Measurement method, measuring device, and observation system

Abstract

To provide a heterodyne scanning tunneling microscope system measurement method, a measuring device, and an observation system capable of measuring the change of state over time of a microstructure that is the measurement object.SOLUTION: The measurement method includes: an arrangement step of arranging a measurement object and an action member that interacts with the measurement object so that the measurement object and the action member form a nonlinear connection part; a first signal input step of inputting, to the nonlinear connection part, a first electromagnetic signal which is a frequency comb composed of a plurality of spectral lines with frequencies aligned at equal intervals; a second signal input step of inputting a second electromagnetic signal to the nonlinear connection part; and a detection step of detecting a heterodyne beat signal generated by interaction between the first and second electromagnetic signals in the nonlinear connection part.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a measurement method, a measurement apparatus, and an observation system.

Background Art

[0002] Conventionally, for the purpose of electron spin detection, a spin polarized scanning tunneling microscope (SP-STM) and a scanning near field optical microscope (SNOM) have been developed. Further, Patent Document 1 discloses a technique for detecting a heterodyne beat signal superimposed on a tunnel current flowing between a measurement target and a probe of a scanning tunneling microscope by introducing two high-frequency signals having different frequencies, and measuring a state such as an electronic state of the measurement target with atomic-level spatial resolution.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the technique of Patent Document 1, when the frequencies of absorption, radiation, excitation, etc. generated by the interaction between the measurement target and the high-frequency signal are unknown, the frequency of one of the high-frequency signals must be swept to detect the frequency at which absorption, etc. occurs. However, when the frequency is swept to detect the frequency of absorption, etc. generated by the interaction with the measurement target, it has not been possible to measure the state change of the fine structure of the measurement target such as the vibration, rotation, and spin of the substance over time.

[0005] The present invention has been made in view of the above, and an object thereof is to provide a measurement method, a measurement apparatus, and an observation system capable of measuring a change in the state of a fine structure to be measured over time. **Means for Solving the Problems**

[0006] In order to solve the above-described problems and achieve the object, a measurement method includes: an arrangement step of arranging the measurement object and the acting member such that the measurement object and the acting member that interacts with the measurement object form a non-linear junction; a first signal input step of inputting a first electromagnetic wave signal, which is a frequency comb composed of a plurality of spectral lines arranged at equal intervals in frequency, into the non-linear junction; a second signal input step of inputting a second electromagnetic wave signal into the non-linear junction; and a detection step of detecting a heterodyne beat signal generated by the interaction of the first electromagnetic wave signal and the second electromagnetic wave signal in the non-linear junction.

[0007] Moreover, in the measurement method according to one aspect of the present invention, the acting member is a sharp probe arranged close to the measurement object.

[0008] Moreover, in the measurement method according to one aspect of the present invention, the first electromagnetic wave signal and the second electromagnetic wave signal are superimposed on a tunnel current flowing between the measurement object and the acting member.

[0009] Moreover, in the measurement method according to one aspect of the present invention, in the detection step, the acting member detects the heterodyne beat signal.

[0010] Moreover, in the measurement method according to one aspect of the present invention, a frequency band of the first electromagnetic wave signal includes a frequency band that interacts with the measurement object.

[0011] Moreover, in the measurement method according to one aspect of the present invention, a frequency band of the heterodyne beat signal includes a frequency band that interacts with the measurement object.

[0012] Further, in the measurement method according to one aspect of the present invention, in the first signal input step and the second signal input step, the first electromagnetic wave signal and the second electromagnetic wave signal are controlled by a pulse train having predetermined characteristics, and a pump and a probe, which are heterodyne beat signals generated at a predetermined delay time, are generated.

[0013] Further, in the measurement method according to one aspect of the present invention, the second electromagnetic wave signal is a frequency comb composed of a plurality of spectral lines with equally spaced frequencies.

[0014] Further, in the measurement method according to one aspect of the present invention, the full width at half maximum of each of the plurality of spectral lines in the first electromagnetic wave signal is 10 Hz or less.

[0015] Further, in the measurement method according to one aspect of the present invention, a frequency setting step of setting the center frequency of the first electromagnetic wave signal or the heterodyne beat signal to a frequency that interacts with the measurement target is included.

