Emitter

Abstract

An emitter (1) comprises: an electron source (2); and a heater (3) for heating the electron source (2). The electron source (2) has: an electron-emitting member (10) which is formed of a first material; and an enclosing member (20) which is formed of a second material having a work function greater than that of the first material. The electron-emitting member (10) has: a first section (11); and a second section (12) which is formed integrally with the first section (11). The enclosing member (20) is fixed to the electron-emitting member (10), and encloses the first section (11) when viewed from a prescribed direction. The enclosing member (20) has a minimum thickness of at least 20 μm. The heater (3) is in contact with the second section (12).

Description

Emitter

[0001] One aspect of the present disclosure relates to an emitter.

[0002] For example, Patent Document 1 describes an emitter including an electron source and a heater. In this emitter, the electron source includes a columnar portion having electron emission characteristics and an electron emission limiting member arranged to surround the columnar portion. The heater is in contact with the electron emission limiting member and heats the columnar portion via the electron emission limiting member. The heated columnar portion emits electrons.

[0003] International Publication No. 2021 / 215335

[0004] In the emitter described above, it is preferable that the fluctuation of the electron emission characteristics is small, that the generation of excess electrons can be effectively suppressed, and that the structure is stable.

[0005] Therefore, one aspect of the present disclosure aims to provide an emitter that can suppress fluctuations in electron emission characteristics, effectively suppress the generation of excess electrons, and improve structural stability.

[0006] An emitter according to one aspect of the present disclosure is [1] "an emitter comprising: an electron source; and a heater for heating the electron source; the electron source having an electron-emitting member formed of a first material; and a surrounding member formed of a second material having a work function greater than that of the first material; the electron-emitting member having a first portion and a second portion formed integrally with the first portion; the surrounding member being fixed to the electron-emitting member and surrounding the first portion when viewed from a predetermined direction; the surrounding member having a minimum thickness of 20 μm or more; and the heater being in contact with the second portion."

[0007] In this emitter, a first portion of the electron emitting member is surrounded by a surrounding member made of a second material having a work function greater than that of the first material constituting the electron emitting member. This suppresses the generation of excess electrons from areas other than the tip of the first portion, allowing for optimal electron emission. Furthermore, in this emitter, a heater contacts a second portion of the electron emitting member. This allows the heater to directly heat the electron emitting member. Therefore, compared to, for example, a case in which the heater contacts the surrounding member and heats the electron emitting member via the surrounding member, the heater can heat the electron emitting member more stably. As a result, fluctuations in electron emission characteristics can be suppressed, even with long-term use. Furthermore, in this emitter, the minimum thickness of the surrounding member is 20 μm or more. This effectively suppresses the generation of excess electrons by the surrounding member. Furthermore, the thick surrounding member ensures the strength of the surrounding member, improving structural stability. Therefore, this emitter can suppress fluctuations in electron emission characteristics, effectively suppress the generation of excess electrons, and improve structural stability.

[0008] The emitter according to one aspect of the present disclosure may be [2] "the emitter according to [1]," in which an end of the first portion opposite the second portion is tapered so as to become thinner toward the tip. In this case, electrons can be suitably emitted from the first portion.

[0009] An emitter according to one aspect of the present disclosure may be [3] "the emitter according to [1] or [2], in which the surrounding member is bonded to the electron-emitting member by a bonding material, and the bonding material is formed of the same material as the second material." In this case, the bonding strength between the surrounding member and the electron-emitting member can be increased.

[0010] The emitter according to one aspect of the present disclosure may be [4] "the emitter according to [3], wherein a boundary between the first portion and the second portion is not surrounded by the surrounding member but is covered by the bonding material." In this case, generation of excess electrons from other than the tip end of the first portion can be effectively suppressed.

[0011] An emitter according to one aspect of the present disclosure may be [5] "the emitter according to any one of [1] to [4], wherein in a width direction perpendicular to the predetermined direction, a width of the second portion is wider than a width of the first portion, and the electron source is fixed to the heater by sandwiching the second portion between the heaters along the width direction." In this case, damage or the like can be suppressed at a portion of the electron source fixed by the heater, and structural stability can be further improved.

