CN106645808A - Kelvin probe force microscope synchronously measuring multiple parameters - Google Patents

Abstract

A Kelvin probe force microscope for multi-parameter simultaneous measurement, relating to a Kelvin probe force microscope, the purpose is to solve the problem that the traditional Kelvin probe force microscope cannot realize the simultaneous characterization of the surface morphology, mechanical properties and surface local potential of a sample . The DC power supply of the present invention is used to generate a DC signal, and load the DC signal between the conductive probe and the sample. The signal generator generates three identical signals, the frequency of which is the same as the second-order resonance frequency of the conductive probe, and the first channel Superimposed with the signal generated by the arbitrary wave generator, it is used to control the No. 3 piezoelectric controller, so that the No. 3 piezoelectric controller drives the piezoelectric ceramic on the probe hand; the second channel is sent as a reference signal to the phase-locked Amplifier; the third channel is loaded between the conductive probe and the sample through a phase shifter of 90 degrees; the signal output by the lock-in amplifier is sent to the host computer. The invention is applicable to the measurement of the surface morphology, mechanical properties and surface local potential of samples.

Description

A Kelvin probe force microscope for simultaneous measurement of multiple parameters

technical field

The present invention relates to Kelvin probe force microscopy.

Background technique

Kelvin Probe Force Microscopy (KPFM) is a member of the Scanning Probe Microscopy (SPM) family, which combines Kelvin probe technology with Atomic force microscopy (AFM) to achieve Characterization of the local potential on the sample surface. The traditional Kelvin probe force microscope can realize the characterization of the surface morphology, mechanical properties and surface local potential of the sample through different measurement methods. For example, the "lift-up mode" can obtain the surface topography and local potential of the sample through two scans, and the "resonance mode (tapping mode)" can obtain the surface topography and local potential of the sample at the same time through one scan. The "peak force mode" is an intermittent contact mode. When scanning, two scans are performed per line. The first scan obtains the surface morphology and mechanical properties of the sample, and then the "lift mode" is used for the second scan. Obtain the surface local potential of the sample. Although the existing methods can realize the characterization of the surface morphology, mechanical properties and surface local potential of the sample, they cannot realize the simultaneous characterization of these parameters, that is to say, the surface morphology, mechanical properties and local surface potential of the sample cannot be simultaneously obtained through one scan. electric potential.

Contents of the invention

Mechanical properties and local surface potentials are very important for understanding the function of microelectronic devices, microbial activity, and many electromechanical and biological phenomena, and many measurements have time-sensitive and electromechanical coupling characteristics. In addition, the contact potential difference between the probe and the sample will cause errors in the measurement of the sample surface topography. Therefore, it is very meaningful to simultaneously measure the surface morphology, mechanical properties and surface local potential of the sample. In view of the fact that the traditional Kelvin probe force microscope cannot realize the simultaneous characterization of the surface morphology, mechanical properties and surface local potential of the sample, the present invention provides a multi-parameter simultaneous measurement Kelvin probe force microscope.

A Kelvin probe force microscope for multi-parameter synchronous measurement according to the present invention includes an XY micro-positioning stage 12, an XYZ nano-positioning stage 13, a Kelvin scanning sample stage 15, an XYZ micro-positioning stage 8, and a one-dimensional large-scale adjustment micro-platform 10 , probe hand bracket 9, probe hand 7, host computer, DC power supply, arbitrary wave generator, acquisition card, signal generator, phase shifter, lock-in amplifier, four-quadrant position detector, semiconductor laser generator, a Piezoelectric controller No. 2, Piezoelectric controller No. 2 and Piezoelectric controller No. 3;

The Kelvin scanning sample stage 15 is fixed on the XYZ nanopositioning stage 13, and the XYZ nanopositioning stage 13 is fixed on the XY micron positioning stage 12; the probe hand 7 is equipped with a conductive probe 7-4 and can drive the conductive probe 7-4 The piezoelectric ceramic 7-2 moving along the vertical direction, that is, the Z direction, the probe hand 7 is fixed on the probe hand support 9, the probe hand support 9 is fixed on the XYZ micron positioning table 8, and the XYZ micron positioning table 8 is fixed on the One-dimensional large-range adjustment micro-platform 10;

