A high-order mode enhancement device for atomic force microscope probe

Abstract

The present invention discloses a high-order modal enhancement device for an atomic force microscope probe. The device utilizes mechanical constraints to improve a single-end clamped micro-cantilever probe system of an atomic force microscope into a micro-cantilever probe system with segmented coupling constraints. The micro-cantilever probe system with segmented coupling constraints consists of a commercial probe, a probe holder (5A), a pressure plate (5B), and a spring sheet (5C). One end of the spring sheet (5C) is fixed to a groove of the pressure plate (5B), and the other end contacts a crossbeam (5D) for clamping a probe substrate (5G). The present invention applies a segmented coupling constraint to the commercial probe. The commercial probe is affected by the constraint position, and its dynamic characteristics change. The system produces a coupling effect, thereby enhancing the high-order modal response of the probe.

Description

Technical Field

[0001] The present invention relates to an atomic force microscope, and more particularly to a method for mounting a probe on a probe clamping device having segmented coupling constraint features, thereby enhancing high-order modal response signals of the probe and obtaining high-order modal images containing more sample information. Background Art

[0002] The atomic force microscope (AFM) is a commonly used nanoscale measurement and characterization instrument. It can operate in a variety of environments, including air, vacuum, and liquid. It detects sample surface information by measuring the interaction forces between the probe and the sample, enabling nanoscale imaging without damaging the sample. In addition to characterizing sample surface topography, AFM is also used to characterize various mechanical and electromagnetic properties of the sample surface. Generally, a typical AFM consists of five major components: a detection unit, a microcantilever probe system, a tip-sample motion unit, a feedback controller, and an image processing and display system. (First edition, February 2016, Amplitude Modulation Atomic Force Microscopy / García, R.) In dynamic AFM, the system applies a fixed frequency (usually the fundamental eigenfrequency of the microcantilever probe system) to the probe as it scans, causing the tip to span a wide range of mutual potential energy, and extracting sample information using the entire force curve. In dynamic AFM, due to the highly nonlinear dynamic characteristics of the cantilever, the probe's resonances and various eigenmodes also contain information about sample properties. The multi-frequency atomic force microscopy (MF-AFM) developed in recent years has provided an important solution to these technical difficulties.

[0003] Multi-frequency atomic force microscopy, a new research hotspot, can simultaneously extract various physical properties of a sample's surface while scanning its topography. It can leverage the cantilever's multiple modes to achieve rapid, high-resolution imaging of the sample surface and quantitative characterization of material properties. Under the influence of different excitation frequencies, the probe's vibration response changes accordingly, forming the modal response curve. When the excitation frequency matches the probe's resonant frequency, the probe's vibration response increases significantly. However, in atmospheric environments, in multi-frequency atomic force microscopy imaging systems, the probe's high-order modal response decreases with increasing modality. Therefore, the signal-to-noise ratio of the response signal obtained using high-order excitation frequencies is too low, making it difficult to discern physical properties of the sample's surface. Summary of the Invention

[0004] To address the technical problem of low probe high-order modal response, the present invention proposes an atomic force microscope (AFM) probe high-order modal enhancement device based on segmented coupling constraints. This device uses a low-cost method to improve a single-end clamped microcantilever probe system into a microcantilever probe system with segmented coupling constraints, thereby enhancing the probe's high-order modal response signal. The AFM probe high-order modal enhancement device applies a segmented coupling constraint to the rectangular cantilever beam probe, thereby improving the microcantilever probe system. The segmented coupling constraint improves the vibration mode of the probe, which originally had a cantilever beam structure, into the vibration mode of a bridge-cantilever beam coupling structure. When the two parts have the same length, width, and height, the first modal natural frequency of the bridge structure is similar to the second mode of the cantilever beam structure, and the second mode of the bridge structure is similar to the third mode of the cantilever beam structure. Similarly, when the probe is excited to vibrate in the nth order eigenmode, the bridge structure vibrates in the n-1th order eigenmode, and the cantilever beam structure vibrates in the nth order eigenmode, thereby enhancing the system's nth order eigenmodal response.

