U.S. patent application number 11/671883 was filed with the patent office on 2007-06-07 for method of forming a heterojunction of a carbon nanotube and a different material, method of working a filament of a nanotube.
This patent application is currently assigned to NEC CORPORATION. Invention is credited to Sumio Iijima, Yuegang Zhang.
Application Number | 20070128101 11/671883 |
Document ID | / |
Family ID | 26477711 |
Filed Date | 2007-06-07 |
United States Patent
Application |
20070128101 |
Kind Code |
A1 |
Zhang; Yuegang ; et
al. |
June 7, 2007 |
METHOD OF FORMING A HETEROJUNCTION OF A CARBON NANOTUBE AND A
DIFFERENT MATERIAL, METHOD OF WORKING A FILAMENT OF A NANOTUBE
Abstract
A carbon nanotube is contacted with a reactive substance which
is a metal or a semiconductor. The reactive substance is heated to
diffuse atoms of the reactive substance into the carbon nanotube so
that the carbon nanotube is partially transformed or converted into
carbide as a reaction product. Thus, a heterojunction of the
reaction product and the carbon nanotube is formed. For example,
the carbon nanotube (2) is contacted with a silicon substrate (1).
The silicon substrate (1) is heated to cause solid-solid diffusion
of Si. As a result, SiC (3) is formed as the heterojunction. At
least a part of a filament material of a carbon nanotube is
irradiated with electromagnetic wave to deform the filament
material.
Inventors: |
Zhang; Yuegang; (Tokyo,
JP) ; Iijima; Sumio; (Tokyo, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
NEC CORPORATION
Tokyo
JP
|
Family ID: |
26477711 |
Appl. No.: |
11/671883 |
Filed: |
February 6, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10623659 |
Jul 22, 2003 |
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11671883 |
Feb 6, 2007 |
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09736220 |
Dec 15, 2000 |
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10623659 |
Jul 22, 2003 |
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09327510 |
Jun 8, 1999 |
6203864 |
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09736220 |
Dec 15, 2000 |
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Current U.S.
Class: |
423/447.1 ;
977/842 |
Current CPC
Class: |
H01L 51/0595 20130101;
H01L 51/0048 20130101; Y10T 428/2902 20150115; Y10S 977/721
20130101; Y10S 977/842 20130101; B82Y 40/00 20130101; H01L 51/002
20130101; H01L 51/0015 20130101; H01L 51/42 20130101; C01B 32/984
20170801; H01L 51/0587 20130101; B82Y 10/00 20130101; Y10S 977/744
20130101; B82Y 30/00 20130101; Y10T 428/21 20150115; C01B 32/168
20170801; Y10S 977/742 20130101; Y10S 977/844 20130101 |
Class at
Publication: |
423/447.1 ;
977/842 |
International
Class: |
D01F 9/12 20060101
D01F009/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 8, 1998 |
JP |
1998-158765 |
Apr 16, 1999 |
JP |
1999-147041 |
Claims
1. A method of working a filament material, comprising the step of
irradiating at least a part of said filament material with
electromagnetic wave to deform said filament material.
2. A method as claimed in claim 1, wherein said electromagnetic
wave is visible light.
3. A method as claimed in claim 1, wherein said filament material
is of a carbon nanotube.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a method of forming a
heterojunction of a carbon nanotube and a different material and,
in particular, to a method of forming a heterojunction of a carbon
nanotube and carbide.
[0002] This invention relates also to a filament, a method of
inducing an electric current therein, and a method of working the
same and, in particular, to a filament having a nanostructure and
adapted for use in a micromachine and an electron source, a method
of inducing an electric current therein, and a method of working
the same.
[0003] A so-called heterojunction formed by heterogeneous or
different materials is an important structure in order to utilize
material-specific characteristics in an electronic device.
[0004] A carbon nanotube comprises a graphite sheet composed of
six-member carbon rings and has a cylindrical structure formed by
rolling the graphite sheet in a manner such that the six-member
carbon rings are aligned in a helical fashion.
[0005] The carbon nanotube, together with a spherical fullerene
represented by C.sub.60, is expected as a useful material for an
electronic device because of its specific electric characteristics.
Particularly, attention is directed to a bond of the carbon
nanotube and carbide.
