JP3569747B2 - Cooled high-quantum-efficiency photocathode-type electron beam source, its fabrication method, laser beam irradiation method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The invention of this application relates to a cooling type high quantum efficiency photocathode type electron beam source and a method for manufacturing the same. More specifically, the invention of this application relates to a cooled high quantum efficiency photocathode electron beam source useful as an electron beam source for an electron microscope, an electron beam accelerator, and an X-ray generator, and a method of manufacturing the same.
[0002]
[Prior art and its problems]
Conventionally, a field emission type electron beam source and a thermionic emission type electron beam source have been generally used as an electron beam source for an electron microscope, an electron beam accelerator, an X-ray generator, etc. Radiation sources are used today in various fields as the brightest electron beam sources. However, even in an electron microscope equipped with a field emission type electron beam source which is the highest brightness electron beam source, the total current of electrons actually emitted is only about 1 μA.
[0003]
When using an electron beam source for an electron microscope, D.E. In order to achieve the effect of "improving the resolution of electron microscopes that can only use a convex lens using electron beam holography" devised by Gabor, it is important to avoid aberrations. In the case of an electron beam source, the number of emitted electrons is small, and the electrons are emitted in all directions perpendicular to the surface of the tip of the cathode. In order to make the electron beam as thin as possible, it is necessary to stop down the electron beam with an electrostatic acceleration lens, and at that time, aberration occurs. Therefore, if a field emission type electron beam source is used as the electron beam source for the electron microscope, the above-mentioned D.E. There is a limit to the effect of improving the resolution by electron beam holography devised by Gabor, and at present, the field emission type electron beam source has been improved only up to about twice since the beginning of practical use. Furthermore, in the field emission type electron beam source, since the total current of the emitted electrons is only about 1 μA, it cannot be expected that the brightness thereof will be dramatically increased in the future. Therefore, there is a need for a new electron beam source that replaces the field emission electron beam source and has extremely high brightness and almost no aberration.
[0004]
Therefore, a photocathode type electron beam source is mentioned as a new electron beam source. The photocathode electron beam source utilizes the photoelectric effect, and is used as an electron beam source by irradiating laser or other light to the cathode whose tip is coated with a material with high quantum efficiency and emitting photoelectrons. can do. For example, a continuous-wave (CW) laser having a wavelength of 488 nm and an output of 1 W is considered to have a quantum efficiency (number of electrons emitted from a material surface by 100 photons (expressed in%)) of 7 to 8% at 488 nm. High Cs₃When Sb is irradiated, as many as 28 to 32 mA of electrons are emitted.
[0005]
This is an electron emission amount that is about 30,000 times larger than that of the field emission type electron beam source, and the photocathode type electron beam source has much higher brightness than the field emission type electron beam source and has almost no aberration. May be a source.
[0006]
Therefore, using a photocathode-type electron beam source in an electron microscope not only improves the brightness of the electron beam and dramatically improves its resolution, but also improves the coherent electron beam diffraction, the positional accuracy of elemental analysis, and the observation of magnetic flux. This leads to improved accuracy and the like. In addition, a photocathode electron beam source having high luminance, having almost no aberration, and having a small energy width in principle may significantly improve various performances of an electron beam accelerator and an X-ray generator. Also, the much higher brightness of the electron beam can lead to unexpected scientific progress.
[0007]
However, the most important element in the photocathode type electron beam source is Cs₃It is known that a substance having high quantum efficiency represented by Sb is chemically very active, and its quantum efficiency decreases with time when it reacts with a trace amount of oxygen. This tendency is accelerated as the temperature of the high quantum efficiency material increases.
[0008]
For this reason, Cs₃Sb, Na₂KSb, Rb₃Materials having high quantum efficiency with respect to visible light, such as Sb and CsI, have been used by vacuum-encapsulating them in glass tubes and irradiating with weak light so that the temperature does not rise. The conventional photocathode-type electron beam source coated does not have a sufficient total current of emitted electrons, has a reduced brightness, and can be used only in a glass tube.
[0009]
Therefore, the invention of this application has been made in view of the circumstances described above, and solves the problems of the prior art, has high luminance, has little aberration, and can be used practically with a cooling type high quantum efficiency photo-sensor. It is an object to provide a cathode-type electron beam source.