[0005] In order to realize the segmented coupling constraint of the probe, the present invention designs a probe clamping device, namely a segmented coupling constraint micro-cantilever probe system, which is composed of a commercial probe, a probe holder (5A), a pressure plate (5B) and a spring sheet (5C). One end of the spring sheet is fixed on the pressure plate, and the other end is in contact with the probe substrate. The metal spring sheet and the crossbeam jointly clamp the middle of the probe substrate to form a bridge structure. The bottom of the probe substrate is engaged in the elliptical groove. The probe needle tip is fixed on the cantilever beam. The opening on the probe holder is to clear the entrance of the tilting rod when changing the needle, so as to facilitate the fixing of the probe. The convex and concave configuration of the pressure plate and the spring sheet (such as Figure 2C The probe clamping device (shown in Figure 1) is designed to resiliently and stably clamp the probe. The spring is mounted in the notch of the concave pressure plate, while the opening of the concave pressure plate is located in the notch of the concave probe substrate. The probe clamping device designed in this invention utilizes a lightweight structure, eliminating the need for significant modifications to the atomic force microscope system, making it more versatile. It also effectively enhances the probe's high-order modal response and improves the high-order modal response signal.

[0006] The present invention designs an atomic force microscope probe high-order mode enhancement device, wherein the phase-locked amplifier first receives the detection control signal V output by the photodetector c ; The second aspect receives the first modal reference signal V1 output by the signal generator; the third aspect receives the second modal reference signal V2 output by the signal generator; the fourth aspect outputs the first modal amplitude signal V3 of the probe; the fifth aspect outputs the second modal amplitude signal V4 of the probe.

[0007] When the atomic force microscope is performing inspections, the signal generator's output is digitally input to the lock-in amplifier, avoiding information loss caused by digital-to-analog conversion. The lock-in amplifier operates in internal reference mode.

[0008] During operation, the demodulation frequencies of the lock-in amplifier are set to F1=f1 and F2=f2.

[0009] The lock-in amplifier uses V1 and V2 to detect the control signal V c After demodulation and amplification processing, the first modal amplitude V3 and the second modal amplitude V4 of the probe are output respectively.

[0010] The first modal amplitude V3 refers to the amplitude of the excitation probe movement at the demodulation frequency F1. The signal is processed by the image processor to obtain a topographic image of the sample surface.

[0011] The second modal amplitude V3 refers to the amplitude of the excitation probe movement at the demodulation frequency F2. After the signal is processed by the image processor, an image of the sample surface with respect to the second modal amplitude of the probe is obtained. After processing, the image can reflect the special physical properties of the sample surface, such as Young's modulus, adhesion, etc.

[0012] The present invention also provides a detection method for multi-frequency atomic force microscopy imaging based on an atomic force microscope based on a probe high-order mode enhancement device. The specific detection steps are:

[0013] Step 1: Select the probe;

[0014] The probe selected for this clamping device is generally a silicon-based commercial probe coated with an aluminum reflective layer.

[0015] Step 2: Install the probe;

[0016] Fix the clamping device on the probe mounting table, insert the tilt rod into the opening slot of the probe holder to lift the spring sheet; then use tweezers to send the probe into the groove and adjust it to the appropriate position, then remove the tilt rod and fix the probe between the spring sheet and the beam.

[0017] The probe is made of a silicon substrate, and the length of the probe substrate is denoted as h. The distance from the elliptical groove on the probe holder to the crossbeam is L. When the ratio of h to L is closer to 2, the segmented coupling constraint fixture has a better effect on enhancing the probe's high-order modal response.

[0018] Step 3: Set the modal frequency;

[0019] Start the atomic force microscope, set the initialization parameters, sweep the probe frequency, and determine the first eigenmode frequency and the second eigenmode frequency of the probe.

