Laminate comprising two-dimensional layered substance and porous film, method for transferring laminate, and method for manufacturing laminate

Abstract

[Problem]　The present invention addresses the problem of providing: a method whereby it is possible to easily transfer a high-quality two-dimensional layered substance to a desired substrate without requiring floating on the surface of water and without causing damage during the transfer process; and a laminate that is used in the method. [Solution]　The present invention provides a laminate comprising a two-dimensional layered substance and a porous film laminated on the two-dimensional layered substance, the laminate being capable of self-support while maintaining a planar structure in the atmosphere.

Description

Laminate containing two-dimensional layered material and porous film, method for transferring laminate, and method for manufacturing laminate

[0001] The present invention relates to a laminate including a graphene film on which a porous film having micropores is laminated, a method for transferring the laminate, and a method for manufacturing the laminate.

[0002] Graphene, with its excellent properties, including optical transparency and high electrical conductivity, is expected to be used in transparent conductive films and other applications. While various methods for producing graphene exist, chemical vapor deposition (CVD) is a useful method for producing high-quality graphene films on large areas. In CVD growth, graphene is deposited on a catalytic metal substrate, such as copper, using a carbon source gas, such as methane. To apply this graphene to transparent conductive films and various devices, it must be transferred from the catalytic metal substrate to the desired substrate. Graphene is a sheet material with a thickness of one atomic layer and cannot stand on its own. Therefore, graphene can be transferred by adhering the graphene to the desired substrate while it is still on the catalytic metal, or by using a transfer support film, such as a polymer coating on the graphene. Both methods require a process that involves peeling or dissolving the metal catalytic substrate. The need for this transfer process is one of the reasons that has hindered the industrial application of graphene. In addition to the complexity of the process, the graphene is prone to damage, such as tearing, and polymer residue.

[0003] In a typical CVD graphene transfer process, polymethyl methacrylate (PMMA) is used as a transfer support film. In this method, a PMMA film is formed on graphene on a metal catalyst (copper) by spin-coating a PMMA solution. The PMMA / graphene / copper laminate is then floated in a copper etching solution. The copper is etched by floating the PMMA / graphene laminate in the etching solution with the copper side in contact with the etching solution. After the copper is completely etched, the remaining PMMA / graphene laminate is transferred to a pool of pure water and floated there. The graphene is washed as needed by repeatedly transferring it to the pure water pool. The PMMA / graphene laminate floating in the pure water is then scooped up onto the desired substrate. After drying, the PMMA present on the top surface of the laminate is dissolved and removed using a solvent such as acetone, completing the transfer of graphene to the desired substrate. Furthermore, if one were to attempt to lift the PMMA-graphene laminate floating on the water surface directly from the water surface using tweezers or the like without scooping it up with the desired substrate, stress within the PMMA film and the surface tension of the water would act, causing the laminate to wrinkle and damaging the graphene. In other words, graphene using the PMMA film as a transfer support film after removing the copper substrate must float on the water surface before and during the transfer process to the desired substrate; it cannot stand on its own in the air. Thus, the need to float the graphene on pure water in the transfer process was one of the main causes of the reduced mass productivity and reproducibility of graphene production.

[0004] Previous research has proposed simpler transfer processes and laminated structures that enable easier graphene transfer. For example, Non-Patent Document 1 reports a graphene transfer method that uses a commercially available laminator and a polyvinyl alcohol (PVA) film. In this method, graphene and a PVA film prepared on copper foil by a CVD method are superimposed on each other, and the graphene and the PVA film are pressed together by passing them through a laminator. Thereafter, when the PVA film is mechanically peeled off from the copper foil, the graphene is also peeled off from the copper foil. This graphene and PVA laminate is then placed on a desired substrate (SiO ２Graphene is transferred by placing the PVA film on a copper foil (a polyolefin substrate) and passing it through a laminator. The PVA film is then dissolved and removed in hot water. This method does not involve skimming the floating laminate off the water surface, but it is difficult to avoid damaging the graphene because it mechanically peels the copper and graphene. Another method proposed is one that utilizes electrochemical transfer and functional tape. Non-Patent Document 2 describes a method in which a UV tape, consisting of a polyolefin coated with a UV-sensitive adhesive, is brought into contact with graphene on copper and then irradiated with UV light to produce a laminate consisting of UV tape, graphene, and copper foil. By peeling the UV tape / graphene laminate from the copper foil using electrochemical transfer, a laminate that can be transferred without floating on water is produced. When this laminate is attached to the desired substrate and heated to 90°C, the tape peels off from the graphene, completing the transfer. This transfer method does not involve dissolving the support material, and the process of peeling the UV tape (support material) from the graphene film can be considered a type of mechanical peeling method.

[0005] As described above, conventional graphene transfer methods either require a process of floating the graphene on water, or utilize mechanical peeling methods that are likely to damage the graphene, or leave residue of the transfer material on the graphene. Therefore, there has been a demand for a method that does not require floating the graphene on the water surface and that can easily transfer high-quality CVD graphene to a desired substrate without causing damage.

[0006] A. Shivayogimath et al., “Do-It-Yourself Transfer of Large-Area Graphene Using an Office Laminator and Water,” Chemistry Materials, 31, pp. 2328-2336 (2019) M. Nakatani et al., “Ready-to-transfer two-dimensional materials using tunable adhesive force tapes,” Nature Electronics, 7, 119-130

[0007] An object of the present invention is to provide a method for easily transferring high-quality two-dimensional layered materials such as graphene onto a desired substrate without the need to float the material on a water surface and without causing damage during the transfer process, and to provide a laminate to be used therefor.

[0008] As mentioned above, irreversible deformation of the graphene occurs when a laminate consisting of a PMMA film and a graphene film, for example, using the PMMA film as a transfer support, is lifted from a floating state on the water surface into the air with tweezers or the like. Damage to graphene in other conventional transfer processes is primarily caused by localized external force concentration in mechanical peeling methods and stress (tensile stress) within the transfer support. After casting a polymer serving as the transfer support onto a graphene film on a metal catalyst, the solvent evaporates, causing the polymer volume to shrink. This results in tensile stress being generated in the transfer support because one surface of the transfer support is constrained by the graphene / copper foil. Furthermore, heating processes such as welding can also cause polymer deformation, and if this occurs at the point of contact with the graphene, it can contribute to damage to the graphene. This tensile stress in the transfer support film exerts a compressive force on the substrate (graphene / copper foil) that constrains the transfer support. In other words, compressive stress is generated in the graphene / copper foil. After etching the copper, the laminate consisting of the transfer support material and the graphene film is left in the atmosphere with nothing to constrain the deformation of the transfer support film other than the graphene, which is one atomic layer thick. This means that the graphene is subjected to a large compressive stress, which is thought to easily wrinkle it. While stress is generated in the laminate in conventional methods, the water-air interface can be used to maintain the planar structure of the laminate. In other words, the hydrophobic nature of PMMA / graphene and the large surface tension of water are thought to counteract the force that tends to shrink the transfer support film.

[0009] To avoid the floating process required in conventional PMMA transfer methods, the laminated structure consisting of a transfer support material and graphene must be self-supporting in the atmosphere and not undergo irreversible deformation. Furthermore, the graphene must be almost free-standing in the laminated structure, and must not be damaged during the final process of removing the transfer support material.

[0010] To solve the above-mentioned problems, the present inventors attempted to produce a laminate consisting of a porous film and graphene. Surprisingly, the laminate after etching the copper foil catalyst metal was able to stand on its own in the atmosphere while maintaining its planar structure, and the graphene in the laminate showed extremely little tearing. Furthermore, by attaching this laminate to a desired substrate and then dissolving the porous film, it was possible to transfer high-quality graphene to the desired substrate with minimal damage, without the need for a process of floating it on water. The present invention was completed based on the above findings and includes the following aspects:

[0011] One aspect of the present invention relates to: [1] a laminate comprising a two-dimensional layered material and a porous film laminated on the two-dimensional layered material, which can stand on its own in the atmosphere while maintaining its planar structure. Here, in one embodiment of the laminate of the present invention, [2] the laminate according to [1] above, characterized in that it is in a dry state. In another embodiment of the laminate of the present invention, [3] the laminate according to [1] or [2] above, characterized in that the porous film has pores with an average pore diameter of 20 nm or more. In another embodiment of the laminate of the present invention, [4] the laminate according to any of [1] to [3] above, characterized in that the area ratio of the pores to the film surface of the porous film is 20% or more. In another embodiment of the laminate of the present invention, [5] the laminate according to any of [1] to [4] above, characterized in that the film thickness of the porous film is 100 nm or more. In one embodiment, the laminate of the present invention is: [6] the laminate according to any one of the above [1] to [5], wherein the porous membrane is a membrane made of a material selected from the group consisting of nitrocellulose, cellulose acetate, polyethersulfone, polytetrafluoroethylene, polyamide, polyvinylidene fluoride, regenerated cellulose, polycarbonate, polypropylene, polyvinylidene chloride, aluminum oxide, glass fiber, quartz fiber, polymethyl methacrylate, polystyrene, polyethylene, polyethylene terephthalate, and ceramic, or a mixed membrane made of two or more materials selected from the group. In one embodiment, the laminate of the present invention is: [7] the laminate according to any one of the above [1] to [6], wherein the porous membrane is a membrane made of a material selected from the group consisting of nitrocellulose, cellulose acetate, polycarbonate, polyvinylidene chloride, polystyrene, and polymethyl methacrylate, or a mixed membrane made of two or more materials selected from the group.

[0012] In another aspect, the present invention relates to [8] a method for transferring the laminate according to any one of the above [1] to [7] to a desired substrate, comprising: (a) adhering the two-dimensional layered material side of the laminate to a desired position on the desired substrate. Here, in one embodiment, the transfer method of the present invention is as follows: [9] the transfer method according to the above [8], characterized in that, after the step (a), it further comprises: (b) removing the porous film of the laminate using a solvent. In another aspect, the present invention relates to

[10] a method for producing the laminate according to any one of the above [1] to [7], comprising: (i) forming a two-dimensional layered material on a metal catalyst substrate by a CVD method, (ii) further forming a porous film on the two-dimensional layered material to produce a laminate, and (iii) removing the metal catalyst substrate by etching. Here, in one embodiment, the method for producing a laminate of the present invention is as follows:

[11] The method for producing a laminate according to the above

[10] , characterized in that the formation of a porous film on the two-dimensional layered material in the step (ii) is carried out by a phase inversion method. Also, in one embodiment, the method for producing a laminate of the present invention is as follows:

[12] The method for producing a laminate according to the above

[10] or

[11] , characterized in that in the step (ii), the solvent for dissolving the polymer used to form the porous film is a mixed solvent containing a good solvent and a poor solvent for the polymer.

[0013] The laminate of the present invention allows high-quality two-dimensional layered materials to be easily transferred to a desired substrate without the need to float them on water and without causing damage during the transfer process. Furthermore, the laminate of the present invention can stand on its own in the air, making it easy to store and transport.