[0010]
[Means for Solving the Problems]
The invention of this application solves the above-mentioned problems. First, a cooled photocathode-type electron beam in which laser light is irradiated on a cathode having a tip coated with a substance having high quantum efficiency. SourceIt has a cathode made by joining a combination of materials with high Peltier cooling efficiency, and by passing current through this cathode, the interface of the combination of materials with high Peltier cooling efficiency is cooled and the tip of the cathode is locally cooled.A cooling type high quantum efficiency photocathode type electron beam source characterized by the above features.
[0011]
Second,N-type semiconductor and p-type semiconductor are the materials of the combination with high Peltier cooling efficiencyA cooling type high quantum efficiency photocathode type electron beam source characterized by the above features.
[0012]
Third,A cathode unit that joins the cathode with a cathode substrate having high electrical and thermal conductivity is mechanically loaded, and the block with high electrical and thermal conductivity is cooled by the heat absorbing surface of the Peltier cooling module with which it contacts. Characterized byProvided is a cooled high quantum efficiency photocathode type electron beam source.
[0013]
Fourth, the invention of this application is:The heating surface of the Peltier cooling module is cooled by a metal plate that circulates a highly electrically insulating liquid inside.Provided is a cooled high quantum efficiency photocathode type electron beam source.
[0014]
Fifth,The tip of the sharply pointed cathode, which includes a surface that has been processed to have a concave shape so that the emitted electrons are converged to enhance brightness by converging the emitted electrons, is made of a metal that is resistant to pickling. It is characterized by being plated and further coated with a high quantum efficiency materialProvided is a cooled high quantum efficiency photocathode type electron beam source.
[0015]
Sixth, a laser beam is applied to the cathode by an optical fiber, the tip of the optical fiber is rounded, and a mini convex lens is attached to the tip of the optical fiber. Efficient photocathode electron beam sourceLaser irradiation methodAlso provide.
[0016]
Seventh, the tip of the cathode is observed with an industrial endoscope that can remotely control the position of the cathode with an XYZ precision stage. Cooled high quantum efficiency photocathode-type electron beam source that accurately irradiates the position of the cathode tipLaser irradiation methodI will provide a.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
The cooled high quantum efficiency photocathode electron beam source according to the invention of this application is a cooled photocathode electron beam source in which laser light is irradiated to a cathode having a tip coated with a material having high quantum efficiency. Thus, in a cooled photocathode electron beam source having a cathode unit in which a cathode is joined to a cathode substrate having high electric conductivity and high heat conductivity, the cooling photocathode electron beam source main body and the atmosphere are of ultra-high purity. The cathode unit is removed from the sealed container in which the cathode unit, which has been turned into an active gas, is enclosed in the same atmosphere as the inside of the sealed container, and the work cover in the inert gas with the glove to be loaded into the electron beam source body is removed. The cathode unit can be loaded into the electron beam source main body without exposing the high quantum efficiency substance to oxygen because it is connected and integrated as much as possible. In addition, the above-mentioned cover for working in an inert gas has a high air-tightness to the extent that the original purity of the ultra-high-purity inert gas enclosed by the cover during use is not impaired.
[0018]
In addition, in a coating apparatus in which a working cover in an inert gas with gloves as described above is attached, a high quantum efficiency material is coated on the cathode tip of the cathode unit in a vacuum state, and then evacuated by a valve operation. Was stopped, and the inside of the coating apparatus and the inside of the inert gas working cover which had been evacuated in advance were filled with an ultra-high purity inert gas so that the gloves of the inert gas working cover could be used. Later, the entire cathode unit is confined in an airtight container using a glove together with ultra-high-purity inert gas, and the airtight container is taken out of the coating device, whereby the high quantum efficiency material can be taken out of the coating device without being exposed to oxygen. Then, the cathode unit and the ultra-high height are installed inside the gloved working cover in inert gas attached to the vacuum device having the electron beam source body. After inserting the hermetically sealed container containing the inert gas through the inlet and outlet, the outlet is closed, and the inside of the vacuum device and the working cover in the inert gas is evacuated, and then the ultra-high purity inert gas is used. Expose the high quantum efficiency material to oxygen by filling, removing the entire cathode unit from the sealed container using gloves, and further loading the entire cathode unit into the electron beam source body inside the vacuum device using gloves. And can be loaded into an electron beam source.