[0020] Step 4: applying incentives;

[0021] Mechanical excitation with frequencies F1 = f1 and F2 = f2 is applied to the probe at the same time, and the scanning stage uses the detection control signal V cThe probe is operated in constant amplitude mode, and the relative distance between the probe and the sample remains unchanged.

[0022] Step 5: Information collection;

[0023] A lock-in amplifier is used to extract morphological information and surface physical property information, such as Young's modulus and adhesion force, from the first mode and the second mode respectively.

[0024] The technical effects achieved by the atomic force microscope probe high-order mode enhancement device designed in the present invention are:

[0025] (1) The atomic force microscope modified based on the present invention can significantly enhance the high-order modal response of the probe, and then extract the morphological information and other physical characteristic information of the sample surface from the first mode and the second mode of the probe respectively.

[0026] (2) The atomic force microscope modified based on the present invention simultaneously uses dual-mode scanning of the sample surface, thereby improving the measurement speed and reducing the measurement error.

[0027] (3) The probe used in the atomic force microscope probe high-order mode enhancement device designed by the present invention does not require ion beam etching of the cantilever beam, and does not need to consider the specifications and dimensions of the needle tip and the cantilever, and is widely applicable. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is based on the improved atomic force microscope system structure block diagram.

[0029] Figure 2 It is a schematic structural diagram of a micro-cantilever probe system with segmented coupling constraints for realizing probe high-order mode enhancement according to the present invention.

[0030] Figure 2A yes Figure 2 Diagram of the structure of the probe holder.

[0031] Figure 2B yes Figure 2 Structural diagram of the probe holder from another perspective.

[0032] Figure 2C yes Figure 2 Assembly structure diagram of the intermediate pressure plate and spring leaf.

[0033] Figure 2D yes Figure 2 Middle spring structure diagram.

[0034] Figure 2E yes Figure 2 Schematic diagram of the commercial probe structure.

[0035] Figure 3 It is the Bode plot of the modal frequency response of the cantilever beam system before improvement.

[0036] Figure 4 It is the Bode plot of the modal frequency response of the improved rear axle-cantilever beam coupling system.

[0037] Figure 5 It is a schematic diagram of the bridge-cantilever beam coupled resonance structure of the present invention.

[0038] Figure 6 is the modal response curve of the probe before improvement.

[0039] Figure 7 This is the modal response curve of the improved probe of the present invention.

[0040] DETAILED DESCRIPTION

[0041] The present invention will be further described in detail below with reference to the accompanying drawings and examples. The parameters listed are merely exemplary embodiments of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention.

[0042] See also Figure 1 The atomic force microscope shown is a conventional atomic force microscope that is constructed by adding a clamping device with a restraining force (such as Figure 2 The present invention provides an atomic force microscope (AFM) probe high-order modal enhancement device for enhancing the probe's high-order modal response. The AFM comprises at least an AFM controller 1, a graphic display 2, a scanner 3, a sample stage 4, a segmented coupled-constrained microcantilever probe system 5, an AFM probe actuator 6, a laser 8, a photodetector 9, a lock-in amplifier 10, and a signal generator 11.

[0043] (1) AFM controller 1

[0044] The AFM controller 1 first receives a detection control signal V output by the photodetector. c ; The second aspect is to control the scanner 3 according to the detection control signal; the third aspect is to receive the path data of the scanner; the fourth aspect is to receive the probe first modal amplitude signal V3 and the probe second modal amplitude signal V4 output by the phase-locked amplifier 10 for image processing; the fifth aspect is to output the image information to the graphic display 2.

[0045] (2) Graphics Display 2

[0046] The graphic display 2 is used to display the imaging results.

[0047] (3) Scanner 3

[0048] A sample stage 4 is mounted on the scanner 3 , and the scanner 3 is used to move the sample on the sample stage 4 .

[0049] (IV) Sample stage 4

[0050] The sample stage 4 is used to carry samples.