[0016] Further, a measurement apparatus according to one aspect of the present invention includes an acting member that interacts with a measurement target and is arranged to form a non-linear junction with the measurement target, a first electromagnetic wave signal that is a frequency comb composed of a plurality of spectral lines with equally spaced frequencies input to the non-linear junction, and a detection unit that detects a heterodyne beat signal generated by the interaction of the first electromagnetic wave signal and a second electromagnetic wave signal input to the non-linear junction in the non-linear junction.

[0017] Further, an observation system according to one aspect of the present invention includes the measurement apparatus according to claim 1 and a scanning unit that scans the acting member.

[0018] Further, an observation system according to one aspect of the present invention includes a first signal generation device that generates the first electromagnetic wave signal and a second signal generation device that generates the second electromagnetic wave signal.

Advantages of the Invention

[0019] According to the present invention, it is possible to realize a measurement method, a measurement device, and an observation system capable of measuring changes in the state of a fine structure of a measurement target over time.

Brief Description of the Drawings

[0020]

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BEST MODE FOR CARRYING OUT THE INVENTION

[0021] The embodiments (embodiments) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the contents described in the following embodiments. Further, the constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be combined as appropriate.

[0022] (Embodiment) 〔Configuration of Heterodyne Scanning Tunneling Microscope System Using Frequency Comb〕 FIG. 1 is a block diagram showing the configuration of a heterodyne scanning tunneling microscope system which is an observation system using a frequency comb according to the embodiment. As shown in FIG. 1, the heterodyne scanning tunneling microscope system 1 using a frequency comb according to the present embodiment includes a probe 2 as an operating member and a detection unit, a scanning tunneling microscope controller 3, a first electromagnetic wave signal generator 4, a second electromagnetic wave signal generator 5, a program pulse generator 6, a coupler 7, and an RF spectrum analyzer 8.

[0023] The probe 2 is placed on the sample S to be measured. The probe 2 and the sample S are arranged so as to form a non-linear heterojunction (hereinafter referred to as the non-linear junction NL). The probe 2 is made of, for example, a sharp Pt / Ir alloy.

[0024] The scanning tunneling microscope controller 3 operates the position of the probe 2 three-dimensionally. The scanning tunneling microscope controller 3 may also have a function of analyzing the signal obtained by two-dimensionally scanning the position of the probe 2 using Fourier transform.

[0025] The first electromagnetic wave signal generator 4 is realized by using, for example, a microwave generator. The first electromagnetic wave signal generator 4 generates a first electromagnetic wave signal (hereinafter referred to as the first signal or signal F1). The first signal includes a high-frequency signal and an optical wave signal. The signal F1 is a frequency comb composed of a plurality of spectral lines with equally spaced frequencies (referred to as the signal F1 comb). The intensity of the signal F1 comb decreases symmetrically around the center frequency f 10 centered. The frequency component f1 of the signal F1 can be expressed as f1 = f 10 + nfr (n is an integer, fr is the interval between spectral lines). The frequency band of the signal F1 is set to include the frequency band that interacts with the sample S. Note that the interval between the plurality of spectral lines in the signal F1 corresponds to the energy resolution measurable by the heterodyne scanning tunneling microscope system 1 using the frequency comb.

[0026] The second electromagnetic wave signal generator 5 is realized by using, for example, a microwave generator. The second electromagnetic wave signal generator 5 generates a second electromagnetic wave signal (hereinafter referred to as the second signal or signal F2). The second signal includes a high-frequency signal and an optical wave signal. The signal F2 is, for example, an alternating current signal with a single frequency f2 (referred to as the signal F2CW).

[0027] The program pulse generator 6 generates a pulse train with predetermined characteristics according to a pre-created pulse sequence program (a program that defines pulse width, pulse intensity, pulse shape, and the time interval between pulses), and controls the electromagnetic wave outputs from the first electromagnetic wave signal generator 4 and the second electromagnetic wave signal generator 5. Further, the program pulse generator 6 is characterized by also having the function of an arbitrary waveform generator. In this way, by controlling the first electromagnetic wave signal generator 4 and the second electromagnetic wave signal generator 5 according to the pulse sequence of the program pulse generator 6, a pulse signal of an electromagnetic wave having an arbitrary pulse profile is generated. The center frequencies of the electromagnetic wave signals F1 and F2 can be seamlessly changed by the first electromagnetic wave signal generator 4 and the second electromagnetic wave signal generator 5 from 0.1 MHz to several GHz. According to the program pulse generator 6, the density, interval, intensity, etc. of the spectral lines of the signals F1 and F2 can be arbitrarily set.

