CN109470732B

CN109470732B - Electronic optical system

Info

Publication number: CN109470732B
Application number: CN201810517125.XA
Authority: CN
Inventors: 乔山
Original assignee: Shanghai Institute of Microsystem and Information Technology of CAS
Current assignee: Shanghai Institute of Microsystem and Information Technology of CAS
Priority date: 2017-09-07
Filing date: 2017-09-07
Publication date: 2020-11-24
Anticipated expiration: 2037-09-07
Also published as: WO2019047986A1; CN109470732A

Abstract

The present invention provides an electron optical system, comprising at least: the lens comprises a magnetic field and a non-axisymmetric lens group, wherein the magnetic field is used for separating the movement tracks of initial incident electrons and emergent electrons and realizing deflection of the movement direction of the electrons, so that the initial incident electrons deflect a first set angle and the emergent electrons deflect a second preset angle; the non-axisymmetric lens group is used for compensating the asymmetry of the electron-optical characteristics of the magnetic field in the vertical and parallel magnetic field directions, reducing aberration, and is matched with the magnetic field to enable the electron beam to simultaneously image on an image plane in the vertical magnetic field direction and the parallel magnetic field direction. Meanwhile, the non-axisymmetric electric lens can realize the deflection function of the electron beam, so that the debugging of the electron optical system is simpler.

Description

Electronic optical system

The present application is a divisional application of a patent with an application date of 07/09/2017 and an application number of 201710800610.3, entitled image type electron spin analyzer.

Technical Field

The invention relates to the technical field of electron spin analysis, in particular to an electron optical system.

Background

Currently, there are mainly Mott type, Spin-LEED type, and VLEED type analyzers for measuring electron Spin. The measurement mode of the Mott type analyzer is as follows: the method comprises the steps of accelerating electrons to 20-100KeV kinetic energy, scattering the electrons on a target made of a material (generally composed of high atomic number elements) with high spin-orbit interaction, and measuring the spin of incident electrons by measuring the asymmetry of the intensity of the scattered electrons; Spin-LEED analyzers measure the Spin of electrons by measuring the asymmetry in the intensity of the diffracted spots of electrons at a single crystal surface of a material with high Spin-orbit interaction (e.g., tungsten, iridium, platinum, topological insulators, etc.); VLEED is a new analyzer that has been recently developed and is measured by: the electron kinetic energy is first accelerated (decelerated) to 6eV, then the reflectivities of the electrons on the ferromagnetic targets magnetized in the + Z direction and the-Z direction are respectively measured, and the spin of the incident electrons in the Z direction is measured by measuring the relative difference of the two reflectivities. VLEED is the most efficient electron spin analyzer to measure at present.

Fig. 1 is a schematic diagram of the electron spin measurement principle of a conventional single-channel VLEED analyzer. The incident electron at the point a on the initial electron plane 11 passes through the electron lens 12, is incident on the scattering target 13, is scattered by the scattering target 13, and then passes through the electron lens 14 to reach the point a of the electron detector 15. Similarly, the incident electron at point B on the initial electron plane 11 reaches point B of the electron detector through a similar path. If the incident electrons vertically enter the scattering target 13, the emergent electrons elastically scattered by the scattering target 13 also vertically scatter the scattering target 13, the paths of the emergent electrons and the incident electrons are the same, and the electron detector will intercept the incident electron beam, so the classical VLEED spin analyzer adopts the method of obliquely emitting the incident electrons to the scattering target 13. Since the measurement efficiency of VLEED decreases with increasing incidence angle (i.e. the angle between the electron beam and the normal to the scattering target), a smaller incidence angle is required, and the incidence angle is usually selected to be 7 ° because the incidence angle cannot be too small in consideration of the size of the electron lens 12 and the electron lens 14. Since the incident angle is not zero, the incident electron orbit and the emergent electron orbit are different, and the incident electron and the emergent electron cannot adopt the same electron lens. In order to obtain a smaller incident angle, the electron