[0051] (V) Segmented coupling constrained microcantilever probe system 5

[0052] See also Figure 2 The micro-cantilever probe system 5 with segmented coupling constraint is mounted on the operating platform of a conventional atomic force microscope (AFM) probe actuator 6 via a probe holder 5A. The micro-cantilever probe system with segmented coupling constraint consists of a commercial probe, a probe holder 5A, a pressure plate 5B, and a spring sheet 5C.

[0053] See also Figure 2 The segmented coupled constrained micro-cantilever probe system 5 shown is designed as a clamping device with a constraining force, capable of providing a constraining force for a commercial probe during operation. A pressure plate 5B is fixed to the probe holder 5A of the segmented coupled constrained micro-cantilever probe system 5. One end of a spring plate 5C is fixed (by welding) to the B opening groove 5B1 of the pressure plate 5B, and the other end of the spring plate 5C contacts the probe substrate 5G (during assembly, the spring plate 5C is lifted by a tilting lever, the probe substrate 5G of the commercial probe is placed in the elliptical groove 5A8, and the spring plate 5C is lowered so that the other end of the spring plate 5C contacts the probe substrate 5G). The spring plate 5C provides a constraining force for the commercial probe during operation. A crossbeam (5D) is provided at the A opening groove (5A3) of the probe holder (5A). The crossbeam (5D) cooperates with the other end of the spring plate 5C to clamp the probe substrate 5G.

[0054] See also Figure 2A 、 Figure 2B As shown, the probe holder 5A is equipped with an A-opening slot 5A3, a circular positioning hole 5A1, an elliptical positioning hole 5A2, a wiring hole 5A7, and multiple A-through holes 5A6. The top panel of the probe holder 5A is provided with an elliptical groove 5A8, located at the base of the A-opening slot 5A3 and used to accommodate the tail of the probe substrate 5G. A crossbeam 5D is located at the A-opening slot 5A3. The circular positioning hole 5A1 and the elliptical positioning hole 5A2 are positioned opposite the A-opening slot 5A3. The circular positioning hole 5A1 is used to accommodate the convex cylinder on the AFM probe actuator 6, while the elliptical positioning hole 5A2 is used to accommodate the convex elliptical cylinder on the AFM probe actuator 6. The A-through hole 5A6 is used to pass rivets. Rivets passing through the A-through hole 5A6 and the B-through hole 5B2 secure the probe holder 5A to the pressure plate 5B.

[0055] See also Figure 2CAs shown, the pressure plate 5B is provided with a B-opening slot 5B1 and a plurality of B-through holes 5B2. The B-through holes 5B2 are used for rivets to pass through. One end of a spring piece 5C is fixed (by welding) at the base of the B-opening slot 5B1, and the other end of the spring piece 5C contacts the probe substrate 5G.

[0056] See also Figure 2 、 Figure 2C 、 Figure 2D As shown, one end of spring leaf 5C is fixed (by welding) to opening slot 5B1 of pressure plate 5B, while the other end of spring leaf 5C contacts probe substrate 5G. Spring leaf 5C provides restraining force for cantilever beam 5E during operation. In the present invention, spring leaf 5C is folded at an angle δ in the middle, typically ranging from 115 to 150 degrees. The dimensions of spring leaf 5C are designed as follows: the folded length b = 2900 μm to 3100 μm, the width a = 1450 μm to 1550 μm, and the thickness c = 290 μm to 310 μm.

[0057] See also Figure 2 、 Figure 2E As shown, a commercial probe generally includes a probe tip 5F, a cantilever beam 5E and a probe substrate 5G. The cantilever beam 5E is located between the probe tip 5F and the probe substrate 5G, and the probe tip 5F is located at the end of the cantilever beam 5E.

[0058] The micro-cantilever probe system 5 with segmented coupling constraint designed in the present invention first secures one end of a spring plate 5C to slot B of a pressure plate 5B. Rivets then secure the pressure plate 5B to the probe holder 5A. Finally, the probe holder 5A is secured via a circular positioning hole 5A1, an elliptical positioning hole 5A2, and two protrusions on an AFM probe actuator 6. The AFM probe actuator 6 applies an excitation force to the probe holder 5A, which in turn drives the probe to vibrate.

