Patent Publication Number: US-2012025413-A1

Title: Method of manufacturing graphene

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims priority from Korean Patent Application No. 10-2010-0072486, filed on Jul. 27, 2010, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     Methods and apparatuses consistent with exemplary embodiments relate to manufacturing graphene. 
     2. Description of the Related Art 
     Currently, materials based on carbon, for example, carbon nanotubes, diamond, graphite, and graphene have been studied in various nano technology fields. Such materials are currently being used or will be used in field effect transistors (FETs), biosensors, nano composites, or quantum devices. 
     Graphene is a two-dimensional semiconductor material having a zero band gap. In recent years, various research results have been reported with respect to electrical characteristics of graphene. The electrical characteristics of graphene include a bipolar supercurrent, spin transport, and a quantum hole effect. Currently, graphene is receiving attention as a material to be used as a basic unit for integration of carbon based nano electronic devices. 
     As interest in graphene increases, there is a need to develop a method of producing high quality graphene in large quantities. 
     SUMMARY 
     One or more exemplary embodiments provide a method of manufacturing high quality and large area graphene in large quantities and an apparatus therefor. 
     According to an aspect of an exemplary embodiment, there is provided a method of manufacturing graphene, the method including: placing a supporting belt, on which a catalyst layer is loaded, into a chamber; increasing a temperature of the catalyst layer by injecting a carbon source into the chamber; forming graphene on the catalyst layer by cooling the catalyst layer; and taking out the supporting belt, on which the catalyst layer, on which the graphene is formed, is loaded, from the chamber to an outside, wherein a ratio of a melting point Tmp of the supporting belt to a maximum temperature Tmax of the catalyst metal layer may be equal to or less than 0.6. 
     The method may include performing a reel-to-reel method. 
     The supporting belt may include at least one of zirconium (Zr), chromium (Cr), vanadium (V), rhodium (Rh), technetium (Tc), hafnium (Hf), ruthenium (Ru), boron (B), iridium (Ir), niobium (Nb), molybdenum (Mo), tantalum (Ta), osmium (Os), rhenium (Re), and tungsten (W). 
     The placing the supporting belt, on which the catalyst layer is loaded, into the chamber may include conveying a portion of the supporting belt, on which a portion of the catalyst layer is loaded, into the chamber; separating the portion of the supporting belt from the portion of the catalyst layer after taking out the portion of the supporting layer, on which the portion of the catalyst layer is loaded, from the chamber; and conveying the portion of the supporting belt, on which another portion of the catalyst layer is loaded, into the chamber. 
     The method may further include separating the supporting belt from the catalyst layer on which the graphene is formed. 
     The method may further include removing the catalyst layer from the catalyst layer on which the graphene is formed after the forming the graphene. 
     The removing the catalyst layer may include removing the catalyst layer by etching the catalyst layer. 
     The method may further include forming a graphene protection film on the graphene between the forming of the graphene and the removing the catalyst layer. 
     The chamber may be maintained at a pressure in a range from 10 −3  to 10 −2  torr. 
     According to an aspect of another exemplary embodiment, there is provided an apparatus for manufacturing graphene, the apparatus including a supporting belt provider which loads a catalyst layer on a supporting belt and provides the supporting belt on which the catalyst layer is loaded; and a chamber which receives the supporting belt, on which the catalyst layer is loaded, provided from the supporting belt, increases a temperature of the catalyst layer while receiving a carbon source from an outside, forms graphene on the catalyst layer by cooling the catalyst layer, and outputs the supporting belt on which the catalyst layer, on which the graphene is formed, is loaded. 
     In the apparatus, a ratio of a melting point of the supporting belt to a maximum temperature of the catalyst layer that the catalyst layer is heated in the chamber may be equal to or less than 0.6. 
     In providing the supporting belt on which the catalyst layer is loaded to the chamber, the supporting belt provider may: convey a portion of the supporting belt, on which a portion of the catalyst layer is loaded, into the chamber; separate the portion of the supporting belt from the portion of the catalyst layer after taking out the portion of the supporting layer, on which the portion of the catalyst layer is loaded, from the chamber; and convey the portion of the supporting belt, on which another portion of the catalyst layer is loaded, into the chamber. 
     The supporting belt may include at least one of zirconium Zr, chromium Cr, vanadium V, rhodium Rh, technetium Tc, hafnium Hf, ruthenium Ru, boron B, iridium Ir, niobium Nb, molybdenum Mo, tantalum Ta, osmium Os, rhenium Re, and tungsten W. 
     The chamber may be maintained at a pressure in a range from 10 −3  to 10 −2  torr. 
     A plurality of the catalyst metal layers having a panel shape may be conveyed into the chamber by the supporting belt. 
     According to the exemplary embodiments, high quality graphene may be produced in large quantities. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features aspects will become more apparent by describing in detail exemplary embodiments with reference to the attached drawings, in which: 