[0028] The combiner 7 includes a power splitter 71, a directional coupler 72, a bias T 73, and a frequency selection filter 74. The power splitter 71 combines the signal F1 from the first electromagnetic wave signal generator 4 and the signal F2 from the second electromagnetic wave signal generator 5. The directional coupler 72 separates the traveling wave and the reflected wave. The separated traveling wave or reflected wave is input to the RF spectrum analyzer 9. The bias T 73 separates the signal of the probe 2 into a DC component and an AC component. Among these, the AC component is input to the RF spectrum analyzer 8 via the frequency selection filter 74. The frequency selection filter 74 selects a signal in the frequency band to be observed from among the AC components separated by the bias T 73.

[0029] The RF spectrum analyzer 8 is used to measure the input signal. A signal F1 is input to the RF spectrum analyzer 8 from the first electromagnetic wave signal generator 4. A signal F2 is input to the RF spectrum analyzer 8 from the second electromagnetic wave signal generator 5. A traveling wave or a reflected wave separated by the directional coupler 72 is input to the RF spectrum analyzer 8. A signal in the frequency band to be observed, which is selected by the frequency selection filter 74 from the AC component of the signal from the probe 2 separated by the bias T73, is input to the RF spectrum analyzer 8.

[0030] The sample S is not particularly limited, but in the following examples, highly oriented pyrolytic graphite (HOPG) was used.

[0031] 〔Measurement method using a heterodyne scanning tunneling microscope system with a frequency comb〕 FIG. 2 is a flowchart showing the processing in the measurement method according to the embodiment. As shown in FIG. 2, first, the sample S to be measured and the probe 2 that interacts with the sample S are arranged so as to form a non-linear junction NL (step S1: arrangement step).

[0032] FIG. 3 is a diagram schematically showing the configuration of the sample and the probe shown in FIG. 1. As shown in FIG. 3, in the heterodyne scanning tunneling microscope system 1 with a frequency comb, the probe 2 is installed on the sample S in a vacuum to form a non-linear junction NL.

[0033] Subsequently, a signal F1 is input to the sample S with respect to this non-linear junction NL, separately from the DC voltage E (step S2: first signal input step). The signal F1 is an electromagnetic wave signal that is a frequency comb composed of a plurality of spectral lines with equally spaced frequencies.

[0034] Furthermore, for this non-linear junction NL, a signal F2 is input to the sample S separately from the DC voltage E (step S3: second signal input step). The signal F2 may be an electromagnetic wave signal that is a frequency comb consisting of a plurality of spectral lines with equally spaced frequencies, or it may be a CW light with a single frequency.

[0035] Then, the heterodyne scanning tunneling microscope system 1 detects, by means of the probe 2, a heterodyne beat signal generated by the interaction of the signal F1 and the signal F2 at the non-linear junction NL (step S4: detection step).

[0036] Now, using the angular frequencies ω1 = 2πf1 and ω2 = 2πf2 of their center frequencies, let the center frequencies of the respective signals be represented as F1C = ksin(ω1t) and signal F2C = ksin(ω2t). At this time, I{E + ksin(ω1t) + ksin(ω2t)} = I(E) + I′(E)k(sin(ω1t) + sin(ω2t)) + (1 / 2)I′′(E)k 2 {1 + cos(ω1 - ω2)t - cos(ω1 + ω2)t - (1 / 2)cos(2ω1t) - (1 / 2)cos(2ω2t)} + ··· can be expressed. I(E) is the DC component of the tunnel current. ksin(ω1t) and ksin(ω2t) are the AC components of the tunnel current. And due to this heterodyne mixing, the signal F1C and the signal F2C interact, and a heterodyne beat signal including a difference frequency component (1 / 2)I′′(E)k 2 cos(ω1 - ω2)t and a sum frequency component (1 / 2)I′′(E)k 2 cos(ω1 + ω2)t is generated (an AC signal generated by a non-linear effect). The same applies to the other frequencies constituting the comb. The heterodyne scanning tunneling microscope system 1 using a frequency comb detects, among the generated heterodyne beat signals, a frequency component suitable for observation generated by heterodyne down-conversion, for example, a component of the difference frequency (f2 - f1) (hereinafter referred to as the third signal or signal F3). This component of the difference frequency is the second derivative of the tunnel current (I′′(E) = d 2 I(E) / dV 2Since it is proportional to the component of (), very fine changes in the tunneling current can be detected with very high sensitivity.

