A coaxial alignment method for micropillars in micropillar compression experiments in an SEM environment

Abstract

The present invention discloses a method for coaxially aligning an indenter with a micropillar during a micropillar compression test in a scanning electron microscope (SEM) environment. The method involves first adjusting the micropillar position so that the indenter is located above the micropillar and within the same field of view of the scanning electron microscope (SEM). The micropillar is then moved until its midline is collinear with the indenter's midline. The depth of field is then determined, and the micropillar's depth boundary point is determined. The micropillar is then moved backwards by a distance Δf / 2 + (R-r) from the depth boundary point to complete the coaxial alignment of the indenter and micropillar. The present invention utilizes a nanomechanical testing system in conjunction with a scanning electron microscope (SEM), combined with specific operating steps, to achieve precise alignment of the indenter and micropillar. The method is simple and easy to operate, effectively reducing test errors in micropillar compression.

Description

Technical Field

[0001] The present invention relates to the technical field of microcolumn characterization, and in particular to a method for coaxially aligning an indenter microcolumn in a microcolumn compression experiment in a SEM environment. Background Art

[0002] Visualized in-situ micro-nanomechanical testing technology enables real-time online observation of the indentation process, allowing for the study of deformation and damage mechanisms on the material surface under load. Micropillar compression is a typical in-situ mechanical test. By slowly applying a compressive load to an indenter above the micropillar and recording the load-displacement curve, the strength, hardness, and elastic modulus of the micropillar can be assessed. During micropillar compression, although a large indenter can easily cover the top surface of the micropillar, the bottom of the indenter can easily block the micropillar during compression, affecting observation. Furthermore, when the micropillar is to the side of the indenter, the micropillar may be subjected to uneven force, affecting data accuracy.

[0003] An indenter with a surface area slightly larger than or equal to the micropillar tip is most suitable, but alignment between the indenter base and the micropillar tip is difficult. This is because the camera image in the scanning electron microscope's field of view is a flat image, while we need to observe dynamic changes in three-dimensional space. This visual error makes it difficult to align the indenter base and micropillar tip. Therefore, how to accurately align an indenter with a surface area slightly larger than or equal to the micropillar tip during testing is a pressing issue. Summary of the Invention

[0004] The present invention aims to solve the problem that an indenter with a surface area slightly larger than or equal to that of the micropillar top is difficult to accurately align with the micropillar during existing micropillar compression testing. The present invention provides a method for coaxial alignment of an indenter and micropillars for micropillar compression experiments in an SEM environment, which is simple and easy to operate and can achieve precise alignment between the indenter and the micropillar.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for coaxially aligning an indenter and micropillars in a micropillar compression experiment in a SEM environment, comprising the following steps:

[0006] (1) The base of the micropillar is mounted on the base of a scanning electron microscope, so that the indenter in the nanomechanical testing system and the micropillar are in the same field of view of the scanning electron microscope, and the radius r (μm) of the micropillar is measured. The present invention combines the nanomechanical testing system with a scanning electron microscope, utilizing the imaging capability of the SEM to observe the mechanical characterization process in real time, thereby realizing visual in-situ micro-nanomechanical testing to study the deformation and damage mechanism of the material surface under load. The nanomechanical testing system is an instrument for realizing quantitative mechanical and tribological characterization of materials at the nanometer and micrometer scales. It is a device well known in the art and will not be described in detail. Different sizes of compression flat heads can be selected according to the diameter of the micropillar. The radius of the micropillar is measured by scanning electron microscopy.

[0007] (2) Raise the base of the microcolumn so that the bottom surface of the indenter and the projection of the indenter on the base of the microcolumn coincide with each other.

[0008] (3) Lower the base of the micropillar and adjust the position of the micropillar so that the indenter is above the micropillar and in the same field of view of the scanning electron microscope. The indenter is located above the micropillar to ensure that the indenter will not collide with the micropillar when it is subsequently moved.

[0009] (4) Adjust the base position of the microcolumn so that the microcolumn moves to the point where the midline of the microcolumn and the midline of the indenter are collinear.

