Abstract:
Disclosed is graphene. More particularly, disclosed are a method for manufacturing graphene to grow graphene with high quality and graphene manufactured by the same. The method includes preparing a thermal-expansion compensation substrate, forming a metal layer on the thermal-expansion compensation substrate, and forming graphene on the metal layer.

Description:
[0001]    Pursuant to 35 U.S.C. §119(a), this application claims the benefit of Korean Patent Application No. 10-2013-0067198, filed on Jun. 12, 2013, which is hereby incorporated by reference as if fully set forth herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to graphene and more particularly, to a method for manufacturing graphene to grow graphene with high quality and graphene manufactured by the same. 
         [0004]    2. Discussion of the Related Art 
         [0005]    Substances containing carbon atoms include fullerene, carbon nanotube, graphene and graphite. Of these, graphene is a single atom layer whose structure is a two-dimensional planar array of carbon atoms. 
         [0006]    In particular, graphene has considerably stable and superior electrical, mechanical and chemical properties as well as excellent conductivity and thus more rapidly carries electrons than silicone and enables application of higher electrical current than copper, which has been actively researched since it was demonstrated through experimentation based on discovery of a method of separating graphene from graphite in 2004. 
         [0007]    Such graphene attracts much attention as a base material for electronic circuits because it may be produced over large areas and has electrical, mechanical, chemical stability as well as excellent conductivity. 
         [0008]    In addition, electrical properties of graphene may change according to crystal direction of graphene with a predetermined thickness. For this reason, electrical properties are expressed in a direction selected by a user and devices can be thus easily designed. Accordingly, graphene is effectively used for carbon-based electronic or electromagnetic devices. 
         [0009]    As such, graphene may be formed on a metal layer which is a catalyst substrate. In this regard, graphene has a negative thermal expansion coefficient, while a metal has a positive thermal expansion coefficient. Accordingly, the difference in thermal expansion coefficient may cause formation of wrinkles in graphene during manufacture of the graphene. 
       SUMMARY OF THE INVENTION 
       [0010]    Accordingly, the present invention is directed to a method for manufacturing graphene to grow graphene with high quality and graphene manufactured by the same that substantially obviate one or more problems due to limitations and disadvantages of the related art. 
         [0011]    An object of the present invention is to provide a method for manufacturing graphene and graphene manufactured by the same to compensate phenomena which may be generated by difference in thermal expansion between a metal layer and graphene formed on the metal layer and thereby grow graphene with high quality. 
         [0012]    Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
         [0013]    To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a method for manufacturing graphene includes preparing a thermal-expansion compensation substrate, forming a metal layer on the thermal-expansion compensation substrate, and forming graphene on the metal layer. 
         [0014]    In accordance with another aspect of the present invention, a method for manufacturing graphene includes preparing a thermal-expansion compensation substrate containing a thermal expansion control substance, forming a metal layer on the thermal-expansion compensation substrate, and forming graphene on the metal layer, wherein the thermal expansion control substance has a lower thermal expansion coefficient than the metal layer or a negative thermal expansion coefficient. 
         [0015]    In accordance with another aspect of the present invention, a method for manufacturing graphene includes preparing a thermal-expansion compensation substrate comprising a support substrate and a thermal expansion control substance disposed on the support substrate, wherein the thermal expansion control substance has a thermal expansion coefficient of −50 ppm/K to 5 ppm/K, forming a metal layer on the thermal-expansion compensation substrate, and forming graphene on the metal layer. 
         [0016]    It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The accompanying drawings, which are included to provide further understanding of the disclosure and are incorporated in and constitute a part of this application, illustrate embodiments of the disclosure and together with the description serve to explain the principle of the disclosure. In the drawings: 
           [0018]      FIG. 1  is a flowchart illustrating an example of a method for manufacturing graphene; 
           [0019]      FIG. 2  is a sectional view illustrating an example of formation of a metal layer on a thermal-expansion compensation substrate; 
           [0020]      FIG. 3  is a sectional view illustrating another example of formation of a metal layer on a thermal-expansion compensation substrate; and 
           [0021]      FIG. 4  is a sectional view illustrating an example of formation of graphene on the metal layer. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Reference will now be made in detail to the specific embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
         [0023]    However, the present invention allows various modifications and variations and specific embodiments thereof are described in drawings and will be described in detail. The present invention should not be construed as limited to the embodiments set forth herein and includes modifications, variations, equivalents, and substitutions compliant with the spirit or scope of the present invention defined by the appended claims. 
