阅读说明：本技术 一种低能电子衍射仪 (Low-energy electron diffractometer ) 是由 乔山 于 2018-05-28 设计创作，主要内容包括：本发明提供一种低能电子衍射仪,包括：电子发生装置、带电粒子光学系统、样品及二维图像型电子探测器。电子发生装置用于生成电子;带电粒子光学系统包括磁场及非轴对称电透镜群,磁场用于分离入射及出射带电粒子的运动轨道,并实现带电粒子运动方向的偏转；非轴对称电透镜群用于补偿磁场光学特性在垂直及平行磁场方向的非对称性,减小像差,并使带电粒子束在像平面上在沿垂直磁场方向和平行磁场的两个方向上同时成像。本发明的低能电子衍射仪可以实现入射和出射带电粒子轨道的分离,从而避免各个部件的几何配置困难,实现无电子枪阴影的低能电子衍射测量并使时间分辨低能电子衍射测量更为便利。(The invention provides a low-energy electron diffractometer, comprising: an electron generating device, a charged particle optical system, a sample, and a two-dimensional image type electron detector. The charged particle optical system comprises a magnetic field and a non-axisymmetric electric lens group, wherein the magnetic field is used for separating the movement tracks of incident and emergent charged particles and realizing the deflection of the movement direction of the charged particles; the non-axisymmetric electric lens group is used for compensating the asymmetry of the magnetic field optical characteristics in the vertical and parallel magnetic field directions, reducing aberration and enabling the charged particle beams to be imaged on an image plane in two directions along the vertical magnetic field direction and the parallel magnetic field simultaneously. The low-energy electron diffractometer can realize the separation of the incident charged particle orbit and the emergent charged particle orbit, thereby avoiding the difficulty of the geometric configuration of each part, realizing the low-energy electron diffraction measurement without the shadow of an electron gun and enabling the time-resolved low-energy electron diffraction measurement to be more convenient.)

1. A low energy electron diffractometer, comprising at least: the device comprises an electron generating device, a charged particle optical system, a sample and a two-dimensional image type electron detector; wherein the content of the first and second substances,

The electron generating device is used for generating electrons;

The charged particle optical system is used for deflecting electrons generated by the electron generating device by a first preset angle to form a focused parallel beam to be incident on the surface of the sample, and deflecting the electron beam diffracted from the surface of the sample by a second preset angle to form an image on the two-dimensional image type electron detector; the charged particle optical system comprises a magnetic field and a non-axisymmetric electric lens group, wherein the magnetic field is used for separating the movement tracks of incident and emergent charged particles and realizing the deflection of the movement direction of the charged particles; the non-axisymmetric electric 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 charged particle beams to be imaged on an image plane in the two directions along the vertical magnetic field direction and the parallel magnetic field simultaneously.

2. the low energy electron diffractometer of claim 1, wherein: the first set angle is greater than 0 ° and less than 360 °, and the second set angle is greater than 0 ° and less than 360 °.

3. The low energy electron diffractometer of claim 2, wherein: the first set angle is any one of 5 degrees, 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees, 45 degrees, 60 degrees, 90 degrees, 120 degrees, 135 degrees or 180 degrees; the second predetermined angle is any one of 5 °, 10 °, 15 °, 20 °, 25 °, 30 °, 45 °, 60 °, 90 °, 120 °, 135 °, or 180 °.

4. The low energy electron diffractometer of claim 1, wherein: the non-axisymmetric electric lens group comprises a plurality of electric lens groups, wherein at least one electric lens group is a non-axisymmetric electric lens group.

5. The low energy electron diffractometer of claim 4, wherein: the non-axisymmetric electric lens group at least comprises one non-axisymmetric electric lens.

6. The low energy electron diffractometer of claim 5, wherein: the non-axisymmetric electric lens is a cylindrical electric lens and is an electric multipole lens constructed by dividing a plurality of cylindrical electric lenses.

7. The low energy electron diffractometer of claim 6, wherein: the non-axisymmetric electric lens is an electric quadrupole lens, an electric hexapole lens or an electric octopole lens.

8. The low energy electron diffractometer of claim 6, wherein: the deflection of the charged particle beam can be achieved by adjusting the electrode voltages of the electric multipole lens.

