+G band is a band of combined tones of the D and G bands. The G band originates from the stretching vibrations of the carbon-carbon double bond, while the D band originates from ring deformation vibrations and CC stretching vibrations. In particular, the D band is associated with edges and defects in the graphite structure. This is due to structural disorder. It is preferable that the D band appears as a shoulder band to a broad G band. Having such a shoulder band is characteristic of the Raman spectrum of amorphous carbon.

[0040] Furthermore, the molar ratio of carbon atoms to oxygen atoms in the structure, obtained by measuring the surface of the carbon film using SEM-EDX, is preferably 2.50 or higher. A molar ratio of carbon atoms to oxygen atoms within the above range indicates that the carbon quantum dots have been sufficiently carbonized and a carbon film has been formed. The molar ratio of carbon atoms to oxygen atoms is preferably 4.00 or higher, more preferably 4.50 or higher, even more preferably 6.00 or higher, and particularly preferably 10.00 or higher. There is no particular upper limit to this molar ratio. For example, the range of this molar ratio may be 2.50 to 100.00, 4.00 to 100.00, 4.50 to 100.00, 6.00 to 100.00, or 10.00 to 100.00. It may also be 2.50 to 20.00. This molar ratio can be increased by increasing the voltage or lengthening the electrophoresis process, and can be decreased by decreasing the voltage or lengthening the electrophoresis process.

[0041] Surface SEM-EDX measurements are performed using the following procedure. Using a JEOL JSM-6010LA type benchtop FE-SEM with an EDX analyzer, the surface of the carbon film is measured at an acceleration voltage of 10kV and a magnification of 300x. At this time, the carbon film is observed from a direction perpendicular to the surface constituting the carbon film. EDX analysis is performed on the surface of the carbon film within the observation field, and the molar ratio of carbon atoms to metal atoms derived from the metal substrate is calculated. By measuring the surface, the coverage of the carbon film can be evaluated more favorably.

[0042] Furthermore, the structure may have a molar ratio of carbon atoms to oxygen atoms of 2.50 or higher, obtained by measuring the cross-section of the carbon film using SEM-EDX. Specifically, the cross-sectional SEM-EDX measurement is performed using the following procedure. A carbon film is cut using a Hitachi IM-4000 type ion milling system to obtain a cross-section of the carbon film. The obtained sample cross-section is observed using a Hitachi SU-5000 type analytical FE-SEM system with an EDX analyzer at an acceleration voltage of 3kV and a magnification of 40,000x. EDX analysis of the carbon film in the observed field of view is performed to calculate the molar ratio of carbon atoms to oxygen atoms. Even by measuring the cross-section of such a carbon film, the molar ratio of oxygen atoms to oxygen atoms can be measured. The molar ratio of carbon atoms to oxygen atoms obtained by measuring the cross-section of the carbon film is preferably 4.00 or higher, more preferably 4.50 or higher, even more preferably 6.00 or higher, and particularly preferably 10.00 or higher. There is no particular upper limit to this molar ratio. For example, the range of this molar ratio may be 2.50 to 100.00, 4.00 to 100.00, 4.50 to 100.00, 6.00 to 100.00, or 10.00 to 100.00. It may also be 2.50 to 20.00.

[0043] Furthermore, if the conductive substrate is a metal substrate, the coverage rate (covering state) of the carbon film can be evaluated by measuring the molar ratio of carbon atoms to metal atoms using SEM-EDX. Specifically, the molar ratio of carbon atoms to metal atoms derived from the metal substrate, obtained by measuring the surface of the carbon film using SEM-EDX, is preferably 0.30 or higher. A molar ratio of carbon atoms to metal atoms derived from the metal substrate being within the above range indicates that the carbon film on the surface of the conductive substrate is densely formed. The molar ratio of carbon atoms to metal atoms derived from the metal substrate is preferably 0.40 or higher, more preferably 0.50 or higher, even more preferably 1.00 or higher, even more preferably 1.40 or higher, and particularly preferably 4.00 or higher. The upper limit is not particularly limited, as a higher value indicates a better coating state as a carbon film. For example, the molar ratio may be in the range of 0.30-10.00, 0.40-10.00, 0.50-10.00, 1.00-10.00, 1.40-10.00, or 4.00-10.00. It may also be 0.30-5.00. Here, the metal atoms originating from the metal substrate are, for example, copper atoms if the metal substrate is copper. This molar ratio can be increased by increasing the voltage or lengthening the electrophoresis process, and can be decreased by decreasing the voltage or lengthening the electrophoresis process.

