JP2005339843A - Photocathode and electron tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photocathode and an electron tube capable of detecting light of a comparatively long wavelength and enabled to be manufactured in a simple manufacturing process. <P>SOLUTION: The electron tube 10 is provided with a photocathode 11, a positive electrode 17 and a vacuum vessel 18. The photocathode 11 is provided with a substrate 12, a light absorption layer 14 excited by an incident light to generate photoelectron e2, and an active layer 15 lowering work function of the surface of the light absorption layer 14. The light absorption layer 14 contains carbon nanotube (CNT), and a catalyst layer 13 is provided for growing the CNT between the light absorption layer 14 and the substrate 12. The positive electrode 17 is arranged in opposition to the photocathode 11 to collect photoelectron e2 emitted from the CNT of the light absorption layer 14. An exciting wavelength of the CNT depends on its shape, and a photocathode capable of detecting a long-wavelength incident light L2 of, for instance, a wavelength of not less 1 μm, can be realized in a simple process. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photocathode that absorbs incident light to excite photoelectrons and emits photoelectrons to the outside, and an electron tube including the photocathode.

  Conventionally, a photocathode used for detecting light of a predetermined wavelength and an electron tube including the photocathode are known. The photocathode has a light absorption layer that absorbs light of a predetermined wavelength and emits photoelectrons. Light is incident on the light absorption layer and this light is converted into photoelectrons to detect light. Can do.

  As conventional photocathodes, in addition to those having a light absorption layer containing an alkali metal such as Cs, those using a pn junction made of InP / InGaAsP (see Patent Document 1) have been put into practical use. FIG. 5 is a cross-sectional view showing the configuration of the photocathode 100 disclosed in Patent Document 1. As shown in FIG. The photocathode 100 was formed on the semiconductor substrate 101 made of p-type InP, the light absorption layer 102 made of p-type InGaAsP and formed on the surface of the semiconductor substrate 101, and the light absorption layer 102 made of p-type InP. The electron emission layer 103, the contact layer 104 made of n-type InP and formed on the electron emission layer 103 in a predetermined pattern, the electrode 105 formed on the contact layer 104, and the back surface of the semiconductor substrate 101 are formed. Electrode 106. Then, a voltage is applied between the electrode 105 and the electrode 106 by the power source 107, whereby an electric field is formed inside the photocathode 100. When light enters the light absorption layer 102, photoelectrons are excited inside the light absorption layer 102. Photoelectrons are accelerated by the electric field and are emitted to the outside of the photocathode 100 through the electron emission layer 103. With such a configuration, the photocathode 100 can detect light having a relatively long wavelength exceeding 1 μm.

In addition, as a technique relevant to this invention, what was disclosed by patent document 2-4 other than patent document 1 is mentioned, for example.
Japanese Patent No. 2923462 JP 2001-176378 A JP 2001-202873 A JP 2002-270861 A

  The photocathode disclosed in Patent Document 1 includes the following problems. That is, since the photocathode disclosed in Patent Document 1 has a heterostructure of compound semiconductors such as InP and InGaAsP, it is necessary to epitaxially grow these semiconductor layers with high quality. Further, when forming the contact layer 104 having a predetermined pattern, advanced semiconductor process technology such as microfabrication technology is required. Therefore, the manufacturing process becomes complicated and the cost increases.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a photocathode and an electron tube that can detect light having a relatively long wavelength and can be manufactured by a simple manufacturing process.

  In order to solve the above-described problems, the photocathode according to the present invention is a photocathode that emits photoelectrons in response to incident light, and is formed on the substrate and excited by the incident light to generate photoelectrons. A light absorption layer, and the light absorption layer includes carbon nanotubes.

