U.S. patent application number 10/831786 was filed with the patent office on 2004-10-07 for apparatus for making carbon nanotube structure with catalyst island.
This patent application is currently assigned to The Board of Trustees of the Leland Stanford Junior University. Invention is credited to Dai, Hongjie, Kong, Jing, Quate, Calvin F., Soh, Hyongsok.
Application Number | 20040194705 10/831786 |
Document ID | / |
Family ID | 22461049 |
Filed Date | 2004-10-07 |
United States Patent
Application |
20040194705 |
Kind Code |
A1 |
Dai, Hongjie ; et
al. |
October 7, 2004 |
Apparatus for making carbon nanotube structure with catalyst
island
Abstract
Carbon nanotube growth is achieved in a high-yield process.
According to an example embodiment of the present invention, a
furnace chamber is adapted to grow a carbon nanotube device via
catalyst islands. The carbon nanotube device includes a catalyst
island, such as Fe.sub.2O.sub.3, and a carbon nanotube extending
therefrom. In one more specific implementation, the catalyst island
is disposed on a top surface of a substrate. The carbon nanotube
device is useful in a variety of implementations and applications,
such as in an atomic force microscope (AFM), in resonators (e.g.,
where a free end of the carbon nanotube is adapted to vibrate) and
in electronic circuits (e.g., where the carbon nanotube is
electrically coupled between two nodes, such as between the
catalyst island and a circuit node). In addition, growing carbon
nanotubes with such a catalyst island is particularly useful in the
high-yield growth of a large number of nanotubes.
Inventors: |
Dai, Hongjie; (Sunnyvale,
CA) ; Quate, Calvin F.; (Stanford, CA) ; Soh,
Hyongsok; (Stanford, CA) ; Kong, Jing;
(Stanford, CA) |
Correspondence
Address: |
Robert J. Crawford
Crawford Maunu PLLC
Suite 390
1270 Northland Drive
St. Paul
MN
55120
US
|
Assignee: |
The Board of Trustees of the Leland
Stanford Junior University
Palo Alto
CA
|
Family ID: |
22461049 |
Appl. No.: |
10/831786 |
Filed: |
April 26, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10831786 |
Apr 26, 2004 |
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10042426 |
Jan 7, 2002 |
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10042426 |
Jan 7, 2002 |
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09133948 |
Aug 14, 1998 |
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6346189 |
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Current U.S.
Class: |
118/719 |
Current CPC
Class: |
B82Y 40/00 20130101;
G11C 17/165 20130101; G11C 17/16 20130101; Y10S 977/842 20130101;
Y10S 977/876 20130101; G01N 27/127 20130101; Y10S 977/894 20130101;
Y10T 428/2975 20150115; B82Y 30/00 20130101; G01Q 70/12 20130101;
B82Y 10/00 20130101; B82B 1/00 20130101; Y10S 977/957 20130101;
Y10S 977/843 20130101; Y10S 977/895 20130101; C01B 2202/02
20130101; Y10S 977/746 20130101; Y10S 977/742 20130101; Y10S
427/102 20130101; C01B 32/162 20170801; Y10T 428/2918 20150115;
B82B 3/00 20130101; G11C 13/025 20130101 |
Class at
Publication: |
118/719 |
International
Class: |
C23C 016/00 |
Claims
What is claimed is:
1. A system for manufacturing a carbon nanotube device, comprising:
first chamber means for forming at least one island of catalyst
material; and second chamber means for contacting the catalyst
island with a carbon-containing gas and forming a carbon nanotube
extending from the catalyst island.
2. The system of claim 1, wherein the second chamber means is
adapted to create conditions suitable for reacting the
carbon-containing gas with the catalyst island for growing the
carbon nanotube.
3. The system of claim 1, wherein the second chamber means
comprises: a chemical vapor deposition (CVD) apparatus configured
and arranged for growing single wall carbon nanotubes.
4. The system of claim 3, wherein the CVD apparatus is configured
and arranged to introduce carbon feedstock gas for growing carbon
nanotubes in the second chamber means.
5. The system of claim 3, wherein the CVD apparatus is configured
and arranged to introduce the carbon feedstock gas to a catalyst
for growing carbon nanotubes in the second chamber means.