optical lenses

12 and 14 are smaller in size, resulting in a larger aberration, that is, each incident electron from point a forms a larger beam spot centered on point a on the electron detector, and each incident electron from point B forms a larger beam spot centered on point B on the electron detector, and the beam spot centered on point a and the beam spot centered on point B partially overlap due to the larger beam spots, so that the classical VLEED analyzer cannot distinguish the source position of the incident electron, that is, whether the incident electron comes from point a or B. Such an electron spin analyzer that cannot distinguish the source position of incident electrons is called a single-channel electron spin analyzer; analyzers that can distinguish the source location of incident electrons are called multi-channel analyzers or image-type analyzers. The electron spin analyzers currently in operation are almost single channel. In order to improve the efficiency of electron spin measurement, the realization of multi-channel measurement of electron spin has been the focus of attention of scientific research technicians.

There are two types of multi-channel electron spin analyzers reported today. One is Spin-LEED image-type Spin analyzer created by the Kirschner research group of germany. Incident electrons of the analyzer are incident to a W (100) target at an incident angle of 45 degrees, an included angle of 90 degrees is formed between the incident electron beam and a scattered electron beam, and an imaginary image plane and an electron detector plane formed by the incident electrons on the back surface of the W (100) target are both vertical to an electron optical axis, so that an electron optical system has smaller aberration and can distinguish the source positions of the incident electrons. However, spin-LEED analyzers based on spin-orbit interactions are only one percent more efficient than VLEED analyzers based on strongly correlated interactions. Another VLEED type multi-channel electron spin analyzer, invented by the applicant, has been granted chinese patent number 201310313572. The invention introduces the magnetic field to realize the separation of the movement tracks of incident electrons and emergent electrons, thereby realizing high-efficiency VLEED type multi-channel electron spin measurement, and adopts the auxiliary magnetic field to remove the electron optical asymmetry of the main magnetic field along the magnetic field direction and the vertical magnetic field direction, but the construction and debugging of the main magnetic field and the auxiliary magnetic field are difficult, thereby being incapable of realizing extremely small aberration and being beneficial to application and popularization.

Disclosure of Invention

In view of the above-mentioned shortcomings of the prior art, the present invention provides an electron optical system, which can solve the problems of low measurement efficiency, large aberration, difficult debugging of the optical system, etc. of the multi-channel electron spin analyzer in the prior art when used in the multi-channel electron spin analyzer.

To achieve the above and other related objects, the present invention provides an electron optical system, including at least: a magnetic field and a non-axisymmetric lens group, wherein,

the magnetic field is used for separating the movement tracks of initial incident electrons and emergent electrons and realizing deflection of the movement direction of the electrons, so that the initial incident electrons deflect a first set angle and the emergent electrons deflect a second set angle; the non-axisymmetric lens group is used for compensating the asymmetry of the electron-optical characteristics of the magnetic field in the vertical and parallel magnetic field directions, reducing aberration, and enabling the electron beam to be imaged on an image plane simultaneously in the vertical magnetic field direction and the parallel magnetic field direction by matching with the magnetic field.

Preferably, the first set angle is (0 °, 360 °), and the second set angle is (0 °, 360 °).

More preferably, the first set angle and the second set angle are any one or two of 10 °, 15 °, 20 °, 25 °, 30 °, 45 °, 60 °, 90 °, 120 °, 135 ° or 180 °.

Preferably, the non-axisymmetric lens group includes a plurality of lens groups, wherein at least one lens group is a non-axisymmetric lens group.

More preferably, the non-axisymmetrical lens group includes a first lens group, a second lens group, and a third lens group.

More preferably, the non-axisymmetric lens group includes at least one non-axisymmetric lens.

More preferably, the non-axisymmetric lens is a cylindrical electric lens and an electric multipole lens constructed by dividing the cylindrical electric lens into a plurality of sections.

More preferably, the non-axisymmetric lens is an electric quadrupole lens.

More preferably, the deflection of the electron beam may be achieved by adjusting the electrode voltage of the electric multipole lens.

