JP2013134874A - Filament and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a filament, in which welding of filament strands having a small radius of curvature and serving as a high luminance electron beam source and a diameter reducing process of a thermionic emission part can be simply performed by a single welding work.SOLUTION: The problem can be solved using a filament 11. The filament has two strands 23, 24 and a diameter reduced toward a tip 21a thereof. The tip 21a has a radius of curvature rof 100 μm or less, and the materials of the two strands 23, 24 is the same metal or alloy.

Description

The present invention relates to a filament and a manufacturing method thereof. In particular, a thermoelectron emission type filament having a small radius of curvature of a thermoelectron emission portion and a large thermoelectron emission current density, which is made by utilizing a phenomenon that a liquid forms a conical tailor cone by a high electric field, and one time The present invention relates to a production method that can be easily produced by welding.

Tungsten hairpin filaments are thermionic emission filaments that are formed simply by bending a thin wire and can be easily manufactured. Therefore, the tungsten hairpin filament is economical and is most often used as an electron beam source in a scanning electron microscope (SEM).

FIG. 1 is a schematic view showing an example of a trajectory of thermoelectrons emitted from a tungsten hairpin filament when this tungsten hairpin filament is used as an electron beam source of a scanning electron microscope.
The thermoelectrons jumping out of the tungsten hairpin filament 150 bent in a U shape are once focused under the Wehnelt by the electrostatic lens effect due to the bias voltage of the Wehnelt 152 and then spread at an opening angle α. The electron beam is not completely focused on one point, but has a certain extent. The most focused point is called a crossover point 153 and becomes a light source in electron optics. Crossover point 153 is represented by a circle of the focusing radius _{r c.} The region near the tip of the tungsten hairpin filament 150 that can be seen from the crossover point 153 (hereinafter, the tip) is the thermal electron emission range.
The luminance B at the crossover point is expressed by the following equation (1) as a function of the current density I per unit solid angle.

The opening angle α is a function of the radius of curvature r ₀ of the tip of the tungsten hairpin filament 150 and the distance f from the center of curvature of the tip to the crossover point, and is expressed by the following equation (2).

The current density I is determined only by the filament material and operating temperature, according to the Richardson-Dushman equation.
From the above, it can be seen that in order to increase the luminance B, the radius of curvature r ₀ at the tip should be decreased. When the curvature radius r ₀ of the tip is reduced, also reduced focusing radius r _c of the cross-over point, the resulting luminance B come approximated bright becomes point light source is observed at high magnification becomes possible.
In addition, when the tungsten hairpin filament 150 is bent into a V shape, the resistance at the bent portion increases and local overheating occurs, so that there is a problem that the life of the filament is shortened in bending.

For this reason, various other filaments have been proposed in order to increase the luminance B (Patent Document 1).
FIG. 2 is a conventional example of another filament.
The filament 161 shown in FIG. 2 (a) is an example of a point filament, and machined surfaces 155a and 155b are formed by machining or electrolytic polishing at the tip of the tungsten hairpin filament shown in FIG. However, the tip is sharpened and the radius of curvature is reduced.

Further, the filament 162 shown in FIG. 2B is an example of a sharpened filament, and the tungsten hairpin filament shown in FIG. 1 has another processed surface by machining, electrolytic polishing, or the like. 156a is formed, the tip is sharpened, and the radius of curvature is reduced.

  Furthermore, the filament 163 shown in FIG. 2 (c) is an example of a semi-point filament. After the needle-like member 157 is welded to the tip of the tungsten hairpin filament shown in FIG. It is processed by polishing so that the tip of the needle-like member 157 is sharpened to reduce the radius of curvature.

Moreover, the related art of these conventional examples is described in Japanese Patent Application No. 2011-105592 and the nonpatent literature 1, for example. Japanese Patent Application No. 2011-105592 relates to a method for welding a high melting point ultrafine metal and alloy wire and a high melting point metal / alloy thin wire joined body, and a Re-W ultrafine thermocouple by a high voltage discharge welding method using a metal needle. Is described. Non-Patent Document 1 relates to observation of a field emission pattern of a tungsten point filament, and describes a bonded / polished tungsten point filament.