[0006] This is because carbide itself has very interesting electric
characteristics. For example, SiC has semiconducting features. TiC
has metallic features. Fe.sub.3C acts as a ferromagnetic material.
NbC attracts the attention as a superconducting material. BC.sub.x,
serves as an insulator. Thus, carbide has a wide variety of
electric characteristics.
[0007] On the other hand, a single-wall carbon nanotube has
specific electric characteristics. That is, the single-wall carbon
nanotube acts as a semiconductor or a metal in dependence upon a
diameter and a helical condition (an angle formed between an axial
direction of the nanotube and an aligning direction of carbon
atoms) (M. S. Dresselhaus et al "Science of Fullerenes and Carbon
Nanotubes" (Academic Press, New York, 1996)). It is expected that
various functional devices can be achieved by a combination of
carbide and the carbon nanotube.
[0008] However, no conventional technique exists to form such
heterojunction of carbide and the carbon nanotube. This is because
the carbon nanotube has a very high Young's modulus and is
therefore difficult to be mechanically processed or deformed.
[0009] In order to produce a carbide nanorod using the carbon
nanotube as a starting material, use has been made of a technique
of contacting a multiwall carbon nanotube with volatile oxide such
as SiO and B.sub.2O.sub.2 or halide such as SiI.sub.4, TiI.sub.4,
NbI.sub.4, and FeCl.sub.3 to cause high-temperature reaction (H.
Dai et al "Synthesis and characterization of carbide nanorods",
Nature, Vol. 375, pp. 769-772, (1995); D. Zhou et al "Production of
silicon carbide whiskers from carbon nanoclusters", Chem. Phys.
Lett., Vol. 222, pp. 233-238 (1994); W. Han et al "Continuous
synthesis and characterization of silicon carbide nanorods", Chem.
Phys. Lett., Vol. 265, pp. 374-378 (1997)). Another technique is
disclosed in EP 60388 A2 (1993) in which carbon fiber is
transformed or converted into a SiC rod by the use of SiO
vapor.
[0010] In the above-mentioned techniques of producing the carbide
nanorod by the use of vapor-solid reaction, the carbon nanotube is
exposed to reactive vapor to transform a whole of the carbon
nanotube into carbide. Therefore, those techniques can not be
applied to formation of the heterojunction. In other words, in
order to realize the heterojunction, a part of the carbon nanotube
must be selectively transformed into carbide with a remaining part
protected from the reaction. However, no conventional technique can
achieve such selective reaction.
[0011] Since a single-wall carbon nanotube (SWCNT) having a
nanostructure has been discovered (Iijima et al, "Pentagons,
heptagons and negative curvature in graphite microtubule growth",
Nature, vol. 356, p776, (1992)), physical properties of the SWCNT
are gradually revealed and research and development for practical
applications are actively carried out.
[0012] The SWCNT comprises a hexagonal network graphite plane
rolled into a cylindrical shape. The SWCNT has an electron
structure widely varied depending upon a tube diameter and a chiral
angle. Therefore, the electric conductivity of the SWCNT is
variable between that of a metal and that of a semiconductor. The
SWCNT is believed to have a feature similar to one-dimensional
electric conductivity.
[0013] For example, the SWCNT is applicable to a filament having a
nanostructure. For use as the filament, the SWCNT must be deformed
into a desired shape. A technique of selectively deforming the
SWCNT is expected to be useful in application to micromachines and
in facilitating the preparation of high-resolution probes (see H.
Dai et al "Nanotubes as nanoprobes in scanning probe microscopy",
Nature, Vol. 384, pp. 147-150 (1996) and S. S. Wong et al
"Covalently functionalized nanotubes as nanometre-sized probes in
chemistry and biology", Nature, Vol. 394, pp. 52-55 (1998)).
[0014] On the other hand, a technique of selectively feeding an
electric current to the filament having a nanostructure, such as
the SWCNT, shows a possibility of development of electronic devices
having a microstructure (S. J. Tans et al "Room-temperature
transistor based on a single carbon nanotube", Nature, Vol. 393,
pp. 49-52 (1998)). In addition, this technique is useful as one of
the high-resolution techniques in analysis evaluation. Thus, this
field of technique is highly expected.
[0015] To meet such expectation, proposal is made of a filament of
a field emission type (Jean-Marc Bonard et al "Field emission from
single-wall carbon nanotube films", Appl. Phys. Lett. Vol. 73, pp.