9. The low energy electron diffractometer of claim 1, wherein: the two-dimensional image type electronic detector comprises a micro-channel plate, a fluorescent plate and a camera.

10. the low energy electron diffractometer of claim 1, wherein: the two-dimensional image type electronic detector comprises a microchannel plate and a delay line detector.

11. The low energy electron diffractometer of any one of claims 1 to 10, wherein: the electron generating device comprises a field emission electron gun.

12. The low energy electron diffractometer of any one of claims 1 to 10, wherein: the electron generation device includes: the field emission electron gun in a critical state generates a pulse electron beam through a photoelectric effect under the irradiation of the laser, so that time-resolved low-energy electron diffraction measurement is realized.

13. The low energy electron diffractometer of claim 12, wherein: the magnetic field comprises an equilateral triangle magnetic field, the laser is positioned on the outer side of the vertex angle of the magnetic field, the electron gun is positioned on the outer side of the bottom edge of the equilateral triangle magnetic field, and the laser and the electron gun are both positioned on the extension line of the middle line of the equilateral triangle magnetic field; the sample is positioned on the outer side of one side of the equilateral triangle magnetic field, and the two-dimensional image type electronic detector is positioned on the outer side of the other side of the equilateral triangle magnetic field.

Technical Field

The invention relates to the field of charged particle optics and low-energy electron diffraction, in particular to a low-energy electron diffractometer.

Background

Electric lens systems have found widespread use, ranging from picture tubes in first generation televisions to scientific instruments such as electronic energy analyzers. Magnetic fields and magnetic lens systems play an important role in the imaging of high energy electrons and ion beams. Time-reversal antisymmetry of magnetic fields on moving charged particles has been applied to the separation of incident and exiting particle trajectories. The magnetic field has different optical properties for charged particles in the directions perpendicular and parallel to the magnetic field. In the direction perpendicular to the magnetic field, the charged particles emitted from the same point will converge again after being bent by 180 degrees due to the action of the Roron magnetic force; in the direction parallel to the magnetic field, the charged particles are not stressed and maintain linear motion. In order to eliminate this asymmetry, a common method at present is to construct a compensation magnetic field, and the asymmetry is eliminated by adjusting the compensation magnetic field. The charged particle optical system constructed by the invention adopts the asymmetry of the non-axisymmetric electric lens to compensate the asymmetry of the optical characteristic of the magnetic field, and meanwhile, the electric multipole lens can also provide the function of a deflector, so that the structure of the charged particle optical system is simpler and the adjustment is more convenient. Low-energy electron diffraction (coherent back scattering) can measure atomic structural information of a substance surface. The current low-energy electron diffractometers all adopt a mode of placing an image type detector in front of a sample to directly observe backscattered electrons for measurement, and because an electron gun and the detector are both positioned in front of the sample, the shadow of the electron gun is inevitably generated in a diffraction image, so that the information of diffraction spots with small diffraction angles is lost. To reduce the effect of this shadow on the measurement, a smaller size electron gun and a larger detector are required.

In addition, time-resolved low-energy electron diffraction is achieved by irradiating a field emission electron gun tip in a critical state with a pulsed laser light to generate pulsed electrons using a photoelectric effect. However, the electron gun and the detector of the current low-energy electron diffractometer are both positioned on the front surface of the sample, and laser beams can only be incident from the side surface of the needle point, which is not beneficial to the generation of high-quality pulse electrons; meanwhile, although the field emission electron gun has the advantages of simple structure, good monochromaticity and easy generation of electron pulses, the field emission electron gun has small emission current due to the high price of a large-sized high-sensitivity two-dimensional detector (such as a multi-channel plate), and is not easy to be applied to a conventional low-energy electron diffractometer.

Disclosure of Invention

In view of the above-mentioned shortcomings of the prior art, it is an object of the present invention to provide a low-energy electron diffractometer for solving the above-mentioned problems of the prior art low-energy electron diffractometers.

