JP2012251209A - Copper foil for producing graphene, and method for producing graphene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper foil for producing graphene producible of large area graphene at low cost, and a method for producing the graphene using the same.SOLUTION: The copper foil for producing graphene contains Cu with the purity of 99.95 mass% or higher.

Description

  The present invention relates to a copper foil for producing graphene and a method for producing graphene.

  Graphite has a layered structure in which a number of flat carbon 6-membered ring layers are stacked, and those having a single atomic layer to several atomic layers are called graphene or graphene sheets. Graphene sheets have unique electrical, optical and mechanical properties, and in particular have a high carrier moving speed. For this reason, graphene sheets are expected to have a wide range of applications in the industry, such as fuel cell separators, transparent electrodes, conductive thin films for display elements, mercury-free fluorescent lamps, composite materials, and drug delivery system (DDS) carriers. ing.

As a method of producing a graphene sheet, a method of peeling graphite with an adhesive tape is known, but the number of layers of the obtained graphene sheet is not constant, it is difficult to obtain a large area graphene sheet, and it is not suitable for mass production There's a problem.
Thus, a technique (chemical vapor deposition (CVD) method) has been developed in which a graphene sheet is grown by bringing a carbon-based material into contact with a sheet-like single crystal graphitized metal catalyst and then performing heat treatment (Patent Literature). 1). As this single crystal graphitized metal catalyst, a metal substrate of Ni, Cu, W or the like is described.
Similarly, a technique for forming graphene by chemical vapor deposition on a copper layer formed on a Ni or Cu metal foil or Si substrate has been reported. In this technique, for example, a copper foil having a thickness of 25 μm is used, and the copper purity of the copper foil used in the catalog is 99.8%. (Non-patent document 2). The graphene film is formed at about 1000 ° C. in a mixed gas atmosphere of argon, hydrogen, and methane (Non-Patent Documents 1 and 2).

JP 2009-143799 A

SCIENCE Vol.324 (2009) P1312-1314 APPLIED PHYSICS LETTERS 97,183109 (2010)

However, as in Patent Document 1, it is not easy to manufacture a single crystal metal substrate, which is extremely expensive, and it is difficult to obtain a large-area substrate, and thus it is difficult to obtain a large-area graphene sheet. . On the other hand, Non-Patent Document 1 describes that Cu is used as a substrate, but graphene does not grow in the surface direction in a short time on the Cu foil, and the Cu layer formed on the Si substrate is annealed. The substrate is formed as coarse particles. In this case, the size of graphene is limited by the Si substrate size, and the manufacturing cost is high. In addition, since the technology described in Non-Patent Document 2 uses copper foil, the cost of the substrate is lower than that of using a copper single crystal or Si substrate, and there is a possibility that a large area of graphene may be obtained. I can say that.
Here, the reason why copper is excellent as a catalyst for graphene growth is that copper hardly dissolves carbon. Then, copper acts as a catalyst, and carbon atoms generated by the thermal decomposition of hydrocarbon gas form graphene on the copper surface. Furthermore, since the copper covered with graphene loses its catalytic action, the hydrocarbon gas is not further thermally decomposed at that portion, and the graphene hardly forms a plurality of layers, so that a single graphene layer can be obtained. Therefore, although a copper single crystal is excellent in this respect as a substrate for producing graphene, it is expensive and limited in size, and thus is not suitable for forming a large area graphene.
On the other hand, the copper foil is easy to increase in area, but when the present inventor manufactured graphene using the copper foil described in Non-Patent Document 2 as a substrate, the sheet resistance of the graphene increases and is suitable for practical use. It turns out that quality is not obtained.
That is, an object of the present invention is to provide a copper foil for producing graphene capable of producing large-area graphene at a low cost and in a quality required for practical use, and a method for producing graphene using the same.

In order to solve the above problems, the copper foil for producing graphene of the present invention is made of Cu having a purity of 99.95% by mass or more.
The purity of Cu is preferably 99.995 mass% or less, and the oxygen concentration is preferably 200 mass ppm or less.

  The method for producing graphene of the present invention uses the copper foil for producing graphene, arranges the heated copper foil for producing graphene in a predetermined chamber and supplies a carbon-containing gas, and the surface of the copper foil for producing graphene A graphene forming step of forming graphene on the surface, and a graphene transfer step of laminating a transfer sheet on the surface of the graphene and transferring the graphene onto the transfer sheet while removing the graphene-producing copper foil by etching .

  ADVANTAGE OF THE INVENTION According to this invention, the copper foil which can produce a large area graphene by the quality requested | required practically at low cost is obtained.

It is process drawing which shows the manufacturing method of the graphene which concerns on embodiment of this invention.

  Hereinafter, the copper foil for graphene manufacture which concerns on embodiment of this invention, and the manufacturing method of graphene are demonstrated. In the present invention, “%” means “% by mass” unless otherwise specified.