The host computer drives the piezoelectric ceramics on the Kelvin scanning sample stage 15 through the No. 1 piezoelectric controller, drives the piezoelectric ceramics on the XYZ nanopositioning stage 13 through the No. 2 piezoelectric controller, and drives the piezoelectric ceramics on the XYZ nanopositioning stage 13 through the No. 3 piezoelectric controller. The piezoelectric ceramics on the probe hand 7 move;

The laser light generated by the semiconductor laser generator 18 is incident on the conductive probe 7-4, and the laser light reflected by the conductive probe 7-4 is incident on the four-quadrant position detector 4;

The detection signal of the four-quadrant position detector 4 is sent to the host computer through the acquisition card, and the detection signal is also sent to the lock-in amplifier as a feedback signal;

The DC power supply is used to generate a DC signal under the control of the host computer, and load the DC signal between the conductive probe 7-4 and the sample 15-8;

The signal generator generates three identical signals (the signal frequency is the same as the second-order resonance frequency of the conductive probe 7-4), and the signal generated by the first path and the arbitrary wave generator is superimposed by the adder to control the third voltage. The electric controller makes the piezoelectric controller No. 3 drive the piezoelectric ceramic 7-2 on the probe hand 7; the second path is sent to the lock-in amplifier as a reference signal; the third path is loaded after the phase shifter is shifted by 90 degrees Between the conductive probe 7-4 and the sample 15-8;

The signal output by the lock-in amplifier is sent to the host computer through the acquisition card.

The present invention has the following advantages: 1. It breaks through the characteristic that the traditional KPFM cannot simultaneously characterize the mechanical properties and local potential of the sample, and realizes the simultaneous measurement of the surface morphology, mechanical properties and local potential difference of the sample in the case of one scan; 2. 1. The Kelvin probe force microscope device for multi-parameter simultaneous measurement enables AFM to be used for multi-parameter measurement of the sample surface, including morphology, mechanical properties and local potential; 3. The Kelvin probe force microscope device for multi-parameter simultaneous measurement is further It provides a technical basis to realize the multi-parameter measurement expansion (such as conductivity and resistivity) of the test object. Compared with the traditional Kelvin probe force microscope, this method can meet the requirements of timeliness and multi-parameter coupling characteristics in the measurement, and compensate the error caused by the electrostatic force on the shape measurement. The biological field has higher usability and operability, and has high practical value.

Description of drawings

Fig. 1 is the schematic diagram of the principle of the Kelvin probe force microscope described in Embodiment 1, wherein 21 is a semiconductor laser generator, 22 is a four-quadrant position detector,

Fig. 2 is a waveform diagram of the driving signal, the force feedback signal and the phase feedback signal of the piezoelectric ceramic 7-2 on the probe hand 7 driven by the No. 3 piezoelectric controller in the first embodiment. The overall driving signal is Gaussian, superimposed on it The sinusoidal waveform is U _m ;

3 is a schematic structural view of the mechanical part of the Kelvin probe force microscope described in Embodiment 1, wherein,

1: Rack; 2: Four-quadrant position detector two-dimensional adjustment micro-platform; 3: One-dimensional adjustment micro-platform I; 4: Four-quadrant position detector; 5: Reflecting laser convex lens; 6: Laser mirror; 7: Detection Needle hand; 8: XYZ micro-positioning stage; 9: Probe hand support; 10: One-dimensional large-scale adjustment micro-platform; 11: Table top; 12: XY micro-positioning stage; 13: XYZ nano-positioning stage; 14: Sample stage support ;15: Kelvin scanning sample stage; 16: incident laser focusing convex lens; 17: one-dimensional adjustment micro-platform II; 18: semiconductor laser generator; 19: laser generator angle adjustment mechanism; 20: optical microscope;

4 is a schematic structural diagram of the probe hand in Embodiment 1, wherein, 7-1: the base of the probe hand; 7-2: piezoelectric ceramics; 7-3: the probe holder; 7-4: the conductive probe; 7-5: shielding sheet; 7-6: conductive probe fixing plate; 7-7: terminal block;

5 is a schematic structural view of the Kelvin scanning sample stage in Embodiment 1, wherein (a) is a front view of the Kelvin scanning sample stage, and (b) is a top view of (a); 15-1: Kelvin scanning sample stage base; 15-2: piezoelectric ceramics; 15-3: sample holder; 15-4: connecting wire; 15-5: set screw; 15-6: wire harness block; 15-7: copper pressing piece; 15-8: Sample; 15-9: Insulation set screw;

