US20070041889A1

US20070041889A1 - Process and device for upgrading current emission

Info

Publication number: US20070041889A1
Application number: US11/430,058
Authority: US
Inventors: Kuo-Chu Hwang
Original assignee: National Tsing Hua University NTHU
Current assignee: National Tsing Hua University NTHU
Priority date: 2002-12-05
Filing date: 2006-05-08
Publication date: 2007-02-22

Abstract

An art is provided to realize a current emitting device capable of emitting current of higher density under the same or lower onset emission voltage. The current emitting device is preferably an array of carbon nanotubes or a film including carbon nanotubes. The art is based on using O₂, and/or O₃, and/or CO₂, and/or NO₂, and/or SO₂, and/or SO₃to oxidize a current emitting device composed of material including carbon, until the current emitting device has at least part thereof changed in shape. The current emitting device thus processed works better with a display, or becomes capable of emitting current of higher density under the same or lower onset emission voltage. As far as experiments showed, the emitted current density achieved by the art can be eight times the amount emitted by an array of nanotubes having not been processed according to the art, and the onset emission voltage can be lowered by the art from 0.8 V/μm to 0.5 V/μm.

Description

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of prior, pending application Ser. No. 10/313,757, filed on Dec. 5, 2002.

FIELD OF THE INVENTION

The present invention generally relates to a current emitting device, and particularly to a carbon nanotube used for emitting electrons, and to a process applied thereto.

