JP3115021B2 - Atomic force microscope / scanning tunnel microscope and control method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a surface shape or analyzing a material by bringing a sharply pointed probe close to a sample surface and detecting a physical quantity depending on a distance between the tip of the probe and the sample surface. Among those related to scanning probe microscopes that perform high spatial resolution, such as the atomic force microscope, which detects the force such as the atomic force acting on the tip of the probe and the surface of the sample to measure the surface shape, the tip of the probe and the surface of the sample BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an atomic force microscope / scanning tunnel microscope which is combined with a scanning tunnel microscope for measuring a surface shape and an electronic property by detecting a tunnel current flowing therebetween, and a control method thereof.

[0002]

2. Description of the Related Art A scanning tunneling microscope (hereinafter abbreviated as STM) can observe and analyze the surface of a conductive material at a high resolution of an atomic order, and can use an atomic force microscope (AFM).
(Abbreviated as) is attracting attention because the surface can be observed at a high resolution of an atomic order irrespective of the conductivity.
Atomic force microscope / scanning tunneling microscope (hereinafter abbreviated as AFM / STM), which is a combination of these devices, is highly capable of observing the surface shape and analyzing electronic characteristics of a surface on which a conductive material and a non-conductive material are mixed. Attention has been paid to the fact that they can be formed at the same time with spatial resolution. For example, it is described in the Journal of the Japan Institute of Metals, Vol.

The configuration and operation of a conventional AFM / STM are as follows. That is, when a soft leaf spring with a sharp and sharp probe attached is brought close to the sample surface,
A repulsive or attractive force acts between the tip of the probe and the surface of the sample due to an atomic force, and the leaf spring bends. The amount of deflection can be detected with very high sensitivity by the amount of tunnel current flowing between another probe on the back of the leaf spring and the back of the leaf spring and the amount of light detected by a photodetector based on the principle of optical leverage. Further, when a bias voltage is applied between the sample and the probe using a conductive probe / leaf spring, a tunnel current due to a tunnel phenomenon flows between the sample and the probe when the sample is conductive. Since this interatomic force and tunnel current greatly depend on the distance between the sample and the probe, the physical quantity is detected while raster-scanning the sample in the XY directions (in-plane directions), and the sample is moved in the Z direction so that it becomes constant. By performing feedback control in a direction (perpendicular to the sample surface), the surface shape of the sample can be observed in the atomic order. For example, on a surface where a conductive material and a non-conductive material are mixed, feedback control is performed so that the atomic force is constant, and the tunnel current is mapped while corresponding to the raster scan. The distribution can be observed with high spatial resolution. Further, by detecting the interatomic force while performing feedback control so that the tunnel current becomes constant, the force acting between the sample and the probe during the STM observation can be measured.

There is a technique called scanning tunneling spectroscopy (hereinafter abbreviated as STS) in which a spectral function is added to the STM method. In this method, a tunnel current signal is input while sweeping a bias voltage while a relative position between a sample and a probe is once fixed at each XY scanning point, and an I (tunnel current) -V (bias voltage) characteristic is measured. By doing
Attention has been paid to a method capable of analyzing electronic characteristics at each XY scanning point with high resolution. For example, Journal of the Physical Society of Japan vo
l. 46, no. 4 (1991), pp. 293-295.

[0005]

However, in the above-mentioned AFM / STM according to the prior art, a tunnel which flows when a bias voltage set to a certain value is applied between a sample and a probe under a constant condition of an atomic force. Only a spatial distribution image of a current value, that is, an image of a spatial distribution of conductivity at a specific bias voltage and an uneven image of a sample surface are obtained, and there is no spectral mechanism.
Therefore, even if it is desired to observe a sample surface on which a plurality of substances having different electrical characteristics such as IV characteristics between the sample and the probe are mixed even if the conductivity at the specific bias voltage is the same, When it is desired to obtain detailed electronic characteristics such as this, there is a problem that this cannot be performed.

