U.S. patent application number 12/248096 was filed with the patent office on 2010-09-16 for method for electrostatic deposition of graphene on a substrate.
This patent application is currently assigned to UNIVERSITY OF LOUISVILLE RESEARCH FOUNDATION, INC.. Invention is credited to Robert W. Cohn, Romaneh Jalilian, P. J. Ouseph, Anton N. Sidorov, Gamini Sumanasekera, Mehdi M. Yazdanpanah.
Application Number | 20100233382 12/248096 |
Document ID | / |
Family ID | 42669609 |
Filed Date | 2010-09-16 |
United States Patent
Application |
20100233382 |
Kind Code |
A1 |
Sumanasekera; Gamini ; et
al. |
September 16, 2010 |
METHOD FOR ELECTROSTATIC DEPOSITION OF GRAPHENE ON A SUBSTRATE
Abstract
A method for electrostatic deposition of graphene on a substrate
comprises the steps of securing a graphite sample to a first
electrode; electrically connecting the first electrode to a
positive terminal of a power source; electrically connecting a
second electrode to a ground terminal of the power source; placing
the substrate over the second electrode; and using the power source
to apply a voltage, such that graphene is removed from the graphite
sample and deposited on the substrate.
Inventors: |
Sumanasekera; Gamini;
(Louisville, KY) ; Sidorov; Anton N.; (Louisville,
KY) ; Ouseph; P. J.; (Louisville, KY) ;
Yazdanpanah; Mehdi M.; (Louisville, KY) ; Cohn;
Robert W.; (Louisville, KY) ; Jalilian; Romaneh;
(Louisville, KY) |
Correspondence
Address: |
STITES & HARBISON, PLLC
400 W MARKET ST, SUITE 1800
LOUISVILLE
KY
40202-3352
US
|
Assignee: |
UNIVERSITY OF LOUISVILLE RESEARCH
FOUNDATION, INC.
Louisville
KY
|
Family ID: |
42669609 |
Appl. No.: |
12/248096 |
Filed: |
October 9, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60978516 |
Oct 9, 2007 |
|
|
|
Current U.S.
Class: |
427/458 |
Current CPC
Class: |
H01L 21/02425 20130101;
H01L 21/02488 20130101; C23C 14/22 20130101; H01L 21/02527
20130101; H01L 21/02381 20130101; C23C 14/0605 20130101; H01L
21/02631 20130101 |
Class at
Publication: |
427/458 |
International
Class: |
B05D 1/00 20060101
B05D001/00 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] This invention was made with support from NASA Cooperative
Agreement NCC5-571 and Grant No. W9113M-04-C-0024 awarded by the
U.S. Army Space and Missile Defense Command. The government has
certain rights in the invention.
Claims
1. A method for electrostatic deposition of graphene on a
substrate, comprising the steps of: securing a graphite sample to a
first electrode; electrically connecting the first electrode to a
positive terminal of a power source; electrically connecting a
second electrode to a ground terminal of the power source; placing
the substrate over the second electrode; and using the power source
to apply a voltage, such that graphene is removed from the graphite
sample and deposited on the substrate.
2. The method as recited in claim 1, and further comprising the
step of interposing an insulator between the second electrode and
the substrate.
3. The method as recited in claim 2, in which the insulator is a
mica sheet.
4. The method as recited in claim 1, in which the graphite sample
is highly oriented pyrolytic graphite (HOPG).
5. The method as recited in claim 4, and further comprising the
step of cleaving the sample of highly oriented pyrolytic graphite
(HOPG) to provide an appropriate surface for securing the first
electrode to the sample.
6. The method as recited in claim 1, in which the graphite sample
is secured to the first electrode using an epoxy.
7. The method as recited in claim 1, in which the substrate
includes a trench, with graphene being deposited on the substrate
and over the trench, such that a portion of the graphene is
suspended over the substrate.
8. A method for electrostatic deposition of graphene on a
substrate, comprising the steps of: securing a graphite sample to a
first electrode; electrically connecting the first electrode to a
positive terminal of a power source; electrically connecting a
second electrode to a ground terminal of the power source; placing
an insulator on the second electrode; placing the substrate over
the insulator; and using the power source to apply a voltage, such
that graphene is removed from the graphite sample and deposited on
the substrate.
