U.S. patent application number 13/164664 was filed with the patent office on 2011-10-06 for graphene sheet and method of preparing the same.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Jae-young CHOI, Hyeon-Jin SHIN, Seon-mi YOON.
Application Number | 20110244210 13/164664 |
Document ID | / |
Family ID | 40614121 |
Filed Date | 2011-10-06 |
United States Patent
Application |
20110244210 |
Kind Code |
A1 |
CHOI; Jae-young ; et
al. |
October 6, 2011 |
GRAPHENE SHEET AND METHOD OF PREPARING THE SAME
Abstract
An economical method of preparing a large-sized graphene sheet
having a desired thickness includes forming a film, the film
comprising a graphitizing catalyst; heat-treating a gaseous carbon
source in the presence of the graphitizing catalyst to form
graphene; and cooling the graphene to form a graphene sheet. A
graphene sheet prepared according to the disclosed method is also
described.
Inventors: |
CHOI; Jae-young; (Yongin-si,
KR) ; SHIN; Hyeon-Jin; (Yongin-si, KR) ; YOON;
Seon-mi; (Yongin-si, KR) |
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Suwon-si
KR
|
Family ID: |
40614121 |
Appl. No.: |
13/164664 |
Filed: |
June 20, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12169114 |
Jul 8, 2008 |
7988941 |
|
|
13164664 |
|
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|
Current U.S.
Class: |
428/220 ;
427/249.1; 428/333; 977/734 |
Current CPC
Class: |
C01B 32/186 20170801;
C01B 32/194 20170801; C01B 2204/02 20130101; B82Y 30/00 20130101;
B82Y 40/00 20130101; C23C 16/0281 20130101; C23C 16/01 20130101;
C01B 2204/32 20130101; C01B 2204/04 20130101; Y02E 60/32 20130101;
C23C 16/26 20130101; C23C 16/56 20130101; Y10T 428/261
20150115 |
Class at
Publication: |
428/220 ;
428/333; 427/249.1; 977/734 |
International
Class: |
B32B 5/00 20060101
B32B005/00; C23C 16/26 20060101 C23C016/26 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 29, 2007 |
KR |
10-2007-0108860 |
Mar 13, 2008 |
KR |
10-2008-0023457 |
Claims
1. A graphene sheet manufactured by a method comprising: forming a
film consisting of a graphitizing catalyst; where the width of the
film is one millimeter or greater; heat-treating a gaseous carbon
source in the presence of the graphitizing catalyst to form
graphene, while maintaining the shape of the film; and cooling the
graphene to form a graphene sheet, wherein a width and a length of
the graphene sheet are each about 1 millimeter or greater.
2. The graphene sheet of claim 1, wherein the graphene sheet
comprises about 1 graphene unit layer to about 60 graphene unit
layers.
3. The graphene sheet of claim 1, wherein the graphene sheet
comprises about 1 graphene unit layer to about 300 graphene unit
layers.
4. The graphene sheet of claim 1, wherein a width and a length of
the graphene sheet are each about 10 millimeter or greater.
5. The graphene sheet of claim 1, wherein a width and a length of
the graphene sheet are each about 1 millimeter to about 1,000
millimeters.
6. The graphene sheet of claim 1, wherein a peak ratio of a D band
intensity to a G band intensity of the graphene sheet is equal to
or less than about 0.2 when determined from a Raman spectrum of the
graphene sheet.
7. The graphene sheet of claim 11, wherein a D band is not observed
in a Raman spectrum of the graphene sheet.
8. A graphene substrate comprising: a substrate; and a graphene
sheet formed on the substrate, wherein the graphene sheet is
derived from a polycyclic aromatic molecule, wherein a plurality of
carbon atoms are covalently bound to each other, wherein the
graphene sheet comprises about 1 layer to about 300 layers, and
wherein each of a width and a length of the graphene sheet is 1 mm
or greater.
9. The graphene substrate of claim 8, further comprising a
graphitizing catalyst layer interposed between and in intimate
contact with the substrate and the graphene sheet.
10. The graphene substrate of claim 9, wherein the graphitizing
catalyst layer comprises a metal catalyst in the form of a thin
film or a thick film.
11. The graphene substrate of claim 9, further comprising a
blocking layer interposed between the substrate and the
graphitizing catalyst layer.