[0019]
In other words, since the high quantum efficiency material is not exposed to oxygen consistently from the process of coating the high quantum efficiency material on the cathode tip to the process of loading the cathode unit into the electron beam source, the quantum efficiency of the high quantum efficiency material is reduced. It can prevent the drop.
[0020]
Further, the cooled high quantum efficiency photocathode type electron beam source of the present invention has a cathode formed by bonding a combination of materials having high Peltier cooling efficiency by soldering, and applying a current to the cathode to perform Peltier cooling. Since the interface of the highly efficient combination of materials is cooled and the tip of the cathode is locally cooled, it is possible to prevent the quantum efficiency of the high quantum efficiency material coated on the cathode from decreasing with time. At this time, an n-type semiconductor and a p-type semiconductor can be used as a combination of substances having high Peltier cooling efficiency.
[0021]
In addition, a block having high electric conductivity and heat conductivity, in which a cathode unit in which a cathode is joined to a cathode base having high electric conductivity and heat conductivity is mechanically mounted, is a heat absorbing surface of a Peltier cooling module with which the block contacts. In addition, the heat generation surface of the Peltier cooling module is further cooled by a metal plate that circulates a liquid having high electrical insulation inside, thereby further preventing a decrease in quantum efficiency.
[0022]
Also, the tip of the cathode is sharpened sharply to prevent a decrease in the amount of emitted electrons due to the space charge effect, and the emitted electrons are converged by forming a concave surface at the tip of the cathode so that the brightness is further increased. To In addition, the tip of the cathode is plated with a metal that is resistant to pickling, and then coated with a high quantum efficiency material, so that when the quantum efficiency of the high quantum efficiency material decreases using the cathode, the cathode By washing the tip with acid, it is possible to remove the high quantum efficiency material without damaging the cathode tip, so that the removal and coating of the high quantum efficiency material can be repeated as many times as possible, and the cathode can be recycled. Become.
[0023]
Gold is an example of a metal that is resistant to pickling. However, since it is difficult to plate gold directly on the tip of the cathode, it is preferable to plate gold after plating nickel.
[0024]
In addition, by irradiating the laser beam to the cathode with an optical fiber, it is possible to avoid the danger of blindness due to a high-power laser, and furthermore, the laser beam emitted from one laser generator is separated by a beam splitter. By splitting into a plurality of laser beams, a plurality of photocathode-type electron beam sources can be irradiated with the laser beams.
[0025]
In addition, by changing the angle of the polarization plane of the two polarizing plates by remote control, the intensity of the laser beam applied to the cathode can be continuously changed from zero.
[0026]
Observe the cathode tip with an industrial endoscope that can remotely control its position with an XYZ precision stage, and remotely control the XYZ precision stage equipped with an optical fiber while watching the TV monitor to accurately position the laser beam at the position of the cathode tip. Can be irradiated. After the setting of the irradiation position of the laser beam, the industrial endoscope can be evacuated to a position that does not cause a discharge when emitting electrons.
[0027]
In addition, the mini-convex lens is attached to the tip of the optical fiber after processing the tip of the optical fiber, so that it is possible to converge the laser light more distantly, and the diameter of the electron beam emitted by the photoelectric effect. Can be made smaller and its brightness can be made higher.
[0028]
Hereinafter, embodiments will be described with reference to the accompanying drawings, and embodiments of the present invention will be described in more detail. Of course, the present invention is not limited to the following examples, and it goes without saying that various aspects are possible in detail.
[0029]
【Example】
As shown in FIG. 1, in the cooled high quantum efficiency photocathode electron beam source of this example, a vacuum device (1) having a cooled photocathode electron beam source body, an atmosphere of ultra-high purity argon gas and Then, the cathode unit (3) in which the cathode unit (2) is confined as shown in FIG. 3 is removed from the cathode unit (3) in the same ultra-high purity argon gas atmosphere as in the cathode unit (3). 2) A work cover (5) with a glove (4) and an inert gas working space to be taken out and loaded into the electron beam source body is detachably connected and integrated.
