Electron emission element and electron tube

Abstract

This electron emission element emits electrons in response to incidence of electromagnetic waves, and comprises: a support body having a support surface formed of an electrically insulating material; a plurality of three-dimensional structures disposed on the support surface and formed of a conductive material; and a functional layer disposed on the plurality of three-dimensional structures and including a carbon layer formed of a material containing carbon.

Description

Electron-emitting device and electron tube

[0001] The present disclosure relates to an electron-emitting device and an electron tube.

[0002] An electron tube including an electron-emitting element including a metasurface that emits electrons in response to the incidence of electromagnetic waves, and an electron multiplier that multiplies the electrons emitted from the electron-emitting element is known (see, for example, Patent Document 1).

[0003] Japanese Patent Translation Publication No. 2023-549000

[0004] Regarding the electron-emitting element as described above, it may be advantageous for electrons to be emitted regardless of the characteristics of the incident electromagnetic waves (for example, the peak electric field strength of the incident electromagnetic waves, the frequency band of the incident electromagnetic waves, the polarization characteristics of the incident electromagnetic waves, etc.).

[0005] An object of the present disclosure is to provide an electron-emitting device capable of improving the electron emission performance, and an electron tube including such an electron-emitting device.

[0006] The electron-emitting device according to one aspect of the present disclosure is [1] "an electron-emitting device that emits electrons in response to the incidence of electromagnetic waves, including a support having a support surface formed of an electrically insulating material, a plurality of three-dimensional structures disposed on the support surface and formed of a conductive material, and a functional layer disposed on the plurality of three-dimensional structures and having a carbon layer formed of a carbon-containing material".

[0007] In the above electron-emitting device, a functional layer having a carbon layer formed of a carbon-containing material is disposed on a plurality of three-dimensional structures formed of a conductive material. Thereby, electrons can be emitted in response to the incidence of electromagnetic waves regardless of the difference in the characteristics of the incident electromagnetic waves (for example, at least one of the peak electric field strength of the incident electromagnetic waves, the frequency band of the incident electromagnetic waves, the polarization characteristics of the incident electromagnetic waves, etc.). Therefore, according to the above electron-emitting device, improvement in the electron emission performance can be realized.

[0008] An electron-emitting element in one aspect of the present disclosure may be [2] "the electron-emitting element according to [1] above, wherein a plurality of first corners are formed by the support and the plurality of three-dimensional structures, and the carbon layer covers the plurality of first corners." With this electron-emitting element, electric field concentration occurs at each first corner, so an improvement in electron emission performance can be reliably achieved.

[0009] An electron-emitting element in one aspect of this disclosure may be [3] "an electron-emitting element according to [1] or [2] above, wherein a plurality of second corners are formed by the plurality of three-dimensional structures, and the carbon layer covers the plurality of second corners." With this electron-emitting element, electric field concentration occurs at each second corner, so an improvement in electron emission performance can be reliably achieved.

[0010] An electron-emitting element in one aspect of this disclosure may be [4] "an electron-emitting element according to any one of [1] to [3] above, wherein a plurality of corners are formed by the plurality of three-dimensional structures, and the carbon layer covers the plurality of corners." With this electron-emitting element, electric field concentration occurs at each corner, so an improvement in electron emission performance can be reliably achieved.

[0011] An electron-emitting element in one aspect of this disclosure may be [5] "an electron-emitting element according to any one of [1] to [4] above, wherein the carbon layer is a graphene layer." This electron-emitting element can reliably achieve improved electron emission performance.

[0012] An electron-emitting element in one aspect of this disclosure may be [6] "an electron-emitting element according to any one of [1] to [5] above, wherein the functional layer further comprises an alkali metal layer formed of an alkali metal material." This electron-emitting element can reliably achieve improved electron emission performance.

[0013] One aspect of the present disclosure is an electron tube comprising [7] "an electron emission element described in any one of [1] to [6] above, and an output unit that performs an output based on the electrons emitted from the electron emission element."

[0014] According to the above-mentioned electron tube, since the electron emission performance of the electron emission element is improved, it is possible to improve the detection sensitivity of electromagnetic waves.

[0015] According to this disclosure, it is possible to provide an electron emission element that can improve electron emission performance, and an electron tube equipped with such an electron emission element.

