JP2002358873A - Surface treatment method of carbon matter material for field electron emission material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve electron emission characteristics by putting carbon matter material used for field electron emission member of a field electron emission element under surface reforming treatment through electrolysis. SOLUTION: In an electrolytic bath 300, electrolyte solution 12 containing electrolyte is filled in a glass vessel 11, and a platinum foil cylindrical electrode 13 and a carbon matter material 15 are put inside the electrolyte solution 12. The cylindrical electrode 13 is connected to direct-current electrolyte power source 10 through a lead wire 14, and the carbon matter material 15 is hung from a support rod 16 through a clamp 17, and further, connected to the direct- current electrolyte power source 10 through the lead wire. When electrolytic reaction begins as voltage is impressed between the cylindrical electrode 13 and the carbon matter material 15 that are to be two electrolyte electrodes, hydrogen gas or oxygen gas is generated from the surface of the carbon matter material 15 according to its polarity, and hydrogenation or oxidization treatment is made.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in electron emission characteristics of a carbon material used in a field emission device.

[0002]

2. Description of the Related Art As an electron-emitting device used for a key device such as an information display tube, a microwave tube, and a sensor that supports an information network, it has a characteristic of energy saving and resource saving in place of a conventional hot cathode. However, there is a demand for practical use of a cold cathode that is compatible with modern manufacturing process technology.
At present, field electron emission devices have received the most attention for practical use as cold cathodes. As a field electron emission material of this field electron emission element, a carbon material is classified from the viewpoints of being chemically stable, being compatible with environmental problems, and being advantageous in resources.

FIG. 2 is a schematic diagram showing a field emission device and a circuit for applying a voltage to the field emission device and measuring the voltage. As shown in FIG. 2, the field emission device 100
Is a field electron emission member 1 made of a field electron emission material;
It comprises a substrate 2 on which a field electron emission member 1 is mounted. The anode 3 is disposed so as to face the field emission device 100. Then, the space within the dotted line including the field emission device 100 and the anode 3 is evacuated to a vacuum state, whereby the diode 200 is formed. An anode voltage Va is applied to the diode 200 from a DC voltage power supply or a pulse voltage power supply 6 from outside. Here, the anode 3 is positive, and the field emission device 100 is negative. When the anode voltage Va from the pulse voltage power supply 6 exceeds a predetermined value, electrons e are emitted, and the field emission electron current Ie is measured by the current measuring device 5.

Generally, in order for electrons of a substance to be emitted, a work function φ (e
V) barriers need to be overcome. In a normal hot cathode,
Heat was applied from the outside to give thermal energy to the electrons, thereby jumping over the barrier.

On the other hand, in the field emission device 100, by applying a strong electric field F (V / cm) to the surface of a material, the thickness of the barrier is reduced rather than jumping over the barrier, instead of jumping over the barrier. Electrons are emitted by passing through the barrier that has been tunnelled. When the same electric field F is applied, the lower the work function φ, the thinner the barrier. That is, for the field emission device 100,
The lower the work function φ, the more advantageous. Further, the larger the electric field F on the front surface of the field emission device 100 obtained by applying the same anode voltage Va, the more advantageous the field emission device 100 is. That is, the larger the electric field voltage coefficient β (1 / cm) when F = βVa is, the more advantageous the field electron emitting device 100 is. The theoretical equation (Fowler-Nordhei equation) that expresses the field emission electron current Ie by the applied voltage Va and the electron emission area S (cm ² , not the element area but the area of the part that actually emits electrons) is:
As shown in the equation (1), it consists of physical constants, work functions φ, and electric field voltage coefficients β, in addition to Va and S.

(Equation 1)

[0006] From the above, the field electron emission device 100
The purpose of this modification is to reduce the work function φ, increase the electric field voltage coefficient β, and increase the electron emission area S.

