Abstract:
Provided are a method of manufacturing graphene, graphene manufactured by the method, a conductive thin film including the graphene, a transparent electrode comprising the graphene, and a radiating or heating device comprising the graphene. The method includes: preparing a graphene member including a base member, a hydrophilic oxide layer formed on the base member, a hydrophobic metal catalyst layer formed on the oxide layer, and graphene grown on the metal catalyst layer; applying water to the graphene member; separating the metal catalyst layer from the oxide layer; and removing the metal catalyst layer using an etching process.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims priority from Korean Patent Application No. 10-2009-0089289, filed on Sep. 21, 2009 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, and more particularly to a method of manufacturing graphene, graphene manufactured by the method, a conductive thin film including the graphene, a transparent electrode including the graphene, and a radiating or heating device including the graphene. 
     2. Description of the Related Art 
     Recently, graphite materials such as fullerenes, carbon nanotubes, graphene, and graphite have attracted attention. 
     In particular, experiments have been performed on carbon nanotubes and graphene. Because graphene can be formed into large scale films and has electrical, mechanical, and chemical stability, in addition to high conductivity, graphene has drawn much attention as a basic element for electronic circuits. 
     In recent years, techniques for manufacturing large scale graphene have greatly improved. A method of manufacturing graphene using a chemical vapor deposition (CVD) method is disclosed in the article “Large-Scale Pattern Growth of Graphene Films for Stretchable Transparent Electrodes” published in Nature Magazine, No. 07719, on Jan. 14, 2009, the contents of which are incorporated herein by reference in their entirety. 
     A related art method of manufacturing graphene using a CVD method is as follows. First, a silicon wafer having a silicon oxide (SiO 2 ) is prepared. Next, a metal catalyst layer is formed by depositing a metal catalyst, such as Ni, Cu, Al, or Fe, on the silicon oxide layer using a sputtering apparatus or an e-beam evaporator. 
     Next, the silicon wafer on which the metal catalyst layer is formed and a gas containing carbon, such as CH 4 , C 2 H 2 , C 2 H 4 , or CO, are put into a reactor for performing inductive coupled plasma chemical vapor deposition (ICP-CVD). Then, the reactor is heated so that carbon can be absorbed into the metal catalyst layer. Next, the reactor is rapidly cooled to crystallize and separate the carbon from the metal catalyst layer, thus growing graphene. 
     The grown graphene undergoes a transfer process before use. For this purpose, an etching method is used. 
     SUMMARY OF THE INVENTION 
     Exemplary embodiments provide a method of rapidly separating graphene from a graphene member on which the graphene is formed. 
     According to an aspect of an exemplary embodiment, there is provided a method of manufacturing graphene, including: preparing a graphene member including a base member, a hydrophilic oxide layer formed on the base member, a hydrophobic metal catalyst layer formed on the oxide layer, and growing graphene on the metal catalyst layer; applying water to the graphene member; separating the metal catalyst layer from the oxide layer; and removing the metal catalyst layer using an etching process. The base member may include silicon (Si). 
     The oxide layer may include silicon oxide (SiO 2 ). 
     The metal catalyst layer may include at least a metal selected from the group consisting of Ni, Cu, Al, Fe, Co, and W. Also, the metal catalyst may be Ni or Cu in a foil state not a metal catalyst layer based on a wafer. 
     The preparing the graphene member may further include disposing a transfer member onto the graphene. 
     The transfer member may include a material selected from the group consisting of polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), polyimide, glass, synthesized rubber, and natural rubber. 
     In the applying water to the graphene member, a gap may be generated between the oxide layer and the metal catalyst layer by water penetrating between the oxide layer and the metal catalyst layer. 
     The applying water to the graphene member may include ultrasonic wave processing of the graphene member. 
     The applying water to the graphene member may be performed by soaking the graphene member in water in a water bath. 
     The separating the metal catalyst layer from the oxide layer may be performed while the graphene member is soaked in water in the water bath. 
     The separating the metal catalyst layer from the oxide layer may be performed by applying a predetermined force to the graphene member. 
     The etching process may be performed by using at least one solution selected from the group consisting of an acid, a hydrogen fluoride solution, a buffered oxide etch (BOE) solution, a FeCl 3  solution, and a Fe(No 3 ) 3  solution. 
     The method may further include, after the removing the metal catalyst layer using the etching process, transferring the graphene onto a substrate or a device. 
     According to an aspect of another exemplary embodiment, there is provided graphene obtained from the methods described above. 
     According to an aspect of another exemplary embodiment, there is provided a conductive thin film including the graphene obtained from the methods described above. 
     According to an aspect of another exemplary embodiment, there is provided a transparent electrode including the graphene obtained from the methods described above. 