Further, when observing a surface containing a non-conductive material, a feedback control method cannot be used so that a tunnel current is constant, but a feedback control is performed so that an atomic force is constant. However, in this case, the tunnel current has higher resolution in the vertical direction than the interatomic force (distance dependence is large), so the fluctuation of the tunnel current due to feedback control error is large, and it is possible to distinguish different conductive materials. There was a problem that it was difficult.

[0007] The present invention has been made to solve the above problems, and one object of the present invention is to include a non-conductive substance.
Feedback control error when observing
The fluctuation of tunnel current due to different conductive materials
AF that can distinguish between and observe their substance distribution
It is to provide M / STM.

[0008] Another object of the present invention is to add to the above.
Furthermore, although the electrical characteristics are different, operation at a specific bias voltage
Observation of sample surface where multiple substances with the same electrical conductivity are mixed
Another object of the present invention is to provide an AFM / STM capable of measuring detailed electronic characteristics such as a surface state density .

[0009]

In order to achieve the above purpose SUMMARY OF THE INVENTION In the atomic force microscope / scanning tunneling microscope and the control method thereof of the present invention, a sample, and the probe, the sample-probe A scan control unit for scanning and controlling a relative position of the sample surface in the in-plane direction between the sample and a feedback control unit for performing feedback control of a relative position between the sample and the probe in a direction perpendicular to the sample surface; A bias voltage controller for applying a bias voltage to a sample or the probe, an atomic force detector for detecting a force acting between the sample and the probe, and a tunnel current for detecting a current flowing between the sample and the probe In an atomic force microscope / scanning tunnel microscope composed of a detection unit,
The feedback control unit may be an atomic force signal output from the atomic force detection unit and a tunnel current detection unit.
Simultaneously input both tunnel current signals output from
And, wherein the function to these parameters as the feedback signal
Depending on the conductive / non-conductive nature of the sample surface Gyosu Fidoba <br/> click system is characterized in Rukoto.

[0010] In addition, also in order to achieve the above purpose,
In atomic force microscopy / scanning tunneling microscope and the control method thereof of the present invention, among the above atomic force microscope / scanning
In the tunneling microscope, the bias voltage control unit
Is a voltage generator that changes the bias voltage with a predetermined voltage waveform.
The feedback control unit comprises a sample and a probe.
Scanning control of the relative position of the sample surface between the needles in the in-plane direction.
In the process, the value of the interatomic force acting between the sample and the probe and
Tunnel flowing between the sample and the probe due to the bias voltage
The function using both the current values as parameters is called the feedback signal.
The test is performed according to the conductive / non-conductive properties of the sample surface.
The relative position between the sample and the probe in the direction perpendicular to the sample surface is
Feedback control to keep the bias voltage within a certain range.
In while sweeping speed is characterized and this <br/> inputting a tunnel current signal.

[0011]

In the atomic force microscope / scanning tunneling microscope (AFM / STM) of the present invention, the feedback control unit comprises:
Signal of tunnel current and signal of interatomic force acting between sample and probe
Input both at the same time and use them as parameters.
Feedback control is performed using the number as a feedback signal. For example,
The part where the tunnel current flows is determined to be conductive, and
Feedback giving priority to keeping the channel current constant
The part where the tunnel current does not flow is non-conductive
Judgment is made, and the atomic force is kept constant and the feedback system is
I will do it. In this way, the feedback control unit
Feedback control by inputting multiple signals of current and atomic force
Control to observe the surface containing non-conductive substances.
Error in the feedback control,
To reduce flow fluctuations and distinguish between different conductive materials
That enables you to.