         FIG. 1  is a flowchart schematically showing a method of manufacturing graphene according to an exemplary embodiment; 
         FIG. 2  is a schematic drawing showing a process system of the method of manufacturing graphene of  FIG. 1 , according to an exemplary embodiment; 
         FIG. 3  is a graph showing a change in strength of a metal according to variations in temperature, according to an exemplary embodiment; 
         FIG. 4  is a schematic lateral cross-sectional view of a catalyst metal layer transported according to an operation of conveying a catalyst metal layer of  FIG. 1 , according to an exemplary embodiment; 
         FIG. 5  is a schematic lateral cross-sectional view of graphene formed on a catalyst metal layer according to operations of injecting a gaseous carbon source, forming graphene, and taking out the catalyst metal layer of  FIG. 1 , according to an exemplary embodiment; 
         FIG. 6  is a schematic lateral cross-sectional view of a graphene protection film formed according to an operation of forming the graphene protection film of  FIG. 1 , according to an exemplary embodiment; and 
         FIG. 7  is a schematic lateral cross-sectional view of graphene from which a catalyst metal layer is removed according to an operation of removing the catalyst metal layer of  FIG. 1 , according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Exemplary embodiments will now be described more fully with reference to the accompanying drawings. The exemplary embodiments may, however, be changed or modified in many different forms and should not be construed as being limited thereto; rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the inventive concept to those of ordinary skill in the art and the scope of the inventive concept is defined by the appended claims. The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting the inventive concept. In the current specification, the singular forms include the plural forms unless the context clearly indicates otherwise. It will be further understood that the terms “comprise” and/or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, and/or components. It will be understood that, although the terms first, second, etc., may be used herein to describe various constituent elements, these constituent elements should not be limited by these terms. These terms are only used to distinguish one constituent element from another constituent element. 
     A catalyst metal layer used in the current specification may be only one single layer. Alternatively, the catalyst metal layer may be a layer formed on the outermost layer of a specific substrate having a plurality of layers. That is, the catalyst metal layer denotes one single layer or the outermost layer of a plurality of layers. 
     Hereinafter, for convenience of explanation, one single catalyst metal layer is described. 
       FIG. 1  is a flowchart schematically showing a method of manufacturing graphene according to an exemplary embodiment.  FIG. 2  is a schematic drawing showing a process system of the method of manufacturing graphene of  FIG. 1 , according to an exemplary embodiment. As depicted in  FIG. 2 , the method of manufacturing graphene may be performed by a reel-to-reel method. 
     In operation S 110 , a supporting belt  30  on which a catalyst metal layer  401  is loaded enters into a chamber  100 . That is, the catalyst metal layer  401  is conveyed into the chamber  100  by the supporting belt  30 . Referring to  FIG. 2  and  FIG. 4 , the catalyst metal layer  401  is supplied by a reel  10 , rollers  11  and  13 . 
     The catalyst metal layer  401  may be formed of at least one of copper (Cu) and nickel (Ni). 
     Since the temperature of the chamber  100  is maintained at a high temperature, the mechanical strength of the catalyst metal layer  401  is reduced in the chamber  100 , and thus, the catalyst metal layer  401  is weakened by its own weight (i.e., self-weight). As a comparative embodiment, if a single layer of the catalyst metal layer  401  is introduced into the chamber  100 , high quality graphene may not be formed due to non-elastic deformation of the catalyst metal layer  401 . However, the supporting belt  30  disposed under the catalyst metal layer  401  prevents strength reduction of the catalyst metal layer  401  and prevents quality reduction of graphene  402  due to the strength reduction of the catalyst metal layer  401 . The catalyst metal layer  401  and the graphene  402  produced accordingly will be described in relation to operations S 120  through S 140 . 
       FIG. 3  is a graph showing a change in strength S of a metal according to variations in temperature T. In  FIG. 3 , Tm denotes a melting point of the metal. Section A is a region where the strength of the metal is barely affected by temperature. Section B is a region where the strength of the metal begins to be affected by temperature, and thus, the deformation rate of the metal is evidently increased. Section C is a region where the metal becomes weak due to its self-weight, and thus, the mechanical strength of the metal is rapidly reduced. 
     Therefore, in order to support the catalyst metal layer  401  in the chamber  100  in terms of strength, the supporting belt  30  having a homologous temperature T H , that is, the supporting belt  30  formed of a material having a ratio of a maximum temperature Tmax of the catalyst metal layer  401  to a melting point Tmp of the supporting belt  30  being equal to or less than 0.6, is used. In other words, the supporting belt  30  formed of a material having 0.6Tmp that is equal to or greater than Tmax is used. This relationship may be expressed as shown in Equation 1. 
     