[0059] (6) AFM probe actuator 6

[0060] The AFM probe actuator 6 receives the dual-frequency sinusoidal mechanical excitation signal V output by the signal generator 11. a .

[0061] (8) Laser 8

[0062] The laser light generated by the laser 8 is irradiated onto the probe tip 5F and the sample.

[0063] (9) Photodetector 9

[0064] The photodetector 9 is used to receive the reflected signal of the laser, which reflects the amplitude response of the cantilever during vibration, and output a detection control signal V c .

[0065] (10) Lock-in amplifier 10

[0066] In the present invention, the lock-in amplifier 10 first receives the detection control signal V output by the photodetector 9. c ; The second aspect is to receive the first modal reference signal V1 output by the signal generator 11; the third aspect is to receive the second modal reference signal V2 output by the signal generator 11; the fourth aspect is to output the first modal amplitude signal V3 of the probe; the fifth aspect is to output the second modal amplitude signal V4 of the probe.

[0067] During inspections in the atomic force microscope designed in this invention, the output of signal generator 11 is digitally added to lock-in amplifier 10, avoiding the information loss associated with complex digital-to-analog conversion by an external analog signal adder. Furthermore, because the lock-in amplifier operates in internal reference mode, the delay between the two signal paths during demodulation is reduced.

[0068] During operation, the demodulation frequency of the lock-in amplifier is set to F1=f1, F2=f2, where F2 represents the first demodulation frequency, F2 represents the second demodulation frequency, f1 represents the first modal frequency and f2 represents the second modal frequency.

[0069] The lock-in amplifier uses V1 and V2 to detect the control signal V c After demodulation and amplification processing, the first modal amplitude V3 and the second modal amplitude V4 of the probe are output respectively.

[0070] The first modal amplitude V3 refers to the amplitude of the excitation probe movement at the demodulation frequency F1. After the signal is processed by the image processor, an image of the sample surface with respect to the first modal amplitude of the probe is obtained. After processing, a topographic image of the sample surface can be obtained.

[0071] The second modal amplitude V3 refers to the amplitude of the excitation probe movement at the demodulation frequency F2. After the signal is processed by the image processor, an image of the sample surface with respect to the second modal amplitude of the probe is obtained. After processing, an image of the physical property distribution of the sample surface, such as Young's modulus distribution, adhesion force, etc., can be obtained.

[0072] In the present invention, the lock-in amplifier is preferably the HF2LI dual lock-in amplifier produced by Zurich Instruments.

[0073] (10) Signal generator 11

[0074] In the present invention, the signal generator 11 first outputs a mechanical excitation signal V a to the AFM probe exciter 6; secondly, outputting the first modal reference signal V1 to the lock-in amplifier 10; and thirdly, outputting the second modal reference signal V2 to the lock-in amplifier 10.

[0075] Two single-frequency sinusoidal signals V1 and V2 are generated in digital form in the signal generator 11; these two digital signals are used as demodulation reference signals to act on the phase-locked amplifier 10 for signal demodulation; secondly, these two digital signals are subjected to high sampling rate digital-to-analog conversion, and the analog sinusoidal signal after digital-to-analog conversion is recorded as V a Acts on the AFM probe actuator.

[0076] The present invention relates to an atomic force microscope probe high-order mode enhancement device. Using the improved atomic force microscope, a dual-frequency atomic force microscope test is performed as an example. The signal connection method is as follows:

[0077] (1) The signal generator generates a sinusoidal signal V1 with the same frequency as the first eigenmode f1 of the probe and a sinusoidal signal V2 with the same frequency as the second eigenmode f2 of the probe as the demodulation reference signals of the first modal channel and the second modal channel, respectively, and outputs them to the lock-in amplifier;

[0078] (2) The signal generator mixes the sinusoidal signal V1 and the sinusoidal signal V2 as the mechanical excitation signal V a Acting on the AFM probe actuator;

[0079] (3) The AFM probe actuator drives the probe with a dual-frequency sinusoidal signal V a applying mechanical drive;

