Transmission electron microscope sample preparation method for lunar soil space weathered surface and application

Abstract

The invention discloses a transmission electron microscope sample preparation method for a lunar soil space weathered surface and application, and the method comprises the following steps: pasting target lunar soil particles on a carbon conductive adhesive tape, and enabling the target flat surfaces of the target lunar soil particles to be placed back to the carbon conductive adhesive tape; plating a layer of carbon film on the surface of the target lunar soil particle to obtain a scanning electron microscope sample of the target lunar soil particle; screening out a plurality of target research areas on the carbon film corresponding to the target flat surface; uniformly plating a layer of gold film on the carbon film corresponding to the target lunar soil particle scanning electron microscope sample; deposition operation of a research area protection layer is carried out on the gold film corresponding to the target research area through an electron beam and an ion beam in sequence; and performing slicing operation perpendicular to the target flat surface on the target lunar soil particle scanning electron microscope sample to obtain the target lunar soil particle transmission electron microscope sample. According to the method, lunar soil space weathering characteristics can be truly reserved, and an accurate and reliable sample is provided for lunar soil space weathering research.

Description

Technical Field

[0001] This invention relates to the field of transmission electron microscopy (TEM) sample preparation technology, specifically to a method and application for TEM sample preparation of lunar regolith weathered surfaces. Background Technology

[0002] As an important component of the lunar surface, lunar regolith's microstructure and composition analysis are crucial for revealing the Moon's geological evolution and space weathering processes. Lunar regolith particles exhibit a complex microstructure resulting from space weathering, including primitive mineral crystals, nano-metal particles, fully amorphous layers, partially amorphous layers, sputtered deposits, and evaporated deposits. Transmission electron microscopy (TEM) is a vital tool for studying the microstructure of lunar regolith; however, prior to TEM analysis, sample preparation of lunar regolith particles is necessary using scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS) and focused ion beam scanning electron microscopy (FIB-SEM).

[0003] Currently, in the preparation of lunar soil TEM samples, to address the poor conductivity of lunar soil particles, a common practice is to first apply a conductive coating, followed by electron beam deposition and ion beam deposition of a protective layer. This method typically involves depositing one of the conductive materials—gold, platinum, or carbon—on the surface of the lunar soil particles to form a nanoscale conductive layer to eliminate charge effects. Then, in FIB-SEM, electron beam and ion beam-induced platinum or carbon protective layers are deposited sequentially to further enhance conductivity and protect the sample surface. However, a single conductive coating material cannot adequately accommodate the diverse microstructures of lunar soil particle surfaces. During subsequent electron beam deposition and ion beam deposition of the protective layer, the coating and protective layer materials intrude and damage the surface structure of the lunar soil particles. Different structures on the lunar soil particle surface exhibit varying degrees of adaptability to conductive materials, particularly for amorphous layers and evaporation-deposited layers with a thickness of only 10-200 nm, where this intrusion is particularly significant. The intrusion of conductive materials severely disrupts the space weathering microstructure of lunar soil particles, distorting TEM analysis results and significantly hindering in-depth research into the space weathering mechanism of lunar soil. Summary of the Invention

[0004] To address the technical problems in the prior art, this invention provides a transmission electron microscopy (TEM) sample preparation method and application for lunar soil weathering surfaces, which can accurately preserve the characteristics of lunar soil weathering and provide accurate and reliable samples for lunar soil weathering research.

[0005] Specifically, the present invention includes the following.

[0006] A first aspect of the present invention provides a method for preparing a transmission electron microscope (TEM) sample of a space-weathered surface of lunar regolith, comprising: Step 1, attaching selected target lunar regolith particles to a carbon conductive adhesive sheet, with the target flat surface of the target lunar regolith particles facing away from the carbon conductive adhesive sheet, wherein the target flat surface is the largest flat surface on the surface of the target lunar regolith particles; Step 2, uniformly depositing a carbon film on the surface of the target lunar regolith particles to obtain a scanning electron microscope (SEM) sample of the target lunar regolith particles; Step 3, selecting several target study areas on the carbon film corresponding to the target flat surface, wherein different target study areas correspond to different space weathering processes and degrees; Fourth, uniformly deposit a gold film on the carbon film corresponding to the target lunar regolith particle scanning electron microscope sample; fifth, sequentially deposit a protective layer for the research area on the gold film corresponding to all the target research areas using electron beam and ion beam, so that the gold film corresponding to each target research area is covered with a protective layer for the target research area; sixth, slice the target lunar regolith particle scanning electron microscope sample perpendicular to the target flat surface along the edge of each target research area to obtain a target lunar regolith particle transmission electron microscope sample, wherein each target lunar regolith particle transmission electron microscope sample contains only one target research area.

[0007] Optionally, in step one above, the method for screening the target lunar soil particles includes: providing a number of lunar soil particles, and using tweezers and glass dishes sterilized with ethanol under an optical microscope inside an inert gas glove box to screen out the lunar soil particles with a particle size greater than or equal to 50 μm as the target lunar soil particles.

[0008] Optionally, in step two above, the step of uniformly depositing a carbon film on the surface of the target lunar regolith particles to obtain a scanning electron microscope (SEM) sample of the target lunar regolith particles includes: placing the target lunar regolith particles, which are adhered to the carbon conductive adhesive tape, into a vacuum carbon plating instrument; setting the current of the vacuum carbon plating instrument to 70-75A, the carbon spraying time to 5-7s, the number of carbon sprayings to 8-13, and the interval between each carbon spraying to 1-1.5min, so as to uniformly deposit a carbon film with a thickness of 50-100nm on the surface of the target lunar regolith particles to obtain a scanning electron microscope (SEM) sample of the target lunar regolith particles.