9. The method as recited in claim 8, in which the substrate is a
conducting material.
10. The method as recited in claim 8, in which the graphite sample
is highly oriented pyrolytic graphite (HOPG).
11. The method as recited in claim 10, and further comprising the
step of cleaving the sample of highly oriented pyrolytic graphite
(HOPG) to provide an appropriate surface for securing the first
electrode to the sample.
12. The method as recited in claim 8, in which the substrate
includes a trench, with graphene being deposited on the substrate
and over the trench, such that a portion of the graphene is
suspended over the substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional
Patent Application Ser. No. 60/978,516 filed on Oct. 9, 2007, the
entire disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0003] Graphene is a single planar sheet of sp.sup.2 bonded carbon
atoms. This two-dimensional structure provides the building block
for the formation of three-dimensional graphite, one-dimensional
nanotubes, and fullerenes (or "bucky balls.") Graphene is predicted
to have remarkable physical properties, including large thermal
conductivity as compared to the in-plane value of graphite,
superior mechanical properties, and excellent electronic transport
properties. Furthermore, the charge carriers in graphene are
predicted to have zero effective mass, and the transport properties
are expected to be governed by the relativistic Dirac equation
rather than the Schrodinger equation.
[0004] Mechanical cleavage has been widely used to separate a few
layers of graphene from highly oriented pyrolytic graphite (HOPG).
Ribbons and terraces with step edges of graphene have been obtained
by peeling off the surface layers of HOPG using scotch tape.
Alternative methods, such as exfoliation and epitaxial growth on
single-crystal silicon carbide substrates, have produced multilayer
graphene sheets, but not single layer graphene sheets. In any
event, known methods of producing graphene sheets are tedious and
labor-intensive. Furthermore, none of the known methods address how
to place the graphene sheets in a desired location, which is of
great importance in constructing electrical experiments and
assembling heterogeneous electronic systems.
SUMMARY OF THE INVENTION
[0005] The present invention is a method for electrostatic
deposition of graphene on a substrate.
[0006] One side of a graphite sample, such as a highly oriented
pyrolytic graphite (HOPG) sample, is first cleaved using the scotch
tape technique (or other similar technique) to obtain a clean
surface. Then, the other side of the graphite sample is secured to
an electrode. This electrode is then electrically connected to the
positive terminal of a high voltage power source. A second
electrode is then electrically connected to the ground terminal of
the power source. A substrate is then placed on the second
electrode, and the power source is used to apply a voltage, such
that graphene is removed from the graphite sample and deposited on
the substrate.
[0007] Furthermore, in some implementations, an insulator is
interposed between the second electrode and the substrate, which is
intended to prevent a short circuit between the first and second
electrodes.
[0008] Thus, the method of the present invention allows for the
positioning of graphene on a suitable substrate at a selected
location, which is important both for studying the fundamental
properties of graphene and developing graphene-based devices. The
method of the present invention also requires minimal resources and
labor, yet allows for the deposition of a monolayer of graphene in
a short period of time on any given substrate without the use of
any chemical additives.
DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic representation of an exemplary method
for electrostatic deposition of graphene on a substrate in
accordance with the present invention;
[0010] FIG. 2 is a schematic representation of another exemplary
method for electrostatic deposition of graphene on a substrate in
accordance with the present invention, in which a trench is formed
in the substrate;
[0011] FIG. 2A is an illustration of the deposited graphene over
the trench formed in the substrate;
[0012] FIG. 3 is a schematic representation of an exemplary method
for electrostatic deposition of graphene on a substrate in
accordance with the present invention, in which the substrate is a
conductive material in the form of a ball; and
[0013] FIG. 4 is a schematic representation of another exemplary
method for electrostatic deposition of graphene on a substrate in
accordance with the present invention, in which no insulator is
interposed between the second electrode and the substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The present invention is a method for electrostatic
deposition of graphene on a substrate. Through the use of scanning
tunneling microscopy (STM), it has been observed that there are
numerous small sheets of graphene, of from one to several layers,
on the surface of certain graphite samples, for example, freshly
cleaved highly oriented pyrolytic graphite (HOPG). The sheets are
loosely bound to the bulk graphite and can be removed from the
surface by an electrostatic attractive force, for instance, by
applying an electrostatic field from an STM tip.
