KR20220102847A - Carbon Nano-Structure for Field Emitter - Google Patents

Abstract

The present invention relates to a carbon structure for an emitter, a deposition device for preparing the carbon structure for an emitter, and a preparation method of the carbon structure for an emitter. Particularly, the present invention provides the carbon structure for an emitter which comprises: a vine structure in which one-dimensional carbon bodies are randomly entangled and extended, wherein a two-dimensional carbon body randomly protrudes on a surface of the vine structure.

Description

Carbon Nano-Structure for Field Emitter

The present invention relates to a carbon structure for a field emission emitter, a method for manufacturing the same, and an apparatus for manufacturing the same, and more particularly, to a carbon structure for an emitter that easily generates a field concentration, has a low threshold voltage, and has stable field emission characteristics. .

Field emission (field emission) is a phenomenon in which electrons in a material are emitted in a vacuum when an electric field of generally 10 MV/m or more is applied to the surface of a material. As a common material used for this field spinning, carbon nanotubes (CNTs) or a carbon film structure having needles (CCNS, see FIG. 1 ) are mentioned. Carbon nanotubes or carbon film structures having needle-like projections have a high electric field concentration coefficient due to their high aspect ratio in the shape of a long and thin pipe, and have excellent radiation characteristics. The field emission characteristic (IV characteristic) is a curve showing the relationship between the applied voltage V and the field emission current (emission current) I by applying a voltage V between the anode and the cathode having a field emission function, and the voltage at which field emission starts (operation onset voltage or threshold voltage) or the slope or shape of the curve.

Under vacuum, an anode (target) made of a metal with good X-ray generation efficiency, such as tungsten, is placed opposite the cold cathode, and a negative voltage is applied to the cold cathode to ground the anode, then electrons are emitted by field radiation from the cold cathode. There is a cold cathode X-ray tube in which the emitted electrons are accelerated by the voltage applied between the electrodes and collide with a target to generate X-rays.

In order to generate X-rays, it is necessary to emit electrons with a certain amount and energy. The current-voltage (IV) characteristic curve, with the emission current (I) representing the amount of electrons as the vertical axis and the voltage (V) between the anode and the cathode as the horizontal axis, showing the electron emission performance of the cold cathode.

When a carbon film structure is applied to a cold cathode X-ray tube, in general, a tube voltage of 30 kV or more and a tube current of 0.01 mA or more are required. In addition, in the X-ray tube, the residual gas in the vacuum inside the tube generates ions by electrons emitted from the carbon film structure. These ions are accelerated by the electric field and collide with the carbon film structure (emitter). As a result, the electron emission state is changed, and a stable X-ray output cannot be obtained.

It has been considered that the ratio of the curvature of the end to the length of the tube is good for the carbon film structure so that an electric field is efficiently applied at the end. In fact, the aspect ratio of the carbon film structure is very large.

However, not all grown crystals have the same aspect ratio, and there is a discontinuous distribution of aspect ratios. Therefore, at a low applied voltage, an elongated or unusually large aspect ratio emits electrons first, but it is destroyed and annihilated as the voltage rises, and then an elongated object with a large aspect ratio emits electrons. In this way, the structure emitting electrons changes with respect to the applied voltage. This is what is commonly referred to as flickering of electron emission.

If this phenomenon is considered as the entire carbon film structure, when voltage is applied and gradually raised, electron emission occurs in some regions of the carbon film structure. As this is not achieved, the electron emission moves to another region and another electron emission occurs.

When the carbon film structure is applied to an electron tube or an X-ray tube using electric field electron radiation, it limits the increase in current, prevention of flickering of electrons, and stabilization of performance. Therefore, first of all, at an applied voltage V with a low operation start voltage, electrons are emitted from the entire film rather than from some regions where the electric field concentration coefficient β, which is a factor of electron emission of the carbon film structure, is large, and field emission that provides stable IV characteristics. Realization of a carbon film for emitters has been demanded.

Republic of Korea Patent Publication No. 2020-0090715

It is an object of the present invention to provide a carbon structure having a low threshold voltage, enabling a large current, and preventing electron flickering and having stable field emission characteristics.

The carbon structure according to the present invention is a carbon structure for a field emission emitter, and includes a vine structure in which a one-dimensional carbon body is randomly entangled and stretched, and has a structure in which a two-dimensional carbon body randomly protrudes from the surface of the vine structure.

In the carbon structure for an emitter according to an embodiment, the two-dimensional carbon body may include graphene.

In the carbon structure for an emitter according to an embodiment, the protrusion direction of the two-dimensional carbon body may include a direction normal to a surface on which the two-dimensional carbon body is positioned.

In the carbon structure for an emitter according to an embodiment, the two-dimensional carbon body protrudes into a thorn-shaped aggregate in which two or more two-dimensional carbon bodies are assembled on the surface of the tendril structure, at least the outer edge of the two-dimensional carbon body constituting the aggregate The parts may be spaced apart from each other.

In the carbon structure for an emitter according to an embodiment, the aggregate may be spaced apart from the one-dimensional carbon body in a radially disorderly manner.

