JP3085960B2 - Scanning tunneling potential spectroscopy microscope and scanning tunneling potential spectroscopy information detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] Scanning Tunneling Microsc
opy: STM) is a microscope that can measure the shape of a conductive surface at the atomic resolution using the electron tunneling phenomenon.

The STM applies a bias voltage between the sharp probe and the sample, scans the probe while keeping the tunnel current flowing between the probe and the sample constant, and detects the unevenness of the sample from the position information of the probe. Obtain an STM image to reflect.

Tunnel current reflects the distance between the sample and the probe, the microscopic electronic properties of the sample, and the local potential of the sample.
The STM image contains information on the microscopic roughness of the sample surface, microscopic changes in electronic physical properties, and the potential distribution on the sample surface.
Therefore, scanning tunneling spectroscopy (Scanning Tunneling S) is used to separate the surface roughness image and the change image of the electronic properties of the surface from the tunnel current and extract the change image of the electronic properties of the surface.
pectroscopy: STS). In addition, the method of extracting the potential distribution on the sample surface from the tunnel current is described as Scanning Tunneling Potentiometry: S
TP).

The present invention measures the unevenness of a sample, and also measures a local potential distribution and a local electronic state of a conductive sample surface using a scanning potential spectroscopy microscope (Scannig Tunnel).
ing Potentio-Spectroscopy: STPS).

Applying a bias voltage U _B between the [prior art] conductive sample and the probe,
When the probe approaches the sample to a distance of about 10 °, a tunnel current flows between the probe and the sample. The STM scans the probe on the XY surface parallel to the sample surface while keeping the tunnel current constant, and records the movement of the probe to obtain an STM image.
Tunneling current I _T denotes the exponential existence as follows with respect to the probe-sample distance S.

I _T = U _B / R _T exp (−BS√φ) (1) where B is a numerical coefficient of about 1.025 / Å√eV, R _T is a tunnel resistance, and φ is a tunnel barrier height (φ = (φ ₁ +
φ ₂ ) / 2, φ ₁ : Work function of probe, φ ₂ : Work function of sample
It is. Since the tunnel barrier height φ for the clean metal surface is about 1~5eV, (1) from the equation, S is the tunneling current I _T When changes 1Å it can be seen that the changes by about one digit. ST
M detects the distance S between the sample-probe from the tunnel current I _T,
The probe or the sample is finely moved in the Z direction using a piezoelectric fine movement element, and the distance S is controlled by servo control so as to keep the tunnel current constant. This control is performed according to the following system. By recording the control voltage simultaneously with the XY scanning movement of the probe, a three-dimensional atomic order microscopic image,
An STM image is obtained.

The barrier height φ, the tunnel resistance R _T ,
If the bias voltage U _B was measured a certain sample regardless of the location, the resulting STM images faithfully represent the unevenness of the sample surface.
However, many of the samples to be actually measured have local variations in the surface potential distribution that determines the barrier height φ, the tunnel resistance R _T , and the bias voltage. An STM image obtained by measuring such a sample includes a difference in surface potential depending on the surface irregularities, the energy state of tunneling electrons, and the location.

As a method of separating information about the energy state of electrons from the tunnel current, a bias voltage U _T of the tunnel current is used.
Dependent _{∂I T / ∂U T, (∂I} T / ∂U T) / (∂U T / ∂I T), ∂ 2
Differential conductance spectroscopy to find the distribution of states of electrons and phonons from I _T / ∂ ² U _T etc. and the distribution of tunnel barrier height φ from the sample probe distance dependence of tunnel current ∂lnI _T / ト ン ネ ル S There is barrier height spectroscopy. These are collectively called scanning tunneling spectroscopy microscopes (STS).