[0037] In addition, although FIG. 3 shows an example in which the signal F1 and the signal F2 are applied to the sample S, the signal F1 and the signal F2 may be input to the probe 2. Further, the signal F1 and the signal F2 may be irradiated as electromagnetic waves to the nonlinear junction NL between the sample S and the probe 2. Alternatively, they may be input to the sample S, the probe, and the space respectively. The combinations include input to the sample and the probe respectively, input to the sample and the space respectively, input to the probe and the space respectively, and input to the sample, the space, and the probe respectively.

[0038] 〔Examples of measurements by a heterodyne scanning tunneling microscope system using a frequency comb〕 (Example 1) FIG. 4 is a diagram for explaining the relationship between the signals. Since the signal F1 comb is set in a frequency band that interacts with a specific mode of the sample S (the fine structure of the measurement target such as the vibration, rotation, or spin of the sample), at least one of the phenomena such as absorption of the signal F1 comb, emission of a new signal, and excitation of the mode occurs due to this interaction, and the waveform of the signal F1 comb changes. In other words, by scanning the center frequency (the carrier frequency of the electromagnetic wave) of the signal F1 comb to the frequency that interacts with a specific mode of the sample S, an unknown phenomenon can be measured. FIG. 4 shows an example in which a part of the signal F1 comb is absorbed in the region A1. This change in the waveform is also transferred to the signal F3 comb generated by the signal F1 comb and the signal F2CW, as shown in the region A2 of FIG. 4. Then, the heterodyne scanning tunneling microscope system 1 using the frequency comb measures the state change of a specific mode of the sample S with high sensitivity by selectively detecting the signal F3 with the frequency selection filter 74.

[0039] According to Example 1, within the frequency band of the signal F1 comb, the interaction between the fine structure of a specific mode such as the vibration, rotation, or spin of the sample S and the signal F1 comb can be detected as a change in waveform. As a result, it becomes possible to detect the interaction between the specific mode of the sample S and the signal F1 comb within the frequency band of the signal F1 comb as a snapshot that cuts out the state at that time. The shutter speed (sampling time) is set to less than 0.00000001 seconds (10 nanoseconds) by fast Fourier transform. By acquiring this snapshot multiple times along the time series, the time change of the interaction can be detected. As a result, it becomes possible to measure the change in the state of the measurement target such as relaxation dynamics over time by the heterodyne scanning tunneling microscope system 1 using the frequency comb.

[0040] Also, according to Example 1, under the control of the program pulse generator 6, the center frequency (carrier frequency of the electromagnetic wave) of the signal F1 comb, the profile (density, interval, intensity) of the spectral lines of the signal F1 comb, and the shape of each spectral line constituting the profile are arbitrarily set. For example, not only a rectangular wave but also an arbitrary aggregate of pulse waveforms with arbitrarily controlled density and interval composed of an arbitrary function is set. Therefore, the interaction between the specific mode of the sample S and the signal F1 comb in a desired frequency band can be detected as a change in waveform.

[0041] Also, according to Example 1, since the signal F3 is a heterodyne beat signal superimposed on the tunneling current generated when the sample S and the tip of the probe 2 are brought close to about 0.000000001 m, it can be measured with atomic-level spatial resolution.

[0042] (Example 2) In Example 2, the frequency band of the signal F3 comb, which is a heterodyne beat signal generated by the interaction between the signal F1 comb and the signal F2CW, is set to include the frequency band that interacts with a specific mode of the sample S (the fine structure of the measurement target such as the vibration, rotation, or spin of the sample).

[0043] FIG. 5 is a diagram for explaining the relationship between each signal. As shown in FIG. 5, at least one phenomenon such as absorption of the signal F3 comb, emission of a new signal, and excitation of a mode occurs due to the interaction between a specific mode of the sample S (fine structure of the measurement target such as vibration, rotation, or spin of the sample) and the signal F3 comb, and the waveform (envelope) of the signal F3 comb changes. In other words, by setting the center frequency of the signal F3 comb to a frequency that interacts with a specific mode of the sample S (fine structure of the measurement target such as vibration, rotation, or spin of the sample), the phenomenon assumed in advance can be measured. FIG. 5 shows an example in which a part of the signal F3 comb is absorbed in the region A3. By detecting the amount of decrease in the signal F3 comb due to this absorption, the heterodyne scanning tunneling microscope system 1 measures the state change of a specific mode of the sample S (fine structure of the measurement target such as vibration, rotation, or spin of the sample). In this way, the state (real signal) of a specific mode of the sample S (fine structure of the measurement target such as vibration, rotation, or spin of the sample) in the region A3 near -140 dBm is detected with high sensitivity as a waveform change of the F3 comb even in an observation environment near -120 dBm with a higher noise flow.

