WO2021020111A1 - Measuring device, atomic force microscope, and measurement method - Google Patents

Abstract

A measuring device (10A, 110) comprises: a generation unit (202A) that generates a reference signal having a reference frequency set close to a resonance frequency of a vibrator (11); an amplitude detection unit (204A) that detects, on the basis of a displacement signal of the vibrator (11) and the reference signal generated by the generation unit (202A), a thermal vibration amplitude of the vibrator (11) within a prescribed range including the reference frequency; and a calculation unit (206A) that calculates the resonance frequency of the vibrator (11) on the basis of the detected thermal vibration amplitude.

Description

Measuring device, atomic force microscope, and measuring method

The present disclosure relates to a measuring device, an atomic force microscope, and a measuring method.

The scanning probe microscope (SPM) detects the interaction between the probe and the sample that occurs when the probe (probe) is brought close to the sample surface, and the probe and the probe are kept constant. The surface shape image is acquired by controlling the distance between the samples and scanning the probe or the sample two-dimensionally. Among the SPMs, the atomic force microscope (AFM: Atomic Force Microscopy) is the most widely used device, and it has a cantilever with a probe at its free end, an optical displacement sensor that detects the displacement of the cantilever, and an optical displacement sensor. , It is equipped with a scanner that scans the cantilever and the sample relative to each other. The AFM creates a mechanical interaction between the mechanical probe and the sample, and obtains sample information based on the deformation of the cantilever caused by the mechanical interaction.

Japanese Unexamined Patent Publication No. 2002-277378 (Patent Document 1) discloses an ultrasonic atomic force microscope (UAFM: Ultrasonic Atomic Force Microscopy). In this UAFM, with the probe attached to the cantilever in contact with the sample, the cantilever is vibrated so that the cantilever is always in a resonance state, and the amplitude of the cantilever in the resonance state is detected and detected. The Q value of the cantilever can be obtained based on the amplitude.

JP-A-2002-277378

In UAFM according to Patent Document 1, it is necessary to vibrate the cantilever by using a piezoelectric element (ultrasonic oscillator) or the like so that the cantilever is always in a resonance state. On the other hand, since the resonance frequency also exists in the cantilever and the peripheral parts of the sample such as the cantilever holder, if the frequency applied to the piezoelectric element matches this, the entire probe-sample system vibrates greatly. In this case, in the frequency spectrum, the resonance characteristics (amplitude and phase) of the cantilever are greatly distorted by the peak (spurious peak) of the parasitic vibration appearing near the resonance frequency of the cantilever. Therefore, the probe-sample system is vibrated at a frequency different from the original resonance frequency, which causes problems such as damage to the sample and the probe and incorrect viscoelastic information.

Further, Non-Patent Document 1 focuses on the thermal noise vibration of the cantilever, and scan-type thermal vibration as a method of obtaining viscoelastic information of the sample surface without vibrating the sample or the cantilever by frequency analysis of the thermal noise vibration. A microscope (STNM: Scanning Thermal Noise Microscopy) is disclosed. In this method, the vibration waveform of the cantilever is recorded and the frequency analysis is performed by the fast Fourier transform, so it is necessary to take time for the measurement. In this respect, the method disclosed in Non-Patent Document 1 has room for improvement.

An object of the present disclosure is to provide a measuring device capable of measuring the resonance frequency of the vibrating body at a higher speed without vibrating the vibrating body, an atomic force microscope including the measuring device, and a measuring method. Is to provide.

A measuring device according to an embodiment is based on a generator that generates a reference signal having a reference frequency set near the resonance frequency of the vibrating body, and a displacement signal of the vibrating body and a reference signal generated by the generating unit. It also includes an amplitude detection unit that detects the thermal vibration amplitude of the vibrating body within a predetermined range including the reference frequency, and a calculation unit that calculates the resonance frequency of the vibrating body based on the detected thermal vibration amplitude.

Atomic force microscopes according to other embodiments are provided with the above measuring device. The vibrating body is a cantilever. The atomic force microscope further includes an image generation unit that generates an image of the resonance frequency of the cantilever calculated by the measuring device by scanning the probe provided at the tip of the cantilever relative to the sample.

The measurement method according to still another embodiment is based on the step of generating a reference signal having a reference frequency set in the vicinity of the resonance frequency of the vibrating body, and the displacement signal of the vibrating body and the generated reference signal. The step includes a step of detecting the thermal vibration amplitude of the vibrating body within a predetermined range including the reference frequency, and a step of calculating the resonance frequency of the vibrating body based on the detected thermal vibration amplitude.

According to the present disclosure, it is possible to measure the resonance frequency of the vibrating body at a higher speed without vibrating the vibrating body.

It is the schematic which shows the whole structure of the AFM according to this embodiment. It is a figure which shows the harmonic oscillator model of a cantilever. It is a figure for demonstrating the configuration example 1 of the signal detection apparatus. It is a figure which shows the thermal vibration spectrum of a cantilever. It is a figure for demonstrating the change of a noise amplitude. It is a functional block diagram of a signal detection device and a computer according to the configuration example 1. It is a figure which shows the configuration example 2 of the signal detection apparatus. It is a figure for demonstrating the noise amplitude detected by the configuration example 2. FIG. It is a functional block diagram of a signal detection device and a computer according to the configuration example 2. It is a figure which shows the structure of a part of the configuration example 3 of a signal detection device. It is a figure which shows the noise amplitude which changes according to the fluctuation of a reference signal. It is a figure which shows the noise amplitude which changes according to the fluctuation of a reference signal. It is a figure which shows the noise amplitude which changes according to the fluctuation of a reference signal. It is a figure which shows the structure which added the lock-in amplifier to the structure of FIG. It is a figure which shows the center frequency dependence of the output signal of a lock-in amplifier. It is a figure which shows the whole structure of the configuration example 3 of a signal detection device. It is a functional block diagram of a signal detection device and a computer according to the configuration example 3. It is a figure which shows the measurement example 1 of a sample. It is a figure which shows the configuration example 4 of the signal detection apparatus. It is a figure for demonstrating the relationship between the time average amplitude and Q value. It is a figure which shows the measurement example 2 of a sample. It is a figure which shows the configuration example 5 of the signal detection apparatus. It is a figure which shows the measurement example 3 of a sample. It is a figure which shows the structural example 6 of the signal detection apparatus.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are designated by the same reference numerals. Their names and functions are the same. Therefore, the detailed description of the same parts of them will not be repeated.

<Overall configuration>
FIG. 1 is a schematic view showing an overall configuration of an AFM 100 according to the present embodiment. With reference to FIG. 1, the AFM 100 includes a scanning mechanism 5, a table 8, a signal detection device 10, a cantilever 11, a laser light source 14, a displacement detector 15, a computer 110, a feedback circuit 120, and Z. It includes a driver 132 and an XY driver 134.

The cantilever 11 which is a vibrating body has, for example, a cantilever structure made of silicon, one end of which is supported by a housing (not shown) of the AFM100, and the other end of which has a probe 12. The probe 12 of the cantilever 11 comes into contact with the surface of the measurement sample 2 arranged on the table 8. The laser light source 14 irradiates the back surface of the cantilever 11 with a laser beam. The displacement detector 15 is composed of, for example, an optical lever type optical displacement sensor, and detects a displacement signal of the cantilever 11 based on a laser beam reflected from the back surface of the cantilever 11. Specifically, the displacement detector 15 detects as a displacement signal a signal indicating an angular displacement proportional to the displacement of the tip of the cantilever 11. The displacement detector 15 may detect a signal indicating the displacement of the tip of the cantilever 11 as a displacement signal. The detected displacement signal is output to the signal detection device 10 and the feedback circuit 120.