FIG. 6 is the measurement result of the polystyrene/photocurable adhesive grating in the second embodiment.

detailed description

Specific Embodiment 1: This embodiment is described in conjunction with FIG. 1. A Kelvin probe force microscope for multi-parameter synchronous measurement described in this embodiment includes an XY micro-positioning stage 12, an XYZ nano-positioning stage 13, and a Kelvin scanning sample stage 15. , XYZ micron positioning table 8, one-dimensional large-scale adjustment micro-platform 10, probe hand bracket 9, probe hand 7, host computer, DC power supply, arbitrary wave generator, acquisition card, signal generator, phase shifter, lock phase amplifier, four-quadrant position detector, semiconductor laser generator, piezoelectric controller No. 1, piezoelectric controller No. 2 and piezoelectric controller No. 3;

The Kelvin scanning sample stage 15 is fixed on the XYZ nanopositioning stage 13, and the XYZ nanopositioning stage 13 is fixed on the XY micron positioning stage 12; the probe hand 7 is equipped with a conductive probe 7-4 and can drive the conductive probe 7-4 The piezoelectric ceramic 7-2 moving along the vertical direction, that is, the Z direction, the probe hand 7 is fixed on the probe hand support 9, the probe hand support 9 is fixed on the XYZ micron positioning table 8, and the XYZ micron positioning table 8 is fixed on the One-dimensional large-range adjustment micro-platform 10;

The host computer drives the piezoelectric ceramics on the Kelvin scanning sample stage 15 through the No. 1 piezoelectric controller, drives the piezoelectric ceramics on the XYZ nanopositioning stage 13 through the No. 2 piezoelectric controller, and drives the piezoelectric ceramics on the XYZ nanopositioning stage 13 through the No. 3 piezoelectric controller. The piezoelectric ceramic 7-2 on the probe hand 7 moves;

The laser light generated by the semiconductor laser 18 generator is incident on the conductive probe 7-4, and the laser light reflected by the conductive probe 7-4 is incident on the four-quadrant position detector 4;

The detection signal of the four-quadrant position detector 4 is sent to the host computer through the acquisition card, and the detection signal is also sent to the lock-in amplifier as a feedback signal;

The DC power supply is used to generate a DC signal under the control of the host computer, and load the DC signal between the conductive probe 7-4 and the sample 15-8;

The signal generator generates three identical signals, the frequency of which is the same as the second-order resonance frequency of the conductive probe 7-4, the first signal and the signal generated by the arbitrary wave generator are superimposed by the adder and used to control the third piezoelectric The controller makes the piezoelectric controller No. 3 drive the piezoelectric ceramic 7-2 on the probe hand 7; the second path is sent to the lock-in amplifier as a reference signal; the third path is loaded into the Between the conductive probe 7-4 and the sample 15-8;

The signal output by the lock-in amplifier is sent to the host computer through the acquisition card.

The principle of the measurement method for multi-parameter synchronous measurement of the present invention is shown in Figure 2. This invention breaks through the traditional use of sinusoidal signals as the drive signal for force-displacement curve measurement, and uses Gaussian signals as the drive signal for force-displacement curve measurement. Therefore , when the probe is detached from the sample surface, the distance between the probe and the sample will remain stable (only sub-nanometer second-order vibration, between point D and point E), this invention makes full use of the void in traditional testing methods The stroke realizes the multi-parameter simultaneous measurement of the sample. The specific test process is as follows:

Step 1. Drive the piezoelectric ceramic 7-2 on the probe hand 7 through the No. 3 piezoelectric controller, so that the conductive probe 7-4 keeps reciprocating up and down;

Step 2. Drive the XYZ nanopositioning stage 13 to move upward and approach the sample through the No. 2 piezoelectric controller, so that the conductive probe 7-4 is in contact with the sample 15-8, and the maximum force between the conductive probe and the sample continues Increase until the maximum interaction force between the conductive probe 7-4 and the sample 15-8 reaches the set value and maintains;

Step 3, drive the XYZ nanopositioning stage 13 to move downward through the No. 2 piezoelectric controller, and the moving distance is less than the range of the Kelvin scanning sample stage 15;

