U.S. patent application number 17/091018 was filed with the patent office on 2021-03-18 for transferring graphitic thin films with a liquid gallium probe.
The applicant listed for this patent is VAON, LLC. Invention is credited to Keith Andrew, John Gilbert, Richard C. Pape, Henry Steen.
Application Number | 20210078316 17/091018 |
Document ID | / |
Family ID | 1000005240037 |
Filed Date | 2021-03-18 |
United States Patent
Application |
20210078316 |
Kind Code |
A1 |
Gilbert; John ; et
al. |
March 18, 2021 |
TRANSFERRING GRAPHITIC THIN FILMS WITH A LIQUID GALLIUM PROBE
Abstract
The present invention generally relates to a process for
transferring a graphitic thin film and a kit for the same.
Inventors: |
Gilbert; John; (Bowling
Green, KY) ; Steen; Henry; (Bowling Green, KY)
; Andrew; Keith; (Bowling Green, KY) ; Pape;
Richard C.; (Bowling Green, KY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VAON, LLC |
Bowling Green |
KY |
US |
|
|
Family ID: |
1000005240037 |
Appl. No.: |
17/091018 |
Filed: |
November 6, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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16196187 |
Nov 20, 2018 |
10857774 |
|
|
17091018 |
|
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|
|
62588994 |
Nov 21, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B 37/025 20130101;
B32B 9/007 20130101; B32B 2037/243 20130101; B32B 38/10 20130101;
B32B 2264/108 20130101; B32B 37/24 20130101; C23F 1/18 20130101;
C23F 1/08 20130101 |
International
Class: |
B32B 37/00 20060101
B32B037/00; B32B 9/00 20060101 B32B009/00; B32B 37/24 20060101
B32B037/24; C23F 1/08 20060101 C23F001/08; C23F 1/18 20060101
C23F001/18; B32B 38/10 20060101 B32B038/10 |
Claims
1. A kit for transferring a graphitic thin film, comprising: (a) a
gallium probe. comprising: (i) a shank with 1.sup.st and 2.sup.nd
ends; (ii) a loop attached to the 1.sup.st end of the shank; (iii)
a drop of gallium in contact with the loop; and (iv) a heat source
capable of liquefying gallium; and (b) an etching container,
comprising: (i) a 1.sup.st chamber comprising: an etchant solution,
a 1.sup.st port, and a 2.sup.nd port, wherein the etchant level is
above the level of the ports and is in contact with the metal layer
of the graphitic-metal material; (ii) a 2.sup.nd chamber adjacent
to the 1.sup.st chamber, comprising: the etchant solution and a
1.sup.st port in liquid contact with the 1.sup.st port of the
1.sup.st chamber, wherein the etchant level is above the level of
the 1.sup.st port; and, (iii) a 3.sup.rd chamber adjacent to the
1.sup.st chamber, comprising: the etchant solution and a 1.sup.st
port in liquid contact with the 2.sup.nd port of the 1.sup.st
chamber, wherein the etchant level is above the level of the
1.sup.st port.
2. The kit of claim 1, wherein the heat source, comprises: a coil
of resistance wire surrounding, but not touching the shank and in
close enough proximity to the gallium drop to liquefy it.
3. The kit, of claim 1, wherein the heat source, comprises: a
plurality of coils of resistance wire surrounding, but not touching
the shank and in close enough proximity to the gallium drop to
liquefy it.
4. The kit of claim 1, further comprising: (c) a
micromanipulator.
5. The kit of claim 1, wherein the shank and loop are tungsten.
6. The kit of claim 1, wherein the diameter of the loop is 1 mm.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This Application is a Divisional of U.S. application Ser.
No. 16/196,187 filed Nov. 20, 2018, which claims priority to U.S.
Provisional Application No. 62/588,994 filed Nov. 21, 2017, all of
which are incorporated herein in their entirety by reference.
FIELD OF THE INVENTION
[0002] The present invention generally relates to a process for
transferring a graphitic thin film and a kit for the same.