[0009] Optionally, in step three above, the step of selecting several target study areas on the carbon film corresponding to the target flat surface includes: using a scanning electron microscope equipped with a dispersive X-ray spectrometer to capture 16K high-resolution images of each target lunar regolith particle SEM sample at a magnification of 100-500x to obtain its surface morphology features, and acquiring chemical composition information of each target lunar regolith particle SEM sample at a magnification of 500-2000x and a resolution of 1K; based on the surface morphology features and chemical composition information of each target lunar regolith particle SEM sample, selecting each target study area corresponding to each target lunar regolith particle SEM sample on the carbon film corresponding to the target flat surface, wherein each target study area is a rectangular area with a length of 10-13 μm and a width of 1-1.5 μm.

[0010] Optionally, in step four above, the step of uniformly depositing a gold film on the carbon film corresponding to the target lunar regolith particle scanning electron microscope sample includes: placing the target lunar regolith particle scanning electron microscope sample after selecting several target research areas into a magnetron sputtering instrument; setting the current of the magnetron sputtering instrument to 30-35mA, the gold sputtering time to 40-50S each time, and the number of gold sputtering times to 1-2 times, thereby uniformly depositing a gold film with a thickness of 50-100nm on the carbon film corresponding to the target lunar regolith particle scanning electron microscope sample.

[0011] Optionally, in step five above, the deposition of a protective layer for the research area is performed sequentially on the gold film corresponding to all the target research areas using electron beams and ion beams, so that each gold film corresponding to the target research area is covered with a protective layer for the target research area. This includes: depositing a first protective layer of 10-15 μm long × 2 μm wide × 0.5 μm high on the gold film corresponding to all the target research areas using electron beam induction of a focused ion beam scanning electron microscope, and each first protective layer completely covers its corresponding target research area; and depositing a second protective layer of 10-15 μm long × 2 μm wide × 1 μm high on all the first protective layers using ion beam induction of a focused ion beam scanning electron microscope, and each second protective layer completely covers its corresponding first protective layer. The first and second protective layers together constitute the protective layer for the target research area.

[0012] Optionally, the deposition materials of the first study area protective layer and the second study area protective layer are any one of platinum, carbon, silicon oxide and tungsten metal, but not limited to platinum, carbon, silicon oxide and tungsten metal.

[0013] Optionally, the first deposition material corresponding to the protective layer of the first study area and the second deposition material corresponding to the protective layer of the second study area may be the same or different.

[0014] Optionally, in step six above, the step of slicing the target lunar regolith particle scanning electron microscope sample perpendicular to the target flat surface along the edge of each target research region to obtain a target lunar regolith particle transmission electron microscope sample, wherein each target lunar regolith particle transmission electron microscope sample contains only one target research region, includes: using a focused ion beam scanning electron microscope to slice the target lunar regolith particle scanning electron microscope sample perpendicular to the target flat surface along the edge of each target research region to obtain a target lunar regolith primary transmission electron microscope sample with a length of 10-13 μm × width of 0.5-1 μm × height of 5-10 μm, wherein each target lunar regolith primary transmission electron microscope sample contains only one target research region; welding the target lunar regolith primary sample to a copper grid, and then performing thinning and purging operations on the target lunar regolith primary sample to reduce its thickness to 70-90 nm to obtain the target lunar regolith particle transmission electron microscope sample, wherein each target lunar regolith particle transmission electron microscope sample contains only one target research region.

[0015] A second aspect of the present invention provides an application of the transmission electron microscopy (TEM) sample preparation method for space weathering of lunar soil according to any one of the preceding claims in the field of TEM sample preparation of lunar soil.

[0016] The specific contents of this invention are as follows:

[0017] (1) Particle sorting: Under an optical microscope inside an inert gas glove box, using tweezers and glass dishes sterilized with ethanol (99.9%), larger lunar regolith particles (>50 μm) (including mineral, rock, glass, and cement particles) were carefully sorted. The operation inside the inert gas glove box and the sterilization of experimental tools with ethanol were chosen to avoid contamination of the lunar regolith particles by the external Earth environment, ensuring that the particles remained in their original state. Selecting larger (>50 μm) lunar regolith particles made them easier to handle and process during subsequent FIB-SEM sample preparation, thus ensuring the accuracy and stability of the sample preparation.

[0018] (2) Sample mounting: Apply carbon conductive tape to the sample stage, and then attach the sorted lunar regolith particles to the conductive tape under an optical microscope. When handling the particles, care should be taken not to damage the particle surface with tweezers. When attaching the particles, ensure the flatter side of the lunar regolith particles faces upwards. This not only ensures the uniformity of subsequent coating and protective layer deposition but also facilitates subsequent SEM-EDS observation and FIB-SEM sample preparation. Simultaneously, the size of the lunar regolith particles on a single sample stage should not vary too much to avoid collisions with instrument components during subsequent observation and sample preparation. The carbon conductive tape serves two purposes: firstly, it fixes the lunar regolith particles; secondly, its good conductivity facilitates subsequent electron beam-related operations.

[0019] (3) Carbon Coating of Samples: The adhered lunar soil particles were placed in a vacuum carbon coating instrument (Cressington 108C). The current was set to 75A, the carbon spraying time was 6s, and the process was repeated 8-13 times with a 1min interval between each time. This resulted in a uniform carbon film with a thickness of 50-100nm on the surface of the lunar soil particles, enhancing their conductivity. The resulting lunar soil particles were then observed under a scanning electron microscope. The selection of a carbon conductive material for coating was to reduce interference caused by the overlap of characteristic peaks of platinum, gold, and other elements in subsequent EDS analysis. The selection of a specific vacuum carbon coating instrument and the setting of corresponding parameters were to precisely control the thickness and uniformity of the carbon film. By spraying carbon at low intensity and repeating the operation, a uniform and appropriately thick carbon conductive layer could be formed on the sample surface, avoiding damage to the fragile surface structure of the lunar soil particles due to excessive coating intensity or time.