In the atomic force microscope / scanning tunneling microscope (AFM / STM) of the present invention, the above A
Scanning tunneling spectroscopy (STS) method for FM / STM
By adding the spectroscopic function of
At each scanning point in scanning control of the relative position between hands,
At the same time as changing the bias voltage at a high frequency with a predetermined waveform,
Measured the number of tunnel current signals,
The IV characteristic at each scanning point is obtained.
So that As a result, electrical characteristics are different but specified
Substances with the same conductivity at different bias voltages
Observation of material distribution on the surface of the existing sample,
Measurement of Shii electronic properties that enable a high spatial resolution.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an AFM showing a first embodiment of the present invention.
FIG. 3 is a configuration diagram of / STM. However, for simplicity,
For feedback control, only the value of the atomic force signal is
Let's take the case where the parameter function is used as the feedback signal.
You. As the parts constituting the AFM / STM in the present embodiment, 1 in the figure is a sample, 2a is a probe, 2b is a leaf spring, 2
c is a laser oscillator, 2d is a photodetector, 2e is an XYZ axis piezoelectric element, 2f is a tunnel current detector, 3 is a feedback control circuit, 4 is a scanning waveform generation circuit, 5 is a bias voltage with a predetermined waveform. Bias voltage control circuit, 6
Reference numerals a and 6b denote storage oscilloscopes. Leaf spring 2
b, the laser transmitter 2c and the photodetector 2d correspond to an atomic force detecting unit for detecting a force (atomic force) acting between the sample 1 and the probe 2a . The sample 1 is placed on an XYZ-axis piezoelectric element 2e, and the probe 2a has an orthogonal axis on a plane (in-plane direction) parallel to the surface of the sample 1 as an XY axis and a direction perpendicular to the surface of the sample 1 as a Z axis. Relative position is controlled.

The connection configuration of each unit and the function of each unit are as follows. The probe 2a is fixed to the tip of the leaf spring 2b, and is arranged close to the surface of the sample 1. Here, when an atomic force acts between the surface of the sample 1 and the tip of the probe 2a, the leaf spring 2b integrated with the probe 2a bends. The amount of deflection changes the course of the laser light transmitted from the laser transmitter 2c, which is detected by the photodetector 2d and output as an atomic force signal. That is, the difference signal between the respective light detection amounts of the two right and left light detection portions constituting the light detector 2d detects the deflection of the leaf spring 2b with high sensitivity. The feedback control circuit 3 receives an atomic force signal from the photodetector 2d, performs feedback control so that the signal becomes constant, and outputs the result as a Z applied voltage signal. For example, for a feedback signal obtained by subtracting a fixed reference value from an atomic force signal, the feedback signal is integrated with a predetermined time constant so that the feedback signal always approaches zero, and a signal proportional to the feedback signal is calculated. Amplify the signal that added
Output as a Z applied voltage signal. Z applied voltage signal is XY
Input to the Z application terminal of the Z-axis piezoelectric element 2e,
By changing the position in the axial direction, the sample 1 and the probe 2
The distance between a is constantly controlled. Scanning waveform generation circuit 4
Transmits an X, Y sweep signal for scanning control of the sample 1 in the X, Y directions by a raster scan method to the XYZ-axis piezoelectric element 2.
Output to the X, Y application terminal b. The storage oscilloscope 6a receives the Z applied voltage signal from the feedback control circuit 3 and the X and Y sweep signals from the scanning waveform generation circuit 4 and associates them with each other so that the AF indicating the unevenness of the sample 1 is obtained.
The M image is displayed as a three-dimensional figure or a gray scale. The bias voltage control circuit 5 outputs a high-frequency triangular wave to the sample 1. It flows between the sample 1 and the probe 2a, and the bias voltage and the sample 1
Is changed by the tunnel current detector 2f connected to the leaf spring 2b and output to the storage oscilloscope 6b. The storage oscilloscope 6b is a tunnel current detector 2f
, A tunnel voltage signal is input from the bias voltage control circuit 5, and an X, Y sweep signal is input from the scanning wave generation circuit 4. An STS image showing electronic characteristics such as distribution and surface state density is displayed as a three-dimensional figure or a gray scale.