Conventionally, a surface treatment modification method for a carbon material, which is the field electron emission member 1, is performed by, for example, irradiating a carbon nanotube with a laser in an oxygen atmosphere, or heating the carbon nanotube in the atmosphere or carbon dioxide to form a tip. An oxidation treatment method for removing a closed cap (SC Tsa
ng et al., Nature Vol. 362, pp. 520
-522 (1993)), a hydrogenation method (N. EIM) in which a diamond thin film formed by a chemical vapor deposition method (CVD) is exposed to hydrogen plasma to make the electron affinity of the surface negative.
ORI et al., Jpn. J. Appl. Phys. Vol.
33 (1994) pp. 6312-6315). In particular, the above-mentioned hydrotreating method is important as a hydrogen termination treatment of the electron emission portion of the carbon material.

[0008]

However, the above-described oxidation treatment method and hydrogenation treatment method have conventionally been performed by separate apparatuses, and the configuration of the apparatuses has been complicated.

Therefore, in order to simultaneously perform the oxidation treatment and the hydrogenation treatment on the carbonaceous material, it is necessary to carry out the treatments in separate apparatuses, which makes the treatment complicated.
If you don't own the kind of equipment you could do it.

Accordingly, the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to reform a carbon material used as a field electron emission member by performing oxidation treatment and / or Another object is to provide a surface treatment method for performing a hydrogenation treatment.

[0011]

Means for Solving the Problems In order to achieve the above object, the surface treatment method for a carbon material for a field electron emission material according to the present invention has the following features.

(1) A voltage is applied between a carbon material as one electrode and another electrode in a solution containing an electrolyte, and an electrolytic reaction for generating oxygen or hydrogen on the surface of the carbon material as needed. This is a surface treatment method to raise.

In a solution containing an electrolyte, a carbon material as a field electron emission material is used as a positive electrode, and the other electrode is used as a negative electrode. Oxygen in a nascent state with high reactivity is generated, and the generated oxygen is oxidized with the carbon material, whereby the carbon material can be modified by an oxidation treatment.

On the other hand, in a solution containing an electrolyte, a carbon material is used as a negative electrode and the other electrode is used as a positive electrode to apply a voltage higher than the hydrogen overvoltage, so that the surface of the carbon material is highly reactive. Hydrogen in a nascent state is generated, and the generated hydrogen is subjected to a hydrogenation reaction with the carbonaceous material, whereby the carbonaceous material can be reformed by a hydrogenation treatment.

Further, the oxidation reaction or the hydrogenation reaction can be performed by simply changing the polarity and voltage value of the applied voltage without changing the structure of the electrolytic cell in which the above-described electrolytic reaction is caused. Can be selected. Furthermore, it is also possible to set up a continuous processing step such as performing an oxidation reaction and then performing a hydrogenation reaction.

(2) The surface treatment method according to the above (1), wherein the electrolyte is an alkali metal salt or an alkaline earth metal salt.

By using an alkali metal salt or an alkaline earth metal salt as the electrolyte, the electrolytic reaction is promoted.

(3) The surface treatment method according to the above (1), wherein a low interfacial tension substance is added to a solution containing an electrolyte.

The surface tension of the electrolyte can be reduced by adding a low interfacial tension substance to the electrolyte containing the electrolyte. Thus, the bubbles of the oxygen gas and the hydrogen gas generated on the surface of the carbon material are easily separated from the surface of the carbon material without greatly growing. Therefore, a uniform surface treatment can be performed, and the modification of the carbon material can be improved.

(4) The surface treatment method according to the above (3), wherein the low interfacial tension substance is any one of alcohols, ketones, and mixtures thereof.

By using any of alcohols, ketones or a mixture thereof as a low interfacial tension substance,
After the surface modification treatment, it evaporates away from the surface of the carbonaceous material and can be easily washed away. Accordingly, there is no possibility that the low interfacial tension substance remains on the surface of the carbon material to impair the electron emission characteristics.