  In the above-described photocathode, photoelectrons are excited by causing light of a predetermined wavelength to enter a carbon nanotube (CNT: Carbon NanoTube), and the photoelectrons are emitted to the outside. The present inventors have found that the wavelength of light at which photoelectrons are excited in the CNT depends on the shape (particularly the diameter) of the CNT, and is sensitive to light having a wavelength of 1 μm or more such as infrared light. Further, since CNT can be manufactured by a simpler process than a compound semiconductor having a heterostructure, the above-described photocathode can be manufactured by a simple manufacturing process. Therefore, according to the above-described photocathode, a photocathode capable of detecting light having a relatively long wavelength such as 1 μm or more can be manufactured by a simpler manufacturing process than in the past.

  In the present invention, the CNT is preferably a single-walled carbon nanotube (SWCNT), but may be a multi-walled carbon nanotube (MWCNT). In addition, CNTs having various shapes such as those whose diameter changes in the longitudinal direction, those whose tip is closed or open, those having a cavity at the center or those having no cavity may be used. Further, the longitudinal directions of the CNTs may be aligned (so-called oriented CNTs) or may not be aligned.

  The photocathode may further include an active layer that is provided on the surface of the light absorption layer and reduces the work function of the surface of the light absorption layer. Thereby, the photoelectrons generated in the light absorption layer are efficiently emitted to the outside of the photocathode, so that the photoelectric conversion efficiency of the photocathode can be further increased.

  In addition, an electron tube according to the present invention includes any one of the above-described photocathodes, an anode for collecting photoelectrons emitted from the photocathodes directly or indirectly, and a vacuum container that holds a path of photoelectrons in a vacuum state. It is characterized by that. According to this electron tube, an electron tube capable of detecting light having a relatively long wavelength can be manufactured by a simpler manufacturing process than before.

  ADVANTAGE OF THE INVENTION According to this invention, the photocathode and electron tube which can detect the light of a comparatively long wavelength and can be manufactured by a simple manufacturing process can be provided.

  Hereinafter, embodiments of a photocathode and an electron tube according to the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
FIG. 1 is a cross-sectional view showing a configuration of a first embodiment of a photocathode according to the present invention. The photocathode emits photoelectrons e1 in response to incident light L1 having a predetermined wavelength. Referring to FIG. 1, the photocathode 1 of this embodiment includes a substrate 2, a catalyst layer 3, and a light absorption layer 4.

  The substrate 2 is a member for mechanically supporting the catalyst layer 3 and the light absorption layer 4. The material of the substrate 2 is not particularly limited as long as the material has a strength capable of mechanically supporting the catalyst layer 3 and the light absorption layer 4. Examples of the material of the substrate 2 include metal, glass, sapphire, quartz, and silicon.

  The catalyst layer 3 is provided between the substrate 2 and the light absorption layer 4. As will be described later, the light absorption layer 4 of the present embodiment is formed to contain CNTs. The catalyst layer 3 includes a component that becomes a catalyst for growing the CNTs of the light absorption layer 4. Examples of the catalyst for growing CNTs include Ni and Fe. The catalyst layer 3 is formed by depositing these catalysts on the substrate 2. The thickness of the catalyst layer 3 is, for example, 50 mm. When the substrate 2 is made of (or includes) a catalyst such as Ni or Fe, the catalyst layer 3 may be omitted.

  The light absorption layer 4 is a photocathode for generating photoelectrons e1 when excited by the incident light L1. The light absorption layer 4 mainly includes CNT (SWCNT in the present embodiment). CNT is a tube-shaped substance mainly made of carbon and having an average diameter of less than 1 μm. The CNT of the light absorption layer 4 is formed by growing carbon on the catalyst layer 3 by a chemical vapor deposition (CVD) method or the like. At this time, the diameter of the CNT changes depending on the thickness of the catalyst layer 3.

