U.S. patent application number 13/307510 was filed with the patent office on 2012-11-29 for templated growth of graphenic materials.
This patent application is currently assigned to CxNanophysics, LLC. Invention is credited to Nolan Nicholas.
Application Number | 20120301625 13/307510 |
Document ID | / |
Family ID | 40508671 |
Filed Date | 2012-11-29 |
United States Patent
Application |
20120301625 |
Kind Code |
A1 |
Nicholas; Nolan |
November 29, 2012 |
TEMPLATED GROWTH OF GRAPHENIC MATERIALS
Abstract
A method is disclosed for producing graphenic materials by
templated growth along a preformed graphenic material lattice edge,
wherein at least one of the graphenic material or template is
translated during growth of the graphenic material. A method for
preparing CNTs from preformed CNT substrates in the presence of
cylindrical templating structures and a reactive carbon source in a
fluid phase is also disclosed, wherein at least one of the CNT
substrate or the cylindrical templating structure is translated
during addition of carbon atoms to the CNT substrate. A method is
also disclosed for preparing CNTs from preformed CNT substrates in
the presence of cylindrical templating structures and a carbon
source in a fluid phase, wherein non-thermalized excited states are
produced on the CNT substrate and at least one of the CNT substrate
or the cylindrical templating structure is translated during
addition of carbon atoms to the CNT substrate.
Inventors: |
Nicholas; Nolan; (S.
Charleston, WV) |
Assignee: |
CxNanophysics, LLC
South Charleston
WV
|
Family ID: |
40508671 |
Appl. No.: |
13/307510 |
Filed: |
November 30, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12135914 |
Jun 9, 2008 |
8088434 |
|
|
13307510 |
|
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60943041 |
Jun 9, 2007 |
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Current U.S.
Class: |
427/457 ;
427/282; 977/842 |
Current CPC
Class: |
C01B 32/16 20170801;
B82Y 30/00 20130101; C30B 29/02 20130101; C30B 29/602 20130101;
B82Y 40/00 20130101 |
Class at
Publication: |
427/457 ;
427/282; 977/842 |
International
Class: |
B05D 5/00 20060101
B05D005/00 |
Claims
1. A method for production of a structured material, comprising
placing a preformed substrate in contact with a templating
structure; providing a reactive source of atoms from a fluid phase;
depositing atoms from the fluid phase to the preformed substrate;
and translating at least one of the preformed substrate and the
templating structure during the depositing, while maintaining the
contact, so as to grow the preformed substrate in to the structured
material.
2. The method of claim 1, wherein the structured material comprises
a graphenic material.
3. A method for production of a CNT, comprising placing a preformed
CNT substrate open on at least one end in contact with a
cylindrical templating structure; providing a reactive source of
carbon in a fluid phase; depositing carbon from the fluid phase to
the open end of said CNT substrate; and, translating at least one
of said CNT substrate and said cylindrical templating structure
during the depositing, while maintaining the contact.
4. The method of claim 3, wherein the cylindrical templating
structure contacts the exterior of the CNT substrate.
5. The method of claim 4, wherein (a) the open end of the CNT
substrate lies within the interior of the external templating
structure, (b) the open end of the CNT substrate is bonded to a
nanoparticle, and (c) the end of the CNT opposite that bonded to
the nanoparticle is attached to an inert support.
6. The method of claim 3, wherein at least one metal atom selected
from the group consisting of periodic table Groups 3-12, the
lanthanide elements, and combinations thereof is bonded to the open
end of the CNT substrate.
7. The method of claim 6, wherein the metal atoms are attached to
the CNT lattice edge by electrochemical deposition.
8. The method of claim 3, wherein an electric potential is applied
to the CNT substrate.
9. The method of claim 8, wherein the template structure has a
lower electrical conductivity than the tip of the growing CNT
substrate.
10. The method of claim 3, wherein a position-controlling structure
contacts the exterior of each CNT substrate as it is
translated.
11. The method of claim 10, wherein positional control of a CNT
substrate is achieved by steps comprised of (a) positioning a wall
structure completely penetrated by a SWCNT conduit between the
inert support anchor point of the CNT substrate and the CNT
substrate lattice edge, wherein (a1) a CNT substrate penetrates the
wall structure, each through the interior of a SWCNT conduit, (a2)
said SWCNT conduits are larger than the CNT substrate they contain
by at least one graphite lattice unit spacing, and (a3) the inert
support is capable of translational motion; (b) growing the CNT
substrate via templated growth from a fluid phase carbon source;
and (c) translating the grown CNT substrate through a SWCNT
conduit.
12. The method of claim 11, wherein translation of the grown CNT
substrate is achieved through a spooling motion.
13. The method of claim 3, wherein a CNT simultaneously functions
as a growth substrate and template.
14. A method for production of a CNT, comprising placing a
preformed CNT substrate open on at least one end in contact with a
cylindrical templating structure, wherein said CNT substrate
contacts said cylindrical templating structure within thermal
variation, and aligns with said cylindrical templating structure in
a coaxial fashion within thermal variation.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/135,914 filed Jun. 9, 2008 which claims
benefit and priority of U.S. patent application Ser. No. 60/943,041
filed Jun. 9, 2007, which is hereby incorporated by reference as if
written herein in its entirety.
BACKGROUND
[0002] Carbon nanotubes (CNTs) are an allotrope of carbon having an
exceedingly long length-to-diameter ratio. These cylindrical carbon
molecules possess novel properties, including exceptional strength
and unique electrical properties, making them of substantial
interest for applications in diverse fields of nanotechnology,
electronic devices, optical devices and materials science.
Inorganic nanotubes are also known. Efficient methods for
production of CNTs is therefore an area of intense research.
[0003] A number of techniques are available for synthesizing CNTs.
Many methods for synthesizing CNTs produce mixtures of multi-walled
carbon nanotubes (MWCNTs) and SWCNTs. For CNTs to be optimally
utilized, methods for efficient production of SWCNTs having
controlled properties, such as length, diameter, chirality, and
number of walls are desired. Further, efficient methods are desired
to manipulate synthesized CNTs into multi-nanotube arrays with
controlled placement of the CNTs, which may be used in electronic,
optical and mechanical applications, such as electronic
devices.
SUMMARY
[0004] In the most general sense, the embodiments disclosed herein
relate to a method for producing a structured material through a
process comprised by 1) placing a preformed graphenic material
substrate into contact with a templating structure, 2) providing a
reactive source of atoms from a fluid phase, 3) depositing atoms
from the fluid phase to the preformed substrate and 4) translating
at least one of the preformed substrate and the templating
structure during the depositing, while maintaining the contact, so
as to grow the preformed substrate in to the structured
material.
[0005] In one aspect, the embodiments disclosed herein relate to a
method for producing a CNT, through a process comprised by 1)
placing a preformed CNT substrate open on at least one end into
proximity of a cylindrical templating structure, such that the CNT
substrate contacts the templating structure and aligns with the
templating structure in a coaxial fashion within thermal variation,
2) binding a CNT substrate and templating structure to separate
inert supports capable of independent translation, 3) providing a
reactive carbon source in a fluid phase, and 4) depositing carbon
from the fluid phase to the open end of a CNT substrate, wherein at
least one of the CNT substrate or templating structure is
translated during the depositing.
[0006] In another aspect, the embodiments disclosed herein relate
to a method for producing a CNT, through a process comprised by 1)
placing a preformed CNT substrate open on at least one end into
proximity of a cylindrical templating structure, such that the CNT
substrate contacts the templating structure and aligns with the
templating structure in a coaxial fashion within thermal variation,
2) binding a CNT substrate and templating structure to separate
inert supports capable of independent translation, 3) producing
non-thermalized excited states in a CNT substrate lattice edge, and
4) depositing carbon from a fluid phase to the open end of a CNT
substrate, wherein at least one of the CNT substrate or templating
structure is translated during addition of carbon to the CNT
substrate.
[0007] The foregoing has outlined rather broadly the features of
the present disclosure in order that the detailed description that
follows may be better understood. Additional features and
advantages will be described hereinafter which form the subject of
the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] For a more complete understanding of the present disclosure,
and the advantages thereof, reference is now made to the following
descriptions to be taken in conjunction with the accompanying
drawings, in which:
[0009] FIG. 1 shows an embodiment of the co-axial arrangement of an
inert templating structure and CNT substrate in the present
disclosure.
[0010] FIG. 2 shows an embodiment of a winding mechanism in the
present disclosure used to translate the CNT substrate.
[0011] FIG. 3 demonstrates an embodiment of a method whereby an
array of CNT seeds can be produced from a single CNT of known type
as described in the present disclosure.
[0012] FIG. 4 shows an alternative embodiment for arraying CNTs in
the present disclosure, whereby an array of CNT seeds is prepared
on the surface of a spooling mechanism from a single CNT.
[0013] FIG. 5 shows an embodiment of self-regulated growth of CNTs
under electrochemical deposition conditions.
[0014] FIG. 6 shows an embodiment of a CNT positional control
system.
