CN113109595B - An atomic force microscopy method and system for analyzing electrostatic and electromechanical coupling responses - Google Patents

Abstract

The embodiment of the invention discloses an atomic force microscopy method and system for analyzing electrostatic and electromechanical coupling responses. An atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses, comprising: synthesizing excitation signals from sub-waveforms with different characteristic parameters in two frequency bands according to a preset splicing sequence; applying the excitation signals to a target to be measured, and obtaining Amplitude images corresponding to different characteristic parameters of the target to be measured; decoupling and reconstruction are performed according to the target decoupling model and the dual-mode amplitude image of the target to be measured to generate a strain image and an electrostatic image of the target to be measured. Solve the problem that the electromechanical coupling strain measurement is easily affected by static electricity and the results are inaccurate, and realize the effect of accurately obtaining the electromechanical coupling strain image and electrostatic response image of the target to be measured by quantitatively analyzing the dual-mode data with the target decoupling model.

Description

An atomic force microscopy method and system for analyzing electrostatic and electromechanical coupling responses

technical field

Embodiments of the present invention relate to microscopic imaging technology, in particular to an atomic force microscopy method and system for analyzing electrostatic and electromechanical coupling responses.

Background technique

In the past decade, the emergence of dynamic excitation measurement modes based on atomic force microscopy (AFM), represented by piezoelectric response force microscopy (PFM) and electrochemical strain microscopy (ESM), has greatly promoted the mechanism of a series of materials. Research and performance optimization. However, in actual measurements, the response is not limited to the expected electro-induced strain, but is also disturbed by electrostatic forces.

In the existing technology, different probes, high-order modes of the probes, and AFM hardware modification are often used in the measurement to qualitatively eliminate the interference of electrostatic force. However, the actual effect cannot be effectively verified, and the strength of the electric strain response of different sample materials relatively difficult.

Contents of the invention

The present invention provides an atomic force microscopy method and system for analyzing electrostatic and electromechanical coupling responses, so as to realize the acquisition of dual-mode test result data in one scan, obtain the test results of strain and electrostatic force through quantitative analysis, and reduce the impact on specific The probe needs to improve the applicability effect.

In the first aspect, an embodiment of the present invention provides an atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses, including:

Multiple sub-waveforms with different characteristic parameters in two frequency bands are synthesized into excitation signals according to the preset splicing sequence;

applying the excitation signal to the target to be measured, and obtaining dual-mode amplitude images corresponding to different characteristic parameters of the target to be measured;

Decoupling and reconstruction are performed according to the target decoupling model and the dual-mode amplitude image of the target to be measured to generate a mechatronic coupling strain image and an electrostatic response image of the target to be measured.

Optionally, before synthesizing a plurality of sub-waveforms with different characteristic parameters into an excitation signal according to a preset splicing sequence, it also includes: constructing a decoupling model; the constructing a decoupling model includes:

Calibrate the vibration parameters of the probe of the atomic force microscope;

Constructing an initial decoupling model based on vibration parameters of the probe;

Based on the measurement data of the atomic force microscope, the reliability of the initial decoupling model is verified, and the target decoupling model is obtained.

Optionally, the vibration parameters of the probe include dual-mode stiffness and optical lever conversion coefficient of coupled resonance between the probe and the sample to be measured.

Optionally, the spectrum range of the excitation signal covers frequencies corresponding to the dual modes.

Optionally, applying the excitation signal to the target to be measured, and obtaining amplitude images corresponding to different characteristic parameters of the target to be measured includes:

Applying the excitation signal to the target to be tested sequentially through the probe of the atomic force microscope to obtain a corresponding response signal;

separating amplitude images corresponding to different characteristic parameters in the response signal.

Optionally, the separating amplitude images corresponding to different characteristic parameters in the response signal includes:

Demodulating the full-time vibration response signals under the different characteristic parameters to obtain the characteristic information of the target under different characteristic parameters and different modes;

According to the feature information and a preset fitting algorithm, dual-mode amplitude images correspondingly included in the target to be measured under different characteristic parameters are obtained.

Optionally, performing decoupling and reconstruction according to the target decoupling model and the amplitude image of the target to be measured to generate a strain image and an electrostatic image of the target to be measured includes:

Demodulating the full-time domain amplitude response data of the target to be measured to obtain the intrinsic amplitude and phase of the target to be measured under the excitation signal applied by the probe;

According to the eigenamplitude and the eigenphase, the target decoupling model reconstructs the decoupled data to obtain the electromechanical coupling strain image and the electrostatic response image of the target to be measured.

