Focusing method and device based on time-of-flight mass spectrometer

Abstract

The present invention relates to a focusing method and device based on a time-of-flight mass spectrometer, comprising: arranging n+n' identical electrode sheets coaxially and insulatingly, wherein the distance between the first electrode sheet and the nth electrode sheet is L 1 , the distance between the nth electrode and the n+n'th electrode is L 2 ; Set electric field shielding nets on the first electrode sheet, the nth electrode sheet, and the n+n'th electrode sheet to isolate the electric field on both sides of the electrode sheet; connect the first electrode sheet to the n+n'th electrode sheet to the voltage source respectively; generate a length of L between the electrode sheet and the electric field shielding net 1 , L 2 , the intensity is E 1 、E 2 The field strength E can be adjusted by adjusting the voltage applied to the electrodes at both ends. 1 、E 2 , by adjusting the field strength E 1 、E 2 Time-of-flight focusing is achieved for charged particles of any given speed.

Description

Technical Field

[0001] The invention relates to a focusing method and device based on a time-of-flight mass spectrometer, and relates to the field of charge-to-mass ratio identification and momentum measurement of charged particles. Background Art

[0002] There are many kinds of microscopic particles, and identification is the basis for studying microscopic particles. Measuring the ratio of the charge to the mass number of microscopic particles (charge-to-mass ratio) is one of the basic means of identifying charged microscopic particles. At present, the most commonly used equipment for measuring the charge-to-mass ratio is the time-of-flight mass spectrometer, referred to as TOF (Time of Flight). This method places charged particles in a known electric field to fly a certain distance, measures the time taken by the particles to fly this distance, and obtains the charge-to-mass ratio of the particles based on the electric field strength, flight distance and flight time. Under current technical conditions, the measurement accuracy of the time-of-flight mass spectrometry method mainly depends on the dispersion of the initial velocity and the starting position of the particles. Reducing these two dispersions can greatly improve the ability to identify the charge-to-mass ratio.

[0003] In kinetic experiments, it is not only necessary to identify the types of particles, but also to measure the initial velocity of the particles to conduct kinetic research. Reducing the influence of the dispersion of the starting position of the particles can improve the measurement accuracy of the initial velocity of the particles. In TOF, changes in the starting position of the particles will cause changes in the flight time of the particles, which in turn affects the accuracy of the restoration of the charge-to-mass ratio and the initial velocity. However, it is difficult to reduce the position dispersion of microscopic particles. Even if it can be achieved through technical means, in most cases it means reducing the number of particles participating in the reaction, which brings adverse effects.

[0004] The prior art reduces the influence of position dispersion on flight time by combining electric fields without reducing the dispersion of the starting position of particles, that is, flight time focusing, thereby improving the measurement accuracy of charge-to-mass ratio and initial velocity. The prior art proposes to achieve time focusing by using two sections of acceleration fields and one section of zero-field drift zone. If the intensity of the two sections of acceleration fields is set to be the same, this scheme is simplified to a two-section type of one section of acceleration zone and one section of drift zone. This is the flight time focusing scheme with a ratio of the length of the acceleration zone to the length of the drift zone of 1:2 that was widely used later. Based on this scheme, researchers later designed a combination scheme of multiple sections of acceleration zones and one section of drift zone to achieve high-order focusing capability. In order to prevent the electric field of the acceleration zone from leaking to the zero-field drift zone, these schemes require the installation of an electric field shielding net at the boundary between the two fields. Since the ratio of the length of the two fields is fixed, it is usually necessary to install a shielding net near the starting position of the particle. For situations where a grid cannot be installed at this position, such as the longitudinal reaction microscopic imaging spectrometer, an important research equipment for atomic collision dynamics, these schemes are not applicable, which seriously limits the momentum resolution improvement of the longitudinal reaction microscopic imaging spectrometer. In addition, the simplified scheme of 1:2 ratio of acceleration zone length to drift zone length can only achieve ideal focusing for particles with zero velocity, but cannot achieve ideal focusing for particles with any given velocity. This is a serious limitation in dynamic research and affects the scope of application of this scheme.

