JPH0398245A - Tiling electric field type secondary electron multiplier - Google Patents

Abstract

PURPOSE:To provide a secondary electron multiplier with which occurrence of ion feedback is suppressed, which permits stable operation even at low vacuum, has high multiplying efficiency and enables large output current by narrowing an output end of a channel with high electron density. CONSTITUTION:A first channel base 31 and a second channel base 32 are tiltingly placed so that a channel 34 formed between the two is narrowed toward an output end 36 side, so that a tilting electric field is formed perpendicularly to an equipotential surface. Primary electrons 13 are incident from an input end 35 side to the channel 34 between the first channel base 31 and the second channel base 32 being formed with such tilting electric field and when the electrons 13 collide against the first channel base 31 to have secondary electrons 14 generated, the secondary electrons 14 perform movement close to cycloidal movement and repeat colliding against a secondary electron multiplier face 43 of the first channel base 31. Therefore the secondary electrons 14 are multiplied permitting secondary electron flow to be taken out from a collector 37.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gradient electric field type secondary electron multiplier in which an electric field for accelerating secondary electrons in a channel is gradient.

[Prior Art] Generally, a secondary electron multiplier has a structure in which a plurality of dynodes, which are electrodes for multiplying secondary electrons, are separated, and a secondary electron multiplier tube has a structure in which dynodes, which are electrodes for multiplying secondary electrons, are separated. There is a continuous die/-done secondary electron multiplier called a channel type secondary electron multiplier.

A continuous dynode secondary electron multiplier has a parallel plate-like channel base or pipe shape, and has a high resistance secondary electron emitting surface on the inner surface. An example of a conventional continuous tie node secondary electron multiplier of this type is shown in FIG.

The secondary electron multiplier 1 has a secondary electron emitting surface 4 made of a high-resistance secondary electron emitting material on opposing surfaces of flat channel substrates 2 and 3 made of glass or ceramics arranged parallel to each other. .5 is formed respectively.

The secondary electron emitting surfaces 4 and 5 formed on each of the channel bases 2 and 3 are connected to high-voltage direct current at the input end 7 and output end 8 of the channel 6 formed between the channel bases 2 and 3. Connected to power supply 9. This high-voltage DC power supply 9 generates an electric field in the axial direction of the channel 6 for accelerating the secondary electrons emitted from the secondary electron emission surfaces 4 and 5 of the channel substrates 2 and 3. In addition, the output terminal 8 of the channel 6
A collector 11 for collecting the secondary electrons multiplied within the channel 6 is provided opposite to the collector 11 .

Between this collector 11 and the output end 8 of the channel 6, an electric field #12 is connected for generating an electric field that guides the secondary electrons that are multiplied and output from the output end 8.

3 4 - When primary electrons 13 enter from the input end 7 side of the secondary electron multiplier tube 1, the primary electrons 13 reach the secondary electron emitting surface of each channel substrate 2, 3, as shown by the solid line in FIG. 4,
5 and generates secondary electrons l4. This secondary electron l4 is accelerated by the electric field, and while drawing a parabolic trajectory, it collides with the secondary electron emitting surfaces 4 and 5 of each channel substrate 2 and 3, and further emits secondary electrons l4 from there. , and thereafter, this is repeated and the secondary electrons l4 multiplied in an avalanche manner are collected in the collector 1l.

In channel 6 of the secondary electron multiplier l having the above structure, the equipotential surface is perpendicular to the axial direction of the secondary electron multiplier l, as shown by the dotted line in Figure 3. . Therefore, the trajectory of the secondary electrons 14 between the channel substrates 2 and 3 becomes parabolic, and the secondary electron emission surface 4 of the secondary electrons 14
, 5 is proportional to the ratio of the axial distance of the channel 6 to the distance between the channel substrates 2, 3. Therefore, in order to obtain a high-gain secondary electron multiplier, it is necessary to increase the value of the above ratio, and also to uniformly align the equipotential surfaces perpendicular to the axes of the channel substrates 2 and 3. , the axial length must be further increased.

In order to solve these problems of conventional continuous dynode electron multipliers, for example, Japanese Patent Publication No. 5016145, Japanese Patent Publication No. 50-25303, and Japanese Patent Publication No. 52-3
No. 8378 and other publications propose a gradient electric field type secondary electron multiplier tube that utilizes a gradient electric field to accelerate secondary electrons and obtains an effective gain with a low acceleration voltage.