6. The system of claim 1, wherein the second chamber means is
configured and arranged to grow carbon nanotubes from a catalyst
island on a substrate in the chamber.
7. The system of claim 1, wherein the second chamber means is
further configured and arranged to grow a carbon nanotube extending
between the catalyst island and a circuit node.
8. The system of claim 1, wherein the second chamber means is
further configured and arranged to grow a circuit including a
carbon nanotube extending between two circuit nodes and adapted for
conducting electricity between the two circuit nodes.
9. The system of claim 1, wherein the second chamber means is
further configured and arranged to grow a carbon nanotube extending
from a cantilever tip.
10. The system of claim 9, wherein the second chamber means is
further configured and arranged for holding a wafer including a
multitude of cantilever tips and to grow carbon nanotubes extending
from a plurality of the multitude of cantilever tips.
11. The system of claim 1, wherein the second chamber means is
further configured and arranged to grow a carbon nanotube extending
between two catalyst islands.
12. The system of claim 1, wherein the second chamber means is
further configured and arranged to grow a carbon nanotube from a
catalyst island including an alumina-supported iron catalyst.
13. The system of claim 1, wherein the second chamber means is
further configured and arranged to grow a plurality of carbon
nanotubes extending from catalyst islands patterned on a
substrate.
14. The system of claim 1, wherein a gas supply is configured and
arranged for introducing the carbon feedstock gas to the second
chamber means.
15. The system of claim 14, wherein the gas supply is configured
and arranged for introducing a carbon feedstock gas including
Methane to the second chamber means to grow the carbon
nanotube.
16. The system of claim 1, wherein the second chamber means is
configured and arranged to grow the carbon nanotube from catalyst
particles lithographically patterned on a substrate.
17. The system of claim 1, wherein the carbon nanotube is grown at
a temperature of less than about 1000 degrees Celsius.
18. The system of claim 17, wherein the carbon nanotube is grown at
a temperature of between about 850 and 100 degrees Celsius.
19. A system for manufacturing a carbon nanotube device, the system
comprising: a chamber apparatus adapted to provide internal heat at
at least one controlled level; and a gas supply configured and
arranged with the chamber apparatus for contacting a catalyst
island in the chamber with a carbon-containing gas and forming,
under said at least one controlled level of heat, a carbon nanotube
extending from the catalyst island.
20. The system of claim 19, wherein the gas supply and the chamber
apparatus are adapted to contact the carbon-containing gas to the
catalyst island for a period of time sufficient to form carbon
nanotubes.
21. The system of claim 19, wherein the chamber apparatus is
further adapted for heating the catalyst island.
22. The system of claim 19, wherein the gas supply is configured
and arranged for contacting the catalyst island with a carbon
containing gas that has been reacted using a catalyst.
23. The system of claim 19, wherein the chamber apparatus is
configured and arranged to heat a substrate to decompose a catalyst
material to form the catalyst island.
24. The system of claim 19, wherein the chamber apparatus is
configured and arranged to heat the substrate while introducing a
carbon feedstock gas to the catalyst material and growing an
aligned carbon nanotube extending from the catalyst material and
across the trench.
Description
RELATED PATENT DOCUMENTS
[0001] This is a divisional of U.S. patent application Ser. No.
10/042,426 (STFD.021C1) filed on Jan. 7, 2002 and entitled "Carbon
Nanotube Structure Having A Catalyst Island," which is a
continuation of U.S. patent application Ser. No. 09/133,948
(STFD.021PA/S98-049) filed on Aug. 14, 1998, now U.S. Pat. No.
6,346,189, and entitled "Carbon Nanotube Structures made Using
Catalyst Islands," to which priority is claimed under 35 U.S.C.
.sctn.120.
FIELD OF THE INVENTION
[0002] The present invention relates generally to carbon nanotubes
and more particularly to the growth of carbon nanotubes using
catalyst islands.
BACKGROUND
[0003] Carbon nanotubes including single-walled carbon nanotubes
(SWNT) are ideal quantum systems for exploring basic science in
one-dimension. These novel molecular-scale wires, derived by
bottom-up chemical synthesis approaches are also promising as core
components or interconnecting wires for electronics and other
applications. Rich quantum phenomena have been revealed with SWNTs
and functional electronic devices such as transistors, chemical
sensors and memory devices have been built. In these and other
devices, it is sometimes desirable to use individual, high quality
SWNTs.
