Measuring device, observation system, and measurement method

Abstract

To provide a measuring device that measures the change of state of a microstructure that is the object to be measured along with the passage of time.SOLUTION: The measuring device comprises: an action member that interacts with an object to be measured; a first signal generator that generates a first electromagnetic signal which is a first frequency comb; a second signal generator that generates a second electromagnetic signal; a third signal generator that generates a reference signal; a detection unit that, with the action member located so as to form a nonlinear connection part with the object being measured, detects a heterodyne beat signal generated by interaction between the first and second electromagnetic signals and the object being measured in the nonlinear connection part; a phase-sensitive detector that extracts a specific frequency component from the heterodyne beat signal using the reference signal and demodulates precision spectroscopic information that is included; and an oscillator that synchronizes frequency precision degrees and phases of the first and second electromagnetic signals and the reference signal by using vibration of a matter having a frequency stability higher than or equal to a frequency precision degree of transition vibration of quartz or rubidium.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Conventionally, for the purpose of electron spin detection, Spin Polarized-Scanning Tunneling Microscopy (SP-STM), Scanning Near field Optical Microscopy (SNOM), etc. have been developed.

[0003] Further, Patent Document 1 discloses a technique of 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. 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 is swept to detect the frequency at which absorption, etc. occurs.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the technique of Patent Document 1, when detecting the frequency of absorption or the like by sweeping the frequency of either one of the two high-frequency signals, it has not been possible to measure the state change of fine structures such as vibration, rotation, and spin of the measurement target with atomic resolution over time.

[0006] The present invention has been made in view of the above, and an object thereof is to provide a measuring device, an observation system, and a measuring method capable of measuring changes in the state of a fine structure to be measured over time.

Means for Solving the Problems

[0007] In order to solve the above-described problems and achieve the object, the measuring device includes an acting member that interacts with the measurement target, a first signal generation device that generates a first electromagnetic wave signal that is a first frequency comb composed of a plurality of spectral lines with equal intervals between the frequencies of the adjacent spectral lines, a second signal generation device that generates a second electromagnetic wave signal, a third signal generation device that generates a reference signal, a detection unit that detects a heterodyne beat signal generated by the interaction between the first electromagnetic wave signal input to the non-linear junction and the second electromagnetic wave signal input to the non-linear junction in a state where the acting member is arranged to form a non-linear junction with the measurement target, a phase-sensitive detector that extracts a specific frequency component from the heterodyne beat signal using the reference signal and demodulates the contained precise spectroscopic information, and an oscillator that synchronizes the frequency accuracy and phase of the first electromagnetic wave signal, the second electromagnetic wave signal, and the reference signal using the vibration of a substance having a frequency stability equal to or higher than the frequency accuracy of the transition vibration of quartz or rubidium.

[0008] Further, in the measuring device according to an aspect of the present invention, the oscillator synchronizes the phases of the first electromagnetic wave signal, the second electromagnetic wave signal, and the reference signal using the vibration of quartz, rubidium, cesium, ytterbium, strontium, or an optical lattice.

[0009] Further, in the measuring device according to an aspect of the present invention, the oscillator synchronizes the frequency accuracies of the first electromagnetic wave signal, the second electromagnetic wave signal, and the reference signal using the vibration of quartz, rubidium, cesium, ytterbium, strontium, or an optical lattice.

[0010] Further, in the measuring device according to one aspect of the present invention, the second electromagnetic wave signal is a second frequency comb different from the first frequency comb, and is a second frequency comb composed of a plurality of spectral lines with an equal interval between the frequencies of adjacent spectral lines.

[0011] Further, in the measuring device according to one aspect of the present invention, the first frequency comb and the second frequency comb are different from each other by a predetermined amount in terms of the interval, and each of the plurality of spectral lines constituting the first frequency comb forms a pair in proximity to any one of the plurality of spectral lines constituting the second frequency comb. The difference in frequency between the paired spectral lines is such that, among the pairs adjacent to each other, the pair with the larger absolute value of the average frequency of the paired spectral lines is larger or smaller by the predetermined amount.

[0012] Further, in the measuring device according to one aspect of the present invention, the first frequency comb and the second frequency comb are frequency combs in which the interval is different by a predetermined amount and the center frequencies of each other are equal.

[0013] Further, in the measuring device according to one aspect of the present invention, the first frequency comb and the second frequency comb are frequency combs in which the interval is different by a predetermined amount and the center frequencies of each other are separated by a predetermined frequency.

[0014] Further, in the measuring device according to one aspect of the present invention, the actuating member is a sharp probe arranged in proximity to the measurement object.

[0015] Further, in the measuring device according to one aspect of the present invention, the first electromagnetic wave signal and the second electromagnetic wave signal are superimposed on the tunnel current flowing between the measurement object and the actuating member.

[0016] Further, in the measuring device according to one aspect of the present invention, the heterodyne beat signal is superimposed on the tunnel current flowing between the measurement object and the actuating member.

[0017] Further, an observation system according to an aspect of the present invention is characterized by including the above-described measuring device and a scanning unit that two-dimensionally or three-dimensionally scans the acting member with respect to the measurement object.