The tungsten hairpin filament shown in FIG. 1 can be easily manufactured for bending, but it is difficult to reduce the radius of curvature and cannot be used as a high-intensity electron beam source. The filaments shown in FIGS. 2 (a) to 2 (c) can have a small radius of curvature, but it is necessary to further machine or spot weld the tungsten hairpin filament and then sharpen the tip by electrolytic polishing. There is a problem that the fabrication is not easy. Furthermore, there is a problem that costs are increased.

As a method for producing the filament, a welding method in which a high voltage is applied at a close distance, a glow discharge is generated, and a metal element wire is butted to perform welding is also conceivable. It is known that when a high voltage is applied, a large electric field is applied to the molten metal, and when the electric field strength increases, the interfacial tension of the molten metal is overcome and is drawn to the counter electrode to form a conical shape with a sharp tip. Called tailor cone.

FIG. 3 is a perspective view showing an example of a state in which a strand is attached to a strand holding jig of a conventional metal strand welding apparatus using high-voltage discharge. The wire holding jig 180 is generally composed of a plate member 181 made of metal or alloy having a substantially rectangular shape in plan view, and a magnet 182 disposed on one surface of the plate member 181.

The plate member 181 is provided with holes 181c penetrating both surfaces. One end of the strand 125 is disposed so as to protrude from the corner of the plate member 181, and the strand 125 is disposed on one surface of the plate member 181 so as to be substantially parallel to the diagonal direction from the corner of the plate member 181. After fixing the strand 125 with the magnet 182 and holding the strand, the strand holding jig 180 is rotated around the center of the through hole 181c as a rotation center, and similarly held with the same configuration. The ends of the jig wires are brought into contact with each other and then welded.
However, in the conventional welding apparatus, the crossing angle β cannot be set to 20 ° or less, and a filament having a small curvature radius at the tip cannot be formed.

JP 11-67055 A

Takematsu et al., Observation of field emission pattern of tungsten point filament, (pages 55-60)

An object of the present invention is to provide a thermoelectron emission type filament having a small radius of curvature and a high thermoelectron emission current density, and a manufacturing method thereof that can be easily manufactured by one welding.

The present inventor has reviewed the mechanism of the conventional welding apparatus, and can precisely control two wire holding jigs and metal needle jigs with four axes of x, y, z and tilt axes, respectively. By reexamining the configuration of the wire holding jig, the position of the tips of the two refractory metal strands can be precisely controlled, the crossing angle between the tips can be reduced, and welding can be performed. did. It was discovered that by using this apparatus, a filament having a tip having a radius of curvature of 100 μm or less could be easily produced, and the present invention was completed.
The present invention has the following configuration.

(1) Two strands are melt-bonded, but the diameter is reduced toward the joint tip by a strong electric field applied at this time, and the radius of curvature of the tip is 100 μm or less. A filament characterized in that the material is the same metal or alloy.

(2) The filament according to (1), wherein the melting point of the material is 2400 ° C. or higher.
(3) The filament according to (2), wherein the material is any one metal selected from the group of W and Re, or an alloy composed of two or more of these metals.
(4) The filament according to (3), wherein the material is a 3% Re-W alloy.

(5) The filament according to any one of (1) to (4), which has a semi-elliptical portion in a cross section including a perpendicular at the tip.

(6) The ends of two strands made of the same metal or alloy are butted at an intersection angle of 20 ° or less, the tip of the metal needle is brought close to 100 μm or less to the tip of the two strands, A method for producing a filament, comprising a step of welding an end of the two strands by applying an electric field between the ends of the two strands and the tip of the metal needle.

(7) The pressing pressure does not become zero until the ends of the two strands are abutted with each other with a pressing pressure of 1 mN or more and the ends of the two strands are welded (6). The manufacturing method of the filament as described in any one of.

(8) The method for producing a filament according to (6) or (7), wherein the applied electric field is 50 V / μm or more.
(9) The method for producing a filament according to any one of (6) to (8), wherein a diameter of the two strands is 100 μm or less.