[0080] (4) The probe vibrates under mechanical drive, and the light beam generated by the laser is focused to the top of the cantilever of the AFM probe actuator. The reflected laser beam is received by the photodetector and outputs a detection control signal V c to the lock-in amplifier;

[0081] (5) The lock-in amplifier uses the demodulated reference signals V1 and V2 to detect the received control signal V c After demodulation and amplification, the probe first modal amplitude V3 and the probe second modal amplitude V4 are output to the AFM controller respectively;

[0082] (6) AFM controller detects the control signal V c To output the start command to the scanner to perform three-dimensional scanning of the sample;

[0083] (7) The scanner outputs the path data to the AFM controller;

[0084] (8) The AFM controller outputs the image signal V5 to the graphic display, so that the graphic display draws an image of the sample surface with respect to the first modal amplitude and the second modal amplitude of the probe.

[0085] The present invention provides a constrained probe for realizing an atomic force microscope with enhanced high-order modal response. The functions realized by the added components are as follows:

[0086] In the present invention, an atomic force microscope is used to enhance the high-order modal response of the probe using an atomic force microscope probe high-order modal enhancement device. The imaging process of the AFM imaging system is as follows:

[0087] Imaging process 1: Probe selection:

[0088] The probe selected for this clamping device is generally a commercial probe etched on a silicon substrate, such as the PPP-FMR model of the Nanosensor Group.

[0089] Imaging process 2, probe installation:

[0090] Fix the clamping device on the probe mounting table, push the tilt rod deep into the probe holder from the entrance, lift the spring sheet, and then use tweezers to put the probe into the groove and adjust it to the appropriate position. Then remove the tilt rod, the spring sheet falls, and the probe is fixed between the spring sheet and the beam.

[0091] Imaging process three: Initialize the atomic force microscope system and obtain the resonance frequency of the AFM probe actuator F = (f1, f2, ..., f i ); Determine the first modal frequency f1 and the second modal frequency f2 of the probe; where f i The identification number representing the i-th eigenmode frequency of the probe.

[0092] Imaging process 4: The signal generator generates a sinusoidal signal V1 with the same frequency as the first eigenmode f1 of the probe and a sinusoidal signal V2 with the same frequency as the second eigenmode f2 of the probe. The V1 and V2 are mixed and then used as the mechanical excitation signal V a Output to AFM probe actuator;

[0093] Imaging process 5, the AFM probe actuator follows the mechanical excitation signal V a Applying mechanical excitation to excite the probe to vibrate;

[0094] Imaging process 6: The probe is stimulated by the mechanical excitation signal V a The laser beam is focused to the cantilever tip of the AFM probe actuator, and the reflected laser beam is received by the photodetector and outputs a detection control signal V. c to the lock-in amplifier;

[0095] In the seventh imaging process, the scanning stage uses the detection control signal to make the probe work in the constant amplitude mode, and the relative distance between the probe and the sample remains unchanged;

[0096] Imaging process eight, the phase-locked amplifier works in the internal reference mode, using the demodulated reference signals V1 and V2 to detect the received control signal Vc After demodulation and amplification, the probe first modal amplitude V3 and the probe second modal amplitude V4 are output to the AFM controller respectively;

[0097] Imaging process nine, the AFM controller outputs the detection control signal V c , the probe first modal amplitude V3 and the probe second modal amplitude V4 are given to the image display, so that the image display draws the first modal amplitude image and the second modal amplitude image of the sample surface.

[0098] Example 1

[0099] The present invention provides an atomic force microscope probe high-order modal enhancement device, which applies a preload constraint to the middle of the substrate of a rectangular cantilever beam structure probe, so that when the cantilever beam side of the probe is constrained to vibrate in the nth order eigenmode, the side of the probe close to the excitation source vibrates in the n-1th order eigenmode. Therefore, when the excitation probe vibrates in the nth order eigenmode, the side close to the excitation source vibrates in the n-1th order eigenmode, and the cantilever beam side vibrates in the nth order eigenmode. The overall nth order modal response of the system is enhanced due to the coupling effect of the two. In order to achieve a better modal enhancement effect, the preferred dimensions of the present invention are as follows:

[0100] The included angle δ of the spring piece 5C is 135 degrees, and the lengths of the spring piece before folding are b=3000 μm, a=1500 μm, and c=300 μm.