[0044] FIG. 6 is a diagram showing the frequency spectrum of the first signal. FIG. 6 is an enlarged view near the center frequency (carrier frequency of the electromagnetic wave) of the frequency spectrum of the first signal. The signal F1 shown in FIGS. 6 and 7 is a frequency comb composed of a plurality of spectral lines with frequencies arranged at equal intervals around the center frequency f 10 = 500000000 Hz (5 gigahertz). This comb signal provides high detection sensitivity because it has a dynamic range exceeding 70 dBm.

[0045] FIG. 8 is a diagram showing an enlarged spectrum of a region that is the third harmonic counted from the center frequency (carrier frequency of electromagnetic waves) of the comb shown in FIG. 7. That is, FIG. 8 is an enlarged view near arrow A4 in FIG. 7. As shown in FIG. 8, the full width at half maximum of the peak of the third harmonic is less than 2 Hz and the energy resolution is 8 femto - eV. The resolution bandwidth (RBW) of the heterodyne scanning tunneling microscope system 1 using the frequency comb is 1 Hz. Thus, when the full width at half maximum of each spectral line in signal F1 is 10 Hz or less, more preferably 3 Hz or less, the energy resolution can be increased.

[0046] FIG. 9 is a diagram showing the time variation of the first signal. That is, FIG. 9 is a diagram showing signal F1' obtained by performing a fast Fourier transform (FFT) on the signal F1 comb shown in FIG. 6. As shown in FIG. 9, the period T of signal F1' is 0.029 s, and the pulse repetition frequency is 34.6 Hz. This shows that due to the symmetry of the rectangular wave in the time domain of signal F1', the center frequency of signal F1 and the interval between spectral lines can be precisely controlled in the frequency domain.

[0047] FIG. 10 is a diagram showing the frequency spectrum of the second CW signal. As shown in FIG. 10, a single - frequency alternating current signal F2CW with a frequency f2 = 500003000 Hz was generated. FIG. 11 is a diagram showing an enlarged spectrum near the peak frequency of the second signal. That is, FIG. 11 is an enlarged view near arrow A5 in FIG. 10.

[0048] As shown in FIG. 11, the full width at half maximum of the peak of signal F2 is less than 2 Hz and the energy resolution is 8 femto - eV. The resolution bandwidth of the heterodyne scanning tunneling microscope system 1 is 1 Hz. From FIGS. 8 and 11, it can be seen that the dynamic range is as wide as 70 dBm.

[0049] FIG. 12 is a diagram showing the frequency spectrum of the third signal. FIG. 12 shows the center frequency f 10Shows the result of introducing a signal F1 comb with a frequency of f1 = 500000000 Hz and a signal F2 CW with a frequency of f2 = 500000772 Hz into a non - linear junction NL. In FIG. 12, for each set point of the tunnel current I S (I S = 40, 90, 140, 180, 230, 290 pA), the frequency spectrum obtained as a result of performing a fast Fourier transform on the tunnel current is shown. From FIG. 12, regardless of the value of the tunnel current I S , the center frequency f 30 of the signal F3 comb is 772 Hz, and by satisfying f 30 = f2 - f 10 , it can be confirmed that the signal F3 comb is a frequency comb generated by heterodyne down - conversion of the signal F1 comb and the signal F2 CW.

[0050] FIG. 13 is a diagram showing the peak intensities of the fundamental wave (0th order) and the 1st, 3rd, and 5th order harmonics as functions of the tunnel current. In FIG. 13, the peak intensities for each tunnel current of the fundamental wave (0th order) and the 1st, 3rd, and 5th order harmonics in FIG. 12 are shown. The signal F3 comb, which is an AC component, is in a linear relationship with the tunnel current I S . In FIG. 13, for the fundamental wave (0th order) and the 1st, 3rd, and 5th order harmonics, the lines connecting the respective peak intensities are substantially straight lines, and since the peak intensity and the tunnel current I s are in a substantially linear relationship, it shows that the signal F3 comb is generated as a tunnel current in a local non - linear junction.