[0012] An emitter according to one aspect of the present disclosure may be [6] "the emitter according to any one of [1] to [5], in which the surrounding member is made of a sintered body." In this case, it is possible to effectively suppress the generation of excess electrons and effectively improve structural stability.

[0013] According to one aspect of the present disclosure, it is possible to provide an emitter that can suppress fluctuations in electron emission characteristics, effectively suppress the generation of excess electrons, and improve structural stability.

[0014] 3 is a cross-sectional view of an emitter according to an embodiment, an electron source and a heater, and a cross-sectional view of an electron source taken along line III-III in FIG.

[0015] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following description, the same or equivalent elements will be designated by the same reference numerals, and redundant description will be omitted.

[0016] As shown in FIG. 1 , the emitter 1 includes an electron source 2, a heater 3, an insulator 4, a pair of electrode pins 5, and a suppressor electrode 6. The electron source 2 emits electrons. Details of the electron source 2 will be described later. The electron source 2 is fixed to the heater 3 and heated by the heater 3. The heater 3 is formed in a block shape from, for example, pyrolytic carbon, and generates heat when electricity is passed through the pair of electrode pins 5. The electrode pins 5 are provided to penetrate the insulator 4 and are connected to the heater 3. The suppressor electrode 6 is disposed around the electron source 2. The suppressor electrode 6 suppresses lateral electron emission from the electron source 2. In the emitter 1, the electron source 2 is heated by passing electricity through the heater 3, and a voltage is applied between the electron source 2 and an extraction electrode (not shown), causing electrons to be output from the tip of the electron source 2.

[0017] 2 and 3, the electron source 2 includes an electron-emitting member 10 and a surrounding member 20. The electron-emitting member 10 is made of a first material (electron-emitting material) having electron emission properties. The surrounding member 20 is made of a second material (electron-emission limiting material) having a work function greater than that of the first material.

[0018] The first material is a material that can be heated to emit electrons. The first material has a lower work function than the second material. An example of the first material is lanthanum boride (LaB ６ ), cerium boride (CeB ６ ) and other rare earth borides; high melting point metals such as tungsten, tantalum, and hafnium, as well as their oxides, carbides, and nitrides; and noble metal-rare earth alloys such as iridium and cerium. The work functions of these materials are as follows: ６ ): 2.8 eV Cerium boride (CeB ６ ): 2.8 eV Tantalum carbide: 3.2 eV Hafnium carbide: 3.3 eV

[0019] The second material has a work function greater than that of the first material. By surrounding the electron emitting member 10 made of the first material with the surrounding member 20 made of the second material, electron emission from the side surface of the electron emitting member 10 is suppressed. The difference in work function between the second material and the first material is preferably 0.5 eV or more, more preferably 1.0 eV or more, and even more preferably 1.6 eV or more.

[0020] The second material preferably includes a high-melting point metal or its carbide, and preferably includes at least one of metallic tantalum, metallic titanium, metallic zirconium, metallic tungsten, metallic molybdenum, metallic rhenium, tantalum carbide, titanium carbide, and zirconium carbide. The second material may include at least one of boron carbide and graphite (carbon material). The second material may include at least one of niobium, hafnium, and vanadium. Glassy carbon (for example, Glassy Carbon (trade name, manufactured by Rayho Manufacturing Co., Ltd.)) may be used as the second material. The work functions of these materials are as follows: metallic rhenium: 4.9 eV; boron carbide: 5.2 eV; graphite: 5.0 eV

[0021] The first material and the second material may be appropriately selected based on, for example, the work function and strength of both materials, and may be used in combination. A suitable example of the first material is lanthanum boride (LaB ６ ), cerium boride (CeB ６ ), hafnium carbide, and iridium cerium. Suitable examples of the second material include metallic rhenium, boron carbide, and graphite (including glassy carbon). Some of the materials that can be used as the first material can also be used as the second material. For example, a material with a work function of approximately 3.2 to 4.5 eV can be used as both the first and second materials. Examples of such materials include metallic tungsten (work function: 4.5 eV), metallic tantalum (work function: 3.2 eV), and hafnium carbide (work function: 3.3 eV).