The scanning mechanism 5 moves the sample 2 and the probe 12 relative to each other in three dimensions. The scanning mechanism 5 includes a Z scanner 6 and an XY scanner 7. The Z scanner 6 is arranged on the XY scanner 7, and the sample 2 is placed via a table 8 fixed to the upper portion of the Z scanner 6 in the vertical direction. The Z scanner 6 is composed of, for example, a piezoelectric element, and moves the sample 2 in the Z direction with respect to the probe 12 in response to the voltage indicated by the Z driver 132. The XY scanner 7 is composed of, for example, a piezoelectric element, and moves the sample 2 in the XY direction with respect to the probe 12 in response to the voltage indicated by the XY driver 134. The Z direction is the vertical direction, that is, the direction perpendicular to the plane on which the sample 2 is placed among the planes of the table 8, and the XY direction is the coordinate axes on the plane orthogonal to the Z direction.

The feedback circuit 120 generates a Z control signal based on the displacement signal of the cantilever 11 so that the amount of deflection of the cantilever 11 becomes constant. For example, the feedback circuit 120 generates a Z control signal so that the output signal that has passed through a low-pass filter (not shown) among the displacement signals has a predetermined constant value, and sends the Z control signal to the Z driver 132. Supply. The Z driver 132 controls the Z scanner 6 according to the supplied Z control signal. As a result, the distance between the sample 2 and the probe 12 is controlled so that the output signal becomes a constant value.

The signal detection device 10 detects the thermal vibration amplitude of the cantilever 11 based on the displacement signal of the cantilever 11, and viscoelastic information (for example, resonance frequency, Q value) of the cantilever 11 based on the detected thermal vibration amplitude. ) Is detected. The specific configuration of the signal detection device 10 will be described later.

The computer 110 is, for example, a desktop personal computer. Typically, the computer 110 has a hardware configuration such as a processor composed of a CPU (Central Processing Unit) and the like, a memory such as a RAM (Random Access Memory), a ROM (Read-Only Memory), and a hard disk, and an operator. It includes an input device (for example, a keyboard, a mouse, etc.) that receives an instruction input from the computer, a communication interface for transmitting and receiving various signals, a display for displaying various information, and the like.

The computer 110 receives the Z control signal from the feedback circuit 120. The computer 110 sends a scanning signal to the XY driver 134 to scan the XY scanner 7 in the XY direction. The computer 110 stores the position of the table 8 in the Z direction corresponding to the Z control signal when the table 8 moves in the XY axis direction. The computer 110 generates various images by scanning the probe 12 relative to the sample 2 while the probe 12 is in contact with the sample surface. Specifically, the computer 110 generates a surface shape image of the sample 2 and displays it on the display by plotting the stored position in the Z direction in the coordinate system of the XYZ axes. Further, the computer 110 calculates the resonance frequency and the Q value of the cantilever 11 based on the signal from the signal detection device 10, generates an image showing the viscoelasticity of the surface of the sample 2, and displays it on the display. For example, the signal detection device 10 and the computer 110 realize a measuring device that measures the resonance frequency and the Q value of the cantilever 11.

<Configuration of signal detection device>
(Introduction)
FIG. 2 is a diagram showing a harmonic oscillator model of a cantilever. With reference to FIG. 2, m ^* , γ, and _kz indicate the effective mass, damping constant, and spring constant of the cantilever, respectively. In the present embodiment, the probe 12 is controlled to be in contact with the sample 2. In this case, the contact elasticity k ^* and the contact viscosity γ _s on the sample 2 side affect the resonance characteristics (resonance frequency and Q value) of the cantilever 11. Therefore, the viscoelastic information of the sample surface can be obtained by obtaining the resonance characteristics of the cantilever 11 at the time of contact between the cantilever 11 and the sample. Further, when the subsurface structure of the sample 2 affects the viscoelasticity of the sample surface, the subsurface structure can be visualized.

Here, when the cantilever or the sample is vibrated as in Patent Document 1, the spurious peak described above is generated, and there are also the following adverse effects. For example, the frequency spectrum obtained by excitation often shows vibration amplitude dependence, and a large amplitude distorts the frequency spectrum. Further, for a soft sample, the probe may be greatly pushed into the sample due to the vibration of the probe, which may damage the sample. Therefore, it is desirable to obtain the resonance frequency of the cantilever (hereinafter, also referred to as “contact resonance frequency”) at the time of contact between the cantilever and the sample in a non-invasive manner without vibrating the cantilever.

Here, the cantilever is constantly vibrating due to the thermal fluctuation of the surroundings without applying a vibrating external force. This vibration is referred to as thermal noise vibration or thermal vibration, the magnitude of the energy, the Boltzmann constant k _B, when the environmental temperature is T, is given by k B _T. Therefore, the root mean square <x _th (t) ² > of the displacement x _th (t) due to thermal vibration is expressed by the following equation (1).

Because cantilever is vibrated at constant energy density per unit frequency band at all frequencies by thermal fluctuation, the frequency spectrum N _th of the thermal oscillation _(omega) (i.e., displacement noise density) angular frequency dependence following formula It is represented by (2).

ω ₀ is the resonance angular frequency of the cantilever, and is given by ω ₀ = (k _z / m ^* ) ^1/2 . Q, which is defined by the ratio of the resonance frequency to the resonance peak width, is given by Q = k _z / (ω ₀ γ) and is called the Q value. The following equation the frequency spectrum N _th of the thermal vibrations of the _(omega) is integrated over the entire frequency range (3) is obtained.

From this, the integrated value of the square of the frequency spectrum N _th (ω) (that is, the displacement noise density) in the entire frequency domain agrees with the time average <x _th (t) ² >.

In the method according to Non-Patent Document 1, the displacement signal of the cantilever is recorded at each scanning point of the contact mode AFM, the frequency spectrum of the thermal vibration amplitude is obtained by Fourier transform, and this is compared with the equation (1). The contact resonance frequency and Q value of the cantilever were acquired. However, since the amplitude of thermal vibration is very small, the sensitivity is low and the measurement time becomes long.

Therefore, in the measurement apparatus according to the present embodiment (the signal detection apparatus 10 and the computer 110), the contact resonance frequency of the cantilever 11 (hereinafter, simply referred to as "resonant frequency f _c.") Near the reference frequency set in the vicinity of detecting the thermal vibration amplitude in the frequency range, measuring the resonance frequency f _c on the basis of the thermal vibration amplitude. Thus, it is possible to measure the resonant frequency f _c in real time can be greatly shortened measurement time. Hereinafter, configuration examples 1 to 6 of the signal detection device 10 will be specifically described.

(Configuration Example 1)
FIG. 3 is a diagram for explaining a configuration example 1 of the signal detection device 10. The probe 12 of the cantilever 11 is set in contact with the surface of the sample 2. For example, the operator adjusts the positions of the laser light source 14 and the displacement detector 15 with the sample 2 away from the probe 12 so that a displacement signal representing the deflection of the cantilever 11 can be obtained with optimum sensitivity. When these positions are adjusted, the Z driver 132 operates the Z scanner 6 to bring the sample 2 into contact with the probe 12. The feedback circuit 120 supplies the Z driver 132 with a Z control signal that makes the output signal of the low-pass filter constant among the displacement signals that change due to contact. The Z driver 132 controls the Z scanner 6 according to the Z control signal. As a result, the probe 12 is controlled to be in contact with the surface of the sample 2.

With reference to FIG. 3, the signal detection device 10A corresponding to the configuration example 1 detects a signal related to the thermal vibration of the cantilever 11 in a state where the probe 12 is in contact with the sample 2. The signal detection device 10A includes a lock-in amplifier 20 and an oscillator 25. The signal detection device 10A corresponds to the signal detection device 10 shown in FIG. 1, but is provided with an additional reference numeral such as “A” for convenience in order to distinguish it from the following other configuration examples. This also applies to other configuration examples.

The oscillator 25 is a voltage controlled oscillator (VCO: Voltage-Controlled Oscillator) that controls the transmission frequency with a control voltage. The oscillator 25 generates a signal cos (2πf _ref t) that changes with a frequency f _ref . This signal is used as a reference signal V _x of the lock-in amplifier 20.

The lock-in amplifier 20 is, for example, a two-phase lock-in amplifier, and includes multipliers 21 and 21A, low-pass filters (LPF) 22, 22A, a phase shifter 24, and a vector calculation circuit 27. .. The displacement signal of the cantilever 11 is input to the multipliers 21 and 21A. Further, the reference signal V _x output from the oscillator 25 is input to the multiplier 21. The signal V _y obtained by passing the reference signal V _x through the phase shifter 24 at + 90 ° is input to the multiplier 21A as a reference signal.

