KR20230144861A - Potential gradient microscopy and operating method thereof - Google Patents

Abstract

While the tip of the cantilever scans the material at a predetermined distance from the surface of the material, the potential gradient microscope provides a light beam incident on the cantilever and detects the reflected beam as the light beam reflects off the cantilever to detect a deflection signal. . Additionally, a potential gradient microscope applies direct and alternating current voltages to the cantilever while scanning the material, and images the material based on the amplitude and phase of the deflection signal.

Description

Potential gradient microscope and its operating method {POTENTIAL GRADIENT MICROSCOPY AND OPERATING METHOD THEREOF}

The disclosure relates to a potential gradient microscope and a method of driving the same.

Scanning probe microscopy (SPM) is a technology that analyzes the surface and internal properties of materials using a tip. Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) ) is a technology that collectively refers to Among them, the most commonly used imaging mode of material properties using AFM is divided into contact mode and non-contact (tapping) mode. Representative contact modes include piezoresponse force microscopy (PFM), which images ferroelectric domains within materials, and conductive atomic force microscopy (c-AFM), which measures current. Non-contact modes include surface Representative examples include electrostatic force microscopy (EFM), which images electric charges, and Kelvin probe force microscopy (KPFM), which images surface potential.

Ferroelectric domain imaging using SPM mainly uses PFM, and is also possible through EFM or KPFM. Recently, a new technology has emerged to image ferroelectric domains by scraping off surface screening charges through charge gradient microscopy (CGM).

Existing imaging technologies, PFM and CGM, are contact technologies and have the potential to change the surface morphology, surface potential, or surface charge state depending on imaging conditions, while EFM is a qualitative measurement technology and has limitations in its principles. . KPFM, which measures the surface potential using the difference in work function between the SPM tip and the material, can change the value of the potential depending on the measurement conditions, and the measurement conditions are very difficult. For example, when using Asylum Research's KPFM mode, the tip must have a higher potential than the material to measure surface potential, and it is often difficult to measure surface potential depending on the measurement environment (temperature, humidity, etc.) and conditions.

Some embodiments may provide potential gradient microscopy to image potential gradients through a non-contact mode to overcome the limitations of contact techniques.

According to one embodiment, a potential gradient microscope may be provided including a cantilever with a tip, a detector, and a control system. The detector provides a light beam incident on the cantilever while scanning the material with the tip at a predetermined distance from the surface of the material and detects the reflected beam as the light beam reflects off the cantilever to generate a deflection signal. It can be detected. The control system may apply direct current and alternating current voltages to the cantilever while scanning the material and image the material based on the amplitude and phase of the deflection signal.

In some embodiments, the mode for scanning the material may correspond to the NAP mode of amplitude modulation Kelvin probe force microscopy (AM-KPFM).

In some embodiments, prior to the nap mode scan, the control system may shape the surface of the material through an oscillating scan in a range that does not tap the surface of the material.

In some embodiments, the control system may include a feedback controller that controls to minimize the difference between the true voltage and the amplitude of the deflection signal according to feedback of the amplitude of the deflection signal.

In some embodiments, the feedback controller may include a proportional-integral-differential (PID) controller or a proportional-integral (PI) controller. The control system may set the proportional gain of the feedback controller lower than a first threshold value and the integral gain of the feedback controller lower than a second threshold value.

In some embodiments, the first threshold may be 20.

In some embodiments, the second threshold may be 20.

In some embodiments, the control system may image the material based on the amplitude and phase of the deflection signal along a scan direction.

In some embodiments, the scan direction may include a first scan direction and a second scan direction that is 90 degrees different from the first scan direction.

In some embodiments, the alternating current waveform may be a sinusoidal waveform.

In some embodiments, the cantilever may be coated with a conductive material.

In some embodiments, the conductive material may be made of at least one of platinum (Pt), iridium (Ir), chromium (Cr), or conductive diamond.

In some embodiments, the material may be comprised of at least one of ferroelectrics, oxide semiconductors, metals, composites, or block copolymers.

