Method for in-situ preparation of crystal electron source based on transmission electron microscope

Abstract

The invention relates to the technical field of field emission electron sources, and discloses a method for in-situ preparation of a crystal electron source based on a transmission electron microscope. According to the method provided by the invention, in the TEM high-vacuum chamber, in-situ controllable physical or electric heating excitation is carried out on the cathode material by using the nano-hand, so that single-crystal or polycrystal nano-particles with clear sizes, shapes and crystal structures can be controllably prepared in a specific area on the surface of the cathode material; surface pollutants are also removed in the process, so that the preparation is clean; after preparation is completed, in-situ field emission testing can be carried out immediately, it is ensured that the tested performance is intrinsic performance of the cathode material and an ideal structure, and performance degradation caused by disjunction of preparation, transfer and testing links in a traditional method is thoroughly avoided; by utilizing the method, the high-reliability electron source with an ideal nano structure, a clean surface and excellent field emission performance can be directly produced, and the conversion efficiency and the reliability of the high-performance electron source from laboratory research to tip instrument commercialization are greatly promoted.

Description

Technical Field

[0001] This invention relates to the field of field emission electron source technology, and in particular to a method for in-situ preparation of crystal electron sources based on transmission electron microscopy. Background Technology

[0002] As a core component of modern cutting-edge electron optical instruments, the performance of field emission electron sources directly determines the performance boundaries of scanning electron microscopes (SEM), transmission electron microscopes (TEM), and a series of electron beam-based micro- and nano-devices and devices. In electron microscopy, the quality of the electron source directly affects the resolution, contrast, and stability of the image. An ideal field emission cathode not only requires the material itself to have low work function characteristics, but more importantly, the cathode surface must possess a nanoscale sharp protrusion structure capable of generating an extremely high local electric field enhancement factor (β). The electric field enhancement factor describes the amplification effect of the cathode surface geometry on the electric field. Nanoscale sharp protrusions can significantly increase the β value, thereby inducing a strong electron tunneling effect under a relatively low average macroscopic electric field, achieving stable, high-brightness, high-coherence, and low-dispersion electron beam emission. Furthermore, field emission performance is extremely sensitive to the state of the cathode surface. Surface contaminants (such as adsorbed gas molecules, oxides, or hydrocarbons) can significantly increase the effective work function, cause drastic fluctuations in the emission current, and even lead to premature cathode failure. Therefore, the optimal performance of a cathode is a combination of intrinsic material properties, geometric structure, and surface cleanliness.

[0003] To construct structures on the cathode surface that significantly enhance emission performance, the main fabrication techniques currently employed in the field of field emission electron sources include chemical vapor deposition (CVD), focused ion beam cutting (FID), and arc discharge (ACD). CVD is a method for growing nanostructures on a substrate through gas-phase reactions. Specifically, a precursor gas is introduced into a specific substrate, reacting at high temperatures to generate carbon nanotubes or semiconductor nanowire arrays, which are then subsequently transferred and assembled onto the cathode holder. This method can produce nanostructures with high aspect ratios, but it is difficult to achieve targeted growth on the already formed cathode tip, and the growth process is affected by various factors such as temperature, gas flow rate, and catalyst, leading to uncontrollable size, morphology, and distribution of the nanostructures. Furthermore, the transfer and assembly processes may introduce mechanical stress, contamination, or damage, thus affecting cathode performance. FID is a technique that uses a high-energy ion beam to precisely cut bulk cathode materials (such as tungsten) at the nanoscale to directly sculpt a tapered tip. This method can achieve high precision, but ion beam bombardment can cause surface damage, lattice defects, and redeposited material. These defects can act as electron scattering centers, reducing emission efficiency. Furthermore, focused ion beam equipment is expensive, complex to operate, and has low processing efficiency, making it unsuitable for large-scale production. Arc discharge, on the other hand, generates instantaneous high-temperature plasma by applying a high voltage between two electrodes, randomly depositing nanoparticles or disordered carbon nanofilms on the cathode surface. This method is simple and fast, but the resulting nanoparticles have uncontrollable size and random positions, lacking repeatability. In addition, the arc process can introduce impurities and contamination, leading to instability on the cathode surface.