[0015] FIG. 7 shows an embodiment whereby multiple coaxial CNTs can
be grown simultaneously to form a beveled CNT tip.
DETAILED DESCRIPTION
[0016] In the following description, certain details are set forth,
such as specific quantities and sizes, to provide a thorough
understanding of embodiments disclosed herein. However, it will be
understood by those skilled in the art that the present disclosure
may be practiced without such specific limitations. In many cases,
details concerning such considerations and the like have been
omitted inasmuch as such details are not necessary to obtain a
complete understanding of the present disclosure and are within the
skills of persons of ordinary skill in the relevant art.
[0017] The present disclosure generally relates to a method for
providing templated growth of structured materials, which may
include a graphenic material. The templated growth may be along
pre-existing graphenic material lattice edges under influence of a
templating structure. Graphenic materials are formed from one or
more graphene sheets and demonstrate comparable chemical reactivity
to graphene. Graphenic material lattices may include both
substitutional and interstitial atoms. In the present disclosure, a
preformed graphenic substrate and a templating structure are
brought into proximity of one another, such that the preformed
graphenic substrate and templating structure are in contact. The
contact may be a reduced energy contact, wherein the contacted
system is reduced in energy compared to the two separated bodies. A
reactive source of atoms is provided in a fluid phase, and atoms
are deposited to the graphenic substrate from the fluid phase under
influence of the templating structure, while at least one of the
preformed graphenic substrate and templating structure is
translated during the depositing. Deposition may occur at a lattice
edge of the substrate. The reactive source of reactive atoms may be
provided as either a monoatomic or polyatomic chemical species.
Translation is embodied as either a linear motion or a spooling
motion where the graphenic material is wound on to a spool as it is
grown. The method may also be practiced wherein more than one
preformed graphenic substrate and a single templating structure per
preformed graphenic substrate are used to simultaneously grow more
than one new graphenic material. One skilled in the art will
recognize that graphene, graphenic materials, CNTs, and like
structures possess similar chemical reactivity, and the methods of
the present disclosure may be used interchangeably for templated
growth on these entities through minimal modifications of the
disclosure provided herein. Generation of reactive atoms in the
fluid phase may be accomplished herein by several different
methods, the advantages of which for a given application will be
easily recognizable to those of skill in the art.
[0018] When the templated growth of graphenic materials is
practiced as described herein, a number of advantages are realized
for the production of graphenic materials, CNTs, and related
structured materials. CNTs produced by this method may be SWCNTs or
MWCNTs. DWCNTs are exemplary of MWCNTs. Templated growth
accomplishes production of graphenic materials on a pre-existing
substrate, wherein van der Waals and Pauli interactions between the
template structure and the graphenic substrate define the topology
of the graphenic material produced. In particular, production of
CNTs under templated growth conditions allows CNTs to be produced
that are free of lattice defects and maintain the chirality of the
template CNT. Another advantage of the present method is that if
either the templating structure, graphenic substrate, or both are
translated during addition of atoms to the graphenic substrate,
graphenic materials of arbitrary length may be produced from a
fixed length templating structure, provided that the graphenic
substrate maintains contact with the templating structure. The
disclosure herein describes a method to produce CNTs of arbitrary
length from a fixed length templating structure. The CNTs produced
as described herein have their positions defined at two fixed
points, such that the CNTs may be advantageously handled with high
precision through mechanical manipulation methods known to those
having skill in the art. The methods described herein may be
readily conducted in parallel to provide two- and three-dimensional
arrays composed of multiple CNTs.
[0019] While most of the terms used herein will be recognizable to
those having skill in the art, the following definitions are
nevertheless put forth to aid in the understanding of the present
disclosure. It should be understood, however, that when not
explicitly defined, terms should be interpreted as adopting a
meaning presently accepted by those of skill in the art.
[0020] "Graphene," as defined herein, is a single sheet of carbon
atoms covalently bonded in a two-dimensional hexagonal lattice. A
graphene sheet may be viewed as a crystal basal plane bounded by
termination of the crystal at a lattice edge.
[0021] "Graphite," as defined herein, is an ordered collection of
graphene sheets stacked on top of one another to form a crystalline
structure with van der Waals forces interacting between the
graphene sheets and covalent bonding forces interacting within the
graphene sheets. Although this definition is true for perfect
crystals, in reality graphite has a small percentage of covalent
linkages between the graphene sheets.
[0022] "Template or templating structure," as defined herein, is an
entity that determines the geometry of produced graphenic materials
by providing a reduced energy pathway for growth of said graphenic
materials. The interaction of the graphenic lattice and template is
such that no persistent covalent bonding is produced between the
two. Such interaction is achieved through non-covalent forces,
including, but not limited, to van der Waals and Pauli
interactions.
[0023] "Reduced energy contact," as defined herein is the condition
wherein non-covalent forces, including, but not limited to, van der
Waals and Pauli exclusion forces, lead to a local potential minima
as two bodies are brought to an interatomic distance wherein the
potential energy between them is near this minima. In the reduced
energy contact, the contacted system is reduced in energy compared
to the energy of the two separated bodies. The interatomic distance
of the reduced energy contact is defined with respect to a spacing
between nuclei.
[0024] "Array," as defined herein is a two-dimensional or
three-dimensional arrangement of graphenic material structures.
[0025] "Pirhana," as defined herein is a mixture of sulfuric acid
and hydrogen peroxide.
[0026] The graphenic materials in the present disclosure may
constitute graphene, multiple layers of graphene, all-carbon
graphenic materials, non-carbon graphenic materials, and graphenic
materials having both carbon and non-carbon atoms. Graphenic
materials are particularly embodied in one instance by CNTs.
Graphenic materials may be utilized to form graphenic substrates
suitable for templated growth. Graphenic materials may be composed
of hexagonal lattices of carbon. Graphenic materials are
illustrative of substrates herein. It will be understood that other
substrate materials which form hexagonal lattices, such as
two-dimensional boron nitride are contemplated. Further, materials
which form hexagonal lattices mixed with another geometric shape
(e.g a triangular lattice), such as elemental boron, are
contemplated. One skilled in the art will recognize that simple
modifications of the methods described herein may be utilized to
template non-carbon atoms on to all-carbon graphenic substrates or
carbon atoms on to non-carbon graphenic substrates.
[0027] The templating structures in the present disclosure provide
a reduced energy pathway for growth of graphenic materials having
controlled geometrical properties on to a pre-existing graphenic
substrate. The attractive interaction of the graphenic substrate to
the templating structure does not produce persistent covalent
bonding between the two. Intimate physical contact between the
graphenic substrate and the templating structure ensures efficient
transfer of structural features from the templating structure to
the newly produced graphenic material lattice edge, thus
eliminating lattice edge defects and providing the same chirality
to the lattice edge as embodied in the templating structure. The
lack of covalent bonding between the templating structure and
graphenic substrate allows a wide variety of graphenic materials
having known geometry to be produced through simple modifications
of the disclosure provided herein.
[0028] Atoms are added to the graphenic substrate/template
structural interface from a fluid phase, which provides a source of
reactive carbon or like atoms which form graphenic lattices. One
skilled in the art will recognize that the exact chemical mechanism
whereby addition of atoms, in particular carbon atoms, to the
graphenic substrate occurs may differ depending on the chosen fluid
phase atom source. The fluid phase may be a gaseous phase, such as
a vapor phase. The vapor phase entity from which the reactive atom
species arises may be a solid, liquid, or gas in its standard state
at room temperature. The suitability of a particular vapor phase
reactive atom source toward a given application will depend on
conditions specific to the application and be evident to one having
skill in the art. The choice of a particular reactive atom source
for a given application should not be considered limiting when
other reactive atom sources may be utilized within the spirit and
scope of the disclosure.
[0029] The fluid phase may be a carbon-containing gas, wherein
carbon atoms are deposited on to the graphenic substrate by
chemical vapor deposition (CVD). One skilled in the art will
recognize that the gas phase carbon-containing compounds may derive
from gases, liquids, or solids having high vapor pressures, wherein
the reactive carbon atom source is generated from these gas phase
compounds by known methods. Suitable carbon-containing compounds
for generating a gas phase carbon atom source may include, but are
not limited to, at least one member of the group consisting of
methane, ethane, propane, butane, isobutane, ethylene, propene,
1-butene, cis-2-butene, trans-2-butene, isobutylene, acetylene,
propyne, 1-butyne, 2-butyne, benzene, toluene, carbon monoxide,
methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol,
2-methyl-2-propanol, cyclopropane, cyclobutane, acetonitrile,
propionitrile, butyronitrile, acetone, butanone, formaldehyde,
acetaldehyde, propionaldehyde, and butyraldehyde.
