JPS601717A - Needle-shaped emitter of field emission type liquid metal ion source - Google Patents

Abstract

PURPOSE:To smooth feeding of a liquid metal to the tip of a needle-shaped emit ter for giveng high performance and high reliability by forming the needle-shaped emitter in a shape, in which a change of the side shape from the columnar part to the conical part or from the square pillar part to the pyramid part is gentle without any steep boundary. CONSTITUTION:Either one of conductors having high melting points such as boride TiB2, CrB2 compound boride BN-TiB2, carbide TiC or the like is used for an emitter material. And, for instance, a columnar piller 11 having a square section is cut out from a parent metal 10, followed by being machined into a columnar pillar 12 for further being machined into a needle-shaped emitter 13 by mechanically grinding the tip side thereof. Said needle-shaped emitter 13 is further machined into the needle-shaped emitter 14 having a smooth boundary by mechanically grinding the boundary part changing from the columnar pillar to a cone. Thereby, a liquid metal can be fed smoothly to the tip for obtaining the stable ion emissive properties while making it possible to emit an ion beam with the taking-out voltage of low threshold value due to a sufficient amount of supply of the liquid metal serving as an ion source.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a needle-shaped emitter of a field emission liquid metal ion source, and is particularly intended to emit an ion beam with high brightness and stability. .

[Background of the invention]

A field emission type liquid metal ion source using a needle emitter is well known as a high-intensity ion source.

FIG. 1 shows a cross-sectional view and an electric circuit diagram of a conventionally used field emission type liquid metal ion source. In Figure 1,
Reference numeral 1 denotes a needle-shaped emitter extending from a support part and an ion emitting part integrally formed on the tip side of the support part, 2 a liquid metal reservoir, 6 a molten metal, 4 an insulating heat conductor, and 5 a A holding part that holds the rear end side of the support part of the needle emitter 1, 6 a heating resistance wire, 7 a heating power source, 8 an ion beam extraction power source,
9 is an ion beam extraction electrode. An opening is made at the tip of the liquid metal reservoir 2, and the needle-shaped emitter 1 projects out of the metal reservoir 2 from the opening with a small gap (approximately 0.1 mm') maintained. It is maintained as follows.

1. By placing the metal to be ionized in the liquid metal reservoir 2 and heating it by passing a current through the heating resistance wire B.
The metal in the liquid metal reservoir 2 melts. This molten metal 3 is
The liquid metal flows overflowing into the needle-shaped emitter 1 protruding from the liquid metal reservoir 2 and is supplied to the ion emitting part at the tip side of the needle-shaped emitter 1. At this time, when the electric field at the tip of the needle-shaped emitter 1 covered with liquid metal exceeds a certain threshold, the electrostatic force applied to the liquid metal surface exceeds the contraction force due to the surface tension of the liquid metal, causing a Taylor cone. At the same time as this occurs, ion emission begins at the tip of the cone. In this way, in order to emit ions, it is necessary to apply a high electric field to the tip of the needle-like emitter 1, so the ion-emitting part of the needle-like emitter 1 has a conical shape (tip curvature: 1 to 10 μm) as shown in FIG. ) has been processed. In Fig. 2, 1-1 is a cylindrical support part, 1-2
indicates a conical ion emitting part, and these support parts 1-1
and the ion emitting section 1-2 are integrally made of the same material to constitute the needle-like emitter 1. Incidentally, a structure in which the support portion 1-1 has a prismatic shape and the ion emitting portion 1-2 has a pyramid shape has also been conventionally employed.

In such a liquid metal ion source, it is necessary to smoothly supply the liquid metal dissipated by ion beam emission to the emitter tip, but in conventional ion sources, special consideration is given to the smooth supply of liquid metal. Because it had not been properly cleaned, it had a built-in factor that made it unstable as an ion source.

[Purpose of the invention]

The present invention has been made in view of these points.6
- Smoothly supplies liquid metal to the tip of the needle emitter,
The object of the present invention is to provide a needle-like emitter for a field emission type liquid metal ion source that has high performance and high reliability.

[Summary of the invention]

A feature of the present invention is that, in order to achieve the above object, the shape of the support part is made into a substantially cylindrical or prismatic shape, and the shape of the ion emitting part integrally formed on the tip side of this support part is made into a substantially conical or pyramidal shape. In a needle-shaped emitter for a field emission type liquid metal ion source manufactured in Furthermore, the needle-shaped emitter has at least one groove formed on its side surface from the support section to the ion emitting section.

Needle-shaped emitters have conventionally been manufactured by (1) machining a high melting point conductive base material, or (2) electrolytically polishing a high melting point metal wire. When the support part is cylindrical, when using the method (1) above, 4. The ion emitting part is processed into a cone with linear side surfaces as shown in Figure 2 (a), and the method (2) is used. According to Fig. 2 (
It is usually polished into a cone with concave sides as shown in b). However, in such a needle-shaped emitter, since the boundary where the cylindrical part changes to the conical part has a sharp angle (a), the flow of liquid metal covering the emitter surface is disturbed at this boundary, and the liquid metal The supply of ions to the tip of the ion emitting section was not smooth. In order to solve this problem, the present invention eliminates the boundary between the change in shape from a cylindrical part to a conical part, and provides a needle-like emitter with a shape that smoothly changes from a cylindrical part to a conical part.