[0005] In order to achieve time focusing without installing a grid, the prior art also proposed an electrostatic lens solution, which can well achieve position focusing perpendicular to the TOF direction by using electric field distortion, but this solution requires a lot of simulation work and is complex to design. At the same time, because the electric field is irregular, it impairs the focusing ability in the TOF direction. In addition, for dynamic research, it is often necessary to measure ions and electrons at the same time, and this solution is extremely unfavorable for measuring electron momentum. Summary of the invention

[0006] In view of the above problems, one of the objects of the present invention is to provide a focusing method based on a time-of-flight mass spectrometer, which can solve the problem that the position of the electric field shielding grid is fixed in the existing two-stage TOF focusing scheme and can only achieve ideal focusing for charged particles with zero velocity; the second object of the present invention is to provide a focusing device based on a time-of-flight mass spectrometer.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a focusing method based on a time-of-flight mass spectrometer, comprising:

[0009] n+n' annular electrode sheets are coaxially insulated and arranged, wherein the distance between the first electrode sheet and the nth electrode sheet is L 1 , the distance between the nth electrode and the n+n'th electrode is L 2 ;

[0010] An electric field shielding net is arranged on the first electrode sheet, the nth electrode sheet, and the n+n'th electrode sheet to isolate the electric field on both sides of the electrode sheet;

[0011] Connect the first electrode sheet to the n+n'th electrode sheet to a voltage source respectively;

[0012] The lengths of L are generated between the electrode sheet and the electric field shielding net. 1 , L 2 , the intensity is E 1 、E 2 Two connected uniform electric fields;

[0013] The field strength E can be adjusted by adjusting the voltage applied to the electrodes at both ends. 1 、E 2 , by adjusting the field strength E 1 、E 2 Time-of-flight focusing is achieved for charged particles of any given speed.

[0014] The focusing method based on time-of-flight mass spectrometer, further, the intervals between the n+n' electrode sheets are l 1 l 2 …l n+n’-1 ,in,

[0015] The focusing method based on the time-of-flight mass spectrometer further applies a voltage U to each electrode sheet. 1 U 2 …U n+n’ The electric field E generated when 1 、E 2 They are:

[0016]

[0017]

[0018] In a second aspect, the present invention provides a focusing device based on a time-of-flight mass spectrometer, the device comprising:

[0019] Ring-shaped electrode sheets, the number of which is n+n', and the n+n' electrode sheets are coaxially insulated and arranged;

[0020] An electric field shielding net, which is arranged on the first electrode sheet, the nth electrode sheet, and the n+n'th electrode sheet, and is used to isolate the electric field on both sides of the electrode sheets;

[0021] A voltage source is provided, wherein the voltage source is connected to the first electrode sheet to the n+n'th electrode sheet respectively.

[0022] The focusing device based on the time-of-flight mass spectrometer, further, the intervals between the n+n' electrode sheets are l 1 l 2 …l n+n’-1 ,in

[0023] The focusing device based on the time-of-flight mass spectrometer, further, each of the electrode sheets applies a voltage U 1 U 2 …U n+n’ When the electric field is generated between the electrode sheet and the electric field shielding net, the intensity is E 1 、E 2 The uniform electric field is:

[0024]

[0025]

[0026] The focusing device based on the time-of-flight mass spectrometer further comprises the annular electrode sheet which is a metal ring with an inner diameter of 10 cm, an outer diameter of 14 cm and a thickness of 1 mm.

[0027] The focusing device based on time-of-flight mass spectrometer further comprises: the electric field shielding net is a metal net.

[0028] The focusing device based on a time-of-flight mass spectrometer further comprises: the voltage source adopts an adjustable DC power supply or a voltage divider circuit.

[0029] The present invention adopts the above technical solution, and has the following characteristics:

[0030] 1. The present invention solves the problem that the shielding grid of the existing TOF focusing solution has a fixed installation position and can only achieve ideal focusing on charged particles with a speed of 0, broadens the application scope of the time-of-flight focusing solution, and can theoretically reduce the flight time dispersion caused by position dispersion by an order of magnitude.

[0031] 2. The present invention realizes time-of-flight focusing by combining two sections of uniform electric fields with adjustable field strengths, and the installation position of the electric field shielding grid is flexibly adjustable. At the same time, it can realize ideal time-of-flight focusing for charged particles of any given speed. Compared with the electrostatic lens focusing solution, the present invention is simple in design and has better time-of-flight focusing capability.

