U.S. patent application number 11/375743 was filed with the patent office on 2010-05-13 for processes for growing carbon nanotubes in the absence of catalysts.
Invention is credited to Gillian Althea Maria Reynolds, David Herbert Roach.
Application Number | 20100119435 11/375743 |
Document ID | / |
Family ID | 42165375 |
Filed Date | 2010-05-13 |
United States Patent
Application |
20100119435 |
Kind Code |
A1 |
Roach; David Herbert ; et
al. |
May 13, 2010 |
Processes for growing carbon nanotubes in the absence of
catalysts
Abstract
Processes for increasing the production rate of single-wall
carbon nanotubes using a disordered carbon target are disclosed.
The processes use a disordered carbon target and include
vaporization of the target in the presence of a non-oxidizing gas.
The single-wall nanotubes produced can be incorporated into
electronic devices such as diodes and transistors.
Inventors: |
Roach; David Herbert;
(Hockessin, DE) ; Reynolds; Gillian Althea Maria;
(Wilmington, DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1122B, 4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
42165375 |
Appl. No.: |
11/375743 |
Filed: |
March 15, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60661974 |
Mar 15, 2005 |
|
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|
Current U.S.
Class: |
423/447.2 ;
423/447.1; 977/750; 977/844 |
Current CPC
Class: |
D01F 9/12 20130101 |
Class at
Publication: |
423/447.2 ;
423/447.1; 977/750; 977/844 |
International
Class: |
D01F 9/12 20060101
D01F009/12 |
Claims
1-8. (canceled)
9. A process for making a single wall carbon nanotube comprising
(a) providing a target having a density of 0.01 to 2 g/cm.sup.3
comprising disordered carbon and a metal catalyst, wherein the
disordered carbon consists essentially of carbon black, and wherein
the disordered carbon has a density of less than 2.2 g/cm.sup.3;
(b) laser ablating the target at a temperature of between about
900.degree. C. and 1500.degree. C. and at a pressure of about
10.sup.-3 Torr to about 10.sup.+3 Torr in the presence of a
non-oxidizing gas; and (c) forming a product comprising at least
one single-wall carbon nanotube.
10. The process of claim 9 wherein the pressure is about 300 Torr
to about 600 Torr.
11. The process of claim 9 wherein the temperature is about
1000.degree. C. to about 1300.degree. C.
12. The process of claim 9 wherein the non-oxidizing gas is
selected from the group consisting of argon, neon, helium, nitrogen
and mixtures thereof.
13. A single-wall carbon nanotube produced by the process of claim
9.
14. The process of claim 9 wherein the catalytic metal comprises
yttrium.
15. The process of claim 9 further comprising a step of subjecting
a product comprising at least one single-wall carbon nanotube to
additional cycles of vaporization and single-wall carbon nanotube
formation.
16. The process of claim 9 further comprising a step of annealing
the product.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to processes for single-wall
carbon nanotube production. By using a disordered carbon target,
the processes can provide increased production rates as compared to
known processes.
BACKGROUND OF THE INVENTION
[0002] In the field of molecular nanoelectronics, few materials
show as much promise as nanotubes, and in particular carbon
nanotubes, which comprise hollow cylinders of graphite. Nanotubes
can be incorporated into electronic devices such as diodes and
transistors, depending on the nanotube's electrical
characteristics. Nanotubes are unique for their size, shape, and
physical properties. Structurally, a carbon-nanotube resembles a
hexagonal lattice of carbon rolled into a cylinder.
[0003] Besides exhibiting intriguing quantum behaviors at low
temperature, carbon nanotubes exhibit the following important
characteristics: a nanotube can be either metallic or semiconductor
depending on its chirality (i.e., conformational geometry).
Metallic nanotubes can carry extremely large current densities.
Semiconducting nanotubes can be electrically switched on and off as
field-effect transistors (FETs). The two types may be covalently
joined (sharing electrons). These characteristics point to
nanotubes as excellent materials for making nanometer-sized
semiconductor circuits.