  Here, FIG. 2 is a graph schematically showing a correlation (spectral sensitivity characteristic) between the wavelength of the incident light L1 and the photoelectric sensitivity (quantum efficiency when the incident light L1 is converted into photoelectrons e1) in the CNT. In FIG. 2, graphs G1 to G3 show correlations when the diameter of the CNT is relatively thin (G1), when it is relatively thick (G3), and when it is in the middle (G2). As shown in FIG. 2, when the diameter of the CNT is reduced, the limit on the long wavelength side of the light having sensitivity to the CNT shifts to the short wavelength side. On the contrary, when the diameter of the CNT is increased, the limit on the long wavelength side of the light having sensitivity to the CNT shifts to the long wavelength side. This is because the energy gap of CNT (particularly SWCNT) is inversely proportional to the diameter of CNT. As described above, in the CNT, the wavelength of the incident light L1 that excites the photoelectrons e1 changes according to the diameter of the CNT. Therefore, it is possible to realize a desired spectral sensitivity characteristic by controlling the diameter of the CNT. is there. For example, in the case of SWCNT, when the diameter is changed from 0.7 nm to 2.0 nm, the limit on the long wavelength side of light with which the CNT is sensitive can be changed from about 1.1 μm to about 3.0 μm. As described above, since the diameter of the CNT can be arbitrarily set by changing the thickness of the catalyst layer 3, for example, a light absorption layer having sensitivity to incident light L1 having a relatively long wavelength such as an infrared region. 4 can be formed easily. Further, the light absorption layer 4 having desirable spectral sensitivity characteristics can be more suitably realized by changing the length, density, structure, etc. of the CNTs.

  Note that the CNT formation method is not limited to CVD, and for example, arc discharge, laser ablation, laser vapor deposition, or the like may be used. In addition to growing the CNTs on the catalyst layer 3, a solvent containing CNTs may be applied to the substrate 2, or the CNTs may be fixed to the substrate 2 with a binder (adhesive).

  The photocathode 1 is provided at least in part between the substrate 2 and the light absorption layer 4, and is a conductive layer such as an electrode 5 that is electrically connected to the light absorption layer 4 and supplies electrons to the light absorption layer 4. It is preferable to provide. For example, a power source 7 is connected between the gate electrode 6 and the electrode 5 provided in the photoelectron emission direction of the light absorption layer 4, and an electric field is formed in the thickness direction of the light absorption layer 4, thereby exciting the CNT. The photoelectrons e1 thus accelerated are accelerated toward the outside of the photocathode 1.

  The photocathode 1 having the above configuration operates as follows. When the incident light L1 is incident from the surface of the light absorption layer 4, the number of photoelectrons e1 corresponding to the amount of the incident light L1 is generated inside the CNT of the light absorption layer 4. The photoelectrons e1 are accelerated by the electric field applied in the thickness direction of the light absorption layer 4 and are emitted to the outside of the photocathode 1.

  The effect by the photocathode 1 of this embodiment is demonstrated. The photocathode 1 includes CNT in the light absorption layer 4. As described above, the wavelength of the incident light L1 at which the photoelectron e1 is excited in the light absorption layer 4 depends on the shape of the CNT, and the light absorption layer 4 is also effective for incident light L1 having a relatively long wavelength such as a wavelength of 1 μm or more. It can have sensitivity. Further, since the photocathode 1 does not have a compound semiconductor heterostructure, it can be manufactured by a simple process. Therefore, according to the photocathode 1 of the present embodiment, it is possible to provide a photocathode that can detect the incident light L1 having a relatively long wavelength and can be manufactured by a simpler manufacturing process than the conventional one.

  In addition, according to the photocathode 1 of the present embodiment, it is possible to provide a photocathode that is low in cost and easy to increase in area by simplifying the manufacturing process. Furthermore, in a conventional photocathode using a compound semiconductor, it is necessary to select a material having an energy gap according to the wavelength of incident light. At this time, defects are introduced unless the lattice constant of the heterostructure is accurately matched. Although there was a problem that the performance deteriorated, according to the photocathode 1 of the present embodiment, it is possible to easily cope with incident light of various wavelengths only by controlling the shape of the CNT. Moreover, since CNT consists of carbon, while the atmospheric stability of the light absorption layer 4 becomes favorable, the influence on natural environment can be restrained low.