In the carbon structure for an emitter according to an embodiment, the protrusion height of the aggregate may be 5 to 500 nm based on the surface on which the aggregate is located.

The carbon structure for an emitter according to an embodiment may further include a carbon film in which carbon particles are aggregated in the form of a film, and the tendril structure may be in a state bound to the carbon film.

The present invention includes the above-described carbon structure (carbon emitter) deposition apparatus for emitter.

A carbon emitter deposition apparatus according to the present invention includes: a first electrode on which a substrate is mounted and in a grounded state; a second electrode spaced apart from and opposed to an upper portion of the first electrode; a coil electrode surrounding a periphery of a deposition region that is a space between the first and second electrodes spaced apart and opposed to each other; a first power supply for applying a voltage to the second electrode; and a second power supply for applying a voltage to the coil electrode.

In the carbon emitter deposition apparatus according to an embodiment, the coil electrode may be positioned on the side of the first electrode in the deposition region.

In the carbon emitter deposition apparatus according to an embodiment, the length of the coil electrode may satisfy 0.3 to 0.8 by setting the separation distance between the first electrode and the second electrode as 1.

In the carbon emitter deposition apparatus according to an embodiment, a plasma may be formed in the deposition region by a DC voltage applied to the second electrode, and a rotational flow may be induced in the gas in the plasma by the coil electrode.

In the carbon emitter deposition apparatus according to an embodiment, the carbon emitter deposition apparatus includes: a chamber in which the first electrode, the second electrode, and the coil electrode are provided and providing an internal space in which deposition is performed; a gas supply means for supplying a gas phase including a carbon source to the inner space; and an exhaust means for adjusting the pressure of the inner space.

The present invention includes a carbon emitter deposition method using the above-described carbon emitter deposition apparatus.

The present invention includes the carbon emitter deposition method (manufacturing method) described above.

In the carbon emitter deposition method according to the present invention, a) a substrate is mounted on the first electrode positioned below the first electrode and the second electrode spaced apart from each other in the direction of gravity, hydrogen gas is introduced, and a voltage is applied to the second electrode. forming a hydrogen plasma by applying it; and b) supplying a gaseous carbon source to the hydrogen plasma and forming a rotational flow in the gas in the plasma adjacent to the substrate at least by using the coil electrode.

In the carbon emitter deposition method according to an embodiment, a temperature difference between the first electrode side and the second electrode side may be generated by the plasma in step b).

In the carbon emitter deposition method according to an embodiment, an ascending flow in which the gas in the plasma rises from the center of the substrate toward the second electrode and a descending flow in which the gas in the raised plasma descends toward the substrate are formed by the temperature difference, , the rising flow, the falling flow, or the rising flow and the falling flow may be rotated by the coil electrode.

The carbon structure for an emitter according to the present invention has the advantage of lowering the threshold voltage compared to the conventional carbon nanotube or carbon film structure and having a very stable IV characteristic.

1 is a scanning electron microscope photograph of a conventional carbon film structure,
2 is a cross-sectional view showing a structure of a deposition apparatus for depositing a carbon structure for an emitter according to an embodiment of the present invention;
3 is a scanning electron microscope photograph of observing the carbon structure for an emitter according to an embodiment of the present invention;
4 is another scanning electron micrograph of observing the carbon structure for an emitter according to an embodiment of the present invention;
5 is another scanning electron micrograph of observing the carbon structure for an emitter according to an embodiment of the present invention;
6 is another scanning electron micrograph of observing the carbon structure for an emitter according to an embodiment of the present invention;
7 is a view showing measurements of IV characteristics (B) and IV characteristics (A) of a conventional carbon film structure of the carbon structure for emitters according to an embodiment of the present invention;
8 is a scanning electron microscope photograph of the conventional carbon film structure of FIG. 1 observed at high magnification.

Hereinafter, a carbon structure for an emitter of the present invention, a method for manufacturing the same, and an apparatus for manufacturing the same of the present invention will be described with reference to the accompanying drawings. The drawings introduced below are provided as examples in order to sufficiently convey the spirit of the present invention to those skilled in the art. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be exaggerated to clarify the spirit of the present invention. At this time, if there is no other definition in the technical terms and scientific terms used, it has the meaning commonly understood by those of ordinary skill in the art to which this invention belongs, and the gist of the present invention in the following description and accompanying drawings Descriptions of known functions and configurations that may be unnecessarily obscure will be omitted.

Also, the singular forms used in the specification and appended claims may also be intended to include the plural forms unless the context specifically dictates otherwise.

In this specification and the appended claims, terms such as first, second, etc. are used for the purpose of distinguishing one component from another, not in a limiting sense.

In this specification and the appended claims, the terms include or have means that a feature or element described in the specification is present, and unless specifically limited, one or more other features or elements are added. This does not preclude the possibility that it will be.

In this specification and the appended claims, when a part of a film (layer), region, component, etc. is said to be on or on another part, not only when it is directly on top of another part in contact with it, but also another film ( layer), other regions, and other components are also included.