[0051] FIG. 14 is a diagram showing the frequency spectrum of the third comb signal (signal F3 comb) when the frequency of the second CW signal (signal F2CW) is changed. FIG. 14 shows the measurement results when the center frequency of signal F1 comb is fixed at 500000000 Hz and the frequencies of signal F2CW are 500000230, 500000770, 500001770, 500002770, and 500004770 Hz. At this time, the center frequencies of signal F3 comb are 230, 770, 1770, 2770, and 4770 Hz, respectively. Also, in the signal F3 comb of each frequency, the interval between the spectral lines and the relationship between the intensities of the fundamental wave (0th order), 1st order, 3rd order, and 5th order harmonics did not change. Therefore, by changing the frequency of signal F2CW, the frequency band of signal F1 comb can be adjusted to a desired band while maintaining the interval between the spectral lines of signal F1 comb and the relationship between the intensities of the fundamental wave (0th order), 1st order, 3rd order, 5th order, etc. of the harmonics. In other words, signal F1 comb can be down-converted to signal F3 comb in an arbitrary frequency band without changing the interval between the spectral lines and the relationship between the intensities of the fundamental wave (0th order), 1st order, 3rd order, 5th order, etc. of the harmonics.

[0052] FIG. 15 is a diagram showing the frequency spectrum of the third signal (signal F3 comb) when the pulse repetition frequency of the first signal (signal F1 comb) is changed. FIG. 15 shows a state where signal F3 comb with a center frequency of 2927 Hz is generated with the center frequency of signal F1 comb being 500000000 Hz and the frequency of signal F2CW being 500002927 Hz. Then, when the pulse repetition frequency of signal F1 comb is changed to 52, 72, 112, 152, and 212 Hz, the interval between the spectral lines of signal F3 comb increases as the pulse frequency increases. Thus, the interval between the spectral lines of signal F3 comb can be set to a desired magnitude by changing the pulse repetition frequency of signal F1 comb.

[0053] As described above, according to Example 2, by setting the center frequency of the signal F3 comb, the density and interval of the spectral lines of the signal F3 comb, it is possible to measure the interaction exerted on the signal F3 by a specific mode of the sample S (the fine structure of the measurement target such as the vibration, rotation, or spin of the sample) in a desired frequency band.

[0054] Also, according to Example 2, when the magnitude of the tunnel current is as small as about several pA to several tens of pA, by using the signal F3 comb with a small intensity that occurs, in order to detect the interaction with a specific mode of the sample S (the fine structure of the measurement target such as the vibration, rotation, or spin of the sample), it is possible to perform the measurement without disturbing the state of the specific mode of the sample S (the fine structure of the measurement target such as the vibration, rotation, or spin of the sample). Specifically, according to Example 2, it is possible to detect a fine structure signal with a noise flow smaller than -120 dBm. Such a fine structure signal can include the signal of a single spin.

[0055] Furthermore, according to Example 2, similar to Example 1, since it is possible to detect the interaction between the signal F3 comb and a specific mode of the sample S (the fine structure of the measurement target such as the vibration, rotation, or spin of the sample) within the range where the signal F3 comb has frequency components as a snapshot, by acquiring a plurality of such snapshots along the time series, it is possible to detect minute signals that vary over time. The shutter speed (sampling time) is set to less than 0.00000001 seconds by fast Fourier transform. Note that the minute signal that varies over time is, for example, a signal caused by any of the Larmor precession motion of the spins on the surface of the measurement target, the vibration of molecules, or the rotation.

[0056] (Modification Example 1) In the embodiment, an example in which only the signal F1 is a frequency comb has been described, but both the signal F1 and the signal F2 may be frequency combs. Figures 16 to 18 described below are the measurement results obtained by inputting the signals F1 and F2 into a double-balanced mixer.

[0057] FIG. 16 is a diagram showing the frequency spectrum of the first signal in Modification 1 of the embodiment. The signal F1 comb shown in FIG. 16 is a frequency comb with a center frequency f 10 of 1000000000 Hz.

[0058] FIG. 17 is a diagram showing the frequency spectrum of the second signal in Modification 1 of the embodiment. The signal F2 comb shown in FIG. 17 is an AC signal with a frequency f2 of 1400000000 Hz.

