JP3270750B2 - Scanning tunneling microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning tunnel microscope for scanning a probe close to a sample surface to detect a tunnel current and obtain a scan image of the sample surface.

[0002]

2. Description of the Related Art When a probe is brought close to a sample to about 1 nm or less where atoms at the tip of the probe and electron clouds of atoms of the sample overlap, and a voltage is applied between the probe and the sample in this state, a tunnel current flows. . This tunnel current has a voltage of several mV.
When the voltage is up to several volts, it becomes about 1 to 10 nA, and changes depending on the distance between the sample and the probe. Therefore, by measuring the magnitude of the tunnel current, the distance between the sample and the probe can be measured very precisely, and the surface shape of the sample can be obtained.

[0003] The scanning tunneling microscope (STM) controls the height of the probe so that the tunnel current becomes constant.
This is a device that observes the surface shape of a sample based on the height trajectory of the probe when the probe is moved in a horizontal plane, and is a device that has attracted attention in analyzing the surface atomic arrangement. When observing the surface shape (concavo-convex image) of the sample by tunnel current, first, the probe is moved close to the sample to about 0.1 μm by coarse movement, and further from 0.1 μm to 1 nm by fine movement.
The probe is brought close to the sample until Angstrom order control is performed.

FIG. 12 is a diagram showing a schematic configuration of a scanning tunnel microscope. In the figure, 42 is a sample, 43 is a probe, 44 is a head, 46, 48 and 49 are piezoelectric elements, 45 and 47 are insulating plates, 51 is an electrode, 52 is an XY scanning circuit, 53 is a servo circuit, and 54 is a tunnel. A current amplifier, 55 is a bias power supply, and 56 is a display device.

In the STM unit, a probe 43 is attached to a head 44 and the head 44 is
5, 47 and the piezoelectric elements 46, 48, 49. The piezoelectric elements 46, 48, and 49 have an X axis, a Y axis, and a Z axis.
A three-dimensional actuator consisting of a shaft and a piezoelectric element 4
6 drives the Z axis, the piezoelectric element 48 drives the X axis, and the piezoelectric element 49 drives the Y axis. A drive voltage is applied to the electrodes 51 arranged on both sides of each of the piezoelectric elements 46, 48, 49 constituting the three-dimensional actuator. In the control of the three-dimensional actuator, the probe 43 is moved in the X-axis and Y-axis directions by sweeping the voltage applied to the piezoelectric elements 48 and 49 in the X-axis and Y-axis directions by the XY scanning circuit 52, and scanning is performed. Meanwhile, the voltage to the Z-axis direction piezoelectric element 46 is controlled through the servo circuit 53 so that the tunnel current becomes constant. Then, by displaying this control voltage value on the display device 56, the surface shape (concavo-convex image) of the sample 42 can be observed.

[0006]

FIG. 13 and FIG. 14 are views for explaining an example of a conventional scanning method.

As described above, in a tunnel microscope, a piezoelectric element is generally used for scanning a sample or a probe. However, since the piezoelectric element has hysteresis, when driven by a triangular wave, the same voltage is applied. There is a problem that the position is shifted on the way back.

Therefore, conventionally, as shown in FIG. 13, image display of a return portion has not been performed by X-direction scanning and Y-direction scanning by blanking. That is, when the probe scans in the direction of the solid line on the sample as shown in FIG. 14A, an image is displayed as shown in FIG.
Erasing is performed when scanning is performed in the direction of the dotted line. Moreover,
Since the servo circuit for controlling the Z-direction drive of the search is always operating, the speed of the return scan cannot be increased because the probe does not hit the sample surface. Therefore, the return scan is a dead time.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has as its object to provide a scanning tunneling microscope which takes an image not only in going but also in returning when driven by a triangular wave and effectively uses the scanning tunnel microscope. It is.

For this purpose, the present invention relates to a scanning tunneling microscope for scanning a probe or a sample in the XY directions by bringing the probe close to the sample surface and detecting a tunnel current to obtain a scan image of the sample surface. the video signal of the forward scan of X scanning in the scanning, and the video signal of the backward path of scanning of the X scanning in the scanning of the forward path of the Y scanning, run X during the backward scan of the Y scanning
The video signal of the forward scan of the inspection and the return scan of the Y scan
A scanning image of the sample is obtained based on the video signal of the backward scanning of the X scanning .

[0011]

According to the scanning tunneling microscope of the present invention, since a scanning image is obtained in each direction of the reciprocal scanning, comparison information between an image obtained by going scanning and an image obtained by returning scanning can be obtained. It can be used effectively without waste.

