CN117766365A - High-energy electron microscope system based on high-repetition frequency microwave acceleration - Google Patents

Abstract

The invention discloses a high-energy electron microscope system based on high-repetition frequency microwave acceleration, which comprises the following steps: generating an initial electron beam using an electron gun; compressing or accelerating the initial electron beam to obtain a first electron beam; performing energy dispersion reduction or acceleration operation on electrons in the first electron beam to obtain a second electron beam; shaping the transverse size of the electrons of the second electron beam to obtain a third electron beam; electrons of the third electron beam that have been back-scattered by the sample to be detected are imaged by means of a detector. The invention can solve the problems of low energy of the commercial direct current mirror, large volume of the traditional high-energy direct current mirror, low current intensity of the microwave acceleration electron microscope system and large energy dissipation.

Description

High-energy electron microscope system based on high-repetition frequency microwave acceleration

Technical Field

The invention relates to the technical field of electron microscope systems, in particular to a high-energy electron microscope system based on high-repetition frequency microwave acceleration.

Background

An electron microscope is a microscopic detection device capable of achieving sub-nanometer level spatial resolution. The basic system comprises an electron source, an electron gun, a magnetic lens system, a sample and a detection module. Electrons are scattered on a sample and a lattice after the processes of generating, accelerating and modulating, and are imaged on a detection screen after passing through an intermediate mirror and a projection mirror. Different atomic types, lattice structures, crystal axis angles correspond to different imaging results. Due to the high sensitivity of electron microscopes to material structures, they have an irreplaceable role in research in the fields of materials science and biology, etc.

The theoretical spatial resolution of the electron microscope is determined by the wavelength of the electron de broglie wave. For the determined camera, the number N of the pixel points and the size d of each pixel point are unchanged; for a fixed sample and camera length L, the Debroil wavelength λ of the radiation source is inversely proportional to the reciprocal spatial resolution 1/r of the camera. The energy of the radiation (e.g., electron beam) emitted by the radiation source is increased and the de broglie wavelength lambda is correspondingly decreased. Thus, as the energy of the radiation source increases, the spatial resolution r correspondingly increases.

Most electron sources used in conventional commercial electron microscopes are field emission electron sources, which are dc electron sources. The advantage of such a direct current electron source is the high quality of the electron beam. Because the energy of the direct current electron microscope is low, the electron emittance can be reduced to the picometer level by matching with a grid cap and a collimation system in the electron gun, and the average current intensity can also reach the mA magnitude; in recent years, in order to further improve the spatial resolution of electron microscopes, electron microscope systems for reducing astigmatism during imaging such as an chromatic aberration correction positron microscope and an spherical aberration correction electron microscope have been developed. However, the electron beam energy of the existing commercial direct current electron microscope is not more than 300keV, the electron beam energy is limited by the electron energy, the resolution improvement is limited, and the penetration capability is poor due to low energy, so that samples such as materials, chips, biological cells and the like with larger thickness can not be imaged.

Aiming at the problem of low energy of the current commercial electron microscope, two solutions exist. The first solution is to increase the electron gun size based on a dc mirror with hundred keV energy and increase the cavity voltage without changing the electric field gradient, but such solutions tend to be very large in equipment size, difficult to build, and not widely used worldwide. Representative of the scheme is an ultra-high voltage direct current mirror of university of osaka, japan, the electron energy of the electron mirror is 2-3 MeV, high-energy electron imaging can be realized, but the total height of the equipment is 13 meters, and the construction and maintenance cost is high; another representative is a 1.2MeV spherical aberration correcting cold field emission dc mirror of the japanese national center institute (Central Research Laboratory, hitachi, ltd.) which can achieve a spatial resolution of 50pm or less, but which is bulky in the high voltage module and the electron gun portion, and only the size of the electron gun portion reaches 3 meters.

