JP2022129983A - Photocathode with protective film - Google Patents

Abstract

To provide a photocathode with a protective film having high brightness and a long life even in a relatively easily obtained high vacuum environment (for example, 10-5 Pa or higher), a manufacturing method of the same.SOLUTION: A photocathode with a protective film includes a photocathode 2 made of an alkaline metal thin film, a protective film 4 which is a monoatomic layer or an electron-permeable thin film provided on the surface of the photocathode 2, and a sealing material 3 that encloses and airtightly packages the photocathode 2 and the protective film 4. In addition, after facing the protective film 4 provided on a mesh-shaped second substrate 4a toward the photocathode 2, the first substrate 2a and the second substrate 4a are airtightly sealed to the photocathode 2 formed on the first substrate 2a in a vacuum environment.SELECTED DRAWING: Figure 1

Description

The present invention relates to a photocathode with a protective film (photocathode) with high brightness and long life even in a relatively easily obtained high vacuum environment (for example, 10 ⁻⁵ Pa or higher), its manufacturing method and manufacturing apparatus. .

Negative electron affinity (NEA) semiconductors or photocathodes such as alkali metal thin film photocathode have extremely high quantum efficiency (QE) of several to several ten percent in short pulses (order of picoseconds to nanoseconds). is obtained. Therefore, they are used in recent advanced electron accelerators such as free electron lasers, electron microscopes, electron beam lithography, and a small number of electron sources and devices that require high-brightness electron beams.

However, since these photocathodes are chemically active, specifically due to their high reactivity with the residual gas in the apparatus, an ultra-high vacuum environment is essential for their use. A favorable vacuum environment of 10 ⁻⁷ Pa or less is required, and there is also the drawback that the service life is short. In addition, when using the photocathode, periodic maintenance is required, and the current situation is that the application is limited.

Recent advanced electron accelerators and future plans require a photocathode that can stably generate a high-current and high-brightness electron beam for a long time. Cathodes have been proposed and found to have the potential to achieve lifetimes several orders of magnitude longer than conventional ones.

However, in practical use, it is necessary to airtightly provide a protective film of a certain size on the photocathode, and Non-Patent Document 1 cannot solve this point.

U.S. Pat. No. 8,823,259

Therefore, the present invention provides a high-luminance, long-life photocathode with a protective film (photocathode) even in a relatively easily obtained high-vacuum environment (for example, 10 ⁻⁵ Pa or higher), its manufacturing method, and manufacturing apparatus. intended to

In order to solve the above problems, the present invention is
(1)
a photocathode of an alkaline metal thin film;
a protective film that is a monoatomic layer or an electron-permeable thin film provided on the surface of the photocathode;
a sealing material that encloses and airtightly packages the photocathode and the protective film;
A film photocathode with a protective film, comprising:
(2)
(1) wherein the photocathode is a photocathode formed on a first substrate, and the protective film is a protective film that covers and adheres to a second substrate having a mesh portion, covering the mesh portion; A photocathode with a protective film according to .
(3)
The photocathode with a protective film according to (2), wherein the seal is a low-melting-point, low-outgassing hot-melt compression bond of an indium wire.
(4)
A method for using a photocathode with a protective film according to (1), wherein the photocathode with a protective film can be used in a vacuum environment of 10 ⁻⁵ Pa or higher.
(5)
A method for producing a film photocathode with a protective film according to (1),
The first substrate and the second substrate are formed on the photocathode formed on the first substrate in a vacuum environment, and the protective film provided on the mesh-like second substrate is directed toward the photocathode. is hermetically sealed.
(6)
An apparatus for manufacturing a film photocathode with a protective film used in the method for manufacturing a film photocathode with a protective film according to (1),
a vacuum chamber;
a first stage for fixing the first substrate within the vacuum chamber;
a second stage that holds the second substrate in the vacuum chamber and has a heater;
After moving and pressing either or both of the first stage and the second stage,
An apparatus for manufacturing a film photocathode with a protective film, wherein a heat-soluble sealing material placed on the first substrate is heated and melted by the heater to airtightly seal the first substrate and the second substrate. .
(7)
The apparatus for producing a film photocathode with a protective film according to (6), wherein the hot-melt sealing material is an annular seal, and the heater is a heater for heating the annular seal part in an annular shape.
and

Here, a conventional photocathode can be adopted as the photocathode.

The protective film may consist of a monoatomic layer such as graphene, silicene, hexagonal boron nitride (hBN), or a sufficiently thin thin film that is permeable to light and electrons, but impermeable to gases, and is directed against the photocathode. Inert (no adverse effects) and chemically stable (resistant to reactions and ion collisions) against common residual gases (hydrogen, methane, water, carbon monoxide, nitrogen, oxygen, carbon dioxide, etc.) It is a uniform, chemically and physically strongly bonded film with a side length of several millimeters or more.