In the second aspect, the present invention also provides an atomic force microscopy system for analyzing electrostatic and electromechanical coupling responses, including:

The signal generation module is used for synthesizing the excitation signal from multiple sub-waveforms with different characteristic parameters in the two frequency bands according to the preset splicing sequence;

An image acquisition module, configured to apply the excitation signal to the target to be measured, and obtain dual-mode amplitude images corresponding to different characteristic parameters of the target to be measured;

The data processing module is used to perform decoupling and reconstruction according to the target decoupling model and the dual-mode amplitude image of the target to generate the electromechanical coupling strain image and electrostatic response image of the target to be measured.

Optionally, the atomic force microscopy system for analyzing electrostatic and electromechanical coupling responses further includes: a decoupling model construction module, and the decoupling model construction module includes:

The parameter calibration unit is used to calibrate the vibration parameters of the probe of the atomic force microscope;

an initial model construction unit, configured to construct an initial decoupling model based on the vibration parameters of the probe;

The model verification unit is configured to verify the reliability of the initial decoupling model based on the measurement data of the atomic force microscope to obtain the target decoupling model.

Optionally, the data processing module includes:

An intrinsic characteristic acquisition unit, configured to demodulate the full-time amplitude response data of the target to be measured to obtain the intrinsic amplitude and phase of the target to be measured under the excitation signal applied by the probe;

A result acquisition unit, configured to reconstruct the decoupled data according to the eigenamplitude and eigenphase, the target decoupling model to obtain the electromechanical coupling strain image and the electrostatic response image of the target to be measured .

In the present invention, multiple sub-waveforms with different characteristic parameters in two frequency bands are synthesized into an excitation signal according to a preset splicing sequence; the excitation signal is applied to the target to be measured, and dual-mode amplitude images corresponding to different characteristic parameters of the target to be measured are obtained ; Decoupling and reconstruction are performed according to the target decoupling model and the dual-mode amplitude image of the target to be measured, and the electromechanical coupling strain image and the electrostatic response image of the target to be measured are generated; The problem of electrostatic influence and inaccurate results can be solved, and the effect of accurately obtaining the electromechanical coupling strain image and electrostatic response image of the target to be measured can be obtained by quantitatively analyzing the dual-mode data with the target decoupling model.

Description of drawings

FIG. 1 is a schematic flowchart of an atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses provided by Embodiment 1 of the present invention;

2 is a schematic diagram of signal synchronization of an atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses provided by Embodiment 1 of the present invention;

3 is a schematic diagram of the response spectrum corresponding to different vibration modes of an atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses provided by Embodiment 1 of the present invention;

4A is a schematic diagram of the total response amplitude of the excitation signal of an atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses provided by Embodiment 1 of the present invention;

Fig. 4B is a schematic diagram of the strain force response of an atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses provided by Embodiment 1 of the present invention;

FIG. 4C is a schematic diagram of an electrostatic force response of an atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses provided by Embodiment 1 of the present invention;

5A is a schematic flowchart of another atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses provided by Embodiment 1 of the present invention;

5B is a schematic sub-flow diagram of another atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses provided by Embodiment 1 of the present invention;

FIG. 6 is a schematic structural diagram of an atomic force microscopy system for analyzing electrostatic and electromechanical coupling responses provided by Embodiment 2 of the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, but not to limit the present invention. In addition, it should be noted that, for the convenience of description, only some structures related to the present invention are shown in the drawings but not all structures.

Embodiment one

Figure 1 is a schematic flow chart of an atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses provided by Embodiment 1 of the present invention. This embodiment can be applied to the situation where electrostatic and strain tests are performed on target samples. This method can be performed by a An atomic force microscopy system for analyzing electrostatic and electromechanical coupling responses is implemented, which specifically includes the following steps:

Step 110, combining multiple sub-waveforms with different characteristic parameters in the two frequency bands into an excitation signal according to a preset splicing sequence.

Usually, when the atomic force microscope (Atomic Force Microscope, AFM) tests various properties of the sample, it needs to perform multiple dynamic and/or static scans, and correspondingly needs to collect test result data multiple times for processing, and switch between different harmonic scans. longer. Since the eigenamplitude of the target to be measured is usually very weak and is easily covered by the system noise of the instrument, it is necessary to use resonance excitation to amplify the response.