12. The graphene substrate of claim 9, wherein the blocking layer
comprises a compound selected from the group consisting of
SiO.sub.x, TiN, Al.sub.2O.sub.3, TiO.sub.2, Si.sub.3N, and a
combination comprising at least one of the foregoing compounds.
13. The graphene substrate of claim 8, wherein the substrate
comprises silicon.
Description
[0001] This application is a divisional application of U.S.
application Ser. No. 12/169,114, filed on Jul. 8, 2008, which
claims priority to Korean Patent Application No. 10-2007-0108860,
filed on Oct. 29, 2007 and Korean Patent Application No.
10-2008-0023457, filed on Mar. 13, 2008, and all the benefits
accruing therefrom under 35 U.S.C. .sctn.119, the contents of which
in their entirety are herein incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This disclosure relates to a graphene sheet and a method of
preparing the same.
[0004] 2. Description of the Related Art
[0005] Generally, graphite is a stack of two-dimensional graphene
sheets formed from a planar array of carbon atoms bonded into
hexagonal structures. Recently, testing of graphene sheets has
revealed beneficial properties of single or multiple-layered
graphene sheets.
[0006] One beneficial property of graphene is that electrons flow
in an entirely unhindered fashion in a graphene sheet, which is to
say that the electrons flow at the velocity of light in a vacuum.
In addition, graphene sheets exhibit an unusual half-integer
quantum Hall effect for both electrons and holes. The electron
mobility of conventional graphene sheets is about 20,000 to 50,000
cm.sup.2/Vs.
[0007] In some applications carbon nanotubes can be used as a
conductor. However carbon nanotubes are expensive due to low yields
during synthesis and purification processes. Also single wall
carbon nanotubes exhibit different metallic and semiconducting
characteristics according to their chirality and diameter.
Furthermore, single wall carbon nanotubes having identical
semiconducting characteristics have different band gap energies
depending on their chirality and diameter. Thus, single wall carbon
nanotubes are preferably separated from each other in order to
obtain the desired semiconducting or metallic properties. However,
separating single wall carbon nanotubes is problematic.
[0008] On the other hand, it is advantageous to use graphene sheets
because, in a device, graphene sheets can be engineered to exhibit
the desired electrical characteristics by arranging the graphene
sheets so their crystallographic orientation is in a selected
direction since the electrical characteristics of a graphene sheet
depend upon crystallographic orientation. It is envisaged that the
characteristics of graphene sheets can be applied to future
carbonaceous electrical devices or carbonaceous electromagnetic
devices.
[0009] However, although graphene sheets have these advantageous
characteristics, a method of economically and reproducibly
preparing a large-sized graphene sheet has not yet been developed.
Graphene sheets can be prepared using a micromechanical method or
by SiC thermal decomposition. According to the micromechanical
method, a graphene sheet can be separated from graphite attached to
the surface of Scotch.TM. tape by attaching the tape to a graphite
sample and detaching the tape. In this case, the separated graphene
sheet does not include a uniform number of layers and the ripped
portions do not have a uniform shape. Furthermore, a large-sized
graphene sheet cannot be prepared using the micromechanical method.
Meanwhile, in SiC thermal decomposition, a SiC single crystal is
heated to remove Si by decomposition of the SiC on the surface
thereof, the residual carbon C then forming a graphene sheet.
However, the SiC single crystal material used as a starting
material in SiC thermal decomposition is very expensive, and
formation of a large-sized graphene sheet is problematic.
BRIEF SUMMARY OF THE INVENTION
[0010] Disclosed is an economical method of preparing a large-sized
graphene sheet having a desired thickness.
[0011] Also disclosed is a graphene sheet prepared using the
disclosed method.
[0012] Disclosed is a membrane, a hydrogen storage medium, an
optical fiber and an electrical device using the graphene
sheet.
[0013] Disclosed a graphene substrate including the graphene
sheet.
[0014] In an embodiment, there is provided a method of preparing a
graphene sheet, the method comprising forming a film, the film
comprising a graphitizing catalyst; heat-treating a gaseous carbon
source in the presence of the graphitizing catalyst to form
graphene; and cooling the graphene to form a graphene sheet.
