JPH0864110A - Carbide film coating electron emitting material and manufacture thereof - Google Patents

Abstract

PURPOSE: To provide a long-life electron emitting material which excels in heat resistance and provides a stable emission current even under a bad vacuum condition by applying a carbonized tantalum film comprising a predetermined composition ratio to the peripheral surface of a tungsten filament. CONSTITUTION: In a carbide film coating electron emitting material in which a carbide film is applied to the surface of an electron emitting material made of tungsten, a carbide coating is a carbonized tantalum film comprising a composition ratio of 1<C/Ta<1.2. The film thickness of the carbide film can be 1 to 50μm and the electron emitting material made of tungsten can be a tungsten filament 1. In a method of manufacturing the carbide film coating electron emitting material, a metal Ta is evaporated in a vacuum and at the same time a C2 H2 gas is introduced thereinto and the carbonized film comprising a composition ratio of 1<C/Ta<1.2 is applied to the surface of the electron emitting material made of tungsten by making both of them react to each other at the evaporation medium pressure/film formation speed of 6.0×10<-2> Pa.min/μm or above by a reactant type ion plating method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron emitting material coated with a carbide film and a method for producing the same, and more specifically, an electron emitting material cathode ray tube, an electron microscope, an Auger electron spectroscopy analyzer, and an electron beam exposure apparatus for a VLSI. The present invention relates to a carbide film-coated electron emitting material used for an electron source such as an electron gun used for metal dissolution or vapor deposition, and a method for producing the same.

[0002]

2. Description of the Related Art Tungsten (W) has been conventionally known as an electron emitting material. Since tungsten has a high melting point, it has little deformation even at a high temperature, and has a low vapor pressure. Was used. Tungsten is also used as a strong field electron emission material.

A filament formed by coating the surface (outer peripheral surface) of a thorium-tungsten wire with a carbonized layer is disclosed in Japanese Patent Laid-Open No.
-147055.

The applicant of the present invention has previously disclosed in Japanese Patent Laid-Open No. 61-250927 that a good electron emitting material (for example, Ti
It has been proposed to use the one coated with C) as an electron emitter.

[0005]

It is used as THE INVENTION Problems to be Solved] The conventionally thermionic emission material Tungsten 10 ^{- 6} adsorbed residual gases such as carbon dioxide increases the work function in a more vacuum Pa, therefore radiation The current decreases rapidly. Further, in tungsten, the emission current is unstable because of the surface migration of the adsorbed residual gas molecules and ion bombardment.

Further, in order to obtain a high-brightness electron current as a thermionic emission material, it is necessary to heat it to an extremely high temperature, and there is a problem that the life is short due to remarkable vaporization.

Further, the filament disclosed in Japanese Patent Laid-Open No. 52-147055 is coated with a carbonized layer, and the formed filament has a filament structure so that the carbonized layer is not damaged even by external mechanical vibration or impact. It is a device that has been devised to retain and hold the.

Further, as proposed in Japanese Patent Laid-Open No. 61-250927,
A thin metal wire coated with a good electron emitting material (for example, TiC) can guarantee sufficient electron emission even at a relatively low temperature, thereby reducing wear and wear rate and compensating for thermal stress and tensile stress. effective.

Therefore, miniaturization and diversification of electron emitting materials,
With the increase in efficiency and the like, the emergence of an electron emitting material having excellent heat resistance, high emission current and long life has been demanded.

It is an object of the present invention to provide a carbide film-coated electron emitting material which has excellent heat resistance, can stably obtain a radiation current even in a bad vacuum state, and has a long life, and a method for producing the same.

[0011]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventor has found that tantalum (Ta) and molybdenum (Mo), including tungsten (W), which has been widely used as an electron emitting material in the past. When the surface is coated with a carbide film of a transition metal such as titanium (Ti) or tantalum (Ta), the work function becomes smaller, and the residual gas such as carbon dioxide is less adsorbed, and the reactivity with it is reduced. Since it is stable and stable, it can be used even in a vacuum of relatively high pressure.

The electron emitting material having a surface coated with a carbide film has the following advantages. Transition metal carbides have a smaller work function than tungsten, tantalum, and molybdenum (W: 4.54eV, Ta: 4.01eV, Mo: 4.03eV, TiC: 3.25eV, Zr.
C: 3.0eV, NbC: 3.50eV, TaC: 3.40eV, HfC: 3.40eV). Therefore, radiation efficiency is good because the operating temperature may be low. Further, the transition metal carbide has a higher melting point than the metal (W: 3380 ℃, Ta: 2998 ℃, Mo: 2617 ℃, TiC: 3450 ℃, ZrC:
3830 ℃, NbC: 4170 ℃, TaC: 4160 ℃, HfC: 4180 ℃). Also, the evaporation rate is almost the same as or lower than that of the metal.