In this embodiment, high-throughput technology is used to synthesize multiple sub-waveforms into excitation signals according to a preset splicing sequence, and the sub-waveforms have different characteristic parameters, and the sub-waveforms are sine waves. The different characteristic parameters include different frequencies, different periods, and different amplitudes. value and different phases, the sequentially synthesized stimulus signal contains multiple sub-waveforms with different characteristic parameters, so the sequentially synthesized stimulus signal has multiple test functions. Further, the frequencies of the sub-waveforms of the synthesized excitation signal belong to two preset frequency bands, that is, the spectrum range of the excitation signal covers the frequencies corresponding to the dual modes, and the frequencies of the sub-waveforms are in a discrete state. The excitation signal synthesized by a plurality of frequency discrete sine waves used in this embodiment can obtain a test result that meets the accuracy requirement, and at the same time, compared with the method of using continuous frequency wavelets for testing, the test rate is improved. Using the above-mentioned excitation signal waveform to excite the scanning area to obtain the scanning information of the electrostatic response and the electromechanical coupling strain response achieves the effect of simply and efficiently obtaining large data with high physical correlation. At the same time, the excitation energy is concentrated on multiple key frequencies, which reduces data redundancy while improving the signal-to-noise ratio.

Specifically, the excitation signal for the test is customized according to the resonance frequency range of the scanning area of the target material. In the experiment, the "AFM" software is usually used to find the area to be scanned and confirm the resonance frequency range of the material. Before synthesizing the excitation signal, it is necessary to set the starting frequency, ending frequency, driving voltage, instrument sampling rate, fitting points and other parameters in advance to customize the signal, and generate a series of sub-waveforms with equal difference frequency according to the conversion of the above parameters, and then The generated frequency sub-waveforms are spliced to generate an excitation signal. The intermediate parameters that need to be used in the conversion process include the frequency difference interval, the number of cycles per frequency, and the phase lag. The excitation signal covers two frequency ranges, such as a signal containing a first-order frequency and a wavelet signal of a second-order frequency. Since the resonance effect is closer to the sample eigenfrequency, the response intensity is greater, so the technical solution provided by this embodiment can better cover each formant frequency range than other traditional techniques, so as to obtain more reliable response information. Exemplarily, the first-order frequency interval of the scanning area is 330kHZ-360kHZ, and 15 frequency points are usually used to cover this interval, so the frequency interval is 2Khz.

Step 120, applying the excitation signal to the target to be measured, and acquiring dual-mode amplitude images of different characteristic parameters of the target to be measured.

The scanning probe applies an excitation signal to the target to be measured, generating a very weak interatomic interaction force, which will cause the cantilever connected to the scanning probe to deform or change its motion state. When scanning the sample, use the sensor to detect these changes, and then the force distribution information can be obtained, so as to obtain the surface topography structure information and physical information such as current and deformation with nanoscale resolution. In this embodiment, the dual-mode amplitude image obtained by applying the excitation signal is specifically: the response amplitude image of the target under the action of the electric field excitation signal of the probe, and its contribution comes from the electrostatic force response between the target to be measured and the probe and the sum of the target's own electrostrain response.

Wherein, step 120 specifically includes:

S1. Apply the excitation signal to the target to be measured sequentially through the probe of the atomic force microscope to obtain a corresponding response signal.

S2. Separate amplitude images corresponding to different characteristic parameters in the response signal.

The arbitrary waveform generator converts the generated excitation signal into an analog signal with a preset sampling frequency and sends it to the scanning microscope probe. When converting the excitation signal into an analog signal with a preset sampling frequency, the arbitrary waveform generator Marking is used to distinguish different frequency signals at intervals to ensure that there is no crosstalk during excitation and post-processing. Specifically, different sub-waveforms are distinguished and marked by a fixed-length blank value reserved in the middle. The scanning probe sequentially applies analog signals to the target to be tested, so that multiple test result signals can be obtained from one scan of the target sample. The test result signal is the collected sample response signal, and the test result signal generates a variety of test results respectively according to the preset splicing sequence of the synthetic excitation signal. is the vibrational response of the probe, and the decoupling results are the electrostatic and strain properties of the target sample.

Exemplarily, as shown in Figure 2, the excitation signal is composed of multiple frequency discrete sine waves connected in time sequence within a preset time span, and a fixed-length blank value is reserved at the connection of different frequency sub-waveforms that make up the excitation signal. Marking, used to identify the response signals generated by different sub-waveforms during post-processing, to ensure that different frequency sub-waveforms do not interfere with each other during excitation and post-processing; multiple different frequency signals are used to excite the sample through the scanning probe, and the scanning probe treats The measurement target is scanned in line order, and the response signal is collected and transmitted to the post-processor. The MATLAB software in the post-processor performs segmental cutting and analysis on the collected response signals of different modes, and the reverse solution is obtained The corresponding amplitude and phase are then fitted, and finally the amplitude and phase diagrams of different modes are obtained.

Step 130 , decoupling and reconstructing according to the target decoupling model and the amplitude image of the target to be measured, and generating the electromechanical coupling strain image and electrostatic response image of the target to be measured.

Optionally, step 130 specifically includes:

Step 131 , demodulating the full-time domain amplitude response data of the target to be measured to obtain the intrinsic amplitude and phase of the target to be measured under the excitation signal applied by the probe.

