KR20210126267A - Graphene transfer method without residue - Google Patents

Abstract

The present invention relates to a graphene transfer method that transfers graphene formed on a first substrate to a second substrate and, more specifically, to a graphene transfer method comprising: (a) a step for forming a support layer on a first substrate layer with a sublimable material so as to cover the graphene that has been formed thereon; (b) a step for separating a layer made of the support layer and graphene from the first substrate; (c) a step for transferring the layer made of the support layer and graphene to a second substrate, thereby making the graphene face the second substrate; and (d) a step for subliming the support and removing the same from the second substrate.

Description

How to transfer graphene without residue {GRAPHENE TRANSFER METHOD WITHOUT RESIDUE}

The present invention relates to a method of transferring graphene, and more particularly, to a method of transferring graphene without a residue using a sublimable material.

The two-dimensional material refers to a material composed of one or several layers in an atomic unit. Each layer of a two-dimensional material is mainly bound by van der Waals (vdW) forces. The physical properties of two-dimensional materials exhibit electrical, mechanical, chemical, and optical properties different from those of bulk materials due to the quantum limiting effect.

A representative example of a two-dimensional material is graphene. Graphene is a material composed of sp ² bonds of carbon, and each carbon atom forms a hexagonal lattice, and carbon atoms are arranged at the vertices of the hexagon. Graphene has excellent physical properties such as high tensile strength and elastic modulus due to the strong bonding force of vdW, and at the same time has the advantage of electrical conductivity.

For large-area synthesis of graphene, chemical vapor deposition (CVD) is used. In the chemical vapor deposition method, a catalytic transition metal (Cu, Ni, Pt, Re) is used as a graphene-forming substrate, and graphene is deposited on the graphene-forming substrate. In order to use graphene deposited on the graphene-forming substrate as a device, a process of transferring it to a substrate suitable for the purpose of use is required, which is called a transfer process.

When the growth substrate is removed during the transfer process, thin graphene is easily broken. To prevent this, a support layer is formed before removing the growth substrate to protect the graphene. As the support layer, poly (methyl methacrylate) (PMMA), poly (dimethylsiloxane) (PDMS), or a thermal release tape is used. Graphene is transferred to the target substrate by removing the post-growth substrate on which the support layer is formed. In order to use graphene as an actual device, the previously used support layer must be removed. In the process of removing the support layer, processes such as the use of an organic solvent and high-temperature heating are added, and damage and performance degradation occur in the graphene in the additional process. For example, in Korean Patent Application Laid-Open No. 2019-0101235 or 2017-0111573, a process such as an organic solvent or heat treatment is essential to remove the polymer used for graphene transfer, and graphene is damaged due to organic solvent or heat treatment. A problem arises.

Accordingly, the present inventors intend to propose a method capable of minimizing performance degradation due to damage to graphene during the transfer process.

Korean Patent Publication No. 2019-0101235 Korean Patent Publication No. 2017-0111573 Korean Patent Publication No. 2017-0110133

It is an object of the present invention to provide a method for transferring a graphene from a first substrate to a second substrate to be used without residue by using a sublimable material as a support layer.

On the other hand, other objects not specified in the present invention will be additionally considered within the range that can be easily inferred from the following detailed description and effects thereof.

In order to achieve the above object, a method of manufacturing graphene according to an embodiment of the present invention is a method of transferring graphene formed on a first substrate to a second substrate and transferring graphene: (a) graphene is formed forming a support layer of a sublimable material on a first substrate to cover the graphene; (b) separating the support layer and the graphene layer from the first substrate; (c) transferring a layer made of the support layer and the graphene to the second substrate such that the graphene faces the second substrate; and (d) sublimating the support layer to remove it from the second substrate.

In one embodiment, the sublimable material may be characterized in that the sublimation at room temperature and pressure.

In one embodiment, the sublimable material may be characterized in that cyclododecaine or naphthalene.

