Method for facet orientation processing of regular morphology single crystal catalyst based on fib

Abstract

The present application relates to a kind of methods for the crystal face directional processing of regular morphology single crystal catalyst based on FIB, comprising the following steps: find regular morphology single crystal catalyst under the field of view of electron beam, judge the angle of the crystal face to be observed in three-dimensional space, the projection direction of target crystal face normal in horizontal plane is adjusted to predetermined position by controlling sample table to rotate in horizontal plane;Again, sample table is tilted, so that FIB carrier net and vertical direction form specific angle, the theoretical value of the specific angle β is equal to the angle α between target crystal face normal and horizontal plane;Then catalyst particle and FIB carrier net are fixed together at specific angle, the rotation of catalyst grain in three-dimensional space is realized, so that the fixed-point sampling and thinning of different exposed crystal face are realized, and the directional processing of any exposed crystal face in three-dimensional space can be realized by this method.

Description

Technical Field

[0001] This invention relates to the field of micro-nano fabrication and materials characterization technology, specifically to the preparation of transmission electron microscopy (TEM) samples, and particularly to a method for crystal plane orientation processing of single-crystal catalysts with regular morphology based on FIB. Background Technology

[0002] In catalysis research, single-crystal catalysts with regular morphologies are important research subjects. Different exposed crystal facets exhibit different surface atomic arrangements, coordination structures, and electronic states, thus displaying significantly different catalytic activities, selectivity, and stability. Therefore, atomic-scale microstructural characterization of different crystal facets of catalysts with specific morphologies is crucial for understanding their structure-activity relationships.

[0003] Currently, high-resolution transmission electron microscopy (HRTEM) is the core method for this type of characterization. However, for single-crystal catalysts with regular geometric morphologies, there is still a lack of systematic methods to achieve directional processing of specific crystal planes in three-dimensional space. For catalysts with small sizes (<100 nm), samples with different orientations are usually randomly selected on a grid (such as a copper grid) and the crystal structure is directly observed using TEM. However, this method relies on random orientation and cannot achieve directional analysis and preparation of specific crystal planes. For single-crystal particles with sizes ranging from hundreds of nanometers to several micrometers, electron beams have difficulty penetrating them, and thinning techniques must be used to prepare electron-transparent sheets (usually <100 nm). Due to its precise positioning and strong processing capabilities, FIB-SEM technology has become a routine method for TEM sample preparation.

[0004] Conventional FIB sampling procedures (such as the "lift-out" method) operate along a fixed direction, including "vertical sampling" (the surface to be observed is parallel to the electron beam) and "horizontal sampling" (the plane to be observed is perpendicular to the electron beam). However, when the crystal plane to be observed of the catalyst is at other angles to the electron beam (not 0° or 90°), traditional processing methods struggle to achieve effective and precise directional thinning and sampling. Therefore, there is an urgent need to establish a complete process flow to address the directional processing requirements of arbitrary crystal planes in catalysts with different morphologies. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a method for crystal face orientation processing of regular-morphology single-crystal catalysts based on FIB. By analyzing the catalyst morphology and crystal structure to determine the spatial orientation of the target crystal face, and by coordinating the planar rotation of the catalyst and the spatial tilt of the sample stage, the catalyst particles are redirected, thereby achieving point sampling and thinning of any preset crystal face.

[0006] The technical solution adopted in this invention is as follows:

[0007] The present invention proposes a method for crystal plane orientation processing of single-crystal catalysts with regular morphology based on FIB, which specifically includes the following steps: S1. Sample positioning and orientation analysis; S2, Three-dimensional spatial rotation orientation: (a) In-plane rotational orientation: Control the sample stage to rotate in the horizontal plane so that the projection direction of the target crystal plane normal in the horizontal plane is adjusted to the predetermined position; (b) Deposit a protective layer on the top of the catalyst and pull out the sample vertically; (c) Out-of-plane tilt orientation: Tilting the sample stage so that the FIB netting forms a specific angle with the vertical direction; the theoretical value of the specific angle is equal to the angle between the normal of the target crystal plane and the horizontal plane; S3. Oriented fixation: After completing step S2, the catalyst particles are fixed at a certain angle on the TEM grid dedicated to FIB. S4. Directional thinning: The fixed catalyst is thinned along a direction perpendicular to the normal of the target crystal plane using a focused ion beam, and finally an electronic transparent sheet for TEM observation is prepared.