[0030]
This cooling type high quantum efficiency photocathode type electron beam source and a coating device (6) equipped with a work cover (5) in an inert gas similar to the above are used to attach Cs to the tip of the cathode.₃Between the step of coating Sb and the step of loading the cathode unit (2) into the body of the electron beam source, Cs which is a high quantum efficiency material is used.₃A method for preventing Sb from being exposed to oxygen will be described.
[0031]
As shown in FIG. 1A, the high quantum efficiency material Cs₃An inert gas working cover (5) is detachably attached to the coating device (6) for coating the Sb on the cathode tip in advance, and the inside of the cover is detached using an oil diffusion pump or the like. 1 × 10^-2A vacuum of about Pa is kept.
[0032]
Here, the cover (5) for working in an inert gas is a durable one made of vinyl chloride, and is welded for bonding between vinyls, bonded with THF (tetrahydrafuran), and a commercially available special adhesive ( Super X) was used. The cover (5) for working in an inert gas is provided with a glove (4) as shown in detail in FIG. 2, and the glove (4) is fitted to a finger so that fine work can be performed. Commercial work gloves were used. Further, a soft O-ring made of vinyl chloride was specially prepared, and this was bonded to a vinyl sheet using THF. At present, when the inside of the cover (5) for working in an inert gas is evacuated by two steps using an oil diffusion pump and an oil rotary pump, the degree of vacuum in the cover is about 5 × 10^-3Pa (~ 3.8 × 10^-5(Torr), the working cover (5) in inert gas is airtight.
[0033]
This is to such an extent that the produced work cover in inert gas (5) does not impair the original purity of the ultra-high-purity argon gas (purity 99.9999% in the market) enclosed by the use of the cover in use. It is a degree of vacuum that guarantees high airtightness.
[0034]
The cover (5) for working in an inert gas is for a "special coating device" for coating a high quantum efficiency material on the tip of the cathode by vacuum deposition, and for a "photocathode type electron beam source test device". And "for a 120 kV electron microscope equipped with a photocathode-type electron beam source".
[0035]
Furthermore, Cs is applied to the cathode tip by vacuum evaporation.₃After coating with Sb, the vacuum exhaust valve (7) in the coating device (6) is closed, and then ultra-high purity argon gas is supplied until the pressure reaches atmospheric pressure. At the same time, the evacuation of the working cover (5) in the inert gas is stopped, and the ultrahigh-purity argon gas is supplied to atmospheric pressure by operating the valve.
[0036]
After that, the vacuum flange (9) is raised using the handle (8) and the cover (5) for working in an inert gas is expanded so that the state shown in FIG. Thereafter, the user puts his hand into the glove (4) attached to the working cover (5) in an inert gas, and as shown in FIG.₃The cathode unit (2) coated with Sb is put in the cathode unit closed container (3) which has been placed in the coating device (6) in advance, and the sealing O-ring (10) is tightened with the thumb screw (11). Thus, the cathode unit closed container (3) in which the cathode unit (2) is confined with the ultra-high purity argon gas is put into the inner pocket (12).
[0037]
Thereafter, the cathode unit closed container access port (13) is opened to take out the cathode unit closed container (3). Next, the cathode unit closed container (3) containing the cathode unit (2) is detachably attached to the vacuum apparatus (1) having the electron beam source in the state of FIG. 1 (A). The cathode unit is inserted into the inside pocket (12) of the active gas working cover (5) through the inlet / outlet (13) of the closed casing of the cathode unit.
[0038]
After the cover (14) of the cathode unit closed container inlet / outlet (13) is tightened with an O-ring as shown in FIG. 2, the inside of the cover (5) for working in an inert gas is opened using an oil diffusion pump or the like. Evacuate. 1 × 10^-2After a high degree of vacuum of Pa or less is obtained, an ultrahigh-purity argon gas is introduced into the working cover (5) in an inert gas until the atmospheric pressure is reached. At the same time, the vacuum evacuation valve (7) of the vacuum apparatus (1) having the electron beam source which has been evacuated to a high vacuum is closed, and ultra-high purity argon gas is introduced to atmospheric pressure.
[0039]
Thereafter, the vacuum flange (9) is raised so that the state shown in FIG. 1 (B) is reached, the work cover (5) in the inert gas is spread, and the cathode is closed from the cathode unit closed container (3) using the glove (4). Take out the unit (2). The cathode unit (2) is loaded into the electron beam source with the empty cathode unit closed container (3) kept in the inner pocket (12). After the charging, the vacuum flange (9) is lowered while gradually evacuating the ultra-high purity argon gas, and the state shown in FIG. Thereafter, the vacuum device (1) having an electron beam source is evacuated in earnest. In addition, the cathode unit closed container inlet / outlet (13) is opened, and the empty closed container (3) is taken out.