Step 4. Use the No. 1 piezoelectric controller to drive the Kelvin scanning sample stage 15 instead of the No. 2 piezoelectric controller to drive the XYZ nanopositioning stage 13. Repeat step 2 to make the maximum interaction force between the conductive probe and the sample reach the set value , superimpose the mechanical excitation U _m on the No. 3 piezoelectric controller through the signal generator, and apply the AC voltage U AC sin(ωt) between the conductive probe and the sample through the phase shifter, and apply the AC voltage U _AC sin(ωt) to the conductive probe and the sample through the DC power supply A DC compensation voltage U _DC is applied between the samples;

Among them, in one movement cycle of the conductive probe, the interaction between the conductive probe and the sample is as follows:

Step 4-1. Drive the piezoelectric ceramic 7-2 on the probe hand 7 to move downward through the No. 3 piezoelectric controller. When the attraction force between the conductive probe and the sample is greater than the stiffness of the conductive probe, the conductive probe Will be attracted to come into contact with the sample surface, this time point is point A;

Step 4-2. After the conductive probe is in contact with the sample, the piezoelectric ceramic 7-2 on the probe hand 7 is driven to continue to move downward through the No. 3 piezoelectric controller, so that the maximum effect between the conductive probe and the sample The force continues to increase until the maximum interaction force between the conductive probe and the sample reaches the set value, and this time point is point B;

By recording the Z-direction coordinate value of the Kelvin scanning sample stage 15 at point B, the surface topography image of the current scanning point of the sample is obtained; the deformation of the conductive probe at point B and the movement of the piezoelectric ceramic 7-2 from the equilibrium position point A' to point B are recorded Displacement, to obtain the maximum indentation depth image of the current scanning point of the sample, the maximum indentation depth = the displacement of the piezoelectric ceramic 7-2 from the equilibrium position point A' to point B - the deformation of the conductive probe; the equilibrium position point A' After point A, during the contact process between the conductive probe and the sample, the force feedback signal of the conductive probe is equal to the time point when the force feedback signal of the conductive probe is not in contact with the sample;

Step 4-3, controlling the reverse movement of the conductive probe;

When the deformation force of the conductive probe is greater than the adhesive force between the conductive probe and the sample surface, the conductive probe suddenly detaches from the sample surface. This time point is point C. Record the force on the conductive probe at point C as the sample The maximum adhesion force image between the conductive probe and the current scanning point;

Convert the force-piezoelectric ceramic 7-2 displacement data between point B and point C into the force-distance data between the conductive probe and the sample, and use the DMT model to fit the sample at the scanning point. Equivalent Young's modulus image, the force refers to the force on the conductive probe, where the DMT model is shown in the following formula:

where F is the interaction force between the probe and the sample, F _adh is the maximum adhesion force between the sample and the probe, R is the tip radius of the probe, δ is the indentation depth, and E ^* is the equivalent Young's modulus;

Obtain the Young's modulus E of the sample according to the Poisson's ratio of the equivalent Young's modulus and the sample;

Step 4-4. When the conductive probe is separated from the sample, the conductive probe continues to rise to the set height h and then stops moving. This time point is point D, h is greater than 0, and the conductive probe is kept at this height for a period of time , namely point D to point E;

Between point D and point E, the phase of the lock-in amplifier output is used as a feedback signal to measure the surface potential difference between the conductive probe and the sample; the time interval between the initial point where the surface local potential difference begins to compensate and point C is greater than that of the conductive probe The time constant τ of 7-4, τ=2Q/ω, Q is the quality factor, ω is the angular frequency, the total potential difference between the conductive probe and the sample is:

ΔU＝U _DC -U _CPD +U _AC sin(ωt)

where U _CPD is the intrinsic surface potential difference between the probe and the sample surface;

At this time, the electrostatic force between the conductive probe and the sample surface is:

where C and z are the capacitance and distance between the probe and the sample, respectively. It can be seen from the above formula that when U _DC = U _CPD , the influence of electrostatic force on the conductive probe at ω frequency will be eliminated, and the phase and amplitude information of the probe feedback signal at this frequency can be obtained by using the lock-in amplifier. The phase signal output by the lock-in amplifier is input to the host computer as feedback, and the host computer eliminates the output phase offset of the lock-in amplifier by adjusting U _DC . When U _DC = U _CPD , the lock-in amplifier output phase offset will be eliminated. By recording U _DC at this time, an image of the surface local potential difference (U _CPD ) between the corresponding conductive probe and the sample surface can be obtained.