As a result of continuous research to solve the above problems, the present applicant has formed a large amount of small thorn-shaped protruding structures having sharp tips on the surface of the carbon structure based on the carbon structure in which the one-dimensional carbon body has grown in the shape of a vine. , confirmed that a large emission current occurs at a low voltage, and as a result of repeated improvements to the vine-shaped carbon structure with a small thorn-shaped protrusion structure, a large emission current stably even in the process of increasing the voltage from low voltage to high voltage The present invention has been completed by developing a carbon structure in which electron radiation is generated substantially from the entire carbon structure.

The carbon structure according to the present invention based on the above study is a carbon structure for a field emission emitter. The carbon structure according to the present invention includes a vine structure in which a one-dimensional carbon body is randomly entangled and stretched, and has a structure in which a two-dimensional carbon body randomly protrudes from the surface of the vine structure.

The carbon structure for emitter according to the present invention is based on a one-dimensional carbon vine structure, and a large amount of two-dimensional carbon body protrusions (protrusions) are formed on the entire surface of the vine structure, so that electron emission can occur throughout the carbon structure, and low voltage It can have a very high emission current and exhibit stable I-V characteristics.

In one embodiment, the one-dimensional carbon body may be a fibrous graphene aggregate. The fibrous graphene aggregate may be one in which graphene is randomly overlapped and aggregated to form a fibrous form, or one-dimensional carbon nanostructures such as graphene and carbon nanotubes are randomly mixed and aggregated to form a fibrous form. In this case, it goes without saying that both the one-dimensional carbon body and the two-dimensional carbon body are conductive carbon bodies. The diameter of the one-dimensional carbon body may be at the level of 10 ¹ nm to 10 ² nm, specifically at the level of 10 nm to 900 nm, more specifically at the level of 10 nm to 500 nm, and the length of the one-dimensional carbon body is at the level of 100 μm to ^{10 2} μm, Specifically, it may be at a level of 10 μm to 900 μm, but is not limited thereto.

In one embodiment, the tendril structure is a structure in which one-dimensional carbon bodies are randomly entangled and stretched, and one one-dimensional carbon body is bent and entangled and/or two or more one-dimensional carbon bodies are entangled and stretched out, one side (virtual side) ) may have a structure extending to spread on one surface in the in-plane direction. At this time, if the one-dimensional carbon body in the vine structure is regarded as a stem, the vine structure may have a form in which two or more branches are branched from the stem. In the vine structure, the region from which the one-dimensional carbon body extends and the region entangled with each other are randomly distributed and can form a macroscopic film shape.

In one embodiment, protrusions including two-dimensional carbon bodies may be positioned on the surface of the vine structure, and a large number of two-dimensional carbon body protrusions may be randomly positioned substantially on the entire surface of the vine structure.

A cluster-like shape such as a vine does not exhibit field emission characteristics by suppressing voltage concentration, but the voltage is concentrated on the protrusion protruding from the surface of the vine structure and electrons can be emitted.

The two-dimensional carbon body of the protrusion may be a two-dimensional nano-carbon body, and the two-dimensional nano-carbon body may include graphene. In this case, graphene may refer to a single-layer graphene and/or a graphene sheet in which a plurality of graphenes are stacked.

When the protrusion is formed of graphene, the electric field concentration applied to the protrusion is weakened by the two-dimensional structure, and the non-uniformity of the electric field concentration can be suppressed. release can be achieved. Accordingly, instead of reducing the number of electrons generated from one protrusion, substantially all of the protrusions may emit electrons, and each protrusion may emit electrons substantially equally (evenly).

Graphene has an area of 0.0001 μm ² to 0.100 μm ² level, specifically 0.005, so that the non-uniformity of electric field concentration can be more effectively reduced by the two-dimensional structure and low aspect ratio. To 0.050 μm ² , more specifically 0.005 to 0.020 μm ² Fine graphene is preferable. Substantially, the diameter of the graphene may be 10 nm to 500 nm, substantially 50 to 400 nm, more substantially 100 to 300 nm.

Advantageously, the projection direction of the two-dimensional carbon body, specifically graphene, may include a direction normal to the surface of the tendril structure on which the two-dimensional carbon body is located. That is, graphene may protrude in the form of standing in a vertical direction on the one-dimensional carbon body positioned on the surface of the tendril structure. Such protrusion in the normal direction is advantageous because the emitted electrons can easily escape out of the carbon structure. However, in the present invention, the protrusion direction of the two-dimensional carbon body (for example, graphene) cannot be interpreted as being limited only to the normal direction of the surface where the protrusion is located, and the two-dimensional carbon body (for example, the normal direction) in several directions including the normal direction. , graphene) is reasonable to interpret as protruding. As a practical example, the two-dimensional carbon body (graphene) may protrude at various angles from being substantially parallel to the surface to standing perpendicular to the surface.

In one embodiment, the protrusion may be a single two-dimensional carbon body and/or an aggregate in which a plurality of two-dimensional carbon bodies are aggregated. When the protrusion is an aggregate, the aggregate may have a visible shape macroscopically, and microscopically, outer edge portions of the two-dimensional carbon body constituting the aggregate may be spaced apart from each other. In this case, the outer side may mean one end side of the two-dimensional carbon body protruding. As the outer edges of the two-dimensional carbon bodies constituting the aggregate have a structure spaced apart from each other, each two-dimensional carbon in the aggregate is substantially independent of the number of spherical two-dimensional carbon bodies constituting the aggregate, the shape of the aggregate, the protrusion angle of the aggregate, etc. At each of the edges of the sieve, the emission of electrons may be made substantially equal to and identical to each other.