The quantitative decoupling method based on the probe vibration principle and dual-mode big data can accurately reflect the real strain of the material induced by the electric field at the tip and the interference of the additional electrostatic force. As shown in Figure 3, the eigenamplitude of the material to be measured under the induction of the probe electrostatic force is inversely proportional to its stiffness, and the difference is obvious in different vibration modes, but the eigenamplitude caused by strain is not affected by this. It can also distinguish the electrostatic effect associated with the change of the internal properties of the material, for example, the electrostatic effect induced by the change of ferroelectric polarization and the change of ion concentration.

Step 132 , according to the eigenamplitude and eigenphase, the target decoupling model reconstructs the decoupled data to obtain the electromechanical coupling strain image and electrostatic response image of the target to be measured.

Before decoupling, the standard sample periodic lithium niobate (PPLN) is used to calibrate the probe. Due to the interference of electrostatic force, some domain responses in different polarization regions of PPLN are enhanced, and some are weakened. This is due to Due to the different polarization directions of different domains, when the electrostatic force is in the same direction as the sample polarization direction, the response is enhanced, and when the direction is opposite, they cancel each other out. From the first-order and second-order amplitude distributions decoupling through the target decoupling model, the amplitude distribution of the piezoelectric response distribution map conforms to the real domain structure distribution, the domain regions in different directions have the same amplitude, and there is a lower response at the domain boundary. The obtained first-order amplitude and second-order amplitude images are decoupled according to the target decoupling model to obtain the distribution of the electromechanical coupling strain map of the sample. Furthermore, the decoupling according to the target decoupling model can be better used to compare the electrostatic force response and electromechanical coupling strain response of different materials. The corresponding amplitudes of electromechanical coupling strain and electrostatic response in different modes are shown in Figure 4A, Figure 4B and Figure 4C. The amplitude of the response varies in proportion.

The technical solution of the embodiment of the present invention synthesizes the excitation signal by combining multiple sub-waveforms with different characteristic parameters in two frequency bands according to the preset splicing sequence; applies the excitation signal to the target to be measured, and obtains the different characteristic parameters of the target to be measured. Dual-mode amplitude image; decoupling and reconstruction are performed according to the target decoupling model and the dual-mode amplitude image of the target to be measured to generate a mechatronic coupling strain image and an electrostatic response image of the target to be measured; Coupled strain measurement is easily affected by static electricity and the results are inaccurate, and the quantitative analysis of dual-mode data by the target decoupling model can accurately obtain the electromechanical coupling strain image and electrostatic response image of the target to be measured, and reduce the impact on specific probes. demand, and improve the effect of applicability.

On the basis of the above technical solution, as shown in Figure 5A, before step 110, it also includes:

Step 100, constructing a decoupling model.

As shown in FIG. 5B , it specifically includes: step 101 , calibrating the vibration parameters of the probe of the atomic force microscope.

Scanning probe microscopy applies an AC voltage to the conductive probe, and under the action of the tip electric field, the piezoelectric sample is deformed under the action of the inverse piezoelectric effect, which enhances the deformation and displacement transmitted to the probe, and enhances the signal through resonance amplification. , the deformation of the sample is quantified by detecting the displacement change of the probe with a laser detector. While the AFM is measuring, due to the capacitive effect between the probe and the sample, electrostatic interaction will be introduced, which will increase the additional contribution of the probe amplitude. Since the electrostatic effect is significantly affected by the stiffness of the probe, it is necessary to calibrate the vibration parameters of the probe before constructing the decoupling model.

Wherein, optionally, the vibration parameters include dual-mode stiffness and optical lever conversion coefficient of coupled resonance between the probe and the sample to be measured.

According to the vibration principle of the probe, the stiffness of different modes of the probe under free resonance can be measured experimentally, and then the stiffness of the dual mode can be obtained through beam theory conversion. The optical lever conversion coefficient can be calibrated by measuring the pure electrostatic effect or changing the integrated position of the laser spot on the cantilever of the AFM probe.

Step 102, constructing an initial decoupling model based on the vibration parameters of the probe.

Step 103, performing reliability verification on the initial decoupling model based on the measurement data of the atomic force microscope, to obtain a target decoupling model.

In order to test the effectiveness of the decoupling model, a variety of AFM routine measurements can be used to verify whether the response magnitude matches or not. Among them, since the electrostatic force is a long-range force, after the resonance measurement, the AFM probe can be raised to a few nanometers on the sample surface, and the same excitation signal is applied; at this time, it is in a non-contact state, and the probe vibration is no longer affected by the sample deformation. The amplitude is determined by the pure electrostatic force gradient, so the electrostatic force can be accurately measured by varying the probe height and applying different DC biases. Finally, the applicability of the decoupling model was tested by using probes with different stiffnesses and different samples, such as lithium iron phosphate, cerium oxide, methylamine lead iodine, etc. The verified decoupling model is determined as the target decoupling model.