         [0024]    It will be understood that when an element such as a layer, area or substrate is referred to as being “on” another element, it can be directly on the element, or one or more intervening elements may also be present therebetween. 
         [0025]    In addition, it will be understood that although terms such as “first” and “second” may be used herein to describe elements, components, areas, layers and/or regions, the elements, components, areas, layers and/or regions should not be limited by these terms. 
         [0026]      FIG. 1  is a flowchart illustrating a method for manufacturing graphene. Hereinafter, the method for manufacturing graphene will be described in detail with reference to  FIG. 1 . 
         [0027]    As shown in  FIG. 1 , first, a thermal-expansion compensation substrate is prepared (S 10 ). 
         [0028]    Next, as shown in  FIG. 2 , a metal layer  20  is formed on the thermal-expansion compensation substrate  10  (S 20 ). 
         [0029]    The thermal-expansion compensation substrate  10  may contain a substance having a low thermal expansion coefficient or a negative thermal expansion coefficient. 
         [0030]    For example, the thermal-expansion compensation substrate  10  may have a low thermal expansion coefficient or a negative thermal expansion coefficient of 5 ppm/K or less within a depth range from several nanometers (nm) to several tens of nanometers (nm) from the substrate. 
         [0031]    In addition, the thermal-expansion compensation substrate  10  may be prepared using a substance which does not produce a compound through reaction with the metal layer  20  at a high temperature. 
         [0032]    The thermal-expansion compensation substrate  10  may contain a thermal expansion control substance  11 . For example, as shown in  FIG. 2 , the thermal-expansion compensation substrate  10  may be manufactured using the thermal expansion control substance  11 . 
         [0033]    In addition, the thermal-expansion compensation substrate  10  may be manufactured by forming the thermal expansion control substance  11  on a support substrate  12 , as shown in  FIG. 3 . 
         [0034]    Accordingly, the thermal expansion control substance  11  may directly contact the metal layer  20 . 
         [0035]    The support substrate  12  may contain at least one of silicon (Si), silicon oxide (SiO 2 ), sapphire and quartz, but the present invention is not limited thereto. 
         [0036]    The thermal expansion control substance  11  may contain at least one of silicon carbide (SiC), graphite, graphene, carbon nanotube, diamond, M 2 B 3 O 12 , AX 2 O 8  and A 2 P 2 WO 12  wherein M represents Al, Sc, In, Y, Zr, Hf or a lanthanide metal, B represents W, Mo or P, X represents W or Mo, and A represents Zr or Hf. 
         [0037]    The substance such as M 2 B 3 O 12 , AX 2 O 8  or A 2 P 2 WO 12  has a negative thermal expansion coefficient. 
         [0038]    The thermal expansion coefficient of the thermal expansion control substance  11  may range from −50 ppm/K to 5 ppm/K. 
         [0039]    In addition, when the metal layer  20  is formed on the thermal-expansion compensation substrate  10  containing the thermal expansion control substance  11 , a combination layer including the thermal-expansion compensation substrate  10  and the metal layer  20  may have a thermal expansion coefficient of −20 ppm/K to 10 ppm/K. 
         [0040]    The metal layer  20  may be formed of a catalyst metal enabling formation of graphene and the catalyst metal may include a metal such as Ni, Co, Fe, Pt, Au, Al, Cr, Cu, Mg, Mn, Mo, Rh, Si, Ta, Ti, W, U, V or Zr. 
         [0041]    The catalyst metal generally has a positive thermal expansion coefficient. For example, a copper (Cu) has a thermal expansion coefficient of 16.4 ppm/K. 