[0018] Further, an observation system according to an aspect of the present invention is characterized by including an image generation device that generates a two-dimensional image or a three-dimensional image based on the position information of the acting member scanned by the scanning unit.

[0019] Further, an observation system according to an aspect of the present invention is characterized by including an image generation device that generates a two-dimensional image or a three-dimensional image of the demodulated precise spectroscopic information based on the position information of the acting member scanned by the scanning unit.

[0020] Further, a measurement method according to an aspect of the present invention includes an arrangement step of arranging an acting member that interacts with a measurement object so as to form a non-linear junction with the measurement object, and using vibrations of a substance having a frequency stability equal to or higher than the frequency accuracy of the transition vibration of quartz or rubidium, a synchronization step of synchronizing the frequency accuracy and phase of a first electromagnetic wave signal, a second electromagnetic wave signal, and a reference signal, which are a first frequency comb composed of a plurality of spectral lines having an equal interval between the frequencies of adjacent spectral lines; a first signal input step of inputting the first electromagnetic wave signal to the non-linear junction; a second signal input step of inputting the second electromagnetic wave signal to the non-linear junction; a reference signal input step of inputting the reference signal to a phase-sensitive detector; 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 with the measurement object at the non-linear junction; an extraction step of extracting a specific frequency component from the heterodyne beat signal by the phase-sensitive detector using the reference signal; and a demodulation step of demodulating precise spectroscopic information included in the specific frequency component.

Effects of the Invention

[0021] According to the present invention, it is possible to realize a measuring apparatus, an observation system, and a measuring method capable of measuring changes in the state of a fine structure to be measured over time.

Brief Description of Drawings

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[0023] 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 content 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 substantially the same ones. Furthermore, the constituent elements described below can be combined as appropriate.

[0024] (Embodiment 1) 〔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 Embodiment 1. As shown in FIG. 1, the heterodyne scanning tunneling microscope system 1 using a frequency comb according to Embodiment 1 of the present invention includes a probe 2 as an acting member and a detecting unit, a scanning tunneling microscope controller 3 as a scanning unit, a phase-sensitive detector 4, an oscillator 5, a first electromagnetic wave signal generator 6, a second electromagnetic wave signal generator 7, a third signal generator 8, a program pulse generator 9, a power combiner 10, a directional coupler 11, a bias T 12, an image generator 13, a spectrum analyzer 14, and an FFT analyzer 15.

[0025] The probe 2 is arranged close to the sample S on the sample S to be measured and interacts with the sample S. The probe 2 and the sample S are arranged so as to form a non-linear heterojunction (hereinafter referred to as a non-linear junction NL). The probe 2 is made of, for example, a sharp Pt / Ir alloy. Further, the probe 2 detects a heterodyne beat signal.

[0026] The scanning tunneling microscope controller 3 scans the probe 2 two-dimensionally or three-dimensionally with respect to the sample S. Further, the scanning tunneling microscope controller 3 may have a function of analyzing the signal obtained by two-dimensionally scanning the position of the probe 2 using Fourier transform.

[0027] The phase-sensitive detector 4 extracts a specific frequency component from the heterodyne beat signal using the reference signal generated by the third signal generator 8. The phase-sensitive detector 4 demodulates the precise spectroscopic information included in the extracted specific frequency component.

[0028] The oscillator 5 synchronizes the frequency accuracy and phase of the first electromagnetic wave signal, the second electromagnetic wave signal, the reference signal, and the program pulse generator 9 using, for example, the transition oscillation of quartz or rubidium. For the oscillator 5, a substance having a frequency stability higher than the frequency accuracy of the transition oscillation of quartz or rubidium may be used, and cesium, ytterbium, strontium, or an optical lattice may be used.

[0029] The first electromagnetic wave signal generator 6 includes, for example, a microwave generator and generates a first electromagnetic wave signal (hereinafter referred to as the first signal or signal F1). The first signal includes an optical wave signal. The signal F1 is a first frequency comb composed of a plurality of spectral lines with equal intervals between the frequencies of adjacent spectral lines (referred to as the signal F1 comb). The intensity of the signal F1 comb decreases symmetrically around the center frequency f 10 centered at. The frequency component f1 of the signal F1 is f1 = f 10It can be expressed as +nfr (n is an integer, including positive integers, 0, and negative integers, and fr is the interval between spectral lines). The frequency band of signal F1 is set to include the frequency band that interacts with sample S. Note that the interval between multiple spectral lines in signal F1 corresponds to the energy resolution measurable by the heterodyne scanning tunneling microscope system 1 using a frequency comb.

[0030] The second electromagnetic wave signal generator 7 includes, for example, a microwave generator and generates a second electromagnetic wave signal (hereinafter referred to as the second signal or signal F2). The second signal includes an optical wave signal. Signal F2 is, for example, an AC signal with a single frequency f2 (referred to as signal F2CW), but may also be a frequency comb consisting of a plurality of spectral lines with equally spaced frequencies (referred to as signal F2 comb).

[0031] The third signal generator 8 generates a stable frequency (hereinafter referred to as the reference signal or signal F3) in which the frequency accuracy and phase of signal F1, signal F2, and the reference signal F3 are synchronized by oscillator 5.