Exemplarily, when there is an electrostatic force, the total amplitude response measured by the AFM is composed of a piezoelectric response and an electrostatic response, as shown in formula (1):

Among them, A _total is the total response amplitude, A _p is the piezoelectric amplitude, A _e is the electrostatic amplitude, d is the _{piezoelectric} coefficient of the sample, V _ac is the AC voltage of the tip, k is the system stiffness of the probe sample, and C' is Capacitance gradient between the needle tip and sample, V _dc is the direct current voltage of the probe, and V _sp is the surface potential of the sample.

In order to obtain the real piezoelectric response of the sample, using the multi-order resonance mode properties of the probe, the dynamic stiffness of the probe will increase with the increase of the resonance mode, while the probe stiffness is inversely proportional to the magnitude of the electrostatic response, while Does not affect the piezoelectric strain, so by using dual-mode PFM, the real piezoelectric response A _p and electrostatic response A _e are decoupled from the total amplitudes A _w1 and A _w2 of different modal responses. The amplitude response contribution is as follows, F _e is the electrostatic force as shown in formulas (2) and (3):

The standard sample PPLN is used to calibrate the probe, and the system parameters invOLS ₁ , invOLS ₂ , k ₁ , k ₂ are obtained. The piezoelectric coefficient of the standard sample PPLN is a known value d ₃₃ =7.5pm/V. The sample is composed of strip domains that are periodically distributed and arranged upward and downward. The amplitude responses of the domains in different polarization directions are the same. The phase is opposite, and the amplitude response is lowest at the domain boundary. The value of the needle tip AC voltage V _ac is set during the experimental measurement, and A _w1 and A _w2 are the amplitude values of different orders of the probe obtained from the experimental measurement. According to the difference in dynamic stiffness k ₁ and k ₂ of the probe under different modes, the piezoelectric response can be obtained by formula (4):

In the SSPFM (Switching spectroscopy piezoresponse force microscopy, piezoelectric response force flip spectrum microscopy) mode, set a DC voltage scan with a linear change of 0-15V, and the AC amplitude is 1V, and measure the different polarizations of the probe on the PPLN sample. The first-order resonance response and the second-order resonance response of the region.

Perform linear fitting on the intersecting line segments, and the intersection point is the real piezoelectric amplitude value of the sample. The amplitude value at this time is obtained through static invOLS conversion, so it is necessary to remove the static invOLS first to obtain the original signal, static invOLS=95.99nm/ V, calibrated by Cypher ES through thermal noise test. Then use the known piezoelectric coefficient d33 of the standard sample to recalculate invOLS1 and invOLS2 under different resonance modes, as shown in formulas (5) and (6):

From the above formula, invOLS1=51.166nm/V, invOLS2=126.711nm/V.

Then through the slope b1=5.4264pm/V and b2=0.223pm/V of the line segment fitted by the first-order mode and the second-order mode, the ratio β of the dynamic stiffness k2 to k1 can be obtained, as shown in formula (7):

This gives β = 6.5.

Thus, after all the system parameters have been calibrated, only the amplitude response values in the first-order mode and the second-order mode can be obtained through experimental testing, and the real piezoelectric response contribution can be separated through the decoupling formula.

On the basis of the above-mentioned technical solution, sub-step S2 in step 120 preferably includes:

S21. Demodulate the full-time-domain vibration response signals under the different characteristic parameters to obtain characteristic information of the target under different characteristic parameters and different modes.

Since the arbitrary waveform generator marks the analog signal and distinguishes the signal intervals corresponding to different characteristic parameters, the obtained full-time vibration response signals under different characteristic parameters can be obtained after demodulation. parameters and corresponding feature information in different modes. The characteristic information includes one or more of amplitude, phase offset, resonance frequency and quality factor.

S22. According to the feature information and a preset fitting algorithm, obtain the dual-mode amplitude images correspondingly contained in the target to be measured under different characteristic parameters.

Draw the corresponding characteristic information of each pixel under different characteristic parameters to the complex plane, and fit the corresponding physical model to obtain the intrinsic amplitude and phase of the target to be measured, and reconstruct the amplitude corresponding to the dual mode. Value plots and phase plots.

Embodiment two

Fig. 6 is an atomic force microscopy system for analyzing electrostatic and electromechanical coupling responses provided by an embodiment of the present invention. As shown in Figure 6, an atomic force microscopy system for analyzing electrostatic and electromechanical coupling responses includes:

The signal generation module 510 is configured to synthesize the excitation signal from multiple sub-waveforms with different characteristic parameters in the two frequency bands according to a preset splicing sequence.

