Four-dimensional electron microscope

Abstract

The four-dimensional electron microscope comprises a light source assembly, an electron source, an electron optical assembly and a detector, and the light source assembly is used for emitting pulse laser. The electron source comprises an excitation optical fiber coupled with the light source assembly and an electron emission layer, the electron emission layer at least comprises an electron excitation layer, and the electron excitation layer is arranged on a light emitting path of pulse laser emitted by the excitation optical fiber so that the electron excitation layer can emit electron beams under excitation of the pulse laser; the electron excitation layer comprises at least one of a zero-dimensional material, a one-dimensional material and a two-dimensional material. The electron optical assembly is arranged on the electron beam emergent side of the electron source, the electron optical assembly is used for adjusting the deflection direction of an electron beam so that the electron beam can be incident on a sample, and the detector is arranged on one side of the sample and used for collecting a reflection electron signal of the electron beam incident on the sample or a transmission electron signal of the electron beam penetrating through the sample.

Description

Technical Field

[0001] This application relates to the technical field of electron microscopes, and particularly to a four-dimensional electron microscope. Background Art

[0002] An electron microscope can achieve three-dimensional characterization at the nanoscale or even the atomic scale. However, with the development of electron microscope technology, three-dimensional characterization can no longer meet people's usage requirements, and a four-dimensional electron microscope that can achieve characterization including the time dimension has gradually emerged.

[0003] However, the scanning stability of the four-dimensional electron microscopes in the related art is poor. Summary of the Invention

[0004] Based on this, it is necessary to provide a four-dimensional electron microscope to address the problem of poor scanning stability of the four-dimensional electron microscopes in the related art.

[0005] A four-dimensional electron microscope is used to scan a sample. The four-dimensional electron microscope includes:

[0006] A light source assembly for emitting pulsed laser light;

[0007] An electron source including an excitation optical fiber coupled to the light source assembly and an electron emission layer. The electron emission layer at least includes an electron excitation layer. The electron excitation layer is disposed on the light path of the pulsed laser light emitted from the excitation optical fiber so that the electron excitation layer can emit an electron beam under the excitation of the pulsed laser light. The electron excitation layer includes at least one of a zero-dimensional material, a one-dimensional material, and a two-dimensional material;

[0008] An electron optical assembly disposed on the electron beam output side of the electron source. The electron optical assembly is used to adjust the deflection direction of the electron beam so that the electron beam is incident on the sample; and

[0009] A detector disposed on one side of the sample for collecting the reflected electron signal of the electron beam incident on the sample or the transmitted electron signal of the electron beam penetrating the sample.

[0010] In one embodiment, the light source assembly includes a light source and a first optical fiber. The light source is coupled to one end of the first optical fiber, and the excitation optical fiber is connected to the other end of the first optical fiber;

[0011] The light source is used to emit the pulsed laser light, and the first optical fiber is used to transmit the pulsed laser light emitted by the light source to the excitation optical fiber.

[0012] In one embodiment, the light source assembly further includes a first optical fiber splitter, a second optical fiber, and a first optical fiber delay line;

[0013] The first optical fiber splitter has a first input end coupled to the light source and a first output end opposite to the first input end, and the first output end is respectively connected to the first optical fiber and the second optical fiber;

[0014] One end of the second optical fiber away from the first optical fiber splitter extends towards the sample;

[0015] The first optical fiber delay line is coupled to the second optical fiber to perform time delay on the light beam propagating in the second optical fiber.

[0016] In one embodiment, the reflected electron signal includes a secondary electron signal;

[0017] The sample has an incident surface disposed opposite to the electron beam exit side of the electron source;

[0018] The detector includes a backscattered electron detector or a secondary electron detector, and the backscattered electron detector or the secondary electron detector is used to face the incident surface of the sample so that the secondary electron detector receives the secondary electron signal or the backscattered electron detector receives the backscattered electron signal.

[0019] In one embodiment, the reflected electron signal includes a cathodoluminescence signal;

[0020] The sample has an incident surface disposed opposite to the electron beam exit side of the electron source;

[0021] The detector includes a cathodoluminescence analysis system, and the cathodoluminescence analysis system is used to face the incident surface of the sample to receive the cathodoluminescence signal.

[0022] In one embodiment, the sample has an incident surface disposed opposite to the electron beam exit side of the electron source and an exit surface opposite to the incident surface;

[0023] The detector includes a receiving screen, and the receiving screen is used to face the exit surface of the sample to receive the electron beam penetrating the sample.

[0024] In one embodiment, the light source assembly further includes a second optical fiber splitter, a third optical fiber, and a second optical fiber delay line;

[0025] The second optical fiber splitter has a second input end coupled to the light source and a second output end opposite to the second input end, and the second output end is respectively connected to the first optical fiber and the third optical fiber;

[0026] One end of the third optical fiber away from the second optical fiber splitter extends towards the sample;

[0027] The second optical fiber delay line is coupled to the third optical fiber and is configured to perform time delay on the light beam propagating in the third optical fiber.

[0028] In one embodiment, the four-dimensional electron microscope further includes a housing;

[0029] The housing has a vacuum chamber, and the electron source and the electron optical assembly are sequentially disposed in the vacuum chamber;

[0030] The housing is provided with an opening communicating with the vacuum chamber, and the light incident end of the excitation optical fiber of the electron source is exposed through the opening and is coupled to the light source assembly.

[0031] In one embodiment, the outer peripheral wall of the excitation optical fiber is sealingly connected to the inner side wall of the opening.

[0032] In one embodiment, the excitation optical fiber includes a core for transmitting laser light and a cladding layer wrapped around the core, and the end face of the light output end of the excitation optical fiber is disposed at an angle with respect to the extending direction of the core;

[0033] The electron emission layer is disposed on the end face of the light output end of the excitation optical fiber, and the electron excitation layer covers the core of the excitation optical fiber. The laser light emitted from the core can directly irradiate the electron emission layer, so that the electron excitation layer is excited by the laser light emitted from the core and emits electrons.

[0034] In one embodiment, the excitation optical fiber includes a core for transmitting laser light and a cladding layer wrapped around the core;

[0035] The light output end of the excitation optical fiber is configured with a light leakage notch along the radial direction of the excitation optical fiber;

[0036] The electron excitation layer is disposed on the bottom wall surface of the light leakage notch. The bottom wall surface of the light leakage notch is configured as a plane, and the projection of the electron excitation layer on the bottom wall surface covers the projection of the core on the bottom wall surface;

[0037] The electron excitation layer further extends to the light output end of the optical fiber.

[0038] In one embodiment, the excitation optical fiber is configured as a perforated optical fiber, and the perforated optical fiber has a light guiding hole;

[0039] The electron excitation layer is at least disposed on the side wall of the light guiding hole and extends to the light output end of the excitation optical fiber along the longitudinal extension direction of the light guiding hole.

[0040] In one embodiment, the excitation optical fiber is configured as a perforated optical fiber, and the perforated optical fiber has a light guiding hole;

[0041] The electron emission layer is disposed on the end face of the light-emitting end of the porous optical fiber, and the electron excitation layer covers one end of the light-guiding hole located on the end face of the light-emitting end;

[0042] The laser emitted by the porous optical fiber can directly irradiate the electron emission layer, so that the electron excitation layer is excited by the laser emitted by the porous optical fiber and emits electrons.

[0043] In one embodiment, the light-emitting end of the excitation optical fiber is provided with a pointed end portion;

[0044] The electron excitation layer covers the surface of the pointed end portion of the excitation optical fiber;

[0045] The excitation optical fiber includes a core for transmitting laser, and the laser emitted by the core can directly irradiate the electron emission layer, so that the electron excitation layer is excited by the laser emitted by the core and emits electrons.

[0046] In one embodiment, the electron source further includes a conductive connection layer, which is disposed on the excitation optical fiber and electrically connected to the electron excitation layer.

[0047] In one embodiment, the electron source further includes an anode, the anode has a first electron channel, and the electron optical component has a second electron channel communicating with the first electron channel;

[0048] A preset electric field is provided between the anode and the electron excitation layer, and the electron beam can pass through the first electron channel and the second electron channel under the drive of the preset electric field and be incident on the sample.

[0049] In one embodiment, the thickness of the electron excitation layer is less than or equal to 50 nm.

[0050] In one embodiment, the included angle between the axial direction of the one-dimensional material in the electron excitation layer and the emission direction of the pulsed laser is 0 to 90°;

[0051] In one embodiment, the electron excitation layer includes at least two two-dimensional materials stacked in sequence along the emission direction of the pulsed laser; or

[0052] The electron excitation layer includes at least two two-dimensional materials with different materials connected to each other on the same plane.

[0053] In one embodiment, the electron excitation layer includes zero-dimensional materials and zero-dimensional materials disposed at the end portion and / or side portion of the one-dimensional material.

[0054] In one embodiment, the electron excitation layer includes a zero-dimensional material and a two-dimensional material, and the zero-dimensional material is disposed on the surface of the two-dimensional material.

[0055] In one embodiment, the electron excitation layer includes a one-dimensional material and a two-dimensional material, and the one-dimensional material is disposed on the surface of the two-dimensional material.

[0056] The above four-dimensional electron microscope can form an electron beam with pulse characteristics by exciting the electron excitation layer with a pulsed laser. The electron beam irradiates the sample to be measured, and the signal obtained by exciting the sample to be measured is received, thereby realizing the scanning of the sample to be measured. It can be understood that the setting of forming an electron beam by exciting the electron excitation layer with a pulsed laser in this application abandons the complex spatial light coupling structure set due to the introduction of an external laser, making the four-dimensional electron microscope less affected by the environment and having a stable electron beam, thereby improving the scanning stability of the sample to be measured. In addition, the electron source in this application uses a low-dimensional material as the material for emitting electrons. Since the electron excitation layer has a strong light-material interaction and a rich electron bandgap, the pulsed laser can better interact with the electron excitation layer to excite the electrons in the electron excitation layer, and the electrons emitted from the electron excitation layer have the characteristics of small energy dispersion, high brightness, and high stability. And by modulating the pulsed laser through the fiber optic component, the electron beam excited by it can be modulated, thereby reducing the influence on the scanning quality when modulating the electron beam, and further enabling stable scanning of the sample to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 The structural schematic diagram of an embodiment showing the four-dimensional electron microscope of this application detecting secondary electron signals.

[0058] Figure 2 The structural schematic diagram of an embodiment showing the four-dimensional electron microscope of this application detecting cathode fluorescence signals.

[0059] Figure 3 The structural schematic diagram of an embodiment showing the four-dimensional electron microscope of this application detecting the electron beam penetrating the sample.

[0060] Figure 4 Shows Figures 1-3 The enlarged view of part A in

[0061] Figure 5 The structural schematic diagram of an embodiment showing that the end face of the light-emitting end of the excitation optical fiber in this application is arranged at an angle with the extending direction of the fiber core.

[0062] Figure 6 The structural schematic diagram of an embodiment showing that the light-emitting end of the excitation optical fiber in this application is provided with a light leakage notch.

[0063] Figure 7 shows Figure 6 side view of

[0064] Figure 8 shows the structural schematic diagram of the embodiment in the present application where the electron excitation layer is disposed on the side wall of the light guiding hole of the porous optical fiber.

[0065] Figure 9 shows Figure 8 magnified schematic diagram at C of

[0066] Figure 10 shows the structural schematic diagram of the embodiment in the present application where the electron excitation layer is disposed on the end face of the light output end of the porous optical fiber.

[0067] Figure 11 shows Figure 10 magnified schematic diagram at D of

[0068] Figure 12 shows the structural schematic diagram of the embodiment in the present application where the light output end of the excitation optical fiber is provided with a pointed end portion.

[0069] Figure 13 shows Figure 12 magnified schematic diagram at E of

[0070] Figure 14 shows the structural schematic diagram where the auxiliary layer is disposed on one side of the end face of the electron excitation layer close to the light output end.

[0071] Figure 15 shows the process schematic diagram of the preparation method of the electron source in an embodiment of the present application.