  Patent Document 2 discloses a field emission electron source using CNTs. This field emission electron source emits electrons by applying an electric field to CNTs. Patent Document 3 discloses a cathode for emitting photoelectrons or secondary electrons using CNTs. In this photoelectron or secondary electron emission cathode, CNT is not a material for photoelectric conversion but is used as an underlayer for improving the crystallinity of a photocathode made of an alkali antimony compound. Patent Document 4 discloses an optical functional film using CNT. In this optical functional film, SWCNT is used as photoelectron emission particles by utilizing the internal photoelectric effect of SWCNT. However, the techniques disclosed in Patent Documents 2 to 4 are completely different from the present invention that utilizes the external photoelectric effect of CNTs in terms of configuration and operational effects.

  In the light absorption layer 4, the diameter of the CNT may be determined so that the photoelectron e1 of the CNT is excited by, for example, incident light L1 having a wavelength of 1 μm or more. According to such a photocathode 1, incident light L1 having a wavelength of 1 μm or more can be easily detected by a simple method of controlling the diameter of the CNT.

  In addition, as in the present embodiment, the photocathode 1 preferably includes a catalyst layer 3 serving as a catalyst for forming CNTs included in the light absorption layer 4 between the substrate 2 and the light absorption layer 4. Accordingly, CNT can be suitably formed regardless of the material of the substrate 2, so that various materials can be used for the substrate 2.

(Second Embodiment)
FIG. 3 is a cross-sectional view showing the configuration of the electron tube according to the second embodiment of the present invention. This electron tube is a device that detects incident light L2 by generating photoelectrons e2 corresponding to the amount of incident light L2 having a predetermined wavelength. Referring to FIG. 3, the electron tube 10 of this embodiment includes a photocathode 11, an anode 17, and a vacuum container 18. The photocathode 11 is a so-called transmissive photocathode in which the surface that receives the incident light L2 and the surface that emits the photoelectrons e2 are different. The photocathode 11 includes a substrate 12, a catalyst layer 13, a light absorption layer 14, an active layer 15, and an electrode 16. In addition, about the structure of the catalyst layer 13 and the light absorption layer 14 of this embodiment, since it is the same as that of the structure of the catalyst layer 3 and the light absorption layer 4 of the said 1st Embodiment, detailed description is abbreviate | omitted.

  The substrate 12 is a member that mechanically supports the catalyst layer 13, the light absorption layer 14, and the active layer 15 and serves as an incident window for receiving the incident light L2. The material of the substrate 12 is not particularly limited as long as it is a material that transmits the incident light L2 having a predetermined wavelength. As a material of the substrate 12, for example, glass, sapphire, quartz and the like are suitable. The substrate 12 has a light emitting surface 12a and a light incident surface 12b. Incident light L2 enters the light incident surface 12b, passes through the substrate 12, and exits from the light exit surface 12a. The catalyst layer 13 and the light absorption layer 14 are formed on the light emission surface 12 a of the substrate 12.

  The active layer 15 is a layer for reducing the work function of the surface of the light absorption layer 14. Since the active layer 15 is formed on the surface of the light absorption layer 14, it is formed at the tip portion of the CNT included in the light absorption layer 14. The active layer 15 includes, for example, an alkali metal, an alkali metal oxide, an alkali metal fluoride, or an alkali halide compound. In the present embodiment, the active layer 15 is formed by thinly applying Cs, which is an alkali metal, or an oxide thereof on the surface of the light absorption layer 14. As a material for the active layer 15, for example, K, Rb, Na, Li, or an oxide thereof can be suitably used in addition to Cs and Cs oxide. By including such a material, the active layer 15 curves the band structure near the surface of the light absorption layer 14 and lowers the work function of the surface of the light absorption layer 14. Photoelectrons e2 generated by the incident light L2 entering the light absorption layer 14 are efficiently emitted to the outside of the photocathode 11 through the active layer 15.