Usually, when the atomic force microscope (Atomic Force Microscope, AFM) tests various properties of the sample, it needs to perform multiple dynamic and/or static scans, and correspondingly needs to collect test result data multiple times for processing, and switch between different harmonic scans. longer. Since the eigenamplitude of the target to be measured is usually very weak and is easily covered by the system noise of the instrument, it is necessary to use resonance excitation to amplify the response.

This embodiment uses high-throughput technology to synthesize multiple sub-waveforms into excitation signals according to a preset splicing sequence, and the sub-waveforms have different characteristic parameters, and the sub-waveforms can be sine waves. The different characteristic parameters include different frequencies, different periods, different One or more of amplitude and different phases, the sequentially synthesized excitation signal contains multiple sub-waveforms with different characteristic parameters, so the sequentially synthesized excitation signal has multiple test functions. Further, the frequencies of the sub-waveforms of the synthesized excitation signal belong to two preset frequency bands, that is, the spectrum range of the excitation signal covers the frequencies corresponding to the dual modes, and the frequencies of the sub-waveforms are in a discrete state. The excitation signal synthesized by a plurality of frequency discrete sine waves used in this embodiment can obtain a test result that meets the accuracy requirement, and at the same time, compared with the method of using continuous frequency wavelets for testing, the test rate is improved. Using the above-mentioned excitation signal waveform to excite the scanning area to obtain the scanning information of the electrostatic response and the electromechanical coupling strain response achieves the effect of simply and efficiently obtaining large data with high physical correlation. At the same time, the excitation energy is concentrated on multiple key frequencies, which reduces data redundancy while improving the signal-to-noise ratio.

The image acquisition module 520 is configured to apply the excitation signal to the target to be measured, and acquire dual-mode amplitude images of different characteristic parameters of the target to be measured.

The scanning probe applies an excitation signal to the target to be measured, generating a very weak interatomic interaction force, which will cause the cantilever connected to the scanning probe to deform or change its motion state. When scanning the sample, use the sensor to detect these changes, and then the force distribution information can be obtained, so as to obtain the surface topography structure information and physical information such as current and deformation with nanoscale resolution. In this embodiment, the dual-mode amplitude images obtained by applying the excitation signal are specifically: the amplitude image of the electrostrain response of the target to be measured under the action of the excitation signal of the probe, and the amplitude image of the electrostatic force response between the target to be measured and the probe.

The excitation signal is composed of multiple frequency discrete sine waves connected in time sequence within a preset time span, and a fixed-length blank value is reserved at the connection of different frequency sub-waveforms that make up the excitation signal for marking, which is used to identify different sub-waveforms during post-processing. The response signal generated by the waveform ensures that different frequency sub-waveforms do not interfere with each other during excitation and post-processing; multiple different frequency signals are used to excite the sample through the scanning probe, and the scanning probe scans the target to be measured in row order, and the collected The response signal is transmitted to the post-processor, and the MATLAB software in the post-processor performs segmental cutting and analysis on the collected response signals of different modes, reversely solves to obtain the corresponding amplitude and phase, and then performs fitting. Finally, the magnitude diagram and phase diagram of different modes are obtained.

The data processing module 530 is configured to perform decoupling and reconstruction according to the target decoupling model and the amplitude image of the target to be measured, and generate the electromechanical coupling strain image and the electrostatic response image of the target to be measured.

By synthesizing the excitation signal, the first-order and second-order modal responses are continuously measured at the same point, and the in-situ scanning of the dual-mode response amplitude in the whole area is completed, and the first-order amplitude and second-order amplitude images are extracted from the original data through the MATLAB program , and then perform decoupling operations according to the target decoupling model to obtain the piezoelectric response map distribution of the target sample to be tested, that is, the test result image of the target to be tested.

Optionally, the atomic force microscopy system for analyzing electrostatic and electromechanical coupling responses further includes a decoupling model construction module 500 . The decoupling model construction module 500 specifically includes:

The parameter calibration unit is used to calibrate the vibration parameters of the probe of the atomic force microscope.

While the AFM is measuring, due to the capacitive effect between the probe and the sample, electrostatic interaction will be introduced, which will increase the additional contribution of the probe amplitude. Since the electrostatic effect is significantly affected by the stiffness of the probe, it is necessary to calibrate the vibration parameters of the probe before constructing the decoupling model. Wherein, optionally, the vibration parameters include dual-mode stiffness and optical lever conversion coefficient of coupled resonance between the probe and the sample to be measured.

