JPS6148213B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to mass spectrometers of various types (thermionic type, gas type, etc.), and more particularly to mass spectrometers capable of luminosity and multi-collection of magnetic sectors. In other words, it concerns the possibility of simultaneously providing a plurality of analytical collectors in the image plane of a mass spectrometer.

(Prior technology) The magnetic sector of a mass spectrometer
In the space required by the magnetic sector, the luminosity of the magnetic sector is limited by the aperture aberration of the magnetic sector.

It is known to reduce or even cancel the aperture aberration by appropriately selecting the radii of curvature of the input and output surfaces of the magnetic sector. However, this generally results in an increase in the angle of inclination of the image plane with respect to the perpendicular to the optical output axis of the magnetic sector. Since this angle is of large value (more than 80°), multi-collection analysis is not possible for different collectors for different masses. Even if possible, problems with electron recoil and secondary electrons compromise the analysis.
In addition, the use of a mass spectrometer having a hexapole electrostatic lens on the input side and a hexapole electrostatic lens on the output side, and the excitation of the hexapole electrostatic lens on the input side or the curvature of the input surface of the magnetic sector and the output surface of the magnetic sector. It is known to cancel aperture aberration by adjusting the curvature of the output side hexapole electrostatic lens or the excitation of the output hexapole electrostatic lens while fixing the other two parameters. In such a hexapole electrostatic lens, the sample
It is known to cancel the tilt angle of the image plane by modifying the distance between magnetic sectors and the distance between the magnetic sectors and the image plane. However, this adjustment has the disadvantage that it completely interferes with the adjustment made to cancel the aperture aberration, which becomes significant when the image plane tilt is reduced to zero.

(Problems and Summary of the Invention) The present invention has been made to eliminate the drawbacks of the prior art as described above. The purpose is to enable multi-collection analysis using a mass spectrometer that stands at right angles.

According to the invention, a magnetic sector having one optical axis and having an input surface with a radius of curvature R1 and an output surface with a radius of curvature R2 along the optical axis, and a coupling coefficient k
a hexapole electrostatic lens having an inclination angle i, and an image plane having an inclination angle i, respectively, in series, and R1, R2, and k represent the mass spectrometry due to aberrations in the radial and axial planes of the mass spectrometer. There is provided a mass spectrometer characterized in that aberration coefficients A and B related to shifts in the radial plane of the device are smaller than 1 in absolute value, and the inclination angle i is smaller than 10 degrees in absolute value. Ru.

Further, according to the present invention, the input side hexapole electrostatic lens has one optical axis and has a coupling coefficient k1, an input surface with a radius of curvature R1, and an output surface with a radius of curvature R2. a magnetic sector having a coupling coefficient k2, an output hexapole electrostatic lens having a coupling coefficient k2, and an image plane having an inclination angle i, respectively, in series, and R1, R2, k1, and k2 are Aberration coefficients A and B related to shifts in the radial plane of the mass spectrometer due to aberrations in the radial and axial planes are smaller than 1 in absolute value, and the inclination angle i is smaller than 10 degrees in absolute value. A mass spectrometer is provided that has certain features.

(Structure and operation of the invention) An embodiment of the present invention will be described below with reference to the accompanying drawings. Note that the same elements are given the same reference numerals in each drawing.

FIG. 1 is a schematic diagram of a thermionic mass spectrometer according to the present invention. This mass spectrometer is equipped with the following elements in series.

- a filament 1 on which the sample to be analyzed is placed; - a so-called moving optical system 2, represented diagrammatically by two lenses; - defining what is usually called a slit source, the central position of which is marked with the symbol H. a screen slit 3 shown; - a first hexapole electrostatic lens 4; - a magnetic sector 5 for deflecting ions originating from the sample and coming from the slit 3; - a second hexapole electrostatic lens 6; - an assembly 7 of three ion collectors arranged in the image plane P of the mass spectrometer;

In addition, in FIG. 1, the axis XX is the optical axis of the mass spectrometer, which has a radius of curvature R and a deflection angle a at the magnetic sector 5, and L1 and L
2 is the length of the hexapole electrostatic lenses 4 and 6, respectively, D
1 and D2 are the diameters of the hexapole electrostatic lenses 4 and 6, respectively, L3 is the distance between the slit source 3 and the hexapole electrostatic lens 4, and L4 is the distance between the hexapole electrostatic lens 4 and the input surface of the magnetic sector 5. L5 is the distance between the output surface of the magnetic sector 5 and the hexapole electrostatic lens 6,
L6 is the distance between the hexapole electrostatic lens 6 and the image plane P,
R1 and R2 are the radii of curvature of the input and output surfaces of the magnetic sector 5, respectively, b1 and b2 are the inclination angles of the input and output surfaces of the magnetic sector 5, respectively, i is the inclination angle of the image plane P, and J is the optical axis X. -X and the image plane P intersect.

The mass spectrometer according to claim 1 of the present specification is capable of performing conventional mass spectrometry due to the curvature of the input and output surfaces of the magnetic sector 5 and the presence of the two hexapole electrostatic lenses 4 and 6. Distinguished from equipment. The purpose of these elements will be explained later.

