Atomic force microscope probe high-order modal enhancement device

Abstract

The invention discloses a high-order modal enhancement device for an atomic force microscope probe. A micro-cantilever probe system of a single-end clamping atomic force microscope is improved into a segmented coupling constraint micro-cantilever probe system by utilizing mechanical constraint. The segmented coupling constraint micro-cantilever probe system is composed of a commercial probe, a probe support (5A), a pressing plate (5B) and a spring piece (5C), one end of the spring piece (5C) is fixed to a groove of the pressing plate (5B), and the other end of the spring piece (5C) makes contact with the cross beam (5D) and is used for clamping a probe substrate (5G). Segmented coupling constraint is applied to the commercial probe, the commercial probe is influenced by the constraint position, the dynamic characteristics are changed, the system generates a coupling effect, and the high-order modal response of the probe is enhanced.

Description

Technical Field

[0001] The present invention relates to an atomic force microscope, and more particularly to a method of 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 a high-order modal image containing more sample information. Background Art

[0002] Atomic force microscope (AFM) is a commonly used nano-measurement and characterization instrument. It can work in a variety of environments such as atmosphere, vacuum, and liquid. It detects the surface information of the sample by detecting the interaction force between the probe and the sample, and can achieve nano-level imaging without damaging the sample. While characterizing the surface morphology of the sample, AFM is also used to characterize various mechanical and electromagnetic physical properties of the sample surface. Generally speaking, an ordinary AFM has five major components, including a detection unit, a micro-cantilever probe system, a needle tip-sample motion unit, a feedback controller, and an image processing and display system. (First edition in February 2016, Amplitude Modulation Atomic Force Microscopy / (West) García (García, R.)). For dynamic atomic force microscopy, the system applies a fixed frequency (usually the basic eigenfrequency of the micro-cantilever probe system) to the probe while it is scanning, so that the needle tip spans a large range of mutual potential energy and uses the entire force curve to extract sample information. For dynamic atomic force microscopy, due to the high nonlinearity of the cantilever dynamic characteristics, the resonance of the probe and the eigenmodes of each order also contain sample property information. The multi-frequency atomic force microscopy (MF-AFM) developed in recent years provides an important solution to these technical problems.

[0003] As a new research hotspot, multi-frequency atomic force microscopy can extract various physical properties of the sample surface while scanning the sample surface morphology. It can use the multiple modes of the cantilever to achieve fast high-resolution imaging of the sample surface and quantitative characterization of material properties. Under the excitation of different frequencies, the vibration response of the probe also changes, which is the modal response curve. When the excitation frequency matches the resonant frequency of the probe, the vibration response of the probe will increase greatly. However, in the atmospheric environment, in the multi-frequency atomic force microscope imaging system, the high-order modal response of the probe decreases step by step with the increase of the mode. Therefore, the signal-to-noise ratio of the response signal obtained using the high-order excitation frequency is too low, which is not conducive to resolving the physical property information of the sample surface. Summary of the invention

[0004] In order to solve the technical problem that the high-order modal response of the probe is too low, the present invention proposes a high-order modal enhancement device for an atomic force microscope probe based on a segmented coupling constraint, which is a low-cost means to improve the single-end clamped micro-cantilever probe system into a micro-cantilever probe system with a segmented coupling constraint, thereby realizing the enhancement of the high-order modal response signal of the probe. The probe high-order modal enhancement device in the atomic force microscope is to improve the micro-cantilever probe system by applying a segmented coupling constraint to the rectangular cantilever beam structure probe. The segmented coupling constraint improves the vibration mode of the probe originally a cantilever beam structure to the vibration of the bridge-cantilever beam coupling structure. And when the length, width and height of the two parts are consistent, 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. By analogy, when the excitation probe vibrates 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, so that the nth order eigenmode response of the system is enhanced.

[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 make way for 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 designed in the present invention uses a lightweight structure and does not require a major change in the atomic force microscope system, so it is more versatile; on the other hand, it can effectively enhance the high-order modal response of the probe and improve the high-order modal response signal.

[0006] The present invention designs a high-order mode enhancement device for an atomic force microscope probe, wherein a lock-in amplifier first receives a detection control signal V output by a photodetector. c ; The second aspect is to receive the first modal reference signal V1 output by the signal generator; the third aspect is to receive the second modal reference signal V2 output by the signal generator; 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.

[0007] When the atomic force microscope is performing detection work, the output of the signal generator is digitally input to the phase-locked amplifier, avoiding information loss caused by digital-to-analog conversion. The phase-locked amplifier works in internal reference mode.

[0008] When working, the demodulation frequency of the phase-locked amplifier is set to F1=f1, F2=f2.