[0020] (4) SEM-EDS Observation: SEM samples of lunar regolith particles were observed using an EDS-equipped SEM. 16K high-resolution images of each particle were captured at 100-500x magnification to obtain its surface morphology characteristics. Chemical composition information for each particle was acquired at 1K resolution at 500-2000x magnification. Based on the combined surface morphology and chemical composition, target study areas (10-13 μm long × 1.5 μm wide) were selected. Before loading the samples, the SEM samples of lunar regolith particles were purged with a syringe to remove adhering dust and prevent particles from falling off in the SEM vacuum system. Based on the surface morphology observed by SEM, areas that had undergone different space weathering processes and degrees were selected, such as surfaces with well-preserved mineral morphology and impact craters. These areas reflect the different weathering histories of lunar regolith in space. Simultaneously, based on the chemical composition detected by EDS, different minerals were distinguished, and regions with significantly different proportions of elements from common lunar minerals and the presence of rare lunar elements were selected. These special regions are of great significance for studying the unique geological processes and evolution of the Moon. Through this step, target areas with research value can be screened out, providing a basis for subsequent precise sample preparation.

[0021] (5) Gold Coating of Samples: The SEM sample of lunar regolith particles observed by SEM-EDS was placed in a magnetron sputtering instrument (Hitachi MSP-1S), with a current of 35mA, and gold sputtering for 40s, repeated 1-2 times to uniformly coat the sample surface with a gold film of 50-100nm thickness. This step is to further enhance the conductivity on the basis of the carbon film to meet the higher requirements of conductivity and surface quality of the lunar regolith particles for subsequent FIB-SEM sectioning, thereby improving the accuracy of FIB-SEM sample preparation. This step is placed after SEM-EDS observation mainly to avoid large gold particles (8-12nm) obscuring the high-resolution morphological information of the sample.

[0022] (6) FIB-SEM sectioning: Using FIB-SEM, firstly, a platinum protective layer (10-15 μm long × 2 μm wide × 0.5 μm high) is deposited to completely cover the target area after the above treatment and screening by electron beam induction. Then, a platinum protective layer (10-15 μm long × 2 μm wide × 1 μm high) is deposited again on the protective layer deposited by electron beam induction. Next, a vertical cut is made in the protective layer area to extract a sample with a length of 10-13 μm × width of 0.5-1 μm × height of 5-10 μm. The sample is then welded to a copper grid using platinum. The sample is then gradually thinned and swept to 70-90 nm by reducing the current (30 kV, 700 pA, 300 pA, 100 pA) and the voltage (30 kV to 5 kV and 2 kV, 10 pA) to obtain a transmission electron microscope sample of lunar soil particles. At this time, the sample can be observed and analyzed on the transmission electron microscope. The purging process also thins the sample, but it also reduces amorphous material on the surface. A double protective layer eliminates damage to the target area from electron and ion beams during subsequent FIB-SEM sectioning, while further enhancing the sample's conductivity. Lunar soil particles for transmission electron microscopy (TEM) are 10-13 μm long, 5-10 μm high, and 70-90 nm wide. This thickness (width) ensures electron beam penetration for TEM observation while maximizing the preservation of the sample's microstructure.

[0023] The technical effects of this invention include, but are not limited to:

[0024] This invention employs a combined coating method of a carbon initial conductive layer and a gold reinforcement layer. The coating is applied in a layered, staged manner, first using carbon spraying followed by gold. An initial conductive layer is formed using low-intensity carbon spraying to avoid excessive elemental interference during EDS analysis, and to prevent large gold particles (8-12 nm) from obscuring the sample's morphology and causing damage to the fragile space-weathered structures on the lunar regolith due to excessive intensity. After SEM-EDS (a combined scanning electron microscope and energy dispersive spectroscopy EDS instrument used to observe the sample surface morphology and simultaneously perform micro-area elemental composition analysis), a second conductive coating is applied using gold material. This prevents the subsequent platinum protective layer deposition during FIB-SEM from intruding into and damaging the space-weathered structures on the lunar regolith, while simultaneously enhancing conductivity to ensure the accuracy of FIB-SEM sample preparation.

[0025] The beneficial effects of this invention are as follows:

[0026] (1) The present invention uses a combination of carbon initial conductive layer and gold reinforcement layer to avoid the invasion and damage of the platinum protective layer on the surface of lunar soil particles by subsequent FIB-SEM electron beam and ion beam deposition, thus truly preserving the space weathering characteristics of lunar soil and providing accurate and reliable samples for the study of space weathering of lunar soil.

[0027] (2) In this invention, gold coating is performed on the sample after SEM-EDS observation, which avoids large gold particles (8-12nm) from obscuring the morphological information of the sample. If gold coating is performed first and then the target research area is screened, a large number of large gold particles will appear on the gold film, and these large gold particles will obscure the morphological features of the sample.

[0028] (3) The present invention uses gold material for secondary coating to further enhance the conductivity of the sample to improve the sample preparation accuracy of FIB-SEM, and can accurately obtain the transmission electron microscope sample of the target area.

[0029] (4) The sample preparation method of the present invention has good repeatability and practicality, fully considers the complexity and diversity of lunar soil surface structure, and is not only applicable to transmission electron microscopy sample preparation of lunar soil samples of different sources and properties, but can also be extended to electron microscopy sample preparation of other celestial samples (such as asteroids and Mars) through parameter adjustment, providing a universal and highly reliable technical solution for microscopic analysis in the field of planetary science. Attached Figure Description

[0030] Figure 1 This is a schematic flowchart illustrating the implementation steps of a transmission electron microscopy sample preparation method for a space-weathered surface of lunar soil according to an embodiment of the present invention.

[0031] Figure 2 The images show HAADF images of the lunar soil glass particles from Embodiment 1 of the present invention, as well as elemental distribution diagrams of C, Si, Pt, and Au.

