JPH0783607A - Control method for scan type probe microscope - Google Patents

Abstract

PURPOSE:To provide a control method for a scanning probe microscope wherein both an interatomic farce microscope image and a scanning tunnelling microscope image are obtained with the same probe at the same time. CONSTITUTION:At measurement points on a material surface, a bias voltage is applied between a conductive needle tip 1 and a material surface 4, and while they are made to relatively came near each other, the tunnelling current flowing between them is measured, and a position of the conductive needle tip 1 in the direction of Z-axis, at the time the value is a specified value, is taken as scanning tunnelling microscope data. Then, the bias voltage is cut off and the conductive needle tip 1 is brought into contact with the material surface 4, and deflection amount at a free end of a cantilever 3 is measured so that the displacement amount of the cantilever 3 in the direction of Z-axis, at the time the displacement amount is a specified value, is taken as interatomic force microscope data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a scanning probe microscope which has both the function of an atomic force microscope and the function of a scanning tunneling microscope for examining the structure of a material surface at the molecular / atomic level using a probe. It is about.

[0002]

2. Description of the Related Art In recent years, a scanning tunneling microscope and an atomic force microscope have been developed as a scanning probe microscope capable of observing a solid surface at an atomic / molecular level. First, the principle of the scanning tunneling microscope will be described. When a conductive needle tip with a sharpened tip is brought close to the material surface by about several nm and a bias voltage is applied between the conductive needle tip and the material surface, a gap between the conductive needle tip and the sample surface is obtained. A tunnel current flows through. The material surface is scanned while feedback controlling the distance between the conductive needle tip portion and the material surface by the Z-axis position control piezoelectric body and the control circuit so as to keep the tunnel current constant. Since the tunnel current reflects the difference in the electron cloud and the potential change on the surface of the material, it is possible to distinguish the individual atoms and molecules that make up the surface of the material by imaging this feedback control amount. .

Next, the principle of the atomic force microscope will be described. In the atomic force microscope, a cantilever having a conductive needle tip and a length of about 100 μm to 200 μm is used to detect a minute force. When the material surface is brought close to the conductive needle tip, the cantilever is bent by the atomic force acting between the conductive needle tip and the material surface. The surface of the substance is scanned while the distance between the cantilever and the substance surface is feedback-controlled by the piezoelectric body for position control in the Z-axis direction and the control circuit so as to keep this amount of deflection constant. The amount of deflection of the cantilever (that is, the force acting between the conductive needle tip and the substance surface) reflects the unevenness of the substance surface. Therefore, by imaging this feedback control amount, the atoms and molecules that make up the substance surface can be visualized. Can be distinguished.

[0004]

With a scanning probe microscope such as a scanning tunneling microscope or an atomic force microscope, it is possible to observe the arrangement of atoms on the surface of a substance such as metal, semiconductor or insulator. However, when a cantilever having a conductive needle tip is brought close to the surface of the material by a distance of several nm, attractive force such as van der Waals force acts, causing the cantilever to bend toward the surface of the material, and the conductive needle tip is positioned at that position. It is impossible to stand still. Therefore, an apparatus that simultaneously achieves the function of the scanning tunneling microscope and the function of the atomic force microscope by using the same probe has not been developed yet, and identification of atomic species on the surface of the substance has been impossible. The present invention has been made to solve the above problems, and an object thereof is to obtain a control method for a scanning probe microscope having both the function of an atomic force microscope and the function of a scanning tunneling microscope. There is.

[0005]

In order to achieve the above object, a method of controlling a scanning probe microscope according to the present invention is a conductive needle provided near a free end of a cantilever at each measurement point on a material surface. A bias voltage is applied between the tip and the material surface, the conductive needle tip approaches or contacts the material surface, and a tunnel current flowing between the conductive needle tip and the material surface and the A method for controlling a scanning probe microscope that measures a surface state of the substance while detecting a force generated between a conductive needle tip portion and the substance surface, wherein the conductive needle tip is provided at each of the measurement points. Section and the substance surface are separated from each other, the substance surface and the fixed end of the cantilever are relatively brought close to each other, and the tunnel current and the force generated between the conductive needle tip and the substance surface are Configured to measure There. In the above configuration, it is preferable to turn off the bias voltage when the tunnel current flowing between the conductive needle tip portion and the substance surface reaches or exceeds a predetermined set value. In addition, imaging the surface state based on the position of the conductive needle tip portion or the displacement of the cantilever when the tunnel current flowing between the conductive needle tip portion and the substance surface reaches a predetermined set value. Is preferred. Alternatively, it is preferable to image the surface state based on the tunnel current value flowing between the conductive needle tip portion and the material surface at the reference position of the conductive needle tip portion or the displacement of the cantilever. Alternatively, it is preferable to image the surface state based on the position of the conductive needle tip portion or the tunnel current value at the time when the displacement of the cantilever reaches a predetermined set value. Or
It is possible to image the surface state based on the position of the conductive needle tip or the displacement of the cantilever when the tunnel current flowing between the conductive needle tip and the material surface reaches a predetermined set value. preferable. Further, it is preferable to move the cantilever relatively from one measurement point on the substance surface to the next measurement point after the conductive needle tip is separated from the substance surface.

