JPH04237941A - Electrode for electric field sector - Google Patents

Abstract

PURPOSE:To obtain small electrodes which are easy to manufacture and can easily control the electric field. CONSTITUTION:Two main electrodes 2L, 2R are arranged rotation-symmetrically with the Z-axis between two auxiliary electrodes 6, 7 arranged plane- symmetrically with the X-axis. The main electrode 2L is divided into three split electrodes 3L, 4L, 5L, and the main electrode 2R is likewise divided into three split electrodes 3R, 4R, 5R. The split electrodes 3L, 3R; 4L, 4R; 5L, 5R are provided in pairs respectively.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of an electrode for an electric field sector used in a mass spectrometer or the like.

0002

2. Description of the Related Art In a mass spectrometer, an electric field sector and a magnetic field sector are usually arranged. The electric field sector and the magnetic field sector can be arranged independently in series in the order of the electric field sector and the magnetic field sector along the optical axis (hereinafter, the optical axis is referred to as the Z axis), or they can be arranged at the same position and overlapped. It can also form a field. Electrodes for electric field sectors are those with a so-called multi-electrode structure, in which multiple linear electrodes are arranged on an insulator, or those with a so-called Matsuda plate, which are placed above and below two main electrodes arranged on the left and right. Structures in which auxiliary electrodes are arranged are known.

FIG. 11 is a diagram showing an example of the former configuration, with FIG. 11A being a plan view and FIG. 11B being a side view taken along line AA in FIG. 11A. An upper resistive film electrode 40 and a lower resistive film electrode 41 are arranged above and below the Z axis, respectively, and an inner electrode 42
and outer electrodes 43 are arranged at a predetermined interval. The upper resistive film electrode 40 and the lower resistive film electrode 41 are
Linear electrodes made of platinum and having a width of, for example, 0.2 mm are formed on each resistive film at a pitch of, for example, 2.5 mm. Therefore, for example, when a predetermined negative potential is applied to the inner electrode 42 and a positive potential is applied to the outer electrode 43, the equipotential surface formed between the upper resistive film electrode 40 and the lower resistive film electrode 41 is As shown in 46 of 11B,
Therefore, since the electric field is in the direction shown by the arrow 47 in the figure, the positively charged ion beam is bent in the opposite direction to the arrow 47, that is, toward the inner electrode 42. In addition,
In FIG. 11A, shunt plates 44 and 45 are arranged at a predetermined distance d at the entrance and exit ports of the electric field sector, respectively.

FIG. 12 is a perspective view showing an example of the structure of the latter electrode. Main electrodes 50 and 51 are arranged rotationally symmetrically with respect to the Z axis and function as a deflector. , there are auxiliary electrodes 52, 5 commonly called Matsuda plates.
It has 3. A predetermined voltage is applied to the auxiliary electrodes 52 and 53 so that they have the same potential. In addition, the main electrode 5
0 and 51, when the ion is an anion, Vd and -Vd (Vd > 0) are applied, respectively, and when the ion is a cation, -Vd and Vd are applied, respectively.

[0005]

[Problem to be solved by the invention] However, FIG.
In the electrode with the configuration, it is not only possible to control the electric field strength over a wide range according to theoretical calculations, but also to
Since the gap G between the upper resistive film electrode 40 and the lower resistive film electrode 41 can be narrowed to about 15 mm or less, when a superimposed field is formed by arranging magnetic poles above and below the electric field sector, Although it has the advantage of reducing the ampere-turns required to form the magnetic field, it requires high precision in the position of the linear electrodes, which poses manufacturing problems, especially when there are a large number of linear electrodes. is difficult to manufacture. Another problem is that the resistance value of the insulator forming the linear electrode gradually decreases over time, which cannot be avoided. In addition, the electrode with the configuration shown in Fig. 12 has a simple structure and is easy to manufacture.Moreover, by changing the voltage applied to the auxiliary electrode, the focusing condition can be kept constant over a wide range of electric field strength and magnetic field strength. However, in order to use the electrode in a superimposed field and obtain good resolution, the auxiliary electrode 52,
The gap G between 53 and 53 is required to be about 30 to 40 mm, which not only increases the size, but also requires many ampere turns to obtain a predetermined magnetic field strength. There is a problem in that distortion occurs and the third-order coefficient of the electric field increases, resulting in a decrease in resolution as a superimposed field mass spectrometer. The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an electrode for an electric field sector that is small, easy to manufacture, and allows easy control of the electric field.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the electric field sector electrode of the present invention includes a main electrode arranged rotationally symmetrically with respect to an optical axis between auxiliary electrodes arranged oppositely to each other. The electric field sector electrode comprising electrodes is characterized in that the main electrode comprises a plurality of pairs of electrodes.

