Preparation method of transmission electron microscope ultrathin sample with cross section made of electron beam sensitive material

Abstract

The invention provides a preparation method of a transmission electron microscope ultrathin sample with a cross section of an electron beam sensitive material, which comprises the following steps: selecting a specific region as a to-be-extracted sample region for the electron beam sensitive material by adopting an electron beam imaging technology; depositing a protective layer on the surface of the to-be-extracted sample area by adopting an electron beam and / or an ion beam; bombarding a to-be-extracted sample area by utilizing a high-energy ion beam, extracting an electron beam sensitive material cross section sample from the to-be-extracted sample area, and fixing the extracted sample to a metal bracket; performing pre-thinning treatment on the extracted sample by using a focused ion beam to obtain a first thinned sample of which the thickness is reduced to be less than a first thickness; and transferring the first thinned sample into a micro-beam fixed-point ion thinning system, and carrying out multi-time stepped low-energy ion beam fine thinning treatment on the first thinned sample by using inert gas ion micro-beams to obtain a second thinned sample which is clean in surface and free of a surface ion damage layer and has the thickness reduced to be less than a second thickness, and taking the second thinned sample as a transmission electron microscope ultrathin sample.

Description

Technical Field

[0001] The present invention relates to the technical field of sample preparation for ultra-thin specimens of transmission electron microscopes, and particularly to a method for preparing an ultra-thin specimen of a cross-section of an electron beam-sensitive material for a transmission electron microscope, and more specifically to a method for preparing an ultra-thin specimen of a cross-section of an electron beam-sensitive double-sided heteroatomic structure carbon nanotube for a transmission electron microscope. Background Art

[0002] As excellent one-dimensional nanomaterials, single-walled carbon nanotubes have unique mechanical, thermal, electrical, and optical properties. In recent years, using single-walled carbon nanotubes as templates to further construct double-sided heteroatomic boron nitride nanotubes, molybdenum sulfur selenium nanotubes, etc., can form one-dimensional coaxial metal-insulator-semiconductor heterojunctions or hetero-nanotube structures that can be used as p-n diodes. These unique structures have great application potential in technical fields such as optical sensing, light-emitting devices, and solar cells. Microstructural analysis of such one-dimensional coaxial heterojunction carbon nanotube materials is of great significance for constructing the structure-activity relationship of carbon nanotubes. A transmission electron microscope (TEM) is a large-scale microscopic analysis device that uses a high-energy electron beam as a light source for magnified imaging. It can directly image the microstructure of materials, explore and construct the structure-activity relationship of materials from the atomic scale, and is a key tool for the microstructural analysis of carbon nanotube materials. However, currently, conventional transmission specimen preparation techniques such as ultra-thin sectioning and ion thinning techniques cannot accurately achieve the thinning process of specific structural regions of carbon nanotubes. The focused ion beam thinning technique, although it can perform selected area thinning with precise positioning of carbon nanotube heterojunctions, has the problem of damage to the surface structure of carbon nanotubes caused by the bombardment of the sample surface by high-energy ion beams during the processing, resulting in the inability to achieve precise microstructural analysis of heterojunctions such as double-sided heteroatomic carbon nanotubes under a transmission electron microscope.

[0003] Currently, the focused ion beam thinning technique is mainly used to prepare carbon nanotube cross-section samples. However, due to the problem of damaging the sample structure in the preparation of the cross-section of double-sided heteroatomic carbon nanotubes by this technique, conventional sample preparation methods cannot prepare an ultra-thin and non-destructive transmission electron microscope specimen that can completely retain the cross-section structure of electron beam-sensitive double-sided heteroatomic carbon nanotubes.

[0004] Therefore, how to provide a method for preparing an ultra-thin and non-destructive transmission electron microscope ultra-thin specimen that can completely retain the cross-section structure of electron beam-sensitive double-sided heteroatomic carbon nanotubes is a problem to be solved. Summary of the Invention

[0005] In view of this, the embodiments of the present invention provide a method for preparing an ultra-thin and non-destructive transmission electron microscope ultra-thin specimen that can completely retain the cross-section structure of electron beam-sensitive materials, so as to eliminate or improve one or more defects existing in the prior art.

[0006] A method for preparing a transmission electron microscope ultra-thin specimen of a cross-section of an electron beam sensitive material provided by the present invention includes the following steps:

[0007] In a dual-beam focused ion beam system, use electron beam imaging technology for the electron beam sensitive material to select a specific area as the sample area to be extracted;

[0008] In the dual-beam focused ion beam system, deposit a protective layer on the surface of the sample area to be extracted using an electron beam and / or an ion beam;

[0009] In the dual-beam focused ion beam system, use a high-energy gallium ion beam to bombard the sample area to be extracted with the deposited protective layer, and extract a cross-section sample of the electron beam sensitive material from the sample area to be extracted, and fix the extracted cross-section sample of the electron beam sensitive material to a metal bracket;

[0010] In the dual-beam focused ion beam system, use a focused ion beam to perform pre-thinning treatment on the extracted cross-section sample of the electron beam sensitive material to obtain a first thinned sample with a thickness reduced to below a first thickness;

[0011] Transfer the first thinned sample to a microbeam fixed-point ion thinning system, and use an inert gas ion microbeam to perform multiple stepped low-energy ion beam fine thinning treatments on the first thinned sample to obtain a second thinned sample with a thickness reduced to below a second thickness, thereby obtaining a transmission electron microscope ultra-thin specimen with a complete cross-section structure and a clean surface of the electron beam sensitive material.