[0072] Explanation of reference numerals:

[0073] 10, four-dimensional electron microscope;

[0074] 100, electron source; 110, excitation optical fiber; 111, core; 112, cladding layer; 1101, light input end; 1102, light output end; 11021, end face; h, light leakage notch; h1, bottom wall surface; h2, side wall surface; k, side wall of the light guiding hole; j, pointed end portion; j1, surface; 120, electron emission layer; 121, electron excitation layer; 1211, first part; 1212, second part; 122, auxiliary layer; 130, conductive connection layer; 131, first conductive part; 132, second conductive part;

[0075] 2. Light source assembly; 29. Light source; 21. First optical fiber; 22. Second optical fiber; 23. Third optical fiber; 24. First optical fiber beam splitter; 25. Second optical fiber beam splitter; 26. First optical fiber delay line; 27. Second optical fiber delay line; 28. Optical switch; 3. Electro-optical assembly; 31. Magnetic lens; 32. Intermediate lens; 33. Projection lens; 4. Detector; 41. Receiving screen; 42. Photography chamber; 5. Sample; 6. Housing;

[0076] 20. Temporary substrate;

[0077] 30. Perforated glass slide;

[0078] 40. Annular heating sheet. Detailed implementation manners

[0079] To make the above objects, features, and advantages of the present application more apparent and understandable, the following will describe the detailed implementation manners of the present application with reference to the accompanying drawings. Many specific details are set forth in the following description to facilitate a thorough understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the spirit of the present application. Therefore, the present application is not limited by the specific embodiments disclosed below.

[0080] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. These are only for convenience in describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present application.

[0081] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0082] In this application, unless otherwise clearly defined and limited, terms such as "installed", "connected", "linked", "fixed", etc. shall be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two components or the interaction relationship between two components, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0083] In this application, unless otherwise clearly defined and limited, the first feature being "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature can be that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is at a higher horizontal level than the second feature. The first feature being "under", "beneath" and "underneath" the second feature can be that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is at a lower horizontal level than the second feature.

[0084] It should be noted that when an element is referred to as "fixed to" or "disposed on" another element, it can be directly on the other element or there can also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "up", "down", "left", "right" and similar expressions used herein are only for illustrative purposes and do not represent the only implementation.

[0085] Electron microscopy is an important means for microstructural characterization. Using electron microscopy, three-dimensional characterization at the nanoscale and even the atomic scale can be achieved. However, limited by the response time of electron detectors, the time detection scale of electron microscopy systems is often limited to the macroscopic order of magnitude, such as the microsecond and millisecond order of magnitude, and cannot perform time characterization at the ultrafast scale, such as the picosecond to femtosecond order of magnitude.

[0086] In the four-dimensional electron microscope in the related art, an optical window is opened on the side of the outer shell near the electron source of an ordinary electron microscope, and pulsed light is focused on the electron source in the cavity to emit pulsed electrons, thereby realizing the function of the four-dimensional electron microscope. However, opening the optical window on the outer shell near the electron source causes damage to the cavity formed by the damaged outer shell, which easily affects the performance of the electron microscope and causes instability of the pulsed electron beam. That is, the scanning stability of the four-dimensional electron microscope in the related art is poor, thus affecting its scanning quality. Moreover, the four-dimensional electron microscope in the related art needs to set up structures such as an electron beam shutter to modulate the electron beam, resulting in a relatively large volume of the four-dimensional electron microscope, which is not conducive to the miniaturized design of the four-dimensional electron microscope.

[0087] In traditional technology, thermionic electron sources mainly select materials with metallic properties such as tungsten filaments and lanthanum hexaboride. When heated to thousands of degrees Celsius, electrons are thermally excited and detached from the material surface to form vacuum electrons. Field emission electron sources mainly select metal tips such as tungsten. Under the action of a strong external electric field, a tip discharge effect is generated. Among them, the electron beam emitted by the thermionic electron source can work in a relatively poor vacuum environment, has good environmental adaptability and stability, but has low brightness and poor coherence. The electron beam of the field emission electron source has high brightness and good coherence, but has high requirements for vacuum degree and is very sensitive to vibration. Whether it is a thermionic electron source or a field emission electron source, the regulation of electron emission properties is limited, and it is impossible to balance the performance and stability of the emitted electrons.

[0088] In traditional technology, a photoemission electron source uses a metal material such as Au as the material of the electron emission layer, and the thickness is more than 50 nm, even reaching hundreds of nanometers. However, the inventors of the present application have found through research that the electron emission layer of the metal material has a relatively large thickness, and the distance between the bottom layer directly interacting with the laser and the surface layer of electron emission is relatively far (50 nm to hundreds of nanometers). During the process of electrons excited from the bottom layer passing through the electron emission layer, they are easily affected by metal lattice scattering, thereby affecting the emission efficiency. Moreover, the metal material is easily damaged under high-power laser irradiation, affecting the service life of the electron emission layer, and thus affecting the emission efficiency and stability of electrons.

[0089] In traditional technology, there is also a case where a photoemission electron source excites electrons by an external laser incident on the surface of a metal tip, and the size of the metal tip is on the nanometer scale, resulting in a relatively high difficulty in aligning the laser spot to the metal tip. If a high-magnification microscope is set up to align the external laser to the metal tip, it will lead to an increase in the overall cost and a deterioration in stability.

[0090] In addition, in traditional technology, graphene is used as a saturable absorber. Graphene has broadband saturable absorption characteristics and a fast recovery time, and is used in the Q-switching and mode-locking of lasers, or the laser spectrum is adjusted by graphene to achieve sensing detection.

[0091] Based on this, it is necessary to provide an electron source that can take into account both electron emission efficiency and stability.

[0092] This application uses low-dimensional materials such as zero-dimensional materials, one-dimensional materials, or two-dimensional materials as the material of the electron emission layer. Under laser irradiation, the low-dimensional materials emit electrons through effects such as the photoelectric effect, multi-photon emission, and optical field emission. The low-dimensional materials have atomic-level thickness, no dangling bonds, and stable properties, thus having characteristics such as good stability and high service life. Moreover, the low-dimensional materials can be directly integrated with the excitation optical fiber 110, and the excitation optical fiber 110 can provide a stable excitation source with adjustable wavelength, polarization, and optical mode, and can be applicable to different application scenarios, such as being applicable to the four-dimensional electron microscope described below.

[0093] This application provides a four-dimensional electron microscope 10 for scanning a sample 5, which can improve the stability of scanning the sample 5, has relatively high scanning quality compared with the prior art, and is conducive to the miniaturized design of the device.

[0094] Please refer to Figure 1 , please refer to in combination with Figure 2 and Figure 3 As shown, the four-dimensional electron microscope 10 provided by this application includes a light source assembly 2, an electron source 100, an electron optical assembly 3, and a detector 4. The light source assembly 2 can emit pulsed laser light, and the pulsed laser light propagates to the electron source 100 to excite the electron source 100 to form an electron beam. The electron beam is modulated by the electron optical assembly 3 and projected onto the sample 5 to emit corresponding signals, and the detector 4 receives the corresponding signals to be able to obtain information about the sample 5 based on the corresponding signals. The electron source 100 includes an excitation optical fiber 110 and an electron emission layer 120. The excitation optical fiber 110 has a light input end 1101 coupled to the light source assembly 2 and a light output end 1102 relative to the light input end 1101, that is, the excitation optical fiber 110 is coupled to the light source assembly 2. The electron emission layer 120 at least includes an electron excitation layer 121, and the electron excitation layer 121 is arranged on the light output path of the pulsed laser light emitted by the excitation optical fiber 110 so that the electron excitation layer 121 can emit an electron beam under the excitation of the pulsed laser light. In other words, the excitation optical fiber 110 includes a core 111 for transmitting pulsed laser light, and the electron emission layer 120 is arranged on the light output path of the pulsed laser light emitted by the core 111, so that the electron excitation layer 121 configured as the electron emission layer 120 can emit an electron beam along the direction outward from the light output end 1102 under the excitation of the pulsed laser light transmitted by the core 111. It can be understood that with the excitation of the pulsed laser light, the emitted electron beam has a pulsed nature, that is, the electron source 100 itself can emit a pulsed electron beam, and there is no need to open an optical window at the position of the outer shell 6 of the four-dimensional electron microscope 10 close to the electron source 100 to introduce the pulsed electron beam, resulting in damage to the cavity formed by the breakage of the outer shell 6, and four-dimensional detection can be achieved.

[0095] With reference to Figures 1-3 As shown, in some embodiments, the four-dimensional electron microscope 10 further includes a housing 6 having a vacuum chamber. The electron source 100 and the electron optical assembly 3 are sequentially disposed in the vacuum chamber. The electron source 100 penetrates through one end of the housing 6 along its longitudinal direction. In other words, an opening communicating with the vacuum chamber is provided on the housing 6. The light incident end 1101 of the excitation optical fiber 110 of the electron source 100 is exposed through the opening and is coupled to the light source assembly 2. Moreover, the outer peripheral wall of the excitation optical fiber 110 is hermetically connected to the inner side wall of the opening, thereby ensuring the airtightness of the cavity and improving the overall quality of the cavity. The arrangement of the electron source 100 in this application can emit pulsed electron beams without additionally opening an optical window on the housing 6 near the position of the electron source 100 for the pulsed electron beams to enter, that is, without damaging the cavity of the electron microscope and without affecting the performance of the electron microscope. Further, this application can modify the existing electron microscope. When modifying, only replacing the electron source 100 can realize the output of pulsed electron beams, and there is no need to open an optical window on the housing 6 near the electron source 100, without damaging the cavity of the existing electron microscope. That is, the modification is simple, the modification cost is low, and the detection effect after modification is good.

[0096] In some embodiments, a through hole is provided at a position of the housing 6 close to the sample 5 for the third optical fiber 23 to extend into the housing, so that the excitation light can irradiate on the sample and cooperate with the electron beam to characterize the sample.

[0097] It can be understood that the excitation optical fiber 110 is a transmission medium for laser and a carrier for the low-dimensional material of the electron emission layer 120. The excitation optical fiber 110 can be a single-mode optical fiber, a multi-mode optical fiber, a polarization-maintaining optical fiber, a holey optical fiber, or a multi-core optical fiber, etc. It should be noted that regardless of which of the above types the excitation optical fiber 110 adopts, the electron emission layer 120 is located in the vacuum chamber.

[0098] The electron excitation layer 121 includes low-dimensional materials, such as at least one of zero-dimensional materials, one-dimensional materials, and two-dimensional materials. During the process that the laser transmitted in the core 111 of the excitation optical fiber 110 is transmitted to the light output end 1102 of the excitation optical fiber 110 and exits, this part of the laser can interact with the electron excitation layer 121, so that the electrons in the electron excitation layer 121 absorb the photons of the laser, and undergo energy transition to escape outside the electron excitation layer 121, and electrons are emitted outward from the light output end 1102.

[0099] It should be noted that the wavelength of the laser can be the wavelength at which electrons in the electron excitation layer 121 absorb a photon and transition. For example, the wavelength is in the visible - near - infrared - ultraviolet range, or it can be the wavelength at which electrons in the electron excitation layer 121 absorb multiple photons and transition. For example, the wavelength is outside the visible - near - infrared - ultraviolet range. No specific limitation is made here.

[0100] The electron source 100 of the present application uses low - dimensional materials such as zero - dimensional materials, one - dimensional materials, or two - dimensional materials as the material of the electron excitation layer 121, and the electron excitation layer 121 is arranged on the excitation optical fiber 110 to achieve the excitation of electrons. It abandons the complex spatial light coupling structure set due to the introduction of external lasers, and also abandons the high - magnification microscope set to solve the alignment problem of metal tips, which can reduce the process cost of the four - dimensional electron microscope 10.