(5) The surface treatment method according to the above (4), wherein the low interfacial tension substance is ethanol, methanol, propanol, butanol, 2-phenylethanol or acetone or methyl ethyl ketone.

By using alcohols or ketones having a short carbon chain length, they evaporate after completion of the surface modification treatment,
In addition, it can be easily removed from the surface of the carbonaceous material by washing, and can be prevented from remaining on the surface. Thereby, there is no possibility that the electron emission characteristic of the carbon material is impaired.

(6) The surface treatment method according to any one of (1) to (5) above, wherein the carbon material is graphite.

Graphite is suitable as a field electron emission material because it is soft and has good processing characteristics and can be formed on a substrate having a large area by chemical vapor deposition (CVD).

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partial sectional view of an electrolytic apparatus for performing a surface treatment of a carbon material, which is a field electron emission material used for a field electron emission element.

As shown in FIG. 1, the electrolyzer comprises an electrolyzer 3
00 and a DC electrolysis power supply 10. The electrolytic cell 300
This is an electrolytic cell for performing a surface modification treatment of a carbon material. In the electrolytic cell 300, a glass container 11 is filled with an electrolytic solution 12 containing an electrolyte, and a cylindrical electrode 13 made of platinum foil and a carbon material 15 are arranged in the electrolytic solution 12. The cylindrical electrode 13 is connected to the DC electrolytic power supply 10 via a lead wire 14. On the other hand, the carbon material 15
The support rod 16 is suspended from a support rod 16 via a clamp 17, and is connected to the DC electrolytic power supply 10 via a lead wire.

The lead wire 14 and the support rod 16 are attached to a stand (not shown) fixed to the table 18 while being electrically insulated.

Further, a cylindrical electrode 13 serving as two electrolytic electrodes
A glass cylinder 19 is arranged between the carbon material 15 and the carbon material 15, and the two electrolytic electrodes are separated by the glass cylinder 19. Further, it is preferable that the liquid level of the electrolytic solution 12 is higher than the upper surface of the cylindrical electrode 13 and lower than the glass cylinder 19. The hole 20 provided in the lower part of the glass cylinder 19 allows the electrolyte 1
Numeral 2 is electrically connected inside and outside the glass cylinder 19 so that the same liquid level is formed.

The role of the glass cylinder 19 is as follows.
A cylindrical electrode 13 which is an electrolytic electrode by a DC electrolytic power supply 10
And a voltage is applied between the carbon material 15 and the electrolytic reaction starts, and from the surface of the cylindrical electrode 13 and the carbon material 15,
Hydrogen gas and oxygen gas, or oxygen gas and hydrogen gas are generated, respectively.
Hydrogen gas or oxygen gas generated on the surface of the cylindrical electrode 13 can be guided to the liquid surface of the electrolytic solution 12 without touching the carbon material 15. As a result, the oxidation treatment or the hydrogenation treatment of the carbon material 15 can be favorably performed.

In the present embodiment, it is preferable that the electrolyte contained in the electrolyte solution 12 is appropriately selected from alkali metal salts or alkaline earth metal salts or a mixture thereof. Further, the electrolyte solution 12 preferably contains a low interfacial tension substance, and it is preferable to use, for example, alcohols or ketones or a mixture thereof, which is easily dissolved in an aqueous electrolyte solution. Examples of alcohols include methanol, ethanol, propanol, butanol, and phenylethyl alcohol (particularly, 2-phenylethyl alcohol (C ₆ H ₅ C, also referred to as 2-phenylethanol).
H ₂ CH ₂ OH)) is preferable, and as the ketones, for example, acetone and methyl ethyl ketone are preferable.