Regarding STS, the present inventors have proposed in Japanese Patent Application No. 1-170663 a unique method of detecting a spectral signal using a time-varying tunnel current with a time-varying bias voltage or a probe sample interval. I have. This method will be described with reference to FIG. Sample 102 and probe 104
Bias voltage U _B that periodically changes between
While applying the sine waveform voltage shown in FIG.
Using Z fine movement mechanism 108, the closer the probe 104 into the sample 102, tunnel current I _T which oscillates at the fundamental period of the bias voltage as shown in FIG. 13 (b) flows. At this time, servo is applied so as to keep the distance between the sample and the probe constant as in the case of a normal STM. At this time, to prevent the distance between the sample and the probe from being affected by the oscillation of the tunnel current,
Absolute value detector 114 (or vibration detector) and servo circuit 112
Is set to a sufficiently long time that is at least five times the basic period of the bias voltage. The tunnel current is converted into a voltage by the current / voltage converter 110 and input to the absolute value detector 114. The absolute value detector 114 detects the absolute value of the tunnel current shown in FIG. 13 (c). The servo circuit 112 adjusts the distance between the sample probes with the signal shown in FIG. 13 (e) like the signal shown in FIG. 13 (d) so that the tunnel current intensity becomes constant at a specific time average. This is a servo system that can control and set the servo time constant so as not to catch up with the bias voltage fluctuation. The probe 104 is scanned at such a speed that the distance between the sample and the probe does not change. A servo signal when the probe 104 is scanned in such a setting becomes information on the unevenness of the sample surface. When the servo time constant and the basic period are set as described above, the servo operation can be performed using an arbitrary bias voltage waveform including a frequency component higher than the basic frequency.

In addition, in order to obtain spectral information in real time, the tunnel current and the bias voltage are input to the analog arithmetic unit 116, and arithmetic processing (for example, ΔI _T / ΔU _T , (ΔI _T / ΔU _T ) /
(∂U _T / ∂I _T ), spectral information (differential conductance, state density, etc.) within the range of the bias voltage amplitude can be obtained in real time. The response frequency of these analog signal systems is at least higher than the basic frequency of the applied bias voltage. The analog operation unit 116 is formed by combining differential addition, subtraction, multiplication, and division to extract spectral information from the tunnel current and the bias voltage signal. Since the calculation processing for obtaining the spectral data is performed in real time, there is no need for post-processing such as numerical differentiation of the data. The spectral data obtained for one voltage level corresponds to the unevenness data on a one-to-one basis. In this way, real-time detection of the spatial distribution of spectral information (STS image) can be performed simultaneously with the uneven image.

On the other hand, for samples with potential gradients or potential distributions on the surface, such as semiconductor pn junctions or semiconductor laser heterostructures, the spread of space charge layers depending on the applied junction voltage and In order to obtain information on the local conductivity such as the conductive mechanism, it is necessary to separate and measure the surface potential distribution and the unevenness with high resolution without disturbing the surface potential distribution. In the STM, the tunnel current flows due to a local potential difference between the sample surface and the tip of the probe, so that a local change in the bias voltage due to a difference in the surface potential distribution affects the tunnel current value. Therefore, a method of applying a bias voltage has been devised, and a scanning tunnel potentiometry (STP) that can simultaneously measure the unevenness of the sample surface and the distribution of the local surface potential has been proposed.

The STP will be described with reference to FIG. Sample 1
22 has an Au film 120 on an SiO ₂ substrate 118 and two electrodes 124 and 126 for applying a potential gradient ΔU, a modulation voltage U _T , and an offset voltage UREG are added to the Au film 120. Between these electrodes 124 and 126, for example, ΔU shown in FIG.
= U ₂ −U ₁ is supplied from the power supply 136. Due to ΔU, the sample 122 forms a potential distribution as shown in FIG. 6 reflecting the surface conductivity. In STP, the distance control between the probe samples is
For example, the modulation voltage U _T = U _T sin of the fundamental period ω ₀ from the oscillator 134
ω ₀ t is added to the entire sample, the intensity of the ω ₀ component of the tunnel current is detected by the lock-in amplifier 138, and the logarithmic amplifier 140
To linearize the dependence on the distance, control the probe so that the ω ₀ component of the tunnel current becomes constant by the proportional and integral control 142, record the control voltage, and measure the STM image. Although the bias voltage U _T is a signal which becomes zero on average, deviated from the average is 0 tunneling current position of the probe by the potential distribution of the sample. At that time, the offset voltage UREG is added to the potential of the entire sample by the feedback from the integrator 136 to return the deviation from the current detection system, and the bias voltage is fed back so that the average of the tunnel current becomes zero. UREG corresponds to a local potential of the sample corresponding to the position of the tip of the probe. By recording the offset value UREG together with the scanning, local potential information on the sample surface can be obtained, and the potential distribution can be recorded simultaneously with the unevenness of the sample. At this time, the potentials of the electrodes 124 and 126 are respectively U ₁
= UREG + U _T sinωt, become _{U 2 = UREG + U T sinωt} + ΔU. Due to this potential feedback, no stationary current other than the tunnel current flowing in the basic period flows between the probe and the sample.