918-920 (1998)). The filament comprises a plurality of SWCNT
filaments scattered over a plurality of electrodes formed on a
substrate. By applying a predetermined voltage between the
electrodes, electrons are emitted from the filaments.
[0016] As compared with a typical thermionic emission type, the
above-mentioned filament is advantageous in the following respects.
Specifically, heating is unnecessary so that energy efficiency is
high. The filament comprises carbon atoms alone and is manufactured
at a low cost. In recent years, much attention is directed to this
field of technique.
[0017] In order to individually and selectively deform the
filament, for example, a manipulation technique is necessary.
Manipulation of those filaments using the SWCNTs and having a
nanostructure requires high resolution comparable to that required
in manipulation of atoms. Therefore, it is in fact impossible to
selectively deform the filament.
[0018] In addition, there is no existing technique of selectively
inducing an electric current in the filament of a nanostructure.
Thus, it is impossible to selectively induce the electric current
in the filament using the SWCNT having a nanostructure.
SUMMARY OF THE INVENTION
[0019] It is therefore an object of this invention to provide a
method of forming a heterojunction of a carbon nanotube and
carbide, which is useful for an electronic device.
[0020] It is therefore an object of this invention to provide a
filament such as a SWCNT having a nanostructure which can be
individually and selectively deformed into a desired shape.
[0021] It is another object of this invention to provide a filament
such as a SWCNT having a nanostructure in which an electric current
can be selectively induced.
[0022] It is still another object of this invention to provide a
method of inducing an electric current in the above-mentioned
filament.
[0023] It is yet another object of this invention to provide a
method of selectively deforming the filament.
[0024] According to this invention, there is provided a method of
producing a heterojunction of a carbon nanotube and carbide,
wherein a part of the carbon nanotube is contacted with a reactive
substance to cause reaction of the carbon nanotube and the reactive
substance by solid-solid diffusion.
[0025] With the above-mentioned method, the reaction of the carbon
nanotube is restricted to a contacting area where the carbon
nanotube is contacted with the reactive substance and an adjacent
zone around the contacting area. In a most part of a noncontacting
area, the carbon nanotube is not changed in structure. Therefore,
it is possible to form a heterojunction of the carbon nanotube and
carbide.
[0026] According to this invention, there is provided a filament
comprising a filament material which is deformed by irradiation of
electromagnetic wave to at least a part thereof.
[0027] Preferably, the filament material is a nanotube.
[0028] Preferably, the nanotube is a single-wall nanotube.
[0029] Preferably, the nanotube has a bundled structure.
[0030] Preferably, the nanotube is a carbon nanotube.
[0031] According to this invention, there is provided a method of
inducing an electric current in a filament, comprising the step of
irradiating at least a part of a filament material with
electromagnetic wave to selectively induce the electric current in
the filament material.
[0032] According to this invention, there is provided a method of
working a filament, comprising the step of irradiating at least a
part of a filament material with electromagnetic wave to deform the
filament material.
[0033] Preferably, the electromagnetic wave is visible light.
BRIEF DESCRIPTION OF THE DRAWING
[0034] FIGS. 1A and 1B are schematic views for describing a method
of forming a heterojunction according to this invention;
[0035] FIG. 2A is an electron micrograph showing a heterojunction
of a bundle of a plurality of single-wall carbon nanotubes and SiC;
and
[0036] FIG. 2B is an electron micrograph showing a heterojunction
of a single-wall carbon nanotube and SiC.
[0037] FIGS. 3A and 3B are optical micrographs for describing a
method of working a filament according to one embodiment of this
invention;
[0038] FIGS. 4A and 4B are optical micrographs showing deformation
of the filament illustrated in FIGS. 3A and 3B at different levels
of irradiation energy;
[0039] FIG. 5 is an optical micrograph showing the filament
illustrated in FIGS. 3A and 3B irradiated with a laser beam;
and
[0040] FIG. 6 is a view showing the result of measurement of an
electric current induced in the filament illustrated in FIG. 5.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0041] Now, description will be made about a preferred embodiment
of this invention with reference to the drawing.
[0042] As a reactive substance, use is made of a metal such as Ti,
W, Mo, V, Fe, and Nb or a semiconductor such as Si. A part of a
carbon nanotube is contacted with the reactive substance.