For example, in the above-mentioned Japanese Patent Publication No. 50-25303, there is
As shown in the figure, it consists of a first flat plate 21 whose inner surface has secondary electron emitting properties and a second flat plate 22 which has high resistance, and these first flat plate 2l and second flat plate 22 are A channel 230 formed between the human power end 24 and the output end 2
Secondary electron multiplier tubes 26 are shown arranged such that the interval becomes wider toward the 5th side. The first flat plate 2
The equipotential surface formed between the first and second flat plates 22 forms an acute angle with respect to the first flat plate 2l, as shown by the dotted line in FIG. becomes high potential. As a result, the secondary electrons 14 take a trajectory as shown by the solid line and reach the first flat plate 2.
The secondary electrons collide with the secondary electron multiplication surface 27 of No. 1, are multiplied, and are captured by the collector 28.

[Problems to be Solved by the Invention] By the way, in the conventional secondary electron multiplier 26 described above, the channel 23 has the first flat plate 21 and the second flat plate 21 on the input end 24 side.
Since the distance between the channel 23 and the flat plate 22 is narrow, and the distance increases toward the output end 25, the input end 2 of the channel 23
In order to make the charged particles incident on the electron beam 4, it is necessary to narrow down the incident beam of the charged particles as narrowly as possible. In addition, when the incident beam of charged particles cannot be focused narrowly, multiple sets of secondary electron multiplier tubes 26, . . . , 26 are directed toward the incident position of the charged particles, and 24 must be aligned and arranged in a fan shape, which increases the overall size, and in practical terms, there is a problem in that it becomes extremely troublesome to mount it on a mass spectrometer or the like.

In addition, in general, in a secondary electron multiplier tube, the density of electrons is high at the output end due to multiplication of secondary electrons, so the electrons collide with the residual gas, and this residual gas is ionized, which is the opposite of the electrons. However, in the conventional secondary electron multiplier tube 26, since the distance between the first flat plate 22 and the second flat plate 22 is wide on the output end 25 side, the ions become secondary electrons. There is a problem in that so-called ion feedback occurs in which secondary electrons are generated by returning to the electron multiplier tube 26 side and colliding with the second flat plate 22.

An object of the present invention is to provide a gradient electric field type secondary electron multiplier tube that suppresses the occurrence of ion feedback, operates stably even in low vacuum, has high multiplication efficiency, and can obtain a large output current. It is.

[Means for Solving the Problems] Therefore, the present invention provides a flat first channel substrate for secondary electron multiplication, and a flat first channel substrate for generating a gradient electric field, which is disposed opposite to the first channel substrate. A channel is formed between the second channel substrate and the secondary electrons generated by the collision of charged particles incident on one end of the first channel substrate along the direction of the gradient electric field. A secondary electron multiplier tube is configured to sequentially multiply in an avalanche manner while moving while colliding with the first channel substrate, and to obtain a multiplied secondary electron flow from the other end of the first channel substrate, 1 channel substrate is its 2nd channel substrate
The surface facing the channel substrate is made of a material that is resistive and has a large secondary electron emission coefficient, and the second channel substrate is made of a material that faces the first channel substrate and is resistive. The first channel base and the second channel base are arranged such that the interval on the input end side of the channel is larger than the interval on the output end side, and the interval decreases toward the output end side, and the above-mentioned The present invention is characterized in that a DC high voltage is applied between one end and the other end of the first channel substrate and between one end and the other end of the second channel substrate to form the gradient electric field.

Another feature of the present invention is that the surface of the second channel substrate facing the first channel substrate is subjected to a surface treatment to reduce the secondary electron emission rate.

Furthermore, another feature of the present invention is that the second channelless substrate is shifted from one end of the first channel substrate toward the other end of the first channel substrate. It is said that

Furthermore, the present invention provides that the first channel substrate and the second channel substrate are arranged such that one end of each of the first channel substrate and the second channel substrate of the second channel substrate coincide with each other; Another feature is that the other end of each of the first channel substrates is provided with a gradient electric field forming electrode extending between the first channel substrate and the second channel substrate.

[Function] Near the other end of the first channel substrate, the electron density is high because the multiplied secondary electron flow is output, and the electrons collide with the residual gas, causing the residual gas to act in the opposite direction to the secondary electrons. ionized into charged ions.

These ions try to head into the channel between the first channel substrate and the second channel substrate, but since the output end of the channel is narrow, the probability of returning from this output end into the channel is small. Ion feedback is less likely to occur.