[0004] Obtaining individual, high quality, single-walled nanotubes
has proven to be a difficult task, particularly when manufacturing
the nanotubes in bulk quantities. Previous methods for the
production of nanotubes yield bulk materials with tangled
nanotubes. Nanotubes in such bulk materials are typically in a
bundled form. These tangled nanotubes are difficult to purify,
isolate, manipulate, and use as discrete elements for making
functional devices. For example, in making functional microscopic
devices, bulk tangled nanotubes are difficult to implement due to
the difficulty of isolating one individual tube from the tangled
nanotubes, manipulating the tube, and constructing a functional
device using the isolated tube. Also, carbon nanotubes manufactured
in this manner tend to exhibit molecular-level structural defects
that result in weaker tubes with poor electrical characteristics.
These and other difficulties have presented challenges to the
manufacture of carbon nanotubes for implementation in a variety of
applications, such as functional microscopic devices.
SUMMARY OF THE INVENTION
[0005] The present invention is directed to carbon nanotubes and
the fabrication thereof. The present invention is exemplified in a
number of implementations and applications, some of which are
summarized below.
[0006] In one example embodiment of the present invention, an
individual, distinct nanotube device includes a catalyst island and
a nanotube extending therefrom. In one implementation, the nanotube
is a single-walled carbon nanotube. The nanotube device is adapted
to be implemented in one or more semiconductor microstructures. In
one implementation, a chamber arrangement is adapted as a system
for manufacturing a carbon nanotube device. The arrangement
includes first chamber means for forming at least one island of
catalyst material, and second chamber means for contacting the
catalyst island with a carbon-containing gas and forming a carbon
nanotube extending from the catalyst island.
[0007] In another implementation, a chamber apparatus is configured
and arranged to heat a substrate while introducing a carbon
feedstock gas to an overlying catalyst material and growing an
aligned carbon nanotube extending from the catalyst material and
across the trench
[0008] In another implementation, the catalyst island is located on
a top surface of a semiconductor substrate, which may, for example,
include silicon, alumina, quartz, silicon oxide or silicon nitride.
The catalyst may include Fe.sub.2O.sub.3 or other catalyst
materials including molybdenum, cobalt, nickel, or zinc and oxides
thereof. In one implementation, the catalyst island is between
about 1 and 5 microns in size.
[0009] In another example embodiment of the present invention,
individual, distinct single-walled nanotubes are grown from
catalyst islands. The nanotubes are grown using a hydrocarbon gas
that is introduced to the catalyst islands, where the hydrocarbon
gas is reacted. The nanotube growth is confined to selected
locations, and the resulting nanotubes can be easily addressed and
integrated into structures to obtain functional microscopic
devices.
[0010] In another example embodiment of the present invention, a
nanotube-tipped atomic force microscope (AFM) device includes a
nanotube extending from a catalyst island on a cantilever tip. The
cantilever is adapted for use as a scanning tip in conventional AFM
applications.
[0011] In another example embodiment of the present invention, a
carbon nanotube device includes a substrate with two electrically
conductive catalyst islands coupled to one another by a nanotube
extending between the islands. The nanotube and the catalyst island
are adapted for electrically coupling to other circuitry, such as
via a conductive interconnect. In one implementation, the nanotube
is freestanding above the substrate and adapted for use as a high
frequency, high-Q resonator. In another implementation, one of the
catalyst islands is replaced by a conductive metal pad.