[0032] Figure 3 The image shows a HAADF image of a lunar soil glass particle sample with metallic iron particles on its surface, as well as elemental distribution diagrams of C, Si, Fe, Pt, and Au, from Embodiment 2 of the present invention.

[0033] Figure 4 The images show the HAADF images of the lunar soil apatite transmission electron microscope sample from Example 3 of this invention, as well as the elemental distribution diagrams of C, O, Pt, and Au.

[0034] Figure 5 The image shows the HAADF image of the lunar soil glass particle transmission electron microscope sample of Comparative Example 1 of this invention, as well as the elemental distribution diagram of C, Si and Pt.

[0035] Figure 6 The images shown are HAADF images of the lunar soil ilmenite transmission electron microscope sample of Comparative Example 2 of this invention, as well as elemental distribution diagrams of Ti, Pt, and Au.

[0036] HAADF (High Angle Annular Dark Field) is an imaging technique in scanning transmission electron microscopy that uses a ring detector to collect electron signals scattered at high angles. Detailed Implementation

[0037] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0038] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that the upper and lower limits of the range and each intermediate value between them are specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0039] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention is described. While only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail. Unless otherwise stated, “%” means percentage based on weight.

[0040] Those skilled in the art will understand that other steps or operations may be included before, after, or between any steps in this embodiment, for example, to further optimize and / or improve the method described in this invention.

[0041] like Figure 1 As shown in the figure, the overall technical solution of a transmission electron microscopy sample preparation method for lunar regolith weathered surface in this embodiment is as follows:

[0042] Step S101: The selected target lunar soil particles are pasted onto carbon conductive tape, with the target flat surface of the target lunar soil particles facing away from the carbon conductive tape. The target flat surface of the target lunar soil particles and the carbon conductive tape are parallel, and the target flat surface is the largest flat surface on the surface of the target lunar soil particles.

[0043] Step S102: A carbon film is uniformly deposited on the surface of the target lunar soil particles to obtain a scanning electron microscope sample of the target lunar soil particles. In the actual carbon film deposition, the carbon film not only covers the entire flat surface of the target, but also covers most of the other surfaces of the target lunar soil particles.

[0044] Step S103: Several target study areas are selected on the carbon film corresponding to the target flat surface. Different target study areas correspond to different space weathering processes and degrees. Specifically, this step selects several target study areas based on the surface morphology characteristics (cleanliness, impact craters, beaded iron particles, and sputtering blankets, etc.) of the target flat surface to observe the microstructure and composition of the target study areas up to 1 μm deep from the surface.

[0045] Step S104: A gold film is uniformly deposited on the carbon film corresponding to the target lunar soil particle scanning electron microscope sample, wherein the gold film completely covers the carbon film.

[0046] Step S105: Deposit a protective layer for the research area sequentially on the gold film corresponding to all the target research areas using an electron beam and an ion beam, so that the gold film corresponding to each target research area is covered with a protective layer for the target research area, wherein each protective layer for the target research area completely covers the target research area corresponding to it.

[0047] Step S106: Along the edge of each target study region, slice the target lunar regolith particle scanning electron microscope (SEM) sample perpendicular to the target flat surface to obtain a target lunar regolith particle transmission electron microscope (TEM) sample. Each target lunar regolith particle TEM sample contains only one target study region. The slices are 10-13 μm long, approximately 5-10 μm high, and 70-90 nm thick to meet TEM requirements. The height refers to the depth of the vertical cut inwards. The length * thickness corresponds to the selected target study region in the SEM image (10-13 μm long * 1.5 μm wide). This step slices the sample based on the edge of the target study region.

[0048] Example 1

[0049] (1) Particle sorting: Under an optical microscope inside an inert gas glove box, tweezers and glass dishes that have been sterilized with ethanol (99.9%) were used to carefully sort out several lunar soil glass particles with larger diameters (>50μm).

[0050] (2) Sample mounting: Place carbon conductive tape on the sample stage, and carefully attach the flatter side (the flattest side) of the sorted lunar soil glass particles with relatively uniform particle size (~200μm×~300μm) to the carbon conductive tape under an optical microscope.

[0051] (3) Carbon coating of sample: The glued lunar soil glass particles are placed in a vacuum carbon coating instrument (model Cressington108C), the current is set to 75A, the carbon spraying time is 6s, and the carbon spraying is repeated 11 times with an interval of 1min each time, so as to uniformly coat a carbon film with a thickness of 70-90nm on the sample surface, enhance the conductivity, and obtain the scanning electron microscope sample of lunar soil glass particles.

[0052] (4) SEM-EDS observation: First, use a syringe to blow away the SEM sample of lunar regolith glass particles to remove the dust adhering to the surface and check whether the lunar regolith glass particles are firmly attached. Use an SEM equipped with EDS to observe the SEM sample of lunar regolith glass particles. Take 16K high-resolution images of each particle at 200-350x magnification to obtain its surface morphology characteristics. Collect chemical composition information of each particle at 1K resolution at 1000-1500x magnification. Combine the surface morphology characteristics and chemical composition information to screen out the areas on the surface of lunar regolith glass particles with elongated and granular metallic iron.

[0053] (5) Gold coating on the sample: The scanning electron microscope sample of lunar soil glass particles observed by SEM-EDS was placed in a magnetron sputtering instrument (model Hitachi MSP-1S), the current was set to 35mA, the gold sputtering time was 40s, and it was repeated twice to uniformly coat the sample surface with a gold film with a thickness of 60-100nm, which further enhanced the conductivity.