[Problems to be Solved by the Invention] The STP can measure the potential distribution in the XY plane of the sample and calculate the potential gradient in the XY plane from the measured potential distribution. This information is based on the local resistance of the sample. It reflects the rate, the mobility of the charge. However, information on the movement of the charge in the Z direction is not obtained from the STP measurement. Further, it is not possible to identify a substance local to the sample that has led to the formation of the potential distribution. Furthermore, information on the energy state of the charge contributing to the propagation of the current cannot be obtained. Meanwhile, ST
In S, spectral information of a sample having a potential gradient cannot be obtained without disturbing the current flowing through the sample.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a scanning tunneling potential spectroscopy microscope capable of measuring unevenness of a sample and simultaneously measuring local potential distribution and spectral information of the sample.

[Means for Solving the Problems] A scanning tunneling potential spectroscopy microscope according to the present invention includes a means for applying a bias voltage including a modulation voltage having a predetermined waveform, which changes with time in a constant cycle, to a sample; Means for detecting a tunnel current flowing between the sample and the sample, means for detecting an absolute value of the tunnel current, and a distance between the sample and the probe using the absolute value of the tunnel current. A means for performing servo control with a time constant of 5 times or more, a means for obtaining unevenness data of a sample from an output servo signal, and a means for performing feedback control so that a tunnel current becomes 0 on average per one cycle of a bias voltage. Means for controlling the offset voltage of the bias voltage, means for detecting local potential data of the sample from the offset voltage,
Means for performing real-time analog calculation of differential conductance by an analog arithmetic unit from a tunnel current and a modulation voltage to obtain differential conductance data, and a state in which the distance between the sample and the probe is kept constant, and simultaneously with the irregularity data. Means for real-time measurement of the differential conductance data and the local potential data.

[Operation] The operation of the scanning tunneling potential spectroscopy microscope of the present invention will be described with reference to FIG. Electrode for the sample 10 to apply a potential gradient ΔU and the bias voltage U _B
14,16 are provided. If there is no need to artificially apply a potential gradient, one electrode may be used. The potential servo circuit 2 is applied to both electrodes 14 and 16 by a predetermined waveform voltage (for example, a sine wave U _T sin ω ₀ t) that changes with time in a fixed cycle from the oscillator 20.
Bias voltage U _B which offset voltage UREG is added output from 2 is applied. Further, a voltage ΔU for giving a potential gradient in the X direction generated from the potential difference generator 18 is applied to the electrode 16. That is, the potential of the electrode 14 is
U _1, when the potential of the electrode 16 and _{U 2, U 1 = UREG +} U T sinω
₀ t, which is _{U 2 = UREG + U T sinω} 0 t + ΔU. Zero potential probe
When brought close to 12 to about several nm on the surface of the sample 10, a tunnel current flows I _T corresponding to a potential difference between the probe 12 and the sample 10. The potential difference between the electrode 14 and the sample surface at the probe position is represented by U _S (x)
When, when the tunneling current I _T, which is detected by the current detector 26 becomes 0, on average, the average of the U ₁ + U _S (x) becomes 0V. _{Thus, <U S (x) +} UREG + U T sinω 0 t> = 0, i.e., U _S (x) = - becomes Ureg. Fed back to UREG using the average value of the tunneling current I _T, controls the offset voltage UREG as tunneling current average value becomes 0, the potential distribution of the sample surface by recording the -UREG U _S (x) Is measured.