[0014] FIG. 1 is a schematic diagram illustrating one embodiment of a laminate according to the present invention. The laminate comprises a porous membrane and a two-dimensional layered material. FIG. 2A shows a scheme of one embodiment of a laminate transfer method according to the present invention. FIG. 2A shows a method of transferring a laminate (porous membrane / two-dimensional layered material) loaded on a membrane by placing a substrate 11 on the laminate and transferring the laminate 1 to the substrate 11. FIG. 2B shows a scheme of one embodiment of a laminate transfer method according to the present invention. FIG. 2B shows a method of transferring a laminate loaded on a membrane onto a substrate. FIG. 2C shows a scheme of one embodiment of a laminate transfer method according to the present invention. FIG. 2C shows a method of transferring a laminate directly onto a substrate without using a membrane. FIG. 2D is a schematic diagram of exposing the laminate to acetone vapor to dissolve and remove the porous membrane. FIG. 3A shows a scheme of one embodiment of a laminate manufacturing method according to the present invention. FIG. 3B shows a scheme for manufacturing a graphene electrode using a conventional PMMA transfer support membrane. FIG. 4 shows an SEM image of the porous membrane surface of the porous membrane / graphene laminate prepared in Example 1 below. FIG. 5 shows a histogram of pore sizes present on the porous membrane surface of a porous membrane / graphene laminate prepared in Example 1 below. FIG. 6 shows a histogram of pore sizes present on the porous membrane surface of a porous membrane / graphene laminate prepared in Example 1 below. FIG. 7(a) shows an image of a PMMA membrane / graphene membrane laminate scooped onto a membrane and dried, as performed in Example 3 below. Meanwhile, FIG. 7(b) shows an image of a cellulose mixed ester / graphene membrane laminate scooped onto a membrane and dried. FIG. 8 shows an SEM image of the surface of a cellulose mixed ester membrane prepared in Example 5 below. FIG. 8(a) shows an SEM image of the surface of a cellulose mixed ester membrane prepared using an acetone solvent, and FIG. 8(b) shows an SEM image of the surface of a cellulose mixed ester membrane prepared using an acetone / formamide mixed solvent. FIG. 9 shows SEM images of the porous membrane surfaces of six types of porous membrane / graphene laminates prepared by the casting method in Example 5 below.The concentrations of the cellulose mixed ester solutions and the conditions for immersion in ultrapure water in Figures 18(a) to (f) are as follows: (a) 4% by mass, no immersion; (b) 4% by mass, with immersion; (c) 8% by mass, without immersion; (d) 8% by mass, with immersion; (e) 12% by mass, without immersion; and (f) 12% by mass, with immersion. Figure 10(a) shows the Raman spectrum of a porous cellulose mixed ester film / graphene film / quartz substrate laminate prepared in Example 5 below. Figure 10(b) shows the Raman spectrum of a graphene film on a quartz glass substrate from which the porous cellulose mixed ester film has been removed. Figure 11 shows an SEM image of the cellulose mixed ester film in a laminate consisting of a porous cellulose mixed ester film / graphene film / copper foil prepared in Example 6 below. Figure 11(a) shows an SEM image of a laminate in which the applicator gap height during preparation of the cellulose mixed ester film was 25 μm. 11(b) to 11(d) show SEM images of laminates in which the applicator gap height during preparation of the cellulose mixed ester film was 50 μm, 75 μm, and 100 μm, respectively. FIG. 12 shows an image of the cellulose mixed ester film prepared in Example 7 below, where the applicator gap height was 300 μm. FIG. 13 shows an image of the cellulose mixed ester film prepared in Example 7 below (prepared with an applicator gap height of 100 μm, 200 μm, or 300 μm) transferred to a slide glass. FIG. 14 shows an image of the cellulose mixed ester film formed on graphene grown on copper foil (prepared with an applicator gap height of 100 μm, 200 μm, or 300 μm) prepared in Example 7 below. FIG. 15 shows an image of the laminate prepared in Example 8 below, where one of six types of porous films was formed on a copper foil / graphene film. Figure 16 shows SEM images of the porous film surface when a cellulose acetate film, a nitrocellulose film, or a cellulose mixed ester film is formed on a copper foil / graphene film, as prepared in Example 8 below. Figure 17 shows SEM images of the porous film surface when a PMMA film, a PVDF film, or a PES film is formed on a copper foil / graphene film, as prepared in Example 8 below.FIG. 18 shows an image of a porous membrane / graphene film / quartz substrate laminate prepared in Example 9 below. FIG. 19 shows an image of the process of recovering a laminate from an etching solution in the laminate manufacturing method performed in Example 10 below. The left image of FIG. 19 shows the process of recovering the laminate using a membrane filter, in which the membrane is brought into contact with the support membrane side of the laminate floating on the etching solution surface and the laminate is pulled up. The center image of FIG. 19 shows the process of immersing the laminate adhering to the membrane filter in a water tank for cleaning. The right image of FIG. 19 shows the process of drying the laminate on the membrane filter (graphene surface facing up). FIG. 20 shows an image of a porous membrane / graphene film laminate prepared in Example 10 below, placed on a membrane filter. CN, MCE, PMMA, PVDF, and PES were used as porous films. FIG. 21 shows an SEM image of the graphene surface of a porous membrane / graphene film laminate prepared in Example 10 below. CN, MCE, PMMA, PVDF, and PES were used as porous films. Figure 22 shows images of each process of transferring a graphene / porous film freestanding laminate to quartz glass, as performed in Example 11 below. Figure 20(1) shows a graphene / porous film freestanding laminate placed on a membrane filter. Figures 22(2) and (3) show the membrane filter placed under the porous film moistened with pure water. Figure 22(4) shows the state in which pure water has been dropped onto the graphene film of the laminate. Figures 22(5) and (6) show the state in which a 20mm x 20mm quartz substrate with gold / chromium (5mm x 5mm) vapor-deposited on the four corners is placed on the laminate. Figure 23 is a graph showing the Raman spectrum of the graphene film on a quartz substrate prepared in Example 11 below. FIG. 24 shows an optical microscope image obtained during Raman spectroscopy of a graphene film on a quartz substrate prepared in Example 11 below. FIG. 25 shows an optical microscope image obtained during Raman spectroscopy of a graphene film on a quartz substrate prepared in Example 12 below. ２ 2 shows images of a single-layer graphene film on a PVDF / Si substrate. Fig. 26 shows images of each step in the transfer process performed in Example 12 below. Fig. 27 is a graph showing the transmittance spectrum of a PVDF / graphene / quartz substrate laminate in a water / glycerin solution measured in Example 13 below.

[0015] One aspect of the present invention provides a laminate comprising a two-dimensional layered material and a porous film laminated on the two-dimensional layered material, which can stand on its own in the atmosphere while maintaining its flatness. One embodiment of the laminate according to this aspect is shown in FIG. 1. As shown in FIG. 1, laminate 1 comprises a two-dimensional layered material 2 and a porous film 3. The porous film constituting the laminate of the present invention has uniformly distributed pores within the film, thereby dispersing internal stress evenly without localized concentration. The internal stress is relieved by the internal space, improving the overall structural stability of the laminate. Furthermore, the pores deform to disperse stress evenly in response to external pressure, making the porous film itself resistant to deformation. The laminate of the present invention utilizes a porous film as a transfer support film. Furthermore, porous films such as cellulose mixed ester films and nitrocellulose films that can be used in the laminate of the present invention are highly soluble in solvents such as acetone, making it possible to obtain a transfer film with extremely little polymer residue. Furthermore, since the transfer support material is a porous film, the solvent can easily penetrate into the transfer support material during the process of dissolving the transfer support material, making it possible to quickly and almost completely remove the transfer support material from the two-dimensional layered material.

[0016] As used herein, the term "two-dimensional layered material" refers to a material capable of forming atomically thin layers. Examples of such two-dimensional layered materials include, but are not limited to, graphene, doped graphene, graphene oxide, hydrogenated graphene, fluorinated graphene, hexagonal boron nitride, molybdenum sulfide, vanadium oxide, silicon, covalent organic frameworks, and layered transition metal dichalcogenides (e.g., MoS). ２ , TiS ２ etc.), two-dimensional oxides (e.g., graphene oxide, NiO ２ , etc.), layered Group IV and Group III-metal chalcogenides (e.g., SnS, PbS, GeS, etc.), silicene, germanene, and layered binary compounds of Group IV and Group III-V elements (e.g., SiC, GeC, SiGe).

[0017] The two-dimensional layered material may be formed of a single layer or multiple layers. When a multiple-layer two-dimensional layered material is used as a transparent conductive film, it is preferable that the two-dimensional layered material has two or three layers from the viewpoint of light transmittance, but is not limited thereto.

[0018] Furthermore, the two-dimensional layered material is preferably a continuous film. A continuous film refers to a film in which the components constituting the film are continuously connected without any holes or tears. A continuous two-dimensional layered material is preferable because it has a uniform surface and can reduce sheet resistance. As used herein, the term "continuous film" means that the two-dimensional layered material in the laminate is formed and adhered to the porous film surface as a continuous film. When the two-dimensional layered material is transferred to the porous film surface as a pattern, each of the two-dimensional layered materials constituting the pattern is adhered to the porous film surface as a continuous film. The laminate of the present invention is capable of transferring a continuous two-dimensional layered material to a desired substrate as a continuous film. A continuous two-dimensional layered material refers to a case in which, when the two-dimensional layered material is transferred to a specific region of the porous film surface (e.g., the entire porous film surface or a portion thereof), the coverage of the two-dimensional layered material in the specific region is 95% or more. In a preferred embodiment, the coverage of the two-dimensional layered material is 96% or more, 97% or more, 98% or more, 99% or more, or 99.5% or more. The coverage can be measured by immersing a laminate of the two-dimensional layered material / porous film in SiO ２ After transferring the material onto a Si substrate and removing the porous film, an optical microscope image of the two-dimensional layered material is taken and measurement can be performed by combining Raman mapping with a method of calculating the color ratio of the single layer portion.

[0019] In this specification, when a two-dimensional layered material is referred to as a single layer, it includes multiple two-dimensional layered materials, but also includes two-dimensional layered materials that are substantially formed as a single layer. A two-dimensional layered material that is substantially formed as a single layer refers, for example, to a two-dimensional layered material in which the area covered by multiple two-dimensional layered materials on the two-dimensional layered material is 15% or less, 10% or less, 5% or less, or 3% or less. When the area covered by multiple two-dimensional layered materials on the two-dimensional layered material is 3% or less, the coverage rate of the single two-dimensional layered material within the two-dimensional layered material is 97% or more.

[0020] In a preferred embodiment, the two-dimensional layered material is graphene. When the two-dimensional layered material is graphene, the graphene film may be doped by substituting carbon atoms of graphene with nitrogen or boron or by molecular adsorption. In a multi-layer graphene film, metal chlorides or the like may be intercalated between the layers.