[0054] (6) FIB-SEM sectioning: Using FIB-SEM, a platinum protective layer (13 μm long × 2 μm wide × 0.5 μm high) was first deposited on the target area with elongated and granular metallic iron on the surface of the lunar regolith glass particles screened in step (4) by electron beam induction. Then, a platinum protective layer (13 μm long × 2 μm wide × 1 μm high) was deposited again on the protective layer deposited by electron beam induction by ion beam induction. This was done to eliminate the damage to the target area caused by electron beam and ion beam during the subsequent FIB-SEM sectioning process and to further enhance the conductivity of the target location. Then, a vertical cut was made in the protective layer area to obtain a sample with a length of 11 μm × width of 1 μm × height of 7.5 μm. The sample was then welded to a copper grid using platinum, and then thinned and swept to 80 nm to finally obtain a lunar regolith glass particle transmission electron microscope sample with a length of 11 μm × width of 80 nm × height of 7.5 μm. Transmission electron microscopy (TEM) HAADF images and elemental distribution maps (C, Si, Pt, and Au) of lunar regolith glass particles were observed using the sample preparation method described in Example 1. Figure 2 As shown, the HAADF plot from top to bottom represents the protective layer, gold film, carbon film, and glass. The dashed lines in the elemental distribution plot represent the boundaries of each element. A comparison of the elemental distribution plots for C, Si, Pt, and Au shows that the lunar regolith glass surface treated using the method described in Example 1 (carbon coating + gold coating) was not damaged by the intrusion of the conductive coating material or the platinum material deposited in the protective layer during FIB-SEM sectioning.

[0055] Example 2

[0056] (1) Particle sorting: Under an optical microscope inside an inert gas glove box, tweezers and glass dishes that have been sterilized with ethanol (99.9%) were used to carefully sort out several lunar soil glass particles with larger diameters (>50μm).

[0057] (2) Sample mounting: Place carbon conductive tape on the sample stage, and carefully attach the sorted lunar soil glass particles with relatively uniform particle size (~200μm×~300μm) with the flatter side (the flattest side) facing up onto the carbon conductive tape under an optical microscope.

[0058] (3) Carbon coating of sample: The glued lunar soil glass particles are placed in a vacuum carbon coating instrument (model Cressington108C), the current is set to 75A, the carbon spraying time is 6s, and the carbon spraying is repeated 8 times with an interval of 1min each time, so as to uniformly coat a carbon film with a thickness of 50-70nm on the sample surface, enhance the conductivity, and obtain the scanning electron microscope sample of lunar soil glass particles.

[0059] (4) SEM-EDS observation: First, use a syringe to blow away the SEM sample of lunar regolith glass particles to remove the dust adhering to the surface and check whether the lunar regolith glass particles are firmly attached. Use an SEM equipped with EDS to observe the SEM sample of lunar regolith glass particles. Take 16K high-resolution images of each particle at 200-350x magnification to obtain its surface morphology characteristics. Collect chemical composition information of each particle at 1K resolution at 1000-1500x magnification. Combine the surface morphology and chemical composition to screen out the areas on the surface of lunar regolith glass particles with elongated and granular metallic iron.

[0060] (5) Gold coating on the sample: The scanning electron microscope sample of lunar soil glass particles observed by SEM-EDS was placed in a magnetron sputtering instrument (model Hitachi MSP-1S), the current was set to 35mA, the gold sputtering time was 40s, and it was repeated twice to uniformly coat the sample surface with a gold film with a thickness of 50-90nm, which further enhanced the conductivity.

[0061] (6) FIB-SEM sectioning: Using FIB-SEM, a platinum protective layer (12 μm long × 2 μm wide × 0.5 μm high) was first deposited on the target area with elongated and granular metallic iron on the surface of the lunar regolith glass particles screened in step (4) by electron beam induction. Then, a platinum protective layer (12 μm long × 2 μm wide × 1 μm high) was deposited again on the protective layer deposited by electron beam induction by ion beam induction. This was done to eliminate the damage to the target area caused by electron beam and ion beam during the subsequent FIB-SEM sectioning process and to further enhance the conductivity of the target location. Then, a vertical cut was made in the protective layer area to obtain a sample with a length of 10 μm × width of 0.5 μm × height of 8 μm. The sample was then soldered to a copper grid using platinum, and then thinned and blown to 80 nm to finally obtain a lunar regolith glass particle transmission electron microscope sample with a length of 10 μm × width of 80 nm × height of 8 μm.

[0062] Transmission electron microscopy (TEM) HAADF images and elemental distribution maps (C, Si, Fe, Pt, and Au) of lunar soil glass particles were observed using the sample preparation method described in Example 2. Figure 3As shown, the HAADF plot, from top to bottom, represents the protective layer, gold film, carbon film, iron particles, and glass. The dashed lines in the elemental distribution plot represent the boundaries of each element. A comparison of the elemental distribution plots for C, Si, Fe, Pt, and Au shows that the lunar soil glass and iron particles treated using the sample preparation method of Example 2 (carbon coating + gold coating) were not damaged by the intrusion of the conductive coating material or the platinum material deposited in the protective layer during FIB-SEM sectioning.

[0063] Example 3

[0064] (1) Particle sorting: Under an optical microscope inside an inert gas glove box, tweezers and glass dishes that have been sterilized with ethanol (99.9%) were used to carefully sort out multiple lunar soil rock and mineral particles with larger particle sizes (>50μm).

[0065] (2) Sample mounting: Place carbon conductive tape on the sample stage, and carefully attach the sorted lunar soil rocks and mineral particles with relatively uniform particle size (~200μm×~300μm) with the flatter side (the flattest side) facing up onto the carbon conductive tape under an optical microscope.

[0066] (3) Carbon coating of samples: The adhered lunar regolith and mineral particles were placed in a vacuum carbon coating instrument (model Cressington108C), the current was set to 75A, the carbon spraying time was 6s, and the carbon spraying was repeated 13 times with an interval of 1min each time, so as to uniformly coat a carbon film with a thickness of about 100nm on the sample surface, enhance the conductivity, and obtain the scanning electron microscope sample of lunar regolith and mineral particles.