BACKGROUND OF THE INVENTION
[0003] The transfer of graphitic thin films from one surface to
another is hindered by one or more of the following: 1) the films
are brittle, being typically from one to ten atoms thick; 2)
graphitic thin films are difficult to locate with the unaided eye,
being nearly completely transparent to white light; and, 3) current
transfer methods involve the application of polymers such as
polymethyl methacrylate (PMMA) or polyethylene terephthalate (PET),
contaminating the film.
[0004] In view of the above, it would be advantageous to discover
new ways of transferring graphitic thin films.
SUMMARY OF THE INVENTION
[0005] In an aspect, the present invention provides a novel method
of transferring a graphitic thin film.
[0006] In another aspect, the present invention provides a novel
kit for transferring a graphitic thin film.
[0007] These and other aspects, which will become apparent during
the following detailed description, have been achieved by the
inventors' discovery that liquid gallium can be used to transfer a
graphitic thin film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a drawing of a three-chamber etching container
useful in the present invention.
[0009] FIG. 2 is a photograph of a three-chamber etching
container.
[0010] FIG. 3 is a photograph of a Brewster's angle microscope with
etching container.
[0011] FIG. 4 is a photograph of a gallium probe on the end of a
micromanipulator.
[0012] FIG. 5 shows before and after Raman spectra.
DETAILED DESCRIPTION OF THE PREFERRED ASPECTS
[0013] FIG. 1 shows a drawing of a three-chamber etching container
useful in the present invention, wherein the chambers are
interconnected by a tube (or ports) (dimensions are in inches). The
exterior openings of the tubes (or ports) are tapped to receive
threaded plugs during the etching process. A variant having a
height of approximately 0.5'' was used for the experiment described
in the Examples.
[0014] FIG. 2 is a photograph of a three-chamber etching container
(shown with threaded plugs in place and made transparent to
illustrate the interconnecting tube and fluid levels), with the
bottom of its concave meniscus set level to that of the convex
meniscus of the regulator container. The etching container is
connected to a fluid level regulation container via a siphon tube
(orange). A titration column is suspended above the opposite
chamber.
[0015] FIG. 3 is a photograph of a Brewster's angle microscope with
etching container (black, center of frame) in place on the stage
and under the gallium probe (red, center of frame).
[0016] FIG. 4 is a photograph of a gallium probe on the end of a
micromanipulator. The gallium probe has a gallium drop suspended by
a wire loop under a resistance wire heating coil.
[0017] FIG. 5 shows Raman spectra before (top) and after (bottom)
contact with the gallium probe of the present invention. The
spectra show Si/SiO.sub.2 peaks at 511 cm.sup.-1 and 965 cm.sup.-1,
and graphitic layer peak shifts of 1343 cm.sup.-1 to 1349 cm.sup.-1
(D peak), 1574 cm.sup.-1 to 1577 cm.sup.-1 (G peak), and 2691
cm.sup.-1 to 2689 cm.sup.-1 (2D peak), respectively.
[0018] In an aspect, the present invention provides a novel method
of transferring a graphitic thin film, comprising; [0019] (a)
contacting a liquid-suspended graphitic thin film with a liquid
gallium probe, wherein the graphitic thin film adheres to the
liquid gallium of the probe to form a gallium-suspended graphitic
thin film; and, [0020] (b) transferring the graphitic thin film to
a substrate by contacting the graphitic thin film with the
substrate, wherein the graphitic thin film adheres to the substrate
to form a graphitic thin film-coated substrate.
[0021] Graphitic thin film is a layer of material, primarily
comprising: graphene (a crystalline allotrope of carbon typically
of a single atomic plane of graphite having a 2-dimensional
hexagonal lattice structure of carbon atoms). The film is typically
from 1, 2, 3, 4, 5, 6, 7, 8, 9, to 10 atomic layers in
thickness.
[0022] In another aspect, the graphitic thin film is suspended in
water. In another aspect, the water is deionized water.
[0023] In another aspect, the substrate of step (b) is an oxidized
Si wafer. For example, the wafer can be an 800 .mu.m thick
wafer.