BACKGROUND OF THE INVENTION

Pretty much effort has been made by many to explore or discover new schemes for emitting electrons to drive a display screen or another device. This is particularly crucial when application of a display to a mobile apparatus becomes popular and size minimiion of apparatus including a display is eagerly expected. The most significant one among the new schemes explored or discovered for his purpose is to have a current emitting device easily made to be of smaller size while being capable of emitting electrons for driving a display screen, without need of higher onset emission voltage or even with lower onset emission voltage in order to minimize voltage source capacity. Obviously a current emitting device of smaller size, and a voltage source of smaller capacity and/or lower voltage level, both will significantly contribute to the size minimization of an apparatus including a display screen. An apparatus requiring lower operating voltage (due to lower onset emission voltage for emitting electrons to drive the display screen) consumes less energy, resulting in longer operating time period on the basis of the same battery capacity. These are particularly crucial to a mobile apparatus with a display thereon.
To realize a current emitting device with features described above, many kinds of means have been tried, among which a carbon nanotube array or film (ie., an array composed of a plurality of carbon nanotubes, or a film including a plurality of carbon nanotubes) has received significant attention. However wishfilly a carbon nanotube is used as a current emitting device, it suffers from its incapability of emitting sufficient electrons to drive a display screen under a realizable onset emission voltage. It can thus be understood that a critical condition for a carbon nanotube to be used as a current emitting device for driving a display screen is its capability of emitting sufficient electrons to drive a display screen under a realizable onset emission voltage.
As carbon nanotubes have been so far regarded as the best potential current emitting device for driving a display screen (particulary if the display is expected to be as small as possible, or to be installed where capacity and/or voltage-level of power source is limited), attepts have been made by scientists to have a carbon nanotube capable of emitting more electrons under an onset emission voltage which is more realizable. An impressive one among the attempts was described in a paper disclosed by Lee and his co-workers. According to Lee's paper, carbon nanotube arrays were grown on iron/silica substrate, and then peeled off and reversed with its bottom side (originally contacting the substrate) facing upward, resulting in open-ended carbon nanotubes, leading to a very low turn-on voltage of 0.6-1.0 V/μm (conventional onset emission voltage of vertically aligned carbon nanotubes formed by CVD process is reported to be in the range of 4-0.9V/μm). Although the attempt achieves low onset emission voltages, the required process includes peeling off and reversing an array or film of nanotubes, which requires sophisticated skill and is difficult to implement, particularly when commercializtion of a product is concerned. This is why a lot of attempts are still being made to achieve a current emitting device which can be easily produced to emit sufficient electrons for driving a display screen under an economically realizable onset emission voltage. One of the most promising among those attempts is to have carbon nanotubes or the like which can be easily formed and better applied to practical products.
Research and experiments for the present invention were therefore initiated long before a significant achievement was reached in March, 2001 by the applicants, with disclosure thereof received by American Institute of Physics on Dec. 27, 2001, and published thereby on Jun. 24, 2002 (Applied Physic Letters, Volume 80, Number 25).
US Patent Application 2003/0143398 discloses an art in which use of oxygen plasma
is suggested for etching the tip of nanotube to have the tip opened for improving the field emission characteristics of the nanotube. The use of oxygen plasma is much more complicated and expensive compared to the use of O₂, or O₃, or CO_2,or NO_2,or SO₂, or SO₃embodied according to the present invention for oxidizing a nanotube to have at least a depression or a tip formed thereon for upgrading the electron emission capability thereof.
US Patent Application 2002/0197474, filed Jun. 3, 2002 (almost half a year after the disclosure of the present invention was received by American Institute of Physics), not necessarily a prior art to the present invention, disclosed an art in which use of argon/oxygen plasma is suggested to functionalize carbon nanotubes for improving electrical and mechanical properties of the nanotubes, wherein carboxylate, hydroxyl, aldehyde, or ketone group is thereby attached on the carbon nanotubes. No suggestion of forming a depression or a tip on a nanotube to improve the electron emission capability of the nanotube is found in the art of US Patent Application 2002/0197474. The present invention differs from the art (not necessary qualified as a prior art) in that nanotubes are oxidized, according to the present invention by using O₂, or O₃, or CO₂, or NO₂, or SO₂, or SO₃, to have a depression or a tip formed on the nanotube for upgrading the current emission capability of the nanotube. The art provided by the present invention to oxidize a nanotube until a depression or a tip is formed thereon for upgrading the current emission capability thereof, is neither disclosed nor suggested by US Patent Application 2002/0197474, not to mention the fact that US Patent Application 2002/0197474 is not necessarily qualified as a prior art.
For more information about carbon nanotubes, reference to U.S. Pat. Nos. 6,303,094 and 6,380,671, and inventor's paper published Jun. 24, 2002 shall be made.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a process applied to a current emitting device composed of material including carbon, for the current emitting device to be capable of working better with a display screen, particularly a display on a mobile or compact apparatus, or those on an apparatus with power source limited to lower voltage level or lower capacity.
It is therefore another object of the present invention to provide a process applied to an object composed of material including carbon, for the object to work better with a display.