<Composition of copper foil>
The copper foil is made of Cu having a purity of 99.95% by mass or more. As described above, when graphene is manufactured using a copper foil as a substrate, the sheet resistance of the graphene may increase and the quality may deteriorate. This is because the area of the copper foil that partially inhibits the growth of graphene exists and the catalytic function becomes uneven on the surface, and the hydrocarbon gas is not thermally decomposed at that part and the bonding of graphene carbon atoms occurs. It is considered that the sheet resistance is increased.
For this reason, the present inventor has determined that the presence of copper atoms on the surface of the copper foil as a catalyst affects the quality of graphene, and that the entire surface of the copper foil can have a catalytic function uniformly. The elements other than copper contained in the copper foil were adjusted to a certain amount or less (that is, the purity of Cu was 99.95% or more).
However, the present inventor initially thought that the impurities in the foil may be in solid solution or may be present as inclusions such as oxides and sulfides, regardless of their form. In general, CVD is used as a method of forming graphene on the surface of the copper foil, and CVD is performed in a mixed atmosphere of hydrocarbon gas, hydrogen gas, and inert gas at 1000 ° C. or higher. At this time, even if there is cuprous oxide, copper sulfide, etc. on the copper foil surface, it is easily reduced by hydrogen contained in the atmosphere of the CVD, so that the presence of impurities does not affect the quality of graphene. Thought. However, it has been found that the presence of impurities on the surface as oxides or sulfides affects the quality of graphene obtained by reduction or once melting at 1000 ° C. That is, it is preferable that oxygen and sulfur are less. In addition, as elements other than copper solid-solved in the copper foil, in addition to the elements originally present in the copper as impurities, elements actively added to the copper material can be mentioned, but the purity of copper is 99.95% If it is above, it does not affect the quality of graphene.
Although the kind of impurity in copper foil is not limited, P and Ag are mentioned in addition to O and S, and additive elements include Ag, Sn, Ti, Ni, Mg, In and the like.

In addition, when Cu purity in copper foil is made high, while manufacturing cost will become high, intensity | strength will fall and manufacture of foil will become difficult and enlargement will become difficult. For this reason, the purity of Cu in the copper foil is preferably 99.995% by mass or less.
Moreover, it is preferable that the oxygen concentration in copper foil is 200 mass ppm or less.
When oxygen exceeds 200 ppm, the amount of oxides increases, and when they are reduced during CVD, the growth of graphene may be inhibited, and the sheet resistance of graphene may increase. In addition, although it is so good that there is also little sulfur in copper foil, sulfur is known as an impurity which worsens the manufacturability of copper, and if it is a range which does not have a bad influence on manufacturability, it hardly affects the quality of graphene.

<Copper foil thickness>
The thickness of the copper foil is not particularly limited, but is generally 5 to 150 μm. Furthermore, it is preferable to set the thickness of the copper foil to 12 to 50 μm in order to easily perform the etching removal described later while ensuring the handleability. If the thickness of the copper foil is less than 12 μm, it may be easily broken and inferior in handleability, and if the thickness exceeds 50 μm, it may be difficult to remove by etching.

<60 degree gloss of copper foil>
Both the 60-degree glossiness (JIS Z 8741) of the copper foil in the rolling parallel direction and the direction perpendicular to the rolling is preferably 400% or more, and more preferably 500% or more.
As will be described later, after producing graphene using the copper foil for producing graphene of the present invention, it is necessary to transfer the graphene from the copper foil to the transfer sheet. However, if the surface of the copper foil is rough, transfer is difficult. May be damaged. Therefore, it is preferable that the surface unevenness of the copper foil is smooth.
The upper limit of 60 degree gloss in the rolling parallel direction and the direction perpendicular to the rolling is not particularly limited, but the upper limit of 60 degree gloss in the rolling parallel direction and the direction perpendicular to the rolling is practically about 800%.
In order to facilitate the transfer of graphene to the transfer sheet as described above, the arithmetic average roughness Ra of the copper foil surface specified in JIS B0601 is preferably 0.25 μm or less.

<Average crystal grain size>
Moreover, by heating the copper foil after completion of the final cold rolling at 1000 ° C. for 1 hour, the copper foil is also heated, and the average crystal grain size of the copper foil grows to 100 μm or more.
If the average crystal grain size of the copper foil is smaller than 100 μm, it may become an obstacle when growing graphene, and it may be difficult to grow graphene in the plane direction.
The heating for 1 hour at 1000 ° C. simulates the conditions for heating the graphene-producing copper foil to a temperature higher than the decomposition temperature of the carbon-containing gas when producing graphene.
The average crystal grain size is determined by measuring the copper foil by the cutting method of JIS H0501.