[0007]

[Operation] The two main electrodes, which are arranged rotationally symmetrically with respect to the optical axis, are each divided into the same number of parts, and the corresponding divided electrodes of each main electrode form a pair.

[0008]

Embodiments Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a diagram showing the configuration of an embodiment in which an electric field sector electrode according to the present invention is applied to a superimposed field type mass spectrometer, with FIG. 1A being a cross-sectional view and FIG. 1B being a plan view. The outer main electrode 2L includes three electrodes 3L, 4L, and 5L, and the inner main electrode 2R includes three electrodes 3R, 4R, and 5R.
It is equipped with three electrodes. electrode 3L and electrode 3R,
The electrode 4L and the electrode 4R, and the electrode 5L and the electrode 5R form a pair, and are arranged in rotationally symmetrical positions with respect to the Z axis. Auxiliary electrodes 6 and 7 are arranged above and below the outer main electrode 2L and the inner main electrode 2R, respectively, in plane symmetry with respect to the x-axis. Pole pieces 1 and 10 are arranged above and below the electric field sector electrode, which is composed of four types of electrodes: the outer main electrode 2L, the inner main electrode 2R, and the auxiliary electrodes 6 and 7, respectively, so that the superimposed field is It is formed. In addition, in FIG. 1B, the pole pieces 6 and 7 are omitted, and 8 is a Herzog shunt on the entrance side, and 9 is a Herzog shunt on the entrance side.
indicates the Herzog shunt on the exit side. A voltage as shown in FIG. 1A is applied to each electrode. That is, the electrode 3L
A voltage V2 is applied to the electrode 5L, a voltage V1 is applied to the electrode 3R and the electrode 5R, and a voltage V3 is applied to the auxiliary electrodes 6 and 7. When a voltage V4 (V4>0) is applied to the electrode 4L, a voltage of -V4 is applied to the electrode 4R.

Next, the generated electric field will be explained.

By the way, the ion optical characteristics of an electric field rotationally symmetrical about the Z axis as shown in FIG.
The potential φ at any point (x, y) on the y plane is expressed as (
1) Coefficient Ui0 (i=1,2
,...), that is, it is known that it is determined by the rate of change of the potential φ in the x direction.

[0011]

[Math 1]

[0012] However, as shown in FIG. 1B, a is the radius of rotation of the Z axis, and the coefficient Ui0 is

[0013]

[Math 2]

It is expressed as: Therefore, E0 is a value determined by -E/U10 using the first-order potential coefficient U10, where E is the electric field strength at the origin of the xy plane.

In ion optics, it is sufficient to consider up to the 4th order coefficient for the electric potential, that is, up to the 3rd order coefficient for the trajectory, so the ion optical characteristics of the superimposed field are
It is determined by four coefficients: 10, U20, U30, and U40. Note that these are given by the following equations (3), (4), (5), and (6), respectively.

[0016]

[Math 3]

[0017]

[Math 4]

[0018]

[Math 5]

[0019]

[Math 6]

[0020] Here, V is the ion acceleration voltage. And these four coefficients U10, U20, U30, U40
The value of is the four voltages V1 and V2 applied to each electrode.
, V3 and V4, and the coefficient U1
By determining 0, U20, U30, U40, the values of fifth-order or higher coefficients U50, U60, . . . are automatically determined. Note that the second-order coefficient U20 is a coefficient that governs the first-order aberration of the orbit, the third-order coefficient U30 is a coefficient that governs the second-order aberration of the orbit, and the fourth-order coefficient U40 is the coefficient that governs the third-order aberration of the orbit. It is a coefficient that affects U10, U20, U30
, U40, and thus the values of the voltages V1, V2, V3, V4 applied to each electrode, can be determined using the surface charge method and the simplex
By performing a simulation in combination with the X) method, it can be determined with high accuracy. An example of this will be explained below.

