KR20120001121A - Fabrication method of graphene films using physical vapor deposition techniques - Google Patents

Abstract

PURPOSE: A method of manufacturing a graphene film using physical vapor deposition techniques is provided to form a grapheme film by heat-treating a carbon film with a general rapid heat-treatment device. CONSTITUTION: A method of manufacturing a graphene film using physical vapor deposition techniques comprises steps of preparing a metal film on a substrate, metal foil, or a metal substrate(30), forming a carbon film on the metal film, the metal foil, or the metal substrate through physical vapor deposition, and heat-treating the carbon film to form a grapheme film(100). The metal film, metal foil, or metal substrate is made from the combination of one or more selected from the group consisting of Ni, Co, Fe, Cu, Ru, Pt, Pd, Ta, Mo, W, Ir, Ti, V, Mn, Al, Mg, and transition metal including Zn.

Description

Fabrication method of graphene films using physical vapor deposition techniques

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a graphene thin film, wherein a carbon thin film is formed on a metal film, a metal foil, or a metal substrate by physical vapor deposition, and then thermally annealed. The present invention relates to a method for forming a graphene thin film using physical vapor deposition which can easily obtain a large area graphene thin film.

Graphene is a word that refers to a thin film laminated within about 1 ~ 10 layers based on the monoatomic layer where carbon atoms are bonded in hexagonal honeycomb shape, and has a high charge mobility of 200,000cm ² / Vs and a high mechanical temperature at room temperature. Due to its excellent properties such as strength, flexibility, and high transmittance to visible light, it is a very promising new material for ultra-fast nano semiconductors, transparent electrode materials, and various sensor materials.

M. Taghioskoui published Materials Today 2009, Vol. 12, No. 10 p. Referring to the review of “Trends in graphene research” published in 34-37, the representative methods for obtaining graphene thin film by the existing technology are as follows.

(1) Mechanical peeling is performed from graphite.

(2) Graphene is peeled off by chemical method using redox reaction to obtain graphene.

(3) The silicon carbide (SiC) is heat-treated at a high temperature of 1500 ° C. or more to sublimate silicon on the surface of the silicon carbide to form an epitaxial graphene thin film on the silicon carbide substrate, leaving only a carbon atom layer.

(4) a raw material gas containing carbon such as CH ₄ , C ₂ H ₄ , C ₂ H ₆ , C ₃ H _8, and the like on a transition metal including Ni, Cu, Co, Ru, and H _2; Gas, Ar, N ₂ and the like are mixed to form a thin film of graphene by chemical vapor deposition (chemival vapor deposition) at a temperature of approximately 900 ~ 1000 ℃.

These existing technologies have their own advantages and disadvantages.

In case of (1), it is the most unfavorable method for large area and mass production. In case of (2), mass production is possible, but J.K. Wassei and R.B. Kaner et al., Materials Today 2010, Vol. 13, No. 3, p. As pointed out in “Graphene, a promising transparent conductor,” pp. 52-59, the quality of graphene films is likely to be less than expected. (3) The price of silicon carbide substrates is very high and unfavorable to large area. there is a problem.

Therefore, the most advantageous method for large-area and mass production for commercialization is generally recognized as the chemical vapor deposition method of (4). However, there are some disadvantages in the case of chemical vapor deposition. (I) First of all, a separate dedicated chemical vapor deposition apparatus is needed to deposit the graphene thin film, and (ii) CH ₄ , C ₂ H ₄ , C ₂ H Due to the use of flammable and explosive gases such as ₆ , C ₃ H ₈ , H _2, etc., there is a safety problem, and a separate safety device for treating exhaust gas is required. (Iii) 900 to form a graphene thin film. Since the process is performed for approximately several ten minutes or more at a temperature of ~ 1000 ℃ has a disadvantage that the thermal budget (thermal budget) is significant.

The present invention is to solve the problem of the conventional technology for forming a graphene (graphene) thin film, the carbon by a physical vapor deposition method on a metal film (metal foil), a metal foil (metal foil) or a metal substrate (metal substrate) It is an object of the present invention to provide a method for forming a graphene thin film using a physical vapor deposition method which can easily obtain a large area graphene thin film through thermal anneal after forming a thin film.