[0032] The program pulse generator 9 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 output from the microwave generator of the first electromagnetic wave signal generator 6. In addition, the program pulse generator 9 also has the function of an arbitrary waveform generator. In this way, by controlling the microwave generator according to the pulse sequence of the program pulse generator 9, a pulse signal of an electromagnetic wave with an arbitrary pulse profile is generated. As a result, the center frequencies of signal F1 and signal F2 can be seamlessly changed from 0.1 MHz to several GHz by the microwave generator. According to the program pulse generator 9, the density, interval, intensity, etc. of the spectral lines of signal F1 and signal F2 can be arbitrarily set. These pulses and spectra are stabilized to the accuracy of oscillator 5.

[0033] The power combiner 10 combines the signal F1 from the first electromagnetic wave signal generator 6 and the signal F2 from the second electromagnetic wave signal generator 7.

[0034] The directional coupler 11 branches the signal input from the power combiner 10 and outputs it to the bias T12 and the spectrum analyzer 14 respectively. The directional coupler 11 may have a configuration capable of branching signals, and may be a circulator or the like.

[0035] The bias T12 separates the signal of the probe 2 into a DC component and an AC component. Among these, the AC component with a low frequency is input to the phase-sensitive detector 4 via the scanning tunneling microscope controller 3.

[0036] The image generation device 13 generates a two-dimensional image or a three-dimensional image based on the position information of the probe 2 scanned by the scanning tunneling microscope controller 3. The image generation device 13 is, for example, a personal computer, a server system, or a workstation. The image generation device 13 is realized by, for example, a processor composed of a CPU (Central Processing Unit) etc. and a memory (main storage unit) composed of a RAM (Random Access Memory), a ROM (Read Only Memory), etc. The image generation device 12 loads a program into the work area of the main storage unit and executes it, and realizes a function that matches a predetermined purpose by controlling each component etc. through the execution of the program. The image generation device 13 may generate a two-dimensional image or a three-dimensional image of the precise spectroscopic information demodulated by the phase-sensitive detector 4 based on the position information of the probe 2.

[0037] The spectrum analyzer 14 is, for example, a vector signal analyzer, and decomposes and displays the signal input from the directional coupler 11 on the time axis and the frequency axis.

[0038] An FFT (Fast Fourier Transform) analyzer 15 analyzes a signal input from a scanning tunneling microscope controller 3 by fast Fourier transform.

[0039] The sample S is not particularly limited, but in the following examples, highly oriented pyrolytic graphite (HOPG) was used.

[0040] 〔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 Embodiment 1. As shown in FIG. 2, first, the sample S to be measured and the probe 2 are arranged so as to form a non-linear junction NL with the sample S (step S1: arrangement step).

[0041] 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 the atmosphere or in vacuum to form a non-linear junction NL.

[0042] Subsequently, the oscillator 5 synchronizes the frequency accuracy and phase of the first electromagnetic wave signal, the second electromagnetic wave signal, and the reference signal (step S2: synchronization step). The oscillator 5 uses the vibrations of quartz or rubidium having a stable natural frequency of frequency accuracy and phase to accurately synchronize the frequency accuracy and phase of the first electromagnetic wave signal, the second electromagnetic wave signal, and the reference signal, so that the signal obtained by extracting a specific frequency component from the heterodyne beat signal can be synchronized with the frequency and phase of the reference signal of the phase-sensitive detector 4.

[0043] Thereafter, separately from the DC voltage E, a signal F1 is input from the first electromagnetic wave signal generator 6 to the non-linear junction NL (step S3: first signal input step). The signal F1 is a high-frequency signal or an electromagnetic wave signal that is a frequency comb composed of a plurality of spectral lines with equally spaced frequencies. The signal F1 is superimposed on the tunnel current flowing between the sample S and the probe 2.

[0044] Furthermore, separately from the DC voltage E, a signal F2 is input from the second electromagnetic wave signal generator 7 to the non-linear junction NL (step S4: second signal input step). The signal F2 may be a high-frequency signal or an electromagnetic wave signal that is a frequency comb composed of a plurality of spectral lines with equally spaced frequencies, or may be a CW light (electromagnetic wave) with a single frequency. The signal F2 is superimposed on the tunnel current flowing between the sample S and the probe 2.

[0045] Then, a signal F3 is input from the third signal generator 8 to the phase-sensitive detector 4 (step S5: reference signal input step).

[0046] Thereafter, the heterodyne scanning tunneling microscope system 1 detects, by means of the probe 2, a heterodyne beat signal FH1 generated by the interaction of the signals F1 and F2 with the sample S at the non-linear junction NL (step S6: detection step).

[0047] Furthermore, a specific frequency component is extracted from the heterodyne beat signal FH1 by means of the phase-sensitive detector 4 using the signal F3 (step S7: extraction step).

[0048] Then, the phase-sensitive detector 4 demodulates the precise spectroscopic information contained in the extracted specific frequency component (step S8: demodulation step).

