Amplitude measuring device and amplitude measuring method

Abstract

To provide an amplitude measuring device and an amplitude measuring method capable of reducing latency.SOLUTION: The amplitude measuring device includes: a high-pass filter 41 for removing low-frequency components of a periodic waveform; a first squaring circuit 45 for squaring a low-frequency-removed signal which has passed through the high-pass filter 41; a differentiator 43 for differentiating the low-frequency-removed signal; a second squaring circuit 46 for squaring a waveform which has passed through the differentiator 43; and an adder 47 for adding an output signal of the first squaring circuit 45 and an output signal of the second squaring circuit.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an amplitude measurement device and an amplitude measurement method for measuring the amplitude of periodic vibration generated in a cantilever. [Background technology]

[0002] High-speed atomic force microscopes (hereafter referred to as "high-speed AFMs") are used to measure objects such as biomolecules in real space at a video rate. Conventional high-speed AFMs scan objects at a scanning speed of about 200 [μm / s]. For this reason, it is necessary to measure the area of, for example, 200 × 200 [nm 2 The limit is that a scan range of 10 ...

[0003] High-speed AFMs use an amplitude modulation method (AM modulation method), which requires measuring the vibration amplitude of the cantilever, and the low measurement bandwidth of this vibration amplitude hinders the speedup of scanning. In other words, conventional high-speed AFMs detect the vibration amplitude of the cantilever with an amplitude measuring device that uses a method called the Fourier type, and when this method is used, a latency (delay time) equal to the vibration period of the cantilever occurs, and this latency causes a decrease in the scanning speed.

[0004] Furthermore, in the technology disclosed in Non-Patent Document 1, a phase shifter (PS: Phase Shifter) type amplitude measuring device is used, and it has been experimentally shown that when the cantilever is vibrated at 500 kHz, the latency is 0.38 times the vibration period of the cantilever. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] A novel phase-shift-based amplitude detector for a high-speed atomic force microscope.Atsushi Miyagi, and SimonScheuring.Citation: Review of Scientific Instruments 89, 083704 (2018);doi: 10.1063 / 1.5038095 Summary of the Invention [Problem to be solved by the invention]

[0006] However, although the above-mentioned phase shifter type amplitude measuring device can reduce latency, latency still occurs, and there has been a growing demand for further reduction in latency.

[0007] The present invention has been made to solve the above-mentioned problems in the conventional art, and an object of the present invention is to provide an amplitude measurement device and an amplitude measurement method that are capable of further reducing latency. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the amplitude measuring device of the present invention is an amplitude measuring device that measures the amplitude of a periodic waveform generated in a cantilever used in an atomic force microscope, and is characterized in that it comprises a high-pass filter that removes low-frequency components from the periodic waveform, a first squaring circuit that squares the low-frequency removed signal that has passed through the high-pass filter, a differentiator that differentiates the low-frequency removed signal, a second squaring circuit that squares the waveform that has passed through the differentiator, and an adder that adds the output signal of the first squaring circuit and the output signal of the second squaring circuit.

[0009] The amplitude measurement method of the present invention is an amplitude measurement method for measuring the amplitude of a periodic waveform generated on a cantilever used in an atomic force microscope, and is characterized by comprising the steps of: removing low-frequency components from the periodic waveform; squaring a low-frequency removed signal from which the low-frequency components have been removed; differentiating the low-frequency removed signal; squaring the differentiated waveform; and adding a signal obtained by squaring the low-frequency removed signal and a signal obtained by squaring the differentiated signal. Effect of the Invention

[0010] According to the amplitude measurement device of the present invention, it is possible to reduce latency. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram showing the configuration of a high-speed atomic force microscope in which an amplitude measurement device according to an embodiment of the present invention is employed. [Diagram 2] FIG. 2 is an explanatory diagram showing two photodetectors provided in the photodiode and the irradiated laser light. [Diagram 3] FIG. 3 is a block diagram showing a detailed configuration of the amplitude measurement device according to this embodiment. [Figure 4] FIG. 4 is a graph showing the relationship between the carrier frequency and the gain and phase of the amplitude spectrum. [Diagram 5] FIG. 5 is a graph showing the relationship between the carrier frequency and the frequency band of the amplitude measurement device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a block diagram showing the configuration of a high-speed AFM 100 (high-speed atomic force microscope) equipped with an amplitude measurement device 20 according to an embodiment of the present invention. The high-speed AFM 100 according to this embodiment scans a sample to be measured while vibrating a cantilever 11 at a predetermined frequency, measuring the unevenness of the sample in a so-called tapping mode, and imaging the surface shape of the sample.