[0008] Furthermore, the regular morphology includes, but is not limited to, cubes, octahedrons, rods, sheets, or other polyhedra.

[0009] Furthermore, step S1 includes: selecting regular-shaped single-crystal catalyst particles to be processed under electron beam field of view, and determining the angle of the crystal plane to be observed in three-dimensional space based on the morphology and crystal structure of the catalyst.

[0010] Furthermore, in step S2, the rotation and tilting operations of the sample stage are implemented based on the sample stage motion control module of the FIB-SEM system.

[0011] Furthermore, in step S2, if the target crystal plane normal is already in the horizontal plane, then only in-plane rotational orientation is required.

[0012] Furthermore, in step S4, a protective layer needs to be deposited in a specific area of ​​the catalyst before and during the thinning process to prevent ion beam damage.

[0013] Compared with the prior art, the present invention has the following advantages: 1. This invention achieves the orientation of catalysts with regular morphology in three-dimensional space through the coordinated orientation of "planar rotation" and "spatial tilt", breaking through the limitations of traditional FIB fixed-direction processing, and can meet the crystal plane processing requirements of arbitrary spatial orientation, effectively solving the problem that traditional fixed-direction processing mode cannot cope with complex spatial angle crystal planes.

[0014] 2. This invention transforms the requirement of "crystal orientation" into a clear and quantifiable sample stage rotation angle and tilt angle. The operation steps are clear and standardized, the parameters are clear, and it has good repeatability and controllability.

[0015] 3. Based on the geometric morphology and spatial angle of the catalyst, this invention is applicable in principle to any single crystal material with a regular shape (such as cube, octahedron, rod, etc.), and is not limited to a specific chemical composition.

[0016] 4. This invention can reliably prepare TEM samples with specific orientations, providing key technical support for studying the structure-activity relationship between catalyst surface structure and performance at the atomic scale. Attached Figure Description

[0017] Figure 1 These are morphological diagrams of hexagonal prism-shaped molybdenum trioxide catalysts and orientation diagrams of different exposed crystal faces; Figure 2 This is a flowchart illustrating the three-dimensional rotation of hexagonal prism-shaped molybdenum trioxide with different exposed crystal faces. Figure a shows the image of the hexagonal prism-shaped molybdenum trioxide after tilting within a horizontal plane; Figure b shows the image after a protective layer (carbon) is deposited on the top of the particle; Figure c shows the image of the particle being lifted vertically (z-direction) using a robotic arm; Figures d and e show the spatial relationship between the catalyst and the FIB mesh when the observed crystal face is the B crystal face and the FIB mesh β=30°; Figures f and g show the spatial relationship between the catalyst and the FIB mesh when the observed crystal face is the A crystal face and the FIB mesh β=90°; Figures h and i show the spatial relationship between the catalyst and the FIB mesh when the observed crystal direction is the y-axis and the FIB mesh β=0°.

[0018] Figure 3 This is a flowchart of the directional thinning process of hexagonal prism-shaped molybdenum trioxide; where, Figure a is a SEM image of the catalyst transferred to the FIB grid; Figure b is a SEM image of the FIB grid tilted to be parallel to the ion beam direction, since the catalyst particles have completed spatial rotation, the top is missing a protective layer at this time; Figure c is a SEM image after a protective layer has been redeposited on the top of the catalyst particles; Figure d is a SEM image of the catalyst after directional thinning. Detailed Implementation

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] The present invention proposes a method for crystal plane orientation processing of single-crystal catalysts with regular morphology based on FIB, which specifically includes the following steps: S1. Sample Positioning and Orientation Analysis: Under electron beam field of view, select the single-crystal catalyst particles with regular morphology to be processed, and determine the angle of the crystal face to be observed in three-dimensional space based on the morphology and crystal structure of the catalyst. The regular morphology includes, but is not limited to, cubes, octahedrons, rods, plates, or other polyhedra; the sample includes, but is not limited to, catalysts or other materials.