In the present embodiment which describes the operation of the first embodiment configured as described above, the bias voltage control circuit 5 sweeps the bias voltage with a predetermined voltage waveform, so that the STS ( It has a spectral function by scanning tunneling spectroscopy. FIG. 2A shows an example of the relationship between the X sweep signal and the material distribution on the sample surface, the electrical characteristics of each material, the bias voltage, and the tunnel current in this embodiment.
(B-1), (b-2), (c) and (d) show. As shown in FIG. 2A, the sample is composed of a substance A, a substance B, and a substance C at a portion corresponding to the value of the X sweep signal, and the substance C is a non-conductive substance. It is assumed that the electrical characteristics have the bias voltage dependence of the tunnel current shown in FIGS. 2 (b-1) and 2 (b-2). For example, p
Some type semiconductors and n-type semiconductors have such electrical characteristics. As a bias voltage having a predetermined voltage waveform, it is appropriate to use a high-frequency triangular wave as shown in FIG. 2 (c).
The result is as shown in FIG. By associating the tunnel current waveform with the X and Y sweep signals, the distribution of each substance on the sample surface can be observed. In addition, it is also possible to obtain information on electronic properties such as the surface state density of each conductive portion according to the STS method. On the other hand, when the bias voltage is DC as in the conventional example, the tunnel current does not flow in each part of the substance B and the substance C at the positive bias voltage, so that it is impossible to distinguish between them. And substance C cannot be distinguished.

As described above, the conventional AFM / STM has the STS
By adding the spectroscopic function according to the method described above, for example, the IV characteristics between the sample and the probe of the substances A, B, and C may be shown on the surface where the conductive substance and the non-conductive substance are mixed. electrical characteristics distribution observation and a plurality of conductive substance is a conductive same bias voltage of different but specific cases, measurement of detailed electronic properties of the surface state density and the like becomes possible with a high spatial resolution.

Next, a second embodiment of the present invention will be described.

FIG. 3 is a block diagram of a digitally controlled AFM / STM showing a second embodiment of the present invention.
a is a probe, 2b is a leaf spring, 2c is a laser transmitter, 2d
Is a photodetector, 2e is an XYZ-axis piezoelectric element, 12a and 12b
Is an A / D converter, and 12c, 12d, 12e, and 12f are D / D converters.
A / A converter, 13 is a DSP unit (digital signal processor unit), and 14 is a control computer.

The structures of the sample 1, probe 2a, leaf spring 2b, laser transmitter 2c, photodetector 2d, and XYZ-axis piezoelectric element 2e are the same as those in the first embodiment. A / D converter 12a
Detects a tunnel current flowing between the sample 1 and the probe 2a, converts this into a digital signal, and outputs the digital signal to the DSP unit 13. The A / D converter 12b receives an atomic force signal from the photodetector 2d, converts the signal into a digital signal,
Output to the SP unit 13. The D / A converter 12c converts the digital bias voltage signal input from the DSP unit 13 into an analog signal, and outputs the analog signal to the sample 1. D / A converter 1
2d and 12e convert the digital X and Y sweep signals input from the DSP unit 13 into analog signals and output the analog signals to the X and Y application terminals of the XYZ axis piezoelectric element 2e. D / A converter 1
2f converts the digital Z applied voltage signal input from the DSP unit 13 into an analog signal, and converts it into an XYZ axis piezoelectric element 2e.
To the Z application terminal. The DSP unit 13 inputs the tunnel current signal and the atomic force signal from the A / D converters 12a and 12b in order according to a method instructed by the control computer 14 in advance, and outputs the signals to the D / A converters 12c, 12d and 12c.
By outputting a bias voltage signal, an X sweep signal, a Y sweep signal, and a Z applied voltage signal in order to e and 12f, the sample 1
Feedback control for keeping the distance between the probes 2a constant and scanning control for scanning the sample 1 in the X and Y directions;
Performs bias voltage control. The control computer 14
It instructs the DSP unit 13 on a method of feedback control, scanning control, and bias voltage control, inputs data obtained from the DSP unit 13, and displays, stores, and processes the data. Specifically, an image showing unevenness due to the Z applied voltage signal with respect to the X and Y sweep signals or an image showing electrical characteristics such as conductivity by the tunnel current signal is obtained.