[0015] The gaseous carbon source may be any compound containing
carbon, specifically a compound containing 6 or fewer carbon atoms,
more specifically a compound containing 4 or fewer carbon atoms,
and most specifically a compound containing 2 or fewer carbon
atoms. Exemplary gaseous carbon sources include at least one
selected from the group consisting of carbon monoxide, ethane,
ethylene, ethanol, acetylene, propane, propylene, butane,
butadiene, pentane, pentene, cyclopentadiene, hexane, cyclohexane,
benzene and toluene.
[0016] The film may be a thin film or a thick film.
[0017] The thickness of the thin film may be between about 1 nm to
about 1000 nm.
[0018] The thickness of the thick film may be between about 0.01 mm
to about 5 mm.
[0019] Hydrogen may also be supplied with the gaseous carbon
source. Hydrogen can be used to control gaseous reactions by
cleaning the surface of a metal catalyst. The amount of hydrogen
may be about 5% to about 40% by volume, specifically about 10% to
about 30% by volume, and more specifically about 15% about 25% by
volume based on the total volume of a container.
[0020] The heat-treatment may be performed at a temperature of
about 300.degree. C. to about 2000.degree. C.
[0021] The thickness of the graphene may be controlled by
regulating the heat-treatment time.
[0022] The graphitizing catalyst may include at least one element
selected from the group consisting of Ni, Co, Fe, Pt Au, Al, Cr,
Cu, Mg, Mn, Mo, Rh, Si, Ta, Ti, W, U, V, and Zr.
[0023] The cooling may be performed at a rate of about 0.1.degree.
C./min to about 10.degree. C./min.
[0024] The method may further include separating the formed
graphene sheet from the graphitizing catalyst by removing the
graphitizing catalyst using an acid treatment after cooling the
heat-treated resultant.
[0025] Also disclosed is a graphene sheet prepared according to the
disclosed method.
[0026] A peak ratio of the Raman D band/G band of the graphene
sheet can be equal to or less than about 0.2, and preferably about
0 (zero) when a Raman spectrum of the graphene sheet is
measured.
[0027] Also disclosed is a graphene sheet derived from a polycyclic
aromatic molecule, wherein a plurality of carbon atoms are
covalently bound to each other, wherein the graphene sheet
comprises about 1 graphene unit layer to about 300 graphene unit
layers, and wherein each of the width and length of the graphene
sheet is about 1 mm or greater.
[0028] The graphene sheet may have about 1 graphene unit layer to
about 60 graphene unit layers, and specifically about 1 graphene
unit layer to about 15 graphene unit layers.
[0029] Each of the width and the length of the graphene sheet may
be about 1 mm to about 1,000 mm.
[0030] In exemplary embodiments, each of the width and length of
the graphene sheet may be about 10 mm or greater.
[0031] Also disclosed is a graphene substrate; and a graphene sheet
formed on the substrate.
[0032] The graphene substrate may further include a graphitizing
catalyst layer interposed between the substrate and the graphene
sheet.
[0033] The graphene substrate may further include a blocking layer
interposed between the substrate and the graphitizing catalyst.
[0034] The blocking layer may be formed of SiO.sub.x, TiN,
Al.sub.2O.sub.3, TiO.sub.2 or Si.sub.3N.
[0035] The substrate may be a silicon substrate.
[0036] The graphitizing catalyst may include a metal catalyst in
the form of a thin film or a thick film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] The above and other aspects, features and advantages will
become more apparent by describing in further detail exemplary
embodiments thereof with reference to the attached drawings in
which:
[0038] FIG. 1 schematically illustrates a method of preparing a
graphene sheet according to an embodiment;
[0039] FIG. 2 is a photographic image of a graphene sheet prepared
according to Example 1;
[0040] FIG. 3 is a graph illustrating Raman spectra of graphene
sheets prepared according to Examples 1 to 3;
[0041] FIG. 4 is a scanning electron microscope ("SEM") image of a
graphene sheet prepared according to Example 1;
[0042] FIG. 5 is a SEM image of a graphene sheet prepared according
to Example 2;
[0043] FIG. 6 is a SEM image of a graphene sheet prepared according
to Example 6; and
[0044] FIG. 7 is a graph illustrating a Raman spectrum of a
graphene sheet prepared according to Example 6.
DETAILED DESCRIPTION OF THE INVENTION
[0045] Hereinafter, embodiments are described more fully with
reference to the accompanying drawings, in which exemplary
embodiments are shown.