[0101] Compared with setting a metal layer on the optical fiber tip and directly interacting the laser transmitted in the optical fiber with the metal layer to excite electrons (electrons are easily affected by lattice scattering during the process of passing through the metal layer, resulting in low electron emission efficiency, wide energy dispersion, and serious heat accumulation), the low - dimensional material has an atomic - level thickness, no dangling bonds, and stable properties, thus having characteristics such as good stability and high service life. In addition, the low - dimensional material also has a strong light - matter interaction and a rich electron bandgap, enabling the laser to better interact with the electron excitation layer 121 to excite electrons in the electron excitation layer 121. These electrons are excited and detached into the vacuum, forming an electron beam, and the electron beam tunneling - emitted from the electron excitation layer 121 has the characteristics of small energy dispersion, high brightness, and high stability.

[0102] Moreover, the low - dimensional material can be directly integrated with the excitation optical fiber 110. The excitation optical fiber 110 can provide a stable excitation source with adjustable wavelength, polarization, and optical mode, and can be applicable to different application scenarios. And the stability of the electron beam emitted by the interaction of the pulsed laser and the low - dimensional material is higher. Compared with the ordinary electron excitation layer 121, the distance that electrons move in the low - dimensional material is shorter, and it is not easily affected by the thickness of the electron excitation layer 121, thereby improving the controllability of the formed electron beam, making the electron beam more stable, and having a higher detection quality.

[0103] In some embodiments, the thickness of the electron excitation layer 121 is less than or equal to 50 nm.

[0104] It can be understood that the thickness of the electron excitation layer 121 is in the nanometer order and the thickness of the electron excitation layer 121 is small. In this way, it is more conducive to reducing the process of in - body transmission of the excited electrons in the electron excitation layer 121, more conducive to improving the electron emission efficiency and emission density, and then an electron beam with ultrashort pulses can be realized by using this electron source 100.

[0105] Optionally, the electron excitation layer 121 may include zero-dimensional materials, which refer to materials with dimensions in the nanoscale range in the three spatial dimensions, such as nanoparticles, atomic clusters, and quantum dots, etc., generally composed of a small number of atoms and molecules. There are many zero-dimensional carbon nanomaterials, such as carbon black, nanodiamond, diamond color center, nano-fullerene C 60 or carbon-coated metal nanoparticles, etc. Zero-dimensional materials have typical discrete energy levels. Under the action of laser excitation, electrons are mainly excited by tunneling from the discrete energy levels, so that the electron beam tunneling and emitting from the electron excitation layer 121 have the characteristics of concentrated energy and small energy dispersion.

[0106] Optionally, the electron excitation layer 121 may also include one-dimensional materials. Electrons in one-dimensional materials can be transported along the linear chain of the one-dimensional materials. Combined with the fact that the electron excitation layer 121 is disposed on the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110, it is beneficial for the electrons emitted by the electron source 100 to be emitted efficiently along the longitudinal extension direction of the excitation optical fiber 110. One-dimensional materials have the characteristics of a small curvature radius (nanoscale), which can enhance the interaction between light and matter and provide a large field enhancement factor, ensuring multi-photon emission, optical field emission, etc., and are applied to scenarios where a high-brightness electron source 100 is required.

[0107] One-dimensional materials can be nanotubes, nanorods or nanowires, nanoribbons or coaxial nanocables, etc.

[0108] The nanotube can be a carbon nanotube, which can be regarded as a seamless tubular structure formed by winding single-layer or multi-layer graphite according to certain rules. The nanotube can also be a silicon (Si) nanotube, a selenium (Se) nanotube, a tellurium (Te) nanotube, a bismuth (Bi) nanotube, a boron nitride (BN) nanotube, a boron-nitrogen co-doped carbon nanotube (BCN nanotube), a tungsten disulfide (WS2) nanotube, a molybdenum disulfide (MoS2) nanotube or a titanium dioxide (TiO2) nanotube, etc.

[0109] The material of the nanowire can be silicon (Si) or germanium (Ge); the nanowire can also be an oxide nanowire, such as tin oxide (SnO) or zinc oxide (ZnO), etc.; of course, the nanowire can also be a nitride nanowire, such as gallium nitride (GaN) or silicon nitride (Si3N4), etc.; the nanowire can also be a sulfide nanowire, such as cadmium sulfide (CdS) and zinc sulfide (ZnS), etc.; the nanowire can also be a ternary compound nanowire, such as barium titanate (BaTiO3) and lead titanate (PbTiO3), etc.

[0110] The nanoribbon is quite different from the above two kinds of nanostructures (nanotubes and nanowires). Its cross-section is not close to circular like that of nanotubes or nanowires, but is quadrilateral, and the aspect ratio distribution range is generally from several to more than a dozen. The material of the nanoribbon can be an oxide, such as tin oxide (SnO) or zinc oxide (ZnO), etc.

[0111] The nanocoaxial cable can be a graphite / boron nitride (C / BN) nanocoaxial cable or a silicon carbide / sulfur dioxide (CSi / SiO2) nanocoaxial cable, etc.

[0112] In some embodiments, the angle between the axial direction of the one-dimensional material in the electron excitation layer 121 and the emission direction of the emitted laser is 0 to 90°, for example, it can be 0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80° or 90°.

[0113] In some embodiments, the axial direction of the one-dimensional material is the same as the emission direction of the laser, so that point emission of the electron source 100 can be achieved, and the resolution is high. If a low-density arrangement of one-dimensional materials is adopted, the energy dispersion of the emitted electrons is low and the brightness is high. If a high-density arrangement of one-dimensional materials is adopted, a large electron beam of the electron source 100 can be achieved. Among them, low density refers to the number of one-dimensional materials per unit area. For example, a density less than 1 per nm 2 is low density, and greater than 1 per nm 2 is high density.

[0114] In some embodiments, there is an angle between the axial direction of the one-dimensional material and the emission direction of the laser, and the angle can be a right angle or an acute angle. Laser excitation of the one-dimensional material can generate a linear electron source.

[0115] Optionally, the electron excitation layer 121 may also include a two-dimensional material. The electrons in the two-dimensional material can be transmitted along the two-dimensional plane. Combining with the electron excitation layer 121 being disposed on the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110, in this way, it is beneficial for the electrons emitted by the electron source 100 to be emitted efficiently along the longitudinal extension direction of the excitation optical fiber 110; and compared with setting a thin metal layer on the excitation optical fiber 110, it will cause the melting point of the metal layer to decrease, and then lead to the problem that the metal layer is easily damaged. The two-dimensional material selected in this application has no dangling bonds, is relatively stable, has a high melting point, is not easily damaged, and is suitable for high-power excitation and large electron beams of the electron source 100. In addition, the energy levels of the two-dimensional material are more discrete, and the energy of the electron beam emitted by tunneling emission is more concentrated and the energy dispersion is smaller.

[0116] Two-dimensional materials are characterized by including different atomic layer thicknesses. The thickness of two-dimensional materials can be the thickness of a single atomic layer or the thickness of multiple atomic layers. During the interaction of pulsed laser with two-dimensional materials, it hardly affects the light transmission mode and has high stability. Moreover, the excited electrons can be directly emitted without scattering inside the material, ensuring the purity of the properties of the emitted electrons and an extremely narrow pulse width.

[0117] Two-dimensional materials can be graphene, transition metal sulfides, two-dimensional perovskites, two-dimensional diamond, boron nitride, etc.

[0118] Taking graphene as an example of two-dimensional materials for illustration, the carbon atoms of graphene are bonded in the plane in the form of covalent bonds, forming a hexagonal honeycomb planar structure. The electron excitation layer 121 can have a thickness of one atomic layer, about 0.34 nanometers; the electron excitation layer 121 can also have a thickness of several or dozens of atomic layers.

[0119] Of course, the present application is not limited thereto. The electron excitation layer 121 also includes two or more of zero-dimensional materials, one-dimensional materials, and two-dimensional materials.

[0120] In some embodiments, the electron excitation layer 121 includes at least one layer of two-dimensional material.

[0121] Optionally, the electron excitation layer 121 includes at least two layers of two-dimensional materials stacked in sequence along the laser emission direction, or the electron excitation layer 121 includes at least two two-dimensional materials with different materials connected to each other on the same plane.

[0122] In some embodiments, at least two layers of two-dimensional materials are stacked, or at least two layers of two-dimensional materials are spliced to form the same plane. Further, the materials of two adjacent two-dimensional materials are different, thereby forming a vertical heterojunction or a planar heterojunction. The heterojunction structure can enhance the interaction between light and two-dimensional materials, realize efficient electron emission under low laser power, and the heterojunction has the function of interfacial energy band regulation. Through material design and twist angle regulation, special interfacial states can be obtained to realize high-brightness and low-energy-dispersion electron emission.

[0123] Of course, the present application is not limited thereto. The electron excitation layer 121 also includes two or more of zero-dimensional materials, one-dimensional materials, and two-dimensional materials.

[0124] In some embodiments, the materials in the electron excitation layer 121 include one-dimensional materials and zero-dimensional materials disposed at the ends and / or sides of the one-dimensional materials.

[0125] In this application, by combining zero-dimensional materials with one-dimensional materials and arranging the zero-dimensional materials at the ends or sides of the one-dimensional materials, that is, using zero-dimensional materials to modify the surface structure of one-dimensional materials. Both zero-dimensional materials and one-dimensional materials have typical discrete energy levels. Under the action of laser, electrons are mainly excited by tunneling from the discrete energy levels, and the emitted electrons have the characteristics of concentrated energy, small energy dispersion, and high emission efficiency.

[0126] In some embodiments, the electron excitation layer 121 includes a zero-dimensional material and a two-dimensional material, and the zero-dimensional material is arranged on the surface of the two-dimensional material.

[0127] In this application, the zero-dimensional material is arranged on the surface of the two-dimensional material. The two-dimensional material can not only serve as a support layer for carrying the zero-dimensional material, but also avoid the addition of a conductive layer by using a conductive two-dimensional material. That is, the two-dimensional material can serve as an auxiliary layer for the zero-dimensional material to achieve the functions of support and conduction.

[0128] In some embodiments, the electron excitation layer 121 includes a one-dimensional material and a two-dimensional material, and the one-dimensional material is arranged on the surface of the two-dimensional material. Optionally, the axial direction of the one-dimensional material forms an angle of 0 to 90° with the surface of the two-dimensional material.

[0129] In this application, the one-dimensional material is arranged on the surface of the two-dimensional material. The two-dimensional material can not only serve as a support layer for carrying the one-dimensional material, but also avoid the addition of a conductive layer by using a conductive two-dimensional material. That is, the two-dimensional material can serve as an auxiliary layer for the one-dimensional material to achieve the functions of support and conduction.

[0130] In some embodiments, the angle between the axial direction of the one-dimensional material in the electron excitation layer 121 and the emission direction of the pulsed laser is 0 to 90°, for example, it can be 0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80° or 90°.

[0131] In some embodiments, the zero-dimensional material, one-dimensional material or two-dimensional material independently includes a doping element.

[0132] In this application, by doping elements into the low-dimensional materials, the conductivity of the low-dimensional materials is improved, the work function is changed, and the electron emission performance is adjusted. For example, alkali metals and alkaline earth metal elements can improve the conductivity of the low-dimensional materials and reduce the work function of the low-dimensional materials at the same time to enhance the emission beam current. Elements such as B, C, N, O, F and rare earths can create discrete energy levels to obtain an electron beam with narrow energy.

[0133] Optionally, the doping element includes at least one of alkali metals, alkaline earth metals, transition metals, rare earth elements, halogen elements and light elements (B, C, N, O, F).

[0134] Refer to in combination Figures 1-3As shown, the electron optical component 3 is provided on the electron beam emission side of the electron source 100. The electron optical component 3 is used to adjust the deflection direction of the electron beam so that the electron beam is incident on the sample 5. In some embodiments, the electron optical component 3 includes structures such as a magnetic lens 31, which is mainly used to modulate the deflection direction of the electron beam so that it can be projected onto the sample 5. The detector 4 is provided on one side of the sample 5 to collect the reflected electron signal of the electron beam incident on the sample 5 or the transmitted electron signal of the electron beam penetrating the sample 5. That is, through the setting of the detector 4, the four-dimensional electron microscope 10 of the present application can achieve the functions of a scanning electron microscope and a transmission electron microscope.