Further, with respect to the tunnel current I _T to be detected, Japanese Patent Application No. 1
By the above-mentioned servo operation described in
By recording the servo voltage while keeping the distance between the probe 10 and the probe 12 constant, a normal STM image showing irregularities on the sample surface can be obtained.

To obtain spectroscopic information in real time, the tunnel current
The I _T and a bias voltage U _T is input to an analog arithmetic unit 32, real-time processing (e.g. _{∂I T / ∂U T, (∂I} T / ∂
(U _T ) / (∂U _T / ∂I _T ), spectral information (differential conductance state density, etc.) within the range of the bias voltage amplitude can be obtained in real time. Here, the response frequency of the analog signal system is at least higher than the basic frequency of the applied bias voltage.

The calculation processing for obtaining the spectral data is performed in real time,
No post-processing such as numerical differentiation is required for the data. The spectral data obtained for one voltage level corresponds to the unevenness data on a one-to-one basis. Therefore, the spatial distribution (STS image) and the local surface potential distribution (STP image) of the spectral information can be detected in real time simultaneously with the uneven image.

Embodiment A first embodiment of the present invention will be described with reference to FIG.

The sample 10 is a resistor having a carbon resistance, and is a sample surface on which good conductive carbon and a binder of an insulator are mixed. The probe 12 uses a PtIr electrolytic polishing needle. The servo circuit 28 is an integral servo circuit. Modulation signal generator 20
Outputs a sine wave U _T sin ω ₀ t. The potential servo circuit 22 is of an integral type, and the response frequency is set to 1/5 or less of the bias modulation frequency so that the offset voltage does not catch up with the bias voltage modulation.

The analog arithmetic unit 32 calculates the differential conductance ∂I _{T in} real time from the time-varying bias voltage and tunnel current.
/ Calculate the ∂U _T. The analog operation unit 32 for calculating the differential conductance has the circuit configuration shown in FIG. 2, and its operation principle model is shown in FIG. The local current-voltage characteristics between the sample and the tip depend on the position of the atom,
It has a unique shape as shown in FIG. FIG. 3 (b)
When the bias voltage U _T of the sine wave shown in is applied,
The tunnel current reflects the I-U characteristic shown in FIG. 3A, as shown in FIG. 3C. Fig. 3 (c)
2 and the bias voltage shown in FIG. 3 (c) are respectively differentiated by the differentiating circuit 34 shown in FIG.
And 36, and the time difference ΔI _T / shown in FIG.
The ∂t signal and the ∂U _T / ∂t signal shown in FIG. 3 (e) are obtained. These two signals are input to the division circuit 38, and the differential conductance ΔI _T shown in FIG.
/ ∂U _T is calculated.

The STM data and the STP data have a single value for each scanning point, but the STS data varies depending on the bias voltage value. Therefore, it is necessary to always output the differential conductance value at a specific voltage using the sampling circuit shown in FIG. The sample-and-hold amplifier 40, the differential conductance value output from the differential conductance arithmetic circuit shown in FIG. 2 (∂I _T / ∂U _T) is input. Bias voltage U _T and reference voltage V ₀ is the comparator 42
At the timing when U _T = V ₀ , a pulse having a pulse width τ _P for sampling by the sample & hold amplifier 40 is generated from the shot pulse generator 44. In this way, the value of the differential conductance at U _T = V ₀ (∂I _T / ∂U _T | UT = V0) is always output.

The scanning speed of the probe is set to such a speed that the uneven servo system can respond to the change in the unevenness and the potential servo can respond to the change in the local bias potential. sample·
The distance between the tips is kept constant, the potential of the sample located at the tip of the tip is set near 0, and the surface irregularity information, the surface local potential value, and the differential conductance value at the bias voltage V ₀ correspond to the XY scanning signal. Therefore, by using the three display methods shown in FIG. 5 together, the spatial correspondence between the concavo-convex image, the local potential image, and the differential conductance image can be displayed and compared in real time.