[0012] The above summary of the present invention is not intended
to describe each illustrated embodiment or every implementation of
the present invention. The figures and detailed description that
follow more particularly exemplify these embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The invention may be more completely understood in
consideration of the detailed description of various embodiments of
the invention that follows in connection with the accompanying
drawings, in which:
[0014] FIG. 1 shows a first step in making nanotubes, according to
an example embodiment of the present invention;
[0015] FIG. 2 shows a second step in making nanotubes, according to
another example embodiment of the present invention;
[0016] FIG. 3 shows a third step in making nanotubes, according to
another example embodiment of the present invention;
[0017] FIG. 4 shows a top view of a substrate with three catalyst
islands, according to another example embodiment of the present
invention;
[0018] FIG. 5 shows a top view of a single catalyst island that has
been used to grow nanotubes, according to another example
embodiment of the present invention;
[0019] FIG. 6 shows an apparatus that has a nanotube connected
between a catalyst island and a metal pad, according to another
example embodiment of the present invention;
[0020] FIG. 7 shows metal covers disposed on top of catalyst
islands and portions of nanotubes, according to another example
embodiment of the present invention;
[0021] FIGS. 8A-8C illustrate the metal covers, such as those of
FIG. 7, being made according to another example embodiment of the
present invention;
[0022] FIG. 9 shows a side view of a resonator made from a
freestanding nanotube supported by the ends of the nanotube,
according to another example embodiment of the present
invention;
[0023] FIG. 10 shows a top view illustrating a carbon nanotube
device, such as that shown in FIG. 9, being made according to
another example embodiment of the present invention;
[0024] FIGS. 11A and 1B illustrate a method of making a carbon
nanotube device, such as that shown in FIG. 9, according to another
example embodiment of the present invention;
[0025] FIG. 12 shows an atomic force microscope tip undergoing
manufacture, according to another example embodiment of the present
invention; and
[0026] FIGS. 13A-13D illustrate a method of producing a carbon
nanotube on a tip of an atomic force microscope cantilever,
according to another example embodiment of the present
invention.
[0027] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the
invention.
DETAILED DESCRIPTION
[0028] The present invention is believed to be applicable to a
variety of different devices and implementations, and the invention
has been found to be particularly suited for manufacturing carbon
nanotubes. While the present invention is not necessarily limited
to such applications, various aspects of the invention may be
appreciated through a discussion of various examples using this
context.
[0029] According to an example embodiment of the present invention,
a carbon nanotube device includes a single-walled carbon nanotube
extending from a catalyst particle. The particle may, for example,
be located on a surface, such as a top surface of a semiconductor
substrate or on a cantilever tip of an AFM. In one implementation,
the carbon nanotube device includes a plurality of catalyst islands
on a top surface of a substrate, each island having a carbon
nanotube extending therefrom.
[0030] FIGS. 1-5 show individually distinct carbon nanotubes being
grown, according to another example embodiment of the present
invention. In FIG. 1, a layer of resist 20 is disposed and
patterned on a top surface of a substrate 22 using, for example,
electron beam (e-beam) lithography. The substrate 22 is made of
material that may, for example, include one or more of silicon,
alumina, quartz, silicon oxide or silicon nitride, and in one
implementation, includes a metal film on the top surface. The
patterning results in at least one hole 24 in the resist 20 that
exposes the underlying substrate 22. In one implementation, holes
formed in the resist are about 3-5 microns in size and are spaced
apart by a distance 26 of about 10 microns.
[0031] In FIG. 2, a catalyst layer 28 is deposited on the surfaces
of the resist 20 and substrate 22. The catalyst layer may include
one or more of a variety of catalysts. In one implementation, the
catalyst includes a solution of Fe(NO.sub.3).sub.3 in methanol,
mixed with alumina nanoparticles having a diameter of about 15-30
nanometers. In other implementations, the catalyst includes one or
more of: elemental metals; oxides of elemental metals (e.g., iron,
molybdenum and zinc oxides); a mixture of iron, molybdenum and
ruthenium oxides; and iron salts such as Fe(SO4).
[0032] The nanoparticles can be made of many ceramic materials,
depending upon the application and available materials. For
instance, one or more of refractory oxide ceramic materials such as
alumina and silica can be used. In one particular application using
Fe(NO.sub.3).sub.3, the catalyst preparation includes mixing 4.0
grams of alumina nanoparticles with 1.0 gram of
Fe(NO.sub.3)*9H.sub.2O in 30 mL methanol for 24 hours. The mixture
is applied to the substrate and the methanol is evaporated, leaving
a layer 28 of alumina nanoparticles coated with Fe(NO.sub.3).sub.3
adhering to the resist and in the holes 24. In FIG. 3, a lift-off
process is performed, leaving isolated islands 29 of catalyst
(e.g., Fe(NO.sub.3).sub.3-coated nanoparticles) adhering in regions
where holes 24 existed. FIG. 4 shows a top view of the catalyst
islands 29.