[0044] The thickness of the carbon film is not particularly limited, but may be 25-200 nm, 25-150 nm, or 25-125 nm. The thickness of the carbon film can be increased by increasing the voltage or lengthening the electrophoresis process, and decreased by decreasing the voltage or lengthening the electrophoresis process. The thickness of the carbon film can be obtained by cross-sectioning the carbon film using ion milling and measuring the obtained cross-section using SEM, or by calculating it using FIB-SIM images.

[0045] When using FIB-SIM images, perform the measurement using the following procedure. Using a Hitachi High-Tech FB-2100 focused ion beam processing and observation system, a tungsten deposition protective sacrificial film is deposited on the surface of a structure, and cross-sectional etching is performed by Ga ion beam sputtering. Subsequently, a cross-sectional SIM image is obtained under the conditions of an acceleration voltage of 40kV, aperture diameter of 5μm, probe (beam) diameter of 10nm (resolution of 6nm), and probe (beam) current of 6pA. From the obtained cross-sectional SIM image, the thickness of the carbon coating film is calculated considering the cross-sectional inclination (45°). [Examples]

[0046] The following examples will provide further details. This disclosure is not limited to these examples unless it exceeds the essence of the disclosure.

[0047] <Example 1> 1.2 g of sucrose (Fujifilm Wako Pure Chemical Industries, Ltd., Wako Special Grade) and 0.3 g of ethylenediammonium dichloride (Fujifilm Wako Pure Chemical Industries, Ltd., Wako Special Grade) were added to 12.8 g of deionized water and homogeneously mixed by magnetic stirring. The mixture was then hydrothermally treated at 170°C for 1 hour. The resulting brown solution was placed in a visking tube (dialysis cellulose tube, molecular weight cutoff approximately 3500, purchased from AS ONE Corporation) and dialysis was performed in 100 mL of deionized water at room temperature for 24 hours. The solution after dialysis (extramembrane solution) was designated as electrophoresis solution s-NCQD_1. Figure 1 is an explanatory diagram showing the fluorescence characteristics of the electrophoresis solution. Specifically, Figure 1 shows the fluorescence characteristics of s-NCQD_1 measured with an Aqualog type three-dimensional fluorescence analyzer manufactured by Horiba, Ltd. The horizontal axis shows the excitation wavelength (EX Wavelength) (nm), and the vertical axis shows the emission wavelength (EM Wavelength) (nm). From Figure 1, it can be seen that a CQD with characteristic emission characteristics was created, having an emission center that shows maximum emission intensity mainly at an excitation wavelength of approximately 385 nm and an emission wavelength of approximately 500 nm (green emission).

[0048] The total organic carbon (TOC) and total nitrogen (TN) content of s-NCQD_1, obtained by measuring with a Shimadzu Corporation TOC-L / TNM-L type total organic carbon / nitrogen meter, were 0.52 wt% and 0.057 wt%, respectively. Furthermore, the zeta potential of s-NCQD_1 was measured in the neutral pH range equivalent to distilled water (specifically pH=5~6) using an Otsuka Electronics ELSZ-1000 type zeta potential / particle size analyzer, and the zeta potential was found to be +25 mV or higher. This indicates that the CQD structure produced by the above procedure... It is thought that this is because it contains pyrrole-like and pyridine-like surface functional groups, which result in the formation of a positively charged surface structure in water.

[0049] An electrophoresis system was constructed by placing 3.5 mL of s-NCQD_1 in a rectangular cell, setting a Cu plate (4.5 cm × 0.25 cm) as the negative electrode and a platinum wire as the positive electrode, with an electrode distance of approximately 0.5 cm, and using a constant voltage current device (DCP3003 model, manufactured by AS ONE Corporation) as the power supply. Using this electrophoresis system, the front and back surfaces of the Cu plate each had a coverage area of ​​0.7-0.8 cm². 2 Constant voltage negative electrode electrophoresis was performed to obtain a surface-coated copper substrate as a structure, coated with a carbon film. The electrophoresis voltage was kept constant at 3.8V. The electrophoresis times were set to 3 hours, 10 hours, and 24 hours. In this electrophoresis process, a certain amount of low negative electrode current (around 10 mA) was initially generated after the process began. Then, the negative electrode current gradually increased over the course of several hours. After these initial stages, the negative electrode current began to increase more rapidly, and after 7-8 hours, a gradual increase was observed again. During these processes, the color of the electrophoresis solution gradually became lighter, and a decrease in the pH value of the electrophoresis solution was also observed. From this, it is thought that this electrophoresis process involves an electrochemical reaction.