As described above, the electron optical system of the present invention has the following advantageous effects:

the electronic optical system of the invention realizes the separation of the incident electron orbit and the emergent electron orbit by introducing the magnetic field, thereby avoiding the difficulty of the geometric configuration of the electronic optical system and the electronic detector, and enabling the lens system to adopt larger size to obtain smaller aberration; the non-axisymmetric lens introduces the asymmetry of the compensation magnetic field in the electron optics in the directions vertical to and parallel to the magnetic field, so that simultaneous imaging in the two directions is realized, real two-dimensional imaging is realized, and aberration is reduced. Meanwhile, the function of the non-axisymmetric lens for deflecting the electron beam enables the debugging of the electron optical system of the invention to be simpler. When the electron optical system of the present invention is used for a multi-channel electron spin analyzer, the number of channels for electron spin measurement can be increased.

Drawings

Fig. 1 shows a schematic diagram of electron spin measurement principle of a prior art single channel VLEED analyzer.

Fig. 2 shows a first embodiment of the image type electron spin analyzer of the present invention.

Fig. 3 shows a second embodiment of the image type electron spin analyzer of the present invention.

Fig. 4 is a schematic diagram illustrating the working principle of the quadrupole lens of the present invention.

Description of the element reference numerals

11 initial electron plane

12. 14 electron lens

13 scattering target

15 electronic detector

2 initial electron plane

31. 32, 33 first to third lens groups

4 scattering target

5 two-dimensional image type electronic detector

6 magnetic field

e1, e2, e3, e4 first to fourth plates

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.

The detailed description is provided with reference to fig. 2-4. It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the invention, and the components in the drawings are not drawn according to the number, shape and size of the components in the actual implementation, and the type, number and proportion of the components in the actual implementation may be changed, and the layout of the components may be more complicated.

The present invention can provide an image type electron spin analyzer, which includes at least: an electronic optical system, a scattering target 4, and a two-dimensional image type electronic detector 5; the electron optical system comprises a non-axisymmetric lens group and a magnetic field 6, wherein the non-axisymmetric lens group is matched with the magnetic field 6 to enable initial incident electrons to deflect a first set angle and then to be imaged on the scattering target 4 plane or any plane behind the scattering target 4 plane, and then enable emergent electrons elastically scattered by the scattering target 4 to deflect a second set angle and then to be imaged on the two-dimensional image type electronic detector 5 plane, so that an emergent electron path is separated from an incident electron path, and a two-dimensional electron intensity image is formed on the two-dimensional image type electronic detector 5.

Specifically, the electron optical system includes a magnetic field 6 and a non-axisymmetric lens group, and is configured to implement imaging of the electron intensity distribution on the initial electron plane 2 onto the scattering target 4 plane or any plane behind the scattering target 4 plane, and then implement imaging of the electron intensity distribution on the scattering target 4 onto the plane of the two-dimensional image type electron detector 5. The electron optical system can be arranged according to the requirement of the installation space of the image type electron spin analyzer, thereby increasing the freedom degree of the geometric configuration of each component of the image type electron spin analyzer.

As shown in fig. 2, in the first embodiment of the present invention, the non-axisymmetrical lens group includes three lens groups, namely, a first lens group 31, a second lens group 32 and a third lens group 33, and the number of lens groups can be set as required in practical applications, which is not limited to this embodiment. In this embodiment, in order to meet the requirement of the installation space of the image type electron spin analyzer, the initial electron plane 2, the scattering target 4 and the two-dimensional image type electron detector 5 are disposed at the right portion of the electron spin analyzer, the first lens group 31, the second lens group 32 and the third lens group 33 are disposed at the center of the electron spin analyzer and at one side of the magnetic field 6, and the magnetic field 6 is disposed at the left portion of the electron spin analyzer. The electron optical subsystem composed of the first lens group 31, the magnetic field 6 and the second lens group 32 realizes point-to-point imaging of the initial electron plane 2 to the scattering target 4. The electron optical subsystem composed of the second lens group 32, the magnetic field 6 and the third lens group 33 realizes point-to-point imaging of the scattering target 4 to the two-dimensional image type electron detector 5.