The filament of the present invention is reduced in diameter toward the tip of the joint by melting and joining two strands, the radius of curvature of the tip is 100 μm or less, and the material of the two strands is the same metal Or since it is a structure which is an alloy, it can manufacture easily and becomes a high-intensity electron beam source. By simply replacing it with a tungsten hairpin filament used in a general-purpose scanning electron microscope, even the same apparatus can be observed at a higher magnification than before, and an improvement in performance can be expected easily. In addition, an analysis apparatus using an electron beam such as EPMA can increase analysis signals. The field emission type high resolution scanning electron microscope (FE SEM) operates at a vacuum degree of 10 ⁻³ to 10 ⁻⁴ Pa as compared with a vacuum degree of 10 ⁻⁷ .

In the method for producing a filament of the present invention, the tips of two strands made of the same metal or alloy are butted at an intersection angle of 20 ° or less, and the tip of the metal needle is placed at the tip of the two strands of 100 μm or less. Since the electric field is applied between the tip of the two strands and the tip of the metal needle and the tips of the two strands are welded to each other, The shape of the welded portion can be sharpened, and a filament having a radius of curvature of 100 μm or less at the tip can be easily produced by a single welding.

It is the schematic diagram which showed an example of the spread of the electron radiated | emitted from a tungsten hairpin filament. It is a prior art example of another filament. It is a perspective view which shows an example of the state which attached the strand to the conventional strand holding jig. It is a figure which shows an example of the filament of this invention. It is a perspective view which shows an example of the state which attached the strand to the strand holding jig. It is a figure explaining a welding process. It is a figure explaining a welding process. It is a figure explaining a welding process. 2 is a photograph of the filament of Example 1. 2 is a photograph of a filament of Comparative Example 1.

(First embodiment of the present invention)
<Filament>
First, the filament which is the 1st Embodiment of this invention is demonstrated.
4A and 4B are diagrams illustrating an example of a filament according to an embodiment of the present invention. FIG. 4A is a plan view, and FIG. 4B is a cross-sectional view taken along the line AA ′ in FIG. It is sectional drawing and FIG.4 (c) is a bottom view.
As shown in FIG. 4, the filament 11 according to the embodiment of the present invention has a shape in which two strands 23 and 24 are fused and reduced in diameter toward the tip 21 a.
The curvature radius _{r 11} of the tip 21a is a 100μm or less.

The material of the two strands 23 and 24 is the same metal or alloy.
The melting point of the material is preferably 2400 ° C. or higher. This is because even when the same material is used, by increasing the temperature, the amount of thermionic emission increases and the luminance can be increased.
For example, Ir having a melting point of 2454 ° C. can be cited as the refractory metal.

The filament material is preferably a material having a low work function. This is because, even at the same temperature, the lower the work function, the greater the amount of thermionic emission, and the higher the luminance.

The material is preferably any one metal selected from the group of W and Re, or an alloy composed of two or more of these metals. In particular, the material is preferably a 3% Re—W alloy. As a result, the brightness can be increased at high temperatures.

The melt-bonded portion 21 has a semi-elliptical shape in a cross section including a perpendicular at the tip 21a.

The intersection angle β between the two strands 23 and 24 is set to 20 ° or less. The diameter m of the two strands 23 and 24 is 100 μm or less. Thus, it is possible to reduce the radius of curvature _{r 11} of the filament of the tip 21a.

<Manufacturing method of filament>
Next, the manufacturing method of the filament which is the 1st Embodiment of this invention is demonstrated.
The manufacturing method of the filament which is embodiment of this invention has welding process S1.

(Welding process S1)
First, two strands made of the same metal or alloy are prepared. The strand diameter is preferably 100 μm or less. Thereby, the filament which made the curvature radius of the tip small can be manufactured by welding.
Next, one strand is attached to one strand holding jig, and the other strand is attached to another strand holding jig.

FIG. 5 is a perspective view showing an example of a state in which the strand is attached to the strand holding jig.
As shown in FIG. 5, the wire holding jig 69 includes a plate member 71 made of metal or alloy having a substantially rectangular shape in plan view, a tube 75 attached to a side surface 71 d of the plate member 71, and one surface of the plate member 71. The plate magnet 73 is arranged roughly at 71a.