[0050] Figures 2A to 2H are explanatory diagrams showing the observation results of the structures. Specifically, Figures 2A, 2C, 2E, and 2G are images of the surfaces of the copper substrate before electrophoresis, the surface-coated copper substrate obtained after 3 hours of electrophoresis, the surface-coated copper substrate obtained after 10 hours of electrophoresis, and the surface-coated copper substrate obtained after 24 hours of electrophoresis, observed using a high-resolution zoom lens optical microscope (Keyence Z500R type, manufactured by Keyence Corporation). Figures 2B, 2D, 2F, and 2H are images of the surfaces of the copper substrate before electrophoresis, the surface-coated copper substrate obtained after 3 hours of electrophoresis, the surface-coated copper substrate obtained after 10 hours of electrophoresis, and the surface-coated copper substrate obtained after 24 hours of electrophoresis, observed using a scanning electron microscope (SEM, Hitachi S-4300 type, acceleration voltage: 3V).

[0051] In optical microscope images, the surface of the copper substrate gradually changed from reddish-brown to black as the electrophoresis time increased. Furthermore, the streaky pattern observed in Figure 2A disappeared in Figures 2C, 2E, and 2G, confirming that the copper surface was covered with a film. SEM images also showed that after 3 hours of electrophoresis, the copper surface was already covered with particles of several tens of nanometers in size (e.g., 20-30 nm) (Figure 2D). This confirmed that the carbon film contained aggregates of carbon nanoparticles. In Figure 2D, the carbon film coverage was relatively loose, with relatively large particle spacing. However, after 10 hours of electrophoresis, and especially after 24 hours, the particle spacing almost disappeared, indicating that the carbon film had become quite dense.

[0052] Furthermore, EDX analysis was performed on each surface-coated copper substrate. Figures 3A and 3B show the results of surface SEM-EDX (energy-dispersive X-ray spectroscopy) analysis of the structures. Figures 3A and 3B show that the carbon film was mainly composed of carbon and was formed on the copper substrate. The carbon film also contained oxygen. In Figures 3A and 3B, the results of Example 1 are indicated by white circles. Furthermore, when the electrophoresis time was varied from 3 hours to 24 hours, the molar ratio of carbon atoms to oxygen atoms increased from 4.91 to 8.04, and the molar ratio of carbon atoms to copper atoms increased from 0.33 to 0.69. From these results, it was found that a reaction process involving carbonization was taking place during this electrophoretic process.

[0053] <Example 2> The electrophoretic solution s-NCQD_2 was prepared and evaluated in the same manner as in Example 1, except that the hydrothermal treatment temperature was changed to 175°C. Figure 4 is an explanatory diagram showing the fluorescence characteristics of the electrophoretic solution. As shown, s-NCQD_2 was formed, exhibiting fluorescence properties similar to s-NCQD_1. The total organic carbon (TOC) and total nitrogen (TN) content of s-NCQD_2 were 0.48 wt% and 0.055 wt%, respectively. The zeta potential was +30 mV at pH = 5.6. Electrophoresis was performed in the same manner as in Example 1, except that s-NCQD_2 was used and the electrophoresis time was set to 24 hours. The front and back surfaces of the Cu plate each had a coverage area of ​​approximately 0.72 cm². 2 A surface-coated copper substrate, which is coated with a carbon film, was obtained as a structural component.

[0054] Figure 5 is an explanatory diagram showing a cross-sectional SEM image of the coating film. Specifically, Figure 5A shows a cross-sectional SEM image of the coating film obtained by ion milling. Figure 6 is an explanatory diagram showing the EDX analysis results of the coating film. Specifically, Figure 6 shows an EDX analysis diagram using an elemental mapping diagram. From Figure 5, it can be seen that a carbon film with a thickness of approximately 51 nm coats the copper surface. The carbon film is mainly composed of carbon, and it was found that a carbon film was formed on the copper substrate. The carbon film also contained oxygen. Cross-sectional SEM-EDX analysis was performed on the obtained carbon film. From the EDX analysis results of the area limited to the carbon film (the area enclosed by the white square line in Figure 5), the molar ratio of carbon atoms to oxygen atoms was 6, and the molar ratio of carbon atoms to copper atoms was 1.47.