[0012] When the electron beam sensitive material is a carbon nanotube heterojunction with a double-sided heteroatom structure (or a carbon nanotube heterojunction with a double-sided heteroatom structure), the method includes the following steps:

[0013] In a dual-beam focused ion beam system, use electron beam imaging technology for the carbon nanotube heterojunction material with a double-sided heteroatom structure that has been transferred to a substrate to select a carbon nanotube area with double-sided heteroatom structure characteristics as the sample area to be extracted;

[0014] In the dual-beam focused ion beam system, deposit a carbon protective layer on the surface of the sample area to be extracted using an electron beam and / or an ion beam;

[0015] In the dual-beam focused ion beam system, use a high-energy gallium ion beam to bombard the sample area to be extracted with the deposited carbon protective layer, and extract a cross-section sample of the carbon nanotube from the sample area to be extracted, and fix the extracted cross-section sample of the carbon nanotube to a metal bracket;

[0016] In the dual-beam focused ion beam system, use a focused ion beam to perform pre-thinning treatment on the extracted cross-section sample of the carbon nanotube to obtain a first thinned sample with a thickness reduced to below a first thickness;

[0017] Transfer the first thinned sample to a microbeam fixed-point ion thinning system, and use an inert gas ion microbeam to perform multiple stepped low-energy ion beam fine thinning treatments on the first thinned sample to obtain a second thinned sample with a thickness reduced to below the second thickness, thereby obtaining a transmission electron microscopy ultra-thin specimen of the cross-section of a carbon nanotube with the double-sided heteroatom structure completely retained and the surface clean.

[0018] In some embodiments of the present invention, before using the electron beam imaging technique on the double-sided heteroatom structure carbon nanotube heterojunction material, the double-sided heteroatom structure carbon nanotube heterojunction material is transferred onto the substrate through the following steps: transfer the double-sided heteroatom structure carbon nanotube heterojunction material into deionized water; pick up the double-sided heteroatom structure carbon nanotube heterojunction material with the substrate, and let the deionized water volatilize.

[0019] In some embodiments of the present invention, the step of depositing a carbon protection layer on the surface of the sample area to be extracted using an electron beam and / or an ion beam includes: first depositing a carbon protection layer using an electron beam, and then depositing a carbon protection layer using an ion beam, the total thickness of the deposited layer is 1 - 2.5 μm, and the deposited carbon protection layer completely covers the sample area to be extracted.

[0020] In some embodiments of the present invention, the second thickness is much smaller than the first thickness.

[0021] In some embodiments of the present invention, the pre-thinning treatment includes multiple pre-thinning processes, the multiple pre-thinning processes include two or more pre-thinning processes corresponding to different processing depths; each or at least one of the two or more pre-thinning processes with different processing depths is repeatedly executed once or more times; wherein, during the pre-thinning treatment process, the working parameters of the multiple pre-thinning processes are adjusted by observing the electron beam window and the ion beam window.

[0022] In some embodiments of the present invention, the multiple stepped low-energy ion beam fine thinning treatment includes multiple fine thinning processes, the multiple fine thinning processes include two or more fine thinning processes with a stepwise decreasing processing depth; each or at least one of the two or more fine thinning processes is repeatedly executed once or more times; wherein, during the fine thinning treatment process, the working parameters of the multiple fine thinning processes are adjusted by characterizing the reduction of the thickness of the carbon protection layer on the sample surface through a high-resolution transmission electron microscope.

[0023] In some embodiments of the present invention, the parameter ranges of the pre-thinning process include: the working voltage of the ion beam varies from 5 kV to 30 kV, the ion beam current is from 10 pA to 1 nA, and the thinning depth is from 10 nm to 2 μm; the tilting angle range of the sample stage is: -3° to 3°; the processing parameters of the fine-thinning process include: the working voltage of the ion beam varies from 200 eV to 2 keV, the ion beam current is 180 μA, the tilting angle of the sample stage is -10 to 30°, and the thinning time is from 5 min to 60 min.

[0024] The method for preparing a transmission electron microscope specimen of the cross-section of a double-sided heteroatom-structured carbon nanotube according to the present invention prepares an ultrathin sample of the cross-section of an electron beam-sensitive double-sided heteroatom-structured carbon nanotube by jointly using a dual-beam focused ion beam micro-nano processing system and an inert gas microbeam fixed-point ion thinning system, so that the double-sided heteroatom cross-sectional structure of the sample can be completely retained, and the ion implantation damage layer and the amorphous layer on the sample surface can be cleaned, and an ultrathin and non-destructive transmission electron microscope sample can be prepared.

[0025] Additional advantages, objects, and features of the present invention will be partially described below, and will become partially apparent to those of ordinary skill in the art after studying the following text, or can be learned from the practice of the present invention. The objects and other advantages of the present invention can be achieved and obtained by the structure specifically pointed out in the specification and the drawings.