[0013] As shown in Fig. 1, the high-speed AFM 100 includes a sample stage 13 on which a sample 12 to be measured is placed, and a scanner 15 that is provided below the sample stage 13 and supports the sample stage 13. In the following, the plane of the sample stage 13 is defined as the XY plane, and the direction perpendicular to the XY plane (the normal direction) is defined as the Z direction. The XY plane is, for example, a horizontal plane, and the Z direction is, for example, a vertical direction. A motor 16 that moves the scanner 15 in the Z direction is provided below the scanner 15.

[0014] The scanner 15 includes a piezo actuator (hereinafter referred to as "Z piezo 15a") that displaces the sample stage 13 in the Z direction. The scanner 15 includes a piezo actuator (hereinafter referred to as "XY piezo 15b") that displaces the sample stage 13 in the XY plane direction.

[0015] A cantilever 11 having a cantilever spring structure is provided near the upper portion of the sample stage 13. A probe 11a is provided at the tip of the cantilever 11, which approaches a sample 12 placed on the sample stage 13 and causes a deflection in the cantilever 11. The rear end of the cantilever 11 is supported by a support member (not shown).

[0016] The cantilever 11 is provided with a piezo actuator (hereinafter referred to as an "excitation piezo 14") that applies a sine wave (periodic waveform) vibration to the cantilever 11. The Z piezo 15a, the XY piezo 15b, the motor 16, and the excitation piezo 14 are connected to a control unit 21.

[0017] The control unit 21 includes a drive signal generating unit 210, a Z piezo control circuit 211, an XY piezo control circuit 212, a motor control circuit 213, and a sine wave output circuit 214.

[0018] The drive signal generating unit 210 outputs a drive command signal for displacing the Z piezo 15a in the Z direction to the Z piezo control circuit 211 based on an amplitude value output from the amplitude measuring device 20 described later. The drive signal generating unit 210 also outputs a drive command signal for applying a sine wave of a predetermined frequency to the cantilever 11 to the sine wave output circuit 214.

[0019] The drive signal generating unit 210 also outputs a drive command signal for scanning the scan area of ​​the sample 12 with the cantilever 11 to the XY piezo control circuit 212. The drive signal generating unit 210 also outputs a drive command signal for moving the scanner 15 in the Z direction to the motor control circuit 213.

[0020] The Z piezo control circuit 211 outputs a control signal to the Z piezo 15a based on the drive command signal output from the drive signal generating unit 210. The XY piezo control circuit 212 outputs a control signal to the XY piezo 15b based on the drive command signal output from the drive signal generating unit 210. The motor control circuit 213 outputs a control signal to the motor 16 based on the drive command signal output from the drive signal generating unit 210. The sine wave output circuit 214 outputs a sine wave excitation signal to the excitation piezo 14 based on the drive command signal output from the drive signal generating unit 210.

[0021] By applying control signals to the Z piezo 15a and the XY piezo 15b, the sample stage 13 can be minutely displaced in the Z direction and on the XY plane on the order of nanometers (nm). By outputting a sine wave excitation signal to the excitation piezo 14, the cantilever 11 can be made to vibrate in a sine wave.

[0022] A laser diode 17 (marked as "LD" in the figure) and a photodiode 18 (marked as "PD" in the figure) are provided above the cantilever 11. The laser diode 17 is, for example, a semiconductor laser, and irradiates a laser beam onto the back surface of the probe 11a of the cantilever 11. The photodiode 18 receives the light reflected by the cantilever 11. Note that mirrors and beam splitters that reflect the laser beam are provided between the laser diode 17 and the cantilever 11, and between the cantilever 11 and the photodiode 18, but are not shown in FIG. 1.

[0023] 2 is an explanatory diagram showing an example of the configuration of the photodiode 18. The photodiode 18 has photodetectors 18a and 18b divided into two blocks as shown in FIG. 2(a). The photodetector is not limited to being divided into two, and a photodetector divided into four can also be used. The photodiode 18 is connected to a differential amplifier 19. The differential amplifier 19 is connected to an amplitude measurement device 20.