The multiplier 21 multiplies the reference signal V _x by the displacement signal, and the multiplied displacement signal is output to the LPF 22. The LPF 22 removes the high frequency component of the displacement signal and outputs it to the vector calculation circuit 27. The output signal of LPF22 is X (= _Arms cosφ). _Arms is the amplitude effective value of the displacement signal. φ is the phase difference between the reference signal V _x and the displacement signal. The multiplier 21A multiplies the reference signal V _y by the displacement signal, and the multiplied displacement signal is output to the LPF 22A. The LPF 22A removes the high frequency component of the displacement signal and outputs it to the vector calculation circuit 27. The output signal of LPF22A is _{Y (=} A rms _sinφ).

The vector calculation circuit 27 calculates the absolute value R and the argument θ of the complex input (X + jY). Here, the absolute value R is (X ² + Y ² ) ^1/2 , and the argument θ is arg (Y / X). The absolute value R (hereinafter, also referred to as “signal R”) corresponds to the amplitude effective value _Arms of the displacement signal. On the other hand, the declination θ corresponds to the phase difference φ between the reference signal V _x and the displacement signal.

If the cutoff frequency of LPF22,22A and _{f LPF,} the lock-in amplifier 20 is a band pass filter equivalent to extract only signal component included in the scope of _{f ref} ± _{f LPF} in frequency space. In this case, the signal R is the square root of the integral value of the squares of the random signal components included in the range of f _ref ± f _LPF centered on the frequency f _ref , that is, the root mean square (RMS) value. Equivalent to. That is, the signal R roughly corresponds to the thermal vibration amplitude (hereinafter, also referred to as “noise amplitude”) in the integrated frequency range (that is, _fref ± f _LPF ). The declination θ is a random value because it is the phase difference between the random signal component included in the range of f _ref ± f _LPF and the reference signal V _x . Therefore, no meaningful information can be obtained from the declination θ.

FIG. 4 is a diagram showing a thermal vibration spectrum of the cantilever 11. With reference to FIG. 4, the frequency spectrum 301 represents the frequency dependence of the displacement noise density of the cantilever 11. The horizontal axis shows the frequency, and the vertical axis shows the displacement noise density. Displacement noise density is maximized at the resonance frequency f _c of the cantilever 11. The area of the region 305 (shaded portion in FIG. 4) over the frequency range (f _ref ± f _LPF ) roughly corresponds to the R signal (that is, the noise amplitude).

Frequency f _ref of the reference signal has been set slightly higher resonant frequency f _c, the setting is performed as follows. The computer 110 records the displacement signal of the cantilever 11 at the scanning start point where the probe 12 and the sample 2 are in contact with each other according to the operator's instruction. The computer 110 acquires the thermal vibration spectrum at the scanning start point by Fourier transforming this displacement signal. The operator, from thermal oscillation spectrum, determines the resonance frequency _{f c} of the cantilever 11 at the scan start point (e.g., 100kHz so). Oscillator 25 in accordance with the instruction of the operator to set the frequency _{f ref} in the vicinity of the resonance frequency _{f c} (e.g., increase the number kHz). Note that oscillator 25 is slightly lower than the resonance frequency _{f c} the frequency _{f ref} (e.g., by a few kHz lower) may be set to.

FIG. 5 is a diagram for explaining a change in noise amplitude. Referring to FIG. 5, for example, to move from one scan point to another scanning point, if the resonant frequency f _c from the state of FIG. 4 was shifted in the negative direction, the frequency spectrum 301, as the frequency spectrum 303 Change. The area of the region 307 corresponding to the signal R after the change in the frequency spectrum 303 is smaller than the area of the region 305 corresponding to the signal R before the change (see FIG. 4).

Signal R (i.e., noise amplitude) decrease in the other case where the shifted resonance frequency f _c is in the negative direction as the frequency spectrum 303, shifted greatly resonance frequency f _c is in the positive direction as shown in the frequency spectrum 304 It can also occur when the integrated frequency range is to the left of the center of the resonance curve, or when the Q value changes and the sharpness of the resonance curve changes. However, for example, also the scanning point is changed to the next scanning point, not the resonance frequency f _c is large shifts in the positive direction, and, if it can be assumed that the Q value is not greatly changed, the change of the signal R is generally represents the change in the resonant frequency _{f c.}

Thus, the computer 110, based on a signal R from time to time detected from the scan starting point can be calculated the resonance frequency f _c of the cantilever 11 at each scanning point. For example, let R _s be the signal R detected at the scanning start point, and let f _cs be the resonance frequency f _c at the scanning start point. When the signal R changes from R _s by ΔR, the computer 110 calculates the resonance frequency as f _cs + Δ f. It should be noted that Δf, which is the change in the resonance frequency f _c when R _s changes by ΔR, is acquired in advance by actual measurement or simulation, and is stored in the memory.

FIG. 6 is a functional block diagram of the signal detection device and the computer according to the configuration example 1. With reference to FIG. 6, the signal detection device 10A includes a generation unit 202A (for example, corresponding to the oscillator 25) and an amplitude detection unit 204A (for example, corresponding to the lock-in amplifier 20) as main functional configurations. Including. The computer 110 includes a calculation unit 206A and an image generation unit 208A as main functional configurations. Note that these functional configurations may be realized by other hardware.

Generating unit 202A, the reference frequency set in the vicinity of the resonance frequency _{f c} of the cantilever 11 (e.g., a frequency _{f ref)} for generating a reference signal having a. The amplitude detection unit 204A detects the noise amplitude (that is, signal R) of the cantilever 11 in a predetermined range including the reference frequency (for example, _fref ± f _LPF ) based on the displacement signal of the cantilever 11 and the reference signal. To do. Calculator 206A, based on the detected noise amplitude, to calculate the resonance frequency f _c of the cantilever 11. The image generation unit 208A calculated the resonance frequency by scanning the probe 12 relative to the sample 2 in a state where the probe 12 provided at the tip of the cantilever 11 is in contact with the surface of the sample 2. An image (resonant frequency image) relating to f _c is generated.

According to the signal detection unit 10A and the computer 110, the noise amplitude of the cantilever 11 (i.e., signal R) by observing the changes in, without vibrating the cantilever 11 can calculate the resonant frequency f _c in real time. Further, an image of the resonance frequency corresponding to the signal R can be displayed on the display. In the above, when it can be assumed that the resonance frequency does not change even if the scanning point changes, the change in the signal R generally represents the change in the Q value. Assuming that the Q value at the scanning start point is Q _s , the computer 110 (for example, the calculation unit 206A) calculates the Q value as Q _s + ΔQ when the signal R changes from R _s to ΔR. Note that ΔQ, which is the amount of change in the Q value when R _s changes by ΔR, is stored in the memory in advance. In this case, the computer 110 (for example, the image generation unit 208A) may generate an image relating to the calculated Q value.

(Configuration Example 2)
In Structural Example 1, for example, assuming that Q value is not changed, the change of the signal R has been described structure for calculating the resonant frequency f _c is regarded as a change in the resonant frequency f _c. In Structural Example 2, a configuration of calculating the resonance frequency f _c without the above assumption.

FIG. 7 is a diagram showing a configuration example 2 of the signal detection device 10. Similar to the first configuration example, the probe 12 of the cantilever 11 is in contact with the sample 2. This also applies to the following configuration examples. With reference to FIG. 7, the signal detection device 10B corresponding to the configuration example 2 includes a lock-in amplifier 20_1, 20_2, an oscillator 25_1, 25_2, an adder / subtractor 31, 32, an adder 33, and a PI controller (Proportional). -Integral Controller) 34 and included. In FIG. 7, the configurations of the lock-in amplifiers 20_1 and 20_2 are shown in a simplified manner in order to facilitate the illustration, but these configurations are the same as those of the lock-in amplifier 20 in FIG. Although the oscillators 25_1 and 25_2 are described as separate oscillators for the sake of simplification of description, they may be configured to be realized by one oscillator.