[0021] Methods for forming two-dimensional layered materials and graphene films are known to those skilled in the art (see, for example, T. Watanabe et al., "Single-layer graphene as a transparent electrode for electrogenerated chemiluminescence biosensing", Electrochemistry Communications, 138, 107290 (2022). https: / / doi.org / 10.1016 / j.elecom.2022.1 (Reference 1)). For example, chemical vapor deposition (CVD) is preferred. Note that graphene films formed by known methods such as mechanical exfoliation, chemical exfoliation, SiC pyrolysis, and graphene oxide reduction can also be used as long as the laminate 1 functions.

[0022] The porous film 3 is laminated on a first surface of the two-dimensional layered material 2. The porous film 3 may be laminated so as to cover the entire surface of the two-dimensional layered material 2, or may be laminated so as to cover a portion of the surface. The porous film 3 is preferably capable of supporting the two-dimensional layered material grown on the metal catalyst substrate so that the two-dimensional layered material can maintain its shape in the atmosphere after the metal catalyst substrate is removed by etching in order to transfer the two-dimensional layered material grown on the metal catalyst substrate to a desired substrate.

[0023] The thickness of the porous film 3 is preferably 100 nm or more. If the film thickness is thinner than 100 nm, the support strength of the two-dimensional layered material formed by the CVD method will be insufficient, increasing the possibility of tearing during transfer. In a preferred embodiment, the lower limit of the film thickness of the porous film 3 is 100 nm or more, and in a more preferred embodiment, it is 1 μm or more. In an even more preferred embodiment, it is 5 μm or more. In a preferred embodiment, the upper limit of the film thickness of the porous film 3 is 300 μm or less, and in a more preferred embodiment, it is 100 μm or less. If the film is too thick, even if it has a porous structure, the residual stress of the support material will increase, and the quality of the two-dimensional layered material after transfer will be impaired.

[0024] Examples of porous membranes 3 that can be used in the present invention include, but are not limited to, membranes made of a material selected from the group consisting of nitrocellulose, cellulose acetate, polyethersulfone, polytetrafluoroethylene, polyamide, polyvinylidene fluoride, regenerated cellulose, polycarbonate, polypropylene, polyvinylidene chloride, aluminum oxide, glass fiber, quartz fiber, polymethyl methacrylate, polystyrene, polyethylene, polyethylene terephthalate, and ceramic, or mixed membranes made of two or more materials selected from the group. From the perspective of porous membranes that are easily soluble in solvents, membranes made of a material selected from the group consisting of nitrocellulose, cellulose acetate, polycarbonate, polyvinylidene chloride, polystyrene, and polymethyl methacrylate, or mixed membranes made of two or more materials selected from the group. Furthermore, the porous membrane 3 may be a laminate of two or more types of porous membranes. A preferred example of a mixed membrane made of two or more materials is a cellulose mixed ester, which is a mixture of cellulose acetate and nitrocellulose. For example, when a mixed membrane of cellulose acetate and nitrocellulose is used, the weight ratio of the cellulose acetate to nitrocellulose mixed solution used to form the porous membrane is preferably in the range of 1:1 to 1:3, and more preferably 1:2 or more. Preferred examples of the porous membrane 3 include nitrocellulose, cellulose acetate, and mixed cellulose esters.

[0025] After transferring the laminate onto the desired substrate, the porous film can be dissolved in a solvent. Thus, in a preferred embodiment, the porous film is a film made of a material that is easily soluble in a solvent, such as nitrocellulose, cellulose acetate, mixed cellulose esters, polymethyl methacrylate, or polystyrene. Using a porous film that is easily soluble in a solvent can reduce damage to the two-dimensional layered material when removing the porous film from the two-dimensional layered material after transfer, and is also preferred in that no residue of the porous film remains on the two-dimensional layered material film.

[0026] Although not limited to the following, the average pore size of the porous membrane 3 is preferably 20 nm to 20 μm. A value less than 20 nm is undesirable because it reduces the stress relaxation function. A value greater than 20 μm is undesirable because it reduces the density of the porous membrane, weakening the support strength when transferring the two-dimensional layered material and increasing the likelihood of membrane tearing. In a preferred embodiment, the average pore size of the porous membrane 3 is 200 nm to 10 μm. The average pore size of the porous membrane 3 refers to the average value of the pore sizes of the pores present on the surface of the porous membrane. The average pore size of the pores can be determined, for example, by observing the surface of the porous membrane using a scanning electron microscope (SEM) or the like and measuring the area of ​​several hundred randomly selected pores (e.g., 300 pores). From the area of ​​each pore, the diameter of each pore, assuming that the pore is circular, is calculated as the pore size, and the average value of these values ​​can be used as the surface average pore size.

[0027] Although not limited thereto, the porous film 3 preferably has a pore area ratio of 20% or more relative to the interface area between the two-dimensional layered material and the porous film. A pore area ratio of less than 20% is undesirable because it reduces the stress relaxation function and makes the two-dimensional layered material more susceptible to damage. The upper limit of the pore area ratio relative to the interface area between the two-dimensional layered material and the porous film is not limited as long as the porous film 3 functions as a transfer support film for the two-dimensional layered material 2, but can be set to, for example, 80% or less. In a preferred embodiment, the pore area ratio relative to the interface area between the two-dimensional layered material and the porous film is 25% or more, and in a more preferred embodiment, the pore area ratio relative to the film surface is 30% or more. The pore area ratio relative to the interface area between the two-dimensional layered material and the porous film of the porous film 3 refers to the ratio of the total area of ​​all pores present on one surface of the porous film to the geometric area of ​​that surface. Those skilled in the art can measure the pore area of ​​a two-dimensional layered material using known techniques. For example, when the two-dimensional layered material is graphene, the area of ​​the pores is measured by observing the structure of the porous film at the graphene film / porous film interface from the graphene side using an SEM or the like.

[0028] In one embodiment, when the two-dimensional layered material is a continuous film of single-layer graphene, the electrical resistance of the single-layer graphene film in the laminate according to the present invention can be 500 Ω / sq or less. In a more preferred embodiment, the electrical resistance of the single-layer graphene film is 400 Ω / sq or less, or 300 Ω / sq or less. In an even more preferred embodiment, the electrical resistance of the single-layer graphene film is 200 Ω / sq or less. Sheet resistance is the electrical resistance of a substantially conductive film, defined as specific resistance / film thickness. The electrical resistance of the laminate can be measured by the van der Pauw method.

[0029] Another aspect of the present invention provides a method for transferring the above-described laminate to a desired substrate, the method comprising the steps of: (a) adhering the two-dimensional layered material side of the laminate to a desired position on a desired substrate. The transfer method of the present invention does not require floating the two-dimensional layered material on the surface of water, and the two-dimensional layered material can be easily transferred to a desired position on a desired substrate.

[0030] The transfer method of the present invention includes a step of (a) adhering the two-dimensional layered material side of the laminate to a desired position on a desired substrate. The "desired substrate" is not limited as long as it is capable of adhering the two-dimensional layered material and is resistant to a solvent that dissolves the porous film. Examples of such substrates include transparent insulating substrates, SiO ２ Examples of suitable substrates include a silicon substrate. The shape of the substrate is not limited to a flat surface, and the substrate may have a curved surface. In addition, since the transfer method of the present invention does not require the laminate to be floated on the water surface during the transfer step, the substrate may be fixed to a building or the like (for example, fixed vertically) like a window pane.

[0031] Transparent insulating substrates that can be used in the present invention include, but are not limited to, quartz, glass, other transparent glass materials, sapphire glass, polyethylene terephthalate, polyester, acrylic resin, polyethylene, nylons, polyvinyl chloride, polyimide, and the like.

[0032] Furthermore, the term "desired position" refers to the position on the desired substrate where the two-dimensional layered material is to be transferred. In conventional transfer methods, it was necessary to float the layered material on the water surface and then scoop up the layered material with the desired substrate, making it difficult to precisely adjust the transfer position. On the other hand, according to the transfer method of the present invention, the layered material itself can stand on its own in the atmosphere, making it easy to transfer to the desired position on the substrate. Furthermore, according to the transfer method of the present invention, it is possible to transfer a large-area two-dimensional layered material onto the desired substrate, which was previously difficult. When a two-dimensional layered material is said to have a large area, it is meant to be, for example, 5 cm ２ In a preferred embodiment, the graphene film after transfer using the laminate of the present invention has a thickness of 10 cm ２ More preferably, the area is 25 cm ２ It has an area of ​​more than 100m2.

[0033] To bond the two-dimensional layered material side of the laminate to a desired position on a desired substrate, a small amount of a solvent such as water may be applied to the two-dimensional layered material side of the laminate and / or the substrate beforehand, and then the laminate and the substrate are brought into contact. After contacting the laminate with the substrate, it is preferable to allow the laminate to stand or to artificially dry the solvent such as water. Artificial drying includes, but is not limited to, heating or blowing air using an incubator or blower. The solvent such as water used to bond the laminate and the substrate is not limited as long as it can promote adhesion due to the van der Waals forces generated between the laminate and the substrate. Such a solvent is preferably volatile and does not dissolve the porous film. Examples include, but are not limited to, water, hexane, heptane, isobutanol, diethyl ether, toluene, etc.

[0034] The laminate of the present invention may be used without removing the porous film after transfer to the desired substrate, or may be used as a two-dimensional layered material with the porous film removed. When used as a laminate consisting of a two-dimensional layered material and a porous film without removing the porous film, it is preferable that the laminate is transparent depending on the target element (substrate). For this reason, the voids of the porous film may be filled with the material constituting the porous film or another type of material with the same refractive index as the material constituting the porous film. If the porous film does not have an absorption band in the visible light wavelength range, the laminate will be transparent.

[0035] An example of a method for filling the voids of the porous membrane with another type of substance having the same refractive index as the substance constituting the porous membrane is a method for filling the voids of the porous membrane with a solvent having a refractive index matching that of the porous membrane. Those skilled in the art can appropriately prepare or adjust a solvent having a refractive index matching that of the porous membrane. Examples of such solvents include, but are not limited to, a combination of solvents with different refractive indices, such as a combination of glycerin and water, and adjusting the composition ratio to match that of the porous membrane. The solvents that can be used are not limited as long as they do not interfere with the use of the laminate as an electrode.

[0036] In one embodiment, the transfer method of the present invention can further comprise, after step (a), a step (b) of removing the porous film of the laminate using a solvent. The solvent for dissolving the porous film can be any known solvent capable of dissolving the porous film, and can be appropriately selected depending on the porous film. Examples of such solvents include ketones such as acetone and acetic acid, alcohols, or combinations thereof. The laminate can be immersed in these solvents, or the solvent can be heated and the laminate can be exposed to the solvent vapor to dissolve and remove the porous film.