The operation and operation of the second embodiment configured as described above will be described.

First, the operation of the feedback control, scanning control, and bias voltage control performed by the DSP unit 13 will be described. FIG. 4 is a flowchart showing the control method, where V is a bias voltage value, I is a tunnel current signal value, F is an atomic force signal value, and Z is an applied voltage signal value.
When the absolute value of the tunnel current is equal to or less than this value, IB is a boundary value where only the atomic force is subject to feedback control, F
B is a boundary value for which only the tunnel current is subjected to feedback control when the atomic force is equal to or less than this value and the absolute value of the tunnel current is equal to or more than IB, and FS is a probe such that the atomic force is equal to this value. IS is a set reference value for performing feedback control in the Z direction, and IS is a set reference value for performing feedback control of the probe in the Z direction so that the absolute value of the tunnel current is constant at this value. (F-FS) or (| I | −IS) is a feedback signal for feedback control. ZF, ZI, and ZFI are feedback control functions for obtaining a Z applied voltage signal value from a feedback signal in each case.

The DSP unit 13 first outputs a bias voltage V, and then inputs a tunnel current signal I and an atomic force signal F. If the absolute value | I | of the tunnel current signal is smaller than the boundary value IB, it is determined that there is a high possibility that the tunnel current signal is a non-conductive material, and only the atomic force is subjected to feedback control, and (F-FS) ) Is calculated as a feedback signal. If the absolute value | I | of the tunnel current signal is equal to or larger than the boundary value IB and the atomic force signal F is smaller than the boundary value FB, the tunnel current signal is determined to be a material having high conductivity, and the tunnel having a high Z-direction resolution is determined. The feedback control function of ZI is calculated with only the current as the target of feedback control and (│I│-IS) as the feedback signal.
In other cases, it is judged that there is a high possibility that it is conductive but not sufficient, and both atomic force and tunnel current are subjected to feedback control. Depending on the purpose, the value of the coefficient in the control function of the ZFI is selected as described later, and the feedback control function of the ZFI is calculated using only the tunnel current or only the interatomic force as the object of the feedback control. Next, the Z applied voltage signal Z obtained from the feedback function in this manner is output,
Finally, the XY scanning point is advanced to the next scanning point, and the above control is repeated.

Next, each feedback control function will be specifically described. One-variable feedback control function Z
F and ZI are as follows when using the digital PID feedback method. In other words, the time sequence of X _n to the feedback control function Z _n of the feedback _{signal, Z n = -pX n -iX '} n -d (X n -X n-1) X' n = X 'n-1 + X _n (X _'o values situation according to) p: proportionality gain factor i: integral gain factor d: as .X _o is zero indicating the value of the time of the feedback control of one time before the derivative gain factor (n-1 Is also possible.)

For the two-variable feedback control function ZFI, the time sequence of two feedback signals (│I _n │−I
S) and (F _n −FS) using a linear sequence X _n ,
What is necessary is just to substitute into the feedback control function of one variable mentioned above. That may be calculated feedback control function of the above 1 variable for the time sequence _{X n = a (F n -FS} -FC) + b (│I n │-IS-IC) + c. Here, if a / b to 0, feedback control is performed for almost only the atomic force, and b / b
If a to 0, feedback control is performed for almost only the tunnel current. For each gain coefficient p, i, d of the feedback control function ZF, ZI, ZFI,
The suffix of F, I, FI is added in order, and pF, iF,
..., dFI, the tunnel current I and the atomic force F
Feedback control functions ZF, Z
1: a: b = pFI: pF: pI = iFI: iF: iI so that I and ZFI are continuous
= DFI: dF: dI = 1: IC: FC, IC = IB-IS, FC = FB-FS, c = bIC (=
aFC) and each coefficient are appropriate.