The method used to display the planar distribution of the uneven image, the local potential image, and the spectral image in two dimensions is as follows. The data signal is added to the Y scanning signal as shown in FIG. 5 and the XY display mode of the storage oscilloscope 46 is used. The signal is input to the Y axis, and the X scanning signal is input to the X axis. In the storage mode, a bright point is left, and X and Y are added to the luminance signal as shown in FIG.
This is a method of inputting a trigger calculated by the AND gate 47 to enable display in one direction of scanning.

FIGS. 7A to 7C respectively show the surface of the carbon resistor measured simultaneously in air in accordance with this notation.
The unevenness image, the local potential image, and the spectral image of the area of 100 nm × 70 nm are shown.

During the measurement, the modulation voltage U _T is a sine wave having an intensity of 0.6VP-P at frequency 4.1KHz, the average tunneling current is set to 5 nA. The potential gradient in the X direction of the sample is 9mV / 100nm
It is. FIG. 7A shows the unevenness of the sample surface, FIG. 7B shows the level of the differential conductance sampled at a modulation voltage of −50 mV, and FIG. 7C shows the potential distribution on the surface. 7A, 7B, and 7C, the conductivity is high in the flat portion without unevenness on the left side of the screen, the value of the differential conductance is stable, and the fluctuation of the potential is relatively smooth. is there. On the other hand, in the area where the uneven image is a hill,
The differential conductance value is unstable, and the potential distribution fluctuates drastically.

From what has been described above, it can be seen that the left portion has carbon and the right portion has a structure in which carbon particles adhere to the binder. Further, by connecting the analog operation data sampling circuits in parallel, the differential conductance can be independently sampled at a large number of reference voltages, so that local values of the differential conductance at a plurality of bias voltage levels can be simultaneously held. That is, many spectral images can be displayed simultaneously.

Next, a second embodiment of the present invention will be described. In this embodiment, the measurement is performed on a sample having no artificial potential gradient. In this case, instead of the electrodes for forming the voltage gradient shown in FIG. 1, a highly conductive metal film such as gold is used as shown in FIG. 48 is provided on the back surface of the sample 10. In FIG. 8, the same members as those in FIG. 1 are denoted by the same reference numerals.
In this configuration, the measured concavo-convex image, potential image, and tunneling spectroscopic image are images reflecting differences in physical properties of the sample itself or physical properties of the sample surface, respectively.

FIG. 9 is a diagram schematically illustrating how an image is viewed based on the conductive mechanism of the sample 10. As shown in FIG. 9 (a), it is assumed that the sample includes three regions: a region A composed of an n-type semiconductor, a region B composed of a p-type semiconductor, and a region C composed of a metal. As shown in FIG. 9 (b), the semiconductor in the region A and the semiconductor in the region B have an asymmetric I _T -U _T characteristic. Then, the offset voltage URE
G deviates from 0 potential. When the probe is scanned from the region A to the region C, as shown in FIG. 9 (c), the potential data shows Ua and Ub in the n-type semiconductor region A and the p-type semiconductor region B, respectively. Indicates a potential, and becomes 0 in the metal region C reflecting a symmetric current-voltage characteristic.

FIG. 9D schematically shows the dependence of the differential conductance on the bias voltage. For simplicity, assuming that sampling the differential conductance data when the modulation voltage becomes a certain voltage V _0, in each region, actually applied by which the bias voltage U _B are each V ₀ + Ua, V ₀ This means that data at + Ub, V ₀ is being measured. For example, in FIG. 9D, when data is measured when the bias voltages are V1 and V2, the sampling operation is performed when the actual bias voltages are V1 'and V2'. So if the modulation voltage U _T of the input of the comparator 42 in Figure 4 to the bias voltage U _B, is sampled at the timing of V1 and V2. By applying feedback to the bias voltage U _B, if it contains many circuit noise, in order to prevent malfunctions during the sampling, it is necessary to provide a low pass filter in the preceding stage to the comparator.

FIGS. 9 (e) and (f) show U _B = V1 and U _B = V2, respectively.
5 shows a scanning cross section of differential conductance data when sampling is performed in step (1). As described above, even when the bias voltage is uniformly applied to the sample, the physical property distribution of the sample can be measured from a large number of measured images.