In the second embodiment of the present invention, as shown in fig. 3, in order to adapt to the installation space requirement of the image type electron spin analyzer, the initial electron plane 2, the scattering target 4 and the two-dimensional image type electron detector 5 are oppositely arranged at an angle of 120 °, and the electron optical subsystem consisting of the first lens group 31, the magnetic field 6 and the second lens group 32 realizes point-to-point imaging of the initial electron plane 2 to the scattering target 4. The electron optical subsystem composed of the second lens group 32, the magnetic field 6 and the third lens group 33 realizes point-to-point imaging of the scattering target 4 to the two-dimensional image type electron detector 5.

More specifically, the magnetic field 6 is used to separate the movement trajectories of the incident electrons and the emergent electrons, and the deflection of the movement direction of the electrons is realized, thereby avoiding the difficulty in the geometrical configuration of the initial electron plane 2, the scattering target 4 and the two-dimensional image type electron detector 5. After the initial incident electrons enter the magnetic field 6, the moving direction is deflected by the first set angle under the action of the magnetic field 6, the first set angle is (0 degrees, 360 degrees), and the first set angle is preferably any one of 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees, 45 degrees, 60 degrees, 90 degrees, 120 degrees, 135 degrees or 180 degrees. After entering the magnetic field 6, the emitted electrons scattered by the scattering target 4 are deflected by the second set angle in the moving direction under the action of the magnetic field 6, the second set angle is (0 degrees and 360 degrees), and the second set angle is preferably any one of 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees, 45 degrees, 60 degrees, 90 degrees, 120 degrees, 135 degrees or 180 degrees. In practical use, the first setting angle and the second setting angle can be set according to geometric configuration requirements, and the first setting angle and the second setting angle can be the same or different; when the second setting angle is different from the first setting angle, a special magnetic field geometry structure is required to realize different deflection angles, which is not described herein again.

In the first embodiment of the present invention, as shown in fig. 2, the first set angle is set to 180 °. The initial incident electrons emitted from the initial electron plane 2 pass through the first lens group 31 to enter the magnetic field 6 along the left direction, are deflected by 180 degrees under the action of the magnetic field 6 to move along the right direction along the horizontal direction, and pass through the second lens group 32 to be imaged on the scattering target 4. The second setting angle is the same as the first setting angle and is set to 180 °. Electrons scattered by the scattering target 4 are incident to the magnetic field 6 from the plane of the scattering target 4 along the horizontal left direction through the second lens group 32, are deflected by 180 degrees under the action of the magnetic field 6, move to the right along the horizontal direction, and are imaged on the two-dimensional image type electronic detector 5 after passing through the third lens group 33.

In the second embodiment of the present invention, as shown in fig. 3, the first set angle is set to 120 °, the initial incident electrons are emitted from the initial electron plane 2 and then incident on the magnetic field 6 through the first lens group 31 in the vertical upward direction, and are deflected by 120 ° by the magnetic field 6 and then imaged on the scattering target 4 through the second lens group 32. The second setting angle is the same as the first setting angle and is set to 120 °. The emitted electrons scattered by the scattering target 4 are emitted from the scattering target 4 plane, and then are incident to the magnetic field 6 again through the second lens group 32, and are deflected by 120 degrees under the action of the magnetic field 6, and then are imaged on the two-dimensional image type electronic detector 5 through the third lens group 33.

The magnetic field 6 has different electro-optical properties in the perpendicular magnetic field direction and in the parallel magnetic field direction. Assuming that the electron beam is deflected by 180 ° in the magnetic field 6, if the electron beam at the entrance of the magnetic field 6 is a divergent beam emitted from the entrance point, the electron makes a circular motion in the direction perpendicular to the magnetic field due to the centripetal force provided by the lorentz force, and after being deflected by 180 °, the electron is focused again at the exit of the magnetic field; in the direction parallel to the magnetic field, the electrons are not stressed and remain dispersed. Therefore, the magnetic field 6 has different electron-optical characteristics in the vertical magnetic field direction and the parallel magnetic field direction, and if the magnetic field is matched with the axisymmetric lens group, the electron-optical system has different focal lengths in the vertical magnetic field direction and the parallel magnetic field direction, so that simultaneous imaging in the two directions is impossible, and finally, the aberration presented on the two-dimensional image type electronic detector 5 is relatively large. The invention compensates the asymmetry of the electron optical characteristics of the magnetic field 6 in the direction of the vertical magnetic field and the direction of the parallel magnetic field by introducing the non-axisymmetric lens group, and enables the electron beam to simultaneously image in the two directions of the vertical magnetic field and the parallel magnetic field on the image plane, thereby reducing aberration and realizing multi-channel measurement of electron spin. In this embodiment, the image plane includes the scattering target 4 plane, an arbitrary plane behind the scattering target 4 plane, and the two-dimensional image type electronic detector 5 plane.