[0040]
By doing so, Cs₃After Sb is coated on the cathode tip in a vacuum, it can be taken out of the coating device (6) without exposure to oxygen, and can be further loaded into a vacuum device (1) having an electron beam source.₃Since Sb does not react with oxygen, Cs₃A decrease in the quantum efficiency of Sb can be prevented.
[0041]
Thereafter, a laser beam having a wavelength of 488 nm was irradiated while cooling the tip of the cathode, and an electron dose was measured using a Faraday cup in the apparatus, and emission of almost expected amount of photoelectrons was confirmed.
[0042]
As shown in FIG. 2, the cover for work in inert gas (5) is formed by digging a groove for an O-ring in the circumferential direction of the upper and lower vacuum flanges (9) and welding to the cover (5). The upper and lower O-rings are inserted and the hermeticity is maintained by using a ring-shaped O-ring fastening tool (9 ') from the outside.
[0043]
FIG. 4A shows a state in which the cathode (16) is irradiated with the argon ion laser beam (15). The cathode (16) is placed in the electron beam source as a cathode unit (2) as shown in FIG.
[0044]
As a combination of materials having high Peltier cooling efficiency used as the cathode (16), n-type Bi having an impurity amount of 0.2 appm is used.₂Te₃And p-type Bi₂Te₃Were prepared by a melting method, crushed into powder, placed in a quartz tube, vacuum-sealed in a thick quartz tube, and melt-molded into a cylindrical shape having a diameter of 2 mm.
[0045]
FIG. 6 shows the tip of the cathode, and as shown in FIG. 6B, the cathode (16) is an n-type semiconductor Bi.₂Te₃(17) and p-type semiconductor Bi₂Te₃(18) is joined by solder having a melting point of 215 to 221 ° C. so as to reduce the contact resistance, and the cathode tip is used to prevent a reduction in the amount of electrons emitted from the cathode tip (19) due to the space charge effect. It is manufactured so that (19) is sharply pointed.
[0046]
Further, soldering (melting point: 177 to 183 ° C.) was performed to join the cathode (16) to the copper cathode base (20).
[0047]
6B, that is, the n-type semiconductor Bi.₂Te₃(17) From p-type semiconductor Bi₂Te₃When an electric current is caused to flow toward (18), heat absorption occurs at the joint surface due to the Peltier effect. N-type semiconductor Bi₂Te₃(17) and p-type semiconductor Bi₂Te₃Heat is generated at the joint surface of the copper cathode substrate (20) having high thermal conductivity and high electrical conductivity, which is joined by soldering (18) to reduce the contact resistance.
[0048]
The amount of heat absorbed is determined by the n-type semiconductor Bi.₂Te₃(17) and p-type semiconductor Bi₂Te₃In the case of (18), if the doping amount is optimal, the current is 0.112 W per 1 A, and if a current of 10 A flows, the heat absorption is 1.12 W (the contact resistance of the soldered joint and the contact resistance). The current value with the highest cooling efficiency is determined by the competition with Joule heat caused by the electric resistance of the semiconductor itself).
[0049]
If the contact resistance between the two joining surfaces by soldering is sufficiently small, the smaller the area of the joining surface, the lower the temperature of the cathode tip portion (19). Polishing of the cathode tip (19) after bonding is performed so that the cathode tip (19) coincides with the bonding surface. As shown in FIG. 6B, in order to supplement the strength of the bonding surface by soldering and to prevent damage to the bonding surface and increase in contact resistance when the cathode tip (19) is polished, as shown in FIG. The object (21) is adhered.
[0050]
Further, as shown in FIG. 6C, the tip of the cathode (16) is slightly concave. By doing so, the photoelectrons emitted from the tip surface of the cathode (16) by the photoelectric effect travel perpendicular to the electric field, so that the crossover position of the electrons (a little from the cathode to the anode side) can be achieved even if the laser light is not extremely small. (A position distant from) can be made sufficiently thin without being affected by aberration.