[0016] Figure 1 is a plan view of an example electron emission element. Figure 2 is a plan view of the three-dimensional structure shown in Figure 1. Figure 3 is a cross-sectional view of a part of the electron emission element shown in Figure 1. Figure 4 is a configuration diagram of an electron multiplier tube equipped with the electron emission element shown in Figure 1. Figure 5 is a configuration diagram of an image intensifier equipped with the electron emission element shown in Figure 1. Figure 6 is a graph showing the relationship between the peak electric field strength of the terahertz wave and the output of the electron multiplier tube. Figure 7 is a graph showing the relationship between the frequency of the terahertz wave and the output of the electron multiplier tube. Figure 8 is a graph showing the intensity distribution of electron emission in the electron emission element. Figure 9 is a graph showing the intensity distribution of electron emission in the electron emission element. Figure 10 is a graph showing the intensity distribution of electron emission in the electron emission element. Figure 11 is a plan view of a modified three-dimensional structure. Figure 12 is a plan view of a modified three-dimensional structure. Figure 13 is a plan view of a modified three-dimensional structure. Figure 14 is a graph showing the relationship between the time elapsed since the start of terahertz wave incidence and the output of the electron multiplier tube.

[0017] An example of this disclosure will be described in detail below with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations are omitted. [Configuration of the electron emission element]

[0018] The electron-emitting element 1 shown in Figure 1 is an element that emits electrons in response to the incidence of electromagnetic waves. The electromagnetic waves are, for example, electromagnetic waves in a predetermined band included in the frequency range from millimeter waves to infrared light, and in this example, terahertz waves. As shown in Figure 1, the electron-emitting element 1 comprises a support 2, a plurality of three-dimensional structures 3, a pair of electrodes 4, and a functional layer 5. In Figure 1, the functional layer 5 is shown by a dashed line.

[0019] The support 2 is formed of an electrically insulating material that is transparent to electromagnetic waves (for example, silicon oxide, silicon, quartz, sapphire, zinc selenide, diamond, etc.). The support 2 has a surface (support surface) 2a. Surface 2a is a surface formed of an electrically insulating material (i.e., an electrically insulating surface). As an example, the support 2 is a substrate and, for example, has the shape of a rectangular plate. In that case, surface 2a is one of the main surfaces of the support 2. Hereinafter, the direction perpendicular to surface 2a will be called the X-axis direction, one direction perpendicular to the X-axis direction will be called the Y-axis direction, and the direction perpendicular to both the X-axis direction and the Y-axis direction will be called the Z-axis direction.

[0020] Multiple three-dimensional structures 3 and a pair of electrodes 4 are arranged on the surface 2a of the support 2. In other words, multiple three-dimensional structures 3 and a pair of electrodes 4 are arranged on the support 2. The multiple three-dimensional structures 3 are arranged two-dimensionally along the surface 2a. Each three-dimensional structure 3 is made of a conductive material (e.g., gold, platinum, aluminum, silver, copper, etc.). The pair of electrodes 4 are located on both sides of the multiple three-dimensional structures 3 in the Z-axis direction. Each electrode 4 is made of a conductive material (e.g., the same material as each three-dimensional structure 3).

[0021] As shown in Figure 2, each three-dimensional structure 3 includes a pair of antenna portions 31 facing each other in the Y-axis direction. In the electron-emitting element 1, the pair of antenna portions 31 constitute an antenna, and the multiple three-dimensional structures 3 constitute a metasurface. As an example, the pair of antenna portions 31 constitute a bowtie antenna, where the vertices of each triangular antenna portion 31, each with a side length of several tens of micrometers, face each other at a distance of 1 to several micrometers. Focusing on one three-dimensional structure 3, one antenna portion 31 is electrically connected to one electrode 4 via wiring 6, and the other antenna portion 31 is electrically connected to the other electrode 4 via wiring 7. Each wiring 6 and 7 is made of a conductive material (for example, the same material as each three-dimensional structure 3).