[0049] Now, using the angular frequencies ω1 = 2πf1 and ω2 = 2πf2 of the 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, signal F1C and signal F2C interact with each other, and the difference frequency component (1 / 2)I′′(E)k 2 cos(ω1 - ω2)t and the sum frequency component (1 / 2)I′′(E)k 2 cos(ω1 + ω2)t are included (the heterodyne beat signal FH1 which is an AC signal generated by the non - linear effect). The same holds for the other frequencies that make up the frequency comb. The heterodyne scanning type tunnel microscope system 1 using the frequency comb detects, among the generated heterodyne beat signals FH1, the frequency components suitable for observation generated by heterodyne down - conversion, for example, the component of the difference frequency (f2 - f1) (hereinafter referred to as the difference frequency signal or signal FH2). This component of the difference frequency is proportional to the second - order differential of the tunnel current (I′′(E) = d 2 I(E) / dV 2 ), so very fine changes in the tunnel current can be detected very sensitively and with high sensitivity.

[0050] Note that in FIG. 3, an example of applying signal F1 and signal F2 to the sample S is shown, but signal F1 and signal F2 may be input to the probe 2. Further, signal F1 and signal F2 may be irradiated as electromagnetic waves to the non - linear junction NL between the sample S and the probe 2. Or they may be input to the sample S, the probe, and the space respectively. The combinations are 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.

[0051] [Example of Measurement by Heterodyne Scanning Tunneling Microscope System Using Frequency Comb] FIG. 4 is a diagram for explaining the relationship between each signal. 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 phenomenon such as absorption of the signal F1 comb, radiation of a new signal, or 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 (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 FH2 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 extracts the signal FH2 by the phase-sensitive detector 4, and measures the state change of a specific mode of the sample S with high sensitivity.

[0052] By this measurement, 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 the waveform. As a result, it becomes possible to detect the interaction between a specific mode of the sample S and the signal F1 comb within the frequency band of the signal F1 comb as a snapshot of 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 a plurality of such snapshots along the time series, the time change of the interaction can be detected. As a result, it becomes possible to measure the state change of the measurement target such as relaxation dynamics over time by the heterodyne scanning tunneling microscope system 1 using the frequency comb.

[0053] Also, according to this measurement, by controlling the first electromagnetic wave signal 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 can be arbitrarily set. For example, not only a rectangular wave but also an arbitrary set of pulse waveforms with arbitrarily controlled density and interval and composed of an arbitrary function can be set. Therefore, the interaction between a specific mode of the sample S in a desired frequency band and the signal F1 comb can be detected as a change in the waveform.

[0054] Also, according to this measurement, since the signal FH1 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 each other to about 0.000000001 m, it can be measured with atomic-level spatial resolution.

[0055] FIG. 5 is a diagram for explaining the relationship between the signals. As shown in FIG. 5, when a specific mode of the sample S (fine structure of the measurement target such as vibration, rotation, or spin of the sample) interacts with the signal FH2 comb, at least one phenomenon such as absorption of the signal FH2 comb, emission of a new signal, or excitation of the mode occurs, and the waveform (envelope) of the signal FH2 comb changes. In other words, by setting the center frequency of the signal FH2 comb to the 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), a phenomenon assumed in advance can be measured. FIG. 5 shows an example in which a part of the signal FH2 comb is absorbed in the region A3. By detecting the amount of decrease in the signal FH2 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 can be detected with high sensitivity as a waveform change of the FH2 comb even in an observation environment near -120 dBm with a higher noise floor.

[0056] (Example 1) FIG. 6 is a diagram showing the frequency spectra of the first electromagnetic wave signal and the second electromagnetic wave signal. The signal F1 comb shown in FIG. 6 is a frequency comb (constituting the grating of a precision spectroscope) composed of a plurality of spectral lines whose frequencies are equally spaced (interval: 555 Hz) around the center frequency f 10 = 500000049 Hz. Since this comb signal has a dynamic range exceeding 70 dBm, it provides high detection sensitivity. The signal F2 CW is an AC signal of a single frequency with a frequency f2 = 500003048 Hz.

[0057] FIG. 7 is an enlarged view of region A4 in FIG. 6. On the low-wavelength side of the signal F1 comb shown in region A5 of FIG. 7, the peak P5, which is the fifth harmonic, is set to be about 13 dB smaller than the peak P7, which is the seventh harmonic.

[0058] FIG. 8 is a diagram showing the frequency spectrum of the difference frequency signal. The peaks P0 to P9 in FIG. 8 are the peaks of the signal FH2 comb, which is a difference frequency signal, and the peaks PS1 to PS5 represent the peaks due to self-heterodyne.

[0059] FIG. 9 is a diagram comparing the frequency spectra of the first electromagnetic wave signal and the difference frequency signal. Below and to the left of FIG. 9, the frequency and signal intensity of the signal F1 comb are shown, respectively. Above and to the right of FIG. 9, the frequency and current of the signal FH2 comb are shown, respectively. Similar to the signal F1 comb, it can be confirmed that the signal intensity of the peak P5, which is the fifth harmonic, is smaller than that of the peak P7, which is the seventh harmonic, in the signal FH2 comb. This indicates that the change in the waveform of the frequency spectrum due to absorption or the like in the signal F1 comb is transferred to the signal FH2 comb. In other words, by measuring the signal FH2 comb, the interaction between the sample S and the signal F1 comb within the frequency band of the signal F1 comb can be detected.