[0055] <Example 3> Electrophoresis was repeated five times on the same copper substrate, varying the electrophoresis time, in the same manner as in Example 2. The electrophoresis time was 24 hours for the first to fourth runs, and 12 hours for the fifth run. As a result, the coating area of ​​approximately 0.80 cm² was obtained on both the front and back surfaces of the Cu plate. 2 A surface-coated copper substrate, which is coated with a carbon film, was obtained as a structural component. Figures 7A to 7D are explanatory diagrams showing the observation results of the structure. Specifically, Figures 7A and 7B are images of the surface of the surface-coated copper substrate obtained in Example 2, observed using a scanning electron microscope (SEM). Figures 7C and 7D are images of the surface of the surface-coated copper substrate obtained in Example 3, observed using a scanning electron microscope (SEM).

[0056] Even after five repeated electrophoretic reactions, the surface of the copper substrate was still covered with a carbon film. Furthermore, EDX analysis was performed on the surface-coated copper substrate. Figures 3A and 3B show the results of the surface SEM-EDX analysis (energy-dispersive X-ray analysis). From Figures 3A and 3B, the molar ratio of carbon atoms to oxygen atoms was 13.3, and the molar ratio of carbon atoms to copper atoms was 4.52. In Figures 3A and 3B, the results for Example 3 are indicated by black circles. Therefore, it was revealed that the carbonization of the coating film and the coating effect of the film could be greatly improved together by repeated electrophoresis reactions. Further, FIG. 8 is an explanatory diagram showing the Raman spectrum of the carbon film. From the results of the Raman spectrum in FIG. 8, in Example 2 and Example 3, the G band near 1587 cm -1 , the D band near 1408 cm that appears as a shoulder peak of the G band -1 , the 2D band corresponding to the D band, the 2G band corresponding to the G band, and the G+D band corresponding to the D band and the G band were observed. Therefore, it was confirmed that the carbon nanoparticles contained in the carbon film are composed of amorphous carbon.

[0057] <Example 4> Electrophoresis was carried out in the same manner as in Example 2 except that the voltage was changed to 2V, 3V, 3.5V, 3.8V, and 4V, and a surface-coated copper substrate as a structure coated with a carbon film with a coating area of about 0.24 cm 2 on each of the front and back surfaces of the Cu plate was obtained. FIGS. 9A to 9F and FIGS. 10A to 10F are explanatory diagrams showing the observation results of the structure. Specifically, FIGS. 9A, 9C, 9E, 10A, 10C, and 10E are images of the front surface of the copper substrate before electrophoresis, the surface-coated copper substrate obtained by performing electrophoresis at 2V, the surface-coated copper substrate obtained by performing electrophoresis at 3V, the surface-coated copper substrate obtained by performing electrophoresis at 3.5V, the surface-coated copper substrate obtained by performing electrophoresis at 3.8V, and the surface-coated copper substrate obtained by performing electrophoresis at 4V, respectively, observed using a high-resolution zoom lens optical microscope (manufactured by Keyence Corporation, Keyence Z500R type). Further, FIGS. 9B, 9D, 9F, 10B, 10D, and 10F are images of the front surface of the copper substrate before electrophoresis, the surface-coated copper substrate obtained by performing electrophoresis at 2V, the surface-coated copper substrate obtained by performing electrophoresis at 3V, the surface-coated copper substrate obtained by performing electrophoresis at 3.5V, the surface-coated copper substrate obtained by performing electrophoresis at 3.8V, and the surface-coated copper substrate obtained by performing electrophoresis at 4V, respectively, observed using a scanning electron microscope (SEM, Hitachi S-4300 type, acceleration voltage: 3V). [[ID=​​​ Figures 9C and 9D show that at a voltage of 2V, almost no carbon film was formed on the copper surface. Figures 9E and 9F show that at a voltage of 3V, nearly spherical primary particles with a size of approximately 50 nm formed aggregates of secondary particles, which adhered to the copper substrate, forming a carbon film. When the voltage was further increased, the aggregates of spherical particles became more densely packed, covering the copper surface (Figures 10A and 10B). At voltages of 3.8V and 4V, a fairly dense carbon film was formed (Figures 10C-10F). Figure 11 is an explanatory diagram showing a cross-sectional FIB-SIM image of the coating film. From the cross-sectional FIB-SIM image in Figure 11, it can be seen that at a voltage of 3.8V, a carbon film with a thickness of approximately 110 nm coats the copper surface. Figures 12A to 12B are explanatory diagrams showing the surface EDX analysis results of the coating film. Surface SEM-EDX analysis results (Figures 12A and 12B) showed that as the applied electrophoretic voltage increased, the molar ratio of carbon atoms to oxygen atoms in the carbon film slightly increased. Note that in Figures 12A and 12B, the results for Example 4 are shown as open circles. On the other hand, the molar ratio of carbon atoms to copper atoms increased significantly. This indicates that increasing the electrophoretic voltage increased the density of the coating film. This suggests that increasing the electrophoretic voltage primarily contributes to improving the density of the coating film.

