JPS5836463B2 - ion source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion source suitable for use in a mass spectrometer,
In particular, it relates to an ion source that ionizes a sample by colliding high-speed neutral particles with it.

As ionization methods for ion sources used in mass spectrometers, electron impact type, chemical ionization type, stable field ionization type, field desorption type, and the like have been developed and put into practical use one after another.

Recently, a new ionization method has been proposed in which high-energy high-speed neutral particles (such as Ar atoms) collide with a sample, and the sample is ionized using that energy. ) The survival rate of not only positive ions but also negative ions is high. (3) There is no need for thermal vaporization, so there is less thermal decomposition of the sample. (4) Since the particles are neutral, there is no charge-up, and even insulating materials can be easily ionized. It is expected to be developed in the future as a method that has many advantages such as the ability to

The present invention relates to the improvement of an ion source based on this proposed method. By arranging an auxiliary electrode near the neutral particle collision surface of the target and applying a different potential to the electrode than the target, ions generated from the target can be efficiently It is characterized in that it can be taken out by passing through the drawer slit.

The present invention will be explained in detail below using the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, and numeral 1 indicates a neutral particle source for generating a neutral particle beam, for example, an Ar atomic beam.

The particle source includes an Ar ion gun 6 equipped with a filament 2, a cathode 3, an anode 4, and an electrode 5, and a high-velocity Ar ion beam 7 taken out from the ion gun 6 that collides with Ar gas filled inside. The speed is determined by the collision chamber 8 in the housing 1, which removes only the charge from the ions and neutralizes them into Ar atoms.
and A mixed in the high-speed Ar atomic beam exiting the collision chamber.
It consists of a deflector 9 for deflecting and removing r ions.

The high-speed atomic beam 10 generated by the neutral particle source 1VIC is introduced into the ionization box 12 through the notch 11, and the atomic beam 10 of the target 13 inserted into the ionization box from behind. collides with a target surface that is tilted relative to the target surface.

The target 13 is made of copper, for example, and is attached to the tip of the introducing glove 1 via an insulator 14, and is connected to the acceleration power source 1.
An acceleration voltage Va of, for example, about 3 KV is applied from 6 to 3 KV.

Between the target 13 and the ionization box 12, a variable output positive power source 1.gamma. or a negative power source 18 is selectively connected by a switch 19.

Reference numerals 20 to 23 represent a group of slit electrodes for extracting and accelerating ions generated from the target 13, and appropriate voltages obtained by dividing the acceleration voltage by a voltage divider 24 are applied to each group.

In such a configuration, Ar ions ionized in the ion gun 6 and accelerated at high speed with a high voltage of several KV collide with Ar gas (Ar atoms) in the collision chamber 8 and lose only their charge, forming a high-velocity Ar atomic beam. is converted to

High speed A and atomic beam 1 taken out from the collision chamber 8
0 proceeds approximately parallel to the slit electrode groups 21 to 23,
It collides with a target surface that is inclined at an angle of about 20' to 45 degrees with respect to the direction of travel.The collision surface is coated with a sample prepared by mixing glycerin and the test substance, for example, and The analyte is ionized by the collision of Ar atoms and ejected from the surface.

The ions generated in this way are extracted by the slit electrode group, accelerated, and guided to the mass spectrometer. It has been found that the amount of ions that can be extracted through the slit electrode can be increased by an order of magnitude by lowering the amount of ions.

This is presumed to be due to the following reasons.

In other words, the surface of the sample coated on the target surface may be a smooth plane, but it may have a complex shape, bulges, or unevenness, so ions generated from the surface may be oriented in a specific direction and ions may be oriented in other directions. It often happens that there is a direction, such that there are few.

Ions may also be generated with strong directionality due to the positional relationship between the atomic beam irradiation point and the slit and other reasons.

If the direction in which most of these ions are generated is in the direction of the slit as shown in Figure 2 a, there will be no problem, but in reality this is rarely the case and the ions are removed from the slit as shown in Figure 2 b and c. In most cases, the amount of ions that can be released is extremely small.

Therefore, by making the potential of the ionization box 12 different from the target potential by several to several tens of volts, an electric field is generated between the ionization box and the target in a direction perpendicular to the ion extraction direction (in the direction of arrow E). Due to the electric field, the second
A large amount of ions can be taken out by bending the direction (2) in Figures b and c toward the slit direction.

In this case, it is thought that the main factor involved in the deflection of ions is the electric field formed between the tilted target surface and the part of the ionization chamber facing the target surface. In the case of FIG. 2b, the positive ions generated from the target are deflected downward by connecting the positive power source 17 and making the potential of the ionization box 12 higher than the target potential.
In the case of C in the figure, on the contrary, it is necessary to connect the negative power supply 18 to deflect the positive ions generated from the target upward.

In this way, since the part of the ionization box facing the target surface is involved in deflection, if there is no ionization box, an ionization box is placed near the target and facing the target surface to assist. The electrodes may be arranged so that a potential different from that of the target can be applied to the auxiliary electrode.

In the above-described embodiment, positive ions were extracted from among the ions generated by atomic beam irradiation, but it is possible to extract negative ions in exactly the same way by simply considering the polarity of the voltage supplied to each electrode. Not even 1.

As described in detail above, according to the present invention, ions can be extracted efficiently with a simple configuration in which auxiliary electrodes are arranged.

Further, in the embodiment shown in FIG. 1, since an ionization box is used as an auxiliary electrode, the construction is particularly simple.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of one embodiment of the present invention.
The figure is a diagram for explaining the directionality of ions. DESCRIPTION OF SYMBOLS 1... Neutral particle source, 2... Filament, 3... Cathode, 4... Anode, 5... Electrode, 6... ...Ar ion L
7.----Ar ion beam, 8... Collision chamber, 9... Deflector, 10... High-speed Ar
Atomic beam, 11... Notch, 12...
...Ionization box, 13...Target, 14.
... Insulator, 16 ... Acceleration power supply, 17.
...Positive power supply, 18...Negative power supply, 19...
...Switch, 20-23...Slit electrode.

Claims (1)

[Scope of Claims] 1. An ion source in which neutral particles given a high velocity collide with a sample held on a target to ionize the sample, and the generated ions are extracted and accelerated through an extraction slit. An ion source characterized in that an auxiliary electrode is disposed near the neutral particle collision point and is configured to apply a different potential to the electrode than the target. 2. The ion source according to claim 1, wherein an ionization box containing the target is used as the auxiliary electrode.