[0030] The gas phase carbon atom source may be a molecule in an
excited state, wherein increased reactivity with the graphenic
substrate may be achieved. When the vapor phase contains an excited
state species, the collision rate of the excited state species in
the vapor phase may be selected to be sufficiently low so as to
avoid generation of unwanted reactive species from non-excited
state vapor phase molecules. In some embodiments, the excited state
is a vibrational excited state. In other embodiments, the excited
state is a radical state. Suitable radical states may include, but
are not limited to, C.sub.2H and C.sub.2H.sub.3. In still more
embodiments, the excited state is an excited electronic state. A
representative excited electronic state is non-dissociatively
excited acetylene, which has been excited by electromagnetic
radiation having a wavelength of about 220 nm, although other
excited electronic states can also be utilized within the spirit
and scope of the disclosure. The foregoing list of excited state
species is meant to be representative of excited state entities
suitable for bringing the disclosure to practice and should not be
considered limiting for this purpose. One skilled in the art will
recognize that an energetically excited state species having
suitable reactivity for a given application may be generated by a
number of techniques and utilized equivalently in the spirit and
scope of the methods described herein.
[0031] The fluid phase may also be a carbon-containing liquid.
Suitable carbon-containing liquids include, but are not limited to,
at least one member of the group consisting of benzene, toluene,
xylenes, and like liquids having high carbon content.
[0032] The fluid phase may also be a molten metal containing a
dissolved carbon source, wherein the molten metal pool is in
physical contact with the graphenic substrate. The molten metal
source is selected from at least one metal known to provide
significant solvation for carbon. Said metals may be chosen from
periodic table groups 1-12, the lanthanide elements, and alloys
thereof. In certain embodiments, suitable metals include, but are
not limited to, at least one member of the group consisting of Fe,
Co, Ni, Au, and alloys thereof. Non-metallic elements including,
but not limited to Si and P, may optionally be included in the melt
to modify the effective carbon saturation (reactivity) and
deposition potential. Sulfur and copper are particularly known to
decrease the surface energy of carbon-containing molten metal
melts, and these elements may also optionally be included. One
skilled in the art will recognize that choice of a particular metal
solvent system for a given application will be governed by a number
of factors, including, but not limited to, melting point,
equilibrium solubility of carbon in the molten metal, and
reactivity of the carbon species in the chosen molten metal
solvent. In a molten metal bath, direct solvation of carbon allows
growth of graphenic materials to take place as a quasi-equilibrium
thermodynamic crystal growth process controlled by melt
supersaturation. The level of supersaturation determines the growth
mode from solution in accordance with the Gibbs free energy of
carbon in solution versus carbon bound in a lattice. By maintaining
the carbon level in the molten metal solvent at slightly
supersaturated conditions, growth of graphenic materials from
solution is driven to pre-existing graphenic material lattice edge
sites.
[0033] The dissolved carbon source in the molten metal bath may be
introduced from a vapor phase carbon species in certain instances.
One skilled in the art will recognize that the vapor phase
carbon-containing species may derive from gases, liquids, or solids
having low vapor pressures. Said carbon-containing compounds may
contain at least one additional element besides carbon, which may
include, but not be limited to, the group consisting of hydrogen,
oxygen, sulfur, nitrogen, fluorine, chlorine, bromine, iodine,
silicon and phosphorus. It is well known in the art of
carbon-containing molten metal solutions that the presence of other
atoms in solution may affect the carbon activity and growth mode of
carbon deposition. For example, other elements may reduce the
surface tension of the molten metal bath and lower the interfacial
energy between the metal melt and non-wetting surfaces it contacts.
Sulfur and copper are particularly known to decrease the surface
energy of carbon-containing molten metal melts, and these elements
may optionally be included in the molten metal baths described
herein. Non-metallic elements including, but not limited to Si and
P, may optionally be included in the melt to modify the effective
carbon saturation (reactivity) and deposition potential. Suitable
carbon-containing compounds for generating a vapor phase carbon
source may include, but are not limited to, at least one member of
the group consisting of methane, ethane, propane, butane,
isobutane, ethylene, propene, 1-butene, cis-2-butene,
trans-2-butene, isobutylene, acetylene, propyne, 1-butyne,
2-butyne, benzene, toluene, carbon monoxide, methanol, ethanol,
1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-2-propanol,
cyclopropane, cyclobutane, acetonitrile, propionitrile,
butyronitrile, acetone, butanone, formaldehyde, acetaldehyde,
propionaldehyde, and butyraldehyde.
[0034] The vapor phase may optionally contain an inert diluent gas
in addition to the carbon-containing source, such that the molten
metal bath is exposed concurrently to both the gas phase
carbon-containing compound and inert diluent gas. Suitable diluent
gases may include, but are not limited to, at least one component
selected from the group consisting of helium, argon, and nitrogen.
The vapor phase may optionally contain an etchant component in
addition to the carbon-containing source, such that the molten
metal bath is exposed concurrently to both the gas phase
carbon-containing compound and etchant vapor. In certain cases, it
is desirable that the vapor phase contain both the etchant
component and diluent gas along with the carbon-containing
compound, such that the molten metal bath is concurrently exposed
to all three substances. Suitable etchants include, but are not
limited to, at least one component selected from the group
consisting of water, carbon dioxide, ammonia, and hydrogen.
[0035] In certain embodiments, the carbon source in the molten
metal bath may be a solid carbon source in direct contact with the
bath. Such a carbon source may be dissolved preferentially over the
carbon substrate. Preferential dissolution of the carbon source may
be achieved through various techniques, such as through applied
electrical potentials or by constructing the solid carbon source
from a less energetically stable carbon form, such as amorphous
carbon.
[0036] In certain embodiments, one or more graphenic materials may
be grown concurrently from individual, isolated carbon-containing
molten metal baths.
[0037] One or more metal atoms may be attached to the graphenic
material lattice edge in certain embodiments. In high temperature
gas phase growth of CNTs, some metal atoms are known to function as
effective catalyst species for promoting CNT growth. Bonding of at
least one catalytic metal atom to the graphenic material lattice
edge may likewise enhance chemical reactivity of the graphenic
substrate toward templated growth along the graphenic material
lattice edge. Suitable metal atoms may include, but are not limited
to, at least one member of periodic table groups 3-12, the
lanthanide elements, and combinations thereof. The catalytic metal
atoms may be bound to the graphenic material lattice edge through
methods resulting in a controlled number and density of metal atoms
on the lattice edge.
[0038] In some embodiments, catalytic metal atoms are introduced to
the graphenic material lattice edge by coupling reactions between
mixtures of metal atom bearing species and non-metal bearing
species having comparable reactivity toward reactive groups on the
graphenic material lattice edge. The density of metal atom
incorporation on the graphenic substrate may be controlled simply
by adjusting the ratio of metal-bearing to non-metal bearing
species in the coupling reaction. Suitable metal atom bearing
species may include, but are not limited to, functionalized
metallocenes (eg., ferrocene), metal-EDTA derivatives, and related
organometallic and metal-ligand complexes. Non-metal bearing
species having comparable reactivity to these specific examples may
include the functionalized non-metallated ligand or similar
compound having comparable reactivity toward the reactive groups on
the graphenic material lattice edge. One skilled in the art will
recognize that a wide variety of non-metallated compounds having
like reactive functionality to the functionalized metal bearing
compound may be used to control the density of metal atom
deposition. These competing non-metallated species may bear no
structural resemblance to the metallated species in certain
instances, while still maintaining comparable chemical reactivity
to the parent metal bearing compound. A convenient functional group
for attaching the metal bearing species and their non-metal bearing
counterparts to graphenic material lattice edges is a carboxylic
acid, although other functional groups may be manipulated to couple
with graphenic material lattice edges through methods known to
those skilled in the art. In the instance where the reactive
functional group on the metal-bearing compound is a carboxylic
acid, the metal bearing species may be attached to surface
graphenic material lattice edge OH groups via an esterification
reaction through various coupling reaction methodologies known to
those skilled in the art. The range of reactions utilized to couple
to the graphenic material lattice edge is not limited to
esterifcation, and other coupling strategies including, but not
limited to, alkoxylation and amidation are viable alternatives for
linking metal atoms to the graphenic material lattice edge.
[0039] Ligand binding sites on the graphenic material lattice edge
may be reacted with metal ion solutions having variable
concentration and pH. The ligand binding sites may be pre-existing
in certain embodiments, including, but not limited to, terminal
carboxylic acid moieties at the graphenic material lattice edge. A
suitable ligand may also be synthesized on the graphenic material
lattice edge. One skilled in the art will recognize that certain
metal ion solutions will require pH and reaction temperatures
having values within a defined range to efficiently bind to the
surface ligands. Furthermore, for a given metal salt, a finite
attainable concentration range and chemical compatibility profile
will be realized due to the innate physical properties of the metal
salt.
[0040] An aspect of the present disclosure is the translation of at
least one of the graphenic substrate or templating structure during
addition of carbon or like graphenic atoms to the graphenic
substrate. As practiced herein, the graphenic substrate and
templating structure are bound to inert supports, which are capable
of independent motion and utilized to translate the graphenic
substrate, templating structure, or both, wherein the translation
is coplanar to the growth of the graphenic substrate. In certain
embodiments, the direction of translation is anti-parallel to the
direction of graphenic substrate growth. In some embodiments, the
support to which the graphenic substrate is bound is independently
translated. In other embodiments, the support to which the
templating structure is bound is independently translated. In still
further embodiments, both supports are translated concurrently.