       
         
           
             
               
                 
                   Th 
                   = 
                   
                     
                       Tmax 
                       Tmp 
                     
                     ≤ 
                     
                       0.6 
                        
                       
                           
                       
                        
                       or 
                        
                       
                           
                       
                        
                       0.6 
                        
                       
                           
                       
                        
                       Tmp 
                     
                     ≥ 
                     Tmax 
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     According to the current exemplary embodiment, the temperature Tc of the chamber  100  forms an equilibrium with the temperature of the catalyst metal layer  401  after a predetermined period of time. Accordingly, the temperature Tc of the chamber  100  is increased to increase the temperature of the catalyst metal layer  401 . For example, since the temperature of the chamber  100  is approximately 1,000° C., a melting point of the supporting belt  30  that satisfies Equation 1 must be greater than approximately 1,667° C. Preferably but not necessarily, the melting point of the supporting belt  30  may be greater than about 1,850° C. A material that satisfies this condition may be at least one of zirconium (Zr), chromium (Cr), vanadium (V), rhodium (Rh), technetium (Tc), hafnium (Hf), ruthenium (Ru), boron (B), iridium (Ir), niobium (Nb), molybdenum (Mo), tantalum (Ta), osmium (Os), rhenium (Re), and tungsten (W). 
     The supporting belt  30  that satisfies the condition of Equation 1 may also be formed of a material that includes carbon, such as, carbon nanotubes, which can withstand a high temperature, or a silicon material. 
     The supporting belt  30  may be formed to have, for example, a caterpillar type. 
     In the current exemplary embodiment, the catalyst metal layer  401  formed of Cu or Ni is described. However, the material for forming the catalyst metal layer  401  is not limited thereto. For example, the catalyst metal layer  401  may also be formed of at least one of cobalt (Co), iron (Fe), platinum (Pt), gold (Au), aluminum (Al), Cr, magnesium (Mg), manganese (Mn), Rh, silica (Si), and titanium (Ti). 
     In operation S 120 , a gaseous carbon source is injected into the chamber  100 . Referring to  FIG. 2 , while injecting the gaseous carbon source into the chamber  100  through an inlet  110  formed on the chamber  100 , carbon atoms are deposited onto the catalyst metal layer  401  by heat-treating the catalyst metal layer  401  using a heater  140 . 
     The heater  140  increases the temperature of the chamber  100  enough to separate the carbon atoms from the gaseous carbon source and simultaneously increases the temperature of the catalyst metal layer  401 . For example, the temperature of the chamber  100  is greater than approximately 1,000° C. Methane (CH 4 ) gas, which is the gaseous carbon source, decomposes into carbon atoms and hydrogen atoms through a heat treatment process performed at approximately 1,000° C., and the separated carbon atoms are deposited onto the catalyst metal layer  401 . In this case, the chamber  100  may be maintained at a pressure in a range from about 10 −3  to about 10 −2  torr. 
     In the current exemplary embodiment, methane is described as the gaseous carbon source. However, the gaseous carbon source is not limited thereto. For example, the gaseous carbon source may be at least one material that contains carbon, such as carbon dioxide, ethane, ethylene, ethanol, acetylene, propane, propylene, butane, butadiene, pentane, pentene, cycloropentadien, hexane, cyclohexane, benzene, or toluene. 
