U.S. patent application number 12/313935 was filed with the patent office on 2009-09-24 for carbon nanotube needle and method for making the same.
This patent application is currently assigned to Tsinghua University. Invention is credited to Shou-Shan Fan, Liang Liu, Yang Wei.
Application Number | 20090239072 12/313935 |
Document ID | / |
Family ID | 41089217 |
Filed Date | 2009-09-24 |
United States Patent
Application |
20090239072 |
Kind Code |
A1 |
Wei; Yang ; et al. |
September 24, 2009 |
Carbon nanotube needle and method for making the same
Abstract
A carbon nanotube needle comprising: an end portion and a broken
end portion, the broken end portion comprising a single carbon
nanotube tip. A method for manufacturing a carbon nanotube needle,
the method comprising the steps of: (a) providing a carbon nanotube
film comprising of a plurality of commonly aligned carbon
nanotubes, a first electrode, and a second electrode; (b) fixing
the carbon nanotube film to the first electrode and the second
electrode, the carbon nanotube film extending from the first
electrode to the second electrode; (c) treating the carbon nanotube
film with an organic solvent to form at least one carbon nanotube
string; and (d) applying a voltage to the carbon nanotube string
until the carbon nanotube string snaps.
Inventors: |
Wei; Yang; (Beijing, CN)
; Liu; Liang; (Beijing, CN) ; Fan; Shou-Shan;
(Beijing, CN) |
Correspondence
Address: |
PCE INDUSTRY, INC.;ATT. Steven Reiss
458 E. LAMBERT ROAD
FULLERTON
CA
92835
US
|
Assignee: |
Tsinghua University
Beijing City
CN
HON HAI Precision Industry CO., LTD.
Tu-Cheng City
TW
|
Family ID: |
41089217 |
Appl. No.: |
12/313935 |
Filed: |
November 26, 2008 |
Current U.S.
Class: |
428/402 ;
264/430 |
Current CPC
Class: |
B82Y 30/00 20130101;
C01B 32/168 20170801; C01B 2202/06 20130101; C01B 2202/04 20130101;
C01B 2202/08 20130101; C01B 32/162 20170801; B82Y 40/00 20130101;
B81C 1/00111 20130101; B81B 2201/055 20130101; C01B 2202/34
20130101; C01B 2202/02 20130101; Y10T 428/2982 20150115; C01B
2202/36 20130101 |
Class at
Publication: |
428/402 ;
264/430 |
International
Class: |
D01F 9/12 20060101
D01F009/12; H05B 6/00 20060101 H05B006/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 19, 2008 |
CN |
200810066128.2 |
Claims
1. A carbon nanotube needle comprising: an end portion and a broken
end portion, the broken end portion comprising a single carbon
nanotube tip.
2. The carbon nanotube needle as claimed in claim 1, wherein the
broken end portion comprises a tapered-shaped structure formed by a
plurality of carbon nanotubes.
3. The carbon nanotube needle as claimed in claim 1, wherein a
diameter of the carbon nanotube needle ranges from 1 to 20 microns,
and a length thereof ranges from 0.01 to 1 millimeter.
4. The carbon nanotube needle as claimed in claim 1, wherein the
carbon nanotube needle is a carbon nanotube string.
5. The carbon nanotube needle as claimed in claim 4, wherein the
carbon nanotube needle comprises a plurality of substantially
parallel carbon nanotubes.
6. The carbon nanotube needle as claimed in claim 5, wherein the
carbon nanotubes are joined end to end via van der Waals attractive
force therebetween.
7. The carbon nanotube needle as claimed in claim 5, wherein the
carbon nanotubes in the end portion includes single-walled carbon
nanotubes, double-walled carbon nanotubes, or multi-walled carbon
nanotubes.
8. The carbon nanotube needle as claimed in claim 7, wherein
diameters of the single-walled carbon nanotubes, the double-walled
carbon nanotubes, and the multi-walled carbon nanotubes is,
respectively, in a range from 0.5 to 50 nanometers, 1 to 50
nanometers, and 1.5 to 50 nanometers.
9. The carbon nanotube needle as claimed in claim 1, wherein the
broken end portion has a diameter of less than 5 nanometers and
approximately 2-3 walls.
10. The carbon nanotube needle as claimed in claim 1, wherein the
carbon nanotube that composes the tip extends 5 nanometers to 50
nanometers from adjacent carbon nanotubes.