[0046] Disclosed is an economical method of preparing a large-sized
graphene sheet having a desired thickness. The graphene sheet
prepared using this method can be applied to various fields in
various applications without limitation on the shape of a substrate
even if the graphene sheet has a complicated or topographically
modulated structure.
[0047] The term "graphene sheet" as used herein indicates graphene
in the form of a film derived from polycyclic aromatic molecules in
which a plurality of carbon atoms are covalently bound to each
other. While not wanting to be bound by theory, the covalently
bound carbon atoms form 6-membered rings as a repeating unit, but
can also form 5-membered rings and/or 7-membered rings.
Accordingly, in the graphene sheet the covalently bound carbon
atoms (usually, sp.sup.2 bonded carbon) are thought to form a
single layer. The graphene sheet can have various structures and
the structure can vary according to the amount of the 5-membered
rings and/or the 7-membered rings. The graphene sheet can comprise
a single layer of graphene, or the graphene sheet can comprise a
plurality of layers of graphene, up to about 300 layers. Generally,
the carbon atoms at the edge of the graphene are saturated with
hydrogen atoms.
[0048] The graphene sheet may be formed according to the method
illustrated in FIG. 1. In the disclosed method a graphene sheet 140
can be formed by forming a film, the film comprising a graphitizing
catalyst 100, forming graphene 130 by heat-treating a gaseous
carbon source 120 in the presence of the graphitizing catalyst 100
while supplying the gaseous carbon source 120 thereto, and cooling
the graphene 130 to thereby grow a graphene sheet 140, as is
illustrated in FIG. 1. That is, when a gaseous carbon source 120 is
heat-treated in the presence of a graphitizing catalyst 100 at a
selected temperature for a selected period of time while the
gaseous carbon source 120 is supplied to a chamber containing the
graphitizing catalyst 100 at a selected pressure, carbon atoms in
the gaseous carbon source 120 are bound to each other in a planar
hexagonal structure to form graphene. When the graphene 130 is
cooled at a selected rate, a graphene sheet 140 having a uniform
arrangement can be obtained.
[0049] Any substance that comprises carbon and is a gas at about
300.degree. C. or higher can be used as the gaseous carbon source
in the formation of the graphene sheet without limitation. The
gaseous carbon source can be any compound containing carbon,
preferably a compound containing 7 or fewer carbon atoms, more
specifically a compound containing 4 or fewer carbon atoms, and
most specifically a compound containing 2 or fewer carbon atoms.
The gaseous carbon source can comprise a compound having about 1 to
about 6 carbon atoms. The gaseous carbon source can comprise a
polycyclic aromatic molecule. Exemplary gaseous carbon sources
include carbon monoxide, ethane, ethylene, ethanol, acetylene,
propane, propylene, butane, butadiene, pentane, pentene,
cyclopentadiene, hexane, cyclohexane, benzene, toluene, or the
like, or a combination comprising at least one of the foregoing
compounds. The gaseous carbon source can thus be one or a
combination of the foregoing compounds.
[0050] The carbon source can be supplied to a chamber including a
graphitizing catalyst at a selected pressure, and the chamber can
include only the carbon source, or can further include an inert gas
such as helium and argon. The pressure of the carbon source in the
chamber can be about 10.sup.-6 to about 10.sup.4 torr, specifically
10.sup.-3 to about 760 torr.
[0051] In addition, hydrogen can be supplied with the gaseous
carbon source. Thus the carbon source can also include hydrogen.
Hydrogen can be used to control gaseous reactions by cleaning the
surface of a metal catalyst. The amount of hydrogen can be about 5%
to about 40% by volume, specifically about 10% to about 30% by
volume, and more specifically about 15% about 25% by volume, based
on the total volume of the chamber.
[0052] When the gaseous carbon source is supplied to a chamber, and
the chamber and graphitizing catalyst heated to a selected
temperature, graphene is formed on the surface of the graphitizing
catalyst. The heat-treatment temperature is an important factor in
the formation of graphene and can be a temperature between about
300.degree. C. to about 2000.degree. C., specifically about
500.degree. C. to about 1500.degree. C., more specifically about
700.degree. C. to about 1300.degree. C. When the heat-treatment is
performed at a temperature lower than about 300.degree. C.,
graphene is not formed at an acceptable rate. On the other hand,
when the heat-treatment is performed at a temperature higher than
2000.degree. C., graphene may not form in the form of a film but in
the form of particles or fibers.