[0059] FIG. 18 is a diagram showing the frequency spectrum of the third signal in Modification 1 of the embodiment. FIG. 18 is a heterodyne beat signal generated by the signal F1 comb shown in FIG. 16 and the signal F2 comb shown in FIG. 17, and is a frequency comb with a center frequency of 400000000 Hz. In this example, since the signal F2 is also a frequency comb, the noise floor is -140 dBm and the peak intensity is -100 dBm. A finer ultrafine structure signal can be detected than in the embodiment.

[0060] (Modification 2) In the embodiment, an example in which the pulse generated by the program pulse generator 6 is input to the first electromagnetic wave signal generator 4 and the second electromagnetic wave signal generator 5 has been described, but the present invention is not limited thereto. FIG. 19 is a block diagram showing the configuration of a heterodyne scanning tunneling microscope system using a frequency comb according to Modification 2 of the embodiment. As shown in FIG. 19, in the coupler 7A of the heterodyne scanning tunneling microscope system 1A according to Modification 2 of the embodiment, the power splitter 71 combines the signals generated by the first electromagnetic wave signal generator 4 and the second electromagnetic wave signal generator 5, and the ultrafast electronic chopper 10A modulates this signal under the control of the program pulse generator 6A.

Description of Reference Numerals

[0061] 1, 1A Heterodyne scanning tunneling microscope system 2 Probe 3 Scanning tunneling microscope controller 4 First electromagnetic wave signal generator 5 Second electromagnetic wave signal generator 6, 6A Program pulse generator 7, 7A Coupler 8 RF spectrum analyzer 10A Ultra-high-speed electronic chopper 71 Power splitter 72 Directional coupler 73 Bias T 74 Frequency selection filter

Claims

1. An arrangement step of arranging the measurement object and the acting member so that the measurement object and the acting member that interacts with the measurement object form a non-linear joint; A first signal input step of inputting a first electromagnetic wave signal, which is a frequency comb composed of a plurality of spectral lines with equally spaced frequencies, into the non-linear joint; A second signal input step of inputting a second electromagnetic wave signal into the non-linear joint; A detection step of detecting a heterodyne beat signal generated by the interaction of the first electromagnetic wave signal and the second electromagnetic wave signal at the non-linear joint; A measurement method characterized by including the above.

2. The measurement method according to claim 1, wherein the acting member is a sharp probe arranged close to the measurement object.

3. The measurement method according to claim 1, wherein the first electromagnetic wave signal and the second electromagnetic wave signal are superimposed on a tunnel current flowing between the measurement object and the acting member.

4. The measurement method according to claim 1, wherein in the detection step, the acting member detects the heterodyne beat signal.

5. The measurement method according to claim 1, wherein the frequency band of the first electromagnetic wave signal includes a frequency band that interacts with the measurement object.

6. The measurement method according to claim 1, wherein the frequency band of the heterodyne beat signal includes a frequency band that interacts with the measurement object.

7. In the first signal input step and the second signal input step, the first electromagnetic wave signal and the second electromagnetic wave signal are controlled by a pulse train having predetermined characteristics, and a pump and a probe, which are heterodyne beat signals generated at a predetermined delay time, are generated. The measurement method according to claim 1, characterized by the above.

8. The measurement method according to claim 1, wherein the second electromagnetic wave signal is a frequency comb composed of a plurality of spectral lines with equally spaced frequencies.

9. The measurement method according to claim 1, wherein the full width at half maximum of each of the plurality of spectral lines in the first electromagnetic wave signal is 10 Hz or less.

10. The measurement method according to claim 1, characterized by including a frequency setting step of setting the center frequency of the first electromagnetic wave signal or the heterodyne beat signal to a frequency that interacts with the measurement object.

11. An actuating member that interacts with a measurement object and is arranged to form a non-linear joint with the measurement object A detection unit that detects a heterodyne beat signal generated by the interaction of a first electromagnetic wave signal, which is a frequency comb composed of a plurality of spectral lines with equally spaced frequencies input to the non-linear joint, and a second electromagnetic wave signal input to the non-linear joint, at the non-linear joint A measuring device, characterized by comprising the above

12. The measuring device according to claim 11 An observation system, characterized by comprising a scanning unit that scans the actuating member

13. A first signal generator that generates the first electromagnetic wave signal A second signal generator that generates the second electromagnetic wave signal The observation system according to claim 12, characterized by comprising the above

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