[0022] The electron emitter 10 has a first portion 11 and a second portion 12 formed integrally with the first portion 11. In this example, the first portion 11 has an octagonal columnar portion 13 and a tapered portion 14. The columnar portion 13 extends from the second portion 12 along direction A (a predetermined direction). The tapered portion 14 is provided on the opposite side of the columnar portion 13 from the second portion 12 (upper side in FIG. 2 ), and constitutes an end portion 11a of the first portion 11 opposite the second portion 12. The tapered portion 14 is tapered so as to become thinner toward the tip. The end surface 10a of the electron emitter 10 (tapered portion 14) is an electron emission surface. The end surface 10a is, for example, a flat surface perpendicular to direction A, and electrons are emitted from the end surface 10a along direction A.

[0023] The second portion 12 is formed to have a shape wider than the column portion 13. That is, in direction B (width direction) perpendicular to direction A, the width W12 of the second portion 12 is wider than the width W11 of the first portion 11. In this example, the second portion 12 is sandwiched between the heaters 3 along direction B, thereby fixing the electron source 2 to the heaters 3. The heaters 3 are in contact with the second portion 12. In this example, the heaters 3 are in contact with the entire second portion 12 in direction A. The second portion 12 is formed to have, for example, a rectangular shape in a cross section perpendicular to direction A.

[0024] The surrounding member 20 is formed in a substantially cylindrical shape and surrounds the first portion 11 of the electron emitting member 10 when viewed from direction A. More specifically, the surrounding member 20 does not cover the end 11b of the first portion 11 on the second portion 12 side (the boundary between the first portion 11 and the second portion 12), but surrounds the entire first portion 11 except for the end 11b. In other words, a gap is formed between the surrounding member 20 and the second portion 12 of the electron emitting member 10 in direction A. The end 11b is covered with a bonding material 30, which will be described later.

[0025] The surrounding member 20 has a first surrounding portion 21 that surrounds the column portion 13 of the first section 11, and a second surrounding portion 22 that surrounds the tapered portion 14 of the first section 11. In this example, the second surrounding portion 22 also surrounds the end of the column portion 13 on the tapered portion 14 side. The first surrounding portion 21 is formed in a cylindrical shape, for example, having a rectangular outer shape. The second surrounding portion 22 is formed in a tapered shape that becomes thinner toward the tip. The taper angle of the outer surface of the second surrounding portion 22 is larger than the taper angle of the outer surface of the tapered portion 14. As a result, the thickness of the second surrounding portion 22 becomes thinner toward the tip side (the side opposite the second section 12).

[0026] In this example, the surrounding member 20 is made of glass-like carbon. More specifically, the surrounding member 20 is made of a sintered body of glass-like carbon formed by vacuum sintering a phenolic resin. The minimum thickness of the surrounding member 20 is 20 μm or more. In this example, the surrounding member 20 is thinnest at the tip of the second surrounding portion 22, and the thickness is, for example, 40 μm. The thickness of the first surrounding portion 21 is, for example, approximately 150 μm. The minimum thickness of the surrounding member 20 is preferably 25 μm or more, and more preferably 30 μm or more.

[0027] The surrounding member 20 is bonded to the electron emitter 10 by a bonding material 30. The bonding material 30 is disposed between the first surrounding portion 21 of the surrounding member 20 and the column portion 13 of the first portion 11 of the electron emitter 10. The bonding material 30 is also disposed between the first surrounding portion 21 and the second portion 12 of the electron emitter 10. As a result, as described above, the bonding material 30 covers the end 11b of the first portion 11 on the second portion 12 side (the portion of the first portion 11 exposed from the surrounding member 20). In this example, the bonding material 30 is formed of the same material (e.g., glassy carbon) as the second material constituting the surrounding member 20. More specifically, the bonding material 30 is formed of a sintered body of glassy carbon formed by placing phenolic resin in predetermined locations and then vacuum sintering it.