More specifically, the non-axisymmetric lens group includes a plurality of lens groups, wherein at least one lens group is a non-axisymmetric lens group. Each lens group is composed of a plurality of lenses, and the non-axisymmetric lens group at least comprises one non-axisymmetric lens. The number of the lens groups and the number of the lenses in each lens group can be set according to actual needs. In this embodiment, the first lens group 31 and the third lens group 33 are both non-axisymmetrical lens groups for compensating the asymmetry of the electro-optical characteristics of the magnetic field 6 in the vertical magnetic field direction and the parallel magnetic field direction. The present invention preferably provides a non-axisymmetric electric lens which compensates for the asymmetry of the magnetic field electron optical characteristics in the vertical and parallel magnetic field directions, and which may be an electric multipole lens constructed by dividing a cylindrical lens into a plurality of cylindrical lenses, including but not limited to a quadrupole lens, a hexapole lens and an octopole lens, and which can adjust the non-axisymmetric electron optical characteristics by adjusting the voltages of the respective plates of the multipole lens. In both the first and second embodiments of the present invention, a quadrupole lens is used, and the simplest structure of the quadrupole lens is to divide a cylindrical lens into four parts as a first plate e1, a second plate e2, a third plate e3 and a fourth plate e4, as shown in fig. 4. If the first plate e1 and the second plate e2 are at the potential U12, and the third plate e3 and the fourth plate e4 are at the potential U34, the difference between the focal lengths of the quadrupole lens in the x direction and the y direction can be adjusted by adjusting the potential difference between the potential U12 and the potential U34. Matching the x-direction and the y-direction with the vertical magnetic field direction and the parallel magnetic field direction allows simultaneous imaging in both directions on the scattering target 4 plane or any plane behind the scattering target 4 plane and on the two-dimensional image type electronic detector 5, thereby reducing aberration. In addition, due to machining and mounting errors, a deflector needs to be additionally installed in an actual electron optical system to compensate for the errors. The multi-polar lens of the invention can realize the non-axisymmetric electron optical characteristics and simultaneously realize the deflector function by adjusting the electric potential of each polar plate. Specifically, the deflection of the electron beam in the y direction can be realized by adjusting the voltage between the first plate e1 and the second plate e 2; the deflection of the electron beam in the x direction can be realized by adjusting the voltage between the third plate e3 and the fourth plate e 4.

Specifically, the angle between the central axis of the electron optical system and the normal of the scattering target 4 may be any angle between (-90 °, 90 °), preferably any one or two angles of 0 °, ± 15 °, ± 20 °, ± 25 °, ± 30 °, ± 45 ° or ± 60 °. Preferably, the central axis of the electron optical system may be at 45 ° to the normal of the scattering target 4 and image the electron beam current at the rear of the scattering target 4 and become a virtual image of the electron optical subsystem consisting of the scattering target and the subsequent lens, and at this time, the angle between the central axis of the reflected beam current and the central axis of the incident beam current is 90 °.

In the first and second embodiments of the present invention, as shown in fig. 2 and 3, it is preferable that the angles between the central axis of the incident electron beam and the central axis of the scattered electron beam of the electron optical system and the normal of the scattering target 4 are all 0 °, and the initial incident electron is deflected, perpendicularly incident on the scattering target 4, and perpendicularly scattered from the scattering target 4.