[0024] In another aspect, contacting step (a) and transferring step
(b) are performed by using a micromanipulator to maneuver the probe
to the graphitic thin film and then the gallium-suspended graphitic
thin film to the substrate.
[0025] In another aspect, the liquid gallium probe, comprises:
[0026] (i) a shank with 1.sup.st and 2.sup.nd ends; [0027] (ii) a
loop attached to the 1.sup.st end of the shank; [0028] (iii) a drop
of gallium in contact with the loop; and [0029] (iv) a heat source
capable of liquefying gallium.
[0030] The shank of the probe is made of a material (or materials)
that does not readily alloy or react with gallium. In another
aspect, the shank is tungsten. The dimensions of the shank are
determined by the dimensions of the etching chamber. As an example,
the shank can vary from a hair-like thickness to 18 gage wire.
[0031] At the 1.sup.st end of the shank is a loop, which is also
made of a material (or materials) that does not readily alloy or
react with gallium. In another aspect, the loop is tungsten. In
another aspect, the loop itself is about 1 mm in diameter. The
thickness of the loop is similar to that of the shank. As an
example, the loop can vary from a hair-like thickness to 18 gage
wire.
[0032] The drop of gallium is typically of a size sufficient to
adhere both to the loop and to the graphitic layer being
transferred. In another aspect, the drop is about 0.25 mm.sup.3. In
another aspect, the drop of gallium is suspended from the loop in
an inverted cone shape. The drop of gallium used in the
transferring process is in a liquid form. This form is still dense
enough to "stick" to the loop of the probe, but liquid enough to be
able to adhere to the graphitic thin film. In another aspect, the
drop of gallium is heated to slightly above its melting point
(about 30.5.degree. C.) prior to contacting with the graphitic thin
film.
[0033] In another aspect, the heat source, comprises: a coil (or a
plurality of coils) of resistance wire surrounding, but not
touching the shank and in close enough proximity to the gallium
drop (but, not touching it) to liquefy it. Typically the resistance
wire leads (the two ends of the coil) are connected to a power
supply (e.g., 0.5 V at 2A DC). In another aspect, the resistance
wire is a nickel chromium wire. In another aspect, the thickness of
the resistance, wire is about 20, 22, to 24 gage.
[0034] In another aspect, the process, prior to step (a), further
comprises: [0035] (a1) placing a graphitic-metal material,
comprising: the graphitic thin film and a metal layer, into a
1.sup.st chamber of an etching container, comprising: [0036] (i) a
1.sup.st chamber comprising: an etchant solution, a 1.sup.st port,
and a 2.sup.nd port, wherein the etchant level is above the level
of the ports and is in contact with the metal layer of the
graphitic-metal material: [0037] (ii) a 2.sup.nd chamber adjacent
to the 1.sup.st chamber, comprising: the etchant solution and a
1.sup.st port in liquid contact with the 1.sup.st port of the
1.sup.st chamber, wherein the etchant level is above the level of
the 1.sup.st port; and, [0038] (iii) a 3.sup.rd chamber adjacent to
the 1.sup.st chamber, comprising: the etchant solution and a
1.sup.st port in liquid contact with the 1.sup.st port of the
1.sup.st chamber, wherein the etchant level is above the level of
the 1.sup.st port; [0039] (a2) inserting, after the etchant has
dissolved the metal layer of the graphitic-metal sample, a first
end of a siphon below the etchant level of the 2.sup.nd chamber and
the second end into a water-containing fluid level regulation
container, [0040] (a3) introducing water into the 3.sup.rd chamber
at a rate and amount sufficient to replace the etchant in the
1.sup.st chamber with water by causing; [0041] (i) the etchant
solution to exit the 3.sup.rd chamber and enter the 1.sup.st
chamber; [0042] (ii) the etchant solution to exit the 1.sup.st
chamber and enter the 2.sup.nd chamber; and, [0043] (iii) the
etchant solution to exit the 2.sup.nd chamber and into the fluid
level regulation chamber via the siphon.