[0021] S2, Three-dimensional spatial rotation orientation: (a) In-plane rotational orientation: Control the sample stage to rotate in the horizontal plane so that the projection direction of the target crystal plane normal in the horizontal plane is adjusted to the predetermined position; (b) A protective layer is deposited on the top of the catalyst, and the sample is lifted vertically using a robotic arm; (c) Out-of-plane tilt orientation: Tilting the sample stage so that the FIB netting forms a specific angle with the vertical direction; the theoretical value of the specific angle is equal to the angle between the normal of the target crystal plane and the horizontal plane.

[0022] If the target crystal plane normal is already in the horizontal plane, then only in-plane rotational orientation is required.

[0023] The rotation and tilting of the sample stage are both achieved through the sample stage motion control module of the FIB-SEM system.

[0024] S3. Orientation Fixation: After completing the spatial orientation described in step S2, the catalyst particles are fixed at a certain angle on the TEM grid dedicated to FIB.

[0025] S4. Directional thinning: The fixed catalyst is thinned along a direction perpendicular to the normal of the target crystal plane using a focused ion beam, and finally an electronic transparent sheet for TEM observation is prepared.

[0026] Before and during the thinning process, a protective layer needs to be deposited in specific areas of the catalyst to prevent ion beam damage.

[0027] This invention determines the angle of the exposed crystal facet in three-dimensional space based on the morphology and crystal structure of the catalyst. By controlling the rotation of the sample stage in the horizontal plane, the projection direction of the target crystal facet normal in the horizontal plane is adjusted to a predetermined position. Then, the sample stage is tilted so that the FIB carrier forms a specific angle with the vertical direction. The theoretical value of the specific angle β is equal to the angle α between the target crystal facet normal and the horizontal plane. Then, the catalyst particles and the FIB carrier are fixed together at a specific angle, realizing the rotation of the catalyst grains in three-dimensional space. This allows for point sampling and thinning of different exposed crystal faces. This method can achieve directional processing of any exposed crystal facet in three-dimensional space.

[0028] The present invention will be further illustrated below through specific embodiments: This embodiment describes the directional processing of molybdenum trioxide with different exposed crystal planes in a regular hexagonal prism morphology. The focused ion beam (FIB) equipment used is a Thermoscientific Helios 5 CX model. The specific process of the processing method is as follows: S1. Sample Localization and Orientation Analysis: The catalyst powder was ultrasonically dispersed with ethanol, dropped onto a silicon wafer, and dried. Monodisperse catalyst particles with regular morphology were located in the FIB-SEM field of view. The position of the normal direction of the hexagonal prism's observed crystal plane in three-dimensional space was determined. For example, the B crystal plane is shown in the appendix. Figure 1 .