11. A method for manufacturing a carbon nanotube needle, the method
comprising the steps of: (a) providing a carbon nanotube film
comprising of a plurality of commonly aligned carbon nanotubes, a
first electrode, and a second electrode; (b) fixing the carbon
nanotube film to the first electrode and the second electrode, the
carbon nanotube film extending from the first electrode to the
second electrode; (c) treating the carbon nanotube film with an
organic solvent to form at least one carbon nanotube string; and
(d) applying a voltage to the carbon nanotube string until the
carbon nanotube string snaps.
12. The method as claimed in claim 11, wherein in step (a), the
carbon nanotube film provided is formed by the substeps of: (a1)
providing an array of carbon nanotubes; and (a2) pulling out a
carbon nanotube film from the array of carbon nanotubes, by using a
tool.
13. The method as claimed in claim 11, wherein in step (c), the
organic solvent is a volatile organic solvent and is selected from
a group consisting of ethanol, methanol, acetone, dichloroethane,
and chloroform.
14. The method as claimed in claim 11, wherein step (c) further
comprises the substeps of: putting the organic solvent onto the
carbon nanotube film or putting the carbon nanotube film, the first
electrode and the second electrode in the organic solvent.
15. The method as claimed in claim 11, wherein a distance between
the first electrode and the second electrode ranges from 50
micrometers to 2 millimeters.
16. The method as claimed in claim 11, wherein step (d) further
comprises the substep of: (d1) placing the first electrode and the
second electrode with the carbon nanotube string thereon in a
chamber; and wherein applying the voltage between two opposite ends
of the carbon nanotube strings is done via the first electrode and
the second electrode for a period of time to snap the carbon
nanotube string, thereby acquiring at least one carbon nanotube
needle with a break-end.
17. The method as claimed in claim 16, wherein in step (d), wherein
carbon nanotube string can reaches a temperature ranging
approximately from 2000 to 2400 kelvins before snapping.
18. A method for manufacturing a carbon nanotube needle, the method
comprising the steps of: (a) providing a carbon nanotube string
comprising of a plurality of carbon nanotubes, a first electrode,
and a second electrode; (b) fixing the two opposite sides of the
carbon nanotube string to the first electrode and the second
electrode; and (c) applying a voltage between two opposite ends of
the carbon nanotube string until the carbon nanotube string snaps,
thereby obtaining at least one carbon nanotube needle; wherein the
at least one carbon nanotube needle has an end portion and a broken
end portion; the broken end portion has a single tip carbon
nanotube protruding from the broken end portion; and the carbon
nanotubes are aligned along a same direction.
19. The method as claimed in claim 18, wherein a plurality of the
carbon nanotubes that comprise the carbon nanotube string are
substantially parallel and joined end-to-end.
20. The method as claimed in claim 18, wherein step (c) further
comprises the substep of: (c1) placing the carbon nanotube strings,
the first electrode and the second electrode in a chamber; and
wherein applying the voltage between two opposite ends of the
carbon nanotube strings is done via the first electrode and the
second electrode for a period of time to snap the carbon nanotube
string, thereby acquiring at least one carbon nanotube needle.
Description
RELATED APPLICATIONS
[0001] This application is related to commonly-assigned
applications entitled, "METHOD FOR MAKING FIELD EMISSION ELECTRON
SOURCE HAVING CARBON NANOTUBES", filed ______ (Atty. Docket No.
US18587); "FIELD EMISSION ELECTRON SOURCE HAVING CARBON NANOTUBES",
filed ______ (Atty. Docket No. US18672); "ELECTRON EMISSION
APPARATUS", filed ______ (Atty. Docket No. US18178); "ELECTRON
EMISSION APPARATUS AND METHOD FOR MAKING THE SAME", filed ______
(Atty. Docket No. US18177). The disclosure of the respective
above-identified application is incorporated herein by
reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The invention relates to a carbon nanotube needle and the
method for making the same.
[0004] 2. Discussion of Related Art
[0005] Carbon nanotubes (CNTs) produced by means of arc discharge
between graphite rods were first discovered and reported in an
article by Sumio Iijima, entitled "Helical Microtubules of
Graphitic Carbon" (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). CNTs
also feature extremely high electrical conductivity, very small
diameters (much less than 100 nanometers), large aspect ratios
(i.e. length/diameter ratios greater than 1000), and a tip-surface
area near the theoretical limit (the smaller the tip-surface area,
the more concentrated the electric field, and the greater the field
enhancement factor). These features tend to make CNTs ideal
candidates for use in many materials and devices, such as composite
materials, field emission devices, and micro electrical
devices.