Oscillator 25_1 generates a signal that varies at a frequency _{f 1.} This signal is used as a reference signal for the lock-in amplifier 20_1. Lock-in amplifier 20_1 multiplies the reference signal generated by the displacement signal and the oscillator 25_1, high frequency components are removed by LPF, and outputs the signal R ₁ by performing a vector operation. The signal R ₁ corresponds to the noise amplitude in the integrated frequency range centered on the frequency f ₁ (that is, f ₁ ± f _LPF ). The frequency f ₁ is set to be slightly lower than the resonance frequency f _c .

Oscillator 25_2 generates a signal that varies at the frequency _{f 2.} This signal is used as a reference signal for the lock-in amplifier 20_2. The lock-in amplifier 20_2 multiplies the displacement signal by the reference signal generated by the oscillator 25_2, removes the high frequency component by the LPF, executes a vector calculation, and outputs the signal R ₂ . The signal R ₂ corresponds to the noise amplitude in the integrated frequency range around the frequency f ₂ (ie, f ₂ ± f _LPF ). The frequency f ₂ is set slightly higher than the resonance frequency f _c .

FIG. 8 is a diagram for explaining the noise amplitude detected by the configuration example 2. Referring to FIG. 8, the area of the region 313 corresponds to the integral frequency range of the left than the resonance frequency _{f c} (i.e., _{f 1} ± _{f LPF)} noise amplitude in (i.e., signal _{R 1).} Area of the region 315 corresponds to the right side of the integrating frequency range than the resonance frequency _{f c} (i.e., _{f 2} ± _{f LPF)} noise amplitude (i.e., signal _{R 2).}

Here, when the signal R ₁ and the signal R ₂ are the same (that is, the area of the region 313 and the area of the region 315 are the same), the intermediate value between the frequency f ₁ and the frequency f ₂ is the resonance frequency _fc. It becomes. At this time, f _c = (f ₁ + f ₂ ) / 2. This is because, Q value of the cantilever 11 is high (e.g., 10 or higher) when is the resonance characteristics and displacement noise density curve can be regarded as symmetrical around the f _c. Therefore, the resonance frequency f _c is adjusted by adjusting the frequency f ₁ and the frequency f ₂ so that the signal R ₁ and the signal R ₂ coincide with each other while keeping the difference between the frequency f ₁ and the frequency f ₂ constant. Can be sought.

Referring again to FIG. 7, the adder-subtractor 31 calculates the difference between the signal R ₁ and the signal R _2, and outputs the difference to a PI controller 34. The PI controller 34 outputs a frequency (that is, (f ₁ + f ₂ ) / 2) at which this difference becomes 0 (that is, the signal _R1 and the signal R ₂ coincide). Subtracter 32, the offset frequency _{f off {= (f 2 -f} 1) / 2} from the frequency subtracts. This subtraction value is frequency _{f 1} of the reference signal oscillator 25_1. The adder 33 adds the frequency and the offset frequency _off . This added value becomes the frequency _{f 2} of the reference signal oscillator 25_2. The output signal of the PI controller 34 is input to the computer 110, the computer 110 calculates the output signal as a resonance frequency _{f c.}

According to the signal detection device 10B, at each scanning point, the difference between the frequencies f ₁ and f ₂ is constant, and the signal R ₁ and the signal R ₂ and the frequencies f ₁ to become the _same, f ₂ is set To. Thus, the computer 110 may generate an image of the resonant frequency _{f c} in real time based on the frequency _f 1, _{f 2.} It is also possible to estimate the change in the Q value by observing the changes in the signals R ₁ and R ₂ . For example, let R _s be the signals R ₁ and R ₂ at the scanning start point, and let Q _s be the Q value at the scanning start point. Computer 110 observes the change of the signal _R 1, _{R 2} accepts input signals _R 1, _{R 2.} When the signals R ₁ and R ₂ change by ΔR from R _s , the computer 110 calculates the Q value as Q _s + ΔQ. It should be noted that ΔQ, which is the amount of change in the Q value when R _s changes by ΔR, is acquired in advance by actual measurement or the like and stored in the memory. As a result, the Q value can be obtained in real time.

FIG. 9 is a functional block diagram of the signal detection device and the computer according to the configuration example 2. With reference to FIG. 9, the signal detection device 10B includes a generation unit 202B, an amplitude detection unit 204B, and a setting unit 210B as main functional configurations. The generation unit 202B corresponds to, for example, oscillators 25_1, 25_2. The amplitude detection unit 204B corresponds to, for example, lock-in amplifiers 20_1 and 20_2. The setting unit 210B corresponds to the adder / subtractor 31, 32, the adder 33, and the PI controller 34. The computer 110 includes a calculation unit 206B and an image generation unit 208B as main functional configurations.

Specifically, the generating unit 202B has a first reference frequency which is set in the vicinity of the resonance frequency _{f c} (e.g., a frequency _{f 1)} and the first reference signal having a second reference frequency (e.g., frequency _f 2) To generate a second reference signal having. The amplitude detection unit 204B detects the noise amplitude (for example, signal R ₁ ) within a predetermined range (for example, f ₁ ± f _LPF ) including the frequency f ₁ based on the displacement signal of the cantilever 11 and the first reference signal. Then, based on the displacement signal of the cantilever 11 and the second reference signal, the noise amplitude (for example, signal R ₂ ) within a predetermined range including the frequency f ₂ (for example, f ₂ ± f _LPF ) is detected. Setting unit 210B is in a state of fixing the difference of frequencies _{f 1} and frequency _{f 2,} to set the frequency _{f 1} and frequency _{f 2} as the signal _{R 1} and the signal _{R 2} are identical. The calculation unit 206B calculates the resonance frequency f _c {= (f ₁ + f ₂ ) / 2} of the cantilever 11 based on the set frequencies f ₁ and f ₂ . Image generation unit 208B, by which relatively scans the probe 12 and the sample 2, and generates an image (resonance frequency image) relating to the resonance frequency f _c which is calculated.

According to the signal detection device 10B and a computer 110, noise amplitude at two integration frequency ranges (i.e., signal R _1, R ₂₎ with, without the cantilever 11 to vibrate, high accuracy and real-time resonance frequency f _c Can be calculated. This allows displaying an image of high precision resonance frequency f _c to the display in real time.

(Configuration Example 3)
In the configuration example 1, a configuration in which the frequency of the reference signal is fixed has been described. In Structural Example 3, the reference signal frequency-modulated (FM: Frequency Modulation) to, by using a reference signal which is frequency modulated, a configuration of calculating the resonance frequency f _c of the cantilever 11. In the following, in order to facilitate understanding, first, a part of the configuration of the configuration example 3 will be described with reference to FIGS. 10 to 13. Next, the configuration of another part of the configuration example 3 will be described with reference to FIGS. 14 and 15. Then, with reference to FIG. 16, the final configuration of the configuration example 3 will be described.

FIG. 10 is a diagram showing a partial configuration of the configuration example 3 of the signal detection device 10. With reference to FIG. 10, the signal detection device 10C corresponding to the configuration example 3 includes a lock-in amplifier 20 and oscillators 41 and 43. Oscillator 41 supplies a cosine wave of a frequency _{f m} of the (modulated signal) as a control voltage of the oscillator 43, the oscillator 43. The center frequency of the oscillator 43 and _{f ctr,} the maximum frequency shift with respect to the control voltage and _{f dev.} In this case, the frequency _{f vco} of the oscillator frequency, i.e. the reference signal input to the lock-in amplifier 20 of oscillator _{43 f vco = f ctr + f dev} cos (2πf m t) , and the variation in the frequency _{f m} (modulation) .. Therefore, the signal R output from the lock-in amplifier 20 changes according to the fluctuation of the reference signal.

11 to 13 are diagrams showing noise amplitudes that change according to fluctuations in the reference signal. Specifically, FIG. 11, the center frequency _{f ctr} of the reference signal indicates a change in noise amplitude is smaller than the resonance frequency _{f c (i.e., f} ctr _{<f c).} FIG. 12 shows the change in noise amplitude when the center frequency f _ctr is larger than the resonance frequency f _c (that is, f _{c tr} > f _c ). FIG. 13 shows the change in noise amplitude when the center frequency f _ctr is the same as the resonance frequency f _c (that is, f _{c tr} = f _c ).