[0004] Nanotubes can be formed as single-wall carbon nanotubes
(SWNTs) or multi-wall carbon nanotubes (MWNTs). SWNTs can be
produced, for example, by arc-discharge and laser ablation of a
carbon target. Local growth of tubes on a surface can also be
obtained by chemical vapor deposition (CVD). The growth of the
nanotubes is made possible by the presence of metallic particles,
such as Co, Fe, and/or Ni, acting as catalyst. The resultant carbon
nanotubes typically contain contaminants, e.g., catalyst particles.
For some potential nanotube applications the use of clean nanotubes
can be important, such as, for example, where nanotubes are
incorporated as an active part of electric devices. The presence of
contaminating atoms and particles can alter the electrical
properties of the nanotubes. The metallic particles can be removed;
however the process of cleaning or purifying the nanotubes can be
complicated and can alter the quality of the nanotubes.
[0005] U.S. patent application Ser. No. 2004/0035355 discloses a
method for growing single-wall nanotubes comprising providing a
silicon carbide semiconductor wafer comprising a silicon face and a
carbon face, and annealing the silicon carbide semiconductor wafer
in a vacuum at a temperature of at least about 1,350.degree. C.,
thereby inducing formation of single-wall carbon nanotubes on the
silicon face. The disclosed process is carried out at 10.sup.-9
Torr, which is not generally conducive to high material production
rates.
[0006] SWNTs have been identified as potential components of
electronic devices in varied applications. Therefore, a need exists
for new and/or improved processes for growing single-wall carbon
nanotubes.
SUMMARY OF THE INVENTION
[0007] One aspect of the present invention is a process
comprising:
[0008] a) providing a target comprising disordered carbon and a
metal catalyst, wherein the carbon target has a density of 0.01 to
2 gm/cm.sup.3;
[0009] b) vaporizing the target at a temperature from about
900.degree. C. to about 1500.degree. C. and at a pressure from
about 10.sup.-3 Torr to about 10.sup.+3 Torr in the presence of a
non-oxidizing gas; and
[0010] c) forming a product comprising at least one single-wall
carbon nanotube.
[0011] In some preferred embodiments, the target comprises about 10
weight percent or less of the metal catalyst.
[0012] Another aspect of the present invention is a single-wall
carbon nanotube made by a process comprising:
[0013] a) providing a target comprising disordered carbon and a
metal catalyst, wherein the carbon target has a density of 0.01 to
2 gm/cm.sup.3;
[0014] b) vaporizing the target at a temperature from about
900.degree. C. to about 1500.degree. C. and at a pressure from
about 10.sup.-3 Torr to about 10.sup.+3 Torr in the presence of a
non-oxidizing gas; and
[0015] c) forming a product comprising at least one single-wall
carbon nanotube.
[0016] These and other aspects of the present invention will be
apparent to those skilled in the art, in view of the following
description and the appended claims.
BRIEF DESCRIPTION OF THE DRAWING
[0017] FIG. 1 shows the production rate as a function of target
density according to an embodiment of present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0018] All documents cited herein are expressly incorporated herein
by reference in their entirety. Applicants also incorporate herein
by reference the co-owned and concurrently filed application
entitled "PROCESSES FOR GROWING CARBON NANOTUBES IN THE ABSENCE OF
CATALYSTS". (Attorney Docket # CL 2626).
[0019] When an amount, concentration, or other value or parameter
is given as either a range, preferred range, or a list of upper
preferable values and lower preferable values, this is to be
understood as specifically disclosing all ranges formed from any
pair of any upper range limit or preferred value and any lower
range limit or preferred value, regardless of whether ranges are
separately disclosed. Where a range of numerical values is recited
herein, unless otherwise stated, the range is intended to include
the endpoints thereof, and all integers and fractions within the
range. It is not intended that the scope of the invention be
limited to the specific values recited when defining a range.