[0135] In some embodiments, the electron source 100 further includes an anode. There is a preset electric field between the anode and the electron emission layer 120. The electron beam can be incident on the sample 5 under the drive of the preset electric field. That is to say, the electron emission layer 120 emits an electron beam under the excitation of a pulsed laser, forming a cathode opposite to the anode. The electrons can move towards the sample 5 under the action of the electric field between the anode and the electron emission layer 120. Combining with the electron optical component 3 being provided on the side of the electron source 100 that emits the electron beam and being used to adjust the deflection direction of the electron beam, the electron beam emitted from the electron emission layer 120 can be incident on the sample 5, and then the corresponding signal emitted from the sample 5 is received by the detector 4 for detection to obtain information about the sample 5. In some embodiments, the anode has a first electron channel, and the electron optical component 3 has a second electron channel communicating with the first electron channel, so that the electron beam can pass through the first electron channel and the second electron channel under the drive of the preset electric field and be incident on the sample 5. That is, the electron beam is driven by the electric field to pass through the first electron channel and is regulated by the electron optical component 3 when passing through the second electron channel, and the deflection direction of the electron beam changes, and finally it is incident on the sample 5, and then the detector 4 receives the reflected electron signal or the transmitted electron signal emitted by the sample 5. It can be understood that the anode can be set as a hollow ring, and the middle of the ring-shaped anode is the first electron channel for the electron beam to pass through. Thus, the anode can cooperate with the electron emission layer 120 to form an electric field for driving the electron beam and does not affect the passing of the electron beam.

[0136] In some embodiments, the four-dimensional electron microscope 10 further includes a sample stage 5. The electron source 100, the electron optical component 3, and the sample stage 5 are sequentially arranged at intervals along the propagation direction of the electron beam. The sample stage 5 is used to carry the sample 5. In some embodiments, a channel through which the electron beam penetrating the sample 5 can propagate is provided in the middle of the sample stage 5. That is, the electron beam penetrating the sample 5 will not be blocked by the sample stage 5 and can continue to propagate, so as to facilitate the four-dimensional electron microscope 10 to achieve transmission scanning detection.

[0137] In some embodiments, the light source assembly 2 includes a light source 29 and a first optical fiber 21. The light source 29 is configured to emit pulsed laser light. The first optical fiber 21 is connected between the light source 29 and the excitation optical fiber 110 and is used to transmit the pulsed laser light emitted by the light source 29 to the excitation optical fiber 110. In other words, the light source 29 is coupled to one end of the first optical fiber 21, and the excitation optical fiber 110 is connected to the other end of the first optical fiber 21. In some embodiments, devices such as an optical switch 28 can be provided between the first optical fiber 21 and the excitation optical fiber 110 to control whether the optical path is open or not.

[0138] The four-dimensional electron microscope 10 of the present application can perform scanning detection on the surface of a sample, that is, realize the function of a scanning electron microscope. Refer to Figure 1 As shown, in some embodiments, the reflected electron signals include secondary electron signals and backscattered electron signals, that is, the four-dimensional electron microscope 10 of the present application can detect secondary electron and backscattered electron signals excited from the surface of the sample. In this embodiment, the light source assembly 2 further includes a first optical fiber beam splitter 24, a second optical fiber 22, and a first optical fiber delay line 26. The pulsed laser light can be divided into two parts by the first optical fiber beam splitter 24. One part is used to excite the electron beam, and the other part is irradiated onto the surface of the sample 5 after time delay modulation to achieve time-resolved imaging analysis, that is, to display the characteristics in the time dimension. It can be understood that the first optical fiber beam splitter 24 has a first input end coupled to the light source 29 and a first output end opposite to the first input end. The first output end is respectively connected to the first optical fiber 21 and the second optical fiber 22. That is to say, the first optical fiber beam splitter 24 divides the pulsed laser light emitted by the light source 29 into two parts and transmits them into the first optical fiber 21 and the second optical fiber 22 respectively.

[0139] Refer to Figure 1As shown, the sample 5 has an incident surface disposed opposite to the electron beam exit side of the electron source 100. One end of the second optical fiber 22 away from the first optical fiber splitter 24 extends towards the incident surface of the sample 5, so as to be able to emit the optical fiber transmitted inside the second optical fiber 22 onto the sample 5. Wherein, the receiving surface of the sample 5 can be inclined relative to the propagation direction of the electron beam or perpendicular to the propagation direction of the electron beam, which is not limited herein. In some embodiments, the first optical fiber delay line 26 is coupled to the second optical fiber 22 and is used to perform time delay on the light beam propagating in the second optical fiber 22, so that the light in the second optical fiber 22 and the light in the first optical fiber 21 used to excite the electron beam have a preset time delay. It can be understood that based on the photoelectric effect, in the related art, an electron microscope uses the difference in the yield of photoelectrons at different spatial positions of a sample as image contrast for projection imaging. The present application combines the use of an ultrafast optical pump-probe technique to provide high time resolution capabilities for an electron microscope. In this embodiment, the electron beam excited by the pulsed laser in the first optical fiber 21 is used to excite the sample 5, and then the pulsed laser with time delay in the second optical fiber 22 is used as the probe light and irradiated on the sample 5 to excite the material, so that the reflection or transmission condition of the electron beam incident on the sample 5 changes, forming the required secondary electron signal or backscattered electron signal with time characterization characteristics. When using the pulsed laser with time delay in the second optical fiber 22 as the probe light, the time delay of the pulsed laser in the second optical fiber 22 can be changed by adjusting the first optical fiber delay line 26, and thus it is possible to know the changes occurring at different time points after the material is excited by the laser, so as to realize time-resolved electron beam imaging and be able to detect the ultrafast dynamics process on the surface of the sample 5 in real time at an ultra-high spatio-temporal resolution scale. In this embodiment, the detector 4 includes a backscattered detector 4 or a secondary detector 4. The backscattered detector 4 or the secondary detector 4 is disposed towards the incident surface of the sample 5 and is used to receive the secondary electron signal and perform imaging.

[0140] Referring to Figure 2 As shown, in the embodiment of scanning and detecting the surface of the sample, the cathode fluorescence signal of the sample 5 can also be detected and analyzed. The cathode fluorescence signal on the surface of the sample 5 is excited by the electron beam. The detector 4 includes a cathode fluorescence analysis system. The cathode fluorescence analysis system faces the incident surface of the sample 5 and is used to receive the cathode fluorescence signal on the surface of the sample 5. The cathode fluorescence analysis system can be set as a time-resolved single photon counting system (TCSPC), and time-resolved cathode fluorescence analysis is performed on the cathode fluorescence signal through the time-resolved single photon counting system, which will not be elaborated herein.

[0141] The four-dimensional electron microscope 10 of the present application can also perform transmission detection on the sample, that is, realize the function of a transmission electron microscope. Referring to Figure 3As shown, the sample 5 further includes an exit surface relative to the incident surface. In some embodiments, the detector 4 includes a receiving screen 41 disposed on the side of the sample 5 away from the electron source 100 and configured to receive the electron beam penetrating the sample 5. The receiving screen 41 can be set as a fluorescent screen. The electron beam passes through the sample and projects the information of the sample onto the fluorescent screen, and then imaging and photographing are performed through structures such as the photographic chamber 42 to obtain experimental results, such as bright field images, dark field images, electron diffraction spectra, high-resolution images, and chemical information. In this embodiment, a high-angle annular dark field detector 4, a low-angle annular dark field detector 4, or an annular bright field detector 4 can also be correspondingly disposed on the side of the exit surface of the sample 5 to obtain a high-angle annular dark field image, a low-angle annular dark field image, or an annular bright field image of the electron-transmitted sample 5, and detect the sample 5 to achieve the function of a transmission scanning electron microscope.

[0142] In some embodiments, the electron optical assembly 3 further includes an intermediate lens 32 and a projection lens 33 sequentially disposed between the sample 5 and the receiving screen 41. The intermediate lens 32 converges the electron beam, and the projection lens 33 is used to adjust the radial size of the electron beam to facilitate imaging of the electron beam projected on the receiving screen 41 by structures such as the photographic chamber 42.

[0143] In some embodiments, the light source assembly 2 further includes a second optical fiber beam splitter 25, a third optical fiber 23, and a second optical fiber delay line 27. The first optical fiber beam splitter 24 can divide the pulsed laser into two parts, one part for exciting the electron beam and the other part as the detection light, which is irradiated onto the surface of the sample 5 after time delay modulation to achieve time-resolved imaging analysis. The second optical fiber beam splitter 25 has a second input end coupled to the light source 29 and a second output end relative to the second input end. The second output end is respectively connected to the first optical fiber 21 and the third optical fiber 23, that is, the second optical fiber beam splitter 25 divides the pulsed laser emitted by the light source 29 into two parts and transmits them into the first optical fiber 21 and the third optical fiber 23 respectively. One end of the third optical fiber 23 away from the second optical fiber beam splitter 25 extends toward the sample 5 to be able to emit the light transmitted inside the third optical fiber 23 onto the sample 5. The second optical fiber delay line 27 is coupled to the third optical fiber 23 and is used to perform time delay on the light beam propagating in the third optical fiber 23, so that the light in the third optical fiber 23 and the light in the first optical fiber 21 for exciting the electron beam have a preset time delay, thereby achieving time-resolved electron beam imaging.

[0144] When the electron source 100 of the present application is in use, the pulsed laser can be transmitted along the core 111 of the excitation optical fiber 110, so that the pulsed laser transmitted in the core 111 can propagate to the end face 11021 of the light output end 1102 and exit, and interact with the electron excitation layer 121. The electrons in the electron excitation layer 121 absorb the photons of the laser and undergo an energy transition to escape outside the electron excitation layer 121, realizing the excitation of electrons. The electron source 100 realizes the excitation of electrons by arranging the electron excitation layer 121 on the excitation optical fiber 110, abandoning the complex spatial light coupling structure set due to the introduction of external lasers, and can reduce the process cost of the electron source 100. In addition, the electron source 100 of the present application uses low-dimensional materials as the materials for emitting electrons. Since the electron excitation layer 121 has strong light-matter interaction and rich electron band gaps, the pulsed laser can better interact with the electron excitation layer 121 to excite the electrons in the electron excitation layer 121, and the electrons tunneling and emitting from the electron excitation layer 121 have the characteristics of small energy dispersion, high brightness and high stability.

[0145] The present application has various embodiments for the setting manners of the excitation optical fiber 110 and the electron excitation layer 121.

[0146] In some embodiments, please refer to Figure 5 , the excitation optical fiber 110 includes a core 111 for transmitting the laser and a cladding layer 112 wrapped around the core 111. The end face 11021 of the light output end 1102 of the excitation optical fiber 110 is set at an angle α with the extending direction of the core 111, and the angle α is selected between 0 and 90 degrees. The electron emission layer 120 is arranged on the end face 11021 of the light output end 1102 of the excitation optical fiber 110, and the electron excitation layer 121 covers the core 111 of the excitation optical fiber 110. The pulsed laser emitted from the core 111 can directly irradiate on the electron emission layer 120, so that the electron excitation layer 121 is excited by the pulsed laser emitted from the core 111 and emits electrons.

[0147] It can be understood that the electron excitation layer 121 is located on the light output path of the laser emitted from the core 111.

[0148] In this way, the oblique incidence on the electron excitation layer 121 can be realized, and the photoelectric field perpendicular to the end face 11021 of the light output end 1102 can be realized. The emission angle of electrons can be changed by changing the angle α, or the emission angle of electrons can be adjusted by adjusting the polarization state of the laser in the excitation optical fiber 110, which is beneficial to broadening the application range of the electron source 100.

[0149] In some embodiments, please refer to Figure 6 and Figure 7, a light leakage notch h is formed along the radial direction of the excitation optical fiber 110 at the light output end 1102 of the excitation optical fiber 110. The electron excitation layer 121 is disposed on the bottom wall surface h1 of the light leakage notch h, and the bottom wall surface h1 of the light leakage notch h is configured as a plane. The projection of the electron excitation layer 121 on the bottom wall surface h1 covers the projection of the fiber core 111 on the bottom wall surface h1. The electron excitation layer 121 also extends to the light output end 1102 of the excitation optical fiber 110.