The seal uses materials with low gas permeability and low outgassing. For example, an indium wire ring can be exemplified, and when the first substrate and the second substrate are bonded, the bonding portion is heated for a short time to melt the indium to ensure airtightness. It is preferable to use a device that locally heats only the junction so that the photocathode does not become hot during heating. Since K ₂ CsSb, which is the photocathode of the alkali metal thin film, is stable up to about 70° C., it is possible to airtightly join the substrates by placing an indium wire around it and instantly heating and melting it. .

Since the present invention is configured as described above, it has the following effects. As shown in FIG. 5, by airtightly providing a protective film on the surface of the photocathode, residual gases (hydrogen, water, carbon monoxide, oxygen, carbon dioxide, etc.) active against the photocathode in the electron source Electrons (e ⁻ ) generated in the photocathode by light irradiation (hv) pass through the protective film and are taken out.

By airtightly providing this protective film, the photocathode can be used for a long time while maintaining high quantum efficiency in a high-vacuum environment (pressure higher than 10 ⁻⁵ Pa), which has hitherto been difficult to use. Photoelectrons can be efficiently extracted in a high vacuum (approximately 10 ⁻⁵ Pa) easily obtained by a general roughing exhaust system (a combination of a rotary pump and a turbo-molecular pump, etc.).
Therefore, it can be used as an electron source for equipment in which it is difficult to generate an ultra-high vacuum. Furthermore, the electron beam generated from the semiconductor or alkali metal thin film photocathode is brighter than the thermoelectron source generally used, and the measurement with time resolution is also possible by using the short-pulse electron beam. It becomes possible.
In addition, even in an ultra-high vacuum environment, the life of the photocathode is much longer than that of a conventional photocathode, so there is a possibility that it can be used as a maintenance-free electron source that does not require regular maintenance of the photocathode. be.
Therefore, the photocathode of the present invention can be widely used for electron sources such as electron microscopes and electron beam lithography, as well as advanced electron accelerators that require high-current electron beams.

FIG. 1 is a schematic view showing a partial cross-section of the method for producing a photocathode with a protective film according to the present invention. FIG. 2 is an enlarged view of the vicinity of the photocathode portion and protective film portion in FIG. FIG. 3 is a cross-sectional schematic diagram showing a state in FIG. 1 in which the first stage is moved by a rod and pressed against the second stage to form an airtight seal. FIG. 4 is a partially enlarged schematic cross-sectional view of the photocathode with a protective film after airtight sealing in FIG. FIG. 5 is a schematic diagram for explaining electron generation by a photocathode with a protective film.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the present invention is not limited to the following embodiments.

A photocathode with a protective film according to the present invention, its manufacturing method and manufacturing apparatus will be described with reference to FIGS. 1 to 4. FIG.

<Photocathode with protective film>
As shown in FIGS. 4 and 5, the photocathode 1 with a protective film includes a photocathode 2 made of an alkali metal thin film and a protective film which is a monoatomic layer or a thin film through which electrons can pass, provided on the surface of the photocathode 2. 4 and a sealing material 3 for enclosing and airtightly packaging the photocathode 2 and the protective film 4 .

More specifically, as shown in FIG. 4, the photocathode 2 is formed in a vacuum environment on the first substrate 2a by a film forming apparatus (not shown) suitable for the material of the photocathode thin film, such as vacuum deposition. . The first substrate 2a is made of metal, semiconductor, or the like, and comprises a film forming area 2c in which the photocathode 2 is formed and walls on both sides of a concave portion 2b surrounding the film forming area 2c. An annular sealing material 3 is placed in the recess 2b.

The protective film 4 covers the mesh portion 4b of the second substrate 4a having the mesh portion 4b and adheres thereto 4c, for example, by Van der Waals force. The second substrate 4a is made of metal or the like, and emits electrons generated by light irradiation through the mesh portion 4b.

The protective film 4 is grown, for example, on a substrate suitable for growth of the protective film in its film forming apparatus (not shown). After the film is formed, the substrate on which the protective film 4 is formed is transferred (transferred) to the second substrate 4a by a method suitable for the type of protective film, and used as the second substrate 4a with the protective film 4 for packaging.

The sealing material 3 is, for example, a low-melting-point, low-outgassing hot-melt compression bond made of indium wire, and seals the portions of the first substrate 2a and the second substrate 4a that are not covered with the photocathode 2 and the protective film 4. They are brought into close contact at the joining portion 3a.

The photocathode 1 with a protective film packaged in this way does not come into direct contact with residual gas active on the photocathode, and electrons (e ⁻ ) generated in the photocathode 2 by light irradiation (hv) are protected. Releases through membrane 4 . In addition, the photocathode 2 can be used for a long time while maintaining high quantum efficiency even in a vacuum environment (pressure higher than 10 ⁻⁵ Pa) that is not ultra-high vacuum.