The low interfacial tension substance as described above is applied to the electrolyte 12
, The surface tension of the electrolyte 12 can be reduced. Thereby, bubbles of oxygen gas or hydrogen gas generated on the electrode surface by the electrolytic reaction in the electrolytic cell 300 are easily released from the surface, and as a result, the surface modification treatment of the carbon material 15 is performed uniformly. Become. Even if the low interfacial tension substance as in the present embodiment is not added to the electrolyte solution 12, bubbles of oxygen gas or hydrogen gas are generated on the surface of the carbon material 15 by the electrolytic reaction, and the surface modification treatment is performed. Although it can be performed, since the electrolyte solution containing no low interfacial tension substance has a large surface tension, the generated bubbles are hard to be detached from the surface, so that the bubbles grow on the surface and become large bubbles. As a result, carbon material 1
In the surface modification treatment of No. 5, unevenness is likely to occur, and a desired surface modification treatment may not be performed.

The low interfacial tension substance in this embodiment is
It is preferable that the carbon material 15 can be easily removed after the surface modification treatment. Carbon material 15 after surface modification
This is because if the low interfacial tension substance remains, the electron emission characteristics may deteriorate when used as a field electron emission member.

[0035]

Examples are shown below.

<Apparatus for Surface Modification of Carbon Material and Surface Modification Method> The surface modification treatment of the carbon material was performed using the electrolytic apparatus shown in FIG. The electrolytic cell 300 is 40 mm × 50
It is a small electrolytic cell that is small enough to perform a surface modification treatment of a carbon material having a diameter of less than 1 mm. The glass container 11 is suitably a commercially available 200 ml beaker having a diameter of 68 mm, and the cylindrical electrode 13 has a diameter of 45 mm.

As the electrolytic solution 12, an aqueous solution 10 of an alkali metal salt or an alkaline earth metal salt having a concentration of 0.1 mol / l is used.
A solution in which a low interfacial tension substance was added to 0 ml in the amount described below was used.

Examples of the carbon material 15 include graphite “PG” manufactured by Advanced Ceramics Co., USA, graphite sheet “PGS” manufactured by Matsushita Electronic Components Co., Ltd. Paraffin soot "PS" was used.

The surface modification treatment was carried out by using a carbon material 15 as a negative electrode or a positive electrode in the apparatus shown in FIG. 1 and flowing an electrolytic current of 65 mA / cm ² for 8 seconds.

<Evaluation Method> In order to compare the quality of the electron emission characteristics of the field electron emission member using the carbon material subjected to the surface modification, the magnitude of the applied voltage required for electron emission to occur generally is compared. Can be evaluated by In other words, it can be said that as the electron emission can be performed with a lower applied voltage, the field emission member is more excellent.

Therefore, as a field electron emission member 1 shown in FIG. 2, a carbon material subjected to a surface modification treatment is reduced to a size of 2 mm square, and then attached to a substrate 2 to form a field electron emission element 100. 0 .0 from the upper surface of the field emission member 1.
The diode 200 provided with the anode 3 at a distance of 1 mm was formed, and the applied voltage Va was measured. Here, the applied voltage Va supplied from the DC voltage power supply or the pulse voltage power supply 6 is gradually increased between the field electron emitting device 100 and the anode 3, and the field emission electron current Ie of 300 nA is increased by the current measuring device 5. The measured applied voltage Va was measured as the electron emission start voltage.

Embodiment 1 Table 1 below shows measured values of the electron emission start voltage when the surface modification treatment of the carbon material was performed and when it was not performed. Note that "N
o. "No. 1" is made of graphite "PG" manufactured by Advanced Ceramics Co., USA, and "No. 2" and "N.
o. No. 4 to No. 10 use the graphite sheet "PGS" manufactured by Matsushita Electronic Components Co., Ltd.
o. No. 3 "used the above paraffin soot" PS ". Note that “PG” and “PGS” are crystalline graphite, and the c-plane (crystal plane perpendicular to the c-axis) was used as the electron emission surface of the field electron emission member.