[0051]
At the cathode tip (19), a high quantum efficiency material, Cs, is directly applied to the cathode tip (19).₃Although Sb (22) may be coated, in this example, electroless plating is performed in the order of nickel (23) and gold (24), and Cs is further formed thereon.₃It is coated with Sb (22). By doing so, the cathode tip (19) can be washed with acid to prevent the cathode tip (19) from being damaged.₃Sb (22) can be removed, and Cs can be removed many times.₃The coating and removal of Sb (22) can be repeated, and the cathode (16) can be recycled.
[0052]
As shown in FIG. 5, the contact portion (25) of the cathode unit (2), the surface of which is plated with gold, is mounted on the cylindrical portion (27) of the copper electrode block (26) of the electron beam source. The surface of the cylindrical portion (27) is plated with gold, and the cylindrical portion (27) is cut with a spring.
[0053]
The copper electrode block (26) is adapted to allow current to flow, and can be cooled by contacting the cooling surfaces of two commercially available Peltier cooling modules (28). Further, the heating surface of the commercially available Peltier cooling module (28) is cooled by contacting the metal plate (30) (in this case, an aluminum plate) to be cooled by circulating the electrically insulating oil (29). The reason for using the electrically insulating oil (29) is that a high voltage is applied between the cathode (16) and the ground. The electrically insulating oil (29) is cooled and circulated by a commercially available liquid cooling / circulating device (not shown). Most of the piping through which the electrically insulating oil (29) flows is also made of an electrical insulator [Teflon (registered trademark)] or the like.
[0054]
As described above, the electrode itself to which the cathode unit (2) was attached was cooled to cool the cathode (16), and the cathode tip (19) was locally cooled. This time, cooling experiments were performed using a "photocathode-type electron beam source test device" and a "non-vacuum cathode cooling test device". Since the diffusion of heat is smaller in a vacuum than in a non-vacuum, it is possible to cool more. As a result, the temperature of the cathode tip (19) can be cooled to -10 to 30 ° C.
[0055]
In Peltier cooling, heat is transferred by electric current, and the speed of heat removal is much faster than that of heat conduction. The heat entering the cathode tip (19) is almost instantaneously removed by laser irradiation, and cooling efficiency is improved. It is possible to prevent a decrease in quantum efficiency of a high quantum efficiency material. Even when the tip of the cathode (19) was actually irradiated with 0.1 W of laser light focused to 0.3 mm in diameter, the temperature rise was 5 ° C. or less.
[0056]
The cooling temperature depends on the temperature and circulation speed of the electrically insulating oil, the cooling power of the commercially available Peltier cooling module, the heat capacity of the cathode mounting block, and the Peltier cooling capacity of the n-type semiconductor and the p-type semiconductor pair. If the selection is made, the temperature of the tip of the cathode irradiated with the laser can be further reduced.
[0057]
Next, the improvement in irradiating the laser beam to the electron beam source will be described in detail.
[0058]
FIG. 7 shows a case where an argon ion laser beam (32) emitted from one CW (continuously) oscillating argon ion laser oscillator (31) (maximum output at a wavelength of 488 nm: about 5 W) is converted into a laser branch concentrator. (33) and an optical fiber (34) are shown leading to a plurality of electron beam sources such as an electron beam accelerator (35), an X-ray generator (36), and an electron microscope (37).
[0059]
FIG. 8 shows the inside of the laser splitter / condenser (33). The argon ion laser beam (32) can be split into two when the laser beam passes, as shown in FIG. And a plurality of reflection mirrors (39), the beam can be branched into a required number (eight in the figure) of laser beams. Therefore, one argon ion laser oscillation device (31) can be shared by a plurality of electron beam sources. Since the oscillation of the commercially available CW laser oscillation argon ion laser oscillation device (31) is about 10 W, even if the laser light is divided into に and used, the laser beam of sufficient intensity is used for the electron beam source. Since irradiation can be performed, one office can share an expensive laser oscillation device, which is extremely economical.
[0060]
The split laser light is opened and closed by each stopper (40) as needed by a remote control device in a room where each electron beam source is installed. Each branched laser beam is guided into each optical fiber (34) by a convex lens (41).