[0024] The differential amplifier 19 detects a difference signal between the signals detected by the photodetectors 18 a and 18 b , and outputs the difference signal to an amplitude measurement device 20 .

[0025] For example, as shown in Fig. 2(a), when the center of the laser light Q1 indicated by the dotted line substantially coincides with the center N1 of the photodiode 18, the difference signal between the detection signal Sa of the photodetector 18a and the detection signal Sb of the photodetector 18b is substantially zero. That is, the above-mentioned difference signal has a small value. On the other hand, as shown in Fig. 2(b), when the center of the laser light Q1 is deviated from the center N1 of the photodiode 18, the difference signal between the detection signals Sa and Sb becomes large. Therefore, the difference signal becomes large.

[0026] When the cantilever 11 vibrates in a sine wave, the output of the differential amplifier 19 also vibrates in a sine wave. Therefore, the output of the differential amplifier 19 is a sine wave. The sine wave output from the differential amplifier 19 is represented as "A sinωt" using the amplitude A.

[0027] The amplitude measurement device 20 converts the envelope of the amplitude of the sine wave output from the differential amplifier 19 into an amplitude value. The amplitude value serves as an index showing the amount of deviation of the laser light irradiation position from the center N1 of the photodiode 18. The amplitude value converted by the amplitude measurement device 20 is output to the feedback circuit 22 and the image formation circuit 31. The detailed configuration of the amplitude measurement device 20 will be described later with reference to FIG. 3.

[0028] The feedback circuit 22 generates a control signal whose target value is the amplitude value calculated by the amplitude measurement device 20 , and outputs this control signal to the image processing circuit 31 and the Z piezo control circuit 211 .

[0029] The image generating circuit 31 acquires the control signal output from the feedback circuit 22, and creates an image of the surface shape of the sample 12 based on this control signal.

[0030] That is, as described above, a sinusoidal excitation signal is applied to the cantilever 11 to vibrate it, and a control voltage is applied to the Z piezo 15a to control the distance between the probe 11a and the sample 12 so that the displacement of the cantilever 11 is constant. Furthermore, the XY piezo 15b is subjected to planar scanning on the XY plane. Specifically, the entire XY plane is scanned by reciprocating the scan in the X direction in a zigzag manner.

[0031] As a result, the amount of movement of the scanner 15 in the Z direction indicates the size of the sample 12 in the Z direction, i.e., the unevenness of the sample 12, and unevenness data of the sample 12 on the XY plane is obtained. The image generating circuit 31 adds contrast based on this unevenness data to image the surface shape of the sample 12.

[0032] Next, details of the amplitude measurement device 20 according to this embodiment will be described. Fig. 3 is a block diagram showing the configuration of the amplitude measurement device 20. As shown in Fig. 3, the amplitude measurement device 20 includes a high-pass filter 41 (hereinafter, referred to as "HPF 41"), a phase shifter 42, a differentiator 43, a changeover switch 44 (a changeover unit), a first squaring circuit 45, a second squaring circuit 46, an adder 47, and a square root calculation circuit 48.

[0033] The HPF 41 receives as its input the sine wave "A sinωt" ("A" is amplitude) output from the differential amplifier 19, and outputs a low-pass filtered signal in which the low-frequency components of the sine wave have been removed. By removing the low-frequency components, the effects of the displacement of the DC component of the cantilever 11 are avoided. Specifically, the effects on the feedback signal caused by the output of a component that is in phase opposite to the input signal are avoided.

[0034] The phase shifter 42 generates a phase-shifted waveform by delaying the phase of the sine wave (low-frequency removed signal) that has passed through the HPF 41 by 90°. That is, the phase shifter 42 outputs a phase-shifted waveform "-Acosωt" by shifting the phase of the sine wave.

[0035] The differentiator 43 generates a phase shift waveform by differentiating the sine wave (low-frequency removed signal) that has passed through the HPF 41. That is, the differentiator 43 outputs a phase shift waveform "Acosωt" by differentiating the sine wave.