Furthermore, if the surface of the second channel substrate facing the first channel substrate is made of a resistive material and has been subjected to a surface treatment to reduce the secondary electron emission rate, the above-mentioned ion No secondary electrons are emitted due to collisions, and ion feedback is suppressed.

Furthermore, since the first channel substrate and the second channel substrate are formed of a continuous and uniform resistor, an equipotential surface connecting the equal potentials generated in the first channel substrate and the second channel substrate is formed. is formed. Therefore,
If the first channel base is shifted in the axial direction with respect to the second channel base, or if an electrode for forming an inclined electric field is formed between the first channel base and the second channel base, An equipotential surface formed between the first channel substrate and the second channel substrate is inclined.

The tilt of this equipotential surface forms the gradient electric field.

[Effects of the Invention] According to the present invention, since the output end of the channel where electron density is high is narrow, the ions generated when electrons collide with residual gas at the output end of the channel are directed toward the output end side of the channel. The probability of returning to ion becomes smaller, the occurrence of ion feedback is reduced, and the occurrence of noise is also suppressed.

Further, according to the present invention, by subjecting the second channel substrate to a surface treatment that reduces the secondary electron emission rate, even if ions collide with the second channel substrate, no secondary electrons are emitted, and the ions The occurrence of feedback can be more effectively suppressed, stable operation can be obtained even in low vacuum, and a large output current can be obtained without the effect of suppressing gain due to space charges.

Furthermore, according to the present invention, the first channel substrate and the second
A gradient electric field can be easily formed by shifting and arranging the channel substrates, or by simply forming electrodes for forming a gradient electric field on the first channel substrate and the second channel substrate.

[Examples] Examples of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows the structure of an embodiment of a gradient field type secondary electron multiplier according to the present invention.

The gradient electric field type secondary electron multiplier 30 includes a flat first channel substrate 3l for multiplying secondary electrons, and a second flat channel substrate 3l for generating a gradient electric field, which is disposed opposite to the first channel substrate 3l. It consists of a channel base 32.

The first channel substrate 31 has resistance and a large secondary electron emission coefficient, for example, ZnO.
-Tie type ceramic material.

Further, the second channel base 32 is also made of the same material as the first channel base 3l. However, the surface 33 of the first channel-free substrate 31 facing the second channel substrate 32 is intentionally roughened by, for example, argon ion bombardment, and a surface treatment is applied to reduce the secondary electron emission rate. has been done.

As can be seen from FIG. 1, the distance between the first channel base 3l and the second channel base 32 on the input end 35 side of the channel 34 formed between them is greater than the distance on the output end 36 side. They are arranged so that the intervals become smaller as they go toward the output end 36 side.

In order to collect the secondary electrons l4 that are multiplied within the channel 34 between the first channel substrate 31 and the second channelless substrate 32 and eject from the output end 36, the A collector 37 is arranged.

An electrode 38a formed on one end 31a of the first channel base 31 and an electrode 3 formed on the other end 3lb.
8b, an electrode 39a formed on one end 32a of the second channel base 32 and an electrode 3 formed on the other end 32b.
9b, a high DC voltage is applied from a high voltage DC power supply 41. Further, a DC power supply 42 is connected between the collector 37 and the electrode 38b at the other end 3lb of the first channel base 31l4 and the electrode 39b at the other end 32b of the second channel base 32.
DC voltage is applied.

With such a structure, the first channel base 31 and the second channel-free base 32 have electrodes 31a and 3l.
A uniform accelerating electric field is formed between the electrodes 39a and 39b and between the electrodes 39a and 39b by the high DC voltage applied from the high voltage DC power supply 41. As a result, the surface connecting the equal potentials of the first channel substrate 31 and the second channel substrate 32 becomes an equipotential surface.

However, as described above, the first channel base 31 and the second channel base 32 are arranged such that the channel 34 formed therebetween is narrower on the output end 36 side.
Since they are arranged at an angle, an equipotential surface is formed that is inclined at an acute angle from a position perpendicular to the first channel base 3l toward the first channel base 31, as shown by the dotted line in FIG. be done. Therefore, a gradient electric field is formed perpendicular to this equipotential surface. Primary electrons 13 enter the channel 34 between the first channel substrate 31 and the second channel substrate 32 in which such a gradient electric field is formed from the manual end 35 side, and enter the first channel substrate 31. When the secondary electrons 14 are generated by collision, the secondary electrons 14 move in a cycloidal motion in the above-mentioned gradient electric field,
The secondary electrons 14 are repeatedly collided with the secondary electron multiplier surface 43 of the second channel substrate 3l, and the secondary electrons 14 are multiplied, and a stream of secondary electrons is taken out from the collector 37.