[0032] In summary, the present invention can be widely used in microscopic particle identification and dynamics research. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Throughout the accompanying drawings, the same reference numerals are used to represent the same components. In the accompanying drawings:

[0034] Figure 1 The relationship between the ratio of the two electric field intensities and the length ratio when the charged particles with zero velocity are ideally focused under the two-stage electric field combination structure of the embodiment of the present invention;

[0035] Figure 2 A schematic diagram of a structure for generating a two-stage uniform electric field with adjustable field strength according to an embodiment of the present invention;

[0036] Figure 3 This is a schematic diagram of a test solution for an embodiment of the present invention;

[0037] Figure 4 1 is the test result of an embodiment of the present invention: momentum distribution of recoil ion He+ in the single capture reaction of 120keV He2+ and He. DETAILED DESCRIPTION

[0038] The exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0039] It should be understood that the terms used herein are only for the purpose of describing specific example embodiments and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "one", "an" and "said" as used herein may also be meant to include plural forms. The terms "include", "comprise", "contain", and "have" are inclusive, and therefore specify the existence of stated features, steps, operations, elements and / or parts, but do not exclude the existence or addition of one or more other features, steps, operations, elements, parts, and / or combinations thereof. The method steps, processes, and operations described herein are not interpreted as necessarily requiring them to be performed in the specific order described or illustrated, unless the execution order is clearly indicated. It should also be understood that additional or alternative steps may be used.

[0040] For ease of description, spatially relative terms may be used herein to describe the relationship of one element or feature relative to another element or feature as shown in the figures, such as "inside", "outside", "inner side", "outer side", "below", "above", etc. Such spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation depicted in the figures.

[0041] The focusing method and device based on the time-of-flight mass spectrometer provided by the present invention include: arranging n+n' electrode sheets coaxially and insulatingly, wherein the distance between the first electrode sheet and the nth electrode sheet is L 1 , the distance between the nth electrode and the n+n'th electrode is L 2 ; Set electric field shielding nets on the first electrode sheet, the nth electrode sheet, and the n+n'th electrode sheet to isolate the electric field on both sides of the electrode sheet; connect the first electrode sheet to the n+n'th electrode sheet to the voltage source respectively; generate a length of L between the electrode sheet and the electric field shielding net 1 , L 2 , the intensity is E 1 、E 2 The field strength E can be adjusted by adjusting the voltage applied to the electrodes at both ends. 1 、E 2 , by adjusting the field strength E 1 、E 2 The invention realizes time-of-flight focusing for charged particles of any given speed. The invention realizes time-of-flight focusing by combining two sections of uniform electric fields with adjustable field strengths, and the installation position of the electric field shielding grid is flexible and adjustable, and can realize ideal time-of-flight focusing for charged particles of any given speed.

[0042] The focusing method based on the time-of-flight mass spectrometer provided by the present invention adopts a combination of two uniform electric fields with adjustable field strengths to achieve time-of-flight focusing, and at the same time obtains a flexible installation position of the electric field shielding grid, which can conveniently achieve ideal time-of-flight focusing for charged particles of any given speed. The specific principle is:

[0043] Assume that the charged particle passes through two adjacent uniform electric fields one after another, and the lengths of the electric fields are L and 1 , L 2 , the intensity is E 1 、E 2 , the total flight time is T, then the electric field relationship satisfies formula (1), That is, ideal focus of the flight time is achieved.

[0044]

[0045] Where m is the mass of the charged particle, q is the charge of the charged particle, and v is the velocity of the charged particle.

[0046] The above formula (1) shows that the electric field strength E 2 By L 1 , L 2 、E 1 , m, q, and v are jointly determined, which means adjusting the electric field strength E 2 In theory, it is possible to achieve ideal time-of-flight focusing for charged particles with any given velocity v, and it is also possible to achieve ideal time-of-flight focusing for charged particles with any given velocity v at any L 2 / L 1 Time-of-flight focusing can be achieved under certain conditions, that is, the installation position of the electric field shielding grid is flexible.

[0047] Taking the time-of-flight focusing of charged particles with a speed of zero as an example, formula (1) can be simplified to formula (2):

[0048]

[0049] At this time, the ratio of the intensity of the two electric fields is only related to the ratio of the lengths of the electric fields. In order to more intuitively understand the relationship between the two ratios, formula (2) is expressed as Figure 1 As shown. hour, like Figure 1 As shown in point A, this condition is a conventional time-of-flight focusing method in which the ratio of the length of the acceleration zone to the length of the zero-field drift zone is 1:2. This is taken as an example, but is not limited to this.

[0050] Based on the above principle, the time-of-flight mass spectrometer focusing provided by the present invention only needs two connected uniform electric fields with adjustable field strength to achieve time-of-flight focusing of charged particles of any given speed. Therefore, the present invention generates two connected uniform electric fields with adjustable field strength to generate two sections with lengths L and L respectively. 1 , L 2 , the intensity is E 1 、E 2 The electric field is taken as an example to explain in detail.