[0059] <Comparative Example 1> The electrophoretic solution s-CQD was prepared and evaluated in the same manner as in Example 1, except that ethylenediammonium dichloride was not used and the hydrothermal treatment time was changed to 1.5 hours. Figure 13 shows the fluorescence properties of s-CQD. Unlike the fluorescence properties of s-NCQD_1 and s-NCQD_2, it can be seen that s-CQD has a emission center that shows maximum emission intensity mainly at an excitation wavelength of approximately 340 nm and an emission wavelength of approximately 425 nm (blue emission). The total organic carbon (TOC) content and total nitrogen (TN) content of s-CQD were 3.9 wt% and 0 wt%, respectively. Furthermore, the zeta potential was approximately -50mV. This is thought to be because the CQD structure produced by the above procedure mainly contains oxygen-containing functional groups on its surface, and a negatively charged surface structure resulting from these groups is generated in water.

[0060] An electrophoresis system was constructed by placing 4 mL of s-CQD in a cylindrical cell, setting a Cu plate (2 cm × 0.25 cm) as the positive electrode and a platinum wire as the negative electrode, with an electrode distance of approximately 1 cm, and supplying power with a constant voltage current device (DCP3003 model, manufactured by AS ONE Corporation). Using this electrophoresis system, negative electrode electrophoresis was performed at 3.8 V for 17 hours. The front and back surfaces of the Cu plate each had a coverage area of ​​0.24 cm². 2 We attempted to form a coating film to achieve this result.

[0061] Figures 14A to 14D are explanatory diagrams showing the observation results of the structure. Figures 14A and 14C are images of the copper substrate before and after electrophoresis, respectively, observed using a high-resolution zoom lens optical microscope (Keyence Z500R type, manufactured by Keyence Corporation). Figures 14B and 14D are images of the copper substrate before and after electrophoresis, respectively, observed using a scanning electron microscope (SEM, Hitachi S-4300 type, acceleration voltage: 3V).

[0062] In the optical microscope images, the copper substrate after electrophoresis was a reddish-copper color, not significantly different from the copper substrate before electrophoresis. Furthermore, the SEM image in Figure 14D showed that carbon particles of several tens of nanometers in size were only partially scattered on the copper substrate. In addition, surface SEM-EDX analysis of the copper substrate after electrophoresis revealed a molar ratio of carbon atoms to copper atoms of 0.29. Note that in Figures 3B and 12B, the results for Comparative Example 1 are indicated by triangles. These results indicate that a sufficient carbon coating film covering the copper surface was not formed. Therefore, it is considered important to include a nitrogen source in the raw materials when synthesizing the electrophoretic solution. The CQD obtained using a nitrogen source was advantageous for negative electrode electrophoresis because it had positively charged surface sites due to the contained nitrogen functional groups.