[0012]

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

FIG. 1 is a diagram showing the configuration of one embodiment of a tunnel microscope according to the present invention, FIG. 2 is a waveform diagram showing one embodiment of the X scanning mode, and FIG. 3 is a waveform showing another embodiment of the X scanning mode. FIG. 4 and FIG. 4 are waveform diagrams for explaining the Y scanning mode.
8 are diagrams showing examples of correspondence between scanning and display images.

1 is a Y scanning circuit, 2 is an X scanning circuit, 3 is a constant voltage generating circuit, 4 is a switching amplifier, 5 is an adding circuit, 6
Is a Y drive amplifier, 7 is an X drive amplifier, 8 is an X display amplifier, 9 is a Y display amplifier, 10 is a display CRT, 11 is a blank circuit, 12 is a video amplifier, 13 is a Z control circuit, 14
Denotes an X drive element, 15 denotes a Y drive element, and 16 denotes a Z drive element.

In FIG. 1, an X drive element 14, a Y drive element 15, and a Z drive element 16 are, for example, piezoelectric elements.
It constitutes a three-dimensional actuator. The X scanning circuit 2 and the Y scanning circuit 1 are circuits that generate X and Y scanning signals, respectively.
These control the voltages applied to the X drive element 14 and the Y drive element 15 based on the respective scanning signals. The Z control circuit 13 detects a tunnel current and controls a voltage applied to the Z drive element 16 so that the tunnel current becomes constant, and the signal becomes a video signal. The switching amplifier 4 switches between the non-inverting mode in which the X-scanning signal A is directly sent to the (B) adding circuit 5 as shown in FIG. ,
+ → − → +...). In the latter inversion mode, the X scanning circuit 2 is used when switching from going to returning.
Is switched over by the timing signal x. As shown in FIGS. 2 and 3, the constant voltage generating circuit 3 generates a constant voltage C which is inverted by the timing signal x every half cycle of the X scanning signal. The adding circuit 5 adds the output B of the switching amplifier 4 and the output C of the constant voltage generating circuit 3 and supplies a display scanning signal D to the X display amplifier 8.

Next, the operation will be described.

First, the X scanning circuit 2 generates an X scanning signal having a triangular waveform shown in FIGS. 2A and 3A.
The sample or the probe is moved in the X direction by being amplified by MP7 and supplied to the X drive element 14 composed of a piezoelectric element.
Also, the Y scanning circuit 1 generates a Y scanning signal having a waveform having a slow gradient corresponding to the required number of X scanning lines as shown in FIG. 4A, amplifies the signal by the Y driving AMP 6, and supplies the Y driving signal to the Y driving element 15. The supply moves the sample or the probe in the Y direction.

Therefore, when the switching amplifier 4 is in the inversion mode, for X display, the output B of the switching amplifier 4 and the output C of the constant voltage generating circuit 3 are shown in FIG. 2 every time the direction of the X scanning signal A changes. The addition is performed as shown, and the addition is performed by the addition circuit 5 to halve. As a result, a waveform shown in FIG. 2D is obtained as an output of the adding circuit 5, and the signal D is amplified by the X display amplifier 8 and used for X deflection of the display CRT 10. Then, when the inclination of the output D of the display amplifier 8 changes, the image is canceled with the waveform shown in FIG. 2E. As for the Y display,
The Y deflection of the CRT is performed using the Y scanning signal as it is.
In this way, as shown in FIG. 5, the image formed by the forward scan and the image formed by the return scan are displayed as left-right symmetric images.

When the switching amplifier 4 is in the non-inverting mode, the output of the switching amplifier 4 becomes X as shown in FIG. 3B.
It becomes the same as the scanning signal A, and an image by forward scanning and an image by backward scanning are displayed in parallel as shown in FIG.

Further, a dashed line portion (constant voltage generation circuit 3, switching amplifier 4, addition circuit 5) of FIG.
In addition, if both the X and Y displays are set to the inversion mode of FIG. 2, four images vertically and horizontally symmetrically as shown in FIG. 7 are obtained. Similarly, when both the X and Y displays are set to the non-inverting mode of FIG. 3, four images in the same direction are obtained as shown in FIG.

FIG. 9 is a diagram showing another embodiment of the present invention using a frame memory, FIG. 10 is a diagram showing a configuration example of a frame memory, and FIG. 11 is a diagram for explaining the relationship between scanning and memory addresses. 21 is a controller, 22, 2
3 and 29 are D / A conversion circuits, 24 is an A / D conversion circuit, 2
5 is a frame memory, 26 is a Y drive amplifier, 27 is an X drive amplifier, 28 is a Z control circuit, 30 is a monitor CRT,
1 indicates an X drive element, 32 indicates a Y drive element, and 33 indicates a Z drive element.