In order to achieve the above object, the present invention, the first to prepare a metal foil (metal foil) or a metal substrate (metal foil) composed entirely of the same material without using a metal film (metal film) formed on the substrate or a separate substrate Steps; A second step of forming a carbon film on the metal film, the metal foil or the metal substrate by physical vapor deposition; The method of forming a graphene thin film using a physical vapor deposition method comprising a; three steps of forming a graphene thin film by heat-treating the carbon thin film (thermal anneal) as a technical gist.

In addition, the carbon thin film formation by the physical vapor deposition method of the second step is carbon evaporation (carbon evaporation), sputtering of the carbon target (carbon target), laser ablation of the carbon source (carbon source) It is preferable that it consists of).

In addition, the metal film, the metal foil or the metal substrate of the first step is a transition metal and Al, including Ni, Co, Fe, Cu, Ru, Pt, Pd, Ta, Mo, W, Ir, Ti, V, Mn, Zn Preference is given to using one or two or more combinations of metals selected from the group consisting of Mg.

In addition, the metal film, the metal foil, or the metal substrate of the first step is preferably using a metal having no carbon and solid solubility.

In addition, the heat treatment of the third step is preferably performed by rapid thermal anneal having a temperature increase rate of 5 ° C./sec to 300 ° C./sec up to the heat treatment temperature.

In addition, when using a metal film formed on the substrate in the first step, it is preferable to form a separate block layer between the metal film and the substrate, the material of the block layer is preferably an oxide film or a nitride film.

In addition, the carbon thin film may be formed by using physical vapor deposition on a metal film, a metal foil, or a metal substrate made of a metal having solid solubility to carbon. After deposition, the graphene thin film is formed by performing heat treatment by rapid thermal anneal having a temperature rising rate of 5 ° C./sec to 300 ° C./sec to a heat treatment temperature. The method of forming the graphene thin film is another technical gist.

In addition, the carbon thin film may be formed by using physical vapor deposition on a metal film, metal foil, or metal substrate made of a metal having no solid solubility to carbon. After the deposition, a method of forming the graphene thin film using the physical vapor deposition method characterized in that the graphene thin film is formed by performing a heat treatment is another technical gist.

By the above problem solving means, the present invention, using the physical vapor deposition method and heat treatment process for the formation of graphene thin film solves all the problems of the conventional dedicated equipment, safety problems, thermal burden problems of the conventional chemical vapor deposition method or There is a mitigating effect.

In addition, evaporation, sputtering, laser ablation, and the like, which are physical vapor deposition methods, are already widely used in silicon standard processes, and use them to deposit carbon thin films. Since the graphene thin film can be formed by heat-treating the carbon thin film, mass production and large-area graphene thin film can be easily and economically obtained.

Figure 1a-shows a metal foil or metal substrate before forming the carbon thin film according to the present invention.
Fig. 1b-A state in which a block layer is formed on an arbitrary substrate according to the present invention and a metal film is formed thereon.
FIG. 1C is a view showing a state in which a carbon thin film is formed on a metal film or a metal foil or a metal substrate by physical vapor deposition according to Example 1 of the present invention. FIG.
FIG. 1D illustrates a state in which carbon atoms are dissolved into a metal film during deposition or rapid heat treatment of a carbon thin film according to Example 1 of the present invention. FIG.
FIG. 1E-A graph showing a state in which a graphene thin film is finally formed on a surface of a metal film after the rapid heat treatment step is finished according to Example 1 of the present invention. FIG.
1f-Temperature-time graph conceptually showing a temperature rising step, a holding step, and a temperature decreasing step in a rapid heat treatment process according to Example 1 of the present invention.
FIG. 2A is a view showing a state in which a carbon thin film is formed on a metal film, a metal foil, or a metal substrate by physical vapor deposition according to Example 2 of the present invention. FIG.
FIG. 2b is a view illustrating a state in which a graphene thin film is finally formed on a metal film, a metal foil, or a metal substrate after heat treatment according to Example 2 of the present invention; FIG.
Figures 3a to 3c-showing the actual experimental results showing the Raman spectrum of each graphene thin film specimen prepared according to Example 1 of the present invention.

The present invention is to form a graphene thin film through thermal anneal after forming a carbon thin film by physical vapor deposition such as evaporation (evaporation), sputtering, laser ablation, etc. on a predetermined substrate.