[0036] Here, the phase shifter 42 generates a phase-shifted waveform (cosine wave) by shifting the phase of a sine wave (sine wave), so a phase delay occurs. On the other hand, the differentiator 43 generates a phase-shifted waveform (cosine wave) by differentiating the sine wave (sine wave), so in principle no phase delay occurs.

[0037] The changeover switch 44 selects either the output signal of the phase shifter 42 or the output signal of the differentiator 43 and outputs the selected signal to the second squaring circuit 46 .

[0038] The first squaring circuit 45 squares the sine wave "A sinωt" that has passed through the HPF 41. That is, (A sinωt) 2 Output.

[0039] The second squaring circuit 46 squares the phase shift waveform "Acosωt" or "-Acosωt" selected by the changeover switch 44. That is, (Acosωt) 2 Output.

[0040] The adder 47 adds the output signal of the first squaring circuit 45 and the output signal of the second squaring circuit 46. The output signal of the adder 47 is a value obtained by squaring the amplitude A of the input signal, "A 2 "

[0041] The square root calculation circuit 48 calculates the value "A 2 " and the amplitude "A" is used as the output signal.

[0042] The differential amplifier 19, amplitude measurement device 20, control unit 21, and image generation circuit 31 constituting the high-speed AFM 100 of this embodiment can be configured, for example, by a general-purpose microcontroller equipped with a CPU, memory, and input / output units.

[0043] [Operation of this embodiment] Next, the operation of the amplitude measurement device 20 according to this embodiment will be described with reference to the graphs shown in Figures 4 and 5. When a sine wave excitation signal is applied to the cantilever 11 shown in Figure 1 and the scanner 15 is operated to scan the sample 12 placed on the sample stage 13, a sine wave "A sinωt" that is amplitude modulated in accordance with the unevenness of the sample 12 is output from the differential amplifier 19.

[0044] This sine wave "Asinωt" is input to the HPF 41 of the amplitude measurement device 20 shown in FIG. 3, where the low frequency components are removed. When the changeover switch 44 is connected to the differentiator 43 side, the sine wave "Asinωt" is differentiated by the differentiator 43. As a result of the sine wave being differentiated by the differentiator 43, a phase shift waveform "Acosωt" is output from the differentiator 43. This phase shift waveform "Acosωt" is input to a second squaring circuit 46. The second squaring circuit 46 calculates the square of the phase shift waveform, and outputs the squared signal (Acosωt) as the result of the calculation. 2 Output.

[0045] On the other hand, a sine wave "Asinωt" is input to the first squaring circuit 45. The first squaring circuit 45 calculates the square of the sine wave, and outputs the squared signal (Asinωt) 2 Output.

[0046] The adder 47 adds the output signals of the first squaring circuit 45 and the second squaring circuit 46. 2 +(Asinωt) 2 By calculating the square of the amplitude "A 2 This calculation result is output to the square root calculation circuit 48.

[0047] The square root calculation circuit 48 calculates the square root of the output of the adder 47 to calculate the amplitude "A".

[0048] The amplitude measurement device 20 outputs the amplitude "A" which is the output signal of the square root calculation circuit 48 as a first output, and the square of the amplitude "A" which is the output of the adder 47 as a second output. 2 " is output.

[0049] The image generating circuit 31 shown in FIG. 2" is used to measure and image the surface shape of the sample 12. In AM-AFM (amplitude modulated AFM), the amount of decrease in the amplitude value is used as a feedback signal. When the distance between the probe 11a and the sample 12 is large, the distance dependency becomes poor, and a problem called the parachute effect occurs. By squaring the amplitude "A", the amplitude decreases sharply with respect to the distance between the probe 11a and the sample 12, and the influence of the parachute effect can be mitigated. In other words, the square of the amplitude "A" 2 By using ", it is possible to generate an image in which the influence of the parachute effect is mitigated.

[0050] Here, in the above process, if latency (delay time) occurs in the amplitude calculation of amplitude measurement device 20, feedback of amplitude control will not be performed correctly, and for example, if a protrusion exists on sample 12, a problem will occur in which probe 11a of cantilever 11 comes into contact with the protrusion. In amplitude measurement device 20 according to this embodiment, the latency in the amplitude calculation is suppressed as described below, thereby avoiding the problem of probe 11a coming into contact with the protrusion.