[0006]

Function At each measurement point on the material surface, first, a bias voltage is applied between the conductive needle tip and the material surface to bring the conductive needle tip and the material surface relatively close to each other. Measure the tunnel current flowing between the tip and the material surface,
The position in the Z-axis direction of the conductive needle tip portion when the tunnel current reaches a predetermined set value is stored as scanning tunneling microscope data. Next, the bias voltage is cut off, the conductive needle tip is brought into contact with the material surface, and the amount of deflection of the free end of the cantilever is measured. The displacement amount of the cantilever in the Z-axis direction at the time when the deflection amount reaches a predetermined set value is stored as atomic force microscope data. After separating the conductive needle tip from the material surface, move the cantilever from one measurement point on the material surface to the next measurement point in the X-axis direction and / or
Alternatively, it is moved relatively in the Y-axis direction. That is, according to the control method of the scanning probe microscope of the present invention, at one measurement point, the conductive needle tip portion is brought relatively close to the material surface in the Z-axis direction from a position distant from the material surface, and Since it is controlled so as to separate from the surface, even if the conductive needle tip comes into contact with the sample surface due to attractive force such as Van der Waals force, by separating the material surface and the conductive needle tip relatively, It becomes possible to measure the tunnel current at a distance of about 1 nm at the measurement point. As a result, it becomes possible to combine the function of the atomic force microscope and the function of the scanning tunneling microscope, and it is possible to identify the atomic species from these images. Similarly, the value of the tunnel current flowing between the conductive needle tip portion and the substance surface at the reference position of the conductive needle tip portion or the displacement of the cantilever, the conductive needle tip when the displacement of the cantilever reaches a predetermined set value. Position or tunnel current value, or the position of the conductive needle tip or the displacement of the cantilever at the time when the tunnel current value flowing between the conductive needle tip and the material surface reaches a predetermined set value. Even if the surface state is imaged, an atomic force microscope image and a scanning tunneling microscope image can be obtained.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a scanning probe microscope control method according to the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing the configuration of a scanning probe microscope suitable for one embodiment of the control method of the scanning probe microscope of the present invention. In FIG. 1, a probe (probe) 100 is composed of a thin film cantilever 3 and a conductive needle tip portion (chip) 1. The conductive needle tip portion 1 is formed of platinum iridium alloy or the like. The thin film cantilever 3 has, for example, a thickness of 0.5 μm, a length of 200 μm, and a width.
It is 40 μm rectangular silicon nitride or the like. The conductive needle tip 1 is
It is fixed near the free end of the thin film cantilever 3 with an adhesive or the like. A metal thin film 2 is provided on the surface of the thin film cantilever 3 to which the conductive needle tip portion 1 is adhered, and the current flowing through the conductive needle tip portion 1 is taken out by the metal thin film 2. The sample 4 is placed on the conductive sample table 8,
It is electrically connected to the conductive sample table 8. The conductive sample stage 8 is attached to a tube type fine movement mechanism composed of position-controlling piezoelectric bodies 5, 6 and 7 in three directions of X axis, Y axis and Z axis. A voltage generator 9 is attached to the conductive sample table 8.
, And the current measuring device 10 is connected to the probe 100.

The bias voltage generated by the voltage generator 9 is applied between the sample 4 and the probe 100 via the conductive sample stage 8. The tunnel current flowing between the conductive needle tip portion 1 and the sample 4 is detected by the current measuring device 10. Scanning of the sample 4 in the horizontal plane (X-axis direction and Y-axis direction) and control in the vertical direction (Z-axis direction) are performed by generating a predetermined voltage by the computer 11 and the piezoelectric body driving device 12, and generating the generated voltage on the X-axis. , A piezoelectric body 5 for position control in the Y-axis and Z-axis directions,
6 and 7 were applied. Cantilever 3
The deflection amount and the twist amount at the free end of the laser light emitted from the semiconductor laser 13 having an output of 5 mW are measured by the lens 14
Was collected on the back surface of the free end of the cantilever, and the reflected light was measured by an optical lever detected by the two-divided photodiode 15.

