JPH0961597A - Device for capturing and supplying charged particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to capture particles of a specific mass and take them out as well as capture particles of a wide range to the outside by supplying pole-like electrodes with a phase-inverting direct-current voltage and giving a direct-current bias acting as the attraction force toward the pole electrodes to charged particles existing between the pole electrodes and an external electrode. SOLUTION: Four pole electrodes 11A to 11D are symmetrically placed around the central axis 12, and an alternating power source 13 supplies an alternating voltage of alternately inverting its phases. The alternating power source 13 is connected to a direct-current power source 14 giving a direct-current bias acting as the attraction force in the direction to a central electrode 11 to charged particles 16 existing in the space between the central electrode 11 and an external electrode 15, and both direct- and alternating-current voltages are simultaneously applied to the central electrode 11. This makes it possible to capture the charged particles of a wide mass range with a high density in the space between the pole electrodes 11A to 11D and the external electrode 15 and select the particles 16 with mass of a specific value or more from the captured particles 16 to take in them from the edge surrounded by the external electrode 15 into the space around the central electrode 11 to take them out to the outside.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for electromagnetically holding charged particles such as electrons and ions in a predetermined space and supplying the particles outside the space.

[0002]

2. Description of the Related Art FIG. 6 shows a conventional method for trapping charged particles in space. FIG. 6A is a so-called quadrupole mass separator, and FIG. 6B is a pole trap that traps charged particles three-dimensionally based on the same principle. Further, FIG. 6C is a so-called Penning trap based on applying an electric field and a magnetic field at right angles.

In FIG. 6 (a), four capture electrodes 31 to 31 are used.
Surround the space where you want to capture charged particles with 4. Of these four electrodes, a high frequency voltage is applied from the AC power supply 2 to the two electrodes 31 and 33 facing each other as shown in the figure, and a high frequency electric field is generated in the space to be captured. This method uses the principle that when a high frequency is applied to an electrode, the force acting on the charged particle placed in the electrode acts in the direction in which the electric field gradient is small when time averaged. Two-dimensionally capture. Further, in FIG. 6B, the trapping electrodes 35 and 36 having a rotating hyperboloid shape and the ring-shaped capturing electrode 37 having an inner surface having a rotating hyperboloid shape are used to three-dimensionally surround the space to be captured. Particles are three-dimensionally captured by the same principle as 6 (a). As is clear from the above principle, in these methods, it is necessary to make the electric field gradient in the space in which the charged particles are desired to be confined smaller than that in the surroundings, and it is necessary to enclose the surroundings with electrodes densely. FIG.
This trapping principle is sensitive to the mass of the charged particles, as can be seen from the widespread use of the configuration of (a) as a mass separator. The reason is that the above trapping principle is based on vibrating charged particles by a high frequency electric field. That is, since the vibration amplitude is small, the force for trapping does not act on the particles having a large mass. In addition, the light particles collide with the electrode because the vibration amplitude is large.

In FIG. 6 (c), a DC power source 3 confines charged particles in the z direction of the figure to an electrode having the same structure as that of FIG. 6 (b), and direct current in the direction of diverging in the horizontal direction (r direction of the figure) is used. Apply voltage. At the same time, a magnetic field 39 in the z direction is generated by the magnet 38. The direct-current voltage causes the charged particles to move away from the center in the horizontal direction. By bending the direction of this movement by the magnetic field 39, the particles are prevented from escaping. Since the force that the particles receive from the magnetic field is proportional to the velocity of the particles, even if the same voltage is applied to the electrodes, the confinement effect by the magnetic field is small for heavy particles. Therefore, in this method, an extremely large magnetic field is required to capture a particle having a large mass such as heavy ions, and therefore the mass and energy of the particle that can be captured are limited to a small value.

As described above, the mass of particles that can be captured by the above conventional method is limited to a narrow range.

FIG. 7 shows a device for trapping charged particles, which was previously filed by the inventor of the present invention (Japanese Patent Laid-Open No. 4-29669).
No. 9). In this method, as shown in the figure, a pair of center electrode 4 and outer electrode 5 is prepared, an alternating voltage is applied from an alternating current power source 6, and a direct current voltage is superposed and applied from a direct current power source 7. An alternating electric field whose strength decreases with an increase in the distance from the central electrode and a direct current electric field exerting a force toward the central electrode are added to the charged particles 8 in the space around the central electrode in a superimposed manner. In this method, charged particles in a wide mass range can be simultaneously captured, but conversely, only particles having a specific mass cannot be selected and taken out.