As a practical example, a macroscopically visible aggregate has a structure in which a plurality of graphenes are scattered, each graphene exists independently from each other, and at least the outer edges of each scattered graphene are not connected and are spaced apart from each other. can In addition, a step may exist between the upper portions (outer end portions) of each graphene constituting the thorn-shaped aggregate, and the upper portion of each graphene may not be flat. In addition, the thorn-shaped aggregate may have a shape such as a planar needle (a flat body with a micro-area having a length of 10 nm to 300 nm on one side), and thus may have a very small curvature. Specifically, the thorn-shaped aggregate is a nanometer-scale graphene (graphene sheet) aggregate of several layers, not long, thick, and long needles like a carbon film structure. have.

In one embodiment, the aggregate may be spaced apart from the one-dimensional carbon body in a radially disorderly manner, specifically, the one-dimensional carbon body positioned on the surface of the tendril structure. Most of the visible aggregates located on the surface of the tendril structure may exist in a linear state, for example, a protrusion angle exceeding 0°, substantially a protrusion angle of 30 to 90°. These thorn-shaped aggregates may be independently spaced apart from each other rather than being located in a cluster. In addition, the visible aggregate may be in a state integrally bound to the first-dimensional carbon body. This can also be interpreted as a prickly aggregate growing from the surface of the vine structure. In this case, the growth direction of the thorn-shaped aggregate may correspond to the protrusion direction, and may be a direction normal to the surface of the vine structure, but is not necessarily limited thereto.

In one embodiment, the height (protrusion height) of the aggregate protruding from the surface of the vine structure may be a few nanometers to several hundred nanometers level, specifically 5 to 500 nm level, and more specifically 5 to 300 nm level. Such a microprotrusion structure is also advantageous in suppressing the non-uniformity of field concentration, so that the carbon structure may exhibit very stable field emission characteristics.

In one embodiment, the carbon structure may further include a carbon film in which carbon particles are aggregated in the form of a film, and the tendril structure may be in a state bound to the carbon film. In this case, the binding to the carbon film may mean that a part of the one-dimensional carbon body forming the vine structure is embedded in the carbon film and/or is fixed by binding with the carbon particles on the surface of the carbon film. In this case, the one-dimensional carbon body may also be expressed as a stem or branch of a vine, and one stem or branch may be randomly fixed to the carbon film at various positions different from each other.

The carbon film may be a film in which carbon particles are continuously connected, or a dense film in which there is practically no empty space between adjacent carbon particles. The diameter of the carbon particles may be 100 nm to ¹⁰² nm level, specifically ⁵ nm to 900 nm level, but is not limited thereto. The carbon film made of conductive carbon particles provides a conductive film that is stable and uniformly energized, and the vine structure is located on the conductive film in a fixed and bound state, so that a stable and uniform voltage can be applied to the entire vine structure. have.

When the carbon structure further includes a carbon film, the aforementioned virtual film may correspond to the surface of the carbon film. Accordingly, the carbon structure may include a carbon film; and a tendril structure extending in an in-plane direction of the surface of the carbon film while one or more one-dimensional carbon bodies are randomly bent and entangled.

In one embodiment, using the carbon structure as an emitter electrode, the threshold voltage at which a current of 0.1 mA is generated may be 2.0 kV or less, specifically 1.9 kV or less under the following field emission conditions.

Field emission conditions: emitter electrode diameter 5 mm, distance between emitter electrode and anode 3 mm, and vacuum of 10 ^-6 Pa

Such a low threshold voltage enables low power consumption of a cold cathode X-ray tube or a field emission device, and a very large emission current can be secured at a lower voltage.

In addition, when the carbon structure is used as an emitter electrode and the voltage is repeatedly swept in the range of 0-2.5V under the same field emission condition, the initial IV characteristic, the IV characteristic at the time of 10 sweeps, and the IV characteristic at the time of 100 sweeps IV properties may be substantially the same. In this case, the IV characteristic includes a threshold voltage, a slope that is an increase in current according to an increase in voltage, a change in slope, and the like. This stable IV property is because the electric field concentration itself is not large as the protrusions in the carbon structure are based on very fine two-dimensional carbon bodies, so damage to the protrusions from which electrons are emitted is prevented. Even if it is possible, there are very many protrusions, and the amount of electrons emitted from each protrusion itself is much smaller than the amount of electrons emitted from the tip existing in the carbon nanotube or carbon film structure. is very insignificant.

The present invention includes a field emission emitter electrode comprising the above-described carbon structure. Hereinafter, the field emission emitter electrode may be collectively referred to as a carbon emitter.

The field emission emitter electrode may include the above-described carbon structure and a support for supporting the carbon structure, and examples of the support include stainless steel, silicon, etc., but is not limited thereto.