By the way, near the other end 31b of the first channel substrate 31, the multiplied secondary electron flow is output, so the electron density is high, and the electrons collide with the residual gas, causing the residual gas to become It is ionized into charged ions M'. Therefore, even if the ions M' try to enter the channel 34 from the output end 36 of the channel 34 between the first channel substrate 3l and the second channel substrate 32, 36 is narrow, so the probability is small.

Then, the ions M' are transferred to the output end 36 of the channel 34.
from the channel 34 to the second channel base 3
2, the second channel substrate 32
Since the surface 33 facing the channel substrate 31 is subjected to a surface treatment to reduce the secondary electron emission rate, no secondary electrons 14 are emitted even when the ions M' collide, and ion feedback is suppressed. . As a result, stable operation can be obtained even in a low vacuum, noise generation due to ion feeder knocks can be suppressed, and a large output current can be obtained without the effect of suppressing gain due to space charges.

Furthermore, since the input end 35 of the channel 34 is wide, there is no need to narrow down the incident beam.

Next, a current embodiment of the present invention is shown in FIG.

The gradient field type secondary electron multiplier 50 shown in FIG. 2 is different from the secondary electron multiplier 30 shown in FIG. One end 31a of the first channel base 3l shifts toward the other end 3lb, and the second channel base 32' is bent in the middle, so that the input end 35 side of the channel 34 becomes wider than the output end 36 side. This is how it was done.

Even with such a structure, the same functions and effects as those shown in FIG. 1 can be achieved.

In addition, in the above embodiment, the first channel substrate 3
1 and the second channel substrate 3 2. 3 2' may be made of glass, ceramics, or the like, and a secondary electron emitting surface made of a secondary electron emitting material may be formed on the surface thereof by a method such as sputtering or vapor deposition.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram schematically showing the structure of an embodiment of a gradient field type secondary electron multiplier according to the present invention, and FIG. 2 is a modification of the gradient field type secondary electron multiplier shown in FIG. 1. FIGS. 3 and 4 are explanatory diagrams each schematically showing the structure of a conventional secondary electron multiplier. 30... Gradient electric field type secondary electron multiplier 17 18 31 - First channel substrate, 32. 32'... Second channel substrate, 33... Opposing surface, 34... Channel, 35 ...input end,
36... Output end, 37 ・Collection 38a, 38b, 3
9a, 39b Electrode, 41... DC high voltage power supply, 42
...DC power supply, 43...Gradient electric field type secondary electron multiplier surface, 50...Secondary electron multiplier tube. evening

Claims (1)

[Scope of Claims] (1) Between a flat first channel substrate for secondary electron multiplication and a flat second channel substrate for generating a gradient electric field, which is disposed opposite thereto. A channel is formed in the process in which secondary electrons generated by the collision of charged particles incident on one end of the first channel substrate move along the direction of the gradient electric field while colliding with the first channel substrate. A secondary electron multiplier tube configured to obtain a secondary electron flow multiplied in an avalanche manner and multiplied from the other end of a first channel substrate, the first channel substrate being The surface facing the channel substrate is made of a material having resistance and a large secondary electron emission coefficient, and the surface of the second channel substrate facing the first channel substrate is made of a material having resistance. , the first channel substrate and the second channel substrate.
The channel base is arranged such that the interval on the input end side of the channel is larger than the interval on the output end side, and the interval becomes smaller as it goes to the output end side, and one end and the other end of the first channel base A gradient electric field type secondary electron multiplier, characterized in that the gradient electric field is formed by applying a DC high voltage between the ends of the second channel substrate and between one end and the other end of the second channel substrate. (2) The gradient electric field type according to claim 1, wherein the second channel substrate has a surface facing the first channel substrate subjected to a surface treatment to reduce the secondary electron emission rate. Secondary electron multiplier. (3) The inclination according to claim 1, wherein the second channel base is shifted from one end of the first channel base toward the other end of the first channel base. Electric field type secondary electron multiplier. (4) The first channel substrate and the second channel substrate are arranged such that one end of the first channel substrate and the other end of the channel substrate coincide with each other, and one end of the second channel substrate and the second channel substrate of the first channel substrate 2. A gradient electric field type secondary electron multiplier according to claim 1, wherein the other end is provided with a gradient electric field forming electrode extending between said first channel substrate and said second channel substrate.