     According to an aspect of another exemplary embodiment, there is provided a radiating or heating device including the graphene obtained from the methods described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects will become more apparent by describing in detail exemplary embodiments with reference to the attached drawings in which: 
         FIG. 1  is a cross-sectional view of a graphene member according to an embodiment; 
         FIGS. 2 through 7  are cross-sectional views for explaining a method of manufacturing graphene according to an embodiment; and 
         FIG. 8  is a flow chart showing a method of manufacturing graphene according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Exemplary embodiments will now be described more fully with reference to the accompanying drawings. 
       FIG. 1  is a cross-sectional view of a graphene member  100  according to an exemplary embodiment. The graphene member  100  includes graphene  140  that is sufficiently grown by using, for example, a conventional chemical vapor deposition method (CVD). The grapheme has not been transferred yet. 
     Referring to  FIG. 1 , the structure of the graphene member  100  will now be described. 
     The graphene member  100  includes a base member  110 , an oxide layer  120 , a metal catalyst layer  130 , and the graphene  140 . 
     The base member  110  is a substrate, such as, for example, a wafer. 
     The material forming the base member  110  is not particularly limited, but according to an exemplary embodiment the material forming the base member  110  is silicon (Si). In an exemplary embodiment, the base member  110  is a silicon wafer. 
     The oxide layer  120  may be formed of silicon oxide (SiO 2 ) and has a thickness greater than, for example, 300 nm. The oxide layer  120  has a hydrophilic property according to the property of silicon oxide. 
     The oxide layer  120  according to an exemplary embodiment is formed of silicon oxide (SiO 2 ), but is not limited thereto. That is, there is no specific limit in selecting the material for forming the oxide layer  120 , and any material can be used as long as the material has a hydrophilic property and can readily form the metal catalyst layer  130 . 
     The metal catalyst layer  130  is formed of Ni on the oxide layer  120  to a thickness of greater than, for example, 100 nm using a sputtering method. The metal catalyst layer  130  has a hydrophobic property according to the property of Ni. 
     The metal catalyst layer  130  according to an exemplary embodiment is formed of Ni, but is not limited thereto. That is, there is no specific limit in selecting the material for forming the metal catalyst layer  130 , and any material can be used as long as the material has a hydrophobic property and can grow graphene by absorbing carbon when a CVD method is performed. In certain embodiments, the metal catalyst layer  130  may be formed of, for example, Cu, Al, Fe, Co, or W. 
     The graphene  140  may have a film shape, and may be grown on an upper surface of the metal catalyst layer  130  using a CVD method. 
     A method of manufacturing graphene will now be described with reference to  FIGS. 2 through 7 , although the ordinarily-skilled artisan will readily recognize that the present invention is not limited by this method of manufacture. 
       FIGS. 2 through 7  are cross-sectional views illustrating a method of manufacturing graphene according to an exemplary embodiment.  FIG. 8  is a flow chart showing a method of manufacturing graphene according to an exemplary embodiment. 
     As described above, a graphene member  100  in which graphene  140  is grown by using a CVD method is prepared (operation S 1 ). 
     Referring to  FIG. 2 , a transfer member  150  is placed on an upper surface of the graphene  140  (operation S 2 ) 
     The transfer member  150  may be formed of, for example, polydimethylsiloxane (PDMS). 
     The transfer member  150  according to an exemplary embodiment is formed of PDMS, but is not limited thereto. That is, the transfer member  150  may be formed of any material that can transfer the graphene  140 . For example, in other embodiments, the transfer member  150  may be formed of, for example, polyethylene terephthalate (PET), polyimide, glass, synthesized rubber, or natural rubber. 
     Referring to  FIG. 3 , the graphene member  100  on which the transfer member  150  is placed soaked in a water bath  160 , and ultrasonic waves generated from an ultra sonic wave generator  170  are radiated onto the graphene member  100  (operation S 3 ). 
     In Operation S 3 , when the graphene member  100  is soaked in the water bath  160 , water generates a gap between the oxide layer  120  and the metal catalyst layer  130  by penetrating between the oxide layer  120  and the metal catalyst layer  130 . This is because the oxide layer  120  has a hydrophilic property and the metal catalyst layer  130  has a hydrophobic property. In particular, ultrasonic waves generated from the ultrasonic wave generator  170  facilitate the penetration of water between the oxide layer  120  and the metal catalyst layer  130 . The ultrasonic waves may be radiated onto the graphene member  100  for approximately 10 seconds. The irradiating time of the ultrasonic waves may vary according to working conditions or size and thickness of the graphene member  100 . 