  The electrode 16 is a conductive layer for supplying electrons to the light absorption layer 14. The electrode 16 is provided at least at a part between the substrate 12 and the light absorption layer 14 and is electrically connected to the light absorption layer 14. The electrode 16 is formed by depositing a conductive material such as metal on the substrate 12. In this embodiment, the electrode 16 is provided along the edge of the light emitting surface 12a of the substrate 12. However, the electrode 16 may be provided on the light emitting surface 12a in various patterns such as a mesh, or The light emitting surface 12a may be provided on the entire surface. In addition, when the electrode 16 is provided on the entire surface of the light emitting surface 12a, the electrode 16 is preferably formed thin enough to allow the incident light L2 to pass through the electrode 16.

  The anode 17 is an electrode for directly collecting the photoelectrons e2 emitted from the photocathode 11 while forming an electric field with the photocathode 11. The anode 17 is provided at a position away from the photocathode 11 so as to face the light emitting surface 12 a of the substrate 12. The anode 17 is preferably disposed at a position close to the photocathode 11. An electric field is formed between the photocathode 11 and the anode 17 by connecting the power source 19 between the anode 17 and the electrode 16 with the anode 17 as the positive voltage side. Photoelectrons e2 generated in the light absorption layer 14 of the photocathode 11 are accelerated toward the anode 17 by this electric field, emitted from the photocathode 11 through the active layer 15, and collected by the anode 17.

  The vacuum container 18 is a container for keeping the path of the photoelectrons e2 in a vacuum. The vacuum vessel 18 has a substantially cylindrical shape, and is constituted by a glass tube, for example. One end of the vacuum vessel 18 is open, and this opening is closed by the photocathode 11. A gap between the photocathode 11 and the vacuum vessel 18 is sealed with, for example, In. An anode 17 is fixed to the other end of the vacuum vessel 18.

  The electron tube 10 having the above configuration operates as follows. When the incident light L2 enters from the light incident surface 12b of the substrate 12, the incident light L2 passes through the substrate 12 and the catalyst layer 13 and reaches the light absorption layer. The incident light L2 excites the CNT of the light absorption layer 14, and a number of photoelectrons e2 corresponding to the amount of the incident light L2 are generated inside the CNT. The photoelectron e2 is accelerated by the electric field formed between the electrode 16 and the anode 17, and reaches the tip of the CNT. Since the work function of the tip of the CNT is lowered by the active layer 15 and the electric field formed between the electrode 16 and the anode 17 is concentrated on the tip of the CNT, the photoelectron e2 reaching the tip of the CNT is a photocathode. 11 (in the vacuum vessel 18) is efficiently discharged. Then, the photoelectrons e2 are collected by the anode 17 and observed as a signal current indicating the amount of incident light L2.

  According to the electron tube 10 and the photocathode 11 according to the present embodiment, since the light absorption layer 14 of the photocathode 11 includes CNT, it is possible to detect the incident light L2 having a relatively long wavelength as in the first embodiment. In addition, it is possible to provide a photocathode and an electron tube that can be manufactured by a manufacturing process simpler than before.

  Further, the photocathode 11 may include a substrate 12 that transmits the incident light L2 as in the present embodiment. When the substrate 12 transmits the incident light L2, the transmissive photocathode 11 can be suitably realized.

  Further, the photocathode 11 preferably includes a conductive layer such as an electrode 16 electrically connected to the light absorption layer 14 between the substrate 12 and the light absorption layer 14 as in the present embodiment. Thus, electrons can be suitably supplied to the light absorption layer 14 containing CNTs, and an electric field can be applied to the photoelectrons e2 in cooperation with the anode 17.