The present invention includes a deposition apparatus and a deposition method capable of producing the above-described carbon emitter.

A carbon emitter deposition apparatus according to the present invention includes: a first electrode on which a substrate is mounted and in a grounded state; a second electrode spaced apart from and opposed to an upper portion of the first electrode; a coil electrode surrounding a periphery of a deposition region that is a space between the first and second electrodes spaced apart and opposed to each other; a first power supply for applying a voltage to the second electrode; and a second power supply for applying a voltage to the coil electrode.

Plasma can be formed in the deposition area by applying a voltage to the second electrode through the first power source from a pair of electrodes (the first electrode and the second electrode) facing each other and spaced apart from each other, and through this, the substrate is subjected to plasma-assisted vapor deposition. A carbon body may be deposited. In this case, the separation direction between the first electrode and the second electrode may be the direction of gravity (the height direction of the device), and the first electrode and the second electrode may have shapes and sizes corresponding to each other, but are not limited thereto. . The first power source may be a DC power source, and the plasma formed in the device may be a plasma formed by DC glow discharge. The second power may be AC power or DC power, specifically, DC power.

The deposition region means a spaced apart space between the first electrode and the second electrode, both ends are defined by the first electrode and the second electrode, and have the same cross-sectional shape as that of the first electrode (or second electrode). can

The coil electrode is a coil-shaped electrode that surrounds the periphery of the deposition region. By applying a voltage to the coil electrode through a second power source, the flow of gas including plasma and decomposition products generated by the plasma during deposition can be controlled. . Hereinafter, the term gas, gaseous phase, or gas in plasma refers to a plasma material and a gaseous decomposition product generated by the plasma, unless specifically limited.

Specifically, the coil electrode may be positioned on the first electrode side among the first electrode side and the second electrode side, which are both end sides of the deposition region. By positioning the coil electrode on the first electrode side, a stable rotational flow of the gas phase on the substrate side can be induced.

In the deposition region, a region to which a force for directly causing rotational flow is applied by the coil electrode may correspond to a region wound by the coil electrode. Accordingly, the size of the region in which the force causing the rotational flow is not applied may be controlled by the length of the coil electrode, which is the distance between both ends of the coil electrode. Advantageously, when the separation distance between the first electrode and the second electrode is 1, the length of the coil electrode (the distance from one end to the other end of the coil electrode) is 0.3 to 0.8, specifically 0.3 to 0.7, more specifically 0.4 to 0.4 0.6 can be satisfied.

As described above, when the coil electrode is located on the side of the first electrode and satisfies the above-described length, a flow of material (gas phase flow) can be caused in various directions while being substantially parallel to the in-plane direction of the substrate, which will be described later. A rotational flow may be formed without interfering with the circulation of an ascending flow and a descending flow of the gas phase in the deposition region, and the above-described carbon structure may be uniformly deposited on the entire substrate.

When the carbon body is deposited on the substrate by plasma-assisted vapor deposition, a temperature difference may occur between the first electrode side and the second electrode side by the plasma, and an upward flow from the center of the substrate from the relatively high temperature first electrode side to the second electrode side This may occur, and a descending flow in which the raised gas phase descends back to the edge of the substrate may occur. By means of the coil electrode, this gas phase upward flow, downward flow or both upward and downward flows can be rotated and flowed.

In one embodiment, the carbon emitter deposition apparatus may further include a chamber having a first electrode, a second electrode, and a coil electrode provided therein, and providing an internal space in which deposition is performed, and a carbon source in the internal space. gas supply means for supplying a gas phase; And it may further include an exhaust means for adjusting the pressure of the internal space. The gas supply means may supply a first gas and a second gas serving as a carbon source for plasma formation to the inner space, respectively, or a mixed gas of the first gas and the second gas to the inner space. The exhaust means may be a vacuum exhaust means for adjusting the degree of vacuum in the internal space. These gas supply means and exhaust means are sufficient as long as they are generally used for injection of gas and control of the degree of vacuum in a typical vapor deposition apparatus.

The first gas supplied by the gas supply means may be hydrogen gas, and thus, the plasma generated in the apparatus may be a hydrogen plasma. The second gas may be a C1-C3 hydrocarbon gas, specifically a C1-C2 hydrocarbon gas, and more specifically, a methane gas, but is not limited thereto. Of course, the decomposition product described above includes the second gas decomposition product by plasma.

The first electrode or the second electrode may be in the form of a circular disk, and an electrode material commonly used in the field of plasma deposition, such as a copper-molybdenum alloy, is sufficient. The coil electrode may be made of titanium, but is not limited thereto.

The present invention includes a carbon emitter deposition method using the above-described carbon emitter deposition apparatus.

The Tasso emitter deposition method according to the present invention comprises a) mounting a substrate on the first electrode positioned below the first electrode and the second electrode spaced apart from each other in the gravitational direction, introducing hydrogen gas, and applying a DC voltage to the second electrode forming a hydrogen plasma by applying and b) supplying a gaseous carbon source (second gas) to the hydrogen plasma and forming a rotational flow in the gas in the plasma adjacent to the substrate at least by using the coil electrode. In this case, the first electrode may be in a ground state.