[0009] The lock-in amplifier uses V1 and V2 to receive the detection 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 an 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 about the second modal amplitude of the probe is obtained. After processing, the image can reflect the special physical property information 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, and the specific detection steps are:

[0013] Step 1: Select the probe;

[0014] The probe selected for the present 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, push the tilt rod deep into the tilt rod entrance of the open groove 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 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 enhancement effect on the high-order modal response of the probe.

[0018] Step 3: Set the modal frequency;

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

[0020] Step 4: applying incentives;

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

[0022] Step 5: Information collection;

[0023] The lock-in amplifier is used to extract the morphology information and surface physical property information, such as Young's modulus and adhesion, 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 by 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 can 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 has wide versatility. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0029] Figure 2 It is a schematic diagram of the structure 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 Another structural diagram of the probe holder from another angle.

[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 structure of a commercial probe.

[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 in conjunction with the accompanying drawings and embodiments. The various parameter demonstrations listed are only preferred embodiments of the present invention. It should be noted that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be considered as the protection scope of the present invention.

[0042] See also Figure 1 The atomic force microscope shown in the figure is a conventional atomic force microscope which is provided with a clamping device having a restraining force (such as Figure 2 The present invention is to design a high-order modal enhancement device for an atomic force microscope probe for enhancing the high-order modal response signal of the probe. The atomic force microscope at least includes an AFM controller 1, a graphic display 2, a scanner 3, a sample stage 4, a micro-cantilever probe system with segmented coupling constraints 5, an AFM probe actuator 6, a laser 8, a photodetector 9, a lock-in amplifier 10 and a signal generator 11.

[0043] (I) 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] (ii) Graphics Display 2

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

[0047] (III) 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 the sample.

[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 table of the conventional atomic force microscope AFM probe actuator 6 through the 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 coupling constrained micro-cantilever probe system 5 shown is designed as a clamping device with constraining force, which can provide constraining force for the commercial probe when it is working. A pressure plate 5B is fixed on the probe holder 5A of the segmented coupling constrained micro-cantilever probe system 5, one end of the spring sheet 5C is fixed (by welding) at the B opening groove 5B1 of the pressure plate 5B, and the other end of the spring sheet 5C is in contact with the probe substrate 5G (when assembling, the spring sheet 5C is lifted by the tilting rod, the probe substrate 5G of the commercial probe is placed in the elliptical groove 5A8, and the spring sheet 5C is lowered so that the end of the spring sheet 5C at the other end is in contact with the probe substrate 5G), and the spring sheet 5C provides constraining force for the commercial probe when it is working. A crossbeam (5D) is provided at the A opening groove (5A3) of the probe holder (5A), and the crossbeam (5D) cooperates with the end of the spring sheet 5C at the other end to clamp the probe substrate 5G.

[0054] See also Figure 2A , Figure 2B As shown, the probe holder 5A is provided with an A opening slot 5A3, a positioning circular hole 5A1, an elliptical positioning hole 5A2, a wiring hole 5A7 and a plurality of A through holes 5A6; an elliptical groove 5A8 is provided on the upper panel of the probe holder 5A, and the elliptical groove 5A8 is located at the root of the A opening slot 5A3, and the elliptical groove 5A8 is used to place the tail of the probe substrate 5G; a crossbeam 5D is provided at the A opening slot 5A3. The positioning circular hole 5A1 and the elliptical positioning hole 5A2 are arranged opposite to the A opening slot 5A3, the positioning circular hole 5A1 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 A through hole 5A6 is used for rivets to pass through, and the rivets passing through the A through hole 5A6 and the B through hole 5B2 realize the fixation of the probe holder 5A and the pressing 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 sheet 5C is fixed (by welding) at the root of the B opening slot 5B1, and the other end of the spring sheet 5C contacts the probe substrate 5G.

[0056] See also Figure 2 , Figure 2C , Figure 2D As shown, one end of the spring sheet 5C is fixed (welded) 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. The spring sheet 5C provides a restraining force for the cantilever beam 5E when it is working. In the present invention, the spring sheet 5C is folded from the middle by an angle δ, and the angle δ is generally 115 degrees to 150 degrees. The size of the spring sheet 5C is designed as follows: the length of the spring sheet before folding is recorded as b=2900μm~3100μm, the width is recorded as a=1450μm~1550μm, and the thickness is recorded as c=290μm~310μm.

[0057] See also Figure 2 , Figure 2E As shown, the 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 by the present invention first fixes one end of the spring sheet 5C at the opening groove B of the pressure plate 5B, then fixes the pressure plate 5B and the probe holder 5A by rivets, and finally fixes the probe holder 5A by a positioning circular hole 5A1, an elliptical positioning hole 5A2 and two protrusions on the AFM probe actuator 6. The AFM probe actuator 6 applies the excitation force to the probe holder 5A, and then drives the probe to vibrate together.