[0022] As shown in Figure 3, the electron emission element 1 has a plurality of first corner ICs 1 and a plurality of corner ECs formed thereon. The plurality of first corner ICs 1 are formed by the support 2 and a plurality of three-dimensional structures 3. More specifically, each first corner IC 1 is a corner formed by the surface 2a of the support 2 and the side surface 31a of each antenna portion 31. The plurality of corner ECs are formed by a plurality of three-dimensional structures 3. More specifically, each corner EC is a corner formed only by the side surface 31a of each antenna portion 31, or a corner formed by the side surface 31a and the top surface 31b of each antenna portion 31. The side surface 31a is a surface of each antenna portion 31 that intersects with the surface 2a of the support 2, for example, a surface perpendicular to the surface 2a. The top surface 31b is a surface of each antenna portion 31 that intersects with the side surface 31a, for example, a surface parallel to the surface 2a.

[0023] The functional layer 5 is arranged on a plurality of three-dimensional structures 3. The functional layer 5 has a graphene layer 51. The graphene layer 51 is a carbon layer formed from a carbon-containing material. As an example, the graphene layer 51 is composed of a single layer or a plurality of graphene films. A single layer graphene film is a graphene film with a thickness of about one atom and can be obtained, for example, by a transfer process or direct synthesis. The graphene layer 51 extends along the surface 2a of the support 2, the side surfaces 31a and top surfaces 31b of each antenna portion 31, and the surface of each electrode 4. The graphene layer 51 covers a plurality of first corners IC1 and a plurality of corners EC. The graphene layer 51 is in contact with each three-dimensional structure 3.

[0024] The functional layer 5 further comprises an alkali metal layer 52. The alkali metal layer 52 is a metal layer formed from a material containing an alkali metal (for example, cesium). As an example, the alkali metal layer 52 is composed of alkali metal deposited on the graphene layer 51 to have a thickness of about one to several atomic layers. The alkali metal layer 52 is in contact with the graphene layer 51. Preferably, in at least the region where the graphene layer 51 covers the three-dimensional structure 3, the alkali metal layer 52 is formed to cover substantially the entire surface of the graphene layer 51.

[0025] In the electron emission element 1 configured as described above, a predetermined potential difference is applied between the pair of antenna portions 31 in each three-dimensional structure 3 via the pair of electrodes 4. When electromagnetic waves are incident on each three-dimensional structure 3 in this state, field electron emission occurs in each three-dimensional structure 3, and electrons are emitted from each three-dimensional structure 3. Note that the potential difference applied between the pair of antenna portions 31 may be zero. In that case, a frame-shaped electrode 4 may be formed on the surface 2a of the support 2 instead of the pair of electrodes 4. [Configuration of an electron tube equipped with an electron emission element]

[0026] As an example of an electron tube equipped with an electron emission element 1, the configuration of the electron multiplier tube 10 shown in Figure 4 will be described. As shown in Figure 4, the electron multiplier tube 10 comprises an electron emission element 1, a plurality of dynodes 11, an anode 12, and a housing 13. The electron emission element 1, the plurality of dynodes 11, and the anode 12 are arranged in a space within the housing 13. This space is a vacuumed space.

[0027] The electron-emitting element 1 is positioned inside the housing 13 with its surface opposite to the surface 2a of the support 2 facing the window portion 13a of the housing 13. When electromagnetic waves W pass through the window portion 13a and enter the electron-emitting element 1, the electron-emitting element 1 emits electrons E in response to the incidence of electromagnetic waves W. Multiple dynodes 11 multiply the electrons E emitted from the electron-emitting element 1. In other words, the multiple dynodes 11 are electron multiplier units. The anode 12 collects the electrons E multiplied by the multiple dynodes 11 and outputs the collected electrons E as a signal current. In other words, in the electron multiplier tube 10, the anode 12 functions as an output unit that outputs based on the electrons E emitted from the electron-emitting element 1.

[0028] As another example of an electron tube equipped with an electron-emitting element 1, the configuration of the image intensifier 20 shown in Figure 5 will be described. As shown in Figure 5, the image intensifier 20 comprises an electron-emitting element 1, an MCP (microchannel plate) 21, a fluorescent film 22, an FOP (fiber optic plate) 23, a window member 24, and a tube body 25. The window member 24 is hermetically fixed to one opening of the tube body 25. The FOP 23 is hermetically fixed to the other opening of the tube body 25. The electron-emitting element 1, the MCP 21, and the fluorescent film 22 are arranged in a space defined by the tube body 25, the window member 24, and the FOP 23. This space is a vacuumed space.

