JP6867568B2 - Nanoscale photocathode electron source - Google Patents

Description

The present invention relates to a photocathode electron source, and more particularly to a nanoscale photocathode electron source capable of generating a highly coherent electron beam.

The DC type photocathode electron source is a method of extracting electrons from the cathode by using the photoelectric effect, does not require a high frequency cavity, and has a simple structure. Such a photocathode electron source is used to generate an electron beam of an accelerator, an electron microscope, or the like. As the photocathode electron source, there are a laser-triggered field electron emission method, a back-illuminated photoelectron emission method, and the like, depending on how electrons are taken out. The laser-triggered field electron emission method irradiates the tip of a sharp needle with a laser to emit electrons. Further, in the back-illuminated photoelectron emission method, a metal thin film formed on glass is irradiated with a laser from the back surface direction to emit electrons (for example, Patent Document 1).

Further, for example, Patent Document 2 discloses an optical cathode in which a transparent electrode layer is provided between a glass substrate of the back-illuminated photoelectron emission method and a photocathode material layer. Further, for example, in the apparatus disclosed in Patent Document 3, a transparent electrode layer is provided between the photoelectron emitting material layer coated with cesium and the glass substrate in order to increase the quantum efficiency. Then, in order to prevent the emission of the electron beam from the cesium provided in the unnecessary area, the metal coating layer is provided in a portion other than the central region where the photoelectron radiation material layer is provided.

In the development of state-of-the-art electron microscope technology, it is required to image a single molecule at the atomic resolution level. In particular, progress in new drug design, low-dose radiation effect evaluation, and single protein structural analysis is expected. As a promising method that enables imaging at the atomic resolution level, research and development of an electron microscope using low-speed coherent electrons in the keV region or less is underway.

Japanese Unexamined Patent Publication No. 2001-143648 Japanese Unexamined Patent Publication No. 11-329215 Japanese Unexamined Patent Publication No. 3-176953

In all of these conventional techniques, the diameter of the emitted electron beam is large. Specifically, in the laser-triggered field electron emission method, the tip of the sharp needle is formed by chemical etching, so that the emitter shape becomes a hemispherical shape. This causes the electron beam to spread radially, so it was necessary to use an electromagnetic field optical lens or the like. Therefore, the coherence of the electron beam deteriorates due to the spherical aberration of the lens, and it is difficult to generate the highly focused electron beam required for the low-voltage coherent electron microscope. Further, in the back-illuminated photoelectron emission method and the device of Patent Document 2, since the diameter of the laser irradiated from the back surface can be reduced, the diameter of the electron beam can be reduced as compared with the general front-facing irradiation. .. However, due to the diffraction limit, the focal diameter of the laser beam cannot be less than the wavelength. For example, in the range from ultraviolet rays to visible light, the limit is that the focal diameter of the laser beam is about 1 μm.

Further, in the case of the apparatus of Patent Document 3, it is necessary to shield the periphery of the photoelectron emitting material layer with a metal coating layer. Therefore, when trying to reduce the diameter of the electron beam by reducing the photoelectron radiation material layer, if the diameter of the central region is less than the wavelength of the laser light, the laser light cannot pass through the central region and an electron beam is generated. It will not be done. Therefore, even in this example, the electron beam diameter could not be reduced to the nanoscale.

In view of such circumstances, the present invention aims to provide a nanoscale photocathode electron source capable of generating a highly coherent electron beam having high beam focusing property.

In order to achieve the above-mentioned object of the present invention, the nanoscale photocathode electron source according to the present invention includes a laser light source capable of irradiating laser light, a substrate having transparency to the laser light from the laser light source, and a laser. A transparent electrode layer made of a conductive material that is transparent to the laser light from the light source, formed on the surface of the substrate facing the surface on which the laser light is irradiated, and to which a predetermined voltage is applied, and transparent. It includes a nanoscale photocathode portion formed on the electrode layer and made of a photocathode material.

Here, the photocathode portion may be embedded so as to be flush with the surface of the transparent electrode layer facing the surface on the side to be irradiated with the laser beam.

Further, the photocathode portion may have a dot shape having a diameter of nanoscale.

Further, the laser light source may be configured so as to have an irradiation diameter as close as possible to the diameter of the dot shape of the photocathode portion.

Further, the photocathode portion may have a fine pattern having a line width of nanoscale.

In this case, the laser light source may be configured to have an irradiation area capable of irradiating the entire fine pattern of the photocathode portion.