According to another embodiment, a method of driving a potential gradient microscope including a cantilever with a tip may be provided. The driving method includes scanning the material while the tip is a predetermined distance away from the surface of the material, applying a voltage of a direct current voltage and an alternating current waveform to the cantilever while scanning the material, During scanning, providing a light beam incident on the cantilever, detecting a deflection signal by detecting a reflected beam as the light beam reflects off the cantilever, and based on the amplitude and phase of the deflection signal, the material It may include the step of imaging.

In some embodiments, the driving method may further include performing feedback control to minimize the difference between the true voltage and the amplitude of the deflection signal according to the feedback of the amplitude of the deflection signal.

In some embodiments, performing the feedback control may include performing the feedback control using a PID controller or a PI controller. The proportional gain used for the feedback control may be lower than a first threshold, and the integral gain used for the feedback control may be lower than a second threshold.

In some embodiments, imaging the material may include imaging the material based on the amplitude and phase of the deflection signal along a scan direction.

In some embodiments, the scan direction may include a first scan direction and a second scan direction that is 90 degrees different from the first scan direction.

1 is a diagram illustrating a potential gradient microscope according to one embodiment.
2 is a diagram illustrating a detector of a potential gradient microscope according to one embodiment.
3 is a diagram illustrating probes and materials used in a potential gradient microscope according to one embodiment.
4 is a diagram illustrating a control system of a potential gradient microscope according to one embodiment.
5 is a diagram illustrating a feedback controller of a potential gradient microscope according to one embodiment.
6A and 6B are diagrams illustrating the vibration amplitude and phase of the cantilever in a potential gradient microscope, respectively, according to one embodiment.
7 is a diagram illustrating materials to be imaged.
Figure 8 is a diagram illustrating imaging results at fast feedback and low feedback.
Figure 9 is a diagram illustrating imaging results according to an increase in I gain.
Figures 10 and 11 are diagrams illustrating imaging results from two scans, respectively.

Below, with reference to the attached drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts that are not related to the description are omitted, and similar parts are given similar reference numerals throughout the specification.

In the description below, expressions described as singular may be interpreted as singular or plural, unless explicit expressions such as “one” or “single” are used.

In the flowchart described with reference to the drawings, the order of operations may be changed, several operations may be merged, certain operations may be divided, and certain operations may not be performed.

Now, with reference to FIGS. 1 to 11 , a potential gradient microscope and its driving method according to various embodiments will be described.

1 is a diagram illustrating a potential gradient microscope according to an embodiment, FIG. 2 is a diagram illustrating a detector of the potential gradient microscope according to an embodiment, and FIG. 3 is a diagram illustrating a detector used in the potential gradient microscope according to an embodiment. This is a drawing illustrating the probe and materials.

Referring to FIG. 1, a potential gradient microscope is a microscope that images a surface potential gradient using SPM, and includes a probe 110, a cantilever holder 120, a control system 130, and a detector 140.

The probe 110 includes a chip 111, a cantilever 112 attached to the end of the chip, and a probe tip (or SPM tip) 113 attached to the end of the cantilever. The probe tip 113 is located on the surface of the material 150. It is used to scan. A conductive material is applied to the cantilever 112 and the probe tip 113. The conductive material may be made of at least one of, for example, platinum (Pt), iridium (Ir), chromium (Cr), titanium (Ti), or conductive diamond.

In some embodiments, material 150 may be ferroelectrics, oxide semiconductors, metals, composites, or other materials that have different surface potentials depending on the composition, state, and properties of material 150. It may be made of at least one of block copolymers.

Referring to FIGS. 1 and 2 , an actuator (not shown) included in the cantilever holder 120 physically vibrates the chip 111 to cause movement of the cantilever 112 and the probe tip 113. In some embodiments, the actuator may be a piezoelectric actuator.

The control system (or control circuit) 130 controls the operation of the potential gradient microscope by applying operation signals to the cantilever 112 and the actuator 121. The detector 140 detects the position of the probe tip 113 and outputs a deflection signal indicating the deflection of the position of the cantilever 112 connected to the probe tip 113. Control system 130 images the surface of material 150 based on the amplitude and phase of the deflection signal output from detector 140.