[0026] Those skilled in the art will understand that the objects and advantages that can be achieved by the present invention are not limited to the above specifically described, and the above and other objects that the present invention can achieve will be more clearly understood according to the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings described herein are used to provide a further understanding of the present invention, form a part of this application, and do not limit the present invention. In the drawings:

[0028] Figure 1 It is a schematic flow chart of a method for preparing an ultrathin transmission electron microscope specimen of the cross-section of a double-sided heteroatom-structured carbon nanotube in an embodiment of the present invention.

[0029] Figure 2 It is an SEM (scanning electron microscope) image of the process of extracting a cross-section of a carbon nanotube with a double-sided heteroatom structure by a focused ion beam in an embodiment of the present invention.

[0030] Figure 3 It is an SEM image of the process of preparing a cross-section of a double-sided heteroatom-structured carbon nanotube by focused ion beam pre-thinning treatment in an embodiment of the present invention.

[0031] Figure 4This is a TEM (transmission electron microscope) image of the thickness change process of an ultrathin specimen of the cross-section of a double-sided heteroatom-structured carbon nanotube prepared in an embodiment of the present invention.

[0032] Figure 5 This is a comparison diagram of a TEM image of the cross-section of a double-sided heteroatom carbon nanotube prepared in an embodiment of the present invention and a TEM image of the cross-section of a double-sided heteroatom carbon nanotube prepared only by the focused ion beam thinning technique.

[0033] Figure 6 This is a comparison diagram of an atomic-level STEM (scanning transmission electron microscope) image of the cross-section of a double-sided heteroatom carbon nanotube prepared in an embodiment of the present invention and an atomic-level STEM image of the cross-section of a double-sided heteroatom carbon nanotube prepared only by the focused ion beam thinning technique.

[0034] Figure 7 This is an atomic-level STEM image of the cross-section of a double-sided heteroatom carbon nanotube prepared in an embodiment of the present invention and the corresponding HRTEM (high-resolution transmission electron microscope) image. Detailed implementation manners

[0035] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the implementation manners and the accompanying drawings. Herein, the illustrative implementation manners of the present invention and their descriptions are used to explain the present invention, but do not limit the present invention.

[0036] Herein, it should also be noted that in order to avoid obscuring the present invention due to unnecessary details, only the structures and / or processing steps closely related to the solution of the present invention are shown in the drawings, while other details less related to the present invention are omitted.

[0037] It should be emphasized that the term "including / comprising" when used herein refers to the presence of features, elements, steps, or components, but does not exclude the presence or addition of one or more other features, elements, steps, or components.

[0038] As can be seen from the foregoing, since the existing conventional transmission electron microscope sample preparation method cannot accurately achieve the thinning process of specific structural regions of carbon nanotubes, it is impossible to prepare an ultrathin transmission electron microscope sample with a complete cross-sectional structure for the electron beam-sensitive double-sided heteroatom-structured carbon nanotube material. And due to the damage to the sample structure by the existing focused ion beam thinning technique, it is also impossible to prepare an ultrathin and non-destructive sample that can completely retain the cross-sectional structure of the electron beam-sensitive double-sided heteroatom carbon nanotube.

[0039] To address this problem, the present invention provides a method for preparing an ultrathin specimen of a transmission electron microscope for the cross-section of an electron beam-sensitive double-sided heteroatom-structured carbon nanotube. As Figure 1 shown, this method includes the following steps:

[0040] Step S110: In a dual-beam focused ion beam (FIB) system, use electron beam imaging technology for a carbon nanotube heterojunction with a double-sided heteroatom structure (or a carbon nanotube heterojunction with a double-sided heteroatom structure) material to select a carbon nanotube region with double-sided heteroatom structure characteristics as the sample region to be extracted.

[0041] When implementing this method, if the carbon nanotube heterojunction material with a double-sided heteroatom structure to be processed has not been transferred to the substrate, before performing step S110, this method further includes a transfer step for the sample to be processed.

[0042] Transfer step for the sample to be processed: Transfer the carbon nanotube heterojunction material with a double-sided heteroatom structure to a clean substrate (such as a silicon substrate) through deionized water. More specifically, it includes:

[0043] First, transfer the carbon nanotube heterojunction material with a double-sided heteroatom structure to deionized water. If the prepared carbon nanotube heterojunction material with a double-sided heteroatom structure is initially located on a ceramic ring, transfer the carbon nanotube heterojunction material with a double-sided heteroatom structure from the ceramic ring to deionized water.

[0044] Then, pick up the carbon nanotube heterojunction material with a double-sided heteroatom structure with a clean silicon substrate and let the deionized water volatilize, for example, leave it standing until the deionized water volatilizes. Thus, the transfer step is completed.

[0045] The dual-beam focused ion beam system is a high-precision micro-nano processing technology integrating the functions of a single-beam focused ion beam and a scanning electron microscope (SEM). The dual-beam focused ion beam system includes an electron gun, an ion source, an acceleration and deflection system, a signal detection system, and a sample chamber, etc. By precisely controlling the interaction between the ion beam and the sample, micro-nano processing, analysis, and imaging of materials can be achieved. The dual-beam focused ion beam system can be implemented by a dual-beam focused ion beam micro-nano processing instrument. Since the dual-beam focused ion beam system itself belongs to an existing system, it will not be elaborated here.