The second scheme is to replace the traditional direct current electron gun with a microwave acceleration electron gun, which well solves the problem of huge volume of an electron source, but the average current intensity, the emittance and the energy dispersion of electrons are all obviously larger than those of the direct current electron gun because the electron gun works in a pulse mode. One representative of this scheme is a u-TEM electron microscope built at Shanghai university of transportation using a hot cathode as an electron source, using a conventional ambient microwave electron gun with a repetition frequency of about several tens to one hundred Hz, although in this scheme a single long electron pulse is selected to improve the signal to noise ratio and a higher harmonic cavity is added to reduce the energy dispersion, the imaging signal to noise ratio is still much lower than that of a dc electron microscope, which is aimed mainly at realizing a single electron imaging mode of a high-energy electron microscope to reduce the damage of space charge forces to beam quality.

The use of high repetition frequency electron sources to improve the signal to noise ratio of imaging systems has been mentioned in previous patents, but the imaging system proposed by this solution is relatively simple in beam quality optimization and control of imaging, relying mainly on subsequent iterative algorithms to optimize the imaging quality.

The current schemes for improving the imaging electron energy have some unavoidable disadvantages. In order to preserve the dc characteristics, the compactness and cost of the device must be sacrificed; in order to maintain the compactness of the device, the signal-to-noise ratio and beam quality of the imaging process need to be sacrificed.

Disclosure of Invention

The present invention aims to solve at least one of the technical problems in the related art to some extent.

Therefore, the invention provides a high-energy electron microscope system based on high-repetition frequency microwave acceleration. The electron emission mode of the invention is laser driving photocathode or field emission, and the beam line is matched with an accelerating tube and an energy selector, so that the problems of low energy of a commercial direct current mirror, large volume of a traditional high-energy direct current mirror, low current intensity of a microwave accelerating electron microscope system and large energy dissipation can be solved. Meanwhile, the high-energy electron microscope keeps a pulse electron emission mode in a photocathode emission mode, so that the high-energy electron microscope has time resolution capability besides spatial resolution capability, and can develop a dynamic pumping-detection process on the basis of static imaging. Compared with a direct current electron microscope, the microblog acceleration high-energy electron imaging system provided by the invention has the advantages that the accumulated effect of electron irradiation damage to the sample is smaller, so that the radiation damage in the imaging process is reduced, and the damage of a beam group to the sample is also reduced.

Another object of the invention is to propose a method for applying a high-energy electron microscopy system based on high-repetition frequency microwave acceleration.

In order to achieve the above object, according to one aspect of the present invention, a high-energy electron microscope system based on high-repetition frequency microwave acceleration is provided, comprising:

a synchronization timing module for providing time synchronization of the system;

a power source module for providing an electromagnetic field required for acceleration of electrons;

an electron gun module for generating an initial electron beam using an electron gun under the electromagnetic field;

the electron beam acceleration module is used for compressing and accelerating the initial electron beam to obtain a first electron beam;

the energy selection module is used for reducing the energy dispersion of electrons in the first electron beam to obtain a second electron beam;

the magnetic lens module is used for shaping the transverse size of the electrons of the second electron beam to obtain a third electron beam;

and the detector module is used for imaging electrons back scattered by the sample to be detected in the third electron beam by using a detector.

In addition, the high-energy electron microscope system based on high-repetition frequency microwave acceleration according to the above embodiment of the present invention may further have the following additional technical features:

further, in one embodiment of the present invention, the method further includes: the laser module comprises a driving laser module and a pumping laser module, wherein the driving laser module and the pumping laser module share one laser source, and the driving laser module comprises a frequency doubling system, a compression system, a widening system and a pulse stacking system;

when the electron gun is a high-repetition-frequency electron gun, the beam splitting laser generated by the laser source is transmitted to the driving laser module to generate driving laser, the driving laser irradiates the cathode position of the high-repetition-frequency electron gun through an image transmission system formed by lenses to generate the initial electron beam, and electrons are generated based on a photoelectric emission principle; when the electron gun is a direct current electron gun, a laser module is not required to be driven, and electrons are generated directly through field emission;

the pump laser module is used for generating pump laser by the beam splitting laser generated by the laser source through the pump laser module and focusing the pump laser on a sample to be detected, and the delay line is adjusted to enable the pump laser and the initial electron beam to be synchronous when reaching the sample.