[0029] The electron emission element 1 is positioned inside the tube 25 with the surface opposite to the surface 2a of the support 2 in contact with the window member 24. When electromagnetic waves W pass through the window member 24 and enter the electron emission element 1, the electron emission element 1 emits electrons E in response to the incidence of electromagnetic waves W. The MCP 21 multiplies the electrons E emitted from the electron emission element 1. In other words, the MCP 21 is an electron multiplication unit. The fluorescent film 22 is formed on the light incidence surface 23a of the FOP 23. When electrons E multiplied by the MCP 21 enter the fluorescent film 22, the fluorescent film 22 emits light L in response to the incidence of electrons E. The FOP 23 guides the light L emitted from the fluorescent film 22 and emits it from the light emission surface 23b. In other words, in the image intensifier 20, the fluorescent film 22 and the FOP 23 function as output units that produce output based on the electrons E emitted from the electron emission element 1. [Operation and Effects]

[0030] In the electron emission element 1, a functional layer 5 having a graphene layer 51 is arranged on a plurality of three-dimensional structures 3 made of a conductive material. As a result, electrons E can be emitted in response to the incidence of electromagnetic waves W, regardless of differences in the characteristics of the incident electromagnetic waves W (for example, at least one of the following characteristics: peak electric field strength of the incident electromagnetic waves W, frequency band of the incident electromagnetic waves W, polarization characteristics of the incident electromagnetic waves W, etc.). Therefore, the electron emission element 1 can improve the emission performance of electrons E.

[0031] In the electron emission element 1, multiple first corner ICs 1 are formed by a support 2 and multiple three-dimensional structures 3, and a graphene layer 51 covers the multiple first corner ICs 1. As a result, electric field concentration occurs at each first corner IC1, thereby reliably improving the electron emission performance E.

[0032] In the electron emission element 1, multiple corner ECs are formed by multiple three-dimensional structures 3, and a graphene layer 51 covers multiple corner ECs. As a result, electric field concentration occurs at each corner EC, thereby reliably improving the electron emission performance E.

[0033] In the electron emission element 1, the functional layer 5 further includes an alkali metal layer 52. This ensures a reliable improvement in the electron emission performance E.

[0034] With the electron multiplier tube 10 and image intensifier 20 equipped with an electron emission element 1, the electron emission performance of the electron emission element 1 is improved, thereby improving the detection sensitivity of electromagnetic waves W.

[0035] Here, we will explain the experimental results demonstrating that the electron emission performance of electrons E is improved by the electron emission element 1. Figure 6 is a graph showing the relationship between the peak electric field strength of the terahertz wave and the output of the electron multiplier tube. In the graph shown in Figure 6, the black circles and solid lines represent the experimental results of Example 1, the white circles and dashed lines represent the experimental results of Example 2, the black squares and dashed lines represent the experimental results of Comparative Example 1, and the black triangles and dashed lines represent the experimental results of Comparative Example 2. The experimental results of Example 1 are from an experiment in which an electron emission element comprising a support, a plurality of three-dimensional structures, a graphene layer, and an alkali metal layer (an electron emission element having the same configuration as the electron emission element 1 described above) was applied to an electron multiplier tube (an electron multiplier tube having the same configuration as the electron multiplier tube 10 described above) (experimental results in which the output of the electron multiplier tube was measured by injecting terahertz waves having each peak electric field strength). The experimental results of Example 2 are from an experiment in which the electron emission element differs from Example 1 only in that it does not have an alkali metal layer. The experimental results for Comparative Example 1 are based on a configuration that differs from Example 1 only in that the electron emission element does not have a graphene layer. The experimental results for Comparative Example 2 are based on a configuration that differs from Example 1 only in that the electron emission element does not have a graphene layer or an alkali metal layer.