As described above, both the tunnel current signal and the atomic force signal are input simultaneously, and the nonconductive material portion has a function of the atomic force on the sample surface where the nonconductive material and the conductive material are mixed. As a feedback signal for feedback control, the portion of highly conductive material is a function of tunnel current with high Z-direction resolution (large dependence on sample-probe distance) as feedback signal for feedback control, and a very thin non-conductive material The target of feedback control is to perform a feedback control using a function that uses both the atomic force and tunnel current as parameters as a feedback signal for portions that are conductive but not sufficient, such as conductive materials covered with an oxide film. Automatically becomes possible.

The effect of enabling the automatic adjustment of the feedback signal to be subjected to the feedback control with respect to the atomic force signal and the tunnel current is as follows. Observe the surface where the conductive material and the non-conductive material are mixed. In this case, the fluctuation of the tunnel current due to the error of the feedback control can be reduced and stabilized. This makes it possible to distinguish different conductive substances and observe their substance distribution. Also, the first
By employing digital control instead of analog control as in the embodiment, it is possible to easily perform post-processing of signals and to eliminate the need to change hardware when adding various additional mechanisms.

Next, a third embodiment of the present invention will be described.
This embodiment is different from the above-described second embodiment in that the bias voltage is always kept constant, but is different from the first embodiment in that a spectral function by the STS is added.

FIG. 5 is a flow chart showing a method of feedback control, scanning control and bias voltage control of the digitally controlled AFM / STM showing the third embodiment. The digitally controlled AFM / STM shown in FIG. ST
This can be realized with the configuration of M. In this case, the feedback control, the scanning control, and the bias voltage control are calculated by the DSP unit 1.
3 does.

In FIG. 5, V, I, F, Z, IB, FB, F
Symbols S, IS, ZF, ZI, and ZFI are as described in the description of FIG. 4 of the second embodiment, and X is the primary coupling between the atomic force and the tunnel current described in the second embodiment. X = a (F−FS−FC) + b (| I | −
IS-IC) + c. △ X is the tolerance of X, △
F and △ I are feedback signals (F-FS) and (│I│-I
S) is the permissible error. m is the number of times the feedback signal has continuously exceeded the allowable error, and n is the maximum number of times the feedback control is repeated at the same scanning point.

The DSP unit 13 first outputs a bias voltage V, and then inputs a tunnel current signal I and an atomic force signal F. If the absolute value | I | of the tunnel current signal is smaller than the boundary value IB, it is determined that there is a high possibility that the tunnel current signal is a non-conductive material, and only the atomic force is subjected to feedback control, and (F-FS) ) Is calculated as a feedback signal. If the absolute value | I | of the tunnel current signal is equal to or larger than the boundary value IB and the atomic force signal F is larger than the boundary value FB, the tunnel current signal is determined to be a material having high conductivity, and the tunnel having a high Z-direction resolution is determined. A feedback control function of ZI is calculated in which only the current is subjected to feedback control and (│I│-IS) is used as a feedback signal.
In other cases, it is judged that there is a high possibility that it is conductive but not sufficient, and both the atomic force and the tunnel current are subjected to feedback control. Depending on the purpose, as described later, the value of the coefficient in the ZFI control function is selected, and the feedback control function of the ZFI is calculated with virtually only the tunnel current or only the interatomic force as the target of the feedback control. After outputting the Z applied voltage signal Z obtained from the feedback function in this manner, the absolute value | F−FS |, || I | −IS of the feedback signal in each case.
If |, | X | is greater than or equal to each of the allowable errors ΔF, ΔI, ΔX, it is determined that the feedback control has not been sufficiently controlled to the target value, and the feedback control is repeated. If, at the same scanning point, the absolute value of the feedback signal is equal to or more than the allowable error for n or more times, it is determined that the portion of the sample surface is not suitable for observation, and at that scanning point, Is given up and the XY scanning point is advanced to the next scanning point. If the absolute value of the feedback signal is less than the allowable error, it is determined that the relative position in the Z direction between the sample and the probe is sufficiently controlled, and the bias voltage is set within a specific range according to the STS method. Input a tunnel current signal several times while sweeping at high speed. Finally, the XY scanning point is advanced to the next scanning point, and the above control is repeated.