[0053] The graphitizing catalyst can be in the form of a film. If
the film comprising the graphitizing catalyst has a thickness
greater than about 0.01 mm, the heat-treatment can be performed at
a temperature equal to or greater than 700.degree. C.
[0054] The film comprising the graphitizing catalyst disclosed
herein can be a thin film or a thick film. If a thin film is used,
it can be formed on a substrate. However, the contact strength
between the thin film and the substrate can become weak, or a part
of the thin film can melt at a temperature higher than about
700.degree. C. Thus, when the heat-treatment is performed at
700.degree. C. or higher, the graphitizing catalyst can be formed
as a thick film without a substrate. If a thin film is desired, the
thickness of the film can be between about 1 nm to about 5,000 nm,
specifically between about 1 nm to about 1,000 nm, more
specifically about 10 nm to about 100 nm. If a thick film is
desired, the thickness of the film can be about 0.01 mm to about 5
mm, specifically about 0.1 mm to about 1 mm.
[0055] The degree of graphene formation can be controlled by
regulating the temperature and time of the heat-treatment. That is,
other parameters being equal, the longer the heat-treatment time,
the greater the amount of graphene formed, and thus the graphene
sheet becomes thicker. On the other hand, the shorter the
heat-treatment time, the less the thickness of the graphene sheet.
Accordingly, the types of the carbon source, the pressure used to
supply the carbon source, the types of the graphitizing catalyst,
the size of the chamber, and the heat-treatment time are key
factors in obtaining a desired thickness of the graphene sheet. The
heat-treatment can be performed for about 0.001 hour to about 1000
hours, about 0.01 hour to about 100 hours, or about 0.1 hour to
about 10 hours. When the heat-treatment is performed for less than
about 0.001 hour, graphene may not be sufficiently obtained. On the
other hand, when the heat-treatment is performed for longer than
about 1000 hours, too much graphene is formed and graphitization
can occur.
[0056] The heat-treatment may be performed by induction heating,
radiant heating, laser, infrared radiation ("IR"), microwaves,
plasma, ultraviolet ("UV") radiation, surface plasmon heating, or
the like, or a combination comprising at least one of the foregoing
heating methods. The heat source can be disposed on the chamber to
increase the temperature in the chamber to a selected level.
[0057] After the heat-treatment, the graphene is cooled. The
cooling is performed to uniformly grow and arrange the carbon atoms
comprising the graphene. Since rapid cooling can cause cracks in
the graphene sheet, the heat-treated graphene can be gradually
cooled. For example, the heat-treated graphene can be cooled at a
rate of about 0.1.degree. C./min to about 10.degree. C./min, about
0.5.degree. C./min to about 5.degree. C./min, or about 1.degree.
C./min to about 3.degree. C./min, or naturally cooled by ambient
convection. In a natural cooling process, the heat source can be
removed so that it is not disposed on the chamber. In this regard,
a sufficient cooling rate can be obtained by removing the heat
source. The graphene sheet obtained after the cooling may have a
thickness of 1 layer, or a thickness of about 1 layer to about 300
layers, specifically about 1 layer to about 60 layers, and more
specifically about 1 layer to about 15 layers. A graphene sheet
having over 300 layers is regarded as graphite, which is distinct
from graphene.
[0058] The heat-treatment and cooling method may be performed as a
single cycle, but a dense graphene sheet having many layers may be
formed by repeating the method several times.
[0059] The film comprising the graphitizing catalyst can be
disposed on a substrate. In particular, if the film comprising the
graphitizing catalyst is a thin film, a substrate can be used for
fabrication convenience. Thus if a substrate is used, the
graphitizing catalyst layer can be interposed between and in
intimate contact with the substrate and the graphene sheet.
[0060] The substrate may be an inorganic substrate such as a Si
substrate, a glass substrate, a GaN substrate, a silica substrate,
or the like, or a combination comprising at least one of the
foregoing inorganic substrates; or the substrate can be a metal
substrate comprising Ni, Cu, W, or the like, or a combination
comprising at least one of the foregoing metals.