Here, the substrate on which the graphene thin film is formed may be a metal film, a metal foil, a metal substrate, or the like, and the metal film may be a metal film deposited on an arbitrary substrate. The metal foil is made of the same metal in its entirety without using a separate substrate. In the present invention, when it needs to be collectively referred to as "metal film".

The metal used for the metal film is selected from the group consisting of transition metals including Ni, Co, Fe, Cu, Ru, Pt, Pd, Ta, Mo, W, Ir, Ti, V, Mn, Zn, and Al, Mg. One or two or more combinations of metals are used.

Among the metals, metals such as Ni, Co, Ru, and the like have solid solubility with respect to carbon, and mean that carbon is dissolved in a metal film or the like during heat treatment. In this case, the heat treatment is performed by a rapid thermal anneal having a temperature rising rate of 5 ° C./sec or more and 300 ° C./sec up to a heat treatment temperature. In addition, in the case of a metal having no solid solubility with respect to carbon such as Cu of the metal to be made by a general heat treatment process. This will be described in detail in the following embodiments.

In addition, when using a metal film (metal film) formed on the substrate, it is possible to form a separate block layer between the metal film and the substrate, the material is SiO ₂ , Si ₃ N ₄ , Al ₂ O ₃ , AlN, TiO ₂ , ZrO ₂ An oxide film or a nitride film such as the above is used.

As such, the present invention is a completely distinct technology from the conventional graphene formation technology using chemical vapor deposition, and it is not only easy to obtain a large-area graphene thin film, but also to conventional chemical It is possible to solve or alleviate all of the dedicated equipment, safety problems, and heat burdens that have been pointed out as vapor deposition problems. In addition, since the deposition of the graphene thin film on the surface of the metal film by physical vapor deposition method conforms to the silicon standard process, it can be advantageously applied to mass production and large area.

Hereinafter, with reference to the accompanying drawings will be described in detail a specific embodiment of the present invention and the actual experimental results obtained by the inventor.

Example  One

1) First step: FIG. 1A shows a metal foil or a metal substrate 30 before forming a carbon thin film, wherein the metal at this time uses a material having a solid solubility with respect to carbon.

FIG. 1B shows a state in which the block layer 20 is formed on an arbitrary substrate 10 and the metal film 30 is formed thereon. As described above, a metal film, a metal foil, or a metal substrate 30 is prepared as shown in FIG. 1A or 1B.

In addition, a carbon thin film is formed on the metal film, the metal foil, or the metal substrate 30. The material of the metal film is Ni, Co, Fe, Cu, Ru, Pt, Pd, Ta, Mo, W, Ir, Ti. One or two or more combinations selected from the group consisting of transition metals including V, Mn, Zn and Al, Mg and the like can be used. An important criterion for selecting a material such as a metal film is that the metal should have solid solubility with respect to carbon (C). That is, carbon should be able to melt in the metal film, and Ni, Co, Ru, and the like are preferred because they satisfy this condition preferentially, but are not limited to these metals.

As described above, the substrate on which the carbon thin film is formed may use a metal foil or a metal substrate made of only a corresponding metal material as shown in FIG. 1A, or an arbitrary substrate as shown in FIG. 1B. It may be used to form a metal film (10) on the (10). The substrate 10 may be any substrate selected according to specific needs such as silicon, sapphire, GaAs, and silicon on insulator (SOI), and between the substrate 10 and the metal film 30 may be SiO ₂ , Si _3. N ₄ , Al ₂ O ₃ , AlN, TiO ₂ , ZrO ₂ It may be desirable to form block layer 20 of any material, including the like. The role of the block layer 20, ① the adhesive layer to assist the adhesion of the substrate 10 and the metal film 30, ② the diffusion of the metal film 30 and carbon to prevent penetration and diffusion into the substrate 10 The protective layer serves as a buffer layer to alleviate thermal stress caused by the thermal expansion coefficient of the substrate 10 and the metal film 30 different from each other. The block layer 20 may be formed by oxidizing the substrate according to its material, or by depositing a thin film of the material on the substrate 10 using evaporation, sputtering, chemical vapor deposition, or other methods. The thickness is preferably 10 nm to 1 μm, but is not limited to this range. When forming the metal film 30 on the substrate 10 as shown in Figure 1b, the method of forming the metal film varies depending on its material, it is preferable to use a method such as evaporation, sputtering, chemical vapor deposition, Its thickness is preferably 100 nm to 1 mu m, but is not limited to this range. If necessary, the metal film 30 may be subjected to a heat treatment. The purpose of the heat treatment is to promote grain growth of the metal film and to relieve internal stress of the metal film and stress with the substrate. In general, the process conditions of the heat treatment can be selected and used in a very wide range, preferably 500 ~ 1000 ℃, heat treatment time from several seconds to several ten minutes, heat treatment atmosphere is H ₂ , Ar, He, N ₂ One or more combinations of gases may be selected and used.