As described above, in this embodiment, the effects of the first and second embodiments are simultaneously exhibited by adding the spectral function by the STS shown in the first embodiment to the second embodiment. . Specifically, by adding a spectroscopic function by the conventional AFM / STM method, on a surface where a conductive material and a non-conductive material are mixed, the electrical characteristics are different but the conductivity at a specific bias voltage is improved. Observation of the distribution of the same plurality of conductive substances and measurement of detailed electronic properties such as surface state density can be performed with high spatial resolution. In addition, by simultaneously inputting both the tunnel current signal and the atomic force signal and automatically adjusting the feedback signal to be subjected to feedback control on the sample surface where non-conductive and conductive materials coexist, feedback control can be performed. Variations in tunnel current due to errors can be reduced and stabilized. This makes it possible to observe the distribution of the conductive material and measure the electronic characteristics with high accuracy.

Furthermore, in addition to the above, when the absolute value of the feedback signal is equal to or more than a certain value, the feedback control is repeated, so that each data is collected when the absolute value of the feedback signal is less than a certain value. Is guaranteed. This means that the accuracy of the obtained data is high.

It should be noted that the above-described embodiments of the present invention are only a part of possible embodiments according to the present invention, and
The present invention can take many embodiments by a combination of the existing methods for TM and STS and the methods described in the above-mentioned embodiments. For example, [a] As a method of detecting the atomic force of the AFM, (1) the optical lever method shown in the embodiment, (2) a method based on the amount of tunnel current flowing between another probe on the back of the leaf spring and the back of the leaf spring. ,
(3) A method based on interference of laser light applied to the back of the leaf spring; [b] To control the relative position between the sample and the probe; (1) To move the position of the sample; (2) To move the position of the probe [C] Measurement environment: (1) in a gas such as an inert gas in the atmosphere; (2) in a liquid such as an electrolytic solution, pure water or oil; (3) in a vacuum such as an ultra-high vacuum; [D] Measurement temperature (1) room temperature, such as room temperature,
(2) High temperature of several hundred degrees to 1000 degrees Celsius, (3) Low temperature of liquid helium to liquid nitrogen temperature, [e] The feedback signal for feedback control is a signal such as tunnel current and (1) setting criteria. What is the difference from the value, (2)
[F] A feedback signal of feedback control is a two-variable function of an atomic force and (1) a tunnel current at a specific bias voltage, (2) two. 2 at the above bias voltage
A function that is a function of three or more variables having at least one tunnel current as a variable [g] A function that derives a feedback signal from a plurality of variables is represented by (1) a linear combination, and (2) a function of two or more nonlinear functions. [H] feedback control method is (1) PID control, (2) fuzzy control, [i] bias voltage is applied to (1) sample,
(2) Various embodiments can be taken by a combination of a device applied to the probe and the like. A specific combination method should be selected optimally according to the sample to be observed and the purpose, but the same effect can be obtained by an appropriate combination.

As described above, the present invention can be variously applied according to the gist thereof and can take various embodiments.

[0036]

As is apparent from the above description, according to the AFM / STM of the present invention, the feedback control unit
Both the signal of the channel current and the signal of the force acting on the sample / tip.
Input at the same time and return
Conduction control by feedback control
When observing a surface where both materials and non-conductive
Small variations in tunnel current due to feedback control error
It can be stabilized. This allows for conductive
Observation of distribution of conductive substances and measurement of electronic properties with high accuracy
Can Ru.