Referring to FIG. 2, the detector 140 includes an optical output device 141 and an optical sensor 142. The light outputter 141 provides a light beam 143 incident on the cantilever 112, and the light sensor 142 detects a reflected beam 144 of the light beam 143. In some embodiments, optical output 141 may include a laser, such as a diode laser, and optical sensor 142 may include a photo diode, such as a position-sensitive photo diode (PSPD). You can.

Movement of the probe tip 113 results in a change in the reflection angle of the reflected beam 144 at which the incident light beam 143 is reflected from the cantilever 112. This may result in a change in the position of the reflected beam 144 on the optical sensor 142. The optical sensor 142 outputs a deflection signal 145 according to a change in the position of the reflected beam 144. Accordingly, detector 140 can monitor the movement of probe tip 113 using beam 144 reflected from cantilever 112 and detected by optical sensor 142. As shown in FIG. 2, the position of the reflected beam 144 is deflected in the vertical direction according to the vibration of the cantilever 112, and a deflection signal 145 having an amplitude (voltage unit) equal to the size of the deflection in the vertical direction is output. It can be.

To image material 150 with a potential gradient microscope, an operation is performed to scan material 150 with probe tip 113. In some embodiments, scanning in amplitude modulation (AM) mode of KPFM, i.e., AM-KPFM, may be performed. In some embodiments, the probe 110 and cantilever 112 are fixed to the cantilever holder 120 and do not move in the xy plane, and the stage on which the material 150 is placed moves in the xy plane so that the scan is performed. In this case, scanning may be performed at a height where the probe tip 113 of the cantilever 112 is a predetermined distance away from the surface of the material 150. This scan is called a nap mode scan. In some embodiments, two scans may be performed. In this case, before the scan in nap mode (second scan) proceeds, a scan (first scan) in which the probe tip 113 of the cantilever 112 oscillates in a range that does not tap the surface of the material 150 ) can be performed.

In some embodiments, during the second scan, the probe tip 113 of the cantilever 112 scans one line in the trace direction and then moves the same line in the opposite direction of the trace direction (retrace direction). You can scan lines. This scan is called a fast scan. Next, after moving one line, high-speed scan can be performed again on the next line. A scan that moves one line is called a slow scan.

Referring to FIG. 3, in the first scan (S310), the control system 130 applies an operation signal to the actuator included in the cantilever holder 120 to operate the actuator. Accordingly, the actuator physically vibrates the probe 110 and the cantilever 112 to cause movement of the probe tip 113. In some embodiments, the cantilever 112 physically vibrates near the first harmonic resonance due to the resonant vibration of the actuator, and an attractive section between the cantilever 112 and the material 150 ( At a height in an attractive regime, the tip of the probe tip 113 oscillates in a range that does not tap the topography 151 of the material 150. The first scan allows you to scan the surface shape. After scanning the surface shape, a scan in nap mode can be performed.

In the second scan (S320), that is, a scan in nap mode, in order to measure the surface potential 152 of the material, the tip of the probe tip 113 is set to a height that is a predetermined distance away from the surface of the material 150. In, the control system 130 applies a voltage of an alternating current (AC) waveform to the cantilever 112. This predetermined distance may be, for example, 10 to 50 nm. In some embodiments, the voltage of the AC waveform may be a sinusoidal voltage (V _ac sin(ωt)). Then, the cantilever 112 electrically vibrates near the first harmonic resonance due to electrostatic force with the material 150. In this case, the resonance amplitude and phase of the cantilever 112 are determined by the voltage, DC voltage, and height of the AC waveform applied to the probe tip 113. Accordingly, control system 130 images material 150 based on the amplitude and phase of the deflection signal detected upon vibration of cantilever 112.

FIG. 4 is a diagram illustrating a control system of a potential gradient microscope according to an embodiment, and FIG. 5 is a diagram illustrating a feedback controller of a potential gradient microscope according to an embodiment.

Referring to FIG. 4, the control system 130 includes a signal generator 131, a digital analog converter (DAC) 132, an analog digital converter (ADC) 133, and a lock-in amplifier. -in amplifier), a controller 136, and a feedback controller 137.