With reference to FIG. 11, the waveform 323 shows the waveform of the signal R (that is, the noise amplitude) output from the lock-in amplifier 20. Waveform 325 shows the waveform of the reference signal that varies at the frequency _{f m} (period _{T m = t 2 -t 1)} . For _{f ctr} <f _c, the signal R changes as a cosine wave reference signal and in phase. On the other hand, referring to FIG. 12, when f _ctr > f _c , the signal R changes like a cosine wave, but changes in the opposite phase to the reference signal. Further, referring to FIG. _13, the case of _f ctr = _{f c,} not appear component of the frequency _{f m} is the signal R, the signal R is twice the frequency (frequencies below _{f m,} both "frequency 2f _m" It changes with).

FIG. 14 is a diagram showing a configuration in which a lock-in amplifier is added to the configuration of FIG. With reference to FIG. 14, the signal detection device 10C further includes a lock-in amplifier 50 in addition to the configuration shown in FIG. The lock-in amplifier 50 is, for example, a one-phase lock-in amplifier, and includes a multiplier 51 and an LPF 52. Lock-in amplifier 50, the component of the frequency f _m in the signal R (i.e., the modulation component) is detected.

Specifically, the signal R output from the lock-in amplifier 20 is input to the multiplier 51. Further, the modulation signal output from the oscillator 41 is input to the multiplier 51 as the reference signal V _xm of the lock-in amplifier 50. The multiplier 51 multiplies the reference signal V _xm by the signal R, and the multiplied signal R is output to the LPF 52. LPF52 outputs the signal to remove high-frequency components of the signal _{R X m (= A m cosφ} m). A _m is the amplitude effective value of the frequency f _m component included in the signal R. φ _m is the phase difference between the reference signal V _{x m} and the signal R. The signal X _m corresponds to the modulation component contained in the signal R.

FIG. 15 is a diagram showing the center frequency dependence of the signal X _m output from the lock-in amplifier 50. With reference to FIG. 15, curve 331 shows the change of signal X _m with respect to the center frequency. For example, when the resonance frequency f _c shifts in the negative direction by Δf as in the frequency spectrum 303, the curve 331 also shifts in the negative direction. At this time, the signal X _m changes by ΔX _m .

Here, when the center frequency _{f ctr} is smaller than the resonance frequency _{f c,} the modulation component of the signal R is the reference signal _{V xm} same phase (i.e., φ _m = 0 °), and the signal _{X m} becomes positive. If the center frequency _{f ctr} is greater than the resonance frequency _{f c,} the modulation component of the signal R is the reference signal _{V xm} opposite phase (i.e., φ _m = 180 °), and the signal _{X m} is negative. When the center frequency f _ctr is located in the vicinity region (shaded region in FIG. 15) of the resonance frequency f _c , the signal X _m changes monotonically. When the center frequency f _ctr coincides with the resonance frequency f _c , the signal X _m becomes zero. Therefore, if the center frequency f _ctr as signal X _m is zero is controlled, so that the center frequency f _ctr coincides with the resonance frequency f _c.

FIG. 16 is a diagram showing an overall configuration of configuration example 3 of the signal detection device 10. With reference to FIG. 16, the signal detection device 10C further includes a PI controller 55 and an adder 57 in addition to the configuration shown in FIG. The PI controller 55 outputs a frequency f _dc feedback-controlled so that the signal X _m becomes zero. Specifically, the PI controller 55 has a current center such that when the signal X _m is negative, the center frequency _fctr coincides with the resonant frequency f _c (ie, the signal X _m is zero). The frequency f _dc that lowers the frequency f _ctr is output. PI controller 55, when the signal _{X m} is positive, so that the center frequency _{f ctr} coincides with the resonance frequency _{f c,} and outputs a frequency _{f dc} to increase the current center frequency _{f ctr.} Frequency _{f dc} is the frequency for adjusting the center frequency _{f ctr} of the reference signal output from the oscillator 43 to the resonant frequency _{f c.} The adder 57 inputs the added value of the frequency _fdc and the modulated signal to the oscillator 43. Thus, the reference signal outputted from the oscillator 43 has a center frequency f _ctr that matches with the resonance frequency f _c, and the signal varying at the frequency f _m.

The frequency f _dc is also supplied to the computer 110. Computer 110 calculates the center frequency _{f ctr} in the initial state stored in advance in the memory, the sum of the frequency _{f dc} as the resonant frequency _{f c.} Thus, the computer 110 may generate an image of the resonant frequency f _c in real time.

FIG. 17 is a functional block diagram of the signal detection device and the computer according to the configuration example 3. With reference to FIG. 17, the signal detection device 10C includes a generation unit 202C, an amplitude detection unit 204C, a modulation component detection unit 212C, and an adjustment unit 214C as main functional configurations. The generator 202C corresponds, for example, to oscillators 41, 43 and adder 57. The amplitude detection unit 204C corresponds to, for example, the lock-in amplifier 20. The modulation component detection unit 212C corresponds to, for example, the lock-in amplifier 50. The adjusting unit 214C corresponds to, for example, the PI controller 55 and the adder 57. The computer 110 includes a calculation unit 206C and an image generation unit 208C as main functional configurations.

Specifically, the generating unit 202C is in the vicinity of the resonance frequency f _c of the cantilever 11, modulates the reference frequency of the reference signal input to the amplitude detector 204C at a predetermined frequency (e.g., frequency f _m). The amplitude detection unit 204C detects the noise amplitude of the cantilever 11 within a predetermined range including the reference frequency (for example, _fref ± f _LPF ) based on the displacement signal of the cantilever 11 and the modulated reference signal. The modulation component detection unit 212C detects the modulation component (for example, signal X _m ) of the noise amplitude (that is, signal R) when the reference frequency of the reference signal is modulated at a predetermined frequency. The adjusting unit 214C adjusts the center frequency _fctr of the modulated reference signal so that the modulation component of the noise amplitude becomes zero. Calculator 206C calculates the adjusted center frequency _{f ctr} as a resonance frequency _{f c} of the cantilever 11. Image generation unit 208C, by which relatively scans the probe 12 and the sample 2, and generates an image (resonance frequency image) relating to the resonance frequency f _c which is calculated.

According to the signal detection device 10C, a frequency-modulated reference signal is input to the lock-in amplifier 20 to detect the noise amplitude (signal R), and the center frequency of the reference signal is set so that the modulation component appearing in the signal R becomes zero. f _ctr is controlled. Thus, without vibrating the cantilever 11 can be calculated with high accuracy the resonant frequency f _c in real time, it can be displayed resonant frequency images on the display.

Although the configuration using the PI controller 55 has been described in the signal detection device 10C, if it can be assumed that the Q value does not change significantly even if the scanning point changes, the resonance frequency is simply recorded by recording the signal X _m. It is also possible to calculate f _c . For example, a signal _{X m} detected by the scanning start point and _{X ms,} the resonance frequency _{f c} at the scan start point and _{f cs.} Here, the center frequency f _ctr at the scanning start point is assumed to be preset to the resonance frequency f _cs. In this case, referring to FIG. 15, when the resonance frequency f _c shifts negatively from f _cs (Δf <0), the signal X _m shifts negatively from X _ms (ΔX _m <0). On the other hand, when the resonance frequency f _c is positively shifted from f _cs (Δf> 0), the signal X _m is positively shifted from X _ms (ΔX _m > 0). Therefore, the computer 110, if the signal _{X m} changes [Delta] X _m from _{X ms,} can be calculated resonant frequency as _{f cs} + _Δf. Incidentally, Delta] f signal X _ms is the change of the resonance frequency f _c in the case of change [Delta] X _m is obtained in advance by actual measurement or simulation, and is stored in the memory.

Further, when it can be assumed that the resonance frequency does not change even if the scanning point changes, the change in the signal X _m generally represents the change in the Q value. Therefore, when the Q value at the scan start point and _{Q s,} the computer 110, if the signal _{X m} changes [Delta] X _m from _{X ms,} calculates a Q value as _{Q s} + Delta] Q. It should be noted that ΔQ, which is the change in the Q value when the signal X _ms changes by ΔX _m , is stored in the memory in advance.