[0006] Generally, the tip-surface area of a CNT is very small. A
single CNT is often used as a needle (i.e., probe, or sharp tip
structure) connected to a base. The CNT needle with the base is
used as a field emission electron source or a detecting probe. The
methods adopted for forming the CNT needle with base mainly include
mechanical and in situ synthesis methods. One mechanical method
involves coating a base (or a cantilever of an atomic force
microscope (AFM)) with an adhesive and touching it to a CNT array,
and pulling one CNT away adhered to the base. However, because CNTs
are so small, using this method is hard to control. Further, the
CNT needle may easily separate from the base. Thus, the performance
of the field emission electron source or detecting probe of AFM
will be decreased and have short life.
[0007] One in-situ synthesis method is performed by coating metal
catalysts on a base and synthesizing a CNT directly on the base by
means of chemical vapor deposition (CVD). However, because CNTs
have a small diameter, the interface of the CNT and the base will
be small, and the mechanical connection between the CNT and the
base will generally be relatively weak and, thus, unreliable.
Further, it is difficult to grow only one CNT on the base.
[0008] What is needed, therefore, is an improved CNT needle and
method for making same.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Many aspects of the present CNT needle can be better
understood with references to the following drawings. The
components in the drawings are not necessarily drawn to scale, the
emphasis instead being placed upon clearly illustrating the
principles of the present CNT needle.
[0010] FIG. 1 is a representation a CNT needle in accordance with a
present embodiment.
[0011] FIG. 2 shows a Scanning Electron Microscope (SEM) image of a
CNT needle.
[0012] FIG. 3 shows a Transmission Electron Microscope (TEM) image
of a CNT needle.
[0013] FIG. 4 is a flow chart of a method for manufacturing a CNT
needle, in accordance with a present embodiment.
[0014] FIG. 5 shows an image of a CNT film treated by an organic
solvent.
[0015] FIG. 6 is a schematic view of an apparatus for fusing CNT
strings.
[0016] FIG. 7 is a schematic view before fusing the CNT strings of
FIG. 6.
[0017] FIG. 8 is a schematic view after fusing the CNT strings of
FIG. 6.
[0018] FIG. 9 shows an image of CNT strings in an incandescent
state.
[0019] FIG. 10 is a graph showing Raman spectrum of an emission tip
of the CNT needle of FIG. 1.
[0020] Corresponding reference characters indicate corresponding
parts throughout the several views. The exemplifications set out
herein illustrate at least one embodiment of the present method, in
one form, and such exemplifications are not to be construed as
limiting the scope of the invention in any manner.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0021] References will now be made to the drawings to describe the
exemplary embodiments of the present CNT needle and the method for
manufacturing the CNT needle, in detail.
[0022] Referring to FIG. 1, the CNT needle 10 is composed of a CNT
string. Each CNT string includes a plurality of continuously
oriented and substantially parallel CNTs joined end-to-end by van
der Waals attractive force. A diameter of the CNT needle 10
approximately ranges from 1 to 20 microns, and a length thereof
ranges from 0.01 to 1 millimeters. The CNT needle 12 includes an
end portion 122 and a broken end portion 124. Referring to FIGS. 2
and 3, the CNTs at the broken end portion 124 form a similar
tapered-shaped structure. One CNT 126 protrudes from the adjacent
CNTs to form a tip 128 of the CNT needle 10. The CNT 126 protrudes
from the adjacent CNTs about 5 nanometers to 50 nanometers. The
CNTs at the broken end portion 124 have smaller diameters and a
fewer number of walls, typically, less than 5 nanometers (nm) in
diameter and have less than 2-3 walls. However, the CNTs 126 in the
CNT needle 10 other than the broken end portion 124 includes
single-walled CNTs, double-walled CNTs, or multi-walled CNTs.
Diameters of the single-walled CNTs, the double-walled CNTs, and
the multi-walled CNTs can, respectively, be in an approximate range
from 0.5 to 50 nanometers, 1 to 50 nanometers, and 1.5 to 50
nanometers.
[0023] Referring to FIG. 4 and FIG. 6, a method for manufacturing
the CNT needle 10 includes the following steps: (a) providing a CNT
film having a plurality of CNTs therein, the CNTs being aligned
along a same direction, a first electrode 22 and a second electrode
24 (b) fixing the two opposite sides of the CNT film on the first
electrode 22 and the second electrode 22 respectively, the CNTs in
the CNT film extending from the first electrode 22 to the second
electrode 24; (c) treating the CNT film with an organic solvent to
form a plurality of CNT strings 28; and (d) applying a voltage
between two opposite ends of the CNT strings via the first
electrode and the second electrode, until the CNT strings
snap/break at a certain points thereof, to achieve a number of CNT
needles 10.