         [0042]    The metal layer  20  may have a thickness of about several angstroms (Å) to about several hundreds of nanometers and preferably have a small thickness of several angstroms (Å) to several tens of nanometers. 
         [0043]    Next, as shown in  FIG. 4 , a graphene  30  is formed on the metal layer  20 . 
         [0044]    The formation of the graphene  30  may be carried out using chemical vapor deposition (CVD). 
         [0045]    In addition, chemical vapor deposition such as thermal-chemical vapor deposition (CVD), inductive coupled plasma chemical vapor deposition (ICP-CVD), plasma-enhanced chemical vapor deposition (PE-CVD) and microwave CVD may be used. Furthermore, various methods such as rapid thermal annealing (RTA), atomic layer deposition (ALD) and physical vapor deposition (PVD) may be used. 
         [0046]    Chemical vapor deposition is a method which grows the graphene  30  by loading the thermal-expansion compensation substrate  10  provided with the metal layer  20  in a chamber (not shown) and supplying a carbon source to the chamber under suitable growth conditions. 
         [0047]    Examples of carbon source include gas-type carbon sources such as methane (CH 4 ) and acetylene (C 2 H 2 ), solid-type carbon sources such as powders and polymers, and liquid-type carbon sources such as bubbling alcohol. 
         [0048]    In addition, various carbon sources such as ethane, ethylene, ethanol, acetylene, propane, butane, butadiene, pentane, pentene, cyclopentadiene, hexane, cyclohexane, benzene and toluene may be used. 
         [0049]    The formation of the graphene  30  may be carried out at a temperature of about 300 to about 1,500° C. The metal layer  20  and the graphene  30  may thermally expand or contract under this temperature condition. 
         [0050]    After formation of the graphene  30  is complete, the graphene  30  formed on the thermal-expansion compensation substrate  10  is cooled to room temperature. 
         [0051]    As described above, the metal layer  20  has a positive thermal expansion coefficient. For example, copper (Cu) has a thermal expansion coefficient of 16.4 ppm/K. 
         [0052]    On the other hand, the graphene  30  formed on the metal layer  20  has a thermal expansion coefficient of −8 ppm/K. A length of the graphene  30  is reduced (contracted), as heat amount increases. 
         [0053]    Accordingly, when the graphene  30  formed on the metal layer  20  at a temperature of 300 to 1,500° C. is cooled, a phenomenon caused by difference in thermal expansion in which the metal layer  20  contacts, but the graphene  30  expands may occur. 
         [0054]    The thermal-expansion compensation substrate  10  compensates the phenomenon which may be generated by difference in thermal expansion between the metal layer  20  and the graphene  30 . 
         [0055]    That is, the thermal expansion control substance  11  having similar thermal expansion properties to the graphene  30  compensates the phenomenon which may be generated by difference in thermal expansion between the metal layer  20  and the graphene  30 . 
         [0056]    Many wrinkles may be produced in the graphene  30  formed without compensating the difference in thermal expansion between the metal layer  20  and the graphene  30 . 
         [0057]    The wrinkles may have negative effects on the graphene  30 . That is, wrinkles produced during cooling of the formed graphene  30  may inhibit electrical properties of the graphene  30 . 
         [0058]    Accordingly, the metal layer  20  having a considerably small thickness of several angstroms (Å) to several tens of nanometers is disposed on the thermal-expansion compensation substrate  10  having a low or negative thermal expansion coefficient and the graphene  30  is formed on the metal layer  20 , thus enabling control of thermal expansion and contraction of the metal layer  20  during heating and cooling of the metal layer  20 . 
         [0059]    A direction of the control is similar to a direction of thermal expansion of the graphene  30 , thus preventing production of wrinkles in the graphene  30 . 
         [0060]    That is, the metal layer  20  does not greatly contract during cooling of the formed graphene  30 , thus enabling production of the graphene  30  which is considerably flat and has low roughness and high performance. 
         [0061]    As such, by compensating the difference in thermal expansion between the graphene  30  and the metal layer  20 , qualities of the graphene  30  can be greatly improved and in particular, electrical properties of the graphene  30  can be greatly improved. 
         [0062]    It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.