In step b), a temperature difference may occur between the first electrode (or substrate) and the second electrode by the hydrogen plasma generated by the first electrode in the ground state and the second electrode to which the DC voltage is applied. In detail, the first electrode may be in a relatively high temperature state than that of the second electrode. Accordingly, an upward flow (updraft) may be formed from the first electrode toward the second electrode, and a descending flow (downdraft) in which the raised gas phase descends again toward the second electrode may be formed. In such a cycle of the rising flow and the falling flow, the rising flow, the falling flow, or both the rising flow and the falling flow may rotate and flow by the coil electrode positioned on the substrate side.

As a specific example of the temperature difference between the first electrode (or substrate) and the second electrode, the temperature of the first electrode (or substrate) may be 900 to 1200°C, specifically 1000 to 1100°C, and the second electrode is the first electrode (or the substrate) may have a temperature of 200 to 500 ℃, specifically 200 to 400 ℃ lower than, but is not limited thereto.

In one embodiment, in step a), a1) after the substrate is mounted on the first electrode, hydrogen gas (first gas) is supplied through a gas supply means, and the pressure in the chamber interior space is 10 to 50 torr through an exhaust means adjusting to become a2) generating a hydrogen plasma by applying a DC voltage to the second electrode through the first power source; By generating the hydrogen plasma before supplying the carbon source, the inside of the chamber including the substrate may be hydrogen cleaned.

In one embodiment, step b) may include b1) supplying a gaseous mixture of a carbon source (second gas) and hydrogen gas into the chamber in which the hydrogen plasma is generated through a gas supply means; b2) applying a voltage to the coil electrode through a second power source; b3) increasing the pressure of the chamber internal space to 60 to 100 torr through the exhaust means and forming a carbon structure on the substrate;

In this case, in step a2), the current by applying the first power may be controlled to a level of 1 to 4A, and in step b3), the current by applying the first power may be controlled to a level of 5 to 10A. In addition, in steps b2) and b3), the coil electrode may be controlled based on the gas flow so that the gas flow in the plasma rotates stably and flows upward and downward. As a practical example, during the deposition of b3) (when forming the carbon structure), the coil electrode may be controlled in a current range of 1 to 10A, but the present invention is not limited thereto. In addition, the deposition of step b3) may be performed for 1 to 5 hours, but is not limited thereto.

2 is a cross-sectional view illustrating the configuration of a deposition apparatus according to an embodiment of the present invention, and corresponds to equipment used for actual deposition. In the chamber 21, the first electrode 24 in a grounded state having a shape corresponding to the second electrode 22 and the substrate 31 and having a mask 39 serving as a sample holder is disposed facing up and down, , the coil electrode 23 extending to the middle of the second electrode 22 and the first electrode 24 is disposed at a position where the substrate 31 is sufficiently covered by the mask 39 . The first electrode 24 is connected to the chamber 21 and grounded. The chamber 21 is provided with a gas supply means 25 for introducing a gas by controlling a predetermined amount of a gas for plasma formation and a film forming gas, and an exhaust means 26 for controlling the degree of vacuum inside the chamber 21 during film formation. The second electrode 22 is connected to a first power source 32 which is a direct current power source, and the coil electrode 23 is connected to a second power source 33 which is a control power source for controlling plasma. The second electrode 22 is a 30% copper-molybdenum alloy electrode in the form of a circular disk.

An example of depositing a carbon structure on a substrate based on the apparatus of FIG. 2 will be described in detail. The gas sent to the inside of the chamber 21 is supplied after mixing and controlling the supply of hydrogen and methane independently, respectively. The mixed gas supply is 5-20 cm ³ per minute. First, the inside of the chamber 21 is exhausted by the exhaust means 26 . Hydrogen gas is introduced into the chamber 21 at a constant flow rate from the gas supply means 25 so that the internal pressure of the chamber 21 becomes 35 torr. Thereafter, a discharge plasma 34 is generated between the second electrode 22 and the first electrode 24 by the application of the first power source 32 . The applied current is increased to 3A with respect to 35 torr inside the chamber 21 and maintained for about 10 minutes. In this way, before the carbon film is formed, the electrodes such as the substrate 31 and the mask 30 are cleaned with hydrogen so that foreign substances are not mixed into the carbon film. Then, the gas supply means 25 mixes hydrogen gas with methane gas and flows it. Thereafter, the pressure inside the chamber 21 is increased to 40 torr and maintained for about 10 minutes. In the meantime, the applied current is raised to about 4A. In this state, decomposition products of the main component of methane in the plasma are generated and spread in the hydrogen plasma (34). In this state, the second power source 33, which is a control power source, is applied to the coil electrode 23 for controlling the plasma to control the generated plasma. Subsequently, the pressure inside the chamber 21 is gradually increased to 75 to 80 torr, and when it reaches 75 torr, the first power source 32 is increased to a level of 6 to 7A. In addition, in order to control the plasma, while watching the gas flow in the plasma, the current value of the second power source 33 was controlled to a level of 4.5 A, and film formation was performed for 2 hours. At the time of film formation, the substrate temperature is about 1000 to 1100°C by the plasma 34 generated on the substrate 31, and the film formation precursor in which methane is decomposed in the plasma is generated by the gas flow 35 in the plasma and the sheath electric field near the substrate. The substrate 31 is reached by a (sheath electric field), and the above-described carbon structure is deposited on the substrate 31 . The coil electrode 23 controlling the plasma rotates the plasma flow 35 and the flow of the methane decomposition product. A temperature difference of about 300 DEG C is generated between the second electrode 22 and the first electrode 24 to change the plasma flow 35 in the vicinity of the substrate to an upward flow. In the plasma 34, rotation is applied by the coil electrode 23 made of titanium to the main upward and downward flow of the material flow 35 in the plasma 34, and the above-described carbon structure is generated on the substrate despite the long film formation time. In FIG. 2 , the flow of the material flow 35 in the plasma rotating and ascending and descending is shown by arrows.