[0046] In this step S110, the silicon substrate carrying the carbon nanotube heterojunction material can be moved to the sample chamber of the dual-beam focused ion beam micro-nano processing instrument, and electron beam imaging technology can be used for scanning and observation to select a carbon nanotube region with double-sided heteroatom structure characteristics on the substrate as the sample region to be extracted.

[0047] As an example, the size of the selected sample region to be extracted is that the sample length is 10 μm, the width is 5 μm, and the sample thickness is 1.5 μm.

[0048] Step S120: Deposit a carbon protection layer on the surface of the sample area to be extracted in a dual-beam focused ion beam system using an electron beam and an ion beam.

[0049] To prevent the ion beam from damaging the sample surface during subsequent sample processing and to protect the target area during thinning, it is necessary to deposit a carbon protection layer on the surface of the sample area to be extracted.

[0050] In a dual-beam focused ion beam system, a gaseous precursor can be released onto the sample surface by means of a gas injection system (GIS) and induced by an electron beam or an ion beam to deposit a protection layer on the sample surface. The GIS precursor is initially solid and needs to be heated to become gaseous during deposition. A carbon protection layer can be deposited by electron beam induced deposition or by ion beam induced deposition. Electron beam induced deposition is to use an electron beam to decompose gaseous molecules, thereby realizing the deposition growth of the decomposed precursor material at specific positions on the substrate; similarly, ion beam induced deposition is to decompose gaseous molecules by the bombardment of an ion beam, thereby realizing the deposition growth of the decomposed precursor material at specific positions on the substrate. Electron beam induced deposition operation has a higher spatial accuracy but a lower deposition rate; ion beam induced deposition has a faster deposition rate but a lower spatial resolution, and ions (such as gallium ions) are likely to introduce impurities or damage the deposition structure.

[0051] In an embodiment of the present invention, a carbon protection layer is deposited under both electron beam and ion beam conditions. Preferably, the carbon protection layer is first deposited under electron beam conditions to prevent damage to the surface structure of the carbon nanotubes during the process of depositing the protection layer under ion beam conditions; then the carbon protection layer is deposited under ion beam conditions to ensure the thickness of the carbon protection layer. As an example, the parameters for depositing the protection layer can be as follows: when depositing the carbon protection layer under electron beam conditions, the working voltage of the electron beam is 2 kV to 5 kV, the current is 0.1 nA to 4 nA, and the deposited thickness is 0.3 μm to 0.6 μm; when depositing the carbon protection layer under ion beam conditions, the working voltage of the ion beam is 30 kV, the current is 50 pA to 1 nA, and the deposited thickness is 0.5 μm to 2.0 μm. The total thickness of the carbon deposition layer can be 1.0 μm to 2.5 μm, for example, preferably 1.5 μm, but the present invention is not limited thereto. The size of the carbon deposition area depends on the size of the carbon nanotube area (sample area to be extracted) with a double-sided heteroatom structure feature selected. The size of the carbon deposition area is required to completely cover the selected carbon nanotube area. As an example, the width of the carbon deposition area is set to 1.5 μm to 2.0 μm, and the length is 5.0 μm to 10.0 μm. Examples of the SEM images of the sample during the deposition of the carbon protection layer using the electron beam, the SEM image of the sample after the deposition of the carbon protection layer using the electron beam, and the SEM image of the sample after the deposition of the carbon protection layer using the ion beam are respectively shown as Figure 2 shown in a - c of

[0052] Step S130: Bombard the area of the sample to be extracted (the area to be thinned), which is deposited with a carbon protective layer, with a high-energy ion beam in a dual-beam focused ion beam system, and extract a cross-sectional sample of carbon nanotubes from the area of the sample to be extracted, and fix the extracted cross-sectional sample of carbon nanotubes to a metal support.

[0053] In this step, the sample can be processed by bombarding the surface of the sample with a high-energy gallium ion beam. First, use the high-energy gallium ion beam to etch the sample to dig pits (as shown by d in Figure 2 ), trim the edges, and perform bottom cutting (as shown by e in Figure 2 ) around the area of the sample to be extracted, to obtain a cantilever-shaped specimen of the cross-section of the carbon nanotube with a double-sided heteroatom structure. Then, bond (such as bonding by welding) the area of the sample to be extracted to the nanomanipulator (such as a tungsten needle) of the dual-beam focused ion beam micro-nano processing instrument to extract a cross-sectional sample of the carbon nanotube with a double-sided heteroatom structure (as shown by f in Figure 2 ), and fix (such as fixing and bonding by welding) the extracted cross-sectional sample of the carbon nanotube with a double-sided heteroatom structure to a copper support (such as a copper mesh), as shown by g - i in Figure 2 .

[0054] As an example, when processing the sample area by bombarding with a gallium ion beam, the working voltage of the ion beam can be 30 kV, the ion beam current is 10 pA - 5 nA, and the tilting angle of the sample stage is 0° - 54°; extract a cross-sectional sample of carbon nanotubes with a length of about 5.0 μm - 10.0 μm, a width of about 5.0 μm - 8.0 μm, and a thickness (i.e., the width covered by the carbon protective layer) of about 1.0 μm - 2.5 μm, and transfer and fix it to a copper support. Here, the listed parameters are only examples, and the present invention is not limited thereto.