The electrolyte used was lithium hydroxide as an electrolyte, and its composition was as follows. (1) 0.1 mol / l aqueous solution of lithium hydroxide 100 ml
+ Ethanol 30 ml (2) 0.1 mol / l lithium hydroxide aqueous solution 100 ml
+ Methanol 22 ml (3) 0.1 mol / l lithium hydroxide aqueous solution 100 ml
+ 2-propanol 15 ml (4) 0.1 mol / l lithium hydroxide aqueous solution 100 ml
+ Acetone 20 ml (5) 0.1 mol / l lithium hydroxide aqueous solution 100 ml
+ Methyl ethyl ketone 22 ml (6) 0.1 mol / l lithium hydroxide aqueous solution 100 ml
+ Ethanol 60ml + 2-phenylethanol 50m
l

[0044]

[Table 1] From Table 1, it was found that the electron emission start voltage can be reduced by 100 V to 600 V by using the surface modification treatment method of the present invention. "No. 5" in Table 1
And “No. 7”, an electrolytic current of 65 mA / cm ² was applied for 8 seconds using the carbon material “PGS” as the first positive electrode,
Next, an electrolytic current of 65 mA / cm ² was passed for 8 seconds using “PGS” as a negative electrode to perform surface modification.

Embodiment 2 FIG. In Example 1, lithium hydroxide was used as the electrolyte, but in this example, cesium nitrate was used as the electrolyte.

The composition of the electrolytic solution is shown below. (7) 0.1 mol / l cesium nitrate aqueous solution 100 ml +
Ethanol 38ml (8) 0.1mol / l cesium nitrate aqueous solution 100ml +
Ethanol 60ml + 2-phenylethanol 50ml

Using these electrolytes, the surface modification treatment of the carbon material was performed using the apparatus shown in FIG. 1 and the electron emission start voltage was pulsed using the apparatus shown in FIG. Table 2 shows the results measured with a voltage power supply. "No.
11 "and [No. 13] used the above-mentioned “PGS” as a negative electrode and applied an electrolytic current of 65 mA / cm ² for 8 seconds to perform surface modification. On the other hand, in “No. 12,” the “PG
S ”as the first positive electrode and an electrolytic current of 65 mA / cm ² of 8
For 65 seconds and then 65 mA / c with "PGS" as the negative electrode.
The surface modification was performed by flowing an electrolytic current of m ² for 8 seconds.

[0048]

[Table 2] In each case, the effect of surface modification was recognized, and it was found that the electron emission start voltage could be reduced by about 500 V.

Embodiment 3 FIG. In Example 3, barium acetate was used as the electrolyte. The composition of the electrolytic solution is shown below. (9) 0.1 mol / ml barium acetate aqueous solution 100
ml + ethanol 38ml

Using this electrolytic solution, the surface modification treatment of the carbon material was performed by the apparatus shown in FIG. Table 3 shows the results of measuring the electron emission start voltage with a pulse voltage power supply using the apparatus shown in FIG. “No. 14” is the same as “PG
"S" was used as a negative electrode, and an electrolytic current of 65 mA / cm ² was passed for 8 seconds to perform surface modification. On the other hand, in “No.
An electrolysis current of 65 mA / cm ² was applied for 8 seconds using the above “PGS” as a positive electrode, and then 6 μM using the “PGS” as a negative electrode.
The surface modification was performed by flowing an electrolytic current of 5 mA / cm ² for 8 seconds.

[0051]

[Table 3] In each case, the effect of surface modification was recognized, and it was found that the electron emission start voltage could be reduced by 260 V to 280 V.

[0052]

As described above, according to the present invention,
Oxidation treatment and hydrogenation treatment can be performed by an extremely simple device, and if necessary, oxidation treatment and hydrogenation treatment can be continued simply by switching the polarity, so that various processes can be easily handled. At the same time, the electron emission starting voltage of the field electron emission member can be reduced.
As a result, a more energy-saving and resource-saving field electron emission device can be provided. Further, a device using the field emission device obtained by the surface treatment of the present invention also includes:
Its performance can be improved.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of an example of an electrolysis apparatus used for surface modification of a carbon material of a field electron emission member according to the present invention.