As described above, although the conventional method can trap charged particles, it can trap particles having a specific mass or particles having a wide mass range. It was not possible to selectively take out charged particles with a specific mass from a wide range of charged particles and automatically supply them to the outside.

[0008]

The present invention is an improvement over the conventional method shown in FIG. 7, in which charged particles in a wide mass range are trapped in a predetermined space, and at the same time, particles having a mass larger than a specific value are automatically generated. The purpose is to selectively and selectively take out and supply it to the outside of the capture space. Such an apparatus is particularly suitable for applying an electromagnetically charged particle capturing method to material processing in a state of being completely isolated from a wall of a container, such as crystal growth in a state of being held in a space. , Was desired to be realized.

[0009]

In order to solve the above problems, the present invention provides a center electrode composed of four or more even columnar electrodes symmetrically arranged around a central axis, and the even number electrode. External electrodes surrounding one end of each of the columnar electrodes, an AC power source connected to each of the even number of columnar electrodes so as to alternately supply an alternating voltage with a reversed phase, and the even number of the AC power source. And a DC power source for applying a DC bias acting as an attractive force toward the columnar electrode to the charged particles existing in the space between the columnar electrode and the external electrode.

Here, the number of even-numbered columnar electrodes may be four, and among the even-numbered columnar electrodes, one end of each half of the columnar electrodes arranged at intervals of The other half of the columnar electrodes may be projected by the same length as the one end portion.

The alternating current voltages whose phases are alternately inverted may be different from each other, and the alternating current power source may be variable in frequency.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a basic embodiment of the present invention, in which a central electrode 11 has four columnar electrodes 11A to 11A.
The case of 11D is shown. As shown, four columnar electrodes 11A symmetrically arranged around the central axis 12
To 11D, the AC power source 13 is connected to the columnar electrodes 11A to 1D.
An alternating voltage whose phase is inverted is alternately supplied to each of 1D. In the figure, an AC power supply 13 is configured by using a transformer, and alternating phases are supplied to every four columnar electrodes with the phase reversed. Further, the external electrodes 15 are provided so as to surround the respective one ends 11a to 11d of the columnar electrodes 11A to 11D. This AC power supply 13 is connected to the center electrode 11
A DC power supply 14 that applies a DC bias acting as an attractive force toward the central electrode 11 to the charged particles 16 existing in the space between the external electrode 15 and the external electrode 15 is connected. In Figure 1,
A common DC bias is applied to all the columnar electrodes 11A to 11D, but if they act as an attractive force, that is, if they have the same polarity, it is not necessary to apply a DC bias of the same value to all of them. In this way, the DC voltage in the direction of attracting the charged particles 16 and the AC voltage are superimposed and applied to the center electrode 11. For example, to capture positive ions, a negative DC voltage is applied to each columnar electrode with respect to the external electrode as shown in the figure. At this time, the purpose of the external electrode 15 is to define the electric field around the center electrode 11, and it is not necessary to surround the center electrode without a gap, and an appropriate gap may be provided as shown in the figure. Further, since only the electric field in the vicinity of the columnar electrode is important in the method of the present invention, it is sufficient that the external electrode simply surrounds the circumference, and the details of its shape are not important. For example, although the external electrode has an axially symmetrical structure in the drawing, it is not always necessary. On the contrary, each columnar electrode preferably has a symmetrical structure around the central axis in order to extract the charged particles with good mass selectivity.

With this configuration, charged particles in a wide mass range can be captured at high density in the space between each of the columnar electrodes 11A to 11D and the external electrode 5, and a specific amount of the captured charged particles can be obtained. A charged particle having a mass equal to or larger than the above value is automatically and selectively taken from one end surrounded by the external electrode of each columnar electrode into the space around the central axis surrounded by each columnar electrode, and through this space, each columnar electrode It can be selectively taken out from the other end side.