3 is a scanning electron microscope (SEM) photograph of observing a carbon structure for an emitter manufactured by the above-described deposition based on the apparatus of FIG. 2 . It can be observed that several vines that grow irregularly on a carbon film in which carbon particles are densely aggregated are entangled. You can see it's growing. Other vines are irregularly intertwined and formed continuously. A vine can become a stem and stand on its own, or there are times when multiple vines are intertwined and growing. The vines are branched and grown in plural, and have an irregular shape. An enlarged SEM photograph of a portion of FIG. 3 is shown in FIG. 4 . As shown in FIG. 4 , it can be seen that nodes such as branches are present on the surface of the vine, which becomes the stem. 5 is an SEM photograph of observing the surface of the vine. Most of the thorns (thorn-shaped aggregates) grown on the surface of the vines exist in a linear state, and they are growing independently rather than clustered together. Compared with the conventional carbon film structure shown in FIG. 1 , this growth pattern can solve the drawback that an electric field is not applied to each crystal tip, and an electric field can be applied intensively to each thorn. The tip of this thorn is sharp, but the height of the thorn is significantly lower than that of a conventional carbon film structure. However, instead of having this low height, a large number of electron generating points are formed. Therefore, since there are many visible numbers that emit electrons from a low voltage and also generate the current value, a very large emission current can be obtained overall. Since this vine is made of a stem (one-dimensional carbon body), the adhesion to the substrate is due to the nature of the vine. Due to this structure, even when a high electric field is applied, peeling or the like does not occur in the electric field. Compared to the conventional carbon film structure, the number of visible rays capable of emitting electrons is significantly greater. Therefore, even if a discharge occurs between the electrodes by applying a voltage, a part of the carbon film is simply destroyed in the existing carbon film and the number of electrons generated drastically decreases. , it is also strong against changes over time. Hereinafter, the carbon structure structure of an embodiment will be described with reference to an SEM photograph. 1 is an SEM photograph showing a conventional carbon film structure, and FIG. 4 is an SEM photograph of a carbon structure based on a vine structure. 1 and 4, it can be seen that the carbon structure has a structure completely different from that of the prior art. In the conventional carbon film structure, a thick needle emitting electrons has a sharp tip, and the height of the needle has a structure to which voltage is easily applied. But the number is not very large. The needle emitting electrons in the existing carbon film structure is actually destroyed when gas molecules remaining in a vacuum container such as an X-ray tube are ionized and accelerated to collide with the cathode. On the other hand, the carbon structure has a tendril-like shape as shown in FIG. 4 . Unlike the carbon nanotube or carbon film structure, a large number of cascading protrusions are formed on the surface of the vine on the normal line. This spine has an effective shape as an emission site. 5 and 6 are SEM photographs of magnified observation of the surface of the vine. It can be seen from FIG. 5 that a number of nanoscale thorns are observed. 6 is an enlarged observation of FIG. 5, and it can be seen that the thorns have a structure in which nano-scale graphene is scattered. An enlarged photographic image of the aggregate that looks like an umbrella of the conventional carbon film structure shown in FIG. 1 is shown in FIG. 8 . As can be seen from FIG. 8 , the carbon film structure has a structure in which graphene sheets are crossed continuously in a large manner so that they do not mechanically fall. An appropriate electric field is not applied to a number of graphene sheets of this type, and efficient electrospinning cannot be performed as in the so-called bundle shape. On the other hand, the carbon structure of the present invention does not contain a coarse graphene sheet as in the prior art. In the carbon structure of the present invention, visible graphene forms a sheet of several layers, and it is seen that the graphene grows in a normal line to the surface of the vine, and the size of the graphene is about 0.3 μm. In addition, the upper part of the graphene (graphene sheet) has a step and is not flat. In the carbon structure of the present invention, graphene exists independently while the conventional carbon film structure is continuously formed. Electron emission is difficult to occur without needles. In the carbon structure of the present invention, the tip of graphene where electron radiation is generated is like a planar needle. Accordingly, the curvature is also remarkably small. Also, the size of graphene is important, and the length from the tip to the root of graphene is only about 0.1 to 0.3 μm. That is, the size of graphene from which electrons are emitted is significantly smaller than that of the conventional carbon film structure. Due to such a nanoscale size, even when a low electric field is applied, electron emission is possible from the visible aggregate. Through scanning electron microscope observation, it can be seen that the above-mentioned thorns grow on the surface of the vine, and the graphene aggregate of 0.01 μm ² in area is radially grown, so there is no continuity aggregation and it exists independently. In addition, the tip of the aggregate (thorn) is essentially the same as the needle tip in the shape of overlapping graphene. Through scanning electron microscope observation, it can be seen that the outer edges of the graphenes at the end of the aggregate are spaced apart from each other. In the observation photograph, the thorn-shaped aggregate (thorn) is an aggregate of several nanometer-scale graphenes, not long, thick, and needle-like, like a carbon film structure. In addition, thorn-shaped aggregates (thorns) were growing at irregular intervals radially with respect to the vine stem, and the height was several 10 to 100 nm. Therefore, when it grows densely like a bundle like carbon nanotubes, the concentration of voltage is suppressed and the field emission characteristics disappear, whereas in the case of a thorn-shaped aggregate, the aggregate is located on the surface of the vine even if there is excessive concentration, and the aggregate is formed. The tip of the pin has a step, and the tip of the graphene is not in contact with the nearby graphene and is scattered in large numbers. Due to this structure, the concentration of the electric field generated in the thorn-shaped assembly is small. Accordingly, the amount of emitted electrons per one graphene is small. However, since it has a visible aggregate structure and an extremely large amount of aggregates are formed, substantially all aggregates emit electrons equally from a low electric field. In this respect, the carbon structure of the present invention has a large aspect ratio, such as a carbon film structure, but is different from conventional emitters that emit electrons only in part because it is uneven. It is possible to lower the operation starting voltage than the carbon film structure, and it can have excellent field emission characteristics including its stability in IV characteristics.