Further, in one embodiment of the present invention, the synchronization timing module includes a signal distribution system, a low level system, and a laser microwave synchronization system;

the reference signal distribution system is used for providing a clock signal for the high-energy electron microscope system based on high-repetition frequency microwave acceleration;

the low-level system is used for using the monitored microwave phase and amplitude of the electron gun as a low-level feedback signal by using a signal acquisition port of the electron gun to adjust the phase and amplitude of the low-level output seed microwave;

the laser microwave synchronization system is used for synchronizing the phases of the driving laser and the pumping laser in the laser module and the microwaves fed into the electron gun.

Further, in one embodiment of the present invention, the power source module is comprised of a microwave system including a solid state amplifier, a high voltage modulator and a klystron when the electron gun is a high frequency electron gun; the low-level system outputs low-power seed microwaves, the low-level system generates first microwaves through amplification of a solid-state amplifier, the first microwaves and high voltage of a modulator are fed into a klystron at the same time, megasecond microwaves are output through the klystron, and the second microwaves are fed into an electron gun or an accelerating tube after passing through a waveguide, a four-terminal circulator and a waveguide coupler to form a resonant accelerating electric field so as to accelerate electrons;

when the electron gun is a direct current electron gun, the power source module comprises a direct current high-voltage power supply, and the direct current high-voltage power supply is used for providing direct current high-voltage to accelerate electrons generated by the direct current electron gun.

Further, in one embodiment of the present invention, the electron beam acceleration module includes a multi-stage acceleration tube; the accelerating tube works in a high-repetition frequency mode;

operating the first section of the accelerating tube at a zero crossing phase to allow compensation for longitudinal compression and partial dispersion of the electron beam; and enabling the rest sections to work in an acceleration phase, so that the initial electron beam is accelerated, and finally the first electron beam is obtained.

Further, in one embodiment of the invention, the energy selection module, including a combination of dipolar irons and a variable collimation aperture,

the dipoles are combined such that electrons of different energies are separated in the lateral direction as they pass through the dipoles, and the desired electrons are selected by varying the aperture and position of the variable collimation holes in the electron path to obtain the second electron beam.

Further, in one embodiment of the present invention, the magnetic lens module includes a condenser lens, an objective lens, a projection lens, and a deflection yoke, wherein,

the condenser is used for adjusting the size and the divergence angle of the second electron beam on the sample within a preset range;

the objective lens is used for imaging scattered electrons in the second electron beam;

the projection lens is used for providing magnetic field intensity;

the deflection yoke is used for providing a transverse magnetic field to deflect the transverse position of the second electron beam.

Further, in one embodiment of the present invention, the apparatus further comprises a sample support module for supporting, moving and cooling the sample;

the sample supporting module comprises a sample card, a mobile motor and a refrigerator; the sample is installed at the sample card, through mechanical connection to the mobile motor, the refrigerator passes through the heat conduction area with the sample card connects.

Further, in one embodiment of the invention, the detector module includes a plurality of selectable detectors; under the diffraction mode, using a phosphor screen to record electronic information in cooperation with an EMCCD camera; in STEM very low charge mode, electronic information is recorded using an EMPAD detector.

Further, in an embodiment of the present invention, the beam measurement module is further configured to install a phosphor screen and a metal mirror with a preset angle on the pulling device, and observe the lateral distribution state of the electrons by using a camera, so as to obtain different lateral distribution situations of the electron beams; and adopting a Faraday cage, and carrying out signal analysis through an oscilloscope to obtain the charge quantity information of different electron beams.

Further, in one embodiment of the invention, the electron gun module, the electron beam acceleration module, the sample support module, and the detector module are in an ultra-high vacuum environment; wherein the ultra-high vacuum environment is constructed by a molecular pump, an ion pump and a getter pump.

In order to achieve the above object, another aspect of the present invention provides a method for applying a high-energy electron microscope system based on high-repetition frequency microwave acceleration, comprising:

performing time synchronization of the whole system;

acquiring an electromagnetic field required by electron acceleration;

generating an initial electron beam by using an electron gun under an electromagnetic field;

compressing and accelerating the initial electron beam to obtain a first electron beam;

reducing the energy dispersion of electrons in the first electron beam to obtain a second electron beam;

shaping the transverse size of the electrons of the second electron beam to obtain a third electron beam;

imaging electrons in the third electron beam, which are subjected to back scattering of the sample to be detected, by using a detector;

and monitoring the state of electrons in different positions after the electrons in the third electron beam are imaged, so as to obtain electronic state information.

