JPH083985B2 - Gradient electric field type secondary electron multiplier - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gradient electric field type secondary electron multiplier having an inclined electric field for accelerating secondary electrons in a channel.

[Prior Art] Generally, a secondary electron multiplier has a structure in which dynodes, which are electrodes for multiplying secondary electrons, are separated into a plurality of parts, and a multiplying path for secondary electrons is provided. It is continuous and there is a continuous dynode secondary electron multiplier called a channel type secondary electron multiplier.

The continuous dynode secondary electron multiplier has a parallel plate-shaped channel substrate or a pipe shape, and has a high resistance secondary electron emission surface on the inner surface. An example of a conventional continuous dynode secondary electron multiplier of this type is shown in FIG.

The secondary electron multiplier 1 has a secondary electron emission surface 4 made of a high resistance secondary electron emission material on the opposing surfaces of flat plate-shaped channel substrates 2 and 3 made of glass or ceramics arranged in parallel with each other. , 5 are formed respectively.

The secondary electron emission surfaces 4 and 5 formed on the respective channel bases 2 and 3 have a high voltage DC power supply 9 at the input end 7 and the output end 8 of the channel 6 formed between the channel bases 2 and 3. Connected to. The 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. Also, facing the output end 8 of the channel 6,
A collector 11 is provided for collecting the secondary electrons multiplied in the channel 6. A power supply 12 is connected between the collector 11 and the output end 8 of the channel 6 to generate an electric field that guides secondary electrons that are multiplied and output from the output end 8.

When primary electrons 13 are incident from the input end 7 side of the secondary electron multiplier 1, the primary electrons 13 are emitted from the secondary electron emission surfaces 4,5 of the channel substrates 2 and 3 as shown by the solid line in FIG. To generate secondary electrons 14. The secondary electrons 14 are accelerated by the electric field, draw a parabolic trajectory, and further collide with the secondary electron emission surfaces 4,5 of the respective channel substrates 2 and 3,
Secondary electrons 14 are further emitted from there, and the secondary electron 14 multiplied by an avalanche by repeating this is collected in the collector 11
Collected in.

In the channel 6 of the secondary electron multiplier 1 having the above structure, the equipotential surface is perpendicular to the axial direction of the secondary electron multiplier 1 as shown by the dotted line in FIG. .
Therefore, the orbits of the secondary electrons 14 between the channel substrates 2 and 3 are parabolic, and the number of collisions of the secondary electrons 14 with the secondary electron emission surfaces 4,5 depends on the distance between the channel substrates 2 and 3. It is proportional to the ratio of the axial distance of the channel 6. Therefore, in order to obtain a high gain secondary electron multiplier, it is necessary to increase the value of the above ratio, and the equipotential surface is evenly aligned perpendicular to the axes of the channel substrates 2 and 3. , The shaft length must be increased.

In order to solve such problems of the conventional continuous dynode secondary electron multiplier, for example, in Japanese Patent Publication No. 50-16145, Japanese Patent Publication No. 50-25303 and Japanese Patent Publication No. 52-38378, the secondary There has been proposed a gradient electric field type secondary electron multiplier which utilizes a gradient electric field for accelerating electrons and obtains an effective gain at a low accelerating voltage.

For example, in Japanese Patent Publication No. 50-25303, as shown in FIG. 4, a first flat plate 21 whose inner surface has a secondary electron emitting property.
And a second flat plate 22 having high resistance. The first flat plate 21 and the second flat plate 22 are spaced apart from each other between the input end 24 and the output end 25 of the channel 23 formed therebetween. The secondary electron multiplier tube 26 is described so as to spread. The equipotential surface formed between the first flat plate 21 and the second flat plate 22 forms an acute angle with the first flat plate 21 as shown by the dotted line in FIG. It becomes a high potential as you go to. As a result, the secondary electrons 14 take a locus as shown by the solid line and move to the first flat plate 21.
The secondary electron multiplication surface 27 is collided with the secondary electron multiplication surface 27 to be multiplied and captured by the collector 28.