In the device of the present invention, the principle of trapping charged particles in the space around the center electrode between the center electrode and the outer electrode is the same as that of the prior invention. That is, the charged particles are captured by the electrostatic attraction due to the DC voltage applied to each columnar electrode.
However, the trapped particles will eventually collide with the columnar electrode only by the attractive force. In the method of the present invention, this is prevented by superimposing and applying the AC voltage. Here, when the strength of the AC electric field decreases with an increase in the distance from the center electrode, the force received by the charged particles from this AC electric field acts as a repulsive force in the direction away from the center electrode when time-averaged. Holds charged particles in space in equilibrium with attractive forces. At this time, the repulsive force due to the AC electric field is 1 / mf ² (m
Is proportional to the mass of the charged particle) and inversely proportional to the mass of the particle. Therefore, the equilibrium position with the attraction due to the DC electric field becomes closer to the center electrode as the mass of the particle increases.

On the other hand, charged particles can be trapped in the inner space surrounded by a plurality of columnar electrodes, that is, the inner space of the central electrode by the same action of the alternating electric field. Further, in the device configuration of the present invention, since one end of each columnar electrode constituting the center electrode is surrounded by the external electrode, charged particles are also captured between this one end of each columnar electrode and the external electrode. A space is formed. Moreover, at the end portion of the center electrode, the repulsive force against the charged particles by the AC electric field is weakest in the center portion, on the center axis of FIGS. 1 and 2. Therefore, the attractive force due to the applied DC bias overcomes the repulsive force to draw the charged particles into the internal space of the center electrode. In this case, since the confinement force does not work in the direction along the length of the columnar electrode, the trapped particles can move freely along the central axis. The principle of such confinement inside is based on the fact that the action of the AC electric field acts as a repulsive force when time averaged.However, if the mass of the particle is too small, the action of the AC electric field is large and the movement of the particle It is accelerated resonantly and cannot be captured stably. This creates a lower limit on the mass of particles that can pass through the inner space of the center electrode. That is, when the AC voltage is represented by V _ac , when V _ac / mf ² becomes equal to or less than a specific value determined by the structure of the columnar electrode, ions can pass through the inner space of the center electrode. As shown in FIG. 1, when a common DC bias is applied to all columnar electrodes, no DC electric field is generated in the internal space, but by changing the DC bias for each columnar electrode, the passage characteristics of particles can be improved. Can be changed.

Therefore, according to the configuration of the present invention, the trapping characteristic of the charged particles in the space outside the center electrode and the trapping characteristic in the inner space are automatically combined so that a wide range of the external space can be obtained. It is possible to capture particles having a mass and at the same time, particles having a mass larger than a specific value can be taken out through the internal space. That is, since particles having a small mass are trapped at a position away from the center electrode when trapped in the external space, they cannot enter the center electrode and are stably trapped. On the contrary, particles with a large mass have a trapping position in the outer space close to the center electrode and are easily taken into the inside, but since they can pass through the inside stably even after being taken in, columnar columns that do not constitute external trapping The other end of the electrode is automatically removed and dispensed.

At this time, the number of columnar electrodes is four, which is the most practical configuration. The quadrupole is usually most mass-sensitive in the passage characteristics of particles in the internal space, as is used in mass spectrometers. However, the principle of the invention of the present application is not limited to the quadrupole, and the same holds for any even number of columnar electrodes such as six.

At this time, the end portions 11a to 11d of the columnar electrodes on the side for trapping particles have the same length as all the columnar electrodes 11A to 11D as shown in FIG.
Even if they are not uniform, the above principle of the present invention is similarly established. However, as shown in FIG. 2B, half of the even number of columnar electrodes, for example, one columnar electrode, for example,
When the end portions 11a and 11b of 1A and 11B are protruded by the same length as the end portions 11c and 11d of the other half of the columnar electrodes 11C and 11D, the configuration shown in FIG.
As compared with the case of (a), the particle trapping property can be improved. That is, in the configuration shown in FIG. 2B, the AC voltages applied to the half long columnar electrodes 11A and 11B and the short half columnar electrodes 11C and 11D have exactly the opposite phases. . As a result, in the space between each columnar electrode and the external electrode 15, the AC voltages whose phases are inverted do not cancel each other out, and the AC electric field of the phase applied to the half long columnar electrodes 11A and 11B is dominant. As a result, the AC electric field is attenuated gradually with respect to the distance from the columnar electrode. This has the effect of increasing the effective repulsive force that acts on the charged particles from the AC electric field, particularly at the portion near the ends of the columnar electrodes, and acts to move the equilibrium position of the trapped particles away from the columnar electrodes. As a result, the trapped particles collide with the columnar electrode or are trapped in a narrow region near the columnar electrode, so that the particles are prevented from being lost due to repulsion between the charged particles, and the trapping property is improved. Thus, even if the lengths of the columnar electrodes are made different, the characteristics of extracting particles through the inside of the columnar electrodes do not change.