[0060] FIG. 10 is a diagram showing an enlarged spectrum of the seventh harmonic of the first electromagnetic wave signal. As shown in FIG. 10, the full width at half maximum of peak P7, which is the seventh harmonic of signal F1 comb, is about 2 Hz. The resolution bandwidth (RBW) of the heterodyne scanning tunneling microscope system 1 using the frequency comb is 300 mHz.

[0061] FIG. 11 is a diagram comparing the frequency spectra of the seventh harmonic of the difference frequency signal and the reference signal. As shown in FIG. 11, it can be seen that the waveform of the seventh harmonic of signal FH2 and the waveform of signal F3 exactly match.

[0062] FIG. 12 is a two-dimensional image generated by the first harmonic of the first electromagnetic wave signal. FIG. 12 is a signal with a frequency of 500001255 Hz, corresponding to the first harmonic on the high-wavelength side of signal F1. The probe 2 is scanned two-dimensionally by the scanning tunneling microscope controller 3 to acquire a signal, and this signal is imaged by the image generation device 12. The length of the white line shown in this image is 0.6 nm. And the spherical bright part included in the image corresponds to one atom of graphite, and it can be seen that an image with atomic resolution has been captured.

[0063] As described above, according to the first embodiment, by setting the center frequency of the signal F1 comb, the density and interval of the spectral lines of the signal F1 comb, and the frequency of the signal F2CW, the interaction exerted 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 the desired frequency band on the signal F1 comb can be measured by the signal FH2. Furthermore, by scanning the probe 2, an image with atomic resolution can be generated.

[0064] (Embodiment 2) In the second embodiment, the first electromagnetic wave signal and the second electromagnetic wave signal are the first and second frequency combs each consisting of a plurality of spectral lines with equal intervals between the frequencies of adjacent spectral lines (referred to as signal F11 comb and signal F12 comb, respectively).

[0065] FIG. 13 is a block diagram showing the configuration of a heterodyne scanning tunneling microscope system using a frequency comb according to Embodiment 2. As shown in FIG. 13, in a heterodyne scanning tunneling microscope system 100 using a frequency comb according to Embodiment 2, the output from a program pulse generator 9 is input to a first electromagnetic wave signal generator 6 and a second electromagnetic wave signal generator 7. As a result, the first electromagnetic wave signal generator 6 outputs a signal F11 comb which is a frequency comb, and the second electromagnetic wave signal generator 7 outputs a signal F12 comb which is a frequency comb.

[0066] (Example 2) FIG. 14 is a diagram for explaining the relationship between the signals. The signal F11 comb and the signal F12 comb are equally spaced such that the frequency interval between adjacent spectral lines differs by a predetermined amount. Also, each of the plurality of spectral lines constituting the signal F11 comb forms a pair in proximity to one of the plurality of spectral lines constituting the signal F12 comb. And the frequency difference between the paired spectral lines is larger by a predetermined amount for the pair with the larger absolute value of the average of the frequencies of the paired spectral lines among adjacent pairs.

[0067] When a part of the signal F11 comb and the signal F12 comb is absorbed in region A11 of FIG. 14 and the waveform of the frequency spectrum changes, this waveform change is also transferred to a signal FH11 comb which is a difference frequency signal generated by the signal F11 comb and the signal F12 comb, as shown in region A12 of FIG. 14. And the heterodyne scanning tunneling microscope system 1 using a frequency comb can highly sensitively measure a state change of a specific mode of the sample S in a wide frequency band by extracting the signal FH11 with a phase sensitive detector 4.

[0068] FIG. 15 is a diagram showing the time change of the voltages of the first electromagnetic wave signal and the second electromagnetic wave signal. As shown in FIG. 15, the signal F11 comb and the signal F12 comb are rectangular waves of 300000 Hz and 300200 Hz, respectively. That is, the difference in the frequency interval between adjacent spectral lines of the signal F11 comb and the signal F12 comb differs by a predetermined amount (200 Hz).

[0069] Figure 16 is a diagram showing the frequency spectra of the first electromagnetic wave signal and the second electromagnetic wave signal. As shown in Figure 16, the signal F11 comb and the signal F12 comb have spectral lines that are close to each other and form a pair.

[0070] Figure 17 is an enlarged view near the peak P11 shown in Figure 16. At the peak P11 located on the lowest frequency side in Figure 16, as shown in Figure 17, the frequency difference between the spectral lines of the signal F11 comb and the signal F12 comb is 200 Hz, which is 1 times a predetermined amount.

[0071] Figure 18 is an enlarged view near the peak P13 shown in Figure 16. At the peak P13 located third from the lowest frequency side in Figure 16, as shown in Figure 18, the frequency difference between the spectral lines of the signal F11 comb and the signal F12 comb is 600 Hz, which is 3 times a predetermined amount.