In the second scan, the signal generator 131 generates an AC waveform ₍ V _dc ) with a DC offset (V dc ) based on a direct current (DC) voltage (V dc ) and an alternating current (AC) voltage (V _{ac sin} (ωt)). +V _ac sin(ωt)) is generated. In some embodiments, signal generator 131 may include a direct digital synthesizer (DDS) to generate an AC voltage (V _ac sin(ωt)). Additionally, the signal generator 131 may receive a DC offset (V _dc ) from the feedback controller 137. The DAC 132 converts the AC waveform generated by the signal generator 131 into an analog signal, and applies the converted analog signal to the cantilever (for example, 112 in FIG. 1).

The ADC 133 converts the bias signal detected by the detector (for example, 140 in FIG. 1) into a digital signal according to the application of the AC waveform. One lock-in amplifier includes a mixer 134a and a low pass filter (LPF) 134b, and mixes the bias signal with a reference signal of a sinusoidal waveform (V _ac sin(ωt)) through the mixer 134a. , the mixed signal is filtered through the LPF 134b to extract the real component (q) of the deflection signal. Another lock-in amplifier includes a mixer 135a and an LPF 135b, which mixes a reference signal of a cosine waveform (V _ac cos(ωt)) with the bias signal through the mixer 135a and mixes it through the LPF 135b. The imaginary component (i) of the bias signal is extracted by filtering the signal. Controller 136 determines the phase (phi) and amplitude (R) of the deflection signal based on the real (q) and imaginary components (i) of the deflection signal. The phase (ϕ) and amplitude (R) of the deflection signal are given as Equations 1 and 2, respectively.

The feedback controller 137 receives the bias signal as feedback and controls the size of the DC offset (V _dc ). The feedback controller 137 can control proportional (P) gain and integral (I) gain. In some embodiments, feedback controller 137 may include a proportional-integral-differential (PID) controller or a proportional-integral (PI) controller that controls the P gain and I gain. there is.

Referring to Figure 5, in some embodiments, the feedback controller 137 may include a subtractor 137a, a control value calculator 137b, a summer 137c, and a processor 137d.

The subtractor 137a subtracts the reference voltage (V _ref ) and the output (V _dc ) of the feedback controller 137 and outputs an error value (e(t)). The control value calculator 137b determines P gain (K _p ), I gain (K _i ), and differential (D) gain (K _d ), P gain (K _p ), I gain (K _i ), Calculate the P gain control value, I gain control value, and D gain control value based on the D gain (K _d ) and error value (e(t)). The summer 137c sums the P gain control value, I gain control value, and D gain control value and outputs a control value. The processor 137d processes the amplitude (V _CPD ) and the control value of the bias signal and outputs a DC offset (V _dc ).

In the feedback controller 137, when the P gain and I gain are high, feedback control becomes faster, and when the P gain and I gain are low, the feedback control becomes slow.

Meanwhile, in the second scan, the electrostatic force (F _es ) between the cantilever 112 (probe tip 113 of the cantilever 112) and the material 150 is given as Equation 3.

는 프로브 팁(113)과 재료(150) 사이 커패시턴스 구배이며, V는 프로브 팁(113)과 재료(150) 사이의 전위차이다. 이러한 전위차는 재료(150)의 표면 전위를 나타낼 수 있다.In Equation 3, C is the capacitance between the probe tip 113 and the material 150,

is the capacitance gradient between the probe tip 113 and the material 150, and V is the potential difference between the probe tip 113 and the material 150. This potential difference may represent the surface potential of the material 150.

The potential difference (V) between the probe tip 113 and the material 150 is the DC voltage (V _dc ) applied from the control system, the voltage of the alternating current waveform (V _ac sin(ωt)), and the probe tip 113 and the material ( 150) is determined by the contact potential difference (CPD) (V _CPD ) between the The potential difference (V) between the probe tip 113 and the material 150 can be given as Equation 4. When the probe tip 113 and the material 150, which have different Fermi levels, come into contact, the Fermi levels of the probe tip 113 and the material 150 are aligned and balanced so that they are the same. Then, a difference in vacuum level occurs equal to the difference in work function between the probe tip 113 and the material 150. The vacuum level difference resulting from the difference in work function between the probe tip 113 and the material 150 is called the contact potential difference (V _CPD ).