In one embodiment, in step (a), the sublimable material is dissolved in an inorganic solvent or liquefied by applying heat, and spin coating or dip coating the sublimable material to form a support layer on the first substrate can be characterized.

In an embodiment, the first substrate is any one transition metal substrate selected from the group consisting of Cu, Ni, Pt, and Re, and the step (b) is performed by etching the first substrate to remove the transition metal. It may be characterized in that it is performed. In this case, after performing the step (b), it may be characterized in that the step of washing the support layer and the graphene in distilled water with distilled water is performed. In addition, after performing step (c), the second substrate is placed in a vacuum chamber to remove distilled water present between the second substrate and the support layer.

In order to achieve the above object, the graphene prepared by the method of manufacturing graphene according to another example of the present invention is (a) a support layer with a sublimable material to cover the graphene on the first substrate on which the graphene is formed. forming a; (b) separating the support layer and the graphene layer from the first substrate; (c) transferring a layer made of the support layer and the graphene to the second substrate such that the graphene faces the second substrate; and (d) sublimating the support layer to remove it from the second substrate.

In another example, it may be characterized in that there are no residues of the first substrate and no residues of the support layer on the second substrate.

The graphene transfer method according to an embodiment of the present invention is performed by forming a sublimable material as a support layer on a first substrate on which graphene is formed, then transferring the support layer and graphene to a second substrate by separating the first substrate, After transfer, the support layer is sublimated and removed at room temperature and pressure without a separate support layer removal process. Therefore, in the graphene transfer method according to an embodiment of the present invention, the performance of graphene is reduced because residues remain, or there is no damage to the graphene due to the removal of the support layer by physical or heat treatment, so the performance of graphene is reduced. there is no

On the other hand, even if it is an effect not explicitly mentioned herein, it is added that the effects described in the following specification expected by the technical features of the present invention and their potential effects are treated as described in the specification of the present invention.

1 is a schematic flowchart of a method for transferring graphene of the present invention.
2 is a schematic diagram schematically illustrating an embodiment of a method for transferring graphene of the present invention.
3 is a photograph taken over time of the sublimation of the support layer after forming the graphene on the first substrate and then coating the sublimable material.
4 is a photograph of (a) crystallizing the sublimable material on graphene, and then recrystallizing the sublimable material by applying heat (b) and (c).
5 is a photograph taken over time of transferring graphene using a support layer on a second substrate.
6 is a photograph taken before and after the graphene is transferred to the second substrate and the support layer is sublimated.
7 shows (a) optical micrographs, (b) Raman spectrum measurement results, and (c) scanning electron micrographs after transferring graphene to the second substrate and sublimating all of the support layers.
8 is (a) a transmission electron micrograph and (b) an electron diffraction pattern result after transferring graphene to the second substrate and sublimating all the support layers.
※ It is revealed that the attached drawings are exemplified as a reference for understanding the technical idea of the present invention, and the scope of the present invention is not limited thereby.

Hereinafter, with reference to the drawings, the configuration of the present invention guided by various embodiments of the present invention and effects resulting from the configuration will be described. In the description of the present invention, if it is determined that the subject matter of the present invention may be unnecessarily obscured as it is obvious to those skilled in the art with respect to related known functions, the detailed description thereof will be omitted.

1 is a schematic flowchart of a method of transferring graphene of the present invention, and FIG. 2 is a schematic diagram schematically illustrating an embodiment of a method of transferring graphene of the present invention.

By using the graphene transfer method according to an embodiment of the present invention, the graphene formed on the first substrate may be transferred to the second substrate.