[0024] In step (a), the CNT film is formed by the following
substeps: (a1) providing a CNT array; and (a2) pulling out a CNT
film from the array of CNTs, by using a tool (e.g., adhesive tape,
pliers, tweezers, or another tool allowing multiple CNTs to be
gripped and pulled simultaneously).
[0025] In step (a1), initially, a substrate is provided, and the
substrate is a P-type silicon or N-type silicon substrate.
Secondly, a catalyst layer is deposited on the substrate. The
catalyst layer is made of a material selected from a group
consisting of iron (Fe), cobalt (Co), nickel (Ni), and their
alloys. Thirdly, the substrate with the catalyst layer is annealed
at a temperature approximately ranging from 700 to 900 degrees
centigrade (.degree. C.) under a protecting gas for approximately
30 minutes to 90 minutes. Fourthly, the substrate with the catalyst
layer is heated to a temperature approximately ranging from
500.degree. C. to 740.degree. C. and a mixed gas including a carbon
containing gas and a protecting gas is introduced for approximately
5 to 30 minutes to grow a super-aligned CNTs array. The carbon
containing gas is a hydrocarbon gas, such as acetylene or ethane.
The protecting gas is an inert gas. The grown CNTs are aligned in
columns parallel to each other and held together by van der Waals
force interactions therebetween. The CNTs array has a high density
and each of the CNTs has an essentially uniform diameter.
[0026] In step (a2), the CNT film can be formed by the substeps of:
(a21) selecting one or more CNTs having a predetermined width from
the super-aligned array of CNTs; and (a22) pulling the CNTs to from
nanotube segments at an even/uniform speed to achieve a uniform CNT
film. In step (a21), the CNT segment having a predetermined width
includes a plurality of CNTs parallel to each other. The CNT
segment is gripped by using an adhesive tape such as the tool to
contact the super-aligned array. In step (a22), the pulling
direction is substantially perpendicular to the growing direction
of the super-aligned array of CNTs.
[0027] More specifically, during the pulling process, as the
initial CNT segments are drawn out, other CNT segments are also
drawn out end to end due to van der Waals attractive force between
ends of adjacent segments. This process of drawing ensures a
substantially continuous and uniform CNT film having a
predetermined width can be formed. The CNT film includes a
plurality of CNTs joined ends to ends. The CNTs in the CNT film are
all substantially parallel to the pulling/drawing direction of the
CNT film, and the CNT film produced in such manner can be
selectively formed to have a predetermined width. The CNT film
formed by the pulling/drawing method has superior uniformity of
thickness and conductivity over a typical disordered CNT film.
Further, the pulling/drawing method is simple, fast, and suitable
for industrial applications.
[0028] The width of the CNT film depends on a size of the CNT
array. The length of the CNT film can be arbitrarily set, as
desired. In one useful embodiment, when the substrate is a 4-inch
P-type silicon wafer as in the present embodiment, the width of the
CNT film is in an approximate range from 0.01 centimeter to 10
centimeters, and the thickness of the CNT film is in an approximate
range from 0.5 nanometers to 100 microns. The CNTs in the CNT film
includes single-walled CNTs, double-walled CNTs, or multi-walled
CNTs. Diameters of the single-walled CNTs, the double-walled CNTs,
and the multi-walled CNTs can, respectively, be in an approximate
range from 0.5 to 50 nanometers, 1 to 50 nanometers, and 1.5 to 50
nanometers.
[0029] In step (b), the first electrode and the second electrode
are separated from each other. A distance between the first
electrode and the second electrode ranges from 50 micrometers to 1
millimeter. The CNT film is suspended between the first electrode
and the second electrode and tensioned thereby.
[0030] Referring to FIG. 5, step (c) can be executed by putting the
organic solvent onto the CNT film or putting the CNT film with the
first electrode and the second electrode in the organic solvent to
soak the entire surfaces of the CNT film. Since the untreated CNT
film is composed of a number of the CNTs, the untreated CNT film
has a high surface-area-to-volume ratio and, thus, may easily
become stuck to other objects. During the surface treatment, the
impending CNT film is shrunk into a plurality of CNT strings after
the organic solvent volatilizing, due to factors such as surface
tension. The CNT string includes a plurality of CNTs, the CNTs
being aligned along a same direction. The surface area to volume
ratio is reduced. Accordingly, the stickiness of the CNT film is
lowered, and strength and toughness of the CNT string is improved.