[0055] Step S140: Perform pre-thinning processing on the extracted cross-sectional sample of carbon nanotubes in a dual-beam focused ion beam system to obtain a first thinned sample with a thickness reduced to below a first thickness.

[0056] As an example, a gallium ion beam can be used to perform focused ion beam pre-thinning processing on the cross-sectional sample of carbon nanotubes extracted in step S130 and fixed to a copper support. The sample thickness can be reduced to below 400 nm (the first thickness). Here, 400 nm is only an example, and the present invention is not limited thereto.

[0057] In some embodiments of the present invention, in the pre-thinning step S140, the thickness change of the sample can be measured by observing the real-time images of the electron beam window and the ion beam window, and based on this, it can be determined whether to adjust the pre-thinning processing parameters or end the pre-thinning process.

[0058] In some other embodiments of the present invention, the pre-thinning process in step S140 may include multiple pre-thinning operations. The multiple pre-thinning operations may include two or more pre-thinning operations corresponding to different processing depths (i.e., thinning depths), and the thinning depth may decrease sequentially in the two or more pre-thinning operations. In some other embodiments of the present invention, each or at least one of the two or more pre-thinning operations with different thinning depths may also be repeatedly performed once or multiple times. The thickness change of the sample can be measured in each pre-thinning operation by observing the real-time image of the electron beam and ion beam window, so as to adjust the processing parameters of the ion beam in the next pre-thinning operation. In some embodiments of the present invention, parameters such as the working voltage and current under the ion beam conditions can be adjusted in real time according to the reduction of the sample thickness during pre-thinning.

[0059] In the embodiments of the present invention, during the pre-thinning process in step S140, both the ion beam processing parameters and the thinning depth for pre-thinning the cross-sectional sample of the extracted carbon nanotubes in the dual-beam focused ion beam system need to change in real time with the sample thickness. The parameter ranges of the focused ion beam pre-thinning operation can be exemplified as follows: the working voltage is 5 kV to 30 kV, the ion beam current is 10 pA to 1 nA, and the thinning depth is 10 nm to 2 μm; the change range of the sample stage tilting angle is: -3° to 3°. These parameters are only examples, and the present invention is not limited thereto.

[0060] Compared with the fine-thinning process in the subsequent step S150, the pre-thinning process in step S140 is a rough-thinning process.

[0061] Step S150: Transfer the first thinned sample to a microbeam fixed-point ion thinning system, and perform multiple stepped low-energy ion beam fine-thinning processes on the first thinned sample using an inert gas ion microbeam to obtain a second thinned sample with a thickness reduced to below the second thickness, thereby obtaining a cross-sectional ultra-thin transmission electron microscope specimen of carbon nanotubes with the double-sided heteroatom structure completely retained and the sample surface clean.

[0062] The microbeam fixed-point ion thinning system uses a low-energy focused argon ion microbeam for finer thinning of the thinned sample. The focused beam spot diameter of the low-energy focused argon ion microbeam is 1 μm, which can effectively remove the ion implantation damage layer introduced by focused ion beam sample preparation and the amorphous layer in the sample without re-deposition phenomenon on the premise of protecting the integrity of the cross-sectional structure. In the embodiments of the present invention, the thickness of the thinned sample is below 50 nm (the second thickness). Here, the second thickness of 50 nm is only an example, and the present invention is not limited thereto, but the second thickness is much smaller than the first thickness. Using the microbeam fixed-point ion thinning system for fine-thinning treatment, an ultra-thin transmission electron microscope sample with a complete sample structure, a clean surface, no surface ion damage layer, and a thickness below 50 nm can be obtained.

[0063] The fine thinning step S150 includes multiple fine thinning processes, which may include two or more fine thinning processes corresponding to different processing depths (i.e., thinning depths). The thinning depth may decrease sequentially in the two or more fine thinning processes, such as in a stepped manner. That is, the first thinning sample is subjected to multiple stepped low-energy ion beam fine thinning treatments. In some other embodiments of the present invention, each or at least one of the two or more fine thinning processes with different thinning depths may also be repeatedly executed once or more times. The thickness reduction of the carbon protection layer on the sample surface can be characterized by a high-resolution transmission electron microscope, and accordingly, parameters such as the working voltage and thinning duration of the argon ion beam can be adjusted in real time to perform multiple stepped low-energy ion beam thinning treatments.

[0064] As an example, the processing parameters of the microbeam fixed-point ion beam fine thinning process are as follows: the working voltage range of the ion beam is 200 eV to 2 keV, the ion beam current is 180 μA, the tilting angle of the sample stage is -10 to 30°, and the thinning time is 5 min to 60 min. These parameters are only examples, and the present invention is not limited thereto.

[0065] The following will illustrate steps S140 and S150 with specific examples.

[0066] As an example, the pre-thinning process of step S140 includes multiple pre-thinning processes ① to ④, and the processing parameters of each pre-thinning process are as follows:

[0067] Pre-thinning process ①: The working voltage of the ion beam is 30 kV, and the ion beam current is 0.5 nA (in actual operation, the current selection range is 0.1 nA to 1 nA, preferably 0.1 nA to 0.5 nA); the thinning depth is 1 μm (the thinning depth selection range is 0.1 μm to 2 μm, preferably 0.5 μm to 1 μm), and the tilting angle of the sample stage is ±1.5° (the tilting angle selection range of the sample stage is -2° to 2°). Pre-thinning process ① is executed several times until the sample thickness in the ion beam window is reduced to 1 to 1.5 μm, as shown in Figure 3 a and b in.