Next, a third embodiment of the present invention will be described. When the substance adsorbed or spread on the sample surface has a resonance point or a relaxation point at a specific frequency, STM measurement can be performed using the difference in the electrical frequency response of the adsorbed substance. When the bias voltage comprises a plurality of frequency components, for example, when the bias voltage is Usinω ₀ t + 0.5sin3ω ₀ waveforms such as t shown in FIG. 10 (a), by detecting the tunnel differential conductance, frequency dependence It is possible to distinguish between places with and without. This is because, if the response of the tunnel current has frequency dependence, different signal values are taken depending on the history of the bias voltage even if the measurement is made at one point without scanning the probe. By the way, when there are two different points where the bias voltage value and the direction of the voltage change are the same, such as point A and point B shown in FIG. 10 (a), as shown in FIG. In the method of determining the sampling timing based on the bias voltage value, a sampling pulse is generated at both the points A and B, so whether the final output signal is the signal at the point A or the signal at the point B is determined. Indistinguishable. Therefore, by using the circuit shown in FIG. 11 based on the timing of the modulation signal, the measured values at the points A and B are distinguished. The shot pulse generator 50 generates pulses in response to the input of the U _T triggers the pulse width tau _D can be set at any time. For example, when measuring point A FIG. 10 (a), when U _T trigger shown in Fig. 10 (b) the shot pulse generator 50 is input, as shown in FIG. 10 (c) In order to output a delayed pulse, the pulse width τ _D of the pulse generator 50 is output.
Is set so that the sampling pulse τ _P shown in FIG. 10D is output from the shot pulse generator 44. To select a measurement point, the pulse width τ
_{Since P} may be adjusted, the signal sampled during one cycle has a single value. STP can be measured simultaneously by sampling the STS using this method.

[Effects of the Invention] According to the present invention, when the bias voltage of the STM includes a component that changes with time in a constant cycle, the servo time constant is appropriately set to perform an operation of keeping the distance between the sample probes constant, By recording the voltage, recording the irregularity data, and returning the offset voltage to the entire sample, the tunnel current flowing into the probe of 0V potential oscillates around 0A. By recording the offset voltage value at this time, the potential distribution of the sample can be recorded, and at the same time, the bias voltage dependency of local spectral data in real time from the tunnel current and the bias voltage maintains the distance between the sample probes. Can be measured in the state. In addition, the surface potential distribution and the bias voltage dependence of the tunnel current can be measured without disturbing the current of the sample, depending on the state of the current flowing through the sample (such as the operating state of a semiconductor laser or the like).

In addition, since the bias voltage value for sampling the spectral data can be set at an arbitrary point within the voltage amplitude of the modulation bias, an arbitrary number of points can be set, so that the potential distribution at the semiconductor junction and the value of the differential conductance at the semiconductor gap voltage can be simultaneously measured. it can.

Since a plurality of measurement points can be provided for the bias voltage value, the required number of points can be measured as the bias voltage dependence data at the same time as the unevenness of the sample surface and the local potential distribution at each point.

Further, since the servo operation is not stopped even when the bias voltage fluctuates, the servo operation accompanying the scanning does not become a step-like response.

