JPH03215703A - Atomic probe microscope - Google Patents

Abstract

PURPOSE:To perform fast servo control over a probe and display a high-accuracy image of a sample surface without any image distortion by providing a detecting circuit for a displacement quantity in the Z direction of a three-dimensional driving body separately from a servo circuit for Z-directional control over the three-dimensional driving body. CONSTITUTION:A scanning type tunneling microscope (STM) which drives the three- dimensional driving body by a voltage control system is provided with a charge detecting circuit 35 which detects a signal for obtaining linear relation between Z- directional extension/contraction displacement and an image display by utilizing the linear characteristic of the amount of charges nearly proportional to the Z-directional extension/contraction displacement of a hollow cylinder type piezoelectric driving body separately from the servo circuit 36. Namely, the output of the circuit 35 is synchronized with an X- and a Y-directional scanning signal to display an image. Consequently, a Z-directional servo signal is prevented from being affected by voltage deviations when an applied voltage is increased and decreased. Further, even if there is phase delay in the circuit 35, no influence is exerted upon the servo control. Further, the probe can be under high-speed servo control and a high-accuracy STM image conforming with the surface shape of the actual sample is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to atomic probes such as scanning tunneling microscopes (STM) and atomic force microscopes (AFM) that can observe the surface of a sample in units of atoms. microscope,
In other words, the present invention relates to a microscope capable of observing samples at the atomic level using a probe.

[Prior Art] Recently, scanning tunneling microscopes (Scanning tunneling microscopes), which can observe the surface of a sample in units of atoms, have become popular.
l1ng Microscope: STM) and atomic force microscope (Atonic Force)
Microscope (AFM) and other atomic probe microscopes (A too+ic probe)
e Microscope (APM) has been developed. These methods utilize tunneling current generated between a probe with a small radius of curvature at the tip and the sample, or the structure of the tip of the probe, and the atomic forces generated between atoms and constituent atoms on the sample surface. At the same time, a servo operation is performed in the Z direction to maintain a constant distance between the sample and the probe, and at the same time, the probe is two-dimensionally scanned over the sample surface in the X and Y directions to determine the fine shape of the sample surface. It is read as movement.

Generally, the proximal end of the probe is fixed to a three-dimensional drive body made of a fine movement element such as a piezoelectric drive body, and the above-mentioned servo operation and two-dimensional scanning of the probe are all performed by this one three-dimensional drive body.
This is done by a dimensional driver.

In addition, as a driving method for the three-dimensional drive body to perform such servo operation, the voltage applied to the piezoelectric drive body that controls the displacement of the probe in two directions is obtained from changes in tunnel current, atomic force, etc. Two known methods are known: a general voltage control method in which the voltage is directly varied by a Z-direction servo signal, and a charge control method in which the amount of charge within the piezoelectric drive body is detected and the voltage applied to the piezoelectric drive body is feedback-controlled based on this.

Further, as a three-dimensional driving body capable of moving a probe in three-dimensional directions, there is, for example, a tube scanner.

As shown in FIG. 5, for example, a three-dimensional drive body called a tube scanner has a plurality of electrodes 12a, 12b, 12c, and 12d provided on the outer surface of a hollow cylindrical piezoelectric drive body 11, and common electrodes 12a, 12b, 12c, and 12d on the inner surface thereof. An electrode 13 is provided. Further, the upper circumferential surface of the piezoelectric drive body 11 is fixed, and a probe 15 is disposed at the center of the lower circular plane via a fixed disk 14. And each electrode 1
High voltage amplifier (not shown) between 2a to 12d and 13
By selectively applying a voltage using, for example, the piezoelectric driving body 11 of the electrode portion to which the voltage is applied is driven to deform (displace). During this drive, the probe 15 becomes a free end and scans the surface of the sample.

[Problems to be Solved by the Invention] By the way, in an atomic probe microscope (hereinafter abbreviated as APM) using a conventional voltage control method, a Z-direction servo signal is converted into a displacement amount in the Z-direction of a three-dimensional driving body. By displaying this as an image in synchronization with a two-dimensional scanning signal, unevenness information indicating the shape of the sample surface is obtained. That is, conventionally, a two-directional servo signal has been used as a signal for detecting the amount of expansion/contraction displacement of a three-dimensional drive body that expands and contracts in accordance with changes in applied voltage.

However, as shown in FIG. 6, the piezoelectric driver 11 exhibits nonlinear characteristics in terms of displacement with respect to applied voltage. That is, when the piezoelectric drive body 11 expands and contracts, the expansion side ■
Even if the displacements are the same on the contraction side (2) and (2), a deviation dV occurs between the voltages when the applied voltage increases and when it decreases.

Therefore, the above deviation dV affects the two-way servo signal,
This appears as image distortion, and has the disadvantage that it is not possible to accurately display the unevenness of the sample surface.