Based on Equation 4, Equation 3 can be rewritten as Equation 5.

은 DC 성분이고,

은 2차 고조파(second harmonic resonance) 성분이다. 프로브 팁(113)과 재료(150) 사이의 정전기력(F_es)은 주파수 대역에서 1차 고조파 성분에 지배적으로 영향을 받는다.In Equation 5, the first harmonic component is given as Equation 6,

is the DC component,

is the second harmonic resonance component. The electrostatic force (F _es ) between the probe tip 113 and the material 150 is predominantly influenced by the first harmonic component in the frequency band.

The feedback controller 137 of the control system 130 provides a DC offset through feedback such that the first harmonic component is minimized (e.g., (V _dc -V _CPD ) (620 in FIGS. 6A and 6B) is zero). Set (V _dc ). In this case, when the feedback control of the feedback controller 137 of the control system 130 is slow (i.e., when the P gain is lower than the first threshold value and the I gain is lower than the second threshold value), the first harmonic component of the first harmonic component is slow. As the magnitude of (V _dc -V _CPD ) increases, the resonance amplitude of the cantilever (i.e., the amplitude of the deflection signal) increases. This resonance amplitude increases where the potential gradient is high, and the phase of vibration of the cantilever 112 is determined depending on the scan direction of the cantilever and the direction of the potential gradient. The phase is 0 degrees when (V _dc -V _CPD ) (620 in FIGS. 6A and 6B) is positive and 180 degrees when it is negative. Accordingly, control system 130 can image the material using the amplitude and phase of the deflection signal.

6A and 6B are diagrams illustrating the vibration amplitude and phase of the cantilever in a potential gradient microscope, respectively, according to one embodiment.

As shown in FIGS. 6A and 6B, when the cantilever 112 scans from a high surface potential 610 to a low surface potential 610, the feedback control is slow and V _dc cannot follow the changing V _CPD (V _dc - V _CPD ) (620) becomes a positive number, and the phase (630) of the deflection signal becomes 0 degrees (①, ③ in FIG. 6A, ②, ④ in FIG. 6B). At this time, in the part where the potential gradient is largest, the absolute value of (V _dc -V _CPD ) 620 is the largest, so the amplitude 640 is the largest. Conversely, when the cantilever 112 scans from a place where the surface potential 610 is low to a place where the surface potential 610 is high, the feedback control is slow and V _dc cannot follow the changing V _CPD , so (V _dc -V _CPD ) (620) is a negative number. The phase 630 of the deflection signal becomes 180 degrees (②, ④ in Fig. 6a, ①, ③ in Fig. 6b). At this time, in the part where the potential gradient is largest, the absolute value of (V _dc -V _CPD ) 620 is the largest, so the amplitude 640 is the largest.

Accordingly, the control system can image the material based on the amplitude and phase changes of the deflection signal.

Next, an example of imaging a material using a potential gradient microscope according to an embodiment will be described.

Figure 7 is a diagram illustrating the results of imaging the material to be imaged with PFM and KPFM, Figure 8 is a diagram illustrating the imaging results at fast feedback and low feedback, and Figure 9 is a diagram illustrating the imaging results according to the increase in I gain. This is an illustrative drawing, and FIGS. 10 and 11 are diagrams illustrating imaging results following two scans, respectively.

As shown in FIG. 7, a box-shaped ferroelectric domain is used as a material in the imaging of FIGS. 8 to 11. In some embodiments, a box pattern ferroelectric domain can be created using a probe tip in a ferroelectric thin film. In this case, the probe tip is grounded (V _Tip = 0), the lower electrode of the outer box is +6 V, which is 2 to 3 times larger than the coercive voltage (±2 V), and the lower electrode of the inner box is -6 V. By applying V, a box-pattern ferroelectric domain can be created with the outer box facing above the film (+z-axis) and the inner box facing down the film (-z-axis). As a result of the example, in the inner box and outside the entire box, the PFM phase is 0 degrees (the direction in which the ferroelectric polarization is down the film), the CPD of the KPFM has a relatively high value, and in the outer box the PFM phase is 180 degrees ( The ferroelectric polarization is toward the top of the film), and the CPD of KPFM has a relatively low value, so the potential gradient has the highest value at the boundary of each box. In some embodiments, the ferroelectric is a ceramic such as barium titanate (BaTiO ₃ ), lead zirconate titanate (PZT), or lithium niobite (LiNbO ₃ ), or polyvinylidine fluoride. Polymers such as polyvinylidene fluoride or polyvinylidene fluoride-co-trifluoroethylene (poly[(vinylidenefluoride-co-trifluoroethylene)) may be used.