When both supports are translated concurrently, the supports may be
translated either toward one another or away from one another. In
some embodiments, the supports are concurrently translated in
opposite directions. In other embodiments, the supports are
concurrently translated in the same direction. The supports may be
moved linearly or rotated in a spooling motion to affect
translation of the graphenic substrate and templating structure. As
a consequence of the translation capability, graphenic materials
produced through templated growth on the graphenic substrate are
permitted to remain in contact with the templating structure during
addition of atoms to the graphenic substrate, while not damaging
the graphenic material during the translation process due to
minimal sliding friction between the two structures. This
arrangement beneficially allows templating structures of finite
physical dimension to direct the growth of graphenic materials to
an arbitrary length. In certain embodiments wherein the templating
structure, graphenic substrate, or both the templating structure
and graphenic substrate are translated, the rate of translation is
matched by the rate of addition of atoms to the graphenic
substrate. If during addition of atoms to the graphenic substrate,
the rate at which the templating structure and graphenic substrate
are translated apart is too slow, then growth of the graphenic
substrate will eventually contact the inert support to which the
templating structure is bound Likewise, if during addition of atoms
to the graphenic substrate, the rate at which the templating
structure and graphenic substrate are translated apart is too
rapid, then growth of the graphenic material will not keep pace
with the rate of translation, and the graphenic substrate will
eventually become disconnected from the templating structure. In
the embodiment of translation described herein, the direction of
translation is parallel and coplanar to the plane of growth of the
graphenic material. In certain embodiments, the direction of
translation is anti-parallel to the direction of graphenic
substrate growth. In still further embodiments, translation of the
graphenic substrate, templating structure, or both the graphenic
substrate and templating structure is accomplished through a
winding motion, wherein the graphenic material is wound on to a
spool mechanism as it is grown. In certain embodiments, the spool
mechanism may be optionally translated parallel to the axis of
winding at the same time it is wound.
[0041] The rate of carbon atom addition to the graphenic substrate
may be controlled in several different manners. In one embodiment,
the growth rate of carbon atom addition to the graphenic substrate
is controlled by spatial modulation of an electromagnetic radiation
field used to produce excited state carbon species in the fluid
phase or used to create reactive excited states at the lattice
edge. The population of excited state species may be controlled by
the physical location and intensity of the electromagnetic
radiation field, such that a population of excited state species
may be produced at the graphenic material lattice edge at a desired
level to give a pre-determined rate of atom addition to the
graphenic substrate. In embodiments where there is translation of
the graphenic substrate, the templating structure, or both the
graphenic substrate and templating structure, the radiation field
is modulated about the axis along which translation occurs, such
that as the graphenic substrate is translated, the population of
excited state species at the lattice edge changes in proportion to
the distance between the spatial illumination and the lattice edge.
Spatial modulation may be utilized to control the growth rate of
carbon atom addition to the graphenic substrate so that the rate of
translation is matched by the growth rate of carbon atom addition.
A benefit of spatially modulated growth of graphenic materials is
that deviations in the growth rate are self-correcting. As such,
when the translation rate outpaces or falls behind the growth rate,
the growth rate adjusts to match. In one embodiment of this
technique, the exciting radiation is in the ultraviolet region of
the electromagnetic spectrum. In some embodiments, the ultraviolet
radiation has an energy of about 3 eV to about 100 eV. In further
embodiments, the ultraviolet radiation has an energy of about 3.1
eV to about 12 eV. In still further embodiments, the ultraviolet
radiation has an energy of about 3.5 eV to about 5.5 eV. It will be
understood by one skilled in the art that depending on the specific
molecule being taken to an excited state in a given application,
other forms of electromagnetic radiation and excitation wavelengths
can be utilized in the spirit and scope of the disclosure to form
the spatially modified radiation field.
[0042] In another embodiment to control the rate of carbon atom
addition to the graphenic substrate, a gradient may be produced in
the chemical potential of the carbon-containing vapor phase. The
gradient may be influenced by a gradient in the carbon
concentration and/or carbon activity. When the gradient is produced
in the chemical potential of the carbon-containing vapor phase, the
carbon-containing vapor is delivered parallel to the direction of
graphenic substrate and the direction of translation. In some
embodiments, the vapor phase optionally contains one or more inert
diluent gases or one or more etchant components in addition to the
carbon source. The gradient in chemical potential of the
carbon-containing vapor phase exists along the common axis created
by the graphenic substrate growth and the direction of translation.
The gradient in carbon-containing vapor phase chemical potential is
maintained in these embodiments through independent modulation of
the carbon source comprising the vapor, inert diluent gas in the
vapor, and etchant component in the vapor.
[0043] A gradient in carbon chemical potential of molten metal
baths may also be utilized to control the growth rate of the
graphenic substrate. In one embodiment of the present disclosure, a
bulk molten metal bath is maintained on one side of a wall of
refractory material having a plurality of small (<10 .mu.m)
holes penetrating through the wall. In other embodiments, the
molten metal bath is maintained on both sides of the wall. In some
embodiments, the molten metal bath resides in the plurality of
small holes. The wall thickness is sufficient to 1) maintain
mechanical integrity, 2) allow the graphenic substrate/template
system to reside in the hole, and 3) allow the growing graphenic
substrate to extend out of the hole. In embodiments having the
molten metal bath maintained on one side of the wall, on the side
of the wall opposite the molten metal bath, templating structures
are bound to an inert support. The side of the wall housing the
bulk molten metal bath is maintained in an atmosphere rich in
etchant component, and on the opposite side of the wall is
maintained in an atmosphere of carbon-containing source gas. One
skilled in the art will recognize that this spatial arrangement
produces a gradient of carbon chemical potential in the molten
metal baths at the point through which the bulk molten metal
penetrates the wall. In a further embodiment, the carbon chemical
potential gradient may be controlled through the rate at which the
carbon-containing source gas is delivered. In a still further
embodiment, the diffusion rate of the carbon-containing source into
the molten metal bath produces a carbon chemical potential
gradient. The carbon-containing species may include, but is not
limited to, at least one of the components selected from the group
consisting of methane, ethane, propane, butane, isobutane,
1-butene, cis-2-butene, trans-2-butene, isobutene, ethylene,
propene, acetylene, propyne, 1-butyne, 2-butyne, benzene, toluene,
carbon monoxide, methanol, ethanol, 1-propanol, 2-propanol,
1-butanol, 2-butanol, 2-methyl-2-propanol, cyclopropane,
cyclobutane, acetonitrile, propionitrile, butyronitrile, acetone,
butanone, formaldehyde, acetaldehyde, propionaldehyde, and
butyraldehyde. Inert diluent gases may include, but are not limited
to, at least one component selected from the group consisting of
helium, argon, and nitrogen. The etchant component may include, but
is not limited to, at least one component selected from the group
consisting of water, carbon dioxide, ammonia, and hydrogen. One
skilled in the art will recognize that these specific examples are
meant to be illustrative of the disclosure herein, and depending on
the requirements for a specific application, different components
or mixtures of components not explicitly cited may be used to
operate within the spirit and scope of the disclosure. In certain
other embodiments of molten metal baths described herein, one or
more molten metal baths are maintained in pits on a refractory
surface, wherein a spatial gradient of carbon chemical potential
exists in the molten metal baths as a result of modulating the rate
at which carbon-containing vapor is introduced to the molten metal
baths and diffusion of carbon into the molten metal solvent takes
place. In all of these embodiments, the gradient of carbon chemical
potential in the metal bath allows the rate of carbon atom addition
to the graphenic substrate to be matched to the rate of
translation.
[0044] The present disclosure also describes in detail herein a
method for producing CNTs, through a process that includes the
steps of 1) placing a preformed CNT substrate open on at least one
end into proximity of a cylindrical templating structure, such that
the CNT is coaxially aligned with the templating structure and
contacts the templating structure within thermal variation, 2)
binding the CNT substrate and templating structure to separate
inert supports capable of independent translation, 3) providing a
reactive carbon source in a fluid phase, and 4) depositing carbon
from the fluid phase to the open end of the CNT substrate where the
CNT substrate lattice edge contacts the cylindrical templating
structure while at least one of the CNT substrate or templating
structure is translated during the depositing. When the disclosure
is practiced in this manner, carbon atoms may be incorporated on
the existing CNT substrate under the influence of the cylindrical
templating structure to prevent the formation of lattice defects
during growth, including end capping of the CNT with carbon
atoms.
[0045] In some embodiments, the cylindrical templating structure
contacts the interior of the CNT substrate. In other embodiments,
the cylindrical templating structure contacts the exterior of the
CNT substrate. In embodiments wherein the templating structure
contacts the interior of the CNT, the templating structure may
extend beyond either end of the CNT substrate. In further
embodiments wherein the cylindrical templating structure contacts
the interior of the CNT substrate, the templating structure is a
CNT having a diameter smaller than that of the CNT substrate, such
that the templating CNT contacts the interior of the CNT substrate.