[0015] FIG. 1 is a schematic representation of an exemplary method
for electrostatic deposition of graphene on a substrate in
accordance with the present invention. In this exemplary
implementation, one side 10a of a graphite sample 10, in this case,
an HOPG sample, is first cleaved using the scotch tape technique
(or other similar technique) to obtain a clean surface. Then, the
other side 10b of the HOPG sample 10 is secured to an electrode 20.
In this exemplary implementation, the HOPG sample 10 is secured to
a copper electrode 20 using a silver epoxy (not shown). This
electrode 20 is then electrically connected to the positive
terminal of a high voltage power source 30 (0-30 kV and 0-10
mA).
[0016] Referring still to FIG. 1, a second electrode 22 is then
electrically connected to the ground terminal of the power source
30. In this exemplary implementation, the second electrode 22 is in
the form of a 3-mm thick copper plate. An insulator 40 is placed on
the second electrode 22. In this exemplary implementation, the
insulator 40, which is intended to prevent a short circuit between
the first and second electrodes 20, 22, and therefore has a high
breakdown voltage, is in the form of a 0.1-mm thick mica sheet. Of
course, to the extent necessary, other insulators or materials with
a high breakdown voltage could also be used to prevent a short
circuit without departing from the spirit and scope of the present
invention.
[0017] Referring still to FIG. 1, a substrate 50 is then placed
over the insulator 40. Various materials could be used as a
substrate, including both conducting and non-conducting materials.
In this exemplary implementation, and as shown in FIG. 1, the
substrate 50 is a 300-nm thick silicon dioxide (SiO.sub.2) layer on
a silicon layer (500 .mu.m thick). By using the power source 30 to
apply a voltage, graphene is pulled from the HOPG sample 10 by an
electrostatic attractive force and deposited on the substrate
50.
[0018] Furthermore, with respect to the exemplary implementation
illustrated in FIG. 1, it has been experimentally observed that by
varying the applied voltage, the number of graphene layers
deposited on the substrate 50 could be changed. For example, for an
applied voltage V.sub.ap in the range of 3 kV<V.sub.ap<5 kV,
mostly single to three-layer thick graphene sheets are deposited on
the substrate 50. For an applied voltage V.sub.ap in the range of 5
kV<V.sub.ap<8 kV, sheets from three to seven layers thick are
deposited on the substrate 50. For V.sub.ap>10 kV, sheets of ten
layers or more are deposited on the substrate. In short, the number
of layers deposited was found to increase with the increasing
applied voltage.
[0019] FIG. 2 is a schematic representation of another exemplary
method for electrostatic deposition of graphene on a substrate in
accordance with the present invention. Similar to the
implementation described above with reference to FIG. 1, one side
110a of an HOPG sample 110 is first cleaved using the scotch tape
technique to obtain a clean surface, and then, the other side 110b
of the HOPG sample 110 is secured to an electrode 120. This
electrode 120 is then electrically connected to the positive
terminal of a high voltage power source 130 (0-30 kV and 0-10 mA).
A second electrode 122 (e.g., a 3-mm thick copper plate) is then
electrically connected to the ground terminal of the power source
130. An insulator 140 (e.g., a 0.1-mm thick mica sheet) is placed
on the second electrode 122. Finally, a substrate 150 is placed
over the insulator 140. In this exemplary implementation, the
substrate 150 again is a 300-nm thick silicon dioxide (SiO.sub.2)
layer on a silicon layer (500 .mu.m thick). However, in the
exemplary implementation, a trench 152 is formed in the substrate
150. Thus, when the power source 130 is used to apply a voltage,
graphene is pulled from the HOPG sample 110 by an electrostatic
attractive force and deposited on the substrate 150 and over the
trench 152. FIG. 2A is an illustration of the deposited graphene
160 over the trench 152 formed in the substrate 150.
[0020] By suspending the deposited graphene 160 over a trench 152
in this manner, the suspended graphene 160 is effectively isolated
from various substrate effects (except, of course, at the supported
ends). For example, the suspended graphene 160 is effectively
isolated from surface adhesion and strain forces, substrate
temperature, substrate conductivity, and parasitic capacitance.