[0059] (VI) 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] (VIII) Laser 8

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

[0063] (IX) 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] When the atomic force microscope designed by the present invention performs detection work, the output of the signal generator 11 is digitally added to the phase-locked amplifier 10, avoiding the information loss caused by the complex digital-to-analog conversion of the external analog signal adder. In addition, because the phase-locked amplifier works in the internal reference mode, the delay between the two signal paths is shorter when the signal is demodulated.

[0068] When in operation, the demodulation frequency of the phase-locked amplifier is set to F1=f1, F2=f2, wherein 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 receive the detection 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 distribution of physical properties of the sample surface can be obtained, such as Young's modulus distribution, adhesion, etc.

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

[0076] The present invention provides an atomic force microscope probe high-order mode enhancement device. Using the improved atomic force microscope, taking dual-frequency atomic force microscope testing 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 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 exciter sends a dual-frequency sinusoidal signal V to the probe. 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 receive the detection control signal V c After demodulation and amplification processing, the first modal amplitude V3 of the probe and the second modal amplitude V4 of the probe are output to the AFM controller respectively;

[0082] (6) The AFM controller detects the control signal V c To output a 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 an atomic force microscope with a constrained probe to enhance high-order modal response. The functions of each added device are as follows:

[0086] In the present invention, an atomic force microscope is used to enhance the high-order modal response of the probe by 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: Select probe:

[0088] The probe selected by the 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, installing the probe:

[0090] Fix the clamping device on the probe mounting table, push the tilt rod deep into the probe holder from the entrance of the tilt rod, lift the spring sheet, then use tweezers to send the probe into the groove and adjust it to a suitable position, then remove the tilt rod, the spring sheet falls, and fix the probe between the spring sheet and the beam;

[0091] Imaging process three: Initialize the atomic force microscope system, apply mechanical excitation to the probe to perform frequency sweep, and obtain the resonant frequency 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, and the V1 and V2 are mixed and then used as the mechanical excitation signal V a Output to the AFM probe actuator;

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

[0094] Imaging process VI: The probe is exposed to 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 imaging process seven, the scanning stage uses the detection control signal to make the probe work in a constant amplitude mode, and the relative distance between the probe and the sample remains unchanged;

[0096] Imaging process 8, the phase-locked amplifier works in the internal reference mode, using the demodulated reference signals V1 and V2 to receive the detection control signal Vc After demodulation and amplification processing, the first modal amplitude V3 of the probe and the second modal amplitude V4 of the probe are output to the AFM controller respectively;

[0097] Imaging process nine, AFM controller outputs 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 the rectangular cantilever beam structure probe, so that when the cantilever beam side of the probe is constrained to perform n-order eigenmodal vibration, the side of the probe close to the excitation source performs n-1-order eigenmodal vibration. Therefore, when the excitation probe performs n-order eigenmodal vibration, the side close to the excitation source performs n-1-order eigenmodal vibration, and the cantilever beam side performs n-order eigenmodal vibration, the overall n-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 being folded are b=3000 μm, a=1500 μm, and c=300 μm.

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

[0102] For the 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 only subjected to a 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 outputs of both the vertical deflection of the free end of the cantilever beam and the deflection slope of the free end of the cantilever beam show a gradually decreasing trend. This is also the working state of the modal response test commonly used by the probe in AFM, which can be shown by the modal frequency response Bode diagram. 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 constraint force to clamp the middle of the probe substrate, a pre-tightening force constraint is applied to the rectangular cantilever beam structure probe fixed at one end 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 to form a bridge-cantilever beam coupling resonance 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 increase of the mode (as shown in Figure 2). Figure 4 As shown in Figure 2, this is the opposite of the rectangular cantilever structure probe. In the application of multi-frequency atomic force microscopy, as the high-order modal response increases, the sensitivity of multi-frequency AFM in detecting sample properties using cantilever high-order modes will also increase.