     In the current exemplary embodiment, the case where only the gaseous carbon source is injected into the chamber  100  is described. However, the inventive concept is not limited thereto. For example, a pretreatment may be performed with respect to a surface of the catalyst metal layer  401  prior to injecting the gaseous carbon source. The pretreatment process is performed to remove foreign materials present on the catalyst metal layer  401  by using a hydrogen gas. The hydrogen gas is supplied through an inlet hole  120  formed on the chamber  100 . 
     Alternatively, the surface of the catalyst metal layer  401  may be washed using an acid/alkali solution before the catalyst metal layer  401  is transported to the chamber  100 . In this way, defects that can occur during the synthesis of graphene in a subsequent process can be reduced. 
     In operation S 130 , the graphene  402  is formed by cooling the catalyst metal layer  401 .  FIG. 5  is a schematic lateral cross-sectional view of the graphene  402  formed on a catalyst metal layer  401  according to operations S 120  through S 140  of  FIG. 1 . Carbon atoms deposited on the surface of the catalyst metal layer  401  are converted to the graphene  402  during cooling. The cooling may be performed in the same space, that is, in the chamber  100  where the temperature of the catalyst metal layer  401  is increased. 
     According to another exemplary embodiment, the cooling process may be performed in an additional cooling chamber (not shown) after taking out the catalyst metal layer  401  from the chamber  100 . Alternatively, the catalyst metal layer  401  may be naturally cooled outside of the chamber  100  by taking out the catalyst metal layer  401  to the outside. 
     In operation S 140 , the catalyst metal layer  401  is conveyed to the outside of the chamber  100  by the supporting belt  30 . That is, the supporting belt  30  is taken out to the outside from the chamber  100  after being used therein for the formation of the graphene  402  in operations S 110  through S 130 . 
     When the supporting belt  30  and the catalyst metal layer  401  are taken out of the chamber  100 , the catalyst metal layer  401  is separated from the supporting belt  30  by a reel  20  and a roller  35 . 
     As depicted in the graph of  FIG. 3 , the mechanical strength of the catalyst metal layer  401  is significantly reduced in the high temperature chamber  100 , and thus, the catalyst metal layer  401  is weakened due to its self-weight. However, since the catalyst metal layer  401  is supported by the supporting belt  30 , tension generated by the reels  10  and  20  and the self-weight of the catalyst metal layer  401  may not affect the catalyst metal layer  401 . 
     As depicted in  FIG. 2 , the supporting belt  30  has a circulating structure. That is, after the supporting belt  30  is used in the process of conveying the catalyst metal layer  401  into the chamber  100  and taking it out of the chamber  100 , the supporting belt  30  performs a new role for conveying the catalyst metal layer  401  into the chamber  100 . The process system of  FIG. 2  includes rollers  31 ,  33 ,  34 ,  35 ,  36 , and  37  for circulating the supporting belt  30 . 
     In operation S 150 , a graphene protection film  600  is formed on the graphene  402 . Referring to  FIG. 2 , when the catalyst metal layer  401  on which the graphene  402  is formed and the graphene protection film  600  are supplied to a protection film forming apparatus  200 , the graphene protection film  600  is formed on the graphene  402  while passing through the protection film forming apparatus  200 .  FIG. 6  is a schematic lateral cross-sectional view of the graphene protection film  600  formed according to operation S 150  of  FIG. 1 . The process system of  FIG. 2  includes a reel  60 , rollers  61 ,  62  and  41  for supplying the graphene protection film  600 . 