Step 5. Move the sample to the next scanning point through the XYZ nanopositioning stage 13, and repeat steps 4 to 5 to obtain the surface topography image, equivalent Young's modulus image and surface potential difference image of the sample.

Ideally, when U _DC =U _CPD , the phase of the lock-in amplifier output in step 4 is 0 degrees, but usually due to the existence of errors, the phase of the lock-in amplifier output is not 0 degrees, by recording the phase of the lock-in amplifier The output phase can obtain the corresponding test phase offset error image.

In order to improve the accuracy of the measurement results, each scanning point repeats step 4 multiple times, and the Z-direction coordinate value of point B Kelvin scanning sample stage 15 of the middle group of test data is selected as the final surface topography of the current scanning point of the sample; The equivalent Young's modulus E ^* value of the group data is used as the final equivalent Young's modulus of the current scanning point of the sample; the surface potential difference value of the corresponding group of data is selected as the final surface potential difference of the current scanning point of the sample;

Among them, the up and down reciprocating movement of the conductive probe 7-4, the Kelvin scanning sample stage 15 maintains the maximum interaction force between the conductive probe 7-4 and the sample 15-8 as the servo motion of the set value, and the XYZ nanopositioning stage 13 The movement to move the sample to the next scan point runs in parallel among the three.

Specific Embodiment 2: This embodiment is described in conjunction with Fig. 1 and Fig. 2. This embodiment is a further limitation of the Kelvin probe force microscope described in Embodiment 1. In this embodiment, the embedding in the host computer is realized by software The measurement module, the measurement module includes the following units:

Force detection unit: collect the deformation of the conductive probe 7-4 detected by the four-quadrant position detector 4 in real time, and calculate the force between the conductive probe 7-4 and the sample according to the deformation; the force is equal to The product of the deformation amount and the stiffness of the conductive probe 7-4;

Surface topography and maximum indentation depth measurement unit: Control the Kelvin scanning sample stage 15 to rise through the No. 1 piezoelectric controller, so that the sample is close to the conductive probe 7-4, when the maximum interaction between the conductive probe 7-4 and the sample When the force reaches the set value, record the Z-direction coordinate value of the piezoelectric ceramic on the sample stage; record the maximum indentation depth at the same time, and the maximum indentation depth is equal to the displacement of the piezoelectric ceramic 7-2 from the equilibrium position point A' to point B The difference from the deformation of the conductive probe 7-4; the time point corresponding to when the force between the conductive probe 7-4 and the sample reaches the set value is point B; the equilibrium position point A' refers to After point A, during the contact process between the conductive probe and the sample, the force feedback signal of the conductive probe is equal to the time point when the force feedback signal of the conductive probe is not in contact with the sample;

Adhesion measurement unit: the piezoelectric ceramic 7-2 is controlled by the No. 3 piezoelectric controller, so that the conductive probe 7-4 moves in the reverse direction, and records the time when the conductive probe 7-4 is separated from the sample during the reverse movement. The applied force is the maximum adhesion force between the conductive probe 7-4 and the sample; the corresponding time point is point C;

Equivalent Young's modulus calculation unit: convert the force-piezoelectric ceramic 7-2 displacement between points B and C into force-indentation depth data, and use DMT model fitting to obtain the equivalent of the sample Effective Young's modulus, the DMT model is:

F is the interaction force between the conductive probe 7-4 and the sample, _{Fa adh} is the maximum adhesion force between the sample and the conductive probe 7-4, R is the tip radius of the conductive probe 7-4, and δ is Indentation depth, E ^* is the equivalent Young's modulus;

Surface local potential difference measurement unit: Control the piezoelectric ceramic 7-2 on the probe hand 7 to move through the No. Keep pin 7-4 at the height h; use the phase output of the lock-in amplifier as a feedback signal to adjust the value of the DC voltage U _DC , so that the signal output by the lock-in amplifier is zero, and record the value of U _DC at this time, the U _DC The value of is the surface local potential difference between the sample and the probe;

Sample moving unit: drive the XYZ nanopositioning stage 13 to move to the next scanning point through the No. 2 piezoelectric controller.

After the above-mentioned measurement module runs once, the measurement of the surface topography, equivalent Young's modulus, and surface local potential difference of the current scanning point of the sample is completed.