[0037] A scheme of one embodiment of the laminate transfer method according to the present invention is shown in Figures 2A to 2C. Figure 2A illustrates a method of transferring a laminate 1 (porous film / two-dimensional layered material) onto a membrane 8 by placing a substrate 11 on the laminate 1. More specifically, the laminate 1 mounted on the membrane 8 is moistened with water, and the substrate 11 is adhered to the laminate 1. The adhered substrate 11, laminate 1, and membrane 8 are then turned upside down, and the membrane 8 is further moistened with water. The membrane 8 is then peeled off from the laminate 1, thereby transferring the laminate 1 to the substrate 11. Subsequently, the porous film 3 in the laminate 1 can be optionally removed, thereby transferring the two-dimensional layered material 2 to the substrate 11. Figure 2B illustrates a method of transferring the laminate 1 mounted on the membrane 8 onto the substrate 11. The desired position on the substrate 11 is moistened with water, and the membrane 8 carrying the laminate 1 is adhered to the substrate 11 so that the substrate 11 comes into contact with the porous film 3 in the laminate 1. The membrane 8 is then further moistened with water and removed, transferring the laminate 1 onto the substrate 11. Optionally, the porous film 3 in the laminate 1 can then be removed to transfer the two-dimensional layered material 2 to the substrate 11. Figure 2C shows a method for directly transferring the laminate 1 onto the substrate 11 without using a membrane. The desired position on the substrate 11 is moistened with water, and the laminate 1 is adhered to the substrate 11 so that the substrate 11 comes into contact with the porous film 3 in the laminate 1, transferring the laminate 1 onto the substrate 11. Optionally, the porous film 3 in the laminate 1 can then be removed using a solvent to transfer the two-dimensional layered material 2 to the substrate 11. Figure 2D shows a schematic diagram of exposing the laminate 1 to acetone vapor to dissolve and remove the porous film 3.

[0038] Another aspect of the present invention provides a method for producing a laminate comprising a two-dimensional layered material and a porous film, the method comprising the steps of: (i) forming a two-dimensional layered material on a metal catalyst substrate by a CVD method; (ii) further forming a porous film on the two-dimensional layered material to produce a laminate; and (iii) removing the metal catalyst substrate by etching.

[0039] Conventionally, manufacturing an electrode having a graphene film as a two-dimensional layered material involves forming a PMMA film as a transfer support film on a graphene film formed on a metal catalyst substrate, etching the metal catalyst substrate, transferring the graphene film to the desired substrate, and then removing the PMMA film. This method requires that the laminate consisting of the graphene film and the transfer support film be floated on the water surface after etching the metal catalyst substrate, necessitating the subsequent transfer to the substrate as a single process. However, according to the method for manufacturing a laminate of the present invention, the resulting laminate is self-supporting in the air and retains its shape even after being lifted from the water surface in the air. This eliminates the need for a single process involving etching the metal catalyst substrate and transferring the graphene film to the substrate. In other words, the transfer of the laminate to the desired substrate can be performed at a convenient time. An example of a manufacturing method scheme according to the present invention is shown in Figure 3A. In the embodiment shown in Figure 3A, a two-dimensional layered material 2 is formed on a metal catalyst substrate 4, and then a porous film-forming solution 3' is applied to the two-dimensional layered material 2 using an applicator. The resulting laminate is then transferred to a water tank containing ultrapure water to promote the formation of a porous film. The resulting laminate 1" (porous membrane / two-dimensional layered material / metal catalyst substrate; wet state) is dried, and the dried laminate 1' (porous membrane / two-dimensional layered material / metal catalyst substrate) is floated in an etching solution in an etching bath to etch the metal catalyst substrate. Finally, the laminate 1 is recovered from the etching solution, thereby completing the production of the laminate. In the embodiment shown in Figure 3A, the laminate 1 is recovered using a membrane 8.

[0040] A manufacturing scheme for a graphene electrode using a conventional transfer support film is shown in Figure 3B. As shown in Figure 3B, in the conventional graphene film transfer method using PMMA as the transfer support film, it is necessary to scoop up the PMMA laminate (PMMA / graphene film) directly from the etching bath 7 (a water bath for subsequent cleaning) with a substrate 11. After the PMMA laminate 10' is scooped up with the substrate 11, the PMMA is removed. Furthermore, in the conventional graphene film transfer method using PMMA as the transfer support film, PMMA residue remains on the graphene film surface after PMMA removal. Such residue unfavorably affects the properties of the graphene film. In contrast, the manufacturing method of the present invention can use a porous film that is easily dissolved in a solvent, which avoids the above-mentioned problems.

[0041] The method for producing a laminate according to the present invention includes (i) the step of forming a two-dimensional layered material on a metal catalyst substrate by a CVD method. Methods for forming a two-dimensional layered material 2 on a metal catalyst substrate 15 by a CVD method are known, and can be carried out by referring to, for example, the above-mentioned Reference 1. The metal catalyst substrate 15 that can be used in the present invention is not limited, and any known substrate used for forming a two-dimensional layered material 2 can be used. Preferred examples include copper substrates, nickel substrates, cobalt substrates, iridium substrates, platinum substrates, gold substrates, and alloy substrates thereof. Alternatively, a substrate formed by vapor-depositing these metals on a heat-resistant substrate may be used.

[0042] After forming a two-dimensional layered material on the metal catalyst substrate in step (i), a step (ii) of forming a porous film on the two-dimensional layered material is carried out. The method for forming the porous film 3 on the two-dimensional layered material is not limited, and known techniques such as spin coating, spray coating, phase inversion using an applicator or bar coater, and vapor deposition can be used. The method for forming a porous film by spin coating will be described below.

[0043] A polymer, which is the raw material for the porous film 3, is dissolved in a solvent to prepare a porous film-forming solution. An appropriate polymer can be selected depending on the porous film 3 to be formed. One or more types of polymers may be used to form the porous film 3. It is known that when forming the porous film 3 by spin coating, the thickness and average pore size of the porous film change depending on conditions such as the solvent selected, the concentration of the polymer in the solvent, the rotation speed of the spin coater, the viscosity of the solution, and the average molecular weight of the polymer (which affects the viscosity). Those skilled in the art can appropriately set the above conditions to form a porous film with the desired thickness and average pore size depending on the polymer and solvent used. The following are examples of conditions for forming the porous film 3 by spin coating, but are not limited to these.

[0044] The solvent is not limited as long as it can dissolve the polymer and form a porous film by spin coating. Examples of solvents that can be used include acetone, methanol, diethyl ether, and ethyl acetate. A low-boiling solvent is preferred. In a preferred embodiment, the solvent has a boiling point of 100°C or less, and in a more preferred embodiment, the solvent has a boiling point of 80°C or less. Generally, low-boiling solvents have a fast evaporation rate. Therefore, using a low-boiling solvent increases the precipitation rate of the polymer in the solution, resulting in random precipitation of the polymer, which is preferable, resulting in the formation of a porous structure. The polymer concentration in the solvent can be 0.5 to 20% by mass. A laminate of a metal catalyst substrate 15 and a graphene film 2 is fixed on a spin coater stage, and the prepared porous film-forming solution is dripped onto the surface and near the center of the graphene film 2. The amount of the dripped porous film-forming solution is sufficient to sufficiently cover the graphene film 2. The rotation speed and rotation time of the spin coater are not limited as long as the desired porous film can be formed. For example, the rotation speed can be set to 200 to 5000 rpm, and the rotation time of the spin coater can be set to 10 to 120 seconds. After that, if any solvent remains, it is dried by heating.

[0045] In a preferred embodiment, the porous membrane 3 can be formed on a two-dimensional layered material by a phase inversion method, such as casting using an applicator. Phase inversion is a method of making a material, such as a polymer, porous by converting it from a liquid phase to a solid phase under controlled conditions. Representative phase inversion methods include nonsolvent-induced phase separation and thermally induced phase separation. Nonsolvent-induced phase separation involves two distinct phenomena: the evaporation of a solvent in a polymer solution containing a nonsolvent or poor solvent, destabilizing the polymer solution and resulting in the precipitation of the polymer in the presence of the nonsolvent; and the nonsolvent contacting the polymer and simultaneously extracting the solvent into the nonsolvent, resulting in the infiltration of the nonsolvent into the polymer solution, destabilizing the polymer solution and resulting in the precipitation of the polymer. The former is called the dry phase inversion method, and the latter is called the wet phase inversion method. There is also a dry / wet phase inversion method, which combines the two. The phase inversion method for forming porous films is well known; see, for example, Masahiro Tamura, Tadashi Uragami, and Mizuho Sugihara, “Permeation Characteristics on Cellulose Nitrate-Cellulose Acetate Blend Polymer Membranes,” Journal of the Japan Society of Color Material, Vol. 50 (6), 317-322 (1977). The nonsolvent-induced phase separation method forms a porous structure by utilizing a solvent exchange process between a good solvent and a poor solvent in a liquid phase. This allows for the formation of a porous film without excessive volume shrinkage due to rapid solvent evaporation, and minimizes damage to graphene at the contact interface with the graphene that occurs during porous film formation. The solvent used in the phase inversion method can be the same as that used in the spin coating method. The polymer concentration in the solvent can be 0.5 to 20% by mass.

[0046] After forming a porous film on the two-dimensional layered material in step (ii), a step (iii) of removing the metal catalyst substrate by etching is carried out. Known methods can be used to remove the metal catalyst substrate 15. For example, when copper foil is used as the metal catalyst substrate 15, etching can be performed using known solutions such as an aqueous ammonium persulfate solution or an aqueous iron (III) nitrate solution. Etching can be performed by floating the laminate on the surface of the etching solution so that the copper foil surface comes into contact with the etching solution. Alternatively, the metal catalyst substrate can be etched by immersing the laminate in the etching solution. Because the laminate of the present invention has high mechanical strength, it can maintain low sheet resistance even when immersed in an etching solution.

[0047] If two-dimensional layered materials are also formed on the back surface of the metal catalyst substrate 15 where the porous film 3 is not formed, the two-dimensional layered materials on the back surface are removed using oxygen plasma treatment or the like before etching the metal catalyst substrate 15. The porous film 3 / two-dimensional layered material 2 / metal catalyst substrate 15 is floated in an etching solution so that the surface from which the two-dimensional layered material has been removed comes into contact with the etching solution, and the metal catalyst substrate 15 is removed. After removing the metal catalyst substrate 15, the laminate consisting of the porous film 3 and the two-dimensional layered material 2 is washed by transferring it to the surface of a pure water pool. It is preferable to perform the washing process three or more times. The laminate 1 floating on this pure water is scooped up using an arbitrary membrane or the like. After scooping up, the laminate 1 is dried, and the production of the laminate is completed.

[0048] The present invention will be specifically described below using examples, but the present invention is not limited to the following embodiments.