[0150] Optionally, the light leakage notch h further has a side wall surface h2 extending along the radial direction of the excitation optical fiber 110, and the bottom wall surface h1 and the side wall surface h2 together define the light leakage notch h.

[0151] Optionally, the bottom wall surface h1 of the light leakage notch h is configured as a plane, and the bottom wall surface h1 of the light leakage notch h extends along the extending direction of the excitation optical fiber 110.

[0152] It can be that the bottom wall surface h1 of the light leakage notch h is spaced apart from the fiber core 111, and the bottom wall surface h1 of the light leakage notch h is parallel to the tangent plane of the outer surface of the fiber core 111; it can also be that the bottom wall surface h1 of the light leakage notch h is tangent to the outer surface of the fiber core 111 (as Figure 7 shown); of course, it can also be that the bottom wall surface h1 of the light leakage notch h is configured as a plane partially formed on the fiber core 111. For example, by cutting the fiber core 111 and the cladding 112 simultaneously to form the light leakage notch h, and making a part of the bottom wall surface h1 of the light leakage notch h be formed on the fiber core 111, and the other part of the bottom wall surface h1 of the light leakage notch h be formed on the cladding 112.

[0153] In this way, the laser transmitted in the fiber core 111 of the excitation optical fiber 110 can generate an evanescent wave at the bottom wall surface h1 of the light leakage notch h, and since the electron excitation layer 121 is disposed on the bottom wall surface h1 of the light leakage notch h, and the projection of the electron excitation layer 121 on the bottom wall surface h1 covers the projection of the fiber core 111 within the bottom wall surface h1, therefore, the laser transmitted in the fiber core 111 of the excitation optical fiber 110 can interact with the electron excitation layer 121 through the evanescent wave, so that the electrons in the electron excitation layer 121 absorb the energy of the evanescent wave and transition, and these electrons can escape outside the electron excitation layer 121, and thus the excitation of electrons can be realized.

[0154] In some embodiments, please refer to Figure 8 and Figure 9 , the excitation optical fiber 110 includes a porous optical fiber, the porous optical fiber has a light guiding hole, the porous optical fiber can include a hollow porous optical fiber, and the hollow porous optical fiber can be a single-hole or multi-hole hollow optical fiber; of course, the porous optical fiber can also include a solid-core porous optical fiber, and the solid-core porous optical fiber can be a single-hole or multi-hole solid-core optical fiber, which is not specifically limited herein.

[0155] The light guide hole is provided with a core 111 composed of air, and the holey optical fiber further includes a cladding layer 112 surrounding the core 111. In some embodiments, the cladding layer 112 is an annular light guide tube body, and the side wall k of the light guide hole is formed on the inner side wall of the annular light guide tube body. Specifically, the material of the annular light guide tube body can be borosilicate, glass or quartz, etc. More specifically, the holey optical fiber is a capillary optical fiber.

[0156] The electron excitation layer 121 is at least provided on the side wall k of the light guide hole, and the electron excitation layer 121 extends along the extending direction of the light guide hole to the light emitting end 1102 of the excitation optical fiber 110.

[0157] When the electron source 100 is in use, during the process of the laser transmitting in the core 111 of the holey optical fiber by means of the light guiding medium, an evanescent wave can be generated at the side wall k of the light guide hole. Since the electron excitation layer 121 is provided on the side wall k of the light guide hole, the laser can interact with the electron excitation layer 121 through the evanescent wave, so that the electrons in the electron excitation layer 121 absorb the energy of the evanescent wave and transition. These electrons can escape outside the electron excitation layer 121, and thus the excitation of electrons can be realized.

[0158] In some embodiments, please refer to Figure 10 and Figure 11 , the excitation optical fiber 110 includes a holey optical fiber, the holey optical fiber has a light guide hole, and the holey optical fiber can include a hollow holey optical fiber, and the hollow holey optical fiber can be a single-hole or multi-hole hollow optical fiber; of course, the holey optical fiber can also include a solid-core holey optical fiber, and the solid-core holey optical fiber can be a single-hole or multi-hole solid-core optical fiber, which is not specifically limited herein.

[0159] The light guide hole is provided with a core 111 composed of air, and the holey optical fiber further includes a cladding layer 112 surrounding the core 111. In some embodiments, the cladding layer 112 is an annular light guide tube body, and the side wall k of the light guide hole is formed on the inner side wall of the annular light guide tube body. Specifically, the material of the annular light guide tube body can be borosilicate, glass or quartz, etc. More specifically, the holey optical fiber is a capillary optical fiber.

[0160] The electron emission layer 120 is provided on the end face 11021 of the light emitting end 1102 of the holey optical fiber, and the electron excitation layer 121 covers one end of the light guide hole located at the end face 11021 of the light emitting end 1102. The pulsed laser emitted by the holey optical fiber can directly irradiate on the electron emission layer 120, so that the electron excitation layer 121 is excited by the pulsed laser emitted by the holey optical fiber and emits electrons.

[0161] Exemplarily, the porous optical fiber is a capillary optical fiber, and the electron excitation layer 121 covers the core 111 of the porous optical fiber. It can be that the electron excitation layer 121 directly covers the core 111 of the porous optical fiber, or it can be that the electron excitation layer 121 indirectly covers the core 111 of the porous optical fiber, and no specific limitation is made here.

[0162] In this way, during the process that the laser transmitted in the core 111 propagates to the end face 11021 of the light output end 1102 and exits, this part of the laser can interact with the electron excitation layer 121, so that the electrons in the electron excitation layer 121 absorb the photons of the laser, and undergo energy transition to escape outside the electron excitation layer 121, realizing the excitation of electrons.

[0163] In some embodiments, please refer to Figure 12 and Figure 13 , the light output end 1102 of the excitation optical fiber 110 is provided with a pointed end j, the electron excitation layer 121 covers the surface j1 of the pointed end j of the excitation optical fiber 110, and the pulsed laser emitted from the core 111 can directly irradiate on the electron emission layer 120, so that the electron excitation layer 121 is excited by the pulsed laser emitted from the core 111 and emits electrons.

[0164] During the process that the laser transmitted in the core 111 of the excitation optical fiber 110 transmits to the pointed end j and exits, this part of the laser can interact with the electron excitation layer 121, so that the electrons in the electron excitation layer 121 absorb the photons of the laser, and undergo energy transition to escape outside the electron excitation layer 121, and thus the excitation of electrons can be realized.

[0165] Optionally, along the extending direction of the core 111, the radial dimension of the pointed end j gradually decreases.

[0166] The electron excitation layer 121 of the present application is arranged on the pointed end j of the excitation optical fiber 110 and covers the surface j1 of the pointed end j of the excitation optical fiber 110. Since the pointed end j of the excitation optical fiber 110 has a geometric structure similar to a needle tip, the field emission enhancement factor is improved, and a higher brightness electron source 100 can be obtained.

[0167] Optionally, in this embodiment, along the extending direction of the core 111, the dimension of the pointed end j is L1, and the dimension of the electron excitation layer 121 is L2, where L1 is greater than L2. Specifically, the dimensions of the pointed end j and the electron excitation layer 121 satisfy the following relationship: L2 > 1 / 2 * L1.

[0168] The electron excitation layer 121 covers the surface j1 of the tip portion j, and the electron excitation layer 121 is disposed around the tip portion j. Since L2 > 1 / 2*L1, thus, the contact area between the electron excitation layer 121 and the surface j1 of the tip portion j can be increased, the bonding strength between the electron excitation layer 121 and the excitation optical fiber 110 can be improved, and it is also beneficial to use the laser transmitted by the fiber core 111 to excite the electron excitation layer 121 to emit electrons outward.

[0169] In some embodiments, with reference to Figures 5-10 As shown, the electron source 100 further includes a conductive connection layer 130. The conductive connection layer 130 is disposed on the excitation optical fiber 110 and is electrically connected to the electron excitation layer 121. The excitation optical fiber 110 further includes a cladding layer 112 that wraps the fiber core 111. The conductive connection layer 130 is at least partially disposed on the cladding layer 112. The conductive connection layer 130 can be a conductive thin film. Specifically, the conductive connection layer 130 can be a metal thin film, a graphite thin film, or a low-dimensional material thin film, etc. The conductive connection layer 130 can be formed on the cladding layer 112 at the light output end 1102 of the excitation optical fiber 110 first, and then the electron excitation layer 121 can be formed at the corresponding position of the fiber core 111. Alternatively, the electron excitation layer 121 can be formed at the corresponding position of the fiber core 111 at the light output end 1102 of the excitation optical fiber 110 first, and then the conductive connection layer 130 can be formed on the cladding layer 112 at the light output end 1102 of the excitation optical fiber 110. No specific limitation is made here.

[0170] It should be added that the conductive connection layer 130 is not disposed on the light output path of the laser emitted from the fiber core 111.

[0171] The electron excitation layer 121 can be electrically connected to the negative electrode of a power source through the conductive connection layer 130. On the one hand, the power source can be used to supply electrons to the electron excitation layer 121, which is beneficial for the electron excitation layer 121 to continuously emit electrons under the excitation of pulsed laser. On the other hand, the direction and convergence of the electrons emitted from the electron excitation layer 121 can be regulated by the voltage applied to the conductive connection layer 130 by the power source.

[0172] Optionally, the electron excitation layer 121 includes a first portion 1211 located on the light output path of the laser emitted from the fiber core 111, and a second portion 1212 connected to the periphery of the first portion 1211. The second portion 1212 is electrically connected to the conductive connection layer 130. Among them, the second portion 1212 can be directly in electrical contact with the conductive connection layer 130 to be electrically connected to the conductive connection layer 130; the second portion 1212 can also be electrically connected to the conductive connection layer 130 through other conductive structures.

[0173] Specifically, such as Figure 5In the illustrated embodiment, the first part 1211 and the second part 1212 are disposed on the end face 11021 of the light output end 1102. The first part 1211 covers the core 111 of the excitation optical fiber 110, and the second part 1212 is disposed around the first part 1211 and is electrically connected to the conductive connection layer 130.

[0174] The first part 1211 may directly cover the core 111 of the excitation optical fiber 110, or may indirectly cover the core 111 of the excitation optical fiber 110, and no specific limitation is made here.

[0175] Specifically, in the embodiments such as Figure 6 and Figure 7 In the illustrated embodiment, the first part 1211 and the second part 1212 are disposed on the bottom wall surface h1 of the light leakage gap h. The projection of the first part 1211 on the bottom wall surface h1 covers the projection of the core 111 on the bottom wall surface h1. The second part 1212 is located outside the first part 1211 and is electrically connected to the conductive connection layer 130.

[0176] Specifically, in the embodiments such as Figure 8 and Figure 9 In the illustrated embodiment, the electron excitation layer 121 includes a first part 1211 that completely covers the side wall k of the light guiding hole, and a second part 1212 that is disposed on the end face 11021 of the light output end 1102 of the fiber with holes. The first part 1211 is connected to the second part 1212, and the second part 1212 is electrically connected to the conductive connection layer 130.

[0177] Specifically, in the embodiments such as Figure 12 and Figure 13 In the illustrated embodiment, the electron excitation layer 121 includes a first part 1211 and a second part 1212 that are disposed on the end face 11021 of the light output end 1102 and are connected to each other. The first part 1211 covers one end of the light guiding hole located on the end face 11021 of the light output end 1102. The second part 1212 is disposed around the first part 1211 and is electrically connected to the conductive connection layer 130.

[0178] Specifically, in the embodiments such as Figure 12 and Figure 13 In the illustrated embodiment, the electron excitation layer 121 includes a first part 1211 and a second part 1212 that are connected. The projection of the first part 1211 in a target plane perpendicular to the extending direction of the core 111 covers the projection of the core 111 in the target plane. The projection of the second part 1212 in the target plane is located outside the projection of the first part 1211 in the target plane, and the second part 1212 is overlapped with the conductive connection layer 130.