The high-energy electron microscope system based on high-repetition frequency microwave acceleration and the application method thereof can solve the problems of low energy of a commercial direct current mirror, large size of a traditional high-energy direct current mirror, low current intensity and large energy dissipation of a microwave acceleration electron microscope system, and have time resolution besides spatial resolution.

The beneficial effects of the invention are as follows:

1) The invention can realize high signal-to-noise ratio imaging of high-energy electrons by utilizing the electron source with high repetition frequency, and can be used for detecting thick samples (in the order of tens of nm) which are difficult to detect by a traditional direct current electron microscope; meanwhile, the structure is relatively compact, and the size of the electron gun part is only 1 meter.

2) The invention adopts a modularized structure, and can realize high-energy electron diffraction, STEM mode or other beam measurement related researches by selectively opening and closing lenses in the magnetic lens module besides a TEM mode.

3) The invention adopts monochromator to select electron energy, and can reduce electron beam energy dispersion to one ten thousandth by changing aperture size of diaphragm.

4) The invention can image common solid material samples and biological samples. The sample temperature can be maintained at the liquid helium temperature by the cooling system of the sample support module, thereby reducing vibration or movement of the sample.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

The foregoing and/or additional aspects and advantages of the invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a high-energy electron microscope system based on high-repetition frequency microwave acceleration according to an embodiment of the invention;

fig. 2 is a flowchart of an application method of a high-energy electron microscopy system based on high-repetition frequency microwave acceleration according to an embodiment of the invention.

Detailed Description

It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other. The invention will be described in detail below with reference to the drawings in connection with embodiments.

In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.

The high-energy electron microscope system based on high-repetition frequency microwave acceleration and the application method thereof according to the embodiment of the invention are described below with reference to the accompanying drawings.

Fig. 1 is a schematic structural diagram of a high-energy electron microscope system based on high-repetition frequency microwave acceleration according to an embodiment of the invention.

As shown in fig. 1, the system includes:

a synchronization timing module 100 for providing time synchronization of the system;

a power source module 200 for providing an electromagnetic field required for acceleration of electrons;

an electron gun module 300 for generating an initial electron beam using an electron gun under an electromagnetic field;

an electron beam acceleration module 400 for compressing and accelerating the electron beam to obtain a first electron beam;

the energy selection module 500 is configured to reduce energy dissipation of electrons in the first electron beam, so as to obtain a second electron beam;

a magnetic lens module 600 for shaping the transverse dimension of the electrons of the second electron beam to obtain a third electron beam;

a detector module 700 for imaging electrons of the third electron beam backscattered from the sample to be detected with a detector.

Specifically, as shown in fig. 1, the high-energy electron microscope system based on high-repetition frequency microwave acceleration of the invention can comprise the following modules:

in some embodiments of the present invention, the synchronization timing module 100 is comprised of a signal distribution system, a low level (Low Level Radio Frequency, abbreviated LLRF) system, and a laser microwave synchronization system. The reference signal distribution system provides a clock signal for the whole system, the low-level system generates seed microwaves, the phase and the amplitude of the microwaves of the electron gun are monitored by using a signal acquisition port (pick-up) of the electron gun as low-level feedback signals, and the phase and the amplitude of the seed microwaves are output by adjusting the low level, so that the phase and the amplitude of the microwaves of the electron gun are more stable. The laser microwave synchronization system synchronizes the phases of the driving laser and the pumping laser in the laser module with the microwaves fed into the electron gun so as to ensure that the emission phase of electrons can be kept stable, and the electrons and the pumping laser can reach the sample at the same time.