When the disclosure is practiced in this manner, mechanical
independence of the growing CNT substrate from the CNT templating
structure is ensured. Likewise, physical and chemical stability of
the CNT templating structure to the growth environment is
maintained, and carbon atom deposition on the CNT templating
structure is suppressed and directed primarily to the CNT
substrate.
[0046] The CNT templating structure and CNT substrate may be
attached to independent supports, which are inert toward the
conditions utilized for fluid phase growth of CNTs. Suitable
support materials depend upon the growth fluid environment. For
example, alumina, magnesia or a combination thereof is well suited
for molten transition metal baths The arrangement of the CNT
templating structure, CNT substrate and inert supports for each is
shown in FIG. 1. The supporting surface attachment points for the
CNT templating structure 101 and CNT substrate 102 are opposite the
point of contact 103 between the CNT templating structure with the
CNT substrate along the common cylindrical axis created by 101 and
102. The supports 100 and 105 to which CNT templating structure 100
and CNT substrate 105 are attached are capable of independent
motion, such that both the CNT templating structure 101 and CNT
substrate 102 may be translated by motion of the supports to which
they are attached. In some embodiments, the support to which the
CNT substrate is bound is independently translated. In other
embodiments, the support to which the CNT templating structure is
bound is independently translated. In still further embodiments,
both supports are translated concurrently. In certain embodiments,
translation of the CNT substrate, CNT templating structure, or both
the CNT substrate and CNT templating structure is accomplished
through a winding motion, wherein the CNT substrate is wound on to
a spool mechanism as it is grown. One embodiment of such a spooling
mechanism for translation of the CNT substrate is shown in FIG. 2.
CNT substrate 203 is translated from CNT templating structure 201,
which is attached to inert support 200. CNT substrate 203 is drawn
on to spooling mechanism 204, which is rotated in direction 206 to
wind CNT substrate 203 on to the spooling mechanism. In certain
embodiments, the spool mechanism may be optionally translated
parallel to the axis of winding at the same time it is wound. As a
consequence of this translation capability, CNTs produced through
templated growth on the CNT substrate are permitted to remain in
contact with the CNT templating structure during addition of carbon
atoms to the CNT substrate, while not damaging either CNT during
the translation process due to minimal sliding friction between the
two structures. This arrangement beneficially allows CNT templating
structures of finite physical dimension to direct the growth of
CNTs to an arbitrary length.
[0047] The methods disclosed herein may be utilized to
simultaneously produce more than one CNT. A two-dimensional or
three-dimensional array of CNT substrates and CNT templating
structures may be produced from a CNT of known type through steps
comprising 1) positioning the CNT of known type on an inert surface
in a known configuration and 2) cutting the CNT of known type into
individual CNT/coaxial CNT templating structures. These CNT `seeds`
may then be manipulated and grown through templated addition of
carbon to the CNT substrate using any of the methods described
herein. In some embodiments of this method, the CNTs are all of
known length. In other embodiments of this method, the CNTs are all
in known positions and may be manipulated with mechanical
precision. Arrayed CNTs and particularly SWCNTs may be particularly
useful for nanoscopic electronic devices such as integrated
circuits and electronic memory. Two-dimensional arrays may be
placed on an electronic device with nanoscale precision, wherein a
precise spacing between the CNTs exists. In other applications,
arrays may be engineered to act as "word-bit" lines in a memory
device.
[0048] Methods are disclosed herein for positioning CNT substrates
and CNT templating structures. A CNT substrate/CNT template pair
may be positioned coaxially. A plurality of CNT substrate/CNT
template pairs may be positioned in an array. It will be understood
that methods of positioning CNT substrates and CNT templating
structures are illustrative of placing a preformed substrate in
contact with a templating structure, wherein the preformed
substrate and template structure are each CNT-based. This in turn
is illustrative of placing a preformed substrate in contact with a
templating structure.
[0049] According to an embodiment, a method for positioning is
illustrated schematically in FIG. 3, wherein CNT substrates and CNT
templating structures may be positioned by steps comprising 1)
preparing a SWCNT of known length held at each end and suspended in
free space, 2) opening at least one end of the SWCNT, 3) filling
the open SWCNT with fullerenes such that the fullerenes are in
contact within the SWCNT (structure 300), 4) polymerizing the
fullerenes to make a second CNT concentric to and inside the SWCNT,
5) placing the resultant DWCNT 301 on a suitable surface in a known
configuration, which may be a parallel configuration, through
methods such as suspending the DWCNT 301 in a photosensitive
polymer above a transparent surface in a known configuration, 6)
cutting DWCNT 301 in regions 302 to leave an array of DWCNT 303,
which may be a parallel array, 7) performing photolithography to
pattern a masking layer 304, such as a refractory metal oxide
layer, on one end of the DWCNT array, 8) etching the exposed ends
of the DWCNTs to leave exposed SWCNTs 305 and masked DWCNTs 306, 9)
removing the masking layer 304, and 10) bonding each end of the
resultant DWCNT/SWCNT array to inert supports 307 and 308, which
are capable of independent translation. The resultant CNT `seeds`
may then be manipulated and grown through templated addition of
carbon to the CNT substrate using any of the methods described
herein. The de novo growth of CNTs inside an existing CNT via
polymerization of fullerenes is commonly known to those skilled in
the art as the `peapod coalescence`.
[0050] In another embodiment of this method, one or more MWCNTs are
suspended in a photosensitive polymer above a transparent surface.
Photolithography is then performed to pattern metal/ceramic
contacts over each MWCNT at two places. The MWCNTs are then held
suspended between the metal/ceramic contact points when the
structure is inverted. The inverted structure is coated with a
photoresist substance, which is then removed around only one of the
metal/ceramic contact points per MWCNT to expose the outer layer of
each MWCNT at each point. The outer layer of the MWCNTs is opened
by methods used to damage CNTs, such as fluorination, light
oxidation with singlet oxygen or ozone, electrical burnout methods,
or controlled etching using oxidizing baths (ie., piranha, nitric
acid, nitric acid/sulfuric acid). One skilled in the art will
recognize that these methods are not necessarily an exhaustive
compilation of methods capable of opening CNTs, and methods not
explicitly listed remain within the spirit and scope of the
disclosure. Following opening of the outer CNTs, the open ends of
the CNTs are etched using methods known to those skilled in the
art, until the open ends of the CNTs are at the desired point
between the metal/ceramic contacts. Suitable etching methods
include, but are not limited to, hydrogen etching, low temperature
piranha etching, and CO.sub.2 etching. The structure is thereafter
inverted again and aligned and bonded to two separate supports.
Carbon atoms are then deposited on to the open end of the resultant
CNT substrates from a fluid phase carbon source as at least one of
the CNT substrate or the CNT templating structure is
translated.
[0051] In yet another embodiment of the present disclosure, as
illustrated in FIG. 4, a CNT substrate 402 and CNT templating
structure 401 bound to inert support 400 may be positioned by steps
comprising 1) wrapping CNT substrate 402 open on at least one end
around a spool mechanism 404, wherein the spool is rotated in
direction 406 to draw the CNT substrate 402 on to the spool while
the spool is simultaneously translated in direction 405 parallel to
the winding axis, thereby winding the CNT substrate 402 on to the
spool 404 to form a helical structure with known pitch, 2) filling
the open CNT on the spool with fullerenes such that the fullerenes
are in contact within the CNT, 3) polymerizing the fullerenes to
make a second CNT inside the original CNT, 4) performing
photolithography to cut the CNT into individual CNT segments 408
while removing CNT segments 407, wherein CNT segments 408 are
aligned in parallel, 5) performing additional photolithography on
the outer CNT of each individual CNT segment 408, wherein the inner
CNT extends beyond the outer CNT, 6) transferring the individual
CNT segments to a surface suitable for CNT growth, wherein the CNTs
segments remain parallel and inner/outer CNTs remain coaxial during
the transfer process, and 7) bonding the inner and outer CNTs from
each segment to supports that can be independently translated. The
aligned CNT `seeds` and CNT templating structures may thereafter be
utilized to grow CNTs using any of the methods described herein. In
alternative embodiments of the alignment process, the second CNT
may be grown following photolithography to cut the CNT into
individual CNT segments 408. In another alternative embodiment of
the alignment process, the second CNT may be grown following
transfer of CNT segments 408 to the surface suitable for CNT
growth.
