Design method of micro-cantilever beam for TEM (Transmission Electron Microscope) measurement mechanics

Abstract

The invention discloses a design method of a micro-cantilever beam for TEM (Transmission Electron Microscope) measurement mechanics, which comprises the following steps of: observing that the normal displacement and the horizontal displacement of the micro-cantilever beam are nanoscale in a TEM, and measuring a normal force and a horizontal force with nanoN-level precision in an experiment; calculating according to Hooke's law to obtain a normal elastic coefficient of the micro-cantilever and a horizontal total elastic coefficient of the micro-cantilever; and then calculating the length, width and thickness of the micro-cantilever and the height of the needle point. According to the invention, the normal force and the horizontal force are calculated by visually measuring the displacement of the needle tip, so that the complexity and uncertainty of mechanical measurement of the micro-cantilever in the AFM are avoided, and the stability is realized; horizontal bending and needle tip torsion of the micro-cantilever are directly observed under the TEM, the problem that horizontal force measurement precision is low due to the fact that horizontal bending of the micro-cantilever cannot be observed in the AFM and a large width-to-thickness ratio exists is solved, the cantilever beam with the small width-to-thickness ratio is designed, and 1 nN high-precision normal force and horizontal force measurement is achieved.

Description

Technical Field

[0001] The invention relates to a micro cantilever beam design method, in particular to a micro cantilever beam design method for TEM mechanics measurement. Background Art

[0002] In recent years, with the development of micro-nano manufacturing technology and semiconductor industry, the scale of micro-nano structures / devices has been continuously reduced. Therefore, the characterization and measurement of materials at the nanoscale have gradually attracted attention. AFM has become an important tool for measuring mechanics of nanomaterials due to its flexibility and non-destructiveness. Its working principle of measuring mechanics is as follows: a beam of laser is irradiated at the end of a micro-cantilever with a needle tip. When there is an interaction force between the needle tip and the sample, the cantilever tip will deflect or its oscillation signal will change (such as amplitude, frequency or phase, etc.), causing the light beam reflected by the cantilever back to the photodetector to deflect. After the deflection is fed back to the detection system, a force-distance curve is drawn according to Hooke's law, thereby performing mechanical measurements.

[0003] However, there are problems in using microcantilever beams for mechanical measurement in AFM: first, the sensitivity of the detector and the change of feedback parameters ultimately determine the performance of the normal and torsional motion of the tip, making it impossible to perform accurate and intuitive mechanical measurements; second, the laser beam needs to be shot at the end of the microcantilever beam to feed back the offset of the tip to the detection system. In this process, only the normal bending of the microcantilever beam and the tip torsion can be detected, but the horizontal bending (in-plane deformation) of the microcantilever cannot be observed. Figure 1 Therefore, the micro cantilever beam of AFM is generally set with a larger width-to-thickness ratio to prevent the horizontal bending of the micro cantilever, thereby making its horizontal spring constant larger, significantly reducing the measurement accuracy of the horizontal force (the measurement accuracy can only reach 10 2 nN level). Summary of the invention

[0004] Purpose of the invention: In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide a design method for a micro cantilever beam for TEM measurement of mechanics that can accurately and effectively perform quantitative measurements.

[0005] Technical solution: The design method of a micro cantilever beam for TEM mechanics measurement described in the present invention comprises the following steps:

[0006] Step 1: The normal displacement and horizontal displacement of the microcantilever beam are observed to be at the nanometer level in the TEM. The experiment needs to measure the normal force and horizontal force with nanonewton level accuracy. The normal elastic coefficient of the microcantilever beam and the horizontal total elastic coefficient of the microcantilever beam are calculated according to Hooke's law.

[0007] Step 2: Calculate the length, width, thickness and tip height of the microcantilever according to the following formula:

[0008]

[0009] In the formula, k N is the normal elastic coefficient of the microcantilever beam, k L′ is the horizontal total elastic coefficient of the micro-cantilever beam, E is the Young's modulus of the micro-cantilever beam, G is the shear modulus of the micro-cantilever beam, w is the width of the micro-cantilever beam, t is the thickness of the micro-cantilever beam, l is the length of the micro-cantilever beam, k L is the elastic coefficient of the microcantilever beam in horizontal bending, k T is the torsional elastic coefficient of the microcantilever tip, and h is the height of the microcantilever tip.

[0010] Furthermore, in step 1, Hooke's law is

[0011] F N =k N ×Δy

[0012] F L =k L′ ×Δx

[0013] In the formula, F N is the normal force, F L is the horizontal force, Δy is the normal displacement, and Δx is the horizontal displacement.

[0014] Furthermore, in step one, a needle tip is provided at one end of the micro cantilever beam, and the needle tip contacts the surface of the target material.