[0072] Figure 19 is an enlarged view near the peak P15 shown in Figure 16. At the peak P15 located fifth from the lowest frequency side in Figure 16, as shown in Figure 19, the frequency difference between the spectral lines of the signal F11 comb and the signal F12 comb is 1000 Hz, which is 5 times a predetermined amount.

[0073] Figure 20 is an enlarged view near the peak P19 shown in Figure 16. At the peak P19 located ninth from the lowest frequency side in Figure 16, as shown in Figure 20, the frequency difference between the spectral lines of the signal F11 comb and the signal F12 comb is 1800 Hz, which is 9 times a predetermined amount.

[0074] As shown in Figures 17 to 20, the signal F11 comb and the signal F12 comb differ by a predetermined amount (200 Hz) in interval, and each of the plurality of spectral lines constituting the signal F11 comb forms a pair in proximity to any one of the plurality of spectral lines constituting the signal F12 comb. And the frequency difference between the paired spectral lines is such that, among the adjacent pairs, the pair with the larger absolute value of the average frequency of the paired spectral lines is larger by a predetermined amount (200 Hz).

[0075] FIG. 21 is a diagram showing the frequency spectrum of the difference frequency signal. As shown in FIG. 21, the signal FH11 comb is a frequency comb composed of a plurality of spectral lines with an equal interval (200 Hz) between the frequencies of adjacent spectral lines.

[0076] FIG. 22 is a diagram showing the relationship between the frequency difference between the first electromagnetic wave signal and the second electromagnetic wave signal and the peak frequency of the difference frequency signal. As shown in FIG. 22, when the horizontal axis represents the frequency difference between the signal F11 comb and the signal F12 comb, and the vertical axis represents the peak frequency of the signal FH11 comb, it can be seen that it is linear, and it can be confirmed that the signal FH11 is the difference frequency signal between the signal F11 comb and the signal F12 comb.

[0077] FIG. 23 is a two-dimensional image generated by the first harmonic of the first electromagnetic wave signal. FIG. 23 is a signal with a frequency of 300000 Hz, corresponding to the first harmonic on the high wavelength side of the signal FH11. The probe 2 was scanned two-dimensionally by the scanning tunneling microscope controller 3 to acquire a signal, and this signal was imaged by the image generation device 12. The length of the white line shown in this image is 0.6 nm. And the spherical bright part included in the image corresponds to one atom of graphite, and it can be seen that an image with atomic resolution has been captured.

[0078] As described above, according to the second embodiment, by setting the center frequencies of the signal F11 comb and the signal F12 comb, and the density and interval of the spectral lines of the signal F11 comb and the signal F12 comb, the specific mode of the sample S in a wide frequency band (the fine structure of the measurement target such as the vibration, rotation, and spin of the sample) can be measured by the signal FH11 for the interaction exerted on the signal F11 comb and the signal F12 comb. Furthermore, by scanning the probe 2, an image with atomic resolution can be generated.

[0079] In addition, in the signal F1 comb and the signal F2 comb, the frequency difference between the paired spectral lines may be smaller by a predetermined amount for the pair with the larger absolute value of the average of the frequencies of the paired spectral lines among adjacent pairs. Similarly in this case, the interaction of 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 wide frequency band on the signal F11 comb and the signal F12 comb can be measured by the signal FH11.

[0080] (Example 3) FIG. 24 is a diagram for explaining the relationship between the signals. As shown in FIG. 24, the first electromagnetic wave signal and the second electromagnetic wave signal are the first and second frequency combs each consisting of a plurality of spectral lines with equal intervals between the frequencies of adjacent spectral lines (referred to as the signal F21 comb and the signal F22 comb, respectively). Also, the signal F21 comb and the signal F22 comb each consist of a plurality of spectral lines with the intervals between the frequencies of adjacent spectral lines differing by a predetermined amount, and are frequency combs with equal center frequencies. And the frequency difference between the signal F21 comb and the signal F22 comb increases as the distance from the center frequency increases.

[0081] When a part of the signal F21 comb and the signal F22 comb is absorbed and the waveform of the frequency spectrum changes, this change in the waveform is also transferred to the signal FH21 comb, which is the difference frequency signal generated by the signal F21 comb and the signal F22 comb. Then, the heterodyne scanning type tunneling microscope system 1 using the frequency comb extracts the signal FH21 by the phase sensitive detector 4, and can highly sensitively measure the state change of the specific mode of the sample S at fine frequency intervals in a desired frequency band.

[0082] FIG. 25 is a diagram showing the time change of the signal intensities of the first electromagnetic wave signal and the second electromagnetic wave signal. As shown in FIG. 25, the signal F21 comb and the signal F22 comb are rectangular waves of 1000000 Hz and 1000700 Hz, respectively.

[0083] FIG. 26 is a diagram showing the frequency spectra of the first electromagnetic wave signal and the second electromagnetic wave signal. The signal F21 comb and the signal F22 shown in FIG. 26 are frequency combs (constituting the grating of a precision spectroscope) composed of a plurality of spectral lines arranged at equal intervals (interval: 555 Hz) with a center frequency f 10 = 500000000 Hz at the center.

[0084] FIG. 27 is an enlarged view near the peak P21 shown in FIG. 26. As shown in FIG. 27, at the peak P21, the frequency difference between the spectral lines of the signal F21 comb and the signal F22 comb is 700 Hz.