[0044] Water is introduced into the 3.sup.rd chamber at a rate that
will cause the etchant solution to flow into the 1.sup.st chamber
and etchant solution to flow from the 1.sup.st chamber into the
2.sup.nd chamber, and finally etchant solution to flow from the
2.sup.rd chamber into the fluid regulation chamber. The rate is
such that the floating graphitic thin film in the 1.sup.st chamber
is left substantially undisturbed. As additional water is added the
fluid flowing will change from etchant to a mixture of etchant and
water and finally just water. Once the fluid of the 1.sup.st
chamber is water or substantially water, the introduction of water
to the 3.sup.rd chamber can be discontinued.
[0045] In another aspect, the process, further comprises: [0046]
(a4) locating the resulting graphitic thin film with a Brewster's
Angle Microscope.
[0047] In another aspect, the process, prior to step (a), further
comprises: [0048] (a5) heating the gallium to a temperature
sufficient to liquefy it.
[0049] The fluid regulation container s filled with water having
its surface level with that of the etchant in the etching
container, as well as level with its own edge or spout. This allows
excess water to spill off into a basin and the container to act as
a fluid level regulator.
[0050] Liquid contact in the etching container means that a liquid
can flow between the chambers that are in contact. For example,
etchant can flow from the 1.sup.st chamber into the 2.sup.nd due to
the liquid contact of the 1.sup.st port in each.
[0051] The ports in the chambers are typically located opposite one
another (when two are present). The ports in the chambers are
typically are at the same level as one another and the other ports
in the container and are near the bottom of their respective
chambers. The ports form a channel between the chambers, near the
bottom of the chambers and below the fluid level.
[0052] In another aspect, "adjacent to" means that the chambers
(e.g., 1.sup.st and 2.sup.nd) partially share a common wall or
boundary. For example, when the chambers are cylindrical, part of
the 1.sup.st and 2.sup.ndchambers (and 1.sup.st and 3.sup.rd) are
touching or share a common portion of their respective cylinders
(e.g., see FIG. 1).
[0053] In another aspect, one or both of the 2.sup.nd and 3.sup.rd
chambers have an external port. In another aspect, the external
port(s) of the etching container is tapped. In another aspect, the
etching container, further comprises: a plug (or plugs) threaded
into the external port(s).
[0054] In another aspect, the 1.sup.st, 2.sup.nd and 3.sup.th
chambers, are cylindrical with open tops (e.g., tops that are
exposed to the atmosphere).
[0055] In another aspect, the 1.sup.st, 2.sup.nd, and 3.sup.rd,
chambers are all housed in one structure. In this aspect, the ports
of the 1.sup.st and 2.sup.nd chambers (1.sup.st and 1.sup.st ports)
and the 1.sup.st and 3.sup.rd chambers (2.sup.nd and 1.sup.st
ports, respectively) are connected (i.e., form a channel between
their respective chambers). In another aspect, the etching
container is a rectangular container. In another aspect. the
etching container is a rectangular container and the 1.sup.st,
2.sup.nd, and 3.sup.rd chambers are cylindrical and are linearly
disposed in the container.
[0056] The metal layer is typically the metal on which the
graphitic thin film was formed. In another aspect, the metal layer
of step (a1) is copper. In another aspect, the metal layer is a
copper-nickel alloy.
[0057] The etchant is a liquid capable of fully dissolving the
metal layer (e.g., copper) but not negatively affecting the
graphitic thin film. In another aspect, the etchant solution of
step (a1)(i) is 1M ferric chloride.
[0058] The water can be introduced to the 3.sup.rd chamber using a
flow control device (e.g., an eye dropper or titration column).
Typically deionized water is used.