FIG. 7 shows the deviation between the actual shape of the sample surface and the total a1 surface unevenness image (APM image) caused by the above-mentioned deviation dV.

For example, if we scan a sample surface with the shape shown in Figure 7(a), the applied voltage must be the same as the inverse shape of the sample surface, as shown by the broken line in Figure 7(b). Even though this should not be the case, the result looks like a solid line shifted by the deviation dV. That is, although the displacements in the two directions of the extension side (2) and the contraction side (2) are the same, the applied voltages are different.

Therefore, as shown by the solid line in FIG. 7(e), the displayed surface unevenness image also differs from the actual shape of the sample surface (broken line).

On the other hand, as shown in FIG. 6, the displacement of the piezoelectric driver 11 exhibits nonlinear characteristics with respect to the applied voltage, but as shown in FIG. It is known that a linear relationship can be obtained between

The amount of charge in the piezoelectric driver 11 is detected using this linear relationship between the displacement of the piezoelectric driver 11 and the amount of accumulated charge, and thereby the voltage applied to the piezoelectric driver 11 is controlled to drive the three-dimensional driver. The above-mentioned charge control type drive circuit is designed to drive this.

For example, as shown in FIG. 9, this drive circuit includes a charge detection means 21 composed of an integrator that detects the amount of charge of the drive body 20, and a charge detection means 21 for driving the drive body 20 using the output of the charge detection means 21. It is mainly composed of a differential amplifier that uses the applied voltage of ing.

According to this circuit, by converting the amount of charge of the piezoelectric driver 11 into voltage and feeding it back, it is possible to obtain an amount of charge that changes linearly with respect to changes in the applied voltage, and at the same time, it is possible to obtain an amount of charge that changes linearly with respect to changes in the applied voltage. On the other hand, a displacement amount that changes linearly is obtained, and a linear relationship is obtained between the applied voltage and the displacement.

However, in this charge control type drive circuit, an integrator is used as the charge detection means 21, and its output is fed back to the differential amplifier, which is the charge injection means 22. As a result, the probe servo control A small feedback loop called an integrator is included in the large feedback loop that performs the operation, and the phase lag in the integrator causes a phase lag in the entire servo system, making it impossible to construct a high-speed servo drive circuit. was there.

Therefore, the present invention aims to provide an atomic probe microscope that is capable of high-speed servo control of the probe, is free from image distortion, and is capable of displaying images of minute irregularities on the surface of a sample with high precision. The purpose is

[Means for Solving the Problems] In order to achieve the above object, the atomic probe microscope of the present invention includes a probe with a small radius of curvature at the tip, and a probe that is A drive circuit for the three-dimensional drive body, comprising a three-dimensional drive body for scanning in the two-dimensional Y direction and displacing the three-dimensional drive body in the Z direction while performing servo control to maintain a constant distance from the sample. and a detection circuit that is provided independently of the servo system and detects the amount of displacement of the three-dimensional driving body in the Z direction.

[Operation] According to the present invention, a linear relationship can be obtained between the expansion/contraction displacement of the three-dimensional driving body in the Z direction and the image display, so that the amount of displacement of the probe in the Z direction can be This makes it possible to read out proportional signals.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows an atomic probe microscope according to the present invention, taking as an example a scanning tunneling microscope (STM) using a tube scanner.

In FIG. 1, a three-dimensional driving body 10 called a tube scanner has a configuration in which, for example, a hollow cylindrical piezoelectric driving body 11 is provided with four electrodes 12a, 12b, 12c, and 12d on the outer surface thereof.

An Xa drive circuit 31 or an xb drive circuit 32 is connected to each of the electrodes 12a and 12b as an electrode for driving in the X direction. Each of the electrodes 12C and 12d has
As a drive electrode in the Y direction, the Ya drive circuit 33 or the Y
b drive circuit 34 is connected.

Further, on the inner surface of the piezoelectric drive body 11, the electrodes 12a,
Each part 1 of the piezoelectric drive body 11 is attached to 12b, 12c, and 12d.
1 a, 1 l b, 1 1 c, 1 1
Common electrodes 13 are provided so as to face each other with d interposed therebetween. This common electrode 13 has a charge detection circuit (piezoelectric charge detection circuit) 35 that detects the total amount of charge of the piezoelectric drive body 11.
is connected.

On the other hand, the upper circumferential surface of the piezoelectric drive body 11 is fixed, and a probe 15 is arranged at the center of the lower circular plane (bottom surface) via a fixed disk 14 so as to face the surface of the sample 16. has been done. A servo circuit 36 is connected to the probe 15, which generates a two-way servo signal for keeping the distance between the sample 16 and the probe 15 constant based on the tunneling current signal. The two-way servo signal from this servo circuit 36 is transmitted to the Xa, Xb, Ya, Yb drive circuit 31.
．． 32, 33, and 34, respectively.