[0021] FIG. 3 is a schematic representation of another exemplary
method for electrostatic deposition of graphene on a substrate in
accordance with the present invention. Similar to the
implementations described above with reference to FIGS. 1 and 2,
one side 210a of an HOPG sample 210 is first cleaved using the
scotch tape technique to obtain a clean surface, and then, the
other side 210b of the HOPG sample 210 is secured to an electrode
220. This electrode 220 is then electrically connected to the
positive terminal of a high voltage power source 230 (0-30 kV and
0-10 mA). A second electrode 222 (e.g., a 3-mm thick copper plate)
is then electrically connected to the ground terminal of the power
source 230. An insulator 240 (e.g., a 0.1-mm thick mica sheet) is
placed on the second electrode 222. Finally, a substrate 250 is
placed over the insulator 240. In this exemplary implementation,
the substrate 250 is composed of a conductive material,
specifically, gold (Au) in the form of a ball. Thus, when the power
source 230 is used to apply a voltage, graphene is pulled from the
HOPG sample 210 by an electrostatic attractive force and deposited
on the substrate 250 (i.e., the gold ball).
[0022] FIG. 4 is a schematic representation of another exemplary
method for electrostatic deposition of graphene on a substrate in
accordance with the present invention. Similar to the
implementations described above with reference to FIGS. 1 and 2,
one side 310a of an HOPG sample 310 is first cleaved using the
scotch tape technique to obtain a clean surface, and then, the
other side 310b of the HOPG sample 310 is secured to an electrode
320. This electrode 320 is then electrically connected to the
positive terminal of a high voltage power source 330 (0-30 kV and
0-10 mA). A second electrode 322 (e.g., a 3-mm thick copper plate)
is then electrically connected to the ground terminal of the power
source 330. A substrate 350 is placed on the second electrode 322,
with no insulator interposed between the second electrode 320 and
the substrate 350. Such a configuration is possible provided that
the current is controlled in another manner to prevent a short
circuit between the first and second electrodes 320, 322. Again,
when the power source 330 is used to apply a voltage, graphene is
pulled from the HOPG sample 310 by an electrostatic attractive
force and deposited on the substrate 350.
[0023] As a further refinement, in order to get a high-yield
deposition of the graphene, it is contemplated that the surface of
the substrate could be modified in some fashion. For example, a
corrugated silicon micro-fabricated substrate may be used instead
of a flat silicon substrate, such that the effective electric field
is enhanced due to the sharp edges.
[0024] As yet a further refinement, it may be possible to control
lateral size of the graphene by depositing it under controlled
vacuum. It has been experimentally observed that by varying the
vacuum pressure, the size of the deposited graphene can be
increased or decreased.
[0025] The above-described method for electrostatic deposition of
graphene on a substrate, which allows for the positioning of
graphene on a suitable substrate at a selected location, is
important both for studying the fundamental properties of graphene
and developing graphene-based devices. For example, graphene can be
deposited and positioned on very delicate structures, such as
suspended microstructures and electronic devices. Furthermore, the
ability to obtain graphene sheets of various thicknesses provides a
unique way to pattern graphene for physical studies. Thus, the
method of the present invention provides a convenient alternative
to the common method of mechanical cleaving of HOPG (or another
graphite sample), with the added benefit of selective deposition.
The method of the present invention also requires minimal resources
and labor, yet allows for the deposition of a monolayer of graphene
in a short period of time on any given substrate. Furthermore,
graphene can be directly deposited without any chemical additives,
thus eliminating a major source of contamination that previously
had been difficult to remove.
[0026] For further details about the method of the present
invention, including its benefits and advantages, reference is made
to the following article, which is incorporated herein by
reference: Sidorov, Anton N.; Yazdanpanah, Mehdi M.; Jalilian,
Romaneh; Ouseph, P. J.; Cohn, R. W.; and Sumanasekera, G. U.,
"Electrostatic deposition of graphene," Nanotechnology 18 (2007)
135301.
[0027] One of ordinary skill in the art will recognize that
additional implementations are also possible without departing from
the teachings of the present invention or the scope of the claims
which follow. This detailed description, and particularly the
specific details of the exemplary implementations disclosed, is
given primarily for clarity of understanding, and no unnecessary
limitations are to be understood therefrom, for modifications will
become obvious to those skilled in the art upon reading this
disclosure and may be made without departing from the spirit or
scope of the claimed invention.
* * * * *