[0021] The electric field for forming a superimposed field that is double focusing on the first order and establishes 3D focusing is U
It is known that 10=-1.0 and U20=0. Further, theoretical studies including experiments by the present inventor have revealed that U30 and U40 are preferably near zero. Then, the ion acceleration voltage V is set to V
= 3.0kV, U10=-1.0, U2
The voltage value at which 0=U30=U40=0 is V1 =V1
0, V2 = V20, V3 = V30, V4 = V40
By calculation, we get the following value. V10=-1.244389×102 (V)
...(7) V20= 3.083180×10
2 (V)...(8)V30=-1.399
793×102 (V) …(9)V4
0=-1.999861×102 (V)
...(10) However, in reality, the first-order focusing condition shifts due to the influence of the fringe field and the edge field, so U10,U
The values of 20, U30, and U40 deviate from the above values, so the voltages applied to each electrode V10, V20, V30, and V40
The values of will also differ. If the values of U10, U20, U30, and U40 at the origin of the x-y plane at this time are set as U100, U200, U300, and U400, respectively,
Changes in Ui0 (i=1, 2, 3, 4) from the origin can be expressed by the following equation. △U1 =U10-U100
...(11)△U2 =U20-U200
…(12)△
U3 = U30-U300
...(13)△U4 =U40-U400
...(14) And at this time, △V1 = V1 - V10, △V2 =
V2 −V20, △V3 =V3 −V30, △V4
=V4 -V40,

[0022]

[Math. 15]

[0023]

[Math. 16]

[0024]

[Math. 17]

[0025]

[Math. 18]

[0026] holds, and also,

[0027]

[Math. 19]

[0028]

[0029]

[Math. 20]

[0030] can be expressed as a matrix, and therefore,

[0031]

[Math. 21]

##EQU1## When the necessary value of Ui0 is found and therefore ΔUi is found, Vi can be found using this equation (21). Note that equation (21) is |△Ui |≒ 1.0 and |△Ui |<1.0
It has been confirmed by the surface charge method that the equations (20) and (21) hold fairly accurately within the range of . Here, U100 = -1, U200 = U300 = U40
It has been determined by simulation that the value of Aij when 0=0 is the value shown in FIG. 3 when the dimensions of each electrode are as shown in FIG. Note that in FIG. 2, the unit of numerical values is mm.

FIG. 4 shows a state in which the values of U20, U30, and U40 are fixed at the origin, that is, U20=U200=0, U30.
= U300 = 0, U40 = U400 = 0, voltage Vi (i = 1, 2
, 3, 4), and FIG. 5 is a diagram showing changes in U10,
A state where the values of U30 and U40 are fixed at the origin, that is, U10
=U100 =-1, U30=U300=0, U40=
6 is a diagram showing changes in voltage Vi when U20 is changed in a state where U400=0, and FIG.
0=U100=-1, U20=U200=0, U40
7 is a diagram showing changes in voltage Vi when U30 is changed in a state where U400=0, and FIG.
U100=-1, U20=U200=0, U30=U
FIG. 3 is a diagram showing a change in voltage Vi when U40 is changed in a state where 300=0. In addition, in FIGS. 4 to 7, the voltage Vi is the deflection reference voltage (V0 = 200
It is normalized and expressed as V. As can be easily understood from FIGS. 4 to 7, when only one of U10, U20, U30, and U40 is changed and the remaining coefficients are fixed, the voltage Vi changes linearly over a wide range. It can be seen that it is expressed as In particular, when U30 is changed, as is clear from FIG. 6, even if U30 changes by about ±1.0, the standardized value (Vi/V0) hardly changes on the graph. Therefore, FIG. 6 shows the deviation from the voltage Vi0 at the origin, that is, ΔVi. According to this, when U30 changes from -1.0 to 1.0, the change △Vi in each Vi is almost 1V or less, and conversely, even if V1, V2, and V3 change slightly, U30 It shows that there is a big change.

Next, a description will be given of how the ion optical focusing characteristics change when Ui0 changes. The change ΔU10 in U10 gives a first-order energy aberration. Therefore, in order to obtain a mass resolution of 3000, △U1
0 must satisfy at least the following conditions.