  Further, it is preferable that an active layer 15 for reducing the work function of the surface of the light absorption layer 14 is formed on the surface of the light absorption layer 14 (that is, the tip portion of the CNT) as in the present embodiment. Accordingly, the photoelectrons e2 generated in the light absorption layer 14 are efficiently emitted to the outside of the photocathode 11, so that the photoelectric conversion efficiency of the photocathode 11 can be further increased. As described above, an alkali metal, an alkali metal oxide, an alkali metal fluoride, or an alkali halide compound is suitable as such a material. Further, the photocathode 11 of the present embodiment can emit photoelectrons e2 from the light absorption layer 14 to the outside without including the active layer 15. Thus, when the photocathode 11 does not include the active layer 15, a photocathode that does not contain an alkali metal (so-called alkali-free photocathode) can be realized.

(Third embodiment)
FIG. 4 is a cross-sectional view showing a configuration of an image intensifier tube (image intensifier) as an electron tube according to the third embodiment of the present invention. This image intensifier tube is an apparatus for enhancing the optical image L3 while maintaining the two-dimensional information of the optical image L3 that is incident light. Referring to FIG. 4, the image intensifier tube 20 of the present embodiment includes a photocathode 21, a side tube portion 28, a micro channel plate (MCP) 31, a phosphor 32, and a fiber optic plate (FOP). Plate) 33 is provided.

  The photocathode 21 is a transmissive photocathode. The photocathode 21 includes a substrate 22, a catalyst layer 23, a light absorption layer 24, an active layer 25, and an electrode 26a. The substrate 22 of the present embodiment is made of a material that transmits the optical image L3, such as borosilicate glass. Further, in the light absorption layer 24 of the present embodiment, at least some of the CNTs are aligned in the longitudinal direction, and the longitudinal direction is along the thickness direction of the light absorption layer 24. Such CNTs are called oriented CNTs. The photocathode 21 converts the light image L3 incident on the light incident surface 22b of the substrate 22 into photoelectrons e3 in the light absorption layer 24 and emits it into the vacuum through the active layer 25. In addition, since it is the same as that of the structure of the photocathode 11 of the said 2nd Embodiment about the structure except the above regarding the photocathode 21 of this embodiment, detailed description is abbreviate | omitted.

  The MCP 31 is an electron multiplier for multiplying the photoelectrons e3 emitted from the photocathode 21 by secondary electrons. The MCP 31 is arranged so that the input end 31 a for inputting the photoelectrons e <b> 3 faces the light emitting surface 22 a of the substrate 22. The MCP 31 has a configuration in which a large number of cylindrical channels whose inner walls are secondary electron emitters are bundled. An electrode 26b is provided around the input end 31a of the MCP 31 where the photoelectrons e3 are incident. A predetermined voltage is applied between the electrode 26 b and the electrode 26 a of the photocathode 21 by a power source 29 a, and an electric field is formed between the photocathode 21 and the input end 31 a of the MCP 31. An electrode 26c is provided around the output end 31b from which the secondary electrons e4 are emitted. A predetermined voltage is applied between the electrode 26b and the electrode 26c by the power source 29b, and an electric field is formed between the input end 31a and the output end 31b of the MCP 31. Then, photoelectrons e3 incident on each channel from the input end 31a side are multiplied while repeatedly colliding with the secondary electron emitter, and are emitted as secondary electrons e4 from the output end 31b side. A protective film for preventing ion feedback may be formed on the input end 31a of the MCP 31.

  The phosphor 32 is made of a material that emits fluorescence when the secondary electrons e4 emitted from the MCP 31 enter. The phosphor 32 is formed by applying a fluorescent material on a light incident surface 33a of an FOP 33 described later, and is provided so as to face the output end 31b of the MCP 31. The phosphor 32 constitutes an anode (anode) together with the electrode 27 provided around the phosphor 32, and a predetermined amount of power is supplied between the electrode 27 and the electrode 26c on the output end 31b side of the MCP 31 by a power source 29c. A voltage is applied. Therefore, an electric field is formed between the output end 31 b of the MCP 31 and the phosphor 32. The secondary electrons e4 emitted from the MCP 31 are accelerated by this electric field and enter the phosphor 32. The phosphor 32 is excited by the secondary electrons e4 and generates a light image L4 by fluorescence. That is, the phosphor 32 indirectly collects the photoelectrons e3 via the MCP 31. Note that a thin conductive film made of, for example, Al may be formed on the surface of the phosphor 32 to prevent the phosphor 32 from being charged up.