2) Second step: From here, it is assumed that the metal foil or the metal substrate 30 is used as shown in FIG. 1A for convenience of description. However, the present embodiment is similarly applied to the case where the metal film 30 is formed and used on the substrate 10 as shown in FIG. 1B. As shown in FIG. 1C, the carbon thin film 90 is formed on the metal film 30.

In order to form the carbon thin film 30, physical vapor deposition such as evaporation of carbon, sputtering of carbon target, and laser ablation of carbon raw material, In addition to using physical vapor deposition, a third technique classified as a physical vapor deposition method other than chemical vapor deposition may be used. When the carbon thin film is deposited by the above methods, in the vapor phase, the carbon atom 80 or the carbon particles 81 composed of two or more carbon atoms is incident on the surface of the metal film 30 to form the carbon thin film 90. To form. When the carbon thin film 90 is formed using the above methods, the temperature of the metal foil 30 may not be artificially heated, or the carbon thin film may be deposited while heating the surface of the metal to a temperature of up to 1100 ° C. have. At this time, the phase of the carbon thin film 90 may vary from amorphous carbon to crystalline graphite. The deposition thickness of the carbon thin film 90 is preferably in the range of 1 nm to 100 nm, but is not limited thereto. However, as the carbon solid solubility of the metal 30 is higher, the thickness of the metal film or the metal foil 30 may be increased. The thicker the thickness, the thicker the carbon thin film 90 needs to be deposited.

When the deposition temperature of the carbon thin film 90 is sufficiently high, as shown in FIG. 1D, some carbon atoms 82 are dissolved in the metal film 30, and the carbon thin film 90 exists on the surface of the metal film 30. In the vicinity, a steady state is formed in which dissolved carbon atoms 82 are present.

3) Third Step: In the second step, the deposition of the carbon thin film 90 is completed, and in the third step, a rapid thermal anneal process is performed. The purpose of the rapid heat treatment step is to dissolve the carbon atoms constituting the carbon thin film 90 in the metal film 30 as shown in FIG. 1D, and the metal film 30 in the temperature reduction step of the rapid heat treatment process as shown in FIG. 1F. The carbon atoms 82 dissolved therein are deposited on the surface of the metal film 30 to finally form the graphene thin film 100 as shown in FIG. 1E. Rapid heat treatment process basically proceeds in three steps as shown in FIG. In the ramp up step, the temperature is rapidly increased at a rate of several tens or 300 degrees Celsius or more at 5 ° C. per second to a desired heat treatment temperature T _A. In the holding step, the temperature is kept constant for several tens of seconds to several minutes at the heat treatment temperature T _A to dissolve the carbon atoms constituting the carbon thin film 90 on the surface of the metal film 30 into the metal film. At the same time, a dynamic equilibrium state is formed in which a part of the carbon atoms 82 dissolved in the metal film 30 is also precipitated to the surface of the metal film 30. In the process of dissolving the carbon atoms in the metal film 30 and depositing them, recombination of the carbon atoms proceeds to form the graphene thin film 100. At this time, the heat treatment temperature T _A is generally preferably in the range of 700 to 1200 ° C., but is not limited thereto. Finally, in the ramp down, the temperature is drastically lowered at a rate of several to several tens of degrees Celsius per second. Since the solid solubility of carbon which can be dissolved in the metal film 30 decreases rapidly as the temperature decreases, a part of the carbon atoms 82 dissolved in the metal film 30 in the temperature lowering step is brought to the surface of the metal film 30. Precipitation forms the graphene thin film 100. At this time, the temperature-fall rate is important. If the temperature-fall rate is too fast, the graphene thin film 100 may not be smoothly formed because there is not enough time for the carbon atoms 82 dissolved in the metal film 30 to precipitate on the metal film surface. . On the contrary, when the temperature reduction rate is too slow, the graphene thin film 100 may not be formed on the surface because the carbon atoms 82 dissolved in the metal film 30 are further diffused into the metal film. Appropriate temperature-fall rate will vary depending on the case, but generally around -10 ℃ / sec is preferred.