[0049] Example 1: Production of a Laminate Composed of Graphene Film and Porous Film In this example, a laminate composed of a single-layer graphene film and a cellulose film (porous film) (hereinafter also referred to as a "porous film / graphene laminate") was produced as follows. Copper foil (35 μm thick) was prepared as a metal catalyst substrate for graphene chemical vapor deposition (CVD) growth. Prior to graphene film formation by CVD, the copper foil was immersed in pure water, ethanol, and acetone, successively, and subjected to ultrasonic treatment to clean the copper foil surface. Thereafter, the copper foil was transferred to a thermal CVD furnace, and hydrogen was introduced, and hydrogen annealing of the copper substrate was performed for 30 minutes under conditions of a hydrogen atmosphere total pressure of 700 Pa and 1000°C. Thereafter, methane was introduced, and graphene was grown by CVD for 10 minutes at a total pressure of 750 Pa, with a flow rate of 2 sccm of methane and 20 sccm of hydrogen.

[0050] Porous films were fabricated on graphene films formed on copper foil using spin coating. Nitrocellulose (CN), cellulose acetate (CA), or a mixed film of nitrocellulose and cellulose acetate (cellulose mixed film) was used as the support layer for graphene transfer. Nitrocellulose (Nacalai Tesque, product number 24728-34), cellulose acetate (Sigma-Aldrich, product number 419028), and acetone as the solvent were prepared as raw materials for the porous film formation solution. Cellulose acetate or nitrocellulose was mixed with acetone to prepare a solution with a 2% cellulose acetate or nitrocellulose content. Three different cellulose mixed solutions with different compositions were also prepared by mixing nitrocellulose, cellulose acetate, and acetone to prepare solutions with a total content of both nitrocellulose and cellulose acetate of 2% by mass and with mass ratios of 3:1, 1:1, and 1:3. A PMMA solution, which has traditionally been used as a support film for graphene transfer, was prepared as a comparison sample. A PMMA solution (Sigma-Aldrich, product number 182265) was prepared by dissolving it in ethyl lactate as a solvent to a content of 4% by mass. Next, the porous film-forming solution was dropped onto a graphene film formed on a copper foil, and spin coating was performed at 2000 rpm to form a nitrocellulose film, a cellulose acetate film, or a mixed cellulose ester film. Under similar conditions, a PMMA film serving as a transfer support film was formed on the graphene film formed on the copper foil. After forming the porous film or transfer support film, the unnecessary graphene film formed on the backside of the copper foil was removed by oxygen plasma treatment. This resulted in a laminate consisting of a porous film / graphene film / copper foil. A comparative example was also obtained, consisting of a PMMA film (transfer support film) / graphene film / copper foil laminate.

[0051] An etching tank was prepared, and a copper etching solution of an aqueous iron (III) nitrate solution (0.5 mol / L) was stored in the tank at 25°C. The size of the porous film / graphene film / copper foil laminate to be subjected to copper etching was 15 mm x 10 mm. The laminate was floated in the copper etching solution so that the copper foil was in contact with the solution, and the copper foil of the laminate was removed by etching for 5 hours. This resulted in a porous film / graphene film laminate comprising a porous film and a graphene film. A PMMA film (transfer support film) / graphene film laminate was also obtained as a comparative example.

[0052] The porous membrane surface of the prepared porous membrane / graphene membrane laminate was observed using a SEM (FE-SEM, manufactured by ZEISS), and the pore size and the percentage of the surface occupied by pores were measured from the captured SEM images. The sample used for SEM observation was a porous membrane / graphene membrane laminate formed on a copper foil after spin coating, with a 3 nm platinum coating on the porous membrane surface. Similarly, the surface of a PMMA membrane was also observed as a comparative example. Figure 4 shows an SEM image. The PMMA membrane had a smooth surface and formed a dense membrane structure without pores. The CN membrane and CA membrane contained pores, but these were composed of small pores, with no pores larger than 100 nm. The CA membrane also had a surface with a low pore density. All prepared cellulose blend membranes had a porous structure, and a tendency for pore diameter to increase with increasing nitrocellulose mass ratio was observed. The diameters of all pores visible in the SEM images were estimated using the scale bar as a reference. The pore diameter data was used to calculate the surface occupancy of the pores in the CN membrane, which is the area ratio of the pores to the membrane surface of the porous membrane. For the blended membranes, the percentage of black area was calculated as the surface occupancy of the pores after converting the SEM image to a black-and-white image. Figures 5 and 6 show the pore size distribution (histograms) of each sample. The histograms were created from the diameter values ​​of all pores visible in the SEM image of Figure 4. Therefore, the histograms shown are for the PMMA membrane, in which no pores were observed, and the CA membrane, which had a low pore density. The CN membrane had only pores with diameters of 40 nm or less, with an average pore diameter of 17 nm. The surface occupancy of the pores in the CN membrane was 2.1%. The cellulose blended membrane with a CN:CA = 1:3 ratio had only pores with diameters of 150 nm or less, with an average pore diameter of 49 nm. The cellulose blend membranes with a CN:CA ratio of 1:1 and CN:CA ratio of 3:1 had pores of 150 nm or larger, with average pore diameters of 140 nm and 880 nm, respectively. The CN:CA ratio of 3:1 had many large pores with diameters of approximately 550 nm, and also had a pore distribution with even larger pore sizes of 1.5 μm or larger. The surface occupancies of the pores in the cellulose blend membranes with a CN:CA ratio of 1:3, CN:CA ratio of 1:1, and CN:CA ratio of 3:1 were 38%, 40%, and 32%, respectively.

[0053] Example 2: Production of a Laminate Comprising a Porous Film, a Graphene Film, and a Transparent Insulating Substrate In this example, the porous film / graphene film laminate produced in Example 1 was transferred onto a transparent insulating substrate to produce a laminate comprising a porous film, a graphene film, and a transparent insulating substrate. A quartz substrate (1 mm thick, 20 mm × 20 mm) was prepared as the transparent insulating substrate. A 10 nm thick chromium layer was deposited on a portion of the quartz substrate using a vacuum deposition apparatus, and a 50 nm thick gold layer was deposited on the chromium. This metal deposition film functions as a conductive electrode when the porous film / graphene film laminate is laminated on the quartz substrate and is necessary when applying the transferred graphene film as a device such as an electrode for electrochemical measurement. A water tank filled with ultrapure water was prepared. After copper etching, the porous film / graphene film laminate floating in the etching solution was transferred to the water surface of the water tank and washed with water. The laminate was then repeatedly washed by transferring it to another water tank. This water washing process was performed three times. The porous film / graphene film laminate floating in a pool of ultrapure water was scooped up using a quartz substrate on which chromium and gold had been vapor-deposited as a conductive electrode. The porous film / graphene film laminate was stacked so that a portion of the conductive electrode overlapped the porous film / graphene film laminate. In this way, a laminate consisting of a quartz substrate (transparent insulating substrate), a porous film, and a graphene film was produced.

[0054] The thickness of the porous film on the laminate was measured using a stylus step gauge (manufactured by BRUKER). The thickness of the laminate on the quartz substrate manufactured using a 2% by weight cellulose acetate and nitrocellulose mixed solution (CN:CA = 3:1) was approximately 400 nm. On the other hand, the thickness of the laminate manufactured using an ethyl lactate solution containing 4% by weight PMMA was approximately 150 nm.

[0055] (Example 3. Preparation of Freestanding Graphene / Porous Film Laminate) A PMMA film / graphene film laminate and a mixed cellulose ester / graphene film laminate (CN:CA = 3:1) prepared under the same conditions as in Example 1 were transferred from the pure water onto a 47 mm diameter membrane filter (ADVANTEC, model number: A045A047A) so that the transfer support material of each laminate was in contact with the membrane filter, and then dried. As a result, the PMMA film / graphene film laminate became wrinkled ( FIG. 7( a) ), whereas the mixed cellulose ester / graphene film laminate maintained its flatness ( FIG. 7( b) ). This difference between the two types of transfer support material likely reflects the porous structure alleviating the internal stress of the laminate. However, when a transfer method ( FIG. 2A ) was attempted using this laminate without floating it on water, the laminate broke during the process of contacting and peeling off the graphene, and it was not possible to transfer it to the substrate. This is thought to be because the adhesion between the porous film produced by this spin coating method and the membrane filter is stronger than that of the thick porous film in the Examples described later. A thin porous film has flexibility that allows it to follow even fine irregularities, so the adhesion area with the membrane filter increases, and the adhesive strength is thought to be stronger.

[0056] Example 4: Verification of Transfer Support Ability of Porous Film In this example, the transfer support ability of a porous film in the etching process of a metal catalyst substrate or the subsequent transfer process to a transparent insulating substrate was verified. A porous film was formed on a graphene film under the same conditions as in Example 1, except that an acetone solution with a 1% by mass concentration of nitrocellulose was used. The thickness of the porous film formed on the graphene film was less than 100 nm. When copper foil was etched after the porous film formation, the film broke due to insufficient support. Furthermore, a porous film was formed on a graphene film under the same conditions as in Example 1, except that an acetone solution with a 6% by mass concentration of nitrocellulose or a 4% by mass concentration of cellulose acetate was used. The thickness of the porous film formed on the graphene film was 1 μm or more. The graphene film was able to be supported in the copper foil etching process after porous film formation, but some peeling from the quartz substrate was observed after transfer to the quartz substrate. On the other hand, when a PET substrate was used instead of the quartz substrate, no peeling occurred even when the porous film was 1 μm or more thick.

[0057] Example 5: Investigation of a Method for Producing a Porous Film / Graphene Laminate by Casting In this example, a cellulose mixed ester film was formed using a casting method using an applicator, and a method for making the cellulose mixed ester film porous was investigated. The cellulose mixed ester film used in this example was produced at a weight ratio of CA:CN = 1:2. First, the solvent was investigated. A porous film-forming solution was prepared by dissolving 12% by mass of cellulose mixed ester in two solvents: acetone and a mixed solvent of acetone and formamide (weight ratio 1:1). The solution was manually cast onto a copper substrate using an applicator with a gap height of 75 μm (BEVS four-sided applicator, width 60 mm, model number: BEVS 1803 / 60 / F13). Figure 8 shows an SEM image of the surface of the cellulose mixed ester film that had been cast and dried (platinum coated to prevent charge buildup). While no pore structure was observed when the acetone solvent was used, a pore structure was observed when the acetone + formamide solvent was used. Acetone is a good solvent for CA and CN, while formamide is a good solvent only for CN and a poor solvent for CA. In the acetone / formamide mixed solvent, as the solvent evaporates, the casting liquid gradually changes into a poor solvent and phase-separates as the acetone, a good solvent, evaporates. This phase separation is thought to be the reason why the acetone / formamide mixed solvent becomes porous. This technique is a dry phase inversion method.