The plate member 71 is provided with a through hole 71c.
The tube 75 is attached so that the tube hole direction is parallel to the side surface 71d and the one surface 71a, and one end 75a of the tube 75 is positioned at the corner of the plate member 71 or above. The tube 75 is attached by, for example, an adhesive.

As the material of the tube 75, a high heat resistant polymer material is used. For example, polyimide (trade name, Kapton) can be given. Other than polyimide, any material can be used as long as it is insulating and has a heat resistant temperature of 200 ° C. or higher.
The inner diameter of the tube 75 is determined according to the diameter of the strand. For example, for a 50 μm strand, 80 μm is used.

As shown in FIG. 5, the strand 25 is disposed through the tube hole. More specifically, the one end 25 a of the strand 25 is arranged so as to protrude from the one end 75 a of the tube 75 by a length of 2 mm or more and 5 mm or less.
This length is preferably 2 mm or more and 5 mm or less. When it is 2 mm or more and 5 mm or less, the control of the pressing pressure and the butt control are facilitated, and the butt portions can be prevented from opening when the strands 25 and 26 are melted. Since the strand is considered to be a cantilever beam pressed by one end 75a of the tube, if it exceeds 5 mm, the deflection at the time of butting becomes too large and the butting control becomes difficult. On the other hand, when the length is less than 2 mm, the tube 75 may be melted by discharge.

One end 25 a of the strand 25 is also arranged so as to protrude from the other end 75 b of the tube 75. The other end 25 b of the strand 25 arranged so as to protrude from the other end 75 b of the tube 75 is fixed with a magnet 73. In FIG. 5, the shape of the magnet 73 is a disc shape, but the shape of the magnet 73 is not limited to this.

Next, another strand 26 is attached to another strand holding jig 70 in the same manner.
The plate member 72 of another strand holding jig 70 is also provided with a hole 72 c, a tube 76 is attached, and the strand 26 is fixed by a magnet 74.
Next, the two wire holding jigs 69 and 70 are attached to a stage capable of precise position control with four axes of x, y, z and tilt axes, respectively (not shown).

6-8 is a figure explaining a welding process.
As shown in FIG. 6, wiring is attached to the plate members 71 and 72 of the two wire holding jigs 69 and 70, respectively. These wires are connected to the ground electrode side of the power supply 78.
The power source 78 is connected to a metal needle 77 having a sharp tip and a terminal on the application electrode side of the power source 78 through another wiring. The metal needle 77 is also attached to a stage (not shown) that can be precisely controlled by four axes of x, y, z, and tilt axes, so that the position can be easily controlled.

As the power supply 78, for example, a pulsed direct current high voltage power supply with a rating of 10 kV and 10 mA is used. If it is below this rated value, the voltage / current value can be set freely, and the voltage drop can be instantaneously restored so as to maintain the output voltage of kV order.

Next, as shown in FIG. 7, the two wire holding jigs 69 and 70 are rotated about the centers of the holes 71c and 72c, respectively, so that the tips of the two wires 25 and 26 are 20 ° or less. Match at the crossing angle β.
The crossing angle β is preferably small, but is limited by the interval between the struts connecting the filaments.

The pressing pressure between the tips is preferably 1 mN or more. Thereby, it can suppress that the strands 25 and 26 leave | separate in the case of discharge.
The pressing direction and position between the tips are precisely controlled by four axes of x, y, z and tilt axes, and the pressing pressure is maintained even if the tip melts by welding, and the pressing direction and position are also Keep it constant. For example, if the pressing direction is deviated from the axis center of the strand, it is separated.

It is necessary that the pressing pressure does not disappear after the ends of the two strands 25 and 26 are abutted with each other with a pressing pressure of 1 mN or more until the ends of the two strands are welded. Thereby, it is possible to reliably manufacture a filament in which the radius of curvature of the tip is reduced by suppressing the separation of the strands 25 and 26 during discharge.

Next, the tip of the metal needle 77 is brought close to 100 μm or less to the tip of the two strands 25 and 26. The distance k between the tips of the two strands 25 and 26 and the tip of the metal needle is preferably about the diameter of the strand, and when a strand having a diameter of 50 μm is used, it is close to 50 μm. Is preferred. Thus, a high voltage can be applied between the tip of the metal needle 77 and the tips of the strands 25 and 26 via the power supply 78, and the applied electric field can be precisely controlled.