[0029] S2. Based on the position of the crystal plane to be observed in three-dimensional space, complete the three-dimensional spatial orientation rotation: For the B crystal plane, its normal direction is outside the xy plane and the angle between it and the xy plane is 30°; (a) First, control the sample stage to rotate in the xy plane so that the projection of its normal direction on the xy plane is parallel to the y-axis; (b) Deposit a protective layer on the top of the hexagonal prism (A crystal plane), insert a robotic arm, fix the robotic arm to the top of the catalyst, and then manipulate the robotic arm to lift the catalyst in the vertical direction (z direction); (c) Use the tilting of the sample stage in space to manipulate the FIB carrier, controlling its angle with the vertical direction (z direction) to be 30°. See Appendix for specific steps. Figure 2 ; Similarly, for crystal plane A, its normal direction is outside the xy plane and makes an angle of 90° with the xy plane. (a) The sample stage is first rotated in the xy plane so that the projection of its normal direction onto the xy plane is parallel to the y-axis; (b) A protective layer is deposited on the top of the hexagonal prism, a robotic arm is inserted, and the robotic arm is fixed to the top of the catalyst. Then, the robotic arm is manipulated to lift the catalyst in the vertical direction (z direction); (c) The FIB carrier is manipulated by tilting the sample stage in space, and its angle with the vertical direction (z direction) is controlled to be 90°. For specific steps, please refer to the appendix. Figure 2 ; Similarly, if viewing directly along the y-axis, simply control the angle between the FIB carrier net and the vertical direction (z-direction) to 0°. See the attached document for specific steps. Figure 2 ; For the C crystal plane, the angle between the normal direction and the xy plane is also 30°, and the operation steps are the same as for the B crystal plane.

[0030] Similarly, for the D crystal plane, the normal direction is in the xy plane, so we only need to perform a rotation in the horizontal plane so that the projection of its normal direction onto the xy plane is parallel to the y-axis.

[0031] S3. Fix the catalyst particles and copper mesh together at the angle confirmed in step S2, cut off the end of the robot arm connected to the catalyst, and transfer the catalyst to the FIB carrier.

[0032] S4. Tilt the sample stage so that the FIB grid is parallel to the ion beam. At this angle, redeposit a protective layer on the top of the catalyst. Thin the catalyst while the FIB grid is parallel to the ion beam. The normal direction of the observed crystal plane of the final catalyst sheet is perpendicular to the FIB grid. See Appendix. Figure 3 .

[0033] All matters not covered in this invention are common knowledge.

[0034] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for crystal plane orientation processing of single-crystal catalysts with regular morphology based on FIB, characterized in that, The method includes the following steps: S1. Sample positioning and orientation analysis; S2, Three-dimensional spatial rotation orientation: (a) In-plane rotational orientation: Control the sample stage to rotate in the horizontal plane so that the projection direction of the target crystal plane normal in the horizontal plane is adjusted to the predetermined position; (b) Deposit a protective layer on the top of the catalyst and pull out the sample vertically; (c) Out-of-plane tilt orientation: Tilting the sample stage so that the FIB netting forms a specific angle with the vertical direction; the theoretical value of the specific angle is equal to the angle between the normal of the target crystal plane and the horizontal plane; S3. Oriented fixation: After completing step S2, the catalyst particles are fixed at a certain angle on the TEM grid dedicated to FIB. S4. Directional thinning: The fixed catalyst is thinned along a direction perpendicular to the normal of the target crystal plane using a focused ion beam, and finally an electronic transparent sheet for TEM observation is prepared.

2. The method for crystal plane orientation processing of regular morphology single-crystal catalysts based on FIB according to claim 1, characterized in that: The regular shapes include, but are not limited to, cubes, octahedrons, rods, sheets, or other polyhedra.

3. The method for crystal plane orientation processing of regular morphology single-crystal catalysts based on FIB according to claim 1, characterized in that: Step S1 includes: selecting regular-shaped single-crystal catalyst particles to be processed under electron beam field of view, and determining the angle of the crystal plane to be observed in three-dimensional space based on the morphology and crystal structure of the catalyst.

4. The method for crystal plane orientation processing of regular morphology single-crystal catalysts based on FIB according to claim 1, characterized in that: In step S2, the rotation and tilting of the sample stage are implemented based on the sample stage motion control module of the FIB-SEM system.

5. The method for crystal plane orientation processing of regular morphology single-crystal catalysts based on FIB according to claim 1, characterized in that: In step S2, if the target crystal plane normal is already in the horizontal plane, then only in-plane rotational orientation is required.

6. The method for crystal plane orientation processing of regular morphology single-crystal catalysts based on FIB according to claim 1, characterized in that: In step S4, a protective layer needs to be deposited in a specific area of ​​the catalyst before and during the thinning process to prevent ion beam damage.

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