[0085] FIG. 28 is an enlarged view near the peak P22 shown in FIG. 26. As shown in FIG. 28, at the peak P22, the frequency difference between the spectral lines of the signal F21 comb and the signal F22 comb is 1400 Hz.

[0086] FIG. 29 is an enlarged view near the peak P23 shown in FIG. 26. As shown in FIG. 29, at the peak P23, the frequency difference between the spectral lines of the signal F21 comb and the signal F22 comb is 2100 Hz.

[0087] FIG. 30 is an enlarged view near the peak P24 shown in FIG. 26. As shown in FIG. 30, at the peak P24, the frequency difference between the spectral lines of the signal F21 comb and the signal F22 comb is 2800 Hz.

[0088] FIG. 31 is a diagram showing the frequency spectrum of the difference frequency signal. As shown in FIG. 31, the signal FH21 comb is a frequency comb composed of a plurality of spectral lines arranged at intervals of 700 Hz.

[0089] FIG. 32 is a diagram showing the relationship between the frequency difference between the first electromagnetic wave signal and the second electromagnetic wave signal and the peak frequency of the difference frequency signal. As shown in FIG. 32, when the horizontal axis represents the frequency difference between the signal F21 comb and the signal F22 comb and the vertical axis represents the peak frequency of the signal FH21 comb, it can be seen that it forms a straight line, confirming that the signal FH21 is the difference frequency signal between the signal F21 comb and the signal F22 comb.

[0090] FIG. 33 is a two-dimensional image generated by the first harmonic of the first electromagnetic wave signal. FIG. 33 shows signals at frequencies of 501000000 Hz and 409000000 Hz, corresponding to the first harmonics on the high-wavelength side and low-wavelength side of signal F1. The probe 2 was two-dimensionally scanned by the scanning tunneling microscope controller 3 to acquire a signal, and this signal was imaged by the image generation device 12. The length of the white line shown in this image is 0.6 nm. And the spherical bright part included in the image corresponds to one atom of graphite, and it can be seen that an image with atomic resolution has been captured.

[0091] As described above, according to Example 3, by setting the center frequencies of signal F21 comb and signal F22 comb, and the density and interval of the spectral lines of signal F21 comb and signal F22 comb, the interaction of a specific mode of sample S in a desired frequency band (the fine structure of the measurement object such as the vibration, rotation, and spin of the sample) on signal F21 comb and signal F22 comb can be measured in detail by signal FH21. Furthermore, by scanning the probe 2, an image with atomic resolution can be generated.

[0092] Note that signal F21 comb and signal F22 comb may be frequency combs composed of a plurality of spectral lines whose frequency intervals between adjacent spectral lines differ by a predetermined amount, and whose center frequencies are separated by a predetermined frequency from each other. Similarly in this case, the interaction of a specific mode of sample S in a wide frequency band (the fine structure of the measurement object such as the vibration, rotation, and spin of the sample) on signal F11 comb and signal F12 comb can be measured by signal FH11.

[0093] (Embodiment 3) FIG. 34 is a block diagram showing the configuration of a heterodyne scanning tunneling microscope system using a frequency comb according to Embodiment 3. In the heterodyne scanning tunneling microscope system 200 using a frequency comb according to Embodiment 3, the first electromagnetic wave signal generator 6 is, for example, a wavelength tunable laser. Then, the first electromagnetic wave signal generator 6 generates infrared light with a wavelength of 1.55 μm (center frequency 190 THz) as the first electromagnetic wave signal.

[0094] The second electromagnetic wave signal generator 7 is, for example, a high-speed optical switch or an optical modulator, and generates a modulation signal obtained by modulating the first electromagnetic wave signal at intervals of 110 Hz.

[0095] The optical power adjuster 21 amplifies or attenuates the modulation signal from the second electromagnetic wave signal generator 7. The optical power adjuster 21 is, for example, an erbium-doped fiber amplifier (EDFA), but may also be a laser amplifier, a doped fiber amplifier, a fiber Raman amplifier, a semiconductor amplifier, or an optical attenuator, etc.

[0096] The condenser lens 22 condenses the light from the optical power adjuster 21 and irradiates the nonlinear junction NL.

[0097] (Example 4) FIG. 35 is a diagram showing the current spectral density in which the modulation signal is superimposed on the tunneling current. FIG. 35 shows the frequency distribution obtained by performing FFT on the modulation signal with a resolution of 1.95 Hz by the FFT analyzer 15. The modulation signal is a frequency comb composed of a plurality of spectral lines in which the frequency intervals between adjacent spectral lines generated by self-heterodyne are equally spaced (110 Hz).

[0098] FIG. 36 is a two-dimensional image generated by the third harmonic of the first electromagnetic wave signal. FIG. 36 is a signal with a frequency of 330 Hz and corresponds to the third harmonic on the high-wavelength side of the modulation signal. The probe 2 was two-dimensionally scanned by the scanning tunneling microscope controller 3 to acquire a signal, and this signal was imaged by the image generator 13. The tunneling current at this time was 130 pA, and the bias voltage applied to the sample S was 1 V. The length of the white line shown in this image is 30 nm. It can be seen from this image that an image with atomic resolution has been captured.