[0033] The substrate 22 is heated and nanoparticles of the catalyst
are decomposed (e.g., the Fe(NO.sub.3).sub.3 is decomposed to
Fe.sub.2O.sub.3). The substrate may be heated, for example, by
placing the substrate in a furnace with an Argon atmosphere and
heating to between about 100-400 degrees Celsius. The decomposed
catalyst nanoparticles are an active catalyst that catalyzes the
formation of carbon nanotubes when exposed to methane gas at
elevated temperature.
[0034] In a more particular example embodiment of the present
invention, the substrate with catalyst islands 29 is heated in a
furnace at about 850-1000 degrees Celsius, and 99.99% pure methane
is flowed over the catalyst islands 29 at a velocity of about 2-20
centimeters per second to grow single-walled nanotubes. In one
implementation, a 1-inch diameter tube is used, wherein methane is
introduced at a flow rate of about 600-6000 cm.sup.3/min to achieve
a velocity of about 2-20 centimeters per second. The amount of time
that the methane is introduced to the catalyst island is sufficient
to react the methane and grow a nanotube, and in one
implementation, is about 10 minutes.
[0035] The nanotubes are formed substantially straight and without
structural flaws (e.g., all the carbon rings in the nanotubes have
6 carbon atoms instead of 5 or 7 carbon atoms). Most of the
nanotubes are single-walled, with diameters in the range of about
1-5 nanometers. At a furnace temperature of about 1000 degrees
Celsius, it has been discovered that about 90% of the nanotubes are
single-walled when grown. At a furnace temperature of about 900
degrees Celsius, about 99% of the tubes are single-walled with most
of the nanotubes having diameters in the range of about 1-2
nanometers. The nanotubes have large length to diameter aspect
ratios (e.g., approaching about 10,000) and are very straight, due
to the absence of structural flaws.
[0036] In another example embodiment of the present invention,
nanoparticles are not used in forming the catalyst. Small
quantities of Iron salts are deposited on the substrate (e.g., by
dissolving the iron salts in a solvent and evaporating the
solvent), and the substrate is heated to decompose the iron salts
without necessarily mixing the iron salts with nanoparticles.
[0037] In another example embodiment of the present invention, a
furnace chamber is configured and arranged for manufacturing carbon
nanotubes. The furnace is adapted to flow a carbon feedstock gas,
such as methane, and to react the carbon feedstock gas using a
catalyst for growing carbon nanotubes. In one implementation, the
furnace chamber is adapted to heat a substrate and catalyst to
between about 850 and 1000 degrees Celsius, and to flow methane gas
at a velocity of about 2-20 centimeters per second to a catalyst in
the furnace. The methane may, for example, be reacted at catalyst
islands on a substrate to form a carbon nanotube.
[0038] FIG. 5 shows a top view of the catalyst island 29 having a
plurality of nanotubes 30 grown therefrom in random directions. The
carbon nanotubes are disposed in contact with the substrate surface
and are firmly attached to the island 29. The nanotubes are grown
in a base-growth mode, where new carbon is added to the nanotubes
30 at the point where they are attached to the island 29, such that
an end of the nanotubes that is opposite the end attached to the
island is free. In one implementation, the nanotubes are adapted to
be used as resonators wherein the free end vibrates.
[0039] In another example embodiment of the present invention, the
carbon nanotubes 30 are not tangled together, are individually
separable and are spaced apart by a substantial distance. In one
implementation, between about 10-50 nanotubes are grown from a
catalyst island. The individually separable nanotubes are
particularly useful for the manufacture of electronic and
micromechanical devices, wherein individual nanotubes are
incorporated into the devices by appropriately locating islands 29.
Electrical and mechanical connections are easily made to individual
nanotubes if they are spatially separated and distinct.
[0040] In another example embodiment of the present invention,
larger numbers of nanotubes are grown (e.g., using a more effective
catalyst). The nanotubes grown in large numbers form bundles that
are useful for many electrical and mechanical devices such as field
effect transistors, single electron transistors, and resonators
that have only one fixed end.