In some embodiments, resistive random-access memory (ReRAM) metal oxide materials may be used. In this case, high-resistance state and low-resistance state regions can be created in a metal oxide (eg, TiO ₂ ) thin film using a probe tip. In this case, the probe tip is in the ground state (V _Tip = 0), and in the high-resistance state, 0 V to -10 V is applied to the lower electrode, and in the low-resistance state, 0 V to -10 V is applied to the lower electrode and then again. It can be made by applying up to 0 V and then up to +10 V.

8 to 11, to image the surface charge state of the material in a scan in nap mode, the height away from the surface is 30 nm, the DC voltage (V _dc ) applied to the cantilever is +7.5 V, and the sine applied to the cantilever is Measurements were performed near resonance with an oscillation amplitude of approximately 5 nm, under the condition that the amplitude of the waveform (V _ac sin(wt)) was 0.5 V.

As shown in Figure 8, under fast feedback with high gain (e.g., I gain of 80 and P gain of 20), which is the normal AM-KPFM imaging condition, the imaged image (amplitude and phase of nap mode) is It had no clear value. On the other hand, in slow feedback with low gain (e.g., I gain of 3 and P gain of 0), the amplitude had a distinct value in the potential gradient region (ferroelectric domain boundary) and the potential gradient region (ferroelectric domain boundary) along the cantilever scan direction. It had a distinct phase of 0 or 180 degrees at the ferroelectric domain boundary. In a trace (T) scan where the cantilever moves to the right, the phase is 0 degrees in areas ① and ③ where the surface potential changes from high to low, and the phase is 180 degrees in areas ② and ④ where the surface potential changes from low to high. am. On the other hand, in a retrace (R) scan where the cantilever moves to the left, the phase is 0 degrees in areas ② and ④ where the surface potential changes from high to low, and in areas ① and ③ where the surface potential changes from low to high. The phase is 180 degrees. In this way, the ferroelectric domain can be imaged through the amplitude and phase in the potential gradient region.

As shown in Figure 9, the material was imaged with the P gain set to 0 and the I gain varied. At low I gains, the surface potential was measured and large resonance amplitudes and phases were observed in the potential gradient region. However, as the I gain increases, the thickness of the resonance amplitude and phase becomes thinner, and when the I gain exceeds approximately 20, distinct noise occurs in the amplitude and phase, making imaging difficult. Likewise, although not shown, when imaging the material while changing the P gain with the I gain set to a value greater than 0, the range of change in resonance amplitude decreased as the P gain increased.

As shown in Figures 10 and 11, the ferroelectric domain boundary can be imaged by performing the scan twice with a 90-degree difference in scan direction. Figure 10 shows an image for which imaging was performed by setting the scan angles to 0 degrees and 90 degrees, respectively, and Figure 11 shows an image for which imaging was performed by setting the scan angles to 45 degrees and -45 degrees, respectively.

As described above, according to some embodiments, the potential gradient microscope may utilize the existing AM mode of KPFM (AM-KPFM). The existing KPFM is a technology that images surface shape and surface potential through two scans. AM-KPFM performs a second scan (nap mode) measuring the height at a predetermined distance from the surface after the first scan to scan the surface shape, and in the second scan, the vibration amplitude of the cantilever due to the electrostatic force between the cantilever and the material is measured. The surface potential is imaged by measuring the tip potential that is minimized. In AM-KPFM, the gain (P gain and I gain) is increased during measurement to minimize this amplitude through feedback of the vibration amplitude. Conversely, in some embodiments, lowering the gain can increase the vibration amplitude. In this case, the vibration amplitude becomes particularly large in places where the potential gradient is high, and the phase of the cantilever vibration can also be determined depending on the scan direction of the cantilever and the direction of the potential gradient. Accordingly, the potential gradient microscope according to some embodiments can image areas where the potential gradient is high using the cantilever vibration amplitude and vibration phase that occur at low gain. Accordingly, imaging can be implemented with easier measurement conditions than the prior art without changing the properties of the material.