     According to an exemplary embodiment, water is applied to the graphene member  100  by soaking the graphene member  100  in the water bath  160  filled with water, but the present invention is not limited thereto. That is, there is no specific limitation in selecting the method of applying water to the graphene member  100 , and any method that can evenly apply water to the graphene member  100  may be used. For example, in other embodiments, the graphene member  100  may be placed in flowing water or may be sprayed with water. 
     According to an exemplary embodiment, the penetration of water between the oxide layer  120  and the metal catalyst layer  130  may be increased by radiating ultrasonic waves, but the present invention is not limited thereto. That is, ultrasonic waves are not necessarily used. 
     Next, referring to  FIG. 4 , the metal catalyst layer  130  is separated from the oxide layer  120  by applying a predetermined force P in a direction indicated by the arrow while the graphene member  100  is soaked in water in the water bath  160  (operation S 4 ). 
     That is, in Operation S 3 , since water penetrates between the oxide layer  120  and the metal catalyst layer  130 , a gap is generated between the oxide layer  120  and the metal catalyst layer  130 . Thus, the metal catalyst layer  130  can be separated from the oxide layer  120  by applying a predetermined force P to the transfer member  150 . 
     In determining the predetermined force P, a magnitude of the force P that can smoothly separate the metal catalyst layer  130  from the oxide layer  120  is determined. Also, the direction of the predetermined force P may be perpendicular to a surface where the oxide layer  120  contacts the metal catalyst layer  130 , parallel to the surface where the oxide layer  120  contacts the metal catalyst layer  130 , may have a predetermined slope with respect to the perpendicular direction to the surface where the oxide layer  120  contacts the metal catalyst layer  130 , or may be a combination of the directions described above. 
     According to an exemplary embodiment, the oxide layer  120  and the metal catalyst layer  130  are separated from each other by applying the predetermined force P while the graphene member  100  is soaked in water, but the present invention is not limited thereto. That is, the oxide layer  120  and the metal catalyst layer  130  can be separated from each other by applying the predetermined force P after the graphene member  100  is taken out from water. In this case, in Operation S 3 , the separation may be performed only when a gap between the oxide layer  120  and the metal catalyst layer  130  is sufficiently formed. 
     Next, referring to  FIG. 5 , after the transfer member  150  is taken out from the water bath  160 , the metal catalyst layer  130  is removed by an etching process (operation S 5 ). 
     In one embodiment, the etching process is performed using an etching solution, for example, an acid, a hydrogen fluoride solution, a buffered oxide etch (BOE) solution, a FeCl 3  solution, or a Fe(No 3 ) 3  solution. 
     The etching process according one embodiment of to the present invention is a wet etching process using an etchant, but is not limited thereto. That is, the etching process may be, for example, a dry process or a process of removing the metal catalyst layer  130  using a sputtering method. 
     When Operation S 4  is finished, the oxide layer  120  is separated from the metal catalyst layer  130 , and thus the entire surface of the metal catalyst layer  130  in Operation S 5  is exposed to the outside. Accordingly, since the etchant acts uniformly on the entire surface of the metal catalyst layer  130 , the process of removing the metal catalyst layer  130  can be rapidly performed. 
     As a result, the graphene  140  transferred onto the transfer member  150  is obtained.  FIG. 6  is a cross-sectional view of the transfer member  150  onto which the graphene  140  is transferred. 
     The state shown in  FIG. 6 , that is, the state in which the graphene  140  is transferred onto the transfer member  150 , may not be the final one. That is, when necessary, the graphene  140  may be transferred to another transfer member from the initial transfer member  150   
     For example, referring to  FIG. 7 , the graphene  140  may be transferred to another transfer member  180  (for example, a final transfer member formed of PET material) from the transfer member  150 . 
     As described above, in the method of manufacturing graphene according to an exemplary embodiment, since the oxide layer  120  has a hydrophilic property and the metal catalyst layer  130  has a hydrophobic property, the separation of the oxide layer  120  from the metal catalyst layer  130  is performed using water. Therefore, the graphene  140  can be rapidly separated from the base member  110  and the oxide layer  120 . 
     Also, according to an exemplary embodiment, since the oxide layer  120  and the metal catalyst layer  130  are separated using water, the entire surface of the metal catalyst layer  130  can be rapidly exposed to the outside. Thus, the metal catalyst layer  130  can be rapidly removed from the graphene  140  in a subsequent process. Accordingly, the transfer process of the graphene  140  can be rapidly performed. 
     Graphene manufactured according to the methods of the exemplary embodiments can be used for various applications such as, but not limited to, transparent electrodes, conductive thin films, radiating or heating devices, flexible display devices, organic light emitting devices, or dye-sensitized solar cells, etc. 
     While exemplary embodiments been shown and described, it will be understood by one 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.