[0041] FIG. 6 is a top view of an electronic device made by
locating the island 29 close to a patterned metal pad 32, according
to another example embodiment of the present invention. A single
nanotube 30a is grown extending from the island 29 to the metal pad
32 and electrically connecting the island 29 and pad 32. The island
29 and pad 32 are spaced apart by a distance in the range of
between about 100 nanometers and 5 microns, with the likelihood
that the nanotube grows to the pad 32 increasing as the distance
between the pad 32 and island 29 is reduced. The island 29 and pad
32 are both electrically conductive, and a patterned conductive
line 33 on the substrate surface electrically connects to the
nanotube 30a on a macroscopic scale. The nanotube 30a with such a
macroscopic electrical connection on each end can be used in many
devices including field-effect transistors, single electron
transistors and low current value fuses. In one implementation, the
conductive line 33 is applied to the substrate 20 before the island
29 is deposited, such that the island rests on top of the
conductive line 33. In another implementation, the conductive line
33 is disposed on top of the islands.
[0042] In another implementation (not shown), when two or more
nanotubes simultaneously electrically connect the island 29 and
metal pad 32, all but one of the nanotubes is broken with an AFM
tip. For instance, an AFM tip can be dragged across the substrate
surface so that it bends unwanted nanotubes until they break.
[0043] In another example embodiment of the present invention, a
second catalyst island is substituted for the metal pad 32. In this
implementation, the nanotube 30a provides electrical contact
between two catalyst islands instead of between the island 29 and
the metal pad 32. Metal line 33 similarly provides electrical
connection to the substituted catalyst island.
[0044] FIG. 7 shows a side view of a substrate 22 in which a metal
cover 34 is deposited on top of each catalyst island 29, according
to another example embodiment of the present invention. The metal
covers 34 include one or more of a variety of metals, such as
platinum or titanium-gold alloy. Each metal cover 34 covers a
portion of each island 29 and covers an end portion 37 of the
nanotube 30a and holds the nanotube 30a rigidly in place.
[0045] In another example embodiment of the present invention, the
substrate is heated to about 300 degrees Celsius in air after the
metal covers are deposited, and Ohmic electrical connection to the
ends of the nanotube 30a are formed. Metal lines, such as line 33
in FIG. 6, can then be connected to the metal covers to provide
macroscopic electrical connection to the nanotube 30a.
[0046] FIGS. 8A-8C show metal covers, such as those shown in FIG.
7, being made using lithographical patterning, according to another
example embodiment of the present invention. Referring to FIG. 8A,
a layer of spin-on resist 60 is deposited on top of catalyst
islands 29 and nanotube 30a. In FIG. 8B, the resist 60 is etched in
regions 61 where the metal covers 34 are to be located. A layer of
metal is then deposited over the resist 60 and catalyst 29 (e.g.,
by physical vapor deposition or CVD). The resist 60 is removed in a
lift-off process in FIG. 8C, leaving the metal covers 34.
[0047] In another example embodiment of the present invention, FIG.
9 shows a side view of a device including a freestanding nanotube
30b capable of acting as a high-Q resonator. The nanotube 30b is
disposed above a surface 36 of an etched trench region 35 in the
substrate 22 between catalyst islands 29 and is supported at ends
39 of the nanotube. In one implementation, the trench 35 and metal
covers 34 are combined in the same apparatus.
[0048] The structure in FIG. 9 is useful in a variety of
applications. In one example embodiment, the nanotube 30b is
resonated by applying a magnetic field thereto (e.g., perpendicular
to the length of the nanotube 30b) and passing an oscillating
current through the nanotube. A conductive film 37 is capacitively
coupled with the nanotube 30b and extracts a resonant signal from
the nanotube. In another implementation, the conductive film 37 is
used to electrostatically excite mechanical vibrations in the
nanotube 30b.
[0049] FIG. 10 shows a top view of a substrate 22 and islands 29,
which can be used to make a nanotube structure as shown, for
example, in FIG. 9. First, a nanotube 30b that connects catalyst
islands 29 is grown. Other nanotubes may also be grown from both
islands, but are not shown for clarity. Then, the substrate is
masked with a resist, such as a spin-on resist, leaving an unmasked
region defined by a box 38. Next, the region inside the box 38 is
exposed to an etchant that removes substrate material without
necessarily affecting the nanotube 30b. The etchant includes one or
more of a variety of etchants, depending upon the composition of
the substrate. For example, hydrofluoric acid can be used to etch
SiO.sub.2 or silicon substrates. Substrate below the nanotube 30b
is etched, resulting in the nanotube being supported only at its
ends 39 as shown in FIG. 9. Metal lines 33 are used to provide
macroscopic electrical connections to the nanotube 30b via the
catalyst islands 29. Metal covers, such as covers 34 in FIG. 8C,
can be deposited before or after etching the trench 35 to provide
Ohmic electrical connections to the nanotube and improved
mechanical stability for the nanotube ends 39.