[0052] At least one metal atom may be optionally bonded to the open
end of the CNT substrate. In certain embodiments, the metal is
selected periodic table groups 3-12, the lanthanide elements, and
combinations thereof. Bonding of one or more metals is known to
enhance the chemical reactivity of CNT substrates toward addition
of carbon atoms. The present disclosure describes methods whereby
catalytic metal atoms may be attached to the CNT lattice edge in
controlled number and density. In some embodiments, metal
deposition to the CNT lattice edge is affected by electrochemical
deposition of suitable metal precursors. Variables such as time- or
current-limited voltage pulses and solution concentration of metal
species may allow electrodeposition to be carried out at variable
rates for a given voltage in order to control the metal density on
the CNT lattice edge. In other embodiments, metal atoms are
attached to the CNT lattice edge by coupling reactions between
mixtures of metal atom bearing species and non-metal bearing
species of comparable reactivity with reactive groups on the CNT
lattice edge. The density of metal atom incorporation on the CNT
lattice edge may be controlled simply by adjusting the ratio of
metal-bearing to non-metal bearing species in the coupling
reaction. Suitable metal atom bearing species may include, but are
not limited to, functionalized metallocenes (e.g., ferrocene),
metal-EDTA derivatives, and related organometallic and metal-ligand
complexes. Non-metal bearing species having comparable reactivity
to these specific examples may include the functionalized
non-metallated ligand or similar compound having comparable
reactivity toward the reactive groups on the CNT lattice edge. One
skilled in the art will recognize that a wide variety of
non-metallated compounds having like reactive functionality to the
functionalized metal bearing compound may be used to control the
density of metal atom deposition. These competing non-metallated
species may bear no structural resemblance to the metallated
species in certain instances, while still maintaining comparable
chemical reactivity to the parent metal bearing compound. A
convenient functional group for attaching the metal bearing species
and their non-metal bearing counterparts to CNT lattice edges is a
carboxylic acid, although other functional groups may be
manipulated to couple with CNT lattice edges through methods known
to those skilled in the art. In the instance where the reactive
functional group on the metal bearing compound is a carboxylic
acid, the metal bearing species may be attached to surface CNT
lattice edge OH groups via an esterification reaction through
various coupling reaction methodologies known to those skilled in
the art. The range of reactions utilized to couple to the CNT
material lattice edge is not limited to esterifcation, and other
coupling strategies including, but not limited to, alkoxylation and
amidation are viable alternatives for linking metal atoms to the
CNT lattice edge. In still further embodiments, ligand binding
sites on the CNT lattice edge may be reacted with metal ion
solutions having variable concentration and pH. The ligand binding
sites may be pre-existing in certain embodiments, including, but
not limited to, terminal carboxylic acid moieties at the CNT
lattice edge. In other embodiments, a suitable ligand may be
synthesized on the CNT lattice edge. One skilled in the art will
recognize that certain metal ion solutions will require pH and
reaction temperatures having values in a defined range to
efficiently bind to the surface ligands. Furthermore, for a given
metal salt, a finite attainable concentration range and chemical
compatibility profile will be realized due to the innate physical
properties of the metal salt.
[0053] A molecule in an excited state may comprise the fluid phase
source of carbon atoms for addition to the CNT substrate, wherein
increased reactivity of the excited state carbon source with the
CNT substrate is realized. When the vapor phase contains an excited
state species, the collision rate of the excited state species in
the vapor phase may be sufficiently low with non-excited state
vapor phase molecules so as not to generate extraneous reactive
species. In some embodiments, the excited state is a vibrational
excited state. In other embodiments, the excited state is a radical
state. Suitable radical states may include, but are not limited to,
C.sub.2H and C.sub.2H.sub.3. In still more embodiments, the excited
state is an excited electronic state. A representative excited
electronic state molecule is non-dissociatively excited acetylene,
which has been excited by electromagnetic radiation having a
wavelength of about 220 nm. One skilled in the art will recognize
that other excited electronic state molecules can also be utilized
within the spirit and scope of the disclosure. The foregoing list
of excited state species is meant to be representative of excited
state entities suitable for bringing the disclosure to practice and
should not be considered limiting for this purpose. One skilled in
the art will recognize that an energetically excited state species
having suitable reactivity for a given application may be generated
by a number of techniques and utilized equivalently in the methods
described herein. The vapor phase containing the excited state
carbon species may optionally contain an inert diluent gas and an
etchant component. Suitable diluent gases may include, but are not
limited to, at least one component selected from the group
consisting of helium, argon, and nitrogen. Suitable etchants may
include, but are not limited to, at least one component selected
from the group consisting of water, carbon dioxide, ammonia, and
hydrogen. In certain embodiments, it may be advantageous to add
both the etchant component and inert diluent gas either separately
or concurrently.
[0054] In certain embodiments, the rate at which the CNT substrate
is translated away from the CNT templating structure is matched by
the growth rate of the CNT substrate through addition of carbon
atoms. If during addition of atoms to the CNT substrate, the rate
at which the CNT templating structure and CNT lattice edge are
translated apart is too slow, the CNT substrate will eventually
contact the inert support to which the CNT templating structure is
bound. Likewise, if during addition of atoms to the CNT substrate,
the rate at which the CNT templating structure and CNT substrate
are translated apart is too rapid, then growth of the CNT substrate
will not keep pace with the rate of translation and the CNT
substrate will eventually become disconnected from the CNT
templating structure.
[0055] The rate of carbon atom addition to the CNT substrate may be
controlled in several different manners. In one embodiment, the
growth rate of carbon atom addition to the CNT substrate is
controlled by a spatial modulation of an electromagnetic radiation
field, such that the population of excited state carbon-containing
fluid phase species at the CNT lattice edge is regulated by the
spatial location of the radiation field relative to the lattice
edge. One skilled in the art will recognize that the population of
excited state species may be controlled by the physical location
and intensity of the electromagnetic radiation field, such that the
population of excited state species may be regulated to a desired
level to give a pre-determined rate of carbon atom addition to the
CNT substrate. In embodiments where there is translation of the CNT
substrate, the CNT templating structure, or both the CNT substrate
and CNT templating structure, the radiation field may be modulated
about the axis along which the translation occurs, such that as the
translation occurs, the population of excited state species changes
in proportion to the distance between the illumination and the CNT
substrate lattice edge. Spatial modulation may therefore be
utilized to control the growth rate of carbon atom addition to the
CNT substrate so that the rate of translation is matched by the
growth rate of carbon atom addition. A benefit of spatially
modulated growth of CNTs is that deviations in the growth rate are
self-correcting. As such, when the translation rate outpaces or
falls behind the growth rate, the growth rate adjusts to match. In
one embodiment, the exciting radiation is in the ultraviolet region
of the electromagnetic spectrum. In some embodiments, the
ultraviolet radiation has an energy of about 3 eV to about 100 eV.
In further embodiments, the ultraviolet radiation has an energy of
about 3.1 eV to 12 eV. In still further embodiments, the
ultraviolet radiation has an energy of about 3.5 eV to about 5.5
eV. It will be understood by one skilled in the art that depending
on the specific molecule being taken to an excited state in a given
application, other forms of electromagnetic radiation and
excitation wavelengths could be utilized in the spirit and scope of
the disclosure to form the spatially modified radiation field.
[0056] The fluid phase source of atoms for addition to CNT
substrates in the present disclosure may be a carbon source
dissolved in a molten metal, wherein physical contact is maintained
between the molten metal and the CNT substrate. The molten metal is
at least one component selected from periodic table groups 1-12,
the lanthanide elements, and alloys thereof. In some embodiments,
the metal may be at least one component selected from the group
consisting of Fe, Co, Ni, Au and alloys thereof. In one embodiment,
the carbon source is a solid in contact with the molten metal. Such
a carbon source may also be preferentially dissolved instead of the
CNT substrate. This feature may be achieved through various
techniques including but not limited to applying electrical
potentials or by constructing the solid carbon source from a less
energetically stable carbon form, such as amorphous carbon In other
embodiments, the carbon source in the molten metal bath is
introduced from a vapor phase carbon-containing species. One
skilled in the art will recognize that the vapor phase
carbon-containing species may derive from gases, liquids, or solids
having low vapor pressures. Said carbon-containing compounds may
contain at least one element other than carbon, and may include,
but not be limited to, the group consisting of hydrogen, oxygen,
sulfur, nitrogen, fluorine, chlorine, bromine, iodine, silicon and
phosphorus. It is well known in the art that presence of other
species in a molten metal solution may affect the carbon activity
and growth mode of carbon deposition from the solution. For
example, the presence of other elements may reduce the surface
tension of the molten metal bath and lower the interfacial energy
between the metal melt and non-wetting surfaces it contacts. Sulfur
and copper are particularly known to decrease the surface energy of
carbon-containing molten metal melts, and these elements may
optionally be included in the molten metal baths described herein.
Non-metallic elements including, but not limited to Si and P, may
optionally be included in the melt to modify the effective carbon
saturation (activity) and deposition potential. In the present
disclosure, the carbon-containing species may include, but is not
limited to, at least one component selected from the group
consisting of methane, ethane, propane, butane, isobutane,
1-butene, cis-2-butene, trans-2-butene, isobutene, ethylene,
propene, acetylene, propyne, 1-butyne, 2-butyne, benzene, toluene,
carbon monoxide, methanol, ethanol, 1-propanol, 2-propanol,
1-butanol, 2-butanol, 2-methyl-2-propanol, cyclopropane,
cyclobutane, acetonitrile, propionitrile, butyronitrile, acetone,
butanone, formaldehyde, acetaldehyde, propionaldehyde, and
butyraldehyde. In a further embodiment of the disclosure, the vapor
phase carbon-containing molecule may be optionally mixed with an
inert diluent gas, such that the molten metal source is exposed
concurrently to both the vapor phase carbon-containing compound and
inert diluent gas. Suitable diluent gases may include, but are not
limited to, at least one component selected from the group
consisting of helium, argon, and nitrogen. In a still further
embodiment, the vapor phase carbon-containing molecule may be mixed
with an etchant component, such that the molten metal source is
exposed concurrently to both the vapor phase carbon-containing
compound and etchant component. In certain embodiments, it is
desirable to add both the etchant component and diluent gas, either
concurrently or separately, along with the carbon-containing
compound. Suitable etchants may include, but are not limited to, at
least one component selected from the group consisting of water,
carbon dioxide, ammonia, and hydrogen. More than one CNT may be
grown simultaneously from individual, isolated carbon-containing
molten metal baths in further embodiments of this method.