It is therefore a further object of the present invention to provide a process applied to an object composed of material including carbon, for the object to be capable of emitting more electrons (i.e., to raise its current emission capability), or be able to emit electrons under lower onset emission voltage (i.e., under smaller applied electric field).
Another further object of the present invention is to provide a current emitting device easily made to be capable of working better with a display, particularly a display on a mobile or compact apparatus, or those on an apparatus with power source limited to lower voltage level or lower capacity.
Other features, advantages, and objects may become apparent from the following detailed description with reference to the drawings.
In this disclosure, “onset emission voltage for emitting a current” means the electric field required for emitting the current, and “turn-on voltage” means the minimum electric field for any current emission.
One aspect of the present invention may be represented by a pross which is applied to a current emitting device having an exposed portion and composed of material including carbon, for the current emitting device to work better with a display or any apparatus requiring electronic current to be emitted from an object. The process comprises a step of oxidizing the current emitting device at an operating temperature until the shape of at least part of the exposed portion changes, wherein the operating temperature is higher than ambient temperature. Here the current emitting device may be in the shape of a tube or a nanotube or a ball (such as a spherical ball or an elliptical ball) with smaller size, or may even be in the shape of a half ellipsoid, and may stretch out (or be grown) from a substrate or a carrier to have a first portion connecting the substrate and a second portion (exposed portion) exposed to the air or space, or stretching outside the substrate (or the carrier). For example, the exposed portion includes a surface for emitting electrons to a display screen wherein the surface of the exposed portion may face or partially face the display screen which is to be driven (i.e., collided) by the electrons emitted from the exposed portion of the current emitting device. All of the second portion, i.e., all the portion which stretches out from the substrate (or carrier), may be regarded as an exposed portion of the nanotube according to the present invention. The exposed portion of the nanotube according to the present invention may have an end part if the nanotube is in the shape of a tube, and may not have an end part if the nanotube is in the shape of a ball. Obviously the end part of the exposed portion of the nanotube according to the present invention may or may not include what is named a “tip” in prior arts.
Another aspect of the present invention may be represented by a process which is applied to a current emitting device composed of material including carbon, for the current emitting device to work better with a display or any apparatus requiring emission of electronic current. Here the current emitting device may have no portion to be regarded as an end. For example, the current emitting device is in the shape of a ball, or in the shape similar to a ball, or a half ball with its flat surface on a substrate or a carrier. The direction the current emitting device emits electrons is not necessarily limited to a certain one or a certain range, and the emission of electrons is not necessarily from an end thereof.
If a current emitting device composed of material including carbon is oxidized by a fluid including O₃, the operating temperature for the oxidization to result in a current emitting device capable of working better with a display screen (or emitting current of higher density) can be as low as −50° C. (negative 50° C.), which simply is any temperature in the real world. Therefore a further aspect of the present invention may be represented by a process of oxidizing the current emitting device by a fluid including O₃at any temperature in the real world, to make the current emitting device capable of emitting current of higher density under the same or lower onset emission voltage.
A current emitting device composed of material including carbon, such as an array of carbon nanotubes, after being oxidized using O₂, or O₃, or CO₂, or NO₂, or SO₂, or SO₃according to the present invention, will usually have carboxylic acid group (—COOH) and/or hydroxyl group (—OH) and/or ketone group (>C═O) and/or aldehyde group (—CHO) and/or alcohol group (—>COH) and/or ester group (—COO—) and/or ether group (C—O—C linear structure) and/or epoxide group (COC tricyclic ring) on at least part of the surface of the nanotube (specifically on the surface of its exposed portion). Therefore another further aspect of the present invention is represented by a current emitting device comprising an array of carbon nanotubes, wherein the nanotube comprises: a first portion connecting a substrate; and a second portion with a surface including at least a depression or a tip and having or partly having thereon an oxygenated group such as carboxylic acid group (—COOH) and/or hydroxyl group (—OH) and/or ketone group (>C═O) and/or aldehyde group (—CHO) and/or alcohol group (—>COH) and/or ester group (—COO—) and/or ether group (C—O—C linear structure), and/or epoxide group (COC tricyclic ring).
For a current emitting device composed of material including carbon, the cause of changing in shape to be capable of emitting electrons of higher density under the same or lower onset emission voltage, is the cleavage of some C═C double bonds of carbon therein. The process according to the present invention is the unique art so far to cause the cleavage of C═C double bonds in a current emitting device composed of material including carbon, for the current emitting device to work better with a display, or to be capable of emitting larger current under the same or lower onset emission voltage. Therefore another still further aspect of the present invention is represented by a process applied to a current emitting device composed of material including carbon, to split the C═C double bonds of the current emitting device, so that the current emission capability of the current emitting device improves, i.e., the current emitting device becomes capable of emitting current of higher density under the same or lower onset emission voltage.
Obviously the application of a current emitting device processed according to the present invention is not necessarily limited to a display. Actually it may be used wherever the current emitted from an object plays a role.