The organic solvent may be a volatilizable organic solvent, such as
ethanol, methanol, acetone, dichloroethane, chloroform, or any
appropriate mixture thereof.
[0031] Referring to FIGS. 6, 7 and 8, the step (d) includes the
following substeps: (d1) placing the CNT strings, along with the
first electrode 22 connected to the second electrode 24 in a
chamber 20; (d2) applying a voltage between two opposite ends of
the CNT strings 28 via the first electrode 22 and the second
electrode 24 of such a magnitude and/or time to cause the CNT
strings 28 to snap. The strings snap at a middle point along an
axis thereof and, thus, acquiring two CNT needles 10 for each
string.
[0032] In step (d1), the chamber 20 is a vacuum or filled with an
inert gas. A diameter of the CNT string 28 approximately ranges
from 1 to 20 micrometers, and a length thereof approximately ranges
from 0.05 millimeters to 1 millimeter. In the present embodiment,
the vacuum chamber 20 can be a vacuum and the pressure thereof is
lower than 1.times.10.sup.-1 Pascal (Pa).
[0033] In step (d2), the voltage can be set according to a diameter
and/or a length of the CNT strings 28. In the present embodiment,
when a length of the CNT string 28 is 300 .mu.m and a diameter
thereof is 2 .mu.m, the voltage is 40 volts (V). A vacuum of the
chamber 20 is less than 2.times.10.sup.-5 Pascal (Pa). In the
present embodiment, vacuum of the chamber 20 is 2.times.10.sup.-5
Pa.
[0034] Referring to FIG. 9, in step (d2), a temperature of the CNT
string 28 increases due to Joule-heating, and the CNT string 28 can
reach a temperature approximately ranging from 2000 to 2400 Kelvin
(K). When the temperature of the CNT string 28 is high enough, the
CNT string 28 is in an incandescent state. Heat in the CNT string
28 is transmitted from the CNT to the electrodes. Since the middle
point of the CNT string is furthest from the electrodes, the
temperature thereof is highest, and then the CNT string 28 is
broken at the middle point. In the present embodiment, after less
than 1 hour, the CNT string 28 is snapped at the middle point.
[0035] Referring to FIG. 8, the CNT string 28 breaks at the middle
point to form two CNT needles 10. Each CNT needle 10 includes an
end portion and an opposite broken end portion. The end portion is
fixed on the first electrode or the second electrode. Each CNT
needle 10 is composed of well-aligned and firmly compacted CNTs.
Referring to FIGS. 2 and 3, the CNTs at the broken end portion 124
have a tapered-shaped structure, i.e., one CNT protruding and
higher than the adjacent CNTs. That is because during snapping,
some carbon atoms vaporize from the CNT string 12. After snapping,
a micro-fissure (not labeled) is formed between two break-end
portions, the arc discharge may occur between the micro-fissure,
and then carbon atoms transform into carbon ions due to ionization.
These carbon ions bombard/etch the break-end portions, and then the
break-end portion 124 forms the taper-shaped structure.
[0036] The CNTs at the broken end portion have smaller diameters
and a fewer number of walls, typically in the present embodiment,
less than 5 nanometers in diameter and only about 2-3 walls.
However, the CNTs away from the break-end portion are about 15 nm
in diameter and have more than 5 walls. The diameter and the number
of the walls of the CNTs are decreased in the vacuum breakdown
process. A wall-by-wall breakdown of CNTs is due to Joule-heating
at a temperature higher than 2000K, with a current decrease
process. The high-temperature process can efficiently remove the
defects in CNTs and, consequently, improve electric and thermal
conductivities and mechanical strength thereof. FIG. 10 shows a
Raman spectrum of the break-end portion 124. After snapping, the
intensity of D-band (defect mode) at 1580 cm.sup.-1 is reduced,
which indicates the structure effects at the break-end portion 124
are effectively removed.
[0037] It is to be understood that the above-described embodiments
are intended to illustrate rather than limit the invention.
Variations may be made to the embodiments without departing from
the spirit of the invention as claimed. The above-described
embodiments illustrate the scope of the invention but do not
restrict the scope of the invention.
[0038] It is also to be understood that above description and the
claims drawn to a method may include some indication in reference
to certain steps. However, the indication used is only to be viewed
for identification purposes and not as a suggestion as to an order
for the steps.
* * * * *