[0057] Molten metal baths are embodied in certain instances wherein
one or more molten metal baths are maintained in individual pits on
a refractory surface. In this embodiment, carbon atoms are added to
one or more CNT substrates from a carbon atom source through
templated growth, while at least one of the refractory surface and
inert support binding the CNT substrate is independently
translated. In another embodiments of molten metal baths, a bulk
molten metal bath is maintained on one side of a wall of refractory
material having a plurality of small (<10 .mu.m) holes
penetrating completely through the wall. In other embodiments, the
molten metal bath is maintained on both sides of the wall. In
additional embodiments, the molten metal bath resides in the
plurality of small holes. The wall thickness is sufficient to 1)
maintain mechanical integrity, 2) allow the CNT substrate/CNT
template system to reside in the hole, and 3) allow the growing CNT
substrate to extend out of the hole. On the side of the wall
opposite the bulk molten metal bath, CNT templating structures may
be bound to an inert support which is stationary with respect to
the refractory material wall. In an alternative embodiment of this
configuration, the CNT templating structures may be bound directly
to the refractory surface wall. In either configuration, carbon
atoms are added to the CNT substrate as translation occurs using
any of the templated growth methods described herein. In yet
another embodiment of molten metal baths, the molten metal bath is
a bead of molten metal localized at the open end of a freestanding
CNT templating structure.
[0058] The rate of carbon atom addition to the CNT substrate may be
controlled by producing a gradient in the chemical potential of the
carbon-containing vapor phase. In some embodiments, the vapor phase
optionally contains one or more inert diluent gases or one or more
etchant components in addition to the carbon source. The gradient
in chemical potential of the carbon-containing vapor phase exists
on the axis of the CNT substrate along the direction of
translation. The gradient in carbon-containing vapor phase chemical
potential is maintained in these embodiments through independent
modulation of the carbon source comprising the vapor, inert diluent
gas in the vapor, and etchant component in the vapor.
[0059] The growth rate of the CNT substrates may be controlled by
creating a gradient of carbon chemical potential in the molten
metal baths as described in the disclosure. In one embodiment, the
growth rate of carbon atom addition to the CNT substrate is
controlled by introducing the carbon-containing vapor at such a
rate that a spatial gradient of carbon chemical potential exists
within the metal bath. In another embodiment, the growth rate of
carbon atom addition to the CNT substrate is controlled by steps
comprising 1) maintaining an etchant component atmosphere on one
side of a refractory substance wall confining a bulk molten metal
bath, wherein a plurality of small (<10 .mu.m) holes penetrate
completely through the wall, and 2) delivering a carbon-containing
source gas on the side of the wall opposite the bulk molten metal
bath, wherein one or more CNT templating structures and CNT
substrates are positioned on the side of the wall opposite the bulk
molten metal bath; the carbon-containing vapor phase is delivered
parallel to the direction of CNT substrate growth; and the
carbon-containing vapor phase maintains a concentration gradient
along the direction of CNT substrate translation through modulation
of at least one of the carbon source, inert diluent gas, and
etchant component in the vapor. One skilled in the art will
recognize that this spatial arrangement produces a gradient of
carbon chemical potential in the molten metal baths at the point
through which the bulk molten metal penetrates the wall. Further, a
skilled artisan will recognize that the chemical potential gradient
will control the growth rate of carbon atom addition to the CNT
substrate as the CNT substrate is translated from the CNT
templating structure. In a further embodiment, the diffusion rate
of the carbon source into the molten metal bath produces a carbon
chemical potential gradient. The vapor phase carbon-containing
species may include, but is not limited to, at least one component
selected from the group consisting of methane, ethane, propane,
butane, isobutane, 1-butene, cis-2-butene, trans-2-butene,
isobutene, ethylene, propene, acetylene, propyne, 1-butyne,
2-butyne, benzene, toluene, carbon monoxide, methanol, ethanol,
1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-2-propanol,
cyclopropane, cyclobutane, acetonitrile, propionitrile,
butyronitrile, acetone, butanone, formaldehyde, acetaldehyde,
propionaldehyde, and butyraldehyde. The inert diluent gas may
include, but is not limited to, at least one component selected
from the group consisting of helium, argon, and nitrogen. The
etchant component may include, but is not limited to, at least one
component selected from the group consisting of water, carbon
dioxide, ammonia, and hydrogen. One skilled in the art will
recognize that these specific examples are meant to be illustrative
of the disclosure described herein, and depending on the properties
required for a specific application, different components or
mixtures of components not explicitly cited may be used to operate
within the spirit and scope of this disclosure.
[0060] In another embodiment of the disclosure provided herein, an
electrical potential is applied to the CNT substrate to produce a
reactive carbon species from the fluid phase for addition to the
CNT substrate. In an alternative embodiment, the electrical
potential enhances the CNT substrate reactivity. In some
embodiments, the electrical potential is utilized to produce
carbon-containing ionic radicals for addition to the CNT substrate
through an electrolytic decomposition reaction of suitable carbon
radical precursors. The carbon-containing ionic radicals may
include, but are not limited to, methyl, ethyl, and vinyl radicals.
Electrochemical deposition has been previously shown to produce
MWCNTs, but the disclosure embodied herein is distinguished from
and superior to known methods in the use of a template to direct
CNT growth. The electrical potential may also be applied in the
presence of an electrically charged carbon source, which results in
attraction of the charged carbon atom species to the CNT substrate.
In a particular embodiment, the charged carbon source may be
dissolved in a molten metal solvent. In another embodiment, the
charged carbon source may be dissolved in an ionic liquid solvent.
The ionic liquid solvent may be a molten alkali halide or alkaline
halide. It has been widely reported that alkali metal carbides and
alkaline metal carbides are soluble in certain alkali metal halide
and alkaline metal halide fused salt systems. These carbides
dissociate to give unbound acetylide (C.sub.2.sup.-2) ions in the
molten salt solution. It has been demonstrated that carbon can be
electrochemically deposited and redissolved under quasi-reversible
conditions in such systems. It has also been demonstrated that
closed graphenic structures are stable in fused alkali halide salt
systems and that these environments are catalytic to the
restructuring of graphenic structures into minimum energy
configurations. The electrical potential may further be applied in
the presence of a neutral and polarizable carbon source, which
results in the establishment of a concentration gradient within the
region throughout which the neutral and polarizable carbon source
is dispersed.
[0061] In certain embodiments wherein an electrical potential is
applied to a CNT substrate, the CNT templating structure has a
lower electrical conductivity than the tip of the growing CNT
substrate. In this instance, the electric field becomes
concentrated at the tip of the growing CNT substrate. The
electrical potential may be adjusted so that the tip of the CNT
substrate develops an excess of electron density (i.e., becomes
electron rich). When the CNT substrate tip becomes electron rich,
the CNT substrate tip may undergo a Diels-Alder type reaction,
wherein the CNT substrate tip serves as the diene component of the
reaction. Suitable dienophile partners for coupling to the CNT
substrate diene may include, but are not limited to, vinyl acetic
acid, acrylic acid, acrylonitrile and dicyanoacetylene. The
electrical potential may also be adjusted such that the CNT
substrate tip develops a net deficiency of electron density (ie.,
becomes electron poor). Comparable cycloaddition reactions to the
electron-deficient CNT substrate may be envisioned by those skilled
in the art.
[0062] An electric field bias may be applied to the growing CNT
substrate such that the field gradient and charge concentration are
varied in the growing CNT substrate through choice of electrode
geometry. In certain embodiments, the electric field bias may be
used to manually regulate the rate of CNT substrate growth. In
other embodiments, the electric field bias may be used to
self-regulate the rate of CNT substrate growth. Self-regulation of
CNT substrate growth may be accomplished by steps illustrated in
FIG. 5 comprising 1) contacting the CNT substrate 502 with an
electrically insulating template structure 501, each individually
bound to supports 504 and 505, 2) applying an electrical potential
to CNT substrate 502 through inert support 505, wherein position
507 is the electrical contact point of CNT substrate 502, and
further wherein the counter-electrode is in a ring configuration
508 surrounding CNT substrate 502 at a distance away from the point
of electrical contact 507, and 3) adding carbon atoms to CNT
substrate 502 as 502 is translated in direction 506, such that the
rate of carbon atom addition to CNT substrate 502 is proportional
to the electric field gradient established at the tip of CNT
substrate 502. In certain embodiments, the electrical potential is
applied at any point on support 505. In additional embodiments, an
electrical potential is applied to CNT templating structure 501
through inert support 504. In further embodiments, the electrical
potential is applied at any point along CNT substrate 502. When the
electrical contact point is applied along the CNT substrate 502,
the site of contact is at point not susceptible to electrochemical
reactions and non-interfering with the electric field established
at the ring counter-electrode. The chosen electrode geometry
ultimately governs placement of ring electrode 508 in this
configuration. In some embodiments, the radius of the ring
counter-electrode determines the distance the ring
counter-electrode is placed away from the point of surface
electrical contact 507. Suitable electrically insulating templates
may include, but are not limited to boron nitride nanotubes and
large band gap CNTs. In the electrode orientation embodied in FIG.
