JPH0748374B2 - Vienna filter - Google Patents

Description

The present invention relates to a charged particle energy analyzer using a filter that superimposes an electric field and a magnetic field, and in particular, an electric field and a magnetic field having different filter lengths. The present invention relates to a Wien filter in which charged particles go straight.

[Conventional technology]

Conventionally, as an energy analyzer for an electron beam or an ion beam, an analyzer called a Wien filter in which uniform electric and magnetic fields are superimposed is known. The Wien filter has excellent characteristics such as high resolution analysis expected and that the beam travels straight in the filter. It is suitable for performing analysis of energy and the like because the energy of is converted into a single color and the optical system can be simplified to simplify the configuration of the analyzer.

FIG. 3 is a perspective view of a conventional Wien filter, in which 1 and 2 are magnetic poles and 3 and 4 are electrodes.

In the figure, a uniform magnetic field is applied to the magnetic poles 1 and 2 and a uniform electric field is applied to the electrodes 3 and 4 in directions orthogonal to each other,
An electron beam is incident in a direction orthogonal to these. In such a Wien filter, the orthogonal uniform electric field E
And magnetic field B are Ew = 2πUo / L, Bw = Ew / Vo under Wien condition, Under, the beam goes straight when the condition B = E / Vo is satisfied. Where Uo
Is the energy of the incident beam, Vo is the particle velocity, L is the length of the filter, Ew and Bw are the electric and magnetic fields that satisfy the Wien conditions. Now, when an electron with an energy such as U = Uo ± ΔU is incident, this deviates from the condition of straight traveling and is bent in the electric field E direction. Therefore, at the exit of the filter, the beam is dispersed according to the magnitude of the energy and can be used as an energy analyzer.

[Problems to be solved by the invention]

By the way, it is easy to satisfy the condition of Vo = E / B in the vicinity of the center of the filter, but particles must enter the filter from the place without the filter and leave the place without the filter again. For example, when a uniform electric field Eo is formed by the parallel plate electrodes 3 and 4 as shown in FIG. 4 (a), the electric field distribution changes gently at both ends of the filter as shown in FIG. 4 (b). The electric field distribution at this edge can be changed as shown in FIG. 5B by placing another plate 5 or 6 in front of or behind the electric field plates 3 and 4 as shown in FIG. 5A. Is possible.

However, the situation is not simple in an analyzer in which an electric field and a magnetic field are superimposed and added, which is the problem here. This is because the edge field of either the electric field E (z) or the magnetic field B (z) must have the same functional form with respect to the length direction z in order to continue satisfying the straight traveling condition of the particle. Usually this is not possible. No matter how the shape of the electrode plate, the shape of the magnetic pole, and the auxiliary electrode plates or iron pieces arranged before and after the electrode plate are changed, some difference in distribution occurs.

Fig. 6 shows the electric field distribution Ex when two kinds of different edge field distributions are assumed (the electric field and the magnetic field have the same edge field distribution).
(Z), magnetic field distribution By (z), x-direction orbit (direction causing dispersion) Xγ, and y-direction orbit Yγ, where (a) and (b) show a smooth edge field. , (C) and (D) of FIG.

In the figure, in the Xγ orbit of the beam incident at 1 m rad,
Zero loss beam and beam with 5 mV energy loss (Vo = 2
(Under 0V) is shown, and it can be seen that a linear dispersion is obtained. Thus, it can be seen that the presence of the edge field does not hinder as long as its distribution is equal in Ey and Bz.

In addition, in Fig. 7 (a) and (b), the electric field distribution should be Ex
(Z), the x-direction trajectory Xγ under a configuration in which the electrode and magnetic pole shapes are devised so that the magnetic field distribution By (z) becomes equal,
And the y-direction trajectory Yγ.

As can be seen from the figure, both distributions Ex (z) and By (z) are very similar, but they cannot be perfectly matched. It can be seen that the curves are slightly shifted when they are overlapped. In this way, if the distributions of Ex and By are different at the edge portions, the trajectory Xγ will be significantly shifted as shown in the figure. In this case, there is a shift of 1.5 mm at the filter outlet. In the figure, the orbits for both the zero-loss beam and the 5 mV loss beam are drawn, and although dispersion has occurred
The loss of 5 mV is on the order of microns, so it cannot be identified in the figure. Even if such a large shift occurs, it can be used as an analysis device by swinging it back out of the filter and then back, but this is by no means desirable in consideration of aberrations and the like.