Preferably, the reactive substance is held in a vacuum or an
inactive gas. At least the reactive substance is heated to diffuse
the reactive substance towards the carbon nanotube. Thus, the
reaction between the carbon nanotube and the reactive substance
proceeds.
Embodiment
[0043] A heterojunction of a single-wall carbon nanotube and SiC
was formed by the use of single crystal silicon as a reactive
substance. At first, a (111) plane silicon wafer was cut into a
dimension of about 7 mm long and about 3 mm wide in a direction
perpendicular to a substrate. Thereafter, mechanical polishing was
performed until the thickness of a center portion is reduced to the
order of several tens of microns. Then, chemical etching was
performed until the thickness is further reduced to the order of
several tens of nanometers. Thus, a silicon substrate 1 was
prepared. As an etchant, a mixed solution of HF and HNO3
(HF:HNO3=1:4) was used. An oxide film on the surface of the silicon
substrate was removed by chemical etching.
[0044] A number of single-wall carbon nanotubes 2 prepared by laser
ablation were dispersed in ethanol and put on the silicon substrate
1 prepared as described above. In this event, most of the carbon
nanotubes 2 were extended, heavily bent, or bundled together. After
ethanol was evaporated from the silicon substrate 1, each of the
carbon nanotube 2 was placed on the silicon substrate 1 with its
three-dimensional structure maintained. As a result, the silicon
substrate 1 and the carbon nanotube 2 were partially contacted in a
small area (FIG. 1A). Thus, a sample was prepared.
[0045] Then, the sample was mounted on a heating stage of a
ultra-high-vacuum transmission electron microscope (UHV-TEM,
JEM-2000FXVII). A vacuum chamber was evacuated to a pressure
between 10-9 and 10-8 Torr.
[0046] The silicon substrate 1 was directly supplied with an
electric current to heat the sample. As a result of measurement by
a pyrometer, the highest temperature of the silicon substrate 1 was
about 1000.degree. C. When the temperature became higher than about
800.degree. C., surface migration of silicon was observed.
[0047] By observation through the transmission electron microscope
(TEM), it was confirmed that heating for several minutes caused
local reaction of silicon and the single-wall carbon nanotube to
produce SiC 3 (FIG. 1B). Heating was carried out for different
heating periods controllably varied within a range from several
minutes to one hour. However, no difference in appearance was
observed in dependence upon the heating periods. The heterojunction
of the single-wall carbon nanotube and SiC thus obtained was shown
in each of FIGS. 2A and 2B as a micrograph taken by the TEM. FIG.
2A shows the heterojunction of a bundle of a plurality of
single-wall carbon nanotubes and SiC while FIG. 2B shows the
heterojunction of one single-wall carbon nanotube and SiC.
[0048] Although the preferred embodiment has been described in the
foregoing, this invention is not restricted thereto but can be
modified in various manners within the scope of this invention. For
example, not only the single-wall carbon nanotube but also a
multiwall carbon nanotube can be used. In the foregoing embodiment,
heating was performed by feeding the electric current to the
substrate. Alternatively, the electric current may be supplied
between the carbon nanotube and the substrate. Instead of the
electric current, use may be made of any other heating means such
as infrared radiation. The heating may be performed not only in the
vacuum but also in an argon or a nitrogen atmosphere.
[0049] As described above, the method according to this invention
comprises the step of partially contacting the carbon nanotube with
the reactive substance to cause the reaction between carbon
nanotube and the reactive substance by solid-solid diffusion of the
reactive substance. Thus, by the above-mentioned method which is
very simple, it is possible to selectively form the heterojunction
between a part of the carbon nanotube and carbide. The
heterojunction of the carbon nanotube and carbide achieved by this
invention is useful in formation of electronic devices and will
make a great contribution to electronic industry.
[0050] Now, description will be made about a filament according to
one embodiment of this invention as well as a method of inducing an
electric current in the filament and a method of working the
filament.
[0051] The filament having a nanostructure comprises a filament
material on the order of nanometers. At least a part of the
filament material is irradiated with electromagnetic wave such as
visible light to deform the filament material into a desired shape,
for example, an arcuate shape or a .eta. shape.