In mass spectrometers, the sensitivity depends in particular on the luminosity of the magnetic sector. This luminosity is primarily limited by aperture aberration in the radial plane, ie, in the plane of FIG.

FIG. 2 is a diagram for explaining aperture aberration in a mass spectrometer. Radius of curvature R in Figure 1
The magnetic sector 5 converts the image of a point H located in the image plane (a point on the optical axis located at the height of the screen) to a point J.
give it to This image is impaired by aperture aberration whose width in the radial plane is R·A·α ² +R·B·β ² . The term R・A・α ² is
Point H that forms an angle α with the optical axis and is included in the radial plane
After passing through the magnetic sector 5, a beam _from
-y corresponds to intersecting the optical axis (perpendicular to the optical axis) in the radial plane. On the other hand, the term R・B・^β2 is
The beam from point H, which forms an angle β with the optical axis and is included in the axial plane (a plane or curved plane perpendicular to the radial plane along the optical axis) at the output of the slit source, is transmitted to the axial plane after the magnetic sector 5. This corresponds to the fact that it is no longer included in The projection of the intersection of this beam with the plane Jyz parallel to Jz (projection onto the axis Jy) intersects the axis Jy at a distance of ^R.B..beta.2 from point J.

As already mentioned, by appropriately selecting the radii of curvature R1, R2 and the inclination angles _b1 , _b2 of the input and output surfaces of the magnetic sector 5, the aperture aberrations ^α2 and ^β2 can be canceled. , it can be seen that the inclination angle i (FIG. 1) of the image plane P becomes considerably large. This makes multi-collection analysis difficult and
In some cases this may not be possible.

According to the mass spectrometer shown in FIG. 1, the aperture aberration defined by the coefficients A and B discussed in connection with the description in FIG. It is possible to correct the inclination angle i at the same time. Experiments have revealed that this aperture aberration and tilt can be corrected by a field created by a hexapole electrostatic lens. Since three coefficients A, B, I have to be corrected, at least three degrees of freedom are required, ie at least three hexapole electrostatic lens arrangements. These three devices can be formed by the curvature of the input and output faces of the magnetic sector 5 and an electrostatic or magnetic sextupole electrostatic lens (reference number 6 in FIG. 1). This hexapole electrostatic lens must be provided in the region where the ion beam to be analyzed is dispersed, that is, after the magnetic sector 5. An additional hexapole electrostatic lens (reference number 4 in FIG. 1) may be provided to provide further degrees of freedom and further increase flexibility during the focusing operation of the mass spectrometer. The hexapole electrostatic lenses 4, 6 and the curvature of the output surface of the magnetic sector 5 in FIG. 1 are used as a hexapole electrostatic lens device, and a flat input surface (R1: infinity) is provided for the magnetic sector 5. You can also use
However, for industrial construction, generally the curvatures of the input and output surfaces of the magnetic sector 5 and the hexapole electrostatic lens provided downstream of the magnetic sector 5 are used as a hexapole electrostatic lens device. is preferred.

By the logic of the quadratic transfer matrix, studying the coefficients A, B, and I with respect to FIG. 1, these coefficients can be written as follows.

A=A ₀ +A ₁・C ₁ +A ₂・C ₂ +A ₃・k ₁ +A ₄・k ₂ B=B ₀ −A ₁・C ₁ +B ₂・C ₂ −A ₃・k ₁ +B ₄・k ₂ I=I ₀ +I ₂・C ₂ +I ₄・k ₂ where C ₁ = R ₁ /R, C ₂ = R ₂ /R, and k ₁ and k ₂
is the excitation coefficient of each hexapole electrostatic lens (k=3/2 1/
The excitation voltage of the hexapole electrostatic lenses 4 and 6 is expressed as r ³ Ve/V ₀ . Note that r=R'/R, and R'=D2/
2 is the radius of the circle inscribed in the path of the hexapole electrostatic lens, Ve=
V = excitation voltage of hexapole electrostatic lens V ₀ = ion charge), A ₀ , A ₁ , A ₂ , A 3 , A ₄ , _{B 0 ,} B ₂ , B ₃ , B ₄ ,
I ₀ , I ₂ , I ₄ are coefficients that depend on the geometrical parameters of the mass spectrometer. These coefficients are obtained by expanding the second-order transfer matrix of the optical system formed as described above. This transfer matrix has various elements (magnetic sector, hexapole electrostatic lens, distance L between elements)
This is a matrix obtained by multiplying the transfer matrices of 3, L4, L5, and L6). These matrices can be found in certain literature (e.g. “A First and Second Order Matrix Theory” by KLBrown).
for the Design of Beam Transport Systems
and Charged Particle Spectrometers”
Advanced in Physics・Volume 1, pp. 71-134
Page, 1967).

For example, when there is no input hexapole electrostatic lens 4, the solution of the following three equations can be found by varying C ₁ , C ₂ and k ₂ .