According to the vibration principle of the probe, the stiffness of different modes of the probe under free resonance can be measured experimentally, and then the stiffness of the dual mode can be obtained through beam theory conversion. The optical lever conversion coefficient can be calibrated by measuring the pure electrostatic effect or changing the integrated position of the laser spot on the cantilever of the AFM probe.

An initial model construction unit, configured to construct an initial decoupling model based on the vibration parameters of the probe.

The model verification unit is configured to verify the reliability of the initial decoupling model based on the measurement data of the atomic force microscope to obtain the target decoupling model.

In order to test the effectiveness of the decoupling model, a variety of AFM routine measurements can be used to verify whether the response magnitude matches or not. Among them, since the electrostatic force is a long-range force, after the resonance measurement, the AFM probe can be raised to a few nanometers on the sample surface, and the same excitation signal is applied; at this time, it is in a non-contact state, and the probe vibration is no longer affected by the sample deformation. The amplitude is determined by the pure electrostatic force gradient, so the electrostatic force can be accurately measured by varying the probe height and applying different DC biases. Finally, the applicability of the decoupling model was tested by using probes with different stiffnesses and different samples, such as lithium iron phosphate, cerium oxide, methylamine lead iodine, etc. The verified decoupling model is determined as the target decoupling model.

Optionally, the image acquisition module 520 includes:

The signal testing unit is used to sequentially apply the excitation signal to the target to be tested through the probe of the atomic force microscope to obtain a corresponding response signal.

An image processing unit, configured to separate amplitude images corresponding to different characteristic parameters in the response signal.

The scanning probe sequentially applies sequentially synthesized excitation signals to multiple pixel points of the target to be tested, so that multiple test result signals can be obtained by one scan of the target sample. The test result signal is the collected sample response signal, and the test result signal generates a variety of test results respectively according to the preset splicing sequence of the synthetic excitation signal. are the electrostatic and strain properties of the target sample.

Optionally, the image processing unit includes:

The characteristic information acquisition subunit is used to demodulate the full-time vibration response signals under the different characteristic parameters to obtain the characteristic information of the target under different characteristic parameters and different modes.

Since the AWG marks the analog signal and distinguishes the signal intervals corresponding to different characteristic parameters, the obtained full-time vibration response signals under different characteristic parameters can be obtained after demodulation under different characteristic parameters and different characteristics of the target to be tested. The feature information corresponding to the mode. The characteristic information includes one or more of amplitude, phase offset, resonance frequency and quality factor.

The amplitude image generating subunit is used to obtain the corresponding dual-mode amplitude images of the target under different characteristic parameters according to the characteristic information and a preset fitting algorithm.

Draw the corresponding characteristic information of each pixel under different characteristic parameters to the complex plane, fit the corresponding physical model to obtain the intrinsic amplitude and phase of the target to be measured, and reconstruct the amplitude corresponding to different modes. Value plots and phase plots.

Optionally, the data processing module 530 includes:

The intrinsic characteristic acquisition unit is configured to demodulate the full-time domain amplitude response data of the target to be measured to obtain the intrinsic amplitude and phase of the target to be measured under the excitation signal applied by the probe.

The quantitative decoupling method based on the probe vibration principle and dual-mode big data can accurately reflect the real strain of the material induced by the electric field at the tip and the interference of the additional electrostatic force.

A result acquisition unit, configured to reconstruct the decoupled data according to the eigenamplitude and eigenphase, the target decoupling model to obtain the electromechanical coupling strain image and the electrostatic response image of the target to be measured .

From the first-order and second-order amplitude distributions decoupling through the target decoupling model, the amplitude distribution of the piezoelectric response distribution map conforms to the real domain structure distribution, the domain regions in different directions have the same amplitude, and there is a lower response at the domain boundary. The obtained first-order amplitude and second-order amplitude images are decoupled according to the target decoupling model to obtain the distribution of the electromechanical coupling strain map of the sample.

The technical solution of the embodiment of the present invention synthesizes the excitation signal by combining multiple sub-waveforms with different characteristic parameters in two frequency bands according to the preset splicing sequence; applies the excitation signal to the target to be measured, and obtains the different characteristic parameters of the target to be measured. Dual-mode amplitude image; decoupling and reconstruction are performed according to the target decoupling model and the dual-mode amplitude image of the target to be measured to generate a mechatronic coupling strain image and an electrostatic response image of the target to be measured; Coupled strain measurement is easily affected by static electricity and the results are inaccurate, and the quantitative analysis of dual-mode data by the target decoupling model can accurately obtain the electromechanical coupling strain image and electrostatic response image of the target to be measured, and reduce the impact on specific probes. demand, and improve the effect of applicability.