[0004] Furthermore, because the cathode fabrication process is disconnected from in-situ TEM testing, researchers cannot observe the dynamic evolution of the cathode from its initial state to its high-performance state. Moreover, during the transfer, assembly, or testing of the cathode after fabrication, its active surface is inevitably exposed to a non-ideal environment, introducing secondary contamination, mechanical stress, or structural damage. These introduced interference variables mean that the final measured field emission performance is not the intrinsic performance of the cathode material and structure, but rather a composite result of multiple negative factors. Therefore, cathodes fabricated using existing techniques suffer from the negative impact of the fabrication process and cannot be directly used as high-performance, high-reliability commercial electron sources, significantly limiting the efficiency of converting laboratory materials into core components of cutting-edge instruments. Summary of the Invention

[0005] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, one objective of the present invention is to provide a method for in-situ preparation of a crystal electron source based on transmission electron microscopy.

[0006] The second objective of this invention is to provide a crystal electron source.

[0007] A third objective of this invention is to provide a system for a method of in-situ preparation of crystal electron sources based on transmission electron microscopy.

[0008] The fourth objective of this invention is to provide an application of this method for in-situ preparation of crystal electron sources based on transmission electron microscopy.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a method for in-situ preparation of a crystal electron source based on transmission electron microscopy, comprising the following steps: S1. Load the cathode material onto the sample holder of the transmission electron microscope and transfer it to the vacuum chamber. Under the real-time observation of the transmission electron microscope, select the crystal particle forming area. S2. Manipulate the piezoelectric ceramic nanohand to move so that the nanoneedle tip at its end approaches the surface of the single crystal particle forming region, and then physically contact and / or electrothermal excite the crystal particle forming region to form single crystal or polycrystalline nanoparticles. S3. In the transmission electron microscope, the field emission performance of the cathode material having the single crystal or polycrystalline nanoparticles is tested in situ.

[0010] In some embodiments of the present invention, the cathode material comprises lanthanum hexaboride crystal.

[0011] In some embodiments of the present invention, the material of the nanoneedle tip is selected from one of the following: high-hardness elemental metals or their alloys, carbon-based materials, silicon-based materials, ceramic materials, and smart and functional materials.

[0012] In some embodiments of the present invention, the high-hardness elemental metal or its alloy material is selected from tungsten, chromium, titanium, iron, zirconium, osmium, vanadium, molybdenum, or an alloy composed of the above-mentioned elemental metals.

[0013] In some embodiments of the present invention, the carbon-based material is selected from diamond, diamond-like carbon materials, graphene, carbon nanotubes, and metal carbides.

[0014] In some preferred embodiments of the present invention, the metal carbide is selected from hafnium carbide, tantalum carbide, and tungsten carbide.

[0015] In some embodiments of the present invention, the silicon-based material is selected from one of monocrystalline silicon, polycrystalline silicon, silicon dioxide, silicon carbide, and silicon nitride.

[0016] In some embodiments of the present invention, the ceramic material is selected from boron nitride, rare earth compounds, and metal oxide ceramic materials.

[0017] In some preferred embodiments of the present invention, the rare earth compound is selected from lanthanum hexaboride and cerium hexaboride.

[0018] In some preferred embodiments of the present invention, the metal oxide ceramic material is selected from one of alumina, zirconium oxide, and lanthanum oxide.

[0019] In some embodiments of the present invention, the intelligent and functional material is selected from shape memory alloys and piezoelectric materials.

[0020] In some preferred embodiments of the present invention, the shape memory alloy comprises nickel-titanium alloy.

[0021] In some preferred embodiments of the present invention, the piezoelectric material is selected from zinc oxide and lead zirconate titanate.

[0022] In some embodiments of the present invention, the radius of curvature of the nanoneedle tip is less than 5 μm.

[0023] In some embodiments of the present invention, after the nanoneedle tip approaches the surface of the crystal particle forming region to a spacing of 400-600 nm, it begins to physically contact and / or electrothermal stimulate the crystal particle forming region.

[0024] In some embodiments of the present invention, the physical contact includes at least one of impact, friction, and scratching.