As described above, it has been found that the life time is remarkably extended because the high temperature characteristics are excellent and the low temperature operation is possible.

The present invention has been made on the basis of the above-mentioned findings. A carbide film-coated electron emitting material is a carbide film-coated electron emitting material obtained by coating the surface of a tungsten electron emitting material with a carbide film. Composition ratio 1 <C / T
It is a tantalum carbide film having a <1.2.

The thickness of the carbide film may be 1 to 50 μm. Further, the tungsten electron emitting material may be a tungsten filament.

In the method for producing a carbide film-coated electron emitting material according to the present invention, metal Ta is evaporated in a vacuum, C ₂ H ₂ gas is introduced at the same time, and both are pressured during deposition by reactive ion plating. characterized by coating the tantalum carbide layer consisting of ² Pa · min / ^μm reacted at least with the composition ratio of 1 on the surface of the tungsten electron-emitting material <C / Ta <1.2 ^- the deposition rate 6.0 × 10.

Further, the electron emitting material made of tungsten may be a tungsten filament.

[0018]

When Ta is vaporized in vacuum and C ₂ H ₂ gas is introduced and reacted by the reactive ion plating method, the surface of the electron emitting material made of tungsten is coated with the carbide film made of TaC.

At this time, the pressure during deposition / film formation rate was 6.0 × 10 ^−
When Ta and C ₂ H ₂ are reacted by the reactive ion plating method at ² Pa · min / μm or more, the composition ratio is 1 <C / Ta <
A tantalum carbide film of 1.2 is coated on the surface of the Dangsten electron emissive material.

This tantalum carbide film having a composition ratio of 1 <C / Ta <1.2 can be operated at a low temperature, so that the life time is significantly extended.

[0021]

EXAMPLE In the present invention, the range of the composition ratio C / Ta of the tantalum carbide (TaC) film coated on the surface of the electron emitting material made of tungsten is 1 <C / Ta <1.2 because the composition ratio C / Ta This is because when Ta is 1 or less, the film becomes an unstable film which is deteriorated at a high operating temperature, and when the composition ratio C / Ta is 1.2 or more, unbonded free carbon causes contamination of the vacuum system.

Further, the thickness range of the tantalum carbide film coated on the surface of the electron emitting material made of tungsten is set to 1 to 50 μm, because when the film thickness is less than 1 μm, it is a portion which is not covered by the base material having a complicated shape. May occur and the film thickness is 50μ
This is because if it exceeds m, the coating is likely to crack and peel off easily.

In the manufacturing method of the present invention, metal Ta is evaporated in a vacuum, C ₂ H ₂ gas is introduced at the same time, and the reaction is performed by the reactive ion plating method to cause the composition ratio on the surface of the tungsten electron emitting material. When coating a tantalum carbide film consisting of 1 <C / Ta <1.2, the deposition pressure / deposition rate was set to 6.
0 × 10 ^{- 2} was a Pa · min / [mu] m or more, evaporation in a pressure / film forming speed is 6.0 × 10 ^{- 2} if less than Pa · min / [mu] m is a single-phase T
aC film can not be obtained, 2 phase containing Ta ₂ C (TaC + Ta ₂
This is because it becomes the film of C). The upper limit value of the deposition in a pressure / film formation rate 2 × 10 Considering that the composition ratio is not proportional to the value ^- may be set to ¹ Pa · min / [mu] m approximately.

In the present invention, the pressure during vapor deposition means C ₂
Shows the total pressure of H ₂ pressure sum produced by the reaction with H ₂ pressure.

First, the basic idea of the present invention will be described.

1. Introduction Transition metal (Ti, Zr, Hf, Ta, Nb, etc.) carbides can be used not only as high-temperature structural materials and wear-resistant materials but also as electron-emitting materials because of their high melting point, high hardness and chemical stability. Is expected. Goodness index "Figure of Merit (φ / Te, however phi work function, Te vapor pressure 10 ^{- 5} Torr to become temperature)" as a measure of evaluation of the hot cathode material W is 1.6 × 10 ^{- 3,} ZrC is 1.5 × 10 ^{- 3,} TiC
It can be said that a ³ is better as this value is smaller ^- is 1.4 × 10 ^{- 3,} TaC is 1.2 × 10.