To achieve the above and other related objects, the present invention provides a low energy electron diffractometer comprising at least: the device comprises an electron generating device, a charged particle optical system, a sample and a two-dimensional image type electron detector; wherein the content of the first and second substances,

The electron generating device is used for generating electrons;

The charged particle optical system is used for deflecting the electrons generated by the electron generating device by a first preset angle to form a focused parallel beam to be incident on the surface of the sample, and deflecting the electron beam diffracted from the surface of the sample by a second preset angle to form an image on the two-dimensional image type electron detector; the charged particle optical system comprises a magnetic field and a non-axisymmetric electric lens group, wherein the magnetic field is used for separating the incident and emergent charged particle motion tracks and realizing the deflection of the motion direction of the charged particles; the non-axisymmetric electric 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 charged particle beams to be imaged on an image plane in the two directions along the vertical magnetic field direction and the parallel magnetic field simultaneously.

Preferably, the first set angle is greater than 0 ° and less than 360 °, and the second set angle is greater than 0 ° and less than 360 °.

Preferably, the first set angle is any one of 5 °, 10 °, 15 °, 20 °, 25 °, 30 °, 45 °, 60 °, 90 °, 120 °, 135 ° or 180 °; the second predetermined angle is any one of 5 °, 10 °, 15 °, 20 °, 25 °, 30 °, 45 °, 60 °, 90 °, 120 °, 135 °, or 180 °.

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

Preferably, the non-axisymmetric electric lens group includes at least one non-axisymmetric electric lens.

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

Preferably, the non-axisymmetric electric lens is an electric quadrupole lens, an electric hexapole lens or an electric octopole lens.

Preferably, the deflection of the charged particle beam is achieved by adjusting the electrode voltages of said electric multipole lens.

Preferably, the two-dimensional image type electron detector includes a microchannel plate, a fluorescent plate, and a camera.

Preferably, the two-dimensional image type electron detector includes a microchannel plate and a delay line detector.

Preferably, the electron generating device comprises a field emission electron gun.

Preferably, the electron generating device includes: the field emission electron gun in a critical state generates electrons through a photoelectric effect under the irradiation of the laser.

Preferably, the magnetic field comprises an equilateral triangle magnetic field, the laser is located outside the vertex angle of the magnetic field, the electron gun is located outside the base of the equilateral triangle magnetic field, and the laser and the electron gun are both located on the extension line of the central line of the equilateral triangle magnetic field; the sample is positioned on the outer side of one side of the equilateral triangle magnetic field, and the two-dimensional image type electronic detector is positioned on the outer side of the other side of the equilateral triangle magnetic field.

As described above, the low-energy electron diffractometer of the present invention has the following advantageous effects:

In the low-energy electron diffractometer, the separation of the incident electron orbit and the emergent electron orbit is realized by introducing the magnetic field, so that the difficulty in geometrical configuration of each part is avoided, and each part can adopt flexible size so as to obtain smaller aberration and certain functions; the asymmetry of optical characteristics of a compensation magnetic field in the vertical and parallel magnetic field directions is introduced through the non-axisymmetric electric lens group, so that simultaneous imaging in the two directions is realized; the non-axisymmetric electric lens simultaneously realizes the deflection of charged particles so as to ensure that the debugging of an optical system is simpler; the separation of the movement tracks of the incident charged particles and the emergent charged particles can realize low-energy electron diffraction measurement without electron gun shadow; compared with the existing low-energy electron diffractometer, the invention can adopt a smaller detector so as to conveniently adopt a microchannel plate detector to realize electron multiplication, thereby adopting a field emission electron gun with simpler structure and better monochromaticity. The combination of the photoelectric effect and the field emission electron gun can conveniently construct a short pulse electron gun so as to realize time-resolved low-energy electron diffraction measurement. The field emission electron gun constructed by the invention is not coaxial with the normal of the sample, so that laser can be introduced from the front of the needle point of the field emission electron gun, and a pulse electron beam with better performance can be generated.

Drawings

FIG. 1 is a schematic diagram showing the structure of the low-energy electron diffractometer of the present invention.

Fig. 2 is a schematic diagram illustrating the working principle of the quadrupole lens of the present invention.

Description of the element reference numerals

2 electron gun

31. 32, 33 first to third electric lens groups

4 samples

5 two-dimensional image type electronic detector

6 magnetic field

7 laser

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.