[0068] Pre-thinning process ②: The working voltage of the ion beam is 16 kV, and the ion beam current is 0.5 / 0.25 nA (the current selection range is 0.1 nA to 1 nA, preferably 0.1 nA to 0.5 nA); the thinning depth is 500 nm (the thinning depth selection range is 0.1 μm to 1 μm, preferably 0.2 μm to 0.5 μm), and the tilting angle of the sample stage is ±1.5° (the tilting angle selection range of the sample stage is -2° to 2°); pre-thinning process ② is executed several times until the sample thickness in the ion beam window is reduced to 0.6 to 1.0 μm (as shown in Figure 3 c and d in);

[0069] Pre-thinning process ③: The working voltage of the ion beam is 16 kV, and the ion beam current is 0.15 nA / 50 pA (the selectable range of the current is 50 pA to 0.5 nA, preferably 50 pA to 0.15 nA); the thinning depth is 200 nm (the selectable range of the thinning depth is 100 nm to 500 nm, preferably 100 nm to 200 nm), and the tilting angle of the sample stage is ±1.5°; Perform pre-thinning process ③ several times until the thickness of the sample in the ion beam window is reduced to 400 nm to 600 nm (as shown in Figure 3 e and f in

[0070] Pre-thinning process ④: The working voltage of the ion beam is 5 kV, and the ion beam current is 16 / 48 pA (the selectable range of the current is 10 pA to 0.1 nA, preferably 10 pA to 48 pA); the thinning depth is 50 / 100 nm (the selectable range of the thinning depth is 10 nm to 200 nm, preferably 10 nm to 100 nm), and the tilting angle of the sample stage is ±3° (the selectable range of the tilting angle of the sample stage is -3° to 3°); Perform pre-thinning process ④ several times until the thickness of the sample in the ion beam window is reduced to 300 nm to 400 nm, and the cross-section of the sample shows a transparent contrast (as shown in Figure 3 g and h in

[0071] Microbeam fixed-point ion beam fine thinning process in step S150: Transfer the carbon nanotube cross-section sample prepared in step S140 to a microbeam fixed-point ion thinning system (such as a microbeam fixed-point ion thinner), and perform fine thinning treatment using a low-energy focused argon ion microbeam. While protecting the integrity of the cross-section structure, effectively remove the ion implantation damage layer caused by focused ion beam sample preparation on the sample surface and the amorphous layer in the sample, and reduce the sample thickness to less than 50 nm, thereby preparing a high-quality ultra-thin transmission electron microscope sample. During the thinning process, synchronously observe and measure the reduction of the carbon protection layer thickness on the sample surface in combination with a transmission electron microscope, as shown in Figure 4 . Adjust the processing parameters of the inert gas argon ion beam according to the reduction of the carbon protection layer thickness on the sample surface. The microbeam fixed-point ion beam fine thinning process in step S150 includes multiple fine thinning processes. As an example, the processing parameters of each fine thinning process are as follows:

[0072] Fine thinning process ①: The working voltage of the ion beam is 900 eV (the selectable range of the working voltage is 200 eV to 2 keV, preferably 500 eV to 900 eV), the current is 180 μA, the tilting angle of the sample stage is ±10° (the selectable range of the tilting angle is -10° to 30°, preferably -10° to 10°), and the thinning time is 15 min for each sample surface (the selectable range of the thinning time is 5 min to 60 min, preferably 5 min to 30 min).

[0073] Perform the fine thinning process ① several times until the thickness of the carbon protective layer deposited under the ion beam on the sample surface ( Figure 4 the black contrast area on the sample surface in Figure 4 ) is reduced by at least half, as shown in a and b of

[0074] Fine thinning process ②: The working voltage of the ion beam is 500 eV (the optional range of the working voltage is 200 eV to 2 keV, preferably 200 eV to 500 eV), the current is 180 μA, the tilting angle of the sample stage is ±10° (the optional range of the tilting angle is -10° to 30°, preferably -10° to 10°), and the thinning time is 10 min for each sample surface (the optional range of the thinning time is 5 min to 60 min, preferably 5 min to 20 min).

[0075] Perform the fine thinning process ② several times until the carbon protective layer deposited under the ion beam on the sample surface is almost completely removed under the transmission electron microscope, as shown in e of Figure 4 ; For the process of gradually and finely thinning the carbon protective layer deposited under the ion beam on the sample surface, please refer to a - e of Figure 4 .

[0076] Fine thinning process ③: The working voltage of the ion beam is 200 eV, the current is 180 μA, the tilting angle of the sample stage is ±10°, the thinning time is 10 min for each sample surface (the optional range of the thinning time is 5 min to 60 min, preferably 5 min to 10 min). When the thickness of the carbon protective layer deposited under the electron beam on the sample surface remains about 200 - 300 nm, the thinning time can be shortened to 5 min for each sample surface.