The surface topography measurement unit measures the Z-coordinate value of the piezoelectric ceramic corresponding to point B at each scanning point, and the Z-coordinate value of the piezoelectric ceramic on the sample table at all scanning points synthesizes the surface topography image of the sample;

The maximum indentation depth measurement unit measures the indentation depth corresponding to point B at each scanning point, and the maximum indentation depth of all scanning points synthesizes the maximum indentation depth image of the sample;

The maximum adhesion force measurement unit measures the adhesion force corresponding to point C at each scanning point, and the maximum adhesion force of all scanning points synthesizes the maximum adhesion force image of the sample;

The equivalent Young's modulus calculation unit measures an equivalent Young's modulus at each scanning point, and the equivalent Young's modulus of all scanning points synthesizes the equivalent Young's modulus image of the sample;

The surface local potential difference measuring unit measures a surface local potential difference at each scanning point, and the surface local potential difference values of all scanning points synthesize the surface local potential difference image of the sample.

Before using the above-mentioned measurement module to measure the surface morphology, mechanical properties and surface local potential difference, some preparatory work must be done first, and the relevant parameters of the measurement module should be set. The specific process is as follows:

1. System initialization, fix the prepared sample 15-8 on the sample holder 15-3, make conductive contact and fix the copper pressing piece 15-7 with the sample 15-8, install the conductive probe 7-4 on the probe On the hand 7, the conductive probe 7-4 is conductively connected to the conductive probe fixing plate 7-6, and the Kelvin scanning sample stage 15 and the probe hand 7 are installed on the sample stage support 14 and the probe hand support 9 respectively, And electrically connect the terminals to the corresponding equipment;

2. The upper computer controls the movement of the XY micron positioning stage 12, initially positions the sample 15-8 through the optical microscope 20, selects a suitable measurement area, and moves this area to the center of the field of view of the optical microscope 20;

3. Move the one-dimensional large-scale adjustment micro-platform 10 and the XYZ micron positioning stage 8, roughly align the conductive probe 7-4, place the conductive probe 7-4 above the measurement area selected in step 2, and adjust the laser direction, so that the laser spot on the conductive probe 7-4 is at the center of the front end of the conductive probe 7-4 cantilever beam;

4. Turn on the sweep frequency exciter to sweep the conductive probe 7-4 to obtain the second-order resonance frequency ω and the corresponding quality factor Q of the conductive probe 7-4, and then obtain the Time constant τ=2Q/ω, and the frequency of the signal generator is set to ω;

5. Roughly adjust the distance between the conductive probe 7-4 and the sample 15-8 through the XYZ micron positioning stage 8, prepare the position servo control, and readjust the laser spot on the conductive probe 7-4 to the conductive probe 7 -4 the center of the front end of the cantilever beam;

6. Arbitrary wave generator generates a control signal, each period of the control signal is a Gaussian signal, and the control signal is sent to the No. 3 piezoelectric controller, so that the No. 3 piezoelectric controller drives the conductive probe 7-4 according to the Gaussian signal. up and down reciprocating motion;

Detect the force on the conductive probe 7-4 by the four-quadrant position detector 4, start the servo control, control the XYZ nanopositioning stage 13 to quickly approach the conductive probe 7-4 along the Z axis and keep the maximum force between the two equal to the set force;

7. Stop the servo control after the servo is successful, lower the XYZ nanopositioning stage 13 to a certain height (less than the stroke of the piezoelectric ceramic 15-2 installed on the Kelvin scanning sample stage 15), and then scan the piezoelectric ceramics installed on the sample stage 15 through Kelvin. Ceramic 15-2 repeats the servo in step 6, and continues to keep the maximum force between the conductive probe 7-4 and the sample 15-8 equal to the set force; usually the servo frequency is 5-10 times the scanning frequency , so multiple servos are performed for each scan point;

8. Apply the mechanical excitation signal U _m at the second-order resonance frequency to the conductive probe 7-4 through the signal generator, and set the calculation point of the phase between point D and point E (as shown in Figure 2, at In one movement cycle of the conductive probe 7-4, the moment when the conductive probe 7-4 comes into contact with the sample during the downward movement is point A, and the conductive probe 7-4 continues to move downward until the distance between the conductive probe 7-4 and the sample When the force reaches the set value, this moment is point B, and then the conductive probe 7-4 starts to move in reverse, and the moment when it separates from the sample is point C, and the conductive probe 7-4 continues to rise to a certain height and then stops moving. And keep at this height for a period of time, that is, between D point and E point, wherein the time between the initial point of surface local potential difference compensation and C point will be greater than the time length number τ), adjust the phase of Um to make the phase of lock-in amplifier The output is zero, wherein the second-order excitation of the conductive probe 7-4 is at a sub-nanometer level, and will not affect the stable contact between the conductive probe 7-4 and the sample 15-8;