[0059] In another aspect, the present invention provides a novel
kit for transferring a graphitic thin film, comprising: [0060] (a)
a gallium probe, comprising: [0061] (i) a shank with 1.sup.st and
2.sup.nd ends; [0062] (ii) a loop attached to the 1.sup.st end of
the shank; [0063] (iii) a drop of gallium in contact with the loop;
and, [0064] (iv) a heat source capable of liquefying gallium; and,
[0065] (b) an etching container, comprising: [0066] (i) a 1.sup.st
chamber comprising: a 1.sup.st port and a 2.sup.nd port; [0067]
(ii) a 2.sup.nd chamber adjacent to the 1.sup.st chamber,
comprising: a 1.sup.st port in liquid contact with the 1.sup.st
port of the 1.sup.st chamber; and, [0068] (iii) a 3.sup.rd chamber
adjacent to the 1.sup.st chamber, comprising: a 1.sup.st port in
liquid contact with the 2.sup.nd port of the 1.sup.st chamber.
[0069] In another aspect, the present invention provides a novel
kit for transferring a graphitic thin film, comprising: [0070] (a)
a gallium probe, comprising: [0071] (i) a shank with 1.sup.st and
2.sup.nd ends; [0072] (ii) a loop attached to the 1.sup.st end of
the shank; [0073] (iii) a drop of gallium in contact with the loop;
and, [0074] (iv) a heat source capable of liquefying gallium; and,
[0075] (b) an etching container, comprising: [0076] (i) a 1.sup.st
chamber comprising: an etchant solution, a 1.sup.st port, and a
2.sup.nd port, wherein the etchant level is above the level of the
ports and is in contact with the metal layer of the graphitic-metal
material; [0077] (ii) a 2.sup.nd chamber adjacent to the 1.sup.st
chamber, comprising: the etchant solution and a 1.sup.st port in
liquid contact with the 1.sup.st port of the 1.sup.st chamber,
wherein the etchant level is above the level of the 1.sup.st port;
and, [0078] (iii) a 3.sup.rd chamber adjacent to the 1.sup.st
chamber, comprising: the etchant solution and a 1.sup.st port in
liquid contact with the 2.sup.nd port of the 1.sup.st chamber,
wherein the etchant level is above the level of the 1.sup.st
port.
[0079] In another aspect, the kit, further comprises: [0080] (c) a
micromanipulator.
[0081] The micromanipulator typically attaches to the 2.sup.nd end
of the shank and allows the operator to selectively move the probe
in order to contact the graphitic thin film when it is floating in
the etching container (e.g., after location with a Brewster's Angle
Microscope) and then contact the gallium-suspended graphitic thin
film with the substrate (e.g., oxidized Si wafer).
[0082] The method of transfer of the present invention is expected
to be useful in the construction of small components that require
the precise placement of submillimeter thin films, to include small
graphene flakes and crystal domains, or other delicate 2D
structures, without damage or supportive layer residue
contamination.
EXAMPLES
[0083] The following examples are meant to illustrate, not limit,
the present invention.
Example 1: General Procedure
[0084] A small piece of a metallic substrate beating a graphitic
sample of approximately 1 mm.sup.2 or less is cut-out (e.g.
punched) of a larger piece to form a sample-bearing substrate. The
sample-bearing substrate is placed in the center chamber (the
etching chamber or 1.sup.st chamber) of a three-chambered etching
container (see FIG. 1) that has been filled with 1M ferric chloride
(or comparable etchant), metallic side down (the graphitic sample,
being on top), so that it floats on the etchant bath and is
confined to the center of the chamber by the concave meniscus in
the fluid.
[0085] The metallic substrate is allowed to dissolve, leaving the
graphitic thin film floating on the surface of the etchant bath.
The etching times will vary depending on substrate thickness,
substrate composition, and etchant used. After dissolution of the
metallic substrate, a small siphon tube, primed with water, is
introduced into one of the remaining two outer chambers (2.sup.nd
chamber) of the etching container. The outlet of the siphon tube is
submerged into water held in another container (the fluid level
regulation container). This container has been filled with water
having its surface level with that of the etchant in the etching
container, as well as level with its own edge or spout that will
allow excess water to spill off into a basin, which allows this
container to act as a fluid level regulator. Using an eyedropper,
titration column, or some other flow controlling apparatus,
approximately 200 mL of deionized water is introduced into the
remaining outer chamber (3.sup.rd chamber) of the etching container
at a rate that maintains the fluid level across the three
interconnected chambers, preserving the concave meniscus in the
center chamber (see FIG. 2). Etchant is removed from the etching
container and into the fluid level regulator chamber by siphon
action, allowing it to be replaced with the water. The separation
of the inflow, sample, and siphoned outflow into three separate
chambers prevents excessive disturbance of the sample that could
result in its damage or loss during the water wash.