[0077] Perform the fine thinning process ③ several times until the thickness of the carbon protective layer deposited under the electron beam on the sample surface remains about 100 - 200 nm (as shown in f of Figure 4 ), then the fine thinning process can be stopped. The specimen obtained at this time can be used as a cross - sectional transmission electron microscope ultra - thin sample of the double - sided hetero - atom - structured carbon nanotube.

[0078] Those skilled in the art should understand that the parameters listed in the present invention are only examples, and the present invention is not limited thereto.

[0079] Figure 5 This is a comparison chart of the TEM images of the cross - section of the double - sided hetero - atom carbon nanotube prepared in an embodiment of the present invention and the TEM image of the cross - section of the double - sided hetero - atom carbon nanotube prepared only by the focused ion beam thinning technology. From Figure 5 it can be seen that the cross - section of the double - sided hetero - atom carbon nanotube prepared in the embodiment of the present invention is an ultra - thin specimen, and its thickness is significantly lower than that of the cross - sectional specimen of the double - sided hetero - atom carbon nanotube prepared only by the focused ion beam thinning technology.

[0080] Figure 6 This is a comparison diagram of the atomic-level STEM (scanning transmission electron microscope) image of the cross-section of double-sided heteroatom carbon nanotubes prepared in an embodiment of the present invention and the atomic-level STEM image of the cross-section of double-sided heteroatom carbon nanotubes prepared only by the focused ion beam thinning technique. From Figure 6 It can be seen that there are a large number of ion implantation damage layers in the cross-section sample of double-sided heteroatom carbon nanotubes prepared only by the focused ion beam thinning technique, resulting in the contamination of the sample surface, and due to the insufficient thickness of the sample, a clear atomic image cannot be obtained; the cross-section sample of double-sided heteroatom carbon nanotubes prepared through the embodiment of the present invention is an ultra-thin transmission electron microscope specimen, the sample surface is clean, no ion damage layer is seen, and the atomic structure is clearly visible, showing that the sample preparation method described in the present invention has excellent sample preparation effects.

[0081] Figure 7 Figures a and b in Figure 7 It can be seen that the ion damage layer and amorphous layer on the surface of the cross-section sample of double-sided heteroatom carbon nanotubes prepared through the embodiment of the present invention are cleaned up during the fine thinning process of the microbeam fixed-point ion beam, and the atomic structure of the carbon nanotubes is completely retained and clearly visible.

[0082] The above results show that the microbeam fixed-point ion thinning based on the above processes in the present invention can completely remove the ion damage layer and amorphous layer on the sample surface, and a carbon nanotube cross-section without surface damage can be obtained.

[0083] The present invention prepares an ultra-thin transmission electron microscope sample of the cross-section of an electron beam-sensitive double-sided heteroatom structure carbon nanotube by jointly using a dual-beam focused ion beam micro-nano processing system and an inert gas microbeam fixed-point ion thinning system. Compared with the sample thinned by using only the dual-beam focused ion beam micro-nano processing system, the double-sided heteroatom cross-section structure of the sample can be completely retained, and the ion implantation damage layer and amorphous layer on the sample surface can be cleaned up, and an ultra-thin and non-destructive transmission electron microscope sample can be prepared. The method of the present invention can also be commonly used for the preparation of ultra-thin transmission electron microscope specimens of the cross-sections of other types of electron beam-sensitive materials (such as perovskite materials).

[0084] When the method of the present invention is used for the preparation of ultra-thin transmission electron microscope specimens of the cross-sections of electron beam-sensitive materials including other types of electron beam-sensitive materials, the corresponding method for preparing ultra-thin transmission electron microscope specimens of the cross-sections of electron beam-sensitive materials includes the following steps S110' to step S150':

[0085] Step S110′, in a dual-beam focused ion beam system, use electron beam imaging technology for the electron beam sensitive material to select a specific area as the sample area to be extracted.

[0086] Among them, the electron beam sensitive material can be, for example, a perovskite material.

[0087] Step S120′, in a dual-beam focused ion beam system, use an electron beam and / or an ion beam to deposit a protective layer on the surface of the sample area to be extracted.

[0088] The deposited material can be matched with the electron beam sensitive material. For example, when the electron beam sensitive material is a perovskite material, a platinum or tungsten protective layer can be deposited on the sample surface.

[0089] Step S130′, in a dual-beam focused ion beam system, use a high-energy gallium ion beam to bombard the sample area to be extracted with the protective layer deposited, and extract a cross-sectional sample of the electron beam sensitive material from the sample area to be extracted, and fix the extracted cross-sectional sample of the electron beam sensitive material to a metal bracket.

[0090] Step S140′, in a dual-beam focused ion beam system, use a focused ion beam to perform pre-thinning treatment on the extracted cross-sectional sample of the electron beam sensitive material to obtain a first thinned sample with a thickness reduced to below a first thickness.

[0091] Step S150′, transfer the first thinned sample to a microbeam fixed-point ion thinning system, and use an inert gas ion microbeam to perform multiple step-by-step low-energy ion beam thinning treatments on the first thinned sample to obtain a second thinned sample with a thickness reduced to below a second thickness, thereby obtaining a transmission electron microscope ultra-thin specimen of the cross-section of the electron beam sensitive material.