Atmosphere of the rapid heat treatment process is preferably used alone or mixed with a gas such as He, Ar, N ₂ , H ₂ . When the temperature reduction step of the rapid heat treatment is completed, the graphene thin film 100 is finally formed on the surface of the metal film 30 as shown in FIG. 1E. The thickness of the graphene thin film 100 can be adjusted through rapid heat treatment conditions as described above. The graphene thin film 100 may be removed from the metal film by performing wet etching using chemicals such as acids and bases capable of selectively dissolving only the metal film 30. For example, in the case of Ni It is common to use FeCl ₃ and the like.

3A to 3C show that a Ni metal film 300 nm is deposited by sputtering on an oxide-covered silicon substrate based on Example 1 of the present invention, and a carbon thin film about 10 nm is deposited on Ni by electron-beam evaporation. After rapid heat treatment at 700 ~ 950 ℃ for several minutes, the results were analyzed by Raman spectroscopy. 3A illustrates a case in which rapid thermal treatment is not performed after the deposition of the carbon thin film, and shows the characteristics of the amorphous carbon thin film. 3b is an analysis result of a specimen cooled at a high rate by heating the temperature at 700 ° C. to 55 ° C./sec and performing rapid heat treatment at 700 ° C. for about 5 minutes, and then setting the temperature reduction rate at about −15 ° C./sec. As crystallization progressed, unique peaks related to graphene began to appear. However, the intensity of the D peak is so high that the quality of the graphene film is still poor. Figure 3c shows the Raman analysis of the specimen cooled at a high speed by performing a heat treatment at 950 ℃ for about 90 seconds and then set the temperature reduction rate to about -15 ℃ / sec. Compared to FIG. 3B, the intensity of the D peak was greatly decreased, and the G peak and the 2D peak were clearly observed to show graphene-specific Raman spectra. However, since the intensity of the 2D peak is lower than that of the G peak, the thickness of the graphene thin film is slightly thicker.

Example  2

1) First step: A metal film 30 formed on a metal foil, a metal substrate, or an arbitrary substrate 10 is prepared in the same manner as in Example 1. The material of the metal film is one or two selected from the group consisting of transition metals including Ni, Co, Fe, Cu, Ru, Pt, Pd, Ta, Mo, W, Ir, Ti, V, Mn, Zn, and Al, Mg, and the like. More than one combination may be used. However, in this case, the material of the metal film 30 is different from that of the first embodiment in that a metal having almost no solid solubility with respect to carbon (C) such as Cu is selected.

As in Example 1, the metal film 30 may be made of a metal foil (metal foil) or a metal substrate (metal substrate) made only of the corresponding metal material as shown in Figure 1a, or as shown in Figure 1b The substrate 10 may be used in the form of a metal film. The substrate 10 may be any substrate selected according to specific needs such as silicon, sapphire, GaAs, and silicon on insulator (SOI), and between the substrate 10 and the metal film 30 may be SiO ₂ , Si _3. It may be desirable to form a block layer 20 of any material, including N ₄ , Al ₂ O ₃ , AlN, TiO ₂ , ZrO ₂ , and the like. As in Example 1, if necessary, the metal film 30 may be heat treated, and the process conditions of the heat treatment may be selected and used in a very wide range, but preferably 500 to 1100 ° C., heat treatment time. From a few seconds to several tens of silver, the heat treatment atmosphere may be used by selecting one or more combinations of gases such as H ₂ , Ar, He, N _2, and the like.