In addition, since analog data and frequency division output spectral data and potential data in real time,
This eliminates the need for post-processing of data due to the above.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of a scanning tunneling potential spectroscopy microscope according to the present invention, FIG. 2 is a diagram showing a configuration of an analog arithmetic unit shown in FIG. 1, and FIG.
FIG. 4 is a diagram showing signals at respective elements of the first embodiment, FIG. 4 is a block diagram of a sampling circuit used in the first embodiment, and FIG.
The figure shows the signal flow when displaying the image on the storage oscilloscope in association with the scanning signal and the measurement data,
FIG. 6 is a diagram showing signals at each element when displayed on a storage oscilloscope, FIGS. 7A to 7C are diagrams showing the surface of a carbon resistor, and FIG. 8 is a scan according to a second embodiment of the present invention. FIG. 9 is a diagram showing a configuration of a scanning tunneling potential spectroscopy microscope, FIG. 9 is a schematic diagram of physical properties for explaining the second embodiment, FIG. 10 is a diagram showing sampling timing in the third embodiment, and FIG. FIG. 12 is a diagram showing a sampling circuit used in the third embodiment, FIG. 12 is a diagram showing a basic configuration of an analog spectroscopic microscope, and FIG. 13 is a diagram showing a relationship between a tunnel current and a servo voltage in the analog spectroscopic microscope of FIG. FIG. 14 is a diagram showing the configuration of a scanning tunnel potentiometer, and FIG. 15 is a model diagram of the potential distribution on the surface of the sample shown in FIG. 12 ... probe, 20 ... oscillator, 22 ... potential servo circuit, 26 ... current detector, 28 ... servo circuit, 30 ... absolute value detector, 32 ... analog operation unit.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Norio Mikoshiba 2-43-2 Hatagaya, Shibuya-ku, Tokyo O-limpus Optical Industrial Co., Ltd. (56) References JP-A-3-43944 (JP, A) Seizor Morita And two others, “Scanning Tunneling Potentiometry / Spectroscopy (STP / STS)”, Japan Journal of Applied Physics, European Journal of Applied Physics, November 20, 1989, November 28, 1989. No. pp. L2034-L2036 Naotake Morita, et al., “Simultaneous Measurement and Data Processing of STS / STM”, Electrotechnical Laboratory, Ohm Co., Ltd., May 20, 1988, Vol. 52, No. 5 No., pp. 717-727 (58) Fields studied (Int. Cl. ⁷ , DB name) G01N 13/10-13/24 G01B 7/34 H01J 37/28 JICST file (JOIS)

Claims (15)