9. Set the phase shifter to shift the phase by 90 degrees and turn it on. Apply the electrical excitation signal U _AC sin(ωt) at the second-order resonance frequency between the conductive probe 7-4 and the sample 15-8. At this time, due to the conductive probe The difference in work function/surface potential between needle 7-4 and sample 15-8, therefore, there is a surface potential difference U _CPD between them, so that the phase of the lock-in amplifier output will shift;

10. Start the Kelvin control program embedded in the host computer, which uses the phase output by the lock-in amplifier as a feedback signal to control the DC power supply to output a DC compensation voltage signal U _DC to act between the conductive probe 7-4 and the sample 15-8 , so as to compensate the local potential difference (U _CPD ) between the conductive probe 7-4 and the surface of the sample 15-8, and finally restore the phase of the lock-in amplifier output to zero, and the voltage (U _DC ) output by the DC power supply will be equal to the conductive The local potential difference (U _CPD ) between probe 7-4 and the surface of sample 15-8;

11. Set the scanning step and scanning points, and then start scanning.

The conductive probe of the above-mentioned Kelvin probe force microscope is simultaneously driven by multiple frequency states, including: 1) mechanical drive (0.5-2kHz) of low-frequency Gaussian signal, 2) mechanical drive in the second-order resonance mode, 3) probe and Electrical excitation at the second-order resonance mode between samples. The upper computer processes the feedback signal of the conductive probe in sections and divides frequency to realize distance control, potential compensation and data fitting, so as to realize the simultaneous measurement of the surface morphology, mechanical properties and local surface potential of the sample.

Use the Kelvin probe force microscope of this embodiment to measure the polystyrene/photocurable grating, the scanning range is 2.56um*2.56um, and the number of scanning points is 256*256. Figure 6 is a polystyrene/photocurable grating sample The scanning image results, where (a) is the surface topography image, the protruding part in the middle is polystyrene, and the concave part on both sides is photocurable adhesive, and the height difference is 60nm; (b) is the maximum adhesion image ; (c) is the maximum indentation depth image; (d) is the equivalent Young's modulus image, the Poisson's ratio of polystyrene is 0.33, therefore, the Young's modulus of polystyrene is 1.93±0.28GPa; ( e) is the surface local potential image; (f) the phase shift error image, and the phase error is -0.05±1.01 degrees. Table 1 shows the measurement results, including maximum adhesion, maximum indentation depth, equivalent Young's modulus, and surface local potential difference.

Table 1 Measurement result data list

Claims (3)

1. a kind of Kelvin probe force microscopy of multiparameter synchro measure, it is characterised in that including XY micron positioning tables (12), XYZ nanometer positioning platforms (13), Kelvin's scanning sample stage (15), XYZ micron positioning tables (8), one-dimensional wide range adjustment microfluidic platform (10), probe handss support (9), probe handss (7), host computer, DC source, Arbitrary Waveform Generator, capture card, signal generator, Phase shifter, lock-in amplifier, four-quadrant position detector, semiconductor laser generator, piezo controller, No. two voltage controls Device processed and No. three piezo controllers；

Kelvin's scanning sample stage (15) is fixed on XYZ nanometer positioning platforms (13), and it is micro- that XYZ nanometer positioning platforms (13) is fixed on XY On rice positioning table (12)；Conducting probe (7-4) is installed on probe handss (7) and conducting probe (7-4) can be driven along vertically side To the piezoelectric ceramics (7-2) of i.e. Z-direction movement, probe handss (7) are fixed on probe handss support (9), and probe handss support (9) is fixed On XYZ micron positioning tables (8), XYZ micron positioning tables (8) is fixed on one-dimensional wide range adjustment microfluidic platform (10)；

Host computer is by the piezoelectric ceramics movement on piezo controller driving Kelvin's scanning sample stage (15), by No. two Piezo controller drives the piezoelectric ceramics on XYZ nanometer positioning platforms (13) to move, drives probe handss by No. three piezo controllers (7) the piezoelectric ceramics movement on；