In some embodiments of the present invention, when the electron gun is a high-frequency electron gun, the power source module 200 functions to generate high-power microwaves to accelerate electrons. The microwave system consists of a solid-state amplifier (Solid state Amplifier, SSA for short), a high-voltage modulator and a Klystron (Kystron). First, the low level system in the synchronous timing module 100 outputs low power seed microwaves, which are primarily amplified by a Solid-state Amplifier (SSA) to generate microwaves of the order of hundred watts. The microwave and the high voltage of the modulator are simultaneously fed into a klystron, and megawatt high-power microwave is output through the klystron. High-power microwaves are fed into an electron gun or an accelerating tube through a waveguide, a four-terminal circulator and a waveguide coupler to form a resonant accelerating electric field for accelerating electrons. When the electron gun is a dc electron gun, the power source module 200 is used as a dc high voltage power source for providing electrons generated by the dc high voltage accelerating dc electron gun.

In some embodiments of the invention, the electron gun module 300 may be a room temperature High-Frequency Very High Frequency electron gun (or VHF gun). The electron gun is a photocathode electron gun driven by laser, and compared with the S/L wave band microwave electron gun commonly used in the existing accelerator device or u-TEM, the electron gun works in a very high frequency band (VHF), the microwave frequency is between 30 and 300MHz, the electron gun can operate in a high repetition frequency mode, the energy of an electron outlet is 1MeV, and the electron energy can be improved to 30MeV at maximum by matching with a subsequent accelerator tube. Heretofore, such electron guns have been used in X-ray free electron lasers, including LCLS-II and Shanghai hard X-ray free electron laser sources, which have been capable of achieving 1MHz stable operation in normal temperature mode. The electron gun module 300 ensures that in the pulse acceleration mode, there is still a sufficiently high imaging beam current, and currently a single hundred pC of imaging charge is achieved.

In some embodiments of the present invention, the high-energy electron microscopy system based on high-frequency microwave acceleration of the present invention further comprises a laser module for generating a driving laser for exciting photoelectron emission and a pump laser for pumping the sample, as will be appreciated.

Specifically, the laser module may be subdivided into a driving laser module and a pumping laser module, which share one laser source, and after being generated from the laser source, are split into two parts by splitting. The driving laser module comprises a frequency multiplication system, a compression system, a widening system and a pulse stacking system, can generate driving laser with any transverse and longitudinal dimensions in a certain range, and is the most flexible and easy-to-operate method for controlling cathode electron generation at present; when the electron gun of the electron gun module 300 is selected as a high-repetition-frequency electron gun, the beam-splitting laser generated by the laser source is transmitted to the driving laser module to generate driving laser, and the laser generated by the driving laser module irradiates the cathode position of the high-repetition-frequency electron gun through an image transmission system formed by lenses, so that photoelectrons are generated by utilizing the photoelectric effect. When the electron gun of the electron gun module 300 is selected as a direct current electron gun, electrons can be generated directly by field emission without driving the laser module. The pump laser module is used for focusing the pump light (usually 800nm infrared light) on the sample to be detected after transmission, and the synchronization of the pump laser and the electron beam when reaching the sample is ensured by adjusting the delay line.

Further, the main function of driving the laser module is to generate electrons at the cathode by the photoelectric effect, which is called photoemission. Electrons can also be generated by using a field emission method, the emission method does not need to drive laser, the cathode is only processed into a needle point shape, electrons are emitted by using a point discharge principle under a strong electric field, and the needle point can be heated in the emission process so as to reduce the threshold value of an emission electric field.

In some embodiments of the invention, the electron beam acceleration module 400 includes a 2-segment or 3-segment acceleration tube. The accelerating tube is operated in a high repetition frequency mode. Each segment of the accelerating tube can independently longitudinally compress or accelerate the electron beam by varying the phase of the microwaves relative to the electron beam. The first accelerating tube is generally selected to work at a zero-crossing phase so as to realize longitudinal compression and partial dispersion compensation of the electron beam; the subsequent accelerating tube works in an accelerating phase to accelerate the whole electron beam, and finally a first electron beam is obtained. The accelerating tube is used for further accelerating the electrons with lower energy (-1 MeV) generated from the electron gun, and the final accelerating energy of the electrons can be continuously adjusted to tens of MeV by changing the feeding power of the accelerating tube.