[0058] Next, a dry-wet phase inversion method was investigated, in which the sample was immersed in ultrapure water after casting. The effect of the solute concentration of the cellulose mixed ester solution on the porous structure was also evaluated. CN and CA were dissolved in an acetone / formamide mixed solvent (1:1 by weight) to prepare a porous membrane solution with a cellulose mixed ester concentration of 4, 8, or 12% by mass. The solution was manually cast onto a copper substrate using an applicator with a gap height of 75 μm. Two types of samples were prepared for each solute concentration: one that was cast and then dried (dry method), and the other that was immersed in ultrapure water for 24 hours 60 seconds after casting and then dried (dry-wet method). The surfaces of the prepared cellulose mixed esters were coated with platinum, and their surface structures were observed using SEM. Figure 9 shows SEM images of the surfaces of the six types of cellulose mixed ester membranes prepared ((a) without 4% immersion, (b) with 4% immersion, (c) without 8% immersion, (d) with 8% immersion, (e) without 12% immersion, (f) with 12% immersion). At all solute concentrations, immersion in water tended to increase the pore diameter. This is because the cast solution was gelled by immersion in water, exchanging the dissolved solvent in the cast solution for water, resulting in phase inversion. The thickness of the porous membranes measured using DekTak is shown in Table 1.

[0059] The film thickness measurements showed a tendency for film thickness to increase with increasing solute concentration and immersion in water. The significant increase in porous film thickness upon immersion in water indicates that the water-immersed sample contains a large amount of voids. The film thickness increased because the amount of solute contained in the casting solution increased with increasing solute concentration. The significant increase in film thickness for the sample immersed in 12% by weight water is thought to be related to the viscosity of the porous film-forming solution. The increased viscosity likely reduced the fluidity of the solute, suppressing aggregation of solutes and thereby reducing the shrinkage of the porous film relative to the applicator gap. Table 2 shows the viscosity of the porous film-forming solution measured using a viscometer (Anton Paar, Model: ViscoQC 100, Spindle: SC4-21).

[0060]

[0061] Next, we investigated whether graphene grown on copper foil using these mixed cellulose esters could be transferred to a quartz substrate. Using a cellulose mixed ester film prepared using an acetone solvent solution, similar to the sample shown in Figure 8(a), as a support material, we attempted to transfer graphene to a quartz substrate using the same procedure as in Example 2. As a result, we found that these laminates peeled off from the quartz substrate during the drying process after transfer, making them untransferable. On the other hand, samples prepared using a porous film-forming solution prepared with a formamide / acetone mixed solvent did not peel off even after drying, and all laminates prepared under the conditions shown in Table 1 were successfully transferred. It is believed that the increased thickness of samples prepared using an applicator compared to spin coating also increases the tensile stress. While the cellulose mixed ester film prepared using an acetone solvent solution did not form a porous structure, the acetone / formamide mixed solvent formed a porous structure throughout the entire film, which likely alleviated the tensile stress and prevented peeling. Thus, we found that by making the support film porous, it was possible to transfer the support film / graphene laminate to a substrate without peeling, even if the film was thicker than 10 μm.

[0062] The Raman spectrum of a porous cellulose mixed ester film / graphene laminate transferred onto a quartz substrate using a support film prepared by immersing a solution with a solute concentration of 12% by mass in pure water is shown in Figure 10(a). －１ and 2950 cm －１ Cellulose CH appears nearby ３ Peaks derived from the C-H and C-H bands were observed, but the 2D peak and G peak derived from graphene were not observed. This is thought to be because the support film was porous and thick, causing the laser light to be scattered by the support film and not reach the graphene. Therefore, the cellulose mixed ester / graphene laminate was immersed in hot acetone for 20 minutes to remove the cellulose mixed ester film, which was the support film, before performing Raman spectroscopy analysis. Figure 10(b) shows the Raman spectrum of graphene after the support film was removed. The 2D peak and G peak derived from graphene were observed, and the peak at 1350 cm －１Since almost no D peak, which indicates defects, was observed near 2950 cm, it can be said that high-quality graphene was produced even when a cellulose mixed ester film prepared by the casting method was used as a support material. －１ The peak due to the C--H of cellulose, which appears around this point, was not observed, which indicates that the cellulose mixed ester was completely removed by immersion in hot acetone.

[0063] Example 6: Preparation of mixed cellulose ester membranes by phase inversion method - thickness change 1 To evaluate the effect of porous membrane thickness, a solution of 12% by mass of cellulose mixed ester with a 2:1 mass ratio of cellulose acetate to nitrocellulose in acetone-formamide mixed solution (acetone:formamide mass ratio 1:1) was used to prepare porous membranes using a four-sided applicator (60 mm wide) with gap heights of 25, 50, 75, and 100 μm. The cellulose solution was applied using the applicator using a Cortec ALC-mini2 fully automatic linear motion coater, which is capable of controlling the running speed during film formation. Graphene was grown on copper foil in the same manner as in Example 1. In this experiment, the running speed during film formation was set to 2 mm / s, and four porous membrane samples with different thicknesses were formed on graphene grown on copper foil. The solution had a high viscosity (609 mPa s) and began to dry immediately after being spread on the graphene. Therefore, the solution did not spread further after being spread with the applicator. After applying the cellulose solution, the copper foil was transferred to a pool of pure water and immersed therein for 1 hour. After removal from the water, the foil was allowed to air-dry. To analyze the surface structure of the prepared porous cellulose mixed ester / graphene laminated film, the film surface was observed using an SEM, as in Example 1. The average pore size and pore surface occupancy were calculated from the captured images. Furthermore, to investigate how the actual film thickness changes with the applicator gap height, film thickness measurements were performed using a laser microscope. Figure 11 shows an SEM image of the cellulose mixed ester film. Comparing the samples, it was observed that the cellulose fiber structure thickened with increasing film thickness. Table 3 shows the film thickness, average pore size, and pore surface occupancy on the film surface. Comparing the four samples, it was observed that the film thickness increased with the applicator gap height. Furthermore, the average pore size and pore surface occupancy decreased with increasing film thickness. This is thought to be because, when the cellulose solution is applied with an applicator and then immersed in water, thick films are less susceptible to solvent replacement, making it less likely for voids to form when dried. These four types of laminates were transferred onto a quartz substrate in the same manner as in Example 2, and no peeling of the film occurred in any of the samples with any thickness even after drying.

[0064]

[0065] (Example 7. Preparation of cellulose mixed ester film by phase inversion method - thickness change 2) To investigate the effect of film thickness when a thicker porous film is formed, a cellulose mixed ester was prepared by the phase inversion method using the same solution as in Example 6 and a multi-vaporized applicator (Co-Tech, width 100 mm, model number: MA100) at gap heights of 100, 200, 300, and 400 μm. First, a porous film was prepared on copper foil on which graphene had not been grown. The coating conditions using the applicator were the same as in Example 6, except for the applicator type, gap height, and running speed. The applicator running speed in this example was 15 mm / s. Figure 12 shows a photograph of a sample coated with a solution at a gap height of 300 μm, immersed in pure water, and dried. Significant warping occurred in the copper foil substrate, suggesting that the increased film thickness led to increased tensile stress within the porous film. Samples with gap heights of 200 μm or more exhibited warping of the copper foil and partial peeling of the porous film. In the samples with a gap height of 100 μm, almost no warping of the copper foil was observed. The unpeeled portions of these porous films (100 mm × 100 mm) were cut into 35 mm × 35 mm pieces, floated in a 10% by weight aqueous solution of ammonium persulfate, and the copper foil was etched. The resulting pieces were then transferred to glass slides (75 mm × 52 mm, Matsunami Glass, product number S9111). The state after transfer is shown in Figure 13. After transfer to the glass slide, the pieces were washed with pure water and dried. When wet, the porous films adhered to the glass slides while maintaining their planar structure. However, samples with gap heights of 200 μm or greater peeled from the glass slides during drying. Only samples fabricated with a gap height of 100 μm remained attached to the glass slides without peeling even after drying. More than 50% of the sample with a gap height of 200 μm peeled, while samples with a gap height of 300 μm or greater peeled almost completely. The film thickness measured by a laser microscope was 37 μm for the sample prepared with a gap height of 100 μm, 75 μm for the sample prepared with a gap height of 200 μm, and 157 μm for the sample prepared with a gap height of 300 μm.

[0066] Next, a 12% by mass (CA:CN = 1:2) cellulose mixed ester film was fabricated on copper foil (35 mm x 70 mm) with single-layer graphene grown at the same four gap heights. Figure 14 shows a photograph of the porous film after immersion in water and drying. It can be seen that the warping of the copper foil increased with increasing gap height. Because cracks occurred in the 400 μm sample, three samples (100, 200, and 300 μm) were cut into 20 mm x 20 mm pieces and transferred to glass slides. Even after washing with pure water and drying, the laminate did not peel from the glass slide. The lack of peeling from the glass slide despite the large stresses, as shown in the photograph in Figure 14, indicates strong adhesion at the graphene / glass slide interface and the graphene / porous film interface. However, for the laminate fabricated at a gap height of 300 μm, cracks occurred during the sample molding process before copper etching, resulting in partial tearing of the laminate after transfer. Thus, it was found that increasing the film thickness increases the tensile stress of the porous film, potentially reducing the quality of graphene in the laminate. As shown in Example 6, increasing the film thickness also facilitates the formation of a layer called a skin layer, which has small pores, on the surface of the porous film. This skin layer is thought to reduce the stress relaxation function of the porous film. On the other hand, results suggest that the smoothness and flexibility of graphene enhance its adhesion to the substrate and improve the adhesive strength due to van der Waals forces. These results also indicate that porous cellulose mixed ester films with a thickness of 100 μm or less have high adhesive properties with graphene and are highly resistant to deformation. Therefore, it can be said that they have sufficient mechanical strength to serve as a graphene transfer support material.

[0067] Example 8: Study of polymer materials suitable for porous films for supporting graphene transfer Six types of polymers were cast onto graphene grown on copper foil by CVD, and an attempt was made to make the film porous by a phase inversion method. To confirm whether the produced polymer film formed a porous structure, SEM observation of the polymer film / graphene laminate was performed. The polymer films used were cellulose acetate (CA), nitrocellulose (CN), mixed cellulose ester (MCE), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), and polyethersulfone (PES).

[0068] Copper foil was cut to 110 mm x 70 mm and immersed in acetic acid for 3 minutes, then immersed in pure water and acetone, and then dried by nitrogen blowing. The copper foil was then transferred to a thermal CVD furnace, hydrogen was introduced, and hydrogen annealing of the copper substrate was performed for 30 minutes under conditions of a hydrogen atmosphere total pressure of 700 Pa and 1000 ° C. Methane was then introduced, and graphene was grown by CVD for 10 minutes at a flow rate of 2 sccm methane and 20 sccm hydrogen at 1000 ° C. and a total pressure of 750 Pa. The copper foil on which graphene was grown was cut to 110 mm x 35 mm. This CVD process was performed three times to prepare six copper foils on which graphene was grown, each measuring 110 mm x 35 mm.

[0069] The compositions of the solutions used to prepare various polymer films are shown in Table 4.