[0036] As shown in Figure 6, it was found that the "minimum value of the detectable peak electric field intensity of terahertz waves" was lower for the "electron emission element comprising a support, a plurality of three-dimensional structures, a graphene layer, and an alkali metal layer" (Example 1: black circles and solid lines) compared with the "electron emission element comprising a support, a plurality of three-dimensional structures, and an alkali metal layer" (Comparative Example 1: black squares and dashed lines) and the "electron emission element comprising a support, a plurality of three-dimensional structures" (Comparative Example 2: black triangles and dashed lines). Furthermore, it was found that the "minimum value of the detectable peak electric field intensity of terahertz waves" was lower for the "electron emission element comprising a support, a plurality of three-dimensional structures, and a graphene layer" (Example 2: white circles and dashed lines) compared with the "electron emission element comprising a support, a plurality of three-dimensional structures" (Comparative Example 2: black triangles and dashed lines). Thus, by incorporating a graphene layer into the electron emission element, the "minimum detectable peak electric field strength of terahertz waves" was lowered. In other words, detection became possible even for terahertz waves with weaker peak electric field strengths, expanding the detection range (dynamic range) in terms of the peak electric field strength of the incident electromagnetic wave. In short, it was possible to improve electron emission performance regardless of differences in the peak electric field strength characteristics of the incident electromagnetic wave.

[0037] Figure 7 is a graph showing the relationship between the frequency of terahertz waves and the output of the electron multiplier tube. The experimental results shown in Figure 7(a) are those obtained using the configuration of Comparative Example 1 described above (i.e., a configuration that differs from Example 1 only in that the electron emission element does not have a graphene layer) (experimental results obtained by incidentally terahertz waves having various frequencies and measuring the output of the electron multiplier tube). The experimental results shown in Figure 7(b) are those obtained using the configuration of Example 1 described above (i.e., a configuration in which the electron multiplier tube is fitted with an electron emission element comprising a support, a plurality of three-dimensional structures, a graphene layer, and an alkali metal layer). As shown in Figures 7(a) and (b), it was found that the "detectable terahertz wave frequency band" is wider when using the "electron emission element comprising a support, a plurality of three-dimensional structures, a graphene layer, and an alkali metal layer" (Example 1: Figure 7(b)) compared to the "electron emission element comprising a support, a plurality of three-dimensional structures, and an alkali metal layer" (Comparative Example 1: Figure 7(a)). Thus, by incorporating a graphene layer into the electron emission element, the "detectable terahertz wave frequency band" was broadened. In other words, detection became possible even for terahertz waves with a wider frequency band, expanding the detection range (dynamic range) in the frequency band. In short, it was possible to improve electron emission performance regardless of differences in the frequency band characteristics of the incident electromagnetic wave.

[0038] Figures 8, 9, and 10 are graphs showing the intensity distribution of electron emission in an electron emission device. The experimental results shown in Figure 8(a) are those obtained with the electron emission device configuration of Comparative Example 3 (experimental results obtained by measuring the intensity distribution of electron emission in an electron emission device by injecting terahertz waves having a predetermined frequency and predetermined electric field oscillation direction). The electron emission device configuration of Comparative Example 3 differs from that of Example 1 only in that it does not have multiple three-dimensional structures. The experimental results shown in Figure 8(b) are those obtained with the electron emission device configuration of Comparative Example 1 described above (i.e., a configuration that differs from that of Example 1 only in that the electron emission device does not have a graphene layer). As shown in Figures 8(a) and 8(b), in the electron emission element comprising a support, a graphene layer, and an alkali metal layer (Comparative Example 3: Figure 8(a)) and the electron emission element comprising a support, a plurality of three-dimensional structures, and an alkali metal layer (Comparative Example 1: Figure 8(b)), the intensity of electron emission in the electron emission element was generally low, and the intensity distribution of electron emission in the electron emission element was non-uniform. In obtaining the experimental results shown in Figure 8(b), the direction in which the pair of antenna parts facing each other was aligned with the direction of the electric field oscillation of the terahertz wave so that the pair of antenna parts constituting the bowtie antenna in each three-dimensional structure emitted electrons in response to the incidence of terahertz waves having a predetermined electric field oscillation direction.

[0039] The experimental results shown in Figure 9(a) are the experimental results for the electron emission element configuration of Example 2 described above (experimental results in which the intensity distribution of electron emission in the electron emission element was measured by incidenting a terahertz wave having a predetermined frequency and predetermined electric field oscillation direction), and are the experimental results when the direction in which the pair of antenna parts face each other is aligned with the electric field oscillation direction of the terahertz wave. The experimental results shown in Figure 9(b) are the experimental results for the electron emission element configuration of Example 2 described above, and are the experimental results when the direction in which the pair of antenna parts face each other is perpendicular to the electric field oscillation direction of the terahertz wave. As shown in Figures 9(a) and (b), in the "electron emission element comprising a support, a plurality of three-dimensional structures, and a graphene layer" (Example 2), the intensity of electron emission in the electron emission element was generally high and the intensity distribution of electron emission in the electron emission element was uniform, regardless of the relationship between the direction in which the pair of antenna parts face each other and the electric field oscillation direction of the terahertz wave. This indicates that, according to the "electron emission element comprising a support, multiple three-dimensional structures, and a graphene layer," it is possible to ensure electron emission performance that is independent of the antenna characteristics (in other words, independent of differences in the polarization characteristics of the incident electromagnetic waves).