[0067] (4) SEM-EDS observation: First, use a syringe to blow away the SEM samples of lunar regolith and mineral particles to remove surface dust and check whether the lunar regolith and mineral particles are firmly attached. Use an SEM equipped with EDS to observe the SEM samples of lunar regolith and mineral particles. Take 16K high-resolution images of each particle at 200-350x magnification to obtain its surface morphology characteristics. Collect chemical composition information of each particle at 1K resolution at 1000-1500x magnification. Combine the surface morphology and chemical composition to screen out the apatite mineral region.

[0068] (5) Gold coating on samples: The SEM-EDS-observed lunar soil rocks and mineral particles were placed in a magnetron sputtering instrument (model Hitachi MSP-1S), the current was set to 35mA, gold was sputtered for 40s, and repeated twice to uniformly coat the sample surface with a gold film with a thickness of 60-100nm, which further enhanced the conductivity.

[0069] (6) Carbon coating of samples: A carbon coating of approximately 30-50 nm thickness was uniformly deposited on the surface of lunar soil rocks and mineral particles using a vacuum carbon coating instrument (model Cressington 108C), with a current of 75 A and a carbon spraying time of 6 s, repeated 6 times with a 1 min interval between each time. Since 6 months had passed since the gold coating of the samples in step (5), the gold film may have developed microcracks, peeled off, or adsorbed contaminants on the surface, reducing conductivity. Therefore, carbon coating was performed again before FIB-SEM sectioning to enhance conductivity.

[0070] (7) FIB-SEM sectioning: Using FIB-SEM, a platinum protective layer (12 μm long × 2 μm wide × 0.5 μm high) was first deposited on the target region of the apatite mineral selected in step (4) above by electron beam induction. Then, a platinum protective layer (12 μm long × 2 μm wide × 1 μm high) was deposited again on the protective layer deposited by electron beam induction by ion beam induction. This was done to eliminate the damage to the target region caused by electron beam and ion beam during the subsequent FIB-SEM sectioning process and to further enhance the conductivity of the target location. Then, a vertical cut was made in the protective layer region to obtain a sample with a length of 10 μm × width of 0.5 μm × height of 7 μm. The sample was then welded to a copper grid using platinum, and then thinned and swept to 80 nm to finally obtain a lunar apatite transmission electron microscope sample with a length of 10 μm × width of 80 nm × height of 7 μm.

[0071] Transmission electron microscopy (HAADF) images and elemental distribution maps (C, O, Pt, and Au) of lunar soil apatite were observed using the sample preparation method described in Example 3. Figure 4 As shown, the HAADF plot from top to bottom represents the protective layer, carbon film, gold film, carbon film again, and apatite. The dashed lines in the elemental distribution plot represent the boundaries of each element. A comparison of the elemental distribution plots for C, O, Pt, and Au shows that the lunar soil apatite surface treated using the method described in Example 3 (carbon coating + gold coating + carbon coating) was not damaged by the intrusion of the conductive coating material or the platinum material deposited in the protective layer during FIB-SEM sectioning.

[0072] Comparative Example 1

[0073] (1) Particle sorting: Under an optical microscope inside an inert gas glove box, tweezers and glass dishes that have been sterilized with ethanol (99.9%) were used to carefully sort out several lunar soil glass particles with larger diameters (>50μm).

[0074] (2) Sample mounting: Place carbon conductive tape on the sample stage, and carefully attach the sorted lunar soil glass particles with relatively uniform particle size (~200μm×~300μm) with the flatter side (the flattest side) facing up onto the carbon conductive tape under an optical microscope.

[0075] (3) Carbon coating of sample: The glued lunar soil glass particles are placed in a vacuum carbon coating instrument (model Cressington108C), the current is set to 75A, the carbon spraying time is 6s, and the carbon spraying is repeated 4 times with an interval of 1min each time, so as to uniformly coat a carbon film with a thickness of 20-30nm on the sample surface, enhance the conductivity, and obtain the scanning electron microscope sample of lunar soil glass particles.

[0076] (4) SEM-EDS observation: First, use a syringe to blow away the SEM sample of lunar regolith glass particles to remove surface dust and check whether the particles are firmly adhered. Use an SEM equipped with EDS to observe the SEM sample of lunar regolith glass particles. Take 16K high-resolution images of each particle at 200-350x magnification to obtain its surface morphology features. Collect chemical composition information of each particle at 1K resolution at 1000-1500x magnification. Combine surface morphology and chemical composition to screen out areas with micro-crater clusters on the surface of lunar regolith glass particles.

[0077] (5) FIB-SEM sectioning: Using FIB-SEM, a platinum protective layer (12 μm long × 2 μm wide × 0.5 μm high) was first deposited on the target area with micro-meteorite crater clusters on the surface of the lunar regolith glass particles selected in step (4) using electron beam induction. Then, a platinum protective layer (12 μm long × 2 μm wide × 1 μm high) was deposited again on the protective layer deposited by electron beam induction using ion beam induction. This was done to eliminate the damage to the target area caused by electron beam and ion beam during the subsequent FIB-SEM sectioning process and to further enhance the conductivity of the target location. Then, a vertical cut was made in the protective layer area to obtain a sample with a length of 10 μm × width of 0.8 μm × height of 10 μm. The sample was then welded to a copper grid using platinum, and then thinned and blown to 90 nm to finally obtain a lunar regolith glass particle transmission electron microscope sample with a length of 10 μm × width of 90 nm × height of 10 μm.

[0078] Transmission electron microscopy (HAADF) images and elemental distribution maps (C, Si, and Pt) of lunar regolith glass particles were observed using the comparative example sample preparation method. Figure 5 As shown, the HAADF plot, from top to bottom, represents the protective layer, carbon film, and glass. The dashed lines in the elemental distribution plot represent the boundaries of each element. By comparing the elemental distribution plots of C, Si, and Pt, it was found that the lunar regolith glass surface treated using the first sample preparation method (only one carbon coating treatment) was penetrated by conductive coated carbon material and platinum material deposited in the protective layer during FIB-SEM slicing, with the deepest penetration reaching 50 nm.