[0179] In this way, by electrically connecting the conductive connection layer 130 to the second part 1212 of the electron excitation layer 121, and considering that the second part 1212 is located on the periphery of the first part 1211, the conductive connection layer 130 can supply electrons to the electron excitation layer 121 without affecting the interaction between the core 111 and the electron excitation layer 121, which is beneficial for the electron excitation layer 121 to continuously emit electrons outward under the excitation of laser light.

[0180] Optionally, the conductive connection layer 130 includes a first conductive part 131 disposed on the light-emitting end 1102 and a second conductive part 132 disposed on the outer peripheral surface of the excitation optical fiber 110. The first conductive part 131 is connected to the second conductive part 132, and the first conductive part 131 overlaps with the second part 1212 of the electron excitation layer 121.

[0181] Specifically, in the embodiments shown in Figure 5 , Figures 10-11 , the first conductive part 131 is disposed on the end surface 11021 of the light-emitting end 1102 and overlaps with the second part 1212 of the electron excitation layer 121. Specifically, in the embodiments shown in Figure 6 and Figure 7 , the first conductive part 131 is disposed on the bottom wall surface h1 of the light leakage notch h and overlaps with the second part 1212 of the electron excitation layer 121. The first conductive part 131 also extends to the light-emitting end 1102. Specifically, in the embodiments shown in Figure 12 and Figure 13 , the first conductive part 131 is disposed on the tip portion j on the light-emitting end 1102 and overlaps with the second part 1212 of the electron excitation layer 121.

[0182] In this way, the conductive connection layer 130 can cover more of the excitation optical fiber 110, improving the bonding strength between the conductive connection layer 130 and the excitation optical fiber 110, and also facilitating better use of the conductive connection layer 130 to supply electrons to the electron excitation layer 121.

[0183] Optionally, the conductive connection layer 130 includes a first metal layer and a second metal layer stacked. The adhesion of the first metal layer is greater than that of the second metal layer, and the corrosion resistance of the first metal layer is less than that of the second metal layer.

[0184] Exemplarily, the material of the first metal layer is titanium, and the material of the second metal layer is gold.

[0185] In this way, the first metal layer with higher adhesion can make the conductive connection layer 130 better adhere to the excitation optical fiber 110, and the second metal layer with better corrosion resistance is used to protect the first metal layer, improving the bonding strength between the conductive connection layer 130 and the excitation optical fiber 110, and also being beneficial for improving the service life of the conductive connection layer 130.

[0186] In some embodiments, the electron emission layer 120 further includes an auxiliary layer 122 , which is stacked on a side of the electron excitation layer 121 close to the excitation fiber 110 , or stacked on a side of the electron excitation layer 121 away from the excitation fiber 110 .

[0187] The auxiliary layer 122 may be stacked on a side of the electron excitation layer 121 close to the end face 1102 of the light output end 1102 of the excitation optical fiber 110 , or the auxiliary layer 122 may be stacked on a side of the electron excitation layer 121 away from the end face 1102 of the light output end 1102 of the excitation optical fiber 110 .

[0188] Of course, the auxiliary layer 122 may also be stacked on a side of the electron excitation layer 121 close to or far from the bottom wall surface h1 of the light leakage gap h.

[0189] Of course, the auxiliary layer 122 may also be stacked on a side of the surface j1 of the electron excitation layer 121 that is close to or far away from the tip j of the excitation optical fiber 110 .

[0190] Figure 10 , Figure 11 and Figure 14 An example is given in which the auxiliary layer 122 is stacked on one side of the end surface 11021 of the electron excitation layer 121 close to the light output end 1102 .

[0191] In the present application, an auxiliary layer 122 is additionally provided. When the electron excitation layer 121 requires structural support, the auxiliary layer 122 is used to provide structural support for the electron excitation layer 121, that is, the electron excitation layer 121 is provided on the auxiliary layer 122; or, when the electron excitation layer 121 cannot be directly connected to the conductive connection layer 130 for conduction, the conductive auxiliary layer 122 is used to connect the conductive connection layer 130, and the auxiliary layer 122 is used to achieve electronic conduction between the electron excitation layer 121 and the conductive connection layer 130.

[0192] Optionally, the auxiliary layer 122 includes at least one of a conductive support layer and a heat dissipation support layer.

[0193] Optionally, the auxiliary layer 122 has a thickness of 0.1 nm to 100 nm.

[0194] Optionally, the light transmittance of the auxiliary layer 122 is greater than 10%, such as 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100%.

[0195] Optionally, the auxiliary layer 122 includes a conductive supporting layer, and the conductive supporting layer is electrically connected to the conductive connecting layer 130 .

[0196] In some embodiments, the auxiliary layer 122 includes a conductive support layer, the material of the conductive support layer includes a conductive metal, the laser wavelength in the excitation optical fiber 110 is 200 nm to 10 μm, the pulse power is 1 nw to 1 w, and the repetition frequency is 0 Hz to 10 GHz.

[0197] In this application, the auxiliary layer 122 uses a conductive metal and controls the laser parameters, thereby avoiding the problem of melting caused by laser irradiation of the conductive metal and ensuring that the auxiliary layer has the functions of support and conduction.

[0198] The auxiliary layer 122 may also include a conductive support layer, such as Figure 10 and Figure 11 As shown, the electron excitation layer 121 is disposed on the end face 11021 of the light output end 1102 through the auxiliary layer 122, and the auxiliary layer 122 has a bearing plane for bearing the electron excitation layer 121. The auxiliary layer 122 may be a light-transmitting material; the auxiliary layer 122 may also be selected as a non-light-transmitting material, and the auxiliary layer 122 has an annular structure, and the orthographic projection of the auxiliary layer 122 on the end face 11021 of the light output end 1102 is located outside the core 111 of the excitation optical fiber 110.

[0199] In this way, both the bearing plane of the auxiliary layer 122 can be utilized to make the electron excitation layer 121 more flatly disposed on the end face 11021 of the light output end 1102, and the interaction between the electron excitation layer 121 and the core 111 of the excitation optical fiber 110 will not be affected, which is beneficial to the formation of an electron beam with concentrated energy and small energy dispersion from the electrons tunneling and emitting within the electron excitation layer 121.

[0200] The auxiliary layer 122 may also include a heat dissipation support layer. Exemplarily, the material of the auxiliary layer 122 may be hexagonal boron nitride. Of course, the material of the auxiliary layer 122 may also be selected as other materials that can dissipate heat for the electron excitation layer 121 and enable the electron excitation layer 121 to be flatly disposed on the end face 11021 of the light output end 1102. In this way, the heat dissipation efficiency of the electron excitation layer 121 can be increased by using the auxiliary layer 122, so that the electron excitation layer 121 can emit a larger electron beam current.

[0201] This application can prepare the electron source 100 through the following steps:

[0202] S210. Provide the excitation optical fiber 110. Among them, the excitation optical fiber 110 includes a core 111 for transmitting laser and a cladding layer 112 wrapped around the core 111.

[0203] Optionally, an excitation optical fiber 110 of an appropriate length can be intercepted, the end coating of the excitation optical fiber 110 can be removed, and one end of the cut excitation optical fiber 110 can be processed to form a light-emitting end 1102. Specifically, a cutting mechanism can be used to cut one end of the cut excitation optical fiber 110 to form the light-emitting end 1102. By forming the light-emitting end 1102 in a cutting manner, the cross-section where the end face 11021 of the light-emitting end 1102 is located can be relatively flat, which is beneficial to forming a flat electron excitation layer 121 on the end face 11021 of the light-emitting end 1102.

[0204] S220. Form an electron excitation layer 121 on the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110. The electron excitation layer 121 covers the core 111 of the excitation optical fiber 110 so that the electron excitation layer 121 is located on the light-emitting path of the laser emitted from the core 111.

[0205] The electron excitation layer 121 can be formed by at least one of dry transfer, wet transfer, and direct growth.

[0206] In some embodiments, the electron excitation layer 121 is prepared by dry transfer. The preparation method includes: transferring zero-dimensional materials, one-dimensional materials, and / or two-dimensional materials to a tape by mechanical exfoliation, and transferring the zero-dimensional materials, one-dimensional materials, and / or two-dimensional materials to the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110.

[0207] Taking two-dimensional materials as an example for illustration, the preparation process of forming the electron excitation layer 121 by dry transfer is as follows:

[0208] (1) The two-dimensional material can be thinned by mechanical exfoliation until an electron excitation layer 121 with a preset thickness is formed. Specifically, the two-dimensional material is adhered to a highly adhesive tape A, and a low-adhesive tape B can be used to mechanically exfoliate along the crystal cleavage plane of the two-dimensional material repeatedly until an electron excitation layer 121 with a preset thickness is formed.

[0209] (2) Transfer the electron excitation layer 121 with the preset thickness to a temporary substrate 20 and remove the tape B on the electron excitation layer 121.

[0210] (3) Transfer the electron excitation layer 121 on the temporary substrate 20 to the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110.

[0211] Optionally, the electron excitation layer 121 is selected as a two-dimensional material, and the material of the temporary substrate 20 can be selected as a polycarbonate propylene ester film.

[0212] Of course, the present application is not limited thereto. The dry transfer method can also be combined with the direct growth method (such as chemical vapor deposition). For example, an electron excitation layer 121 with a preset thickness is grown on the substrate to be peeled off, and then the electron excitation layer 121 is transferred from the substrate to be peeled off to the temporary substrate 20 by etching the substrate to be peeled off with acid or tearing it by hand. Then, the electron excitation layer 121 on the temporary substrate 20 is transferred to the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110. Among them, the substrate to be peeled off can be metal or other materials that can be etched with acid or torn by hand.

[0213] In some other embodiments, the electron excitation layer 121 is prepared by a wet transfer method. The preparation method includes: directly preparing zero-dimensional materials, one-dimensional materials or two-dimensional materials in a solution and floating them on the liquid surface, making the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110 contact the zero-dimensional materials, one-dimensional materials or two-dimensional materials on the liquid surface, and drying the zero-dimensional materials, one-dimensional materials and / or two-dimensional materials on the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110.

[0214] In still some other embodiments, the electron excitation layer 121 is prepared by a direct growth method. The preparation method includes: directly preparing the electron excitation layer 121 on the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110 by at least one of chemical vapor deposition, physical vapor deposition, molecular beam epitaxy and liquid filling.

[0215] Optionally, before or after forming the electron excitation layer 121 on the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110, the preparation method of the electron source 100 further includes:

[0216] S230. Form a conductive connection layer 130 on the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110 so that the conductive connection layer 130 overlaps with the electron excitation layer 121.

[0217] That is to say, the conductive connection layer 130 can be formed first and then the electron excitation layer 121; or the electron excitation layer 121 can be formed first and then the conductive connection layer 130; as long as the electron excitation layer 121 and the conductive connection layer 130 are electrically connected to each other. In this way, electrons can be supplied to the electron excitation layer 121 by means of the conductive connection layer 130, which is beneficial to the continuous emission of electrons from the electron excitation layer 121 under the excitation of laser light.

[0218] Optionally, forming a conductive connection layer 130 on the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110 so that the conductive connection layer 130 overlaps with the electron excitation layer 121 specifically includes:

[0219] S231. Form a core protective layer on the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110, and the core protective layer covers the core 111 of the excitation optical fiber 110.

[0220] It may be that the core protective layer directly covers the core 111 of the excitation optical fiber 110, or it may be that the core protective layer indirectly covers the core 111 of the excitation optical fiber 110, and no specific limitation is made here.

[0221] Optionally, a polymer microsphere solution can be coated on the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110 to form a core protective layer covering the core 111. Exemplarily, the polymer microsphere solution is a polymethyl methacrylate suspension.

[0222] S232. Form a conductive material layer covering the core protective layer on the excitation optical fiber 110.

[0223] The conductive material layer can be formed by evaporation coating. Specifically, a metal evaporation coating device can be used to form the conductive material layer on the excitation optical fiber 110.