2) Second step: From here, it is assumed that the metal foil or the metal substrate 30 is used as shown in FIG. 1A for convenience of description. However, this embodiment is equally applicable to the case where the metal film 30 is formed and used on an arbitrary substrate 10. The carbon thin film 90 is deposited on the metal foil 30 as shown in FIG. 2A using physical vapor deposition such as evaporation, sputtering, laser ablation, or the like. In this case, the thickness of the carbon thin film 90 is important to be thinner than the first embodiment, and preferably about 0.5 to 5 nm. This is because the metal foil, the metal substrate, or the metal film 30 hardly dissolves carbon, and therefore it is not necessary to form the carbon thin film 90 thickly. In addition, when depositing the carbon thin film 90, it is preferable to keep the temperature of the surface of the metal film 30 as high as possible, for example, by maintaining the range of about 900 to 1100 ° C. so that the carbon atoms are formed on the surface of the metal film 30. It is desirable to have high mobility. In this way, the higher the deposition temperature, the higher the possibility that the graphene thin film 100 is immediately formed in step 2.

3) Third Step: In the second step, the deposition of the carbon thin film 90 is completed, and in the third step, a rapid thermal anneal process is performed. However, the difference from Example 1 is that the temperature reduction step is not very important in Example 2. This is because the metal film 30 does not dissolve carbon and there is no carbon dissolution and precipitation process. Instead, it is important to sufficiently set the heat treatment temperature T _A and the heat treatment time of the maintenance step so that the carbon thin film 90 can be easily recombined into the graphene thin film 100, and it may be several minutes to several tens of minutes at the heat treatment temperature of 700 to 1200 ° C. It is preferable to perform heat treatment to a degree. When the deposition temperature of the second stage is sufficiently high, the heat treatment time of the third stage is further shortened. Atmosphere of the rapid heat treatment process is preferably used alone or mixed with a gas such as He, Ar, N ₂ , H ₂ . When the rapid heat treatment is completed, the graphene thin film 100 is formed on the surface of the metal film 30 as shown in FIG. 2B. As in Example 1, the graphene thin film 100 may be separated from the metal film by performing wet etching using various chemicals such as acids and bases capable of selectively dissolving only the metal film 30.

10 substrate 20 block layer
30: metal foil, metal film or metal substrate
80: carbon atom incident on the metal film from the gas phase,
81: Carbon particles incident on the metal film from the gas phase.
82: carbon atom dissolved in the metal film
90: carbon thin film formed on the metal film,
100: graphene thin film

Claims (10)

A first step of preparing a metal foil or a metal substrate formed of the same material as a whole without using a metal film or a separate substrate formed on the substrate;
A second step of forming a carbon film on the metal film, the metal foil or the metal substrate by physical vapor deposition;
Forming a graphene thin film by thermally annealing the carbon thin film; and forming a graphene thin film by using a physical vapor deposition method. The method of claim 1, wherein the carbon thin film formation by the physical vapor deposition method of the second step is performed by carbon evaporation. The method of claim 1, wherein the carbon thin film is formed by physical vapor deposition in the second step. The carbon thin film is formed by sputtering a carbon target. 2. The graphene thin film formation method of claim 1, wherein the carbon thin film formation by the physical vapor deposition method of the second step is performed by laser ablation of a carbon source. Way. The method of claim 1, wherein the metal film, metal foil, or metal substrate of the first step includes Ni, Co, Fe, Cu, Ru, Pt, Pd, Ta, Mo, W, Ir, Ti, V, Mn, Zn. Method of forming a graphene thin film using a physical vapor deposition method using a transition metal and one or two or more combinations of metals selected from the group consisting of Al, Mg. The method of claim 1, wherein the heat treatment in the third step is performed by a rapid thermal anneal having a temperature increase rate of 5 ° C./sec to 300 ° C./sec up to a heat treatment temperature. Formation method of graphene thin film. The method of claim 1, wherein when using a metal film formed on the substrate in the first step, a separate block layer is formed between the metal film and the substrate. Formation method. The method of claim 7, wherein the block layer is formed of an oxide film or a nitride film. Deposition of a carbon thin film using physical vapor deposition on a metal film, metal foil or metal substrate made of a metal having a solid solubility to carbon After that, the graphene thin film is formed by performing heat treatment by rapid thermal anneal having a temperature rising rate of 5 ° C./sec to 300 ° C./sec up to a heat treatment temperature. Formation method of thin film. Deposition of a carbon thin film using physical vapor deposition on a metal film, metal foil or metal substrate made of a metal without solid solubility to carbon. After that, the graphene thin film is formed using a physical vapor deposition method, characterized in that to form a thin film by heat treatment.

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