[0079] Comparative Example 2

[0080] (1) Particle sorting: Under an optical microscope inside an inert gas glove box, tweezers and glass dishes that have been sterilized with ethanol (99.9%) were used to carefully sort out multiple lunar soil rock and mineral particles with larger particle sizes (>50μm).

[0081] (2) Sample mounting: Place carbon conductive tape on the sample stage, and carefully attach the sorted lunar soil rocks and mineral particles with relatively uniform particle size (~200μm×~300μm) with the flatter side (the flattest side) facing up onto the carbon conductive tape under an optical microscope.

[0082] (3) Gold coating on samples: The adhered lunar regolith and mineral particles were placed in a magnetron sputtering instrument (model Hitachi MSP-1S), the current was set to 35mA, the gold sputtering time was 40s, and it was repeated twice to uniformly coat a gold film with a thickness of 40-80nm on the carbon film on the sample surface to enhance conductivity and obtain scanning electron microscope samples of lunar regolith and mineral particles.

[0083] (4) SEM-EDS observation: First, use a syringe to blow away the SEM samples of lunar regolith and mineral particles to remove surface dust and check whether the lunar regolith and mineral particles are firmly attached. Use an SEM equipped with EDS to observe the SEM samples of lunar regolith and mineral particles. Take 16K high-resolution images of each particle at 200-350x magnification to obtain its surface morphology characteristics. Collect chemical composition information of each particle at 1K resolution at 1000-1500x magnification. Combine surface morphology and chemical composition to screen out areas with micro-meteorite crater clusters on the surface of ilmenite.

[0084] (6) FIB-SEM sectioning: Using FIB-SEM, a platinum protective layer (13 μm long × 2 μm wide × 0.5 μm high) was first deposited on the target area with micro-meteorite crater clusters on the ilmenite surface selected in step (4) above by electron beam induction. Then, a platinum protective layer (13 μm long × 2 μm wide × 1 μm high) was deposited again on the protective layer deposited by electron beam induction. This was done to eliminate the damage to the target area caused by electron beam and ion beam during the subsequent FIB-SEM sectioning process and to further enhance the conductivity of the target location. Then, a vertical cut was made in the protective layer area to obtain a sample with a length of 11 μm × width of 0.8 μm × height of 10 μm. The sample was then welded to a copper grid using platinum, and then thinned and blown down to 70 nm to finally obtain a lunar ilmenite transmission electron microscope sample with a length of 11 μm × width of 70 nm × height of 10 μm.

[0085] Transmission electron microscopy (HAADF) images and elemental distribution maps (Ti, Pt, and Au) of lunar ilmenite were observed using the sample preparation method in Comparative Example 2. Figure 6As shown, the HAADF diagram, from top to bottom, shows the ion beam protective layer, electron beam protective layer, gold film, and ilmenite. The dashed lines in the elemental distribution diagram represent the boundaries of each element. By comparing the elemental distribution diagrams of Ti, Pt, and Au, it was found that the lunar ilmenite surface treated using the second sample preparation method (only one gold coating treatment) was penetrated by the conductive gold coating material, with a penetration depth of approximately 38.5 nm.

[0086] This invention addresses the technical problem of coating and protective layer materials invading and damaging the microscopic features of space weathering on the surface of lunar soil particles during existing lunar soil transmission electron microscopy (TEM) sample preparation processes, and proposes a new sample preparation method. This method first selects larger (>50 μm) lunar regolith particles through particle sorting. After the samples are mounted on a stage, a low-intensity carbon spraying treatment is applied to form an initial conductive layer, reducing elemental interference in subsequent energy dispersive spectroscopy (EDS) analysis and preventing large gold particles (8-12 nm) from obscuring the sample morphology information. Next, the target study area (10-13 μm long × 1.5 μm wide) is observed and screened using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). Then, a second conductive coating is applied using gold material to prevent the subsequent platinum protective layer deposition from intruding and damaging the space weathering structure on the lunar regolith surface, while enhancing conductivity to ensure the accuracy of focused ion beam (FIB) sample preparation. Finally, a platinum protective layer (10-15 μm long × 2 μm wide) is deposited in the target study area using dual-beam electron and ion beams via dual-beam electron microscopy (FIB-SEM), and a transmission electron microscopy sample of lunar regolith particles with a length of 10-13 μm, a width of 70-90 nm, and a height of 5-10 μm is obtained by vertical sectioning. This invention can accurately preserve the space weathering characteristics of lunar soil and precisely obtain transmission electron microscopy samples of the target area. It has good repeatability and practicality, providing accurate and reliable samples for the study of space weathering of lunar soil, and also providing a generalized and highly reliable technical solution for microscopic analysis in the field of planetary science.

[0087] Although the invention has been described with reference to exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary embodiments. Various adjustments or changes may be made to the exemplary embodiments described in this specification without departing from the scope or spirit of the invention. The scope of the claims should be interpreted in the broadest possible sense to cover all modifications and equivalent structures and functions.

Claims

1. A method for preparing a transmission electron microscope sample of lunar regolith weathered surface, characterized in that, include: Step 1: Adhere the selected target lunar soil particles to the carbon conductive tape, and place the target flat surface of the target lunar soil particles facing away from the carbon conductive tape, wherein the target flat surface is the largest flat surface on the surface of the target lunar soil particles. Step 2: A carbon film is uniformly deposited on the surface of the target lunar soil particles to obtain a scanning electron microscope sample of the target lunar soil particles. Step 3: Select several target research areas on the carbon film corresponding to the target flat surface. Different target research areas correspond to different space weathering processes and degrees. Step 4: A gold film is uniformly deposited on the carbon film corresponding to the target lunar soil particle scanning electron microscope sample; Step 5: Sequentially deposit a protective layer for the research area on the gold film corresponding to all the target research areas using electron beam and ion beam, so that the gold film corresponding to each target research area is covered with a protective layer for the target research area. Step six: Along the edge of each target study area, perform a slicing operation perpendicular to the target flat surface on the target lunar soil particle scanning electron microscope sample to obtain a target lunar soil particle transmission electron microscope sample, wherein each target lunar soil particle transmission electron microscope sample contains only one target study area.