In addition, these Xa, Xb, Ya, Yb drive circuits 31, 3
A scanning signal generation circuit 37 is connected to 2, 33, and 34.
An X direction scanning signal and a Y direction scanning signal are respectively supplied.

A display device 38 is connected to the scanning signal generation circuit 37, and the display device 38 displays the charge detection signal, which is the output of the charge detection circuit 35, in synchronization with the synchronization signal of the above-described XY direction scanning signal. It has become so.

FIG. 2 shows the configuration of the charge detection circuit 35. As shown in FIG.

The charge detection circuit 35 includes a capacitor 35a and an operational amplifier 35b with extremely high input resistance. Each portion 11a of the piezoelectric drive body 11 is connected to the capacitor 35g.
, llb, llc, and lld, an amount of charge equal to the total amount of charge Q of the amount of charge Qxa, Qxb, Qya, and Qyb accumulated in each of them is stored.

For example, now, the common electrode 13 of the hollow cylindrical piezoelectric drive body 11
is set to a constant potential, a voltage Vx is applied to the electrode 12a, and the voltage Vx is applied to the electrode 12a.
Assume that a voltage -Vx is applied to each of the terminals 2b and 2b. Then,
The portion 11a of the piezoelectric driver 11 corresponding to the electrode 12a extends in the Z direction, that is, the vertical direction in the drawing, and the electrode 12
The portion 1lb of the piezoelectric driver 11 corresponding to b is contracted. As the three-dimensional driving body 10 is deformed in this way, the probe 15 provided at the center of the bottom surface of the three-dimensional driving body 10 moves to the electrode 12.
It is moved almost parallel to the b side (rightward in the drawing).

That is, the common electrode 13 is set at a constant potential, and the electrodes 12a,
When voltages Vx and -Vx are respectively applied to 12b, 3
The dimensional driver 10 changes from the state shown in FIG. 3(a) to the state shown in FIG. 3(b).
is transformed as shown by the solid line. Therefore, the probe 15
will be translated almost parallel to the right. Note that the movement of the probe 15 in the Y direction (back and forth direction in the drawing) is the same, so a description thereof will be omitted here.

On the other hand, when a tunnel current signal flowing when the probe 15 approaches the sample 16 at a distance of several people is supplied to the servo circuit 36, a two-way servo signal from the servo circuit 36 is transmitted to each drive circuit 31. , 32.33.34. Here, for example, each electrode 12a. 12b. 12c,1
Assume that a servo voltage ΔVz is added to and applied to 2d. Then, each electrode 12a, 12b, 12c, 12d
Each part 11a, 1lb, l of the piezoelectric drive body 11 corresponding to
lc, lld are respectively Δ, 9xa, Δjlx in the Z direction
b, ΔIya. The probe 15 is extended by Δlyb, and the position of the probe 15 is also moved in accordance with the deformation of the three-dimensional driving body 10.

That is, for each electrode 12a, 12b, 12c, 12d, the servo voltage Δ from the servo circuit 36 is added to the voltage corresponding to the X and Y direction scanning signals from the scanning signal generation circuit 37.
The voltage obtained by adding Vz is applied to each drive circuit 31 and 32.
．． 33 and 34, the three-dimensional driving body 10 is deformed as shown by the broken line in FIG. 3(b). in this case,
The probe 15 is arranged at the center of the fixed disk 14. Therefore, the amount of movement Δ,Qtip of the probe 15 in the Z direction is ΔI
tip one (Δ47 xa ten ΔII xb+ΔI ya+Δf
lyb)/4.

Here, when the probe 15 is moved by Δltip in the Z direction, each portion 11a, 1lb. ll
The amount of expansion (expansion/contraction displacement) of c and lld is the s load of the capacitor 35a of the charge detection circuit 35! +;: Proportional. Therefore, the amount of change in the total amount of charge Q at that time (the amount of movement ΔjJ
ΔQ (corresponding to the change in tip) is ΔQ−kxΔaltip. However, k is a constant.

In this case, each part 11a, 1 l b of the piezoelectric drive body 11
. It is proportional to the amount.

In the STM having such a configuration, the tip position of the probe 15 is always scanned at a constant distance from the surface of the sample 16 by the action of the servo circuit 36. Therefore, the charge detection signal (unevenness information signal) from the charge detection circuit 35 obtained by detecting the total amount of charge of the piezoelectric drive body 11 is read out in synchronization with the synchronization signal from the scanning signal generation circuit 37. By displaying this on the display device 38, it becomes possible to image the unevenness information on the surface of the sample 16 with high accuracy in the Z direction.