5, one skilled in the art will recognize that the electrical field
in the CNT substrate tip is enhanced as the tip nears the ring
electrode, thus leading to a self-regulated rate matching of
translation to the CNT substrate growth rate.
[0063] In another aspect of the disclosure, an electrical potential
applied to the growing CNT substrate enhances the deposition rate
of carbon to the growing CNT substrate wherein the CNT is
translated from an electrically insulating template structure which
is coaxial and external to the CNT substrate in a carbon-atom
source environment. Specific examples of the electrically
insulating external template may include, but are not limited to,
boron nitride nanotubes and large band gap CNTs, both of which have
a diameter larger than the growing CNT substrate. In one embodiment
of this disclosure, the carbon source is carbon dissolved in a
molten metal, wherein the metal is at least one component selected
from periodic table groups 1-12, the lanthanide elements, and
alloys thereof. In a further embodiment of this method, the metal
is molten cobalt.
[0064] Another aspect of the disclosure provided herein relates to
a method for achieving positional control of CNT substrates by
means of a position-controlling structure contacting the exterior
of each CNT substrate as it is translated as shown in FIG. 6.
Positional control of grown CNT substrates is accomplished by steps
comprised of 1) positioning a wall structure 605 completely
penetrated by one or more SWCNT conduits 604 between the inert
support anchoring point 607 of CNT substrate 602 and the CNT
substrate lattice edge 603, wherein each CNT substrate 602
penetrates wall structure 605 through the interior of a SWCNT
conduit 604; the SWCNT conduits 604 are larger than the CNT
substrate 602 they contain by at least one graphite lattice unit
spacing; and the inert support 607 is capable of translational
motion, 2) growing CNT substrate 602 via templated growth from a
fluid phase carbon source, wherein templating structure 601 is
bound to inert support 606, and 3) translating the grown CNT
substrate 602 through wall structure 605 separating the fluid phase
carbon source from inert support 607, wherein translation of CNT
substrate 602 is affected through a SWCNT conduit 604. In certain
embodiments, the grown CNT substrate is translated through the
position-controlling structure 604 via a spooling motion.
[0065] In certain embodiments CNTs may be prepared via templated
growth, wherein the CNT substrate lies within the interior of an
external templating structure. In this embodiment, the open end of
the internalized CNT substrate may optionally be bonded to a
nanoparticle, and the end of the CNT substrate opposite the
nanoparticle is attached to an inert support. In certain
embodiments, the internal CNT substrate may be translated through
movement of the inert support as atoms are added to the CNT
substrate.
[0066] The disclosure herein also describes an embodiment wherein a
CNT simultaneously functions as both a growth substrate and
templating structure as shown in FIG. 7. In this embodiment, a
MWCNT has its innermost CNT 701 contacting a templating structure
702, which is bound to inert support 703. As carbon atoms are added
to innermost CNT 701 during translation of the MWCNT, the innermost
CNT 701 serves as a template of increasing length to the next layer
CNT 704. This process applies sequentially to all CNTs 704 in the
MWCNT until the outermost CNT 705 is reached. The outermost CNT 705
serves only as a growth substrate. Templated growth embodied in
this sense can be used to create MWCNTs having a beveled tip
700.
[0067] The disclosure herein also provides a method for enhancing
graphene lattice edge reactivity by exciting non-thermalized
excited states in the graphene lattice edge. In a specific
embodiment of this process, a method for production of CNTs is
comprised of 1) placing a preformed CNT substrate open on at least
one end into proximity of a cylindrical templating structure,
wherein the CNT substrate contacts the cylindrical templating
structure within thermal variation and aligns with the cylindrical
templating structure in a coaxial fashion within thermal variation,
2) binding a CNT substrate and cylindrical templating structure to
separate inert supports, wherein each support may be independently
translated, 3) producing non-thermalized excited states in a CNT
substrate, and 4) depositing carbon from a fluid phase to the open
end of a CNT substrate where the CNT substrate lattice edge
contacts the cylindrical templating structure, while at least one
of the CNT substrate or cylindrical templating structure is
translated during the depositing. In some embodiments, the CNT
lattice edge is brought into a non-thermalized excited state
through direct excitation of edge localized states. In polyaromatic
systems, "zig-zag" configurations are known to have localized
electron sites which populate the Dirac point in the density of
states. Transitions from these edge localized states allow the
direct excitation of non-thermalized states at the CNT lattice edge
to enhance reactivity. The edge localized states may include, but
are not limited to, benzyne and carbyne sites on the CNT lattice
edge. In other embodiments, plasmon excitation of the CNT substrate
produces non-thermalized edge state excitation. In certain
embodiments, UV irradiation produces a CNT lattice edge substrate
having non-thermalized excited states.
[0068] The CNT substrate reactivity toward carbon atom addition may
also be enhanced by exciting non-thermalized excited states in CNT
substrates bound to at least one metal atom. The metal atoms may be
at least one component chosen from periodic table groups 3-12, the
lanthanide elements, and combinations thereof. The non-thermalized
excited state may be produced through excitation of the
metal-carbon bond. Alternatively, the non-thermalized excited state
may be produced through direct excitation of the metal atom,
including, but not limited to, interaction of the metal atom with
X-rays.
EXPERIMENTAL EXAMPLES
Prophetic Example 1
Acetylides in Alkali Halide Fused Salts
[0069] A fused molten salt environment comprised of one or more
alkali metal halides will be prepared, wherein the cationic alkali
metal species will be chosen from Li, Na, and K and the anionic
halogen component will be chosen from F, Cl, and Br. Feedstock
species comprised of at least one alkali acetylide, alkaline
acetylide, or a combination thereof will thereafter be prepared in
the molten alkali halide solvent. A graphenic substrate/templating
system will be brought into contact in the molten alkali halide
solvent, and the graphenic sub strate/templating system will be
translated apart as carbon is electrochemically added to the
graphenic substrate under quasi-equilibrium conditions. The
reaction temperature will be sufficient to render the solvent
composition liquid and provide activation energy sufficient to
anneal deposited carbon. Other carbon sources are envisioned to be
utilized in this method, including, but not limited to, alkali
metal carbonates. A method to generate carbide ions in situ from a
carbon electrode or from external acetylene bubbled over the
cathode are also envisioned. In general the potential required to
deposit carbon at quasi-equilibrium conditions will depend upon the
salt system, temperature and counter-electrode, and will be
directly found through a standard CV (cyclic voltammetry)
experiment to identify the acetylide oxidation potential. In
general the working electrode will be the graphenic material
templated growth system. The counter (auxiliary) and reference
electrodes will simply be compatible with the cell; that is they
will be stable in and not contaminate the molten alkali halide
environment, and they will not degrade during the reduction of
alkali ions.
Prophetic Example 2
Iron/Cobalt Alloy Solvent System
[0070] The ability of certain transition metals to dissolve carbon
without forming stable carbides is well known in metallurgy and
widely exploited in the synthesis of carbon nanomaterials such as
CNTs.
[0071] A molten metal ternary alloy comprised of cobalt, iron, and
carbon will be prepared and liquified between about
1115-1135.degree. C. The ratio of cobalt to iron in the ternary
alloy will be between about 3:17 to about 3:7. The carbon
concentration in the ternary alloy will be about 14 to about 17
atomic percent. Carbon saturation will be achieved by placing the
molten cobalt/iron alloy in contact with a carbon source, including
but not limited to amorphous carbon. Once the ternary allow has
been established and temperature adjusted to 1115-1135.degree. C.,
a graphenic substrate/templating system will be brought into
contact in the molten alloy. The environmental pressure will be
maintained below atmospheric pressure and ideally will be
maintained between 10-400 torr to avoid increasing the likelihood
of diamondoid carbon formation while keeping the molten metal bath
from evaporating. The temperature will be raised to slightly above
these conditions (1150.degree. C.), and carbon will then be
deposited into the graphenic substrate when the carbon chemical
potential is just above saturation. As the graphenic substrate is
extended, translation will be performed to maintain the graphenic
substrate and templating structure in contact with one another. The
solvent system will be maintained at near equilibrium carbon
saturation conditions to deliver templated growth of highly perfect
graphenic materials.
* * * * *