[Problems to be Solved by the Invention] In the above-described conventional secondary electron multiplier 26, the channel 23 has the first flat plate 21 and the second flat plate on the input end 24 side thereof.
Since the distance to the input end 24 of the channel 23 is made small, the incident beam of the charged particles needs to be narrowed as much as possible because the distance to the input end 24 of the channel 23 is narrow because the distance to the input end 24 of the channel 23 is narrow. . Further, when the incident beam of charged particles cannot be narrowed down, a plurality of sets of secondary electron multipliers 26, ..., 26 are directed to the incident position of charged particles, and the input end 24 of each channel 23 thereof is set. Since they must be aligned and arranged in a fan shape, the size becomes large as a whole, and there is a problem that mounting on a mass spectrometer or the like becomes very troublesome in practice.

Generally, in the secondary electron multiplier, the electron density is high on the output end side due to the multiplication of secondary electrons, so that the electrons collide with the residual gas, and this residual gas is ionized and is opposite to the electrons. Although the ions have polar charges, in the above-mentioned conventional secondary electron multiplier 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 above-mentioned secondary ions are generated. There was a problem that so-called ion feedback occurs, which returns to the electron multiplier tube 26 side and collides with the second flat plate 22 to generate secondary electrons.

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

[Means for Solving the Problems] For this reason, the present invention provides a first flat plate-shaped first electron multiplication device.
A channel is formed between the first channel substrate and a second channel substrate that is arranged opposite to the first channel substrate and is a flat plate-like second channel substrate for generating a gradient electric field. Collision of charged particles incident on one end of the first channel substrate. The secondary electrons generated by the above are sequentially multiplied by an avalanche in the process of moving while colliding with the first channel substrate along the direction of the gradient electric field.
A secondary electron multiplier adapted to obtain a multiplied secondary electron flow from the other end of the first channel substrate, wherein the first channel substrate has a resistance surface opposite to the second channel substrate. And a material having a large secondary electron emission coefficient, and the second channel substrate is made of a material having a resistance surface on the surface facing the first channel substrate. The second channel base body is arranged such that the gap on the input end side of the channel is larger than the gap on the output end side and the gap becomes smaller toward the output end side, and one end and the other end of the first channel base body. Between and second
The direct current high voltage is applied between one end and the other end of the 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 surface-treated to reduce the secondary electron emission rate.

Furthermore, in the present invention, the second channel substrate is the first channel substrate.
Another feature is that the one end of the channel substrate is shifted toward the other end of the first channel substrate.

Furthermore, according to the present invention, the first channel base body and the second channel base body are arranged so that their one ends and their other ends are aligned with each other, while the one end of the second channel base body and the first channel base body are arranged. Another feature is that the other end of the channel substrate is provided with a gradient electric field forming electrode extending between the first channel substrate and the second channel substrate.

[Operation] In the vicinity of the other end of the first channel substrate, the multiplied secondary electron flow is output, so that the electron density is high, the electrons collide with the residual gas, and the residual gas is opposite to the secondary electrons. Ionized into charged ions. The ions try to go into the channel between the first channel substrate and the second channel substrate, but since the channel has a narrow output end, the probability of returning from this output end into the channel is small, Ion feedback is less likely to occur.

Further, the second channel base body is made of a material whose surface facing the first channel base body has resistance, and
When the surface treatment is performed to reduce the secondary electron emission rate, secondary electrons are not emitted even by the collision of the ions, and the ion feedback is suppressed.

Further, since the first channel base and the second channel base are formed of continuous and uniform resistors, equipotential surfaces connecting equal potentials generated in the first channel base and the second channel base. Is formed. Therefore, the first channel base body is axially shifted with respect to the second channel base body, or the gradient electric field forming electrode is formed between the first channel base body and the second channel base body. Then, the equipotential surface formed between the first channel substrate and the second channel substrate is inclined. The tilted electric field is formed by the tilt of the equipotential surface.

[Effect of the Invention] According to the invention of claim 1, the distance between the first channel substrate and the second channel substrate at the input end of the channel is larger than that at the output end side, and as the distance from the output end side increases. Since the gaps are arranged to be small, the gradient electric field can be generated without using a special power source.