A=0 B=0 I=0 (gives i=0°) Geometric properties: L3+L1+L4=307.1mm (hexapole electrostatic lens 4 is excluded) a=90° b1=40° b2=22.5゜ R=200mm L5=160mm L2=40mm D2=30mm=2R' (see Figure 3) That is, r=R'/R=15/200=0.075 L6=495.6mm, and the air gap of magnetic sector 5 is 15mm. According to a mass spectrometer in which the length is , the six bars of the hexapole electrostatic lens 6 (see Figure 3) each have a diameter of 15 mm, and the ion kinetic energy V ₀ is 4500 eV, R1 = If you choose 78.8mm R2 = 70mm V = 11.29 volts (V and -V: excitation voltage of hexapole electrostatic lens 6 - see Figure 3), A = 0.17 B = -0.38 i = 0°. I (measurement accuracy ±7°) (However, the values of A and B are for a measurement system where the angle is expressed in radians.) is given.

In practice, completely sufficient operating conditions for the mass spectrometer are obtained when A and B are less than or equal to 1 and i is less than 10°.

The optimum excitation voltage for the hexapole electrostatic lens corresponding to the A cancel is between 11.4 and 11.5 volts. Optimal adjustment is made by examining the shape of the analytical peaks. At this time, the coefficient B does not become zero again, but becomes B=-0.3. In order to make B zero, it is necessary to correct the adjustment of the radius of curvature of the input and output surfaces of the magnetic sector, but a small value of B will cause the spectral line to broaden, R = 200 mm, and β = 10 ^-2 radians. On the other hand, 10 _-2 mm or less can be ignored, so the correction of the above adjustment is not necessary.

During the measurement, the radii of curvature R1 and R2 are adjusted by the use of removable pieces located respectively between the concave input surface of the magnetic sector and the surface M and between the surface N and the convex output surface of the magnetic sector. achieved. Other geometric properties of the mass spectrometer, in particular the angles b1, b
2 is selected based on data already obtained through experience with mass spectrometers.

FIG. 3 is a diagram showing how the hexapole electrostatic lens 6 discussed in connection with the description of FIG. 1 is constructed. This hexapole electrostatic lens has six cylindrical metal bars 60 to 65. bar 6
0 to 65 are equally spaced around the optical axis XX, and their principal axes (not shown) are parallel to the optical axis XX. bar 60,6
2 and 64 are joined to a metal ring 66 which is at potential +V by means of a metal spacer provided at 1/3 of their length. Similarly, bar 6
1, 63, and 65 are joined to a metal ring 67, which is at potential -V, by a metal spacer provided at two-thirds of their length. Ring 6 to make the hexapole electrostatic lens a rigid assembly.
The insulating pieces that are joined to the bars 6 and 67 are the bar 60.
~66 are not shown to better illustrate how they are combined in two groups of three.

The invention is not limited to the embodiments described above. The present invention is applicable not only to the use of an electrostatic hexapole electrostatic lens, but also to the use of a magnetic hexapole electrostatic lens, and furthermore, the present invention can be applied to the use of a magnetic hexapole electrostatic lens, and furthermore, the present invention is applicable to the use of a magnetic hexapole electrostatic lens. It is also applicable to the use of a plurality of hexapole electrostatic lenses provided in a.

Furthermore, the present invention provides one magnetic sector in addition to the above magnetic sector.
Alternatively, it is also possible to apply it to a mass spectrometer using a plurality of electrostatic and/or magnetic sectors. These sectors serve to correct the aperture aberration and the tilt angle of the image plane.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a mass spectrometer according to the present invention;
FIG. 2 is a diagram illustrating aberrations in the mass spectrometer, and FIG. 3 is a detailed diagram of one of the elements in FIG. 1. 1... filament, 2... moving optical system, 3...
...Slit screen, 4...First hexapole electrostatic lens, 5...Magnetic sector, 6...Second hexapole electrostatic lens, 7...Assembly, 60-65...Bar, 66, 67 ...Metal ring.

Claims (1)

[Claims] 1. A magnetic sector having one optical axis and having an input surface with a radius of curvature R1 and an output surface with a radius of curvature R2 along the optical axis, and a hexapole electrostatic sector with a coupling coefficient k. A lens and an image plane each having an inclination angle i are included in series, and R1, R2, and k are in the radial plane of the mass spectrometer due to aberrations in the radial plane and the axial plane of the mass spectrometer. A mass spectrometer characterized in that aberration coefficients A and B related to the shift of are smaller than 1 in absolute value, and the inclination angle i is smaller than 10 degrees in absolute value. 2. Coupling along the optical axis with an input hexapole electrostatic lens having a coupling coefficient k1 and a magnetic sector having an input surface with a radius of curvature R1 and an output surface with a radius of curvature R2. An output-side hexapole electrostatic lens having a coefficient k2 and an image plane having an inclination angle i are respectively included in series, and the R1, R2, k1 and k2 are arranged in the radial plane and the axial plane of the mass spectrometer. The aberration coefficients A and B related to shifts in the radial plane of the mass spectrometer due to aberrations are smaller than 1 in absolute value, and the inclination angle i is smaller than 10 degrees in absolute value. Mass spectrometer.