[0010] (5) After the edge of the indenter is clearly focused, the microcolumn is moved back and forth until the front surface of the microcolumn is clearly outlined. At this time, the depth of field Δf (μm) of the clear image is obtained on the SEM imaging plane with the edge of the indenter as the center. Different brands of scanning electron microscopes can use different methods to obtain the depth of field under certain shooting conditions. For example, the depth of field of the Tesken scanning electron microscope can be directly read out in the software, while for electron microscopes produced by companies such as Zeiss and Hitachi, the depth of field under corresponding conditions can be calculated using the depth of field calculation formula. Obtaining the depth of field is a conventional technical means in this field, so it will not be repeated here.

[0011] (6) Move the microcolumn forward to determine the boundary position between the blurred and clear front side of the microcolumn, and use this position as the depth of field boundary point.

[0012] (7) Move the micropillar backward from the depth of field boundary point by a distance Δf / 2+(Rr) to complete the coaxial alignment of the indenter and the micropillar, where R is the indenter radius (μm).

[0013] Preferably, in step (1), the micropillars are in a vertical position, and the bottom surface of the indenter is parallel to the top surface of the micropillars. When the micropillars are in a vertical position, the force is concentrated and uniform; the higher the parallelism between the bottom surface of the indenter and the top surface of the micropillars, the smaller the test error. Therefore, in the present invention, the bottom surface of the indenter and the top surface of the micropillars are kept parallel to each other to reduce the test error of micropillar compression.

[0014] Preferably, in step (1), the bottom surface area of ​​the indenter is equal to or slightly larger than the top surface area of ​​the micropillars. When the bottom surface area of ​​the indenter is equal to or slightly larger than the top surface area of ​​the micropillars, the bottom end of the indenter is less likely to block the micropillars during the compression process, facilitating observation, more uniform force on the micropillars, and improving data accuracy.

[0015] Preferably, in step (3), the distance between the indenter and the micropillar is controlled to be less than 5 μm. The indenter and the micropillar can be seen simultaneously in the lowest magnification field of view of the SEM, and subsequent needle insertion is relatively fast.

[0016] Preferably, the distance between the indenter and the microcolumn is controlled to be 2-3 μm.

[0017] Therefore, the present invention has the following beneficial effects: the indenter-micropillar coaxial alignment method for a micropillar compression test in a SEM environment of the present invention utilizes a nanomechanical testing system and a scanning electron microscope in combination with specific operating steps to achieve precise alignment between the indenter and the micropillar. The method is simple and easy to operate, which is conducive to reducing the test error of the micropillar compression. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is an electron microscope image of the state where the indenter and its projection on the base of the microcolumn overlap in step (2).

[0019] Figure 2 This is an electron microscope image of the state where the pressure head is located above the microcolumn in step (3).

[0020] Figure 3 This is an electron microscope image showing the state in which the midline of the microcolumn and the midline of the indenter are collinear in the upper and lower directions in step (4).

[0021] Figure 4 This is an electron microscope image of the microcolumn at the depth of field boundary point in step (6).

[0022] Figure 5 This is an electron microscope image of the coaxial alignment state of the pressure head and the microcolumn in step (7). DETAILED DESCRIPTION

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0024] In the following examples, the scanning electron microscope used was a Zeiss Sigma 360, with a 3 kV accelerating voltage, a 60 μm aperture, and high beam current mode to ensure sufficient electron load. The working distance was 14.4 mm. The micropillars were printed using two-photon 3D printing technology using a photosensitive material composed of 2-phenylethylthiol and pentaerythritol triacrylate as monomers and metal nanoclusters as photoinitiators. The micropillar radius r was measured to be 4.16 μm and the height 13.09 μm. The indenter used was a Bruker TI-0261 Flat Punch with a 20 μm diameter, a 60° cone angle, a Young's modulus of 1140 GPa, and a Poisson's ratio of 0.07.

[0025] Example 1

[0026] (1) The base of the micropillar is mounted on the base of a scanning electron microscope so that the indenter and the micropillar in the nanomechanical testing system are in the same field of view of the scanning electron microscope. The radius r of the micropillar (4.16 μm) is measured. The micropillar is in a vertical state, the bottom surface of the indenter is parallel to the top surface of the micropillar, and the bottom surface area of ​​the indenter is slightly larger than the top surface area of ​​the micropillar.