In the present invention, as an application of the carbide film in the field of electronic materials, a TaC film having the smallest index of merit is taken up, the production conditions thereof are clarified, and the W filament is coated to obtain thermionic emission characteristics. Was examined.

2. Experimental Method Activated reactive vapor deposition was used to produce the TaC film. Bulk Ta was melted by an electron beam and evaporated, and C ₂ H ₂ or C ₂ H ₄ gas was introduced as a reaction gas. SU on the board
S304 was used. As the evaluation of the produced film, the crystal structure, the lattice constant, the half width of the X-ray diffraction line, the crystal grain size, the chemical composition, the hardness, and the color tone were examined.

3. Experimental Results and Discussion 3-1 In the case of C ₂ H ₂ gas Experimental conditions are shown in Table 1, and characteristics of the produced film are shown in Table 2.

[0030]

[Table 1]

[0031]

[Table 2]

When the incident frequency ratio γ (C ₂ H ₂ ) / γ (Ta) obtained from the pressure during vapor deposition and the film formation rate is 2.6 or more, all Ta
Only phase C. The lattice constant is similar to the value reported for 4.453 to 4.463 (4.455Å), and there is no significant change due to the incidence frequency ratio. The crystal grain size obtained from Scherrer's equation decreases with increasing incidence frequency ratio.

The composition ratio C / Ta of the sample No. 8-K-109 determined from the peak of the spectrum of Auger electron spectroscopy was 1.17.
Met. The micro Vickers hardness of the coating (thickness: 4 μm) was 2000 kg / mm ² , which was a light gold color.

3-2 In the case of C ₂ H ₄ gas Table 3 shows the characteristics of the produced film.

[0035]

[Table 3]

The incidence frequency ratio γ (C ₂ H ₄ ) / γ (Ta) is 4.
Below 1 is the TaC phase only, but 4.9 is mainly Ta ₂ C, where very broad (101) is observed, and other weak TaC.
There is. In the incident frequency ratio from 6.9 to 9.7 TaC is mainly, Ta ₂ C is mixed in addition.

The lattice constant of TaC does not change much with the incidence frequency ratio, and is close to the reported value of bulk. The crystal grain size changes in a complicated manner reflecting the two-phase state.

In the case of C ₂ H ₂ , a single-phase TaC film can be easily obtained, but in the case of C ₂ H ₄ , Ta ₂ C has a low reactivity.
Is a two-phase state including

3-3 Thermionic emission characteristics The W filament was coated with a TaC film to examine thermionic emission characteristics and compared with that without coating. It has been found that the TaC coating increases the thermionic emission current and further extends the life.

In the manufacturing method of the present invention, metal tantalum (Ta) and acetylene (C ₂ H ₂ ) gas are reacted by the reactive ion plating method to coat the surface of the tungsten electron emitting material with the TaC film. At that time, the temperature of the electron emitting material made of tungsten is about 200 to 800 ° C, and the film forming rate is 0.
It is preferably about 05 to 5 μm / min.

Next, specific examples of the present invention will be described together with comparative examples according to the attached drawings.

Example 1 In this example, as the electron emitting material, the thickness shown in FIG. 1 was 0.1 mm.
φ, coil diameter 1mmφ, coil winding number 10, coil length 5
A tungsten (W) coil filament 1 having a thickness of 4 mm and an electrode portion of 4 mm was used. As the evaporation material of the carbide film coating the surface of the coil filament 1, tantalum (T) having a purity of 99% (T
a) was used, and acetylene (C ₂ H ₂ ) gas having a purity of 99% was used as a reaction gas.

The outer peripheral surface of the coil filament was coated with a carbide film by the reactive ion plating method.
The conditions for reactive ion plating are:
^{1.3 × 10 - 4 Pa, 500} ℃ the temperature of the coil filament, T
4kW electron beam output of the evaporation source for heating evaporate a, the pressure during the deposition 4 × 10 ^{- 2} Pa, the probe voltage 50 V, the probe current was 0.5A, the deposition rate and 0.3 [mu] m / min. The deposition in a pressure 4 × 10 ^{- 2} Pa, the deposition rate 0.3 [mu] m / min deposition in a pressure / deposition rate = 1.3 × 10 ^- is ¹ Pa · min / ^μm.

The probe is a ring-shaped electrode installed near the electron beam evaporation source.

Then, as shown in FIG. 2, a carbide film coated electron emitting material 3 in which a tantalum carbide (TaC) film 2 having a film thickness of 3 μm is coated on the outer peripheral surface of the tungsten coil filament 1.
Was produced.