Hereinafter, in InSb crystal (11
0) A method of operating the scanning probe microscope when observing the cleavage plane will be described. An n-type InSb crystal doped with tellurium (Te) was placed on a conductive sample stage 8 and cleaved in an ultrahigh vacuum to expose a (110) clean surface, which was used as a sample 4. In this embodiment, at each measurement point, a bias voltage of +1.0 V is applied to the sample 4, the conductive needle tip 1 approaches the sample 4, and flows between the conductive needle tip 1 and the sample 4. The bias voltage was cut off when the tunnel current exceeded 0.1 nA. Further, when the conductive needle tip portion 1 receives a repulsive force from the sample 4 and the amount of deflection generated at the free end of the cantilever reaches 10 nm or more, the conductive needle tip portion 1 is separated from the sample 4 in the Z-axis direction. Set to. Further, the conductive needle tip portion 1 at the time when the tunnel current and the deflection amount reach the set values.
The position in the Z-axis direction of was measured by the computer 11 as scanning tunneling microscope image data and atomic force microscope image data at the measurement points.

Next, the voltages 16 and 17 applied to the piezoelectric bodies 5 and 7 for position control in the X-axis and Z-axis directions at the time of measurement.
2 shows the relationship among the deflection amount 18 of the cantilever 3, the bias voltage 19 applied to the sample 4, and the tunnel current 20. While detecting the deflection amount of the free end of the cantilever 3 and the tunnel current flowing between the conductive needle tip portion 1 and the sample 4, the voltage applied to the Z-axis position control piezoelectric body 7 is gradually increased, The conductive needle tip portion 1 was brought close to the surface of the sample 4. When the tunnel current reaches the set value,
The voltage 21 applied to the piezoelectric body 7 for position control in the Z-axis direction was stored in the computer 11 as scanning tunneling microscope image data. At the same time, the bias voltage applied to Sample 4 was turned off. Further, the voltage applied to the piezoelectric body 7 for position control in the Z-axis direction was gradually increased to bring the conductive needle tip portion 1 into contact with the surface of the sample 4. After the conductive needle tip portion 1 contacts the surface of the sample 4, the cantilever 3 gradually bends. Cantilever 3
When the amount of deflection at the free end of
The voltage 22 applied to the axial position control piezoelectric body 7 was stored in the computer 11 as atomic force microscope image data. At the same time, the voltage applied to the piezoelectric body 7 for position control in the Z-axis direction was lowered, and the conductive needle tip portion 1 was separated from the sample 4 by 50 nm. Then, a predetermined voltage was applied to the position controlling piezoelectric body 5 in the X-axis direction, and the sample 4 was moved in the X-axis direction by a predetermined distance. After that, a bias voltage was applied to the sample 4 again, the voltage applied to the Z-axis direction position control piezoelectric body 7 was gradually increased, and the same operation was repeated. The measurement interval at each measurement point was about 1 msec. Such measurement was repeated 256 times in the X-axis direction, and scanning for one line was completed. Next, the sample 4 was moved in the Y-axis direction by a predetermined distance by the Y-axis position control piezoelectric body 6, and one line was further scanned by the same operation. 25 in the Y-axis direction
After scanning 6 times, the voltage data of 256 × 256 sets captured in the computer 11 alternately at every measurement point were imaged as a scanning tunneling microscope image and an atomic force microscope image.

An outline of the scanning tunneling microscope image and the atomic force microscope image obtained by the above method is shown in FIGS. 3 and 4. A region indicated by a circle 23 in FIG. 3 is a region where a tunnel current easily flows, and shows an arrangement of In atoms. A large circle 24 in FIG. 4 indicates a region where the sample surface is higher than other regions, and a small circle 25 indicates a region slightly higher than the other regions. When FIG. 3 and FIG. 4 are overlapped, the circles in FIG. 3 match the small circles in FIG. 4, which represent In atoms. Therefore, it can be seen that the large circles in FIG. 4 correspond to Sb atoms. That is, in the conventional scanning tunneling microscope, In
I could only display either atom of Sb or Sb,
According to the scanning probe microscope of the present invention, both atoms can be displayed, and the atomic species can be identified by comparing the obtained scanning tunneling microscope image with the atomic force microscope image.

In the above embodiment, the tunnel current value,
Alternatively, the case where the data at the time when the deflection amount (displacement) of the cantilever reaches a predetermined set value is imaged has been described, but the tunnel current value at the predetermined reference position, the cantilever deflection amount, and the tunnel current value are set to the predetermined values. Also by imaging the deflection amount of the cantilever at the time when the value reaches the value, or the tunnel current value when the deflection amount of the cantilever reaches the predetermined set value,
Various surface information was obtained.

