WO2019156337A1 - Amorphous electron emitting material stable in air and manufacturing method therefor - Google Patents

Abstract

The present invention relates to an electron emitting material and a manufacturing method therefor. More particularly, the present invention relates to an amorphous electron emitting material that is stable in air and allows a large emission current at a low driving voltage thanks to the low work function thereof, and a manufacturing method therefor. The electron emitting material of the present invention exhibits a work function characteristic lower by 30 % or more than the work functions of the commercial electron emitting materials Mo and carbon, which are at a level of around 4.3 eV. Thus, the application of the electron emitting material to FED and fluorescent tubes allows a large emission current at a low driving voltage without structurally changing preexisting devices. In addition, the electron emitting material of the present invention can be manufactured on a mass scale by using simple thermal treatment, melting-solidification, and mechanical grinding processes.

Description

Stable Amorphous Electron Emission Material in Air and Manufacturing Method Thereof

The present invention relates to an electron emitting material and a method of manufacturing the same. More particularly, the present invention relates to an amorphous electron-emitting material that is stable in air, and to a method of manufacturing the same, which can increase the emission current at a low driving voltage due to its low work function.

Field emission display (FED) is a device that emits phosphors and displays images by emitting phosphors, which is one of the core technologies of large area display. In addition, the fluorescent tube or lighting device uses a micro electron source with an electron emitter that emits electrons by a strong current. If the diameter of the tube is reduced by using a material having excellent electron emission characteristics, the tube is not only high luminance but also compact in size. It is possible to apply to the backlight of the non-light-emitting display device, such as liquid crystal.

The prior art used for FEDs or fluorescent tubes utilizes the principle that an electron beam is emitted from the electron emitter and the phosphor is excited to emit light by applying a high voltage between the electron emitter and the electrode material. As the electron-emitting material, a metal or carbon-based material such as Mo is mainly used.

In order to facilitate the driving of the micro electron source, driving at a low voltage is required. In particular, when the electron emission is controlled by turning on / off the driving voltage such as FED, it is essential to lower the driving voltage.

Therefore, there is a need for a material having a small work function that can increase the emission current from the electron emitter at a low driving voltage. Metal or carbon-based materials such as Mo, which are currently used, have a work function directly related to the ease of electron emission at a level of 4 eV, and thus a method of inducing concentration by forming a fine needle structure for electron emission at low voltage is used.

For example, in the case of Mo, processing is required in the form of a cone of about 1 μm in height, and in the case of carbon, it is necessary to use a structure having a diameter of several tens of nm, such as carbon nanotubes. However, the electron emitter structure of such a shape is difficult to process the electrode, and when the electrode spacing is narrowed, problems with device fabrication and driving reliability are involved.

The inventors of the present invention have developed amorphous Hf ₂ S _1-y having a work function of at least 20% lower than that of Mo and carbon-based materials while studying electron emission materials having low work function properties.

Such amorphous Hf ₂ S _{1 -y} is formed on the surface of the crystalline material to a thickness of several tens of nm. Also crystalline Hf ₂ S _{1 -y} is a surface oxide easily create a HfO ₂ layer to lower the work function, but the conductive properties are degraded, such as shrinking, amorphous Hf ₂ S _{1 -y} is maintained on the surface structure compared to crystalline material is It is easy to minimize the deterioration of characteristics.

An object of the present invention is to provide an electron-emitting material containing the amorphous Hf ₂ S _{1 -y} and a manufacturing method thereof.

The present invention provides an amorphous electron emitting material having a composition including Hf and S and represented by the following Chemical Formula 1.

<Formula 1>

Hf ₂ S _1-y (-0.2 ≤ y ≤ 0.2)

In one embodiment of the present invention, the material surface of the formula (1) composition is Hf and S is distributed in a composition ratio of approximately 2: 1, but the amount of S may be locally excessive or insufficient.

The present invention also provides an electron emitter, characterized in that it comprises the amorphous electron-emitting material powder exposed to the surface.

Moreover, this invention provides the fluorescent tube provided with the said electron emitter.

In addition, the present invention comprises a first step of producing a compound raw material by a heat treatment process; Melting and cooling the obtained raw material of the first system to prepare a homogeneous electron-emitting material; And it provides a method for producing an amorphous electron-emitting material powder comprising a third step of crushing and grinding the surface of the material obtained in the third step.

Specifically, the first step of mixing the Hf powder and S powder and then heat treatment at a temperature of 450 to 600 ^o C for 2 to 4 days to obtain a compound raw material; A second step of melting and cooling the compound raw material obtained in the first step; And it provides a method for producing an amorphous electron-emitting material comprising a third step of crushing and grinding the surface of the material prepared in the second step.

The melting is preferably carried out in an inert gas atmosphere.

The second step may be performed once or twice or more times.

In the third step, scraping the surface of the material prepared in the second step may be performed through chemical etching or mechanical polishing.

In the third step, the shaving of the surface of the material prepared in the second step is preferably performed in an inert gas atmosphere for preventing oxidation such as vacuum, argon or nitrogen atmosphere.

The grinding can be done using ball milling, attrition milling, high energy milling, jet milling or grinding using a mortar and pestle.

The grinding can be done by gas atomization.

In the first step, the S powder may be added at a ratio of 0.8 to 1.2 with respect to 2 moles of the Hf powder.

The third step of grinding may be performed in a vacuum or inert gas atmosphere.

The electron-emitting material of the present invention exhibits a very large electron-emitting effect due to the low work function characteristics expressed from the presence of localized electron layers of amorphous Hf ₂ S _{1 -y} material.

Hf ₂ S _{1 -y} included in the electron-emitting material of the present invention does not depend heavily on the value of y and has a value of about 3.0 eV. This is more than 30% lower than the work function of about 4.3 eV level of commercial electron emission material Mo and carbon. When applied to FED and fluorescent tube, it is possible to obtain a large emission current at low driving voltage without changing the existing device structure. .

The method for preparing Hf ₂ S _{1 -y} electron-emitting materials provided in the present invention can easily produce a large amount of materials by simple heat treatment, melt-solidification and mechanical grinding processes.

The electron-emitting material provided in the present invention is easy to manufacture and can emit electrons at a low driving voltage. Therefore, it is possible to implement an electron emitter that forms a relatively large emission current based on the same applied voltage reference can be effectively applied to low-voltage driving FED, fluorescent tube and lighting device.

1 is the amorphous Hf ₂ S _1, the electron-emitting material of the present _invention is a TEM photograph of a microstructure _{y (0.2 ≤ y ≤ 0.2)} . Amorphous Hf ₂ S _{1 -y} material is formed on the crystalline Hf ₂ S surface to a thickness of several tens of nm. Localized electrons exist between the amorphous layer atoms, which is the source of the low work function properties.

FIG. 2 is an X-ray photoelectron spectroscopy (XPS) analysis result of amorphous Hf ₂ S _{1 -y} prepared in Example 1. FIG.

3 is a core level X-ray photoelectron spectroscopy analysis of the amorphous Hf ₂ S _{1 - y} prepared in Example 1. The area of each graph can be obtained to determine the composition of the substance Hf ₂ S _1-y .

4 shows the results of ultraviolet photoelectron spectroscopy (UPS) analysis on amorphous Hf ₂ S _{1 -y} prepared in Example 1. FIG.

FIG. 5 is an analysis result of re-measurement after 30 days of the XPS / UPS result and the measured raw material measured in FIG. 2.

6 is a graph comparing the conductivity of crystalline and amorphous Hf ₂ S _{1 -y} raw materials before and after oxidation. As a result, the conductivity deterioration of the crystalline raw material is severe, but the conductivity deterioration of the amorphous raw material is small.

FIG. 7 is a diagram showing the results of measurement of an electronized sample in a state before polishing and removing the surface oxidized in Example 1 by X-ray photoelectron spectroscopy. It can be seen that the pick due to oxidation is clearly visible on the surface.

Advantages and features of the present invention, and methods for achieving them will be apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings.

However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms.

The embodiments herein are provided to make the disclosure of the present invention complete, and to fully convey the scope of the invention to those skilled in the art, and the present invention is defined by the scope of the claims. It will be.

Thus, in some embodiments, well-known components, well-known operations and well-known techniques may be omitted from specific description in order to avoid obscuring the present invention.

As used herein, the singular forms "a", "an" and "the" include plural unless the context clearly dictates otherwise, and the elements and acts referred to as 'comprises' or 'do' not exclude the presence or addition of one or more other components and acts. .

Unless otherwise defined, all terms used in the present specification (including technical and scientific terms) may be used in a sense that can be commonly understood by those skilled in the art.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

According to one embodiment of the present invention, there is provided an amorphous electron-emitting material of a composition comprising Hf and S and represented by the following formula (1).

<Formula 1>

Hf ₂ S _{1 -y} (-0.2 ≤ y ≤ 0.2)

The electron-emitting material represented by Formula 1 may have a large or small composition of S locally due to the nature of the amorphous material, but the overall composition converges on the Hf ₂ S composition, and the electron-emitting property is not sensitive to the amount of S.

The electron-emitting material exhibits a large electron-emitting effect by its low work function, including localized high-density electrons.

The electron-emitting material may be an amorphous layer existing in the range of several to several tens of nm on the powder or bulk surface.

In addition, according to one embodiment of the invention, (a) preparing a compound raw material by a heat treatment process; And (b) melting and cooling the raw material obtained in step (a) to produce a homogeneous electron emitting material. And (c) there is provided a method for producing an amorphous electron-emitting material powder comprising the step of grinding the material obtained in step (b).

Step (a) is a step of heat-treating a mixture of raw materials for seed phase synthesis prior to the melting process to produce the electron-emitting material.

Specifically, Hf and S raw materials vacuum-sealed in a silica tube is put into a furnace and heat-treated for 2 to 4 days at 450 to 600 ℃.

Step (b) is to increase the purity and homogeneity of the electron-emitting material.

Specifically, the heat-treated mixture prepared in step (a) is placed in an arc melting facility chamber to form an inert gas atmosphere such as argon at a level capable of arc driving after forming a vacuum atmosphere. Thereafter, an arc is applied to melt the heat-treated mixture to solidify to produce an electron-emitting material.

The melting method may be carried out by a commonly used melting method, for example, a process selected from the group consisting of a high temperature tubular furnace, an ultra high temperature electric furnace, and the like, and may be preferably performed by arc melting. However, the present invention is not necessarily limited to these methods, and any method that can be used as a melting method in the art is possible. By using the arc melting method, industrial mass production of electron-emitting materials is possible, and improved physical properties can be obtained even when a general melting method other than the arc melting method is used.

In the arc melting method, in order to prevent oxidation of a mixed raw material, the raw material is melted in a process of making a liquid state by heating the raw material above a melting point in an inert gas atmosphere. It is possible to obtain an electron-emitting material having a size and a shape corresponding to a sample charging part made of a copper material in an arc melting facility chamber. In order to increase the purity and homogeneity of electron-emitting materials, melting by arc melting may be repeated.

Step (c) is a step of preparing a powder.

Specifically, the powder is prepared by using a mechanical grinding process such as ball milling to remove the oxidized portion during the process by scraping off the surface of the material in the form of agglomerates prepared in step (b) and preventing oxidation.

At this time, as a method of removing the oxidized portion of the surface of the material may be a method such as chemical etching, mechanical polishing that can remove the hafnium oxide in an inert gas atmosphere. For example, etching using a mixture of hydrofluoric acid or hydrofluoric acid and various ether organic solvents in a glove box, or polishing using abrasive stone, abrasive paper, grounder, polisher or the like can be used.

The melt-solidified material is pulverized by a method such as ball milling, attrition milling, high energy milling, jet milling, mortar, etc. It can be prepared in the form of a powder, but is not necessarily limited to these, any method that can be used in the art as a method for producing a powder by grinding the raw material in a dry or wet manner.

The powder grinding process of step (c) is preferably performed in an inert gas atmosphere such as vacuum, argon or nitrogen to prevent oxidation of the material.

In addition, the electron-emitting material powder may be prepared by gas atomization (gas atomization). In the gas atomization method, the compound raw material prepared by the melting method is heated to a melting point or more to form a liquid state, and rapidly sputtered by rapid ejection into a space of vacuum or argon atmosphere at room temperature through a nozzle to obtain a spherical raw material powder.

Hereinafter, the present invention will be described in more detail using examples and comparative examples.

Example ₁ Preparation and Characterization of Amorphous Hf ₂ S _{1 -y} (-0.2 ≦ y ≦ 0.2)

Grinded Hf, S powder was pelletized and vacuum-sealed in a silica tube, put into a furnace and sintered at 450 to 600 ℃ for 2 to 4 days. Hf ₂ S _{1 -y} is a phase that appears at high temperature, _whereas S has a very low vaporization point, so pure S is converted into Hf-S through the sintering process in order to minimize the loss of S when melting the material for synthesis. The intermediate materials made by sintering are synthesized by melting and solidifying by arc melting method, and then oxidized surface in the glove box is removed by grinding and then crushed by ball milling.

The prepared raw material naturally forms an amorphous material of Hf ₂ S _{1 -y} composition (0.2 ≦ y ≦ 0.2) on the crystalline Hf ₂ S surface as shown in the TEM photograph shown in FIG. 1.

The oxidation of the prepared raw materials and the valence state of the elements were measured using XPS as shown in FIG. 2. The raw material was crushed inside the XPS equipment. As shown in the data, the material was not oxidized, thus confirming that there was no material degradation due to oxidation.

As shown in FIG. 3, the y value of amorphous Hf ₂ S _{1 -y} was determined by core level XPS measurement. The area of the Hf and S core level graphs can be obtained and substituted into the following equation to obtain the composition.

In this case, n _i I _i S _i is the composition ratio, graph area, and previously reported sensitivity factor for element _i , respectively.

As shown in FIG. 4, of amorphous Hf ₂ S _{1 -y} The work function was 3.0 eV, which was slightly higher than that of the alkali metal, but was lower than that of the commercial product. There was little change in the work function in the range 0.2?

Comparative Example 1. Mo and C Work Function Measurement

The work function was measured in the same manner as in Example 1 for Mo and C.

As shown in FIG. 4, in the case of Mo or a carbon-based material which is widely used as an electron emission material, it has a work function near 4.3 eV. However, in the case of amorphous Hf ₂ S _{1 -y} raw material synthesized by the researchers, it has a work function near 3.0 eV regardless of the composition of y in the range 0.2 ≤ y ≤ 0.2. With a significantly lower work function, electron emission is relatively easy at low voltages.

Table 1 below shows the work function measurement results of amorphous Hf ₂ S _{1 -y} , Mo, and C prepared in Example 1 and Comparative Example 1.

matter	Work function (eV)
carbon nanotube	4.7-4.9
graphene	~ 4.5
Mo	4.36-1.95
Amorphous Hf 2 S 1 -y	3.0 ± 0.1

Example 2. Hf ₂ S _1-y Stability Evaluation

In order to evaluate the stability of Hf ₂ S _{1 -y} , the amorphous Hf ₂ S _{1 -y} powder prepared in Example 1 was measured again after about 30 days. As shown in the XPS and UPS results of FIG. 5, no significant difference was found in the data before / after 30 days and there was no degradation of the work function value.

In addition, as shown in the conductivity results of FIG. 6, it was confirmed that similar values appeared in the data before / after 30 days.

Crystalline Hf ₂ S-based materials are easily oxidized to form HfO ₂ layers having a high work function and low conductivity. Therefore, when manufacturing an electron emission device using crystalline Hf ₂ S, sufficient conductivity may not be obtained, deterioration of characteristics may occur, and thus desired characteristics may not be obtained or reliability of the device may be degraded.

In contrast, since the surface structure of amorphous Hf ₂ S _{1 -y} remains stable, deterioration of material properties is prevented. As a result, it is possible to fabricate devices that are easier to handle and more reliable than conventional crystalline Hf ₂ S based materials.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and variations without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

Claims (12)

1. An amorphous electron emitting material represented by Chemical Formula 1.

   <Formula 1>

   Hf ₂ S _1-y (-0.2 ≤ y ≤ 0.2)
2. An electron emitter comprising the powder of amorphous electron-emitting material of claim 1 exposed on a surface thereof.
3. A fluorescent tube comprising the electron emitter of claim 2.
4. A first step of mixing Hf powder and S powder and then heat-treating at a temperature of 450 to 600 ^° C. for 2 to 4 days to obtain a compound raw material;

   A second step of melting and cooling the compound raw material obtained in the first step; And

   A third step of shaving and grinding the surface of the material prepared in the second step;

   Method for producing an amorphous electron emitting material comprising a.
5. The method of claim 4, wherein

   And the melting is performed in an inert gas atmosphere.
6. The method of claim 4, wherein

   The second step is a method for producing an amorphous electron-emitting material, characterized in that performed repeatedly one or more times.
7. The method of claim 4, wherein

   In the third step, the shaping of the surface of the material prepared in the second step is performed by chemical etching or mechanical polishing method of producing an amorphous electron-emitting material.
8. The method of claim 4, wherein

   The method of manufacturing an amorphous electron-emitting material according to claim 3, wherein the surface of the material prepared in the second step is scraped off in a vacuum or inert gas atmosphere.
9. The method of claim 4, wherein

   The grinding is a method of producing an amorphous electron-emitting material, characterized in that using the milling using a ball mill, attrition milling, high energy milling, jet milling or mortar.
10. The method of claim 4, wherein

    And the pulverization is carried out by gas atomization.
11. The method of claim 4, wherein

    In the first step, the S powder is an amorphous electron-emitting material manufacturing method, characterized in that added in a ratio of 0.8 to 1.2 compared to 2 moles of the Hf powder.
12. The method of claim 4, wherein

    The third step of the grinding process is an electron-emitting material manufacturing method, characterized in that carried out in a vacuum or inert gas atmosphere.

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