When the composition ratio C / Ta of the TaC film 2 coated on the outer peripheral surface of the tungsten coil filament 1 was examined by the peak ratio of the spectrum of Auger electron spectroscopic analysis, the composition ratio C / Ta = 1.17.

[0047] Using the apparatus of the bipolar type thermionic emission properties of the carbide film-coated electron emitting material TaC film is coated on the outer peripheral surface of the tungsten coil filament in the method, pressure 1 × 10 ^- In ⁴ Pa vacuum chamber Examined.

As the thermionic emission characteristics, the temperature (° C.) of the electronic material coated with the carbide film, the applied power (W), the emission current (μA),
The life time (hour) until the filament of the carbide film-covered electronic material evaporates and cut was examined. The temperature (° C.) of the filament was measured by an optical pyrometer, and the anode voltage of the characteristic measuring device was set to 10V. Table 4 shows the results of the examined filament temperature (° C.), emission current (μA), and life time (hour).

Further, input power (W) and radiation current (μA)
3 is shown as a curve A in FIG. 3, and the relationship between the filament temperature (° C.) and the radiation current (μA) is shown as a curve B in FIG.

[0050] Example 2 the electron beam output 4.5 kW, the pressure during the deposition 2 × 10 ^{- 2} Pa, the outer periphery of the tungsten coil filament in the same manner as in Example 1 except that the film formation rate was 0.4 .mu.m / min Film thickness on the surface
A carbide film coated electron emitting material coated with a 3 μm TaC film was prepared. The deposition in a pressure ² × 10 ^- 2 Pa, deposition rate 0.4μm
/ min is deposited in a pressure / deposition rate = 5 × 10 ^- a ² Pa · min / ^μm.

Further, when the composition ratio C / Ta of the TaC film coated on the outer peripheral surface of the tungsten coil filament was examined by the peak ratio of the spectrum of Auger electron spectroscopy analysis, the composition ratio C / Ta = 1.01.

Then, the temperature (° C.), applied power (W), emission current (μA) and life time (hour) of the filament of the carbide film-coated electron emitting material were examined by the same method as in Example 1. Table 4 shows the results of the examined filament temperature (° C.), emission current (μA), and life time (hour).

Further, input power (W) and radiation current (μA)
3 is shown as a curve C in FIG. 3, and the relationship between the filament temperature (° C.) and the radiation current (μA) is shown as a curve D in FIG.

[0054] Example 3 deposited in pressure 3 × 10 ^{- 2} except that the Pa release carbide film-coated electronic coated with TaC film having a thickness of 3μm on the outer circumferential surface of the tungsten coil filament in the same manner as in Example 1 An injection material was prepared. The deposition in a pressure 3 × 10 ^{- 2} Pa, deposition rate
0.3 [mu] m / min is deposited in a pressure / deposition rate ^{= 1 × 10 - 1 Pa ·} min /
μm.

Further, when the composition ratio C / Ta of the TaC film coated on the outer peripheral surface of the tungsten coil filament was examined by the peak ratio of the spectrum of Auger electron spectroscopic analysis, the composition ratio C / Ta = 1.10.

Then, the temperature (° C.), applied power (W), emission current (μA) and life time (hour) of the filament of the carbide film-coated electron emitting material were examined by the same method as in Example 1. Table 4 shows the results of the investigated tungsten coil filament temperature (° C.), radiation current (μA), and life time (hours).

Further, input power (W) and radiation current (μA)
3 is shown as a curve E in FIG. 3, and the relationship between the filament temperature (° C.) and the radiation current (μA) is shown as a curve F in FIG.

Comparative Example 1 Thickness without coating any TaC film as an electron emitting material
A tungsten coil filament having a diameter of 0.1 mm, a coil diameter of 1 mm, a coil winding number of 10, a coil portion length of 5 mm, and an electrode portion of 4 mm was used.

Then, the temperature (° C.) of the tungsten coil filament, the applied power (W), the emission current (μA), and the life time (hour) were examined by the same method as in Example 1. Filament temperature (° C), emission current (μ
Table 4 shows the results of A) and life time (hours).

Further, input power (W) and radiation current (μA)
3 is shown as a curve G in FIG. 3, and the relationship between the filament temperature (° C.) and the radiation current (μA) is shown as a curve H in FIG.

[0061] Comparative Example 2 the electron beam output 4.6KW, deposited in pressure 2 × 10 ^{- 2} Pa, the outer periphery of the tungsten coil filament except that the deposition rate was 0.42 .mu.m / min is the same method as in Example 1 A carbide film-coated electron emitting material having a surface covered with a TaC film having a thickness of 3 μm was produced. The deposition in a pressure ² × 10 ^- 2 Pa, deposition rate 0.42
[mu] m / min is deposited in a pressure / deposition rate ^{= 4.8 × 10 - 2 Pa ·} min / μ
m.

When the composition ratio C / Ta of the TaC film coated on the outer peripheral surface of the tungsten coil filament was examined by the peak ratio of the spectrum of Auger electron spectroscopy analysis, the composition ratio C / Ta = 0.93.

Then, in the same manner as in Example 1, the temperature (° C.) of the filament of the carbide film-coated electron emitting material,
Input power (W), radiation current (μA), life time (hours)
Was examined. Table 4 shows the results of the examined filament temperature (° C.), emission current (μA), and life time (hour).

[0064] Comparative Example 3 deposited in pressure 1 × 10 ^{- 1} except that the Pa is T the thickness 3μm on the outer peripheral surface of the coil filament in the same manner as in Example 1
A carbide film-coated electron emitting material coated with an aC film was prepared. The deposition in a pressure ¹ × 10 ^- 1 Pa, the deposition rate 0.3 [mu] m / min deposition in a pressure / deposition rate = 3.3 × 10 ^- is ¹ Pa · min / ^μm.

When the composition ratio C / Ta of the TaC film coated on the outer peripheral surface of the tungsten coil filament was examined by the peak ratio of the spectrum of Auger electron spectroscopy analysis, the composition ratio C / Ta = 1.25.

Then, the temperature (° C.), input power (W), emission current (μA) and life time (hour) of the filament of the carbide film-coated electron emitting material were examined by the same method as in Example 1. Table 4 shows the results of the examined filament temperature (° C.), emission current (μA), and life time (hour).

[0067]

[Table 4]

As is clear from Table 4, in the first, second and third embodiments of the present invention, T is the same for the same input power.
It can be seen that the filament temperature is lower than that of Comparative Example 1 in which only the W filament is not coated with any aC film, the radiation current is twice or more, and the life is increased 200 times or more. Therefore, it was confirmed that the examples of the present invention had significantly improved electron emission characteristics.

Further, in each of the examples, Comparative Examples 2 and 3 in which the composition ratio C / Ta of the coated TaC film is outside the range of the present invention
It can be seen that when the filament temperature is the same, the radiation current is large and the life is long.

As is apparent from FIG. 3, in Example 1, Example 2 and Example 3, the comparative example 1 (W
The radiation current is more than twice as high as that of the filament alone). Therefore, for example, in order to obtain a radiation current of 20 μA, 20 W of input power is required in Comparative Example 1, but in Example 1, Example 2, and Example 3, the input power is 4 W, and it is confirmed that the efficiency is extremely good. Was done.

As is clear from FIG. 4, in the example 1, the example 2, and the example 3 with respect to the same filament temperature, the radiation current more than twice as much as the comparative example 1 (W filament only) can be obtained. . Therefore, for example, in order to obtain a radiation current of 20 μA, it is necessary to set the filament temperature to 2800 ° C. in Comparative Example 1 (W filament only), but in Example 1, Example 2 and Example 3, the filament temperature is 1800 ° C. It was confirmed that the temperature can be lowered by 1000 ° C. from the temperature of Comparative Example 1 (W filament only), whereby the life can be significantly extended and the life of the electron emitting material can be extended.

Example 4 In this example, electron emission characteristics were examined when the thickness of the tantalum carbide film covering the outer peripheral surface of the tungsten coil filament was changed.

The thickness of the tantalum carbide film is 1 μm and 10 μm.
m, 15 μm, 30 μm, 50 μm, except that tantalum carbide (composition ratio C / Ta
= 1.17) Each carbide film-coated electron emitting material having a different film thickness was prepared.

Regarding each of the carbide film-coated electron emitting materials having different tantalum carbide film thicknesses, the above-mentioned Example 1 was applied.
In the same manner as in (3), the temperature of the filament of the electron emission material coated with a carbide film (° C.), input power (W), emission current (μA),
The life time (hour) was examined. Table 5 shows the results of the examined filament temperature (° C.), emission current (μA), and life time (hour).

[0075]

[Table 5]

As is clear from Table 5, when the film thickness of the carbide (TaC) film coating the surface of the tungsten coil filament is in the range of 1 μm to 50 μm, the emission current has no great difference with the film thickness, but the life time Was confirmed to increase with the film thickness.