[0061] In the case of a silica substrate, the surface of the silica
substrate can be coated with a blocking layer in order to prevent
undesirable reactions between the substrate and the graphitizing
catalyst. The blocking layer can be interposed between the
substrate and the graphitizing catalyst to inhibit reduction in the
efficiency or reduction in the rate of graphene formation that can
be caused by reactions between the graphitizing catalyst and the
substrate. The blocking layer can comprise a compound such as
SiO.sub.x, TiN, Al.sub.2O.sub.3, TiO.sub.2, Si.sub.3N, or the like,
or a combination comprising at least one of the foregoing
compounds, and the blocking layer can be disposed on the substrate
by a method comprising sputtering, vapor deposition, or the like.
The blocking layer can have a selected thickness between about 0.1
nm to about 1000 .mu.m, about 1 .mu.m to 500 .mu.m, or about 10
.mu.m to about 100 .mu.m. When the thickness of the blocking layer
is less than about 0.1 nm, the desired effect of the blocking layer
may not be obtained. On the other hand, when the thickness of the
blocking layer is greater than about 1000 .mu.m, costs can be
increased.
[0062] In the disclosed method, the graphitizing catalyst contacts
the carbon source and assists carbon elements supplied from the
carbon source to be bound to each other to form a planar hexagonal
structure. Any catalyst used to synthesize graphite, induce
carbonization or prepare carbon nanotubes can be used as the
graphitizing catalyst. Exemplary graphitizing catalysts include the
metals Ni, Co, Fe, Pt, Au, Al, Cr, Cu, Mg, Mn, Mo, Rh, Si, Ta, Ti,
W, U, V, Zr, or the like, or a combination comprising at least one
of the foregoing metals. Thus the graphitizing catalyst can
comprise a metal selected from the group consisting of Ni, Co, Fe,
Pt Au, Al, Cr, Cu, Mg, Mn, Mo, Rh, Si, Ta, Ti, W, U, V, Zr, and the
like, and a combination comprising at least one of the foregoing
metals. The graphitizing catalyst can be in the form of a plate and
can comprise one or a combination of the foregoing metals, or the
graphitizing catalyst can be disposed on a substrate by a
deposition method such as sputtering, or the like. A thin film or a
thick film can comprise the graphitizing catalyst, and the
graphitizing catalyst can comprise one or a combination of the
foregoing metals.
[0063] Since the graphene sheet can be prepared by contacting a
graphitizing catalyst with a carbon source, heat-treating, and
cooling the graphene to form a graphene sheet, the process is
simple and economical. In particular, a large-sized graphene sheet
with each of the width and the length thereof being about 1 mm or
greater, specifically about 10 mm or more, and more specifically
about 10 mm to about 1,000 mm, can be prepared. For example, a
large-sized graphene sheet can be prepared by controlling the size
of the substrate on which the graphitizing catalyst is formed. In
addition, since the carbon source is supplied as a gas, the shape
or configuration of the substrate and the graphitizing catalyst are
not limited. Accordingly, a three-dimensional, contoured, or
topographically modulated substrate can be used, and the film
comprising the graphitizing catalyst can have various structures
accordingly.
[0064] The graphene sheet can be identified using a Raman spectrum.
That is, since pure graphene has a G' peak in the vicinity of about
1594 cm.sup.-1, the formation of graphene can be identified by the
presence of an absorption at this wavenumber.
[0065] Surprisingly, it has been observed the disclosed graphene
sheet has a uniform structure without defects. While not wanting to
be bound by theory, the uniformity is thought to be because the
graphene sheet is prepared by a method comprising high-temperature
heat-treatment using a pure gaseous carbon source. A D band
intensity of a Raman spectrum of the graphene sheet can indicate
the presence of defects formed in the graphene. A strong D band
peak can indicate a plurality of defects in the graphene, and a
weak D band peak or no D band peak can indicate few defects.
[0066] A peak ratio can be defined as a ratio of the peak D band
intensity to the peak G band intensity. A peak ratio of a graphene
sheet prepared by a stack formation method using a graphitizing
catalyst comprised of a metal can be equal to or less than about
0.2, specifically equal to or less than about 0.01, more
specifically equal to or less than about 0.001, and can be "0"
(zero). The peak ratio "0" indicates that there are few if any
defects in the graphene.