[0051] [Latency explanation] The difference in latency that occurs when a phase-shifted waveform is generated using the conventional phase shifter 42 and when a phase-shifted waveform is generated using the differentiator 43 employed in this embodiment will be described.

[0052] 4(a) and (b) show the amplitude “A” measured by the amplitude measurement device 20 when an AM modulated signal is used. 2 4(a) is a graph showing the change in gain and phase of the frequency spectrum of "." As shown by the curve s1 in FIG. 4(a), the gain of the frequency spectrum is almost flat over frequencies above 1000 kHz, and only slight attenuation is observed.

[0053] As for the phase curve shown in FIG. 4(b), the result is that the phase decreases with increasing frequency. The curve s2 shown in FIG. 4(b) shows the delay of the amplitude signal, and the curve s3 shows the delay due to the differentiator 43. When the curves s2 and s3 are analyzed based on the dead-time theorem, it is possible to fit the curve s2 well using a single delay component as in the case of the curve s3. This delay is caused by the characteristics of the differentiator 43. In the case of an analog circuit, the frequency band is determined by the differentiator 43. In the case of a digital circuit, the frequency band is determined by the AD / DA converter. As shown in the curve s4 shown in FIG. 4(b), the phase delay of 45° has a frequency band of the carrier frequency of 1100 [kHz], and a detection band higher than the carrier frequency of 500 [kHz] is obtained.

[0054] Fig. 5 is a graph showing the relationship between the carrier frequency and the band frequency of the amplitude measurement device 20. Curves s11, s12, and s13 shown in Fig. 5 respectively show the band frequencies when the differentiator 43 is used, when the phase shifter 42 is used, and when the conventional Fourier type is used.

[0055] The theoretical latency when using a conventional Fourier type is one time the vibration period of the sine wave applied to the cantilever 11. In other words, a phase delay of 360° occurs. As shown by the curve s13, at low frequencies it overlaps with the dashed line indicating a delay of 360°, but as the carrier frequency increases, the phase delay due to the circuit delay is added, resulting in a delay of more than 360°.

[0056] The theoretical latency when the phase shifter 42 is used is 1 / 12 (0.083) times the vibration period of the sine wave applied to the cantilever 11. That is, a phase delay of 30° occurs. As shown by the curve s12, in the low frequency band below 500 [kHz], it is quite close to the theoretical line, but it can be seen that the detector band gradually increases as the carrier frequency increases.

[0057] In contrast, when the differentiator 43 is used, theoretically, the phase delay is 0°, which means zero latency. As shown by the curve s11, the phase delay is higher than 30° in the frequency band of 750 kHz or less, which shows that the band exceeds the theoretical limit when the phase shifter 42 is used.

[0058] On the other hand, it can be seen that the curve is almost flat except for the data at 300 [kHz]. This is because there is no theoretical delay, and as mentioned above, only the delay of the differentiator 43 determines the rate, confirming the zero latency. Therefore, it can be seen that the latency can be significantly reduced by using the differentiator 43.

[0059] In addition, in a frequency band where the carrier frequency is around 500 kHz, the speed is about 10 times faster than the Fourier type when the phase shifter 42 is used. Furthermore, the speed is about twice as fast as when the phase shifter 42 is used when the differentiator 43 is used.

[0060] That is, by differentiating the sine wave "Asinωt" using the differentiator 43 shown in FIG. 3 to generate the phase shift waveform "Acosωt", it is possible to significantly reduce the latency of the amplitude measurement device 20.

[0061] In the above measurements, the HPF 41 was not taken into consideration, but the detector band would be slightly smaller if the HPF 41 were taken into consideration. However, although the cutoff frequency of the HPF 41 is determined by the band of the Z piezo 15a, the effect of the HPF 41 can usually be suppressed by making the resonant frequency of the cantilever 11 sufficiently higher than this band.

[0062] [Description of the embodiment] The inventors used actin fibers as the sample to be observed and evaluated the amplitude measurement device 20 shown in Fig. 3. When imaging was performed at a scan speed of 800 [μm / s], which is four times faster than the conventional method, the results showed that when a Fourier type was used, the fibers were broken due to probe interaction one second after the start of scanning the sample 12. In contrast, when the differentiator 43 was used, a surface image of the sample 12 could be generated without breaking the fibers when scanning for 30 seconds.