[0025] In some embodiments of the present invention, when the physical contact is an impact, the magnitude of the impact force is adjusted by controlling the displacement accuracy of the nanoneedle tip; wherein, a displacement accuracy of 10-1000nm is a high-force impact, and a displacement accuracy of less than 10nm is a low-force impact.

[0026] In some embodiments of the present invention, the completion of a single impact is determined by real-time monitoring of the contrast change in the transmission electron microscope image of the cathode material; a significant change in contrast indicates that the impact is complete.

[0027] In some embodiments of the present invention, the electrothermal excitation includes at least one of Joule heating and field evaporation.

[0028] In some embodiments of the present invention, the Joule heating is achieved by applying a scanning voltage ranging from ±100nV to ±140V, and the heating time is 0.1ms-3600s.

[0029] In some embodiments of the present invention, the crystal particle forming region is monitored in real time by an electron beam from a transmission electron microscope, and it is determined whether a crystal particle with a prominent morphology is formed in the region based on real-time imaging or diffraction signals. When a single crystal or polycrystalline nanoparticle with a prominent morphology is formed in the region, the preparation is completed.

[0030] A second aspect of the present invention provides a crystal electron source, comprising a source prepared using the method described in the first aspect of the present invention.

[0031] In some embodiments of the present invention, the surface of the emitting end of the crystal electron source has single-crystal or polycrystalline nanoparticles with a size of 1-50 nm.

[0032] A third aspect of the present invention provides a system for the method of in-situ preparation of a crystal electron source based on transmission electron microscopy as described in the first aspect of the present invention, comprising: The main body of a transmission electron microscope, including a vacuum chamber; A sample rod is used to load cathode material and transfer it into the vacuum chamber; A piezoelectric ceramic nanohand is integrated onto the sample rod, with a three-dimensionally movable nanoneedle tip at its end; The excitation unit is electrically connected to the piezoelectric ceramic nanohand and the cathode material, and is used to apply controllable electrothermal excitation to the contact area between the nanoneedle tip and the cathode material. A control unit, connected to the piezoelectric ceramic nanohand, is used to drive the nanohand to move and control the displacement accuracy; The monitoring unit is used to monitor the crystal particle forming area in real time using the electron beam of the transmission electron microscope. The field emission test unit is electrically connected to the cathode material and is used to apply a test voltage and collect the emission current to characterize the field emission performance of the cathode material with single-crystal or polycrystalline nanoparticles.

[0033] The fourth aspect of the present invention provides the application of the method for in-situ preparation of crystal electron sources based on transmission electron microscopy as described in the first aspect of the present invention in the preparation of field emission cathodes, thermionic emission cathodes, Schottky cathodes, and photoemission cathode electron sources.

[0034] The basic principles of this invention are explained as follows: The present invention provides a method for in-situ preparation of a crystal electron source based on transmission electron microscopy (TEM). The entire process is carried out within a TEM vacuum chamber. The high-resolution electron beam enables real-time and clear observation of the initial surface morphology of the cathode material, ensuring accurate identification and positioning of the specific region most suitable for modification and field emission testing. After selecting the target region, a controllable localized excitation is applied to the positioned target region by precisely manipulating a piezoelectric ceramic nanohand integrated on the sample holder, including: (1) Physical contact: The nanoneedle tip of the piezoelectric ceramic nanohand impacts or rubs the cathode material surface with controllable force, injecting mechanical energy into the cathode material surface. Through plastic deformation, material peeling or extrusion, the original flat structure is destroyed at the atomic scale, inducing the material to reconstruct and recrystallize, thereby forming nanoscale protrusions. Real-time TEM imaging is used to determine whether the expected contrast change has occurred. When the contrast changes significantly, it indicates that the morphology has changed. Physical contact is especially suitable for cathode materials with high hardness. Different displacement precisions are used for impact according to different materials with different hardness to control the magnitude of the impact force. Under large step displacement (10-1000nm), the acceleration is higher and the impact force is larger. Conversely, under small step displacement (less than 10nm), the impact force is smaller. (2) Electrothermal excitation: The nanoneedle tip is brought into contact with the surface of the cathode material and a scanning Joule heating current is applied. When the current passes through the nanoscale point with huge contact resistance, highly localized Joule heat is generated. This instantaneous high temperature can rapidly melt and spheroidize the material at the contact point and its surroundings, and rapidly cool and recrystallize after the heat source is removed, thereby forming discrete, well-crystallized nanoparticles. During the preparation process, after each operation (physical contact or electrothermal excitation), TEM imaging mode (to observe whether convex contrast appears) or diffraction mode (to verify whether diffraction spots are formed) is immediately used to determine whether the crystal particles have been successfully formed. This ensures that the process can be stopped the instant the ideal structure is reached, avoiding over-processing and guaranteeing the success rate and consistency of the preparation. In addition, physical impact can peel off the surface contaminant layer to a certain extent, while the high temperature of Joule heating can effectively evaporate or decompose the adsorbates and oxide layers on the surface, achieving cleanliness during preparation. Subsequently, under the premise of completely avoiding secondary contamination and structural damage, in-situ field emission tests are immediately performed on the freshly prepared single-crystal or polycrystalline nanoparticles in their cleanest and most active state. This directly and realistically reflects the intrinsic field emission performance of the single-crystal or polycrystalline nanoparticles themselves, thereby directly establishing the structure-property relationship between microstructure and emission performance.