FIG. 18 is a diagram showing measurement example 1 of sample 2. Here, a thin film (film thickness: about 300 nm) obtained by spin-coating a N-methyl-2-pyrrolidone solution of a photopolymer on a silicon substrate and annealing it was used as a sample to be measured. FIG. 18A is a surface shape image of this sample by contact mode AFM. This surface shape image is an image obtained by plotting the position in the Z direction corresponding to the Z control signal from the feedback circuit 120 in the coordinate system of the XYZ axes.

The cantilever used is a silicon cantilever, the spring constant of which is about 1.5 N / m, and the free resonance frequency is about 27.2 kHz. The contact force of the probe was set to about 10 nN. The scanning region of FIG. 18A is 1000 nm × 1000 nm, and the number of pixels is 256 × 256. The time required for the measurement was about 8 minutes. From this surface shape image, it was found that the sample surface was approximately flat, but there were dome-shaped raised regions in some places. FIG. 18B is a cross-sectional profile of the straight line portion 401 of FIG. 18A. From FIG. 18 (b), it was found that the vicinity of the center of this raised region was about 15 nm higher than the periphery.

FIG. 18 (c) shows a contact resonance frequency image acquired at the same time as the image shown in FIG. 18 (a) using the signal detection device 10C. 110kHz contact resonance frequency of the scanning start point approximately, because the Q value was about _90, and _{f ctr = 110kHz, f dev =} 2.5kHz, and f m = 1.1 kHz. FIG. 18D is a cross-sectional profile of the straight portion 403 of FIG. 18C. The position of the straight line portion 401 and the position of 403 in sample 2 are the same. It was found that the contact resonance frequency was lowered by about 2.5 kHz in this raised region.

(Configuration Example 4)
In the signal detection device 10C according to the configuration example 3, the center frequency f _ctr of the reference signal of the lock-in amplifier 20 is controlled so as to coincide with the resonance frequency f _c, it can detect the noise amplitude at the vicinity of the resonance frequency f _c. As shown in the above equation (3), the noise amplitude integrated in the entire frequency domain has no Q value dependence. However, the displacement noise density _{N th} (omega ₀₎ in the vicinity of the resonance frequency _{f c} from the equation (2) is expressed by the following equation (4).

The equation (4), the displacement noise density _{N th} (omega ₀₎ is, Q value (i.e., the sharpness of the resonance peak) seen to be dependent on the square root of. Therefore, if measuring the noise amplitude at the vicinity of the resonance frequency f _c, information about the viscosity of the sample is obtained. The configuration example 4 of the signal detection device 10 adopts the first method for obtaining the Q value in the configuration example 3. Specifically, in the configuration example 4, the Q value is calculated based on the time average amplitude of the signal R output from the lock-in amplifier 20 of FIG.

FIG. 19 is a diagram showing a configuration example 4 of the signal detection device 10. The signal detection device 10D corresponding to the configuration example 4 is a signal detection device 10C (see FIG. 16) corresponding to the configuration example 3 with a lock-in amplifier 20D added. The lock-in amplifier 20D is, for example, a two-phase lock-in amplifier. The time constant of the lock-in amplifier 20D is set larger than the time constant of the lock-in amplifier 20. Specifically, the cutoff frequency of the LPF22D in the lock-in amplifier 20D is set to be smaller than the cutoff frequency of the LPF22 of the lock-in amplifier 20. Other configurations of the lock-in amplifier 20D are the same as those of the lock-in amplifier 20.

In the signal detection device 10D, since the center frequency f _ctr is controlled so as to coincide with the resonance frequency f _c, the signal R output from the lock-in amplifier 20 is modulated at a frequency 2f _m (see FIG. 13) .. However, the sampling rate used in recording the signal R as a digital image, since much slower than the frequency 2f _m, the low-frequency components contained in the consequently signals R amplitude, i.e., the time average amplitude of the signal R Is recorded. Therefore, the time average amplitude of the signal R is considered to correspond to that eliminate frequency 2f _m component through LPF to a signal R.

Therefore, to be smaller than the frequency 2f _m cutoff frequency of LPF22D, signals _{R v} outputted from the lock-in amplifier 20D corresponds to the time average amplitude of the signal R. Instead of adding the lock-in amplifier 20D as in the configuration example 4, an LPF that receives the input of the signal R output from the lock-in amplifier 20 may be provided. The LPF is a signal obtained by removing the frequency 2f _m component from the signal R, is detected as a time average amplitude of the signal R.

FIG. 20 is a diagram for explaining the relationship between the time average amplitude and the Q value. With reference to FIG. 20, frequency spectra 341 and 342 are thermal vibration spectra at scanning points P1 and P2, respectively. Waveforms 343 and 344 indicate waveforms of the signal R at scanning points P1 and P2, respectively. For example, assume that the Q value corresponding to the frequency spectrum 341 is 100 and the Q value corresponding to the frequency spectrum 342 is 90.

Here, it is assumed that the scanning point P1 is moved to the scanning point P2. In the scanning point P1, the signal R at the resonance frequency _{f c} when Q value is 100 to "1", the moment the signal R becomes smallest _{(i.e., f vco = f ctr ± f} dev) is in the signal R "0 If it is .5 ”, the time average amplitude of the signal R is about 0.75 (= (1 + 0.5) / 2). In scanning point P2, the Q value is changed to 90, the signal R at the resonance frequency _{f c} is about 0.95 a ^{(90/100) 1/2.} On the other hand, the signal R at the moment when the signal R becomes the smallest hardly changes and is about 0.51. Therefore, the time average amplitude of the signal R is about 0.73 (= (0.95 + 0.51) / 2). Therefore, the rate of change of the time average amplitude when the Q value decreases by 10% is estimated to be about 3%.

In Configuration Example 4, the Q value is calculated based on the time average amplitude. For example, the time average amplitude of the signal R at the scanning start point is R _vs, and the Q value at the scanning start point is Q _s . The computer 110 calculates the time average amplitude as Q _s + ΔQ when R _vs changes by ΔR _v . It should be noted that ΔQ, which is the change in the Q value when R _vs changes by ΔR _v , is stored in the memory in advance by actual measurement or the like. As a result, the Q value can be calculated in real time.

FIG. 21 is a diagram showing measurement example 2 of sample 2. Specifically, the image shown in FIG. 21 is a time average amplitude image detected by the signal detection device 10D. The image shown in FIG. 21 was obtained at the same time as the image shown in FIG. According to the time average amplitude image shown in FIG. 21, the time average amplitude is slightly smaller in the raised region. Therefore, it is presumed that the Q value is low in the raised region and the viscosity in this region is high.

The signal detection device 10D has, as main functional configurations, the functional configurations of configuration example 3 shown in FIG. 17 (generation unit 202C, amplitude detection unit 204C, modulation component detection unit 212C, adjustment unit 214C) and time average amplitude detection. Including part. Time average amplitude detector, for example, lock-in amplifier 20D (or, LPF to remove the frequency 2f _m component from the signal R) corresponding to. The time average amplitude detector, the reference frequency of the reference signal outputted from the oscillator 43 is a predetermined frequency (e.g., frequency f _m) if it is modulated, the time average amplitude of the noise amplitude (e.g., signal R _v) To detect. The calculation unit 206C (for example, the computer 110) calculates the Q value of the cantilever 11 based on the time average amplitude. According to the signal detection unit 10D and the computer 110 can calculate the resonant frequency _{f c} and Q values in real time.

(Configuration Example 5)
The configuration example 5 of the signal detection device 10 adopts the second method for obtaining the Q value in the configuration example 3. Specifically, in the configuration example 5, Q values based on the amplitude effective value of the components that are modulated at a frequency 2f _m in the signal R is calculated.