  By using the graphene-producing copper foil defined as described above, large-area graphene can be produced at a low cost and with a high yield.

<Manufacture of copper foil for graphene production>
The copper foil for producing graphene according to the embodiment of the present invention can be produced, for example, as follows. First, for example, tough pitch copper (JIS-H3100) or oxygen-free copper (JIS-H3100) is used as it is, or high-purity copper is used as it is, or a predetermined element is added as necessary, and the purity is 99.95. A copper ingot having a mass% or more is produced. However, in the case of tough pitch copper, it is necessary that the oxygen concentration does not exceed 200 ppm. After hot rolling this ingot, annealing and cold rolling are repeated to obtain a rolled sheet. The rolled sheet is annealed and recrystallized, and finally cold-rolled to a predetermined thickness of 80 to 99.9% (preferably 85 to 99.9%, more preferably 90 to 99.9%). To obtain copper foil.

<Graphene production method>
Next, with reference to FIG. 1, a method for producing graphene according to an embodiment of the present invention will be described.
First, the graphene producing copper foil 10 of the present invention described above is placed in a chamber (vacuum chamber or the like) 100, the graphene producing copper foil 10 is heated by the heater 104, and the inside of the chamber 100 is decompressed or evacuated. . Then, the carbon-containing gas G is supplied from the gas inlet 102 into the chamber 100 (FIG. 1A). Examples of the carbon-containing gas G include methane, ethane, propane, ethylene, acetylene, alcohol, and the like. However, the carbon-containing gas G is not limited thereto, and may be one or two or more mixed gases. Further, the heating temperature of the graphene-producing copper foil 10 may be equal to or higher than the decomposition temperature of the carbon-containing gas G, for example, 1000 ° C. or higher. Further, the carbon-containing gas G may be heated to a decomposition temperature or higher in the chamber 100, and the decomposition gas may be brought into contact with the copper foil 10 for producing graphene. And decomposition gas (carbon gas) contacts the surface of the copper foil 10 for graphene manufacture, and the graphene 20 is formed on the surface of the copper foil 10 for graphene manufacture (FIG.1 (b)).

And the copper foil 10 for graphene manufacture is cooled to normal temperature, the transfer sheet 30 is laminated | stacked on the surface of the graphene 20, and the graphene 20 is transcribe | transferred on the transfer sheet 30. FIG. Next, this laminated body is continuously immersed in the etching tank 110 through the sink roll 120, and the copper foil 10 for graphene production is removed by etching (FIG. 1C). Thus, the graphene 20 laminated on the predetermined transfer sheet 30 can be manufactured.
Furthermore, when the laminated body from which the copper foil 10 for producing graphene is removed is pulled up, the substrate 40 is laminated on the surface of the graphene 20, and the transfer sheet 30 is peeled off while transferring the graphene 20 onto the substrate 40, The stacked graphene 20 can be manufactured.

  As the transfer sheet 30, various resin sheets (polymer sheets such as polyethylene and polyurethane) can be used. As an etching solution for etching and removing the copper foil 10 for producing graphene, for example, a sulfuric acid solution, a sodium persulfate solution, hydrogen peroxide, a sodium persulfate solution, or a solution obtained by adding sulfuric acid to hydrogen peroxide can be used. As the substrate 40, for example, Si, SiC, Ni, or Ni alloy can be used.

<Preparation of sample>
A copper ingot (thickness 30 mm, width 100 mm) having the composition shown in Table 1 was produced. Here, for a copper foil having a Cu purity of 99.999%, a 99.9999% copper raw material was redissolved in a vacuum to cast an ingot. For copper foils with a Cu purity of 99.995% or less, oxygen-free copper (JIS-H3100) is used as a raw material and redissolved in a vacuum, and the purity is adjusted by adding impurity elements having the composition shown in Table 1, and an argon atmosphere The ingot was cast with. In addition, when adding oxygen as an impurity, after adding argon gas in the furnace which casts an ingot, copper oxide was added.
The surface of the obtained ingot was machined, then hot-rolled at 800 to 900 ° C., pickled, and cold-rolled to obtain a rolled sheet having a thickness of 1 to 2 mm. This rolled sheet is annealed at 600 to 800 ° C. and recrystallized, and further cold rolled, finally cold rolled to a thickness of 7 to 50 μm with a reduction ratio of 95 to 99.7%, and a thickness of 8 to 70 μm. A copper foil was obtained. In addition, you may repeat annealing and cold rolling before processing to final thickness.

<Measurement of 60 degree glossiness>
The 60-degree glossiness of the surface after the final cold rolling of the copper foils of the examples and comparative examples was measured.
The 60 degree glossiness was measured using a gloss meter (trade name “PG-1M” manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS-Z8741.