In the example shown in FIG. 9, the controller 21
D / A conversion circuit 23 for X, D / A for Y
The data is output to the conversion circuit 22, and a voltage having a waveform shown in FIG. 2A is applied to both the X drive element 31 and the Y drive element 32.

The output from the Z control circuit 28 for keeping the tunnel current constant is output to the A / D conversion circuit 2 at regular intervals.
4 to the controller 21.

If the frame memory 25 has a structure of 512 × 512 pixels as shown in FIG. 10, for example, the X and Y scans are performed on the frame memory 25 as shown in FIG.
An address is generated by an algorithm such as A and data is stored.

The data stored in the frame memory 25 is
The data is read out at a speed corresponding to the cycle of the monitor CRT 30, D / A converted by the D / A conversion circuit 29, added with a synchronization signal, and sent to the monitor CRT 30. By doing so, an image as shown in FIG. 7 can be displayed.

When data is stored in the frame memory 25, if an X-ray and an Y-address are generated by an algorithm as shown in FIG. 11B, an image as shown in FIG. 8 can be displayed.

It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible. For example, although a CRT is used in the above embodiment, XY
A recorder may be used. In that case, with Y-axis modulation,
No luminance signal is required. Also, luminance erasure corresponds to pen-up. Further, the image during the return scan may be stored in another frame memory to form another screen.

[0028]

As is clear from the above description, according to the present invention, since each image is obtained in response to the reciprocating scanning, the images can be displayed side by side at the same time, or by switching the images and displaying the images. , And the state of the hysteresis of the Y drive element. In addition, depending on the shape of the probe, reciprocal images may be inconsistent, so that it can be used for evaluation of the probe. Further, return of sample or probe (return)
Since the scanning period is also used, wasteful time can be eliminated and useful information can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a tunnel microscope according to the present invention.

FIG. 2 is a waveform chart showing one embodiment of an X scanning mode.

FIG. 3 is a waveform chart showing another embodiment of the X scanning mode.

FIG. 4 is a waveform chart for explaining a Y scanning mode.

FIG. 5 is a diagram showing an example of correspondence between scanning and a display image.

FIG. 6 is a diagram showing an example of correspondence between scanning and a display image.

FIG. 7 is a diagram showing an example of correspondence between scanning and a display image. .

FIG. 8 is a diagram illustrating an example of correspondence between scanning and a display image.

FIG. 9 is a diagram showing another embodiment of the present invention using the frame memory of FIG. 9;

FIG. 10 is a diagram illustrating a configuration example of a frame memory.

FIG. 11 is a diagram for explaining the relationship between scanning and memory addresses.

FIG. 12 is a diagram showing a schematic configuration of a scanning tunnel microscope.

FIG. 13 is a diagram for explaining an example of a conventional scanning method.

FIG. 14 is a diagram for explaining an example of a conventional scanning method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Y scanning circuit, 2 ... X scanning circuit, 3 ... constant voltage generation circuit, 4 ... switching amplifier, 5 ... addition circuit, 6 ... Y driving amplifier, 7 ... X driving amplifier, 8 ... X display amplifier, 9 ... Y Display amplifier, 10 ... Display CRT, 11 ... Blank circuit, 1
2 ... Video amplifier, 13 ... Z control circuit, 14 ... X drive element, 15 ... Y drive element, 16 ... Z drive element

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-202447 (JP, A) JP-B-7-92461 (JP, B2) Osamu Nishikawa et al. “Drive element characteristics and STM image” 1986 Proceedings of the 47th Autumn Meeting of the Japan Society of Applied Physics (pp. 229) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 13/10-13/24

Claims (3)

(57) [Claims] 1. A scanning tunneling microscope in which a probe or a sample is scanned in the X and Y directions by bringing a probe close to the sample surface and a tunnel current is detected to obtain a scanned image of the sample surface. the video signal for the outward scan, the image signal of the scanning of the recovery path of the X scanning in the scanning of the forward path of the Y scanning
And the forward scan of the X scan in the backward scan of the Y scan.
Video signal and X-scan return path in Y-scan return path
A scanning tunnel microscope characterized in that a scanning image of a sample is obtained based on a video signal of the scanning. 2. The scanning tunnel microscope according to claim 1, wherein a video signal of the forward scan of the X-scan and a video signal of the backward scan of the X-scan are alternately acquired. 3. In a scanning tunneling microscope in which a probe is brought close to a sample surface to scan the probe or the sample to detect a tunnel current and obtain a scan image of the sample surface, a scan image of the sample based on a video signal of the return scan. A scanning tunnel microscope comprising a switching means for switching the display mode between an inversion mode and a non-inversion mode, and obtaining a scan image of a sample based on a video signal of forward scanning and a video signal of backward scanning. .