     The graphene protection film  600  may be formed of a material such as a thermal exfoliation tape, a photoresist, an aqueous polyurethane resin, an aqueous epoxy resin, an aqueous acryl resin, an aqueous natural polymer resin, a water based adhesive, an alcohol exfoliation tape, acetic acid vinyl emersion adhesive, a hot-melt adhesive, a visible light hardening adhesive, an infrared ray hardening adhesive, an ultraviolet ray hardening adhesive, an electron beam hardening adhesive, a polybenzimidazole (PBI) adhesive, a polyimide adhesive, a silicon adhesive, an imide adhesive, a bismaleimide (BMI) adhesive, or a modified epoxy resin. 
     In operation S 160 , the catalyst metal layer  401  is removed. For example, the catalyst metal layer  401  may be removed by an etching process. Referring to  FIG. 2 , the catalyst metal layer  401  is conveyed to an etching space  300  using rollers  21 ,  22 ,  42  and  43  after the graphene protection film  600  is formed in operation S 140 . The etching space  300  includes a sprayer  310  that sprays an etching solution. The etching solution may be an acid, HF, a buffered oxide etch (BOE) solution, a FeCl 3  solution, or a Fe(No 3 ) 3  solution. 
       FIG. 7  is a schematic lateral cross-sectional view of the graphene  402  from which the catalyst metal layer  401  is removed according to operation S 160  of  FIG. 1 . 
     The graphene  402  from which the catalyst metal layer  401  is removed is collected in a reel  50  after passing through rollers  51  and  52 . 
     As described above, the case where the catalyst metal layer  401  according to the exemplary embodiment is conveyed into the chamber  100  by a reel-to-reel method is described. However, the inventive concept is not limited thereto. That is, besides the reel-to-reel method, if, in order to form a large area graphene, the catalyst metal layer  401  having a large area is conveyed into the chamber  100 , and the mechanical strength of the catalyst metal layer  401  is reduced due to the high temperature of the chamber  100 , deformation of the catalyst metal layer  401  in the high temperature chamber  100  may be prevented or minimized by using the supporting belt  30  according to the exemplary embodiment. For example, in the process of increasing the temperature of the catalyst metal layer  401 , the surface or texture of the catalyst metal layer  401  may become non-uniform due to an internal constituent material or stress, and thus, the quality of the graphene may be degraded. However, in the exemplary embodiment, since the catalyst metal layer  401  is supported by the supporting belt  30 , the catalyst metal layer  401  may maintain a stable shape even if the temperature of the catalyst metal layer  401  is increased. 
     For example, the catalyst metal layer  401  having a rectangular shape and a large area may be conveyed by the supporting belt  30  by being supported only at edges of the catalyst metal layer  401 . When the catalyst metal layer  401  is exposed to a high temperature in a state in which only the edges of the catalyst metal layer  401  are supported, the mechanical strength of the catalyst metal layer  401  is greatly reduced, and, as a result, the catalyst metal layer  401  having a large area weakened due to its self-weight. However, when the supporting belt  30  supports the entire catalyst metal layer  401 , deformation of the catalyst metal layer  401  and quality degradation of the graphene  402  due to the self-weight of the catalyst metal layer  401  may be prevented. 
     While the exemplary embodiments have been particularly shown and described with reference to the corresponding drawings, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the inventive concept as defined by the following claims.