[0101] Commercial probe dimensions: Probe substrate 5G has a length of h = 3340 μm to 3460 μm, a width of l = 1570 μm to 1630 μm, and a thickness of k = 304 μm to 324 μm. Cantilever beam 5E has a length of j = 215 μm to 235 μm, a width of i = 33 μm to 43 μm, and a thickness of k1 = 6 μm to 8 μm. In Example 1, the preferred probe dimensions are: h = 3400 μm, l = 1600 μm, k = 314 μm, j = 225 μm, i = 28 μm, and k1 = 3 μm.

[0102] For a rectangular cantilever beam structure probe, it has a series of resonant frequencies, which can be obtained by calculation. For example, if the fundamental resonant frequency of the rectangular cantilever beam structure probe is f1 (i.e., the first eigenmode), then its second eigenmode f2 = 6.26 × f1, the third eigenmode f3 = 17.54 × f1, and so on. Without additional processing, the modal response of the rectangular cantilever beam structure probe gradually decreases. When the rectangular cantilever beam structure probe is subjected to only one uniformly distributed excitation acting on the entire probe, the modal response Bode diagram of the system is as follows: Figure 3As shown in the figure, the transfer function output for both the vertical deflection and the deflection slope of the cantilever free end shows a gradually decreasing trend. This is also the working state of the probe commonly used in AFM modal response testing, which can be shown using a modal frequency response Bode chart. Figure 3 Refer to November 13, 2006, "IEEE Transactions on Nanotechnology", "Transfer Function Analysis of the Micro Cantilever Used in Atomic Force Microscopy", author F. Javier Rubio-Sierra.

[0103] The present invention is a high-order modal enhancement device for an atomic force microscope probe. By using a clamping device with a constraining force to clamp the middle of the probe substrate, a preload constraint is applied to the rectangular cantilever beam probe with a single end fixed through mechanical constraint, and the probe is divided into a bridge structure at the rear end and a cantilever beam structure at the front end, which together form a bridge-cantilever beam coupling resonant structure. A uniform excitation force u(t) (such as Figure 5 As shown in Figure 2, the modal response of the entire bridge-cantilever beam coupled resonance structure will be significantly enhanced compared to the rectangular cantilever beam structure probe, and the modal response of the system will gradually increase with the improvement of the mode (as shown in Figure 2). Figure 4 In the application of multi-frequency atomic force microscopy, as the high-order modal response improves, the sensitivity of multi-frequency AFM in detecting sample properties using the cantilever's high-order modes also increases.

[0104] like Figure 5 In the schematic diagram of the bridge-cantilever coupled resonant structure shown, a fixed constraint is applied to the bottom surface, dividing the probe into two parts: the clamped bridge structure on the left, connected to the AFM probe actuator via a clamping device, and the cantilever beam on the right. When an excitation force u(t) is applied to the left bridge structure, if the left bridge structure and the right cantilever beam have the same dimensions, the modal vibration frequencies of the bridge structure and the cantilever beam overlap. The natural frequency of these vibration modes can be expressed by a dimensionless coefficient λ, as shown in Table 1.

[0105] Table 1 Dimensionless coefficients for calculating the natural frequency of beam structures

[0106]

[0107] The probe modal response curve of the atomic force microscope without high-order modal enhancement device was tested, and the results were as follows: Figure 6As shown in the figure, the first and second modal resonant frequencies of the probe are approximately 72kHz and 451kHz, respectively, and the ratio of the probe's response peaks at these frequencies is close to 2:1. Because the response signal intensity decreases approximately 10-fold with each mode increase during multi-frequency atomic force microscopy sample testing, the signals in the high-order modal channels, which reflect information about the physical properties of the sample surface, are very weak and easily overwhelmed by noise. For example, the contrast of images of physical information such as the sample surface's Young's modulus and adhesion force decreases significantly with increasing probe mode.