[0035]

[Math. 22]

Next, it can be seen from FIG. 8 that U20 is a coefficient that affects the aberration of first-order directional focusing. That is, FIG. 8A
, B are respectively U10=-1.0 and U30=2.5
, U40=0 and U20 is set to 0,
It is a diagram showing the primary focal point of the beam in the Z direction when the value is -0.05, and it can be understood from this that when U20 is changed, the primary focal point moves. Therefore, the change in U20 ΔU20 needs to satisfy at least the following conditions.

[0037]

[Math. 23]

Next, it can be seen from FIG. 9 that U30 affects the spread of the beam due to the second-order aberration at the focal point of the beam. That is, FIGS. 9A, B, C, and D are each U10
, U20, and U40 are fixed and U30 is set to -5.0, 0, 2.5, and 5.0. This figure shows that changing U30 changes the beam spread based on secondary aberration at the focal point. In addition, in FIG. 9, the values of Ui0 other than U30 are U10=-1.0, U20=-0.05, U4
0=0. And the beam opening angle is ±1/150
(rad), if U30 changes by about 2.5, the beam spread due to second-order aberration will be 50 μm.
It has been confirmed that this will be the case. This has a mass resolution of 6
It corresponds to 000. Therefore, the change in U30 △
U30 must satisfy the following conditions.

[0039]

[Math. 24]

Next, regarding U40, U40 is 10
It has been confirmed that even if the degree changes, the ion path hardly changes based on theoretical calculations. However, simulation results have revealed that when U40 changes, distortion occurs in the electric field due to fifth-order or higher-order aberrations, as shown in FIG. 10A and B are U10=-1, respectively.
．． 0, U20=-0.05, U30=2.5, and U40 is set to 0.45 and -0.45. It can be seen that the distortion of the electric field is smaller in Figure B than in Figure B. In addition,
The dimensions of each electrode are the same as shown in FIG.

From the above, as shown in FIG. 1, by dividing each of the two main electrodes into three parts and applying vertically symmetrical potentials to each electrode, the ion optical focusing conditions can be adjusted.
That is, energy focusing (U10), primary focusing in direction (
U20) and secondary aberration (U30) can be controlled independently, and then the optimal U10, U20 thus obtained can be
It has been confirmed that a good electric field can be obtained by changing U40 for the combination of , U30 and finding a value that provides a good electric field.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above embodiment, the main electrode is divided into three parts, but it can also be divided into two or four or more parts, and by increasing the number of divisions, a more uniform electric field can be generated. It is also possible to configure the auxiliary electrode with multiple electrodes as shown in FIG.
Furthermore, the main electrode can be electrically divided by using separate electrodes in the above embodiments, but by configuring the main electrode with multiple electrodes and changing the voltage applied to the linear electrodes, the main electrode can be electrically divided. It is also possible to do this.

[0043]

As is clear from the above description, according to the present invention, it is possible not only to obtain an electric field sector electrode that is small and easy to produce, but also to improve energy focusing, primary focusing in direction, and Since secondary aberrations can be controlled independently and distortion of the electric field based on higher-order aberrations can also be controlled, an optimal electric field can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of an electric field sector electrode according to the present invention.

FIG. 2 is a diagram showing an example of the dimensions of an electrode.

FIG. 3 is a diagram showing an example of the value of Aij.

FIG. 4 is a diagram showing changes in each electrode voltage when only U10 is changed.

FIG. 5 is a diagram showing changes in each electrode voltage when only U20 is changed.

FIG. 6 is a diagram showing changes in each electrode voltage when only U30 is changed.

FIG. 7 is a diagram showing changes in each electrode voltage when only U40 is changed.

FIG. 8 is a diagram for explaining the shift of the primary focal point of the beam in the Z direction when only U20 is changed.

FIG. 9 is a diagram for explaining beam spread based on second-order aberration when only U30 is changed.

FIG. 10 is a diagram for explaining the distortion of the electric field that occurs when U40 is changed.

FIG. 11 is a diagram showing a conventional multi-electrode.

FIG. 12 is a diagram showing a configuration example of a conventionally used electric field sector electrode.

[Explanation of symbols]

1, 10... Pole piece, 2... Main electrode, 3, 4, 5... Divided electrode, 6, 7... Auxiliary electrode.

Claims (1)

[Claims] 1. An electric field sector electrode comprising a main electrode arranged rotationally symmetrically with respect to an optical axis between auxiliary electrodes arranged facing each other, wherein the main electrode comprises a plurality of pairs of electrodes. Electrode for electric field sector.