As described above, the purpose of making the lengths of the columnar electrodes unequal is to partially prevent the AC voltages whose phases are inverted from canceling each other. Therefore, even if the columnar electrodes having the same length are used, if the alternating voltages having the inverted phases supplied to them are different from each other, the mutual canceling effect is weakened. The effect is exactly the same as when they are made different.

Specific experimental examples will be described below.

With the device having the structure shown in FIG. 3A, the ions of Xe and Ar were captured, and the above characteristics were actually confirmed.
The example of this figure uses the configuration of FIG. 1, that is, the method of disposing four columnar electrodes symmetrical about the central axis. However, in FIG. 3A, illustration of the AC power supply and the DC power supply is omitted. Here, the columnar electrodes 11A to 11D each made of a stainless steel cylinder having a diameter of 1 cm are shown in FIG.
The axis of each cylinder is the central axis 12
Were arranged side by side on a circumference having a radius of 1 cm to form a center electrode. Around that, as the external electrode 15, a diameter of 17 cm,
A cylindrical wire net having a length of 20 cm was arranged. Each columnar electrode projects into it by 15 cm. That is, one end of the columnar electrode is surrounded by the external electrode. A quadrupole mass spectrometer 17 is arranged on the other end side of the columnar electrode in order to detect the ions extracted through the inside of the center electrode, that is, the space surrounded by the columnar electrodes 11A to 11D. Further, in order to detect the ions trapped between the center electrode and the external electrode, an opening 15A was provided in a part of the external electrode 15, and the extraction electrode 18 was arranged behind it. The purpose of this extraction electrode is to apply a negative pulse voltage to the extraction electrode to extract the captured charged particles and measure the mass of the captured particles with the quadrupole mass analyzer 19.

With this experimental apparatus, the characteristics were measured as follows. First, in the circuit using the transformer of FIG. 1, -4V is applied to each of the columnar electrodes 11A to 11D with respect to the external electrode 15.
DC voltage of 100V (V
An alternating voltage of _pp = 200 V) was applied. While maintaining this voltage, Xe or Ar gas is introduced at about 5 × 10 ⁻⁵ Pa. Next, the electron beam source 20 was operated only for 10 ms to pulse-irradiate the electron beam with an energy of about 100 eV to ionize the introduced rare gas and capture it around the center electrode. Then, the trapping characteristics of the ions and the extraction characteristics of the ions passing through the inner space of the center electrode were measured by the above-mentioned two quadrupole mass analyzers 17 and 19.

In FIG. 4, the frequency f of the AC voltage is changed to
This is the result of counting Xe ions and Ar ions passing through the internal space of the center electrode. As described below, f = 500k
Even at Hz, both Xe and Ar ions are trapped in the space around the center electrode, but as shown in the figure, they cannot pass through the center electrode and leak. f is 590 kHz
When it is increased to, the condition of internal passage of the center electrode is satisfied,
The count of Xe ions rises rapidly. Xe as shown
It can be seen that the frequency region in which ions are counted is clearly separated from Ar ions, and mass-selected ions can be extracted. The two regions differ by the square root (= 1.8) of the mass ratio of the ions, and the characteristics are V as designed.
It shows that it is determined by _ac / mf ² .

FIG. 5 shows the results of measuring the trapping life of Xe ions trapped in the space between the center electrode and the outer electrode under the same conditions as above. Here, the trapping lifetime is defined as the time when the number of trapped charged particles becomes 1 / e from the value at the start of trapping. Moreover, in this figure, as shown in FIG. 2A, the case where all the four columnar electrodes have the same length,
As shown in (b), when 2 out of 4 protrudes by 1 cm (therefore, the total length protruding into the external electrode is 15 cm).
cm and 16 cm). In both cases, when the frequency f of the alternating current is increased, the capture life of the particles gradually decreases due to the particle capture position approaching the columnar electrode. Also, at f = 590 kHz, particles begin to flow out through the inside of the center electrode, so that the capture lifetime is rapidly reduced. However, comparing the case where the lengths of the four columnar electrodes are all the same (described as 0 cm in the figure) and the case where two of the four columnar electrodes protrude by 1 cm, the latter has a longer trapping life as f increases. It can be seen that the decrease of is moderate. However, when the length of the protrusion was further increased to 2 cm, the trapping characteristic was deteriorated.