2. The method for preparing a transmission electron microscope sample of lunar regolith weathered surface according to claim 1, characterized in that, In step one, the method for screening the target lunar soil particles includes: A number of lunar soil particles are provided, and under an optical microscope inside an inert gas glove box, tweezers and glass dishes sterilized with ethanol are used to screen out the lunar soil particles with a particle size greater than or equal to 50 μm as the target lunar soil particles.

3. The method for preparing a transmission electron microscope sample of the space-weathered surface of lunar soil according to claim 1, characterized in that, In step two, a carbon film is uniformly deposited on the surface of the target lunar regolith particles to obtain a scanning electron microscope sample of the target lunar regolith particles, including: The target lunar soil particles, which are attached to the carbon conductive adhesive tape, are placed in a vacuum carbon plating instrument; The current of the vacuum carbon plating instrument is set to 70-75A, the carbon spraying time is set to 5-7s, the number of carbon sprayings is set to 8-13, and the interval between each carbon spraying is set to 1-1.5min. A carbon film with a thickness of 50-100nm is uniformly deposited on the surface of the target lunar soil particles to obtain the scanning electron microscope sample of the target lunar soil particles.

4. The method for preparing a transmission electron microscope sample of lunar regolith weathered surface according to claim 1, characterized in that, In step three, the screening of several target study areas on the carbon film corresponding to the target flat surface includes: A scanning electron microscope equipped with an energy-dispersive X-ray spectrometer was used to capture 16K high-resolution images of each target lunar regolith particle scanning electron microscope sample at a magnification of 100-500x to obtain its surface morphology features, and chemical composition information of each target lunar regolith particle scanning electron microscope sample was acquired at a resolution of 1K at a magnification of 500-2000x. Based on the surface morphology features and chemical composition information of each target lunar soil particle scanning electron microscope sample, each target study area corresponding to each target lunar soil particle scanning electron microscope sample is screened on the carbon film corresponding to the target flat surface. Each target study area is a rectangular area with a length of 10-13 μm and a width of 1-1.5 μm.

5. The method for preparing a transmission electron microscope sample of the space-weathered surface of lunar soil according to claim 1, characterized in that, In step four, uniformly depositing a gold film onto the carbon film corresponding to the target lunar soil particle scanning electron microscope sample includes: After selecting several target study areas, the target lunar soil particles were placed into a magnetron sputtering instrument. The current of the magnetron sputtering instrument is set to 30-35mA, the gold sputtering time is set to 40-50s, and the number of gold sputtering times is set to 1-2 times, so that a gold film with a thickness of 50-100nm is uniformly deposited on the carbon film corresponding to the target lunar soil particle scanning electron microscope sample.

6. The method for preparing a transmission electron microscope sample of lunar regolith weathered surface according to claim 1, characterized in that, In step five, the deposition of a protective layer for the research area is performed sequentially on the gold film corresponding to all the target research areas using electron beams and ion beams, so that the gold film corresponding to each target research area is covered with a protective layer for the target research area, including: A first protective layer of 10-15 μm long × 2 μm wide × 0.5 μm high is deposited on the gold film corresponding to all the target study areas by electron beam induction using a focused ion beam scanning electron microscope, and each first protective layer completely covers the target study area corresponding to it. A second protective layer of 10-15 μm long × 2 μm wide × 1 μm high is deposited on the entire first protective layer of the study area using ion beam induction by focusing ion beam scanning electron microscopy, and each second protective layer of the study area completely covers the first protective layer of the study area. The first protective layer of the study area and the second protective layer of the study area together constitute the target protective layer of the study area.

7. The method for preparing a transmission electron microscope sample of space-weathered lunar soil surface according to claim 6, characterized in that, The deposition materials of the first protective layer and the second protective layer of the study area are any one of platinum, carbon, silicon oxide and tungsten metal, but not limited to platinum, carbon, silicon oxide and tungsten metal.

8. The method for preparing a transmission electron microscope sample of space-weathered lunar soil surface according to claim 6, characterized in that, The first deposition material corresponding to the protective layer of the first study area and the second deposition material corresponding to the protective layer of the second study area may be the same or different.

9. The method for preparing a transmission electron microscope sample of the space-weathered surface of lunar soil according to claim 1, characterized in that, In step six, the target lunar regolith particle scanning electron microscope (SEM) sample is sliced ​​perpendicular to the target flat surface along the edge of each target study region to obtain a target lunar regolith particle transmission electron microscope (TEM) sample. Each target lunar regolith particle TEM sample contains only one target study region, including: By using a focused ion beam scanning electron microscope, the target lunar regolith particle scanning electron microscope sample is sliced ​​perpendicular to the target flat surface along the edge of each target study area to obtain a target lunar regolith primary transmission electron microscope sample with a length of 10-13 μm × width of 0.5-1 μm × height of 5-10 μm, wherein each target lunar regolith primary transmission electron microscope sample contains only one target study area. The primary sample of the target lunar regolith particles is welded onto a copper mesh, and then the primary sample of the target lunar regolith particles is thinned and purged to reduce its thickness to 70-90 nm, thus obtaining the transmission electron microscope (TEM) sample of the target lunar regolith particles, wherein each TEM sample of the target lunar regolith particles contains only one target study area.

10. The application of a transmission electron microscopy (TEM) sample preparation method for space-weathered lunar soil surface according to any one of claims 1-9 in the field of TEM sample preparation for lunar soil.

Images