[0108] The atomic force microscope loaded with this embodiment was tested for the probe modal response curve, and the results were as follows: Figure 7 The modal response curve of the probe in the atomic force microscopy imaging system of the present invention is shown. The first and second modal resonant frequencies of the probe are approximately 72kHz and 451kHz, respectively. Under instrument excitation, the improved probe achieves a peak-to-peak ratio of nearly 1:1.5 at each modal response frequency. This effectively enhances the signal extracted by the lock-in amplifier from higher-order modes and reduces noise interference with the measurement.

Claims

1. An atomic force microscope probe high-order mode enhancement device, comprising an atomic force microscope, wherein the atomic force microscope comprises an AFM controller (1), a graphic display (2), a scanner (3), a sample stage (4), an AFM probe actuator (6), a laser (8), a photodetector (9), a lock-in amplifier (10) and a signal generator (11); characterized in that: The atomic force microscope probe high-order mode enhancement device also has a segmented constrained coupled micro-cantilever probe system (5); The segmented coupling constrained micro-cantilever probe system (5) is composed of a commercial probe, a probe holder (5A), a pressure plate (5B) and a spring sheet (5C); the probe holder (5A) is mounted on the operating table of an AFM probe actuator (6); a pressure plate (5B) is fixed on the probe holder (5A), one end of the spring sheet (5C) is fixed at the B opening groove (5B1) of the pressure plate (5B), and the other end of the spring sheet (5C) contacts the probe substrate (5G), and the spring sheet (5C) provides a constraint force for the commercial probe when it is working; the A opening groove (5A3) of the probe holder (5A) is provided with A crossbeam (5D); the crossbeam (5D) and the other end of the spring sheet (5C) jointly clamp the middle of the probe substrate (5G); an elliptical groove (5A8) is further provided on the probe holder (5A), the elliptical groove (5A8) is located at the root of the A opening groove (5A3) of the probe holder (5A), and the A opening groove (5A3) is used to place the tail of the probe substrate (5G); the positioning circular hole (5A1) on the probe holder (5A) is used to place the convex cylinder on the AFM probe actuator (6), and the elliptical positioning hole (5A2) is used to place the convex elliptical cylinder on the AFM probe actuator (6); The first aspect of the phase-locked amplifier (10) receives the detection control signal output by the photodetector (9) ; The second aspect receives a first modal reference signal output by a signal generator (11) ; The third aspect receives the second modal reference signal output by the signal generator (11) ; The fourth aspect outputs the first modal amplitude signal of the probe ; The fifth aspect outputs the second modal amplitude signal of the probe ; When the atomic force microscope performs detection work, the demodulation reference signal output by the signal generator (11) is digitally added to the lock-in amplifier (10), and the lock-in amplifier (10) starts demodulation work based on the demodulation reference signal output by the signal generator (11); When working, the demodulation frequency of the lock-in amplifier (10) is set to , ; represents the first eigenmode frequency of the probe; represents the second eigenmode frequency of the probe; The lock-in amplifier utilizes and The received detection control signal After demodulation and amplification, the first modal amplitude signal is output respectively and the probe's second modal amplitude signal ; The first modal amplitude signal It means the probe moves at the demodulation frequency The signal is processed by the image processor to obtain the topography image of the sample surface; The second modal amplitude signal It means the probe moves at the demodulation frequency The signal is processed by the image processor to obtain an image of the sample surface with respect to the second modal amplitude of the probe.

2. The atomic force microscope probe high-order mode enhancement device according to claim 1, characterized in that: The spring piece (5C) is bent at an angle in the middle , The angle is 115 degrees to 150 degrees; the length of the spring sheet before it is folded is =2900 ~3100 , the width is recorded as =1450 ~1550 , the thickness is recorded as =290 ~310 .

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