<Measurement of surface roughness (Ra, Rz, Sm)>
The surface roughness after the final cold rolling of the copper foils of the examples and comparative examples was measured.
Using a contact roughness meter (trade name “SE-3400”, manufactured by Kosaka Laboratories), the arithmetic average roughness (Ra; μm) based on JIS-B0601 was measured, and the oil pit depth Rz was JIS B0601-. Ten-point average roughness was measured according to 1994. The measurement position is changed 10 times in parallel with the rolling direction under the conditions of a measurement standard length of 0.8 mm, an evaluation length of 4 mm, a cut-off value of 0.8 mm, and a feed rate of 0.1 mm / second, and 10 times in each direction. The value in the measurement was obtained. In addition, the average interval of unevenness (Sm; mm) is a measurement position parallel to the rolling direction under the conditions of a measurement reference length of 0.8 mm, an evaluation length of 4 mm, a cutoff value of 0.8 mm, and a feed rate of 0.1 mm / second. The measurement was repeated 10 times, and the values for 10 measurements were obtained. Note that Sm is defined as “average interval of unevenness” in JIS B0601-2001 (conforms to ISO 4287-1997) in which the surface property is expressed by a contour curve method, and the contour length of each unevenness within the reference length. The average of

<Measurement of average crystal grain size (GS)>
The copper foil after the final cold rolling in each example and comparative example was heated at 1000 ° C. for 1 hour, and then the average crystal grain size on the surface of the copper foil was measured by the cutting method of JIS H0501.

<Tensile strength (TS)>
The tensile strength in the rolling direction was measured with a tensile tester according to JIS-Z2241.

<Manufacture of graphene>
The graphene-producing copper foil of each example (length and width: 100 × 100 mm) was wound around the inner wall of a quartz tube (3 inches) in an infrared image furnace and evacuated (pressure: 0.2 Torr). Next, the infrared image furnace is heated to 1000 ° C. while flowing a mixed gas of hydrogen and argon (H2 / Ar = 10/400 to 5/500 sccm (Standard Cubic Centimeter per Minutes)) into this quartz tube, and further methane gas is added. The reaction was carried out at CH4 / H2 / Ar = 10/10/400 to 10/5/500 sccm and held for 1 hour for reaction.
After sticking a PET film on the graphene side of the copper foil with graphene grown on the surface and etching away the copper foil with acid, the sheet resistance of the graphene was measured by a four-probe method. The reaction time was determined in advance by investigating the relationship between the reaction time and the sheet resistance and stabilizing the sheet resistance.
If the sheet resistance of graphene is 400Ω / □ or less, there is no practical problem.

The obtained results are shown in Table 1. In Table 1, G60 _RD and G60 _TD indicate 60-degree glossiness in the rolling parallel direction and the rolling perpendicular direction, respectively. GS represents an average crystal grain size.
Further, “S + P + Ag <5 ppm” in the table indicates that the total concentration of S, P, and Ag is less than 5 wtppm. In addition, although the sum total of each element in a table | surface is less than 100 mass%, the part is equivalent to the inevitable impurity in copper foil.

As is clear from Table 1, in each of the examples in which the purity of the copper foil was 99.95% by mass or more, the sheet resistance of graphene was 400Ω / □ or less, and the quality was excellent.
Note that the higher the oxygen concentration, the higher the sheet resistance of graphene.
In the case of Example 13 in which the copper foil exceeded 50 μm, it took time to remove the copper foil by etching as compared with the other examples. In the case of Example 14 in which the thickness of the copper foil was less than 12 μm, handling was troublesome as compared with other Examples.

On the other hand, in the case of each comparative example in which the purity of the copper foil was less than 99.95% by mass, the sheet resistance of graphene exceeded 400Ω / □, and the quality of graphene was inferior.
Further, in the case of Comparative Example 1 in which the oxygen concentration exceeds 200 mass ppm, the sheet resistance of graphene exceeds 400Ω / □ and the quality of graphene is inferior although the purity of the copper foil is 99.95 mass% or more. It was.

10 Copper foil for graphene production 20 Graphene 30 Transfer sheet

Claims (4)

  A copper foil for producing graphene made of Cu having a purity of 99.95% by mass or more.   The copper foil for producing graphene according to claim 1, wherein the purity of Cu is 99.995 mass% or less.   The copper foil for producing graphene according to claim 1 or 2, wherein the oxygen concentration is 200 ppm by mass or less. It is a manufacturing method of graphene using the copper foil for graphene manufacture in any one of Claims 1-3,
A graphene forming step of arranging the heated copper foil for producing graphene in a predetermined chamber and supplying a carbon-containing gas and forming graphene on the surface of the copper foil for producing graphene,
A graphene transfer process comprising: laminating a transfer sheet on the surface of the graphene; and transferring the graphene onto the transfer sheet while etching and removing the copper foil for producing graphene.

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