DIFFERENCE BETWEEN THE PRESENT INVENTION AND TYPICAL PUBLISHED ARTS

U.S. Pat. No. 6,250,984 suggests that nanotubes with depressed tips will enhance electron emission. In contrast, either a depression or a tip on the surface of a nanotube oxidized according to the present invention will upgrade the current emission capability of the nanotube, regardless of the location of the depression or the tip on the surface of the nanotube, and regardless of the feature of the surface of the nanotube and the shape of the nanotube (the nanotube may be in the shape of a tube or in the shape of a ball or in any other shape according to the present invention). U.S. Pat. No. 6,250,984 does not suggest nanotubes with surface having oxygenated group thereon.
U.S. Pat. No. 5,698,175 suggests a lump of carbon nanotube powder in which the carbon nanotube includes a depressed tip and has ketone or carboxylic group on the surface thereof. In contrast, the current emitting device according to the present invention comprises an array of carbon nanotubes wherein the nanotube includes a surface having at least a depression or a tip thereon, and having oxygenated groups thereon which are not limited to ketone or carboxylic group, and can also be at least one of the groups of alcohol, aldehyde, ester, ether and epoxide.
US Patent Application 2003/0143398 disclosed an art in which use of oxygen plasma
is suggested for etching the tip of nanotube to have the tip opened for improving the field emission characteristics of the nanotube. In contrast, the carbon nanotube according to the present invention is oxidized by using O₂, or O₃, or CO₂, or NO₂, or SO₂, or SO₃to have a depression or a tip formed on the exposed portion (or surface) of the nanotube for upgrading the current emission capability of the nanotube.
The nanotube according to the present invention can be in the shape of a tube or a ball or in any other shape. The depression on the exposed portion (or surface) of the nanotube according to the present invention does not need to be formed at a tip, and either a depression or a tip can be formed anywhere (either on side wall or at end part of the exposed portion, typically see FIG. 4) on the surface of the nanotube according to the present invention. The depression formed on the surface of a nanotube according to the present invention does not correspond to the depression formed by opening a tip or an end of a nanotube according to U.S. Pat. No. 6,250,984 and US Patent Application 2003/0143398.
US Patent Application 2002/0197474, filed Jun. 3, 2002 (almost half a year after the disclosure of the present invention was received by American Institute of Physics), not necessarily qualified as a prior art to the present invention, disclosed an art in which use of argon/oxygen plasma is suggested to functionalize carbon nanotubes for improving electrical and mechanical properties of the nanotubes, wherein carboxylate, hydroxyl, aldehyde, or ketone group is thereby attached on the carbon nanotubes. No suggestion of forming a depression or a tip on a nanotube to improve the electron emission capability of the nanotube is found in the art of US Patent Application 2002/0197474. In contrast, according to the present invention, nanotube is oxidized by using O₂, or O₃, or CO₂, or NO₂, or SO₂, or SO₃to have a depression or a tip formed on the exposed portion (or surface) of the nanotube for upgrading the current emission capability of the nanotube. The art provided by the present invention to oxidize a nanotube until a depression or a tip is formed thereon for upgrading the current emission capability thereof, is neither disclosed nor suggested by US Patent Application 2002/0197474, not to mention the fact US Patent Application 2002/0197474 is not necessarily qualified as a prior art.
The present invention may best be understood through the following description with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram representing an image picture of two carbon nanotubes taken by a TEM (transmission electron microscope).
FIG. 2 is a diagram representing a picture view of an oxidized carbon nanotube taken by a TEM (transmission electron microscope), wherein oxidization was embodied according to the present invention.
FIG. 3 is a diagram representing another picture view of an oxidized carbon nanotube taken by a TEM (transmission electron microscope), wherein oxidization was embodied according to the present invention.
FIG. 4 is a diagram representing a further picture view of an oxidized carbon nanotube taken by a TEM (transmission electron microscope), wherein oxidization was embodied according to the present invention.
FIG. 5 is a diagram representing Emitted Current-Emission Voltage) plots of an original array of carbon nanotubes and those having been oxidized according to the present invention.
FIG. 6 is a diagram representing plots of 1n(J/E²) vs 1/E according to Fowler-Nordheim field emission theory, for an original array of carbon nanotubes and those having been oxidized according to the present invention.
FIG. 7 is a diagram representing (Emitted Current-Emission Voltage) plots of an original array of carbon nanotubes and those having been oxidized by O₃and BR₂according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, a carbon nanotube's exposed portion 11 has an end part 12 and can be used as a current emitting device to emit electrons. For example, an array of carbon nanotubes' exposed portions 11 may be used to emit electrons for driving a display screen (not shown in figures), i.e., the emitted electrons collide with a display screen to form images on the display screen. The carbon nanotube's exposed portion 11 may be regarded as having another end part 13 on or connecting a substrate or carrier (not shown in figures), or regarded as being grown from a substrate.