[0027] (2) Raise the base of the microcolumn so that the bottom surface of the indenter and the projection of the indenter on the base of the microcolumn coincide with each other (e.g. Figure 1 (3) Lower the base of the microcolumn and adjust the position of the microcolumn so that the indenter is located above the microcolumn. Under the conditions of 500 times magnification and 14.4 mm working distance, it can be seen that the indenter and the microcolumn are in the same field of view of the scanning electron microscope (as shown in FIG. Figure 2 As shown), the distance between the indenter and the micropillar is controlled at 5 μm;

[0028] (4) Adjust the magnification to 2000x and adjust the base position of the microcolumn so that the midline of the microcolumn and the midline of the indenter are aligned vertically (e.g. Figure 3 shown);

[0029] (5) The magnification is set to 3000x. The bottom of the indenter and the microcolumn are in the same field of view. After the edge of the indenter is clearly focused, the microcolumn is moved back and forth until the front surface of the microcolumn is clearly outlined. Under the current shooting conditions, M is 3000, D is 14.4 mm, d is 0.03 μm (the maximum spot of the thermal field emission electron gun is calculated to be d = 0.03), a is 60 μm, and the calculated depth of field Δf is 2.2 μm.

[0030] (6) With the edge of the indenter as the center, move the microcolumn forward to determine the boundary position between the blur and clarity of the front side of the microcolumn, and use this position as the depth of field boundary point (e.g. Figure 4 shown);

[0031] (7) Move the microcolumn backward from the depth of field boundary point by a distance of Δf / 2+(Rr) (i.e., 6.94 μm) to complete the coaxial alignment between the indenter and the microcolumn (e.g., Figure 5 As shown in Figure 2, the micro-pillar compression experiment can be carried out after lowering the indenter to the micro-pillar surface.

[0032] The embodiment described above is only a preferred solution of the present invention and does not limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solution described in the claims.

Claims

1. A method for coaxial alignment of an indenter and micropillars in a micropillar compression experiment in a SEM environment, characterized in that: The following steps are involved: (1) The micropillar base is mounted on the base of a scanning electron microscope so that the indenter and the micropillar in the nanomechanical testing system are in the same field of view of the scanning electron microscope, and the micropillar radius r (μm) is measured; (2) raising the base of the microcolumn so that the bottom surface of the indenter and the projection of the indenter on the base of the microcolumn coincide with each other; (3) Lower the base of the micropillar and adjust the position of the micropillar so that the indenter is above the micropillar and in the same field of view of the scanning electron microscope; (4) Adjust the base position of the microcolumn so that the microcolumn moves to the point where the midline of the microcolumn and the midline of the indenter are collinear; (5) After the edge of the indenter is clearly focused, the micropillar is moved back and forth until the front surface of the micropillar is clearly outlined. At this time, the depth of field Δf (μm) of the clear image is obtained on the SEM imaging plane with the edge of the indenter as the center; (6) Move the microcolumn forward to determine the boundary position between blur and clarity on the front side of the microcolumn, and use this position as the depth of field boundary point; (7) Move the micropillar backward from the depth of field boundary point by a distance Δf / 2+(Rr) to complete the coaxial alignment of the indenter and the micropillar, where R is the indenter radius (μm).

2. The method for coaxially aligning an indenter and micropillars in a micropillar compression experiment in a SEM environment according to claim 1, characterized in that: In step (1), the microcolumns are in a vertical state, and the bottom surface of the indenter is parallel to the top surface of the microcolumns.

3. The method for coaxially aligning an indenter and micropillars in a micropillar compression experiment in a SEM environment according to claim 1, characterized in that: In step (1), the bottom surface area of ​​the indenter is equal to or slightly larger than the top surface area of ​​the microcolumn.

4. The method for coaxially aligning an indenter and micropillars in a micropillar compression experiment in a SEM environment according to claim 1, characterized in that: In step (3), the distance between the indenter and the microcolumn is controlled to be less than 5 μm.

5. The method for coaxially aligning an indenter and micropillars in a micropillar compression experiment in a SEM environment according to claim 4, characterized in that: The distance between the indenter and the microcolumn is controlled at 2-3 μm.

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