[0050] FIGS. 11A and 11B show a suspended carbon nanotube being
manufactured, such as the nanotube shown in FIG. 9, according to
another example embodiment of the present invention. In FIG. 11A, a
substrate 22 is etched to form the trench 35 where a nanotube is to
be suspended. In FIG. 11B, islands 29 are disposed on opposite
sides of the trench 35 and a nanotube 30b is grown from the islands
29 and electrically connects the islands. The distance across the
etched substrate, and thus between the islands 20, is selected for
the characteristics of a particular application, including
manufacturing conditions and materials used. In connection with an
example embodiment of the present invention, it has been discovered
that using catalyst islands having a width of at least 1 micron and
spacing the islands at a distance that is less than about 10
microns apart is particularly useful in forming carbon nanotubes
extending between the two catalyst islands. In addition, if a
number of catalyst islands are spaced at varied distances in an
array, the likelihood of growing a carbon nanotube between islands
is improved. As in the example embodiments above, one of the
islands can be replaced with a metal pad, wherein the nanotube
grows from the island 29 to the pad. In addition, metal covers,
such as covers 34 in FIG. 8C, can be deposited on top of the
nanotube 30b and catalyst islands 29.
[0051] In another example embodiment of the present invention (not
shown), the nanotube 30b is freestanding, such that the nanotube is
supported on only one end by a catalyst island 29 (e.g., the
freestanding nanotube does not extend all the way across the trench
35). In this implementation, the nanotube is a cantilever and is
adapted to be used as a resonator.
[0052] FIG. 12 shows a catalyst particle 45 located on a tip 47 of
an atomic force microscope (AFM) cantilever 42, according to
another example embodiment of the present invention. The cantilever
42 is supported by a base 49 and has a free end 48 opposite the
base 49. The particle 45 may be made of one or more of a variety of
catalyst materials, such as Fe.sub.2O.sub.3 (decomposed from
Fe(NO.sub.3).sub.3) and others, as discussed above. The catalyst
particle 45 may or may not have supporting nanoparticles (e.g.,
silica or alumina particles), and is firmly attached to the tip 47.
Atomically sharp nanotubes 30 are grown from the particle 45, are
firmly attached to the cantilever and are useful as probe tips for
AFM. In one implementation (not shown), the cantilever does not
have a tip 47 and the particle is disposed directly on the
cantilever 42.
[0053] FIGS. 13A-13D show a carbon nanotube on a tip being
manufactured, according to another example embodiment of the
present invention. In FIG. 13A, a substrate 50 is coated with a
gold film 52, and droplets of Fe(NO.sub.3).sub.3 dissolved in
methanol are deposited on the gold surface. The methanol is then
evaporated, leaving only small particles 54 of Fe(NO.sub.3).sub.3
on the gold film 52. Next, an AFM tip 47 is brought into contact
with a particle 54 of Fe(NO.sub.3).sub.3 in FIG. 13B. An electric
field is then applied between the tip 47 and the gold film 52. The
electric field adheres the Fe(NO.sub.3).sub.3 particle to the tip
47. In one implementation, the electric field also causes the
Fe(NO.sub.3).sub.3 to decompose into Fe.sub.2O.sub.3. In FIG. 13C,
the cantilever 42 and tip 47 with the adhered Fe(NO.sub.3).sub.3
particle 54 is removed from the gold film 52. The cantilever 42 and
tip 47 are heated to fully decompose the Fe(NO.sub.3).sub.3
particle 54 into an Fe.sub.2O.sub.3 particle 54 in FIG. 13D (e.g.,
as shown in FIG. 12). Nanotubes 30 are then grown from the catalyst
particle 45.
[0054] While the present invention has been described with
reference to several particular example embodiments, those skilled
in the art will recognize that many changes may be made thereto
without departing from the spirit and scope of the present
invention.
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