Semiconductor laser generator produce laser light incident to conducting probe (7-4), Jing conducting probes (7-4) reflection laser It is incident to four-quadrant position detector；

The detectable signal of four-quadrant position detector is sent to host computer by capture card, and the detectable signal is also as feedback signal Send to lock-in amplifier；

DC source is used to produce direct current signal under the control of host computer, and the direct current signal is loaded into into conducting probe (7- 4) and sample (15-8) between；

Signal generator produces three tunnel identical signals, and the signal frequency is identical with the second-order resonance frequency of conducting probe (7-4), The first via is used to control No. three piezo controllers after being superimposed with the logical adder of the signal that Arbitrary Waveform Generator is produced, and makes No. three piezoelectricity Controller drives the piezoelectric ceramics (7-2) on probe handss (7)；Second tunnel is sent to lock-in amplifier as reference signal；3rd Road is loaded between conducting probe (7-4) and sample (15-8) after 90 degree of phase shifter phase shift；

The signal of lock-in amplifier output is sent to host computer by capture card.

2. Kelvin probe force microscopy according to claim 1, it is characterised in that the host computer is embedded in by software The measurement module of realization, the measurement module is included with lower unit：

Power detector unit：The deformation quantity of the conducting probe (7-4) that Real-time Collection four-quadrant position detector (4) is detected, and root Active force of the conducting probe (7-4) and sample between is calculated according to the deformation quantity；The active force is equal to deformation quantity and conducting probe (7-4) product of rigidity；

Surface topography and maximum depth of cup measuring unit：Kelvin is controlled by a piezo controller and scans sample stage (15) On piezoelectric ceramics rise, the close conducting probe of sample (7-4) is made, when maximum effect of the conducting probe (7-4) and sample between When power reaches setting value, the Z-direction coordinate figure of piezoelectric ceramics on Kelvin's scanning sample stage (15) is recorded；Maximum impression is recorded simultaneously Depth, the maximum depth of cup is equal to piezoelectric ceramics (7-2) from equilbrium position point A ' to the displacement of point B and conducting probe (7- 4) difference of deformation quantity；Active force of the conducting probe (7-4) and sample between reaches time point corresponding during setting value for B Point；The equilbrium position point A ' is referred to after A points, in conducting probe and sample contact process, the force feedback letter of conducting probe Number be equal to conducting probe and sample not in contact with when force feedback signal time point；

Adhesion measuring unit：Piezoelectric ceramics (7-2) is controlled by No. three piezo controllers, conducting probe (7-4) is reversely moved It is dynamic, and conducting probe (7-4) and active force suffered during sample disengaging during reverse movement are recorded, the active force is and leads Maximum adhesion power of the electric probe (7-4) and sample between；Now corresponding time point is C points；

Equivalent Young's modulus computing unit：By the power between B points and C points-piezoelectric ceramics displacement quantity converting to force-depth of cup Data, and using DMT models fittings, the equivalent Young's modulus of sample are just obtained, the DMT models are：

$F-F_{adh}=\frac{4}{3}{E}^{*}\sqrt{{\mathrm{R\δ}}^3}$

F be interaction force of the conducting probe (7-4) and sample between, F_adhFor the maximum between sample and conducting probe (7-4) Adhesion, R for conducting probe (7-4) needle type radius, δ is depth of cup, E^*For equivalent Young's modulus；

Surface local potential difference measurements unit：The piezoelectric ceramics movement on probe handss (7) is controlled by No. three piezo controllers, is made Conducting probe (7-4) continues to move up certain altitude h, h>0, conducting probe (7-4) is maintained at height h；Will lock The phase place of phase amplifier output adjusts DC voltage U as feedback signal_DCValue, make lock-in amplifier export phase signal be Zero, U_DCIt is direct current compensation voltage that DC source is loaded between conducting probe and sample, records U now_DCValue, the U_DC The surface local potential that is between sample and conducting probe of value it is poor；

Sample mobile unit：XYZ nanometer positioning platforms (13) is driven to be moved to next scanning element by No. two piezo controllers.

3. Kelvin probe force microscopy according to claim 1 and 2, it is characterised in that the Arbitrary Waveform Generator is produced Raw gaussian signal, controls conducting probe and moves back and forth up and down by the signal.