[0052] As the filament material, use is advantageously made of a
nanotube (NT), particularly, a single-wall carbon nanotube (SWCNT)
or a plurality of SWCNTs in a bundled structure.
[0053] Next, the method of working the filament will be
described.
[0054] At first, a SWCNT as the filament material is formed by
laser ablation known in the art (see Y. Zhang et al "Microscopic
structure of as-grown single-wall carbon nanotubes by laser
ablation", Philosophical Magazine Letters, Vol. 78, No. 2, pp.
139-144 (1998)).
[0055] Specifically, a graphite target containing 1.2at % of Ni and
Co as catalysts was placed in a furnace heated to 1200.degree. C.,
kept at a pressure of 500 Torr, and supplied with an Ar gas at a
flow rate of about 300 sccm. By the use of a Nd-doped YAG
(yttrium-aluminum-garnet) laser, the graphite target was irradiated
with second harmonic produced by the YAG laser to obtain the SWCNT.
The second-order harmonic wave has a pulse width of about 8 ns and
energy per pulse of about 3J/cm.sup.2.
[0056] Then, the SWCNT was put in a sample cell having a quartz
window with two electrodes arranged inside.
[0057] Within the sample cell, the SWCNT guided by a stream of the
Ar gas was caught between the electrodes. Thereafter, the sample
cell is evacuated to a pressure of 0.1 Torr.
[0058] Next, the SWCNT was irradiated through the quartz window of
the sample cell with visible light emitted from a halogen lamp of
150 W to obtain a filament deformed into a desired shape.
[0059] Referring to FIGS. 3A and 3B, the filament before and after
irradiation of the visible light is shown, respectively. Herein,
the visible light had irradiation energy of about 20
mW/cm.sup.2.
[0060] As will be understood from FIGS. 3A and 3B, the filament can
be deformed into a desired shape by simply irradiating the filament
with the visible light. The deformation of the filament can be
controlled by selecting the irradiation energy of the visible light
and the irradiation area of the filament.
[0061] Referring to FIGS. 4A and 4B, the deformation of the
filament is dependent upon the level of the irradiation energy. In
FIG. 4A, the visible light had the irradiation energy of 30
mW/cm.sup.2. In FIG. 4B, the visible light had the irradiation
energy of 5 mW/cm.sup.2.
[0062] As seen from FIGS. 4A and 4B, the deformation of the
filament apparently depends upon the level of the irradiation
energy.
[0063] Referring to FIG. 5, the filament was irradiated with a
laser beam having a wavelength of 632 nm and irradiation energy of
about 800 mW/cm.sup.2 by the use of a He--Ne laser. The deformation
of the filament was substantially equivalent to that of the
filament illustrated in FIG. 4A.
[0064] Referring to FIG. 6, an electric current was induced in the
filament when the filament was irradiated at the center between two
electrodes with a laser beam having a wavelength of 632 nm and
irradiation energy of about 800 mW/cm.sup.2 by the use of a He--Ne
laser. The result of measurement of the electric current is
illustrated in the figure.
[0065] As seen from FIG. 6, it is possible to selectively induce
the electric current in the filament by irradiating the filament
with the laser beam.
[0066] According to this embodiment, it is possible to individually
and selectively deform the filament of a nanostructure such as
SWCNT by irradiating the filament with electromagnetic wave such as
visible light.
[0067] It is also possible to induce the electric current in the
filament by irradiating the filament with electromagnetic wave such
as visible light.
[0068] In each of the above-mentioned operations, it is sufficient
to simply irradiate at least a part of the filament with the
electromagnetic wave such as visible light. Thus, the operation is
very simple and convenient. The filament can be applied as a
nanoelectronics element.
[0069] In the foregoing, description has been made about one
embodiment of the filament, the method of inducing the electric
current in the filament, and the method of working the filament.
However, this invention is not restricted to the foregoing
embodiment but can be modified in various manners within the scope
of this invention.
[0070] For example, the halogen lamp and the He--Ne laser are used
in the foregoing embodiment. However, similar effect is achieved by
the use of any other light or energy source.
[0071] As described above, according to this invention, it is
possible to individually and selectively deform the filament of a
nanostructure such as the SWCNT into a desired shape.
[0072] By irradiating the filament with electromagnetic wave such
as visible light, it is possible to selectively induce the electric
current in the filament.
* * * * *