FIG. 2 shows a view of a carbon nanotube's exposed portion 21 which has been oxidized according to the present invention to have its end part 22 changed in shape. For example, at least a part 23 of end part 22 becomes depressed, and at least a part 24 thereof turns to be in the shape of a tip or similar to the shape of a tip, thereby the current emission capability of the carbon nanotube improves and/or the onset emission voltage thereof is lowered.
FIG. 3 shows a view of a carbon nanotube 31 which has been oxidized according to the present invention to have its end part 32 changed in shape. For example, at least a part 33 of end part 32 turns to be depressed, and at least parts 34 and 35 thereof turn to be in the shape of a tip or similar to the shape of a tip, thereby the current emission capability of the carbon nanotube improves and/or the onset emission voltage thereof is lowered.
FIG. 4 shows a view of a carbon nanotube 41 which has been oxidized according to the present invention to have at least the parts (indicated by three white arrows 43) of its exposed portion turned to be depressed, thereby the current emission capability of the carbon nanotube improves and/or the onset emission voltage thereof is lowered.
FIG. 5 shows (Emitted Current-Emission Voltage) plots of an original array of carbon nanotubes and those oxidized according to the present invention by gaseous fluid including Oxygen (O₂). Y axis represents emission current density J (unit: μA/cm²), and X axis represents applied electric field E (unit: V/μm). The curve represented by open circles ◯ is for an array of original carbon nanotubes (not oxidized according to the present invention). The curve represented by closed triangles ▴ is for an array of carbon nanotubes having been oxidized for 10 minutes at an operating temperature of 400° C. by gaseous fluid including Oxygen, or oxidized for 10 minutes by gaseous fluid including Oxygen and being at an operating temperature of 400° C. The curve represented by open triangles Δ is for an array of carbon nanotubes having been oxidized for 20 minutes at an operating temperature of 400° C. by gaseous fluid including Oxygen, or oxidized for 20 minutes by gaseous fluid including Oxygen and being at an operating temperature of 400° C. The curve represented by open stars ⋆ is for an array of carbon nanotubes having been oxidized for 25 minutes at an operating temperature of 400° C. by gaseous fluid including Oxygen, or oxidized for 25 minutes by gaseous fluid including Oxygen and being at an operating temperature of 400° C.
It can be seen from FIG. 5 that in terms of current emission capability of the nanotubes, the oxidization of the nanotubes for 10 minutes by gaseous fluid including Oxygen at an operating temperature of 400° C. makes no much difference from the original nanotubes (compare the two curves respectively represented by ▴ and ◯), but the oxidizations of the nanotubes for 20 and 25 minutes by gaseous fluid including Oxygen at an operating temperature of 400° C. make significant differences from the original nanotubes (compare the 3 curves respectively represented by Δ, ⋆, and ◯). For a condition of E (applied electric field)=4.5V/μm, J (emitted current density) of the original nanotubes (see the curve represented by ◯) is about 9 μA/cm², while the J of the nanotubes having been oxidized for more than 25 minutes by gaseous fluid including Oxygen at a temperature of 400° C. can reach 72 μA/cm²which is 8 times the amount of the original nanotubes. The turn-n voltage for field emission (or current emission), as can be observed from the plots of 1n(J/e²) vs 1/E in FIG. 6 according to Fowler-Nordheim field emission theory, decreases from 0.8 V/μm to 0.5 V/μm. These carbon nanotubes may have been grown on a p-Si substrate.
FIG. 6 shows plots of 1n(J/E²) vs 1/E according to Fowler-Nordheim field emission theory. In FIG. 6, Y axis represents 1n(J/E²) and X axis represents 1/E where J is emitted current density (unit: μA/cm²) and E is applied electric field (unit: V/μm). What are meant by the curves (actally lines) represented by ◯, ▴, Δ, and ⋆ in FIG. 6 are on the analogy of those in FIG. 5. The arrow 7 indicates a region of turn-on voltage of field emission (or current emission). It can be seen the turn-on voltage of field emission (or current emission) for the original nanotubes (see line represented by ◯) is about 0.8 V/μm, while the turn-on voltage of field emission (or current emission) for the nanotubes having been oxidized for more than 25 minutes by gaseous fluid including Oxygen at a temperature of 400° C. (see lines represented by Δ, ⋆) can be as low as 0.5 V/μm. If the carbon nanotubes are used to drive a display screen (i.e., to emit electrons colliding with the screen for displaying images thereon), and the spacer between the screen and the emission portion of the nanotubes is 200 μm in thickness, the decrease of turn-on voltage of field emission (or current emission) from 0.8 V/μm to 0.5 V/μm means a decrease of required electric field of 60V, which is extremely significant particularly when the nanotubes are used with a display on a mobile apparatus or with any apparatus with limited capacity or voltage-level of power source, or with limited convenience of accepting higher voltage-level.