[0015] Preferably, the micro cantilever is a single crystal gold micro cantilever. The normal elastic coefficient of the micro cantilever is calculated to be 3 N / m, and the horizontal total elastic coefficient of the micro cantilever is 2 N / m.

[0016] Furthermore, in step 2, G is the shear modulus of the microcantilever beam, which is 25 GPa.

[0017] Furthermore, in step 2, E is the Young's modulus of the microcantilever beam, which is 70 GPa.

[0018] Furthermore, in step 2, the length of the microcantilever is calculated to be 60 μm, the width is 2 μm, the thickness is 2 μm, and the tip height is 7 μm.

[0019] Furthermore, after the size of the micro cantilever beam is designed, the fracture flat surface of the single crystal gold wire is processed by a focused ion beam. The diameter of the single crystal gold wire is 0.2-0.3 mm, and the purity is above 99.9wt.%.

[0020] Design principle: TEM is a characterization method with extremely high atomic-level resolution and ultrafast spatiotemporal resolution, which is often used to study the microstructure of nanomaterials. Therefore, combining the microcantilever in AFM with TEM can not only perform mechanical measurements on nanomaterials, but also characterize the morphological changes of their atomic structures. Since the normal and horizontal movements of the microcantilever tip can be directly observed in TEM, and there is no laser beam irradiation and feedback detection process, the environmental complexity and uncertainty of the microcantilever in mechanical measurement in AFM can be directly solved, thereby achieving the stability of the mechanical measurement of the microcantilever. In addition, the horizontal bending (in-plane deformation) and tip torsion of the microcantilever are observed in real time and directly in TEM, which can solve the problem that the horizontal bending of the microcantilever cannot be observed in AFM and there is a large width-to-thickness ratio, so that the microcantilever under TEM has a smaller width-to-thickness ratio, thereby improving the accuracy of the microcantilever horizontal force measurement, achieving 1nN high-precision normal force and horizontal force measurement, and providing more accurate and effective quantitative measurement for various mechanical tests.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0022] 1. The normal force and horizontal force on the target material can be directly calculated by directly measuring the displacement of the needle tip. This method is direct and convenient, avoiding the environmental complexity and uncertainty of mechanical measurement of the micro-cantilever in AFM, thereby achieving the stability of mechanical measurement of the micro-cantilever;

[0023] 2. By directly observing the horizontal bending and tip twisting of the microcantilever through TEM, a microcantilever with a smaller aspect ratio can be designed for TEM measurement of mechanical processes, which improves the problem of low horizontal force measurement accuracy of traditional AFM microcantilever due to its large aspect ratio, thereby enabling it to achieve 1nN high-precision normal force and horizontal force measurement in TEM, providing more accurate and effective quantitative measurement for various mechanical tests. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the microcantilever mechanical measurement method under AFM;

[0025] Figure 2 It is a schematic diagram of the micro-cantilever beam mechanical measurement method under TEM of the present invention;

[0026] Figure 3 1 is a SEM image of the gold microcantilever of the present invention, wherein (a) is a top view and (b) is a side view;

[0027] Figure 4 It is a real-time data diagram of the normal force and horizontal force measured by the gold microcantilever under the TEM of the present invention. DETAILED DESCRIPTION

[0028] The microcantilever used for TEM measurement of mechanics has a needle tip perpendicular to it at the top and a fixed bottom. The needle tip of the microcantilever is opposite to the target material and perpendicular to the electron beam. The target material is connected to a displacement control mechanism. The needle tip of the microcantilever and the target material are placed under a transmission electron microscope (TEM) to observe their normal displacement changes and lateral displacement changes, and the normal displacement changes and lateral displacement changes are obtained by real-time acquisition of TEM images.

[0029] A design method of a micro cantilever beam for TEM measurement mechanics, comprising the following steps:

[0030] (1) According to the experimental requirements, single crystal gold metal was selected as the material of the microcantilever. The normal displacement and horizontal displacement (i.e., Δy and Δx) of the single crystal gold microcantilever were directly observed in the TEM and were both at the nanometer level, while the experiment required the measurement of mechanical properties with nanonewton-level precision (i.e., nanometer-level F N and F L ). Therefore, according to the actual needs of the experiment and the following formula:

[0031] F N =k N ×Δy (i)

[0032] F L =k L′ ×Δx (ii)

[0033] Calculate k N and k L′ The values ​​are 3N / m and 2N / m respectively.

[0034] In the formula, F N is the normal force, F L is the horizontal force.