[0035] Compared with the prior art, the beneficial effects of the present invention are: The present invention provides a method for in-situ preparation of crystal electron sources based on transmission electron microscopy (TEM). This method utilizes nano-hands to perform in-situ controllable physical or electrothermal excitation on the cathode material within a high-vacuum TEM chamber, allowing for the controlled preparation of single-crystal or polycrystalline nanoparticles with well-defined sizes, morphologies, and crystal structures in specific regions of the cathode surface. This process simultaneously removes surface contaminants, achieving clean preparation. After preparation, in-situ field emission testing can be performed immediately, ensuring that the measured performance reflects the intrinsic characteristics of the cathode material and its ideal structure. This completely avoids the performance degradation caused by the disconnect between preparation, transfer, and testing in traditional methods. This method can directly produce highly reliable electron sources that combine ideal nanostructures, clean surfaces, and excellent field emission performance, greatly promoting the efficiency and reliability of high-performance electron sources from laboratory research to the commercialization of cutting-edge instruments. Attached Figure Description

[0036] Figure 1 These are schematic diagrams of the operating system structure based on transmission electron microscopy in Examples 1 and 2; Figure 2 This is a schematic diagram of the process for preparing the crystal electron source in Examples 1 and 2; Figure 3 The initial TEM characterization image of the lanthanum hexaboride bulk sample in Example 1; Figure 4 The characterization results were obtained at different stages of the preparation process in Example 1; Figure 5 Comparison of TEM characterization results of single-crystal nanoparticles prepared on the surface of lanthanum hexaboride nanocone samples in Example 2; Figure 6 The in-situ field emission test IV curve of the largest single-crystal nanoparticle on the tip of the lanthanum hexaboride nanocone sample in Example 2; Figure 7 The in-situ field emission (FN) curve of the largest single-crystal nanoparticle at the tip of the lanthanum hexaboride nanocone sample in Example 2 is shown. Detailed Implementation

[0037] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments can be obtained from conventional commercial sources or by existing technical methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0038] Example 1 In this embodiment, a polycrystalline electron source is prepared. The preparation process is carried out in an operating system based on transmission electron microscopy. The TEM in-situ electrical sample rod and its field emission testing system are used. The operation is carried out in the vacuum chamber of a high-resolution transmission electron microscope. The tungsten nanoneedle tip prepared by electrochemical etching is assembled into its three-dimensional movable end to form a nanohand.