[0061]
As shown in FIG. 9, the branched laser light is passed through two commercially available heat-resistant polarizing plates (42), and one of the polarizing plates (42) is electrically rotated. The intensity of each branched laser beam can be changed almost continuously from 0 by rotating it by remote control using a stage to be made. The laser light whose intensity was changed was made incident on an optical fiber (34) (core diameter: 50 μm) fixed to an optical fiber holder (43) using a convex lens (41). An optical fiber connector (44) is provided between them, and a photocathode electron beam source test device (accelerates photoelectrons at a voltage of 7 kV at maximum) using an optical fiber (34), and a 120 kV electron microscope equipped with a photocathode electron beam source , And the cathode tip (19) of the "non-vacuum cathode cooling experimental device" can be simultaneously irradiated with laser.
[0062]
In the "photocathode electron beam source test apparatus" and the "120 kV electron microscope equipped with a photocathode electron beam source", as shown in FIG. 4, a metal pipe (45) to which an optical fiber (34) is fixed is used. And an industrial endoscope (46) were mounted on a motorized XYZ precision stage (47), so that its axis could be adjusted remotely by watching a TV monitor (not shown).
[0063]
In the former device (test device), the motorized XYZ precision stage (47) was put in a vacuum device, and in the latter device (electron microscope), the motorized XYZ precision stage (47) was put out of the vacuum device.
[0064]
When the electric XYZ precision stage (47) is placed in a vacuum device, the optical fiber (34), the metal pipe (45), and the cable of the industrial endoscope (46) are vacuum-sealed with an ultra seal using a small O-ring. . When the electric XYZ precision stage (47) is taken out of the vacuum apparatus, an ultra-seal is attached to the metal pipe (45) (stainless steel pipe) containing the optical fiber (34) and the hard industrial endoscope (46). And maintain a high vacuum.
[0065]
In each case, the vacuum seal by the Ultra Tall seal is perfect, and a high degree of vacuum is obtained. In an electron microscope, the tip of the optical fiber needs to be separated from the tip of the cathode by a certain distance (currently, 50 mm in the case of a 120 kV electron microscope) so that no discharge occurs. As shown in FIG. 2 (B), as compared with the case where the tip of the optical fiber is flattened and a mini-convex lens having a diameter of 3 mm or less is adhered to a metal pipe to condense light, as shown in FIG. The laser light can be condensed smaller if the tip of the lens is rounded to a suitable radius of curvature using a micro burner and then condensed by the mini convex lens (48).
[0066]
For example, when a mini convex lens having a focal length of 1.6 mm is used, the minimum beam diameter of the laser beam at a distance of 50 mm ahead is 1.48 mm when the tip of the optical fiber (the diameter of the core portion is 50 μm) is smooth. On the other hand, when the radius of curvature R was rounded to 60 μm, the radius was 1.1 mm. The minimum beam diameter of the laser beam at a distance of 50 mm ahead using a mini convex lens having a focal length of 2.5 mm is 1.05 mm when the tip of the optical fiber is smooth, whereas the radius of curvature R = It was 0.825 mm when the spherical tip was processed to 60 μm.
[0067]
When an optical fiber is not used, the risk of blindness caused by direct exposure to the laser light is likely to occur.However, by irradiating the laser to the photocathode electron beam source using the optical fiber as described above, the laser light can be directly observed. Can be prevented from being blinded, and safety is ensured. Another great advantage is that the photocathode type electron beam source can be manufactured at lower cost.
[0068]
【The invention's effect】
As described above in detail, the invention of this application is useful as an electron beam source such as an electron microscope, an electron beam accelerator, and an electron beam source for an X-ray generator, and has high luminance, little aberration, and high safety. A cooled high quantum efficiency photocathode electron beam source and its fabrication method are provided, and the research on materials, physical properties, basic physics, etc. is progressing by improving the performance of electron microscopes, electron beam accelerators, X-ray generators, etc. For example, an economic effect comparable to the invention of laser in light is expected.
[Brief description of the drawings]
FIG. 1 is a view showing a process for producing a cooled high quantum efficiency photocathode type electron beam source of the present invention.
FIG. 2 is a diagram showing a work cover in an inert gas used for producing a cooled high quantum efficiency photocathode electron beam source of the present invention in detail.
FIG. 3 is a view showing a step of confining a cathode unit of the cooled high quantum efficiency photocathode type electron beam source of the present invention in an airtight container.