Specifically, the material of the scattering target 4 includes, but is not limited to, a ferromagnetic material and a material having a high spin-orbit interaction. Wherein the ferromagnetic material includes, but is not limited to, ferromagnetic iron oxide; materials with high spin-orbit interactions include, but are not limited to, single crystals of tungsten, iridium, gold, topological insulators, or amorphous of tungsten, iridium, gold, topological insulators. Forms of the ferromagnetic material and the material with high spin-orbit interaction include, but are not limited to, bulk and thin film. When the scattering target 4 is made of ferromagnetic iron oxide thin film material, a VLEED type multi-channel electron spin analyzer can be constructed. In one embodiment of the present invention, the scattering target 4 is a ferromagnetic iron oxide thin film formed on a magnesium oxide substrate. When the scattering target 4 is made of a material having a high spin-orbit interaction, such as a tungsten single crystal thin film, an iridium single crystal thin film, a gold single crystal thin film, or a topological insulator single crystal thin film, a spin-LEED type multi-channel electron spin analyzer can be constructed.

Specifically, the two-dimensional image type electron detector 5 may be any device capable of recording the electron intensity distribution. In one embodiment of the present invention, the two-dimensional image type electron detector 5 is composed of a Micro-channel Plate (MCP), a fluorescent Plate, and a high-sensitivity camera. In another embodiment of the present invention, the two-dimensional image type electron probe 5 is composed of a microchannel plate and a Delay Line probe (DLD).

It should be noted that the above description is only illustrative and not restrictive to the present invention, and in fact, any design that uses a non-axisymmetric lens group in combination with a magnetic field to bend an incident electron beam to an angle and then to enter a scattering target at an optimal incident angle and image the electron beam at a specific plane relative to the scattering target, and that can bend an emergent electron beam scattered from the scattering target to an angle and then to reach an optimal emergent angle and image the electron beam on a two-dimensional image type electron detector is included in the scope of the present invention.

As shown in fig. 2, the operation of the image-type electron spin analyzer according to the present invention is described in detail in a first embodiment of the present invention:

as shown in fig. 2, first, the scattering target 4 (ferromagnetic scattering target) is magnetized in a certain direction, for example, in the + Z direction, and then, an incident electron beam from the initial electron plane 2 enters the magnetic field 6 after passing through the non-axisymmetric first lens group 31, and is vertically incident to the scattering target 4 through the second lens group 32 after being bent upward by 180 ° by the magnetic field 6, and is two-dimensionally imaged on the plane of the scattering target 4; then, the outgoing electron beam elastically scattered by the scattering target 4 enters the magnetic field 6 again after passing through the second lens group 32, and vertically reaches and is two-dimensionally imaged on the entrance plane of the two-dimensional image type electronic detector 5 again through the non-axisymmetric third lens group 33 after being bent upward by 180 ° again under the action of the magnetic field 6, and the two-dimensional image type electronic detector 5 includes a high-sensitivity camera for recording a two-dimensional electron intensity image on a fluorescent plate.

Subsequently, the scattering target 4 is magnetized in the-Z direction, and a two-dimensional electron intensity image on the fluorescent plate is recorded again.

Since the electron intensity difference of a certain pixel point in the two-dimensional electron intensity image obtained based on the two measurements is proportional to the spin polarization degree of the incident electron at the corresponding position on the initial electron plane 2 along the Z direction, the above process can measure the spin polarization degree of the incident electron at each point on the initial electron plane 2.

It can be seen from the above that, the separation of the incident electron orbit and the emergent electron orbit can be realized by bending the electron orbit by introducing the magnetic field, and meanwhile, since the initial electron plane, the scattering target plane and the plane of the two-dimensional image type electron detector are all perpendicular to the optical axis, and the incident and scattered electrons near the scattering target pass through the same electron lens group 32, the increase of the size of the electron lens becomes possible, so that the aberration of the whole optical system can be greatly reduced. Therefore, after the incident electron beams from each position point on the initial electron plane are focused, transmitted and scattered by the electron optical system, beam spots formed on the plane of the two-dimensional image type electron detector are very small and are not overlapped with each other, so that each beam spot can correspond to the incident electron beam at the corresponding position point on the initial electron plane, namely the source position of the incident electrons can be distinguished, and the multi-channel measurement of electron spin is realized.