First, the step of forming the graphene 2 on the first substrate 1 is performed. A method of forming graphene on the first substrate may use chemical vapor deposition (CVD). When graphene is formed by chemical vapor deposition, a transition metal selected from the group consisting of Cu, Ni, Pt, Re, and the like as the first substrate is used as the growth substrate. The transition metal acts as a catalyst during the growth of graphene by chemical vapor deposition to improve the physical properties of the formed graphene. The basic principle of the chemical vapor deposition method is to flow a mixed gas of _{CH 4} , H _{2 , and Ar at a high temperature of 800 ℃ or higher.} When the carbon atoms contained in the mixed gas come into contact with the growth substrate, graphene is grown on the surface of the growth substrate during the cooling process due to the catalytic effect or carbon solubility of the substrate.

A known method may be used to form graphene on the first substrate using such a chemical vapor deposition method. Meanwhile, a method other than chemical vapor deposition may be used as a method of forming graphene on the first substrate, and the present invention is not limited to chemical vapor deposition.

) 결합을 할 수 있는 유기물을 이용할 수 있다. 제1기판 상에 그래핀을 형성한 후 승화성 물질인 씨클로도데케인을 스핀 코팅한 후 지지층이 승화하는 단계를 시간의 경과에 따라 촬영한 사진인데, 60분 경과후에 지지층이 모두 승화하였음을 알 수 있다. After the graphene is formed on the first substrate, a process of transferring the formed graphene to the second substrate is required. Therefore, after forming the graphene on the first substrate, the step of forming the support layer 3 to cover the graphene on the first substrate is performed. In the method of transferring graphene according to an embodiment of the present invention, the support layer is formed using a sublimable material. The sublimable material refers to a material that sublimes at room temperature and pressure, and more specifically, refers to a material that is sublimed without a separate temperature control device or pressure control device. For example, as a sublimable material, pi (cyclododecane, naphthalene, etc.)

) can be used for bonding organic matter. After forming graphene on the first substrate, spin-coating cyclododecaine, a sublimable material, and then sublimating the support layer over time. can

In the step of forming the support layer, the sublimable material may be dissolved in an inorganic solvent such as benzene, or used in a liquefied state by applying heat to the sublimable material. That is, a liquid sublimable material is made, and a support layer is formed to a sufficient thickness by spin coating or dip coating on the graphene-formed first substrate on the liquid sublimable material as shown in FIG. 3( a ). The sublimable material is crystallized in the process of evaporating the inorganic solvent or in the process of re-solidifying the sublimable material that was liquefied by heat. As the crystallization uniformity of the sublimable material is constant, the sublimable material supports all parts of the graphene, so that the graphene can be transferred without loss. Therefore, a support layer having a uniform degree of crystallinity can be formed by recrystallizing the sublimable material through an additional heating process. At this time, the heating temperature is 50 to 80 °C, and this temperature is not high, so there is almost no damage to the graphene. In addition, the larger the crystallization size, the more stably support the graphene. In summary, as the thickness of the support layer is sufficiently thick and uniform, and the crystallization size is large, the graphene can be more stably supported and transferred more easily. In addition, in the method of transferring graphene in an embodiment of the present invention, since the support layer is formed of a sublimable material, sublimation starts at the same time as the support layer is formed. Therefore, it is preferable to form the support layer to a sufficient thickness in order to perform a subsequent process.

After forming the support layer, a step of separating the first substrate is performed. When the first substrate is a transition metal, the support layer and the graphene layer are separated from the first substrate by removing the transition metal by etching. If the first substrate is copper (Cu), the first substrate may be separated by etching using _{ammonium persulfate ((NH 4} ) ₂ S ₂ O _{8 ).} However, the present invention is not limited thereto, and the first substrate may be separated from the support layer and graphene by another method. When the first substrate is removed by etching, a step of washing the support layer and graphene in distilled water may be performed.

After the step of separating the support layer and the graphene layer is performed, the support layer and the graphene layer are transferred to the second substrate 4 so that the graphene faces the second substrate. At this time, the graphene and the second substrate are in close contact by an intermolecular force. In addition, in order to remove distilled water remaining during washing performed in the process of separating the first substrate, the support layer and the graphene layer are transferred onto the second substrate and then placed in a vacuum chamber. At this time, as distilled water positioned between the graphene and the second substrate escapes in the vacuum chamber, the graphene and the second substrate are more strongly adhered. Therefore, when distilled water is removed using a vacuum chamber, there is an advantage in that the performance of the transferred graphene is further improved.