[0028] The end face 20a of the surrounding member 20 (second surrounding portion 22) is flush with the end face 10a (electron emission surface) of the electron emitter 10. Furthermore, the side face of the first portion 11 of the electron emitter 10 is covered by the surrounding member 20 and the bonding material 30. Since the side face of the first portion 11 is not exposed in this manner, unnecessary electron emission, i.e., lateral electron emission, can be effectively suppressed. For example, to obtain a larger electron current, the electron source 2 is heated to a high temperature of approximately 1550°C and a high electric field of several kV is applied to the electron source 2. Application of such a high electric field can generate excess electrons from sources other than the tip of the electron source 2. These excess electrons may reduce the brightness of the electron beam from the tip or cause unnecessary heating of surrounding electrode components due to the space charge effect. To prevent this, only the electron emitting portion of the electron source 2 (end surface 10a of the electron emitting member 10) is exposed, and the other surfaces are covered with the surrounding member 20 and the bonding material 30, so that only the high-brightness electron beam can be obtained from the tip.

[0029] Covering the side surfaces of the first portion 11 of the electron emitter 10 with the surrounding member 20 and the bonding material 30 also has the effect of suppressing the occurrence of a phenomenon known as microdischarge. Specifically, in thermionic emission, electrons are emitted by heating the electron source to a high temperature. As a result, the electron-emitting material evaporates and adheres to the surrounding electrode components, forming fibrous crystals called whiskers. Accumulation of charge in these whiskers causes microdischarge. Microdischarge can destabilize the electron beam and reduce device performance. Covering the side surfaces of the first portion 11 with the surrounding member 20 and the bonding material 30 traps the sublimated electron-emitting material, reducing the amount of material adhering to the surrounding electrode components and making microdischarge less likely to occur. The surrounding member 20 and the bonding material 30 do not have a circumferential gap but cover the entire first portion 11. This effectively suppresses lateral electron emission. [Operation and Effects]

[0030] In the emitter 1, the first portion 11 of the electron emitting member 10 is surrounded by a surrounding member 20 made of a second material having a work function greater than that of the first material constituting the electron emitting member 10. This suppresses the generation of excess electrons from areas other than the tip of the first portion 11, enabling favorable electron emission. Furthermore, in the emitter 1, the heater 3 contacts the second portion 12 of the electron emitting member 10. This allows the heater 3 to directly heat the electron emitting member 10. Therefore, compared to, for example, a case in which the heater contacts the surrounding member and heats the electron emitting member via the surrounding member, the heater 3 can heat the electron emitting member 10 more stably. As a result, fluctuations in the electron emission characteristics can be suppressed, even after extended use. That is, for example, if a configuration is adopted in which the heater contacts the surrounding member and heats the electron emitting member via the surrounding member, continued use of the emitter for an extended period (e.g., two months) can cause the surrounding member to wear out due to heating, changing the contact condition between the surrounding member and the electron emitting member, resulting in sporadic fluctuations in output. This is thought to be due to fluctuations in heat conduction from the heater to the electron emitting member caused by changes in the contact state between the surrounding member and the electron emitting member. In this regard, in the emitter 1 of the embodiment, the heater 3 directly heats the electron emitting member 10, thereby suppressing such fluctuations in heat conduction and suppressing fluctuations in electron emission characteristics. Furthermore, in the emitter 1, the minimum thickness of the surrounding member 20 is 20 μm or more. This effectively suppresses the generation of excess electrons by the surrounding member 20. Furthermore, the thick surrounding member 20 ensures the strength of the surrounding member 20, improving structural stability. Therefore, the emitter 1 can suppress fluctuations in electron emission characteristics, effectively suppress the generation of excess electrons, and improve structural stability.