[0067] The graphene sheet can thus be formed on a substrate and/or
on a film comprising the graphitizing catalyst. The graphene sheet
can be used with the graphitizing catalyst, or the graphene sheet
can be separated from the graphitizing catalyst by treating the
graphene sheet with an acid. The acid treatment can be performed
after cooling the graphene sheet.
[0068] If desired, the graphene sheet can be separated from the
substrate.
[0069] The separated graphene sheet can be processed in a variety
of ways according to its desired use. That is, the graphene sheet
can be cut into a selected shape, or the graphene sheet can be
wound to form a tube. The processed graphene sheet can also be
combined with a various articles to be applied in various ways.
[0070] The graphene sheet can be applied in various fields and
applications. The graphene sheet can be efficiently used as a
transparent electrode since it has excellent conductivity and high
uniformity. An electrode that is used on a solar cell substrate, or
the like, is desirably transparent to allow light to penetrate
therethrough. A transparent electrode formed of the graphene sheet
has excellent conductivity and flexibility due to the flexibility
of the graphene sheet. A flexible solar cell can be prepared by
using a flexible plastic as a substrate and the graphene sheet as a
transparent electrode. In addition, where the graphene sheet is
used in the form of a conductive thin film in a display device,
desired conductivity can be obtained using only a small amount of
the graphene sheet and light penetration can thus be improved.
[0071] In addition, the graphene sheet formed in the form of a tube
can be used as an optical fiber, a hydrogen storage medium or a
membrane that selectively allows hydrogen to penetrate.
[0072] The disclosure will now be described in greater detail with
reference to the following examples. The following examples are for
illustrative purposes only and are not intended to limit the scope
of the claims.
Example 1
[0073] A graphitizing catalyst film was formed by depositing Ni on
a 1.2 cm.times.1.5 cm silicon substrate on which 100 nm of
SiO.sub.2 was coated by sputtering to form a Ni thin film with a
thickness of 100 nm. The silicon substrate on which the SiO.sub.2
and Ni thin film were formed was disposed in a chamber, and the
substrate heat-treated at 400.degree. C. for 20 minutes using a
halogen lamp as a heat source while acetylene gas was added to the
chamber at a constant rate of 200 sccm to form graphene on the
graphitizing catalyst.
[0074] Then, a 7 layered graphene sheet having a size of 1.2
cm.times.1.5 cm was formed by removing the heat source and
naturally cooling the interior of the chamber to grow graphene in a
uniform arrangement.
[0075] Then, the substrate including the graphene sheet was
immersed in 0.1 M HCl for 24 hours to remove the Ni thin film. The
graphene sheet separated from the substrate during the immersion.
FIG. 2 is a photographic image of the graphene sheet prepared
according to Example 1.
[0076] FIG. 3 is a graph illustrating a Raman spectrum of the
graphene sheet. Referring to FIG. 3, the formation of graphene can
be identified by the G' peak shown at 1594 cm.sup.-6.
[0077] In addition, FIG. 4 is a scanning electron microscope
("SEM") image of the graphene sheet formed in Example 1. Referring
to FIG. 4, it can be seen that a uniform graphene sheet was
formed.
Example 2
[0078] A 16 layered graphene sheet having a size of 1.2
cm.times.1.5 cm was prepared in the same manner as in Example 1,
except that the heat-treatment was performed at 500.degree. C.
instead of 400.degree. C.
[0079] Then, the substrate including the graphene sheet was
immersed in 0.1 M HCl for 24 hours to remove the Ni thin film. The
graphene sheet separated from the substrate during the
immersion.
[0080] FIG. 3 is a graph illustrating a Raman spectrum of the
graphene sheet. Referring to FIG. 3, the formation of graphene can
be identified by the G' peak shown at 1594 cm.sup.-1.
[0081] FIG. 5 is a SEM image of the graphene sheet formed in
Example 2. Referring to FIG. 5, it can be seen that a uniform
graphene sheet was formed because features are not observed in the
SEM image.
Example 3
[0082] A 32 layered graphene sheet having a size of 1.2
cm.times.1.5 cm was prepared in the same manner as in Example 1,
except that the heat-treatment was performed at 600.degree. C.
instead of 400.degree. C.
[0083] Then, the substrate including the graphene sheet was
immersed in 0.1 M HCl for 24 hours to remove the Ni thin film. The
graphene sheet separated during the immersion.