[0224] S233. Remove the core protective layer and the part of the conductive material layer disposed on the core protective layer to form a conductive connection layer 130.

[0225] Optionally, a solvent that can dissolve the core protective layer and does not interact with the conductive material layer can be used to remove the core protective layer. Specifically, the light-emitting end 1102 of the excitation optical fiber 110 can be soaked in acetone, so that the core protective layer (polymer microspheres) is dissolved, and the part of the conductive material layer disposed on the core protective layer (part of the metal coating) is peeled off to obtain the conductive connection layer 130.

[0226] It can be understood that the core protective layer can be used to make the orthographic projection of the conductive connection layer 130 on the end face 11021 of the light-emitting end 1102 not coincide with the orthographic projection of the core 111 of the excitation optical fiber 110 on the end face 11021 of the light-emitting end 1102, so that the laser transmitted in the core 111 of the excitation optical fiber 110 can better interact with the electron excitation layer 121 covering the core 111 of the excitation optical fiber 110.

[0227] In some embodiments, please refer to Figure 15 , the step S220 of forming the electron excitation layer 121 on the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110 specifically includes the following steps. Specifically, the specific steps of transferring the electron excitation layer 121 on the temporary substrate 20 to the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110 are as follows:

[0228] S221. Set the end face 11021 of the light output end 1102 of the excitation optical fiber 110 and the electron excitation layer 121 opposite to each other and parallel to each other in the first direction.

[0229] Specifically, observe the end face 11021 of the light output end 1102 of the excitation optical fiber 110 and the electron excitation layer 121 under a microscope, and set the electron excitation layer 121 and the end face 11021 of the light output end 1102 of the excitation optical fiber 110 opposite to each other and parallel to each other in the first direction, and make the center connection line of the two extend in the first direction.

[0230] S222. Drive the excitation optical fiber 110 to move in the first direction to contact the electron excitation layer 121.

[0231] S223. Make the electron excitation layer 121 adhere to the end face 11021 of the light output end 1102 of the excitation optical fiber 110 at a preset temperature.

[0232] In this way, the center of the electron excitation layer 121 can be aligned with the center of the end face 11021 of the light output end 1102 of the excitation optical fiber 110 by using a microscope, and the two are adhered to each other at a certain temperature, so that the electron excitation layer 121 and the end face 11021 of the light output end 1102 of the excitation optical fiber 110 can be closely adhered under the action of van der Waals force, improving the bonding fastness of the electron excitation layer 121 on the excitation optical fiber 110, and also facilitating the electron excitation layer 121 to completely cover the core 111 of the excitation optical fiber 110, so that the laser transmitted by the core 111 can better interact with the electron excitation layer 121.

[0233] In some specific embodiments, the step S220 of forming the electron excitation layer 121 on the end face 11021 of the light output end 1102 of the excitation optical fiber 110 specifically includes the following steps. Specifically, the specific steps of transferring the electron excitation layer 121 on the temporary substrate 20 to the end face 11021 of the light output end 1102 of the excitation optical fiber 110 are as follows:

[0234] S2201. Stick a circular heating sheet 40 on the back of the perforated glass slide 30 of the microscope, fix the temporary substrate 20 with the electron excitation layer 121 on the bottom side of the circular heating sheet 40 (the temporary substrate 20 can be fixed on the bottom side of the circular heating sheet 40 by an adhesive fixing method), and make the electron excitation layer 121 on the temporary substrate 20 face downward, and fix the excitation optical fiber 110 below the electron excitation layer 121, so that the central axis of the objective lens of the microscope, the central axis of the perforated glass slide 30, the central axis of the circular heating sheet 40, the center of the electron excitation layer 121 and the center of the core 111 coincide, and the objective lens of the microscope, the perforated glass slide 30, the circular heating sheet 40, the electron excitation layer 121 and the excitation optical fiber 110 are arranged in sequence from top to bottom.

[0235] Optionally, a fixture can be used to fix the excitation optical fiber 110 on the moving platform, and the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110 is arranged upward. The moving platform is used to adjust the position of the excitation optical fiber 110 in the first direction, and to adjust the angle of the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110 relative to the horizontal plane to make it horizontally arranged.

[0236] Optionally, the fixture can be a pneumatic gripper or an electric gripper.

[0237] Optionally, the moving platform can be a six-degree-of-freedom platform. The moving platform can also include a linear drive mechanism and a rotary drive mechanism connected to the linear drive mechanism. The output end of the rotary drive mechanism is connected to the fixture to drive the fixture and the excitation optical fiber 110 clamped by the fixture to rotate around an axis parallel to the horizontal plane, so that the end face 11021 of the light-emitting end 1102 is horizontally arranged. The linear drive mechanism is used to drive the rotary drive mechanism, the fixture and the excitation optical fiber 110 to move in the first direction.

[0238] Wherein, the linear drive mechanism can be a motor or a cylinder, and the rotary drive mechanism can be a motor or a rotary cylinder.

[0239] S2202. Observe the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110 and the electron excitation layer 121 under a microscope, and arrange the electron excitation layer 121 and the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110 to be opposite and parallel to each other in the first direction, and make the center connection line of the two extend in the first direction.

[0240] The center alignment of the end face 11021 of the light-emitting end 1102 and the electron excitation layer 121 can be completed with the aid of a microscope.

[0241] S2203. Connect the annular heating sheet 40 to an external power supply to apply a first preset voltage to the annular heating sheet 40, and preheat the electron excitation layer 121 on the temporary substrate 20 (heat it to the preheating temperature), which is beneficial to make the electron excitation layer 121 flatter.

[0242] Optionally, the first preset voltage is 1V - 1.5V, and the preheating temperature is 50 - 60°C.

[0243] S2204. Drive the excitation optical fiber 110 to move in the first direction to contact the electron excitation layer 121. It can make the end face 11021 of the light-emitting end 1102 and the electron excitation layer 121 contact to form Newton's rings.

[0244] S2205. At a preset temperature, closely attach the electron excitation layer 121 to the end face 11021 of the light output end 1102 of the excitation optical fiber 110. Specifically, apply a second preset voltage to the annular heating sheet 40, and heat the electron excitation layer 121 on the temporary substrate 20 to the preset temperature, which is beneficial for the electron excitation layer 121 to be more closely disposed on the end face 11021 of the light output end 1102.

[0245] Optionally, the second preset voltage is 2.5V - 4V, and the preset temperature is 90 - 100 °C.

[0246] S2206. Remove the temporary substrate 20. The temporary substrate 20 can be removed by a method combining melting heating and solvent immersion. Specifically, apply a third preset voltage to the annular heating sheet 40, and heat the temporary substrate 20 to the melting temperature until it melts. It should be noted that the melting point of the electron excitation layer 121 is much higher than that of the temporary substrate 20.

[0247] Optionally, the third preset voltage is 5.5V - 6V, and the melting temperature is 130 - 150 °C.

[0248] After the electron excitation layer 121 is closely disposed on the end face 11021 of the light output end 1102, the part of the temporary substrate 20 in contact with the annular heating sheet 40 can be melted by melting heating, and the electron excitation layer 121 can be separated from the annular heating sheet 40 and closely attached to the end face 11021 of the light output end 1102 of the excitation optical fiber 110, which is convenient for subsequent removal of the temporary substrate 20 remaining on the electron excitation layer 121. The part of the temporary substrate 20 not in contact with the annular heating sheet 40 remains on the electron excitation layer 121. The excitation optical fiber 110 can be removed from the fixture and the light output end 1102 of the excitation optical fiber 110 can be immersed in acetone to dissolve the temporary substrate 20 remaining on the electron excitation layer 121 and completely remove the temporary substrate 20.

[0249] The following will describe the implementation scheme of the present invention in detail in conjunction with embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. For the experimental methods without specific conditions in the following embodiments, the guidance given in the present invention is preferably referred to, and it can also be in accordance with the experimental manuals or conventional conditions in the art, or in accordance with the conditions recommended by the manufacturer, or refer to the experimental methods known in the art.

[0250] Example 1

[0251] The excitation optical fiber 110 is a single-mode optical fiber. The diameter of the core 111 of the excitation optical fiber 110 is 8.2 μm, the diameter of the excitation optical fiber 110 is 125 μm, the angle ɑ is selected as 30 degrees, that is, the bevel angle of the excitation optical fiber 110 forms a 30-degree angle with the axis of the excitation optical fiber 110, and the wavelength of the laser transmitted in the excitation optical fiber 110 is 1550 nm. The conductive connection layer 130 includes 5 nm of titanium and 60 nm of gold laminated on the excitation optical fiber 110. Among them, the core 111 at the end face 11021 of the light output end 1102 is exposed (without being covered by the conductive connection layer 130). The electron excitation layer 121 is made of graphene two-dimensional material (the thickness of the graphene two-dimensional material is 1 nm). The shape of the graphene two-dimensional material is not limited and can be polygonal, circular, elliptical, etc. The electron excitation layer 121 is disposed on the end face 11021 of the light output end 1102 of the excitation optical fiber 110 and completely covers the core 111 of the excitation optical fiber 110. For example, in the radial direction of the excitation optical fiber 110, the size of the electron excitation layer 121 is 30 - 60 μm (much larger than the diameter of the core 111). In this embodiment, in the radial direction of the excitation optical fiber 110, the size of the electron excitation layer 121 is 50 μm.

[0252] Example 2

[0253] The excitation optical fiber 110 is a single-mode optical fiber. The diameter of the core 111 of the excitation optical fiber 110 is 8.2 μm, the diameter of the excitation optical fiber 110 is 125 μm, and the wavelength of the laser transmitted in the excitation optical fiber 110 is 1550 nm. The conductive connection layer 130 includes 5 nm of titanium and 60 nm of gold laminated on the excitation optical fiber 110. Among them, the core 111 at the light output end 1102 is exposed (without being covered by the conductive connection layer 130). The electron excitation layer 121 is made of graphene two-dimensional material (the thickness of the graphene two-dimensional material is 1 nm). The shape of the graphene two-dimensional material is not limited and can be polygonal, circular, elliptical, etc. The electron excitation layer 121 is disposed on the end face 11021 of the light output end 1102 of the excitation optical fiber 110 and completely covers the core 111 of the excitation optical fiber 110. For example, in the radial direction of the excitation optical fiber 110, the size of the electron excitation layer 121 is 30 - 60 μm (much larger than the diameter of the core 111). In this embodiment, in the radial direction of the excitation optical fiber 110, the size of the electron excitation layer 121 is 40 μm.

[0254] Example 3

[0255] The excitation optical fiber 110 is a single-mode optical fiber. The core 111 of the excitation optical fiber 110 has a diameter of 8.2 μm, the diameter of the excitation optical fiber 110 is 125 μm, and the wavelength of the laser transmitted in the excitation optical fiber 110 is 1550 nm. The above-mentioned conductive connection layer 130 is formed on the outer surface of the excitation optical fiber 110. The conductive connection layer 130 includes 5 nm of titanium and 50 nm of gold laminated on the light-emitting end 1102 of the excitation optical fiber 110. Among them, the core 111 at the light-emitting end 1102 is exposed (not covered by the conductive connection layer 130). An auxiliary layer 122 with a thickness of 1 nm and made of graphene is deposited on the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110; then a plurality of nanotubes are deposited on the auxiliary layer 122, and the axial direction of the nanotubes is parallel to the extension direction of the core 111 to obtain an electron excitation layer 121, and then an electron source 100 is obtained. Among them, the first conductive part 131 of the conductive connection layer 130 is arranged on the end face 11021 of the light-emitting end 1102 of the excitation optical fiber 110 and overlaps with the auxiliary layer 122, and the second conductive part 132 of the conductive connection layer 130 is arranged on the outer peripheral surface of the excitation optical fiber 110.

[0256] Comparative Example 1

[0257] The electron source 100 was prepared according to the structure of Example 1, except that the electron excitation layer 121 in Example 1 was replaced with a gold layer with a thickness of 100 nm, and the gold layer was prepared by deposition.