[0020] The present invention provides processes for producing
single-wall carbon nanotubes (SWNT). In preferred embodiments, the
processes provide increased rates of production of single-wall
carbon nanotubes. It has been found that the use of a relatively
lower density carbon target (sometimes referred to as "softer"
carbon target, e.g., about 2.2 g/cm.sup.3 or less) can provide
increased rates of production of nanotubes as compared with known
methods such as conventional laser ablation of graphite, arc
discharge, chemical vapor deposition, and high pressure carbon
monoxide techniques. As examples only, using a target having a
density of 1.6 g/cm.sup.3, it has been observed that the rate of
production of nanotubes was from about 0.1 to 0.5 grams per hour,
and with a density of 0.9 g/cm.sup.3, the rate observed was about
1.2-1.5 g/hour. It is not intended that the invention be limited by
these recited rates, as variations in the process within the scope
of the invention, which may be made by one skilled in the art, can
result in varied rates of production of nanotubes.
[0021] In highly preferred embodiments, the processes include
providing a target that is a mixture of a metal catalyst and
disordered carbon. Suitable metal catalysts include yttrium, iron;
nickel and cobalt and combinations thereof. By "disordered carbon"
is meant a carbon material having a density less than 2.2
g/cm.sup.3. Forming the target can be accomplished, for example, by
forming a mixture of catalyst, carbon and a graphite cement in a
volatile solvent, allowing the solvent to evaporate, then
compression molding the residual solid. The target thus can have a
density of 0.01 to 2 gm/cm.sup.3. The compression-molded article
can be optionally heated, preferably in an inert atmosphere, to
substantially remove traces of the solvent.
[0022] Vaporization of the target can be carried out by laser
ablation or other suitable methods, such as, for example, radio
frequency induction heating and sputtering. The vaporization can be
carried out at temperatures between about 900.degree. C. and
1500.degree. C., preferably from about 1000.degree. C. to about
1300.degree. C. Also, the vaporization can be carried out at a
pressure of about 10.sup.-3 Torr to about 10.sup.+3 Torr,
preferably from about 300 Torr to 600 Torr. The vaporization is
carried out in the presence of a non-oxidizing gas, such as argon,
neon, helium, nitrogen or mixtures thereof. It is generally
desirable to grow the tubes at pressures preferably 1 millitor or
higher, and more preferably at 500 Torr or higher. In some
preferred embodiments, the pressure is about 1000 Torr. It is
generally not desirable that the pressure be greater than about
1000 Torr. Although a reduction in pressure below about 500 Torr
has not been observed to undesirably affect the rate of growth of
nanotubes, pressures of about 500 Torr or greater are often
practical.
[0023] In one embodiment of this invention, the SWNT-containing
product can serve as a target for one or more additional cycles of
vaporization and SWNT-formation.
[0024] The process can further include an annealing step. The
annealing can be performed in an ultra-high vacuum (UHV) (e.g., at
a pressure less than about 10.sup.-9 Torr), or at higher pressures,
even above atmospheric pressure (760 Torr).
[0025] According to an embodiment of the present invention,
vaporizing the disordered carbon target can induce the growth of
SWNTs. The vaporizing can be performed under reduced pressure
(e.g., at a pressure of about 300-600 Torr) in non-oxidizing
conditions and at temperatures between about 900.degree. C. and
1500.degree. C. The process produces nanotubes, which are
preferably predominately SWNTs. The SWNTs can be very long and have
a good crystalline quality. "Good crystalline quality" means
substantially free of observable defects. By further increasing the
extent of carbon disorder, which is reflected in a decrease in the
density, the production rate of SWNTs can be increased. All of the
compositions and processes disclosed and claimed herein can be made
and executed without undue experimentation in light of the present
disclosure. While the compositions and processes of this invention
have been described in terms of preferred embodiments, it will be
apparent to those of skill in the art that variations can be
applied to the compositions and processes and in the steps or in
the sequence of steps of the method described herein without
departing from the concept, spirit, and scope of the invention. All
such substitution and modifications apparent to those skilled in
the art are deemed to be within the spirit, scope, and concept of
the invention as defined by the appended claims.