[Embodiments of the invention] Examples of the present invention will be described below.

FIG. 6 is a side view of a needle emitter according to an embodiment of the present invention.
(a) shows the case where the shape of the ion emitting part 1-2 is a cone with linear side surfaces, and (b) shows the case where the shape of the ion emitting part 1-2 is a cone with concave sides. , as shown in the figure (b), is made to have sharp boundaries. First, a method for manufacturing a needle emitter having such a shape will be described. For Al ion sources, boride (TI B2
.

A high melting point conductor such as CrB2), composite boride (BNTIB2), or carbide (TiC) is used as the emitter material. A method for manufacturing the needle-shaped emitter of the present invention from the base material as described above will be explained with reference to FIG. In FIG. 4, a prism 11 with a square cross section is cut out from a base material 10 to a size of 0.3 to 1.7 mm on one side of the square, and then machined into a cylinder 12. The tip side of this cylinder 12 is processed into a needle-like emitter 16 by mechanical polishing (grinding, polishing, etc.). Furthermore, the boundary portion where the cylinder transitions to the cone is mechanically polished to form a needle-shaped emitter 14 having a smooth boundary. However, when the support part is made into a prism, machining from the prism 11 to the cylinder 12 is not necessary, and the tip side of the prism 11 is polished into a pyramid, and the transition part from the prism to the pyramid is smoothed. Needless to say, it is better to polish it to

Next, a method for producing the needle-shaped emitter of the present invention by electrolytic polishing using a high melting point metal wire such as a tungsten wire as an emitter material will be explained with reference to FIG. An electrolytic solution 16 is placed in an electrolytic bath 15, and an alternating current or an electric current is applied between the emitter metal wire 171m (17-1) + (17-2)) to be electrolytically polished and the cathode (platinum wire, carbon electrode, etc.) 18. Apply DC voltage. When the metal wire 17 is electrolytically polished in this way, since the metal wire is most likely to be electrolytically polished right below the surface of the electrolytic solution, the needle-shaped emitter 17-1 whose cut surface has a shape as shown in FIG. 2(b), The remaining metal wire 17-2 is separated. At this time, by detecting the flowing current,
The radius of curvature of the tip of the needle emitter is controlled by controlling the electrolytic polishing time after cutting the metal wire 17-2. However, if the acicular emitter remains as it is, the boundary from the cylinder to the cone [(a) in FIG. 2(b)] has a steep boundary corresponding to the electrolyte level.

Therefore, in order to produce the needle-shaped emitter of the present invention, the electrolytic polishing time required for cutting the metal wire is 1/3 to 2/3.
- The metal wire 17 is vibrated by the vertical movement mechanism 19 or brought out of the liquid surface little by little for a period of time to smooth the boundary, and then the metal wire 17 is fixed and further electrolytic polishing is performed. Let's do it. Depending on the manufacturing method, this can be seen in Figure 6 (
Needle-shaped emitters like those shown in b) can be fabricated.

In the ion source using the needle-shaped emitter having the shape shown in FIG. Since the supply of liquid metal per source is sufficient, the ion beam can be emitted at a low threshold extraction voltage. In addition, low temperatures (
Since the liquid metal is stably supplied to the tip of the needle emitter even when the temperature is higher than the melting point), there is an advantage that the characteristics at low temperatures are stable.

Next, as shown in FIG. 6, the characteristics of the ion source using the needle emitter of the present invention and the conventional ion source will be compared. The needle emitter for the present invention is made of composite boride (BN TI
B2) A base material was produced according to the process shown in Fig. 4. The ion source metal is kl. The radius of curvature of the tip of the needle emitter is about 2 to 5 μm.

The characteristics of the needle-shaped emitter of the conventional shape and the needle-shaped emitter of the present invention were compared for two types of conical tip angles of 30 degrees and 45 degrees. First, when we observed the flow of molten A7 on the surface of the needle-shaped emitter, we found that in conventional emitters, A7 stagnates at the steep boundaries of the emitter surface and is difficult to flow to the tip, whereas in the needle-shaped emitter of the present invention It was confirmed that molten Al could be smoothly supplied to the tip. Next, the above-mentioned conventionally shaped needle emitter and the needle emitter according to the present invention were incorporated into an apparatus, and the emitters were actually used as an ion beam source and their characteristics were compared. FIG. 6 shows an example of the experimental results. The characteristics were evaluated based on the correlation between the source current, that is, the total ion emission current 1, and the ion beam extraction voltage.

In terms of performance as an ion beam source, it is necessary that an ion beam can be emitted with a low extraction voltage, that a large source current can be obtained with a slight increase in the extraction voltage, and that the above characteristics are stable. . Figure 6(a), (
b) and (C) are the ion beam extraction voltages when the conventional shaped needle emitter shown in FIG. 2(a) is used, and (d) and (e) are when the needle emitter of the present invention is used. The relationship between and source current (total ion emission current) is shown.