Next, as shown in FIG. 8, while the atmosphere adjustment gas heated from directly above the metal needle 77 is sprayed from a cylindrical gas guide 79 arranged coaxially with the metal needle, the application electrode side is the metal needle 77 and the ground electrode side. Are applied to the metal needle 77 side, and a high voltage is applied between the tips of the two wires 25 and 26 and the tip of the metal needle 77. Thereby, atmospheric pressure pulse discharge plasma is generated.

The glow discharge generated by a high voltage of several kV and a small current of several mA causes the tips of the two strands 25 and 26 to melt at a high temperature in a short time, and the tips of the two strands 25 and 26 are welded. Is done.

In a glow discharge generated by a high voltage of several kV and a small current of several mA, a short pulse discharge of nanosecond order is actually generated with a certain pause interval. This is due to the characteristics of the power supply that suddenly returns the voltage lowered by the discharge to the original voltage, and this allows the discharge to continue in the glow discharge or abnormal glow discharge region, and the strand made of a refractory metal or alloy 25 and 26 can be welded. That is, in general, the DC glow discharge at atmospheric pressure is more likely to shift to arc discharge because the electrode is locally heated compared to the low-pressure discharge. Since it is cooled, glow discharge continues.

When the strands 25 and 26 are welded, the tip ends of the strands are melted and integrated. At this time, the melted portion is attracted to the metal needle 77 by the action of a high electric field between the metal needle and a tailor cone. When the glow discharge is completed, the melted portion is very small and rapidly cooled, so that the shape of the tailor cone is solidified to some extent, so that a sharp tip having a tip radius of 100 μm or less is obtained.

The atmosphere adjustment gas is injected from a cylindrical gas guide 79 disposed coaxially with the metal needle 77 from 5 seconds before the start of discharge to 5 seconds after the end of discharge.
The atmosphere adjustment gas is CO ₂ or the like. This gas is used as a shielding gas for preventing oxidation of a refractory metal or alloy. Shielding can be performed by spraying from the cylindrical gas guide 79 arranged coaxially with the metal needle 77 toward the ends of the two strands 25 and 26. By heating the atmosphere adjusting gas, the shielding effect can be enhanced.

Refractory metals or alloys are susceptible to oxidation. For this reason, in order to prevent oxidation during welding, it is usually necessary to perform welding in a special container under vacuum, in an inert atmosphere or in a reducing gas atmosphere. This configuration is not suitable for continuous processing and causes an increase in processing cost.
However, in this embodiment, a high melting point metal or alloy thin wire is used, the heat input is sharply controlled in the welding process, the influence of heat is locally suppressed, and discharge is performed while CO ₂ is used as a shielding gas. So, it can be welded without oxidization even in open air without using a special container. Thereby, it can apply easily to a continuous process and processing cost can be reduced.

The applied electric field is preferably 50 V / μm or more. When the distance k between the tips of the two strands 25 and 26 and the tip of the metal needle 77 is 100 μm, for example, the applied voltage is 5 kV. When the applied electric field is less than 50 V / μm, stable discharge cannot be obtained.
The applied current is 9 mA, for example.

When a voltage is applied, short pulse discharges are repeatedly generated. The voltage application time is preferably 1 second or less. More preferably, it is 0.8 seconds or less, and further preferably 0.6 seconds or less. If the voltage application time is longer than 1 second, even if the wire tip melts, it may not be integrated and welded.
The welding conditions are not limited to the voltage, current, and frequency values.

Through the above-described welding step S1, a filament with a reduced radius of curvature at the tip can be easily formed in one step.

The filament 11 according to an embodiment of the present invention has a radius of curvature r ₁₁ at the tip of 100 μm or less, and the material of the two strands is the same metal or alloy, and can be easily manufactured by fusion bonding, and has high brightness. A good electron beam source. This filament is a thermionic emission filament and can be easily replaced with a conventional tungsten hairpin filament. By simply replacing it with a tungsten hairpin filament used in a general-purpose scanning electron microscope, even the same apparatus can be observed at a higher magnification than before, and an improvement in performance can be expected easily. In addition, an analysis apparatus using an electron beam such as EPMA can increase analysis signals. Operation is possible at a vacuum level of 10 ⁻³ to 10 ⁻⁴ Pa, compared with a vacuum level of 10 ⁻⁷ Pa of a field emission type high resolution electron microscope (FE SEM).