  The FOP 33 is a member for emitting the light image L4 generated in the phosphor 32 to the outside of the image intensifier tube 20. The FOP 33 has a light incident surface 33 a and a light emitting surface 33 b, and is disposed so that the light incident surface 33 a faces the output end 31 b of the MCP 31. The FOP 33 is formed by bundling a number of glass fibers in a direction intersecting the thickness direction, and can emit the light image L4 incident on the light incident surface 33a from the light emitting surface 33b while maintaining the two-dimensional information. .

  The side tube portion 28 is a vacuum container for keeping the paths of the photoelectrons e3 and the secondary electrons e4 in a vacuum. The side tube portion 28 is made of an insulating material and has a cylindrical shape. One end of the side tube portion 28 is closed by the photocathode 21, and the other end of the side tube portion 28 is closed by the FOP 33. The gap between the side tube portion 28 and the photocathode 21 and the gap between the side tube portion 28 and the FOP 33 are sealed with, for example, In. Thus, the region surrounded by the photocathode 21, the side tube portion 28, and the FOP 33 is maintained in a vacuum state. Further, the photocathode 21, MCP 31, and phosphor 32 are insulated from each other by the side tube portion 28.

  The image intensifier tube 20 of this embodiment operates as follows. When the light image L3 enters the photocathode 21 from the light incident surface 22b of the substrate 22, the light image L3 passes through the substrate 22 and the catalyst layer 23 and reaches the light absorption layer 24. Then, the light image L3 excites the alignment CNTs of the light absorption layer 24, and the number of photoelectrons e3 corresponding to the amount of light of the light image L3 is generated inside the alignment CNTs. The photoelectron e3 is accelerated by the electric field formed between the electrode 26a and the electrode 26b, and reaches the tip of the oriented CNT. The work function of the tip of the oriented CNT is lowered by the active layer 25, and the electric field formed between the electrode 26a and the electrode 26b is concentrated on the tip of the oriented CNT, so that the tip of the oriented CNT reaches the tip of the oriented CNT. The photoelectrons e3 are efficiently emitted into the vacuum.

  The emitted photoelectrons e3 enter the MCP 31. At this time, the photoelectron e3 travels in parallel with the electric field formed between the light absorption layer 24 of the photocathode 21 and the input end 31a of the MCP 31, so that the two-dimensional when the light image L3 enters the image intensifier tube 20. The light enters the MCP 31 while maintaining information. The photoelectrons e3 incident on the MCP 31 are multiplied by about 10,000 to 1,000,000 times within each channel, emitted as secondary electrons e4, and enter the phosphor 32. At this time, a positive voltage is applied to the output end 31b of the MCP 31 with respect to the input end 31a, and a positive voltage is applied to the electrode 27 and the phosphor 32 with respect to the output end 31b of the MCP 31. As a result, an electric field is formed, the secondary electrons e4 enter the phosphor 32 while maintaining the two-dimensional information that the photoelectrons e3 had, and the phosphor 32 emits the light image L4. The light image L4 thus generated passes through the FOP 33 and is emitted to the outside of the image intensifier tube 20. By the above operation, the image (light image L3) incident on the image intensifier tube 20 is enhanced.

  According to the image intensifier tube 20 and the photocathode 21 according to the present embodiment, the light absorption layer 24 of the photocathode 21 includes CNT (aligned CNT), so that a relatively long wavelength is obtained as in the first embodiment. It is possible to provide a photocathode and an electron tube (image intensifier tube) that can detect the light image L3 and can be manufactured by a simpler manufacturing process than in the past. Further, since the longitudinal directions of the CNTs are aligned with each other, the photoelectrons e3 emitted through the CNTs can accurately hold the two-dimensional information of the optical image L3.