In some embodiments of the invention, the energy selection module 500 is used to further reduce the electron energy dispersion. The energy selection module 500 includes a combination of dipoles and variable collimation holes, the combination of dipoles being such that electrons of different energies are separated laterally as they pass through the dipoles, and the desired electrons are selected by changing the aperture and position of the variable collimation holes in the electron path. The smaller the aperture of the collimation hole is, the smaller the electron beam energy dispersion is obtained; the electron beams with different central energies can be selected by changing the lateral position of the collimation holes. The combination of the plurality of dipoles allows the electrons to return to the original direction of motion after energy selection to obtain a second electron beam.

In some embodiments of the invention, a magnetic lens module 600 is used to shape the lateral (perpendicular to the electron transport direction) dimensions of the electrons. The module includes a set of collection optics, an objective lens, a projection lens, and a set of deflection coils, wherein the collection optics and deflection coils are positioned in front of the sample and the objective lens and projection lens are positioned behind the sample. The condenser lens, the objective lens and the projection lens provide a longitudinal magnetic field to modulate the transverse dimension of the electron beam. The size and the scattering angle of the electron beam on the sample can be randomly adjusted within a certain range by adjusting the condensing lens, the objective lens is used for imaging scattered electrons, and the magnetic field intensity of the projection lens is adjusted, so that the imaging of the image plane or the back focal plane of the objective lens on the detector can be realized, and the diffraction or imaging mode can be realized. The deflection coil provides a transverse magnetic field to deflect the transverse position of the electron beam, and the scanning of the electron beam on the sample can be realized in a certain range. During actual operation, different magnetic lenses may be selectively switched to achieve different imaging modes: if only the projection lens and the deflection coil are turned on, STEM mode can be realized; if the condenser, the objective lens and the projection lens are turned on, a TEM mode can be realized. The scheme firstly proposes the design of implanting the scanning coil into the high-energy imaging system so as to further perfect the functions of the high-energy imaging system.

In some embodiments of the present invention, the high-energy electron microscopy system based on high-repetition frequency microwave acceleration of the present invention further comprises a sample support module for supporting, moving and cooling the sample. The module comprises a sample card, a mobile motor and a refrigerator. The sample is mounted on a TEM sample card and mechanically coupled to a mobile motor that includes three dimensions of translational movement and three dimensions of rotational movement. The refrigerator is connected with the sample card through the heat conduction belt and can cool the sample to the liquid helium temperature. At this low temperature, thermal movement of the sample atoms can be suppressed as much as possible. It is appreciated that the sample cooling system is not considered since the current high energy imaging solutions have not considered imaging biological samples.

In some embodiments of the invention, the detector module 700 comprising a plurality of selectable detectors, uses phosphor screens in combination with an EMCCD camera to record electronic information in a diffraction mode; in extremely low charge mode such as STEM, electronic information is recorded using an EMPAD detector.

It can be understood that the currently commercial hundred keV energy direct current mirror adopts a generally commercial electronic amplification array Detector (Electron Magnified pixel-array Detector, EMPAD), which has the advantages of high acquisition speed and large dynamic range, but is only suitable for electron imaging of hundred keV energy, but cannot be used for electron beam imaging of MeV energy; at present, the detector commonly used for MeV energy electronic imaging is an EMCCD, and the detector records electronic imaging information through collecting fluorescence emitted by electrons striking a phosphor screen, so that the applicable electronic energy range is large, but the dynamic range is small, and imaging under a low charge amount is difficult to realize.

In particular, an EMPAD detector which is not applied before and is suitable for high-energy electrons is used in the invention, the detector can realize imaging from single electron to 1000 electrons, and the acquisition speed can reach more than 100 kHz.

In some embodiments of the invention, the system further comprises a beam measurement module for monitoring the charge amount, lateral distribution, etc. properties of the electron beam at different locations. Preferably, a combination of a YAG phosphor screen and a 45-degree metal reflecting mirror is hung on a lifting device, and a CCD camera is used for observing the transverse distribution of electrons; and analyzing the signal by using a Faraday cage through an oscilloscope to obtain the charge amount information of the electron beam.

In some embodiments of the present invention, the electron gun module 300, the electron beam acceleration module 400, the sample support module, and the detector module 700 in the above modules are all in an ultra-high vacuum environment. The ultra-high vacuum environment of the system is maintained by a molecular pump, an ion pump and a getter pump.