[0040] The experimental results shown in Figure 10(a) are those obtained using the electron emission element configuration of Example 2 described above (experimental results obtained by measuring the intensity distribution of electron emission in the electron emission element by incidenting terahertz waves having a predetermined frequency and predetermined electric field oscillation direction), and are those obtained when the graphene layer is composed of a single layer of graphene film having a thickness of approximately one atom. The experimental results shown in Figure 10(b) are those obtained using the electron emission element configuration of Example 2 described above, and are those obtained when the graphene layer is composed of two layers of graphene film. As shown in Figures 10(a) and (b), it was found that in both cases, sufficient height and sufficient uniformity of the electron emission intensity in the electron emission element can be obtained with the "electron emission element comprising a support, a plurality of three-dimensional structures, and a graphene layer" (Example 2). However, it was found that in order to obtain sufficient height and sufficient uniformity of electron emission intensity in an electron emission device, the case in which the graphene layer is composed of two graphene films (Figure 10(b)) is more advantageous than the case in which the graphene layer is composed of a single graphene film (Figure 10(a)).

[0041] Figure 14 is a graph showing the relationship between the time elapsed since the start of terahertz wave incidence and the output of the electron multiplier tube. In the graph shown in Figure 14, the solid line represents the experimental results for the configuration of Example 1 described above (i.e., a configuration in which an electron emission element comprising a support, a plurality of three-dimensional structures, a graphene layer, and an alkali metal layer is applied to an electron multiplier tube) (experimental results in which the output of the electron multiplier tube was measured by injecting terahertz waves of a certain intensity), and the dashed line represents the experimental results for the configuration of Comparative Example 1 described above (i.e., a configuration that differs from Example 1 only in that the electron emission element does not have a graphene layer). As shown in Figure 14, it was found that the electron emission element with a graphene layer (Example 1: solid line in Figure 14) exhibits a higher and more stable output compared to the electron emission element without a graphene layer (Comparative Example 1: dashed line in Figure 14), that is, field electron emission in the electron emission element exhibits a higher and more stable output. In particular, in the electron emission device without a graphene layer (Comparative Example 1: dashed line in Figure 14), the output drops in the initial stages from the start of terahertz wave incidence, but in the electron emission device with a graphene layer (Example 1: solid line in Figure 14), such an output drop is suppressed. [Modification]

[0042] This disclosure is not limited to the example described above. For example, as shown in Figures 11 and 12, the electron emission element 1 may have multiple second corner ICs 2 formed by multiple three-dimensional structures 3. The second corner ICs 2 are parts that indicate the starting point of shape changes of the three-dimensional structure 3 itself, such as branching, joining, and bending, when the three-dimensional structure 3 is viewed from a direction opposite to the surface 2a of the support 2 (a direction along the X-axis). In other words, they can be considered as connection points when multiple independent three-dimensional structures 3 are connected and become one. Such second corner ICs 2 can be said to be corners that are generated by the deformation of the three-dimensional structure 3 itself. In this case as well, since a carbon layer such as a graphene layer 51 covers multiple second corner ICs 2, electric field concentration occurs at each second corner ICs 2, and as a result, an improvement in electron emission performance can be reliably achieved.

[0043] Each three-dimensional structure 3 may be configured as an antenna other than the bowtie antenna (e.g., a dipole antenna, a split-ring antenna, a double split-ring antenna, etc.), or may not be configured as an antenna as shown in FIGS. 11, 12, and 13.

[0044] As shown in FIGS. 11(a) and 11(b), each three-dimensional structure 3 may be formed by a single polygon (e.g., a triangle, a quadrilateral, etc.) wire, or may be formed by a combination of the same or different types of polygon wires. In that case, the length of one side is preferably λ / 10 or more, and the width of the wire is preferably λ or more (λ is the wavelength of the target electromagnetic wave W). Also, when providing a gap, the width of the gap is preferably λ / 10 or more.