(57) [Claims] 1. A scanning tunneling microscope, comprising: means for applying a bias voltage including a modulation voltage having a predetermined waveform which changes with time in a constant cycle to a sample; and a tunnel current flowing between the zero potential probe and the sample. Means for detecting, means for detecting the absolute value of the tunnel current, and servo control of the distance between the sample and the probe using the absolute value of the tunnel current with a time constant at least five times the cycle of the modulation voltage. Means for obtaining the unevenness data of the sample from the output servo signal, and means for controlling the offset voltage of the bias voltage so as to perform feedback control so that the tunnel current becomes zero on average per one cycle of the bias voltage. Means for detecting local potential data of the sample from the offset voltage, and real-time differential conductance of the differential Means for performing differential operation to obtain differential conductance data, and means for real-time measurement of the differential conductance data and the local potential data simultaneously with the unevenness data while maintaining a constant distance between the sample and the probe. A scanning tunneling potential spectroscopy microscope comprising: 2. In a scanning tunneling microscope, a probe is set to 0
To a potential, applying a bias voltage including a modulation voltage of a predetermined waveform that changes with time in a constant cycle as the potential of the sample, detects a tunnel current flowing between the sample and the probe, detects an absolute value of the tunnel current, Using a servo circuit with a time constant set so that the bias voltage does not affect the distance between the sample and the probe, the servo between the sample and the probe is controlled based on the absolute value of the tunnel current. The unevenness data of the sample is obtained from the output, the offset voltage of the bias voltage is controlled so that the tunnel current becomes 0 on average for each cycle of the modulation voltage, the local potential of the sample is obtained from the offset voltage, By performing real-time analog calculation of differential conductance from current and bias voltage, the differential conductance can be obtained simultaneously with the unevenness data while keeping the distance between the sample and the probe constant. Nsu data and scanning tunneling potential spectral information detection method for performing real-time measurement of local electrical potentials data. 3. The scanning tunnel potential spectroscopy microscope according to claim 1, wherein the means for applying the bias voltage to the sample includes a modulation voltage generator, and the modulation voltage generator is a sinusoidal voltage generator. 4. The modulation voltage according to claim 2, wherein the modulation voltage is a sine wave voltage.
The scanning tunneling potential spectral information detection method described in the above. 5. The apparatus according to claim 1, wherein the means for applying the bias voltage to the sample includes a plurality of electrodes provided on the sample, and means for generating a potential gradient in the sample by applying different potentials to the respective electrodes. Item 4. A scanning tunnel potential spectroscopic microscope according to Item 1. 6. The scanning tunneling potential spectral information detecting method according to claim 2, wherein different bias potentials are applied to a plurality of points on the sample to artificially generate a potential gradient. 7. A scanning tunneling microscope, comprising: means for applying a bias voltage including a modulation voltage having a predetermined waveform, which changes with time at a constant period, to a sample; and a tunnel current flowing between the zero potential probe and the sample. Means for detecting, means for detecting a fundamental frequency component of a modulation voltage that changes at a constant period included in the tunnel current, and servo control for controlling a distance between the sample and the probe using the fundamental frequency component. Means for obtaining unevenness data of the sample from the output servo signal, and means for controlling the offset voltage of the bias voltage so as to perform feedback control so that the tunnel current becomes zero on average per cycle. A means for detecting local potential data of a sample from an offset voltage, and a differential conductor from a tunnel current and a modulation voltage by an analog arithmetic unit. Means for obtaining differential conductance data by performing a real-time analog calculation of the impedance, and realizing the differential conductance data and the local potential data simultaneously with the irregularity data while maintaining a constant distance between the sample and the probe. Scanning tunneling potential spectroscopy microscope comprising means for measuring time. 8. A scanning tunneling microscope, wherein a probe is set at 0
A bias voltage including a modulation voltage having a predetermined waveform that changes with time at a constant cycle as a sample potential is applied, and a tunnel current flowing between the sample and the probe is detected, and the voltage changes at a constant cycle included in the tunnel current. The fundamental frequency component of the modulation voltage to be detected is detected, and the servo circuit is used to servo-control the distance between the sample and the probe from the fundamental frequency component of the modulation voltage. The offset voltage of the bias voltage is controlled so that the current becomes 0 on average for each cycle of the modulation voltage, the local potential of the sample is obtained from the offset voltage, and the real-time analog of the differential conductance is obtained from the tunnel current and the bias voltage. By performing the calculation, the differential conductance data and the local potential data can be obtained simultaneously with the unevenness data while keeping the distance between the sample and the probe constant. Scanning tunneling potential spectral information detection method for performing real-time measurement data. 9. An arbitrary voltage within a range of an amplitude of a modulation voltage,
A sample and hold amplifier that holds only the differential conductance data at a specific bias voltage from the local differential conductance data output in real time from the analog arithmetic unit, and a sample and hold amplifier based on the voltage value of the arbitrary waveform generator The scanning tunneling potential spectroscopy microscope according to claim 1, further comprising a sampling circuit to be operated. 10. The scanning tunneling potential spectral information detecting method according to claim 2, wherein a differential conductance at at least one specific bias is obtained from local differential conductance data at an arbitrary voltage within a range of the amplitude of the modulation voltage. 11. A sample for holding only differential conductance data at a specific timing from local differential conductance data output in real time from an analog operation unit at an arbitrary time within one cycle of a modulation voltage. 2. The scanning tunneling potential spectroscopy microscope according to claim 1, further comprising: a &amp; hold amplifier; and a sampling circuit for operating the sample & hold amplifier based on a trigger timing of a bias voltage generator. 12. The scanning tunneling potential spectral information detection according to claim 2, wherein a differential conductance at at least one specific timing is obtained from local differential conductance data at an arbitrary time within one period of the modulation voltage. method. 13. The scanning tunnel potential spectroscopy microscope according to claim 1, wherein a phase compensation circuit for adjusting the phase of the tunnel current and the modulation voltage is provided before the analog operation unit. 14. The tunnel potential spectral information detecting method according to claim 2, wherein the phases of the tunnel current and the bias voltage are adjusted before the analog operation is performed. 15. A means for detecting a tunnel current when a signal from a bias voltage signal is detected by said means for detecting a tunnel current even though a tunnel current does not flow between the probe and the sample. 2. The scanning tunneling potential spectroscopic microscope according to claim 1, further comprising a compensating means for extracting only an original tunnel current signal from the detected tunnel current signal immediately after the step (c).