FIG. 22 is a diagram showing a configuration example 5 of the signal detection device 10. With reference to FIG. 22, the signal detection device 10E corresponding to the configuration example 5 is a signal detection device 10C (see FIG. 16) corresponding to the configuration example 3 to which the lock-in amplifier 20E and the multiplier 65 are added. .. In the signal detection device 10E, since the center frequency _{f ctr} is controlled to coincide with the resonance frequency _{f c,} the signal R is modulated at a frequency 2f _m (see FIG. 13). Lock-in amplifier 20E detects an amplitude effective value of the components that are modulated at a frequency 2f _m contained in the signal R.

The multiplier 65, by squaring the modulated signal of a frequency f _m which is outputted from the oscillator 41, and outputs a signal of frequency 2f _m (2 harmonic signal). The double wave signal is used as a reference signal for the lock-in amplifier 20E. The lock-in amplifier 20E is, for example, a two-phase lock-in amplifier, and is substantially the same as the lock-in amplifier 20. The lock-in amplifier 20E, the reference signal of the lock-in amplifier 20 is output from the signal R, and the frequency 2f _m is input. Lock-in amplifier 20E detects the frequency 2f _m component included in the signal R. Specifically, the lock-in amplifier 20E outputs the amplitude effective value R _{2 m} of the frequency 2 fm component.

As shown in FIG. 13, when the center frequency f _ctr is equal to the resonant frequency f _c, the noise amplitude detected varies near the resonance frequency f _c. Therefore, the amplitude effective value R _2m frequency 2f _m component represents noise amplitude attenuation in the peak and the skirt of the peak of the frequency spectrum 301 (sharpness of resonance). That is, the effective amplitude value R _2m corresponds to the rate of change (slope) between the peak and the tail of the peak.

As in the configuration example 4, it is assumed that the scanning point P1 is moved to the scanning point P2. In the scanning point P1, the signal R and _{R p0} Q value at the resonance frequency _{f c} of the case 100, the instant the signal R becomes smallest _{(i.e., f vco = f ctr ± f} dev) in the signal R is 0.5R _Assuming that it is _p0 , the effective amplitude value of the signal R is about 0.18 (≈ (1-0.5) / (2 * 2 ^1/2 )) R _p0 . In scanning point P2, the Q value is to have changed to 90, the signal R at the resonance frequency _{f c} is about 0.95 R _p0 is ^(90/100) 1/2 _{R p0.} On the other hand, at the moment when the signal R becomes the smallest, the signal R hardly changes and is about 0.51R _p0, so that the effective amplitude value of the signal R is about 0.15 (≈ (0.95-0.51) / (. 2 * 2 ^1/2 )) R _p0 . Therefore, the rate of change of the amplitude effective value when the Q value decreases by 10% is estimated to be about 13%. In the case of Configuration Example 4, the rate of change in the time average amplitude when the Q value decreased by 10% was about 3%, indicating that Configuration Example 5 has higher sensitivity than Configuration Example 4. ..

In Configuration Example 5, the Q value is calculated based on the effective amplitude value. For example, the amplitude effective value of the frequency 2f _m component included in the signal R at the scanning start point and R _{2 ms,} the Q value at the scan start point and Q _s. The computer 110 calculates the Q value as Q _s + ΔQ when the effective amplitude value R _{2 ms} changes by Δ R _{2 m} . It should be noted that ΔQ, which is the change in the Q value when R _2ms changes by ΔR _2m , is stored in the memory in advance by actual measurement or the like. As a result, the Q value can be calculated in real time. Further, since the amplitude effective value R _2m corresponds to the slope between the peak and the tail of the peak, it can be defined as R _2m = (dR / df) / R _p0 = Q / (2f _c R _p0 ). Therefore, it is possible to determine from the resonance frequency f _c and amplitude effective value R _2m, the Q values directly.

FIG. 23 is a diagram showing measurement example 3 of sample 2. The image shown in FIG. 23 is an image obtained by the measurement performed following the measurement result of FIG. Specifically, the image of FIG. 23A shows a surface shape image by the contact mode AFM. The image of FIG. 23B shows a contact resonance frequency image. The image of FIG. 23 (c) is an amplitude effective value image obtained by the configuration example 5. With reference to FIG. 23 (c), since the amplitude effective value is small in the raised region, it is inferred that the Q value is low and the viscosity is high in this region. Compared with the time average amplitude image shown in FIG. 21, it can be seen that the amplitude effective value image is drawn more clearly and has high sensitivity.

The signal detection device 10E has, as main functional configurations, the functional configurations (generation unit 202C, amplitude detection unit 204C, modulation component detection unit 212C, adjustment unit 214C) of configuration example 3 shown in FIG. 17, and amplitude effective value detection. Including the part. The amplitude effective value detection unit corresponds to, for example, the lock-in amplifier 20E. Amplitude effective value detection unit, the reference frequency of the reference signal outputted from the oscillator 43 is a predetermined frequency (e.g., frequency f _m) if it is modulated by, the noise amplitude, double frequency component of a predetermined frequency (e.g. detects the amplitude effective value _{R 2m)} of the frequency 2f _m component. The calculation unit 206C (computer 110) calculates the Q value of the cantilever 11 based on the double frequency component. According to the signal detection unit 10E and the computer 110 can calculate the resonant frequency f _c and Q values at the time of contact between the cantilever 11 and the sample 2 in real time.

(Configuration Example 6)
The configuration example 6 of the signal detection device 10 adopts the third method for obtaining the Q value in the configuration example 3. In Configuration Example 6, the Q value is calculated based on the noise amplitude around the center frequency detected based on the displacement signal of the cantilever 11.

FIG. 24 is a diagram showing a configuration example 6 of the signal detection device 10. With reference to FIG. 24, the signal detection device 10F corresponding to the configuration example 6 is a signal detection device 10C (see FIG. 16) corresponding to the configuration example 3 with an oscillator 75 and a lock-in amplifier 20F added. In the signal detection device 10F, the center frequency _{f ctr} is controlled so as to coincide with the resonance frequency _{f c} (see FIG. 13). Lock-in amplifier 20F, the center frequency _{f ctr} included in the displacement signal (i.e., the resonance frequency _{f c)} detecting the noise amplitude of the surrounding.

The oscillator 75 is composed of the same oscillator as the oscillator 43. Specifically, the maximum frequency shifts in the oscillator 75 and the oscillator 43 are the same. Further, the frequency _fdc output from the PI controller 55 is input to the oscillator 75. Therefore, the center frequencies _fctr of the oscillator 75 and the oscillator 43 are the same. However, unlike the oscillator 43, the modulation signal is not input to the oscillator 75, so that the output signal of the oscillator 75 is not frequency-modulated. The output signal of the oscillator 75 is used as a reference signal of the lock-in amplifier 20F.

The lock-in amplifier 20F is, for example, a two-phase lock-in amplifier, and is substantially the same as the lock-in amplifier 20. The displacement signal of the cantilever 11 and the reference signal output from the oscillator 75 are input to the lock-in amplifier 20F. The lock-in amplifier 20F multiplies the displacement signal and the reference signal, removes the high frequency component by the LPF, executes the vector operation, and outputs the signal R _p . The signal R _p corresponds to the noise amplitude in the integrated frequency range (ie, f _ctr ± f _LPF ) centered on the center frequency f _ctr (ie, resonance frequency f _c ). That is, the signal R _p corresponds to the peak amplitude of the thermal vibration spectrum.

As in the configuration example 4, it is assumed that the scanning point P1 is moved to the scanning point P2. In the scanning point P1, Q value is the signal R (i.e., signal _{R p} corresponding to the peak amplitude) at the resonance frequency _{f c} of the case 100 a and _{R p0.} In scanning point P2, the Q value is to have changed to 90, the signal _{R p} at the resonance frequency _{f c} is about 0.95 R _p0 is ^(90/100) 1/2 _{R p0.} Therefore, the rate of change in peak amplitude when the Q value decreases by 10% is estimated to be about 5%.

In Configuration Example 6, the Q value is calculated based on the peak amplitude. For example, let the signal R _p at the scanning start point be R _ps, and let the Q value at the scanning start point be Q _s . The computer 110 calculates the Q value as Q _s + ΔQ when R _ps changes by ΔR _p . It should be noted that ΔQ, which is the amount of change in the Q value when R _ps changes by ΔR _p , is stored in the memory in advance by actual measurement or the like. As a result, the Q value can be calculated in real time.