In some embodiments, potential gradient microscopy may image localized regions of high surface potential gradients within a material, thereby imaging ferroelectric domain boundaries, dissimilar material boundaries, or regions of different properties. Additionally, potential gradient microscopy is a non-contact imaging technology, and can image without changing the surface potential or surface charge of the material.

In some embodiments, the limitations of KPFM imaging, where the conditions for measuring potential gradient microscopic clouds are difficult and complicated, can be improved, and the limitations of conventional imaging technology can be secured by easily measuring surface potential gradients. This potential gradient microscope can be used in various fields such as ferroelectric domains, surface charges, and differentiating materials.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims are also possible. It falls within the scope of rights.

Claims (18)

a cantilever with a tip,
A detector that detects a deflection signal by providing a light beam incident on the cantilever and detecting a reflected beam that the light beam reflects off the cantilever while scanning the material while the tip is a predetermined distance away from the surface of the material. , and
A control system that applies direct current and alternating current voltages to the cantilever while scanning the material and images the material based on the amplitude and phase of the deflection signal.
Potential gradient microscopy including. In paragraph 1:
The mode for scanning the material corresponds to the napped mode of AM-KPFM (amplitude modulation Kelvin probe force microscopy), potential gradient microscopy. In paragraph 2,
Before the scan in the nap mode, the control system shapes the surface of the material through an oscillating scan in a range that does not tap the surface of the material. In paragraph 1:
The control system includes a feedback controller that controls to minimize the difference between the true voltage and the amplitude of the deflection signal according to the feedback of the amplitude of the deflection signal. In paragraph 4,
The feedback controller includes a proportional-integral-differential (PID) controller or a proportional-integral (PI) controller,
The control system sets the proportional gain of the feedback controller lower than a first threshold and the integral gain of the feedback controller lower than a second threshold.
Potential gradient microscopy. In paragraph 5,
Potential gradient microscopy, wherein the first threshold is 20. In paragraph 5,
wherein the second threshold is 20. In paragraph 1:
wherein the control system images the material based on the amplitude and phase of the deflection signal along the scan direction. In paragraph 8:
The scan direction includes a first scan direction and a second scan direction having a difference of 90 degrees from the first scan direction. In paragraph 1:
Potential gradient microscopy, wherein the alternating current waveform is a sinusoidal waveform. In paragraph 1:
A potential gradient microscope in which the cantilever is coated with a conductive material. In paragraph 11:
The conductive material is made of at least one of platinum (Pt), iridium (Ir), chromium (Cr), or conductive diamond. In paragraph 1:
The material is a potential gradient microscope consisting of at least one of ferroelectrics, oxide semiconductors, metals, composites, or block copolymers. A method of driving a potential gradient microscope including a cantilever with a tip, comprising:
scanning the material while the tip is a predetermined distance away from the surface of the material;
Applying voltages in the form of direct current and alternating current waveforms to the cantilever while scanning the material,
providing a light beam incident on the cantilever while scanning the material,
detecting a deflection signal by detecting a reflected beam that the light beam reflects from the cantilever, and
imaging the material based on the amplitude and phase of the deflection signal.
A driving method comprising: In paragraph 14:
A driving method further comprising performing feedback control to minimize a difference between the true voltage and the amplitude of the deflection signal according to the feedback of the amplitude of the deflection signal. In paragraph 15:
The step of performing the feedback control includes performing the feedback control using a proportional-integral-differential (PID) controller or a proportional-integral (PI) controller,
The proportional gain used for the feedback control is lower than the first threshold, and the integral gain used for the feedback control is lower than the second threshold.
How to drive. In paragraph 14:
Wherein imaging the material comprises imaging the material based on the amplitude and phase of the deflection signal along a scan direction. In paragraph 17:
The scan direction includes a first scan direction and a second scan direction having a difference of 90 degrees from the first scan direction.

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