[0070] The polymeric raw materials shown in Table 4 were weighed into vials, and the solvent was added and stirred. Because PVDF and PES were difficult to dissolve, they were kept at 55°C until dissolved. A copper foil (110 mm x 35 mm) on which graphene had been grown was fixed to the stage using the clamping function of a fully automated linear motion coater, and the solution was applied to the graphene / copper foil using a multi-vaporized applicator. The applicator gap height was set to 160 μm as measured by the attached micrometer. Since the copper foil was 35 μm thick, the gap height between the copper foil and the applicator was estimated to be approximately 125 μm. The applicator travel speed was 15 mm / s. The graphene / copper foils coated with the various solutions were immediately immersed in a pool of pure water and removed after 30 minutes. After removal from the pool, the polymer adhering to the graphene on the backside of the copper foil was removed using a cotton swab moistened with various solvents, and the graphene on the backside of the copper foil was removed by exposure to oxygen plasma. The samples were then cut into 15 mm x 15 mm pieces. Figure 15 shows photographs of the six samples. The four samples coated with PVDF, PES, CN, and MCE exhibited a white color, suggesting the formation of a porous structure. On the other hand, the copper foil color was prominent in the samples coated with CA and PMMA, suggesting that the polymer support film was almost transparent and no porous structure was formed. Platinum was coated on the polymer film side of this polymer film / graphene / copper foil laminate, and SEM observation was performed. Figures 16 and 17 show SEM images. Pores were observed in all polymer films, but the pores on the surfaces of CA, PMMA, and PES were small, and the pores accounted for only a small proportion of the surface. The white color of PES suggests the formation of a skin layer on the surface. The other three samples also showed a small proportion of the pores on the surface, suggesting that the increased applicator gap caused the film to thicken and a skin layer to form.

[0071] Example 9: Transfer of Laminate and Measurement of Laminate Thickness by Conventional Method. The 15 mm × 15 mm polymer support film / graphene / copper foil laminate prepared in Example 8 was floated in a 10% by mass aqueous solution of ammonium persulfate, a copper etching solution, with the copper facing downward. As in Example 2, after all the copper was etched, the polymer support film / graphene laminate floating in the etching solution was transferred to the water surface of a water tank and washed with water. The laminate was then repeatedly washed by transferring it to another water tank. This water washing process was performed three times. The porous film / graphene film laminate floating in the pure water pool was scooped up using a quartz substrate. This polymer support film / graphene / quartz substrate laminate was allowed to air dry. Figure 18 shows a photograph of the polymer support film / graphene laminate transferred to a quartz substrate. The CA / graphene laminate peeled off from the quartz substrate during the drying process. The photograph of CA shows some translucent areas, suggesting a partially porous structure, but most of it is transparent, meaning that a sufficient porous structure was not formed, resulting in tensile stress that exceeded the adhesive strength between the quartz substrate and graphene. The PMMA / graphene laminate was more transparent than the other four types of support film / graphene laminates other than CA, but the entire film was uniformly translucent.

[0072] The film thickness of the support film / graphene laminate transferred onto the quartz substrate was measured using a shape analysis laser microscope (Keyence, VK-X1000). Table 5 shows the film thickness of five types of laminate. The film thickness of the CA film could not be measured because it could not be transferred to the substrate. The difference in film thickness between samples, even with the same applicator gap height, is related to the solute concentration, viscosity of the solution, and the degree of porous structure formation.

[0073] Example 10: Preparation of a graphene / porous support membrane freestanding laminate and structural evaluation by SEM. The 15 mm x 15 mm polymer support membrane / graphene / copper foil laminate prepared in Example 8 was floated in a 10% by mass ammonium persulfate aqueous solution, which was a copper etching solution, with the copper facing downward, as in Example 8. After all of the copper was etched, the graphene / polymer support membrane laminate floating in the aqueous solution, as shown in Figure 19, was lifted onto a cellulose mixed ester membrane filter (ADVANTEC, model number: A045A047A) so that the support membrane and membrane filter were in contact. The membrane filter portion of this laminate was grasped with tweezers, and the membrane filter with the polymer membrane / graphene laminate attached was immersed in a pool of pure water to wash the polymer membrane / graphene laminate. At this time, the laminate was separated from the membrane so that the porous side was in contact with the water surface, allowing it to float on the water surface with the graphene facing upward. After washing in a water tank, the membrane was again lifted so that the porous membrane and the porous membrane were in contact. The laminate floating in the water tank can be easily transferred to a membrane. The laminate removed from the water tank can stand on its own without bending when peeled off from the membrane filter. However, using a membrane filter prevents objects from coming into contact with the graphene side of the laminate, making handling easier. Figure 20 shows a photograph of a graphene / polymer support film laminate placed on a membrane. The PMMA-supported laminate had some thin white areas, but the majority was transparent. The graphene surfaces of five types of graphene / polymer support film laminates were observed using SEM. Figure 21 shows an SEM image. All of the polymer materials used in the transfer support film were electrically insulating, but the transfer of graphene prevented charge buildup. Furthermore, because graphene is a single-atom sheet, an electron beam can penetrate it, allowing the structure of the polymer support film to be observed. CN, MCE, PVDF, and PES, which appeared white to the naked eye, also had a structure in which a skin layer was formed and the surface occupancy of pores was low in the SEM images of the polymer-side surfaces in Figure 16 . However, the structures of these four types of polymers near the graphene / polymer interface were porous structures with sufficient voids.While CN, MCE, and PVDF formed a mesh-like network, PES formed fibers with a pattern more similar to a tree than a mesh. Furthermore, PES was more difficult to observe due to the significant charge-up effect during observation compared to the other four materials, suggesting significant graphene damage and reduced electrical conductivity. SEM images of graphene / PMMA laminates exhibited low contrast and a wavy structure, suggesting that the PMMA was grabbing the graphene film, creating wrinkles. Generally, when polymer films are formed by solution casting, residual stress is generated in the polymer due to shrinkage caused by solvent evaporation. In this study, the polymer film was solidified by solvent exchange rather than solvent evaporation, but volumetric shrinkage can be considered to occur similarly to evaporation. This volumetric shrinkage generates residual stress, which compresses the adherend, i.e., graphene. As the polymer thickens, the stress generated by volumetric shrinkage also increases, resulting in greater compressive forces being applied to the adherend. The absence of wrinkle-like structures observed at the PMMA / graphene interface in the SEM images of CN, MCE, PVDF, and PES is thought to be due to the formation of a porous structure near the interface between the graphene and the support film, which prevents excessive volumetric shrinkage and relieves stress.In the PMMA support film, it is thought that a porous structure sufficient to relieve stress was not formed.

[0074] During SEM observation, if a tear is found in the graphene layer of a sample, exposing the polymer film underneath the graphene layer, it is thought that localized charge buildup will be stronger at that location; however, no such locations were observed in any of the samples.

[0075] Example 11: Transfer of graphene / porous support membrane freestanding laminate and four-terminal resistance measurement. The graphene / porous membrane freestanding laminate prepared in Example 10 was transferred to gold / chromium-deposited quartz glass by the method shown in Figure 22. The graphene / porous support membrane freestanding laminate (Figure 22(1)) placed on the membrane filter shown in Figure 20 was placed on the membrane filter. The membrane filter placed under the porous support membrane was moistened with pure water (Figures 22(2) and (3)). Pure water was then dropped onto the graphene membrane of the laminate (Figure 22(4)). A 20 mm x 20 mm quartz substrate with gold / chromium (5 mm x 5 mm) deposited on the four corners was then placed on top of it (Figures 22(5) and (6)). After the excess water was soaked into a nonwoven fabric such as Bemcot and appropriately dried, water was allowed to soak in from the membrane filter side, allowing the porous support and membrane filter to be easily peeled off. After drying at room temperature, a porous film / graphene laminate transferred to the desired position is obtained as shown in Figure 22 (7).

[0076] A typical CVD graphene transfer process includes a step of scooping up a support film / graphene laminate floated on the surface of a pure water pool, as in Example 2. However, in this method, if a free-standing graphene / porous film laminate is prepared, graphene can be easily transferred to any position on any substrate without the need to float it on water.

[0077] The electrical properties of graphene fabricated using five types of graphene / porous support membrane freestanding laminates were measured using electrical resistance measurements by the van der Pauw method and a Hall effect measurement device (Nanometrics). After measuring the electrical properties, the samples were immersed in acetone to attempt dissolution of the support membrane. CN, MCE, and PMMA could be removed, but PES and PVDF could not be completely dissolved and removed. Hall effect measurements and Raman spectroscopy measurements were also performed on the samples after dissolving the support membrane.

[0078] The PES was then further removed by immersion in NMP, the solvent used in the porous film-forming solution. Similarly, PVDF was immersed in hot DMF for 30 minutes, but the support film was not dissolved to the point where it could no longer be seen. The electrical properties and microscopic Raman spectroscopy measurements of these samples were performed again. Figure 23 shows the Raman spectra. Figure 24 shows optical microscope images taken during Raman spectroscopy. Table 6 shows the electrical properties of five types of samples before and after dissolution of the support film. For comparison, graphene prepared by transfer using the conventional PMMA method had a sheet resistance of approximately 550 Ω / sq.

[0079]

[0080] In the Raman spectra shown in Figure 23, samples prepared using CN, MCE, and PMMA as supports after acetone dissolution exhibited spectra characteristic of single-layer graphene. As shown in Figure 24, samples using PES and PVDF as supports contained a large amount of residue, and peaks other than graphene were observed in the Raman spectra. For the PVDF-supported transfer sample, the peak intensity due to the residue was high, and only a faint 2D peak due to graphene was observed. The sheet resistance of the PVDF-supported transfer sample increased significantly after acetone immersion, but the measured values ​​indicate that graphene was present beneath the polymer residue even after acetone immersion. Optical microscopy after immersion in DMF, as shown in Figure 24, revealed numerous graphene breaks, making it impossible to measure the electrical properties. For the PES-supported transfer sample, the sheet resistance before dissolution of the support film was approximately 10 times higher than that of the MCE and CN-supported transfer films, and the electrical properties could not be measured after acetone immersion. As shown in Figure 24, the optical microscope image indicated that PES residue covered almost the entire sample. After immersion in NMP, the PES was successfully dissolved, but most of the graphene on the substrate was torn and peeled off. Regarding PES support transfer, transfer to a resistance measurement substrate was also performed using the conventional scooping method. The sheet resistance of this sample was 791 Ω / sq, suggesting that many tears likely occurred during the process of lifting the laminate from the floating state on the water surface. As shown in the SEM image in Figure 21, the structure of PES at the contact interface with graphene does not form a mesh structure, unlike CN, MCE, and PVDF. Therefore, it is thought that the strength to support the graphene was insufficient when it was lifted from the water surface. Thus, it can be said that differences in the form of the porous structure of the support material also affect the quality of the transferred graphene.