Explanation of Signs

[0099] 1, 100, 200 Heterodyne Scanning Tunneling Microscope System 2 Probe 3 Scanning Tunneling Microscope Controller 4 Phase Sensitive Detector 5 Oscillator 6 First Electromagnetic Wave Signal Generator 7 Second Electromagnetic Wave Signal Generator 8 Third Electromagnetic Wave Signal Generator 9 Program Pulse Generator 10 Power Combiner 11 Directional Coupler 12 Bias T 13 Image Generator 14 Spectrum Analyzer 15 FFT Analyzer 21 Light Quantity Regulator 22 Condensing Lens

Claims

1. An actuating member that interacts with the object to be measured, A first signal generator that generates a first electromagnetic wave signal which is a first frequency comb composed of a plurality of spectral lines with equal intervals between the frequencies of adjacent spectral lines, A second signal generator that generates a second electromagnetic wave signal, A third signal generator that generates a reference signal, In a state where the actuating member is arranged to form a non-linear junction with the object to be measured, a detection unit that detects a heterodyne beat signal generated by the interaction with the object to be measured in the non-linear junction between the first electromagnetic wave signal input to the non-linear junction and the second electromagnetic wave signal input to the non-linear junction, A phase-sensitive detector that extracts specific frequency components from the heterodyne beat signal using the reference signal and demodulates the contained precise spectroscopic information, An oscillator that synchronizes the frequency accuracy and phase of the first electromagnetic wave signal, the second electromagnetic wave signal, and the reference signal using the vibration of a substance having a frequency stability equal to or higher than the frequency accuracy of the transition vibration of quartz or rubidium, A measuring device, characterized by comprising the above.

2. The oscillator according to claim 1, wherein the oscillator synchronizes the phases of the first electromagnetic wave signal, the second electromagnetic wave signal, and the reference signal using the vibration of quartz, rubidium, cesium, ytterbium, strontium, or an optical lattice.

3. The oscillator according to claim 1, wherein the oscillator synchronizes the frequency accuracies of the first electromagnetic wave signal, the second electromagnetic wave signal, and the reference signal using the vibration of quartz, rubidium, cesium, ytterbium, strontium, or an optical lattice.

4. The second electromagnetic wave signal according to claim 1 is a second frequency comb different from the first frequency comb, and is a second frequency comb composed of a plurality of spectral lines with equal intervals between the frequencies of adjacent spectral lines.

5. The first frequency comb and the second frequency comb Differ by a predetermined amount in the interval, Each of the plurality of spectral lines constituting the first frequency comb forms a pair in proximity to any one of the plurality of spectral lines constituting the second frequency comb. The difference in frequency between the paired spectral lines is such that, among the pairs adjacent to each other, the pair with the larger absolute value of the average of the frequencies of the paired spectral lines is greater or smaller by the predetermined amount. The measuring apparatus according to claim 4.

6. The first frequency comb and the second frequency comb differ by a predetermined amount in the interval, and are frequency combs having equal center frequencies. The measuring apparatus according to claim 4.

7. The first frequency comb and the second frequency comb differ by a predetermined amount in the interval, and are frequency combs with their center frequencies separated by a predetermined frequency. The measuring apparatus according to claim 4.

8. The acting member is a sharp probe arranged close to the measurement object. The measuring apparatus according to claim 1.

9. 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. The measuring apparatus according to claim 1.

10. The heterodyne beat signal is superimposed on a tunnel current flowing between the measurement object and the acting member. The measuring apparatus according to claim 1.

11. The measuring apparatus according to claim 1, and a scanning unit that two-dimensionally or three-dimensionally scans the acting member with respect to the measurement object. An observation system characterized by comprising the above.

12. An image generation device that generates a two-dimensional image or a three-dimensional image based on the position information of the acting member scanned by the scanning unit. The observation system according to claim 11.

13. An image generation device that generates a two-dimensional image or a three-dimensional image of the demodulated precise spectroscopic information based on the position information of the acting member scanned by the scanning unit. The observation system according to claim 11.

14. An arrangement step of arranging an acting member that interacts with a measurement object so as to form a non-linear junction with the measurement object, a synchronization step of synchronizing the frequency accuracy and phase of a first electromagnetic wave signal, a second electromagnetic wave signal, and a reference signal, which are a first frequency comb composed of a plurality of spectral lines with equal intervals between the frequencies of adjacent spectral lines, using the vibration of a substance having a frequency stability equal to or higher than the frequency accuracy of the transition vibration of quartz or rubidium, a first signal input step of inputting the first electromagnetic wave signal into the non-linear junction, A second signal input step of inputting the second electromagnetic wave signal into the non-linear junction; A reference signal input step of inputting the reference signal into a phase-sensitive detector; 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 with the measurement target at the non-linear junction; An extraction step of extracting a specific frequency component from the heterodyne beat signal by the phase-sensitive detector using the reference signal, and a demodulation step of demodulating the precise spectroscopic information included in the specific frequency component. The measurement method is characterized by including these steps.

Images