FIG. 4 is a diagram exemplifying a state in which a cooled high quantum efficiency photocathode type electron beam source of the present invention is irradiated with laser light.
FIG. 5 is a view showing a cooling mechanism of a cathode portion of the cooling type high quantum efficiency photocathode type electron beam source of the present invention.
FIG. 6 is a diagram showing a cathode tip portion of a cooled high quantum efficiency photocathode electron beam source according to the present invention.
FIG. 7 is a diagram illustrating an example in which a plurality of cooled high quantum efficiency photocathode electron beam sources are irradiated with laser light from a laser oscillation device.
FIG. 8 is a diagram illustrating a state in which a laser beam from a laser oscillation device is split into a plurality of laser beams by a beam splitter.
FIG. 9 is a diagram illustrating a state in which the intensity of laser light is adjusted using two polarizing plates.
[Explanation of symbols]
1 vacuum equipment
2 Cathode unit
3 Cathode unit sealed container
4 gloves
5 Work cover in inert gas
6 Coating equipment
7 Evacuation valve
8 Flange hoisting handle
9 Vacuum flange
9 'O-ring fastening tool
10 O-ring for sealing
11 Thumbscrews
12 inside pockets
13 Cathode unit closed container access
14 Lid
15 Argon ion laser light
16 Cathode
17 n-type semiconductor Bi₂Te₃
18 p-type semiconductor Bi₂Te₃
19 Cathode tip
20 Cathode base
21 Insulation for reinforcement
22 Cs₃Sb
23 Nickel
24 Fri
25 Contact part
26 electrode block
27 cylinder
28 Peltier cooling module
29 Electrically insulating oil
30 metal plate
31 Argon ion laser oscillator
32 Argon ion laser light
33 Laser Branch Concentrator
34 Optical Fiber
35 electron beam accelerator
36 X-ray generator
37 Electron microscope
38 Beam splitter
39 Reflection mirror
40 Stopper
41 convex lens
42 Polarizing plate
43 Optical fiber holder
44 Optical fiber connector
45 metal pipe
46 Industrial endoscope
47 Electric XYZ precision stage
48 mini convex lens

Claims (7)

A cooled photocathode-type electron beam source irradiated with laser light to a cathode coated with a material with a high quantum efficiency at the tip, and a cathode made by bonding a combination of materials with high Peltier cooling efficiency A cooled high quantum efficiency photocathode electron beam source characterized in that a current flows through the cathode to cool the interface of a combination of materials having high Peltier cooling efficiency and locally cool the tip of the cathode. 2. The cooled high quantum efficiency photocathode electron beam source according to claim 1, wherein the combination of materials having high Peltier cooling efficiency is an n-type semiconductor and a p-type semiconductor. A cathode unit that joins the cathode with a cathode substrate having high electrical and thermal conductivity is mechanically loaded, and the block with high electrical and thermal conductivity is cooled by the heat absorbing surface of the Peltier cooling module with which it contacts. 3. The cooled high quantum efficiency photocathode type electron beam source according to claim 1, wherein: 4. The cooled high quantum efficiency photocathode electron beam source according to claim 3, wherein the heat generating surface of the Peltier cooling module is cooled by a metal plate for circulating a liquid having a high electrical insulation property. The tip of the sharply pointed cathode, which includes a surface that has been processed to have a concave shape so that the emitted electrons are converged to enhance brightness by converging the emitted electrons, is made of a metal that is resistant to pickling. 5. The cooled high quantum efficiency photocathode type electron beam source according to claim 1, wherein plating is performed, and a high quantum efficiency material is coated thereon. 6. A cooling height according to any one of claims 1 to 5, wherein a laser beam is applied to the cathode by an optical fiber, a tip of the optical fiber is rounded, and a mini convex lens is attached to the tip of the optical fiber. Laser irradiation method for quantum efficiency photocathode electron beam source. Observe the tip of the cathode with an industrial endoscope that can remotely control its position with an XYZ precision stage, and remotely control the XYZ precision stage with the attached optical fiber while watching the TV monitor, and place the laser beam at the position of the cathode tip. 7. The laser beam irradiation method for a cooled high quantum efficiency photocathode electron beam source according to claim 6, wherein the irradiation is performed accurately.

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