Further, in order to suppress the influence of the laser beam from the laser light source, the difference between when the laser beam is irradiated to the optical cathode portion and when the laser beam which passes through the substrate and the transparent electrode layer is irradiated while avoiding the optical cathode portion. It may be provided with a noise removing unit for removing light.

The photocathode portion may be any of Au, Ag, Cu, GaAs, CsTe, CsKSb, and NEA-GaAs.

Further, the transparent electrode layer may be any of ITO, ZnO, and IGZO.

The nanoscale photocathode electron source of the present invention has an advantage that it can generate a highly coherent electron beam having high beam focusing property.

FIG. 1 is a schematic diagram for explaining a nanoscale photocathode electron source of the present invention. FIG. 2 is a schematic side sectional view for explaining another example of the nanoscale photocathode electron source of the present invention. FIG. 3 is a schematic side sectional view for explaining still another example of the nanoscale photocathode electron source of the present invention. FIG. 4 is a schematic plan view of the periphery of the photocathode portion for explaining another example of the photocathode portion of the nanoscale photocathode electron source of the present invention. FIG. 5 is a schematic side sectional view for explaining the method for manufacturing the nanoscale photocathode electron source of the present invention.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the illustrated examples. 1A and 1B are schematic views for explaining a nanoscale photocathode electron source of the present invention, FIG. 1A is a side sectional view, and FIG. 1B is a plan view of the periphery of the photocathode portion. .. As shown in the figure, the nanoscale photocathode electron source of the present invention capable of generating a highly coherent electron beam is mainly composed of a laser light source 10, a substrate 20, a transparent electrode layer 30, and a photocathode portion 40. There is. That is, the photocathode is composed of a substrate 20, a transparent electrode layer 30, and a photocathode portion 40.

The laser light source 10 is capable of irradiating a laser beam. The laser light source 10 may be such that photoelectrons are emitted from the photocathode unit 40 by irradiating the photocathode unit 40, which will be described later, with laser light. Specifically, the laser light source 10 may be any light source capable of outputting, for example, ultraviolet laser light or green laser light. The laser light source 10 may be a CW laser (continuous wave laser) or a pulse laser (mode-locking method, Q-switch method, etc.). Further, the laser light source 10 may be configured by a laser diode or the like.

The substrate 20 is transparent to the laser light from the laser light source 10. That is, for example, if the laser light of the laser light source 10 is an ultraviolet laser light, it may have a high transmittance for ultraviolet rays, and if the laser light is a green laser light, it has a high transmittance for green. If it is good. The substrate 20 may be, for example, a glass substrate. The glass substrate may be, for example, sapphire glass or quartz glass.

The transparent electrode layer 30 is made of a conductive material having transparency to the laser light from the laser light source 10. That is, for example, if the laser light of the laser light source 10 is an ultraviolet laser light, it may have a high transmittance for ultraviolet rays, and if the laser light is a green laser light, it has a high transmittance for green. If it is good. Further, the transparent electrode layer 30 is formed on a surface of the substrate 20 facing the surface on the side to be irradiated with the laser beam. That is, the transparent electrode layer 30 is formed on the back surface of the surface on which the laser beam is irradiated. The transparent electrode layer 30 may be formed on the substrate 20 with a film thickness of 125 nm, to give a specific example. Further, the transparent electrode layer 30 may be specifically, for example, ITO, ZnO, IGZO, or the like. Then, a predetermined voltage is applied to the transparent electrode layer 30.

The photocathode unit 40 is a nanoscale material made of a photocathode conversion material. The photocathode portion 40 is formed in the transparent electrode layer 30. Here, the nanoscale means that the portion that becomes the electron beam radiation surface has a nano size. For example, as shown in FIG. 1B, the photocathode portion 40 may have a nanoscale dot shape. Specifically, the photocathode portion 40 may have a cylindrical shape having a diameter of 30 to 500 nm. The thickness may be, for example, 5 to 40 nm. As described above, the diameter of the photocathode portion 40 used in the nanoscale photocathode electron source of the present invention is nano-sized below the laser wavelength. The shape of the photocathode portion 40 is not necessarily limited to a perfect circular cylinder as shown in the illustrated example, and may be any shape such as an elliptical shape or a square shape. The photocathode unit 40 may be made of, for example, Au, Ag, Cu, GaAs, CsTe, CsKSb, NEA-GaAs, or the like. Then, as shown in the illustrated example, the photocathode portion 40 may be provided so as to be flush with the surface of the transparent electrode layer 30 facing the surface on the side to be irradiated with the laser beam. That is, the transparent electrode layer 30 may be provided with a groove (hole) in which the photocathode portion 40 is embedded, and may be formed in the groove so that the surface of the photocathode portion 40 is exposed. As a result, since the side portion of the photocathode portion 40 is also covered with the transparent electrode layer 30, the emission of the electron beam from the side portion of the photocathode portion 40 is suppressed, and a higher coherent electron beam can be generated.