[0063] In other words, it has been demonstrated that by using the differentiator 43, non-invasiveness can be maintained even when performing high-speed scanning in comparison with the conventional method.

[0064] Furthermore, in the amplitude measurement device 20, when quick response of the phase shift waveform "Acosωt" is not required, the changeover switch 44 is switched to the phase shifter 42 side, and the amplitude "A" can be calculated using the phase shift waveform "-Acosωt" output from the phase shifter 42. By using the phase shifter 42, it is possible to reduce noise.

[0065] That is, the user can select either the phase shifter 42 or the differentiator 43 by operating the changeover switch 44, and can select the phase shifter 42 by switching the changeover switch 44 to the phase shifter 42 side.

[0066] [Description of Modifications] Next, a modified example of the above-mentioned embodiment will be described. In the above-mentioned embodiment, an example in which the amplitude of an amplitude-modulated sine wave signal is calculated to measure the unevenness of the sample 12 is described. In the modified example, an example in which the method is applied to a high-speed AFM (PM-AFM) that employs phase modulation will be described.

[0067] In a modified example, the displacement signal of the cantilever 11, i.e., the sine wave “A sinω mBy inputting a signal obtained by adding "phase difference V(t)" and an excitation signal for vibrating the cantilever 11, i.e., an excitation signal supplied to the excitation piezo 14 shown in Fig. 1 (hereinafter referred to as "added signal V(t)") to the amplitude measurement device 20, information correlated with the phase difference is obtained. This will be explained in detail below.

[0068] Sine wave “Asinω m If the phase difference between "t" and the excitation signal is θ, the excitation signal is "Bsin(ω m Here, B is the amplitude of the excitation signal. Therefore, the sum signal V(t) can be expressed by the following equation (1).

[0069]

number

[0070] By squaring the above equation (1), V 2 (t) can be expressed by the following equation (2).

[0071]

number

[0072] Moreover, by differentiating the sum signal V(t) shown in equation (1) by a differentiator 43, the following equation (3) is obtained.

[0073]

number

[0074] That is, the output signal of the differentiator 43 is given by equation (3).

[0075] By squaring the above equation (3), the following equation (4) is obtained.

[0076]

number

[0077] That is, the output signal of the second squaring circuit 46 is given by equation (4).

[0078] The adder 47 adds the equations (2) and (4), so the square of the amplitude is expressed as "Amp 2 " will result in "Amp 2 " can be expressed by the following equation (5).

[0079]

number

[0080] As can be seen from equation (5), the squared amplitude signal "Amp 2 " is a signal reflecting the phase difference "θ" and amplitudes "A" and "B".

[0081] In addition, for comparison with the calculations of the above expressions (1) to (5), similar calculations will be considered when phase shifter 42 is used.

[0082] In the phase shifter 42, the signal V(t-π / 2) obtained by delaying the added signal V(t) by 90° can be expressed by the following equation (6).

[0083]

number

[0084] In addition, the second squaring circuit 46 squares equation (6) to obtain V 2 (t-π / 2) can be expressed by the following equation (7).

[0085]

number

[0086] The adder 47 adds the equations (2) and (7), and the square of the amplitude is expressed as "Amp 2 " will result in "Amp 2 " can be expressed by the following equation (8).

[0087]

number

[0088] Equation (8) is the same as equation (5) above, and like equation (5) above, the squared amplitude signal "Amp 2 " is a signal reflecting the phase difference "θ" and amplitudes "A" and "B".

[0089] As described above, a signal reflecting the phase difference θ can be obtained by inputting the sum signal V(t) to the amplitude measurement device 20. However, as can be seen from equation (8), the signal is correlated with the phase and the amplitude value. Therefore, in order to obtain information related only to the phase, a condition is required under which both A and B do not change over time.

[0090] First, in the case of AM-AFM used in high-speed AFMs, A is constant, and during acquisition of a topography image, the tip-sample distance is controlled so that B is constant. Therefore, provided that feedback is working properly, it is possible to use this method to reduce latency and scan the sample 12 while acquiring a signal proportional to cosθ.