Since the filament 11 which is an embodiment of the present invention has a structure in which the melting point of the material is 2400 ° C. or higher, it becomes a high-intensity electron beam source by melting it at a high temperature.

The filament 11 according to the embodiment of the present invention has a configuration in which the material is any one metal selected from the group of W and Re, or an alloy composed of two or more of these metals. High brightness electron beam source.

The filament 11 according to an embodiment of the present invention is a structure in which the material is a 3% Re—W alloy, and therefore, the filament 11 becomes a high-intensity electron beam source at a high temperature without melting.

Since the filament 11 according to the embodiment of the present invention has a semi-elliptical portion 21 in a cross section including a perpendicular line at the tip 21a, a tip having a small curvature radius can be formed.

The manufacturing method of the filament 11 which is embodiment of this invention matches the front-end | tips of the two strands 25 and 26 which consist of the same metal or alloy with the crossing angle of 20 degrees or less, and the front-end | tip of the said 2 strands Further, after bringing the tip of the metal needle 77 close to 100 μm or less, a voltage is applied between the tip of the two strands and the tip of the metal needle to weld the tips of the two strands. Since it has a process, the shape of the welded portion can be sharpened by the action of an electric field, and a filament having a tip radius of curvature of 100 μm or less can be easily formed by only one welding.

In the manufacturing method of the filament 11 according to the embodiment of the present invention, the pressing pressure is applied until the ends of the two strands are abutted with each other with a pressing pressure of 1 mN or more, and the ends of the two strands are welded. Since the structure is maintained, a filament having a radius of curvature of 100 μm or less can be easily manufactured without separation.

Since the method of manufacturing the filament 11 according to the embodiment of the present invention has a configuration in which the applied electric field is 50 V / μm or more, the discharge welding and the diameter reduction of the welded portion are completed in one step, and a filament having a radius of curvature of the tip of 100 μm or less is obtained. Easy to produce.

Since the method for manufacturing the filament 11 according to the embodiment of the present invention has a configuration in which the electric field application time is 1 second or less, a filament having a radius of curvature of 100 μm or less can be easily produced in one step without separation.

Since the filament manufacturing method according to the embodiment of the present invention has a configuration in which the diameter of the two strands is 100 μm or less, a filament having a radius of curvature of the tip of 100 μm or less can be easily manufactured in one step.

The filament and the manufacturing method thereof according to the embodiment of the present invention are not limited to the above embodiment, and can be implemented with various modifications within the scope of the technical idea of the present invention. Specific examples of this embodiment are shown in the following examples. However, the present invention is not limited to these examples.

Example 1
<Filament production>
First, a tungsten wire having a diameter of 50 μm was attached to the wire holding jig shown in FIG.
A polyimide tube having an inner diameter of 80 μm was used as the tube.
The strands passed through the polyimide tube and protruded 2 to 5 mm from the tube exit to the metal needle side.

  Next, a voltage was applied with the apparatus configuration shown in FIGS. 6 to 8, and two high-melting-point metals were welded in one step to produce a pointed filament.

Specifically, first, butting was performed so as to apply a force that aligned and pressed the axial centers of the two strands.
The butt angle of the strands at this time was 20 °.

The tip of the strand and the metal needle were separated by 50 μm.
In this state, a positive voltage was applied to the metal needle side with the application electrode side as a metal needle and the ground electrode side as a wire. A maximum of 10 kV was applied to a very narrow electrode spacing of 50 μm.

A high-voltage power supply with a rating of 10 kV and 10 mA was used which can instantaneously recover output control by a pulse method and voltage drop due to discharge.
The voltage was 5 kV, the applied current was 9 mA, and the voltage application time was 0.6 seconds.

A high voltage was applied to the metal needle under the above conditions to generate an atmospheric pressure discharge between the metal needle and the wire butt.

Due to the characteristics of this power source, the discharge was continued in the glow discharge or abnormal glow discharge region, and the refractory metal fine wires were joined.