[0013]

As described above, according to the present invention, a bias voltage is applied between the conductive needle tip portion and the substance surface at each measurement point on the substance surface so that the conductive needle tip portion and the substance surface are separated from each other. While relatively approaching, the tunnel current flowing between the conductive needle tip and the material surface is measured, and the position of the conductive needle tip in the Z-axis direction at the time when the tunnel current reaches a predetermined set value is determined. It is stored as scanning tunneling microscope data, then the bias voltage is cut off, the conductive needle tip is brought into contact with the material surface, and the amount of deflection of the free end of the cantilever is measured.The cantilever at the time when the amount of deflection reaches the specified value Since the displacement amount in the Z-axis direction is stored as atomic force microscope data, an atomic force microscope image and a scanning tunneling microscope image can be simultaneously obtained with the same probe,
Further, there is an effect that a scanning probe microscope capable of identifying atomic species and the like can be obtained from these images.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a scanning probe microscope suitable for a control method of the scanning probe microscope of the present invention.

FIG. 2 is a diagram showing a scanning probe microscope control method according to an embodiment of the present invention, wherein a voltage applied to a piezoelectric body for position control in the X-axis and Z-axis directions, a deflection amount of a cantilever, a bias voltage applied to a sample, and a tunnel. Diagram showing the relationship of current change over time

FIG. 3 is a diagram showing a scanning tunneling microscope image obtained by the control method of the scanning probe microscope of the present invention.

FIG. 4 is a diagram showing an atomic force microscope image obtained by the control method of the scanning probe microscope of the present invention.

[Explanation of symbols]

1: Conductive needle tip 2: Metal thin film 3: Thin film cantilever 4: Sample 5: Piezoelectric body for position control in X-axis direction 6: Piezoelectric body for position control in Y-axis direction 7: Piezoelectric for position control in Z-axis direction Body 8: Conductive sample stand 9: Voltage generator 10: Current measuring device 11: Computer 12: Piezoelectric body driving device 13: Semiconductor laser 14: Condensing lens 15: Two-division photodiode 16: For position control in the X-axis direction Voltage applied to the piezoelectric body 17: Voltage applied to the piezoelectric body for position control in the Z-axis direction 18: Deflection amount of the free end of the cantilever 19: Bias voltage applied to the sample 20: Tunnel current 21: Tunnel current reaches the set value Applied voltage at the time point 22: Applied voltage at the time when the amount of deflection reaches the set value 23: In atom 24: Sb atom 25: In atom 10 : Probe

Claims (7)

[Claims] 1. A bias voltage is applied between a conductive needle tip portion provided near a free end of a cantilever and a material surface at each measurement point on the material surface, and the conductive needle tip portion is moved to the material surface. The surface state of the substance while detecting the tunnel current flowing between the conductive needle tip and the substance surface and the force generated between the conductive needle tip and the substance surface. A method for controlling a scanning probe microscope for measuring, wherein at each of the measurement points, the substance surface and the fixed end of the cantilever are relatively moved from a state where the conductive needle tip portion and the substance surface are separated from each other. A method for controlling a scanning probe microscope, wherein the tunneling current and the force generated between the conductive needle tip portion and the substance surface are measured by approaching each other. 2. The scanning probe microscope according to claim 1, wherein the bias voltage is cut off when the tunnel current flowing between the conductive needle tip portion and the material surface exceeds a predetermined set value. Control method. 3. A surface state is imaged based on the position of the conductive needle tip portion or the displacement of the cantilever when the tunnel current flowing between the conductive needle tip portion and the material surface reaches a predetermined set value. The method for controlling a scanning probe microscope according to claim 1 or 2, characterized by: 4. The surface state is imaged based on the tunnel current value flowing between the conductive needle tip and the material surface at the reference position of the conductive needle tip or the displacement of the cantilever. The control method of the scanning probe microscope according to claim 1. 5. The surface state is imaged based on the position of the conductive needle tip portion or the tunnel current value at the time when the displacement of the cantilever reaches a predetermined set value. A method for controlling the scanning probe microscope according to. 6. The surface state is imaged based on the position or the displacement of the cantilever at the time when the tunnel current value flowing between the conductive needle tip and the material surface reaches a predetermined set value. The method for controlling the scanning probe microscope according to claim 1 or 2. 7. The cantilever is relatively moved from one measurement point on the substance surface to the next measurement point after the conductive needle tip is separated from the substance surface.
7. The method for controlling the scanning probe microscope according to any one of 1 to 6.