  Further, the image intensifier tube 20 preferably includes an electron multiplying means (for example, MCP 31) for multiplying the photoelectrons e3 emitted from the photocathode 21 as secondary electrons as in the present embodiment. As a result, the photoelectrons e3 can be multiplied at a high multiplication factor, and thus the image (optical image L3) can be enhanced with high accuracy at a high S / N ratio. In addition, in the image intensifier tube 20, when it is necessary to obtain a light image L4 with higher brightness, a plurality of MCPs 31 may be provided in order to further obtain a secondary electron multiplication factor. In this way, the incident light image L3 can be further enhanced and the luminance can be increased.

  Further, the image intensifier tube 20 preferably includes a phosphor 32 that emits light when secondary electrons e4 (or photoelectrons) may enter as in the present embodiment. Thereby, the secondary electron e4 or photoelectron can be suitably converted into an optical image. In the image intensifier tube 20 described above, the phosphor 32 is used as a means for emitting light by the secondary electrons e4. However, this means may be any means that can convert secondary electrons or photoelectrons into an image. For example, the same effect can be obtained by providing an image pickup device such as a charge coupled device (CCD) instead of the phosphor, and directly irradiating the image pickup device with photoelectrons or secondary electrons.

  The photocathode and the electron tube according to the present invention are not limited to the above-described embodiments, and various other modifications are possible. For example, in the second embodiment, if an electron multiplier means (for example, the MCP 31 shown in the third embodiment) is provided between the photocathode 11 and the anode 17, a so-called photomultiplier tube can be realized. In such a photomultiplier tube, the electron multiplying means is not limited to MCP, and secondary electron surfaces using alkali antimonide, CuBe or the like may be configured in cascade. In addition, the electron tube 10 of the second embodiment or the photomultiplier tube as described above may have a so-called electron-injected configuration in which accelerated photoelectrons e2 (or secondary electrons) are injected into a photodiode.

FIG. 1 is a cross-sectional view showing a configuration of a first embodiment of a photocathode according to the present invention. FIG. 2 is a graph schematically showing the correlation between the wavelength of incident light and photoelectric sensitivity in CNT. FIG. 3 is a cross-sectional view showing the configuration of the electron tube according to the second embodiment of the present invention. FIG. 4 is a cross-sectional view showing a configuration of an image intensifier tube (image intensifier) as an electron tube according to the third embodiment of the present invention. FIG. 5 is a cross-sectional view showing the configuration of the photocathode disclosed in Patent Document 1.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 11, 21 ... Photocathode, 2, 12, 22 ... Substrate, 3, 13, 23 ... Catalyst layer, 4, 14, 24 ... Light absorption layer, 10 ... Electron tube, 15, 25 ... Active layer, 16, 26a ˜26c, 27 ... electrode, 17 ... anode, 18 ... vacuum vessel, 19,29a-29c ... power source, 20 ... image intensifier tube, 28 ... side tube portion, 31 ... MCP, 32 ... phosphor, 33 ... FOP.

Claims (5)

A photocathode that emits photoelectrons in response to incident light,
A substrate,
A light absorption layer formed on the substrate and excited by the incident light to generate the photoelectrons,
The photocathode characterized in that the light absorption layer contains carbon nanotubes.   The photocathode according to claim 1, wherein the carbon nanotubes are mainly single-walled carbon nanotubes.   The photocathode according to claim 1 or 2, wherein at least some of the carbon nanotubes are aligned in the longitudinal direction.   The photocathode according to any one of claims 1 to 3, further comprising an active layer provided on a surface of the light absorbing layer and reducing a work function of the surface of the light absorbing layer. The photocathode according to any one of claims 1 to 4,
An anode for directly or indirectly collecting the photoelectrons emitted from the photocathode;
An electron tube comprising: a vacuum vessel that holds the photoelectron path in a vacuum state.

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