According to the high-energy electron microscope system based on high-repetition frequency microwave acceleration, the problems that a commercial direct current mirror is low in energy, a traditional high-energy direct current mirror is large in size, the microwave acceleration electron microscope system is low in flow intensity and large in energy dissipation can be solved, meanwhile, high-energy electron signal-to-noise ratio imaging can be achieved, high-energy electron diffraction, STEM mode or other beam measurement related researches can be achieved, imaging can be conducted on a common solid material sample and a biological sample, and damage of pulsed electron beams to the sample is smaller.

In order to implement the above embodiment, as shown in fig. 2, the present embodiment further provides an application method of a high-energy electron microscope system based on high-repetition frequency microwave acceleration, where the method includes:

s1, performing time synchronization of the whole system;

s2, acquiring an electromagnetic field required by electron acceleration;

s3, generating an initial electron beam by using an electron gun under an electromagnetic field;

s4, compressing and accelerating the initial electron beam to obtain a first electron beam;

s5, reducing the energy dispersion of electrons in the first electron beam to obtain a second electron beam;

s6, shaping the transverse size of the electrons of the second electron beam to obtain a third electron beam;

s7, imaging electrons in the third electron beam, which are subjected to back scattering of the sample to be detected, by using a detector;

and S8, monitoring the state of electrons in different positions after the electrons in the third electron beam are imaged, and obtaining electronic state information.

According to the application method of the high-energy electron microscope system based on high-repetition frequency microwave acceleration, the problems that a commercial direct current mirror is low in energy, a traditional high-energy direct current mirror is large in size, the microwave acceleration electron microscope system is low in flow intensity and large in energy dissipation can be solved, meanwhile, high-energy electron signal-to-noise ratio imaging can be achieved, high-energy electron diffraction, STEM mode or other beam measurement related researches can be achieved, imaging can be conducted on a common solid material sample and a biological sample, and damage of a pulse electron beam to the sample is smaller.

In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.

Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In the description of the present invention, the meaning of "plurality" means at least two, for example, two, three, etc., unless specifically defined otherwise.

Claims (12)

1. A high-energy electron microscopy system based on high-repetition frequency microwave acceleration, comprising:

the synchronous timing module is used for providing time synchronization of the whole system;

a power source module for providing an electromagnetic field required for acceleration of electrons;

an electron gun module for generating an initial electron beam using an electron gun under the electromagnetic field;

the electron beam acceleration module is used for compressing and accelerating the initial electron beam to obtain a first electron beam;

the energy selection module is used for reducing the energy dispersion of electrons in the first electron beam to obtain a second electron beam;

the magnetic lens module is used for shaping the transverse size of the electrons of the second electron beam to obtain a third electron beam;

and the detector module is used for imaging electrons back scattered by the sample to be detected in the third electron beam by using a detector.

2. The system of claim 1, further comprising: the laser module comprises a driving laser module and a pumping laser module, wherein the driving laser module and the pumping laser module share one laser source, and the driving laser module comprises a frequency doubling system, a compression system, a widening system and a pulse stacking system;

when the electron gun is a high-repetition-frequency electron gun, the beam splitting laser generated by the laser source is transmitted to the driving laser module to generate driving laser, the driving laser irradiates the cathode position of the high-repetition-frequency electron gun through an image transmission system formed by lenses to generate the initial electron beam, and electrons are generated based on a photoelectric emission principle; when the electron gun is a direct current electron gun, a laser module is not required to be driven, and electrons are generated directly through field emission;

the pump laser module is used for generating pump laser by the beam splitting laser generated by the laser source through the pump laser module and focusing the pump laser on a sample to be detected, and the delay line is adjusted to enable the pump laser and the initial electron beam to be synchronous when reaching the sample.

3. The system of claim 2, wherein the synchronization timing module comprises a signal distribution system, a low level system, and a laser microwave synchronization system;

the reference signal distribution system is used for providing a clock signal for the high-energy electron microscope system;

the low-level system is used for using the monitored microwave phase and amplitude of the electron gun as a low-level feedback signal by using a signal acquisition port of the electron gun to adjust the phase and amplitude of the low-level output seed microwave;

the laser microwave synchronization system is used for synchronizing the phases of the driving laser and the pumping laser in the laser module and the microwaves fed into the electron gun.