[0045] As shown in FIG. 12(a), each three-dimensional structure 3 may be formed by a circular portion and a plurality of protruding portions. In that case, the diameter of the circle is preferably 10λ or less, and the interval between adjacent circular portions is preferably λ / 10 or more. Also, the width of each protruding portion is preferably λ or more.

[0046] As shown in FIG. 12(b), each three-dimensional structure 3 may be formed by a rod-shaped portion. In that case, the length of the rod-shaped portion is preferably λ / 10 or more and 10λ or less, and the length of the rod-shaped portion is preferably equal to or greater than the width of the rod-shaped portion. Also, the interval between adjacent rod-shaped portions is preferably λ / 10 or more.

[0047] If the plurality of three-dimensional structures 3 form a pattern with a plurality of first corners IC1 and a plurality of corners EC, they may be a regular pattern as shown in FIG. 13(a), or may be a random pattern as shown in FIG. 13(b).

[0048] In the electron-emitting device 1, each three-dimensional structure 3 was electrically connected to the electrode 4 via the wirings 6 and 7, but each three-dimensional structure 3 may be electrically connected to the electrode 4 via the graphene layer 51. When each three-dimensional structure 3 is electrically connected to the electrode 4 via the wirings 6 and 7, there is an advantage that the supply of electrons to each three-dimensional structure 3 is stabilized. On the other hand, when each three-dimensional structure 3 is electrically connected to the electrode 4 via the graphene layer 51, there is an advantage that the degree of freedom in the shape and arrangement of each three-dimensional structure 3 is improved. Also, the plurality of three-dimensional structures 3 may be separated from each other or may be connected to each other.

[0049] In the electron-emitting device 1, as a carbon layer formed of a carbon-containing material, a carbon layer other than the graphene layer 51 (for example, a graphite layer, an amorphous carbon layer, a diamond-like carbon layer, a carbon nanotube layer, etc.) may be applied. Even in that case, it is possible to realize an improvement in the emission performance of the electrons E. Also, the support 2 only needs to be such that the surface 2a is formed of an electrically insulating material, and for example, may include a main body portion formed of a conductive material. Also, in the case of the transmission-type electron-emitting device 1, the support 2 needs to be permeable to electromagnetic waves, but in the case of the reflection-type electron-emitting device 1, the support 2 does not necessarily have to be permeable to electromagnetic waves.

[0050] 1... electron-emitting device, 2... support, 2a... surface (support surface), 3... three-dimensional structure, 5... functional layer, 10... electron multiplier tube (electron tube), 12... anode (output portion), 20... image intensifier (electron tube), 22... fluorescent film (output portion), 23... FOP (output portion), 51... graphene layer (carbon layer), 52... alkali metal layer, IC1... first corner portion, IC2... second corner portion, EC... corner portion, W... electromagnetic wave, E... electron.

Claims

1. An electron emission element that emits electrons in response to the incidence of electromagnetic waves, comprising: a support having a support surface formed of an electrically insulating material; a plurality of three-dimensional structures disposed on the support surface and formed of a conductive material; and a functional layer disposed on the plurality of three-dimensional structures and having a carbon layer formed of a carbon-containing material.

2. The electron emission element according to claim 1, wherein a plurality of first corners are formed by the support and the plurality of three-dimensional structures, and the carbon layer covers the plurality of first corners.

3. The electron emission element according to claim 1 or 2, wherein a plurality of second corners are formed by the plurality of three-dimensional structures, and the carbon layer covers the plurality of second corners.

4. The electron emission element according to any one of claims 1 to 3, wherein the plurality of three-dimensional structures form a plurality of corners, and the carbon layer covers the plurality of corners.

5. The electron-emitting element according to any one of claims 1 to 4, wherein the carbon layer is a graphene layer.

6. The electron emission element according to any one of claims 1 to 5, wherein the functional layer further comprises an alkali metal layer formed of a material containing an alkali metal.

7. An electron tube comprising an electron-emitting element according to any one of claims 1 to 6, and an output unit that performs an output based on the electrons emitted from the electron-emitting element.

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