[0031] The end 11a (tapered portion 14) of the first portion 11 opposite the second portion 12 is tapered so as to become thinner toward the tip. This allows electrons to be emitted favorably from the first portion 11. On the other hand, if the end 11a is tapered, it is difficult to accurately form an electron emission suppressing layer (e.g., a layer having a thickness of 10 μm or less) on the end 11a by film deposition. In this regard, in the emitter 1 of the embodiment, the surrounding member 20 surrounding the first portion 11 is configured as a member (structure) having a thickness of 20 μm or more and is bonded to the electron emitting member 10 by a bonding material 30. Therefore, the surrounding member 20 can be formed accurately and then bonded to the electron emitting member 10.

[0032] The surrounding member 20 is bonded to the electron emitting member 10 by a bonding material 30, and the bonding material 30 is made of the same material as the second material constituting the surrounding member 20. This makes it possible to increase the bonding strength between the surrounding member 20 and the electron emitting member 10.

[0033] An end 11b of the first portion 11 on the side of the second portion 12 (a boundary between the first portion 11 and the second portion 12) is not surrounded by the surrounding member 20 but is covered by the bonding material 30. This makes it possible to effectively suppress the generation of excess electrons from other than the tip end of the first portion 11.

[0034] In direction B (width direction), the width W12 of the second portion 12 is wider than the width W11 of the first portion 11, and the electron source 2 is fixed to the heater 3 by sandwiching the second portion 12 between the heater 3 along direction B. This makes it possible to prevent damage or the like from occurring at the fixing points of the electron source 2 by the heater 3, and further improves structural stability. Furthermore, because the width W12 of the second portion 12 is wider than the width W11 of the first portion 11, the second portion 12 is easier to grip, improving handleability.

[0035] The surrounding member 20 is made of a sintered body, which makes it possible to effectively suppress the generation of excess electrons and effectively improve the structural stability.

[0036] The present disclosure is not limited to the above-described embodiments. For example, the materials and shapes of the components are not limited to those described above, and various materials and shapes can be adopted.

[0037] The first portion 11 of the electron emitter 10 may not have a tapered portion 14 and may have a uniform cross-sectional shape along its entire length. The surrounding member 20 may not have a tapered portion (second surrounding portion 22) and may have a uniform cross-sectional shape along its entire length. In the above embodiment, the surrounding member 20 does not cover the end 11b of the first portion 11 on the second portion 12 side. However, the surrounding member 20 may cover the entire first portion 11 in the direction A. The bonding material 30 may be made of a material different from the second material constituting the surrounding member 20. The bonding material 30 is not necessarily provided, and the surrounding member 20 may be fixed to the electron emitter 10 by another method. In the direction B, the width W12 of the second portion 12 may be the same as the width W11 of the first portion 11 or may be narrower than the width W11.

[0038] 1...emitter, 2...electron source, 3...heater, 10...electron emitting member, 11...first portion, 11a...end portion, 11b...end portion, 12...second portion, 20...surrounding member, 30...bonding material, A...direction (predetermined direction), B...direction (width direction), W11, W12...width.

Claims

1. An emitter comprising an electron source and a heater for heating the electron source, wherein the electron source has an electron emission member formed of a first material and a surrounding member formed of a second material having a work function greater than that of the first material, the electron emission member has a first portion and a second portion integrally formed with the first portion, the surrounding member is fixed to the electron emission member and surrounds the first portion when viewed from a predetermined direction, the minimum thickness of the surrounding member is 20 μm or more, and the heater is in contact with the second portion.

2. The emitter according to claim 1, wherein an end portion of the first portion on the side opposite to the second portion is formed in a tapered shape so as to become thinner toward the tip.

3. The emitter according to claim 1 or 2, wherein the surrounding member is joined to the electron emission member by a joining material, and the joining material is formed of the same material as the second material.

4. The emitter according to claim 3, wherein a boundary portion between the first portion and the second portion in the first portion is not surrounded by the surrounding member but is covered by the joining material.

5. The emitter according to claim 1 or 2, wherein in a width direction perpendicular to the predetermined direction, the width of the second portion is wider than the width of the first portion, and the electron source is fixed to the heater by the second portion being sandwiched by the heater along the width direction.

6. The emitter according to claim 1 or 2, wherein the surrounding member is constituted by a sintered body.

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