With the nanoscale photocathode electron source configured in this way, it is possible to configure the photocathode portion 40 having a diameter smaller than the irradiation diameter of the laser light from the laser light source 10. The laser light from the laser light source 10 passes through the substrate 20 and the transparent electrode layer 30 to excite the photocathode portion 40 and emit an electron beam. Therefore, it is possible to generate a highly coherent electron beam having substantially the same size as the photocathode portion 40. The electron beam current can be modulated by modulating the irradiation intensity of the laser light from the laser light source 10 or adjusting the voltage applied to the transparent electrode layer 30.

Here, the laser light source 10 may be focused so as to have an irradiation diameter as close as possible to the diameter of the dot shape of the photocathode portion 40. However, since the diameter of the laser beam of the laser light source 10 is limited to be reduced depending on the wavelength, it cannot be reduced to the size of the nanoscale photocathode portion 40. Therefore, the generated electron beam is emitted in a state where the laser light from the laser light source 10 is included. Regarding this, when it is necessary to suppress the influence of the laser light from the laser light source 10 depending on the application of the electron beam, the component of the laser light can be removed. That is, by providing a noise removing portion that takes the difference between when the photocathode portion 40 is irradiated with the laser beam and when the photocathode portion 40 is avoided and the laser beam transmitted through the substrate 20 and the transparent electrode layer 30 is irradiated. It is possible to subtract the components of the laser beam.

In the above illustrated example, an example is shown in which the photocathode portion 40 is embedded in the transparent electrode layer 30 so as to be flush with each other. However, the present invention is not limited to this. FIG. 2 is a schematic side sectional view for explaining another example of the nanoscale photocathode electron source of the present invention. In the figure, the parts having the same reference numerals as those in FIG. 1 represent the same objects. Only the periphery of the photocathode portion is shown. As shown in the figure, in this example, the photocathode portion 40 is formed on the surface of the transparent electrode layer 30. Even with such a configuration, electrons can be sufficiently supplied from the transparent electrode layer 30, and an electron beam having a diameter sufficiently smaller than that of the prior art can be generated.

Further, the photocathode portion 40 may reach the substrate 20. FIG. 3 is a schematic side sectional view for explaining still another example of the nanoscale photocathode electron source of the present invention. In the figure, the parts having the same reference numerals as those in FIG. 1 represent the same objects. Only the periphery of the photocathode portion is shown. As shown in the figure, in this example, the photocathode portion 40 is formed so as to penetrate the transparent electrode layer 30 and reach the surface of the substrate 20. Even with such a configuration, electrons can be sufficiently supplied from the transparent electrode layer 30, and an electron beam having a diameter sufficiently smaller than that of the prior art can be generated.

Here, the nanoscale photocathode electron source of the present invention is not limited to a dot shape as shown in FIG. 1 (b). FIG. 4 is a schematic plan view of the periphery of the photocathode portion for explaining another example of the photocathode portion of the nanoscale photocathode electron source of the present invention. In the figure, the parts having the same reference numerals as those in FIG. 1 represent the same objects. As shown in the figure, in this example, the photocathode portion 41 has a fine pattern rather than a dot shape. The line width of this fine pattern is nanoscale. The pattern in the illustrated example is just a pattern for explanation, and is not limited to this pattern. When the photocathode portion 41 having such a fine pattern is provided, the laser light source 10 may be configured to have an irradiation area capable of irradiating the entire fine pattern.

The nanoscale photocathode electron source of the present invention configured in this way can transfer a fine pattern to, for example, a predetermined target substrate by forming a photocathode portion composed of a nanoscale fine pattern. .. This makes it possible to easily form a nanoscale fine pattern on the target substrate.

Next, an example of a method for manufacturing the photocathode portion of the nanoscale photocathode electron source of the present invention will be described. The following manufacturing method is merely an example, and is not limited to this manufacturing method. As long as a similar structure can be manufactured, any conventional or future manufacturing method can be applied.