In summary, the image type electron spin analyzer according to the present invention bends electrons by using an electron optical system in which a magnetic field is combined with a non-axisymmetric lens group, so that an incident electron orbit and an emergent electron orbit can be separated, the incident electrons can be incident on a scattering target at an optimal incident angle, the emergent electrons can be incident on a two-dimensional image type electron detector at an optimal incident angle, and a first two-dimensional imaging from an electronic image at an initial plane of the spin detector to a specific plane corresponding to the scattering target and a second two-dimensional imaging from the plane to a plane of the two-dimensional image type electron detector are respectively performed, thereby realizing multi-channel measurement of electron spin. Because the object image plane is vertical to the optical axis of the electronic optical system in the two imaging processes, the real two-dimensional imaging can be ensured. Herein, the true two-dimensional imaging means that a first imaging image plane without considering aberration completely coincides with a specific plane corresponding to the scattering target, and a second imaging image plane without considering aberration completely coincides with a plane of the two-dimensional image type electronic detector.

In summary, the present invention provides an electronic optical system, which at least includes: the lens comprises a magnetic field and a non-axisymmetric lens group, wherein the magnetic field is used for separating the movement tracks of initial incident electrons and emergent electrons and realizing deflection of the movement direction of the electrons, so that the initial incident electrons deflect a first set angle and the emergent electrons deflect a second set angle; the invention realizes the separation of the incident electron orbit and the emergent electron orbit by introducing the magnetic field, thereby avoiding the difficulty of the geometric configuration of the electron lens and the electron detector, and enabling the lens to adopt larger size so as to obtain smaller aberration; the non-axisymmetric lens group is used for compensating the asymmetry of the electron optical characteristics of the magnetic field in the vertical and parallel magnetic field directions and is matched with the magnetic field to enable the electron beam to simultaneously image in the vertical magnetic field direction and the parallel magnetic field direction on the image plane, thereby realizing real two-dimensional imaging and reducing aberration. The invention can be applied not only to the electron spin measurement, but also to other scientific instruments, so the invention effectively overcomes various defects in the prior art and has high industrial utilization value.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Claims

1. An electron optical system, characterized in that it comprises at least: a magnetic field and a non-axisymmetric lens group, wherein,

the magnetic field is used for separating the movement tracks of initial incident electrons and emergent electrons and realizing deflection of the movement direction of the electrons, so that the initial incident electrons deflect a first set angle and the emergent electrons deflect a second set angle, and the magnetic field has different electron optical characteristics in the direction perpendicular to the magnetic field and the direction parallel to the magnetic field; the non-axisymmetric lens group is used for compensating the asymmetry of the electron-optical characteristics of the magnetic field in the vertical and parallel magnetic field directions, reducing aberration, and enabling the electron beam to be imaged on an image plane simultaneously in the vertical magnetic field direction and the parallel magnetic field direction by matching with the magnetic field.

2. The electron optical system according to claim 1, characterized in that: the first set angle is (0 °, 360 °), and the second set angle is (0 °, 360 °).

3. The electron optical system according to claim 2, characterized in that: the first set angle and the second set angle are any one angle or any two angles among 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees, 45 degrees, 60 degrees, 90 degrees, 120 degrees, 135 degrees or 180 degrees.

4. The electron optical system according to claim 1, characterized in that: the non-axisymmetric lens group comprises a plurality of lens groups, wherein at least one lens group is a non-axisymmetric lens group.

5. The electron optical system according to claim 4, characterized in that: the non-axisymmetrical lens group comprises a first lens group, a second lens group and a third lens group.

6. The electron optical system according to claim 4 or 5, characterized in that: the non-axisymmetric lens group includes at least one non-axisymmetric lens.

7. The electron optical system according to claim 6, characterized in that: the non-axisymmetric lens is an electric multipole lens constructed by dividing a cylindrical electric lens into a plurality of parts.

8. The electron optical system according to claim 7, characterized in that: the non-axisymmetric lens is an electric quadrupole lens.

9. The electron optical system according to claim 7, characterized in that: the deflection of the electron beam can be achieved by adjusting the electrode voltage of the electric multipole lens.