[0039] The specific preparation steps are as follows: S11. The (100) oriented lanthanum hexaboride bulk sample prepared by focused ion beam cutting is loaded onto an in-situ electrical sample rod and inserted into the vacuum cavity of a transmission electron microscope. The lanthanum hexaboride bulk sample is initially characterized, and the crystal grain forming region is selected under real-time observation of the transmission electron microscope. S21. Manipulate the movement of the piezoelectric ceramic nanohand so that the tungsten nanoneedle tip at its end approaches the surface of the crystal particle forming region until the distance between the two is about 500nm. S22. Manipulate the piezoelectric ceramic nanohand to impact and rub the surface of the crystal particle forming region, while applying Joule heating current. The heating scanning voltage is ±2V and the scanning time is 100ms. After each operation (physical contact or electrothermal excitation), immediately use TEM imaging mode (to observe whether there is a raised contrast) or diffraction mode (to verify whether diffraction spots are formed) to determine whether the single crystal nanoparticles have been successfully formed. When polycrystalline nanoparticles with prominent morphology are observed to form in the region, the preparation is complete. S23. In-situ field emission tests were performed on polycrystalline nanoparticles on a lanthanum hexaboride bulk sample under a transmission electron microscope.

[0040] Example 2 In this embodiment, a single-crystal electron source is prepared. The preparation process is carried out in an operating system based on transmission electron microscopy. The TEM in-situ electrical sample rod and its field emission testing system are used. The operation is carried out in the vacuum chamber of a high-resolution transmission electron microscope. The tungsten nanoneedle tip prepared by electrochemical etching is assembled into its three-dimensional movable end to form a nanohand.

[0041] The specific preparation steps are as follows: S11. The (100) oriented lanthanum hexaboride nanocone sample prepared by focused ion beam cutting is loaded onto an in-situ electrical sample rod and inserted into the vacuum cavity of a transmission electron microscope. The lanthanum hexaboride nanocone sample is initially characterized, and the crystal particle forming region is selected under real-time observation of the transmission electron microscope. S21. Manipulate the movement of the piezoelectric ceramic nanohand so that the tungsten nanoneedle tip at its end approaches the surface of the crystal particle forming region until the distance between the two is about 500nm. S22. Manipulate the piezoelectric ceramic nanohand to impact and rub the surface of the crystal particle forming region, while applying Joule heating current. The heating scanning voltage is ±2V and the scanning time is 100ms. After each operation (physical contact or electrothermal excitation), immediately use TEM imaging mode (to observe whether there is a raised contrast) or diffraction mode (to verify whether diffraction spots are formed) to determine whether the single crystal nanoparticles have been successfully formed. When single crystal nanoparticles with prominent morphology are observed in the region, the preparation is complete. S23. In situ field emission tests were performed on a random single-crystal nanoparticle on a lanthanum hexaboride nanocone sample under a transmission electron microscope to obtain the IV curve and FN curve.

[0042] Figure 1 These are schematic diagrams of the operating system structure based on transmission electron microscopy in Examples 1 and 2. Figure 1 It is known that the operating system used in the preparation of the crystal electron source in Examples 1 and 2 both include a transmission electron microscope body with a vacuum chamber, a sample rod that can be inserted into the vacuum chamber, a nanohand integrated on the sample rod, an excitation unit, a control unit, a monitoring unit, and a field emission testing unit. The nanohand has a nanoneedle tip at its end, which is used to physically contact and / or electrothermally excite the crystal particle forming area. The control unit is connected to the nanohand via a cable, which can adjust the displacement accuracy of the nanohand and drive the nanohand to move. The excitation unit is electrically connected to the nanohand and the cathode material, and is used to apply controllable electrothermal excitation to the contact area between the nanoneedle tip and the cathode material. The monitoring unit is used to monitor the crystal particle forming area in real time using the electron beam of the transmission electron microscope. The field emission testing unit is electrically connected to the cathode material, and is used to apply a test voltage and collect the emission current to characterize the field emission performance of the cathode material with single-crystal or polycrystalline nanoparticles.

[0043] Figure 2 This is a schematic diagram of the process for preparing the crystal electron source in Examples 1 and 2. Figure 2 It is known that when the nanoneedle tip of the nano hand approaches the surface of the crystal particle forming region, protruding particles can be formed by physical contact and / or electrothermal stimulation of the crystal particle forming region.