[0051] Example 1: Figure 2 As shown, the focusing device based on the time-of-flight mass spectrometer provided in this embodiment includes:

[0052] Electrode sheet 1, electrode sheet 1 is a ring electrode, the number is n+n', n+n' electrode sheets 1 are coaxially insulated and arranged along the central axis, and the intervals between them are l 1 l 2 …l n+n’-1 ,in,

[0053] The electric field shielding net 2 is arranged on the first electrode sheet, the nth electrode sheet, and the (n+n')th electrode sheet to isolate the electric field on both sides of the electrode sheet.

[0054] A voltage source is connected to the first to the n+n'th electrode sheets respectively, and a voltage U is applied to these electrode sheets respectively. 1 U 2 …U n+n’ ,Require Preferably, the voltage source may be an adjustable direct current power supply, or may be replaced by a voltage divider circuit that meets the voltage requirements of the electrode sheet, which is not limited here.

[0055] In a preferred embodiment of the present invention, the electrode sheet 1 may be a metal ring with an inner diameter of 10 cm, an outer diameter of 14 cm, and a thickness of 1 mm.

[0056] In a preferred embodiment of the present invention, the first electrode sheet, the nth electrode sheet, and the n+n'th electrode sheet are provided with a fixed electric field shielding net. For example, on the above-mentioned electrode sheet with an inner diameter of 10 cm and an outer diameter of 14 cm, a plurality of screw holes are reserved on a circle with a diameter of 11 cm. The electric field shielding net 2 is fixed to the side of the electrode sheet 1 using screws and matching pressure rings to ensure that the inner hole of the electrode sheet is completely and evenly covered by the shielding net.

[0057] In a preferred embodiment of the present invention, the n+n′ electrode sheets 1 are insulated from each other. For example, the electrode sheets can be fixed on an insulating material to achieve insulation.

[0058] In a preferred embodiment of the present invention, the electric field shielding net 2 may be a metal net.

[0059] Embodiment 2: This embodiment also provides a focusing method based on a time-of-flight mass spectrometer, comprising:

[0060] S1. Prepare n+n' identical annular electrode sheets 1, wherein the inner holes of three electrode sheets are neatly sealed with an electric field shielding net 2 to isolate the electric field on both sides of the electrode sheets. To ensure the uniformity of the electric field edge, the 1st, nth and n+n' sheets use electrodes with an electric field shielding net, which can be a metal net.

[0061] S2, n+n' electrode sheets 1 are coaxially insulated and fixed along the central axis, and the intervals between them are l 1 l 2 …l n+n’-1 ,in

[0062] S3, apply voltage U to these electrodes respectively 1 U 2 …U n+n’ ,Require At this time, the lengths of L are generated in the annular electrode sheet and between the metal meshes. 1 , L 2 , the intensity is E 1 、E 2 Two connected uniform electric fields.

[0063] S4. The field strength E can be adjusted by adjusting the voltage applied to the electrode 1 、E 2 It should be pointed out that the uniformity index of the electric field needs to be determined according to the specific use requirements. The uniformity of the electric field can be improved by optimizing the electrode parameters, increasing the electrode arrangement density and the number of shielding meshes.

[0064] S5. By adjusting the field strength E 1 、E 2 , to achieve ideal time-of-flight focusing for charged particles with any given velocity v.

[0065] The effectiveness of the focusing method based on time-of-flight mass spectrometer provided by the present invention is verified by specific examples below.

[0066] The velocity (i.e. momentum) dispersion and position dispersion of microscopic particles in TOF will affect the flight time of the particles. The present invention can only reduce the flight time dispersion caused by position dispersion, so the ideal test system of the present invention should be a charged particle system with only position dispersion but no velocity dispersion. However, due to the uncertainty principle, such a system does not exist. Therefore, to test the effect of the present invention, only a charged particle system with as small velocity dispersion as possible and obvious position dispersion can be selected. For this reason, this embodiment uses a He target produced by a supersonic cold target and a He 2+ Ion collision, measurement of He 2+ +He(1s 2 ) → He + (1s)+He + (1s) Recoil ion He produced by the reaction + The momentum along the beam direction (i.e. longitudinal momentum) is a constant value for the momentum transfer of the collision reaction in this direction, so the ion momentum dispersion in this direction mainly comes from the thermal dispersion and position dispersion of the He target before the reaction. The He target produced by the supersonic cold target in the test has a diameter of about 5mm in the collision zone, a thermal dispersion of about 0.04au, and a beam diameter of about 0.5mm.