After transferring the support layer and the graphene layer to the second substrate, only the graphene remains on the second substrate as the support layer is sublimed. Thus, the graphene is transferred from the first substrate to the second substrate by the method of transferring the graphene of the present invention. In particular, when graphene is transferred by the method of transferring graphene of the present invention, there is no need to perform high-temperature heat treatment, apply physical force, or use a separate solvent to remove the support layer. There is no residue, and at the same time, damage to graphene can be minimized. Above all, in the case of the graphene transfer method of the present invention, the transfer can be performed even on a type of substrate that cannot be used under conditions such as an organic solvent or high temperature, high pressure, etc., so there is an advantage in that the degree of freedom in substrate selection is significantly increased. .

In the case of graphene produced by the graphene transfer method described above, the remnants of the first signboard and the remnants of the support layer do not remain on the second substrate.

Example One

When graphene is transferred from the first substrate to the second substrate by the graphene transfer method of the present invention, there should be no change in the Raman spectrum before and after transfer in order to say that there is no performance loss of graphene and no residue, and However, materials other than graphene should not be observed in surface analysis equipment such as scanning electron microscope and transmission electron microscope, and only points forming six-symmetry should appear in electron diffraction analysis equipment.

In order to confirm these results, graphene was transferred in the following way.

First, graphene was formed by chemical vapor deposition on a copper film as a first substrate.

Cyclododecaine dissolved in benzene was coated on the upper portion of the formed graphene, that is, on the upper portion of the first substrate by a spin coating method to form a support layer. Cyclododecane is coated with crystallization on the first substrate (see Fig. 4 (a)). In order to equalize the thickness of the crystallized cyclododecaine and increase the cyclododecaine crystal size, it was placed on a plate at 60° C. to melt the cyclododecaine, and then moved to room temperature for recrystallization (Figs. 4 (b), 4 (c)). Reference).

Then, the first substrate in a 20% concentration of ammonium persulfate solution. The first substrate, which is a copper film, is removed by floating a layer made of graphene and a support layer for about 2 hours to separate the first substrate from the layer made of graphene and a support layer. In order to completely remove the ammonium peroxide from the layer consisting of graphene and the support layer, it is immersed in two batches of deionized water (DI) for 10 minutes.

As the second substrate, silicon dioxide (SiO ₂ ) was used. A layer made of graphene and a support layer was transferred to the second substrate, and placed in a vacuum chamber of ^{10 -2} torr to remove distilled water trapped between the layer made of graphene and the support layer and the second substrate. Distilled water was completely removed in the vacuum chamber, and the support layer was also sublimed after a predetermined time elapsed. Finally, graphene transferred onto the second substrate was obtained. 5 is a photograph taken over time of transferring graphene using a support layer on a second substrate. Referring to FIG. 5 , as time passes, the second substrate 10 and graphene 20 do not change, but in the case of the support layer 30, densely formed crystals become loose as sublimation proceeds. can be checked This sublimation of cyclododecaine can be confirmed with the naked eye, as can be seen in FIG. 6 .

7 shows (a) optical micrographs, (b) Raman spectrum measurement results, and (c) scanning electron micrographs after transferring graphene to a second substrate and sublimating all of the support layers.