EXAMPLES
[0026] These Examples show the effects of the amount of disorder of
the carbon target on the nanotube production rate.
Example 1
[0027] Carbon black powder (66 grams (g), Alfa Aesar, Ward Hill,
Mass.), nickel metal catalyst powder (7.56 g, 2.2-3 .mu.m stock #
10255, Alfa Aesar, Ward Hill, Mass.), cobalt metal catalyst powder
(7.56 g, 1.6 .mu.m stock # 10455, Alfa Aesar, Ward Hill, Mass.),
and Dylon.RTM. graphite cement (grade C, 94.12 g, Dylan Industries,
Inc., Cleveland, Ohio) were incorporated into a homogeneous mixture
using 260 mL of methanol. The mixture was allowed to dry and then
was broken up. The mixture as made provides targets with a high
level of disorder and a density of 0.93 g/cm.sup.3. A portion of
this mixture was placed into a stainless steel die (3.18 cm
diameter by 7.62 cm high). The die was placed in a press and heated
to 130.degree. C. Force up to 40034 Newtons was then applied for 1
hour. The die was allowed to cool before the target was removed.
The targets were then heated in an Ar atmosphere to 1150.degree. C.
The targets were then placed in a non-oxidizing atmosphere of Ar at
500 Torr, heated to 1100.degree. C. and ablated with two Nd:YAG
lasers operating at 1064 nm and 30 Hz. A felt-like material
containing single-wall carbon nanotubes was formed and collected
downstream in a cool zone. This felt-like material was generated at
a rate of 1.3 g/hr.
Example 2
[0028] The target preparation described in Example 1 was repeated
using 187.2 g of Dylan.RTM. graphite cement, 7.56 g of nickel
catalyst powder, 7.56 g of cobalt metal catalyst powder, and 50 mL
of methanol. The mixture as made provided targets with a density of
1.4 g/cm.sup.3 and less disorder than the targets of Example 1. A
portion of this mixture was placed into a stainless steel die (3.18
cm diameter by 7.62 cm high). The die was placed in a press and
heated to 130.degree. C. Force of 40034 Newtons was then applied
for 1 hour. The die was allowed to cool before the target was
removed. The targets were then heated in an Ar atmosphere to
1150.degree. C. The targets were then placed in an atmosphere of Ar
at 500 Torr, heated to 1100.degree. C., and ablated with two Nd:YAG
lasers operating at 1064 nm and 30 Hz. A felt-like material
containing nanotubes was formed and collected downstream in a cool
zone. The felt-like material was generated at a rate of 0.9 g/hour.
This production rate was lower than that obtained with the targets
of 0.93 g/cm.sup.3 density of Example 1.
Example 3
[0029] The target preparation described in Example 1 was repeated
using 94.12 g of Dylon.RTM. graphite cement, 7.56 g of nickel
catalyst powder, 7.56 g of cobalt metal catalyst powder, 66 g of
graphite powder (grade UCP-1-M, Carbone of America, Ultra Carbon
Division, Bay City, Mich.), and 130 mL of methanol. The mixture as
made provides targets with a density of 1.6 g/cm.sup.3 and even
less disorder than the targets of Examples 1 and 2. A portion of
this mixture was placed into a stainless steel die (3.18 cm
diameter by 7.62 cm high). The die was placed in a press and heated
to 130.degree. C. Force up to 40034 Newtons was then applied for 1
h. The die was allowed to cool before the target was removed. The
targets were then heated in an Ar atmosphere to 1150.degree. C. The
targets were then placed in an atmosphere of Ar at 500 Torr, heated
to 1100.degree. C. and ablated with two Nd:YAG lasers operating at
1064 nm and 30 Hz. A felt-like material containing nanotubes was
formed and collected downstream in a cool zone. The felt-like
material was generated at a rate of 0.4 g/hour. This production
rate was lower than that achieved with the targets of 0.93
g/cm.sup.3 or 1.4 g/cm.sup.3 density of Examples 1 and 2.
* * * * *