[0258] Comparative Example 2

[0259] The electron source 100 was prepared according to the structure of Comparative Example 1, except that the electron excitation layer 121 in Comparative Example 1 was replaced with a gold layer with a thickness of 1 nm.

[0260] The electron source 100 was prepared using the above-mentioned examples and comparative examples, and the performance of the prepared electron source 100 was tested. The test results are as follows in the table:

[0261] Table 1

[0262]

[0263]

[0264] Among them, stability refers to when the excitation power of the electron source 100 is 50% or more of the damage power, the vacuum degree is 2X10 -5 Pa, and the continuous emission current is 1 hour. After removing the bad points, the ratio of the difference between the maximum current and the minimum current to the average current is the stability, and the stability can reflect the working stability of the electron source 100. Lifetime refers to when the excitation power of the electron source 100 is 50% or more of the damage power, the vacuum degree is 2X10 -5Pa, continuously emit current until the current decays to less than 10% of the initial value, which is defined as the lifetime. The operating vacuum degree refers to the continuous emission current when the excitation power of the electron source 100 is 50% or more of the damage power. The vacuum degree is gradually increased until a rapid decay of the current occurs (the rapid decay is defined as the current decaying by more than 50% within 1 minute). The vacuum degree at this time is defined as the operating vacuum degree. It can be seen from the above table that: the electron source 100 of the present application has good stability, a long lifetime, and a good operating vacuum degree.

[0265] In the present application, low-dimensional materials such as zero-dimensional materials, one-dimensional materials, and two-dimensional materials have atomic-scale sizes. Electrons incident from the back can be emitted into the vacuum without passing through in-body transmission, which is very suitable for an ultrafast electron source with a narrow pulse width; moreover, low-dimensional materials and different types of optical fibers can be directly integrated, bringing ultra-high stability and integration; in addition, low-dimensional materials have no dangling bonds, are stable, have a high melting point, and are not easily damaged, making them suitable for a large-beam electron source with high-power excitation; low-dimensional materials and a tip can be integrated to obtain a very sharp optical fiber tip, which has large optical field and electric field enhancement factors and provides a large emission beam current; there are many combinations of low-dimensional materials, making them suitable for optoelectronic sources with various properties. Finally, the optical fiber integrated with a low-dimensional material electron source and the low-dimensional material integration have significant advantages. The optical fiber can not only transmit laser light, but also, as a carrier of the low-dimensional material, provide a stable excitation source with adjustable wavelength, polarization, and optical mode, can be applied to different application scenarios, and does not require a complex optical path. It has the characteristics of small volume and high integration. When integrated with other devices, it can achieve stable integration without cracking and modifying the vacuum electronic device.

[0266] The setting of forming an electron beam by the pulsed laser exciting the electron excitation layer 121 in the present application abandons the complex spatial light coupling structure set due to the introduction of external laser light, making the four-dimensional electron microscope 10 less affected by the environment, having a stable-excited electron beam, and thus being able to improve the scanning stability of the sample 5 to be measured. In addition, the electron source 100 of the present application uses a low-dimensional material as the material for emitting electrons. Since the electron excitation layer 121 has a strong light-matter interaction and a rich electron bandgap, the pulsed laser can better interact with the electron excitation layer 121 to excite the electrons in the electron excitation layer 121, and the electrons tunneling and emitting from the electron excitation layer 121 have the characteristics of small energy dispersion, high brightness, and high stability. Moreover, in the present application, an electron beam with pulsed properties can be formed by exciting the electron excitation layer 121 with a pulsed laser, without opening an additional window on the electron microscope to provide a pulsed electron beam, without damaging the electron microscope cavity, facilitating miniaturization design, and by modulating the pulsed laser through the electron optical component 3, the electron beam excited by it can be modulated, thereby reducing the impact on the scanning quality when modulating the electron beam, and thus being able to stably scan the sample 5 to be measured.

[0267] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as falling within the scope described in this specification.

[0268] The above-described embodiments only express several implementation manners of the present application, and the description thereof is relatively specific and detailed. However, it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A four-dimensional electron microscope for scanning a sample, characterized in that, The four-dimensional electron microscope includes: a light source assembly for emitting pulsed laser light; an electron source including an excitation optical fiber coupled to the light source assembly and an electron emission layer. The electron emission layer at least includes an electron excitation layer, and the electron excitation layer is disposed on the light-emitting path of the pulsed laser light emitted by the excitation optical fiber so that the electron excitation layer can emit an electron beam under the excitation of the pulsed laser light. The electron excitation layer includes at least one of a zero-dimensional material, a one-dimensional material, and a two-dimensional material; an electron optical assembly disposed on the electron beam emission side of the electron source, and the electron optical assembly is used to adjust the deflection direction of the electron beam so that the electron beam is incident on the sample; and a detector disposed on one side of the sample for collecting reflected electron signals of the electron beam incident on the sample or transmitted electron signals of the electron beam penetrating the sample.

2. The four-dimensional electron microscope according to claim 1, wherein The light source assembly includes a light source and a first optical fiber. The light source is coupled to one end of the first optical fiber, and the excitation optical fiber is connected to the other end of the first optical fiber; The light source is used to emit the pulsed laser light, and the first optical fiber is used to transmit the pulsed laser light emitted by the light source to the excitation optical fiber.

3. The four-dimensional electron microscope according to claim 2, wherein, The light source assembly further includes a first optical fiber beam splitter, a second optical fiber, and a first optical fiber delay line; The first optical fiber beam splitter has a first input end coupled to the light source and a first output end opposite to the first input end. The first output end is respectively connected to the first optical fiber and the second optical fiber; One end of the second optical fiber away from the first optical fiber beam splitter extends toward the sample; The first optical fiber delay line is coupled to the second optical fiber to perform time delay on the light beam propagating in the second optical fiber.

4. The four-dimensional electron microscope according to claim 3, wherein, The reflected electron signal includes a secondary electron signal or a backscattered electron signal; The sample has an incident surface disposed opposite to the electron beam emission side of the electron source; The detector includes a backscattered electron detector or a secondary electron detector. The backscattered electron detector or the secondary electron detector is used to face the incident surface of the sample so that the secondary electron detector receives the secondary electron signal or the backscattered electron detector receives the backscattered electron signal.

5. The four-dimensional electron microscope according to claim 2, characterized in that, The reflected electron signal includes a cathodoluminescence signal; The sample has an incident surface disposed opposite to the electron beam emission side of the electron source; The detector includes a cathodoluminescence analysis system. The cathodoluminescence analysis system is used to face the incident surface of the sample to receive the cathodoluminescence signal.

6. The four-dimensional electron microscope according to claim 2, wherein The sample has an incident surface disposed opposite to the electron beam emission side of the electron source and an exit surface opposite to the incident surface; The detector includes a receiving screen. The receiving screen is used to face the exit surface of the sample to receive the electron beam penetrating the sample.

7. The four-dimensional electron microscope according to claim 6, characterized in that, The light source assembly further includes a second optical fiber beam splitter, a third optical fiber, and a second optical fiber delay line; The second optical fiber beam splitter has a second input end coupled to the light source and a second output end opposite to the second input end. The second output end is respectively connected to the first optical fiber and the third optical fiber; One end of the third optical fiber away from the second optical fiber splitter extends towards the sample. The second optical fiber delay line is coupled to the third optical fiber and is configured to perform time delay on the light beam propagating in the third optical fiber.

8. The four-dimensional electron microscope according to any one of claims 1-7, characterized in that, The four-dimensional electron microscope further includes a housing. The housing has a vacuum chamber, and the electron source and the electron optical component are sequentially arranged in the vacuum chamber. An opening communicating with the vacuum chamber is provided on the housing, and the light incident end of the excitation optical fiber of the electron source is exposed through the opening and is coupled to the light source component.

9. The four-dimensional electron microscope according to claim 8, characterized in that, The outer peripheral wall of the excitation optical fiber is sealingly connected to the inner side wall of the opening.

10. The four-dimensional electron microscope according to any one of claims 1-9, characterized in that, The excitation optical fiber includes a core for transmitting laser light and a cladding layer wrapping the core, and the end face of the light output end of the excitation optical fiber is arranged at an angle with the extending direction of the core. The electron emission layer is arranged on the end face of the light output end of the excitation optical fiber, and the electron excitation layer covers the core of the excitation optical fiber. The pulsed laser light emitted from the core can directly irradiate on the electron emission layer, so that the electron excitation layer is excited by the pulsed laser light emitted from the core and emits electrons.

11. The four-dimensional electron microscope according to any one of claims 1-9, characterized in that, The excitation optical fiber includes a core for transmitting laser light and a cladding layer wrapping the core. A light leakage notch is formed in the radial direction of the excitation optical fiber at the light output end of the excitation optical fiber. The electron excitation layer is arranged on the bottom wall surface of the light leakage notch. The bottom wall surface of the light leakage notch is configured as a plane, and the projection of the electron excitation layer on the bottom wall surface covers the projection of the core on the bottom wall surface. The electron excitation layer further extends to the light output end of the optical fiber.

12. The four-dimensional electron microscope according to any one of claims 1-9, characterized in that, The excitation optical fiber is configured as a perforated optical fiber, and the perforated optical fiber has a light guiding hole. The electron excitation layer is at least arranged on the side wall of the light guiding hole and extends to the light output end of the excitation optical fiber along the longitudinal extension direction of the light guiding hole.

13. The four-dimensional electron microscope according to any one of claims 1-9, characterized in that, The excitation optical fiber is configured as a perforated optical fiber, and the perforated optical fiber has a light guiding hole. The electron emission layer is arranged on the end face of the light output end of the perforated optical fiber, and the electron excitation layer covers one end of the light guiding hole located at the end face of the light output end. The pulsed laser light emitted from the perforated optical fiber can directly irradiate on the electron emission layer, so that the electron excitation layer is excited by the pulsed laser light emitted from the perforated optical fiber and emits electrons.

14. The four-dimensional electron microscope according to any one of claims 1-9, characterized in that, The light output end of the excitation optical fiber is provided with a pointed end portion. The electron excitation layer covers the surface of the pointed end portion of the excitation optical fiber. The excitation optical fiber includes a core for transmitting pulsed laser light. The pulsed laser light emitted from the core can directly irradiate on the electron emission layer, so that the electron excitation layer is excited by the pulsed laser light emitted from the core and emits electrons.

15. The four-dimensional electron microscope according to any one of claims 10-14, characterized in that, The electron source further includes a conductive connection layer, and the conductive connection layer is arranged on the excitation optical fiber and is electrically connected to the electron excitation layer.

16. The four-dimensional electron microscope according to any one of claims 1-15, characterized in that, The electron source further includes an anode, the anode has a first electron channel, and the electron optical component has a second electron channel communicating with the first electron channel. A preset electric field exists between the anode and the electron excitation layer, and the electron beam can pass through the first electron channel and the second electron channel under the drive of the preset electric field and be incident on the sample.

17. The four-dimensional electron microscope according to claim 1, wherein The thickness of the electron excitation layer is less than or equal to 50 nm.

18. The four-dimensional electron microscope according to claim 1, wherein The included angle between the axial direction of the one-dimensional material in the electron excitation layer and the emission direction of the pulsed laser is 0 to 90°.

19. The four-dimensional electron microscope according to claim 1, wherein, The electron excitation layer includes at least two two-dimensional materials stacked in sequence along the emission direction of the pulsed laser; or The electron excitation layer includes at least two two-dimensional materials with different materials connected to each other on the same plane.

20. The four-dimensional electron microscope according to claim 1, characterized in that, The electron excitation layer includes zero-dimensional materials and zero-dimensional materials disposed at the ends and / or sides of the one-dimensional materials.

21. The four-dimensional electron microscope according to claim 1, wherein The electron excitation layer includes zero-dimensional materials and two-dimensional materials, and the zero-dimensional materials are disposed on the surfaces of the two-dimensional materials.

22. The four-dimensional electron microscope according to claim 1, characterized in that, The electron excitation layer includes one-dimensional materials and two-dimensional materials, and the one-dimensional materials are disposed on the surfaces of the two-dimensional materials.

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