As mentioned above, in STM that drives a three-dimensional drive body using a voltage control method, the expansion and contraction in the Z direction is performed using the linear characteristic of the amount of accumulated charge that is approximately proportional to the expansion and contraction displacement in the Z direction of the hollow cylindrical piezoelectric drive body. A circuit for detecting a signal that provides a linear relationship between displacement and image display is provided separately from the servo circuit.

That is, a charge detection circuit for detecting the total amount of charge of the piezoelectric drive body is provided independently, and the output of this circuit is synchronized with the X and Y direction scanning signals to display an image. This makes it possible to prevent the voltage deviation between when the applied voltage increases and when the applied voltage decreases from affecting the two-way servo signal.

Further, even if there is a phase delay in this circuit, it will not have any adverse effect on servo control. Therefore, it becomes possible to faithfully scan the probe along the unevenness of the sample surface at high speed, and it becomes possible to obtain an STM image that matches the actual surface shape of the sample.

In the above embodiment, an inverting charge detection circuit is used in which a capacitor that stores a charge amount equal to the total amount of charge stored in the piezoelectric driver is connected between the negative input terminal and the output terminal of the operational amplifier. Although the explanation has been given using an example, the present invention is not limited to this, and it is also possible to configure a non-inverting type as shown in FIG. 4, for example.

Furthermore, the piezoelectric drive body constituting the three-dimensional drive body is not limited to a hollow cylindrical type; for example, the displacement in the X and Y directions is
A tripod-type three-dimensional drive body that does not affect displacement in the directions can be easily applied by providing the piezoelectric charge detection circuit described above to the piezoelectric drive body in two directions.

Further, the present invention can be fully applied to a hollow four-sided cubic type or cantilever type three-dimensional driving body in which a plurality of piezoelectric parts are integrally formed. In this case, a piezoelectric charge detection circuit may be provided for each piezoelectric portion, and calculation processing may be performed to output only the amount of displacement in the Z direction among the displacements of the three-dimensional driving body obtained by this circuit. .

It goes without saying that the present invention can also be easily applied to other atomic probe microscopes such as AFM.

It goes without saying that various other modifications can be made without departing from the gist of the invention.

[Effects of the Invention] As described in detail above, according to the present invention, in addition to the servo circuit for two-direction control of a three-dimensional drive body driven by a voltage control method, the Z Since a detection circuit is provided to detect the amount of displacement in the direction, high-speed servo control of the probe is possible, and there is no image distortion.
It is possible to provide an atomic probe microscope that can display images of minute irregularities on the surface of a sample with high precision.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a scanning tunneling microscope showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of a charge detection circuit, and FIG. 3 is a diagram for explaining the movement of a probe. FIG. 4 is a diagram showing another example of the configuration of the charge detection circuit, FIG. 5 is a perspective view showing the configuration of the three-dimensional drive body, and FIG. 6 is for explaining the relationship between applied voltage and displacement of the piezoelectric drive body. Characteristic diagram shown in 7th
The figure is shown to explain the deviation between the actual sample surface shape and the APM image caused by the voltage deviation between when the applied voltage increases and when it decreases. Figure 8 shows the amount of charge accumulated in the piezoelectric drive body. Characteristic diagram shown to explain the relationship between and displacement, No. 9
The figure is a configuration diagram showing a drive circuit for a three-dimensional drive body using a charge control method. 10... Three-dimensional drive body, 11... Hollow cylindrical piezoelectric drive body, 12a, 12b, 12c. 12d--electrode, 1
3... Common electrode, 15... Probe, 16... Sample,
31, 32, 33. 34... Drive circuit, 35... Charge detection circuit, 36... Servo circuit, 37... Scanning signal generation circuit, 38... Display device. Figure 3 Figure 4 Figure 5 Variable applied voltage Figure 6 Figure 7 Figure 9

Claims (5)

[Claims] (1) A probe with a small radius of curvature at the tip, and scanning the probe in the two-dimensional directions of X and Y on the surface of the sample,
A scanning tunneling microscope (STM) or an atomic force microscope (AF) has a three-dimensional drive body for displacing in the Z direction while controlling the distance from the sample to be constant.
In an atomic probe microscope such as M), a drive circuit for the three-dimensional drive body is provided independently of the servo system, and a Z
An atomic probe microscope characterized by comprising a detection circuit that detects the amount of directional displacement. (2) The atomic probe microscope according to claim 1, wherein the detection circuit is a piezoelectric charge detection circuit that detects the amount of charge of the three-dimensional driving body. (3) The atomic probe microscope according to claim 1 or 2, wherein the three-dimensional drive body is a hollow cylindrical piezoelectric drive body. (4) The atomic probe microscope according to claim (1) or (2), wherein the three-dimensional drive body is a tripod piezoelectric drive body. (5) The atomic probe microscope according to claim 1 or 2, wherein the three-dimensional drive body is a cantilever type piezoelectric drive body.