[0092] The above steps are similar to Steps S110 to S150, except that: Steps S110 to S150 are for an electron beam sensitive double-sided heteroatom-structured carbon nanotube heterojunction, and Steps S110′ to S150′ are for electron beam sensitive materials that can include double-sided heteroatom-structured carbon nanotube heterojunctions and other electron beam sensitive materials; based on the specific processing object, the specific working parameters may be different.

[0093] Those of ordinary skill in the art should understand that the various exemplary components, systems, and methods described in connection with the embodiments disclosed herein can be implemented in hardware, software, or a combination of both. Specifically, whether to implement it in hardware or software depends on the specific application and design constraints of the technical solution. A person skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention. When implemented in hardware, it can be, for example, an electronic circuit, an application-specific integrated circuit (ASIC), appropriate firmware, a plug-in, a functional card, and so on. When implemented in software, the elements of the present invention are programs or code segments used to perform the required tasks. The program or code segment can be stored in a machine-readable medium or transmitted through a data signal carried in a carrier wave on a transmission medium or a communication link.

[0094] It should be clear that the present invention is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order between steps after understanding the spirit of the present invention.

[0095] In the present invention, the features described and / or illustrated for one embodiment can be used in the same or a similar manner in one or more other embodiments, and / or combined with the features of other embodiments or replace the features of other embodiments.

[0096] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, various changes and variations can be made to the embodiments of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a transmission electron microscope ultra-thin specimen of a cross-section of an electron beam sensitive material, characterized in that, The method includes the following steps: In a dual-beam focused ion beam system, an electron beam imaging technique is used for an electron beam sensitive material to select a specific area as the sample area to be extracted; In the dual-beam focused ion beam system, an electron beam and / or an ion beam is used to deposit a protective layer on the surface of the sample area to be extracted; In the dual-beam focused ion beam system, a high-energy gallium ion beam is used to bombard the sample area to be extracted with the deposited protective layer, and a cross-sectional sample of the electron beam sensitive material is extracted from the sample area to be extracted, and the extracted cross-sectional sample of the electron beam sensitive material is fixed to a metal bracket; In the dual-beam focused ion beam system, a focused ion beam is used to perform a pre-thinning process on the extracted cross-sectional sample of the electron beam sensitive material to obtain a first thinned sample with a thickness reduced to less than a first thickness; The first thinned sample is transferred to a microbeam fixed-point ion thinning system, and an inert gas ion microbeam is used to perform multiple stepped low-energy ion beam fine thinning processes on the first thinned sample to obtain a second thinned sample with a thickness reduced to less than a second thickness, thereby obtaining a transmission electron microscope ultra-thin specimen of the cross-section of the electron beam sensitive material.

2. The method according to claim 1, characterized in that The electron beam sensitive material is a carbon nanotube heterojunction with a double-sided heteroatom structure; The specific area is a carbon nanotube area with double-sided heteroatom structure characteristics; The protective layer is a carbon protective layer.

3. The method according to claim 2, characterized in that, The method further includes: before using the electron beam imaging technique for the carbon nanotube heterojunction material with a double-sided heteroatom structure, transferring the double-sided heteroatom structure carbon nanotube heterojunction material to the substrate through the following steps: Transfer the double-sided heteroatom structure carbon nanotube heterojunction material to deionized water; Lift the double-sided heteroatom structure carbon nanotube heterojunction material with the substrate and let the deionized water evaporate.

4. The method according to claim 1 or 2, characterized in that, The step of depositing a protective layer on the surface of the sample area to be extracted by using an electron beam and / or an ion beam includes: First, an electron beam is used to deposit a protective layer, and then an ion beam is used to deposit a protective layer. The total thickness of the deposited layer is 1-2.5 μm, and the deposited protective layer completely covers the sample area to be extracted.

5. The method according to claim 1 or 2, characterized in that, The second thickness is much smaller than the first thickness.

6. The method according to claim 1 or 2, characterized in that, The pre-thinning process includes multiple pre-thinning procedures, and the multiple pre-thinning procedures include two or more pre-thinning procedures corresponding to different processing depths; Among them, during the pre-thinning process, the working parameters of the multiple pre-thinning procedures are adjusted by observing the electron beam window and the ion beam window.

7. The method according to claim 6, wherein Each or at least one of the two or more pre-thinning procedures with different processing depths is repeated once or more times.

8. The method according to claim 1 or 2, characterized in that, The multiple stepped low-energy ion beam fine thinning process includes multiple fine thinning procedures, and the multiple fine thinning procedures include two or more fine thinning procedures with a stepwise decreasing processing depth; Among them, during the fine thinning process, the working parameters of the multiple fine thinning procedures are adjusted by characterizing the reduction of the carbon protective layer thickness on the sample surface through a high-resolution transmission electron microscope.

9. The method according to claim 8, characterized in that, Each or at least one of the two or more fine thinning procedures is repeated once or more times.

10. The method according to claim 8, characterized in that, The working parameter ranges of the pre-thinning process include: the ion beam working voltage varies from 5 kV to 30 kV, the ion beam current is from 10 pA to 1 nA, and the thinning depth is from 10 nm to 2 μm; the sample stage tilting angle varies from -3° to 3°; the working parameter ranges of the fine-thinning process include: the ion beam working voltage varies from 200 eV to 2 keV, the ion beam current is 180 μA, the sample stage tilting angle is from -10° to 30°, and the thinning time is from 5 min to 60 min.

Images