[0081] The graphene transferred using CN and MCE as supports maintained high electrical conductivity and no breaks across the entire surface even after acetone immersion. Both samples achieved sheet resistances below 200 Ω / sq, an extremely low value for single-layer graphene. This low sheet resistance is evidence of the transfer of high-quality graphene without breaks. Residue was visually observed on the PMMA-supported transfer sample after acetone immersion, and it was not removed even by immersion in hot acetone. Optical microscope images after acetone immersion revealed that most of the graphene was broken. The SEM image in Figure 21 suggests that the formation of a thick film with insufficient porosity, resulting in large tensile stress, is the cause of the frequent breaks. The residue that did not dissolve in hot acetone is likely due to PMMA wrapped around broken graphene remaining on the substrate surface.

[0082] These results suggest that porous MCE or CN films are the optimal support materials for graphene transfer, as their porous structure eliminates stress and allows for easy dissolution after graphene transfer. Furthermore, the graphene-coated laminate is self-standing, demonstrating the feasibility of high-quality graphene transfer using a simple method not previously possible. This invention is highly valuable for the industrial application of graphene and is expected to be a major help in advancing research into the utilization of graphene.

[0083] Example 12: Large-area graphene transfer using a porous film / graphene laminate In this example, a laminate (hereinafter also referred to as a porous film / graphene laminate) consisting of a single-layer graphene film and a cellulose film (porous film) was produced as follows. Copper foil (65 mm × 90 mm, 35 μm thick) was prepared as a metal catalyst substrate for chemical vapor deposition (CVD) of graphene, and a graphene film was formed by CVD in the same manner as in Example 8. Prior to forming the graphene film, the copper foil was immersed in pure water, ethanol, and acetone, successively, and subjected to ultrasonic treatment to clean the copper foil surface. Thereafter, the copper foil was transferred to a thermal CVD furnace, and hydrogen was introduced. The copper substrate was subjected to hydrogen annealing for 30 minutes under conditions of a hydrogen atmosphere total pressure of 700 Pa and 1000°C. Thereafter, methane was introduced, and graphene was grown by CVD at a flow rate of 2 sccm of methane and 20 sccm of hydrogen at 1000° C. under a total pressure of 750 Pa for 10 minutes.

[0084] A porous film was fabricated on a graphene film formed on copper foil using a phase inversion method. A mixed film (cellulose mixed film) of nitrocellulose (CN) and cellulose acetate (CA) was used as the support layer for graphene transfer. Nitrocellulose (Nacalai Tesque, product number 24728-34), cellulose acetate (Sigma-Aldrich, product number 419028), and the solvents acetone and formamide were prepared as raw materials for the solution used to form the porous film. The cellulose acetate and nitrocellulose were dissolved in a 1:1 acetone-formamide mixed solvent at a mass ratio of 4% by mass and 8% by mass, respectively, to prepare a solution for forming the porous film.

[0085] Next, a copper foil having a graphene film formed on its surface by CVD was fixed to the stage of a fully automatic linear motion coater, and a multi-vaporized applicator (100 mm wide) was used to uniformly spread the solution on the graphene at a gap height of 100 μm and a running speed of 15 mm / s. The graphene / copper foil laminate on which the solution was spread by the applicator was immersed in a pool of pure water and left at room temperature for 1 hour. The graphene / copper foil laminate with the porous film formed was removed from the pool of pure water and dried at room temperature. The graphene film formed on the copper foil opposite the surface with the porous film was then removed by oxygen plasma treatment. The porous film / graphene / copper foil laminate was then cut into a 65 mm x 65 mm piece. A 10% by mass aqueous solution of ammonium persulfate, a copper etching solution, was stored in an etching bath, and the laminate was floated so that the copper foil surface was in contact with the etching solution. After approximately 4 hours, complete etching of the copper was confirmed, and the ammonium persulfate aqueous solution was drained from the etching bath while pure water was introduced to wash the porous film / graphene laminate. The resulting laminate was 10 μm thick or thicker and strong enough to withstand removal from pure water. After removal, the laminate was placed on a 90 mm diameter membrane filter (ADVANTEC, model number: A045A090C) with the porous membrane side in contact with the membrane surface and allowed to dry at room temperature. The resulting laminate was self-supporting in the atmosphere without irreversible deformation.

[0086] After drying the laminate and the membrane filter, the laminate can be peeled off from the membrane, making it possible to handle the laminate alone. This cellulose mixed ester / graphene laminate was then attached to a SiO 2 membrane with chromium / gold vapor-deposited in four places on the surface. ２ / In order to transfer to a Si substrate (4 inches diameter), pure water was dropped onto the substrate, and then the graphene film of the laminate was transferred to SiO ２ The laminate including the membrane filter was placed at a desired position on the substrate so that the SiO 2 / Si substrate side was facing the membrane filter. ２The membrane filter was placed so that it would come into contact with the four chromium / gold portions deposited on the SiO2 / Si. This transfer method does not require floating on water, making it easy to finely adjust the transfer position. Then, pure water was dripped onto the membrane filter to moisten it, and the membrane filter was peeled off from the porous film. Then, the SiO2 / Si film was removed. ２ The laminate on the Si substrate was dried at room temperature. ２ After drying the Si substrate, the porous cellulose mixed ester film was dissolved by exposing it to acetone vapor. Figure 25 shows a photograph of the single-layer graphene after dissolving the cellulose mixed ester support film. ２ / Oxide film (SiO ２ The thickness of the oxide layer was 300 nm, an oxide thickness suitable for visualizing single-layer graphene, and it was confirmed that a large graphene size of 65 mm x 65 mm was transferred. Furthermore, the uniform color was observed, and no change in color due to residue was observed, demonstrating that this transfer technique is an excellent method with very little graphene breakage or support material residue. The sheet resistance measured by the van der Pauw method was 354 Ω / sq. The fact that such a low sheet resistance was obtained demonstrates that the graphene / porous film laminate of the present invention can transfer even large areas of graphene with very little breakage. Figure 26 shows images taken at each step in the transfer process of this example.

[0087] Example 13: Making porous film / graphene laminate transfer film transparent A PVDF / graphene laminate electrode was fabricated by a casting method using an applicator with a gap height of 100 μm, following the same procedure as in Example 9. A PVDF porous film-forming solution was prepared by dissolving PVDF (Sigma-Aldrich, product number: 347078) at 12 mass % in a 1:1 acetone / dimethylformamide (DMF) mixed solvent. The fabricated PVDF / graphene / quartz substrate laminate was immersed in methanol for hydrophilization, and then impregnated with water or a water / glycerin solution, and a cover glass was placed on top, and transmittance measurements were performed. The transmittance spectrum is shown in FIG. 27. The transmittance at 550 nm of the laminate in which the PVDF membrane was impregnated with water was 39%, whereas the transmittance of the laminate in which the PVDF membrane was impregnated with a water / glycerin solution with a mass ratio of water:glycerin = 4:6 was 89%, and the PVDF porous membrane / graphene laminate was successfully made transparent.

[0088] Example 14: Evaluation by Raman Mapping of Graphene Transferred by a Transfer Method Using a Porous Film / Graphene Laminate Using the same procedure as in Example 9, a 20 mm × 20 mm cellulose mixed ester / graphene laminate prepared by a casting method was transferred to a 20 mm × 20 mm quartz glass substrate using an applicator with a gap height of 100 μm. After removing the porous film using acetone vapor, the graphene on the quartz substrate was subjected to Raman mapping using a WITec Raman imaging microscope alpha300 to examine the graphene coverage. The measurement conditions were as follows: the entire 20 mm × 20 mm quartz substrate was measured every 1 mm vertically and horizontally to obtain a 20 × 20 grid mapping image. The measurement was also performed using an autofocus function. The presence of graphene was determined by the presence or absence of a 2D peak. Of the 361 grids (19 × 19 grids) excluding the outermost grids of the mapping image, only one grid did not show a 2D peak and only one grid showed a cellulose peak. Therefore, it was confirmed that 99% or more of the transferred graphene was graphene without any support film residue or breaks.

[0089] DESCRIPTION OF SYMBOLS 1 Laminate (porous film / two-dimensional layered material) 1' Laminate (porous film / two-dimensional layered material / metal catalyst substrate) 1'' Laminate (porous film / two-dimensional layered material / metal catalyst substrate; wet state) 2 Two-dimensional layered material 3 Porous film 3' Porous film forming solution 4 Metal catalyst substrate 5 Applicator 6 Water tank 7 Etching tank 8 Membrane 9 PMMA 10 PMMA laminate (PMMA / graphene film / metal catalyst substrate) 10' PMMA laminate (PMMA / graphene film) 11 Substrate

Claims

1. A laminate comprising a two-dimensional layered material and a porous membrane laminated on the two-dimensional layered material, the two-dimensional layered material is a continuous film; The laminate is capable of standing on its own in the atmosphere while maintaining its planar structure.

2. The laminate according to claim 1, The laminate in its dry state.

3. The laminate according to claim 1, The porous film has pores with an average pore diameter of 20 nm or more.

4. The laminate according to claim 1, A laminate in which the area ratio of pores to the membrane surface of the porous membrane is 20% or more.

5. The laminate according to claim 1, A laminate wherein the porous membrane is a membrane made of a material selected from the group consisting of nitrocellulose, cellulose acetate, polyethersulfone, polytetrafluoroethylene, polyamide, polyvinylidene fluoride, regenerated cellulose, polycarbonate, polypropylene, polyvinylidene chloride, aluminum oxide, glass fiber, quartz fiber, polymethyl methacrylate, polystyrene, polyethylene, polyethylene terephthalate, and ceramic, or a mixed membrane made of two or more materials selected from the group.

6. The laminate according to claim 1, A laminate, wherein the porous membrane is a membrane made of a material selected from the group consisting of nitrocellulose, cellulose acetate, polycarbonate, polyvinylidene chloride, polystyrene, and polymethyl methacrylate, or a mixed membrane made of two or more materials selected from the group.

7. A method for producing the laminate according to any one of claims 1 to 6, comprising the steps of: (i) forming a two-dimensional layered material on a metal catalyst substrate by a CVD method; (ii) forming a porous film on the two-dimensional layered material to produce a laminate; (iii) removing the metal catalyst substrate by etching; Including, A method for manufacturing a laminate.

8. A method for producing the laminate according to claim 7, The method for producing a laminate, wherein the formation of a porous film on the two-dimensional layered material in step (ii) is carried out by a phase inversion method.

9. The manufacturing method according to claim 8, The production method, wherein in the step (ii), the solvent for dissolving the polymer used to form the porous membrane is a mixed solvent containing a good solvent and a poor solvent for the polymer.

10. A method for transferring the laminate according to any one of claims 1 to 6 to a desired substrate, comprising: (a) bonding the two-dimensional layered material side of the laminate to the desired position on the desired substrate; A transfer method comprising:

11. The transfer method according to claim 10, After the step (a), (b) removing the porous membrane of the laminate using a solvent; The transfer method further comprises: