WO2020130642A1

WO2020130642A1 - Cold cathode comprising graphene film, and electron gun using same

Info

Publication number: WO2020130642A1
Application number: PCT/KR2019/018029
Authority: WO
Inventors: 박건식; 사토로프맛랍전; 홍동표
Original assignee: 서울대학교산학협력단
Priority date: 2018-12-19
Filing date: 2019-12-18
Publication date: 2020-06-25
Also published as: KR20200076641A

Abstract

The present invention relates to a cold cathode comprising a graphene film, and an electron gun using same. More particularly, the present invention relates to a cold cathode comprising a graphene film and an electron gun using same, which can be used in vacuum electronic devices having a range of millimeter and sub millimeter frequencies. The present invention provides a cold cathode comprising a graphene film and capable of stably emitting electrons having a high current density, and an electron gun comprising same. Specifically, a cold cathode including a thin graphene film having a high aspect ratio can maintain a high current density and current.

Description

Cold cathode containing graphene film and electron gun using the same

The present invention relates to a cold cathode comprising a graphene film and an electron gun using the same. More particularly, the present invention relates to a cold cathode including a graphene film and an electron gun using the same, which can be used in vacuum electronic devices having a range of millimeter and sub millimeter frequencies.

Interest in millimeter and terahertz radiation has recently been spotlighted by advances in microfabrication and modeling tools, and the need for new biomedical and security technologies. Potential applications include biological and chemical spectroscopy and biomedical diagnostics, radar and high-speed communication systems, weapon or threat detection, remote high-resolution imaging, and material research. Slow-wave vacuum electronics (such as oscillators) are currently the most widely distributed medium-function radiation sources in the millimeter and sub-millimeter wavelength range, and generally the power of these available sources decreases rapidly with increasing frequency. Especially in the terahertz range, the reduction is even greater. All classical electron sources of coherent electromagnetic radiation rely on the general physical principle of converting the kinetic energy of an electron current into electromagnetic field energy. The limitations of these devices are related to the device's circuitry and the cathode's power handling capabilities, namely heat-related issues. Most vacuum electronics use thermal ions or hot cathodes, but they are problematic in the high frequency range because they are bulky and cause heating of the surrounding device to provide insufficient emission current density. Accordingly, in recent years, cold-cathode electron emitters have begun to be used as a source of high-density electron beams that cannot be achieved with current thermal ion cathodes, and these cold-cathode electron emitters are used for medical imaging, high-resolution field emission electron microscopy, flat panel displays and border security. Or, various applications such as X-ray sources for vacuum electronics for satellite communication are being studied.

The cathode means an electron emitting surface or a cathode surface of the electron tube. The cathode refers to an electrode that emits electrons from the cathode electron tube. If categorized according to the emission principle, there are hot cathode, photocathode, and cold cathode. The cold cathode means a cathode that emits electrons without heating the cathode, and there are those using secondary electron emission due to collision of electrons or ions and those using field emission (field emission cathode). Field emission is a kind of electron emission, which means drawing electrons from a metal surface by a strong electric field. The general cold cathode has a problem that its stability and life are significantly lower than that of a hot cathode.

Field emission occurs in high electric fields between about 10 MV/cm and 100 MV/cm, which exceeds the typical vacuum breaking strength at approximately 100 kV/cm. Therefore, in order to avoid destruction and satisfy the above conditions, the field emission source can have a high aspect ratio emitting surface such as a lightning rod. That is, it is required to have a very sharp emission surface of tens to tens of nanometers for electric field strengthening.

For stable performance, the emitted electron beam must be uniform. Therefore, it is important to control the emission surface with a sharp and high aspect ratio to improve the field. In the case of a field emission electron microscope, the emission surface of the point emitter (e.g., LaB ₆ single crystal) was uniformized by reactive ion etching (RIE), electric discharge processing, electric aging, and focused ion beam (FIB) processing. Alternatively, carbon nanotube (CNT) tips have been used.

On the other hand, flat panel displays and X-ray sources use arrays, flakes or yarn emitters formed by a collection of individual electron emitting elements to obtain large emission areas and emission currents. This flat panel display has a non-uniform field emission surface because the individual field emission points are not the same due to the limitations of the manufacturing method. The non-uniform field emission surface inevitably involves local evaporation of the emission element. Therefore, it causes local electric field emission and consequently electrical damage due to poor vacuum. This not only causes non-uniform electron emission, but is an important obstacle that determines the life of the field emission device. To solve this problem, the individual field emission points must be homogenized and the surface treated using methods such as plasma treatment, laser surface treatment, electric discharge machining, and controlled electrical blocking treatment. Although it is possible to obtain a more stable and uniform field emission using this method, the random nature of the individual field emission points included in the manufacturing method cannot be fully compensated. Therefore, there is a problem that the lifetime of most field emission cathodes is significantly lower than that of a thermal ion cathode having a stable lifetime.

Recently, a field emission cathode using a graphene oxide film that can be mechanically freely cut to form a desired field emission surface has been developed, which uses a modified Hummer method. However, there is a problem in that it is difficult to uniformly control the shape of the surface in the micro-region of the order of tens of nanometers from the surface where the field emission occurs.

A field emission cathode using a graphene oxide film rolls graphene paper to form an array and a graphene cannon capable of producing a maximum current density of 3A/cm ² and 6mA. The graphene cannon is fixed vertically to the metal base, and the voltage applied between the metal base and the anode controls the emission characteristics. The field strengthening factor of this graphene canon is less than other types of graphene sheet emitters previously reported. However, it still has a high turn-on field, so the current density and current to be achieved are still below the limits of the thermal ion cathode.

An electron gun (electron beam) is a device that makes a beam of electrons that are well aimed to move at a specific speed, and is generally made of a narrow and long vacuum tube, and a vacuum electronic device and a cold cathode electron emitter are used for this. Therefore, it has the problems of a general vacuum electronic device and a cold cathode electron emitter.

Accordingly, the technical problem of the present invention is conceived in this regard, and the object of the present invention is to provide a cold cathode having a very high current density of 10,000 A/cm ² or more and 10 mA/mm or more, and a power higher than the vacuum terahertz range. In order to do, the cold cathode according to an embodiment of the present invention includes a graphene film.

Another object of the present invention is to provide an electron gun that emits an electron beam stably by improving a problem of thermal contact of a graphene field emission device by using a cold cathode including a graphene film capable of generating a high current density. .

To solve this problem, the cold cathode according to an embodiment of the present invention includes a graphene film, and the graphene film has an aspect ratio of 30,000:1 or more.

The graphene film may be doped with tungsten.

The cold cathode may emit an electron beam with a current density of 10 mA/mm or more.

The cold cathode may emit an electron beam with a current density of 10000 A/cm ² or higher.

The electron gun according to an embodiment of the present invention includes a cathode base, a cold cathode fixed to the cathode base, an anode spaced apart from the cathode base, and the cold cathode includes a graphene film, and the graphene film is 30,000: It has an aspect ratio of 1 or more.

The graphene film may be doped with tungsten.

As described above, the present invention includes a graphene film, and provides a cold cathode capable of stably emitting electrons having a high current density and an electron gun including the same. Specifically, a cold cathode including a thin graphene film having a high aspect ratio can maintain a high current density and current.

1 is a perspective view of a cold cathode sheet electron gun using an electrostatic focusing lens.

2 is a cross-sectional view of a cold cathode sheet electron gun using a stand-alone vertically aligned graphene film.

3 is a perspective view showing a cold cathode including a graphene film according to an embodiment of the present invention.

4 is a view showing a simulated temperature distribution in the cathode geometry due to the contact between the graphene film of the cold cathode including the graphene film according to FIG. 3 and the substrate.

5 is a view showing a simulation graph of the temperature distribution versus the discharge current of the cold cathode including the graphene film according to FIG. 4.

6 is a SEM image of a vertically aligned tungsten-doped graphene oxide film in a cold cathode including a graphene film according to an embodiment of the present invention.

7 is a perspective view of performing an electric aging and electric field emission test on a cold cathode including a graphene film according to an embodiment of the present invention.

8 is a diagram showing a graph of current density according to an applied voltage tested in a diode mode of a cold cathode including a graphene film according to an embodiment of the present invention.

9 is an image showing a W-rGO emission pattern of a cold cathode including a graphene film according to an embodiment of the present invention.

FIG. 10 is a graph showing a current graph of stand-alone graphene cold cathodes vertically aligned in a diode mode of a cold cathode including a graphene film according to an embodiment of the present invention.

11 is a diagram showing a current graph by simulation and experiment of a cold cathode including a graphene film according to an embodiment of the present invention.

12 is a perspective view of an electron gun according to an embodiment of the present invention.

13 is a view showing the electron beam trajectory in the XZ (cathode wide side) and YZ plane (cathode height side) of the electron gun according to an embodiment of the present invention.

14 is a graph showing the emission pattern of the graphene sheet and the electric field emission of the graphene sheet to the graphene sheet emitter in a general graphene film emitter.

15 is a general graphene film emitter (a) a photo of an rGO thin film, (b) a schematic view of the manufacture of a cylindrical graphene sheet emitter, (c) a photograph of a cylindrical graphene sheet emitter, and (d) a cylindrical graphene sheet emitter. It shows the circular radiation pattern of.

16 is a graph showing the field emission results of a graphene canon of a typical graphene film emitter.

17 is a view showing an rGO-film cutting edge by various cutting methods of a general electron gun.

18 is a schematic view of (a) rGO film mounting method of an electron gun according to an embodiment of the present invention (b) total test setting (c) showing an experimental apparatus installed in a vacuum chamber.

19 is a graph showing a field emission trend graph saturated by sequential electrical aging of a cold cathode including a graphene film according to an embodiment of the present invention.

The present invention can be applied to various changes and can have various forms, and the embodiments are described in detail in the text. However, this is not intended to limit the present invention to a specific disclosure form, and it should be understood that all modifications, equivalents, and substitutes included in the spirit and scope of the present invention are included. In describing each drawing, similar reference numerals are used for similar components. Terms such as first and second may be used to describe various components, but the components should not be limited by the terms.

The terms are used only for the purpose of distinguishing one component from other components. The terms used in this application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In this application, terms such as “comprise” or “consist of” are intended to indicate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, and that one or more other features are present. It should be understood that the existence or addition possibilities of fields or numbers, steps, actions, components, parts or combinations thereof are not excluded in advance.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains. Terms, such as those defined in a commonly used dictionary, should be interpreted to have meanings consistent with meanings in the context of related technologies, and should not be interpreted as ideal or excessively formal meanings unless explicitly defined in the present application. Does not.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the drawings.

The present invention relates to a cold cathode comprising a graphene film and an electron gun including the same. Graphene films can have very high aspect ratios aligned vertically. The cold cathode including the graphene film having such a high aspect ratio can emit an electron beam with a current density of 10 mA/mm or more or a current density of 10000 A/cm ² or more.

The graphene film can be doped with tungsten, in which case the electrical and thermal properties of the cold cathode can be improved.

Hereinafter, a cold cathode including a graphene film according to an embodiment of the present invention and an electron gun including the same will be described with reference to the drawings.

1 is a perspective view of a cold cathode sheet electron gun using an electrostatic focusing lens. 2 is a cross-sectional view of a cold cathode sheet electron gun using a vertically aligned graphene film. 3 is a perspective view showing a cold cathode including a graphene film according to an embodiment of the present invention.

Referring to FIG. 1, the cold cathode sheet electron gun 100 includes a cathode base 110, a graphene film 111, a gate 120, and an anode 130. 2 and 3, the graphene film 111 may be positioned to protrude over the cathode base 110. At this time, the protruding height may be about 0.5 mm.

Then, the graphene film included in the cold cathode of the present invention will be described in detail below. The graphene film 111 included in the cold cathode of the present invention may be doped with tungsten. In addition, the graphene film 111 may have a very high aspect ratio vertically aligned.

The cold cathode including the graphene film 111 of the present invention can be produced by a chemical process using a Hummer method and a hydrothermal synthesis process. During the hydrothermal process, the oxygen functional group of the graphene film 111 may be reduced to restore graphene properties. The graphene film 111 is flexible and can control its thickness and shape. When the aspect ratio of the length to thickness of the graphene film 111 is high, it may have a high heat transfer coefficient under an applied electric field.

Also, for further reduction, the graphene film 111 may be annealed at a temperature of 800° C. in a nitrogen atmosphere. After the annealing process, when the graphene film 111 is irradiated using energy dispersive X-ray spectroscopy (EDS), a decrease in oxygen ratio can be confirmed. For example, the weight percent of carbon and oxygen before annealing may be 69% and 24%, respectively, and after annealing may be 79% and 12%. In this way, the graphene film 111 may partially recover broken sp2 bonds due to oxygen in the graphene structure through annealing.

In this embodiment, the graphene film 111 included in the cold cathode may be a multi-layer graphene film (rGO film). In order for the field emission to occur in the graphene film 111, it is necessary to form a field emission surface. Hereinafter, a method for forming a field emission surface will be described.

The rGO film can be cut in various ways such as RIE, laser cutting, knife cutting, microtome and FIB to form a uniform field emission surface.

The FIB method has the highest uniformity. However, graphene such as rGO film is inefficient and time consuming because it is resistant to ion bombardment, the mechanism of the FIB cutting method. Since the rGO film is independent to improve the field emission performance, it is difficult to adhere the film during ion etching. Therefore, the RIE method in which uniform etching cannot be performed is not suitable. Uniformity of the cutting edge is important to use the graphene film as a cold cathode. The laser cutting method is also not suitable for forming a uniform emission surface because it concentrates high-density energy at local points and burns the material to form debris.

Therefore, it is preferable to use a knife cutting and a microtome to cut the graphene film 111. The rGO film can be processed manually due to its excellent flexibility and rigidity, and can be cut mechanically. When the rGO film is cut with a knife cutting and a microtome, excellent surface uniformity can be obtained. To apply the microtome, a rectangular shaped pre-formed rGO film can be prepared using a knife-cutting method and stored by being embedded in paraffin wax during microtome manipulation. After molding using a microtome, paraffin wax can be removed using a diluted xylene solution. The protrusions and non-uniformities of less than 100 nm remaining on the emitting surface of the graphene film can be uniformized through electrical aging by field emission.

The cold cathode including the graphene film according to the present embodiment may represent a thermal analysis simulation result as shown in FIG. 4.

4 is a view showing a simulated temperature distribution in the cathode geometry due to the contact between the graphene film of the cold cathode including the graphene film according to FIG. 3 and the substrate. 4(a) is a normal contact conductance, and FIG. 4(b) is a 20.5 W/m ² contact conductance.

As illustrated in FIG. 4B, when the graphene film is burned due to high temperature, the thermal contact conductance between the cathode base 110 and the graphene film 111 may be changed to find the lowest conductance.

FIG. 5 shows temperature distribution versus emission current by simulating FIG. 4. Fig. 5(a) is a normal contact conductance, and Fig. 5(b) is a 20.5 W/m ² contact conductance. Referring to FIG. 5(b), it was confirmed that the rGO film was burned at a contact conductance of 20.5 W/m ² . That is, as illustrated in FIG. 5, when the thermal contact conductance is 20.5 W/m ² , the temperature inside the graphene may match the experimental data in which the graphene film is burned.

In order to use the graphene film as a cold cathode, the graphene film 111 may be cut into a rectangular shape. 6 is a SEM image of a vertically aligned tungsten-doped graphene oxide film in a cold cathode including a graphene film according to an embodiment of the present invention. The graphene film in FIG. 6 can be cut into a rectangular shape with a discharge edge of 3 mm and a length of 5 mm.

As shown in Figure 3, the cut rGO film can be sandwiched between the cathode base 110. The cathode base 110 may be made of stainless steel, and the height of the film protruding from the cathode surface may be 0.5 mm.

Referring to FIG. 7, an ultra-high vacuum chamber equipped with a rotary pump, a turbo pump, and an ion pump may be used in the electric aging and field emission test. The diode-type experiment apparatus shown in FIG. 7 can be prepared by inserting a ceramic insulator spacer between the film-mounted cathode base 110 and the

molybdenum anodes

710 and 720 and placing it in a vacuum chamber. The distance from the field emission surface to the anode is 0.5 mm, the thickness of the ceramic insulator is 1 mm, and the height of the mounted film can be maintained at 0.5 mm.

A vacuum level of 10 ^-7 to 10 ^-8 Torr can be generated before starting the experiment, which can be maintained during the experiment. For the experiment, a DC voltage source with a maximum output voltage of 5 kV and a current of 250 mA can be used. The current collected at both

anodes

710 and 720 can be measured using a current meter in the nano-amp range connected to the computer.

During the experiment, there is a risk of sudden electrical breakdown due to the rate of gas removal generated by electrons striking the anode surface. To avoid this, a sufficient ramp-up voltage can be applied in the early stages of the experiment. A design process in which the voltage applied with a lamp of 100 V is strengthened to create a uniform radiation surface by electrical treatment can be implemented. As the number of voltage cycles increases, lower voltages may be required to achieve the same field emission current level in the low voltage region (1.5-2.5 kV). As the conditioning process continues, the emission current may gradually stabilize. The maximum applied voltage limit can be kept below 4 kV during conditioning to avoid vacuum breakage.

FIG. 8 is a graph showing a current density according to an applied voltage experimentally tested in a diode mode of a cold cathode including a graphene film according to an embodiment of the present invention. As shown in Fig. 8, the IV curve can finally reach a stable emission current. The change in current density before conditioning is significant, but can be neglected after conditioning. This may indicate that the release edge of the rGO film gradually clears after a series of electrical aging. Referring to FIG. 8, the IV characteristic demonstrates that the radiated current density reaches about 10,000 A/cm ² at the applied DC voltage (3.7 kV) in stable operation. That is, the graphene film according to the present embodiment can maintain a current density of 10,000 A/cm ² or more.

9 is an image showing an emission pattern of a tungsten-doped graphene oxide film (W-rGO) of a cold cathode including a graphene film according to an embodiment of the present invention. To characterize emission uniformity, field emission luminescence can be performed using a phosphor screen on a conductive ITO glass used as an anode. In order to avoid burning of the fluorescent material on the ITO glass, the applied potential was kept below 2.5 kV. Therefore, it emits a lower current. For example, when taking a picture of the ITO glass surface, the emission current may be less than 1.25mA. Before conditioning, the beam is wide and non-uniform, and very bright spots expected to be caused by the uneven surface with protrusions are observed, but a clear and uniform sheet-like beam mark may appear as shown in FIG. 9 after electrical adjustment. The width of the beam mark can match the width of the rGO emission edge.

10 shows time tracking of current density at a fixed applied voltage of 3 kV for a vertically aligned rGO film after the conditioning process. Referring to FIG. 10, electron emission was observed for 1,100 hours or more on a graphene cathode having a uniform emission surface through electrical treatment after mechanical molding. Despite operating at a very high current density of about 10,000 A/cm ^2, the emission current variability during the entire stability test period was less than 5%. That is, it was confirmed that the graphene film according to the present embodiment has very improved stability when used as a cold cathode (emission surface) of an electron gun.

11 is a diagram showing a current graph by simulation and experiment of a cold cathode including a graphene film according to an embodiment of the present invention. 11 is for comparing the experimentally observed I-V curve and the simulated curve, it was confirmed that the simulation and experimental values are very similar.

The high aspect ratio and vertically aligned shape of the rGO film according to an embodiment of the present invention can emit many electrons with high current density by increasing the emission area and improving the electric field applied to the emission surface. This field emission characteristic can be further improved if the emission surface is properly conditioned. In particular, when the rGO film is doped with tungsten or the like to improve the electrical conductivity and thermal conductivity of the rGO film, emission characteristics may be further improved.

12 is a perspective view of an electron gun according to an embodiment of the present invention. The electron gun according to an embodiment of the present invention may include a cold cathode including the graphene film described above.

As illustrated in FIG. 12, the electron gun may have a potential of 1 kV applied to the

gate

120, 5 kV applied to the cathode base 110 and the anode 130 grounded. The emitted electrons have a high rate of divergence, ie a higher vertical velocity, due to the natural rapid coulomb expansion (space-charge). As a result, the electron beam may collide with the gate and the anode.

13 is a view showing the electron beam trajectory in the XZ (cathode wide side) and YZ plane (cathode height side) of the electron gun according to an embodiment of the present invention. 13, a combination of an electrostatic lens and a magnetic system may be used to focus and transmit the electron beam 1010 through the slow-wave beam tunnel 1120. 13(a) is an electron beam trajectory in XZ (cathode wide side), and (b) is an electron beam trajectory in YZ plane (cathode height side). The solenoid magnet 1110 focuses a highly divergent electron beam through the gate. Solenoids of 0.4 Tesla and magnetic field strengths of Tesla of 0.2 or less can be used.

Thus, the cold cathode including graphene and the electron gun including the graphene according to the present embodiment can be used in a miniaturized terahertz vacuum electronic device requiring a high current density and a uniform and long-term stable cold cathode.

Hereinafter, an emission surface of the graphene sheet according to an embodiment of the present invention will be described. In order to emit electrons from the graphene sheet, the graphene sheet may overlap horizontally and the edges may be cut evenly. Release can occur only at the edge of the graphene sheet. When the graphene sheet is fixed vertically, the graphene sheet may be aligned vertically to emit electrons. Therefore, the emission region and emission pattern can be precisely controlled.

14 is a graph showing the emission pattern of the graphene sheet and the electric field emission of the graphene sheet to the graphene sheet emitter in a general graphene film emitter. Field emission measurements can be performed in a high vacuum chamber with a diode of 1 mm in diameter and a space of 300 μm. The graphene sheet can be held vertically as a cathode between two metal rectangles. A phosphor may be deposited on the ITO glass to investigate the emission of the graphene film emitter. The emission pattern is shown in FIG. 14. As illustrated in FIG. 14, electrons coming from the edge of the graphene sheet cause phosphors to form electron beams and generate emission patterns. Through the FE test of the graphene sheet shown on the right side of FIG. 14, it was confirmed that the on field was 2V/µm, the FE current density was about 10A/cm ^2, and the current was 2mA.

15 is a general graphene film ejector (a) a photo of an rGO sheet, (b) a schematic view of the manufacture of a cylindrical graphene sheet ejector, (c) a photograph of a cylindrical graphene sheet ejector, and (d) a cylindrical graphene sheet ejector. It shows a circular radiation pattern. The graphene film of FIG. 14 can be rolled as shown in FIG. 15 to form a canon cathode. This is because the graphene film is flexible.

16 is a graph showing the field emission results of the graphene canon of the graphene film emitter. Referring to FIG. 16, the emission current density increases initially and has some fluctuation, and after 1 hour, the emission current density becomes flat. The emission current density may decrease by 6% after 6 hours of continuous emission.

Hereinafter, the uniformity of the cut surface according to the graphene film cutting method will be described.

17 is a view showing uniformity of rGO-film cutting edges of various cutting methods of a general electron gun. Referring to FIG. 17, it can be confirmed that the cutting surface when cutting with a knife and a microtome is most effective as described above.

18 is a schematic view of (a) rGO film mounting method of an electron gun according to an embodiment of the present invention (b) electron gun test setting (c) is a diagram showing an experimental apparatus installed in a vacuum chamber. 19 is a graph showing a field emission tendency graph to be saturated by sequential electrical aging of a cold cathode including a graphene film according to an embodiment of the present invention.

Referring to FIG. 18, the W-rGO film can be cut into a rectangular shape with a discharge edge length of 3 mm and a height of 5 mm. The precisely cut W-rGO film can be sandwiched between the cathode blocks made of stainless steel and screwed so that the height of the film protruding from the cathode surface is 0.5 mm. Ultra-vacuum chambers equipped with rotary pumps (Varian, SD-300), turbo pumps (Varian, Turbo-V301) and ion pumps (Varian, Vacion plus 500) can be used for electrical aging and field emission tests. A ceramic insulator spacer is inserted between the cathode block on which the graphene film is mounted and the molybdenum anode, and placed in a prepared vacuum chamber to prepare a die-shaped experimental apparatus. The distance from the field emission surface to the anode is 0.5 mm, the thickness of the ceramic insulator is 1 mm, and the height of the mounted film can be maintained at 0.5 mm. The circuit diagram and the photo image of the test setup composed of the diode settings are as shown in FIGS. 18(b) and 18(c), respectively.

Before starting the experiment, a vacuum level of 10 ^-7 -10 ^-8 Torr is created and can be maintained during the experiment. A DC voltage source with a maximum output voltage of 5 kV and a current of 250 mA can be used. The output current can be measured using a current meter in the nanometer range connected to the computer. Because of the high rate of gas removal generated by electrons striking the anode surface, there is a high risk of sudden electrical breakage, so a low voltage can be applied for a sufficient time in the early stages of the experiment to avoid this. A process in which the voltage applied in steps of 100 V is enhanced to produce a uniform emission surface by electrotreatment can be implemented. As the number of voltage cycles increases, lower voltages may be required to achieve the same field emission current level in the low voltage region (1.5 kV or more and 2.5 kV or less).

In addition, referring to FIG. 19, if the conditioning process continues, the emission current may gradually stabilize. A high applied voltage limit of 3.5 kV can be maintained during conditioning to avoid vacuum failure. As can be seen in Figure 19, the IV curve can finally reach a narrow range with stable emission currents (4th and 5th curves). This means that the release edge of the W-rGO film gradually becomes clean after a series of electric aging as shown in FIG. 19. The IV characteristic shows that the discharge current reaches a maximum of about 8 mA in a stable operating state, and the applied DC voltage may be 3.5 kV. The calculated maximum current density was about 3,000 A/cm ^2, and it was confirmed that the maximum current density in stable operation reached an emission current density of about 10,000 A/cm ² at an applied DC voltage of 3.7 kV.

Although described above with reference to embodiments, those skilled in the art can variously modify and change the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. You will understand that there is.

Claims

Graphene film,

The graphene film is a cold cathode having an aspect ratio of 30,000:1 or more.
According to claim 1,

The graphene film is a cold cathode doped with tungsten.
According to claim 1,

The cold cathode is a cold cathode capable of emitting an electron beam with a current density of 10 mA/mm or more.
According to claim 1,

The cold cathode is a cold cathode capable of emitting an electron beam with a current density of 10000 A/cm 2 or higher.
Cathode base;

A cold cathode fixed to the cathode base;

And an anode spaced apart from the cathode base,

The cold cathode includes a graphene film,

The graphene film is an electron gun having an aspect ratio of 30,000: 1 or more.
The method of claim 5,

The graphene film is an electron gun doped with tungsten.
The method of claim 5,

The cold cathode is an electron gun capable of emitting an electron beam with a current density of 10 mA/mm or more.
The method of claim 5,

The cold cathode is an electron gun capable of emitting an electron beam with a current density of 10000 A/cm 2 or higher.