Further, it was experimentally confirmed that C ₁₁ clusters can be selectively taken out from methane gas as a raw material in the same apparatus as above under substantially the same conditions. In this case, a methane gas of about 10 ⁻⁴ Pa and a He gas of about 10 ⁻³ Pa were introduced into the apparatus, and this was continuously irradiated with an electron beam having an energy of about 100 eV. Frequency f of AC voltage is 590 kHz
When kept at z, it passed through the inner space of the center electrode and C ₁₁
It was confirmed that ⁺ cluster ions flowed out. It is considered that the C ₁₁ clusters were formed by the reaction of CH _x ⁺ ions trapped in the space between the columnar electrode and the external electrode with the CH _x radicals also formed by electron beam irradiation.

From the above experiments, the effectiveness of the method of the present invention could be confirmed.

When only specific charged particles are targeted, the frequency of the AC voltage may be fixed to a predetermined value. However, as described above, it is preferable to change the frequency of the AC power source when a plurality of types of charged particles are targeted.

[0028]

According to the apparatus of the present invention, charged particles over a wide mass range and energy range can be captured at a high density, and charged particles having a mass of a specific value or more can be selectively taken out and supplied to the outside. Therefore, the apparatus of the present invention has a remarkable effect when it is used for the purpose such as the growth of microcrystals using the trapped particles as a seed, the material treatment in a space isolated state such as the reaction between the trapped particles and the reaction gas. To be

[Brief description of drawings]

FIG. 1 is a diagram showing a principle configuration of the present invention when a center electrode composed of four columnar electrodes is used.

FIG. 2 is a side view showing a typical structure of a columnar electrode and an external electrode.

FIG. 3 is a diagram showing a device configuration of a specific experimental example.

FIG. 4 is a diagram showing the structure of FIG. 3 in which the frequency of the alternating voltage is changed and Xe ions and A
It is a figure which shows the result of having counted the r ion.

FIG. 5 is a diagram showing the results of measuring the capture lifetime of Xe ions trapped in the space between the center electrode and the outer electrode under the same conditions as in FIG.

FIG. 6 is a diagram showing a conventional method.

FIG. 7 is a diagram showing a charged particle capturing device previously filed by the inventor of the present invention.

[Explanation of symbols]

2 AC power source used in the conventional method 3 DC power source used in the conventional method 4 Center electrode of the prior application method 5 External electrode of the prior application method 6 AC power source of the prior application method 7 DC power source of the prior application method 11 Center electrodes 11A, 11B , 11C, 11D Columnar electrodes 11a, 11b, 11c, 11d One end of columnar electrode 12 Center axis 13 AC power source 14 DC power source 15 External electrode 16 Charged particle 17, 19 Mass spectrometer 18 Extraction electrode 20 Electron beam source 31, 32, 33, 34 Trapping Electrode Used in Conventional Method 35, 36 Rotating Hyperboloidal Trapping Electrode Used in Conventional Method 37 Ring Trapping Electrode with Inner Surface Rotating Hyperboloid Used in Conventional Method 38 Magnet Used in Conventional Method 39 Magnetic field used in conventional methods

Claims (5)

[Claims] 1. A center electrode composed of four or more even-numbered columnar electrodes symmetrically arranged around a central axis, an external electrode surrounding one end of each of the even-numbered columnar electrodes, and the even number. AC power supply connected to each of the columnar electrodes of the book so as to supply alternating voltage of which phases are alternately inverted, and the charging present in the space between the even-numbered columnar electrodes and the external electrodes in the AC power supply. A device for trapping and supplying charged particles, comprising: a DC power supply that applies a DC bias acting as an attractive force to the particles toward the columnar electrodes. 2. The charged particle supply / supply device according to claim 1, wherein the number of the even-numbered columnar electrodes is four. 3. The one end of each of the half of the even number of columnar electrodes, which is arranged at every other one of the even number of columnar electrodes,
The charged particle trapping / supplying device according to claim 1 or 2, wherein the other half of the columnar electrodes are protruded by the same length from the one end of each of the columnar electrodes. 4. The charged particle capturing / supplying device according to claim 1, wherein the alternating voltages whose phases are alternately inverted are different from each other. 5. The charged particle capturing / supplying apparatus according to claim 1, wherein the AC power source has a variable frequency.