Although the experiments for the curves in FIGS. 5 and 6 were based on the operating temperature of 400° C., the oxidization to achieve the object of the present invention can actually be implemented for a proper time period at any temperature higher than ambient temperature, preferably higher than or equal to 70° C.
FIG. 7 shows (Emitted Current-Emission Voltage) plots of an original array of carbon nanotubes and those oxidized according to the present invention by gaseous fluid including Ozone (O₃) or Br₂. Y axis represents emission current density J (unit: μA/cm²), and X axis represents applied electric field E (unit: V/μm). The curve represented by open circles ◯ is for an array of original carbon nanotubes (not oxidized according to the present invention). The curve represented by symbols x is for an array of carbon nanotubes having been oxidized for 20 minutes at room temperature by gaseous fluid including Br₂. The curve represented by symbols ∇ is for an array of carbon nanotubes having been oxidized for 1 minutes at room temperature by gaseous fluid including O₃. The curve represented by symbols □ is for an array of carbon nanotubes having been oxidized for 3 minutes at room temperature by gaseous fluid including O₃. The curve represented by symbols Δ is for an array of carbon nanotubes having been oxidized for 5 minutes at room temperature by gaseous fluid including O₃. The curve represented by symbols
is for an array of carbon nanotubes having been oxidized for 7 minutes at room temperature by gaseous fluid including O₃. The curve represented by symbols + is for an array of carbon nanotubes having been oxidized for 9 minutes at room temperature by gaseous fluid including O₃.
It can be seen from FIG. 7 that in terms of current emission capability of carbon nanotubes, the oxidization of carbon nanotubes for 1 minute by gaseous fluid including O₃at room temperature, or the oxidization of carbon nanotubes for 20 minutes by gaseous fluid including Br₂at room temperature, makes no much difference from the original nanotubes (compare the 3 curves respectively represented by ∇, x, and ◯), but the oxidization of the nanotubes for 3 or more minutes by gaseous fluid including O₃at room temperature makes a significant difference from the original nanotubes (compare the 5 curves respectively represented by □, Δ,
, +, and ◯). It must be noted that the oxidization of carbon nanotubes for longer time period by gaseous fluid including O₃at room temperature does not necessarily always result in better capability of emitting electrons. For example, among the oxidizations of carbon nanotubes respectively for 3, 5, 7, and 9 minutes by gaseous fluid including O₃at room temperature, the shorter time period for which the carbon nanotubes are oxidized, the better the carbon nanotubes are capable of emitting electrons, as can be seen from the 4 curves represented by □, Δ,
, and +. It may be understood that a prolonged oxidization of an array of carbon nanotubes by O₃at room temperature leads to oxidative damage along the walls of the nanotubes, resulting in a decrease of current emission.
Experiments showed that as long as ambient temperature is equal to or higher than negative 50° C. (i.e., −50° C.), an array of carbon nanotubes can be oxidized by O₃to significantly improve its capability of emitting electronic current (i.e., to be capable of emitting electronic current of higher density) under the same or lower onset emission voltage.
The cause of a carbon nanotube changing in shape (existent tips become sharper, or new tips or depressions are formed, for example) to be capable of emitting electrons of higher density under the same or lower onset emission voltage, is the cleavage of some C═C double bonds of carbon in the carbon nanotube, where C represents Carbon. The process according to the present invention is the unique art so far to cause the cleavage of C═C double bonds in a carbon nanotube for the carbon nanotube to work better with a display, or to be capable of emitting current of higher density under the same or lower onset emission voltage.
Although the experiments for the curves in FIGS. 5 and 7 are mainly based on oxidants of O₂and O₃, the process according to the present invention is not necessarily limited to adopting O₂and O₃as oxidant, and may actually be implemented by an oxidant selected from among O₂, O₃, CO₂, NO₂, SO₂, and SO₃, or the combination of at least two thereof, or by whatever can cause the cleavage of some C═C double bonds of carbon in the carbon nanotube, where O, C, N, S respectively represents Oxygen, Carbon, Nitrogen, and Sulphur.
It is observed from experiments that the sharper a tip of a carbon nanotube is, the lower an onset emission voltage can be for current to be emitted therefrom, and the larger a current can be emitted therefrom.
Although oxidants in the form of liquid fluid may also be used for the oxidization according to the present invention, gaseous oxidants are preferred.
Obviously, to achieve the object of the present invention, it is not necessary to expose a whole carbon nanotube to oxidant in the process according to the present invention. For example, if only an end part of a carbon nanotube is expected to emit electronic current, then only the end part needs to be exposed to oxidant.
It can be understood the process of oxidizing an array of nanotubes by an oxidant (or a fluid including an oxidant) at an operating temperature higher ambient temperature may comprise the steps of:

- heating the oxidant (or the fluid) until the oxidant (or the fluid) reaches the operating temperature; and
- exposing at least part (an end part, for example) of the nanotube to the oxidant (or the fluid) until the shape of at least part of the nanotube changes.

While the invention has been described in terms of what are presently considered to be the most practical and preferred embodiments, it shall be understood that the invention is not limited to the disclosed embodiment. On the contrary, any modifications or similar arrangements shall be deemed covered by the spirit of the present invention.

Claims

1. A process applied to a current emitting device having an exposed portion and being composed of material including carbon, comprising:

oxidizing said current emitting device at an operating temperature until the shape of at least part of said exposed portion changes, said operating temperature being higher than ambient temperature.

2. The process according to claim 1 wherein said current emitting device is in the shape of a tube.

3. The process according to claim 1 wherein said current emitting device is in the shape of a ball.

4. The process according to claim 1 wherein said current emitting device is a carbon nanotube.

5. The process according to claim 1 wherein said operating temperature is at least 70° C.

6. The process according to claim 1 wherein at least part of said exposed portion is exposed to one type of gaseous material.

7. The process according to claim 6 wherein said gaseous material is at least one selected from among O₂, O₃, CO₂, NO₂, SO₂, and SO₃.

8. The process according to claim 1 wherein the shape of said exposed portion changes in such a way that at least part of said exposed portion becomes to be in the shape of a tip.

9. The process according to claim 1 wherein the shape of said exposed portion changes in such a way that at least part of said exposed portion is depressed.

10. A process applied to a current emitting device composed of material including carbon, comprising:

oxidizing said current emitting device by a fluid including O₃until said current emitting device has at least part thereof changed in shape.

11. The process according to claim 10 wherein said current emitting device is oxidized at a temperature which is at least negative 50° C.

12. The process according to claim 10 wherein said current emitting device has the shape thereof changed in such a way that at least part thereof becomes to be in the shape of a tip.

13. The process according to claim 10 wherein said current emitting device has the shape thereof changed in such a way that at least part thereof is depressed.

14. A process applied to a current emitting device composed of material including carbon, comprising:

splitting some C═C double bonds of carbon in said current emitting device until the shape of at least part of said current emitting device changes in such a way that the current emission capability of said current emitting device increases.

15. A current emitting device comprising an array of carbon nanotubes, wherein said nanotube comprises:

a first portion for connecting a carrier; and

a second portion with a surface including at least a depression and having an oxygenated group thereon.

16. The current emitting device according to claim 15 wherein said oxygenated group includes at least one of alcohol group (—>COH), ester group (—COO—), ether group (C—O—C linear structure), and epoxide group (COC).

17. The current emitting device according to claim 15 wherein said oxygenated group includes at least one of carboxylic acid group (—COOH), hydroxyl group (—OH), ketone group (>C═O), and aldehyde group (—CHO).

18. A current emitting device comprising an array of carbon nanotubes, wherein said nanotube comprises:

a first portion for connecting a carrier; and

a second portion with a surface including at least a tip and having an oxygenated group thereon.

19. The current emitting device according to claim 18 wherein said oxygenated group includes at least one of alcohol group (—>COH), ester group (—COO—), ether group (C—O—C linear structure), and epoxide group (COC tricyclic ring).

20. The current emitting device according to claim 18 wherein said oxygenated group includes at least one of carboxylic acid group (—COOH), hydroxyl group (—OH), ketone group (>C═O), and aldehyde group (—CHO).