FIG. 2 is a schematic diagram showing a voltage application and current measurement circuit to a diode having a field emission device.

[Explanation of symbols]

1 field electron emission member, 2 substrate, 3 anode, 5
Current measuring instrument, 6 DC voltage power supply or pulse voltage power supply, 10 DC electrolytic power supply, 11 glass container, 12 electrolyte, 13 cylindrical electrode, 14 lead wire, 15 carbon material, 16 support rod, 17 clamp, 18 units, 1
9 glass cylinder, 20 holes, 100 field emission device, 200 diode, 300 electrolytic cell.

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[Procedure amendment]

[Submission date] July 27, 2001 (2001.7.2)
7)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction contents]

On the other hand, in the field electron emission device 100, by applying a strong electric field F (V / cm) to the surface of a substance, the thickness of the barrier is reduced rather than jumping over the barrier. Electrons are emitted by passing through the barrier that has been tunnelled. When the same electric field F is applied, the lower the work function φ, the thinner the barrier. That is, for the field emission device 100,
The lower the work function φ, the more advantageous. Further, the larger the electric field F on the front surface of the field emission device 100 obtained by applying the same anode voltage Va, the more advantageous the field emission device 100 is. That is, the larger the electric field voltage coefficient β (1 / cm) when F = βVa is, the more advantageous the field electron emitting device 100 is. Field emission electron current Ie of the applied voltage Va and the electron emission area S (cm ^2, rather than the element area actually part area of doing electron emission) theoretical formula representing the (Fowler-Nordhei m type) is,
As shown in the equation (1), it consists of physical constants, work functions φ, and electric field voltage coefficients β in addition to Va and S.

(Equation 1)

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0049

[Correction method] Change

[Correction contents]

Embodiment 3 FIG. In Example 3, barium acetate was used as the electrolyte. The composition of the electrolytic solution is shown below. (9) 0.1 mol / l barium acetate aqueous solution 100 ml +
38 ml of ethanol

Continuation of the front page (72) Inventor Kenji Ijima 1-10-14 Itabashi, Itabashi-ku, Tokyo Inside the Tokyo Cathode Research Laboratory (72) Inventor Yasushi Tawa 1-10-14 Itabashi, Itabashi-ku, Tokyo Stock In the Tokyo Cathode Research Laboratory (72) Inventor Maki Kanai 1-10-14 Itabashi, Itabashi-ku, Tokyo Stock Company In the Tokyo Cathode Research Laboratory (72) Inventor Teruo Yajima 1-10-14 Itabashi, Itabashi-ku Tokyo 4G046 CB01 CB09 CC10

Claims (6)

[Claims] 1. A voltage is applied between a carbon material as one electrode and another electrode in a solution containing an electrolyte,
A surface treatment method for a carbon material for a field electron emission material, wherein an electrolysis reaction for generating oxygen or hydrogen is caused on the surface of the carbon material as needed. 2. The surface treatment method according to claim 1, wherein the electrolyte comprises an alkali metal salt or an alkaline earth metal salt. 3. The surface treatment method according to claim 1, wherein a low interfacial tension substance is added to the solution containing the electrolyte. 4. The surface treatment method according to claim 3, wherein the low interfacial tension substance is an alcohol, a ketone, or a mixture thereof. Surface treatment method. 5. The carbon for a field electron emission material according to claim 4, wherein the low interfacial tension substance is ethanol, methanol, propanol, butanol, 2-phenylethanol or acetone or methyl ethyl ketone. Surface treatment method for material. 6. The method according to claim 1, wherein the carbon material comprises graphite. 6. The method according to claim 1, wherein the carbon material comprises graphite.