[0104] like Figure 5 In the schematic diagram of the bridge-cantilever beam coupled resonance structure shown, a fixed constraint is applied to the bottom surface to divide the probe into two parts: the clamped bridge structure on the left side connected to the AFM probe exciter through a clamping device and the cantilever beam part on the right side. When the excitation force u(t) is applied to the left bridge structure, if the left bridge structure part is the same size as the right cantilever beam, the modal vibration frequency of the bridge structure and the modal vibration frequency of the cantilever beam structure overlap, and the natural frequency of the vibration mode 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 the high-order modal enhancement device was tested, and the results were as follows: Figure 6As shown. The first and second modal resonance frequencies of the probe are around 72kHz and 451kHz, respectively, and the ratio of the probe's response peaks at these frequencies is close to 2:1. During the multi-frequency atomic force microscope sample detection process, the response signal intensity decreases by about 10 times with each increase in the mode. This results in the signal of the high-order modal channel reflecting the physical properties of the sample surface being very weak and easily submerged by noise. For example, the contrast of the physical information image such as the Young's modulus and adhesion of the sample surface will drop significantly with the increase in the probe mode used.

[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, and the first and second modal resonance frequencies of the probe are about 72kHz and 451kHz respectively. Under the excitation of the instrument, after improvement, the response peak ratio of the probe at each modal response frequency is close to 1:1.5, which can effectively enhance the signal extracted by the lock-in amplifier from the high-order mode and reduce the interference of noise on the measurement.

Claims

1. A high-order mode enhancement device for an atomic force microscope probe, the atomic force microscope at least comprising 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: There is also a segmented constrained coupled microcantilever 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 an 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), the other end of the spring sheet (5C) is in contact with a probe substrate (5G), and the spring sheet (5C) provides a restraining force for the commercial probe when it is working; a crossbeam (5D) is provided at the A opening groove (5A3) of the probe holder (5A); the positioning circular hole (5A1) on the probe holder (5A) is used to place a convex cylinder on the AFM probe actuator (6), and the elliptical positioning hole (5A2) is used to place a convex elliptical cylinder on the AFM probe actuator (6); 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; When the atomic force microscope performs detection work, the demodulation reference signal output by the signal generator (11) is digitally added to the phase-locked amplifier (10), and the phase-locked amplifier (10) starts demodulation work based on the demodulation reference signal output by the signal generator (11); When in operation, the demodulation frequency of the phase-locked amplifier (10) is set to F1=f1, F2=f2; The lock-in amplifier uses V1 and V2 to receive the detection 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; The first modal amplitude V3 refers to the amplitude of the excitation probe movement at the demodulation frequency F1, and the signal is processed by the image processor to obtain the topographic image of the sample surface; 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.

2. The atomic force microscope probe high-order mode enhancement device according to claim 1, characterized in that The imaging process of the AFM imaging system is: Imaging process 1: Select commercial probes: Imaging process 2, installing the probe: Fix the clamping device on the probe mounting table, push the tilt rod deep into the base from the entrance of the tilt rod, lift the spring sheet, then use tweezers to send the probe into the groove and adjust it to a suitable position, then remove the tilt rod and fix the probe between the spring sheet and the beam; Imaging process three, initializing the atomic force microscope system, applying mechanical excitation to the probe to perform frequency sweeping, and obtaining multiple resonant frequencies F of the AFM probe actuator; finally determining the first modal frequency f1 and the second modal frequency f2 of the probe; 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, and the V1 and V2 are mixed and then used as the mechanical excitation signal V a Output to the AFM probe actuator; Imaging process 5: The AFM probe actuator drives the mechanical excitation signal V a Applying mechanical excitation to excite the probe to vibrate; Imaging process VI: The probe is exposed to 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; In imaging process seven, the scanning stage uses the detection control signal to make the probe work in a constant amplitude mode, and the relative distance between the probe and the sample remains unchanged; Imaging process 8, the phase-locked amplifier uses the demodulated reference signals V1 and V2 to receive the detection control signal V c After demodulation and amplification processing, the first modal amplitude V3 of the probe and the second modal amplitude V4 of the probe are output to the AFM controller respectively; Imaging process nine, AFM controller outputs 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 an image of the sample surface with respect to the probe first modal amplitude and the second modal amplitude.

3. The atomic force microscope probe high-order mode enhancement device according to claim 1, characterized in that: The size of the spring sheet (5C) in the segmented constraint coupled micro-cantilever probe system (5) is that the spring sheet (5C) is folded at an angle δ from the middle, and the angle δ is generally 115 degrees to 150 degrees; the length of the spring sheet before folding is recorded as b=2900μm~3100μm, the width is recorded as a=1450μm~1550μm, and the thickness is recorded as c=290μm~310μm.

4. The atomic force microscope probe high-order mode enhancement device according to claim 1, characterized in that: When the first and second order eigenresonant frequencies of the probe are 72kHz and 451kHz respectively, the ratio of the response peak values ​​of the probe at the first and second order eigenmodal response frequencies is close to 1:1.5, which can effectively enhance the extraction of high-order modal signals from the mixed signal by the lock-in amplifier and improve the signal-to-noise ratio of the high-order modal signals.

Images