FIG. 7 is a diagram illustrating measurement of IV characteristics using the produced carbon structure as an emitter electrode. In FIG. 7, A is an IV characteristic curve by the conventional carbon film structure (FIG. 1), and B is an IV characteristic curve by the carbon structure according to the present invention. The measurement conditions were that the diameter of the emitter electrode was 5 mm, the distance between the emitter electrode and the anode was 3 mm, and the vacuum pressure at the time of measurement was 1 × 10 ^-6 Pa. Comparing the curve A and the curve B, it can be seen that the current rise occurs at a lower voltage in the carbon structure according to the present invention. As is known, the carbon film structure generates a current at a lower voltage than the carbon nanotube. The carbon structure according to the present invention has a lower voltage than that of the carbon film structure. Looking at the voltage at which a current of 0.1 mA starts to occur (operation starting voltage or threshold voltage, V), the conventional carbon film structure has a threshold voltage of about 2.5 kV, and the carbon structure according to the present invention is 1.9 kV has a threshold voltage of If the threshold voltage is lowered like this, the cathode circuit can be directly controlled by semiconductor devices such as IGBTs and MOSFETs in fields that use high voltages, such as X-ray tubes, so that the amount of emitted current can be freely handled.

As described above, the carbon structure for an emitter according to the present invention has a film structure in which the tendril structure is irregularly grown. On the surface of this vine structure, there are many thorns, which are graphene aggregates, in a normal line. In addition, the thorn is composed of a collection of independent graphene composed of several layers with a very small area. Graphene consists of nanometer planes, and there is no continuity between individual graphenes. Individual graphenes are intermingled while standing in a normal line to the vine. Electron radiation is emitted from the tip of the graphene that is on the normal line.

As described above, the present invention has been described with specific matters and limited examples and drawings, but these are only provided to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments, and the present invention is not limited to the above embodiments. Various modifications and variations are possible from these descriptions by those of ordinary skill in the art.

Therefore, the spirit of the present invention should not be limited to the described embodiments, and not only the claims described below, but also all those with equivalent or equivalent modifications to the claims will be said to belong to the scope of the spirit of the present invention. .

Claims (7)

One-dimensional carbon bodies include randomly entangled and stretched tendril structures,
A carbon structure for an emitter in which a two-dimensional carbon body randomly protrudes on the surface of the vine structure. The method of claim 1,
The two-dimensional carbon body is a carbon structure for an emitter comprising graphene. The method of claim 1,
The projection direction of the two-dimensional carbon body is a carbon structure for an emitter including a normal direction of the surface on which the two-dimensional carbon body is located. The method of claim 1,
The two-dimensional carbon body protrudes into a thorn-shaped aggregate in which two or more two-dimensional carbon bodies are assembled on the surface of the vine structure, and at least the outer edge portions of the two-dimensional carbon bodies constituting the aggregate are spaced apart from each other. 5. The method of claim 4,
The aggregate is a carbon structure for an emitter that is spaced apart radially and disorderly in the one-dimensional carbon body. 5. The method of claim 4,
A carbon structure for an emitter having a protrusion height of the aggregate of 5 to 500 nm based on the surface on which the aggregate is located. The method of claim 1,
The carbon structure further includes a carbon film in which carbon particles are aggregated in the form of a film, and the vine structure is a carbon structure for an emitter bound to the carbon film.

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