[0035] (2) Then, it is known that the Young's modulus E and shear modulus G of gold are 70 GPa and 25 GPa respectively, according to the following formula:

[0036]

[0037] The designed gold microcantilever has a length l of 60 μm, a width w of 2 μm, a thickness t of 2 μm, and a tip height h of 7 μm.

[0038] In the formula, k N is the normal elastic coefficient of the microcantilever beam, k L′ is the horizontal total elastic coefficient of the micro-cantilever beam, E is the Young's modulus of the micro-cantilever beam, G is the shear modulus of the micro-cantilever beam, w is the width of the micro-cantilever beam, t is the thickness of the micro-cantilever beam, l is the length of the micro-cantilever beam, k L is the elastic coefficient of the microcantilever beam in horizontal bending, k Tis the torsional elastic coefficient of the microcantilever tip, and h is the height of the microcantilever tip.

[0039] Next, according to the designed size of the gold microcantilever, the flat surface of the fracture of a single-crystal gold wire (0.25 mm, purity 99.9 wt.%) can be processed by a focused ion beam (Dualbeam Helios 5CX), thereby achieving nanonewton-level mechanical measurement of single-crystal gold microconvex bodies. Due to some processing errors, the final processing results are as follows Figure 3 As shown, the length l is 58.58 μm, the width w is 2.88 μm, the thickness t is 2.39 μm, and the tip height h is 7.34 μm.

[0040] The designed and processed gold microcantilever was used in TEM to carry out coordinated measurement of normal force and horizontal force, such as Figure 4 As shown, they can all achieve nanonewton-level high precision and 1nN accuracy, thus realizing accurate and effective mechanical measurement.

Claims

1. A design method for a micro cantilever beam for TEM measurement mechanics, characterized in that: The following steps are involved: Step 1: The normal displacement and horizontal displacement of the microcantilever beam are observed to be at the nanometer level in the TEM. The experiment needs to measure the normal force and horizontal force with nanonewton level accuracy. The normal elastic coefficient of the microcantilever beam and the horizontal total elastic coefficient of the microcantilever beam are calculated according to Hooke's law. Step 2: Calculate the length, width, thickness and tip height of the microcantilever according to the following formula: In the formula, k N is the normal elastic coefficient of the microcantilever beam, k L′ is the horizontal total elastic coefficient of the micro-cantilever beam, E is the Young's modulus of the micro-cantilever beam, G is the shear modulus of the micro-cantilever beam, w is the width of the micro-cantilever beam, t is the thickness of the micro-cantilever beam, l is the length of the micro-cantilever beam, k L is the elastic coefficient of the microcantilever beam in horizontal bending, k T is the torsional elastic coefficient of the microcantilever tip, and h is the height of the microcantilever tip.

2. The design method of a micro cantilever beam for TEM measurement of mechanics according to claim 1, characterized in that: In step 1, Hooke's law is F N =k N ×Δy F L =k L′ ×Δx In the formula, F N is the normal force, F L is the horizontal force, Δy is the normal displacement, and Δx is the horizontal displacement.

3. The design method of a micro cantilever beam for TEM measurement of mechanics according to claim 1, characterized in that: In the step 1, a needle tip is provided at one end of the micro cantilever beam, and the needle tip contacts the surface of the target material.

4. The design method of a micro cantilever beam for TEM measurement of mechanics according to claim 1, characterized in that: In the step 1, the micro cantilever is a single crystal gold micro cantilever.

5. The method for designing a micro cantilever beam for TEM measurement of mechanics according to claim 4, characterized in that: In the step 1, the normal elastic coefficient of the micro cantilever beam is calculated to be 3 N / m, and the horizontal total elastic coefficient of the micro cantilever beam is 2 N / m.

6. The method for designing a micro cantilever beam for TEM measurement of mechanics according to claim 4, characterized in that: In the step 2, G is the shear modulus of the microcantilever beam, which is 25 GPa.

7. The method for designing a micro cantilever beam for TEM mechanics measurement according to claim 4, characterized in that: In the step 2, E is the Young's modulus of the microcantilever beam, which is 70 GPa.

8. The method for designing a micro cantilever beam for TEM measurement of mechanics according to claim 4, characterized in that: In the step 2, the length of the micro cantilever is calculated to be 60 μm, the width is 2 μm, the thickness is 2 μm, and the tip height is 7 μm.

9. The method for designing a micro cantilever beam for TEM measurement of mechanics according to claim 1, characterized in that: After the size of the micro cantilever beam is designed, the fracture flat surface of the single crystal gold wire is processed by a focused ion beam.

10. The method for designing a micro cantilever beam for TEM mechanics measurement according to claim 9, characterized in that: The single crystal gold wire has a diameter of 0.2-0.3 mm and a purity of more than 99.9 wt.%.

Images