Since bulk transition metal carbides have high hardness and brittleness, it is extremely difficult to process them into a desired shape. However, a metal material of an electron emitting material is preliminarily coiled, hairpin-shaped, tip-shaped, cylindrical-shaped, Since it is easy to process into a flat plate shape and to cover the surface of the processed product with a carbide film, there are various uses as electron emission sources having various shapes.

Further, by coating the surface of the tungsten filament with a thin film of tantalum carbide, the work function becomes small, the residual gas is hardly adsorbed, and stable electron emission characteristics are exhibited.

Carbide Film-Coated Electron Emissive Material 3 of the Above Example
Is a tungsten coil filament 1 as shown in FIG.
The TaC film 2 was coated on the entire outer peripheral surface of the
The film may be coated on a portion of the tungsten coil filament.

Further, although the tungsten coil filament is used in the above-mentioned embodiment, tungsten is used as a material, and various shapes such as a hairpin shape, a chip shape, a cylindrical shape and a flat plate shape are formed according to the purpose, and the surface thereof is coated with a TaC film. You may do it.

In the above-described embodiment, the emission current is a minute current of about several tens of μA, but it can be used as an electron beam source of several hundred A or more as an electron beam source used for metal melting or vapor deposition.

In the above embodiment, the application to thermionic emission was carried out, but it can also be used as a strong field electron emission.

[0083]

When the carbide film-coated electron emitting material of the present invention is used, the composition ratio on the surface of the tungsten electron emitting material is reduced.
Since the tantalum carbide film with 1 <C / Ta <1.2 is coated, the work function can be made small and the adsorption of residual gas can be made small, so that electron emission in a relatively high vacuum is performed. Is possible.

Further, since the electron emission efficiency is improved by the small work function, it is possible to operate at a low temperature, efficiently use a small amount of electric power, and prolong the service life.

Further, according to the method for producing the carbide film-covered electron emitting material, the metal Ta is evaporated in a vacuum and, at the same time, C ₂ H ₂ gas is introduced, and the pressure during deposition / composition is increased by the reactive ion plating method. film speed ^{6.0 × 10 - 2 Pa · min} / μ
m, and both were reacted to coat the surface of the tungsten electron emitting material with a tantalum carbide film having a composition ratio of 1 <C / Ta <1.2, so that the work function is small, the residual gas is not adsorbed, and the temperature is low. There is an effect that it is possible to easily manufacture a tungsten carbide film-coated electron emitting material which is operable and has a significantly extended life.

Since the carbide film can be coated after processing tungsten into various shapes by using the manufacturing method of the present invention, there are various uses as electron emission sources having various shapes.

[Brief description of drawings]

FIG. 1 is a schematic view of a tungsten coil filament used in one embodiment of the present invention,

FIG. 2 is a cross-sectional view of a carbide film-coated radiant material produced by the method of the present invention,

FIG. 3 is a characteristic diagram showing the relationship between the input power and the emission current of a comparative example and a carbide film-coated emission material produced by the method of the present invention;

FIG. 4 is a characteristic diagram showing a relationship between a filament film-coated radiation material manufactured by the method of the present invention and a filament temperature and radiation current of a comparative example.

[Explanation of symbols]

1. Tungsten coil filament, 2 carbide film, 3 carbide film coated electron emitting material.

Claims (5)

[Claims] 1. A carbide film-coated electron-emitting material comprising a tungsten electron-emitting material whose surface is coated with a carbide film,
The carbide film-coated electron emitting material, wherein the carbide film is a tantalum carbide film having a composition ratio of 1 <C / Ta <1.2. 2. The carbide film-coated electron emitting material according to claim 1, wherein the tantalum carbide film has a thickness of 1 to 50 μm. 3. The carbide film-coated electron emitting material according to claim 1, wherein the tungsten electron emitting material is a tungsten filament. 4. The metal Ta is vaporized in a vacuum, and at the same time C
₂ by introducing H ₂ gas, during the deposition of both the reactive ion plating method pressure / deposition rate ^{6.0 × 10 - 2 Pa · min} / μ
A method for producing a carbide film-coated electron-emitting material, which comprises reacting at a temperature of m or more for coating a surface of a tungsten electron-emitting material with a tantalum carbide film having a composition ratio of 1 <C / Ta <1.2. 5. The method for producing a carbide film-coated electron emitting material according to claim 4, wherein the tungsten electron emitting material is a tungsten filament.