From 5 seconds before the start of discharge to 5 seconds after the end of discharge, CO ₂ heated to 100 ° C. was jetted from a gas guide having an inner diameter of 8 mm as an atmosphere adjusting gas (shield gas).
As described above, the filaments of Example 1 were manufactured by welding the strands by high voltage discharge.

(Comparative Example 1)
A hairpin filament used for JEOL JSM-5310LV SEM was prepared, and this was used as the filament of Comparative Example 1.

<Filament evaluation>
FIG. 11 is a photograph of the filament of Example 1, FIG. 11A is a photograph as it is, and FIG. 11B is a photograph showing the radius of curvature r _j1 .
The curvature radius r _j1 of the tip of the filament of Example 1 was about 19 μm.
The reason why the filament of Example 1 has a very small radius of curvature is considered to be due to the influence of the electric field strength during welding.

12 is a photograph of the filament of Comparative Example 1, FIG. 12 (a) is a photograph as it is, and FIG. 12 (b) is a photograph showing the radius of curvature r _h1 .
The curvature radius r _h1 of the tip of the filament of Comparative Example 1 was about 200 μm.

From (1) and (2), the brightness increases when the radius of curvature of the tip is reduced. Therefore, the filament of Example 1 can have the radius of curvature of the tip one order of magnitude smaller than that of the filament of Comparative Example 1, and the beam aperture angle. It was found that the brightness at the crossover point (point light source) can be increased by reducing the height of the electron beam, resulting in an electron beam source with high brightness.

The filament of the present invention and the manufacturing method thereof are related to a filament having a radius of curvature of 100 μm or less using a wire having a wire diameter of 100 μm or less and up to 50 μm, and a method for manufacturing the same. Since it can be used as a filament serving as a high-intensity electron beam source, it can be used in FED (field emission display) manufacturing industry, SEM manufacturing industry, EPMA manufacturing industry, etc. that require such an electron emission source.

DESCRIPTION OF SYMBOLS 11 ... Filament, 21 ... Fusion joined part, 21a ... Tip, 23, 24 ... Wire, 25 ... Wire, 25a ... One end, 25b ... Other end, 26 ... Wire, 69, 70 ... Wire holding jig, 71, 72: plate-like member, 71a: one surface, 71c, 72c ... hole, 71d ... side surface, 73, 74 ... magnet, 75, 76 ... tube, 75a ... one end, 75b ... other end, 77 ... metal needle, 78 ... Power source, 79 ... cylindrical gas guide, 125 ... wire, 150 ... filament, 152 ... Wenert, 153 ... crossover point, 155a, 155b, 156a ... machined surface, 157 ... needle members, 161, 162,163 ... conventional Of other filaments, 180 ... strand holding member, 181 ... plate-like member, 181c ... hole, 182 ... magnet.

Claims (9)

By melting and joining two strands, the diameter is reduced toward the tip of the joint, the radius of curvature of the tip is 100 μm or less, and the material of the two strands is the same metal or alloy Characteristic filament. The filament according to claim 1, wherein the melting point of the material is 2400 ° C. or more. 3. The filament according to claim 2, wherein the material is any one metal selected from the group of W and Re, or an alloy made of two or more of these metals. The filament according to claim 3, wherein the material is a 3% Re—W alloy.   The filament according to any one of claims 1 to 4, wherein the filament has a semi-elliptical portion in a cross section including a perpendicular at the tip. The ends of two wires made of the same metal or alloy are butted at a crossing angle of 20 ° or less, the tip of the metal needle is brought close to 100 μm or less to the tips of the two wires, and then the two wires A method for producing a filament, comprising the step of applying an electric field between the tip of the element wire and the tip of the metal needle to perform high-voltage discharge welding of the tip of the two element wires. The pressing pressure does not become zero until the ends of the two strands are butted against each other with a pressing pressure of 1 mN or more until the ends of the two strands are welded. Filament manufacturing method. The method for producing a filament according to claim 6 or 7, wherein the applied electric field is 50 V / µm or more. The method for producing a filament according to any one of claims 6 to 8, wherein a diameter of the two strands is 100 µm or less.