Looking at the optical micrograph of FIG. 7( a ), it can be confirmed that no residues other than the graphene monolayer and the bilayer patch are observed. Looking at the results of the Raman spectrum of FIG. 7(b), it can be seen that a D peak near ^{1380 cm -1} , a G peak near ^{1580 cm -1} , and a 2D peak near ^{2700 cm -1 are observed.} The degree of defects in graphene can be known through the ratio (ID/IG) of the intensity of the D peak (ID) and the intensity of the G peak (IG). A lower ratio (ID/IG) means fewer defects in graphene. 7(b), it can be seen that the ID/IG is very low, and it can be seen that the graphene transferred according to the method of transferring the graphene of the present invention has almost no defects. In the scanning electron microscope image of FIG. 7(c), it can be confirmed that no residues other than the graphene monolayer and the bilayer patch were observed, as in FIG. 7(a).

Example 2

Graphene was transferred in the same manner as in Example 1 using a TEM grid as a second substrate for measurement of a transmission electron microscope (TEM). There is no difference from Example 1 except that the second substrate is a TEM grid.

8 is (a) a transmission electron micrograph and (b) an electron diffraction pattern result after transferring graphene to the second substrate and sublimating all the support layers.

Transmission electron microscopy is a method for observing materials on an atomic basis. Referring to the transmission electron micrograph of FIG. 8(a), it can be seen that other materials than graphene are not observed and the hexagonal structure of graphene is maintained. . That is, it was confirmed that the support layer did not remain on the graphene surface without a separate process of removing the support layer through the method for producing the graphene of the present invention, and the graphene was supported without loss in the transfer process.

The electron diffraction analysis pattern is a measurement method that can confirm the periodicity of the atomic structure. Referring to the image showing the electron diffraction analysis pattern of FIG. 8(b), it can be observed that the observed ^{points have a periodicity of 60 o} . Through this, it can be seen that the graphene transferred on the TEM grid maintains an ideal hexagonal structure.

The protection scope of the present invention is not limited to the description and expression of the embodiments explicitly described above. In addition, it is added once again that the protection scope of the present invention cannot be limited due to obvious changes or substitutions in the technical field to which the present invention pertains.

Claims (10)

A method of transferring graphene for transferring graphene formed on a first substrate to a second substrate, comprising:
(a) forming a support layer of a sublimable material to cover the graphene on the first substrate on which the graphene is formed;
(b) separating the support layer and the graphene layer from the first substrate;
(c) transferring a layer made of the support layer and the graphene to the second substrate such that the graphene faces the second substrate; and
(d) sublimating the support layer to remove it from the second substrate; graphene transfer method comprising a.
According to claim 1,
The step (a) is a method for transferring graphene, characterized in that after the support layer is formed on the first substrate, it is further heated to recrystallize the support layer,
According to claim 1,
The method for transferring graphene, characterized in that the sublimable material is sublimed at room temperature and pressure.
According to claim 1,
The method for transferring graphene, characterized in that the sublimable material is cyclododecaine or naphthalene.
According to claim 1,
In step (a), the sublimable material is dissolved in an inorganic solvent or liquefied by applying heat, and the sublimable material is spin-coated or dip-coated to form a support layer on the first substrate. How to fight.
According to claim 1,
The first substrate is any one transition metal substrate selected from the group consisting of Cu, Ni, Pt, and Re, and the step (b) is performed by etching the first substrate to remove the transition metal. How to transfer graphene.
7. The method of claim 6,
Method for transferring graphene, characterized in that the step of washing the support layer and the graphene in distilled water with distilled water after performing step (b).
8. The method of claim 7,
After performing step (c), the second substrate is placed in a vacuum chamber to remove distilled water present between the second substrate and the support layer.
As graphene prepared by a method of transferring graphene formed on a first substrate to a second substrate and transferring graphene:
(a) forming a support layer of a sublimable material to cover the graphene on the first substrate on which the graphene is formed;
(b) separating the support layer and the graphene layer from the first substrate;
(c) transferring a layer made of the support layer and the graphene to the second substrate such that the graphene faces the second substrate; and
(d) sublimating the support layer to remove it from the second substrate; graphene prepared by a method of transferring graphene comprising a.
10. The method of claim 9,
Graphene, characterized in that there is no residue of the first substrate and the residue of the support layer on the second substrate.

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