[0044] Figure 3 This is the initial TEM characterization image of the lanthanum hexaboride bulk sample in Example 1. Figure 4 The characterization results are obtained at different stages of the preparation process in Example 1, wherein, Figure 4 Images (a), (b), (c), and (d) are TEM images of the preparation process. Figure 4 Image (e) in the image is a high-magnification TEM image of polycrystalline nanoparticles. Figure 4 In the diagram, (f) is the Fourier transform diffraction spot pattern corresponding to (e), derived from... Figure 3and Figure 4 It can be seen that when the nanohand approaches and contacts the bulk lanthanum hexaboride sample, the material in the contact area deforms, shrinks or spheroidizes during the application of mechanical force or Joule heating, gradually forming discrete polycrystalline nanoparticles. The Fourier transform diffraction pattern shows a series of regularly arranged diffraction spots, confirming that the prepared particles are polycrystalline, rather than amorphous impurities.

[0045] Figure 5 This is a comparison of the TEM characterization results of single-crystal nanoparticles prepared on the surface of lanthanum hexaboride nanocone samples in Example 2, wherein... Figure 5 (a) in the image shows the initial morphology of the lanthanum hexaboride nanocone sample. Figure 5 Image (b) is a magnified view of the tip of the lanthanum hexaboride nanocone sample. Figure 5 (c) in the image represents the tip of the lanthanum hexaboride nanocone cathode sample after the single-crystal particle preparation is completed. Figure 5 Image (d) in the image is a high-magnification characterization photograph of the prepared single-crystal nanoparticles. Figure 5 As can be seen, after several physical contacts and Joule heating cycles in the embodiment, a large number of obvious particles were generated at the tip of the lanthanum hexaboride nanocone sample. The curvature radius of the crystal particles was 1.9-5.77 nm. The largest single crystal particle (curvature radius 5.77 nm) had clear same crystal plane stripes, showing its single crystallization. Moreover, its position was independent of other particles, and it had a high field enhancement factor.

[0046] Figure 6 The in-situ field emission (IV) curve of the largest single-crystal nanoparticle at the tip of the lanthanum hexaboride nanocone sample in Example 2 is obtained from... Figure 6 It can be seen that the voltage point at which the current begins to rise sharply is significantly reduced in the lanthanum hexaboride nanocone sample after the preparation of single-crystal particles. Figure 7 The in-situ field emission (FN) curve of the largest single-crystal nanoparticle at the tip of the lanthanum hexaboride nanocone sample in Example 2 is obtained from... Figure 7 As can be seen, the FN curve exhibits a good linear relationship, which not only confirms that electrons are emitted through quantum tunneling, but the change in its slope can also indirectly reflect the increase in the field enhancement factor β. In-situ field emission test results show that this invention improves the field enhancement factor of the cathode material by preparing nanocrystalline particle protrusions on a relatively smooth cathode material surface, thereby reducing the field emission threshold voltage and making it easier for the cathode to emit a high-brightness electron beam.

[0047] In Examples 1 and 2, polycrystalline nanoparticles and monocrystalline nanoparticles were formed on the surfaces of different cathode materials using the same preparation process. This is mainly related to the thickness of the cathode material and the initial surface layer structure, as analyzed in detail below: 1) The source material in Example 1 was cut from a monocrystalline bulk material using a focused ion beam method with a large beam current. Its surroundings were cut by a large focused ion beam current, resulting in crystal damage at the surface position, changing from monocrystalline to polycrystalline. After exposure to the atmosphere, an amorphous oxide layer will form on the surface. That is, the lanthanum hexaboride bulk sample in Example 1 has a structure from the inside out: monocrystalline (inner) - polycrystalline (subsurface) - amorphous (outermost surface). During in-situ sample preparation, the crystal orientation of the prepared crystal particles is difficult to control, and because the action is performed at a relatively surface position, the prepared particles are polycrystalline nanoparticles. 1) The source material in Example 2 is a lanthanum hexaboride nanocone with a very small thickness and a single crystal orientation, obtained by removing the polycrystalline layer with surface damage using a small current. Therefore, it is still a single crystal structure. However, after exposure to the atmosphere, an amorphous oxide layer will form on the surface. That is, the source material in Example 2 has a single crystal (inner) - amorphous (outermost) structure from the inside out. Therefore, the prepared particles are single crystal nanoparticles. 2) The source material in Example 1 is a bulk material with a relatively large thickness, with a length, width and height all greater than 1 μm. Therefore, the prepared particles are larger, with a radius of curvature of about 25 nm. The nanocone in Example 1 has a curvature of only 15 nm, which is 2-3 orders of magnitude smaller than the bulk sample in Example 1. Therefore, the smaller the particles, the more likely they are to form single crystals, with a radius of curvature of 1.9-5.77 nm.