The above-mentioned signal detection device 10F has, as main functional configurations, a functional configuration (generation unit 202C, amplitude detection unit 204C, modulation component detection unit 212C, adjustment unit 214C) of configuration example 3 shown in FIG. 17, and a signal generation unit. , Includes a peak amplitude detector. The signal generator corresponds to, for example, the oscillator 75. The peak amplitude detection unit corresponds to, for example, the lock-in amplifier 20F. The signal generation unit generates a reference signal having the center frequency _fctr adjusted by the adjustment unit _214C as a reference frequency. Based on the displacement signal of the cantilever 11 and the reference signal generated by the signal generation unit, the peak amplitude detection unit has a noise amplitude (for example, _fctr ± f _LPF ) within a predetermined range including the reference frequency of the reference signal. For example, the signal R _p ) is detected. The calculation unit 206C (for example, the computer 110) calculates the Q value of the cantilever 11 based on the noise amplitude. According to the signal detection unit 10F and the computer 110 can calculate the resonant frequency _{f c} and Q values in real time.

<Advantage>
According to this embodiment, the resonance frequency and the Q value can be calculated in real time based on the noise amplitude of the cantilever 11 without vibrating the cantilever 11. Therefore, it is not necessary to add a special high-frequency excitation mechanism such as a piezoelectric element to the existing AFM, and the viscoelasticity of the sample surface and the structure under the sample surface can be visualized at the same time as normal sample surface observation. In addition, the measurement time of the sample can be significantly reduced.

<Other embodiments>
(1) In the above-described embodiment, the configuration for calculating the resonance frequency and the Q value of the cantilever by using the noise amplitude of the cantilever of the AFM has been described, but the configuration is not limited to this. For example, not only cantilever but all vibrating bodies (mechanical resonators) are thermally vibrated. Therefore, the resonance frequency and Q value of the vibrating body can be calculated based on the noise amplitude of the vibrating body (for example, a MEMS (Micro Electro Mechanical Systems) sensor or the like) in which it is difficult to excite the vibration from the outside. For example, by preparing a displacement detection device for detecting the displacement of the vibrating body, a signal detecting device 10, and a computer 110, the resonance frequency and the Q value can be calculated in real time based on the noise amplitude of the vibrating body. Can be done.

(2) In the above-described embodiment, the lock-in amplifier 20 composed of the two-phase lock-in amplifier is used, and the noise amplitude (R signal) is set as the root mean square (RMS) value of the displacement noise density in a certain frequency range. The configuration to be detected has been described, but the configuration is not limited to this configuration. For example, a spectrum analyzer may be used instead of the lock-in amplifier 20 to detect an R signal in a certain frequency range.

(3) In the above-described embodiment, the configuration for calculating the resonance frequency and the Q value of the cantilever by using the noise amplitude when the cantilever of the AFM is brought into contact with the sample has been described, but the configuration is not limited to this. .. Specifically, even if the cantilever is not in contact with the sample, the cantilever resonates when an interaction force acts on the probe of the cantilever (for example, when the cantilever is close to the sample placed in water). The frequency changes. Therefore, the resonance frequency and the Q value of the cantilever may be calculated by using the noise amplitude detected without bringing the cantilever into contact with the sample. In this case, the displacement detector 15 may detect as a displacement signal a signal indicating a time change (velocity) of the displacement of the tip of the cantilever 11.

(4) The configuration exemplified as the above-described embodiment is an example of the configuration of the present invention, can be combined with another known technique, and a part thereof is not deviated from the gist of the present invention. It is also possible to change the configuration by omitting it. Further, in the above-described embodiment, the configuration described in the other embodiments may be appropriately adopted and implemented.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is shown by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

2 sample, 5 scanning mechanism, 6 Z scanner, 7 XY scanner, 8 table, 10, 10A to 10F signal detector, 11 cantilever, 12 probe, 14 laser light source, 15 displacement detector, 20, 20D to 20F, 50 Lock-in amplifier, 21,21A, 51,65 multiplier, 24 phase shifter, 25,41,43,75 oscillator, 27 vector arithmetic circuit, 31,32 adder / subtractor, 33,57 adder, 34,55 PI controller , 110 computer, 120 feedback circuit, 132 Z driver, 134 XY driver, 202A, 202B, 202C generator, 204A, 204B, 204C amplitude detector, 206A, 206B, 206C calculation unit, 208A, 208B, 208C image generator, 210B setting unit, 212C modulation component detection unit, 214C adjustment unit.

Claims (8)

1. A generator that generates a reference signal having a reference frequency set near the resonance frequency of the vibrating body,
   An amplitude detection unit that detects the thermal vibration amplitude of the vibrating body within a predetermined range including the reference frequency based on the displacement signal of the vibrating body and the reference signal generated by the generating unit.
   A measuring device including a calculation unit that calculates a resonance frequency of the vibrating body based on the detected thermal vibration amplitude.
2. The generation unit generates a first reference signal having a first reference frequency set in the vicinity of the resonance frequency and a second reference signal having a second reference frequency set in the vicinity of the resonance frequency.
   The amplitude detection unit detects the first thermal vibration amplitude of the vibrating body within the predetermined range including the first reference frequency based on the displacement signal of the vibrating body and the first reference signal, and detects the vibration. Based on the body displacement signal and the second reference signal, the second thermal vibration amplitude of the vibrating body within the predetermined range including the second reference frequency is detected.
   With the difference between the first reference frequency and the second reference frequency fixed, the first reference frequency and the second reference frequency are set so that the first thermal vibration amplitude and the second thermal vibration amplitude match. It also has a setting unit to set
   The measuring device according to claim 1, wherein the calculation unit calculates the resonance frequency of the vibrating body based on the set frequency of the first reference signal and the frequency of the second reference signal.
3. The generator modulates the reference frequency of the reference signal with a predetermined frequency in the vicinity of the resonance frequency of the vibrating body.
   A modulation detection unit that detects a modulation component of the thermal vibration amplitude when the reference frequency of the reference signal is modulated at the predetermined frequency.
   Further provided with an adjusting unit for adjusting the center frequency of the reference signal being modulated so that the modulation component of the thermal vibration amplitude becomes zero.
   The measuring device according to claim 1, wherein the calculation unit calculates the adjusted center frequency as a resonance frequency of the vibrating body.
4. Further, a first detection unit for detecting the time average amplitude of the thermal vibration amplitude when the reference frequency of the reference signal is modulated at the predetermined frequency is provided.
   The measuring device according to claim 3, wherein the calculation unit calculates a Q value of the vibrating body based on the time average amplitude.
5. Further, a second detection unit for detecting a frequency component twice the predetermined frequency in the thermal vibration amplitude when the reference frequency of the reference signal is modulated at the predetermined frequency is provided.
   The measuring device according to claim 3, wherein the calculation unit calculates the Q value of the vibrating body based on the frequency component twice the thermal vibration amplitude.
6. A signal generation unit that generates another reference signal whose reference frequency is the center frequency adjusted by the adjustment unit, and
   A third detection unit that detects the thermal vibration amplitude within the predetermined range including the reference frequency of the other reference signal based on the displacement signal of the vibrating body and another reference signal generated by the signal generation unit. And with more
   The measuring device according to claim 3, wherein the calculation unit calculates a Q value of the vibrating body based on the thermal vibration amplitude within the predetermined range including the reference frequency of the other reference signal.
7. The measuring device according to any one of claims 1 to 6 is provided.
   The vibrating body is a cantilever,
   An atomic force microscope further comprising an image generation unit that generates an image relating to the resonance frequency of the cantilever calculated by the measuring device by scanning a probe provided at the tip of the cantilever relative to a sample.
8. A step of generating a reference signal having a reference frequency set near the resonance frequency of the vibrating body, and
   A step of detecting the thermal vibration amplitude of the vibrating body within a predetermined range including the reference frequency based on the displacement signal of the vibrating body and the generated reference signal.
   A measurement method including a step of calculating a resonance frequency of the vibrating body based on the detected thermal vibration amplitude.

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