According to the second aspect of the present invention, the second channel substrate is subjected to the surface treatment to reduce the secondary electron emission rate, so that the secondary electron emission is achieved even if the ions collide with the second channel substrate. Therefore, the generation of ion feedback can be suppressed more effectively, stable operation can be obtained even in a low vacuum, and a large output current can be obtained without the effect of suppressing the gain due to space charge.

Furthermore, according to the third and fourth aspects of the present invention, the first channel base body and the second channel base body are shifted and arranged, or the gradient electric field is applied to the first channel base body and the second channel base body. A gradient electric field can be easily formed only by forming electrodes for formation.

Embodiments Embodiments of the present invention will be described below with reference to the accompanying drawings.

The structure of one embodiment of the gradient electric field type secondary electron multiplier according to the present invention is shown in FIG.

The gradient electric field type secondary electron multiplier 30 includes a flat plate-shaped first channel substrate 31 for secondary electron multiplication and a flat plate-shaped second channel substrate 31 arranged to face it. And a channel base 32.

The first channel substrate 31 has resistance and a large secondary electron emission coefficient, for example, ZnO-Ti.
It is made of O ₂ -based ceramic material.

The second channel base 32 is also made of the same material as the first channel base 31. However, the surface of the first channel substrate 31 facing the second channel substrate 32 is subjected to a surface treatment to intentionally roughen the surface 33 facing the second channel substrate 32 by, for example, the impact of argon ions to reduce the secondary electron emission rate. There is.

The first channel substrate 31 and the second channel substrate
As can be seen from FIG. 1, 32 indicates that the spacing between the channels 34 formed between them on the side of the input end 35 is larger than that on the side of the output end 36, and the spacing decreases toward the side of the output end 36. Is located in.

The first channel substrate 31 and the second channel substrate
A collector 37 is arranged opposite the output 36 in order to collect the secondary electrons 14 which have been multiplied in the channel 34 between them and which emerge from the output 36.

Then, between the electrode 38a formed on one end 31a of the first channel base 31 and the electrode 38b formed on the other end 31b, the electrode 39a formed on one end 32a of the second channel base 32 and the other end. A high DC voltage is applied from a high-voltage DC power supply 41 to the electrode 39b formed on 32b. Further, the collector 37, the electrode 38b at the other end 31b of the first channel base 31, and the electrode 39 at the other end 32b of the second channel base 32.
A DC voltage is applied from the DC power supply 42 between the voltage and b.

With this configuration, the first channel base 31 and the second channel base 32 are applied from the high voltage DC power supply 41 between the electrodes 31a and 31b and between the electrodes 39a and 39b. A uniform accelerating electric field is formed by DC high voltage. As a result, the surface connecting the same potentials of the first channel base 31 and the second channel base 32 becomes an equipotential surface. But,
As described above, the first channel base body 31 and the second channel base body 32 are the channels formed between them.
Since 34 is arranged so as to be inclined so that the output end 36 side becomes narrow, as shown by the dotted line in FIG. 1, from the vertical position to the first channel base 31, the first channel base 31 side An equipotential surface that is inclined at an acute angle is formed. Therefore, a gradient electric field is formed perpendicularly to this equipotential surface without using a special power source. The primary electrons 13 are incident on the channel 34 between the first channel base body 31 and the second channel base body 32, in which such a gradient electric field is formed, from the input end 35 side thereof, and then the first channel base body 31. When the secondary electrons 14 collide with each other and generate secondary electrons 14, the secondary electrons 14 make a motion close to a cycloidal motion in the gradient electric field and repeatedly collide with the secondary electron multiplying surface 43 of the first channel substrate 31. The multiplication of the secondary electrons 14 is performed, and the secondary electron flow is taken out from the collector 37.

By the way, in the vicinity of the other end 31b of the first channel substrate 31, since the multiplied secondary electron flow is output, the electron density is high, the electrons collide with the residual gas, and the residual gas is opposite to the secondary electrons. It is ionized into a charged ion M ⁺ . Therefore, even if the ion M ⁺ tries to enter the channel 34 from the output end 36 of the channel 34 between the first channel base 31 and the second channel base 32, the output end 36 of the channel 34 becomes narrow. Therefore, the probability is small.