[0048] This invention utilizes the precise manipulation capabilities of nano-hands to prepare particles in specific areas on the surface of cathode materials, overcoming the spatial randomness of traditional preparation methods. It uses real-time TEM imaging / diffraction signals as the basis for terminating the preparation process, ensuring that the preparation operation stops the instant single-crystal or polycrystalline particle formation, thus guaranteeing a high success rate. The preparation of single-crystal or polycrystalline particles significantly improves the field emission performance of the cathode material. Compared to traditional preparation techniques, this invention fundamentally avoids the unavoidable randomness of uneven particle distribution and uncontrollable size, further ensuring the reliability of in-situ field emission test results and the practical application of the cathode.

Claims

1. A method for in-situ preparation of a crystal electron source based on transmission electron microscopy, characterized in that, Includes the following steps: S1. Load the cathode material onto the sample holder of the transmission electron microscope and transfer it to the vacuum chamber. Under the real-time observation of the transmission electron microscope, select the crystal particle forming area. S2. Manipulate the movement of the piezoelectric ceramic nanohand so that the nanoneedle tip at its end approaches the surface of the crystal particle forming region, and then physically contact and / or electrothermal stimulate the crystal particle forming region to form single crystal or polycrystalline nanoparticles. S3. In the transmission electron microscope, the field emission performance of the cathode material having the single crystal or polycrystalline nanoparticles is tested in situ.

2. The method according to claim 1, characterized in that, The nanoneedle tip is made of a material selected from high-hardness elemental metals or their alloys, carbon-based materials, silicon-based materials, ceramic materials, and smart and functional materials.

3. The method according to claim 1, characterized in that, The physical contact includes at least one of impact, friction, and scratching.

4. The method according to claim 3, characterized in that, When the physical contact is an impact, the magnitude of the impact force is adjusted by controlling the displacement accuracy of the nanoneedle tip; wherein, a displacement accuracy of 10-1000nm is a high-force impact, and a displacement accuracy of less than 10nm is a low-force impact.

5. The method according to claim 1, characterized in that, The electrothermal excitation includes at least one of Joule heating and field evaporation.

6. The method according to claim 5, characterized in that, The Joule heating is achieved by applying a scanning voltage, which ranges from ±100nV to ±140V, and the heating time is from 0.1ms to 3600s.

7. A crystal electron source, characterized in that, It includes preparations made using the method described in any one of claims 1-6.

8. The crystal electron source according to claim 7, characterized in that, The surface of the emitting end of the crystal electron source has single-crystal or polycrystalline nanoparticles with a size of 1-50 nm.

9. A system for the method of in-situ preparation of a crystal electron source based on transmission electron microscopy as described in any one of claims 1-6, characterized in that, include: The main body of a transmission electron microscope, including a vacuum chamber; A sample rod is used to load cathode material and transfer it into the vacuum chamber; A piezoelectric ceramic nanohand is integrated onto the sample rod, with a three-dimensionally movable nanoneedle tip at its end; The excitation unit is electrically connected to the piezoelectric ceramic nanohand and the cathode material, and is used to apply controllable electrothermal excitation to the contact area between the nanoneedle tip and the cathode material. A control unit, connected to the piezoelectric ceramic nanohand, is used to drive the nanohand to move and control the displacement accuracy; The monitoring unit is used to monitor the crystal particle forming area in real time using the electron beam of the transmission electron microscope. The field emission test unit is electrically connected to the cathode material and is used to apply a test voltage and collect the emission current to characterize the field emission performance of the cathode material with single-crystal or polycrystalline nanoparticles.

10. The method for in-situ preparation of crystal electron sources based on transmission electron microscopy according to any one of claims 1-6 is used in the preparation of field emission cathodes, thermionic emission cathodes, Schottky cathodes, and photoelectric emission cathode electron sources.

Images