<Method and apparatus for manufacturing photocathode with protective film>
As shown in FIG. 1-4, the apparatus 10 for manufacturing a photocathode with a protective film comprises a first stage 11 on which the first substrate 2a is placed and a second stage 14 on which the second substrate 4a is held.

In this example, the protective film-equipped photocathode manufacturing apparatus 10 further includes a retainer 12 for fixing the first substrate 2a to the first stage 11, and the first stage 11 moving back and forth with respect to the direction of the second stage 14. and a rod 13 that allows the

Although the first stage 11 is moved and pressed against the second stage 14 here, the second stage 14 may be moved, or both the first and second stages 11 and 14 may be moved. The first stage 11 can also be used when moving the photocathode 2 from the film forming apparatus to the vacuum chamber 15 .

They are used for hermetic packaging in vacuum chamber 15 . That is, the photocathode 2 and the protective film 4 are sandwiched between the first substrate 2a and the second substrate 4a, and the first substrate 2a and the second substrate 4a are joined with the sealing material 3 to enclose the photocathode 2 and the protective film 4.

The first stage 11 has a rod 13 fitted in an internal recess, has a recessed mounting portion 11a on the upper surface for mounting the first substrate 2a, and has a flange 11b formed at the end. One substrate 2a is fixed.

The flange 11b is used when the first stage is fixed to a film formation device for the photocathode 2, and the photocathode 1 with a protective film is fixed to an installation destination such as an electron gun. The shape and other fixing and installation means may be selected as appropriate.

The second stage 14 is equipped with an annular heater 14e in an annular groove 14c between the inner frame 14a and the outer frame 14b of the internal cavity 14d, holds the second substrate 4a in the vacuum chamber 15, and holds the second substrate 4a in the state of FIG. The sealing material 3 is heated in an annular shape.

It should be noted that the second stage 14 is fixed to a moving rod (not shown) and configured to be inserted into and removed from the vacuum chamber 15 . After packaging, the second stage 14 is pulled out from the vacuum chamber 15. At that time, the second substrate 4a is fused to the first substrate 2a. separates.

As a result, in a vacuum environment, the photocathode 2 and the protective film 4 can be sandwiched between the first substrate 2a and the second substrate 4a, and then enclosed and hermetically sealed.

In this way, the photocathode 2 packaged so as to block the environmental atmosphere by the first and second substrates 2a, 4a, the protective film 4, and the sealing material 3 is attached to various devices while being packaged, and used as an electronic device. used as a source. In order to ensure greater stability, it is desirable to move and transport the device under vacuum until it is attached to a device under a vacuum environment.

1 Photocathode with Protective Film 2 Photocathode 2a First Substrate 2b Recess 2c Film Forming Area 3 Sealing Material 3a Joining Portion 4 Protective Film 4a Second Substrate 4b Mesh Portion 4c Adhesion 10 Photocathode with Protective Film Manufacturing Apparatus 11 First Stage 11a Mounting portion 11b Flange 12 Presser 13 Rod 14 Second stage 14a Inner frame 14b Outer frame 14c Groove 14d Cavity 14e Heater 15 Vacuum chamber

Claims (7)

a photocathode of an alkaline metal thin film;
a protective film that is a monoatomic layer or an electron-permeable thin film provided on the surface of the photocathode;
a sealing material that encloses and airtightly packages the photocathode and the protective film;
A film photocathode with a protective film, comprising: 2. The photocathode is a photocathode formed on a first substrate, and the protective film is a protective film that covers the mesh portion and adheres to the second substrate having the mesh portion. A photocathode with a protective film according to . 3. A photocathode with a protective film according to claim 2, wherein said seal is a low-melting-point, low-outgassing hot-melt compression bond made of indium wire. A method of using a photocathode with a protective film according to claim 1, wherein the photocathode with a protective film can be used in a vacuum environment of 10 ^-5 Pa or higher. A method for manufacturing a film photocathode with a protective film according to claim 1,
The first substrate and the second substrate are formed on the photocathode formed on the first substrate in a vacuum environment, and the protective film provided on the mesh-like second substrate is directed toward the photocathode. is hermetically sealed. An apparatus for manufacturing a film photocathode with a protective film used in the method for manufacturing a film photocathode with a protective film according to claim 5,
a vacuum chamber;
a first stage for fixing the first substrate within the vacuum chamber;
a second stage that holds the second substrate in the vacuum chamber and has a heater;
After moving and pressing either or both of the first stage and the second stage,
An apparatus for manufacturing a film photocathode with a protective film, wherein a heat-soluble sealing material placed on the first substrate is heated and melted by the heater to airtightly seal the first substrate and the second substrate. . 7. The apparatus for producing a film photocathode with a protective film according to claim 6, wherein said heat-meltable sealing material is an annular seal, and said heater is a heater for heating said annular seal portion in an annular shape.

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