FIG. 5 is a schematic side sectional view for explaining the method for manufacturing the nanoscale photocathode electron source of the present invention, and FIGS. 5 (a) to 5 (g) are views in each process. In the figure, the parts having the same reference numerals as those in FIG. 1 represent the same objects. First, as shown in FIG. 5A, the substrate 20 is prepared, polished and washed. The substrate 20 is, for example, SiO ₂ . Then, as shown in FIG. 5B, a transparent electrode layer 30 is formed on the substrate 20 by a sputtering method. The transparent electrode layer 30 is, for example, ITO. Next, as shown in FIG. 5C, the transparent electrode layer 30 is coated with the acrylic resin layer 31 and heat-treated. The acrylic resin layer 31 is, for example, PMMA. Further, the coating treatment is carried out, for example, by dropping PMMA onto the substrate 20 and using a spin coater at 5000 rpm for 30 seconds. The heat treatment is performed at 180 degrees for 5 minutes, for example. Then, as shown in FIG. 5D, an aluminum layer 32 is formed on the acrylic resin layer 31 by a sputtering method. Next, as shown in FIG. 5 (e), a hole is drilled by a focused ion beam. Specifically, by irradiating an ion beam with gallium ions, a hole is formed which penetrates the aluminum layer 32 and the acrylic resin layer 31 and reaches the transparent electrode layer 30. In the illustrated example, a dot-shaped hole can be formed. This may be done by machining a groove with a fine pattern. Focused ion beams enable nanoscale fine drilling. Further, the depth of the hole may be adjusted so that the transparent electrode layer 30 is dug down by, for example, 5 to 40 nm so as to be the thickness of the photocathode portion 40 to be formed later. Then, as shown in FIG. 5 (f), a gold film 33 is formed on the aluminum layer 32 by a sputtering method. As a result, gold is also filled in the holes formed in the process of FIG. 5 (e). Finally, as shown in FIG. 5 (f), the acrylic resin layer 31, the aluminum layer 32, and the gold film 33 are peeled off by lift-off, and the photocathode portion 40 made of gold is formed in the hole formed in the transparent electrode layer 30. The formed nanoscale photocathode electron source is obtained.

The nanoscale photocathode electron source of the present invention is not limited to the above-mentioned illustrated examples, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

10 Laser light source 20 Substrate 30 Transparent electrode layer 31 Acrylic resin layer 32 Aluminum layer 33 Gold film 40, 41 Photocathode

Claims (8)

A nanoscale photocathode electron source capable of generating a highly coherent electron beam, the nanoscale photocathode electron source is
A laser light source that can irradiate laser light and
A substrate that is transparent to the laser light from the laser light source,
A transparent electrode layer made of a conductive material that is transparent to the laser light from the laser light source, formed on the surface of the substrate facing the surface on which the laser light is irradiated, and to which a predetermined voltage is applied. When,
A nanoscale photocathode portion formed on the transparent electrode layer and made of a photocathode material,
In order to suppress the influence of the laser beam from the laser light source, the difference between when the laser beam is irradiated to the optical cathode portion and when the laser beam which passes through the substrate and the transparent electrode layer is irradiated while avoiding the optical cathode portion is calculated. The noise remover to take and
A nanoscale photocathode electron source comprising. In the nanoscale photocathode electron source according to claim 1, the photocathode portion is embedded so as to be flush with the surface of the transparent electrode layer facing the surface on which the laser beam is irradiated. Nanoscale photocathode electron source. The nanoscale photocathode electron source according to claim 1 or 2, wherein the photocathode portion has a nanoscale dot shape in diameter. In the nanoscale photocathode electron source according to claim 3, the laser light source is configured to be focused so as to have an irradiation diameter as close as possible to the dot-shaped diameter of the photocathode portion. Nanoscale photocathode electron source. The nanoscale photocathode electron source according to claim 1 or 2, wherein the photocathode portion has a fine pattern having a line width of nanoscale. The nanoscale photocathode electron source according to claim 5, wherein the laser light source is configured to have an irradiation area capable of irradiating the entire fine pattern of the photocathode portion. .. The nanoscale photocathode electron source according to any one of claims 1 to 6 , wherein the photocathode portion is any one of Au, Ag, Cu, GaAs, CsTe, CsKSb, and NEA-GaAs. Nanoscale photocathode electron source. The nanoscale photocathode electron source according to any one of claims 1 to 7 , wherein the transparent electrode layer is any of ITO, ZnO, and IGZO.

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