[0091] In the case of FM-AFM, the sample surface is scanned while detecting the phase and performing feedback so that the frequency shift is constant. In this method, AGC (Automatic Gain Control) is used to control the amplitude value to be constant, so contrary to AM-AFM, A is constant and B varies over time. Even in this case, both A and B can be fixed by using a signal with the same phase as A and the same amplitude as B as the input signal instead of A. In that case, the above-mentioned formula (5) becomes the following formula (9).

[0092]

number

[0093] Furthermore, in the case of FM-AFM, self-excited oscillation is performed so that the phase delay of the oscillation of the cantilever 11 is 90°, so that the following formula (10) is obtained.

[0094]

number

[0095] In Non-Patent Document 1, there is no particular explanation and it is written as "A (Ext+Cant) " It is stated that it is best to keep it at 2 × cos45° of B.

[0096] Since 2×cos45°=√2, it can be seen that the same relationship as equation (10) above can be obtained.

[0097] PM-AFM (phase-modulated AFM) often uses a setup that does not use AGC, but if AGC is used, a signal related to the phase change can be obtained based on a similar principle.

[0098] In this way, the amplitude measurement device 20 according to the modified example can acquire not only the amplitude value but also the phase signal at high speed. In high-speed AFM measurement, it becomes possible to map viscoelastic information by acquiring the phase signal together with the shape image.

[0099] In the above-described embodiment and modified examples, a sine wave has been used as an example of a periodic waveform for vibrating the cantilever 11, but the present invention is not limited to a sine wave, and other periodic waveforms can also be used.

[0100] Although the embodiment of the present invention has been described above, the description and drawings forming a part of this disclosure should not be understood as limiting the present invention. Various alternative embodiments, examples and operating techniques will become apparent to those skilled in the art from this disclosure. [Explanation of symbols]

[0101] 11 Cantilever 11a Probe 12 Samples 13 Sample stage 14 Excitation Piezo 15 Scanner 15a Z Piezo 15b XY Piezo 16 Motor 17 Laser Diode 18 Photodiode 18a, 18b Photodetector 19 Differential Amplifier 20 Amplitude measuring device 21 Control section 22 Feedback Circuit 31 Image generation circuit 41 High Pass Filter (HPF) 42 Phase Shifter 43 Differentiator 44 Changeover switch (changeover section) 45 First squaring circuit 46 Second squaring circuit 47 Adder 48 Square root calculation circuit 210 Drive signal generating unit 211 Z Piezo Control Circuit 212 XY Piezo Control Circuit 213 Motor control circuit 214 Sine wave output circuit

Claims

1. An amplitude measurement device for measuring the amplitude of a periodic waveform generated on a cantilever used in an atomic force microscope, comprising: a high-pass filter for removing low-frequency components of the periodic waveform; a first squaring circuit that squares the low-frequency removed signal that has passed through the high-pass filter; a differentiator for differentiating the low-frequency removed signal; a second squaring circuit for squaring the waveform that has passed through the differentiator; an adder that adds an output signal of the first squaring circuit and an output signal of the second squaring circuit; An amplitude measuring device comprising:

2. a phase shifter for shifting the phase of the low-frequency removed signal; a switching unit that selects either the output signal of the differentiator or the output signal of the phase shifter, The second squaring circuit squares the output signal selected by the switching unit.

2. The amplitude measuring device according to claim 1 .

3. The phase shifter delays the phase of the low-frequency removal signal by 90°.

3. The amplitude measuring device according to claim 2 .

4. a square root calculation circuit for calculating the square root of the output added by the adder, The output of the adder is a first output, and the output of the square root calculation circuit is a second output.

4. The amplitude measuring device according to claim 1, wherein

5. An excitation signal that outputs a periodic waveform to the cantilever and a sum signal obtained by adding a displacement signal of the cantilever are used as an input signal, and a signal correlated with a phase difference of the cantilever is obtained. The amplitude measuring device according to any one of claims 1 to 4,

6. 1. An amplitude measurement method for measuring the amplitude of a periodic waveform generated on a cantilever used in an atomic force microscope, comprising: removing low frequency components from the periodic waveform; Squaring the low-frequency removed signal; differentiating the low-pass removed signal; squaring the differentiated waveform; adding a signal obtained by squaring the low-frequency removed signal and a signal obtained by squaring the differentiated signal; An amplitude measurement method comprising:

Images