The atomic force microscopy system for analyzing electrostatic and electromechanical coupling responses provided by the embodiments of the present invention can execute the atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses provided by any embodiment of the present invention, and has corresponding functional modules and Beneficial effect.

Note that the above are only preferred embodiments of the present invention and applied technical principles. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and can also include more other equivalent embodiments without departing from the concept of the present invention, and the present invention The scope is determined by the scope of the appended claims.

Claims (10)

1. An atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses, characterized in that it comprises: Multiple sub-waveforms with different frequencies in two frequency bands are synthesized into excitation signals according to the preset splicing sequence; Applying the excitation signal to the target to be measured, acquiring dual-mode amplitude images corresponding to different frequencies of the target to be measured; Decoupling and reconstruction are performed according to the target decoupling model and the dual-mode amplitude image of the target to be measured to generate a mechatronic coupling strain image and an electrostatic response image of the target to be measured. 2. The atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses according to claim 1, characterized in that, before the multiple sub-waveforms with different frequencies in the two frequency bands are synthesized into excitation signals according to a preset splicing sequence , also includes: constructing a decoupling model; said constructing a decoupling model includes: Calibrate the vibration parameters of the probe of the atomic force microscope; Constructing an initial decoupling model based on vibration parameters of the probe; Based on the measurement data of the atomic force microscope, the reliability of the initial decoupling model is verified, and the target decoupling model is obtained. 3. the atomic force microscopy method of analyzing static electricity and electromechanical coupling response according to claim 2, is characterized in that, the vibration parameter of described probe comprises the double-mode stiffness of probe and sample coupling resonance and optical lever conversion coefficient. 4. The atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses according to claim 1, wherein the frequency spectrum of the excitation signal covers the frequencies corresponding to the dual modes. 5. The atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses according to claim 1, wherein the excitation signal is applied to the target to be measured, and the dual-mode corresponding to different characteristic frequencies of the target to be measured is obtained. State amplitude images include: Applying the excitation signal to the target to be tested sequentially through the probe of the atomic force microscope to obtain a corresponding response signal; Amplitude images corresponding to different frequencies in the response signal are separated. 6. The atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses according to claim 5, wherein said separating amplitude images corresponding to different frequencies in said response signal comprises: Demodulating the full-time vibration response signals at different frequencies to obtain the characteristic information of the target to be measured at different frequencies and different modes; According to the feature information and a preset fitting algorithm, dual-mode amplitude images correspondingly included in the target to be measured at different frequencies are obtained. 7. The atomic force microscopy method for analyzing electrostatic and electromechanical coupling responses according to claim 1, wherein the decoupling and re-coupling are carried out according to the target decoupling model and the dual-mode amplitude image of the target to be measured. structure, generating the electromechanical coupling strain image and the electrostatic response image of the target to be measured, including: Demodulating the full-time domain amplitude response data of the target to be measured to obtain the intrinsic amplitude and phase of the target to be measured under the excitation signal applied by the probe; According to the eigenamplitude and the eigenphase, the target decoupling model reconstructs the decoupled data to obtain the electromechanical coupling strain image and the electrostatic response image of the target to be measured. 8. An atomic force microscopy system for analyzing electrostatic and electromechanical coupling responses, characterized in that it includes: The signal generating module is used for synthesizing multiple sub-waveforms with different frequencies in two frequency bands into an excitation signal according to a preset splicing sequence; An image acquisition module, configured to apply the excitation signal to the target to be measured, and obtain dual-mode amplitude images corresponding to different frequencies of the target to be measured; The data processing module is used to perform decoupling and reconstruction according to the target decoupling model and the dual-mode amplitude image of the target to generate the electromechanical coupling strain image and electrostatic response image of the target to be measured. 9. The atomic force microscopy system for analyzing electrostatic and electromechanical coupling responses according to claim 8, further comprising: a decoupling model construction module, the decoupling model construction module comprising: The parameter calibration unit is used to calibrate the vibration parameters of the probe of the atomic force microscope; an initial model construction unit, configured to construct an initial decoupling model based on the vibration parameters of the probe; The model verification unit is configured to verify the reliability of the initial decoupling model based on the measurement data of the atomic force microscope to obtain the target decoupling model. 10. The atomic force microscopy system for analyzing electrostatic and electromechanical coupling responses according to claim 8, wherein the data processing module comprises: An intrinsic characteristic acquisition unit, configured to demodulate the full-time amplitude response data of the target to be measured to obtain the intrinsic amplitude and phase of the target to be measured under the excitation signal applied by the probe; A result acquisition unit, configured to reconstruct the decoupled data according to the eigenamplitude and eigenphase, the target decoupling model to obtain the electromechanical coupling strain image and the electrostatic response image of the target to be measured .

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