In FIG. 6, (a) shows the characteristics of a conventional structure emitter with a tip angle of 45 degrees at a relatively low temperature above the melting point of Al, the threshold voltage is high, and the ion emission characteristics with respect to voltage, i.e. The slope of the curve is gentle. This shows that, especially at relatively low temperatures, the amount of molten Al that passes along the surface of the needle emitter and is supplied to the tip is large enough. In addition, (b) and (C) show the characteristics of emitters with conventional structures with tip angles of 45 degrees and 30 degrees, respectively, when the melting temperature of kl is increased and they are used for a longer time. In comparison, the threshold voltage decreases,
Although a steepening of the emission characteristics with respect to voltage was achieved, such a state was not stable, and unstable characteristics similar to (a) were occasionally observed to occur. On the other hand, (d
) and (e) are the characteristics when the needle emitter of the present invention is adopted, and the threshold voltage is the same as the corresponding conventional characteristic (b).
) and (C), and a steep release characteristic with respect to voltage was obtained. Further, almost no dependence on the melting temperature of A7, which was observed in the case of the emitter with the conventional structure, was observed, and furthermore, no unstable fluctuations in the characteristics were observed. From the above, the effects of the present invention were demonstrated.

As shown in FIG. 6, the smaller the tip angle of the needle-shaped emitter, the lower the threshold voltage becomes orange. However, according to the needle-shaped emitter manufacturing method shown in FIG. It is easy to obtain a tip angle of about 30 degrees. Generally, a tip angle range of 60 degrees to 90 degrees can be used as a needle emitter.

Note that an even greater effect can be produced by providing one or more grooves on the surface of the needle-shaped emitter from the supporting portion toward the ion emitting portion to further facilitate the flow of the molten metal.

〔Effect of the invention〕

・１１・ As explained above, according to the present invention, since molten metal can be smoothly supplied to the tip of the needle emitter, the liquid metal that is emitted as ions can be immediately replenished, and the molten metal that disappears as an ion beam can be replaced with the molten metal that disappears as an ion beam. Since the balance with the supplied molten metal is not lost, the threshold voltage is low.
A needle-shaped emitter for a field emission type liquid metal ion source that has little temperature dependence, is rich in reproducibility, and is highly reliable can be obtained.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional configuration diagram for general explanation of a field emission type liquid metal ion source, and Figure 2 is a side view of a conventional needle-shaped emitter (a
) is the one in which the ion emitting part has a straight side surface, (b) is the one in which the ion emitting part is on the concave side surface, and FIG. 3 is a side view of the needle-shaped emitter of the present invention (
(a) shows a case where the ion emitting part is straight and has a concave side surface; (b) shows a case where the ion emitting part is a concave side surface; FIG. 4 and FIG. FIG. 2 is a comparison diagram of the characteristics of the present invention and a conventional ion source. Explanation of symbols ・12・ 1... Needle emitter 1-1... Support part 1-2...
- Ion emitting part 2... Liquid metal reservoir 3... Molten metal 4... Insulating thermal conductor 5... Holding part 6... Heating resistance wire 7... Heating power supply 8...・Drawer power supply 9
...Extraction electrode 10...Base material 11...Prismatic column 12...Cylinder 16...Acicular emitter 14...Acicular emitter with smooth boundary 15...Electrolytic cell 16...Electric field Liquid 17'-1, 17-2... Metal wire for emitter 18...
・Cathode 19... Vertical movement mechanism patent applicant Junnosuke Nakamura, patent attorney representing Nippon Telegraph and Telephone Public Corporation

Claims (2)

[Claims] (1) The support part and the ion emitting part integrally formed on the tip side of the support part are formed so that the shape of the support part is approximately cylindrical or prismatic, and the shape of the ion emitting part is approximately conical. Or, in the needle-shaped emitter of a field emission type liquid metal ion source made in the shape of a pyramid, the change in side shape from the cylindrical part to the conical part or from the prismatic part to the pyramidal part is gradual and does not have a sharp boundary. Features a needle-shaped emitter of a field emission type liquid metal ion source. (2) Consisting of a support part and an ion emitting part integrally formed on the tip side of the support part, the support part has an approximately cylindrical or prismatic shape, and the ion emitting part has an approximately conical or prismatic shape. In the needle-shaped emitter of the field emission type liquid metal ion source made in the shape of a pyramid, the change in side shape from the cylindrical portion to the conical portion or from the prismatic portion to the pyramidal portion is gradual and does not have a steep boundary, and . A needle-shaped emitter for a field emission type liquid metal ion source, characterized in that at least one groove is formed on a side surface from the support section toward the ion emitting section. (b) The field emission type liquid metal according to claim 1 or 2, wherein the ion emitting section is an ion emitting section whose tip angle is formed at 60 degrees to 90 degrees. Needle emitter of ion source.