According to the AFM / STM of the present invention,
The above AFM / STM is provided with a spectral function by the STS method.
By adding, in addition to the above effects, conductive material
Electrical characteristics are different on the surface where both and non-conductive substances are mixed
Have multiple conductors with the same conductivity at a particular bias voltage.
Observation of distribution of conductive materials and detailed electronic information such as surface state density
That Do possible with high spatial resolution measurement of a property.

[Brief description of the drawings]

FIG. 1 shows an atomic force microscope / first embodiment of the present invention.
Configuration diagram of scanning tunneling microscope

FIGS. 2 (a), (b-1), (b-2), (c),
(D) is a diagram showing an example of the relationship between the X sweep signal and the material distribution on the sample surface, the electrical characteristics of each material, the bias voltage, and the tunnel current showing the operation of the first embodiment.

FIG. 3 is a configuration diagram of a digitally controlled atomic force microscope / scanning tunnel microscope showing a second embodiment of the present invention.

FIG. 4 is a flowchart of a control method of the atomic force microscope / scanning tunnel microscope according to the second embodiment.

FIG. 5 shows an atomic force microscope / third embodiment of the present invention.
Flowchart of control method for scanning tunneling microscope

[Explanation of symbols]

Reference Signs List 1 sample, 2a probe, 2b leaf spring, 2c laser transmitter, 2d photodetector, 2e XYZ axis piezoelectric element, 2
f: tunnel current detector, 3: feedback control circuit, 4: scanning waveform generation circuit, 5: bias voltage control circuit, 6a, 6b: storage oscilloscope, 12a,
12b A / D converter, 12c, 12d, 12e, 12
f ... D / A converter, 13 ... Digital signal processor unit (DSP unit), 14 ... Control computer.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-110402 (JP, A) JP-A-3-43944 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B 21/00-21/32 G01B 7/00-7/34 G01N 37/00 G01N 13/12 G01N 13/14

Claims (4)

(57) [Claims] A scanning control unit configured to scan and control a relative position of the sample surface between the sample and the probe in an in-plane direction; and a scanning control unit configured to scan the sample surface between the sample and the probe. A feedback control unit that performs feedback control of a relative position in a vertical direction; a bias voltage control unit that applies a bias voltage to the sample or the probe; and an atomic force detection that detects a force applied between the sample and the probe. And an atomic force microscope / scanning tunneling microscope comprising a tunnel current detector for detecting a current flowing between the sample and the probe, wherein the feedback controller is configured to detect the current from the atomic force detector. Atomic force microscope / scanning, wherein a function using both an output atomic force signal and a tunnel current signal output from a tunnel current detector as parameters is feedback-controlled as a feedback signal. Tunneling microscope. 2. The process of scanning control of the relative position of the sample surface between the sample and the probe in the in-plane direction and the value of the interatomic force acting between the sample and the probe and the distance between the sample and the probe. The relative position between the sample and the probe in the direction perpendicular to the sample surface is determined in accordance with the conductivity / non-conductivity of the sample surface as a feedback signal using a function having both parameters of the flowing tunnel current as parameters. A control method for an atomic force microscope / scanning tunnel microscope, wherein the control method is feedback control. 3. The method according to claim 1, wherein the bias voltage control section controls a predetermined voltage wave.
The bias voltage is changed in the form of
Current detector detects the bias voltage at the scan point in the scan control.
The atomic force microscope / scanning tunnel microscope according to claim 1 , wherein a plurality of different tunnel current signals are input . (4)Atomic force microscope / scanning type according to claim 1
In a tunnel microscope,  The relative position between the sample and the probe in the in-plane direction of the sample surface
Inspection control processsoOf the atomic force acting between the sample and the probe
Value andBy the bias voltageFlow between the sample and probe
Function with both parameters of the tunnel current
The return signal corresponds to the conductive / non-conductive properties of the sample surface.
Between the sample and the probe in the direction perpendicular to the sample surface.
Position feedback controlAnd specify the bias voltage
Within range Multiple tunnel current signals while sweeping
Enter the issueAtomic force microscope / scanning type
How to control a tunnel microscope.