[0067] This embodiment uses a combination of an accelerating electric field and a decelerating electric field to test He + Time-of-flight focusing effect: In order to keep the detector and the electric field shielding net away from the beam, an angle of 120 is set between the electric field direction and the beam direction. Figure 3 In addition to the beam direction, the collision causes the recoil ion He +A continuous momentum distribution is obtained in other directions, resulting in excessive dispersion of the initial momentum of the recoil ion in the electric field direction. This momentum dispersion leads to serious flight time dispersion, so it is impossible to measure the recoil ion He + The flight time directly verifies the focusing effect. This embodiment verifies the focusing effect by restoring the momentum dispersion in the beam direction. During the test, the length of the accelerating electric field is 28.8 cm, the length of the decelerating electric field is 9.2 cm, and the two fields are composed of an electrode sheet with an electric field shielding net ( Figure 3 During the experiment, the voltage in the acceleration zone was 29.6V, the voltage in the deceleration zone was 28.2V, and He + The flight time is 19.86 μs. Under unfocused conditions, the momentum dispersion caused by a 5 mm target thickness is about 0.85 au. Due to the flight time focusing, the measured resolution is 0.054 au. Figure 4 As shown. The component in the direction perpendicular to the electric field is not focused, and the momentum dispersion caused by the position dispersion in this direction is about 0.2 au, and the momentum dispersion transferred to the beam direction is about 0.04 au. Considering that the thermal dispersion of the He target is about 0.04 au, the current test scheme cannot measure the focusing limit capability of the present invention, but it proves that the application of the present invention reduces the measured momentum dispersion from about 0.85 au to 0.054 au.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A focusing method based on a time-of-flight mass spectrometer, characterized in that include: Will n+n' The annular electrode sheets are coaxially insulated and arranged, wherein the first annular electrode sheet to the n The spacing between the ring electrodes is L 1, no. n Ring electrode sheet to n+n' The spacing between the ring electrodes is L 2; Place the first ring electrode sheet, n Ring electrode sheet, n+n' An electric field shielding net is arranged on each of the annular electrode sheets to isolate the electric field on both sides of the annular electrode sheets, and the electric field shielding net is made of a metal net; Place the first ring electrode sheet to the n+n' The annular electrode sheets are respectively connected to a voltage source; The lengths of the annular electrode sheet and the electric field shielding net are L 1. L 2, strength is E 1. E 2 two connected uniform electric fields; The field strength can be adjusted by adjusting the voltage applied to the ring electrodes at both ends. E 1. E 2. By adjusting the field strength E 1. E 2. Time-of-flight focusing of charged particles of any given speed is achieved; wherein, n+n' The intervals between the annular electrodes are l 1, l 2 …l n+n’-1 , in, , ; Voltage is applied to each ring electrode U 1, U 2 … U n+n’ The electric field generated when E 1. E 2 are: ； 。 2. The focusing method based on a time-of-flight mass spectrometer according to claim 1, characterized in that: The annular electrode sheet is a metal ring with an inner diameter of 10 cm, an outer diameter of 14 cm and a thickness of 1 mm.

3. A focusing device based on a time-of-flight mass spectrometer, characterized in that: The device includes: Ring-shaped electrode sheets, the number of which is n+n' indivual, n+n' The annular electrode sheets are coaxially insulated and arranged; The electric field shielding net is arranged between the first annular electrode sheet and the second n Ring electrode sheet, n+n' The electric field shielding net is a metal net on the annular electrode sheet to isolate the electric field on both sides of the annular electrode sheet; the electric field shielding net is a metal net; A voltage source, the voltage source is connected to the first annular electrode sheet to the n+n' Ring electrode sheet, wherein: n+n' The intervals between the annular electrodes are l 1, l 2 …l n+n’-1 , in , ; Each of the annular electrodes is applied with a voltage U 1, U 2 … U n+n’ When the intensity of the electric field generated in the annular electrode sheet and between the electric field shielding nets is E 1. E 2 uniform electric field: ； 。 4. The focusing device based on a time-of-flight mass spectrometer according to claim 3, characterized in that: The annular electrode sheet is a metal ring with an inner diameter of 10 cm, an outer diameter of 14 cm and a thickness of 1 mm.

5. The focusing device based on a time-of-flight mass spectrometer according to claim 3, characterized in that: The voltage source is an adjustable DC power supply or a voltage divider circuit.

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