Then, even if the ions M ⁺ return from the output end 36 of the channel 34 into the channel 34 and collide with the second channel substrate 32, the second channel substrate 32 faces the first channel substrate 31. Since 33 is surface-treated to reduce the secondary electron emission rate, the secondary electrons 14 are not emitted even by the collision of the ions M ⁺ , and the ion feedback is suppressed. As a result, stable operation can be obtained even in a low vacuum, generation of noise due to ion feedback can be suppressed, and a large output current can be obtained without the effect of suppressing gain due to space charge.

Also, since the input end 35 of the channel 34 is wide, it is not necessary to narrow the incident beam.

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

In the gradient electric field type secondary electron multiplier 50 shown in FIG. 2, in the secondary electron multiplier 30 of FIG. 1, the second channel substrate 32 ′ is different from that of the first channel substrate 31. One end 31a of the first channel base 31 shifts toward the other end 31b, and the second channel base 32 'bends in the middle, so that the input end 35 side of the channel 34 becomes wider than the output end 36 side. It was done like this.

Even with such a configuration, the same operation and effect as those of FIG. 1 can be obtained.

In the above embodiments, the first channel substrate
31 and the second channel bases 32, 32 'are made of glass, ceramics or the like, and the secondary electron emitting surface made of a secondary electron emitting substance is formed on the surface thereof by a method such as sputtering or vapor deposition. May be

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing the structure of one embodiment of a gradient electric field type secondary electron multiplier according to the present invention, and FIG. 2 is a modification of the gradient electric field type secondary electron multiplier of FIG. FIG. 3 is an explanatory diagram schematically showing the structure of an example, and FIGS. 3 and 4 are explanatory diagrams schematically showing the structure of a conventional secondary electron multiplier. 30 …… Gradient electric field type secondary electron multiplier, 31 …… First channel substrate, 32, 32 ′ …… Second channel substrate, 33 …… Opposed surface, 34 …… Channel, 35 …… Input End, 36 ...... Output end, 37 …… Collector, 38a, 38b, 39a, 39b …… Electrode, 41 …… DC high voltage power supply, 42 …… DC power supply, 43 …… Gradient electric field type secondary electron multiplication surface , 50 …… Secondary electron multiplier.

Claims (4)

[Claims] 1. A channel is formed between a flat plate-shaped first channel base body for secondary electron multiplication and a flat plate-shaped second channel base body for generating a gradient electric field which is arranged so as to face it. The secondary electrons generated by the collision of the charged particles incident on the one end of the first channel substrate move while colliding with the first channel substrate along the direction of the gradient electric field, and sequentially increase in an avalanche manner. A secondary electron multiplier tube that is adapted to obtain a multiplied secondary electron flow from the other end of the first channel substrate, wherein the first channel substrate is connected to the second channel substrate. The opposing surface is made of a material having resistance and a large secondary electron emission coefficient, and the second channel substrate is made of a material having resistance at the opposing surface to the first channel substrate. Channel of Base and second
The channel base is arranged such that the gap on the input end side of the channel is larger than the gap on the output end side and the gap becomes smaller toward the output end, and one end and the other end of the first channel base A gradient electric field type secondary electron multiplier, wherein a high direct current voltage is applied between the first and second ends of the second channel substrate to form the gradient electric field. 2. The inclination according to claim 1, wherein the surface of the second channel substrate facing the first channel substrate is surface-treated to reduce the secondary electron emission rate. Electric field type secondary electron multiplier. 3. The second channel base body is arranged so as to be shifted from one end of the first channel base body toward the other end of the first channel base body. Gradient electric field type secondary electron multiplier. 4. The first channel body and the second channel body are arranged so that their one ends and their other ends are aligned with each other, while one end of the second channel body and said first channel are arranged. 2. The gradient electric field type secondary electron multiplier according to claim 1, wherein the other end of the substrate is provided with a gradient electric field forming electrode extending between the first channel substrate and the second channel substrate. tube.