The present invention is to solve the above problems, and an object of the present invention is to provide a Wien filter that can bring the orbit to the vicinity of the center even if the distribution of the edges of the electric field Ex and the magnetic field By is different. To do.

[Means for solving problems]

Therefore, the Wien filter of the present invention is arranged between a pair of opposing linear electrodes arranged between a pair of electric field adjusting mirrors and a pair of magnetic field adjusting mirrors, and is orthogonal to an electric field formed by the electrodes. A Wien filter comprising a pair of opposed linear magnetic poles for generating a magnetic field, which is designed to cause a charged particle of interest to go straight, wherein the length of the electrode is made longer than the length of the magnetic pole, and goes straight through the filter field. It is characterized in that the charged particles are allowed to pass straight through the edge field.

[Action]

The Wien filter of the present invention, by making the length of the linear electric field filter arranged between the pair of electric field adjusting mirrors longer than the length of the linear magnetic field filter arranged between the magnetic field adjusting mirrors, the edge field It is possible to correct the bending of the trajectory of the charged particles due to the effect.

〔Example〕

 Embodiments will be described below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the Wien filter according to the present invention. FIG. 1A is a horizontal sectional view and FIG. 1B is a vertical sectional view. In the figure, 11 and 12 are magnetic poles, 13 and 14 are electrodes, 15 is a magnetic field distribution adjusting mirror, and 16 is an electric field distribution adjusting mirror.

In the figure, the distance dm between the magnetic poles 11 and 12 and the magnetic field distribution adjusting mirror 15 made of iron pieces placed before and after the magnetic poles 11 and 12 and the electrodes 13 and 14 are shown.
And the distance de between the electric field distribution adjusting mirror 16 made of a metal piece are equal (dm = de = 10 mm), and the magnetic pole gap Sm and the electrode distance Se are
If and are equal (Sm = Se = 10mm), the electrode length Le
Is defined as Le = Lm + dLe for the magnetic pole length Lm.

Fig. 2 shows the Xγ and Yγ orbits when dLe was changed from 0.4 mm to 0.7 mm. The Yγ orbit hardly changes, but the Xγ orbit changes greatly with dLe. Figure 3,
That is, the change is extremely remarkable as compared with the case of dLe = 0. As is clear from the figure, under the conditions shown above, dL
Good results were obtained at e = 0.6 mm. In this case, X
The γ orbit only shifts 30-40 μm at z = 90 mm, and the dispersion due to the energy loss of 5 mV is also clearly visible.

In this way, by making the filter length of the electric field different from the filter length of the magnetic field, it is possible to correct the curve of the beam trajectory due to the influence of the edge field and go straight.

In the above embodiment, the distance to the mirror for defining the electric field distribution of the edge field is the same in the electric field and the magnetic field, but this is a desirable condition.
It does not have to be necessary.

〔The invention's effect〕

As described above, according to the present invention, as in the Wien filter, energy of a type in which an electric field and a magnetic field are superimposed and added, or in a mass spectrometer, the filter length of the electric field is made longer than the filter length of the magnetic field. The orbital bending due to the effect of the edge field can be corrected to obtain an orbit close to the particle trajectory expected when the edge field is not present.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a Wien filter according to the present invention, FIG. 2 is a diagram showing Xγ orbits and Yγ orbits when dLe is changed from 0.4 mm to 0.7 mm, and FIG. 3 is a conventional Wien filter. Fig. 4 is a perspective view showing the configuration of Fig. 4, Fig. 4 is a diagram showing an edge field distribution relating to an electric field, Fig. 5 is a diagram showing an edge field distribution when an electric field adjusting mirror is used, and Fig. 6 is an electric field distribution and a magnetic field. FIG. 7 is a diagram showing an Xγ orbit when the distributions match, and FIG. 7 is a diagram showing an Xγ orbit when the electric field distribution and the magnetic field distribution are similar to each other. 11, 12 ... Magnetic poles, 13, 14 ... Electrodes, 15 ... Mirrors for adjusting magnetic field distribution, 16 ... Mirrors for adjusting electric field distribution.

Claims (1)

[Claims] 1. A magnetic field which is disposed between a pair of opposing linear electrodes arranged between a pair of electric field adjusting mirrors and a pair of magnetic field adjusting mirrors and which is perpendicular to the electric field formed by the electrodes. It consists of a pair of linear magnetic poles facing each other,
A Wien filter adapted to cause the charged particles of interest to go straight, wherein the length of the electrode is made longer than the length of the magnetic pole so that the charged particles that go straight through the filter field continue to go straight through the edge field. The Vienna filter characterized by having done.