[0086] The remaining thin film sample is invisible or nearly
invisible to the naked eye. The etching container, with the thin
film sample in the etching chamber, is transported to the
Brewster's Angle Microscope (BAM). The bottom of the center
(etching) chamber is designed to have a low laser reflectivity. In
this example, the chamber is black in color and equipped with a 665
nm longpass filter at its floor. The BAM's laser (in this example a
630 nm red He--Ne laser with p-polarizing filter), having
previously been calibrated to the Brewster's angle of the air-water
interface, is fired into the center chamber of the etching
container. The etching chamber is manipulated under the laser to
search for the sample floating on the water's surface using two
video cameras: one directly above looking through the microscope
lens and one looking down the axis of the anticipated reflection
angle (see FIG. 3). The etching chamber is searched until a
reflection is detected at the laser's point of entry into the
water, indicating the presence of the sample.
[0087] Once the sample is located on the surface of the water in
the etching container, a micromanipulator holding a probe is
positioned above it. The probe, comprises: [0088] a. a downward
sloping shank, made of material that will not readily alloy or
react with gallium (e.g. tungsten), with an approximately 1 mm
diameter horizontal loop at the lowest end; [0089] b. one to
several turns (a plurality of coils) of small gage resistance wire
wrapped around, but not touching, the shank and having power leads;
and, [0090] c. a drop of gallium metal (approximately 0.25 mm.sup.3
for a 1 mm loop) suspended from the shank's loop in an inverted
cone shape. The resistance wire leads are connected to a power
supply (e.g., approximately 0.5V at 2A DC), producing heat from the
wire wrappings that heats the gallium drop to slightly above its
melting point (approximately 30.5.degree. Celsius)(see FIG. 4).
[0091] The liquid gallium drop is lowered onto the floating sample
in the etching container via the micromanipulator controls. The
sample sticks to the gallium drop due to Van der Waals forces. The
sample can then easily be transported to and deposited on another
substrate (in this experiment, the SiO.sub.2 surface of a Si wafer)
by touching the sample bearing gallium probe tip to the new
substrate.
Example 2: Comparison of Wet Transfer Versus Gallium Transfer
[0092] A 1.2 mm round sample of graphene bearing copper substrate,
punched from a larger piece, was transferred to the SiO.sub.2
surface of an oxidized Si wafer by a previously established wet
transfer method. This method involves dropping the floating sample
onto the wafer after etching by positioning the wafer beneath the
sample and lowering the fluid level until the graphene rests on the
SiO.sub.2 surface. This process does not involve touching the
sample with gallium and, therefore, acts as a control sample. This
control sample was then inspected using a 532 nm wavelength Raman
spectrometer, with a beam width of .about.35 micrometers. to
establish a baseline spectrum for a graphene sample without gallium
contamination.
[0093] A second 1.2 mm round sample of graphene bearing copper
substrate was prepared from the same larger piece and transferred
to the SiO.sub.2 surface of an oxidized Si wafer using the gallium
probe method described in Example 1. This experimental sample was
then inspected using a Raman spectrometer to establish a spectrum
for a graphene sample after having been in contact with
gallium.
[0094] The above process was repeated three times and the resulting
gallium transfer spectra were compared to their respective control
spectra. As shown in FIG. 5, the comparison showed no discernable
difference between the sample and control spectra in the number of
peaks, peak shift, peak height, or background curve that might
indicate the presence of gallium contamination.
[0095] Numerous modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to he understood that within the scope of the appended
claims, the invention may be practiced otherwise that as
specifically described herein.
* * * * *