4. The system of claim 3, wherein the power source module is comprised of a microwave system when the electron gun is a high-frequency heavy-duty electron gun, the microwave system comprising a solid state amplifier, a high-voltage modulator, and a klystron; the low-level system outputs low-power seed microwaves, the low-level system generates first microwaves through amplification of a solid-state amplifier, the first microwaves and high voltage of a modulator are fed into a klystron at the same time, megasecond microwaves are output through the klystron, and the second microwaves are fed into an electron gun or an accelerating tube after passing through a waveguide, a four-terminal circulator and a waveguide coupler to form a resonant accelerating electric field so as to accelerate electrons;

when the electron gun is a direct current electron gun, the power source module comprises a direct current high-voltage power supply, and the direct current high-voltage power supply is used for providing direct current high-voltage to accelerate electrons generated by the direct current electron gun.

5. The system of claim 1, wherein the electron beam acceleration module comprises a multi-segment acceleration tube; the accelerating tube works in a high-repetition frequency mode;

operating the first section of the accelerating tube at a zero crossing phase to allow compensation for longitudinal compression and partial dispersion of the electron beam; and enabling the rest sections to work in an acceleration phase, so that the initial electron beam is accelerated, and finally the first electron beam is obtained.

6. The system of claim 1, wherein the energy selection module comprises a combination of dipolar irons and a variable collimation aperture,

the dipoles are combined such that electrons of different energies are separated in the lateral direction as they pass through the dipoles, and the desired electrons are selected by varying the aperture and position of the variable collimation holes in the electron path to obtain the second electron beam.

7. The system of claim 1, wherein the magnetic lens module comprises a condenser lens, an objective lens, a projection lens, and a deflection yoke, wherein,

the condenser is used for adjusting the size and the divergence angle of the second electron beam on the sample within a preset range;

the objective lens is used for imaging scattered electrons in the second electron beam;

the projection lens is used for providing magnetic field intensity;

the deflection yoke is used for providing a transverse magnetic field to deflect the transverse position of the second electron beam.

8. The system of claim 1, further comprising a sample support module for supporting, moving and cooling a sample;

the sample supporting module comprises a sample card, a mobile motor and a refrigerator; the sample is installed at the sample card, through mechanical connection to the mobile motor, the refrigerator passes through the heat conduction area with the sample card connects.

9. The system of claim 1, wherein the detector module comprises a plurality of selectable detectors; under the diffraction mode, using a phosphor screen to record electronic information in cooperation with an EMCCD camera; in STEM very low charge mode, electronic information is recorded using an EMPAD detector.

10. The system of claim 1, wherein the beam measuring module is further configured to install a phosphor screen and a metal mirror with a preset angle on the pulling device, and observe the lateral distribution state of the electrons by using a camera to obtain different lateral distribution conditions of the electron beams; and adopting a Faraday cage, and carrying out signal analysis through an oscilloscope to obtain the charge quantity information of different electron beams.

11. The system of any one of claims 1-10, wherein the electron gun module, the electron beam acceleration module, the sample support module, and the detector module are in an ultra-high vacuum environment; wherein the ultra-high vacuum environment is constructed by a molecular pump, an ion pump and a getter pump.

12. A method for application to the high-energy electron microscopy system based on high-repetition frequency microwave acceleration of claim 1, characterized in that it comprises the steps of:

performing time synchronization of the whole system;

acquiring an electromagnetic field required by electron acceleration;

generating an initial electron beam by using an electron gun under an electromagnetic field;

compressing and accelerating the initial electron beam to obtain a first electron beam;

reducing the energy dispersion of electrons in the first electron beam to obtain a second electron beam;

shaping the transverse size of the electrons of the second electron beam to obtain a third electron beam;

imaging electrons in the third electron beam, which are subjected to back scattering of the sample to be detected, by using a detector;

and monitoring the state of electrons in different positions after the electrons in the third electron beam are imaged, so as to obtain electronic state information.