[0084] FIG. 3 is a graph illustrating a Raman spectrum of the
graphene sheet. Referring to FIG. 3, the formation of graphene can
be identified by the G' peak shown at 1594 cm.sup.-1.
Example 4
[0085] A 22 layered graphene sheet having a size of 1.2
cm.times.1.5 cm was prepared in the same manner as in Example 1,
except that the heat-treatment was performed for 1 hour instead of
20 minutes.
[0086] Then, the substrate including the graphene sheet was
immersed in 0.1 M HCl for 24 hours to remove the Ni thin film. The
graphene sheet separated during the immersion.
Example 5
[0087] An 11 layered graphene sheet having a size of 1.2
cm.times.1.5 cm was prepared in the same manner as in Example 1,
except that methane was used as a carbon source instead of
acetylene.
[0088] Then, the substrate including the graphene sheet was
immersed in 0.1 M HCl for 24 hours to remove the Ni thin film. The
graphene sheet separated during the immersion.
Example 6
[0089] A Ni foil having a size of 1.2 cm.times.1.5 cm and a
thickness of 0.5 mm was prepared. The Ni foil was deposited in a
chamber, and heat-treated at 1000.degree. C. for 5 minutes using a
halogen lamp as a heat source while acetylene gas was added to the
chamber at a constant rate of 200 sccm to form graphene on the
graphitizing catalyst.
[0090] Then, a 10 layered graphene sheet having a size of 1.2
cm.times.1.5 cm was formed by removing the heat source and
naturally cooling the interior of the chamber to grow graphene in a
uniform arrangement.
[0091] Then, the substrate including the graphene sheet was
immersed in 0.1 M HCl for 24 hours to remove the Ni foil. The
graphene sheet separated during the immersion. FIG. 6 is a SEM
image of the separated graphene sheet and a uniform structure was
identified by the absence of features.
[0092] FIG. 7 is a graph illustrating a Raman spectrum of the
graphene sheet. Referring to FIG. 7, the formation of graphene can
be identified by the G' peak shown at 1594 cm.sup.-1 and it can
also be identified that a uniform graphene without defects was
formed a D band was not observed.
[0093] Disclosed is an economical method of preparing a large-sized
graphene sheet and efficiently controlling the thickness of the
graphene sheet. One of ordinary skill in the art will understand
that the graphene sheet can be efficiently applied to a transparent
electrode, a hydrogen storage medium, an optical fiber, an
electrical device, or the like, since a desired thickness of the
graphene sheet can be obtained.
[0094] The terms "the", "a" and "an" do not denote a limitation of
quantity, but rather denote the presence of at least one of the
referenced item. The suffix "(s)" as used herein is intended to
include both the singular and the plural of the term that it
modifies, thereby including at least one of that term (e.g., the
colorant(s) includes at least one colorants).
[0095] Unless defined otherwise, technical and scientific terms
used herein have the same meaning as is commonly understood by one
of skill in the art.
[0096] As used herein, approximating language can be applied to
modify any quantitative representation that can vary without
resulting in a change in the basic function to which it is related.
Accordingly, a value modified by a term or terms, such as "about"
and "substantially," can not to be limited to the precise value
specified, in some cases. In at least some instances, the
approximating language can correspond to the precision of an
instrument for measuring the value. Thus the modifier "about" used
in connection with a quantity is inclusive of the stated value and
has the meaning dictated by the context (e.g., includes the degree
of error associated with measurement of the particular
quantity).
[0097] All ranges disclosed herein are inclusive of the endpoints
and are independently combinable. The endpoints of all ranges
directed to the same component or property are inclusive and
independently combinable (e.g., ranges of "less than or equal to
about 25 wt %, or, more specifically, about 5 wt % to about 20 wt
%," is inclusive of the endpoints and all intermediate values of
the ranges of "about 5 wt % to about 25 wt %," etc.).
[0098] "Optional" or "optionally" means that the subsequently
described event or circumstance can or can not occur, and that the
description includes instances where the event occurs and instances
where it does not. As used herein, "substrate" or "substrates" can
be used interchangeably with "surface" or "surfaces."
[0099] While the disclosed embodiments have been particularly shown
and described with reference to exemplary embodiments thereof, 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 disclosure as defined by
the following claims.
* * * * *