[0063] Examples of the inventions identified from the above disclosures are as follows: [Configuration 1] A structure comprising a conductive substrate and a carbon film on the surface of the conductive substrate, The carbon film comprises an aggregate of carbon nanoparticles, A structure in which the carbon nanoparticles are made of amorphous carbon. [Configuration 2] The structure according to configuration 1, wherein the carbon nanoparticles are spherical particles. [Configuration 3] The structure according to configuration 1 or 2, wherein the number-average particle diameter of the carbon nanoparticles is less than 100 nm. [Structure 4] When the carbon film was measured using Raman spectroscopy with an excitation wavelength of 532 nm and a Raman spectrum was obtained, the Raman spectrum showed 1587 cm⁻¹. -1 Nearby G-band, 1408cm -1 A structure according to any one of configurations 1 to 3, wherein a nearby D band, a 2D band corresponding to the D band, a 2G band corresponding to the G band, and a D+G band corresponding to the D band and the G band are observed. [Composition 5] The structure according to any one of configurations 1 to 4, wherein the molar ratio of carbon atoms to oxygen atoms, obtained by measuring the surface of the carbon film using SEM-EDX, is 2.50 or more. [Composition 6] The structure according to any one of configurations 1 to 5, wherein the conductive substrate is a metal substrate or a conductive glass substrate. [Composition 7] The structure according to configuration 6, wherein the conductive substrate is a metal substrate, and the molar ratio of carbon atoms to metal atoms derived from the metal substrate, obtained by measuring the surface of the carbon film using SEM-EDX, is 0.30 or more. [Structure 8] A method for manufacturing the structure described in any of configurations 1 to 7, The manufacturing method includes an electrophoresis step of electrophoresis of a carbon quantum dot solution, The carbon quantum dots contained in the carbon quantum dot solution have a positive surface charge, A method for manufacturing a structure, wherein the conductive substrate is used as the negative electrode in the electrophoresis step. [Configuration 9] A method for manufacturing the structure according to configuration 8, wherein the voltage in the electrophoresis step is 2.5 to 4.5 V. [Configuration 10] The method for manufacturing the structure includes a preparation step of preparing the carbon quantum dot solution, The aforementioned preparation step is A hydrothermal treatment step involves hydrothermally treating an aqueous solution containing sugars and one or more selected from the group consisting of organic amines and organic amine salts. Removal process to remove molecules with a molecular weight of 3500 or more from the aqueous solution obtained in the aforementioned hydrothermal treatment step. To what extent, A method for manufacturing the structure according to configuration 8 or 9, including the method described in configuration 8 or 9. [Composition 11] A method for manufacturing the structure according to configuration 10, wherein the temperature in the hydrothermal treatment step is 120 to 220°C.

Claims

1. A structure comprising a conductive substrate and a carbon film on the surface of the conductive substrate, The carbon film comprises an aggregate of carbon nanoparticles, A structure in which the carbon nanoparticles are made of amorphous carbon.

2. The structure according to claim 1, wherein the carbon nanoparticles are spherical particles.

3. The structure according to claim 1, wherein the number-average particle diameter of the carbon nanoparticles is less than 100 nm.

4. When the carbon film was measured using Raman spectroscopy with an excitation wavelength of 532 nm and a Raman spectrum was obtained, the Raman spectrum showed 1587 cm⁻¹. －１ Nearby G-band, 1408 cm －１ The structure according to claim 1, wherein a nearby D band, a 2D band corresponding to the D band, a 2G band corresponding to the G band, and a D+G band corresponding to the D band and the G band are observed.

5. The structure according to claim 1, wherein the molar ratio of carbon atoms to oxygen atoms, obtained by measuring the surface of the carbon film using SEM-EDX, is 2.50 or more.

6. The structure according to claim 1, wherein the conductive substrate is a metal substrate or a conductive glass substrate.

7. The structure according to claim 6, wherein the conductive substrate is a metal substrate, and the molar ratio of carbon atoms to metal atoms derived from the metal substrate, obtained by measuring the surface of the carbon film using SEM-EDX, is 0.30 or more.

8. A method for manufacturing the structure according to any one of claims 1 to 7, The manufacturing method includes an electrophoresis step of electrophoresis of a carbon quantum dot solution, The carbon quantum dots contained in the carbon quantum dot solution have a positive surface charge, A method for manufacturing a structure, wherein the conductive substrate is used as the negative electrode in the electrophoresis step.

9. The method for manufacturing the structure according to claim 8, wherein the voltage in the electrophoresis step is 2.5 to 4.5 V.

10. The method for manufacturing the structure includes a preparation step of preparing the carbon quantum dot solution, The aforementioned preparation step is A hydrothermal treatment step involves hydrothermally treating an aqueous solution containing sugars and one or more selected from the group consisting of organic amines and organic amine salts. A removal step is performed to remove molecules with a molecular weight of 3500 or more from the aqueous solution obtained in the aforementioned hydrothermal treatment step, A method for manufacturing the structure according to claim 8, including the method described in claim 8.

11. The method for manufacturing the structure according to claim 10, wherein the temperature in the hydrothermal treatment step is 120 to 220°C.

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